Date of Award

Spring 2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical Engineering

Committee Director

Min Song

Committee Member

Linda L. Vahala

Committee Member

Frederic D. McKenzie

Call Number for Print

Special Collections LD4331.E55 G67 2007

Abstract

Wireless Local Area networks (WLAN) and Wireless Personal Area Networks (WPAN) provide complimentary services using the same unlicensed radio frequency band of operation. The 802.11b WLAN operates in the 2.4 GHz band and uses a Direct Sequence Spread Spectrum technique. It is designed to cover large areas ranging up to 100 meters in diameter, which may connect hundreds of computers. Bluetooth (BT) WPAN also operates in the same frequency band as the IEEE 802.lib and it uses a Frequency Hopping Spread Spectrum technique. BT is primarily used for communications between notebooks, palm units and other personal computing devices within relatively short distances ranging up to 10 meters. As the benefits of utilizing these services become increasingly apparent, the likelihood of mutual interference may also increase.

In this thesis an algorithm called Interference Aware Scheduling-Adaptive Frequency Hopping (IAS-AFH) is proposed to evaluate the performance of 802.11b devices in the presence of Bluetooth (BT) devices. It is an appropriate combination of Bluetooth Interference Aware Scheduling (BIAS) and Adaptive Frequency Hopping (AFH) techniques aimed at modifying the BT frequency hopping sequence. BIAS would be ideal where the interference levels change rapidly. AFH may be more suitable for slow changing environments. It is conjectured that an appropriate combination of using BIAS and AFH

within the same scenario should give a better performance than either method alone. BIAS could be used to respond to the changes quickly to a change in the environment and AFH could be used if the interference persists for a long interval of time. The BT devices sense the channel to check for any transmission in a particular frequency slot. If the slot is "bad" or occupied, the transmission is withdrawn until the slot becomes "good" or available. This continues for a particular amount of time and if the interference persists for a longer period, then the frequency hopping sequence is modified to replace the bad channel with good ones to increase the available number of channels for hopping. The withdrawal time period is chosen based on the amount of delay, which can be acceptable without affecting the systems performance. An analytical channel model for AFH and IAS-AFH based on standard path loss-log normal shadowing-AWGN-Rayieigh multi-path fading channel model is developed. The probability of collision (Pc) due to BT on 802.11b at Medium Access Control (MAC) layer is calculated in terms of the network and radio propagation parameters. Based on Pc the packet error rate and the throughput of the 802.11b system are calculated.

Simulations and analysis of the model was done in MATLAB to calculate the throughput of the system using the existing algorithms and the proposed algorithm and the results were compared. The results show an improvement with the proposed IAS-AFH in terms of packet error rate and throughput.

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DOI

10.25777/3zdw-cf56

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