Introduction

Digital modulation techniques can be largely divided into two categories. One is single-carrier modulation, which utilizes a single radio frequency (RF) to transmit data. The other is multi-carrier modulation, which utilizes simultaneously modulated multiple RF carriers in order to combat inter symbol interference (ISI) while increasing communication bandwidth. This chapter focuses on a particular type of multi-carrier modulation known as Orthogonal Frequency Division Multiplexing (OFDM). The idea of OFDM [1] was proposed in the 1960s followed a few years later by the Discrete Fourier Transform (DFT) based implementation algorithm [2]. Then, OFDM became practical and has been popular in a number of applications such as asymmetric digital subscriber line (ADSL), wireless local area network (WLAN), digital TV broadcasting (DTV). It also has become a strong candidate for 4th generation cellular land mobile radio system.

It is well known that OFDM modulation and demodulation can be implemented by IDFT and DFT. But in actual implementation, not only those DFTs but also several error compensation mechanisms are indispensable because orthogonality between parallel transmitted subcarrier signals are easily destroyed by synchronization errors such as RF error, clock sampling rate error, and FFT window position shift. When applying OFDM technology for mobile communication, Doppler induced RF errors easily distort a reception performance. Therefore the main contents of this chapter are two fundamental techniques to realize high-performance OFDM communication systems. These are Diversity technologies and Synchronization error Detection and Compensation methods. After this, real hardware implementation examples and their data are summarized.