Secondary Network Optimization for Overlaid Wireless Networks with MIMO Spatial Multiplexing

This paper investigates the transmission capacity of the secondary network in overlaid ad hoc networks with multi-antenna spatial multiplexing. Based on stochastic geometry tools, we study the effects of the node density and the transmission power of the secondary network on the transmission capacity performance. We derive the optimal node density for the secondary network, and subsequently the optimal transmit power ratio between the primary network and the secondary network. Our findings show that increasing the node density of the secondary network will result in an increase in the transmission capacity of the secondary network under a reasonable target outage probability assumption. The optimal node density and transmit power ratio are mainly influenced by the target outage probability and the permitted outage probability increment. On the other hand, numerical results show that the transmission capacity increases over the antenna number. Moreover, the antenna number has little effect on the optimal transmission power ratio.