Geometric design of cooperative spectrum sensing for cognitive radios

Cooperative spectrum sensing is widely known to collect sensing information from cooperative sensors to assist cognitive radio transmitter to better judge the transmission opportunities, with appearance of hidden primary system terminals. However, it is usually ignored that a successful transmission can go through by requiring not only the spectrum availability at cognitive radio transmitter, but also spectrum availability at cognitive radio receiver. Using this special observation, we use Poisson distributed nodes and Boolean random network model to analyze the geometric region allowing CR transmission with the help of cooperative sensors. Contrary to intuition, we find that cooperative sensing is not always helpful and the region allowing CR transmission is no longer circular anymore. Using this geometric property, we further find that transmission link can remain bidirectional only under certain geometric conditions. Due to these observations, we develop a complete methodology so that a secondary transmitter can select helpful cooperative sensors corresponding to different receivers.