5.1 Introduction

The aim of this chapter is to provide some theoretical background on the OFDM transmission technique. A brief introduction to OFDM is given in Section 5.2. We review the block diagram of a "classic" OFDM system, which employs a GI to mitigate the impairments of the multipath radio channel. We also discuss several design considerations related to hardware properties and derive the mathematical model for an idealized system, leading to the conclusion that data symbols can be transmitted independently of each other [i.e., without ISI and intercarrier interference (ICI)]. Moreover, the effects of synchronization imperfections are analyzed, like carrier-frequency and phase offsets and timing errors.

Section 5.3 introduces a method of calculating uncoded BERs for this idealized OFDM system model. This method is largely based on work presented in [1]. Differential and coherent detection schemes can be evaluated for Rayleigh and Rician fading channels. We also show that, for the system proposal under investigation, differential detection in time direction is much preferable to differential detection in frequency direction. Imperfect synchronization and channel estimation may be assessed by extending the system model used and by incorporating the SNR degradations due to ICI and ISI. Basic aspects are discussed in this chapter. Issues for further refinement of the methods are addressed.

Section 5.4 presents conclusions and recommendations.

5.2 OFDM Introduction and System Model

OFDM is a parallel transmission scheme, where a high-rate serial data stream is split up into a set of low-rate substreams, each of which is modulated on...