Puheliikenteen suorituskyky pistekoodinointifunktiota käyttävässä WLAN:ssa

IEEE 802.11 (WLAN) has been designed primarily for non-real-time data applications with Distributed Coordination Function (DCF). For transmission of real-time data, the supplementary medium access protocol Point Coordination Function (PCF) is used, which resides on top of DCF and uses a centralized polling scheme. This thesis implements the basic Point Coordination Function algorithm in a time-driven simulation program written in C language, and evaluates the performance of voice transmission in a Wireless LAN with PCF supported. The evaluation covers the throughput, delay distribution, the frame loss rate, and compares the performance for two kinds of PCM payload length. The simulation results show that the proper superframe size should be approximately similar to the traffic interval, which results in good performance. Further, the simulation shows that long payload provides higher throughput and lower frame loss rate than short payload, but meanwhile, long payload brings longer access delay. When the number of VoIP mobile stations increases, the performance degrades dramatically. Therefore, PCF provides limited good service differentiation to the real-time applications