We investigate a collision-sensitive secondary network that intends to opportunistically aggregate and utilize spectrum of a primary network to achieve higher data rates. In opportunistic spectrum access with imperfect sensing of idle primary spectrum, secondary transmission can collide with primary transmission. When the secondary network aggregates more channels in the presence of the imperfect sensing, collisions could occur more often, limiting the performance obtained by spectrum aggregation. In this context, we aim to address the following fundamental query: How much spectrum aggregation is worthy with imperfect sensing? For collision occurrence, we focus on two different types of collision: One is imposed by asynchronous transmission, and the other is imposed by imperfect spectrum sensing. The collision probability expression has been derived in closed form with various secondary network parameters: primary traffic load, secondary user transmission parameters, spectrum sensing errors, and number of aggregated subchannels. In addition, the impact of spectrum aggregation on data rate is analyzed under the constraint of collision probability. Then, we solve an optimal spectrum aggregation problem and propose the dynamic spectrum aggregation approach to increase the data rate subject to practical collision constraints. Our simulation results clearly show that the proposed approach outperforms the benchmark that passively aggregates subchannels with lack of collision awareness.
- Collision probability
- opportunistic spectrum access
- secondary networks
- spectrum aggregation