Fundamental limits of spectrum-sharing in fading environments

TLDR

Spectrum licensing traditionally grants exclusive rights, protecting licensees from interference, but in practice secondary users can share bands if their interference is harmless; in fading environments, a secondary user can opportunistically transmit at high power when its signal is deeply faded at the primary receiver. In this paper we investigate the capacity gains offered by this dynamic spectrum sharing approach when channels vary due to fading. We quantify the relationship between secondary channel capacity and primary‑user interference, and evaluate and compare capacity under various fading distributions. Our results indicate a significant gain in spectrum access in fading environments compared to the deterministic case.

Abstract

Traditionally, the frequency spectrum is licensed to users by government agencies in a rigid manner where the licensee has the exclusive right to access the allocated band. Therefore, licensees are protected from any interference all the time. From a practical standpoint, however, an unlicensed (secondary) user may share a frequency band with its licensed (primary) owner as long as the interference it incurs is not deemed harmful by the licensee. In a fading environment, a secondary user may take advantage of this fact by opportunistically transmitting with high power when its signal, as received by the licensed receiver, is deeply faded. In this paper we investigate the capacity gains offered by this dynamic spectrum sharing approach when channels vary due to fading. In particular, we quantify the relation between the secondary channel capacity and the interference inflicted on the primary user. We further evaluate and compare the capacity under different fading distributions. Interestingly, our results indicate a significant gain in spectrum access in fading environments compared to the deterministic case