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Improving Wireless Link Throughput via Interleaved FEC

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Improving Wireless Link Throughput via Interleaved FEC Ling-Jyh Chen, Tony Sun, M. Y. Sanadidi, Mario Gerla Computer Science Department, University of California at ... – PowerPoint PPT presentation

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Title: Improving Wireless Link Throughput via Interleaved FEC


1
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

2
Background
Improving Wireless Link Throughput via
Interleaved FEC
  • Dealing with packet losses
  • End-to-end
  • ARQ Retransmission in TCP
  • FEC Robust Audio Tool (RAT) 14
  • Partial Correctness Interleaving as in Video
    transfer protocols RFC 2354
  • Link Layer Level
  • ARQ as in HDLC, or Bluetooth link layer protocol
  • FEC as in 802.11a and Bluetooth

3
Background
Improving Wireless Link Throughput via
Interleaved FEC
  • Problems
  • ARQ 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

4
Background
Improving Wireless Link Throughput via
Interleaved FEC
  • 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

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
5
Improving Wireless Link Throughput via
Interleaved FEC
Gilbert-Elliott Burst Error Model
6
Burst Error Length
Improving Wireless Link Throughput via
Interleaved FEC
At high Pbb, burst length are too long do not
expect FEC to work
7
Packet Error Rate after FEC
Improving Wireless Link Throughput via
Interleaved FEC
Pgb 0.0005
Packet Size FEC Level Pbb 0.1 Pbb 0.3 Pbb 0.5 Pbb 0.7 Pbb 0.9
100 bytes (15,10) 3.25 9.42 15.44 21.47 28.61
100 bytes (7,4) 3.39 10.24 16.92 23.45 30.18
100 bytes None 32.92 32.93 32.94 32.98 33.23
200 bytes (15,10) 7.40 20.48 31.84 42.00 51.16
200 bytes (7,4) 6.76 19.39 30.79 41.28 50.91
200 bytes None 55.09 55.10 55.11 55.13 55.29
500 bytes (15,10) 16.86 42.59 60.57 73.33 82.68
500 bytes (7,4) 16.09 41.90 60.51 73.76 83.15
500 bytes None 86.49 86.49 86.49 86.50 86.55
  • When Pbb is high, FEC does not help much!

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

9
Improving Wireless Link Throughput via
Interleaved FEC
Proposed Approach I-FEC
  1. Bluetooth DM mode (FECed already!)

(b) I-FEC
  • The FEC overhead is the same as DM mode
  • The latency caused by interleaving is negligible,
    since I-FEC interleaves data in bit level within
    one link layer packet, instead of packet level
    cross different packets

10
Evaluation
Improving Wireless Link Throughput via
Interleaved FEC
  • 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
    NS2 simulator)
  • Simulation Topology (a) one hop (b) two hops

11
Packet Error Rates (1 hop)
Improving Wireless Link Throughput via
Interleaved FEC
Pgb 0.0005
Pbb 0.2
12
TCP Performance
Improving Wireless Link Throughput via
Interleaved FEC
Pbb 0.2
Pbb 0.2
13
TCP Performance
Improving Wireless Link Throughput via
Interleaved FEC
Pgb 0.0003
Pgb 0.0003
14
Conclusion
Improving Wireless Link Throughput via
Interleaved FEC
  • I-FEC, a hybrid approach incorporating the
    robustness of FEC coding to random errors and the
    survivability of interleaving to burst errors
  • I-FEC is simple and applicable to other link
    technologies, as long as FEC is already there

15
T h a n k s
Improving Wireless Link Throughput via
Interleaved FEC
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