Three bits softened decision scheme in cooperative spectrum sensing among cognitive radio networks

Recently, cognitive radio (CR) access has received much attention to overcome spectrum scarcity problem. Spectrum sensing methods are often used for finding free channels to be used by CR. In this paper, one of spectrum sensing method will be investigated. This method is cooperative spectrum sensing which is based on energy detection in CR networks in order to overcome fading, noise and shadowing effects on individual CR user and increase the reliability and efficiency of spectrum sensing. The sensing information from CR users combines at the Fusion center (common receiver) by soft combination or conventional hard combination techniques. Soft combination has excellent performance but, it requires a lot of overhead for feedback observation. In contrast, the conventional hard combination scheme requires only one bit of overhead, but it has worst performance because of loss of information caused by local hard decisions. In this paper, the detection performance improves by increasing the levels of local observations by proposing three-bit softened decision scheme which is not clarified until now. Analytical Expressions of proposed three bits scheme will be derived. Design parameters are optimized to find the detection performance with a given false alarm probability. The simulation results show that, at 90% detection probability, the cooperative signal detection improves by 1.75 dB of signal to noise ratio over conventional hard combination (i.e., one bit scheme). Moreover, comparisons between proposed scheme, one bit and two bits schemes will be made.