Unisys Corporation

Sperry Corporation

Loral Corporation

Sperry Rand Corporation

John W Zscheile, Jr

Alan E Lundquist

Billie M Spencer

Samuel Charles Kingston

Glen D Rattlingourd

Richard J Saggio

Robert J Currie

Michael Wilson

Vaughn Lee Mower

Robert V Jones

Benjamin V Cox, Jr

Steven T Barham

Robert Price

Craig K Rushforth

Robert A Wright

Steven L Bennett

Lowell N Shestag

William S Cady

Curtis M Abrahamson

Lawrence W Pike

Glen S Kirkpatrick

Bellie M Spencer

Willis B Adkisson

In a spread spectrum multipoint-to-point communication system there is provided a novel frequency to phase converter, for automatically synchronizing the PN codes of the user transmitters/receiver with the receiver/transmitter in the central hub. The highly accurate frequency to phase converter generates a highly accurate phase error signal for synchronizing the multiuser network. The frequency to phase converter includes a serial adder and a series to parallel converter and a shift register which integrates the highly accurate phase error signal values and produces a highly accurate frequency value which is applied to the input of the resident processor in the central hub transmitter/receiver. The central hub transmitter/receiver calculates the clock offset for synchronizing each of the user receiver transmitters and generates a clock adjusting signal which is transmitted to the user receiver/transmitters.

Apparatus for synchronizing multipoint-to-point communications systems

Apparatus and method are provided for adaptively modulating or combining a first signal with a second signal. A series of values of the first signal are taken and sequentially stored in a shift register. The maximum absolute value of the oldest N values (where N is an integer) stored in the shift register is then determined. Before, during or after that determination, the maximum absolute value of the remaining (newer) series of values of the shift register is also determined. The lesser of those two maximum absolute values is then determined. This lesser maximum absolute value is then multiplied by a gain factor representing the desired gain to produce a scale factor. The gain factor can be a preset constant, or can be based on the steady-state ratio of the power of the second signal to the power of the first signal. The second signal is then multiplied by the scale factor to produce a scaled signal. Meanwhile, the first signal has been delayed by an amount representative of the total time duration of the first N values in the shift register, or of the total time needed to obtain those first N values, or of the duration of the portion of the signal represented by those first N values. Considering the two peaks separately, combined with using this delay, in effect enables the resulting amplitude tracking to consider prospective as well as past values of the first signal. The scaled signal is then added to the delayed first signal. The amplitude of the scaled second signal thereby tracks the amplitude of the corresponding portion of the first signal, so that the scaled second signal cannot be readily detected unaided during any relatively low amplitude portion of the first signal.

Apparatus and method for amplitude tracking

A novel code division multiple access (CDMA) system and apparatus is provided which permits a plurality of encoded modulated data messages to be transmitted simultaneously on the same channel in one frequency band as a composite CDMA signal. An identification signal is generated and spread by a spreading signal having a duty cycle less than fifty percent to produce a combined signal which is transmitted to a receiver having a tapped delay with a plurality of taps each of which produce a replica of the received combined signal delayed by an odd multiple of the duty cycle of the spreading signal. Each of the replica signals is multiplied by a predetermined weighted value to produce weighted delayed signals and a controller responsive to the received combined signal, is employed for controlling individual weighted delayed signals which are then combined to suppress the spreading signal leaving the identification signal.

Apparatus and method for signal identification

A set of independent pseudonoise (PN) component codes greater than two are combined in a manner which produces one or more I and Q uncorrelated orthogonal pairs of resulting combined PN sequences. At least two of the component codes in a resulting combined PN sequence are combined in a manner which produces an overall imbalance of ones and zeros in the binary expression of the resulting combined PN sequence so that the resulting composite code has a partial correlation with a predetermined one of the PN component codes. In the preferred embodiment, three component codes are combined to produce uncorrelated orthogonal pairs of composite codes wherein at least one of the pairs of composite codes is produced to have a partial correlation with one or more of the component codes.

Apparatus and method for generating and utilizing pseudonoise code

A transmitter is provided which simultaneously transmits waveforms such as with different data rates. These transmissions are modulated (e.g. phase modulated) onto quadrature channels of a common carrier, and are then combined. The resulting composite modulated waveform is upconverted to RF, power amplified, split and routed to separate ports for transmission. The transmitted signals are then received, downconverted and demodulated to produce the original signals.

Multiple channel quadrature communication system and method

Apparatus and a method for increasing the speed of acquisition of PN coded signals includes a novel PN code clock extraction circuit which is coupled in parallel to a code tracking loop and acquisition loop of a PN receiver of the type having a replica PN code generator which is slip controlled to synchronize with the received PN coded signals. The novel PN code clock extraction circuit detects the clock transition of the received PN coded signals and synchronized the replica PN code generator clock transition signals so that there is no misalignment during acquisition. A switch control in the acquisition loop circuit senses the synchronization of the replica PN code generator transition and the received PN code transition and disconnects the PN code clock extraction circuit after synchronization of clock transition and before acquisition of the PN code so that the acquisition loop detects the PN code synchronization with a full strength signal.

