OFDM Communication with Cooperative Relays

Introduction 1.1 Cooperative relay communicationsSignal fading due to multi-path propagation is one of the major impairments to meet the demands of next generation wireless networks for high data rate services.To mitigate the fading effects, time, frequency, and spatial diversity techniques or their hybrid can be used.Among different types of diversity techniques, spatial diversity is of special interest as is does not incur system losses in terms of delay and bandwidth efficiency.Recently, cooperative diversity in wireless network has received great interest and is regarded as a promising technique to mitigate multi-path fading, which results in a fluctuation in the amplitude of the received signal.The cooperative communications is a new communication paradigm which generates independent paths between the user and the base station by introducing a relay channel.The relay channel can be thought of as an auxiliary channel to the direct channel between the source and destination.The basic idea behind cooperation is that several users in a network pool their resources in order to form a virtual antenna array which creates spatial diversity (Laneman et al., 2004; Sendonaris et al., Part I, 2003; Sendonaris et al., Part II, 2003).Since the relay node is usually several wavelengths distant from the source, the relay channel is guaranteed to fade independently from the direct channel, which introduces a full-rank Multiple-input-multiple-output (MIMO) channel between the source and the destination.This cooperative spatial diversity leads to an increased exponential decay rate in the error probability with increasing signalto-noise ratio (SNR) (Liu et al., 2009).Before discussing cooperative OFDM, let us first review some fundamental knowledge of OFDM and MIMO, which is associated with the cooperative OFDM study in this chapter.1.2 Physical layer of cooperative wireless networks (OFDM & MIMO) 1.2.1 OFDM basics In the modern wireless communication, OFDM technology has been widely used due to its spectral efficiency and inherent flexibility in allocating power and bit rate over distinct subcarriers which are orthogonal to each other.Different from a serial transmission, OFDM