To Stay or To Switch: Multiuser Multi-Channel Dynamic Access

In this paper we study opportunistic spectrum access (OSA) policies in a multiuser multi-channel random access cognitive radio network, where users perform channel probing and switching in order to obtain better channel condition or higher instantaneous transmission quality. Prior studies in this area include those on channel probing and switching policies for a single user to exploit spectral diversity, and those on probing and access policies for multiple users over a single channel to exploit temporal and multiuser diversity. By contrast, in this study we consider the collective switching of multiple users over multiple channels. This inevitably necessitates explicit modeling of the effect of collision. Furthermore, we consider finite arrivals, whereby users are not assumed to always have data to send and the demand for channel follows a certain arrival process. Under such a scenario, the users´ ability to opportunistically exploit temporal diversity (the temporal variation in channel quality over a single channel) and spectral diversity (quality variation across multiple channels at a given time) is greatly affected by the level of congestion in the system. We investigate the associated decision process in this case, and show that the optimal policy is given by a nested stopping rule which may be viewed as a type of generalization to results found in existing literature in this area. We analytically and numerically evaluate the extent to which congestion affects potential gains from opportunistic dynamic channel switching.