RESOURCE ALLOCATION IN - MULTIUSER OFDM SYSTEMS

Abstract

communications over a wireless channel but the wireless environment limits the performance by causing time and frequency selective fading. To combat these situations, orthogonal frequency division multiplex (OFDM) is considered as a promising solution because of the robustness against frequency selective fading. OFDM can be used both as a modulation scheme and as a part of the multiple access technique. OFDMA, also referred to as multiuser OFDM, in which resources are allocated adaptively according to the variations of the channel is being considered as a modulation and multiple access method for 4`h generation wireless networks. In a typical multiple access scenario, each user has different QoS and bit rate requirements. The fact that different subcarriers experience different channel conditions for different users in a frequency selective fading environment can be exploited. Different adaptive resource allocation schemes are investigated in this thesis. We propose a new scheme for subchannel allocation in margin adaptive multiuser OFDM systems and its performance is compared with the existing margin adaptive scheme