Synchronous FSK detection

Details Synchronous FSK detection Synchronous FSK detection

1992-05-19

1993-09-14

Safourek, Benedict V.

Pulse or digital communications

Repeaters

Testing

329302, 375 88, 375 97, H04L 2714

Patent

active

052456323

ABSTRACT:
The present invention provides methods and apparatus for synchronous detection of a Frequency Shift Keying (FSK) signal. The demodulation of the FSK signal is performed in the "complex plane" after multiplying the input samples by an unlocked complex carrier in a complex down converter. Two decision bits are generated per real bit. Once bit should be the real decision; the other bit is a "transition" bit between two Bauds. To generate this situation, the last three decisions are considered. If a transition from 0 to 1, or vice-versa, occurs between the first and third bit, then the middle (second) bit should have equal probability to be 0 or 1. If it is 1, timing correction, by moving the sampling window, is done towards the 0 bit. If it is a 0, the sampling window is moved toward the 1 bit. The timing decision is efficiently implemented by taking the three bits as an index to an 8-entry look-up table that generates ADVANCE, DELAY or NO.sub.--OP directions.

REFERENCES:
patent: 4203071 (1980-05-01), Bowles et al.
patent: 4726043 (1988-02-01), Levesque
patent: 4759036 (1988-07-01), Meyers
patent: 4815103 (1989-03-01), Cupo et al.

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