Broadband Access: Wireline and Wireless - Alternatives for Internet Services

14Wireless Broadband Access: Air Interface Fundamentals

14.1 Introduction

In this chapter, we lay down the groundwork needed to understand the technologies that have evolved for wireless broadband access, by discussing various concepts that form the basis of modern wireless communication systems. By nature, the wireless medium is not a closed medium, and it is therefore susceptible to interference and may need to support shared access. Furthermore, due to the propagation characteristics of electromagnetic waves, wireless links can be very unreliable unless several steps are taken to mitigate this shortcoming. In the following sections, we first discuss duplexing techniques used to support two-way communications. We next explore the basic building blocks that comprise the physical layer of a robust wireless communication system, and concepts pertaining to shared access of the medium. Finally, we discuss algorithms such as link adaptation and scheduling, which control the operation of the physical layer and are vital to the performance of the system. As an example application of these concepts, we describe a satellite-based broadband access system.

14.2 Duplexing Techniques

Duplex communications allow the two ends of a communication link to transmit and receive simultaneously. This mode of communications is also referred to as full-duplex, and is in contrast to simplex communications, which is only unidirectional (e.g., broadcast TV). Most broadband access systems tend to use ...