Effects of quantization on bepwalls for soft decision based cooperative sensing

Abstract

This paper focuses on the performance limitations for soft decision (SD) based cooperative spectrum sensing in cognitive radios. Cooperative sensing (CS) is formulated as a composite hypothesis problem where we assume that the distribution of the primary user signal is not known. CS suffers from the Bit Error Probability (BEP) wall phenomenon in the presence of reporting channel errors. If the BEP value of the reporting channels is greater than the so called BEP wall value, then it is impossible to satisfy the imposed performance constraints on the CS at the fusion center even if the sensed signal quality or the sensing time at the secondary user is increased. In this paper, we specifically analyze the effects of quantization on the BEP wall for the case of SD based CS. It is shown that the choice of quantization scheme significantly affects the BEP wall value and needs to be paid sufficient attention during the design of practical cooperative sensing schemes.