Typical Radio Problems

TYPICAL RADIO PROBLEMS AND THIER OPTIMIZATION Posted on

April 30, 2013 by TELNETWORK

TYPICAL RADIO PROBLEMS Several sources of information for optimization: QoS indicators, Coverage predictions, Customer complaints, Drive tests, Abis/A traces, Other teams information (NSS statistics). I. Coverage Problem Bad coverage : A network facing coverage problems has bad RxLev. RxQual can be bad at the same time. Sometimes the RxLev can look OK on the street (i.e. from drivetest) but coverage inside the buildings can be poor due to building losses. Building losses can range from 10 to 30 dB or more. Indications : • Customers complain about dropped calls and/or “No Network” • OMC QoS indicators – TCH failure rate – Call drop rate – Low proportion of better cell HO – High rate of DL & UL Level HO (possibly also DL/UL quality HO) • A interface indicators – High rate of Clear Request message, cause radio interface failure • Drive Test – Poor RxLev ( < -95 dBm) Investigation and Optimization : • If actual coverage OK compared to predicted ones – Improve coverage by adding Macro site, Microcell site (Border or Shadow areas), or IBC site (In-building coverage). – Use parameter setting ex. Bi-layer Handover.

• If actual coverage is not the one predicted by planning tool – Check antenna system (azimuth, crossed sector?) – Check prediction in the tool (EIRP, Clutter Type, Obstructing building?). Most of the time the prediction will be incorrect, as it is only a computer simulation – Increase or decrease antenna down-tilt – Check BTS output power set in the OMC-R (BS_TXPWR_MAX: should always be set at 0) From Drive test or Abis Interface – RxLev < -95 dBm and – RxQual > 4 II. Interference Problem Interference: A network facing interferences problems presents good RxLev and bad RxQual in the same time on some areas. Indications: • Customers complain about bad speech quality (noisy calls) and/or call drops • OMC QoS indicators – SDCCH/TCH Drop – Low proportion of better cell HO – High rate of DL/UL quality HO and interference HO – Low HO success rate • A interface indicators – High rate of Clear Request message, cause radio interface failure • Drive Test

– RxQual > 4 with RxLev > -85 dBm Typical causes: • GSM interferences: Co-channel, adjacent. • Non GSM Interference: Other Mobile Network, Other RF sources. Co-channel interference: • C/I = Carrier-to-interference ratio • +12 dB is taken into account for Alcatel ( +9 dB according to GSM standard) (i.e. interference can be 9  12 dB weaker than serving cell to cause poor RxQual). • Indications: Downlink and/or Uplink Interference, High rate of quality handover, call drop, and call setup failure. • Investigation: Drive test analysis, Lumpini: Co-channel checking, Check prediction to verify which cell could be causing the interference, Frequency plan C/I < 12 dB. • Optimization: Antenna optimization, Change frequency, Reduce BTS power (not an option in TA Orange network), Concentric cell. Adjacent channel interference: • C/A = Carrier-to-adjacent ratio • -6 dB is taken into account for Alcatel ( -9 dB according to GSM standard). • Indications : Downlink and/or Uplink Interference, High rate of quality handover, call drop, and call failure • Investigation: Adjacent HO statistics (if they are defined as neighbors). If they often handover, then adjacent channel interference could be a problem. Drive test analysis ; Lumpini: Adjacent channel checking ; Cell coverage prediction; Frequency plan C/I < -6 dB. • Optimization : Antenna optimization, Change frequency, Reduce BTS power (not an option in TA Orange network), use Concentric cell Non GSM interference : • Other mobile network : Inter-modulation with GSM BTS/MS receiver • Other RF interferers – Radar

– Shop anti-theft mechanism – Medical devices – Other man-made radio transmission – Illegal usage of GSM frequencies (e.g. illegal imported devices, illegal usage of other organization, …) III. Unbalance power budget Problem – A cell facing unbalanced power budget problems presents a too high path-loss difference between UL and DL (often DL>UL) – Lower Rx diversity gain of cross polarized antenna in rural area compared to dense area – Crossed feeders – Traffic not directly in boresight of antenna, where cross-polar discrimination is lower – Loose connectors – Faulty antenna, feeder, TMA – Rule : try to have delta as small as possible to avoid access network possible only in 1 direction (usually BTS->MS : OK and MS->BTS : NOK), i.e. uplink limited Indicators: • OMC QoS indicators – High ratio of Uplink level Handover cause – Low incoming HO success rate – DL level looks OK for HO, but UL is too weak when HO is attempted – Degradation of TCH failures and OC call drop indicators • A interface indicators – High rate of Clear Request message, cause radio interface failure • O&M Alarms

– Voltage Standing Wave Ratio (VSWR) – TMA Investigation : – Abis monitoring: ABS(delta Path loss) > 10Check if problem is occurring for 1 TRX or all. – ABS(delta path loss) = ABS(UL Path loss – DL Path loss) – UL Path loss = MS transmitted power – measured received UL level – DL Path loss = BTS transmitted power – combiner loss – measured received DL level – Large difference between uplink and downlink level triggered HO. – Use PM observation counter (in OMC-R) – RT11 Optimization : This equipment should be checked – TRX types (MP, HP) – Antennas or common RF components, TMA (common to all TRX of the BTS) – TRX RF cables, LNA IV. TCH congestion Problem TCH Congestion : • TCH Congestion rate (TCH Assignment Phase) is too high (more than 2%) • Rule : try to meet the offered traffic (asked by users) by providing the right number of resources (TRX extension) Indications: – Customers complain about “Network busy” – OMC QoS indicators: High “TCH Congestion rate”, “RTCH Assignment fail-Congestion”, Low “incoming Intra/Inter BSC HO success rate” (no TCH available), High “Directed Retry rate or Congestion Relief (Motorola)” if activated, A interface indicators: “BSS Congestion failure in OC”(High rate of Assignment Failure message, No radio resource available) – Drive Test : Handover to better cell is slow, or never occurs Optimization:

– Special events : Foreseeable: (footballs match, important meeting, Exhibition, etc): Add some extra TRXs, Add special mobile BTSs (Cell on Wheel), Activate HR (may not always be possible due to BSC capacity limitations) Not foreseeable: car crash on the highway – Daily periodic problems : At busy hour: Hardware solution: Add TRX(s), concentric cell, new site, Optimize cell boundaries (i.e. antenna optimization) to share traffic with surrounding cells. Software solution: Directed Retry, Traffic Handover, Half Rate (Alcatel), Congestion Relief (Motorola) Flow control (Motorola). Problems and responsible parties • Coverage problem : If the measured RxLev does not match the prediction: – Check the prediction, check panoramic pictures for obstructions – Field Operation team to check physical configuration (tilt, azimuth, antenna height…). Also check for faults in the antenna system (VSWR, sweep antennas, DTF test, etc.) – If Field Operation find no problem, antenna optimization may be required (if necessary) If the field realities match the prediction: RF team to add new sites (tri-sector, micro cellular, indoor cells) to improve poor/no coverage area (Optimizer requests for some new sites to RF team regarding to the drive test result). • Interference problem : Optimization team to identify the interference source and request Spectrum Management team to correct it in case of internal source (new frequency planning…) • Unbalanced power budget problem : Field Operation team to check the impacted BTS (Antenna, TMA, RF cables, LNA, diversity system…) according to request from Optimizer.

• TCH Congestion problem : Regional RF to request TRX expansion.

Interview question of GSM 1) Which channel is used to transmit random access signals? BCCH CCCH Correct! SDCCH TCH 2) Which one of the following is the combination of main BCCH? TCH+SACCH FCH+SCH+BCH+CCCH Correct! SDCCH/8+SACCH/8 FCH+SCH+BCH+SDCCH+SACCH 3) The Value Range of Timing Advance (TA) in GSM is? 0-31 0-127 0-63 Correct! 0-7 4) How many MS can be paged with 1 paging massage with IMSI? 1 2 Correct! 3 4 5) Directed Retry handover means? TCH to TCH SDCCH to TCH Correct! SDCCH to SDCCH None of Above 6) How many neighbors are measured by MS at a time? 5 6 Correct! 7 8 7) Time Duration of Super Frame? 3 Hour 28 minutes 53 seconds 760 ms 6.12 seconds Correct! 235.65 ms 120 ms 8) Maximum number of characters allowed in one SMS? 160 Correct! 170 180 150 9) If you have 5 MHz frequency band what will be the maximum number of

channels as per GSM system? 25 Correct! 35 20 24 10) Which kind of Handovers more desired in the Network? Rx Level Power Budget Correct! Rx Quality Interference 11) SDCCH holding time for Normal location update is 3.8ms 3.5sec Correct! 3.5ms None of them 12) SDCCH holding time for call setup (MOC) is 2.7sec Correct! 3.5sec 2.7ms 3.5ms 13) Same BCCH-BSIC combination in adjacency will lead Will not cause any problem. Massive Handove failaur Call drop B & C Correct! 14) What is the reason of ping-pong handover Cable swap No dominant cell coverage Improper handover margine All of above Correct! 15) If there is interference on the BCCH TRx and the call is going on at the hopping Trx Call will drop Call will be unafected Correct! Call will attempt handover due to this interference None of above 16) If in a cell all KPI is going well but its TCH drop is high, there is no any RF and hardware issue then this TCH drop will be due to Transcoder fail Correct! Lapd fail A&B None of them 17) Which system informations are used in idle mode System information 1,2,3,4,7 & 8 Correct! System information 1,2,3,4,5,6,7 & 8 System information 1,2,3,4,5,6,9 & 10 System information 1,2,3,4,5,6,7,8,9,10,11,12 & 13

18) Which system informations are used for BA list System information 1,2,3 & 4 Correct! System information 5,6,8,9,10 & 12 System information 12 & 13 None of them 19) Which system informations are used for MA list System information 13,10,9 & 4 System information 5 & 6 Correct! System information 12 & 13 None of them 20) Which system informations are used for GPRS System information 9 & 4 System information 5 & 6 System information 12 & 13 Correct! None of them

LTE DRIVE TEST PARAMETERS RSRP :- Reference signal receive power. • RSRP (dBm) = RSSI (dBm) -10*log (12*N)

where RSSI = Received Signal Strength Indicator N: number of RBs across the RSSI is measured and depends on the BW Significance : RSRP is the most basic of the UE physical layer measurements and is the linear average power (in watts) of the downlink reference signals (RS) across the channel bandwidth for the Resource elements that carry cell specific Reference Signals. Knowledge of absolute RSRP provides the UE with essential information about the strength of cells from which path loss can be calculated and used in the algorithms for determining the optimum power settings for operating the network. Reference signal receive power is used both in idle and connected states Range :- -44 to -140 dBm

• RSRP term is used for coverage same as RSCP in 3G RSRQ :Reference signal receive quality RSRQ = RSRP / (RSSI / N) N is the number of resource blocks over which the RSSI is measured RSSI is wide band power, including intra cell power, interference and noise.

Significance :It provides the Indication of Signal Quality . Measuring RSRQ becomes particularly important near the cell edge when decisions need to be made, regardless of absolute RSRP, to perform a handover to the next cell. Reference signal receive quality is used only during connected states Range :- -3 to -19.5 dB • RSRQ term is used for Quality same as Ec/No in 3G. • SINR :- Signal to Noise Ratio. SINR = S / I + N S -- Average Received Signal Power I -- Average Interference power N -- Noise Power Significance : Is a way to measure the Quality of LTE Wireless Connections. As the energy of signal fades with distance i.e Path Loss due to environmental parameters ( e.g. background noise , interfering strength of other simultaneous transmission)

• RSSI :- Received Signal Strength Indicator. < !--[if ppt]--> • RSSI = wideband power = noise + serving cell power + interference power • RSSI=12*N*RSRP • RSSI per resource block is measured over 12 resource elements. N: number of RBs across the RSSI is measured and depends on the BW •

Based on the above: RSRP (dBm) = RSSI (dBm) -10*log (12*N) •

Significance :– Is the parameter represents the entire received power including the wanted power from the serving cell as well as all the co channel power & other sources of noise

• CQI :- Channel Quality Indicator • Range :- 1 to 15 Significance: CQI is a measurement of the communication quality of wireless channels i.e. it indicates the downlink mobile radio channel quality as experienced by the UE .CQI can be a value representing a measure of channel quality for a given channel. Typically, a high value CQI is indicative of a channel with high quality and vice versa.

• CQI is measured in the Dedicated mode only. • < !--[if ppt]--> • CQI depends on the RF conditions. • < !--[if ppt]--> • Better the CQI better the throughput will get and vice versa. • PCI:- Physical Cell Id Range :- 0 to 503 • Significance - PCI used to identify the cell & is used to transmit the data • < !--[if ppt]--> • PCI = PSS + 3*SSS PSS is Primary Synchronization Signal ( Identifies Cell Id ). PSS value can be 0, 1 & 2 SSS is Secondary Synchronization Signal ( identifies Cell Id group). SSS value can be 0 to 167.

•

BLER :- Block Error Rate • Block Error Ratio is defined as the ratio of the number of erroneous blocks received to the total number of blocks transmitted • < !--[if ppt]--> Significance A simple method by which a UE can choose an appropriate CQI value could be based on a set of Block Error Rate (BLER) thresholds . The UE would report the CQI value corresponding to the Modulation Coding Schemes that ensures BLER ≤ 10% based on the measured received signal quality • < !--[if ppt]--> • BLER is Calculated using Cyclic Redundancy error Checking method High BLER leads to loss of Peak rates & efficiency 

BLER threshold should be low i.e. ≤ 10%

DDownlink Throughput -I n E-UTRAN may use a maximum of 2 Tx antennas at the ENodeB and 2 Rx antennas at the UE ( MIMO ). Significance - Target for averaged user throughput per MHz, 3 to 4 times Release 6 HSDPA i.e Higher user throughput as compared to 3G ( Over 300 Mbps downlink as compared to 14 Mbps in UMTS) - The supported user throughput should scale with the spectrum

bandwidth.

Uplink Throughput -I n E-UTRAN uses a maximum of a single Tx antenna at the UE and 2 Rx antennas at the E Node B. - Greater user throughput should be achievable using multiple Tx antennas at the UE ( MIMO ) . - SignificanceTarget for averaged user throughput per MHz, 2 to 3 times Release 6 Enhanced Uplink i.e Higher user throughput as compared to 3G (Over 50 Mbps Uplink as compared to 5.76 Mbps in UMTS).The user throughput should scale with the spectrum bandwidth provided that the maximum transmit power is also scaled.

