Bluetooth: Quality of Service

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Bluetooth Quality of Service

• Reference QoS based scheduling for
  incorporating variable rate coded voice in
  Bluetooth Chawla, S. Saran, H. Singh, M.
  IEEE International Conference on Communications
  (ICC), 2001, pp. 1232 -1237 (BTQoS-1.pdf)

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Introduction

• Voice Activity Detection (VAD)
• Detecting silence periods in speed
• Reducing the coding rate during silence
• Incorporation of variable rate coded voice over
  BT would necessitate a substantial change to the
  scheduling policies
• BT intrinsically allocate 64Kbps to voice
• 1. Adaptive TSCO scheduling
• 2. For QoS of voice, EDD-based scheduling

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Scheduling

• For variable rate coded voice
• 1. Adaptive TSCO
• For voice channels with no error coding, TSCO is
  typically 6 TDD slots to account for 64 Kbps
  bandwidth
• To adapt to the coding rate, the time period of
  scheduling SCO connections can be increased
• For instance, TSCO 16 would correspond to a
  bandwidth usage of 24 Kbps, which is
  approximately the bandwidth allocated to voice in
  GSM during talkspurt
• In this scheme, we dynamically adjust TSCO
  depending on the activity of the call.
  Accordingly, TSCO toggles between two distinct
  values with change in activity of voice

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Scheduling (cont)
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Scheduling (cont)

• 2. Voice over ACL
• Use a QoS based scheduling scheme
• ? Latency based scheduling
• If a connection has latency of n slot, then
  each packet of that connection should be
  scheduled within n slots of its arrival ?
  scheduling based on deadline of packets
• Use a greedy Earliest Due Deadline (EDD) scheme
• EDD is known to give an optimal schedule in the
  sense that if it is possible to satisfy QoS
  requirements of every connection, they are
  satisfied
• Necessitates admission control for the system

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Scheduling (cont)

• For a voice connection, end-to-end latency of
  less than 100 ms is acceptable as it is not
  noticeable to the human ear
• A single hop should be much lesser than 100 ms
• In order to avoid large end to end delay and
  jitter, try to avoid queuing of more than one
  voice packet in the system
• Accordingly, choose max. tolerable scheduling
  delay of a voice connection to be the time gap
  between arrival of two packets
• Thus, the latency of voice for 22.8 Kbps
  connection should be 18 time slots ? corresponds
  to a latency of 11 ms

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Simulation Scenario

• Using Network Simulator
• Two state Markov chain model to simulate
  talkspurt and silence periods for voice
• Voice traffic in bursts of 20 ms length
• Coding rate (similar to that in GSM)
• 22.8 Kbps for talkspurt, 11.4 Kbps for silence
• Latency for voice connections
• 18 slots during activity, 36 slots during silence
• Latency for data connections
• 50 200 slots

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Simulation Results

• Fig. 3
• The scheduling delays for data packets in the
  case of adaptive TSCO are lesser on average than
  those in the case of fixed TSCO
• Fig. 4
• Similar results as Fig. 3
• Fig. 5
• Both proposed scheduling schemes perform better
  than voice over SCO
• Voice over ACL performs best

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Simulation Results (cont)
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Simulation Results (cont)
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Simulation Results (cont)
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Simulation Results (cont)
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Simulation Results (cont)
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Simulation Results (cont)
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Conclusion

• Variable rate coded voice in BT
• 1. Adaptive TSCO
• 2. Voice over ACL (EDD-based scheduling)