Method of, and apparatus for, frequency-hopped frequency-shift-keyed

Abstract

A digital data communications method and system combining frequency agility with a frequency-shift-keyed signal to transmit a unique code word representing a plurality of data states. Each code word comprises a plurality of chips, each of which is an integer subportion of the bit time interval in which one data bit is communicated. The multiple-chip word provides a frequency-hopped spread spectrum signal in which the nominal carrier frequency value is offset for transmitting binary data, or is offset in either frequency direction by different discrete amounts for transmitting multilevel digital data, to allow the data value to be properly decoded at a receiver even if the transmitter instantaneous frequency during at least one chip time interval is jammed by another signal. The frequency offset, can also be provided in complementary fashion during selected chip time intervals to even further encode the data bit being communicated and further reduce the probability of jamming. The multiple-chip code word, of normal or selected-chip-complemented form, modulates a carrier at the transmitter end. The FH-FSK carrier is demodulated at the receiver end by an inverse modulation process which converts the signal into a serial bit stream, for matched filtering transmission and reception apparatus of non-complemented and/or complemented chip-encoded words is described.