The broadband wireless access (BWA) system, the latest technology of the wireless communication system, will become one of the major network types in the future. It is more superior than the other existing wireless systems because of its high data rate. In recent years, scientists and engineers investigate the relay station (RS) for packets forwarding due to the reason of coverage percentage of the base station (BS). The merit of the RS is to provide a longer transmission range and higher data rate to overcome this disadvantage. However, considering the queuing delay, transmission delay, and the propagation delay, the forwarded packets may suffer from the additional delay in the RS. In this paper, we propose an architecture base on the Markov chain model to analyze the potential delays and throughput enhancement caused by the RS. Simulation results show that the RS can provide a higher throughput than the legacy IEEE 802.16d based BWA system and reduce the end-to-end transfer delay. The investigation will give subscribers stations (SSs) a better strategy for data transmission. Moreover, based on the investigation, the BS can also benefit from adjusting the transmission power to achieve a higher throughput.

1 Introduction 1
1.1 History of WiMAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 IEEE 802.16-2004 MAC . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.1 The frame structure of WiMAX . . . . . . . . . . . . . . . . . 2
1.2.2 Process of joining the network . . . . . . . . . . . . . . . . . . 3
1.2.3 Process of transmitting a packet . . . . . . . . . . . . . . . . . 4
1.3 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 WiMAX MAC 8
2.1 WiMAX MAC with Relay Station . . . . . . . . . . . . . . . . . . . . 8
2.2 Relationship between Range and Rate . . . . . . . . . . . . . . . . . 9
2.2.1 Friis Free Space Model . . . . . . . . . . . . . . . . . . . . . . 9
2.2.2 Modulation and Range . . . . . . . . . . . . . . . . . . . . . . 10
2.3 Related Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.1 Backo® . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.2 Multi-rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.3 Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3 Analysis Model Design 13
3.1 Assumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2 Architecture of WiMAX networks with RS . . . . . . . . . . . . . . . 15
3.3 Queuing Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.3.1 Queuing model of SS . . . . . . . . . . . . . . . . . . . . . . . 16
3.3.2 Queuing model of RS . . . . . . . . . . . . . . . . . . . . . . . 19
3.3.3 Queuing model of BS . . . . . . . . . . . . . . . . . . . . . . . 20
3.4 Bandwidth Request Delay Estimation . . . . . . . . . . . . . . . . . . 21
3.5 Throughput Estimation . . . . . . . . . . . . . . . . . . . . . . . . . 22
4 Simulation Model and Results 25
4.1 Simulation Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1.1 Scenario of Simulation . . . . . . . . . . . . . . . . . . . . . . 26
4.2 Simulation Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2.1 Arrival rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2.2 Transmission power . . . . . . . . . . . . . . . . . . . . . . . . 29
5 Conclusion 33
Bibliography 34

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