Gte Government Systems Corporation

William E DeLisle

John W Lovell

Karen Marie Schramm

Seymour Stein

Karen M Sebramm

Circuit for recovery of a plurality of multipath direct sequence spread spectrum signal components received over a time span, wherein the multipath signal components are components of a signal generated from digital data comprised of data bits at a data bit rate modulated by a pseudo-noise code, consisting of a sequence of chips having a chip rate greater than the data bit rate, wherein the sequence of chips is a code repetition period equal or greater than the received time span of the multipath signal components. A plurality of correlators is provided. Each correlator has a first input for coupling to the multipath signal components, a second input, and an output. A pseudo-noise code generator generates a duplicate of the pseudo-noise code. A time delayer is coupled between the second inputs of a mulitiplicity of the correlators and the pseudo-noise code generator for delaying the duplicate of the pseudo-noise code by a multiple of a time delay equal to the time of a chip duration or less. A signal combiner is coupled to the plurality of phase correcting devices.

Apparatus for multipath DSSS communications

Method of demodulating a signal including a plurality of time-dispersed signal components such as resulting from receiving in a multipath environment. A plurality of correlators are provided. The period of expected time uncertainty is scanned to identify the highest energy signal components. Each correlator is assigned to process one of the highest energy signal components. Each of the correlator outputs is pase corrected to compensate for carrier phase differences. The correlator outputs are coherently combined to provide a data output.

Method of multipath dsss communications

A correlator for processing a direct sequence spread spectrum communication system signal, wherein digital data comprised of data bits at a data bit rate is modulated by a first pseudo-noise code comprised of a sequence of chips having a pseudo-noise chip rate greater than the data bit rate, each chip having a chip period, the sequence repeating at a code period, and the pseudo-noise modulated data modulates a carrier resulting in the signal. A sampler produces digital samples of the signal. A pseudo-noise code generator produces a second pseudo-noise code replicating the first pseudo-noise code. Circuity time syncronizes the second pseudo-noise code to maximize a combined value of correlated signal energy, thereby time locking the first pseudo-noise code and the second pseudo-noise code.

Correlator for DSSS communications

Method of processing a direct sequence spread spectrum communication system signal wherein digital data comprised of data bits is modulated by a first pseudo-noise code comprised of a sequence of chips, the pseudo-noise chip rate greater than said date bit rate, each chip having a chip period, said sequence repeating at a code period, and the pseudo-noise modulated data modualates a carrier frequency resulting in the signal. Digital samples are made of the signal. A second pseudo-noise code replicates the first pseudo-noise code. A first correlation is made of the sampled signal and the second pseudo-noise code. A second correlation is made of the sampled signal and the second pseudo-noise code delayed by one chip period. A first correlated signal energy value represents the signal energy of the first correlation. A second correlated signal energy value represents the signal energy of the second correlation. The first and second correlated signal energy values are combined to obtain the combined value of correlated signal energy. The second pseudo-noise code is time syncronized to maximize the combined value of correlated signal energy, thereby time locking the first pseudo-noise code and the second pseudo-noise code.

DSSS communications correlation

Apparatus for indicating the end of an acquisition procedure between a transmitter and receiver in a direct sequence spread spectrum communications system. A transmitter generates a first acquisition code having a first acquisition code period and comprised of digital bits at a first bit rate. A circuit modulates the first digital acquisition code by a pseudo-noise code repeating at a pseudo-noise code period and consisting of a sequence of chips at a chip rate greater than the first bit rate. The first acquisition code period is an integer multiple of the pseudo-noise code period. A circuit modulates a carrier by the first digital acquisition code modulated by the pseudo-noise code. The carrier modulated by said first digital acquisition code modulated by said pseudo-noise code is transmitted for a first period of time. A circuit synchronizes a receiver to the chip rate and carrier frequency. A circuit synchronizes the receiver to the pseudo-noise code period. A circuit synchronizes the receiver to the period of the data bit rate. A circuit synchronizes the receiver to the first acquisition code period. The transmitter generates a second acquisition code having a second acquisition code period and comprised of digital bits at a second bit rate, the second bit rate equal to the bit rate of the first acquisition code period. A circuit modulates the second digital acquisition code by the pseudo-noise code. A circuit modulates the carrier by the second digital acquisition code modulated by the pseudo-noise code. A circuit transmits for a second period of time equal to the second acquisition code period the carrier modulated by the second acquisition code modulated by the pseudo-noise code. A circuit synchronizes the receiver to the second acquisition code, the end of the second acquisition code indicates the end of the acquisition procedure.

Acquisition apparatus for DSSS communications

Method for indicating the end of an acquisition procedure between a transmitter and receiver in a direct sequence spread spectrum communications system. At a transmitter, a first acquisition code having a first acquisition code period and comprised of digital bits at a first bit rate is generated. The first digital acquisition code is modulated by a pseudo-noise code repeating at a pseudo-noise code period and consisting of a sequence of chips at a chip rate greater than the first bit rate, and wherein the first acquisition code period is an integer multiple of the pseudo-noise code period. A carrier frequency is modulated by the first digital acquisition code modulated by the pseudo-noise code. The carrier is modulated by the first digital acquisition code modulated by the pseudo-noise code is transmitted for a first period of time. A receiver is synchronized to the chip rate and carrier frequency, then to the pseudo-noise code period, next to the period of the data bit rate, and then to the first acquisition code period. At the transmitter a second acquisition code is generated having a second acquisition code period and comprised of digital bits at a second bit rate, the second bit rate equal to the bit rate of the first acquisition code period. The second digital acquisition code is modulated by the pseudo-noise code. The carrier frequency is modulated by the second digital acquisition code modulated by the pseudo-noise code. The carrier modulated by the second acquisition code modulated by the pseudo-noise code is transmitted for a second period of time equal to the second acquisition code period. The receiver is sychronized to the second acquisition code, the end of the second acquisition code indicating the end of the acquisition procedure.

Acquisition method for DSSS communications

Method for carrier frequency correction in a direct sequence code division multiple access communication system having a carrier frequency, consisting of an expected carrier frequency and a carrier frequency error, modulated by a pseudo-noise code. A local frequency is produced equal to the expected carrier frequency. Received signals are demodulated of the pseudo-noise and mixed with the local frequency. The demodulated signals consist of in-phase signal components and quadrature signal components and the carrier frequency error. Each of the demodulated signal are converted to digital samples. Each signal digital sample is multiplied by stored digitized samples of a plurality of sinusoidal tones to produce a product corresponding to each tone. Each product corresponding to each tone is squared. The resulting squared products are compared to determine which squared product has the maximum value. The tone which corresponds to the squared product with the maximum value substantially equal to the carrier frequency error. The local frequency is adjusted to compensate for the carrier frequency error.

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Milford, MA, United States of America

William E DeLisle