Abstract: A system for locating a mobile device is disclosed. In one embodiment, the system includes a mobile device having a processor and a receiver, and at least three transceiver devices forming a network of transceiver devices. The mobile device and transceivers can transmit a request (REQ) packet by the mobile device; receive the REQ packet by the at least three transceiver devices; transmit, by a first one of the at least three transceiver devices receiving the REQ packet, a response (RSP) packet; and receive by at least some of the at least three transceiver devices the REQ and the RSP packet. The at least three transceiver devices that receive both the REQ and the RSP packet, the system determines a difference in arrival time between receiving the REQ packet and the RSP packet. The system can determine the location of the mobile device based on determined differences in arrival time.

Abstract: A Loran-C communications technique and system are disclosed involving appropriate encoding of communication messages and logical multiplication and inversion of encoded signals prior to phase modulation of the Loran-C pulses, with novel bit-flip connections for producing complementary plus and minus modulation position shifts in the first and third and second and fourth, etc., of the Loran-C pulse groups, and with perfect balance irrespective of the nature of the raw data and irrespective of skywave interference.

Abstract: A radio signal containing Loran C pulses from stations of interest is received and periodically sampled to convert the input signal to sample data. The data is assigned to memory locations within an acquisition memory at positions in the memory which correspond to specific times within the group repetition interval (GRI) of the Loran chain of interest. A GRI counter assigns the locations in the memory to which the data are written and cycles the memory after the completion of each GRI so that new data corresponding to a new set of pulses from the master and secondary stations of the Loran C chain will be assigned to essentially the same memory locations as data acquired during a previous GRI. The new data is ensemble averaged with the old data contained in the memory locations and the averaged data stored back in the memory.

Abstract: The present invention includes both a system and a method for locating a source of a randomly modulated radio signal. In one form of the invention, at least three receiving stations at known locations receive and process the randomly modulated radio signal. A common reference level is selected for the radio signal at each of the receiving stations. The times of arrival at each receiving station of selected transitions of the radio signal with reference to the common reference level are determined. Each receiving station provides an indication of the times of arrival of the selected transitions to a central facility for processing to provide an indication of the location of the signal source.

Abstract: A Loran-C signal receiving apparatus which achieves accurate measurement of the location of the apparatus without error due to a well-known cycle slip phenomenon. In the Loran-C signal receiving apparatus, a pulse tracking a particular cycle of a carrier wave of the received Loran-C signal is generated, a frequency at which the tracking pulse is generated by a pulse generator (in a PLL circuitry) is monitored and when a frequency error of the generator is derived on the basis of a tracking error of the tracking pulse with respect to the received Loran-C signal, the frequency of the pulse generator is corrected on the basis of the derived frequency error. The apparatus can thus assure a phase tracking of the received Loran-C signal and assure accurate measurement of the location.

Abstract: In a Loran-C message communication system a method of obviating errors in navigation locking caused by sampling reception at the conventional symmetrical pulse modulation time intervals in advance of and in delay from the normal transmission interval, through rendering the pulse modulation assymetrical to a degree that compensates for different cycle amplitudes at sampling points above and below the desired sixth zero crossing used for navigation position determination.

Abstract: A guidance system for aircraft wherein a radio antenna on the ground transmits a beam that sweeps across an aircraft and the aircraft receives the beam and utilizes its amplitude waveform in determining the location of the aircraft from the station. At low elevation angles of the aircraft the portion of received waveform that includes significant amounts of signal reflected from the ground is used in only a preliminary manner. The more reliable, directly radiated, portions of the waveform are utilized to compute by least squares error, the median of a Gaussian beam shape. That median serves as an estimate of the time that the transmitting antenna was pointing directly at the aircraft.

Abstract: Method and apparatus of obviating cycle-locking slippage errors in reception of Loran-C and similar radio-frequency signals covered by receiver location acceleration effects and other distortion effects simulating the same, that comprises, receiving the radio-frequency signals and producing data by sampling and tracking the cycles of the signal with a time-constant filter sufficiently fast to accommodate for the largest acceleration to be experienced by the receiver location to avoid cycle slippage in locating a predetermined cycle zero crossing, and independently post-filtering sufficiently slowly to smooth the data and without interaction with said sampling.

Abstract: The effects of impulse noise on the operation of a microprocessor-controlled Loran-C receiver are reduced by muting or attenuating the received signals in the front end of the receiver ahead of the receiver gain during a time period which preceeds the start time of the pulses being tracked. The attenuation is selectively removed after the start time of each pulse being tracked to permit the receiver to perform its time difference of pulse arrival measurements in the normal manner. The attenuation is also selectively removed during those time periods in which the receiver performs its envelope slope, skywave/groundwave and other such samplings. The attenuation is provided by a muting circuit which is controlled by a time gate signal that derives from the microprocessor of the receiver.