Title: Improving Wireless Link Throughput via Interleaved FEC
1Improving 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
2Background
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
3Background
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
4Background
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
5Improving Wireless Link Throughput via
Interleaved FEC
Gilbert-Elliott Burst Error Model
6Burst Error Length
Improving Wireless Link Throughput via
Interleaved FEC
At high Pbb, burst length are too long do not
expect FEC to work
7Packet 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!
8Proposed 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
9Improving Wireless Link Throughput via
Interleaved FEC
Proposed Approach I-FEC
- 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
10Evaluation
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
11Packet Error Rates (1 hop)
Improving Wireless Link Throughput via
Interleaved FEC
Pgb 0.0005
Pbb 0.2
12TCP Performance
Improving Wireless Link Throughput via
Interleaved FEC
Pbb 0.2
Pbb 0.2
13TCP Performance
Improving Wireless Link Throughput via
Interleaved FEC
Pgb 0.0003
Pgb 0.0003
14Conclusion
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
15T h a n k s
Improving Wireless Link Throughput via
Interleaved FEC