GSM Network Analysis and KPI Optimisation discusses key performance indicators (KPIs) for optimizing GSM networks. It describes the architecture of GSM networks including mobile stations, base station subsystems, switching subsystems and operation support subsystems. It then covers various GSM concepts like channels, frame structure, bursts and call flows. The document outlines different types of KPIs like accessibility, retainability and speech quality for both voice and data services. Finally, it discusses how to optimize specific KPIs like blocking, dropping and handover success rates by checking network parameters and using tools like OSS, MRR and NCS reports.

1. GSM Network Analysis and KPI
Optimisation
By
Isha Chhaya
Intern at Idea Cellular Ltd.

2. Content
• GSM Architecture
• Channel concept
• Network Interfaces
• Frame structure
• Burst, its types
• Call Flow
• Identity Numbers
• KPI and its types
• KPI Optimisation
• GSM concepts used in Optimisation

3. GSM Architecture

4. • Network is divided into 4 subsystems:
Mobile Station(MS)
Base Station Subsystem (BSS)
Switching Subsystem (SS)
Operation and Support Subsystem (OSS)
1. Mobile Station
a. Mobile Equipment
b. SIM (Subscriber Identity Module)
2. Base Station Subsystem (BSS)
a. BTS (Base Transceiver System)
b. BSC (Base Station Controller)
c. TRAU (Transcoding Rate and Adaptation Unit)

5. 3. Switching Subsystem
a. MSC (Mobile Switching Centre)
b. HLR (Home Location Register)
c. VLR (Visitor Location Register)
d. AuC (Authentication Centre)
e. EIR (Equipment Identity Register)
f. GMSC (Gateway MSC)
4. Operation and Support Subsystem

6. Channels
1. Physical Channels
• A single GSM Carrier is divided into eight timeslots.
• Can support up to eight MS subscribers simultaneously.
• Each repetition of this sequence is called a “TDMA frame”.
2. Logical Channels

7. Broadcast Channels (BCH)
BCH channels are all downlink and are allocated to timeslot zero.
• FCCH: Frequency control channel sends the MS a burst of all ‘0’ bits
to allows MS to synchronise to the frequency of BS.
• SCH: Synchronisation channel enables TDMA-Frame number
synchronisation by sending the absolute value of the frame number
(FN), together with the BTS’s BSIC
• BCCH: Broadcast Control Channel sends network-specific
information such as radio resource management and control
messages, Location Area Code etc.

8. Common Control Channels (CCCH)
CCCH contains all point to multi-point downlink channels (BTS to
several MSs) and the uplink Random Access Channel:
• RACH: Random Access Channel is sent by the MS to request a resources
from the network e.g. an SDCCH channel for call setup.
• AGCH: Access Grant Channel is used to allocate a dedicated channel
(SDCCH) to the mobile.
• PCH: Paging Channel sends paging signal to inform mobile of a call.
• CBCH: Cell Broadcast Channel is an optional GSM Phase II implementations
for SMS broadcast messages, for example road traffic reports or network
engineering messages.

9. Dedicated Control Channels (DCCH)
DCCH comprise the following bi-directional (uplink / downlink)point to
point control channels:
• SDCCH: Standalone Dedicated Channel is used for call set up,
location updating and also SMS
• SACCH: Slow Associated Control Channel is used for link
measurements and signalling during a call
• FACCH: Fast Associated Control Channel is used (when needed) for
signalling during a call, mainly for delivering handover messages and
for acknowledgement when a TCH is assigned

10. GSM Network Interfaces

11. Frame Structure

12. Frame Structure
• Hyper Frames
– 2048 consecutive super frames
– Hyper frames are 3hours 29 min nearly
• Super Frames
– 51 consecutive traffic Multi frames or 26 continuous control
Multi frames
– Super frames = 6.12 sec
• Traffic Multi Frames
– Traffic multi frames = 26 continuous traffic frames (4.61ms * 26
= 120ms)
• Control Multi Frames
– Control multi frames = 51 continuous control frames (4.61ms *
51 = 235ms)

13. Bursts and its Types
Burst – Physical content of a time slot.
Normal Burst
Frequency Correction Burst
Synchronisation Burst
Dummy Burst
Access Burst (RACH)

14. GSM Call Flow

16. Key Performance Indicator
• Parameters fixed by service providers to monitor and judge
the performance of their network
• It is measured in two specific hours:
– NBH (Network Busy Hour)
– BBH (Bouncing Busy Hour)

17. Voice KPIs
KPIs are divided into three main types:
• Accessibility
• Retainability
• Speech Quality

18. Accessibility
• Paging Success Rate (>90%)
• Random Access success rate (>=98%)
• SDCCH blocking (<1%)
• SDCCH Drop (<1.4%)
• TCH Blocking (<2%)
• TCH assignment success rate (>98.5%)

