Abstract: An apparatus and method for generating an envelope predistorted radio frequency signal which avoids undesirable spurious emissions. A complex baseband signal, having an in-phase component I and a quadrature component Q, is sampled and filtered in a sampling circuit and filter circuit to obtain samples Ik of the in-phase component and samples Qk, the quadrature component. The magnitude xk of each sample pair is determined in a first calculation circuit. An amplitude and phase distortion factor Dk, based on scaled values of the archyperbolic tangent and the hyperbolic tangent of the baseband sample magnitude is determined in further calculation circuit and a multiplier. Each sample Ik of the in-phase component and Qk of the quadrature component is multiplied by the corresponding distortion factor Dk, and the resulting predistorted components combined and upconverted to provide a predistorted baseband signal which is amplified in a power amplifier having hyperbolic tangent distortion.

Abstract: A radio receiver (10) adapted to receive an AM-MSK modulated carrier signal includes an envelope detector (24) and a transformer (28) which restores the real signal to complex MSK format. A Doppler remover (34) removes any Doppler shift of the MSK due to relative motion of the transmitter and receiver (10). A sample rate reducer (56) may reduce the sample rate used in the Doppler remover (34) to the transmitted symbol rate used during the modulation process.

Abstract: A compensation circuit for phase modulation systems, such as QPSK and QAM systems, which compensates for phase errors in the I and Q components of the QPSK or QAM signals to minimize carry over of such phase errors in analog up and down conversions of such signals. In particular, the invention relates to a relatively simple circuit, which compensates for channel phase errors by providing a direct correction of one of the channels based on the measured correlation between the I and Q components, which should ideally be 0. As such, cross talk between I-Q channels is minimized, which improves the signal-to-noise ratio of transmitted and received QPSK or QAM signals.

Abstract: A steerable antenna array (10) includes a plurality of antenna elements (12a-12f) which receive broad band signals and narrow band interfering signals which together form antenna signals. The antenna signals are combined with weighting signals by combining functions (16a-16f) to form a combined signal, which is filtered by a filter function (30) to filter the narrow band signals. The filtered signals are sent to a weight processor (50) which also receives the antenna signals as an input. The processor (50) generates the weighting signals so that interference from the narrow band signals is reduced.

Abstract: An apparatus for and a method of determining the envelope of a complex baseband signal having an in-phase component I and a quadrature component Q by determining (I2+Q2)½ for sampled values of the baseband signal. The maximum and minimum values of I and Q are detected by detecting the larger of I and Q in a first detection circuit (18) and the smaller of I and Q in a second detection circuit (20). A value x=½{(the detected minimum value)÷(the detected maximum value)}2 is calculated in a first calculation circuit (22). The value of (I2+Q2)½ is then calculated based on the value of x. In a first embodiment the value of (I2+Q2)½ is calculated in a second calculation circuit (24, 26, 28, 30, 32, 34, 36, 38) as the (the detected maximum value)×(1+x)/2+½(1+x−x2+x3−x4+x5−x6).

Abstract: The present invention is an apparatus for and a method of upconverting a (complex) phase and possible amplitude modulated baseband signal for radio transmission, also known in the industry as Quadrature Amplitude Modulation (QAM). The two components of the baseband signal consisting of an in-phase component I and a quadrature component Q, are to be upconverted to a desired real signal at a frequency fdhZ, (normally called the IF or intermediate frequency signal). A subsequent conversion to a higher RF carrier frequency may occur after this process. This invention utilizes to a high degree a single channel for the upconversion process before the signal has been fully upconverted to the desired (IF) frequency fd in order to reduce the processing complexity in a digital upconverter.

Abstract: An apparatus for and a method of generating an envelope predistorted radio frequency signal. A complex baseband signal, having an in-phase component I and a quadrature component Q, is sampled and filtered. The magnitude uk of each complex baseband sample pair is determined by the square root of the sum of the squares of the in-phase component sample and the quadrature component sample. A distortion factor Dk, is determined based on a scaled value of the inverse hyperbolic tangent or archyperbolic tangent (“atanh”) of the baseband sample magnitude divided by that scaled sample magnitude. Each sample of the in-phase component Ik and of the quadrature component Qk is multiplied by the corresponding distortion factor Dk so as to provide predistorted components. The predistorted components are then combined to provide a predistorted baseband signal.

Abstract: Demodulating a DPSK encoded data signal. The received signal has a symbol tracking value determined in a synchronization circuit. Doppler error in the signal is estimated. The signal, the symbol tracking value, and the estimated Doppler error are applied to a demodulator within which the signal is multiplied by a signal at a frequency which is the negative of the estimated Doppler error to remove that Doppler error. The resulting signal is filtered and decimated and normalized to generate the arctangent of the in-phase and quadrature components of the baseband signal. This arctangent signal is stripped of phase angle modulation and applied through loops to remove derivatives of the input phase signal. The arctangent and the resulting angles are mapped in a nearest neighbor map circuit, and the difference between successive angles is applied to a gray code to binary mapping circuit which detects the encoded data.

Abstract: A steerable antenna array (10) includes a plurality of antenna elements (12a-12f) which receive broad band signals and narrow band interfering signals which together form antenna signals. The antenna signals are combined with weighting signals by combining functions (16a-16f) to form a combined signal, which is filtered by a filter function (30) to filter the narrow band signals. The filtered signals are sent to a weight processor (50) which also receives the antenna signals as an input. The processor (50) generates the weighting signals so that interference from the narrow band signals is reduced.

