GB1246142A - Means and method to obtain an impulse autocorrelation function - Google Patents

Abstract

1,246,142. Multiplex pulse code signalling; pulse radar. INTERNATIONAL STANDARD ELECTRIC CORP. 18 Sept., 1968, No. 44281/68. Headings H4D and H4L. [Also in Division G1] In a binary coded pulse signalling system in which correlation techniques are used in the reception of the coded signals to provide an impulse at a defined time, e.g. as in radar or pulse communication systems, the signals are so coded as to provide pairs of co-operating code mates, the two codes of a given pair having co-operating autocorrelation functions whereby upon transmission of signals corresponding to a given pair of code mates to a receiver and detection of the individual mates by respective autocorrelation detectors followed by linear addition of the detector outputs, an impulse function is derived in which an impulse output at a given time occurs and zero output at all other, times within the periodic time of a signal comprising a pair of code mates. Before transmission the two codes may be either time or frequency multiplexed together, and at the receiver they are separated from the multiplex signal, and separately detected to provide their individual autocorrelation functions. These functions are added to produce the required output impulse. The Specification explains that there are 19 unique eight bit codes and that from among these there are three which have autocorrelation functions' which respectively mate with those of another three in the required way. It goes on to show that further suitable pairs of codes may be produced by taking one such suitable code and its mate, complementing one of them and interleaving the other with both the mate and the complement to produce two further codes which mate in the required way. This process can be continued. In a time multiplex system (Fig. 7) signals in both codes S1, S2 are generated at 20, S1 is delayed at 23 and both are modulated at 24, 21 respectively with the same carrier from source 22. The two signals are added at 25, amplified and transmitted. In a frequency multiplex system the delay 23 is omitted and two different frequency carriers are applied to the two respective modulators, In the time multiplex receiver (Fig. 8) the signal is gated at 30, 31 in accordance with the delay 23 to separate the two codes. Replicas of the codes are generated by the source 36 and applied via variable delays, 37, 38 to multipliers 34, 35 to produce the separate autocorrelation functions. These are added at 39 to provide an output at 40. The delays 37, 38 are adjusted in synchronism until an impulse is detected. In the frequency multiplex receiver (Fig. 10, not shown) the gates 30, 31 are replaced by appropriate filters. The Specification diagrammatically illustrates (Fig. 19, not shown) a system for generating two 32 bit code mates from two 8 bit code mates. These are generated using delay lines along which pulses from a generator are transmitted, the outputs or inverted outputs at each of 8 tappings on each line being taken in accordance with the codes and added. The outputs from the adders are delayed and interleaved one also being inverted and interleaved with the other, and this process is repeated.