Audio%20Streaming%20over%20Bluetooth:%20An%20Adaptive%20ARQ%20Timeout%20Approach

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Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach

• Ling-Jyh Chen, Rohit Kapoor, Kevin Lee, M. Y.
  Sanadidi, Mario Gerla

Department of Computer Science, University of
California at Los Angeles
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Outline
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach

• Introduction
• Background and related work
• Proposed approach
• Implementation and experiment results
• Conclusion

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Introduction
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach

• Wireless PAN is becoming popular nowadays.
• Digital media, such as audio/video streaming, is
  becoming more desired than before.
• The varying nature of the wireless link makes
  audio streaming over wireless become a
  challenging problem.
• A well-designed solution should minimize the
  packet loss rate and delay of perceived streaming
  data.

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Bluetooth Overview
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach

• The enabler of Personal Area Network (PAN)
• Low power, low cost, and smaller chips

Mode FEC Packet Packet SymmetricThroughput(kbps) AsymmetricThroughput(kbps) AsymmetricThroughput(kbps)
Mode FEC Size (bytes) Length(slots) SymmetricThroughput(kbps) AsymmetricThroughput(kbps) AsymmetricThroughput(kbps)
DM1 yes 17 1 108.8 108.8 108.8
DM3 yes 121 3 258.1 387.2 54.4
DM5 yes 227 5 286.7 477.8 36.3
DH1 no 27 1 172.8 172.8 172.8
DH3 no 183 3 390.4 585.6 86.4
DH5 no 339 5 433.9 723.2 57.6
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Streaming Overview
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach
SCP
VTP
RAP
Helix
TEAR
Microsoft
TFRC
All of the upper layer streaming protocols has
no ideas about link layer behavior.
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Link Layer Enhancements
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach

• Three potential solutions RFC 3366
• Retransmission (e.g. ARQ)
• Redundancy (e.g. FEC)
• Interleaving
• Challenges
• User-perceived streaming quality
• Random errors vs bursty errors

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Retransmission - ARQ
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach

• Stop-and-wait ARQ retransmit a packet until
  either the acknowledgement of a successful
  reception is received or the retransmission
  timeout is exceeded.

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Redundancy - FEC
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach
Pros Cons
Robustness against random errors Redundancy overhead
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Error Model
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach

• Wireless errors are usually bursty in
  occurrences.

Burst Error Model (aka Gilbert-Elliott model)
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Wireless Channel Model (cont.)
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach
Retransmissions are still required when burst
errors are present!!
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Related Work
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach

• S. Krishnamachari et al proposed to adaptively
  change the maximum number of MAC layer
  retransmissions and FEC encoding level in the
  application layer by using the estimated MAC
  layer link quality (SNR).
• However, the link quality prediction may not be
  appropriate due to the dynamics of wireless
  networks.

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Proposed Approach
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach

• Adaptive ARQ Timeout in Bluetooth
• Problem The deployed stop and wait ARQ is
  harmful to real-time streaming audio over
  Bluetooth, especially in the error prone
  environment.
• Aim to reduce the audio packet delay and loss
  rate
• Ideas
• If we spent too much time on sending packet n,
  then we should decrease RTO on packet n1
• If we save some time on sending packet n, then we
  should increase RTO on packet n1
• If we drop at least two of the last 5 packets,
  then we should reset RTO

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RTO Update Equation
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach

• Initialization
• Update
• Reset

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Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach
Implementation
128kbps MP380 ms/RTP packet
Average DelayRTP Packet Loss Rate
RTP Packet BufferFlush Timeout Packets
RTP Packet RTTLink Quality
DH5 packet
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Measure Link Quality
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach

• Get_Link_Quality function call (in BT spec.)
• Get_Link_Quality This command returns the value
  of the Link Quality. It returns a number between
  0 and 255, with the higher value representing a
  better channel. Each Bluetooth module vendor will
  determine how to measure the link quality
• For CSR Bluetooth Chipsets
• If BER (Bit Error Rate) 0, LQ (Link Quality)
  255
• If BER lt 40/40000, LQ 255 BER 40000
• If 40/40000ltBER lt 4000/40000, LQ 215 ((BER /
  32) 40000)
• If 4000/40000ltBER lt 40000/40000, LQ105 ((BER /
  256) 40000)

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Experiments
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach
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Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach
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Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach
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Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach
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Conclusion
Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach

• Such cross-layer optimization can significantly
  improve application performance in PAN.
• Our proposed approach is simple and applicable to
  other wireless technologies.

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Audio Streaming over Bluetooth An Adaptive ARQ
Timeout Approach

• Thank You!!