Performance Comparison between Adaptive and Fixed Transmit Power in Underlay Cognitive Radio Networks

In this paper, we compare the performance in terms of symbol error probability, data rate and power consumption of the use of fixed transmit power (FTP) and adaptive transmit power (ATP) in underlay cognitive radio networks. The use of FTP alleviates the signaling requirements of underlay cognitive radio networks compared to the ATP. Nevertheless, the use of FTP influences the performances of the underlay cognitive radio networks. To study this influence, we consider three relay selection schemes using FTP: opportunistic decode and forward with FTP (O-DF with FTP), opportunistic amplify and forward with FTP (O-AF with FTP) and partial relay selection with FTP (PR with FTP). We compare the performances of these schemes in terms of symbol error probability, data rate and power consumption with three relay selection schemes using ATP: opportunistic decode and forward with ATP (O-DF with ATP), opportunistic amplify and forward with ATP (O-AF with ATP) and partial relay selection with ATP (PR with ATP). We provide exact and/or lower bound expressions of the symbol error probabilities of O-DF, O-AF and PR with FTP. The analytical study for the data rate and the power consumption is also provided. Our comparison study shows that FTP has a positive impact on the data rate and power consumption performance while it deteriorates the symbol error probability performance.