WCDMA/3G Questions & Answers General

< !--[if !supportLists]-->1. What is the experience and involvement in your current and previous UMTS design projects? Talk about your current and previous projects, your responsibilities, design objectives, tools used, activities involved, challenges, objectives met, etc.

Link Budget

< !--[if !supportLists]-->2. What is a typical NodeB sensitivity level? The service and load determines the NodeB sensitivity; in general, in a no-load condition, the sensitivity is between -115dBm to -125dBm. For Ericsson, the NodeB sensitivity level is calculated at around: CS12.2: -124 dBm PS-64: -119 dBm PS-128: -115 dBm PS-384: -115 dBm

< !--[if !supportLists]-->3. What is a typical UE sensitivity level? The service and load determines the UE sensitivity; in general, in no-load condition, the sensitivity is between -105dBm and -120dBm. For Ericsson, the UE sensitivity level is calculated at around: CS12.2: -119 dBm

PS-64: -112 dBm PS-128: -110 dBm PS-384: -105 dBm HSDPA: -95 dBm

< !--[if !supportLists]-->4. What is a typical NodeB maximum output power? The maximum NodeB output power is usually 20W or 40W, that is, 43dBm or 46dBm.

< !--[if !supportLists]-->5. What is UE maximum transmit power in your link budget? 21dBm.

< !--[if !supportLists]-->6. What is a typical antenna gain? The antenna gain depends on antenna model; in link budget we use around 17dBi.

< !--[if !supportLists]-->7. What is a typical maximum path loss? The maximum path loss is dependent on the service and vendor recommendations; typically it is in between 135 to 140dB for urban areas and between 150 to 160dB for rural areas.

< !--[if !supportLists]-->8. What is difference between dBi and dBd? dBi is the gain in dB from isotropic source; dBd is the gain from a dipole source. dBd + 2.15 = dBi.

< !--[if !supportLists]-->9. What is the difference between dB and dBm? dBm is a unit of power level, measured in milli-watts in logarithm scale, that is, dBm = 10 * log(W*1000) where W is the power in Watts dB is not a unit, it is the difference in dBm.

< !--[if !supportLists]-->10. What is 0dBm? 0dBm = 1 milli-watt.

< !--[if !supportLists]-->11. How does TMA work? A TMA reduces system noise, improves uplink sensitivity and leads to longer UE battery life. Sensitivity is the minimum input power needed to get a suitable signal-to-noise ratio (SNR) at the output of the receiver. It is determined by receiver noise figure, thermo noise power and required SNR. Thermo noise power is determined by bandwidth and temperature, SNR is determined by modulation technique, therefore the only variable is noise figure. The cascading noise figure can be calculated by Friis equation (Herald Friis): NFt = NF1 + (NF2-1)/G1 + (NF3-1)/(G1*G2) + ... + (NFi-1)/(G1*G2*...*Gi) As the equation shows, the first block imposes the minimum and the most prominent noise figure on the system, and the following blocks imposes less and less impact to the system provided the gains are positive. Linear passive devices have noise figure equal to their loss. A TMA typically has a gain of 12dB.

There are typically top jumper, main feeder and a bottom jumper between antenna and BTS. A TMA placed near antenna with a short jumper from antenna provides the best noise figure improvement – the noise figure will be restricted to the top jumper loss (NF1) and TMA ((NF2-1)/G1), and the remaining blocks (main feeder and bottom jumper) have little effect. To summarize, a TMA has a gain that’s close to feeder loss.

< !--[if !supportLists]-->12. What are the pros and cons (advantages and disadvantages) of TMA? On the upside, a TMA reduces system noise, improves uplink sensitivity and leads to longer UE battery life. On the downside, TMA imposes an additional insertion loss (typically 0.5dB) on the downlink and increases site installation and maintenance complexity.

< !--[if !supportLists]-->13. What is typical TMA gain? TMA typically has a 12 dB gain; however, the effective gain comes from noise figure reduction and the gain is close or equivalent to the feeder loss.

< !--[if !supportLists]-->14. Why TMA are installed at the top near the antenna and not the bottom near the NodeB? Based on Friis Equation, having a TMA near the BTS will have the top jumper and main feeder losses (noise figures) cascaded in and a TMA will not be able to help suppress the losses.

< !--[if !supportLists]-->15. What is UMTS chip rate? 3.84MHz.

< !--[if !supportLists]-->16. What is processing gain? Processing gain is the ratio of chip rate over data bit rate, usually represented in decibel (dB) scale. For example, with 3.84MHz chip rate and 12.2k data rate, the processing gain is: PG12.2k = 10 * log (3,840,000 / 12,200) = 25dB

< !--[if !supportLists]-->17. What are the processing gains for CS and PS services? CS12.2: 25dB PS-64: 18dB PS-128: 15dB PS-384: 10dB HSDPA: 2dB

< !--[if !supportLists]-->18. How to calculate maximum number of users on a cell? To calculate the maximum number of users (M) on a cell, we need to know: W: chip rate (for UMTS 3,840,000 chips per second) EbNo: Eb/No requirement (assuming 3dB for CS-12.2k) i: other-cell to in-cell interference ratio (assuming 60%)

R: user data rate (assuming 12,200 kbps for CS-12.2k) η: loading factor (assuming 50%) Take 12.2kbps as example: M = W / (EnNo * (1 + i) * R) * η = 3,840,000 (3 * (1 + 0.6) * 12,200) * 0.5 = 32.8 The number of users could also be hard-limited by OVSF code space. Take CS12.2k for example:

< !--[if !supportLists]--> A CS-12.2k bearer needs 1 SF128 code. < !--[if !supportLists]--> Total available codes for CS-12.2k = 128 – 2 (1 SF64) – 2 (4 SF256) = 124.

< !--[if !supportLists]--> Consider soft-handover factor of 1.8 and loading factor of 50%: 124 / 1.8 *.05 = 34 uers/cell.

< !--[if !supportLists]-->19. What is Eb/No? By definition Eb/No is energy bit over noise density, i.e. is the ratio of the energy per information bit to the power spectral density (of interference and noise) after dispreading. Eb/No = Processing Gain + SIR For example, if Eb/No is 5dB and processing gain is 25dB then the SIR should be -20dB or better.

< !--[if !supportLists]-->20. What are the Eb/No targets in your design? The Eb/No targets are dependent on the service:

< !--[if !supportLists]--> On the uplink, typically CS is 5 to 6dB and PS is 3 to 4dB – PS is about 2dB lower.

< !--[if !supportLists]--> On the downlink, typically CS has 6 to 7dB and PS is 5 to 6dB – PS is about 1dB lower.

< !--[if !supportLists]-->21. Why is Eb/No requirement lower for PS than for CS? PS has a better error correction capability and can utilize retransmission, therefore it can afford to a lower Eb/No. CS is real-time and cannot tolerate delay so it needs a higher Eb/No to maintain a stronger RF link.

< !--[if !supportLists]-->22. What is Ec/Io? Ec/Io is the ratio of the energy per chip in CPICH to the total received power density (including CPICH itself).

< !--[if !supportLists]-->23. Sometimes we say Ec/Io and sometimes we say Ec/No, are they different? Io = own cell interference + surrounding cell interference + noise density No = surrounding cell interference + noise density That is, Io is the total received power density including CPICH of its own cell, No is the total received power density excluding CPICH of its own cell. Technically Ec/Io should be the correct measurement but,

due to equipment capability, Ec/No is actually measured. In UMTS, Ec/No and Ec/Io are often used interchangeably.

< !--[if !supportLists]-->24. What is RSCP? RSCP stands for Received Signal Code Power – the energy per chip in CPICH averaged over 512 chips.

< !--[if !supportLists]-->25. What is SIR? SIR is the Signal-to-Interference Ratio – the ratio of the energy in dedicated physical control channel bits to the power density of interference and noise after dispreading.

< !--[if !supportLists]-->26. What is the loading factor in your design? The designed loading typically is 50%; however, sometimes a carrier may want to design up to 75% load.

< !--[if !supportLists]-->27. Give a simple definition of pole capacity? The uplink noise increases with the loading exponentially. When the uplink noise approaches infinity then no more users can be added to a cell – and the cell loading is close to 100% and has reached its “pole capacity”. Mathematically, to calculate the uplink pole capacity we need to know: W: chip rate (for UMTS 3,840,000 chips per second) R: user data rate (assuming 12,200 kbps for CS-12.2k) f: other-cell to in-cell interference ratio (assuming 65%) EbNo: Eb/No requirement (assuming 5dB) AF: Activity factor (assuming 50%) Pole Capacity = (W/R) / ((1+f) * AF * 10^(EbNo/10)) = 120.6 To calculate the downlink pole capacity we also need to know: α: downlink channels orthogonality factor (assuming 55%) Pole Capacity = (W/R) / ((1- α +f) * 10^(EbNo/10)) = 64.06

< !--[if !supportLists]-->28. What is typical pole capacity for CS-12.2, PS-64, PS-128 and PS-384? With same assumptions as above:

< !--[if !supportLists]--> CS-12.2k: 120.6 (UL), 64.1 (DL). < !--[if !supportLists]--> PS-64k: 34.8 (UL), 12.8(DL). < !--[if !supportLists]--> PS-128k: 16.2 (UL), 8.4 (DL). < !--[if !supportLists]--> PS-384k: 16.2 (UL), 2.8 (DL). PS-384k has only 128k on the uplink, therefore the uplink capacity is the same for both.

< !--[if !supportLists]-->29. How many types of handovers are there in UMTS?

Soft handover, softer handover, inter-frequency handover, inter-RAT handover, inter-RAT cell change (UE moving out of UMTS coverage into GSM/GPRS/EGDGE coverage).

< !--[if !supportLists]-->30. What is soft handover and softer handover? < !--[if !supportLists]--> Soft handover: when a UE is connected to cells owned by different NodeB.

< !--[if !supportLists]--> Softer handover: when a UE is connected to cells owned by the same NodeB.

< !--[if !supportLists]-->31. How does soft/softer handover work? < !--[if !supportLists]--> Soft/softer handover downlink: UE rake receiver performs maximum ratio combining, i.e. UE combines multi-path signals and form a stronger signal.

< !--[if !supportLists]--> Soft handover uplink: RNC performs selection combining, i.e. RNC selects the better signal coming from multiple NodeB.

< !--[if !supportLists]--> Softer handover uplink: NodeB performs maximum ratio combining, i.e. NodeB rake receiver combines signals from different paths and forms a stronger signal.

32. Why is there “soft handover gain”? Soft handover gain comes from the following:

< !--[if !supportLists]--> Macro diversity gain over slow fading. < !--[if !supportLists]--> Micro diversity gain over fast fading. < !--[if !supportLists]--> Downlink load sharing over multiple RF links. By maintaining multiple links each link could transmit at a lower power, resulting in lower interference therefore a gain.

< !--[if !supportLists]-->33. Brief describe the advantages and disadvantages of soft handover? Advantages:

< !--[if !supportLists]--> Overcome fading through macro diversity. < !--[if !supportLists]--> Reduced Node B power which in turn decreases interference and increases capacity.

< !--[if !supportLists]--> Reduced UE power (up 4dB), decreasing interference and increasing battery life. Disadvantages:

< !--[if !supportLists]--> UE using several radio links requires more channelization codes, and more resources on the Iub and Iur interfaces.

< !--[if !supportLists]-->34. What are fast fading and slow fading? Fast fading is also called multi-path fading, as a result of multi-path propagation. When multi-path signals arriving at a UE, the constructive and destructive phases create a variation in signal strength. Slow fading is also called shadowing. When a UE moves away from a cell the signal strength drops down slowly.

< !--[if !supportLists]-->35. What are fast fading margin and slow fading margin? To factor in the fast fading and slow fading, we need to have a margin in the link budget and they are called fast fading margin and slow fading margin. In link budget, the fast fading margin is usually set to 2-3; slow fading margin is set to 7-10.

< !--[if !supportLists]-->36. What is a typical soft handover gain in your link budget?

 CS-12.2k: 3dB (UL), 2dB (DL). < !--[if !supportLists]--> PS-64k: 1dB (UL), 0dB (DL). < !--[if !supportLists]--> PS-128k: 1dB (UL), 0dB (DL). < !--[if !supportLists]--> PS-384k: 1dB (UL), 0dB (DL). < !--[if !supportLists]-->37. What is the percentage in time a UE is expected to be in soft or softer handover? Typically a UE should be in soft handover mode at no more than 35 to 40% of the time; in softer handover mode at about 5% of the time.

< !--[if !supportLists]-->38. What is a typical EiRP? The EiRP depends NodeB transmit power, cable and connector loss and antenna gain. With a sample system of 43dBm transmit power, a 3dB cable and connector loss and a 17dBi antenna gain, the EiRP = 43 – 3 + 17 = 57dBm.

< !--[if !supportLists]-->39. How much power usually a NodeB is allocated to control channels? The power allocated to control channels may depend on equipment vendor recommendation. Typically no more than 20% of the total NodeB power is allocated to control channels, including CPICH. However, if HSDPA is deployed on the same carrier then the total power allocated to control channel may go up to 25 to 30% because of the additional HSDPA control channels required.

< !--[if !supportLists]-->40. What is a typical CPICH power? CPICH power typically takes about 10% of the total NodeB power. For a 20W (43dBm) NodeB, CPICH is around 2W (33dBm). In urban areas where in-building coverage is taken care of by in-building installations, the CPICH may sometimes go as low as 5% because:

< !--[if !supportLists]--> The coverage area is small since users are close to the site, and < !--[if !supportLists]--> More power can be allocated to traffic channels. < !--[if !supportLists]-->41. How much is your HSDPA (max) link power? HSDPA link power is typically 4 to 5dB below the maximum NodeB maximum output power. For example, for 43dBm maximum NodeB power the HSDPA link power is 39dBm.

< !--[if !supportLists]-->42. Consider downlink only, what are the major components in calculating maximum path loss, starting from NodeB?

