System for improving signal-to-noise ratio in a direct sequence

Details System for improving signal-to-noise ratio in a direct sequence System for improving signal-to-noise ratio in a direct sequence

1984-03-23

1987-02-17

Griffin, Robert L.

Multiplex communications

Wide area network

Packet switching

375 1, 375115, H04J 1300, H04L 706

Patent

active

046445234

ABSTRACT:
A plurality of transmitters synchronized to a common clock each transmit a data signal spread by a common bipolar pseudo-random code having a different assigned code sequence shift. A receiver, synchronized to the clock, discriminates the signal transmitted by a predetermined transmitter from signals transmitted by the others by generating a first pseudo-random code that is a replica of the common bipolar pseudo-random code and has a code sequence shift corresponding to that of the predetermined transmitter, and a second bipolar pseudo-random code that is a replica of the common bipolar pseudo-random code and has an unassigned code sequence shift. The difference between the first and second bipolar pseudo-random code sequences, which is a trinary code sequence, is cross-correlated with the incoming signal. The cross-correlation despreads only the signal having the predetermined code sequence shift. Each receiver includes a number of correlation detectors offset from each other by a fraction of a code chip, together with decision circuitry to identify cross-correlation peaks for optimum synchronization. The output of each sub-receiver is processed to extract data using weighting factors selected according to the particular distortion present, to improve signal-to-noise ratio.

REFERENCES:
patent: 4400790 (1983-08-01), Chambers et al.

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