GSM RF Survey & Drive Test
What are the requirement for Drive testing? (Ans) Test the network from the subscribers.Test the complete system, end-to-end (mobile-to-land).Benchmark performance against competitor networks.Test specific important routes and areas.Test in-building coverage for specific buildings (walk test). What are the software required for drive test? there are many software used for drive test for ex huawei using probe 2.3 3.3, Nokia using tems 6.0 8.0 10.0 11.0 , and Nemo drive tool, for cdma we can use agilent. How to do Hardware Configuration for TEMS INVESTIGATION ? Minimum Hardware Configuration for laptop to cope with connected one mobile station and one GPS to standard interface connected to com ports. PC : Pentium III 500MHz , 256 MB Ram Ports : Serial Port, USB Port, and PCMCIA Card will be helpful. Graphics with min. 16 bit High Color Sound Card and Speaker for audio indications. For more mobile connections min. 512 MB Ram and better processor. OS : Windows 2000, Windows XP Software : Min. Internet Explorer 5.0 or more for report generator and online help. Explain the Routine Drive Test? Network is monitored on a regular basis Drive test routes to include all the major roads, important locations, etc Routes regularly drive tested and problems further analyzed and solved May require removing interfering carrier, Power Change to BTS, Frequency Plan change, Neighbor addition , etc. What is Access Fails during Drive Test / RF Optimization? Access failures are the total number of unsuccessful TCH attempts which is calculated by subtracting number of assigned TCH seizures from number of TCH attempts – including the ones during handovers. What is Retainability during Drive Test / RF Optimization? Retainability is the clue to network continuity and targets TCH Call Success rate of the network. It takes all type of drops into consideration. Retainability = TCH Call Access Rate = 1 –TCH Call Drop Rate TCH Call Drop rate is calculated by dividing total number of drop calls to number of total TCHseizures and attempts. Total number of drop calls contains all types of TCH drops including anyradio related, user activated, network activated, ABIS fail, A interface, LAPD, BTS failure orBSCU reset drops. Please note that any TCH re – establishment should be subtracted from TCH call drop rate as call is somehow able to continue. Total number of TCH attempts and seizureswill include any TCH seizures for new calls and TCH to TCH attempts during Handover andnumber of intracell handovers as well. Retainability is wanted to be as near as to 100 percent.For measuring retainability and integrity of a network, long continuous calls must be performedby drive test. What is Accessibility during Drive Test / RF Optimization? Accessibility counter is one of the most important statistics and it is the performance expression of the network at the first glance. Accessibility is calculated by multiplying SDDCH (Standalone Dedicated Control Channel) serviceability by TCH accessibility. Accessibility = SDCCH Serviceability * TCH Accessibility For accessibility performance of the network, repeated short call set–ups must be performed bydrive tests. Explain the Problem Drive Testing? Problems reported by statistical analysis, routine drive testing,customer care centre , etc.List of problematic cells identified and drive tested thoroughly to analyze the problem. Data collection and analysis done simultaneously. What do mean by GSM Drive Test Metrics? Route Plots RxLev Full RxLev Sub RxQual Full RxQual Sub C/I BCCH Events Call Drops Setup Failures HO Failures HO Success
What are the predefined Events in Drive Test?
