Introduction

Wireless communication involves transmission of messages over radio channels which are prone to noise and interference. In order to ensure reliable transmission, several processes are involved both at the transmitting and receiving end. In Chapter 1, the block diagram of a wireless communication system was explained. This chapter will focus on coding, modulation, diversity and equalization techniques.

Source Coding

The end-user generates information that has to be transmitted towards the receiver. The generated user message may contain several redundancies that can be easily omitted such that the user message still remains in understandable format. Removal of redundancies to an acceptable limit is the main function of a source encoder. This main criterion behind the source coding principle leads to two types of coding techniques, namely lossless coding and lossy coding. The former type of source coding techniques ensures that the original user message is reconstructed at the receiver end. These coding variants are also referred to as entropy coding or noiseless coding techniques. On the other hand, in the latter type, the source coding is done in such a way that at the receiver end, only an approximation of the original user message can be reconstructed.

Depending upon the code length of the source encoder output and the corresponding user message length, lossless coding can be classified into four types:

• • Fixed-to-fixed mapping: In this technique, a fixed number of user message symbols are mapped to codeword of fixed length.

• • Fixed-to-variable mapping: In this technique, a fixed number of user message symbols are mapped to codeword of varying length. All the symbols in the user message do not have equal probability of occurrence.