Capacity of voice service over WiMAX networks

Abstract

Voice over Internet Protocol (VoIP) is expected to be widely supported in wireless environment in the coming days. VoIP is a delay-sensitive real time application and thus requires an efficient uplink scheduling algorithm. IEEE 802.16d, formally known as 802.16-2004, defines five scheduling algorithms in providing different levels of quality of service (QoS) for fixed broadband wireless access (BWA). They are known as Unsolicited Grant Service (UGS), Extended Real-time Polling Service (ertPS), Real-time Polling Service (rtPS), Non-real-time Polling Service (nrtPS) and Best Effort (BE). Among all of them, only UGS, ertPS and rtPS are suitable for supporting real time traffic. In this work, I investigate the performance of VoIP services in constant bit rate (CBR) with no silence suppression using G.711 and G.726 as the voice codec under these three scheduling algorithms. The experiment is implemented using QualNet 4.0 software. The simulation is carried out in one single site and site-to-site respectively. In each case, different channel bandwidths are studied. It aims at finding the maximum number of simultaneous voice users that could be supported in UGS, ertPS and rtPS. To determine the upper bound on the number of simultaneous calls, three metrics are looked up: average one-way end-to-end delay, jitter and packet loss rate. Through the analysis of voice capacity, the results show that UGS achieves the best performance in all scenarios while ertPS ranks second and rtPS is the worst.