Cognitive decode-and-forward relaying with successive interference cancelation

In this work, we study the cognitive decode-and-forward (DF) relaying, where a primary user (PU) communicates with an access point (AP), and in the same geographical region, a secondary source (SS) communicates to a secondary destination (SD) with assistance from a secondary relay (SR). Either SR or SD can decode the secondary data directly (DIR) or using the successive interference cancelation (SIC) technique. Based on the decoding methods of SR and SD, we proposed SR-DIR-SD-DIR, SR-DIR-SD-SIC, SR-SIC-SD-DIR, and SR-SIC-SD-SIC-based cognitive DF relaying schemes. The outage probabilities of both primary and secondary systems are analyzed for all the decoding manners. The transmit powers of SS and SR are further determined to minimize the outage probability of secondary system subject to the constraint that the outage performance loss of primary system should not exceed a certain percentage compared with the stand-alone primary network without spectrum sharing. Numerical results show that by using the SIC decoding, the outage probability of secondary system can be greatly decreased, especially when the interference from PU is strong or the transmission rate of primary data is low.