Improving Cognitive Radio link adaptation for avoiding interference with passive primary users

The main challenge for Cognitive Radio Networks (CRNs) is avoiding interference with PUs caused by unlicensed access, especially in any disaster where the Cognitive Radio (CR) nodes may lose the connection to the data base entity. To cope with this challenge, each CR node depends on its observations, such as Signal to Noise Ratio (SNR) and Signal Strength (SS), to define the free channel. However, this scheme is not efficient because there is a probability of interfering with the passive licensed users. In this paper, we develop a link adaptation approach in CR which estimates the distance to the nearest passive primary user and adapts the link configuration parameters to avoid any possible interference. The results show an improvement in Signal to Interference plus Noise Ratio (SINR) and Bit Error Rate (BER) at all possible passive primary users, compared to the literature, without a degradation in the Quality of Service (QoS) requirement of unlicensed users.