Audio Streaming over Bluetooth: Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAn 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
MNSA 20043/24/2004
Outline
Introduction Background and related work Proposed approach Implementation and experiment results Conclusion
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
Introduction
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.
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
Bluetooth Overview
The “enabler” of Personal Area Network (PAN) Low power, low cost, and smaller chips
Mode FEC
Packet SymmetricThroughput
(kbps)
AsymmetricThroughput
(kbps)Size
(bytes)Length(slots)
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
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
Real-time StreamingReal-time Streamingadapt sending rate and stream qualityadapt sending rate and stream quality
Best-effort StreamingBest-effort Streamingadapt sending rateadapt sending rate
Streaming Overview
SCPSCP
RAPRAPTEARTEAR
TFRCTFRC
VTPVTP
HelixHelix
MicrosoftMicrosoft
All of the upper layer streaming protocols has no ideas about link layer behavior.
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
Link Layer Enhancements Three potential solutions [RFC 3366]:
1. Retransmission (e.g. ARQ)
2. Redundancy (e.g. FEC)
3. Interleaving
Challenges User-perceived streaming quality Random errors vs bursty errors
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
Retransmission - ARQ
Stop-and-wait ARQ: retransmit a packet until either the acknowledgement of a successful reception is received or the retransmission timeout is exceeded.
HighHighLowLowRetransmission timeoutRetransmission timeout
Enlarge the delay, and degrade the streaming quality
Increase reliability
More packets will be dropped, and the streaming quality will become poor
Decrease delay
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
Redundancy - FEC
ProsPros ConsCons
Robustness against random errors
Redundancy overhead
Bit 1 Bit 2 Bit 3 . . . Bit 14 Bit 15
Bit 16 Bit 17 Bit 18 . . . Bit 29 Bit 30
Bit 31 Bit 32 Bit 33 . . . Bit 44 Bit 45
. . . . . . . . . . . . . . . . . .
Bit n-14 Bit n-13 Bit n-12 . . . Bit n-1 Bit n
0 1 2 13 14
1
2
3
n/15
Bit sequence in packetAn Example:An Example: Bluetooth DM modeThe FEC coding scheme used in DM mode is a (15, 10) shortened Hamming code, in which each block of 10 information bits is encoded into a 15 bit codeword, and it is capable of correcting single bit error in each block.
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
Error Model
Good Bad Pbb
Pbg
Pgb
Pgg
gbbb
bbg PP
PP
1
1
gbbb
gbb PP
PP
1
Burst Error Model (aka Burst Error Model (aka Gilbert-Elliott model)Gilbert-Elliott model)
• Wireless errors are usually bursty in occurrences.
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
Wireless Channel Model (cont.)
0 0.25 0.5 0.75 1Pgb 0.60.75
0.9Pbb
020406080
100
Burst Error Length
Retransmissions are still required when burst errors are present!!Retransmissions are still required when burst errors are present!!
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
Related Work
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.
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
Proposed 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 n+1
If we save some time on sending packet n, then we should increase RTO on packet n+1
If we drop at least two of the last 5 packets, then we should reset RTO
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
RTO Update Equation
Initialization
Update
Reset
9.0 ; 1.1 ; 25.0
%75)(80min
droppedpacket if ;
SRTTRTT if ;
SRTTRTT if ;
'
)1('
SizeUsedBufferizeMaxBufferSRTO
RTO
RTO
RTO
RTO
RTTSRTTSRTT
)2%,75)((80
SizeUsedBufferizeMaxBufferSMaxRTO
RTTSRTT
)2%,75)((80 SizeUsedBufferizeMaxBufferSMaxRTO
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
RTP Packet
BNEP
L2CAP
HCI
Baseband
Audio Server
BNEP
L2CAP
HCI
Baseband
Audio Client128kbps MP380 ms/RTP packet
RTP Packet BufferFlush Timeout Packets
RTP Packet RTTLink Quality
Average DelayRTP Packet Loss Rate
Implementation
BlueZBlueZ
BluetoothBluetoothDeviceDevice
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
DH5 packet
MNSA 20043/24/2004
Measure Link Quality 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 ChipsetsIf BER (Bit Error Rate) = 0, LQ (Link Quality) = 255
If BER <= 40/40000, LQ = 255 – BER * 40000
If 40/40000<BER <= 4000/40000, LQ = 215 – ((BER / 32) * 40000)
If 4000/40000<BER <= 40000/40000, LQ=105– ((BER / 256)* 40000)
0
50
100
150
200
250
3000
0.01
0.02
0.02
0.03
0.04
0.05
0.06
0.06
0.07
0.08
0.09 0.1
Bit Error Rate
Lin
k Q
ual
ity
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
Experiments
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
0
200
400
600
800
1000
1200
1400
400 450 500 550 600
Tim
e (
mse
c)
RTP seqno
RTT
RTO
drop
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
10
20
30
40
50
60
70
80
90
100
0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004 0.0045
Pa
cke
t R
ate
(%
)
Bit Error Rate
Adapt pkt
Fixed 160 pkt
Fixed 400 pkt
Fixed 1200 pkt
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
100
150
200
250
300
350
400
0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004 0.0045
Avg
. D
ela
y T
ime
(m
s)
Bit Error Rate
Adapt delay
Fixed 160 delay
Fixed 400 delay
Fixed 1200 delay
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
Conclusion
Such cross-layer optimization can significantly improve application performance in PAN.
Our proposed approach is simple and applicable to other wireless technologies.
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
MNSA 20043/24/2004
Thank You!!Thank You!!
Audio Streaming over Bluetooth: An Adaptive ARQ Timeout ApproachAudio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach
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