A system for enciphering or deciphering wherein bit patterns in a binary number notation of a plurality of elements, which an irreducible polynomial in the Galois field GF (2i) has, are stored in registers arranged in a certain correspondence with the bit positions of input data or messages, as random numbers for an encryption key or decryption key. The bit patterns retained in the registers corresponding to the digit of bit "1" in the input data are subjected to a mod 2 addition operation independently for each digit of the random numbers, to thereby obtain encipher or decipher data corresponding to the input data. The elements to be used for the encipher and decipher keys have a specific relationship therebetween in conformity with the periodical characteristic of the elements the irreducible polynomial has.

System for enciphering or deciphering data

A coherent signal generated at a precise frequency determined by an atomic clock is transmitted by a moveable object. A receiver station compares the frequency of the coherent signal received from the moving object with a second coherent signal generated at the same precise frequency by an atomic clock in the receiver to determine the radial component of the velocity of the moveable object relative to the receiver as a function of the doppler shift of the transmitted signal. Low cost, low power, miniature atomic clocks with an accuracy of 10-11 make possible accurate measurements of velocities of only centimeters per second. Such velocity measurement can be used to enhance radar tracking in air traffic control and collision avoidance systems. These velocity measurements can also be used to resolve tracking ambiguities in precision location systems, such as prisoner, geriatric and airport ground control systems, where three or more receiver stations each having an atomic clock measure time of flight of the transmitted coherent signal to triangulate moving object position.

Location and velocity measurement system using atomic clocks in moving objects and receivers

A system for aiding the movement of moving units (aircraft such as helicopters) when flying in formation. Every unit transmits information to every other unit so that bidirectional communication links are established between all units in the formation. Information indicative of the relative position between units is exchanged via the bidirectional communication links such that every unit has redundant position information pertaining to the position of every other unit. By a "data fusion" process performed on the redundant information, every unit accurately determines the position of every unit in the formation. One of the units (the "leader") then transmits "commands" to the other units (the "slaves"). Each command determines the position of a slave within the formation. Utilizing the command transmitted to it by the leader, and utilizing predetermined laws of pilotability, each slave then generates "piloting orders" for directing itself to the position commanded by the leader. These piloting orders may be supplied to an autopilot for automatic control the formation. The distance quantity of the relative position between units may be determined based on the travelling time of the transmissions of the bidirectional communication links between units. The direction quantity of the relative position may be determined based on the detected direction from which the transmission of the bidirectional communication links originated.

System for aiding the movement of moving units in group formation

A maximum length shift register sequence generator capable of changing the format and phase of an M code known as maximum length shift register sequences in the transmitter and receiver. The register is most suitable for use in spread spectrum communication systems adapted to effect transmission by correlation between an M code from the transmitter and such an M code generated in the receiver. The generator includes a latch for storing the format and initial phase of an M code to be generated subsequently, and a microprocessor for setting in the latch necessary data required for changing the M code. A change of the M code is effected by a strobe signal lasting for a time equal to the lasting time of one clock pulse.

Maximum length shift register sequences generator

This is a cipher system for enciphering a stream of binary data by means of a product cipher. A clear message represented in a binary data format is transformed into a cipher message by operating on each bit of clear information with a complex modulo-two addition function. This function is dependent on previous internal cipher digits transmitted and varies for each message bit processed. The function is developed by continually shifting a key matrix under the control of a varying control matrix. The control matrix is formed from the sub-product of the complex function developed in generating each cipher bit.

Variant key matrix cipher system

A binary pseudo-random frequency generator in which a shift register is continuously strobed by a clock and has its informational content altered in accordance with its acquired state A variable count divider counts down to zero from a number set therein from information received from the shift register at the divider zero count in response to frequency signals received from a voltage controlled oscillator Divider zero counts are also compared in a phased lock loop with a reference frequency to set the voltage controlled oscillator frequency

Pseudo-random frequency generator

A means of synchronizing clocks without addressing within a cooperative collision avoidance system which utilizes the time slot of the aircraft requesting synchronization. During its time slot, an aircraft transmitting a collision avoidance message automatically requests clock synchronization. All other aircraft within the collision avoidance network which receive the synchronization request will respond in a random manner with a probability inversely proportional to the number of potential responding aircraft within the collision avoidance network. To accomplish this each cooperating aircraft is equipped to monitor the number of occupied time slots so as to determine the number of potential responding aircraft, determines the probability of its response with respect thereto and determines in accordance with the probability thus derived whether it should respond to this particular synchronization request.

Clock synchronization without addressing for collision avoidance systems

A digital phase tracker includes a memory for storing a signal locked in phase with an external signal and means for maintaining the signal stored within the memory phase synchronized with the external signal as the phase of the external signal varies. The time relationship between positive excursions of the external signal and positive excursions of the stored signal is timed by high-speed clock pulses with clock pulses being added to or subtracted from the memory signal to maintain phase-lock.

Digital phase tracker

Apparatus for synchronizing clocks within a cooperative collision avoidance network wherein an aircraft after operating in an isolated environment for a predetermined time sets its clock in a standby position and listens for start of epoch signals. Upon hearing a start of epoch signal the aircraft immediately starts its clock and begins counting epochs and the time slots contained therein. During own time slot, as determined by its clock, the aircraft transmits a clock synchronization request. If no synchronization responses are received the aircraft will automatically advance its clock by a predetermined amount and once again transmit a synchronization request during its next time slot. If a synchronization response is now received the aircraft will synchronize its clock taking into account the amount of time by which its clock had to be advanced in order to receive the synchronization response. If no response is received the aircraft automatically returns its clock to the standby condition.

Extended range clock synchronization for collision avoidance system

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Pseudo-random frequency generator

Clock synchronization without addressing for collision avoidance systems

Digital phase tracker

Extended range clock synchronization for collision avoidance system