Sperry Corporation

Unisys Corporation

Sperry Rand Corporation

Billie M Spencer

John W Zscheile, Jr

Samuel Charles Kingston

Alan E Lundquist

Glen D Rattlingourd

Robert J Currie

Benjamin V Cox, Jr

Robert Price

William S Cady

Willis B Adkisson

Lawrence W Pike

James Eugene Holladay, Jr

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

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

In a two way ranging system of the type employing pseudonoise spread spectrum codes there is provided a method for correcting the navigational system of one of two moving stations in space to compensate for relative drift. The point positions of the two stations are calculated by the on-board navigation systems of the individual stations at a first and subsequently at a second position after relative movement. The range from station 1 to station 2 is calculated employing the highly accurate pseudonoise communications ranging systems. The range uncertainty of the range calculation and the trigonmetric relation of the two calculated ranges and the include angle between the line of sight of the range directions is employed to calculate a range of uncertainty parallelogram more accurate that the navigation systems. When a station's point position is indicated by its navigation system to be outside the parallelogram, the navigation system is corrected to compensate for relative drift.

Method of correcting navigation system errors caused by drift

A method of rapidly reacquiring a pseudonoise spread spectrum coded signal after short outages includes calculating the new positions of the moving stations relative to the old positions of the moving stations and for determining the accurate displacement and the accurate direction the platforms have moved in their new direction after a short time outage. The method includes calculating a triangle which includes the displacement between the moving stations' old position and the moving stations new position and the included angle between the direction of movement and the line of sight between said moving platforms at the time of outage. A range displacement adjustment is calculated on the basis of the triangle for each moving station and the range factor resulting from this calculation is applied to the PN generators of the receiver and transmitter in each of the moving stations to independently adjust for each station's movement. The directional antennas of the moving stations are pointed in new directions toward the area in which the other moving station will be found. The directional antennas are moved simultaneously toward each other and a sweep or reacquisition adjustment of the PN generators of each moving station is made employing a small window of uncertainty which results in reacquisition of the PN coded signal being transmitted from the other station.

Range estimation using floating reference points

The present invention is concerned with an apparatus and a method of jumping a composite PN code from a current phase position to a desired predetermined phase position so as to enhance acquisition of a composite PN code. The apparatus includes a plurality of individual PN code generators which are connected to a code combiner to produce a composite PN code. Each of the individual PN code generators is driven by its own timing gate for supplying synchronized clock pulses to its own PN code generator. A master clock is connected to a timing gate before being connected to the individual PN code generators. An inhibit input at each of the individual timing gates is provided so that the individual PN generators may be inhibited a predetermined number of clock pulses which causes the PN code generated to be inhibited and has the effect of jumping the PN code a desired number of phase positions.

Method of jumping composite PN codes

A novel maximum likelihood sequence detector is provided for decoding linear cyclic error correction codes. The detector comprises one cyclic correlator for each two shaft sets of the code which have weights greater than one, and a serial correlator for detecting the shift sets of all zero's and all one's. The number of cyclic correlators required to decode linear codes is reduced to less than half the number of shift sets which define all the codewords instead of half the number of codewords where the number of shift sets is always less than the number of codewords.

Maximum likelihood sequence decoder for linear cyclic codes

An accurate radio frequency ranging system is provided for measuring the time required for a signal to be transmitted from a ground station to a remote station and to be returned to the ground station. The ground station is provided with a master reference clock that is employed to drive a first pseudonoise generator. The ranging system in the ground station is started by a unique and predetermined start epoch signal produced by the first pseudonoise generator. The first pseudonoise generated signals are transmitted to the remote station where they are tracked and sensed. When the original start epoch signal is sensed at the remote station, it is employed as a trigger or read signal to initiate the generation of a stop epoch signal. The stop epoch signal is retransmitted to the ground station and stored in a register where it is compared with pseudonoise generated signals being retransmitted from the remote station to the ground station. When the correlation between the two signals occurs, a new epoch stop signal is produced which stops the timing of the ranging system in the ground station. Since the pseudonoise generated signals transmitted from the remote station to stop the ranging system in the ground station are not locked on to the pseudonoise signals being transmitted from the ground station to the remote station, there is no requirement for turn-around coherency.

