Capacity improvement of wireless VoIP system based on resource allocation and cognitive radio

Abstract

Despite of the rapid growth of data services, voice services are still the major revenue earner for network service providers. Accordingly, voice over IP (VoIP) is one of the hottest trends in wireless communication systems because the network service providers can provide high-quality voice services at a relatively lower cost through the VoIP technology, which exploits traditional packet-switched IP networks. There are various research items for VoIP services, such as capacity improvement, QoS provisioning, power saving, VoIP codec, security, mobility management, and so on. In this thesis, we mainly focus on the capacity improvement based on the efficient resource allocation considering rate adaptation and cognitive radio. First, a new algorithm is proposed for wireless VoIP codecs that allocates radio resources in consideration of the variations in packet size and packet-generation period. This algorithm allows resources to be utilized more efficiently in Mobile-WiMAX systems. The outstanding performance of our proposed algorithm with respect to average throughput and average packet dropping probability is shown through intensive numerical analysis and simulations. VoIP capacity is compared with respect to the application of different VoIP codecs (G.729B, adaptive multirate (AMR)) and VoIP header compression schemes (payload header suppression (PHS) and robust header compression (ROHC)). Second, we propose a new framework to analyze performance considering finite-length queuing and adaptive modulation and coding (AMC) for multi-user VoIP services in wireless communication systems. We formulate an uplink VoIP system as a two-dimensional discrete-time Markov chain (DTMC) based on a Markov modulated Poisson process (MMPP) traffic model for VoIP services and MCS (modulation and coding scheme)-level set transition reflecting users` channel variations. We extend the transition modeling of the MCS-level for a single-user to the transition modeling of the MC...