GSM Fundamentals & RF GTL welcomes you to the Basic course on GSM Fundamentals & RF (GTL-GSM RF-001)
What you will learn here? • • • • • • • •
Basic Telecom concepts Various Wireless Technologies Cellular concepts & Principal of cellular Comm. GSM Network Architecture GSM channel Architecture Call Flows in GSM GSM Planning steps (Nominal Plan & RF surveys) GSM Optimization Steps ( Performance, Drive testing & Benchmarking)
BASIC Telephony
•Signaling •Traffic
SWITCH / EXCHANGE
•Off Hook •Dial Tone •Dialing Digits
•Ring
•RBT
•Off Hook & Conversation
•Conversation
Wireless Communication •
Alternative means of wireless communication – Walkie - Talkie – Pagers – Trunked private radios
• Mobile Phone - the magic technology that enables everyone to communicate anywhere with anybody.
Wireless Telephony MSC
BSC BTS
BTS
Mobile Subscriber...
Different Standards Worldwide • Till 1982 Cellular Systems were exclusively Analog Radio Technology. • Advanced Mobile Phone Service (AMPS) – U.S. standard on the 800 MHz Band • Total Access Communication System (TACS) – U.K. standard on 900 MHz band • Nordic Mobile Telephone System (NMT) – Scandinavian standard on the 450 & 900 MHz band
Different Standards Worldwide
Different Standards Worldwide GSM - 900 The term GSM-900 is used for any GSM system which operates in any 900 MHz band. P-GSM - 900 P-GSM-900 band is the primary band for GSM-900 Frequency band for primary GSM-900 (P-GSM-900) : 2 x 25 MHz 890 – 915 MHz for MS to BTS (uplink) 935 – 960 MHz for BTS to MS (downlink) E-GSM - 900 In some countries, GSM-900 is allowed to operate in part or in all of the following extension band. E-GSM900 (Extended GSM-900) band includes the primary band (P-GSM-900) and the extension band : 880 – 890 MHz for MS to BTS (uplink) 925 – 935 MHz for BTS to MS (downlink) R-GSM-900 R-GSM-900 (Railway GSM-900) band includes the primary band (P-GSM-900) and the following extension band: 876 – 890 MHz for MS to BTS (uplink) 921 – 935 MHz for BTS to MS (downlink) GSM-1800 Frequency band: 2 x 75 MHz 1710 – 1785 MHz for MS to BTs (uplink) 1805 – 1880 MHz for BTS to MS (downlink)
Industry Vs Technology Spread • Telecom Service Providers/Operators – – – – –
GSM CDMA Basic-WLL Internet Services Long Distance
• Vendor • Telecom Consultancy
Analog Mobile Telephony • End of 1980’s Analog Systems unable to meet continuing demands – Severely confined spectrum allocations – Interference in multipath fading environment – Incompatibility among various analog systems – Inability to substantially reduce the cost of mobile terminals and infrastructure required
Digital Mobile Telephony • Spectrum space - most limited and precious resource • Solution - further multiplex traffic (time domain) • Can be realized with Digital Techniques only
GSM History and Organization • 1979 • 1982 • 1986 • 1988 • 1990 • 1991
• 1992
Europe wide frequency band reserved for Cellular “Groupe Speciale Mobile” created within CEPT GSM had full time in Paris ETSI takes over GSM Committee The phase 1 GSM Recommendations frozen GSM Committee renamed “Special Mobile Group” and GSM renamed as “Global System for Mobile Communication” GSM launched for commercial operations
Service Industry • Service Provider is not a Equipment Manufacturer. • The Service Provider has a license to operate in a geographical boundary (state/circle/ country). • It buys equipment from OEM Suppliers (Vendors). • Installs & commissions the equipment thus making it’s own Network. • Provides the desired service to it’s subscribers.
Vendor • Vendor is a Equipment Manufacturer. • It supplies Product, Consultancy and Trainings • Service provider has the option of taking the Consultancy and Training
Cellular Communication • A cellular system links Mobile subscribers to Public Telephone System or to another Mobile subscribers. • It removes the fixed wiring used in a traditional telephone installation. • Mobile subscriber is able to move around, perhaps can travel in a vehicle or on foot & still make & receive call.