< !--[if !supportLists]--> NodeB CPICH transmit power. < !--[if !supportLists]--> Jumper and feeder connector loss. < !--[if !supportLists]--> Antenna gain. < !--[if !supportLists]--> Over-the-air loss. < !--[if !supportLists]--> Building / vehicle penetration loss. < !--[if !supportLists]--> Body loss. < !--[if !supportLists]--> Etc. < !--[if !supportLists]-->43. What is maximum path-loss? The maximum path-loss is how much signal is allowed to drop from a transmitter to a receiver and maintains as good signal.

< !--[if !supportLists]-->44. Simple link budget: with a 30dBm CPICH and a -100dBm UE sensitivity, ignoring anything in between, what is the maximum path loss? 30 – (–100) = 30 + 100 = 130dB.

< !--[if !supportLists]-->45. Suppose I have a maximum path-loss of 130dBm, what is the new path-loss if a 5dB body loss is added? 125dB.

< !--[if !supportLists]-->46. What is channelization code? Channelization codes are orthogonal codes used to spread the signal and hence provides channel separation, that is, channelization codes are used to separate channels from a cell.

< !--[if !supportLists]-->47. How many channelization codes are available? The number of channelization codes available is dependent on the length of code. In the uplink the length is defined as between 4 and 256. In the downlink the length is defined as between 4 and 512.

< !--[if !supportLists]-->48. Are channelization codes mutually orthogonal? If so, why is “Orthogonality Factor” required in the link budget? Yes, channelization codes are mutually orthogonal. Nonetheless, due to multi-path with variable time delay, channels from the same cell are no longer perfectly orthogonal and may interfere with each other. A “Downlink Orthogonality Factor”, typically 50-60%, is therefore needed in the link budget to account for the interference – and hence reduces pole capacity.

< !--[if !supportLists]-->49. What is scrambling code? How many scrambling codes there are? Scrambling codes are used to separate cells and UEs from each other, that is, each cell or UE should have a unique scrambling code. There are 512 scrambling codes on the downlink and millions on the uplink.

< !--[if !supportLists]-->50. What is scrambling “code group”? The 512 scrambling codes are divided into 64 code groups – each code group has 8 scrambling codes. Code group i (i = 0 to 63) has codes from i*8 to (i+1)*8-1, i.e. (0-7) (8-15)…(504-511).

< !--[if !supportLists]-->51. Do you divide scrambling code groups into subgroups? Please give an example. Yes, we divide the 64 code groups into subgroups:

< !--[if !supportLists]--> Macro layer group: 24 code groups reserved for macro (outdoor) sites.

< !--[if !supportLists]--> Micro layer group: 16 code groups reserved for micro (inbuilding) sites.

< !--[if !supportLists]--> Expansion group: 24 code groups reserved for future expansion sites.

< !--[if !supportLists]-->52. Which service usually needs higher power, CS or PS? Consider downlink and take CS-12.2 and PS-384k for example. The processing gain is 25 for CS-12.2 and 10 for PS-384. The Eb/No requirement is 7 for CS-12.2 and 5 for PS-384. Therefore the power requirement is higher for CS-12.2 than PS-384.

< !--[if !supportLists]-->53. What is Eb/No requirement for HSDPA? The Eb/No requirement for HSDPA varies with user bit rate (data rate), typically 2 for 768kbps and 5 for 2Mbps.

< !--[if !supportLists]-->54. What is “noise rise”? What does a higher noise rise mean in terms of network loading? For every new user added to the service, additional noise is added to the network. That is, each new user causes a “noise rise”. In theory, the “noise rise” is defined as the ratio of total received wideband power to the noise power. Higher “noise rise” value implies more users are allowed on the network, and each user has to transmit higher power to overcome the higher noise level. This means smaller path loss can be tolerated and the cell radius is reduced. To summarize, a higher noise rise means higher capacity and smaller footprint, a lower noise rise means smaller capacity and bigger footprint.

< !--[if !supportLists]-->55. What is “pilot pollution”? Simply speaking, when the number of strong cells exceeds the active set size, there is “pilot pollution” in the area. Typically the active set size is 3, so if there are more than 3 strong cells then there is pilot pollution. Definition of “strong cell”: pilots within the handover window size from the strongest cell. Typical handover window size is between 4 to 6dB. For example, if there are more than 2 cells (besides the strongest cell) within 4dB of the strongest cell then there is pilot pollution.

< !--[if !supportLists]-->56. What is a typical handover window size in your network? A handover window size is usually between 4 to 6dB.

< !--[if !supportLists]-->57. What is “soft handover” and “softer handover”? “Soft handover” is when UE has connection to multiple cells on different NodeB. “Softer handover” is when UE has connection to multiple cells on same NodeB.

In downlink a UE can combine signals from different cells, improving the signal quality. For uplink and soft handover, RNC selects the best signal from different NodeB. For uplink and softer handover, a NodeB combines the signal from different sectors.

< !--[if !supportLists]-->58. During a handover, if one cell sends a power down request and two cells send a power up request, shall the UE power up or power down? Power down. As long as a good link can be maintained it is not necessary to power up in order to maintain multiple links. Maintaining unnecessary multiple links increases noise rise and shall be avoided.

< !--[if !supportLists]-->59. Suppose we are designing a CS network and a PS network, is there a major difference in the design consideration? Server dominance is the key difference. In a CS network we shall limit the number of strong servers in any given area to no more than the active set size to avoid pilot pollution (in the downlink). In a PS network, however, there isn’t soft handover in the downlink so the server dominance is very important – meaning ideally there should be only one dominant server in a given area.

< !--[if !supportLists]-->60. What is the active set size on your network? 3.

< !--[if !supportLists]-->61. How many fingers does a UE rake receiver have? 4.

< !--[if !supportLists]-->62. What is “compressed mode”? Before UE can perform inter-frequency or IRAT handover, it needs to have some time to lock on to the control channel of the other frequency or system and listen to the broadcast information. Certain idle periods are created in radio frames for this purpose and is called “compressed mode”.

< !--[if !supportLists]-->63. Describe the power control schemes in UMTS? < !--[if !supportLists]--> Open loop – for UE to access the network, i.e. used at call setup or initial access to set UE transmit power.

< !--[if !supportLists]--> Closed outer loop: RNC calculates the SIR target and sends the target to NodeB (every 10ms frame).

< !--[if !supportLists]--> Closed inner loop: NodeB sends the TPC bits to UE to increase or decrease the power at 1,500 times a second.

< !--[if !supportLists]-->64. What is the frequency of power control (how fast is power control)?

< !--[if !supportLists]--> Open loop: depends on parameter setting: T300 – time to wait between RRC retries (100ms to 8000 ms, typical 1500ms)

< !--[if !supportLists]--> Closed outer loop: 100 times a second. < !--[if !supportLists]--> Closed inner loop: 1,500 times a second. < !--[if !supportLists]-->65. Briefly describe why open loop power control is needed and how it works?

< !--[if !supportLists]--> When a UE needs to access to the network it uses RACH to begin the process.

< !--[if !supportLists]--> RACH is a shared channel on the uplink used by all UE, therefore may encounter contention (collision) during multiple user access attempts and interfere with each other.

< !--[if !supportLists]--> Each UE must estimate the amount of power to use on the access attempt since no feedback from the NodeB exists as it does on the dedicated channel.

< !--[if !supportLists]--> The purpose of open loop power control is to minimize the chance of collision and minimize the initial UE transmit power to reduce interference to other UE.

ansmit power = Primary_CPICH_Power – CPICH_RSCP + UL_Interferrnce + constant_Value_Cprach

< !--[if !supportLists]--> Instead of sending the whole message, a “test” (preamble) is sent.

< !--[if !supportLists]--> Wait for answer from NodeB. < !--[if !supportLists]--> If no answer from NodeB increase the power. < !--[if !supportLists]--> Try and try until succeed or timeout. < !--[if !supportLists]-->66. What is power control “headroom”? Power control “headroom” is also called “power rise”. In a non-fading channel the UE needs to transmit a certain fixed power. In a fading chennel a UE reacts to power control commands and usually increases the transmit power. The difference between the average power levels of fading and non-fading channels is called “power rise” or “headroom”.

< !--[if !supportLists]-->67. When in 3-way soft handover, if a UE receives power down request from one cell and power up request from the other 2 cells, should the UE power up or down and why? Power down. Maintaining one good link is sufficient to sustain a call and having unnecessary stronger links creates more interference.

< !--[if !supportLists]-->68. Suppose two UE are served by the same cell, the UE with weaker link (poor RF condition) uses more “capacity”, why does this mean? The UE with weaker RF link will require NodeB to transmit higher traffic power in order to reach the UE, resulting in less power for other UE – therefore consumes more “capacity”.

< !--[if !supportLists]-->69. Under what circumstances can a NodeB reach its capacity? What are the capacity limitations? NodeB reaches its maximum transmit power, runs out of its channel elements, uplink noise rise reaches its design target, etc.

< !--[if !supportLists]-->70. What is “cell breathing” and why? The cell coverage shrinks as the loading increases, this is called cell breathing. In the uplink, as more and more UE are served by a cell, each UE needs to transmit higher power to compensate for the uplink noise rise. As a consequence, the UE with weaker link (UE at greater distance) may not have enough power to reach the NodeB – therefore a coverage shrinkage.

In the downlink, the NodeB also needs to transmit higher power as more UE are being served. As a consequence UE with weaker link (greater distance) may not be reachable by the NodeB.

< !--[if !supportLists]-->71. Is UMTS an uplink-limited or downlink-limited system? A UMTS system could be either uplink-limited or downlink-limited depending on the loading. In a lightly loaded system, the UE transmit power sets a coverage limitation therefore it is uplink-limited. In a heavily loaded system, the NodeB transmit power limits the number of UEs it can serve therefore it is downlinklimited.

< !--[if !supportLists]-->72. What is the impact of higher data rate on coverage? Higher data rate has lower processing gain and therefore a NodeB needs to transmit more power to meet the required Eb/No; this means the coverage is smaller for higher data rate.

< !--[if !supportLists]-->73. What is OCNS? OCNS stands for Orthogonal Channel Noise Simulator. It is a simulated network load usually by increasing the noise rise figure in the NodeB.

UTRAN

< !--[if !supportLists]-->74. What are the interfaces between each UTRAN component? Uu: UE to NodeB Iub: NodeB to RNC Iur: RNC to RNC Iu: RNC to MSC

< !--[if !supportLists]-->75. Briefly describe the UE to UTRAN protocol stack (air interface layers). The radio interface is divided into 3 layers:

< !--[if !supportLists]-->1. Physical layer (Layer 1, L1): used to transmit data over the air, responsible for channel coding, interleaving, repetition, modulation, power control, macro-diversity combining.

< !--[if !supportLists]-->2. Link layer (L2): is split into 2 sub-layers – Medium Access Control (MAC) and Radio Link Control (RLC).

< !--[if !supportLists]--> MAC: responsible for multiplexing data from multiple applications onto physical channels in preparation for over-the-air transmition.

< !--[if !supportLists]--> RLC: segments the data streams into frames that are small enough to be transmitted over the radio link.

< !--[if !supportLists]-->3. Upper layer (L3): vertically partitioned into 2 planes: control plane for signaling and user plan for bearer traffic.

< !--[if !supportLists]--> RRC (Radio Resource Control) is the control plan protocol: controls the radio resources for the access network. In implementation:

< !--[if !supportLists]-->1. UE has all 3 layers. < !--[if !supportLists]-->2. NodeB has Physical Layer. < !--[if !supportLists]-->3. RNC had MAC layer and RRC layer. < !--[if !supportLists]-->76. Briefly describe UMTS air interface channel types and their functions. There are 3 types of channels across air interface – physical channel, transport channel and logical channel:

< !--[if !supportLists]-->1. Physical Channel: carries data between physical layers of UE and NodeB.

< !--[if !supportLists]-->2. Transport Channel: carries data between physical layer and MAC layer.

< !--[if !supportLists]-->3. Logical Channel: carries data between MAC layer and RRC layer.

< !--[if !supportLists]-->77. Give some examples of Physical, Transport and Logical channels.

< !--[if !supportLists]-->1. Logical Channel: < !--[if !supportLists]--> Control channel: BCCH, PCCH, CCCH, DCCH. < !--[if !supportLists]--> Traffic channel: DTCH, CTCH. < !--[if !supportLists]-->2. Transport Channel: < !--[if !supportLists]--> Common control channel: BCH, FACH, PCH, RACH, CPCH. < !--[if !supportLists]--> Dedicated channel: DCH, DSCH. < !--[if !supportLists]-->3. Physical Channel: < !--[if !supportLists]--> Common control channel: P-CCPCH, S-CCPCH, P-SCH, SSCH, CPICH, AICH, PICH, PDSCH, PRACH, PCPCH, CD/CA-ICH.

< !--[if !supportLists]--> Dedicated channel: DPDCH, DPCCH. < !--[if !supportLists]-->78. What are the RRC operation modes? Idle mode and connected mode.

< !--[if !supportLists]-->79. What are the RRC states? There are 4 RRC States: Cell_DCH, Cell_FACH, URA_PCH and Cell_PCH. URA = UTRAN Registration Area.





< !--[if !supportLists]-->80. What are transparent mode, acknowledged mode and unacknowledged mode?

< !--[if !supportLists]--> Transparent mode corresponds to the lowest service of the RLC layer, no controls and no detection of missing data.

< !--[if !supportLists]--> Unacknowledged mode offers the possibility of segment and concatenate of data but no error correction or retransmission therefore no guarantee of delivery.

< !--[if !supportLists]--> Acknowledged mode offers, in addition to UM mode functions, acknowledgement of transmission, flow control, error correction and retransmission.

< !--[if !supportLists]-->81. Which layer(s) perform ciphering function? RRC – for acknowledged mode (AM) and unacknowledged mode (UM). MAC – for transparent mode (TM).

< !--[if !supportLists]-->82. What is OVSF? Orthogonal Variable Spreading Factor.

< !--[if !supportLists]-->83. How many OVSF code spaces are available? < !--[if !supportLists]--> Total OVSF codes = 256. < !--[if !supportLists]--> Reserved: 1 SF64 for S-CCPCH, 1 SF256 for CPICH, P-CCPCH, PICH and AICH each.

< !--[if !supportLists]--> Total available code space = 256 – 4 (1 SF64) – 4 (4 SF256) = 248.