Coherent sequential PN code extractor

Apparatus for rapidly acquiring a high performance gain long PN code having a preamble header in real time includes appratus for rapid acquiring and tracking a short PN code in said preamble header and further includes apparatus for demodulating and tracking a long PN code which follows said preamble header. After acquiring the short PN code, the short PN replica code is applied to the long code demodulation and tracking apparatus. The short PN code is employed to synchronize the long code demodulation and tracking apparatus by detecting the time of occurrence of a sync word in said preamble header and is employed to generate a switch point signal and switch from a short PN replica code to a long PN replica code at the input to the long code demodulation and tracking device in real time.

High processing gain acquisition and demodulation apparatus

A novel PN code acquisition and demodulation circuit comprise an analog receiver coupled to an analog to digital converter. The digital output of the converter is passed through an N chip width parallel correlator. The parallel outputs are coherently accumulated to provide N soft decision data values one of which is indicative of the proper replica code for locking onto the data. All of the soft decision data values are stored in a high speed memory in real time. Subsequently non-coherent accumulated soft decision data is employed to detect the proper PN replica code. Logic selection means accesses the soft decision data stored in the high speed memory in non real time and selects the best estimate for the soft decision data and applies the soft decision data to a demodulator in non-real time to recover the hard data encoded in the received PN coded data.

Asynchronous samples data demodulation system

A high PN code rate receiving system is provided for receiving, recovering and tracking a high rate PN composite code comprising a low rate PN code combined with a high rate PN code and wherein the receiving system comprises a broad band receiver for receiving the high rate PN composite code and further includes a data recovery channel and a tracking loop channel. The data recovery channel comprises a high rate mixer and a low rate mixer for removing the high data rate component code and the low data rate component code to provide a low data rate data stream. The tracking loop channel comprises a high rate early-late tracking system for producing a high rate error signal and further comprises a low rate portion of the tracking loop for producing a low rate error signal which is combined with the data output to provide a clock error signal. The clock error signal is applied to a voltage controlled oscillator to produce a low data rate clock and a high data rate clock which are coupled to a low data rate code generator and a high data rate code generator which synchronize the tracking loop and said data channel.

High rate-low rate PN code tracking system

A novel low speed code sequence generator having a set of parallel flip-flops is provided and comprises a vector generator in series between the outputs and the inputs of the set of parallel flip-flops in the generator. The outputs from the low speed code sequence generator may be multiplexed together to provide an individual high speed code sequence. The selective outputs from a plurality of low speed code sequence generators may be algebraically combined and then multiplexed together to provide a composite code sequence.

High speed code sequence generator

A novel range based acquisition system includes a receiver for receiving PN encoded signals coupled to a novel range based variable dwell correlator which detects and acquires uniquely timed received transmitter PN encoded signals employing different search dwell times for each of the estimated ranges from which the receiver transmitted PN encoded signals are being propagated so as to enhance the speed of acquisition of said PN encoded signals.

Range based acquisition system

In a demodulator circuit for receiving a direct sequence spread spectrum signal having composite PN codes, there is provided a novel detecting and tracking circuit for faster acquisition of the component PN codes. The first component code of the received composite direct sequence spread spectrum code is noncoherently detected in a noncoherent detection branch and the subsequent component codes of the composite code are automatically detected in a coherent lock detection branch to provide faster acquisition than was heretofore possible. Further, while the noncoherent detection branch is acquiring the first component PN code, a novel coherent carrier tracking loop is acquiring and locking onto the direct sequence spread spectrum signal carrier.

Detecting and tracking circuit for component PN codes

Apparatus for generating a complex composite code for fast acquisition by multiple access users is provided which comprises a composite code generator having an in-phase channel code generator and a quadrature channel code generator for generating two linear composite codes. The quadrature channel composite code is modulated onto a carrier which is 90.degree. out of phase with the in-phase carrier. The two linear composite codes are summed together and simultaneously transmitted to the receivers. Each receiver has a plurality of components code generators which generate replica component codes for fast acquisition of the composite code. A plurality of the components codes of the in-phase composite code are derived from the like components code generators in the quadrature channel to enhance speed of acquisition without acknowledgements by the receivers that any of the components codes have been acquired.

Multiple access code acquisition system

The present invention provides a novel burst erasing automatic gain control circuit which includes the basic elements of an automatic gain control circuit and further includes in the loop control circuit, slow response wideband filter means, and a hard limiter which limits the AGC'ed output from the amplifier so that the signal reaching the slow response wideband filter means never exceeds a predetermined value which would cause distortion in the feedback loop. The output of the novel automatic gain control circuit is coupled to a despreading circuit which removes substantially all of the remaining burst jamming signals.

Burst jammer erasure circuit for spread spectrum receivers

A coherent pseudonoise code (PN) tracking loop is provided with apparatus for sensing the absence of PN transition in the incoming data stream to the tracking loop and for switching OFF the data stream to prevent phase error distortion and inherent noise from entering the tracking loop which could be sensed as false or incorrect phase error signals. The apparatus includes a transition switch in the incoming data stream that is responsive to transition gate control logic coupled to the output of the PN replica generator in the tracking loop for switching OFF the incoming data stream when no PN transitions are occurring.

Growing community of inventors

Farmington, UT, United States of America

John W Zscheile, Jr