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

MH MH

MHMH

1 Mbps

11Mbps11Mbps

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

35 m

< 8 m

start at time = 0 s

start at time = 150 s

Node 0

Node 1

Node 2 Node 3

Server

100 Mbps

APRange = 45m

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

1 Mbps

2 Mbps

5.5 Mbps

11 Mbps

RainDrop: A Multi-Rate Multi-Channel WLAN

AP

Notes: 4x antenna “cost” (?)+77% capacity

Multi-Rate Multi-Channel (MRMC) MAC protocol

• Channel association algorithm

1. Beacon (channel, transmission rate, SNR threshold)

2. Get SNR3. Channel association frame

4. Channel association grant

SNRavg = αlpha * SNRavg + (1- αlpha) * SNRnew

APMH

Simulation Evaluation of the MRMC protocol (ns-2)

Experiment 1. Effect of αlpha on throughput

• stationary scenario:

5, 15, 25, 35m

AP

MH

Server

100 Mbps

Simulation Evaluation of the MRMC protocol (ns-2)

Experiment 1. Effect of αlpha on throughput

• stationary scenario:

5, 15, 25, 35m

AP

MH

Server

100 Mbps

mobile scenario:

< 45m

100 Mbps

Simulation Evaluation of the MRMC protocol (ns-2)

Experiment 1. Effect of αlpha on throughput

• stationary scenario:

5, 15, 25, 35m

AP

MH

Server

100 Mbps

mobile scenario:

< 45m

100 Mbps

Simulation Evaluation of the MRMC protocol (ns-2)

Experiment 1. Effect of αlpha on throughput

• stationary scenario:

5, 15, 25, 35m

AP

MH

Server

100 Mbps

mobile scenario:

< 45m

100 Mbps

Experimental Factors

• Experiment 1: Effect of alpha

Stationary Mobile

Distance to AP 5m, 15m, 25m, 35m < 45m

Mobile Speed 0 m/s 0.5m/s, 1m/s, 2m/s, 3m/s, 4m/s

αlpha 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

stationary mobile

SNRavg = αlpha * SNRavg + (1- αlpha) * SNRnew

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)

AP

Server

100 Mbps

Node 1

Node N

< 45m

< 45m

Experiment 3. Static scenario with N mobile hosts

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)

AP

Server

100 Mbps

< 45m

< 45m

Node 1

Node 20

Experiment 4. Mobile scenario with 20 hosts

Simulation Evaluation of the MRMC Protocol (ns-2)

AP

Server

100 Mbps

< 45m

< 45m

Node 1

Node 20

Experiment 4. Mobile scenario with 20 hosts

Simulation Evaluation of the MRMC Protocol (ns-2)

AP

Server

100 Mbps

< 45m

< 45m

Node 1 Node 20

Experiment 4. Mobile scenario with 20 hosts

Simulation Evaluation of the MRMC Protocol (ns-2)

AP

Server

100 Mbps

< 45m

< 45m

Node 1

Node 20

Experiment 4. Mobile scenario with 20 hosts

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