Advantage of Cellular Communication • Mobility
• Flexibility • Convergence • Greater QOS • Network Expansion • Revenue/Profit
WHAT IS CELLULAR TELEPHONY ? CONSIDERATIONS ✻ FREQUENCY Base Station
✻ SUBSCRIBER DENSITY ✻ COVERAGE
Base Station Base Station
Base Station Base Station
Base Station
The Cell • Cellular Radio involves dividing a large service area into regions called “cells.” • Each cell has the equipment to switch, transmit and receive calls. • Cells - Reduce the need of High powered transmission • Cells - Conventionally regarded as being hexagonal, but in reality they are irregularly shaped. • Cell shape is determined by the nature of the surrounding area e.g. Hills , tall building etc.
Cell Size • Large Cells
• Small Cells
• 35 Km
• Near about 1 KM
• Remote Areas
• Urban Areas
• High Transmission Power
• Low Transmission Power
• Few subscribers
• Many Subscribers
Coverage & Capacity • Coverage – Percentage of the geographical area covered by cellular service where mobile telephony is available • Capacity – Number of calls that can be handled in a certain area within a certain period of time. – Capacity can also refer to the probability that users will be denied access to a system due to the simple unavailability of radio channels.
Frequency Spectrum Designation Very Low Frequency Low Frequency Medium Frequency High Frequency Very High Frequency Ultra High Frequency Super High Frequency Extremely High Frequency
Abbreviation VLF LF MF HF VHF UHF SHF EHF
Frequencies 9 kHz - 30 kHz 30 kHz - 300 kHz 300 kHz - 3 MHz 3 MHz - 30 MHz 30 MHz - 300 MHz 300 MHz - 3 GHz 3 GHz - 30 GHz 30 GHz - 300 GHz
Free-space Wavelengths 33 km - 10 km 10 km - 1 km 1 km - 100 m 100 m - 10 m 10 m - 1 m 1 m - 100 mm 100 mm - 10 mm 10 mm - 1 mm
GSM - IN CELLULAR TELEPHONY • Each Cell in the Cellular Network consists of one or more RF carriers. • An RF carrier is a pair of radio frequencies – One used in upward direction by MS - Uplink – Other used in downward direction by BTS - Downlink – The transmit and receive frequencies are separated by a gap of 45 MHz in GSM of 75 MHz in DCS. • There are 124 carries in GSM Band. With each carrier carrying 7 timeslots, only 124 x 7 = 868 calls can be made! • Frequency Reuse is the solution
Ful(n) = 890.0 + (0.2) *n MHz
Fdl(n) = Ful + 45 MHz where n =ARFCN ; 1 ≤ n ≤ 124
dl= 935 to 960 MHz
ul= 890 to 915 MHz
Frequency & ARFCN
Multiple Access Methods Power
Time
Time Power
Power
F DMA
Frequency
Time
CDMA
TDMA
Frequency
Frequency
Multiple Access Methods FDMA Power Tim
Fr
e
y nc e u
eq
TDMA Power Fre
e
CDMA Power Tim
E D CO nc
e
e
Fr
y
nc
e qu
Tim
e qu
y
FDMA: AMPS & NAMPS •Each user occupies a private Frequency, protected from interference through physical separation from other users on the same frequency •TDMA: IS-136, GSM •Each user occupies a specific frequency but only during an assigned time slot. The frequency is used by other users during other time slots. •CDMA •Each user occupies a signal on a particular frequency simultaneously with many other users, but is uniquely distinguishable by correlation with a special code used only by this user
Frequency Reuse Pattern Three types of frequency reuse patterns • 7 Cell reuse pattern • 4 cell reuse pattern • 3 cell reuse pattern
3 Site Reuse Pattern c2 c1 b2
c3 a2
b1 b3
a1 a3 Cell Re-use
c1
c2 c3
FREQUENCY RE - USE – Frequency Re-use
2 7 1 6
3 4
5
D=R
D Cell Dia = R
7/21 cell cluster
(3N)
where N is Cluster size
Principal Of Sectorization • Omni Directional Cells • 120 degree Sectors • 60 Degree sectors – Each Sector in a Site has its own allocation of Radio Carriers • Advantage – By frequent reuse of frequency more capacity can be achieved
Frequency Hopping ★
Multipath Fading results in variations in signal strength which is known as Rayleigh Fading.
