Introduction

Wireless systems provide high flexibility and mobility support to their users. Each wireless system is allocated a fixed part of the available frequency spectrum for communication purposes. Table 3.1 lists the range of frequency allocated for some significant wireless services. A user in any wireless system is assigned a particular frequency within this pre-determined band either on permanent or on demand basis. With ever-increasing user density, planning the allocation of the available spectrum to users within the system has become important. Proper resource planning gives the following benefits: First, it aids in avoiding congestion and interference amongst the users. Second, efficient utilization of the otherwise limited frequency spectrum is obtained.

Vast varieties of multiplexing and access techniques are employed for efficient utilization of resources. Multiplexing is predominantly a physical layer function while access technique selection is a data link layer function of the OSI [Open Systems International] model. Multiplexing techniques help to divide the fixed system resource into multiple non-overlapping channels while access techniques are used to accommodate multiple users in these multiple channels, thus increasing the system user capacity Duplexing is another important process involved in preventing interference between uplink and downlink transmission from the same system entity. As multiplexing, duplexing and access methods are all interlinked in planning the resource allocation, they will be discussed together in this chapter.