초록 ▼

The presence of a supervisory audio tone signal (SAT), superimposed on a voice/data signal transmitted in a cellular telephone system, is carried out by first deleting the voice/data signal, leaving only the SAT signal. Thereafter, the SAT signal power and noise power are determined. During interval

The presence of a supervisory audio tone signal (SAT), superimposed on a voice/data signal transmitted in a cellular telephone system, is carried out by first deleting the voice/data signal, leaving only the SAT signal. Thereafter, the SAT signal power and noise power are determined. During intervals when the SAT signal rises and falls, the SAT noise power and signal power move in opposite directions when the radio carrier turns on and off, respectively. By comparing the SAT noise power to the SAT signal power, a fast, accurate determination can be made as to whether the SAT signal is present. Moreover, the ratio of the SAT signal power to SAT noise power provides a good estimate of the quality of the channel in the cellular telephone system. By repeatedly computing the SAT signal power to noise power ratio, a base station (48) in the cellular telephone system can decide when to hand off, and to which other base station such hand-off should be made.

대표청구항 ▼

[ I claim:] [11.] A system for detecting the presence of a Supervisory Audio Tone (SAT) when superimposed on a voice/data signal to yield a combined voice/data and SAT signal which is periodically sampled, comprising:(a) means for deleting the voice/data signal from a sample of the combined voice/da

[ I claim:] [11.] A system for detecting the presence of a Supervisory Audio Tone (SAT) when superimposed on a voice/data signal to yield a combined voice/data and SAT signal which is periodically sampled, comprising:(a) means for deleting the voice/data signal from a sample of the combined voice/data and SAT signal so that only the SAT remains, said means including(1) a first complex mixer for performing a first complex mixing operation on the combined voice/data and SAT signal sample to shift the sample to an approximate DC value;(2) decimating means for low-pass filtering the approximate DC value produced by the first complex mixer;(3) second complex mixer for performing a second complex mixing operation on the low-pass-filtered, approximate DC value to shift the frequency thereof in accordance with the frequency of the incoming SAT;(b) means for determining the signal power of the remaining SAT, said means including:(1) low-pass filtering means for low-pass filtering the frequency-shifted, approximate DC value;(2) means for determining the square of the low-pass-filtered, frequency shifted, approximate DC value; and(3) an infinite-impulse response filter for filtering the square of the lowpass-filtered, frequency-shifted, approximate DC value;(c) means for determining the noise power of the remaining SAT; and(d) means for comparing the SAT signal power to the SAT noise power to determine if the signal power of the SAT exceeds the noise power of the SAT as occurs when the SAT is present in the combined signal.