Minimum Required Learning and Impact of Information Feedback Delay for Cognitive Users

This paper studies the value of learning for cognitive transceivers in dynamic wireless networks. We quantify the utility improvement that can be obtained by a wideband user that learns the stationary usage pattern of the spectrum occupied by narrowband users and, based on this learned information, adapts its transmission. Specifically, we investigate the basic tradeoff between the learning duration and the achievable performance in stationary environments. We apply optimization and large-deviation theory to analytically derive an upper bound of the minimum required learning duration, given the user's tolerable performance loss and outage probability. Furthermore, since learning techniques require the information feedback of the spectrum usage pattern between the transceivers, we investigate how a cognitive user can further improve its performance by taking into account its feedback delay. The impact of inaccurate delay estimation on the achievable performance is also quantified.