Abstract: Systems, apparatus and methods for determining a set of ranges from selected subcarriers of an OFDM signal sent between a receiver (e.g., first transceiver or a local receiver of a local unit at a first location) and a transmitter (e.g., second transceiver or remote transmitter of a remote unit at a second location) are presented. The set of ranges is ambiguous as to the correct range. Each range in this set of ambiguous ranges represents a possible range between the transmitter and the receiver. Range ambiguities may be resolved by using additional subcarriers from the OFDM signal and/or using a last know position of a receiver and/or finding ranges to two, three or more transmitters. The range may be used with other ranges to find a location estimate of the receiver.

Abstract: Systems, apparatus and methods for determining a set of ranges from selected subcarriers of an OFDM signal sent between a receiver (e.g., first transceiver or a local receiver of a local unit at a first location) and a transmitter (e.g., second transceiver or remote transmitter of a remote unit at a second location) are presented. The set of ranges is ambiguous as to the correct range. Each range in this set of ambiguous ranges represents a possible range between the transmitter and the receiver. Range ambiguities may be resolved by using additional subcarriers from the OFDM signal and/or using a last know position of a receiver and/or finding ranges to two, three or more transmitters. The range may be used with other ranges to find a location estimate of the receiver.

Abstract: A data encryption and decryption system securely geoencrypts data using location-dependent navigation signals. To increase the entropy of the cryptographic key to guard against a brute-force attack, geoencryption is made to depend on largely time-independent characteristics of the navigation signals that are not easily spoofed, including the time difference of arrival, the envelope-to-cycle difference, the differential signal-to-noise, the signal envelope shape, and the directions of arrival of the navigation signal set.

Abstract: In a geo-security system, a device receives RF signals from multiple distinct classes of RF communication systems and extracts location-dependent signal parameters. A current geotag is computed from the parameters by fuzzy extractors involving quantization of the parameters and Reed-Solomon decoding to provide a reproducible unique geotag. The current geotag is compared with a stored geotag, and a geo-secured function of the device is executed based on the result of the comparison. The use of multiple signal sources of different types, combined with special fuzzy extractors provides a robust geotag that allows both lower false rejection rate and lower false acceptance rate.

Abstract: Location systems and methods are implemented using a variety of arrangements and methods. Using one such system location information is provided in response to a utility-line arrangement propagating signals that represent a wireless radio-frequency (RF) communication originating from one or more remote transmitters. The system includes a receiver circuit communicatively coupled and responsive to the utility-line arrangement. The system also includes a signal-processing logic circuit, communicatively coupled and responsive to the utility-line arrangement. The signal processing logic circuit is arranged to derive location information from characteristics of the signals that are indicative of a location of the receiver circuit relative to the remote transmitters.

Abstract: In a geo-security system, a device receives RF signals from multiple distinct classes of RF communication systems and extracts location-dependent signal parameters. A current geotag is computed from the parameters by fuzzy extractors involving quantization of the parameters and Reed-Solomon decoding to provide a reproducible unique geotag. The current geotag is compared with a stored geotag, and a geo-secured function of the device is executed based on the result of the comparison. The use of multiple signal sources of different types, combined with special fuzzy extractors provides a robust geotag that allows both lower false rejection rate and lower false acceptance rate.

Abstract: Various systems, methods and devices are implemented for processing received signals. Consistent with one such embodiment, a method is implemented for use in a signal-communication receiver having a carrier-tracking loop and a processor for operating adaptive algorithms. The method involves interpreting a received signal using space time adaptive processing (STAP). A convergence speed of the adaptive algorithms is set based on a noise bandwidth of a phase-locked loop (PLL) in the carrier-tracking loop. A carrier-phase de-rotation constraint is implemented into weight parameters of the STAP to preserve spatial and temporal degrees of freedom in the STAP.

Abstract: Aspects are applicable to secure encryption such as in the generation of a cryptographic key from location information as may be useful in portable/wireless communication devices. As an example, one embodiment is implemented as a method of generating cryptographic keys from location information derived from a signal received from a publicly-used wireless communication system. The location information is protected from fraudulently generated signals using direction of arrival of the received signal.

Abstract: A data encryption and decryption system securely geoencrypts data using location-dependent navigation signals. To increase the entropy of the cryptographic key to guard against a brute-force attack, geoencryption is made to depend on largely time-independent characteristics of the navigation signals that are not easily spoofed, including the time difference of arrival, the envelope-to-cycle difference, the differential signal-to-noise, the signal envelope shape, and the directions of arrival of the navigation signal set.

Abstract: Various systems, methods and devices are implemented for processing received signals. Consistent with one such embodiment, a method is implemented for use in a signal-communication receiver having a carrier-tracking loop and a processor for operating adaptive algorithms. The method involves interpreting a received signal using space time adaptive processing (STAP). A convergence speed of the adaptive algorithms is set based on a noise bandwidth of a phase-locked loop (PLL) in the carrier-tracking loop. A carrier-phase de-rotation constraint is implemented into weight parameters of the STAP to preserve spatial and temporal degrees of freedom in the STAP.

