Transmission Capacity of Decode-and-Forward Cooperation in Overlaid Wireless Networks

In this paper, we employ a stochastic geometry model to analyze the transmission capacity of the Decode-and-Forward (DAF) cooperation scheme in an overlaid wireless network where a primary (PR) network and a secondary (SR) network coexist together. The PR users employ DAF scheme and have a higher priority to access the channel, whereas the SR users use only direct transmission. Because of the fact of coexistence, the interference from SR network seriously affects the performance of PR network. Assuming that simultaneous transmitters in both networks are randomly located in space according to Poisson point processes, we develop outage probabilities for both DAF and direct transmission schemes in both deterministic and Rayleigh fading channels. By defining transmission capacity in terms of the outage probability, a desired data rate and the density of transmissions, we further quantify transmission capacities for both schemes. It shows that the use of cooperative transmission achieves much better reliability and a larger transmission capacity than the use of direct transmission in the PR network. Furthermore, such performance gain can be manipulated to increase the transmission capacity of the SR network without deteriorating the performance of the PR network. Numerical results also demonstrate the significant improvement on the transmission capacity by using cooperative transmission.