Signal-recognition arrangement using cadence tables

摘要

A call classifier (300, 500) for recognizing cadenced signals (100-103) is based on data tables (110, 111) whose contents define the cadences of the signals that need to be recognized. Consequently, the call classifier may be adapted for recognizing the cadenced signals of various signaling schemes that are used in various countries or telecommunication systems, simply by reprogramming the data contents of the data tables. Each cadenced signal comprises a different pattern of interleaved signal-on (P) intervals and signal-off (S) intervals. A separate cadence timing table-pair (200-204) corresponds to each sequential S/P interval-pair. Each table-pair includes a P table (210) and an S table (211) each having a plurality of entries (220, 221) each corresponding to a different duration of the corresponding P interval and S interval, respectively, and identifying those signals which have the corresponding P interval and S interval duration, respectively, as candidates for a received signal. The durations of sequential ones of the P and S intervals of the cadence pattern of the received signal are measured (303, 304) and applied (305, 306) as pointers to sequential ones of the cadence timing table-pairs to select the corresponding table entries. The selected table entries are ANDed (307) with each other until only one candidate remains in the result (308). The one candidate identifies the received signal. Because reception of a signal can begin anywhere within the signal's cadence pattern, the table-pairs are initially used (500) to identify when the end of one and the beginning of another instance of the cadence pattern has been received.