< !--[if !supportLists]-->84. Can code space limit the cell capacity? Yes, cell capacity can be hard-limited by code space. Take CS-12.2k for example:

< !--[if !supportLists]--> A CS-12.2k bearer needs 1 SF128 code.

< !--[if !supportLists]--> Total available codes for CS-12.2k = 128 – 2 (1 SF64) – 2 (4 SF256) = 124.

< !--[if !supportLists]--> Consider soft-handover factor of 1.8: 124 / 1.8 = 68 uers/cell. < !--[if !supportLists]-->85. Can a user have OVSF code as “1111”? No, because “1111…” (256 times) is used by CPICH.

< !--[if !supportLists]-->86. What are the symbol rates (bits per symbol) for BPSK, QPSK, 8PSK and 16QAM?

< !--[if !supportLists]--> BPSK: 1. < !--[if !supportLists]--> QPSK: 2. < !--[if !supportLists]--> 8PSK: 3. < !--[if !supportLists]--> 16QAM: 4. < !--[if !supportLists]-->87. Briefly describe UMTS frame structure. < !--[if !supportLists]--> UMTS frame duration = 10ms. < !--[if !supportLists]--> Each frame is divided into 15 timeslots. < !--[if !supportLists]--> Each timeslot is divided into 2560 chips. < !--[if !supportLists]--> Therefore 2560 chips/TS * 15 TS/frame * (1000ms/10ms) frame/sec = 3,840,000 chip/sec.

< !--[if !supportLists]-->88. What is cell selection criterion? Cell selection is based on:

< !--[if !supportLists]--> Qmean: the average SIR of the target cell. < !--[if !supportLists]--> Qmin: minimum required SIR. < !--[if !supportLists]--> Pcompensation: a correction value for difference UE classes. S = Qmean - Qmin - Pcompensation

< !--[if !supportLists]--> If S>0 then the cell is a valid candidate. < !--[if !supportLists]--> A UE will camp on the cell with the highest S. < !--[if !supportLists]-->89. Briefly describe Capacity Management and its functions: Capacity Management is responsible for the control of the load in the cell. It consists of 3 main functions:

< !--[if !supportLists]--> Dedicated Monitored Resource Handling: tracks utilization of critical resources of the system.

< !--[if !supportLists]--> Admission Control: accepts/refuses admission requests based on the current load on the dedicated monitored resources and the characteristics of the request

< !--[if !supportLists]--> Congestion Control: detects/resolves overload situations

Planning

< !--[if !supportLists]-->90. What are the major 4 KPIs in propagation model tuning and typical acceptable values? The 4 KPIs are standard deviation error, root mean square error, mean error and correlation coefficient. The typical acceptable values are:

< !--[if !supportLists]--> Standard deviation error: the smaller the better, usually 7 to 9dB.

< !--[if !supportLists]--> Mean error: the smaller the better, usually 2 to3. < !--[if !supportLists]--> Root mean square error: the smaller the better, usually < !--[if !supportLists]--> Correlation coefficient: the larger the better, usually 70% to 90%.

< !--[if !supportLists]-->91. What is the minimum number of bins required for a certain propagation model? The more bins the more likely to come up with a good model. Usually a minimum of 2,000 bines is considered acceptable, but sometimes as low as 500 bins may be accepted.

< !--[if !supportLists]-->92. How many scrambling codes are there? There are 512 scrambling codes in the downlink and 16,777,216 codes in the uplink.

< !--[if !supportLists]-->93. How many scrambling code groups are there for downlink? There are 64 code groups, each group has 8 scrambling codes.

< !--[if !supportLists]-->94. Can we assign same scrambling codes to sister sectors (sectors on same site)? No, because scrambling code on the downlink is used for cell identity. As a requirement, scrambling codes have to maintain a safe separation to avoid interference.

< !--[if !supportLists]-->95. Are scrambling codes orthogonal? No, scrambling codes are not orthogonal since they are not synchronized at each receiver. They are pseudo random sequences of codes.

< !--[if !supportLists]-->96. Can we assign scrambling codes 1, 2 and 3 to sister sectors? Yes.

< !--[if !supportLists]-->97. In IS-95 we have a PN reuse factor (PN step size) and therefore cannot use all 512 PN codes, why isn’t it necessary for UMTS scrambling codes?

Because IS-95 is a synchronized network, different PN codes have the same code sequence with a time shift, therefore we need to maintain a certain PN step size to avoid multi-path problem. For example, if two sectors in the neighborhood have a small PN separation then signal arriving from cell A may run into the time domain of cell B, causing interference. UMTS, on the other hand, is not a synchronized network and all scrambling codes are mutually orthogonal so no need to maintain a step size.

< !--[if !supportLists]-->98. What are coverage thresholds in your UMTS design and why? The coverage thresholds are based on UE sensitivity, fading and penetration loss. Assuming UE sensitivity of -110dBm, fade margin of 5dB:

< !--[if !supportLists]--> Outdoor: -110dBm sensitivity + 5dB fade margin = -105dBm. < !--[if !supportLists]--> In-vehicle: -110dBm + 5dB + 8dB in-vehicle penetration loss = -97dBm.

< !--[if !supportLists]--> In-building: -110dBm + 5dB + 15dB in-building penetration loss = -90dBm.

< !--[if !supportLists]-->99. What is the Ec/Io target in your design? The Ec/Io target typically is between -12 to -14dB. However, if a network is designed for data then the Ec/Io target could go higher to around -10dB because server dominance is more critical for a data network – since there isn’t software in the downlink.

< !--[if !supportLists]-->100. What is“Monte Carlo simulation”? Since UMTS coverage is dependent on the loading, static coverage and quality analysis (RSCP and Ec/Io) represents the network performance in no-load condition. Monte Carlo simulation is therefore used to illustrate network performance under simulated loading consition.

< !--[if !supportLists]-->101. What is the key difference between a static analysis and a Monte Carlo simulation? Static analysis can only show RSCP and Ec/Io in no-load condition. Monte Carlo simulation not only can show RSCP and Ec/Io in simulated loading condition but also can show many more others: mean served, cell loading, uplink and downlink capacity limits reached, etc.

< !--[if !supportLists]-->102. What should be run first (what information should be ready and loaded) before running a Monte Carlo simulation? Before running Monte Carlo simulation, the following should be completed or in place.

< !--[if !supportLists]--> Run prediction. < !--[if !supportLists]--> Spread the traffic. < !--[if !supportLists]--> Define terminal types. < !--[if !supportLists]-->103. How many snap shots and iteration do you usually have when running Monte Carlo simulation? (Depend on software tool recommendations).

< !--[if !supportLists]-->104. What are the design KPI’s?

(RSCP, Ec/Io, mean served, soft handover ratio…)

< !--[if !supportLists]-->105. What plots do you usually check after running Monte Carlo for trouble spots? (RSCP, Ec/Io, service probability, reasons for failure…)

< !--[if !supportLists]-->106. What are the typical reasons of failure in Monte Carlo simulation?

< !--[if !supportLists]--> Downlink Eb/No failure (Capacity). < !--[if !supportLists]--> Downlink Eb/No failure (Range). < !--[if !supportLists]--> Uplink Eb/No failure. < !--[if !supportLists]--> Low pilot SIR. < !--[if !supportLists]--> Noise rise limit reached. < !--[if !supportLists]--> Etc. < !--[if !supportLists]-->107. What does“traffic spread” mean? “Traffic spread” means spreading traffic (number of terminals) in a cell coverage area.

< !--[if !supportLists]-->108. Do you use live traffic or even-load traffic in your design? (Depends). Optimization

< !--[if !supportLists]-->109. What are the optimization tools you use? Drive test, analysis, others?

< !--[if !supportLists]-->110. Are System Information Blocks (SIB) transmitted all the time? No, system information block is multiplexed with synchronization channel. Synchronization channel occupies the first time slot (TS) and SIB occupies the other 9 time slots.

< !--[if !supportLists]-->111. How does UE camp (synchronize) to a NodeB? < !--[if !supportLists]-->1. UE uses the primary synchronization channel (P-SCH) for slot alignment (TS synchronization).

< !--[if !supportLists]-->2. After aligning to NodeB time slot, UE then uses secondary synchronization channel (S-SCH) to obtain frame synchronization and scrambling code group identification.

< !--[if !supportLists]-->3. UE then uses scrambling code ID to obtain CPICH, thus camping to a NodeB.

< !--[if !supportLists]-->112. What could be the cause of soft handover failure?

< !--[if !supportLists]--> UE issue. < !--[if !supportLists]--> Resource unavailable at target NodeB. < !--[if !supportLists]--> Inadequate SHO threshold defined. < !--[if !supportLists]--> Etc. < !--[if !supportLists]-->113. What are the three sets in handover? The 3 sets in handover are:

< !--[if !supportLists]--> Active set – the list of cells which are in soft handover with UE. < !--[if !supportLists]--> Monitored set –the list of cells not in active set but RNC has told UE to monitor.

< !--[if !supportLists]--> Detected set –list of cells detected by the UE but not configured in the neighbor list.

< !--[if !supportLists]-->114. What are the major differences between GSM and UMTS handover decision? GSM:

< !--[if !supportLists]--> Time-based mobile measures of RxLev and RxQual – mobile sends measurement report every SACH period (480ms).

< !--[if !supportLists]--> BSC instructs mobile to handover based on these reports. UMTS:

< !--[if !supportLists]--> Event-triggered reporting – UE sends a measurement report only on certain event “triggers”.

< !--[if !supportLists]--> UE plays more part in the handover decision. < !--[if !supportLists]-->115. What are the events 1a, 1b, 1c, etc.? < !--[if !supportLists]--> e1a – a Primary CPICH enters the reporting range, i.e. add a cell to active set.

< !--[if !supportLists]--> e1b – a primary CPICH leaves the reporting range, i.e. removed a cell from active set.

< !--[if !supportLists]--> e1c – a non-active primary CPICH becomes better than an active primary CPICH, i.e. replace a cell.

< !--[if !supportLists]--> e1d: change of best cell. < !--[if !supportLists]--> e1e: a Primary CPICH becomes better than an absolute threshold.

< !--[if !supportLists]--> e1f: a Primary CPICH becomes worse than an absolute threshold.

< !--[if !supportLists]-->116. What are event 2a-2d and 3a-3d?

Events 2a-2d are for inter-frequency handover measurements and events 3a-3d are for IRAT handover measurements.

< !--[if !supportLists]--> e3a: the UMTS cell quality has moved below a threshold and a GSM cell quality had moved above a threshold.

< !--[if !supportLists]--> e3b: the GSM cell quality has moved below a threshold. < !--[if !supportLists]--> e3c: the GSM cell quality has moved above a threshold. < !--[if !supportLists]--> e3d: there was a change in the order of best GSM cell list. < !--[if !supportLists]-->117. What may happen when there’s a missing neighbor or an incorrect neighbor?

< !--[if !supportLists]--> Access failure and handover failure: may attempt to access to a wrong scrambling code.

< !--[if !supportLists]--> Dropped call: UE not aware of a strong scrambling code, strong interference.

< !--[if !supportLists]--> Poor data throughput. < !--[if !supportLists]--> Poor voice quality. < !--[if !supportLists]--> Etc. < !--[if !supportLists]-->118. What can we try to improve when access failure is high? When access failure is high we can try the following to improve RACH performance:

< !--[if !supportLists]--> Increase maximum UE transmit power allowed: Max_allowed_UL_TX_Power.

< !--[if !supportLists]--> Increase power quickly: power_Offset_P0. < !--[if !supportLists]--> Increase number of preambles sent in a given preamble cycle: preamble_Retrans_Max.

< !--[if !supportLists]--> Increase the number of preamble cycles: max_Preamble_Cycle. < !--[if !supportLists]--> Increase number of RRC Connection Request retries: N300. < !--[if !supportLists]-->119. What are the conditions you typically set to trigger IRAT handover? RSCP and Ec/Io are used to trigger IRAT handover:

< !--[if !supportLists]--> RSCP ≤ -100dBm. < !--[if !supportLists]--> Ec/Io ≤ -16dBm. < !--[if !supportLists]-->120. What are the typical KPIs you use to measure a network and what criteria?

< !--[if !supportLists]--> Access failure rate (≤ 2%).

< !--[if !supportLists]--> Call setup time (CS: over 95% of the time < 6-second for mobileto-PSTN, 9-second for mobile-mobile. PS: over 95% of the time< 5-second).

< !--[if !supportLists]--> Dropped call rate (≤ 2%). < !--[if !supportLists]--> BLER: over 95% of the blocks ≤ 2%. < !--[if !supportLists]--> Average DL/UL throughput for PSD: 210kbps for loaded, 240kbps for unloaded.

< !--[if !supportLists]-->121. What is the typical UE transmit power? Varies - most of the time below 0dBm.

< !--[if !supportLists]-->122. Have your used Ericsson TEMS? If so: < !--[if !supportLists]--> Do you know how to create command sequence? < !--[if !supportLists]--> What are the call sequences you typically have? CS long call, CS short call, PSD call, etc.

< !--[if !supportLists]--> What are the typical commands you have for CS and PS call? < !--[if !supportLists]--> Do you regularly stop and restart a new log file? Why and when to stop and start a new file?

< !--[if !supportLists]--> How do you stop a log file? Stop command sequence first, wait and make sure all equipment are in idle mode before stop logging.

< !--[if !supportLists]-->123. Did you work on neighbor prioritization? < !--[if !supportLists]-->124. What is the typical event sequence of IRAT Handover from 3G to 2G

< !--[if !supportLists]--> Event 2d –entering into compressed mode – measurement of 2G candidates – Event 3a –Verification of 2G resources – Handover from UTRAN Command from 3G RNC to UE

< !--[if !supportLists]-->125. What are the possible causes for an IRAT Failure?

< !--[if !supportLists]--> Missing 2G relations < !--[if !supportLists]--> Non availability of 2G Resources < !--[if !supportLists]--> Poor 2G Coverage < !--[if !supportLists]--> Missing 3G Relations

< !--[if !supportLists]-->126. What is Paging Success Ratio? What is the typical PSR that you have seen in a UMTS network?

