Spatial cognitive access in Zero Forcing beamforming scenarios

Multiple Input Multiple Output (MIMO) opens new challenges to be exploited in Cognitive Radio (CR) by simultaneously serving several users. The spatial domain that is added through MIMO is another system resource that has to be optimized, and shared when possible. In this paper, we present a spatial sharing approach that is carried out through Zero Forcing beamforming (ZFB). Statistical assessment of the primary user´s (high priority user) performance is carried out through two indicators: Quality of Service (QoS) and Probability of Satisfaction (PoS). Closed form expressions are derived for the primary user´s behaviour in the developed scenario and compared its performance to extensive simulations. Interesting results are obtained regarding the number of simultaneous serviced users that can share the spatial domain.