Fast frequency hopping demodulation system with serial accumulation of

Abstract

A system for demodulating a received signal containing repetitive blocks of m frequency hopped pulses having a predetermined hopping sequence. 'm' is an integer greater than one. The system includes m filters respectively tuned to the frequencies of the predetermined hopping sequence; a network for distributing the received signal to all m filters in parallel; and an integrator for integrating at an integer-multiple of the hop rate the output signals from the filters over an interval corresponding to the block of pulses to determine the time of arrival of the last pulse of each block. The filters are optical RF bandpass filters. The integrator includes a signal accumulator having a series of cells respectively coupled to different filters. Signals are accumulated in the cells from the filters at an integer-multiple of the hop rate and the accumulated signals are shifted serially from cell to cell at the integer-multiple of the hop rate to provide a serial output from an end cell. A detector detects when the serial output of the accumulator exceeds a predetermined threshold to thereby determine the arrival of each block. A charge coupled device (CCD) or a surface acoustic wave device (SAWD) is used as the accumulator to provide compactness and speed. The demodulation system can be programmed in accordance with a predetermined code pertaining to the sequence of the respective pulses in each block and/or in accordance with a predetermined binary output code.