< !--[if !supportLists]--> PSR – Paging Responses to the Paging Attempts < !--[if !supportLists]--> About 90%

< !--[if !supportLists]-->127. What are the possible causes for a lower PSR?

< !--[if !supportLists]--> Non-continuous RF Coverage – UE going in and out of coverage area frequently

< !--[if !supportLists]--> Very High‘Periodic Location Update Timer’ – Keeping UEs in VLR long time after it moved out of coverage

< !--[if !supportLists]--> Lower Paging Channel Power < !--[if !supportLists]--> Access Channel Parameter Issues < !--[if !supportLists]--> Delayed Location Update when crossing the LA / CN Boundaries

< !--[if !supportLists]-->128. What are the possible causes for a Drop Call on a UMTS network?

< !--[if !supportLists]--> Poor Coverage (DL / UL) < !--[if !supportLists]--> Pilot Pollution / Pilot Spillover < !--[if !supportLists]--> Missing Neighbor < !--[if !supportLists]--> SC Collisions < !--[if !supportLists]--> Delayed Handovers < !--[if !supportLists]--> No resource availability (Congestion) for Hand in < !--[if !supportLists]--> Loss of Synchronization < !--[if !supportLists]--> Fast Fading < !--[if !supportLists]--> Delayed IRAT Triggers < !--[if !supportLists]--> Hardware Issues < !--[if !supportLists]--> External Interference

< !--[if !supportLists]-->129. A UE is served by 2 or 3 SC in AS. It is identifying a SC from 3rd tier, Stronger and meets the criteria for Event1a or Event1c. But SHO did not happen because of missing neighbor relations? How do you optimize this issue?

< !--[if !supportLists]--> Study the Pilot spillover from the 3rd Tier SC and control its coverage

< !--[if !supportLists]--> Even after controlling the coverage, if the spillover is there, Add the neighbor.

< !--[if !supportLists]-->130. A UE is served by 2 SC in AS, a SC is coming in to Monitored Set and Event1a is triggered. But UE is not receiving Active Set Update from NodeB and the call drops. What could be possible causes for this drop?

< !--[if !supportLists]--> Delayed Handover < !--[if !supportLists]--> Loss of Synchronization < !--[if !supportLists]--> Fast Fading < !--[if !supportLists]--> Pilot Pollution / Spillover issues

< !--[if !supportLists]-->131. What is Hard Handover in UMTS? When will it happen?

< !--[if !supportLists]--> Hard Handover in UMTS is a break before make type Handover < !--[if !supportLists]--> It can happen in the inter RNC boundaries where there is no Iur link.

< !--[if !supportLists]-->132. What is the typical Call Setup Time for a 3G UE to 3G UE Call? What are the possible RF related causes for a delayed CST in this type of call?

< !--[if !supportLists]--> 6 to 9 seconds < !--[if !supportLists]--> Multiple RRC Attempts (UE is on poor coverage – need more than Access Attempt)

< !--[if !supportLists]--> Delayed Page Responses < !--[if !supportLists]--> High Load on Paging and/or Access Channel < !--[if !supportLists]--> Paging / Access Parameters

< !--[if !supportLists]-->133. What is Soft Handover Overhead? What is the typical value in UMTS network?

< !--[if !supportLists]--> Soft Handover Overhead is calculated in two ways. 1) Average Active Set Size – Total Traffic / Primary Traffic. 2) Secondary / Total Traffic

< !--[if !supportLists]--> Typical Values are like 1.7 (Avg Active Set Size) or 35% (Secondary / Total )

< !--[if !supportLists]-->134. What will happen to the Soft Handover Overhead when you apply OCNS on the network? And Why?

< !--[if !supportLists]--> With OCNS, the interference (load) increases. This leads to reduction in Ec/Io of a Pilot, which reduces the pilot spillovers. Reduction in Pilot Spillover will reduce the Soft Handover Overhead.

< !--[if !supportLists]-->135. What are the possible causes for an Access Failure in UMTS?

< !--[if !supportLists]--> Missing Neighbors < !--[if !supportLists]--> Poor Coverage < !--[if !supportLists]--> Pilot Pollution / Spillover < !--[if !supportLists]--> Poor Cell Reselection < !--[if !supportLists]--> Core Network Issues < !--[if !supportLists]--> Non –availability of resources. Admission Control denies < !--[if !supportLists]--> Hardware Issues < !--[if !supportLists]--> Improper RACH Parameters < !--[if !supportLists]--> External Interference

< !--[if !supportLists]-->136. (FOR ERICSSON EXPERIENCED) What is RTWP? What is the significance of it?

< !--[if !supportLists]--> Received Total Wide-band Power

< !--[if !supportLists]--> It gives the Total Uplink Power (Interference) level received at NodeB

< !--[if !supportLists]-->137. (FOR ERICSSON EXPERIENCED) What is the System Reference Point at which all the Power Levels are measured in Ericsson NodeB?

< !--[if !supportLists]--> System Ref Point for E/// NodeB is at the output of TMA (Between TMA and Antenna)

< !--[if !supportLists]-->138. What are the typical values for ‘reportingrange1a’ and ‘reportingrange1b’?

< !--[if !supportLists]--> 3 dB and 5 dB respectively.

< !--[if !supportLists]-->139. What will be the impact when you change ‘reportingrange1a’ from 3 to 4 dB and‘timetotrigger1a’ 100 to 320 ms, without changing any other parameters?

< !--[if !supportLists]--> Reduction in number of Event1a < !--[if !supportLists]--> Delayed Event1a trigger < !--[if !supportLists]--> Reduction in Average Active Set Size < !--[if !supportLists]--> Delay in Event1a could increase DL interference, which could lead to a drop call or increase in Average Power Per User (reduction in cell capacity)

< !--[if !supportLists]-->140. What is Admission Control?

< !--[if !supportLists]--> Admission Control is an algorithm which controls the Resource Allocation for a new call and additional resource allocation for an existing call. Incase, if a cell is heavily a loaded and enough resources in terms of power, codes or CEs are not available, admission control denies permission for the additional resource requirement.

< !--[if !supportLists]-->141. What is Congestion Control?

< !--[if !supportLists]--> Congestion Control monitors the dynamic utilization of specific cell resources and insures that overload conditions do not occur. If overload conditions do occur, Congestion Control will immediately restrict Admission Control from granting additional resources. In addition, Congestion Control will attempt to resolve the congestion by either down switching, or terminating existing users. Once the congestion is corrected, the congestion resolution actions will cease, and Admission Control will be enabled.



< !--[if !supportLists]-->142. What is the maximum number of Channelization Codes that can be allocated for HS, as per 3GPP standard?

< !--[if !supportLists]--> 15 codes of SF 16. < !--[if !supportLists]--> < !--[if !supportLists]-->143. What is‘Code Multiplexing’ in HSDPA?

< !--[if !supportLists]--> Sharing the HS Channelization Codes among more than one HS users within the 2ms TTI period.

< !--[if !supportLists]-->144. (FOR ERICSSON EXPERIENCED) In Ericsson System, how is the Power allocated for HSDPA>

< !--[if !supportLists]--> Power unutilized by R99 PS, CS and Comman Channels, is used for HS (PHS = Pmax - hsPowerMargin - Pnon-HS)

< !--[if !supportLists]-->145. What are Events that can trigger the HSDPA Cell Change?

< !--[if !supportLists]--> Event 1d HS –Change of Best Cell in the Active Set < !--[if !supportLists]--> Event 1b or Event 1c – Removal of the Best Cell from the Active Set

< !--[if !supportLists]-->146. How is typically the Call Setup Time of a CSV call calculated in UMTS using L3 messages?

< !--[if !supportLists]--> CST is calculated as the time difference between ‘Alerting’ and the first RRC Connection Request (Call Initiation) messages.

GSM,WCDMA,RF ,RF Optimization Interview Objective Question Level 2-3 NPO Questions (RF Planning & Optimisation Engg) In the following questions, please select one alternative which you think is the best answer for the particular question. Q1. SMS broadcast is done over which channel 1. SDCCH 2. BCCH 3. TCH 4. A & C

Q2. The parameter number of Slot Spread Trans (SLO)(BTS) is used to allocate a number of CCCH blocks for . a) Paging Channel (PCH) b) Random Access Channel (RACH) c) Access Grant Channel (AGCH) d) Traffic Channel Q3. Which of the following comment is true? a) MAIO step is used to avoid intra-cell interference where as HSN is used to avoid inter-cell interference b) HSN is used to avoid intra-cell interference where as MAIO step is used to avoid inter-cell interference c) Both MAIO step and HSN are used to avoid intra-cell interference. d) Both MAIO step and HSN are used to avoid inter-cell interference Q4. Timer T200 is related with which KPI a) SDCCH Completion rate b) Paging success rate c) TCH assignment success rate d) All of the above Q5. Which parameter defines how often paging messages are sent to MS? a) No of Multi-frames between Paging (MFR) b) Max No of Retransmission (RET) c) No of Slots Spread Transmission (SLO) d) No of Blocks for Access Grant (AG) Q6. Which parameter is used as a margin to prevent ping-pong location updates? a) PLMN-Permitted (PLMN) b) Rx Level Access Minimum (RXP) c) Cell Reselect Hysteresys (HYS) d) Handover Margin Level (LMRG) Q7. Which Parameter describes the minimum received field strength required by an MS to get any service from the network in that cell in Idle mode? a) PLMN-Permitted (PLMN) b) Rx Level Access Minimum (RXP) c) Cell Reselect Hysteresis (HYS) d) Direct Access Level (DAL)

Q8. When is location updates carried out? a) Every time an MS changes its location area under one MSC. b) Every time an MS changes between two different MSCs c) On a periodic basis set by a timer d) All of the above

Q9. Increasing Radio Link Time Out (RLT) from 16 to 24 will improve following KPI a) SDCCH Completion rate b) TCH Completion rate c) Paging Success rate d) All of the above

Q10. If a cell is having TCH congestion, which of the following is true? a) It is having TCH blocking b) It may have TCH blocking. c) It is having TCH Drop. d) All of the above Q11. Which of the parameter is set to zero for cyclic hopping? a) BTS Hopping (HOP) b) Hopping sequence number (HSN) c) MAIO Offset (MAIO) d) All of the above Q12. What is directed retry? a) A feature that allows a recovery system to restore a BCCH to its original TRX after fault has been eliminated. b) It is designed to control the traffic load of a frequency hopping radio network in which frequencies are reused tightly. c) It is used in call set up to assign a TCH to an MS from a cell outside the serving cell due to TCH congestion d) None of the above

Q13. Which of the following is measured as BER?

a) Received Signal Quality (RX QUAL) b) Speech Quality Index (SQI) c) Voice Quality d) All of above Q14. Polarization is characterized by 1. Direction of Magnetic Field 2. Direction of Electric Field 3. Direction of Electromagnetic Field 4. None of Above. Q15 Which one is correct for TMA, TMB and Repeater? 1. Amplifies U/L, Amplifies D/L, and Amplifies both. 2. Amplifies D/L, Amplifies U/L, and Amplifies both. 3. Amplifies U/L, Amplifies D/L, and Amplifies U/L. 4. Amplifies U/L, Amplifies D/L, and Amplifies D/L.

Q16 Define Beam width of Antenna? 1. Angular distance between the points on two opposite sides of the peak direction where the radiation intensity drops to the 1/2 of the peak intensity.

2. Angular distance between the points on two opposite sides of the peak direction where the radiation intensity drops to the 1/3 of the peak intensity.

3. Angular distance between the points on two opposite sides of the peak direction where the radiation intensity drops to the 1/4 of the peak intensity.

4. Angular distance between the points on two opposite sides of the peak direction where the radiation intensity drops to the 1/8 of the peak intensity.

Q17 From which technique we cancel the effect of Rayleigh Fading? 1. Antenna Hoping. 2. Frequency Hoping. 3. Antenna Diversity. 4. MAIO. Q18 If HLR=5 Million subs, VLR/HLR=0.7,mErl/Sub=30.Then how much Capacity is required to cater the subscriber in RF for 70% utilized Network. 1. 150 K Erl 2. 300 K Erl 3. 135 K Erl 4. 165 K Erl Q19 Electrical Tilt antenna limits coverage through? 1. Tilting of Dipoles. 2. Inserting Phase Shift. 3. Inserting attenuation. 4. None of the above. Q20 Which Antenna has the highest front to back Ratio? 1. Loop 2. Yagi

3. Dipole 4. Parabolic

Q21 Select relation between forward power and Reflected Power if load is not connected? 1. VSWR=1 2. VSWR=∞ 3. VSWR=0 4. VSWR=1/2 Q22 What is the difference between splitter and coupler? 1. Even Distribution of Power in coupler and uneven distribution in splitter. 2. Uneven Distribution of Power in coupler and even distribution in splitter. 3. Even Distribution of Power in both. 4. Uneven Distribution of Power in both.

Q23. What are mobility management states in GPRS? 1. Idle,Standby,Ready 2. Dedicated,Standby,Ready 3. Idle,Dedicated,Standby 4. None of above Q24. Which modulation is used for EDGE above MCS-4

1. QPSK 2. GMSK 3. 8PSK 4. PSK

Q25. What does SGSN stands for? 1. Serving Gateway Support node 2. Serving GPRS Support node 3. Serving GMSC Support node 4. None of the above

Q26 In dedicated mode, SMS comes on which channel? a) SDCCH. b) SACCH. c) FACCH. d) None of the above. Q27 In Dedicated Mode, MS receives which system info. Messages? 1. System Info 1, 2, 3. 2. System Info 1, 2, 3,4,13. 3. System Info 5, 6. 4. None of the above.

Q28 Freq used in Uplink of Satellite communication is higher while in GSM it is lower. Why? 1. Loss α freq.

2. Loss α 1/freq. 3. Loss α sqr(freq) 4. None of the above. Q29 AMR is used to improve? 1. SQI 2. Downlink quality. 3. Uplink Quality 4. None of the Above. Q30 In Idle Mode, MS receives which system info. Messages? a) System Info 1, 2,3. b) System Info 1, 2, 3,4,13. 3. System Info 5, 6. d) None of the above Q31 The Common Control channel multiframe consists of? 1. 51 time slots. 2. 50 timeslots 3. 4 Time slots 4. 9 Time slots

Q32 Which of the following are true? 1. Type 1 Paging: can address up to 2 mobiles using either IMSI or TMSI. 2. Type 2 Paging: can address up to 3 mobiles, one by IMSI and the other 2 by TMSI.

