Importance

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Abstract

A syncrhonization arrangement is disclosed for synchronizing a receiver with a transmitter whose frequency is hopping through a sequence of predetermined frequencies arranged pseudo-randomly. The transmitter includes a time base circuit in the form of a string of dividers operated from a stable oscillator. One divider produces (in this example) a 28 bit synchronization signal which changes state once every sixty four hop frequencies. The 28 bits control a keystream generator which produces a pseudo-random output sequence controlling the transmitting frequencies. This 28 bit signal is formatted by repeating it several times successively, with its bits partially re-circulated to a predetermined extent each time, masking bits are added, and the result transmitted to the receiver on one of the hop frequencies. At the receiver, a correlator subtracts the mask, partially re-circulates the bits to offset the partial recirculation at the transmitter, and recognizes receipt of the 28 bits when successive groups of the resultant bits are identical (or do not differ by more than predetermined total error). The 28 bits are used to pre-set a divider at the receiver which then in turn resets the receiver's keystream generator, thereby synchronizing the receiver.

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First Claim