Optimum Spectral Efficiency of Horizontally Spectrum Sharing 2-Link System

Under the horizontal spectrum sharing scenario where two cognitive radios are able to find an unutilised resource and access to the resource is coordinated between them, it is shown in our earlier work that either single or simultaneous transmission at maximum power maximises system spectral efficiency. While in general suboptimal, sequential transmission, an average of two single transmissions, is also investigated as a more fair alternative to single transmission. In this paper, the system spectral efficiencies of simultaneous, single and sequential transmission schemes are compared for the 2-link scenario where the two communication pairs are chosen from uniformly distributed nodes on a disk. The simultaneous transmission scheme is shown to provide smaller expected system spectral efficiency for higher transmit power than sequential or single transmission schemes. Introducing additional interferers, however, significantly reduces the advantage of single and sequential schemes over simultaneous transmission. However, under the scenario of transmission to the closest neighbour, simultaneous transmission is shown to result in higher average system spectral efficiency than the other two schemes over the wide range of transmit powers.