Explain the Cell Coverage Analysis Drive Test? Usually carried out for new planned sites in the network New cells to come on air are thoroughly drive tested to determine their server and coverage areas Optimisation to be carried out for any major deviation from the initially planned design List of drive test Analysis Types? Routine Voice call drive test, short call & long Call. Data Drive. MMS , SMS Drive test. Comparative Drive. Problem specific drive test Cell coverage analysis drive test. Walk test. What is the Cell name in Drive Test? Cell name: It displays the name of the sector which is serving according to the cellfile that is loaded in TEMS. What is the CGI in Drive Test? CGI : It stands for the Cell Global Identity which is unique for every sector of the site. It consists of MCC,MNC,LAC,CI. What is the BCCH ARFCN in Drive Test? BCCH ARFCN: It tells by which BCCH is the mobile station getting served. What is the TCH ARFCN in Drive Test? TCH ARFCN: On which Traffic Freq. call is going on. What is the BSIC in Drive Test? BSIC (Base Station Identity Code) : It is combination of Network Color Code (NCC) (0 – 7) & Base Station Color Code (BCC) (0 – 7). e.g. 62. It is decoded by mobile on every Sync. Channel Message. What is the Mode in Drive Test? Mode: It is shows in which state is mobile operating, Idle, Dedicated & Packet. What are the Channel Types in Drive Test? Channel Type: Type of channel mobile is getting now. Like BCCH / SDCCH/8 + SACCH/C8 or CBCH / TCH/F +FACCH/F +SACCH/F. What is the Channel Mode in Drive Test? Channel Mode :It shows mode of coding like Speech Full Rate of Half Rate. What is the Ciphering Algorithm in Drive Test? Ciphering Algorithm : It shows ciphering algorithm used by the system to protect data for privacy. E.g. Cipher by A5/2. What is the Sub Channel Number in Drive Test? Sub Channel Number: It is displayed at a time when mobile is on dedicated mode at time of call setup when it is getting SDCCH at that time it shows which SDCCH it is getting out of 8 available. E.g. 2. What is the Hopping Channel in Drive Test? Hopping Channel : It shows that current sector is having hopping feature or not. Values are Yes or No. What is the Hopping Frequencies in Drive Test? Hopping Frequencies : It displays no. of freq. on which mobile is allowed to hop. viz. MA List for hopping of that sector. What is the Mobile Allocation Index Offset in Drive Test? Mobile Allocation Index Offset (MAIO): It is the number which tells from which freq. from given MA list for sector hopping has to be started. E.g. 0 means sector will start from first freq. to hop.
What is the Hopping Sequence Number in Drive Test? Hopping Sequence Number (HSN) : Indicates sequence in which frequencies are allowed to hop from the MA List. 0- 63. 0 for Cyclic Hopping, 1 – 63 random hopping sequences. What is the RxLev in Drive Test? RxLev : Receiving level in terms of dBm that mobile is receiving from the site. Range of -30 dBm to -110dBm. What is the RxQual in Drive Test? It is the quality measure of the signals recieved by MS.Better the quality better will be services.it Ranges 0-7where it is best at minimum.It depends on BER,more the BER more will Value of Rx Q and less will be Quality. What is the BER Actual in Drive Test? BER Actual : Ratio of the number of bit errors to the total number of bits transmitted in a given time interval. BER is a measure for the voice quality in network.. Depending on BER RxQual is measured. E,g, BER 0 to 0.2 % corresponds to RxQual 0. Max. BER countable and useful is up to 12.8 % which corresponds to RxQual of max. 7. What is the SQI in Drive Test? SQI : SQI is a more sophisticated measure which is dedicated to reflecting the quality of the speech (as opposed to radio environment conditions). This means that when optimizing the speech quality in your network, SQI is the best criterion to use. SQI is updated at 0.5 s intervals. It is computed on basis of BER and FER. For EFR 30, FR – 21 & HR – 17 are respectively ideal values. What is the MS Power Control Level in Drive Test? MS Power Control Level : Displays range of power control from 0 to 8 depending upon network design. E.g. 0 means no power control and 1 means level that is defined by operator viz. 2 dBm less acc. to airtel. What is the Discontinuous transmission in Drive Test? DTX : Discontinuous transmission (DTX) is a mechanism allowing the radio transmitter to be switched off during speech pauses. This feature reduces the power consumption of the transmitter, which is important for MSs, and decreases the overall interference level on the radio channels affecting the capacity of the network. What is the System Info message Types 1 in Drive Test? Type 1: Cell channel description, RACH control (Only used during Frequency hopping). What is the System Info message Types 2 in Drive Test? Type 2: Neighbor Cell description, NCC permitted, RACH control. 