In conventional cognitive radio, the primary network usually remains unchanged. In some cases, however, the primary network operator may wish to accommodate secondary user access. In this paper, we assess the secondary user VoIP capacity when primary basestation scheduling is designed to be secondary network friendly. Friendliness is measured by the number of connections that can be supported subject to typical quality of service constraints in the presence of delay tolerant primary traffic. An offline scheduler is first derived that maximizes friendliness using an integer linear program formulation. We show that this schedule can be found using a minimum cost flow graph construction in time complexity that is polynomial in the number of time slots. Two online scheduling algorithms are then compared that achieve various levels of friendliness. The first algorithm operates by having the primary network temporally shape its residual capacity subject to satisfying its own packet deadline constraints. The second algorithm assumes virtual secondary calls and applies scheduling to both primary traffic and virtual secondary traffic. Results are presented for a variety of parameters that show the degree to which friendly scheduling can improve secondary user VoIP capacity compared to non-friendly primary scheduling.

In conventional cognitive radio networks it is usually assumed that the primary network remains unchanged. The onus is then placed on the secondary network users to make the best use of any residual radio capacity. In some situations however, the primary network operator may wish to accommodate secondary user access. This objective has motivated recent work which considers simple modifications at the primary user stations that would lead to better secondary spectrum availability. In this paper primary base station scheduling mechanisms are proposed which are designed to be friendly from a secondary network user perspective. We focus on packet scheduling algorithms which maximize friendliness when the secondary users are transmitting real-time VoIP traffic. An optimization problem is first formulated which can maximize friendliness over finite time intervals. An on-line scheduling algorithm is then proposed which attempts to achieve this goal. This is done by having the primary network temporally shape its residual capacity subject to satisfying its own packet deadline constraints. Simulation results are presented which show that our proposed scheme results in better secondary user real-time traffic support compared with conventional scheduling.