  High speed wireless access on 60 GHz spectrum relies on high-gain directional
antennas to overcome the severe signal attenuation. However, perfect alignment
between transmitting and receiving antenna beams is rare in practice and
overheard signals from concurrent transmissions may cause significant
interference. In this paper we analyze the impact of antenna beam misalignment
on the system performance of 60 GHz wireless access. We quantify the signal
power loss caused by beam misalignment and the interference power accumulated
from neighboring concurrent transmissions whose signals are leaked either via
the main-beam pointing in the similar direction or via side-lobe emission, and
derive the probability distribution of the signal to interference plus noise
power ratio (SINR). For scenarios where interfering transmitters are
distributed uniformly at random, we derive upper and lower bounds on the
cumulative distribution function (abbreviated as CDF or c.d.f.) of SINR, which
can be easily applied to evaluate system performance. We validate our
analytical results by simulations where random nodes are uniformly distributed
within a circular hall, and evaluate the sensitivity of average throughput and
outage probability against two parameters: the half-power (3 dB) beamwidth to
main-lobe beamwidth ratio and the beam misalignment deviation to main-lobe
beamwidth ratio. Our results indicate that the derived lower bound performs
well when the half-power beamwidth to main-lobe beamwidth ratio or the number
of concurrent transmission links is small. When the number of active links is
high, it is desirable in antenna design to balance the degradation caused by
beam misalignment (wider beam is better) and the interference from concurrent
transmission (narrower beam is better).
