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Enhancing Bluetooth TCP Throughput via Packet Type Adaptation

Enhancing Bluetooth TCP Throughput via Packet Type Adaptation. Ling-Jyh Chen, Rohit Kapoor, M. Y. Sanadidi, Mario Gerla Dept. of Computer Science, UCLA. Outline of the Talk. The problem : Wireless interference and bit errors severely affect TCP efficiency.

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Enhancing Bluetooth TCP Throughput via Packet Type Adaptation

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  1. Enhancing Bluetooth TCP Throughput via Packet Type Adaptation Ling-Jyh Chen, Rohit Kapoor, M. Y. Sanadidi, Mario Gerla Dept. of Computer Science, UCLA

  2. Outline of the Talk • The problem: Wireless interference and bit errors severely affect TCP efficiency. • The opportunity: Bluetooth offers multiple packet type options with different FEC and packet lengths. Moreover, the link layer API provides link error quality information. Opportunity for cross-layer adaptation. • Key idea: dynamically select packet type based on measured link quality. • The results: we show that the “Adaptive Packet Type” approach in Bluetooth can effectively enhance TCP performance. ICC 2004

  3. Who still remembers Bluetooth? Personal Area Network Designed for “cable” replacement Application Examples • Automatic synchronization of calendars, address books, business cards • Proximity operation (camera to cellphone, etc) ICC 2004

  4. m s m s s s Bluetooth Physical Link • Point to point link • master - slave relationship • radios can function as masters or slaves • Piconet • Master can connect to 7 slaves • Each piconet has max capacity =1 Mbps • Frequency hopping pattern is determined by the master ICC 2004

  5. f1 f5 f3 f4 f2 f6 m s1 s2 625 µsec 1600 hops/sec Piconet MAC Protocol : TDM/Polling ICC 2004

  6. f1 f5 f4 f6 m s1 s2 625 µsec Data rate depends on type of packet Multi Slot Packets ICC 2004

  7. DM1 DH1 DM3 DH3 DM5 DH5 Data Packet Types Asymmetric Symmetric 2/3 FEC Asymmetric Symmetric No FEC ICC 2004

  8. Bluetooth packet types • DH: Stop and Wait ARQ • DM: ARQ as well as 2/3 FEC codes to correct single bit errors • FEC coding scheme: • (15, 10) Hamming code, • each block of 10 information bits is encoded into a 15 bit codeword • can correcting a single bit error in each block. ICC 2004

  9. Throughput Analysis • DH mode: (ARQ)PER:1 hop Throughput:2 hop Throughput: • DM mode: (ARQ+FEC)PER:1 hop Throughput:2 hop Throughput: P: Packet Error Rate, B: Bit Error Rate, S: Packet Size, T: Max Throughput ICC 2004

  10. PER vs BER ICC 2004

  11. Bluetooth Throughput ICC 2004

  12. Proposed Approach • Adaptive Packet Type (APT): • In BT specs, the function call, Get_Link_Quality, returns the Quality of the specified Link. • We read the returned link Quality Value, and adapt packet type so as to optimize throughput. ICC 2004

  13. Simulation 1: Fixed BER Time: 600 secondsTCP Packet Size: 500 bytesBuffer Size: 9000 bytes ICC 2004

  14. Simulation 2: Varying BER Time: 600 secondsTCP Packet Size: 500 bytesBuffer Size: 9000 bytesBER: changes between 0.0001 and 0.0005 every 1 second ICC 2004

  15. Simulation 3: Measured BER Traces • 802.11 interference experiments using CSR chipset • CSR provides LQ vs BER conversion tables: If BER (Bit Error Rate) = 0, LQ (Link Quality) = 255; perfect channel. 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). • Simulation: Time: 600 seconds TCP Packet Size: 500 bytesBuffer Size: 9000 bytesBER: using the BER trace ICC 2004

  16. Simulation 3: measured BER trace ICC 2004

  17. Conclusions • In Bluetooth, TCP throughput collapses with BER above 0.03% (eg, BER caused by near 802.11 interference) • APT (Adaptive Packet Type) approach can restore TCP throughput to acceptable values for much higher BER (we tested up to .3%) • APT technique can be applied to any wireless link with packet length and FEC options, and with link quality (ie BER) feedback. • Further work on BT crosslayer optimization will include: • Adaptive optimization of number of retransmissions (for a mix of TCP and real time traffic) • Interleaved FEC over multiple frames ICC 2004

  18. T h a n k you ICC 2004

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