3. Type 3 Paging: can address up to 4 mobiles using the TMSI only. 4. All of the above.

Q33 In GSM while performing handover 1. The MS breaks connection from source cell and then tunes on the target cell. 2. The MS continues connection from the source, tunes on the target and then releases the source cell. 3. MS gets paging message from the target and replies it on its RACH and gets TCH allocated. 4. MS gets paging message from the target and replies it on its RACH and gets SDCCH allocated. Q34 If E-RACH is used then which of the following is true? 1. GSM range will increase beyond 35Km 2. It will increase no of RACH channels and release congestion on RACH. 3. SDCCH assignment will improve. 4. All above are false. Q35 In dedicated mode the BTS receives handover command on? 1. TCH 2. SDCCH 3. SACCH 4. FACCH Q36 The duration of a single timeslot is?

1. 4.615 ms 2. 1250 ms 3. 0.577 ms 4. 156.25 ms Q37 Modulation used in GSM radio interface is? 1. Phase shift keying (PSK) 2. Gaussian Minimum shift Keying (GMSK) 3. Frequency modulation. 4. 8PSK.

Q38 TIE stands for? 1. Terminal Equipment identifier 2. Transcoder Input Erlang 3. TRX identifier for Edge TRX 4. None of the above Q39 As per GSM Standard in case of frequency hopping the C/I value should be at least? 1. 3 dB 2. 6 dB 3. 9 dB 4. 12 dB

Q40 In inter BSC handover the handover is controlled by? 1. GMSC 2. MSC 3. Source BSC 4. Target BSC

Q41 The maximum no of neighbors that can be defined with a cell is? 1. 8 2. 16 3. 32 4. 64

Q42 The permissible value of VSWR for feeder cable is? 1. < 1.3 2. >1.3 3. > 1 4. <2 Q43 The function of Transcoder is 1. To convert 64 kbps speech channel on A interface to 16 kbps speech channel on Ater Interface and vice versa.

2. To convert 16 kbps speech channel on A interface to 64 kbps speech channel on Ater Interface and vice versa. 3. To convert analogue speech signal from MSC to Digital signal for use of BSC 4. To convert analogue speech signal from BSC to Digital signal for use of MSC Q44 TSC stands for 1. Time Synchronized Channel 2. Temporary subscriber code 3. Transcoder Signaling Controller 4. Training Sequence Code

Q45 If Cell bar is set to “yes” on a cell then 1. It will reject new calls as well as handover calls 2. It will reject new call assignment but will receive calls by Handover 3. It will reject Handover but allow new call to come 4. The BTS will go into locked state.

Q46 DAP stands for 1. Dual Abis pool 2. Dynamic Allocation protocol 3. Dynamic Abis Pool 4. None of the above

Q47 Who can initiate the GPRS detach 1. The MS only 2. The SGSN only 3. Both the MS and the SGSN 4. None of the above

Q48 The mapping of logical name/Host name to IP addresses in the GPRS network is done by 1. Border Gateway 2. SGSN 3. GGSN 4. DNS Q49 Where is the mobility management context established in GPRS 1. In the MSC 2. In the SGSN 3. In the GGSN 4. All of the above

Q50 Which layer uses the functionality of Uplink State Flag (USF)? 1. RLC Layer 2. Physical Layer 3. MAC Layer

4. All of the above Q51 How many TDMA frames are there in a PDCH multiframe? 1. 51 2. 52 3. 26 4. 8 Q52 Which coding scheme does not use Forward Error Correction (FEC)?

1. CS-1 2. CS-2 3. CS-3 4. CS-4 Q53 Which new area is defined in GPRS compared to GSM? 1. Location Area 2. Routing Area 3. Both a and b 4. None of the above

Q54 Which layer is responsible for segmentation and reassembly of LLC PDUs and backward error correction (BEC) procedures? 1. Physical Layer

2. Application Layer 3. RLC Layer 4. MAC Layer

Q55 Which coding scheme has adopted the same coding as used for SDCCH? 1. CS-1 2. CS-2 3. CS-3 4. CS-4 Q56 What is the single timeslot data rate for coding scheme CS-2 1. 7.8 Kbit/s 2. 10.4 Kbit/s 3. 13.4 Kbit/s 4. 21.4 Kbit/s Q57. Combiner works in a) Downlink direction b) Uplink direction c) In both direction d) As a Amplifier

Q58 Number of AMR codec modes used only in FR? 1. 6

2. 4 3. 2 4. 8

Q59 During conference call which channel is used to establish another call1. SACCH 2. SDCCH 3. FACCH 4. TCH

Q60 What is Duplex spacing. 1. Difference between first frequency of Uplink and last frequency of Downlink. 2. Difference between first frequency of Downlink and first frequency of Uplink. 3. Difference between last frequency of Downlink and first frequency of Uplink. 4. None of the above.

Q61 What does MSRN stands for …. 1. Mobile Station Registration Number 2. Mobile System Registration Number 3. Mobile Station Roaming Number 4. Mobile Station Register Number. Q62. If my MCC=404, MNC=05, LAC=100, CI = 14011, then what will be CGI for same??

1. 4040510014011 2. 404056436BB 3. 4040514433273 4. 4040510033273 Q63. Which information is there in Handover Access Command in Layer 3 Message? 1. BCCH & BSIC of Source 2. BCCH & BSIC of Target 3. Handover Reference Value 4. All of above. Q64 What is the use of Immediate Assignment Extended Command? 1. Allocate AGCH for 2 Mobiles 2. Allocate SDCCH for 3 Mobiles 3. Allocate SDCCH for Call and SMS simultaneously. 4. None of Above.

Q65. What is the cause value for normal call release? 1. 16 2. 3 3. 14 4. 45

Q66. Location Update Request falls under which management system? 1. RRM 2. CM 3. CRM 4. MM

Q67. Which system information message contains NCC Permitted Values? 1. SI 6 2. SI 2 3. All of Above. 4. None of Above.

Q68. When timer T3212 expires which process is initiated? 1. Cell Update 2. RAC Update 3. LAC Update 4. Handover Q69. If AMR FR & AMR HR is enabled in network, then what will be the formula for counting GSM FR Traffic with help of EOSFLX KPI Reports ? 1. Total Traffic – AMR FR Traffic 2. Total Traffic – AMR FR Traffic - AMR HR Traffic 3. Total Traffic – GSM HR Traffic – AMR FR Traffic – AMR HR Traffic

4. None of Above.

Q70. By reducing value of RET parameter it will help to improve which KPI? 1. TCH Drop 2. SDCCH Drop 3. HO Success 4. None of above.

Q71. What is the range of AMH TRHO PBGT Margin parameter? 1. -6 to +6, 255 2. -24 to +24, 255 3. -6 to +24, 255 4. +6 to +24, 255

Q72. What is the relation between HO Load Factor and HO Priority Level? 1. Load Factor > Priority Level 2. Load Factor >= Priority Level 3. Load factor < Priority Level 4. Load Factor <=Priority Level

Q73. Which are the basic features helps to distribute traffic in nearby cells? 1. DR 2. IDR 3. AMH

4. All of above

Q74. Using Multi BCF Common BCCH feature operator can expand how many numbers of TRX in one segment without using another BCCH? 1. 16 2. 24 3. 30 4. 36

Q75. While Using Path loss Criterion C2 which parameter should be made “0” so that this particular cell have higher C2 Value even though having poor C1? 1. CRO 2. TEO 3. Penalty Time 4. None of above.

Q76. Common BCCH feature is implemented in network, then which feature will help to access the secondary freq. spectrum directly? 1. DR 2. DADB 3. DADL 4. All of above

Q77. Which types of GSM Reports are generated by Nemo Analyzer? 1. GSM Performance Report 2. GSM Benchmark Report 3. All of above 4. None of above

Q78. What is the range of parameter PMRG? 1. -24to +63 2. -24 to +24 3. -63 to +63 4. 0 to +63

Q79. How many maximum uplink TBF can be there per RTSL? 1. 6 2. 7 3. 8 4. 9 Q80. What should be minimum value of CDED (%) to have 1 RTSL as dedicated GPRS Timeslot considering 2 TRX as GPRS TRX? 1. 0 2. 1 3. 8 4. 10

Q81. What does TRP Value = 3 means? 1. TCH allocation from BCCH TRX for non-amr user and from beyond BCCH TRX for amr USER 2. TCH allocation from beyond BCCH TRX for non-amr user and from BCCH TRX for amr USER 3. All of above 4. None of Above

Q82. How many basic EGPRS MCS Families are there? 1. 1 2. 2 3. 3 4. 4

Q83. Which is / are the main factors affecting the Radio Accessibility for TBF in UL/ DL? 1. Coverage 2. Capacity 3. Interference 4. All of above. Q84. Which parameter setting can help to increase the TBF Retainability? 1. UL Power Control 2. DL Power Control 3. All of above.

4. None of above.

Q85. What should be SDCCH GOS when compared to TCH GOS? 1. SD GOS = TCH GOSDTX 2. SD GOS = 1/2(TCH GOS) 3. SD GOS = 1/4(TCH GOS) 4. SD GOS = 2(TCH GOS) Q86. Which feature/technique is not used to reduce blocking / congestion? 1. Directed Retry 2. Traffic Reason Handover 3. Dynamic SDCCH 4. Intra Cell Handover Q87. Rx Quality = 3 means BER =? 1. 0.2 - 0.4 2. 6.4 - 12.8 3. 1.6 - 3.2 4. 0.8 - 1.6

Q88. Following is false when using Dynamic SDCCH. 1. SDCCH Handover cannot be used. 2. Free TCH is used when SDCCH is required. 3. SDCCH carrying CBCH cannot be used. 4. Every SDCCH request can be fulfilled by Dynamic SDCCH.

Q89. In Link Budget; what has the least importance? 1. GSM Antenna Gain 2. Path Loss 3. Feeder Loss 4. MS Antenna Gain

Q90. When 2 calls are made from different TRXs of same cell having 1*1 RF hopping; what plays important role to neglect C/I? 1. MAL ID 2. HSN 3. MAIO Step 4. MAIO Offset

Q91. Frame loss can be reduced by: 1. Speech Coding 2. Channel Coding 3. Interleaving 4. Burst Formatting Q92. What can be done to overcome combiner loss when cell is upgraded from 2 TRX to 3 TRX? 1. Remove Combiner 2. Air-Combining 3. HOP = OFF 4. TMA Implementation

Q93. What is the Basic feature amongst below: 1. SAIC 2. STIRC 3. AMR Progressive Power Control 4. Freq. Hopping Q94. Out of following channels which one is common channel? 1. AGCH 2. SACCH 3. TCH-FR 4. FACCH Q95. Out of following channels which one is the answer to RACH? 1. SDCCH 2. AGCH 3. FACCH 4. SACCH Q96. In Air-interface TDMA time-slot means how many Seconds? 1. 576.9us 2. 4.615ms 3. 6.12sec 4. 480ms Q97. Which type of antenna is used in MS?

1. Dipole 2. Omni 3. Loop 4. Cross-polar Q98. Choose the correct Erlang Formula? 1. x Erlang= (calls per hour) * (average call duration)/3600 Sec 2. x Erlang= (no. of user)*(3600 sec)/ (calls per hour) 3. x Erlang= (no. of calls)*(no. of user)/ (average call duration) 4. x Erlang= (calls per hour)*(no. of users)/3600 sec Q99. If GOS of an N/W is 3%, what does it mean? 1. 3 out of 100 calls may fails 2. average call duration is 3min 3. at a time 3% of total users can make a call 4. 3% blocking in the N/W is permitted Q100. Which type of message is "Identity Request”? 1. Mobility Management 2. Radio Resource Management 3. Call Control 4. Call related SS message Q101. Paging message type 2 contains. 1. Paging message for 3 mobiles 2. Paging message for 2 mobiles

3. Paging message for 4 mobiles 4. Paging message for >4 mobiles

Q102. Out of following which one is not a part of NSS? 1. Mobility Management 2. Connection Management 3. Radio Resource Management 4. Charging

Q103. In L3 messages, out of following Info messages which one carries Dedicated Mode Information? 1. System Info 2 2. System Info 4 3. System Info 5 4. System Info 13 Q104. Which one out of following is not a part of AMR Codec Modes? 1. 4.6 2. 5.9 3. 7.4 4. 12.2 Q105. Frequency Hopping… 1. Eliminates the problem of fading dips 2. Eliminates the problem of ISI

3. is part of channel coding 4. spreads the problem of fading dips to many mobile stations Q106. ISI is caused by: 1. fading dips 2. the Viterbi equalizer 3. reflection 4. interleaving

Q107. Maximum data throughput / tsl possible incase of GPRS is: X` 1. 18.8kbps 2. 27.2kbps 3. 29.2kbps 4. 21.4kbps Q108. Out of following which element/s in the GSM N/W can not initiate HO? 1. BSC 2. BTS 3. MSC 4. None of Above

Q109. Out of following, which type of antenna has highest directivity? 1. Dipole 2. Helical 3. Log-Periodic

4. Yaagi-Uda Q110. When we say the output power of a Transmitter is 30dBm, how many watts does it mean? 1. 3W 2. 1W 3. 1mW 4. 30mW Q111. Out of following which one is a passive device? 1. Repeater 2. Cross Polar Antenna 3. TMA (Tower Mount Amplifier) 4. TRX Q112. Out of following which can not be observed during Drive-test? 1. Rx Quality 2. Location Update 3. Paging Load 4. GPRS Attach Q113. If a cell is EDGE capable, how much Downlink Throughput can we guarantee to customer? 1. 59.2kbps 2. 473.6kbps 3. 236.8kbps 4. can't guarantee

Q114. How many blocks of AGCH are reserved in non combined mode? 1. 1-7 2. 0-2 3. 0-7 4. None of Above. Q115. What are the contents of authentication triplets? 1. A3,A5,A8 2. SRES,RAND,Kc 3. RAND,A3,A8 4. SRES,Kc,A8

Q116 Frequency hopping in a network: 1. May or may not be implemented 2. Does not provide optimal gain if the hopping frequencies are less than 4 3. Both above are correct. 4. None of the above. Q117 .Which of the following functions is not done by SDCCH CHANNEL: 1. Authentication 2. Transmission of short messages