Abstract: Location systems and methods are implemented using a variety of arrangements and methods. Using one such system location information is provided in response to a utility-line arrangement propagating signals that represent a wireless radio-frequency (RF) communication originating from one or more remote transmitters. The system includes a receiver circuit communicatively coupled and responsive to the utility-line arrangement. The system also includes a signal-processing logic circuit, communicatively coupled and responsive to the utility-line arrangement. The signal processing logic circuit is arranged to derive location information from characteristics of the signals that are indicative of a location of the receiver circuit relative to the remote transmitters.

Abstract: Method and apparatus for reducing radio frequency interference (RFI) using a dual-element patch antenna [10]. The antenna possesses two antenna elements [13, 14] having distinct radiation patterns. Either element may be independently selected using a DC bias voltage. Diodes [20] connected to the elements serve to disable one element when the other is selected. In one selected mode, a nominal radiation pattern provides a broad, hemispherical shaped sensitivity that is designed for acquiring and tracking all navigation satellites above the horizon. This nominal radiation pattern, however, is susceptible to interference that is present near or below the horizon. The second selectable radiation pattern of the dual-element antenna has comparatively higher gain toward zenith, and lower gain at and below the horizon to mitigate interference. This combination of features is packaged in a single antenna unit that can be a direct replacement for existing antennas.

Abstract: A multipath mitigation method consists of locating a multipath-invariant (MPI) point of an ideal autocorrelation function and measuring the distance between the MPI point and DLL. The same MPI point is located in a received correlation function, and the distance between the point and the DLL, now affected by multipath, is measured. The difference between the ideal distance and the actual distance is the code tracking error resulting from multipath. The error is subtracted from the computed pseudorange or used to control the DLL. The method can be used to reduce the effects of all types of tracking error sources, such as signal transmission failure or code noise.

Abstract: Method and apparatus for reducing radio frequency interference (RFI) using a dual-element patch antenna [10]. The antenna possesses two antenna elements [13, 14] having distinct radiation patterns. Either element may be independently selected using a DC bias voltage. Diodes [20] connected to the elements serve to disable one element when the other is selected. In one selected mode, a nominal radiation pattern provides a broad, hemispherical shaped sensitivity that is designed for acquiring and tracking all navigation satellites above the horizon. This nominal radiation pattern, however, is susceptible to interference that is present near or below the horizon. The second selectable radiation pattern of the dual-element antenna has comparatively higher gain toward zenith, and lower gain at and below the horizon to mitigate interference. This combination of features is packaged in a single antenna unit that can be a direct replacement for existing antennas.

Abstract: In wireless communications and navigation systems such as GPS, pseudorange measurements are made between a signal transmitter and a signal receiver based on pseudorandom noise codes modulating the transmitted signals. In the receiver, a code is tracked by forming a correlation function between the received code and a local code replica and locating the peak of the function using a delay-lock loop (DLL). Multipath signals, which reflect from objects before arriving at the receiver, degrade the code tracking performance. Multipath-invariant points are locations of the correlation function whose properties are independent of multipath parameters, and they can therefore be located reproducibly in the presence of multipath. A multipath mitigation method consists of locating a multipath-invariant (MPI) point of an ideal autocorrelation function and measuring the distance between the MPI point and the DLL.

Abstract: Method and apparatus for using a plurality of correlators to improve the estimate of direct signal arrival time by identifying detailed features of a correlation function at and adjacent to the correlation peak. The errors in location of the center point of a correlation function R(.tau.), formed by the received signal and a stored copy of the expected signal, are assumed to be strongly correlated for narrow sample spacing and wide sample spacing of the correlation function. Alternatively, the multipath signal strengths and phases are estimated by a least mean squares analysis, using multiple sampling of a correlation function of an expected signal and an arriving composite signal that includes the direct signal and one or more multipath signals. Times of arrival or path delays of the direct signal and the multipath signals are determined separately. Path delays can be determined by at least three approaches: (1) identification of slope transition points in the correlation function R(.tau.

Abstract: Method and apparatus for using a plurality of correlators to improve an estimate of direct signal arrival time by identifying features of a correlation function at and adjacent to the correlation peak. In a first embodiment, the errors in location of the center point of a correlation function R(.tau.), formed by the incoming composite signal and a stored copy of the expected signal, are assumed to be strongly correlated for narrow sample spacing and wide sample spacing of the correlation function. In a second embodiment, multipath signal strengths and phases are estimated, using multiple sampling of the correlation function R(.tau.). This approach assumes that path delays of the direct signal and of the multipath signals can be determined separately.

Abstract: Method and apparatus for reducing or cancelling impulse noise from a signal containing noise. The desired noise-free signal is assumed to have a representative frequency .omega..sub.3, but may have a range of frequencies adjacent to this frequency, and is assumed to have substantially zero amplitude for all frequencies .omega.<.omega..sub.1 and/or for all frequencies .omega.>.omega..sub.2, where .omega..sub.1 <.omega..sub.3 <.omega..sub.2 or .omega..sub.1 <.omega..sub.2. An input (noisy) signal is filtered and analyzed in a narrow frequency region surrounding .omega.=.omega..sub.1 and/or a narrow frequency region surrounding .omega.=.omega..sub.2 to obtain one or two output signal components n.sub.1 (t) and/or n.sub.2 (t), respectively, that, ideally, contain no contribution from the desired signal. The input signal is also filtered and analyzed in a narrow frequency region surrounding .omega.=.omega..sub.3 to obtain an output signal s(t)+n.sub.3 (t) component including the desired signal s(t).

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: 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.