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: A radio telecommunications system includes a number of locator satellites in low earth orbits. Locatable subscriber units communicate with the satellites. A single subscriber unit communicates with a single satellite using electromagnetic signals so that a measurement processor can obtain Doppler component, propagation duration, and real time measurements of the signals. A location processor converts these measurements into a two-position location solution. The two-position solution includes an actual position and an image position. The actual position may be detected in some situations by identifying a cell within which communications take place. In other situations, the actual position may be distinguished from the image position by detecting the eastward rotation of the earth. A service processor determines which qualifications to apply to communication services offered by the system. These qualifications are based on the subscriber unit's location.

Abstract: A quadraphase shift keyed (QPSK) demodulator employs a pseudo data estimation loop for reducing the loop gain variation. This demodulator has a feedback loop to minimize the cross-coupling between the i anf q channels. This demodulator also provides as outputs the signals representing the amplitude of i and q channels. In addition, by eliminating amplification of some of the internally generated signals, this demodulator may serve as a biphase shift keyed (BPSK) demodulator.

Abstract: A phase shift keyed (PSK) demodulator includes a closed loop wherein a phase error signal is generated to control a voltage controlled oscillator (VCO) to track the carrier frequency of an input signal for demodulation. A frequency discriminator is incorporated with the PSK demodulator to provide a frequency error voltage which is also applied to the VCO to improve the tracking of the carrier frequency by substantially eliminating false locks and removing the dependence of the apparatus on the modulation of the received signal.

Abstract: The Doppler is converted to digital or a square wave signal after which a first counter is used to count total full Doppler cycles by counting the positive going zero crossings, a second counter counts relatively high frequency pulses from the beginning of each cycle until the end or until the reception of a read-out pulse, whichever occurs sooner, and a third counter counts the high frequency clock pulses from the beginning of each cycle until the end. When the read-out pulse is received the partial Doppler cycle count in the second counter is divided by the full Doppler cycle count in the third counter to obtain a fraction indicative of the partial Doppler cycle, which fraction is added to the total full Doppler count in the first counter to obtain a measure of Doppler cycles from the start until the read-out pulse is received.

Abstract: A multiple phase shift keyed data coherent carrier recovery system wherein a coherent carrier tracking loop has attached thereto a signal generator for providing a signal with non-stationary zero-crossing times (e.g. a noise generator), which signal generator chops, or alters the phase of, signals within the loop to prevent the loop from locking on harmonics or subharmonics and to allow AC coupling with DC response therein.

Abstract: A communications system utilizing a noisy reference signal and a noisy information signal wherein the information signal is delayed from the reference signal as a function of the information modulation and then the two signals are combined for simultaneous transmission. The receiver amplifies the combined signal and delays it by a predetermined amount corresponding to the delay in the transmitter. The delayed and undelayed signals are autocorrelated to reconstruct the information signal. The system provides for autocorrelation of signals which have traveled a plurality of signal paths from transmitter to receiver.