★
Rayleigh Fading phenomenon is dependent on path difference and hence frequency of reception.
★
A fast moving mobile may not experience severe effect of this fading since the path difference is continuously changing.
★
A slow moving mobile ( or a halted mobile ) may experience severe deterioration in quality.
★
But, if the frequency of reception is changed when this problem occurs, could solve it.
★
The fading phenomenon is fast and almost continuos, this means the frequency change should also be continuos.
★
This process of continuously changing frequency is known as Frequency Hopping.
Frequency Hopping ★
Frequency Hopping is done in both Uplink and Downlink .
★
Frequency is changed in every TDMA Frame
★
Mobile can Hop on maximum 64 frequencies
★
The sequence of Hopping can be Cyclic or Non-Cyclic
★
There are 63 Non-Cyclic Hopping sequences possible
★
Different Hopping sequence can be used in the same cell.
★
BCH Timeslot can never HOP, but the remaining Timeslots can very well hop.
Frequency Hopping Reduction in Average Interference ★
With Frequency Hopping consistent interference will become bursty.
★
So even though, both the co-channel cells will be using the same set of ARFCN's for Hopping, interference will not be continuos.
★
This is because, GSM cells are not Frame synchronized, and change in frequency is related to Frame nos.
★
If same HSN is used in two cells, then either the interference will be nil , or if a phase correlation exists then it will be continuos.
★
So the two cells should preferably use different HSN's .
★
Sectorial cells ( controlled by the same BTS) can use same HSN, since the sectors don't come up at the same time.
★
Cells if they are synchronized, can use same HSN, if each cell has an offset of some TDMA frames.
★
Offset of TDMA frames is also required to avoid SACCH occurring at the same time in all synchronized cells, as they kills away the objective of DTX.
Cell Sectorisation b2 b1 a2 OMNI CELL 1 ANTENNA
a1
a3
a6
a4 a5 60O CELLS 6 ANTENNAS
b3
120O CELLS 3 ANTENNAS
Features of GSM • Compatibility • Noise Robust • Increased Capacity & Flexibility • Use of Standard Open Interfaces • Improved Security & Confidentiality • Cleaner Handovers • Subscriber Identification • ISDN Compatibility • Enhanced Range of Services
Handovers Hard Handoff Analog, TDMA and GSM
Break before Make
Soft Handoff CDMA
Make before Break
Handovers 197 199
113 200
187 198
70
171
214
225
201
18
215
20
25
175 181
22 216 7 173
41 44
11 218 75
222
71
182 69
132 221
13 120
213 220 219
12
80 19
8 32 28 24 40
73
16
17
Cleaner Handovers • The mobile measures up to 32 adjacent cells for – Signal Strength (RxLevel) – Signal Quality (RxQual) – updated every 480 mS and sends to BTS • Sophisticated Handover based on – RxLevel – Interference – RxQual – Timing Advance – Power Budget
GSM NETWORK ELEMENTS BSC OML
OMC OM
A bis BTS BT S BTS BT S BTS BT
S
BTS BT S BTS BT
S BTS BT S
C
VMSC V
A BTS BT S
TRAU
MSC MS
C
BTS BT S
AUC MSC AU
HLR HL
R VLR VL R BC
B C
MS
BSC PSTN
C EIR EI R
SMSC S
MSC
Mobile Station Identities MSISDN : Human Identity used to call a Mobile Station MSRN : Mobile Station CC NDC SN Roaming No
98
XXX
12345
IMSI : Network Identity unique to a SIM 3 2 10 digits MCC digits MNC digits MSIN
404
XX
TMSI : Identity unique in a LAI
12345
IMEI: Serial number unique to every Mobile Station
TAC
FAC
SNR
S
6 digits 2 digits 6 digits 1 digit
GSM Network Components • Mobile Station consists of two parts– Mobile Equipment (ME) – Subscriber Identity Module (SIM) • ME – Hardware e.g. Telephone, Fax Machine, Computer. • SIM – Smart Card which plugs into the ME.
