  In cognitive radio networks, spectrum sensing is a crucial technique to
discover spectrum opportunities for the Secondary Users (SUs). The quality of
spectrum sensing is evaluated by both sensing accuracy and sensing efficiency.
Here, sensing accuracy is represented by the false alarm probability and the
detection probability while sensing efficiency is represented by the sensing
overhead and network throughput. In this paper, we propose a group-based
cooperative Medium Access Control (MAC) protocol called GC-MAC, which addresses
the tradeoff between sensing accuracy and efficiency. In GC-MAC, the
cooperative SUs are grouped into several teams. During a sensing period, each
team senses a different channel while SUs in the same team perform the joint
detection on the targeted channel. The sensing process will not stop unless an
available channel is discovered. To reduce the sensing overhead, an
SU-selecting algorithm is presented to selectively choose the cooperative SUs
based on the channel dynamics and usage patterns. Then, an analytical model is
built to study the sensing accuracy-efficiency tradeoff under two types of
channel conditions: time-invariant channel and time-varying channel. An
optimization problem that maximizes achievable throughput is formulated to
optimize the important design parameters. Both saturation and non-saturation
situations are investigated with respect to throughput and sensing overhead.
Simulation results indicate that the proposed protocol is able to significantly
decrease sensing overhead and increase network throughput with guaranteed
sensing accuracy.
