Spread spectrum correlation receiver

A system for correlating an input signal against an N-bit reference signal, said system comprising, in combination:

• N correlation circuits, each said circuit having first storage means for storing a sample of said input signal, second storage means for storing a bit of said reference signal and means for providing a correlation output, said second storage means being serially interconnected so that said correlation circuits are arranged in an N-stage sequence;
• scan means for serially loading samples of said input signal into said first storage means, said scan means operating to load said storage means in order according to said N-stage sequence;
• loading means for entering the bits of said reference signal into said second storage means;
• and
• control means for serially shifting the bits of said reference signal through said second storage means in synchronism with the loading of said input signal samples, the sequence of said reference signal bits being arranged such that the last bit is kept in alignment with the newest sample of said input signal and the first bit is kept in alignment with the oldest stored sample of said input signal.

In a spread spectrum communication system including a plurality of transmitters operating to transmit independent audio signals impressed on a pseudo-noise (PN) carrier signal, a receiver comprising in combination:

• correlation means for receiving a composite of said audio signals and for performing a continuous sequence of N-point correlations on said composite signal against a reference signal representing N bits of said PN carrier signal;
• accumulation means for storing the sum of the outputs generated by said correlation means;
• control means for resetting the level stored in said accumulation means to a predetermined reference value after each N correlation operations;
• and
• output means operable prior to each said resetting operation for feeding the output of said accumulation means into an audio output channel to generate an audio signal representing a composite of said transmitted signals.

In an rf communication system, a receiver which provides detection of all multipath components of a signal transmitted in rf form on a pseudo-noise (PN) carrier, said detection being provided independent of phase differences that exist between said components, said receiver comprising:

• synchronous demodulation means for converting the received rf signal into I and Q signal components representing baseband demodulations of said signal at orthogonally related phase-detection angles;
• I correlation means for performing an N-point correlation of said I signal component against a reference signal representing said PN coded carrier;
• Q correlation means for performing an N-point correlation of said Q signal component against a reference signal representing said PN coded carrier;
• means for controlling said I and Q correlation means to serially perform a plurality of said correlations during a sample interval when a high correlation output is likely to occur;
• means for accumulating the outputs from said correlations;
• means for generating a decoded output signal in accordance with the sum of said accumulated correlation outputs;
• and
• a pair of adaptive filter circuits for processing the outputs from said I and Q correlations prior to the presentation thereof to said accumulating means, each said filter circuit including means for multiplying its respective correlation output by a signal function representing an estimation of said correlation output over the duration of said sampling interval.

In a communication system, a receiver for decoding an information signal transmitted on a psuedo-noise (PN) coded carrier comprising, in combination:

• correlation means for performing an N-point correlation of said received signal against a reference signal representing said PN coded carrier by simultaneously comparing the amplitude of N samples of said received signal with N samples of said reference signal;
• means for controlling said correlation means to serially perform a plurality of said correlations during a sampling interval when a high correlation output is likely to occur;
• means for accumulating the output from said correlations;
• means for generating a decoded output signal in accordance with the sum of said accumulated correlation outputs;
• and
• an adaptive filter for processing said correlation outputs prior to the presentation thereof to said accumulating means, said filter comprising means for developing a smoothed correlation function including first signal storage means, second signal storage means for storing the correlation outputs from the last preceding sampling interval, means for combining the signals stored in said first and second signal storage means in accordance with a predetermined filtering function to derive a control signal representing said smoothed correlation function, means for multiplying said correlation outputs by said control signal, and means for transferring the latter for said first signal storage means.

In a communication system, a receiver for decoding an information signal transmitted on a psuedo-noise (PN) coded carrier compring, in combination:

• correlation means for performing an N-point correlation of said received signal against a reference signal representing said PN coded carrier by simultaneously comparing the amplitude of N samples of said received signal with N samples of said reference signal;
• means for controlling said correlation means to serially perform a plurality of said correlation during a sampling interval when a high correlation output is likely to occur, said controlling means further includes synchronization means for controlling said correlation means to perform a continuous sequence of said N-point correlations;
• cycle timing means;
• and means responsive to a correlation output of a predetermined level generated during said continuous sequence of correlations for causing said cycle timing means to generate a series of clock signals for timing said sampling interval;
• means for accumulating the outputs from said correlations;
• and
• means for generating a decoded output signal in accordance with the sum of said accumulated correlation outputs.