Abstract: A satellite tracking system, including a terrestrial transmitter, a plurality of terrestrial receivers, and a controller/analyzer, operates in two modes. In an active mode, the transmitter emits a tracking signal within a spread spectrum to a satellite and at least one of the receivers receives the signal retransmitted by the satellite. The controller/analyzer then determines the satellite position and velocity from the received signal. In a passive mode, at least two receivers each receive a signal transmitted from the satellite during normal operation and the controller/analyzer determines the satellite position and velocity from the received signals. The satellite position and velocity can be used to determine the position of an unknown transmitter that causes interference at the satellite.

Abstract: A method and an apparatus for determining a position of a movable object comprise transmission of a radio wave of a constant frequency from the mobile object. The transmitted radio wave is received at each of a plurality of spaced positions which are disposed in an area where the mobile object is movable. A frequency of the received radio wave is detected at each of these positions and the position of the mobile object is determined based on position data indicating the spaced positions and a frequency deviation between the frequency of the received radio wave detected at each of the positions and the constant frequency. Further, in a mobile communication system a radio wave of a constant frequency, which is transmitted from the mobile object, is received at each of a plurality of spaced base stations which are disposed in an area where the mobile object is movable.

Abstract: A location system relies upon a non-coherent, FDM/TDM communication scheme to measure location parameters. A locator unit moves relative to the locatable unit. A series of messages are communicated between the locator unit and the locatable unit. Through feedback provided from the locator unit to the locatable unit, the locatable unit adjusts its reference frequency and time base so that signals it transmits arrive at the locator unit on a desired frequency and at a desired time slot. The locatable unit estimates Doppler and propagation duration and transmits the estimates to the locator unit. The locator unit measures offsets between desired frequencies and time slots and actual frequencies and time slots. The offsets are combined with the locatable unit's estimates of Doppler and propagation duration to form an integrated Doppler parameter and an integrated propagation duration parameter. The integrated Doppler and propagation duration are used to determine location.

Abstract: An electronics circuit receives a sub frame of encoded doppler data having roups One through N of data words with the first three words of Group N comprising a frame sync signal which is compared to a reference signal with a sync pulse being generated whenever the signals are identical. This sync pulse is supplied to three counters to load each counter with a predetermined count. The first counter counts the number of words in each Group; the second counter counts the number of Groups in a sub frame and the third counter indicates the location of Automatic Gain Control and Word Width data within the sub frame. Encoded within each group of a Sub Frame are one or more clusters of doppler words with a fourth counter indicating the location of these clusters of doppler words. A word decoder circuit in response to a gain signal and a word width data signal decodes each word of each group of the sub frame having doppler data to extract the doppler data.

Abstract: The frequency and power of transmissions in a mobile communication system, such as an air-to-ground telephony system, are stabilized without a priori knowledge of the system gain factors or frequency references. The ground station monitors the available channels and modifies a vacant channel broadcast message to provide information that the channel is available. In this way, the air terminals have knowledge of all available channels. The ground station transmits a pilot signal. Upon request by a user for a dial tone at the air terminal, the air terminal selects a vacant channel and scans for the pilot signal. The air terminal estimates a distance to the ground station and sets a power level of a seizing transmission based on the estimated distance. The air terminal also estimates a Doppler frequency shift of the selected channel due to the relative movement of the air terminal with respect to the ground station and sets a frequency of the seizing transmission based on the estimated Doppler frequency shift.

Abstract: To reduce error introduced by the local oscillator in the velocity calculations, the receiver has two "tracking channels" and a microcomputer. With numbers required to, simultaneously, lock each of the "tracking channels" each to a respective satellite signal, the microcomputer employs a differential doppler technique to calculate the receiver velocity. The microcomputer calculates a number which represents the difference between the apparent doppler frequency shift of the carrier signal which is transmitted by the first "tracking channel" satellite and which is measured over a specific time period and the apparent doppler frequency shift of the carrier signal which is transmitted by the second "tracking channel" satellite and which is measured over substantially the same time period.

