On the Capacity Region of Cognitive Multiple Access over White Space Channels

TL;DR

This paper analyzes the capacity regions for multiple secondary users sharing white space channels with primary users, considering side information and proposing optimal rate and power allocation schemes.

Contribution

It models the white space sharing as a multi-switch channel, derives bounds on achievable rates, and proposes an optimal allocation scheme for cognitive radio systems.

Findings

Side information significantly impacts achievable rates.

The proposed scheme improves sum rate performance.

Bounds are tight in certain scenarios.

Abstract

Opportunistically sharing the white spaces, or the temporarily unoccupied spectrum licensed to the primary user (PU), is a practical way to improve the spectrum utilization. In this paper, we consider the fundamental problem of rate regions achievable for multiple secondary users (SUs) which send their information to a common receiver over such a white space channel. In particular, the PU activities are treated as on/off side information, which can be obtained causally or non-causally by the SUs. The system is then modeled as a multi-switch channel and its achievable rate regions are characterized in some scenarios. Explicit forms of outer and inner bounds of the rate regions are derived by assuming additional side information, and they are shown to be tight in some special cases. An optimal rate and power allocation scheme that maximizes the sum rate is also proposed. The numerical results reveal the impacts of side information, channel correlation and PU activity on the achievable rates, and also verify the effectiveness of our rate and power allocation scheme. Our work may shed some light on the fundamental limit and design tradeoffs in practical cognitive radio systems.