ME (Classmark Information) • Revision Level – Phase of the GSM specs ME comply with. • RF Power Capability – Max power ME is able to Transmit. • Ciphering Algorithm Used – Presently A5 – Phase 2 specifies Algorithms A5/0 to A5/7. • Frequency Capability • SMS Capability
Mobile Equipment Class
Power O/p
1
20 W
2
8W
3
5W
4
2W
5
0.8 W
Typical Settings
SIM(IMSI) • IMSI(International Mobile Subscriber Identity) – Transmitted over Air Interface on initialization – Permanently stored on SIM card – 15 digit Decimal
SIM (TMSI) • Temporary Mobile Subscriber Identity – Periodically changed by the System Management on instances like location update etc. • Reason for use of TMSI – To prevent a possible intruder from identifying GSM users, TMSI is used • Management – Assignment, Administration & Updating is performed by VLR.
Transcoder • Converts 64 Kbps PCM circuits from MSC to 16 Kbps BSS circuits. • Each 30 channel 2 Mbps PCM link can carry 120 GSM specified voice channels.
Base Station System (BSS) • BSS (Base Station System) – BSC (Base Site Controller) – BTS (Base Transceiver Station) – XCDR (Transcoder)
XCDR
BSC
BTS
Network Switching System (NSS)
Base Station System (BSS) • BSC – Controls upto 40 BTS – Conveys information to/from BTS – Connects terrestrial circuits & Air Interface Channels – Controls handovers between BTSs under itself • BTS – Contains RF Hardware – Limited control functionality – 1 - 6 carriers in a BTS Cabinet – 7 - 48 simultaneous calls per BTS
BSS Configuration • Collocated BTS • Remote BTS • Star Configuration • Daisy Chain BTS
Loop Configuration
BSC
BTS BTS
All BTS on 1 E1
BTS
BTS B T S
BSC
BTS
BTS
Network Switching System(NSS) • NSS (Network Switching System) – MSC (Mobile Switching Centre) – HLR (Home Location Register) – VLR (Visitor Location Register) – EIR (Equipment Identity Register) – AUC (Authentication Centre) – IWF (Interworking Function) – EC (Echo Canceller)
GSM Network Component • MSC – Call Switching – Operation & Management Support – Internetwork Interworking – Collects call billing data • Gateway MSC – MSC which provides interface between PSTN & BSS’s in the GSM Network.
Home Location Register (HLR) • Reference database for the Subscriber profiles– Subscriber ID (IMSI & MSISDN) – Current VLR Address – Supplementary Services subscribed – Supplementary Service Information – Subscriber Status (Registered/deregistered) – Authentication Key and AUC functionality – TMSI – MSRN
Visitor Location Register (VLR) • Temporary Data, which exists as long as the subscriber is active in a particular Coverage area. • Contains the following– Mobile Status (Busy/ Free/ No Answer/etc.) – Location Area Identity (LAI) – TMSI – MSRN (Mobile Station Roaming Number)
Equipment Identity Register (EIR) • Contains Database for validating IMEI – White List (valid ME) – Black List (Stolen ME) – Grey List (Faulty ME)
