GPRS/EGPRS Design & Optimization

Reviewing  GPRS/EGPRS

• Understanding voice versus data
  • Deterministic and random
  • Data services and mix of data
  • Voice versus data for system performance
• Standards overview
  • GPRS/EGPRS nodal and interface definitions
    • SGSN
    • GGSN
    • Gb
    • Gn
    • Ga
    • Gr
    • Gd
    • Gs
    • Gi
    • Ge
    • Gx
    • Gy
    • Gz
• GPRS bearer and signaling:  Definitions, groups, and mapping of:
  • RLC/MAC layer
  • PRACH
  • PAGCH
  • PCCCH
  • PDTCH
  • PDCH
  • PACCH
  • Random access requests and packet queuing notifications
  • USF
• GPRS message sequence
  • Attached request
  • PDP context activation
  • Primary/secondary PDP context
  • GTP-U
  • GTP-C
  • GTP’
  • GPRS homing
  • Location areas and updates
  • Routing areas and updates

Systems Engineering Considerations

• Exercises
  • Mapping bearer traffic to total traffic:  Class will walk through several real world scenarios showing the impact of signaling overhead to various coding schemas
  • Simple estimations of throughput with various time slot configurations:  Class will be asked to predict and collectively model in simplistic terms throughput for various timeslot allocation with the effect of IP packet error rate to arrive at a simple, estimated throughput calculation

More on GPRS

• Coding schema
• Temporary block flow – TBF
• Channel assignment:  Hopping versus non-hopping
• BLER
• Throughput versus delay
• C/I ratio
• SR-ARQ
• Automatic retransmission request
• BEC
• FEC

GPRS Problem Areas

• Air Interface
  • Coverage
  • Interference
  • TBF usage
  • Congestion
  • Coding schema non-optimal
  • Transmission time wasted
• Core network
  • Contention at SGSN
  • Packet loss
  • Processing delays at SGSN/GGSN
  • Buffer/overflow

Problems, Causes, and Troubleshooting

• No IP address
• No PDP context
• No GPRS attach
• RAU failure
• No uplink data
• No downlink data
• No GPRS indicator

Final Exercises

• Create a test scenario to simulate parallel GSM and GPRS traffic load on a limited number of theoretical cells
  • Determine the impact of GPRS load on GSM quality
  • When and how to prioritize GPRS over GSM
  • When and how to prioritize GSM over GPRS
• Create a test scenario whereby GPRS traffic demand during the busy hour reaches 25% of total traffic
  • What is the impact on the air interface?  BLER, CS, FEC/BEC, SR-ARQ?
  • What is happening at RA and LA?
  • What about MIP?  How does high versus low mobility provide additional impact?
  • How should this be optimized and where does one begin?
  • How do the eight available coding and modulation schemes available in EGPRS impact throughput?  What are the underlying causes of EGPRS using higher versus lower coding schemes?

Course Recap and Conclusion