| 摘要 |
<p>A selective call communication system (10) transmits a frequency hopped spread spectrum signal as a Reed Solomon code word modulated as a four-level frequency shift keying (4FSK) signal. A base site transceiver (150) receives the signal on a plurality of narrow band channels and a DSP (152) performs an FFT on the signal. The DSP (152) has a comparator (342) that computes energy of a 4FSK symbol. The comparator (342) establishes a ratio of a maximum energy and a next largest energy to an eye-opening threshold to indicate a probability of error. A determinator (344) in response to the probability of error determines when there is a fade, an erasure marker (346) marks a position of a Reed Solomon symbol in the fade as an erasure and error correcting code (348) corrects errors in the Reed Solomon code word with the marked erasure.</p> |
