United States of America As Represented by the Secretary of the Air Force

Itt Manufacturing Enterprises, Inc.

James B Y Tsui

David M Lin

Stephen L Hary

Keith M Graves

John M Emmert

Charles Richard Ward

Stuart Mitchell Lopata

Nicholas A Pequignot

Michael H Stockmaster

William S McCormick

James N Hedge

John J Schamus

Vasu Chakravarthy

Anthony W White

Scott M Rodrigue

Marvin N Potts

Maan J Broadstock

Dennis M Akos

A moderate cost and complexity digital radio receiver system having enhanced instantaneous dynamic range response to the receipt of simultaneous signals and also providing large single signal dynamic range. Multiple signal instantaneous dynamic range improvement is achieved through use of a suppressed zero signal amplitude representation arrangement having a selected number of signal amplitude representing digital bits rather than the larger entire array of digital output bits of the receiver system's analog to digital converter. Digital apparatus for accomplishing the selection of desired high order bits from the analog to digital converter output is also disclosed in detail. Use of a 'Monobit' and related simplified Fourier transformation radio receivers as disclosed in identified previous patents of the recited inventors and colleagues is preferred for embodying the digital radio receiver circuit included in a present system.

Digital receiver instantaneous dynamic range enhancement

An instantaneous frequency measurement (IFM) receiver includes a receiver module for determining a frequency fof a received signal. Also included is a discrete Fourier transform (DFT) module configured to sum values of digital samples of data in a block of data, wherein the values of the digital samples of data are based on the frequency f. A confirmation module confirms the frequency f, if the sum has a value greater than a predetermined threshold. The DFT module is configured to obtain the sum of N-sample points of data which are disposed in the block of data by using a DFT kernel function.

Detection and time-of-arrival estimation using an IFM receiver

A Fourier transformation algorithm implementation in which accommodation is provided for the output attenuation occurring when an input signal falls intermediate two terms of the transformation output series in its frequency. Corrected Fourier transformation terms, achieved by combining the magnitudes of attenuated Fourier transformation terms generated by the input signal at Fourier transformation frequencies distant to the input signal frequency, in either a vectorial or a scalar combination, are substituted for an attenuated Fourier transformation term according to the invention. Noise correction of the substitute Fourier transformation terms is also provided. The invention is disclosed through use of a global position system signal example that is subjected to a double Fourier transformation filtering process to enhance the incoming signal to noise ratio. Normally occurring 3.9 decibel attenuations in each Fourier transformation step are reduced to about 0.9 decibel each through use of the invention.

Accommodating fourier transformation attenuation between transform term frequencies

A Fourier transformation arrangement usable in an electronic warfare radio receiver for analyzing spectral content of multiple transmitter-sourced brief duration incoming signals for their signal characteristics. The disclosed Fourier transformation arrangement includes approximated Kernel function values disposed in a significant plurality of locations about a real-imaginary coordinate axis origin according to disclosed locating principles. The points are displaced from the origin by magnitudes having real and imaginary component lengths of powers of two commencing with zero. Multiplication involving a power of two component length during a Kernel function utilization are preferably achieved by way of an expanded binary shift multiplication algorithm in lieu of a full fledged digital multiplication algorithm. A group of guiding principles for selecting desirable approximation Kernel function locations is included.

Kernel function approximation and receiver

An apparatus for confirming a frequency measurement of a received signal includes a discrete Fourier transform (DFT) module for receiving a sampled digital signal. The DFT module is configured to analyze the received sampled digital signal, and output amplitude values at different frequency components. A threshold comparator is included for receiving the amplitude values of the frequency components and outputting a thresholded-amplitude value exceeding a predetermined threshold value. A frequency confirmation is provided based on the thresholded-amplitude value. The sampled digital signal is sampled at a sampling frequency of f, and the DFT module is configured to analyze the received sampled digital signal at a frequency bandwidth that is equal to or less than f. The frequency bandwidth is equal to the sampling frequency of f, when the received sampled digital signal includes I and Q signals. The DFT module is configured to analyze the received sampled digital signal by examining N frequency components, where N equals the total number of frequency components equally spaced between 0 and the sampling frequency.

Wideband digital IFM receiver with frequency confirmation

An IFM receiver includes a hybrid for outputting I and Q signals from a received input signal; a first ADC for digitizing the I signal to produce a first digital signal at a sampling rate of 1/&#x3c4;, and a second ADC for digitizing the Q signal to produce a second digital signal at the same sampling rate. A processor is configured to (a) delay the first and second digital signals by at least one sample time of &#x3c4;, (b) count the number of samples produced having predetermined phase shifts, and (c) determine the frequency of the received input signal, based on the number of samples having the predetermined phase shifts. The first and second ADCs are each 1-bit analog-to-digital converters. The predetermined phase shifts of 0&#xb0;, 90&#xb0;, &#x2212;90&#xb0; and 180&#xb0; are counted by the processor over a predetermined time interval.