2 bis: Neighbor cell description (extension), RACH control, 2 ter: Additional multiband information, Neighbor cell description (other band). What is the System Info message Types 3 in Drive Test? Type 3: Location area identity, Cell identity, Cell options, Cell selection, RACH control. What is the System Info message Types 4 in Drive Test? Type 4: Location area identity, Cell selection, RACH control, CBCH control & description. What is the System Info message Types 5 in Drive Test? Type 5: Neighbor Cell description. 5 bis: Neighbor cell description (extension). 5 ter: Additional multiband information, Neighbor cell description (other band). What is the System Info message Types 6 in Drive Test? Type 6: Location area identity, Cell identity, Cell options, NCC permitted. What is the System Info message Types 7 in Drive Test? Type 7: System info 7 rest octets have the same format as the sys-info 4. What is the System Info message Types 8 in Drive Test? Type 8: System info 8 rest octets have the same format as the sys-info 4. What is the Serving Neighbor in Drive Test? Cell Name : Name that describes the neighboring cell as per the cellfile. ARFCN : Channel number mobile receives as neighbor. BSIC : BSIC of the neighboring cell. RxLev : Receiving Level in dBm of neighboring cell. C1 & C2 : These are the cell path loss criterion and cell reselection criteria. Valid during idle mode of mobile station. C31 & C32 : GPRS signal strength threshold criterion C31 and GPRS cell ranking criterion C32. Valid both in packet idle and packet dedicated mode. What are the TYPES OF SWAP at BTS Site? Types of Swap at BTS Site 1.PARTIAL SWAP. 2.SECTOR SWAP. Define the SECTOR SWAP in Drive Test? In sector swap total sector is made like for exampleFound in another direction means planned orientation is 1st 70, 2nd 170, 3rd 340, we found 1st 170, 2nd 70, 3rd 240, in sector swap also we found cyclic swap, in That reverse of planned orientation. Find out swap by drive in Idle. Remove the swap by tracing cable.
Define the PARTIAL SWAP in Drive Test? In Partial swap TX RX cable Swap is made. What are the advantage and drawback of Mechanical Tilt? A.Advantages 1.Adjustment of Vertical Tilt Possible 2.Cost Effective 3.Fast adjustment Possible and easy to Change B.Drawbacks 1.Sidelobes are less tilted 2.Accurate adjustment is difficult What are the advantage and drawback of Electrical Tilt? Advantages 1.Same Tilt for Both Main and Side Lobes 2.no adjustment error Drawbacks 1.Adjustment of electrical tilt mostly not possible What is the RxQual_Full measurements in Drive Test? RxQual: Quality of voice which is measuredon basis of BER. Range of RxQual 0 -7. FULL VS SUB Values In GSM, there are two types of values presented for RX QUAL, namelyRXQUAL FULL and RXQUAL SUB, RX LEVEL, the parameter representingthe signal strength also has similar FULL and SUB values.The FULL values are based upon all frames on the SACCH multiframe.If DTX DL is used in the network, the SUB set must be used, and if not, theFULL values are preferred due to their higher confidence. What is the radio link counter in Drive Test? The RLT (radio link counter) is not a parameter that is measured over speech frames; it is set to a value decided by the network operator. This value is in units of SACCH frames. If the mobile is not able to decode a SACCH frame, then this counter decrements by 1. If the decoding is successful, then it is incremented by 2, but it will not exceed the set value. Since the SACCH frame has 40 bits used for the CRC, the probability of detecting bad frames accurately is high. Hence, a decrement in the RLT value indicates a serious situation. When this counter reaches 0, the mobilewill declare radio link failure,consider the call as dropped and return to the idle state.
What is the Definition File in drive test? –Without it, it is impossible to observe overshooing neighbors. –GenDef7.exe can convert FP to definition file.
