the value to be at the appropriate limit of the range the value of rssi_correct_val is then transferred to reverse link excess capacity estimation module 56 which uses the value as described with reference to fig5 below to determine the excess capacity of bts 18 in a last step 100 of process 90 control unit 20 periodically adds an u201c aging factor u201d to the evaluated value of rssi_ref_filt according to equation 2 below control unit 20 typically generates the periodicity age_period for applying equation 2 and the value of the aging factor age_factor in initial step 92 of process 90 typical values for age_period and age_factor are of the order of 1 hour and approximately 0 1 db respectively after step 100 process 90 returns to the beginning of step 94 it will be understood from inspection of process 90 that the value rssi_correct_val is a function of the minimum value of rssi_dbm determined over the time during which process 90 is operated it will also be understood that rssi_correct_val approximates the difference between the vertical axis intercept ev illustrated in fig3 and the noise value nsys of receiving system 24 described above the aging factor age_factor simulates the change in noise value of receiving system 24 over time so that the exemplary values given above increase the noise value of the receiving system with no other change being input to the system by 0 1 db every hour however it will be understood that this change may be overridden by a smaller actual noise value rssi_dbm received by the receiving system fig5 is a flowchart of a process.