RainDrop: A Multi-Rate Multi-Channel Wireless LAN
Tianbo Kuang
Qian Wu
Carey Williamson
Department of Computer Science
University of Calgary
Outline
• Problem Statement and Motivation
• Multi-Rate Multi-Channel (MRMC) protocol
• Simulation Evaluation of MRMC
• Summary and Conclusions
Problem Statement
• The IEEE 802.11b WLAN supports automatic rate selection
• Each station dynamically chooses its transmission rate of
either 1, 2, 5.5, or 11 Mbps, depending on channel conditions
(e.g., rate selection algorithm in Lucent’s WaveLAN-II)
• This is both a good thing and a bad thing...
AP
11Mbps
MH
MH
1 Mbps
MH
11Mbps
MH
1 Mbps
when sharing the
same physical channel
Performance Anomaly of IEEE 802.11b [Heusse et al. 2003]
• An ns-2 network simulation experiment showing the problem
Node 0
Server
Node 1
100 Mbps
AP
Range = 45m
start at
time = 0 s
Node 2
<8m
35 m
start at
time = 150 s
Node 3
Throughput of Node 0 versus time (before vs after)
Our Solution – Multi-Rate Multi-Channel (MRMC) WLAN
• Use multiple physical channels (3 or 4) simultaneously at AP,
each with a different transmission rate (static or dynamic)
1 Mbps
2 Mbps 5.5 Mbps
11 Mbps
RainDrop: A Multi-Rate Multi-Channel WLAN
AP
11 Mbps
5.5 Mbps
2 Mbps
Notes:
4x antenna “cost” (?) 1 Mbps
+77% capacity
Multi-Rate Multi-Channel (MRMC) MAC protocol
• Channel association algorithm
1. Beacon (channel, transmission rate, SNR threshold)
2. Get SNR
3. Channel association frame
MH
AP
4. Channel association grant
SNRavg = αlpha * SNRavg + (1- αlpha) * SNRnew
Simulation Evaluation of the MRMC protocol (ns-2)
Experiment 1. Effect of αlpha on throughput
• stationary scenario:
Server
AP
100 Mbps
5, 15, 25, 35m
MH
Simulation Evaluation of the MRMC protocol (ns-2)
Experiment 1. Effect of αlpha on throughput
• stationary scenario:
mobile scenario:
Server
AP
100 Mbps
100 Mbps
5, 15, 25, 35m
MH
< 45m
Simulation Evaluation of the MRMC protocol (ns-2)
Experiment 1. Effect of αlpha on throughput
• stationary scenario:
mobile scenario:
Server
AP
100 Mbps
100 Mbps
5, 15, 25, 35m
MH
< 45m
Simulation Evaluation of the MRMC protocol (ns-2)
Experiment 1. Effect of αlpha on throughput
• stationary scenario:
mobile scenario:
Server
AP
100 Mbps
100 Mbps
5, 15, 25, 35m
MH
< 45m
Experimental Factors
• Experiment 1: Effect of alpha
Stationary
Distance to AP
Mobile Speed
αlpha
Mobile
5m, 15m, 25m, 35m
0 m/s
< 45m
0.5m/s, 1m/s, 2m/s, 3m/s, 4m/s
0, 0.1,…0.9, 0.92, 0.94,…0.98
Wireless Channel Model: Rayleigh fading, Jakes’ method
Simulation Results: Effect of αlpha on Throughput
SNRavg = αlpha * SNRavg + (1- αlpha) * SNRnew
stationary
mobile
Simulation Evaluation of the MRMC Protocol (ns-2)
Expt 2. MRMC performance in a stationary scenario
(comparison to results for previous problem scenario)
Simulation Evaluation of the MRMC Protocol (ns-2)
Experiment 3. Static scenario with N mobile hosts
Server
Node N
AP
< 45m
100 Mbps
< 45m
Node 1
Experimental Factors and Performance Metrics
• Factors
 Number of nodes N: 2, 4, 6,…50
 MAC layer protocols: MRMC, WaveLAN-II
• Metrics:
 Total throughput of nodes (99% confidence intervals)
 Mean throughput for each node
Simulation Results
Total Throughput
Per-Node Throughput
Simulation Evaluation of the MRMC Protocol (ns-2)
Experiment 4. Mobile scenario with 20 hosts
Server
AP
100 Mbps
< 45m
Node 1
< 45m
Node 20
Simulation Evaluation of the MRMC Protocol (ns-2)
Experiment 4. Mobile scenario with 20 hosts
Server
AP
< 45m
100 Mbps
Node 20
< 45m
Node 1
Simulation Evaluation of the MRMC Protocol (ns-2)
Experiment 4. Mobile scenario with 20 hosts
Server
AP
< 45m
100 Mbps
< 45m
Node 1
Node 20
Simulation Evaluation of the MRMC Protocol (ns-2)
Experiment 4. Mobile scenario with 20 hosts
Server
AP
< 45m
Node 1
100 Mbps
< 45m
Node 20
Experimental Factors and Performance Metrics
• Factors
 Mean moving speed: 0.5 m/s, 1 m/s, 2 m/s, 3 m/s, 4 m/s
 MAC layer protocols: MRMC, WaveLAN-II
• Metrics:
 Total throughput of nodes (99% confidence intervals)
Simulation Results
Conclusions
• The proposed MRMC protocol is promising
• Performance is not very sensitive to value of alpha
• With 4 channels and 4 rates, the MRMC protocol
offers a 450% throughput advantage over the
WaveLAN-II IEEE 802.11b MAC protocol
• Super-linear throughput improvement (450%)
from 77% increase in channel capacity (4x cost?)
• Primary benefit: isolating low-rate/high-rate users
Future Work: Multiple APs