We investigate the effects of multi-user diversity in
a spectrum sharing system where secondary users restrictively
utilize a spectrum licensed to primary users only if interference
perceived at primary users is regulated below a predetermined
level. This interference regulation affects the characteristics of
multiuser diversity gains previously known in non-spectrum
sharing systems. Our numerical and analytical results show
that the multiuser diversity gain in a spectrum sharing system
increases differently according to conditions given by the
transmit power of secondary users, P, and a predetermined
interference temperature, Q – if P is sufficiently larger than
Q, the multiuser diversity gain in terms of capacity scales like
log2 (W (Ns)) similarly to a previously known scaling law in
the non-spectrum sharing systems, where W(·) and Ns denote a
Lambert W function and the number of secondary transmitters,
respectively. However, the scaling law of multiuser diversity gain
becomes log2(Ns) as P becomes sufficiently larger such that
P QNs.