Inter Working Function • Provides function to enable the GSM System to interface with Public/Private Data Networks. • The basic feature of the IWF are – Rate Conversion – Protocol adaptation
• IWF incorporates Modem Bank. e.g. GSM DTE IWF
PSTN DTE Analogue Modem
Echo Canceller • Echo is apparent only in Mobile - Land conversation & is generated at the 2 wire to 4 wire interface. • To avoid it, Echo Canceller (EC) is used. – Echo is irritating to MS Subscriber – Total Round Trip delay of 180 ms in the GSM system – EC is placed on the PSTN side of the Switch – Cancellation up to 68 ms with EC
Operation & Maintenance Centre • Event & Alarm Management • Fault Management • Performance Management • Configuration Management • Security Management
GSM Terrestrial Interfaces Broadly classified into two types of interfaces• Standard Interfaces – 2 Mbps Trunks (E1) – Signalling System No. 7 SS7 ( CCS7) – X.25 (Packet Switched Mode) • GSM Interfaces
GSM Interfaces •
Um
MS
- BTS
•
Abis
BTS
- BSC
•
A
BSC
- MSC
•
B
MSC
- VLR
•
C
MSC
- HLR
•
D
VLR
- HLR
•
E
MSC
- MSC
•
F
MSC
- EIR
•
G
VLR
- VLR
•
H
HLR
- AUC
GSM Protocol Layers GSM protocols are basically divided into three layers:
Layer 1: Physical layer ± Enables physical transmission (TDMA, FDMA, etc.) ± Assessment of channel quality ± Except on the air interface (GSM Rec. 04.04), PCM 30 or ISDN links are used (GSM Rec. 08.54 on Abis interface and 08.04 on A to F interfaces).
Layer 2: Data link layer ± Multiplexing of one or more layer 2 connections on control/signaling channels ± Error detection (based on HDLC) ± Flow control ± Transmission quality assurance ± Routing
Layer 3: Network layer ± Connection management (air interface) ± Management of location data ± Subscriber identification ± Management of added services (SMS, call forwarding, conference calls, etc.)
Basic Processes • AUTHENTICATION • CIPHERING • REGISTRATION • CALL ESTABLISHMENT • HANDOVER / HANDOFF • ROAMING
AUTHENTICATION ALGORITHM NSS
HLR
Ki
AUC
AUTH. ALGORITHMS A3
SRES
COMPARE
RAND
AIR INTERFACE RAND
MS
SIM MS
Ki
AUTH. ALGORITHMS A3
SRES
Ciphering • Data protection is required on air interface. • A specific key called Ciphering Key (Kc), is generated from RAND and A8 algorithm. • A8 is on the SIM.
Ki
RAND
A8 Kc
Ciphering
Kc
Kc Data
A5
Ciphered Data
A5
Data
Transmission Media • Access Network – Microwave 15 /23 GHz • Backbone Network – Microwave 7 GHz – Optical Fibers – Leased Line( From Dot or any other service provider on any media)
Optical Fiber • Different Possible Combinations • Mono Mode Step Index 10 / 125 µm • Mono Mode Graded index • Multi Mode Step Index 100 / 300 µm • Multi Mode Graded Index 75 / 130 µm • Mono Mode Graded Index would have been the best but fabrication not possible 140 Mbps OLTE , Mono Mode Step Index in our case
Channels On Air Interface • Physical Channel • Logical Channel • Physical Channel – Physical channel is the medium over which the information is carried. • Logical Channel – Logical channels consists of the information carried over the Physical Channel.
