ABSTRACT
This chapter discusses the Orthogonal Frequency Division Multiplexing (OFDM) and Spatial Diversity techniques. OFDM is one of the most advanced techniques used in wireless mobile communications. OFDM is a FDM modulation technique for transmitting large amounts of digital data over a radio wave. Code Division Multiple Access (CDMA) was found to perform poorly in a single cellular system, with each cell only allowing 7–16 simultaneous users in a cell, compared with 128 for OFDM. CDMA is a spread spectrum technique that uses neither frequency channels nor time slots. With CDMA, the narrow band message is multiplied by a large bandwidth signal that is a pseudo random noise code. CDMA is achieved by modulating the data signal by a pseudo random noise sequence, which has a chip rate higher then the bit rate of the data. The PN code sequence is a sequence of ones and zeros, which alternate in a random fashion.
