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					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 11Mbps MH 1 Mbps

when sharing the same physical channel

MH 1 Mbps

Performance Anomaly of IEEE 802.11b [Heusse et al. 2003]

• An ns-2 network simulation experiment showing the problem
Server Node 0

100 Mbps

Node 1 AP Range = 45m

start at time = 0 s
Node 2

start at time = 150 s

Node 3

<8m 35 m

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

AP
4. Channel association grant

MH

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:
Server

mobile scenario:

AP
100 Mbps 5, 15, 25, 35m 100 Mbps

< 45m

MH

Simulation Evaluation of the MRMC protocol (ns-2) Experiment 1. Effect of αlpha on throughput
• stationary scenario:
Server

mobile scenario:

AP
100 Mbps 5, 15, 25, 35m 100 Mbps

< 45m

MH

Simulation Evaluation of the MRMC protocol (ns-2) Experiment 1. Effect of αlpha on throughput
• stationary scenario:
Server

mobile scenario:

AP
100 Mbps 5, 15, 25, 35m 100 Mbps

< 45m

MH

Experimental Factors

• Experiment 1: Effect of alpha
Stationary Mobile

Distance to AP Mobile Speed αlpha

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 AP 100 Mbps < 45m Node 1 < 45m

Node N

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 100 Mbps Node 20 < 45m < 45m

Node 1

Simulation Evaluation of the MRMC Protocol (ns-2) Experiment 4. Mobile scenario with 20 hosts

Server AP 100 Mbps < 45m Node 1 Node 20 < 45m

Simulation Evaluation of the MRMC Protocol (ns-2) Experiment 4. Mobile scenario with 20 hosts

Server AP 100 Mbps < 45m < 45m Node 1

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


				
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posted:5/21/2009
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