a single nominal time slot without any of them transmitting too much power as noted above the fcc has imposed limits on the allowable transmit power for a given uwb device over a set measurement time t m as well as the allowable peak to average ratio in particular they have required that the average power of a uwb transmission using root mean square averaging must be below u2212 41 3 dbm mhz averaged over 1 millisecond and that the peak to average power must be below 0 dbm 50 mhz peak in other words under these rules the output power of a uwb device is measured in 1 microsecond blocks corresponding to 1 mhz but the measured power is averaged over one millisecond furthermore this averaged output power must be 41 3 db below a milliwatt in addition the highest peak power of this transmission must be below 1 milliwatt for any 50 mhz bandwidth window across the whole of the usable bandwidth it is expected that regulatory agencies in other countries will impose similar restrictions one way to meet this maximum power limitation is to transmit a constant uwb signal 310 at 100 duty cycle over the measurement period t m which is used to define the nominal time slot length in this embodiment and set the power level of the constant uwb signal 310 such that it will not violate.