  We present a controller and transmission policy design procedure for
nonlinear wireless networked control systems. Our objective is to ensure the
stability of the closed-loop system, in a stochastic sense, together with given
control performance, while minimizing the average power used for
communications. The controller is designed by emulation, i.e., ignoring the
network, and the transmission power is given by threshold policies. These
policies involve waiting a given amount of time since the last successful
transmission instant, as well as requiring that the measured wireless channel
gain is above a given threshold, before attempting a new transmission. Two
power control laws are investigated: i) a constant power and ii) a power level
inversely proportional to the channel gain. We explain how to select the
waiting time, the channel threshold and the power level to minimize the induced
average communication power, while ensuring the desired control objectives.