LOGICAL CHANNELS 3
Normal Burst 3 T
57 encrypted
1 26 1 S training S
57 encrypted
3 T
8.25 GP
577µS
0 1 2 3 4 5 6 7 577µS x 8 = 4.615mS
26 Frame Multi-frame
TDMA Frame
GSM Channels
Traffic Channel Traffic Channels
• Time is divided into discrete periods called “Timeslots”
TCH/F Full rate 22.8kbits/s
TCH/H Half rate 11.4 kbits/s TCH carries payload data - speech, fax, data
• Connection may be: - Circuit Switched - voice or data
or
• TCH may be: • Full Rate (TCH/F) - one channel per user - 13 kb/s voice, 9.6 kb/s data
or
• Half Rate (TCH/H) - one channel shared between two users
- Packet Switched – data
Control Channel Control Channels
BCH ( Broadcast channels ) Downlink only
BCCH Broadcast control channel
Synch. Channels
FCCH
Frequency Correction channel
SCH Synchronization channel
CCCH(Common Control Chan) Downlink & Uplink
RACH
CBCH
Random Access Channel
Cell Broadcast Channel
PCH/ AGCH
Paging/Access grant
DCCH(Dedicated Channels) Downlink & Uplink
SDCCH
Standalone dedicated control channel
FACCH
Fast Associated Control Channel
ACCH
Associated Control Channels
SACCH
Slow associated Control Channel
Broadcast Channels (BCH) BCH channels are all downlink and are allocated to timeslot zero. Channels are: • FCCH: Frequency control channel sends the mobile a burst of all ‘0’ bits which allows it to fine tune to the downlink frequency • SCH: Synchronization channel sends the absolute value of the frame number (FN), which is the internal clock of the BTS, together with the Base Station Identity Code (BSIC) • BCCH: Broadcast Control Channel sends radio resource management and control messages, Location Area Code and so on. Some messages go to all mobiles, others just to those that are in the idle state
Common Control Channels (CCCH) CCCH contains all point to multi-point downlink channels (BTS to several MSs) and the uplink Random Access Channel: • CBCH: Cell Broadcast Channel is an optional channel for general information such as road traffic reports sent in the form of SMS • PCH: Paging Channel sends paging signal to inform mobile of a call • RACH: Random Access Channel is sent by the MS to request a channel from the BTS or accept a handover to another BTS. A channel request is sent in response to a PCH message. • AGCH: Access Grant Channel allocates a dedicated channel (SDCCH) to the mobile • NCH: Notification Channel informs MS about incoming group or broadcast calls
Dedicated Control Channels (DCCH) SDCCH( Standalone Dedicated Control Channel ) Uplink and Downlink Used for call setup, location update and SMS. SACCH( Slow Associated Control Channel ) Used on Uplink and Downlink only in dedicated mode. Uplink SACCH messages - Measurement reports. Downlink SACCH messages - control info. FACCH( Fast Associated Control Channel ) Uplink and Downlink. Associated with TCH only.
BURST • The Time Slots are arranged in a sequence , conventionally numbered 0 to 7. • Each repetition of this sequence is called a TDMA Frame. • The information content carried in one time slot is called a “burst”.
BURST • Information – Main Area where the Speech, Data or Control info is held • Guard Period – To enable the burst to hit the time slot (0.031ms) • Stealing Flags – 2 bits are set when TCH is to stolen by a FACCH • Training Sequence – For estimation of transfer characteristics of physical media • Tail Bits – Used to indicate beginning and end of the burst.
GSM Burst & TDMA Frame 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 FRAME 1
GUARD PERIOD
Information TAIL BITS
FRAME 2
Training Sequence
GUARD PERIOD
Information TAIL BITS
Five Types of Burst • Normal Burst Traffic & Control Channels
Bi-directional
• Frequency Correction Burst FCCH
Downlink
• Synchronization Burst SCH
Downlink
• Dummy Burst BCCH Carrier
Downlink
• Access Burst RACH
Uplink
Call Scenarios • Mobile to Mobile – Intra-city – Inter-city • Mobile to Land – Intra-city – Inter-city • Land to Mobile – Intra-city – Inter-city
Mobile To Land Sequence MS 1 2 3 4
CHANNEL REQUEST DCCH ASSIGN
AGCH
REQUEST FOR SERVICE SDCCH
6
SET-UP
7
EQUIPMENT ID REQUEST
CR
CC
AUTHENTICATION SET CIPHER MODE
MSC
RACH
SIGNALLING LINK ESTABLISHED
5
BSS
SDCCH
Call Info
VLR
HLR
PSTNEIR
Call Contt. 8 9
COMPLELTE CALL
MSSDCCH BSS
CALL PROCEEDING ASSIGNMENT COMMAND
ASSIGNMENT COMPLELTE INITIAL & FINAL ADDRESS (IFAM) ASSIGNMENT COMPLETE (ACM) ALTERING 10 MS HEARS RINGTONE FROM LAND PHONE
SDCCH
RING TONE STOPS
VLR HLR PSTN EIR
(circuit)
(channel) FAACH (TCH)
FACCH
Hello!