Abstract: A radio carrier signal is detected (20) after being converted to digital form and is filtered (22). A noise estimator (24) generates a noise estimate signal by estimating the noise in the detected signal due to atmospheric conditions and the noise due to the gain in noise figure properties of the circuitry. The output of the noise estimator is used to calculate a threshold signal (50) and another detection operation (52) determines whether the power of a signal derived from the detected signal exceeds the threshold. If the threshold is exceeded, the detected signal is passed through a signal conditioner, such as a switch (54) to an output path (56).

Abstract: An automatic frequency control loop implemented by a digital signal processor (14) down converts an IF signal carrier to a residual-carrier within an allowed range of frequencies by a down converter operation (16). A frequency detector (28) detects any error frequency in the residual carrier with reference to a reference frequency, such as 0 Hz, in order to shift the frequency of the residual carrier by a shifter operation (20) which reduces the frequency error in the shifted signal. An envelope detector operation (26) retrieves information from the residual carrier, and the resulting signals are processed by a low pass filter operation (36) to reduce cross talk.

Abstract: An aviation radio receiver provides automatic gain control in three zones including an RF zone employing an RF attenuator (14), an intermediate frequency zone employing an intermediate frequency logarithmic attenuator (26) and a baseband zone implemented in a digital processor (30).

Abstract: A radio receiver (10) processes a carrier signal having a Doppler shifted frequency and carrying a coded signal having variable phase and amplitude. The coded signal is divided into a preamble portion and a message portion. A memory (23) stores samples of the coded signal representing at least some of the predetermined symbols of the preamble. A logic unit (16) divides the stored samples into a plurality of sample groups and identifies one sample group having the minimum variation of envelope amplitude. That sample group is used to provide additional samples by which the Doppler shift of the carrier frequency is estimated (70). The coded signal is delayed by a delay operation (100) and has its Doppler shift reduced. The Doppler reduced coded signal is processed by a filter operation (120) and a demodulator (130).

Abstract: Delay domain multiplexing, differing from coherence multiplexing of digital data signals, may use orthogonal encoding to reduce cross-channel interference compared to traditional techniques. A plurality of photonic encoders may receive laser pulses from a laser pulse source, converting the pulses into n sets of orthogonal codes, such as Walsh codes, depending on the number of channels to be multiplexed. A passive apparatus may use orthogonal codes, creating them fast enough to function in an optical or photonic environment. The orthogonal codes may subsequently be modulated with n digital data signals before being multiplexed and demultiplexed in a delay domain or coherence multiplexing apparatus. At a receiver, the encoded signals are decoded and the original digital data signals are extracted therefrom.

Abstract: An method for stabilized photonic transmission is described. A light source of limited coherence length is wavelength shifted, stabilized, and data encoded to provide a stabilized photonic signal. A modulation synthesizer provides a modulation waveform embedded with the shifting, stabilization and data encoding mechanisms. A variety of modulation techniques are supported. The modulation waveform is optimized for the particular modulation technique. A wavelength error detector provides feedback to the modulation synthesizer. The error signal is used to stabilize the photonic signal and correct channel wavelength errors. Fixed wavelength channels and spread spectrum channels are supported.

Abstract: Optical code-division multiplexing and demultiplexing (CDM) using orthogonal codes with minimum shift keying (MSK) waveforms allows more efficient use of the spectrum and greatly reduces cross-channel interference. Receiving multiple baseband data channels, a derivation mechanism converts the data signals into series of impulses. These impulses may be split into odd and even channels, each at half the original data rate, and transmitted to a plurality of Walsh filters configured to have an impulse response corresponding to one of a plurality of orthogonal MSK waveforms. Odd and even channels, encoded with MSK waveforms, may combine into an in-phase and quadrature channel, 90° out of phase. A laser output may be divided, phase shifted, and modulated with the in-phase and quadrature channels, which divisions are then combined into a single multiplexed output. Walsh filters may decode the incoming signal in order to reproduce the original baseband channels.

Abstract: A compound asymmetric interferometric wavelength converter receives a photonic signal of a first wavelength and bandwidth, and outputs a photonic signal of a second, more stabilized, wavelength and bandwidth. The apparatus may be either propagating or co-propagating, and measures selected photonic signal parameters dynamically and uses this information for self-calibration and to optimize and control signal quality of the photonic output signal.

Abstract: An apparatus and method for storing optical information packets. The apparatus includes an optical circulator set up to receive and circulate an optical packet having an initial frequency and length. The circulator may include a frequency shifter which shifts the frequency of the circulating packet. The circulator may then receive a following packet at the initial frequency. The frequency shifter may then frequency-shift the circulating packets and receive a new packet. This process may be continued thereby creating a frequency-stacked signal composed of information packets at different wavelengths. On the receiving end, frequency shifters may receive the frequency-stacked signal and shift the signal until a desired packet has a desired frequency. The desired packet may then be filtered and detected for transmission. In another embodiment, a tunable filter may be used to filter out a desired packet at some arbitrary frequency.

Abstract: A generic optical modulator includes a first inteferometer receiving a first control signal and a second interferometer receiving a second control signal, and each receive a portion of an incoming light signal. The output of the first interferometer is attached to the output of the second interferometer after that output has passed through a phase shifter. A coupler receives the output of the first interferometer and the second interferometer and generates a modulated signal therefrom.

Abstract: A virtual filter-bandwidth reduction and frequency stabilization via heterodyning shifts the signal to be filtered up and down as it passes through two cascaded fixed filters whereas the alternative structure shifts the filter center frequencies of two cascaded filters up and down respectively and leaves the signal to be filtered alone. Two identical cascaded fixed filters are used to provide the filtering.