ABSTRACT
CONTENTS 4.1 WiMAX-The IEEE 802.16 System .......................................................... 57
4.1.1 Core Components and Topology ................................................. 57 4.1.2 Frequency of Operation and Service Capacity ........................... 58
4.2 The PHY and MAC Layer of WiMAX ..................................................... 58 4.2.1 The PHY ........................................................................................... 58 4.2.2 The MAC ......................................................................................... 60
4.2.2.1 MAC Frame Format ........................................................ 61 4.2.2.2 Aggregation ...................................................................... 62 4.2.2.3 Fragmentation .................................................................. 63 4.2.2.4 Connection Setup and Transmission ............................ 63 4.2.2.5 Automatic Repeat Request ............................................. 64 4.2.2.6 Minislots ........................................................................... 65
4.3 VoIP ............................................................................................................... 65 4.3.1 Quality of VoIP and R-Score ......................................................... 66 4.3.2 Effect of Delay ................................................................................. 67 4.3.3 Effect of Loss ................................................................................... 67 4.3.4 Effect of Delay and Loss on R-Score ............................................ 68
4.4 Supporting VoIP over WiMAX ................................................................. 69 4.4.1 Packet Restore Probability ............................................................. 69
4.4.1.1 Decreasing Payload Keeping Code Length Fixed ...... 69 4.4.1.2 Increasing Code Length Keeping Payload Fixed ........ 70 4.4.1.3 Increasing Both Payload and Code ............................... 70
4.4.2 Enabling ARQ Mechanism ............................................................ 70 4.4.3 Optimal MPDU Size ....................................................................... 71 4.4.4 Dynamic Allocation of Minislots .................................................. 72
4.5 Simulation Model and Results ................................................................. 72 4.5.1 Simulation Parameters ................................................................... 73 4.5.2 Simulation Results .......................................................................... 73
4.6 Conclusions ................................................................................................. 75 References ............................................................................................................. 76
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In spite of the growing popularity of data services, voice services still remain the major revenue earner for the network service providers. The two most popular ways of providing voice services are the packet switched telephone networks (PSTN) and the wireless cellular networks. Deployment of both these forms of networks require infrastructures that are usually very expensive. Alternative solutions are being sought that can deliver good quality voice services at a relatively lower cost. One way to achieve low cost is to use the already existing IP infrastructure. Protocols used to carry voice signals over the IP network are commonly referred to as voice over IP (VoIP) protocols. In more common terms, it signifies the phone service (voice) over the Internet using IP.