ANSWER(ANS)
11 CONNECT
MS C
FACCH FACCH
CONNECT ACKNOWLEDGE TCH
BILLING STARTS
Supplementary Services • Calling Line Identification – Present – Absent • Connect Line Identification – Present – Absent • Closed User Group - CUG – Only incoming – Only outgoing • Operator Controlled Barring
Data Services Data
rates supported as of today are
2.4
Kbps
4.8
Kbps
9.6 Kbps
GPRS
& EDGE implementation takes the data
capability to higher level of the order of 184 kbps and more
Customer..Expectation • • • •
Good coverage – where ever he goes Good quality No blocking Value added services – – – – – –
SMS Voice mail MMS Call forward/call waiting Data/internet at high data rates prepaid
Basic Network Design Objectives The basic objectives of a wireless system are: – COVERAGE: provide sufficient cell sites to deliver RF coverage of the entire desired area. – BUILDING/VEHICLE PENETRATION: deliver sufficient signal levels to adequately penetrate buildings and vehicles where appropriate. – TRAFFIC: ensure that no cell captures more traffic than it can handle at the desired grade of service (i.e., blocking percentage) – PERFORMANCE: design, construct, and adjust the network to deliver reliable service free from excessive origination and call delivery failures, dropped calls, quality impairments, and service outages. – ECONOMICS: provide return on investment sufficient to support operating and capital expenses, expand the network to take advantage of growth opportunities, and retire costs of construction prior to depreciation of the network equipment.
High Level Design
•
Inputs – Coverage objectives • Area coverage objectives • Coverage penetration objectives – Morphology data/clutter information – Terrain data and Vector maps – Traffic objectives • Number of subscribers defined • Traffic per subscriber defined • Desired grade of service defined – City regulations – BTS Hardware specifications – Link Budget – Business and Logistical objectives • Capital budget • Timing: launch data • Operating revenue Vs. total costs Output – Cell database and traffic model – Composite coverage plot – Equal power handoff boundaries plot
“Background” Issues Impacting System Design • Site acquisition – Availability of suitable candidate (building or land) – Owner interest – Cost of leasing – Frequency clearance (SACFA) – Government authority approval – Space constraints and other construction issues • Candidate Location – line of sight to the objective • Clutter type • Terrain variations • Physical Blocking – buildings, hoardings • Water • Mumbai – High end, high traffic areas are very close to water…. Makes RF design much more challenging • Deviation from desired location impacts surrounding site locations
Design considerations of Network (GSM/CDMA) • •
• • • • • • • •
Understand geographical area as per license agreement Define coverage expectations in terms – On road coverage – In-building coverage (different penetration margins) Capacity considerations – busy hour per subscriber call attempts and minutes of use (Erlangs) 1 Erlang is 1 call of 1 hour duration Decide number of sites based on coverage capacity requirement Propagation tools used for this analysis Finalize exact site locations after field survey Initiate candidate identification process Site acquisition/antenna positioning Modify existing design if site location changes
Flow Chart for Network Deployment Market Requirement
System/Site Dimensioning Propagation model verification
RF &Network Planning
Site Search Plan
Site Search & Selection
Site Acquisition Performance Monitoring
Traffic & Growth Analysis
Operational Network
Site Build
System Optimisation
Site Coverage Confirmation
GSM Planning Steps • Various steps are listed below – – – – – –
CW survey Model Tuning Nominal Planning RF site Surveys Realized Planning Frequency Planning
• Implementation • Optimization – Drive Testing – Performance Analysis
Nominal Planning •
•
•
It consists of planning a set of sites on planning tool so as to predict the coverage of the target area Tool needs to be made intelligent so as to predict the coverage as close as possible to actual coverage Coverage plots are based on customer intension of providing indoor and outdoor coverage
Mumbai – Coverage Expectation Boundary
Coverage Maps – Reverse Link. Mazgaon
Indoor Coverage: Penetration Margin Legend
Malabar Hill
>=30dB:: 3-4 wall coverage 25-30dB : 3 Wall Coverage 23-25 dB : 2-3 Wall Coverage 18-23dB: 2-3 Wall Coverage 16-18 dB : 2 Wall Coverage 8-16dB : 1-2wall Coverage 08 dB :