What is the mean opinion score in Drive Test? Another method of measuring speech quality is the MOS (Mean Opinion Score). There are five grades for MOS; grade 5 is excellent and grade 1 is poor. MOS measurements can be done by voice quality systems, which use voice scripts or similar techniques for sending a known voice pattern from a fixed central unit and analyzing it with a mobile receive unit. What is the Frame Erasure Rate in Drive Test? The percentage of frames being dropped due to high number of non corrected bit errors inthe frame. It is the ratio of discarded speech frames to that of received speech frames.It should be 0.0 TO 4% GOOD 4 TO 15 % DEGRADED 15 % < USELESS. What is the Benchmarking in drive test? Performing drive test to get justification about 'our' network. Can compete or not. With comparing the whole network including 'us' in drive test. What is the Undecoded BCCH in drive test? Description: –BSICs can’t be decoded in 5s –Usually consider 3 strongest neighbors Reason: –GCLK shift, only decode same site BSICs –Channel interference –Non-BCCH carrier, no dedicated spectrum for BCC What is the BSIC Undecode in drive test? Description: –BSIC in same site can be decoded but not for other sites –Handover can only happen in intra-site basis –It is similar to former Undecoded BCCH case Reason: –GCLK shift •GCLK recalibration is required •No one monitors OMC-R alarms What is the No Handover in drive test? Description: –Neighbor BSIC is decoded and COMMON handover requirement is fulfilled but there is never a handover Reason: –Missing neighbor •No such neighbor in CM database –Incorrect external neighbor •Target cell’s LAC/BCCH/BSIC in add_neighbor is different from those in equip_rtf •Engineer modifies external neighbor at MMI, not through GUI •Never use OMC-R Proxy Cell to propagate external neighbor information –N < hreqt. Great HO_MARGIN. Improper algorithm 1-7 setting –Missing_rpt =1 –Serving cell overshoots/covers too far away
What is the Delay Handover in drive test? Description: –Neighbor BSIC is decoded but handover occurs in much later time Reason: –All possible neighbors suffer blocking –Large hreqt * hreqave –qual_power_flag is enabled, full BTS/MS power must be reached before handover –Large handover_recognized_period and bssmap_t7 setting. What is the Ping Pong Handover in drive test? Description: –Lot of handovers between cells –“Time between Handover” is around hreqt*hreqave of such HO cause Reason: –Improper hardware calibration –Hardware fault –UL/DL interference –Negative handover –Different coverage footprint for antennas of a cell
What is the Negative Handover in drive test? Description: –Serving cell hands over to a weaker neighbor Reason: –ho_only_max_power is enabled –qual_margin_flag is disabled –ho_margin_usage_flag is enabled with negative ho_margin_rxqual/rxlev –Negative HO_MARGIN –Micro-cellular algorithms are enabled, especially type 5
What is the Overshooting in drive test? Description: –Cell shoots at far distance but that location has closer cells around Reason: –Overshooting cell has small downtilt, 0 degree! –Overshooting cell has too high altitude –Closer cells have overshooting as well –BSIC of closer cells can’t be decoded What is the High Overlapping in drive test? Description: –Cells have major rxlevel difference within ±5dB Reason: –Overshooting –Too many cells in that area
–Poor antenna downtilt What is the No Dominant Server in drive test? Description: –Rxlevel of best neighbors are close to that of serving cell Reason: –Poor antenna downtilt –Lack of near-by site
What is the Unreasonable Serving Area in drive test? Description: –Coverage area of the cell is incoherent to the antenna direction Reason: –Wrong cable connection to antennas –Incorrect record of antenna orientation –Incorrect ANTENNA_SELECT What is the Poor Coverage in drive test? Description: –Low rxlevel with rxquality –In rural area, rxlevel is less than 15 (-95dBm)
–In city center, rxlevel is less than 35 (-85dBm) –Different location has different threshold, noise level is the key point Reason: –Lack of cell site –BSIC of dominant server can’t be decoded –Dominant server has blocking or cell-bar –Handover problem. E.g. missing & incorrect neighbor, negative handover, no & delay handover What is the Drop Call in drive test? Description: –DL case: Radio_link_timeout counter decreases to 0 –UL case: link_fail counter decreases to 0 –Layer 2: BSS/MS send SABM/DISC in every T200 for N200+1 times, and no response from recipient Reason: –All cases in this presentation What is the Handover Failure in drive test? Description: –MS fails to reach target cell, so return to source cell –MS sends HO FAILURE and UL-SABM to source cell and there is response Reason: –Channel interference –Poor coverage –External interference at UL, like wideband repeator What is the MS Power Rapid Increase in drive test? Description: –MS rapidly increases its TX power due to •Optimised Power Control or •UL SACCH multiframes aren’t received for link_fail - link_about_to_fail times Reason: –Sudden UL interference, e.g. wideband repeator, channel interference –Too much rapid power down –l_rxlev_ul_p is too small
What is the Sudden Power Drop in drive test? Description: –Dedicated ARFCN has significant non-power control rxlevel difference from rxlevel of BCCH Reason: –No/improper TX power calibration –Faulty ancillary. E.g. combiner, filter.. –Different cable lengths from BTS to antennas –Due to air combing, so antennas have different coverage footprints
