Signal Processing for Cognitive Radios

15COOPERATIVE COGNITIVE COMMUNICATIONS

15.1 INTRODUCTION

In Chapter 12, we discussed how secondary cognitive radios may make spectrum sensing decisions as a group with the aid of an SSDC. Such spectrum sensing frameworks are normally called cooperative spectrum sensing: Secondary cognitive radios cooperate among themselves to render spectrum sensing more accurate, effective, and efficient. In cognitive radio networks (CRNs), cooperation can, however, be used in a much broader sense than just for cooperative spectrum sensing. Indeed, initially cooperative communication was developed for improving performance of wireless communications systems independent of cognitive radios. The cognitive and intelligent abilities of a cognitive radio, or a CRN, of course provide an ideal platform to fully realize the potential gains of cooperation. Hence, naturally, it was later brought into CRN.

In general, cooperative strategies used among nodes in communications systems can be termed cooperative communications techniques. Cooperative spectrum sensing is just one form of cooperative communications. In fact, it is an incarnation of one of the traditional approaches used for improving the received signal-to-noise ratio (SNR) in wireless communications, namely, the spatial diversity. However, the more direct ancestor to cooperative communications as a broader theme arguably is the multiple-input multiple-output (MIMO), or dual antenna array, communication that was developed during the 1990s. ...