Wireless Communications Systems Design

7Orthogonal Frequency-Division Multiplexing

The Orthogonal Frequency-Division Multiplexing (OFDM) became the most popular transmission technique for a broadband communication system because it has many advantages such as robustness to multipath fading channels and high spectral efficiency. The Orthogonal Frequency-Division Multiple Access (OFDMA) is used for a multiuser system based on the OFDM technique. It allows multiple users to receive information at the same time on different parts of the channels. The OFDMA typically allocates multiple subcarriers to an individual user. Many recent standards use the OFDM/OFDMA technique. For example, European Telecommunications Standards Institute (ETSI) included the OFDM technique in the Digital Video Broadcasting-Terrestrial (DVB-T) system in 1997. The WiFi included the OFDM technique for its physical lаyer in 1999. In addition, IEEE802.16e/m and LTE adopted the OFDMA technology. In this chapter, we design the OFDM system and discuss hardware implementation issues.

7.1 OFDM System Design

We should consider many design parameters of the OFDM system. The first design parameters of the OFDM system for wireless communications are Inter-Carrier Interference (ICI) power, the size of the Discrete Fourier Transform (DFT), and the subcarrier spacing (or the OFDM symbol duration). It is important to determine the optimal DFT size balancing protection against multipath fading, the Doppler shift, and complexity [1]. The DFT size and subcarrier ...