Throughput enhancement of secondary transmitter under target physical layer security rate

In this paper, we investigate the cognitive radio (CR) network, in which the secondary link works as a helper node to improve the physical layer secrecy rate of primary user. Depending upon the operation of secondary link, we consider two operation modes: (i) Spectrum-spatial leasing (SSL), which is introduced in the previous work, and (ii) Spectrum-time leasing (STL), which we propose. In guaranteeing the given secrecy rate and ensuring the throughput of the secondary link, the SSL considers both simultaneously, whereas the STL considers them separately. Therefore, there exists a performance gap between SSL and STL in terms of secrecy rate. We analyze both modes under the constraint of target physical layer secrecy rate compared with no helper node case. Since the performance of both modes has changed over different channel conditions, we propose a mode selection algorithm to increase the expected secondary throughput. We demonstrate that our analysis is in good agreement with the simulation results.