Time-efficient broadcasting in cognitive radio networks

In this paper, we study the delay minimization problem for wireless data broadcasting in cognitive radio networks (CRN). In CRN, each secondary user (SU) has a set of available channels to communicate with each other but there may not be a common available channel set among all the SUs. Therefore, a simple way to shorten the broadcasting delay among them is to select a minimal set of available channels which cover all SUs in the network. However, this scheme may incur a fairness problem in resource sharing among SUs and also lower the system resource utilization. To tackle this problem, we assign channels to SUs for data broadcasting service in downlink sub-frames by jointly considering broadcast delay minimization and fair resource sharing. We formulate this problem as a nonlinear integer programming problem, and show that it is NP-hard by applying a reduction from the 3-dimensional matching problem. We then propose an enumerative algorithm to find an optimal solution and design a greedy-based polynomial-time heuristic algorithm to reduce the computational complexity. The simulation results show that our enumerative algorithm not only effectively reduces the broadcasting delay but also ensures the fairness among SUs in resource sharing. We also show that the performance gap between our enumerative algorithm and our heuristic algorithm is small.