A round-trip, spread-spectrum navigation and locating system achieves high capacity and large processing gains in one-to-many and many-to-one configurations using round-trip signaling with frequency division based upon precise responding device carrier frequency offsets. Reduced cross-correlation is achieved by assigning these very small disparate frequency offsets to replies from interrogated devices so that the long-term correlation between disparate reply sequences is reduced almost to that of random noise of equivalent energy. The invention supports simultaneous interrogation of multiple responding devices, which responding devices respond essentially simultaneously at a fixed delay after receiving the query. The originating and/or responding devices may be fixed or mobile, permanently or temporarily deployed, terrestrial, airbourne or space-based with any source of power including batteries and solar without limitation. The signaling may be electromagnetic or acoustic with the potential for under-water use.

A round-trip, spread-spectrum navigation and locating system achieves high capacity and large processing gains in one-to-many and many-to-one configurations using round-trip signaling with frequency division based upon precise responding device carrier frequency offsets. Reduced cross-correlation is achieved by assigning these very small disparate frequency offsets to replies from interrogated devices so that the long-term correlation between disparate reply sequences is reduced almost to that of random noise of equivalent energy. The invention supports simultaneous interrogation of multiple responding devices, which responding devices respond essentially simultaneously at a fixed delay after receiving the query. The originating and/or responding devices may be fixed or mobile, permanently or temporarily deployed, terrestrial, airbourne or space-based with any source of power including batteries and solar without limitation. The signaling may be electromagnetic or acoustic with the potential for under-water use.

A round-trip, spread-spectrum navigation and locating system achieves high capacity and large processing gains in one-to-many and many-to-one configurations using round-trip signaling with frequency division based upon precise responding device carrier frequency offsets. Reduced cross-correlation is achieved by assigning these very small disparate frequency offsets to replies from interrogated devices so that the long-term correlation between disparate reply sequences is reduced almost to that of random noise of equivalent energy. The invention supports simultaneous interrogation of multiple responding devices, which responding devices respond essentially simultaneously at a fixed delay after receiving the query. The originating and/or responding devices may be fixed or mobile, permanently or temporarily deployed, terrestrial, airbourne or space-based with any source of power including batteries and solar without limitation. The signaling may be electromagnetic or acoustic with the potential for under-water use.

A round-trip, spread-spectrum navigation and locating system achieves high capacity and large processing gains in one-to-many and many-to-one configurations using round-trip signaling with frequency division based upon precise responding device carrier frequency offsets. Reduced cross-correlation is achieved by assigning these very small disparate frequency offsets to replies from interrogated devices so that the long-term correlation between disparate reply sequences is reduced almost to that of random noise of equivalent energy. The invention supports simultaneous interrogation of multiple responding devices, which responding devices respond essentially simultaneously at a fixed delay after receiving the query. The originating and/or responding devices may be fixed or mobile, permanently or temporarily deployed, terrestrial, airbourne or space-based with any source of power including batteries and solar without limitation. The signaling may be electromagnetic or acoustic with the potential for under-water use.

A receiver is provided for acquiring a DSSS signal. The receiver includes a splitter, a first multiplier, a second multiplier and a processor. The splitter is operable to split the DSSS signal into a first DSSS signal and a second DSSS signal. The first multiplier is operable to multiply the first DSSS signal by a shuffled pseudo-noise sequence and a sine function to obtain a first correlation value. The second multiplier is operable to multiply the second DSSS signal by the shuffled pseudo-noise sequence and a cosine function to obtain a second correlation value. The processor is operable to determine an alignment delay based on the first correlation value and the second correlation value.

A method of synchronising a communication signal entering into a receiver. Each frame of the signal includes a learning symbol formed of N repetitions of a learning sequence. The method includes the determination of a total correlation signal by correlating the input signal with a correlation symbol formed of N repetitions of a correlation sequence corresponding to all or part of the learning sequence and duration t.sub.sc, and the determination of a partial correlation signal by correlating the input signal with the correlation sequence. A peak of the total correlation signal is identified at an instant t.sub.pct. At least one threshold is defined from the power of the peak of the total correlation signal, and the power of the partial correlation signal is compared here to the instants t.sub.pctk*t.sub.sc, with k a whole number between 0 and N1.

A method of synchronising a communication signal entering into a receiver. Each frame of the signal includes a learning symbol formed of N repetitions of a learning sequence. The method includes the determination of a total correlation signal by correlating the input signal with a correlation symbol formed of N repetitions of a correlation sequence corresponding to all or part of the learning sequence and duration t.sub.sc, and the determination of a partial correlation signal by correlating the input signal with the correlation sequence. A peak of the total correlation signal is identified at an instant t.sub.pct. At least one threshold is defined from the power of the peak of the total correlation signal, and the power of the partial correlation signal is compared here to the instants t.sub.pctk*t.sub.sc, with k a whole number between 0 and N1.

A receiver includes a reception antenna, a reception unit, and a demodulation unit. The reception unit sequentially receives modulated signals resulting from spread spectrum via the reception antenna. The demodulation unit demodulate a first signal received by the reception unit by performing despreading using a short-period spreading code, the first signal including information for identifying a long-period spreading code. The demodulation unit identifies the long-period spreading code on the basis of the information obtained from the first signal. The demodulation unit then demodulates a second signal received by the reception unit after the first signal by performing despreading using the long-period spreading code.

A receiver includes a reception antenna, a reception unit, and a demodulation unit. The reception unit sequentially receives modulated signals resulting from spread spectrum via the reception antenna. The demodulation unit demodulate a first signal received by the reception unit by performing despreading using a short-period spreading code, the first signal including information for identifying a long-period spreading code. The demodulation unit identifies the long-period spreading code on the basis of the information obtained from the first signal. The demodulation unit then demodulates a second signal received by the reception unit after the first signal by performing despreading using the long-period spreading code.

A method of synchronising a communication signal entering into a receiver. Each frame of the signal includes a learning symbol formed of N repetitions of a learning sequence. The method includes the determination of a total correlation signal by correlating the input signal with a correlation symbol formed of N repetitions of a correlation sequence corresponding to all or part of the learning sequence and duration t.sub.sc, and the determination of a partial correlation signal by correlating the input signal with the correlation sequence. A peak of the total correlation signal is identified at an instant t.sub.pct. At least one threshold is defined from the power of the peak of the total correlation signal, and the power of the partial correlation signal is compared here to the instants t.sub.pctk*t.sub.sc, with k a whole number between 0 and N1.