Wideband digital IFM receiver

A digital cueing radio receiver system embodied using digital memory in lieu of analog delay lines and thereby avoiding delay line implementation difficulties. The cueing receiver system includes a wideband receiver portion providing an output signal employed for tuning a narrowband receiver portion of the system. Signal delay enabling use of the wideband receiver portion output signals for tuning the narrow band receiver portion selection frequency is provided by a digital memory circuit operating on analog-to-digital converted samples of input signal data of the receiver system. Approximated unity value related mathematical multiplication free Kernel function values are employed in the Fourier transformation. Avoidance of analog delay line-elements in embodying the system is a significant practical advantage of the invention.

Digital cueing receiver

An improved apparatus and method for determining the carrier frequency in a biphase coded signal such as the course acquisition code signal in a global position sensing system. The described system may also be used for other purposes. The described system is based on use of the conventional data signal squaring or frequency doubling step to remove biphase coding but performs a series of frequency reducing steps prior to applying the Fourier transformation sequence. The frequency reducing steps include heterodyne mixing and signal averaging. These frequency-reducing steps diminish the speed and capacity requirements imposed on the Fourier transformation sequence and thereby decrease the cost and complexity of the overall system.

Downconvert and average identification of biphase coded signal carrier

A simplified, weak GPS C/A code coherent acquisition method. When performing GPS signal acquisition, the strength of a signal received at a GPS receiver having an outside antenna is generally sufficiently strong such that only 1 ms of data needs to be used in acquisition to find the signal. However, for weak signals received at a GPS receiver, when the antenna is inside a building or vehicle, for example, a long record of data is needed for acquisition. The present invention reduces the calculation burden for GPS signal acquisition for a weak signal.

Signal folding coherent acquisition for weak global positioning system (GPS) C/A coded signal

A global position system radio receiver achieved through use of an electronic warfare receiver, and particularly one of the electronic warfare receiver output frequency channels, as a front-end signal processor for the global position system receiver. Electronic warfare receiver channel selection for such usage is described and the attenuating effect of electronic warfare receiver channel center frequency and global position system signal frequency differences are considered. A favorable comparison of present invention and conventional global position system receiver-generated results in processing a global position system signal are included along with control of a sampling frequency characteristic within the electronic warfare receiver in order to align global position system signal frequency and electronic warfare receiver channel location to an electable better degree.

GPS receiver with electronic warfare receiver front end

An electronic warfare apparatus for determining the location of for example a ground based source of electromagnetic radiation from a platform such as an aircraft. Location is determined using angle of arrival based vector determinations provided by signal differences detected in the ground based signals arriving at platform antennas. Elimination of angle of arrival errors arising from imprecise knowledge of platform electronic warfare antenna characteristics is a focal point of the invention and is accomplished through precision use of global position system information received via the same electronic warfare antennas. Accurate determination of electronic warfare antenna characteristics prior to consideration of the large distance multiplication factors imposed by aircraft to distant signal source geometry enables accurate distant signal source location using the invention.

Phase center measurement of electronic warfare antennas using GPS signals

The present invention uses narrow-band monobit receivers after a digital filter bank to separate simultaneous signals in one channel. The invention improves the capability of wideband digital receivers.

Digital filter bank followed by monobit receivers for signal processing

An arrangement for calibrating the sample frequency determining clock in a global position system receiver using signals received from a Wide Area Augmentation System satellite or other Wide Area Augmentation System signal source. Such Wide Area Augmentation System based clock calibration is free of the Doppler frequency effects impressed on a global position system signal in view of the geo-stationary orbit of a Wide Area Augmentation System satellite. Use of the calibration invention enables correction of the pseudo range determination accomplished with global position system receiver output data. The invention may be considered a new use of signals available from the Wide Area Augmentation System. A noise-considered arrangement for comparing Wide Area Augmentation System and global position system frequencies is included.

Calibrating the sampling frequency of a GPS receiver

Passive microwave direction finding with monobit fourier transformation receiver and matrix coupled antenna

An improved global positioning system satellite signal acquisition method. The method of the invention reduces the number of operations in the block correlation used in determining Doppler frequency and time of the received GPS C/A or P(Y) codes. Reducing the number of operations in block correlation increases acquisition speed making it conducive to commercial and military GPS receivers

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Dayton, OH, United States of America

James B Y Tsui