  In a large-scale wireless ad hoc network in which all transmitters form a
homogeneous of Poisson point process, the statistics of the
signal-to-interference ratio (SIR) in prior work is only derived in closed-form
for the case of Rayleigh fading channels. In this letter, the mean SIR is found
in closed-form for general random channel (power) gain, transmission distance
and power control models. According to the derived mean SIR, we first show that
channel gain randomness actually benefits the mean SIR so that the upper bound
on the mean spectrum efficiency increases. Then we show that stochastic power
control and opportunistic scheduling that capture the randomness of channel
gain and transmission distance can significantly not only enhance the mean SIR
but reduce the outage probability. The mean-SIR-based throughput capacity is
proposed and it can be maximized by a unique optimal intensity of transmitters
if the derived supporting set of the intensity exists.
