Improving Wireless Link Throughput via Interleaved FEC LingJyh

Improving Wireless Link Throughput via Interleaved FEC Ling-Jyh Chen, Tony Sun, M. Y. Sanadidi, Mario Gerla Computer Science Department, University of California at Los Angeles June 2004 ISCC 2004

Improving Wireless Link Throughput via Interleaved FEC Background Dealing with packet losses: n End-to-end n n ARQ: Retransmission in TCP FEC: Robust Audio Tool (RAT) [14] Partial Correctness: Interleaving as in Video transfer protocols [RFC 2354] Link Layer Level n n June 2004 ARQ: as in HDLC, or Bluetooth link layer protocol FEC: as in 802. 11 a and Bluetooth ISCC 2004 2

Improving Wireless Link Throughput via Interleaved FEC Background n Problems: ¨ ARQ n does not perform well for high error rates ¨ FEC works if errors are not bursty ¨ Interleaving introduces latency Our Proposal: I-FEC ¨ combines FEC and Interleaving at Bluetooth link layer for high-rate bursty errors June 2004 ISCC 2004 3

Improving Wireless Link Throughput via Interleaved FEC Background n n n In Bluetooth DM mode, FEC uses a (15, 10) Hamming code Each block of 10 information bits is encoded into a 15 bit codeword Capable of correcting single bit error in each block Packet June 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 ISCC 2004 Asymmetric Throughput (kbps) 4

Improving Wireless Link Throughput via Interleaved FEC Gilbert-Elliott Burst Error Model June 2004 ISCC 2004 5

Improving Wireless Link Throughput via Interleaved FEC Burst Error Length At high Pbb, burst length are too long; do not expect FEC to work June 2004 ISCC 2004 6

Improving Wireless Link Throughput via Interleaved FEC Packet Error Rate after FEC Pgb = 0. 0005 Packet Size 100 bytes 200 bytes 500 bytes n FEC Level Pbb = 0. 1 Pbb = 0. 3 Pbb = 0. 5 Pbb = 0. 7 Pbb = 0. 9 (15, 10) 3. 25 % 9. 42 % 15. 44 % 21. 47 % 28. 61 % (7, 4) 3. 39 % 10. 24 % 16. 92 % 23. 45 % 30. 18 % None 32. 92 % 32. 93 % 32. 94 % 32. 98 % 33. 23 % (15, 10) 7. 40 % 20. 48 % 31. 84 % 42. 00 % 51. 16 % (7, 4) 6. 76 % 19. 39 % 30. 79 % 41. 28 % 50. 91 % None 55. 09 % 55. 10 % 55. 11 % 55. 13 % 55. 29 % (15, 10) 16. 86 % 42. 59 % 60. 57 % 73. 33 % 82. 68 % (7, 4) 16. 09 % 41. 90 % 60. 51 % 73. 76 % 83. 15 % None 86. 49 % 86. 50 % 86. 55 % When Pbb is high, FEC does not help much! June 2004 ISCC 2004 7

Improving Wireless Link Throughput via Interleaved FEC Proposed Approach: I-FEC Inherits both the robustness to random errors from FEC and the survivability to burst errors from Interleaving n Simulated I-FEC in Bluetooth, and to Bluetooth DH (no FEC coding) and DM (FEC coding) modes n June 2004 ISCC 2004 8

Improving Wireless Link Throughput via Interleaved FEC Proposed Approach: I-FEC (a) Bluetooth DM mode (FECed already!) n n (b) I-FEC The FEC overhead is the same as DM mode The latency caused by interleaving is negligible, since IFEC interleaves data in bit level within one link layer packet, instead of packet level cross different packets June 2004 ISCC 2004 9

Improving Wireless Link Throughput via Interleaved FEC Evaluation n Comparison of I-FEC, DH, and DM mode packets using 5 -timeslot Bluetooth packets. ¨ PER with different Pgb and Pbb (using Monte Carlo Simulation) ¨ TCP Throughput with different Pgb and Pbb (using NS 2 simulator) ¨ Simulation Topology: (a) one hop (b) two hops June 2004 ISCC 2004 10

Improving Wireless Link Throughput via Interleaved FEC Packet Error Rates (1 hop) Pbb = 0. 2 June 2004 ISCC 2004 Pgb = 0. 0005 11

Improving Wireless Link Throughput via Interleaved FEC TCP Performance Pbb = 0. 2 June 2004 ISCC 2004 Pbb = 0. 2 12

Improving Wireless Link Throughput via Interleaved FEC TCP Performance Pgb = 0. 0003 June 2004 ISCC 2004 Pgb = 0. 0003 13

Improving Wireless Link Throughput via Interleaved FEC Conclusion I-FEC, a hybrid approach incorporating the robustness of FEC coding to random errors and the survivability of interleaving to burst errors n I-FEC is simple and applicable to other link technologies, as long as FEC is already there n June 2004 ISCC 2004 14

Improving Wireless Link Throughput via Interleaved FEC Thanks June 2004 ISCC 2004 15