Abstract: In a system for deriving position, velocity, and acceleration information from a received signal emitted from an object to be tracked wherein the signal comprises a carrier signal phase modulated by unknown binary data and experiencing very high Doppler and Doppler rate, this invention provides combined estimation/detection apparatus for simultaneously detecting data bits and obtaining estimates of signal parameters such as carrier phase and frequency related to receiver dynamics in a sequential manner. There is first stage for obtaining estimates of the signal parameters related to phase and frequency in the vicinity of possible data transitions on the basis of measurements obtained within a current data bit. A second stage uses the estimates from the first stage to decide whether or not a data transition has actually occurred.

Abstract: Radiodirection finding method and apparatus using Doppler effect frequency modulation for measuring the bearing of a source transmitting a high frequency signal, wherein either on the reception side or on the transmission side, several antenna strands are used in pairs diametrically spaced from each other and spaced evenly apart angularly about a circumference. A first pair of diametrically spaced antenna strands are energized and then the next pair of diametrically spaced antenna strands in turn are selectively energized so as to create, at all times, a mobile fictitious antenna moving diametrically and alternately between the two diametrically opposite antenna strands of the particular pair of antenna strands considered. Different pairs of diametrically opposite antenna strands are successively energized in an angularly rotating sequence from the first pair of antenna strands.

Abstract: A passive doppler differential ranging method for use with respect to an aircraft radar for determining the range, R, of a threat passively, includes the steps of mounting a first receiving antenna and a second receiving antenna on an aircraft and positioning the first and second antennas a known distance, d, apart from each other, and determining the azimuth angle .alpha. of the threat with respect to the aircraft at a first time t.sub.o. A first differential doppler phase shift, .DELTA..phi., between the first and second antennas of a received signal transmitted by the threat at time t.sub.o is then determined. The velocity of the aircraft is measured, and a second differential phase shift, .DELTA..phi..sub.1, between the first and second antennas of a received signal transmitted by the threat at time t.sub.1 is then determined. The differential differential doppler phase shift, .DELTA..DELTA..phi.

Abstract: There is disclosed a system and technique for providing an audio verification of Global Positioning System (GPS) receiver signal acquisition. In a GPS receiver, the correlated output of the GPS signal is generally represented as a data modified CW signal with a Doppler component caused by the movement of a GPS satellite with respect to the receiver. Due to the Doppler component, this signal output provides a signature which is indicative of the particular satellite from which the signal is being received. The signal output is mixed with a local oscillator to produce a beat frequency in the audio band which may be filtered and coupled to an audio amplifier to produce an audio tone. The presence of the audio tone indicates the acquisition of a selected satellite signal and its audio frequency is indicative of the particular satellite signal being received.

Abstract: An improved method of doppler searching in a digital GPS receiver is described. According to the principles of the present invention, an N-point fourier transform is performed on samples of a down converted GPS signal representing the entire range of Doppler-shifted GPS carrier frequencies. The magnitude of the square of each of the output samples is calculated to produce N power quantities, corresponding to N search frequencies. The power quantities for each of the N search frequencies are then summed to produce N quantities proportional to average power. The maximum of the N-power quantities indicates the presence of the corresponding GPS signal.

Abstract: A method and a system are disclosed for measuring the baseline vector b between a pair of survey marks on the ground by radio interferometry using radio signals broadcast from the earth orbiting satellites of the NAVSTAR Global Positioning System (GPS), the radio signals broadcast by the satellites being double-sideband modulated with their carriers suppressed. An antenna is positioned at each survey mark. The signals received by one antenna during a predetermined time span are separated into upper and lower sideband components. These separate components are filtered, converted to digital form, and then multiplied together. Their product is analyzed digitally by means of correlation with quadrature outputs of a local oscillator to determine the power, and the phase relative to that local oscillator, of the carrier wave that is implicit in the double-sideband signal being received from each satellite. Differences in Doppler shift are utilized to distinguish the carriers of different satellites.