Signal Processing for Cognitive Radios

13

SPECTRUM DECISION-MAKING IN DSA COGNITIVE NETWORKS

13.1 INTRODUCTION

As we discussed in Chapter 12, dynamic spectrum sharing (DDS) invariably requires the secondary cognitive radios to have a certain level of spectrum awareness: Cognitive radios must be able to determine when a primary user channel is idle and when it is not. In Chapter 12, we discussed how secondary radios can detect whether a channel is idle or busy based on sensing observations. However, this is only one part of the spectrum sensing problem for DSS. Indeed, recall from Chapter 12 that the overall spectrum sensing problem for DSS is made of three decision-making problems: channel-state detection, channel sensing decision-making, and channel-access decision-making.

Let us again consider the primary–secondary coexistence scenario in which there are an M number of primary channels in the system, K_p number of primary users, and K_s number of secondary users. For simplicity of this discussion, let us assume that the primary transmissions are slotted as in Figure 12.3 and at the beginning of each slot there is a (relatively) short sensing interval during which all primary users will indicate whether they intend to use a particular channel for the duration of the subsequent slot. Before this, secondary cognitive radios need to make decisions on which channel to sense during this sensing interval. This is the channel sensing decision-making problem.

Once the channel state is determined from sensing observations, ...