3. Adaptive power control information from BTS to MS only 4. Assignment of traffic channel to MS. Q118 How many TS can be used at the most with HSCSD? 1. 2 2. 4 3. 6 4. 8 Q119 What should be the value of C/I when you are in hopping mode? 1. Above 9 2. Above 12 3. Less than 9 4. All of the above are correct Q120 Which value of level and quality should be considered for analysis in a DT log 1. Full 2. Sub 3. Both 4. None of the above is correct. Q121 What are the coding schemes observerd in UL/ DL after implementing EDGE in your Network: 1. CS1-CS4 2. MCS1-MCS6

3. MCS5-MCS9 4. MCS1-MCS9

Q122 What does DAP stand for? 1. Dynamic Abis Pool 2. Dynamic Access Pool 3. Dynamic Access Protocol 4. None of the above

Q123 How many codec’s can be defined for AMR HR 1. 5 2. 2 3. 6 4. 4 Q124 How many TRX’s can be accommodated max on a single E1 where DAP pool is assigned for 4 TS in a Ultra site 1. 12 2. 16 3. 18 4. 24 Q125 How much traffic will be offered by a sector having 4 TRX with GOS of 2%

1. 24Erlangs 2. 21.03Erlangs 3. 23.56Erlangs 4. 22.12 Erlangs

Q126 Which ND report would you refer in order to find the discrepancy for Handovers? 1. Report 163 2. Report 166 3. Report 153 4. Report 208

Q127 On what basis would an optimizer decide whether the site serving is overshooting: 1. On the basis of TA 2. From ND report 232 3. Physically verifying whether the cell is having up tilt 4. All of the above

Q128 BBH is generally implemented where: 1. For dense network 2. For small capacity network 3. For cells where tight frequency reuse is required

4. None of the above

Q129 In case of Directed retry HO: 1. HO is performed from TCH of serving to TCH of Adjacent cell 2. HO is performed from SDCCH of serving to TCH of adjacent cell 3. HO is performed from TCH of Serving to SDCCH of adjacent cell 4. HO is performed from SDCCH of serving to SDCCH of adjacent cell Q130 Which alarm indicates the TRX faulty operation in the system: 1. 7601 2. 7602 3. 7725 4. 7745

Q131 C/I estimation during a DT can be done in: 1. U/L 2. D/L 3. Both A&B 4. Cannot be estimated. Q132 Which is the unique feature in TEMS for analsing speech quality: 1. Rx qual Full 2. Rx Qual Sub

3. SQI 4. Rx Qual.

Q133 Drop calls due to Handovers can be caused basically due to: 1. Neighbors with Co-BSIC 2. Neighbor with Co-BCCH 3. Neighbors with Co-BCCH and Co-BSIC 4. All of the above.

Q134 Consider a cell where the no calls are happening, the probable causes would be 1. Wrong definition of LAC,CI 2. DMAX=0 3. Only A is correct 4. Both A&B are correct. Q135 What should be the value of Rxlev Access min set: 1. -47dbm 2. -110dm 3. -65dbm 4. -85dbm Q136 What would be the output of a cell with parameter setting as MstxPwrmax=0db,BsTxPWrMax =30db

1. Cell will carry max.no of calls 2. Cell will carry very few calls 3. Cell will not be latched 4. Cell with a correct parameter setting.

Q137 What would be the power loss after using a combiner in a sector: 1. -2db 2. -1db 3. -3db 4. -4db

Q138 What will happen in case where GTRX=Y(Non Edge TRX),EDGE=Y: 1. TRX will be unlocked 2. System will not allow the TRX to be unlock 3. TRX will go in Block state 4. Both B&C are correct. Q139 Which report would give you the total payload for GPRS: 1. 232 2. 208 3. 228 4. 226.

Q140 In a Flexi BTS 1 physical TRX would logically represent how many Trx: 1. 1 2. 2 3. 3 4. None of the above. Q141 ‘Booster ’ becomes a solution in case of : 1. Capacity 2. Coverage 3. A & B Both 4. None of the above Q142 Recommended value of ITCF is : 1. 2 2. 0 3. 1 4. 4 Q143. Which ND report gives the data for RACH rejection on cell level? 5. 134 6. 132 7. 188 8. 111.

Q144. Which ND report would you refer in order to find the discrepancy for Handovers? 5. Report 163 6. Report 166 7. Report 153 8. Report 208 Q145.On what basis would an optimizer decide whether the site serving is overshooting: 5. On the basis of TA 6. From ND report 232 7. Drive test logs 8. All of the above Q146.Which ND report would give you the total payload for GPRS: 5. 232 6. 208 7. 228 8. 226. Q147 What is a Command to check active alarms on bts: 1. ZERO 2. ZEQO 3. ZEOL 4. ZELO

Q148 Value of BSC Timers can be checked by command: 1. ZEFO 2. ZEDO 3. ZEHO 4. ZEGO

Q149 ND Report 71 Tells: 1. Adjacencies having highest success rate 2. Adjacencies having highest failure rate 3. All adjacencies 4. None of the above Q150.Which report gives value of dedicated data time slots: 1. 051 2. 053 3. 061 4. 063. Q151. Which is ND Report number for AMR Parameters? 1. 051 2. 111

3. 216 4. 053 Q152. Which report shows percentage of HO attempts happening due to GPRS? 1. 150 2. 151 3. 153 4. 154 Q153 Which ND report gives detailed analysis of a cell? 1. 204 2. 216 3. 186 4. 226

Q154 In which ND report we can see hourly Traffic Profile for a cell? 1. 180 2. 181 3. 182 4. 186

Q155. In which ND report we can see hourly call drops due to TCH_RF_NEW_HO counter? 1. 216 2. 213

3. 163 4. 166

Q156. In which ND report we can see adjacency discrepancy between neighbor definitions? 1. 061 2. 060 3. 067 4. 073 Q157. Which are the Coverage Enhancement Features of NSN System? 1. ICE 2. Reverse ICE 3. Smart Radio Concept(SRC) 4. All of Above Q158. Which ND Report shows Paging Success Rate per LA? 1. 213 2. 216 3. 186 4. 222 Q159. Which ND report shows EGPRS KPI? 1. 230 2. 226 3. 229

4. 228

Q160 Which counter shows DL multislot assignment in percentage? 1. msl_13 2. msl_14 3. msl_15a 4. msl_16a Q161. How many 64 Kbps DAP TSLs are required if MS is using MCS 9 (consider: dedicated data timeslot = 4, single data user attached)? 1. 2 2. 4 3. 6 4. 8

Q162. How many maximum Abis timeslots can be handle by PCU ? 1. 64 2. 128 3. 256 4. 264

Q163. What is the Maximum output power of Metrosite BTS in terms of Watt? 1. 5 2. 10 3. 20

4. 40

Q164. What is the maximum number of TRX’s can created per BCSU in BSC 3i with version S12? 1. 110 2. 200 3. 100 4. 220

Q165. Which interface is required to implement combine paging (Voice + Data) 1. Gs 2. DPM ( Dual Paging Mode) 3. Gn 4. DPT ( Dual Paging Transmission)

Q166. In which ND report we can see TRHO Handovers attempt and success? 1. 153 2. 154 3. 155 4. 156

Q167. How many TRX’s can be handled by 1 BB2F Card in Ultra Site BTS? 1. 2

2. 3 3. 4 4. 6

Q168. Which of the following BTS Type do not have combiner in-built in them? 1. Ultra Site 2. Metro Site 3. Flexi BTS 4. None of above Q169. Which report will help to see EDAP Congestion? 1. 280 2. 281 3. 128 4. 082

Q170. In which ND report we can see paging deletion counts for cell level? 1. 180 2. 181 3. 182 4. 186 Q171 Out of following, which is true as per NSN Specification? 1. CDED<=CDEF 2. CDED>CDEF

3. CDED=CDEF+CMAX 4. CDEF=CDED+CMAX Q172. What should be minimum value of CDED(%) to have 1 RTSL as dedicated GPRS Timeslot considering 2 TRX as GPRS TRX? 1. 0 2. 1 3. 8 4. 10 Q173 Which report shows Intra Cell Handover Statistics? 1. 150 2. 153 3. 154 4. 158 Q174 What is the maximum data throughput/timeslot can be achieved in case of MCS 9? 1. 64 Kbps 2. 59.2 Kbps 3. 118 Kbps 4. 230.4 Kbps Q175 Which BTS Type does not support Rx Diversity (RDIV) parameter? 1. Flexi Edge BTS 2. Ultra BTS 3. Metro BTS

4. Talk Family BTS Q176 In case of EDGE which of the following CS offers highest coverage? 1. MCS 1 2. MCS 9 3. MCS 5 4. CS 1 Q177 Which ND Report shows Trx vise quality distribution? 1. 180 2. 269 3. 196 4. 169

Q178 ND Report gives radio timeslot configuration? 1. 111 2. 222 3. 121 4. 051 Q179 Noise separation feature can be implemented in? 1. TCSM 2. BSC 3i 3. Flexi BTS 4. TRX

Q180 Which of the following is not a feature of GSM network alone, but also feature of analog mobile communication network? 1. Digital transmission of user data in air interface 2. Possibility of full international roaming in any country 3. Better speech quality 4. Fully digitized switching exchange Q181 which of the following is parameter affecting cell sites while planning the network 1. Antenna height 2. MS power 3. BTS Power 4. None Of Above Q182 What is E interface? 1. MSC-MSC 2. MSC-VLR 3. MSC-HLR 4. HLR-VLR Q183 In GSM which type of handover occurs? 1. Hard 2. Soft 3. Both of the above 4. Make before break

Q184 Choose the correct bit pattern of a flag in LAP-D format ? 1. 01111110 2. 11111111 3. 10101010. 4. 01010101. Q185 Mobile identity is a part of? 1. Physical layer Info 2. Lap-D Info 3. BSSMAP Info 4. GSM L3 Info

Q186 Maximum PLMN Permitted can be ? a) 7 b) 8 c) 1 d) 2 Q187 how many BSIC possible if NCC=4, no of BCCH ARFCN =8 ? a) 32 b) 64 c) 256 d) 1024 Q188 DTX helps in a) Reducing TCH congestion b) Reducing SDCCH congestion c) Reducing interference d) Improving paging success

Q189. BSSAP needs the services of SCCP to a) Analyze A subscriber data b) To perform Connectionless signaling with the MSC c) Send MAP messages to HLR via the MSC d) To make a virtual connection between the MS and the MSC Q190. Which of the following istrue? a) MAP stands for Mobile Access Part b) LAP-D protocol is used to communicate between MSC and BSC c) MAP is used for communication between MSC and HLR d) BSSAP is used for communicating between BSC and MS

Q191. If an inter MSC handover occurs during a call, the decision to make a handover is done by a) BSC controlling the target cell b) MSC controlling the target cell c) BSC controlling the current cell d) MSC controlling the current cell Q192. Which of the following is notan advantage of the GSM network Compared to other networks which use the same frequency band? a) Lower Carrier to Interference Ratio for signal reception b) Use of MAP signaling c) Frequency reuse is more efficient than in other networks d) Lower bit rate for voice coding Q193. The basic principle of speech coding in a GSM Mobile Station is a) A-Law PCM with 8 bits per sample b)-Law PCM at 104Kbits/s c) A-Law PCM with special filtering at 13Kbits/s d) None of the above Q194. Authentication verification is carried out in a) HLR b) MSC c) VLR d) Authentication Centre Q195. No calls initiating in a cell, handover traffic is present

1. wrong neighbor defined 2. CGI creation problem 3. Same BCCH Allocated in neighbor 4. None of above

Q196. Which of the following facility is not supported by Net monitor? 1. Neighbor Cell Id 2. DTX Status 3. Ciphering status 4. HSN Q 197. In a cell configured with phase diversity, with air combining, what should be ideal distance between two antennas of same sector? 1. At least λ/4 separated 2. At least λ/10 separated 3. 0 distance 4. None of above Q198. Which of the following is supported by remote tune combiner? 1. BB Hopping 2. RF Hopping 3. Cyclic Hopping 4. All of above

Q199. Which of the following is affecting SDCCH capacity on Abis Interface? 1. TRX Signaling Size 2. No of TCH in sector 3. EDAP Pool 4. OMU Signaling Q200. Alarm no. 2993 indicates 1. TCH Drop on Abis Interface 2. TCH Drop on Ater Interface 3. TCH Drop on Air Interface 4. TCH Drop on A Interface What is LTE? LTEi (Long Term Evolution) is initiated by 3GPPi to improve the mobile phone standard to cope with future technology evolutions and needs.  

Login or register to post comments What is goal of LTE? The goals for LTE include improving spectral efficiency, lowering costs, improving services, making use of new spectrum and reformed spectrum opportunities, and better integration with other open standards.

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Login or register to post comments What speed LTE offers? LTE provides downlink peak rates of at least 100Mbit/s, 50 Mbit/s in the uplink and RAN (Radio Access Network) round-trip times of less than 10 ms.

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Login or register to post comments What is LTE Advanced?

LTE standards are in matured state now with release 8 frozen. While LTE Advanced is still under works. Often the LTE standard is seen as 4G standard which is not true. 3.9G is more acceptable for LTE. So why it is not 4G? Answer is quite simple - LTE does not fulfill all requirements of ITU 4G definition. Brief History of LTE Advanced: The ITU has introduced the term IMT Advanced to identify mobile systems whose capabilities go beyond those of IMT 2000. The IMT Advanced systems shall provide best-in-class performance attributes such as peak and sustained data rates and corresponding spectral efficiencies, capacity, latency, overall network complexity and quality-of-service management. The new capabilities of these IMT-Advanced systems are envisaged to handle a wide range of supported data rates with target peak data rates of up to approximately 100 Mbit/s for high mobility and up to approximately 1 Gbit/s for low mobility. See LTE Advanced: Evolution of LTE for more details.  

Login or register to post comments What is LTE architecture? The evolved architecture comprises E-UTRAN (Evolved UTRAN) on the access side and EPC (Evolved Packet Core) on the core side. The figure below shows the evolved system architecture

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Login or register to post comments What is EUTRAN?

