  In this paper, we investigate multiuser diversity in interference-limited
Multiple Access (MAC) underlay cognitive channels with Line-of-Sight
interference (LoS) from the secondary to the primary network. It is shown that
for $N$ secondary users, and assuming Rician interference channels, the
secondary sum capacity scales like
$\log\left(\frac{K^{2}+K}{\mathcal{W}\left(\frac{K e^{K}}{N}\right)}\right)$,
where $K$ is the $K$-factor of the Rician channels, and $\mathcal{W}(.)$ is the
Lambert W function. Thus, LoS interference hinders the achievable multiuser
diversity gain experienced in Rayleigh channels, where the sum capacity grows
like $\log(N)$. To overcome this problem, we propose the usage of single radio
Electronically Steerable Parasitic Array Radiator (ESPAR) antennas at the
secondary mobile terminals. Using ESPAR antennas, we induce artificial
fluctuations in the interference channels to restore the $\log(N)$ growth rate
by assigning random weights to orthogonal {\it basis patterns}. We term this
technique as {\it Random Aerial Beamforming} (RAB). While LoS interference is
originally a source of capacity hindrance, we show that using RAB, it can
actually be exploited to improve multiuser interference diversity by boosting
the {\it effective number of users} with minimal hardware complexity.
