Hybrid opportunistic spectrum access and power allocation for secondary link communication

In cognitive radio (CR) system, the spectrum band licensed to the primary link (PL) is usually divided into multiple sub-channels. Traditionally, the secondary link (SL) accesses the primary spectrum by either opportunistically selecting the idle sub-channels, called opportunistic spectrum access (OSA), or coexisting with the PL in the same band, called spectrum sharing (SS). In this paper, we propose a hybrid opportunistic spectrum access (H-OSA) scheme, in which the SL has the opportunity to access all the sub-channels based on the activity and interference threshold of the PL. Based on the lagrange dual-decomposition theory, the optimal power solution on each sub-channel is derived to maximize the ergodic capacity of the SL. Two cases are studied, i) perfect channel state information (CSI) is available at the SL, and ii) the SL has only imperfect CSI of the interference channels. The SL performance is analysed versus different activity and interference threshold of the PL. Our results indicate that the proposed scheme indeed improves the ergodic capacity of secondary link.