19. Retainability
• TCH Drop (<2%)
• HOSR (>95%)
• DL Rx Quality (>95%)

20. Data KPIs
• Accessibility
– %of cells with hard UL blocking
– %of cells with hard DL blocking
– %of cells with soft DL PDTCH blocking
• Retainability
– %of TBF drop
• Data Quality
– Average DL throughput

21. Voice KPI Optimisation
• TCH blocking
Parameters to be checked
– Number of TRXs
– Hardware fault
– Half rate percentage
Cell Hour TRX TCH Designed Traffic Traffic SDCCH
TCH Blocking (User
Perceived)
CELLA 15 1 6 2.27 0.11 7 86.49
CELLB 20 1 5 1.65 7.68 15 62.70
CELLC 10 1 6 2.27 1.57 7 57.38
CELLD 21 1 6 2.27 11.80 15 40.33
CELLE 21 2 13 7.40 22.95 15 38.48

22. • TCH or SDCCH Drop
Parameters to be checked to reduced drops
– Low Signal Strength
– Bad Quality
– Excessive Timing Advance
– Sudden Lost Connection
Cell Hour TRX TCH
Designed
Traffic
Traffic SDCCH SD Traffic SD Drop
CELLA 15 2 12 6.61 18.86 15 22.10 4.49
CELLB 19 4 28 20.15 13.20 23 3.43 1.90
CELLC 21 2 13 7.40 7.26 15 3.60 3.20
CELLD 21 2 13 7.40 4.72 15 2.28 3.42
CELLE 20 2 13 7.40 5.29 15 3.77 1.89
Cell Hour TRX TCH Designed Traffic Traffic SDCCH TCH Drop
CELLA 20 2 13 7.40 0.80 15 220.00
CELLB 19 4 29 21.03 2.91 15 146.34
CELLC 21 4 28 20.15 6.92 23 132.93
CELLD 20 4 29 21.03 9.40 15 119.43
CELLE 11 2 13 7.40 1.15 15 85.71

23. • HOSR
Parameters to be checked to increase HOSR
– Neighbour tuning
– BCCH-BSIC Code verification
– Optimum neighbour
– AFP tool
Cell Hour TRX TCH
Designed
Traffic
Traffic SDCCH SD Traffic HOSR
CELLA 11 2 14 8.20 0.15 7 0.14 0.00
CELLB 21 4 29 21.03 20.02 15 3.01 7.65
CELLC 23 2 14 8.20 22.88 7 1.02 13.02
CELLD 23 6 45 35.60 24.29 15 1.03 13.99
CELLE 23 4 29 21.03 32.24 15 1.11 19.37
CELLF 20 4 29 21.03 12.69 15 1.44 20.21

24. • SDCCH Blocking
Parameters to be checked
– Traffic capacity
– SDCCH time slots
Cell Hour TRX TCH Designed Traffic Traffic SDCCH SD Traffic SD Blocking
CELLA 15 2 12 6.61 18.86 15 22.10 85.78
CELLB 19 4 28 20.15 13.20 23 3.43 74.67
CELLC 21 2 13 7.40 7.26 15 3.60 55.57
CELLD 21 2 13 7.40 4.72 15 2.28 48.14
CELLE 20 2 13 7.40 5.29 15 3.77 47.12

25. GSM Concepts used in Optimisation
• Adaptive configuration of Logical channels is to minimize
SDCCH congestion by automatically adapting the number
of SDCCHs in a cell to the demand for such channels.
• Power Control
• Frequency Hopping
• Overlaid - Underlaid cells

26. • Power Control
– Used for reducing interference
– Conserving battery life

27. • Frequency Hopping
– Baseband hopping
– Synthesizer hopping
• It is performed in TCH and SDCCH only.

28. • HSN – (Hopping Sequence Number)
• MAIO- (Mobile Allocation Index Offset )
HSN remains same, but frequency used by TRX are different.

29. • Overlaid - Underlaid cells
– Overlaid cells – low output power, small coverage, used in
1800 MHz band
– Underlaid cells – high output power, wider coverage, used
in 900 MHz band

30. Tools used for optimisation
• Map Info Tool
• OSS
– MRR – Measurement & Recording Report
– FAS – Frequency Allocation Support
– NCS – Neighbour Cell Support

31. Conclusion
• Telecom is a vast sector where our ultimate aim to provide
quality service to our customers.
• Thus, performance analysis of one’s network is very essential
to keep up in this competitive sector.
• At Idea Cellular, I learned about GSM fundamentals and
various network performance parameters.
• I also got an opportunity to apply these fundamentals in KPI
optimisation.

32. Thank You