Audio Streaming over Bluetooth An Adaptive ARQ Timeout

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 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Outline Introduction n Background and related work n Proposed approach n Implementation and experiment results n Conclusion n 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Introduction n n 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. 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Bluetooth Overview n n The “enabler” of Personal Area Network (PAN) Low power, low cost, and smaller chips Packet 3/24/2004 Mode FEC Size (bytes) Length (slots) Symmetric Throughput (kbps) DM 1 yes 17 1 108. 8 DM 3 yes 121 3 258. 1 387. 2 54. 4 DM 5 yes 227 5 286. 7 477. 8 36. 3 DH 1 no 27 1 172. 8 DH 3 no 183 3 390. 4 585. 6 86. 4 DH 5 no 339 5 433. 9 723. 2 57. 6 MNSA 2004 Asymmetric Throughput (kbps)

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Streaming Overview Best-effort Streaming Real-time Streaming adapt sending rate and stream quality SCP RAP TEAR TFRC VTP Helix Microsoft All of the upper layer streaming protocols has no ideas about link layer behavior. 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Link Layer Enhancements n Three potential solutions [RFC 3366]: Retransmission (e. g. ARQ) 2. Redundancy (e. g. FEC) 3. Interleaving 1. l Challenges User-perceived streaming quality l Random errors vs bursty errors l 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Retransmission - ARQ n Stop-and-wait ARQ: retransmit a packet until either the acknowledgement of a successful reception is received or the retransmission timeout is exceeded. Decrease delay Low Increase reliability Retransmission timeout More packets will be dropped, and the streaming quality will become poor 3/24/2004 MNSA 2004 High Enlarge the delay, and degrade the streaming quality

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Redundancy - FEC Pros Robustness against random errors Cons Redundancy overhead An Example: Bluetooth DM mode The 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. 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Error Model • Wireless errors are usually bursty in occurrences. Burst Error Model (aka Gilbert-Elliott model) 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Wireless Channel Model (cont. ) Retransmissions are still required when burst errors are present!! 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Related Work n 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). n However, the link quality prediction may not be appropriate due to the dynamics of wireless networks. 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Proposed Approach n 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: n n n 3/24/2004 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 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach RTO Update Equation Initialization n n Update n Reset 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Implementation Audio Client Average Delay RTP Packet Loss Rate Blue. Z RTP Packet BNEP L 2 CAP HCI RTP Packet Buffer Flush Timeout Packets Bluetooth Device Baseband 3/24/2004 Audio Server 128 kbps MP 3 80 ms/RTP packet RTP Packet RTT DH 5 packet Link Quality MNSA 2004 Baseband

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Measure Link Quality n Get_Link_Quality function call (in BT spec. ) n 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 n For CSR Bluetooth Chipsets If 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) 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Experiments 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Conclusion n Such cross-layer optimization can significantly improve application performance in PAN. n Our proposed approach is simple and applicable to other wireless technologies. 3/24/2004 MNSA 2004

Audio Streaming over Bluetooth: An Adaptive ARQ Timeout Approach Thank You!! 3/24/2004 MNSA 2004