Quality of service assessment of opportunistic spectrum access: a medium access control approach [dependability in the ubiquitous wireless access]

Opportunistic spectrum access (OSA) is a promising new spectrum management approach that will allow coexistence of both licensed and opportunistic users in each spectrum band, potentially decreasing the spectrum licensing costs for both classes of users. However, this has significant implications on the QoS experienced by the licensed and opportunistic spectrum users. In this article we investigate how tolerant to secondary user activity a licensed user should be so as to provide dependable communication with sufficient QoS to an opportunistic user. We also look at key multichannel MAC features for such OSA networks proposed in the literature, and discuss how the design of control channel management affects the QoS of opportunistic users as a function of the tolerance of licensed users. We quantify the trade-off between dependability of the OSA network and the dependability of licensed users. The main conclusion is that opportunistic users can indeed achieve good QoS, as long as the licensed users are not highly active. For example, in one of the scenarios we studied, opportunistic users can achieve a delay below 100 ms if licensed user activity stays below 30 percent.