Introduction

The goal of a wireless sensor network (WSN) is to provide the end user with a more intelligent understanding of its life and environment. WSN is a class of special wireless ad-hoc networks. An ad hoc network is a group of wireless nodes that interconnect directly over a common wireless channel. Away from the traditional cryptographic techniques for ensuring security in a wireless system, most researchers started studying secrecy from a physical layer point of view. The increasing number of users demanding service has encouraged intensive research in wireless communications. The idea of cooperative communications came into existence to implement the idea of multiple-input–multiple-output system in a distributed manner. Time diversity, frequency diversity, and space diversity are the three basic techniques for providing diversity to wireless communication systems. The chapter also presents an overview on the key concepts discussed in this book.