Modification of Maximal Ratio Combining Technique for Detection of Spectrum Hole in a Cognitive Radio Network

Spectrum Sensing (SS) is a critical operation in a Cognitive Radio (CR) network to identify spectrum hole thereby preventing licensed users from harmful interference for improving spectrum utilization. However, multipath effects in wireless channel such as multipath fading, shadowing and receiver uncertainty affect the sensing accuracy of CR resulting to high Probability of Missing (PM) that causes interference to Primary User (PU). Maximal Ratio Combining (MRC) technique which was one of the techniques used to solve this problem suffers hardware complexity resulting in high Sensing Time (ST). Therefore, in this paper, modification of MRC technique is carried out to reduce hardware complexity of conventional MRC thereby reducing ST. The modified technique consists of ‘L’ Secondary User (SU) antennas that received the multiple copies of Primary User (PU) signals over Nakagami-m fading channel. The received PU signals are made to passed through separate channel estimator and co-phased to avoid signal cancellation before been summed up. The resultant signa is then made to passed through single RF chain and MF. Output of MF is then used as input to Energy Detector (ED) to obtain the energy of the received signal. The obtained energy is compared with the set threshold to determine the status of spectrum. The modified MRC technique is incorporated with simulation model which consists of PU transmitter that processes the randomly generated data through some signal processing techniques for transmission. Mathematical expression of Probability of False Alarm (PFA) for the modified MRC technique is derived and used to set the thresholds at PFA of 0.01 and 0.05. The modified model is evaluated using PM, Probability of Detection (PD) and PT to determine the performance. The results obtained revealed that modified MRC gives higher PD, lower PM and PT values when compared with conventional MRC.