Transmission capacities for overlaid wireless networks with spatial multiplexing

In this paper, we investigate the performance of open-loop spatial multiplexing in overlaid ad hoc networks. Based on a stochastic geometry model, we derive exact closed-form expressions for the transmission capacity of two coexisting networks (a primary network vs. a secondary network) employing spatial multiplexing with zero-forcing (ZF) receivers. Simulation results confirm the accuracy of our expressions. In addition, we discuss the impact of multi-antenna scheme on the transmission capacity of the overlaid networks. Our findings show that the sum transmission capacity of the overlaid networks will improve significantly over that of a single network if a slight outage probability increase is allowable for the primary network. This improvement can be further boosted if spatial multiplexing is employed with more antennas. But when the antenna number exceeds a certain limit, spatial multiplexing may produce negative effect for the overlaid network.