Quasi coherent two-way ranging apparatus

A non-coherent receiving system is provided with a novel triple-bit matched filter detector system which provides two outputs indicative of the data stream being detected. A preliminary or soft decision is made concerning the state of the bits in the data stream. One of the outputs provides a best estimate of state of the data bit being detected and the other output provides the second best estimate of the state of the data bits being detected. The incoming data stream is processed and modified as it is shifted through a plurality of shift registers in real time employing the data bits subsequently detected. A controller is provided to make a plurality of predetermined evaluations of the state of the bits in the data stream and to provide a final or hard decision of the correct state of the data bits previously detected.

Triple bit non-coherent matched filter receiving system

In a digital data acquisition system, there is provided a coherent direct sequence spread spectrum receiving system. The coherent receiving system comprises an independent carrier tracking loop and three independent branches for detecting and locking on to a received psuedonoise data signal. The psuedonoise data signal being transmitted is provided with a time slot or discrete time portion during which no data is modulated onto the carrier. The carrier signal which is not phase modulated with digital data is tracked by the tracking loop so that the absolute phase of the carrier is never lost. The psuedonoise data signals are now recoverable in a coherent direct sequence spread spectrum receiver without the requirement of absolute phase determination or non-coherent detection.

Coherent spread spectrum receiving apparatus

A system for transmitting desired information is provided which has a very low probability of being intercepted. The system combines a well known narrow bandwidth directional antenna for limiting the interception of the main beam information signal with a novel random noise generated signal which guarantees that the sidelobe signals which also contain the desired information cannot be distinguished as information signals.

Low probability of intercept transmitting apparatus

A novel interleaver-de-interleaver is provided which is adapted to store bits of a data stream after being error encoded. The data bits are stored in a random access memory in addresses identifiable by an array of columns and rows. The interleaver comprises address pointer means and logic for reading the data bits out of the memory addresses in a predetermined reordered sequence to provide a quasi-random pattern sequence of data bits which when transmitted are substantially immune to periodic bursts of radio frequency interference signals.

Apparatus for interleaving and de-interleaving data

An accurate radio frequency ranging system is provided for measuring the time of transmission of a signal from a first station to a second station and back to the first station without coherent turn-around of the signal. Each of the two stations is provided with its own range measuring means and its own reference clock. The first station range measuring device is started by the first station reference marker and is stopped by the second station reference marker start signal transmitted from the second station to provide a first range measurement. The second station range measuring device is started by the second station reference marker and is stopped by the reference marker start signal transmitted from the first station to provide a second range measurement. The sum of the two range measurements contains the data necessary to calculate the true range between stations and the difference between the two range measurements contains the data necessary to calculate the offset between the two reference clocks without the two reference clocks being synchronized or locked to each other.

Noncoherent two way ranging apparatus

A coding system produces a code with enhanced acquisition security by generating a plurality of linear component codes, C.sub.1, C.sub.2, . . . C.sub.n, combining the component codes in accordance with a modulo-2 addition rule to form a linear first composite code, nonlinearizing the first composite code to form a nonlinear second composite code, time delaying the component codes, C.sub.1, C.sub.2, . . . C.sub.n-1, and combining the time delayed codes with the nonlinear second composite code in accordance with a Boolean majority voting rule to form a nonlinear acquisition composite code. Acquisition of the nonlinear acquisition composite code is achieved by generating a plurality of linear reference component codes, R.sub.1, R.sub.2, . . . R.sub.n, that correlate respectively with the linear acquisition component codes, C.sub.1, C.sub.2, . . . C.sub.n, combining the reference component codes in accordance with the modulo-2 addition rule to form a linear third composite code, nonlinearizing the third composite code to form a nonlinear fourth composite code, time delaying the reference component codes, R.sub.1, R.sub.2 , . . . R.sub.n-1, correlating the time delayed codes with the nonlinear acquisition composite code by shifting the phases of the time delayed codes, and correlating the fourth composite code with the acquisition composite code by shifting the phase of the reference component code, R.sub.n.

Coding method and system with enhanced security

A ranging system utilizing continuous-wave radio frequencies having unique relationships which occur at a predictable rate. A radio transmission system used for transmitting data has a portion of its baseband used to determine range to a target. Three frequencies within the portion of the baseband are so chosen that there is a periodic phase conicidence of the three frequencies which occurs at predetermined intervals. The phase coincidence is detected on transmission to and from a target to provide range information.

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Bountiful, UT, United States of America

Billie M Spencer