Multi-User Diversity in a Spectrum Sharing System

Abstract

We investigate the effects of multi-user diversity ina spectrum sharing system where secondary users restrictivelyutilize a spectrum licensed to primary users only if interferenceperceived at primary users is regulated below a predeterminedlevel. This interference regulation affects the characteristics ofmultiuser diversity gains previously known in non-spectrumsharing systems. Our numerical and analytical results showthat the multiuser diversity gain in a spectrum sharing systemincreases differently according to conditions given by thetransmit power of secondary users, P, and a predeterminedinterference temperature, Q – if P is sufficiently larger thanQ, the multiuser diversity gain in terms of capacity scales likelog2 (W (Ns)) similarly to a previously known scaling law inthe non-spectrum sharing systems, where W(·) and Ns denote aLambert W function and the number of secondary transmitters,respectively. However, the scaling law of multiuser diversity gainbecomes log2(Ns) as P becomes sufficiently larger such thatP QNs.