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QoS-Based Scheduling for Bluetooth Voice with Variable Rate Coding

Explore how QoS-based scheduling enhances Bluetooth voice communication with variable rate coding, optimizing throughput and latency. The study compares different schemes for incorporating voice in Bluetooth networks.

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QoS-Based Scheduling for Bluetooth Voice with Variable Rate Coding

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  1. QoS based Scheduling for incorporating Variable Rate Coded Voice in BLUETOOTH Shuchi Chawla, Huzur Saran, Mitali Singh June 13, 2001

  2. BLUETOOTH : A Wireless Personal Area Network • At most 1 master & 7 slaves in a piconet • TDMA for medium access • Slots of length 625μs • MAC is master-driven • Two kinds of links : • SCO – Synchronous Connection Oriented (Voice) • 64Kbps for voice • ACL – Asynchronous Connection Less (Data)

  3. TDD in Bluetooth • Master & slave transmit alternately

  4. Voice: BW requirements • Toll quality voice -- 64Kbps • Compressed voice -- much lesser • Empirical studies: • 60% inactivity in phone calls • Variable Rate Coding(VRC)based on activity • 23.8 Kbps and 11.4 Kbps • More than 110% saving!!

  5. Scheduling Voice in Bluetooth • Standard – Voice over SCO • Throughput improvement by Activity based Variable Rate Coding of voice. • Schemes proposed • Adaptive TSCO • Voice over ACL

  6. Adaptive Tsco • Tsco – period after which SCO connection is scheduled • Increase Tsco when lesser bandwidth for voice is required • Talkspurt: Tsco = 6 64Kbps • Silence: Tsco = 12 32Kbps

  7. Voice over ACL • QoS based scheduling scheme used • Earliest Due Deadline policy • Deadline = arrival time + acceptable latency • Latency for voice: • normally up to 100ms acceptable • Avoid queuing of more than 1 packet • Bandwidth requirement of ~23Kbps imposes a max latency of 11ms  18 time slots.

  8. Voice over ACL: Issues • Paging : All ACL connections put on hold for 18ms • We cannot put voice on hold for so long • During paging ACL voice also scheduled as SCO • This again limits max voice connections to 3. • ACL packets fragmented and reassembled at L2CAP • Send voice down the stack as SCO • At MAC layer schedule them as ACL • Assumption : Knowledge of slave status to master. • Separate Reverse Channel for this info • PiggyBacking – requires very few bits

  9. Scheme implemented Data Throughput (Kbps) Average delay (msec) Without voice 358.40 9.98 Voice over SCO 238.93 21.72 Voice over SCO with adaptive Tsco 257.24 18.09 Voice over ACL 274.24 11.78 Simulation results 1 voice connection

  10. Voice over SCO 119.4 36.47 Voice over SCO with adaptive Tsco 172.2 31.05 Voice over ACL 258.8 15.25 Simulation results 2 voice connections Scheme implemented Data Throughput (Kbps) Average delay (msec) Without voice 358.4 9.98

  11. Voice over SCO 0.0 Voice over SCO with adaptive Tsco 94.2 Voice over ACL 102.6 Simulation results 3 voice connections Scheme implemented Data Throughput (Kbps)

  12. Conclusions • Scheduling over ACL performs best, but changes to standard are required • Second option : Adaptive Tsco, considerable improvement in throughput over current scheme

  13. Bluetooth protocol stack

  14. Paging in Bluetooth

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