Multiple Access Schemes

Multiple access schemes are used whenever there is a need for a number of independent users to share a resource that may be scarce or expensive. This chapter considers some of the popular multiple access schemes. These schemes can be divided into three categories: orthogonal access schemes, controlled access schemes, and random access schemes. The chapter reviews the basic fixed channel access schemes that are the foundation of the orthogonal access schemes. Most multiplexing schemes are based on the concept of dividing a communication link into independent communication channels. Three methods used to divide a communication link into independent channels are as follows: frequency‐division multiplexing (FDM), time‐division multiplexing (TDM), and code‐division multiplexing (CDM). Orthogonal multiple access schemes refer to techniques that allow two or more users to share radio frequency spectrum in a manner that avoids collision. The main concern of the random access schemes is transmission scheduling to minimize the probability of packet collision.