Spectrum monitoring measurements are made by
microcell base stations in a layered
cellular network, while not serving calls or engaged in
processing calls. The
microcell base station transmits a first control message from to a
microcell mobile station, to increase the duration for the
mobile station to reside in the camping state on a
control channel of the microcell
base station. The microcell
base station transmits a second control message from the microcell base
station to the microcell
mobile station, to increase the duration for the mobile
station to reside in a
call origination state while attempting to access a
control channel of the microcell base
station. Then, to perform the spectrum monitoring measurement, the base station's
transmitter is turned off, the
receiver is retuned to the frequency to be monitored, a
signal strength measurement taken on that frequency, the
receiver is retuned back to its assigned frequency, and the
transmitter is turned back on, all in a short time interval. Because the measurement time is so short, it is possible to take spectrum-monitoring measurements without causing inactive mobiles registered on the measuring base station to reselect
control channel. Mobiles initiating a call during a spectrum monitoring measurement by its base station are also delayed in their control channel reselection.