On Road-1 Wall Coverage
00 dB : On Road/No Coverage
Colaba
Composite Coverage Plot •
•
•
•
Propagation models are used to predict coverage from a particular site A composite coverage plot shows the overall coverage produced by each sector in the field of view The color of each pixel corresponds to the signal level of the strongest server at that point Such plots are useful for identifying coverage holes and overall coverage extent
Clutter Types •
Clutter types – – – – – – – –
Dense Urban Urban Sub Urban Rural Water Vegetation Industrial Forest
RF surveys • Each nominal has a search ring defined by the RF Planner • Candidates needs to be identified as close as possible to the nominal within the search ring • Height, orientations & antenna placement at site are the key RF parameter which are based upon the coverage requirement in the area • Major obstructions and clutter type in various directions to be observed on RF survey
RF surveys • Equipment required for RF Survey – – – –
GPS Digital Camera Binoculars Magnetic Compass
• There might be 3 or more candidates surveys for one site • Each candidate would have an RF survey form and panoramic associated with it
Drive Testing • Drive testing is an important activity to get statistics & graphs on coverage, quality & capacity in the downlink direction • Drive test setup – DT tool, Engineering Handset, GPS, accessories • Call in 2 modes •Dedicated – while the mobile is on call •Idle – while the mobile is idle Important parameters observed during drive testing •Coverage – Rx level (Full & Sub) •Quality – RxQual & SQI •Handover, Dropped call, Neighbor list, TA
Selecting and Tuning Propagation Models • Parameters of propagation models must be adjusted for best fit to actual drive-test measured data in the area where the model is applied • The figure at right shows drive-test signal strengths obtained using a test transmitter at an actual test site • Tools automate the process of comparing the measured data with its own predictions, and deriving error statistics • Prediction model parameters then can be “tuned” to minimize observed error
Drive Test Screen
What is Performance Optimization? • •
The words “performance optimization” mean different things to different people, viewed from the perspective of their own jobs System Performance Optimization includes many different smaller processes at many points during a system’s life – recognizing and resolving system-design-related issues (can’t build a crucial site, too much overlap/soft handoff, coverage holes, etc.) – “cluster testing” and “cell integration” to ensure that new base station hardware works and that call processing is normal – “fine-tuning” system parameters to wring out the best possible call performance – identifying causes of specific problems and customer complaints, and fixing them – carefully watching system traffic growth and the problems it causes - implementing short-term fixes to ease “hot spots”, and recognizing problems before they become critical
Optimization • Optimisation is an ongoing process of analysing network performance against Quality of Service targets:
Performance •Measurements of network performance cover: • Traffic in erlangs • TCH and SDCCH Grade of Service (Congestion) • Call success rate • Handover failure • Coverage area • Coverage quality • Subscriber base and growth • Key Performance Indicators (KPI) are measurable dynamic parameters that help to target areas of concern
KPI’s • Appropriate KPIs to use depend on: • The nature of the network • Data sources available • Measurement tools available • Ability of engineering team • Cost of network infrastructure • Sources of data include: • Surveyed data - from drive tests • Network statistics - from OMC • Field engineer reports
Radio Interface Optimization • Transmission Timing • Power Control • VAD Voice Activity Detector and DTX • Multipath Fading • Equalization • Diversity • Frequency Hopping • Antenna Parameters ( Height, Azimuth, Tilts )
Antenna Tilts
Antenna Tilts
Benchmarking •Surveyed data from test-mobile measurements can be used to benchmark system performance against that of a competitor • Problems that may be identified from surveyed data: • Poor coverage • Unexpected interference • Missing handover definitions • Installation problems at BTS • Test-mobile measurements should include: • continuous calls to test coverage • repetitive short calls to test call-success
Overview RF Planning Tool Drive Test Tool Optimization Tool MapInfo
