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Traffic Capacity Challenges for TETRA Application Development

On February 15, 2000, Richard Dewey presented a comprehensive overview of traffic capacity issues in TETRA systems. The presentation delves into the types of bearer services, including individual, group, and broadcast calls, highlighting their performance characteristics. Dewey discusses mixed voice and data traffic profiles, utilizing a simple air interface model to provide insights into traffic performance. The implications of circuit and packet modes for data are examined, along with the factors affecting access and data transmission capacity. Key conclusions emphasize the importance of realistic traffic simulations in addressing these challenges.

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Traffic Capacity Challenges for TETRA Application Development

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  1. Traffic Capacity issues facing the TETRA Application Developer Richard Dewey 15 February 2000

  2. Telecom Consultants International Outline of presentation • TETRA tele and bearer services • Mixed voice + data traffic profiles • Insight from simple air interface model • Typical traffic performance results • Summary

  3. Tele Services Supported by TETRA Clear Speech or Encrypted Speech • INDIVIDUAL CALL (POINT TO POINT) • BROADCAST (POINT TO MULTIPOINT ONE WAY) • GROUP CALL (POINT TO MULTIPOINT) • ACKNOWLEDGED GROUP CALL (POINT TO MULTIPOINT)

  4. Bearer Services Supported by TETRA • Circuit mode unprotected data: 7.2, 14.4, 21.6, 28.8 kbits/sec • Circuit mode low protected data: 4.8, 9.6, 14.4, 19.2 kbits/sec • Circuit mode high protected data: 2.4, 4.8, 7.2, 9.6 kbits/sec • Packet connection oriented data • Packet connectionless data • Short Data Services - • 65535 Status messages (half reserved) • user defined data types • type 1: 16 bits data • type 2: 32 bits data • type 3: 64 bits data • type 4: up to 2047 bits data

  5. Traffic performance criteria • Voice calls • T95 average, T95 maximum • access throughput, blocking probability • system throughput • Data calls • intrinsic delay • throughput

  6. Mixed voice + data traffic profiles • Mixture of individual and group calls? • Mixture of voice and data? • Length of voice calls? • Size of data messages: packet and SDS1234 • Priorities for different voice calls?

  7. Simple model of air interface • Control channel • grants access • allocates traffic chans • carries packet data • Traffic channels • carry circuit mode voice + data SERVERS Control Queue server Queues 1 2 3 4 Data Access

  8. Control mechanisms for air interface • Access priority to get in to the system. • Queue priority gets in to the favoured Q. • Pre-emptive priority removes low priority active user to gain immediate service. SERVERS Control Queue server Queues 1 2 3 4 Data Access

  9. Performance limiting factors • Control channel loading • access on the uplink • capacity on the downlink • Traffic channel loading • availability of channels

  10. Monte Carlo simulation • Define traffic load • subscriber characteristics (individuals, groups, dispatchers, location) • traffic generated by each user • Generate traffic load • Run air interface protocol simulation • Analyse traffic runs • Plot results

  11. Results

  12. Summary • Realistic traffic results only by full simulation. • Will take account of • voice + data traffic mix • voice priority mix • mix of data bearer services (SDS1234 and status). • HOWEVER priority between voice and data is “an implementation issue”. • Supplementary or extended control channels can be set up to give improved data services.

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