Effect of Flat Fading in 802.11 MAC for Cross Layer Evaluation Using Channel Emulator Adriano Almeida Goes goes.adriano@gmail.com Omar Carvalho Branquinho omar.branquinho@puc-campinas.edu.br Norma Reggiani nreggiani@puc-campinas.edu.br Douglas Zambianco douglas.zambianco@gmail.com Pontifícia Universidade Católica de Campinas Centro de Ciências Exatas, Ambientais e de Tecnologias Faculdade de Engenharia Elétrica Rodovia Dom Pedro I km 136 – Campinas – Brasil ABSTRACT WLAN 802.11 operating in 2,4 GHz are being intensely implanted mainly in public environments. In these environments mobility is always a present characteristic. The objective of this work is to analyze the behavior of 802.11 MAC with flat fading. To reach this objective an emulation system was developed to create the flat fading channel phenomenon. With a WLAN and the emulator was possible to show the cross layer effect, evaluating the WLAN performance analyzes in mobility conditions. The experiments evaluated: rate of transmission in each modulation level, data rate in the transport layer, network efficiency, jitter and throughput. The network information was obtained through SNMP. The results show that the 802.11 MAC had problems to support services that need high performance, as VoIP and Streaming. Therefore when the receiver is in movement the degradation does not allow the quality required by these types of services. Keywords  PWLAN, WLAN, Rayleigh, Weibull, Flat fading, wireless, MAC, IEEE802.11. I. INTRODUCTION Each time more 802.11 WLAN (Wireless Local Area Network) [1], are being used in the market in wide scale. The performance depends on the position of the user and its mobility. WLAN used in public environment (PWLAN) can be had accessed by diverse types of equipment, as for example, cellular, palm tops, PDAs, laptops, among others portable and mobile devices. The 802.11 MAC has an anomaly effect that degraded the performance [2][3]. This type of network supports well services that do not need high performance such as, email, HTTP, ftp, among others. However for services like video-on-demand, VoIP, Streaming, among others, that require high availability and functionality, there are serious doubts if the WLAN performance will be good enough. In this work it is studied the efficiency of the net and the effect of cross layer through the emulation of the flat fading channel. For mobile applications the attention must be in the environment conditions, once there are diverse phenomena that degrade the WLAN efficiency significantly, for example, multi path. To analyze WLAN operating in these conditions it is necessary a tool to reproduce these phenomena and take into account the requirements of this type of application. This article presents results of WLAN performance using a work bench to emulate signal strength variation and evaluate the efficiency with Weibull distribution [4] that takes in consideration some factors normally not considered in other models for indoors propagation. The radio propagation tests to evaluate performance always were a laborious task requiring sophisticated equipment. The currently WLAN possess ways of measurement of the signal intensity, signal-noise ratio, number of packets in each modulation level, among others, through the protocol of management of net SNMP (Simple Network Management Protocol). The objective of this work is to emulate the flat fading phenomenon through a work bench and evaluate the WLAN performance with different Weibull distribution factor, to determine the cross layer effect. The work is organized in the following form: in section II presents the flat fading emulation process in 802.11 WLAN operating in 2,4 GHz [5,6,7]. In section III, the software and the hardware used are described. Section IV presents the results network efficiency, as well as an analysis of the obtained results. Section V presents a preliminary test in VoIP. Finally, section VI presents the conclusion. Second International Conference on Systems (ICONS'07) 0-7695-2807-4/07 $20.00 © 2007