The E-UTRAN (Evolved UTRAN) consists of eNBs, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of the X2 interface. The eNBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core), more specifically to the MME (Mobility Management Entity) by means of the S1-MME and to the Serving Gateway (S-GW) by means of the S1-U.  

Login or register to post comments What are LTE Interfaces? The following are LTE Interfaces : (Ref: TS 23.401 v 841)            

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S1-MME :- Reference point for the control plane protocol between E-UTRAN and MME. S1-U:- Reference point between E-UTRAN and Serving GW for the per bearer user plane tunnelling and inter eNodeB path switching during handover. S3:- It enables user and bearer information exchange for inter 3GPP access network mobility in idle and/or active state. S4:- It provides related control and mobility support between GPRS Core and the 3GPP Anchor function of Serving GW. In addition, if Direct Tunnel is not established, it provides the user plane tunnelling. S5:- It provides user plane tunnelling and tunnel management between Serving GW and PDN GW. It is used for Serving GW relocation due to UE mobility and if the Serving GW needs to connect to a non-collocated PDN GW for the required PDN connectivity. S6a:- It enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system (AAA interface) between MME and HSS. Gx:- It provides transfer of (QoS) policy and charging rules from PCRF to Policy and Charging Enforcement Function (PCEF) in the PDN GW. S8:- Inter-PLMN reference point providing user and control plane between the Serving GW in the VPLMN and the PDN GW in the HPLMN. S8 is the inter PLMN variant of S5. S9:- It provides transfer of (QoS) policy and charging control information between the Home PCRF and the Visited PCRF in order to support local breakout function. S10:- Reference point between MMEs for MME relocation and MME to MME information transfer. S11:- Reference point between MME and Serving GW. S12:- Reference point between UTRAN and Serving GW for user plane tunnelling when Direct Tunnel is established. It is based on the Iu-u/Gn-u reference point using the GTP-U protocol as defined between SGSN and UTRAN or respectively between SGSN and GGSN. Usage of S12 is an operator configuration option. S13:- It enables UE identity check procedure between MME and EIR. SGi:- It is the reference point between the PDN GW and the packet data network. Packet data network may be an operator external public or private packet data network or an intra operator packet data network, e.g. for provision of IMS services. This reference point corresponds to Gi for 3GPP accesses. Rx:- The Rx reference point resides between the AF and the PCRF in the TS 23.203. SBc:- Reference point between CBC and MME for warning message delivery and control functions. Login or register to post comments

What are LTE Network elements?

eNB eNB interfaces with the UE and hosts the PHYsical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Control Protocol (PDCP) layers. It also hosts Radio Resource Control (RRC) functionality corresponding to the control plane. It performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated UL QoS, cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of DL/UL user plane packet headers. Mobility Management Entity manages and stores UE context (for idle state: UE/user identities, UE mobility state, user security parameters). It generates temporary identities and allocates them to UEs. It checks the authorization whether the UE may camp on the TA or on the PLMN. It also authenticates the user. Serving Gateway The SGW routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNB handovers and as the anchor for mobility between LTE and other 3GPP technologies (terminating S4 interface and relaying the traffic between 2G/3G systems and PDN GW). Packet Data Network Gateway The PDN GW provides connectivity to the UE to external packet data networks by being the point of exit and entry of traffic for the UE. A UE may have simultaneous connectivity with more than one PDN GW for accessing multiple PDNs. The PDN GW performs policy enforcement, packet filtering for each user, charging support, lawful Interception and packet screening.  

Login or register to post comments What are LTE protocols & specifications? In LTE architecture, core network includes Mobility Management Entity (MME), Serving Gateway (SGW), Packet Data Network Gateway (PDN GW) where as E-UTRAN has E-UTRAN NodeB (eNB). See LTE protocols & specifications for specification mappings. Protocol links are as below            

Air Interface Physical Layer GPRS Tunnelling Protocol User Plane (GTP-U) GTP-U Transport Medium Access Control (MAC) Non-Access-Stratum (NAS) Protocol Packet Data Convergence Protocol (PDCP) Radio Link Control (RLC) Radio Resource Control (RRC) S1 Application Protocol (S1AP) S1 layer 1 S1 Signalling Transport X2 Application Protocol (X2AP)

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X2 layer 1 X2 Signalling Transport Login or register to post comments

What is VoLGA? VoLGA stands for "Voice over LTE via Generic Access". The VoLGA service resembles the 3GPP Generic Access Network (GAN). GAN provides a controller node - the GAN controller (GANC) inserted between the IP access network (i.e., the EPS) and the 3GPP core network. The GAN provides an overlay access between the terminal and the CS core without requiring specific enhancements or support in the network it traverses. This provides a terminal with a 'virtual' connection to the core network already deployed by an operator. The terminal and network thus reuse most of the existing mechanisms, deployment and operational aspects. see VoLGA - Voice over LTE via Generic Access for more details.  

Login or register to post comments What is CS Fallback in LTE? LTE technology supports packet based services only, however 3GPP does specifies fallback for circuit switched services as well. To achieve this LTE architecture and network nodes require additional functionality, this blog is an attempt to provide overview for same. In LTE architecture, the circuit switched (CS) fallback in EPS enables the provisioning of voice and traditional CS-domain services (e.g. CS UDI video/ SMS/ LCS/ USSD). To provide these services LTE reuses CS infrastructure when the UE is served by E UTRAN. See Understanding CS Fallback in LTE for more details.

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Login or register to post comments How does LTE Security works? The following are some of the principles of 3GPP E-UTRAN security based on 3GPP Release 8 specifications:    

The keys used for NAS and AS protection shall be dependent on the algorithm with which they are used. The eNB keys are cryptographically separated from the EPC keys used for NAS protection (making it impossible to use the eNB key to figure out an EPC key). The AS (RRC and UP) and NAS keys are derived in the EPC/UE from key material that was generated by a NAS (EPC/UE) level AKA procedure (KASME) and identified with a key identifier (KSIASME). The eNB key (KeNB) is sent from the EPC to the eNB when the UE is entering ECMCONNECTED state (i.e. during RRC connection or S1 context setup).

See LTE Security Principles for more details.

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Login or register to post comments What is IP Multimedia Subsystem (IMS)? The 3GPP IP Multimedia Subsystem (IMS) technology provides an architectural framework for delivering IP based multimedia services. IMS enables telecom service providers to offer a new generation of rich multimedia services across both circuit switched and packet switched networks. IMS offers access to IP based services independent of the access network e.g. wireless access (GPRS, 3GPP’s UMTS, LTE, 3GPP2’s CDMA2000) and fixed networks (TISPAN’s NGN) IMS defines a architecture of logical elements using SIP for call signaling between network elements and Provides a layered approach with defined service, control, and transport planes. Some of IMS high level requirements are noted below: The application plane provides an infrastructure for the provision and management of services, subscriber configuration and identity management and defines standard interfaces to common functionality. The IMS control plane handles the call related signaling and controls transport plane. Major element of control plane is the Call Session Control Function (CSCF) , which comprises Proxy-CSCF (PCSCF), Interrogating-CSCF (I-CSCF) and Serving-CSCF (S-CSCF). The CSCF (Call/Session Control Function) is essentially a SIP server. The IMS transport plane provides a core IP network with access from subscriber device over wireless or wireline networks.

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Login or register to post comments How does measurements work in LTE? In LTE E-UTRAN measurements to be performed by a UE for mobility are classified as below    

Intra-frequency E-UTRAN measurements Inter-frequency E-UTRAN measurements Inter-RAT measurements for UTRAN and GERAN Inter-RAT measurements of CDMA2000 HRPD or 1xRTT frequencies

See Measurements in LTE E-UTRAN for details.  

Login or register to post comments What is Automatic Neighbour Relation? According to 3GPP specifications, the purpose of the Automatic Neighbour Relation (ANR) functionality is to relieve the operator from the burden of manually managing Neighbor Relations (NRs). This feature would operators effort to provision. Read Automatic Neighbour Relation in LTE for more details.

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 How does Intra E-UTRAN Handover is performed? Intra E-UTRAN Handover is used to hand over a UE from a source eNodeB to a target eNodeB using X2 when the MME is unchanged. In the scenario described here Serving GW is also unchanged. The presence of IP connectivity between the Serving GW and the source eNodeB, as well as between the Serving GW and the target eNodeB is assumed. The intra E-UTRAN HO in RRC_CONNECTED state is UE assisted NW controlled HO, with HO preparation signalling in E-UTRAN. Read LTE Handovers - Intra E-UTRAN Handover for more details.  

Login or register to post comments How does policy control and charging works in LTE? A important component in LTE network is the policy and charging control (PCC) function that brings together and enhances capabilities from earlier 3GPP releases to deliver dynamic control of policy and charging on a per subscriber and per IP flow basis. LTE Evolved Packet Core (EPC) EPC includes a PCC architecture that provides support for finegrained QoS and enables application servers to dynamically control the QoS and charging requirements of the services they deliver. It also provides improved support for roaming. Dynamic control over QoS and charging will help operators monetize their LTE investment by providing customers with a variety of QoS and charging options when choosing a service. The LTE PCC functions include:     

PCRF (policy and charging rules function) provides policy control and flow based charging control decisions. PCEF (policy and charging enforcement function) implemented in the serving gateway, this enforces gating and QoS for individual IP flows on the behalf of the PCRF. It also provides usage measurement to support charging OCS (online charging system) provides credit management and grants credit to the PCEF based on time, traffic volume or chargeable events. OFCS (off-line charging system) receives events from the PCEF and generates charging data records (CDRs) for the billing system.

Refer following whitepapers for more details. Introduction to Evolved Packet Core Policy control and charging for LTE networks Quality of Service (QoS) and Policy Management in Mobile Data Networks  

Login or register to post comments What is SON & how does it work in LTE?

Self-configuring, self-optimizing wireless networks is not a new concept but as the mobile networks are evolving towards 4G LTE networks, introduction of self configuring and self optimizing mechanisms is needed to minimize operational efforts. A self optimizing function would increase network performance and quality reacting to dynamic processes in the network. This would minimize the life cycle cost of running a network by eliminating manual configuration of equipment at the time of deployment, right through to dynamically optimizing radio network performance during operation. Ultimately it will reduce the unit cost and retail price of wireless data services. See Self-configuring and self-optimizing Networks in LTE for details.  

Login or register to post comments How does Network Sharing works in LTE? 3GPP network sharing architecture allows different core network operators to connect to a shared radio access network. The operators do not only share the radio network elements, but may also share the radio resources themselves. Read Network Sharing in LTE for more.

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Login or register to post comments How does Timing Advance (TA) works in LTE? In LTE, when UE wish to establish RRC connection with eNB, it transmits a Random Access Preamble, eNB estimates the transmission timing of the terminal based on this. Now eNB transmits a Random Access Response which consists of timing advance command, based on that UE adjusts the terminal transmit timing. The timing advance is initiated from E-UTRAN with MAC message that implies and adjustment of the timing advance. See Timing Advance (TA) in LTE for further details.

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Login or register to post comments How does LTE UE positioning works in E-UTRAN? UE Positioning function is required to provide the mechanisms to support or assist the calculation of the geographical position of a UE. UE position knowledge can be used, for example, in support of Radio Resource Management functions, as well as location-based services for operators, subscribers, and third-party service providers. See LTE UE positioning in E-UTRAN for more details.

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Login or register to post comments How many operators have committed for LTE?

List of operators committed for LTE has been compiled by 3GAmericas from Informa Telecoms & Media and public announcements. It includes a variety of commitment levels including intentions to trial, deploy, migrate, etc. For latest info visit http://ltemaps.org/  

Login or register to post comments What is Single Radio Voice Call Continuity (SRVCC)? Along with LTE introduction, 3GPP also standardized Single Radio Voice Call Continuity (SRVCC) in Release 8 specifications to provide seamless continuity when an UE handovers from LTE coverage (E-UTRAN) to UMTS/GSM coverage (UTRAN/GERAN). With SRVCC, calls are anchored in IMS network while UE is capable of transmitting/receiving on only one of those access networks at a given time. See Evolution of Single Radio Voice Call Continuity (SRVCC) for more details.

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Login or register to post comments How does Location Service (LCS) work in LTE network? In the LCS architecture, an Evolved SMLC is directly attached to the MME. The objectives of this evolution is to support location of an IMS emergency call, avoid impacts to a location session due to an inter-eNodeB handover, make use of an Evolved and support Mobile originated location request (MO-LR) and mobile terminated location request MT-LR services. Release 9 LCS solution introduces new interfaces in the EPC:   

SLg between the GMLC and the MME SLs between the E-SMLC and the MME Diameter-based SLh between the HSS and the HGMLC

For details read LCS Architecture for LTE EPS and LTE UE positioning in E-UTRAN  

Login or register to post comments How does Lawful Interception works in LTE Evolved Packet System? 3GPP Evolved Packet System (EPS) provides IP based services. Hence, EPS is responsible only for IP layer interception of Content of Communication (CC) data. In addition to CC data, the Lawful Interception (LI) solution for EPS offers generation of Intercept Related Information (IRI) records from respective control plane (signalling) messages as well. See Lawful Interception Architecture for LTE Evolved Packet System for more details.

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Login or register to post comments What is carrier aggregation in LTE-Advanced?

To meet LTE-Advanced requirements, support of wider transmission bandwidths is required than the 20 MHz bandwidth specified in 3GPP Release 8/9. The preferred solution to this is carrier aggregation. It is of the most distinct features of 4G LTE-Advanced. Carrier aggregation allows expansion of effective bandwidth delivered to a user terminal through concurrent utilization of radio resources across multiple carriers. Multiple component carriers are aggregated to form a larger overall transmission bandwidth. See Carrier Aggregation for LTE-Advanced for more details.  

Login or register to post comments What is Relay Node and how does Relaying works in LTE-Advanced? For efficient heterogeneous network planning, 3GPP LTE-Advanced has introduced concept of Relay Nodes (RNs). The Relay Nodes are low power eNodeBs that provide enhanced coverage and capacity at cell edges. One of the main benefits of relaying is to provide extended LTE coverage in targeted areas at low cost. The Relay Node is connected to the Donor eNB (DeNB) via radio interface, Un, a modified version of E-UTRAN air interface Uu. Donor eNB also srves its own UE as usual, in addition to sharing its radio resources for Relay Nodes.