Spatial spectrum holes for cognitive radio with relay-assisted directional transmission

Abstract

Spectrum hole (SH) is defined as a spectrum band that can be utilized by unlicensed users, which is a basic resource for cognitive radio (CR) systems. Most of existing contributions detect SHs by sensing whether a primary signal is present or absent and then try to access them so that the CR and primary users use the spectrum band either at different time slots or in different geographic regions. In this paper, we propose a novel scheme with relays or directional relays for CR users to exploit new spectrum opportunity, called spatial SH. It can provide higher spectrum efficiency by coexistence of primary and CR users at the same region, time, and spectrum band. In particular, when the spectrum opportunity of a direct link from a CR transmitter to a CR receiver does not appear, our scheme may still establish the communication through indirect links, i.e., other CR users act as relay stations to assist the communication by using other spatial domains. Furthermore, we analyze the successful communication probabilities of CR users and demonstrate that the spectrum efficiency can be considerably improved by our scheme.

Ten years of research in spectrum sensing and sharing in cognitive radio

“…With the increase of the number of relays, the outage performance gap decreases. The relays in the CR networks can assist the transmission between the SU transmitter and receiver to reduce the required transmit power and decrease the interference generated to the PU system [119]. The transmission opportunities created through this way are called as spatial SHs.…”