Outage Probability for Cognitive Heterogeneous Networks with Unreliable Backhaul Connections

To enhance the spectrum scarcity of cooperative heterogeneous networks (HetNets) with unreliable backhaul connections, we examine the impact of cognitive spectrum sharing over multiple small-cell transmitters in Nakagami-m fading channels. In this system, the secondary transmitters are connected to macro-cell via wireless backhaul links and communicate with the secondary receiver by sharing the same spectrum with the primary user. Integrating cognitive radio (CR), we address the combined power constraints: (1) the peak interference power and (2) the maximal transmit power. In addition, to exclude the signaling overhead for exchanging channel-state-information (CSI) at the transmitters, the selection combining (SC) protocol is assumed to employ at the receivers. The closed-form statistics of the end-to-end signal-to-noise (SNR) ratio are derived to attain the exact formulas of outage probability and its asymptotic performance to reveal further insights into the effective unreliable backhaul links.