Implementation and Simulation Study of 802.11b-Based Multi Rate WLAN and Ad Hoc Networks

Abstract

Abstract The focus of this project will be on studying the behaviour of throughput changes of the cell when nodes send their data in different bit rate. The main goal of this thesis was to develop techniques and tools that can cope with multiple data rate, behaviour. The project involved the following goals: · Gain a deeper understanding of how 802.11/802.11b works both at the PHY and MAC Layer. · Implementation of 802.11b extension in NS-2. · Simulate maximum achievable throughput for one single UDP session · Analyse throughput, delay and jitter of a station with mobility. · Analyse throughput, delay and jitter of a station with mobility and pause time. · Analyse throughput, delay and jitter of one-hop behaviour where stations in a cell send their data with different bit rate. · Analyse throughput, delay and jitter of two-hop and three-hop behaviour where stations in a cell send their data with different bit rate. After conducting throughput analysis on simulation it is found that the throughput obtained by wireless node is much smaller then the nominal bit rate of 11 Mbps. Co-existence between the fast and slow host in the radio channel decreases the performance of fast host considerably. The main reason for this is the basic CSMA/CA protocol. This access method guarantees that the long-term probability for accessing the channel is equal for all hosts, so when a slow host takes control of the medium for long time it penalizes the fast transmitting host. Furthermore if RTS-CTS mechanism is used it imposes additional delay as these packets are exchanged before any data packets are sent. In the case when there are flows with multi-hop, additional delay will be imposed and the packet drops in the intermediate nodes. This can stem from packet collisions or buffer overflows. However when there are multi-hop flows concurrently with on-hop flows sending at same data rate considerable decrease in throughput for one-hop flow will happen. In the case when there is different and lower data rate for multi-hop flow, it happens that in period the fast host captures the channel leading to starvation for the slower-flows