Abstract: A technique for Crest Factor reduction of multi-carrier signals using phase rotation is described. The multi-carrier signal could be in digital baseband, analog baseband, or analog RF (radio frequency). The multi-carrier signal is converted to individual baseband representatives before each individual baseband signal being phase rotated according to an algorithm which maintains the crest factor to a pre-defined value. The algorithm uses a deterministic phase rotation technique and each phase rotated baseband signals will be individually filtered to remove the unwanted signals. The phase rotated and filtered baseband signals are then up converted and combined to reconstruct the multi-carrier signal. The crest factor reduction is limited by the in band distortion introduced to each individual signal.

Abstract: A technique to boost the output power of portable radio terminals without increasing the power dissipation is described. The input to the terminal transmit amplifier is modified by a peak-to-average reduction and amplitude pre-distortion circuit, prior to being applied to the amplifier. The peak-to-average reduction and pre-distortion circuit clips the baseband samples before applying any amplitude pre-distortion if they exceed a predefined value The peak-to-average reduction and pre-distortion circuit uses a lookup table to pre-distort the peak-to-average reduced signal. The amplitude pre-distortion lookup table is being updated at power up or power down of the terminal radio, during idle time, just before origination of a call, before termination of a call, or while the call is active. During the updating of the lookup table the radio could be in its normal transmit mode, or transmit into a dummy load using an analog transmit switch controlled from the peak-to-average reduction and pre-distortion circuit.

Abstract: A technique for Crest Factor reduction and amplitude pre-distortion of multi-carrier signals is described. The input to the multi-carrier amplifier is modified by a Crest Factor reduction and amplitude pre-distortion circuit, prior to being applied to the amplifier. The Crest Factor reduction and amplitude pre-distortion circuit first clips the amplitude of the signal, converts the clipped signal to baseband to produce the baseband representative of each carrier, filters each baseband representative to remove the unwanted signals, up converts each baseband representative to its multi-carrier baseband frequency and finally the up converted signals are combined to produce the multi-carrier baseband signal. The Crest Factor reduction and amplitude pre-distortion circuit next pre-distort the amplitude of the signal using a look up table before applying the signal to the amplifier.

Abstract: A technique for Crest Factor reduction of multi-carrier signals is described. The input to the multi-carrier amplifier is modified by a Crest Factor reduction circuit, prior to being applied to the amplifier. The Crest Factor reduction circuit clips the amplitude of the signal, converts the clipped signal to baseband to produce the baseband representative of each carrier, filters each baseband representative to remove the unwanted signals, up converts each baseband representative to its multi-carrier baseband frequency and finally the up converted signals are combined to produce the multi-carrier baseband signal. The input to the Crest Factor reduction circuit could be a baseband, an intermediate frequency (IF) or radio frequency (RF) signal. The Crest Factor reduction could be performed in digital or analog domain.

Abstract: A technique for peak-to-average reduction of multi-carrier signals is described. The input to the multi-carrier power amplifier is modified by a peak-to-average reduction circuit, prior to being applied to the amplifier. The peak-to-average reduction circuit uses a phase generator to create appropriate phase for each carrier to suppress the peak of the multi-carrier signal. The peak-to-average reduction circuit clips the multi-carrier input signal's samples before applying any phase rotation if they exceed a predefined value. The input to the peak-to-average reduction circuit could be a baseband, an intermediate frequency (IF) or radio frequency (RF) signal. The peak-to-average reduction is performed in digital domain.

Abstract: A technique for peak suppressing and pre-distorting the input signal to multi-carrier wireless radio frequency amplifiers to improve the power handling or boost the operating point of the amplifier and subsequently significantly improving the power efficiency of the amplifier is described. The input to the multi-carrier amplifier is modified by a peak suppression and pre-distortion circuit, prior to being applied to the amplifier. The peak suppression and pre-distortion circuit uses a phase generator to create appropriate phase for each carrier to suppress the peak of the multi-carrier signal. The peak suppression and pre-distortion circuit uses samples of the output of the amplifier to adaptively adjust a lookup table that is being used for pre-distortion. The input to the peak suppression and pre-distortion circuit could be a baseband, an intermediate frequency (IF) or radio frequency (RF) signal. The peak suppression and pre-distortion is performed in digital domain at baseband.

Abstract: A technique for peak suppressing and pre-distorting the input signal to wireless amplifiers to improve the linearity of the amplifier and subsequently significantly improving the power efficiency of the amplifier is described. The input to the amplifier, prior to being applied to the amplifier, is modified by a peak suppression and pre-distortion circuit. The peak suppression and pre-distortion circuit uses samples of the output of the amplifier to adaptively adjust a lookup table that is being used for pre-distortion. The input and output of the peak suppression and pre-distortion circuit are at the amplifier frequency. The peak suppression and pre-distortion is performed in digital domain at baseband.

Abstract: An interference measurement technique in for example a wireless receiver uses a received, unprocessed signal and correlates it with a signal reconstructed from detected information, then compares a square of the correlated signal with a square of the received signal to produce a signal-to-interference metric useful for evaluating a channel quality, such as in a wireless telecommunication environment.

Abstract: A receiver having an adaptive maximum likelihood sequence (MLSE) estimator and method are provided, in particular in a nonlinear receiver, wherein a channel estimator is used to estimate the channel to be used in the MLSE estimator in order to minimize distortion. In the MLSE estimator, the channel estimation is extracted from the phase of the signal using a known training sequence pattern in the received data frame. The channel estimation is adaptively updated using a Least Mean Square (LMS) algorithm by applying tentative decision in the received signal.

Abstract: An adaptive control system and method is provided in a feed-forward linear amplifier, and in particular a multi-channel linear amplifier, wherein analyzed distortion or error detection of nonlinear distortion components of the output signal of a main amplifier element is used to correct distortion in amplification of an information signal using a two-stage distortion correction circuit. Analysis of the distortion is based on a sweep of the entire operating frequency band from which the distortion components are extracted. I.F. sampling (sub-harmonic sampling) may be used in analog-to-digital conversion of an I.F. signal to detect the distortion within a pass-band.

Abstract: An adaptive control system and method is provided in a feed-forward linear amplifier, and in particular a multi-channel linear amplifier, wherein analyzed distortion or error detection of nonlinear distortion components of the output signal of a main amplifier element is used to correct distortion in amplification of an information signal. Analysis of the distortion is based on a sweep of the entire operating frequency band from which the distortion components are extracted. I.F. sampling (sub-harmonic sampling) may be used in analog-to-digital conversion of an I.F. signal to detect the distortion within a pass-band.

Abstract: An adaptive control system and method for use with a feed-forward linear amplifier, and in particular a multi-channel linear amplifier wherein a distortion (error) detection circuit is used for detecting a nonlinear distortion component of a main amplifier output for using in correcting distortion in amplifying an information signal. The distortion correction can be extracted from a pilot signal, an analysis of distortion from a channel-by-channel sweep or from analysis of selected target channels. Analysis can be based on a single signal, an average of many signals, or a selection of maxima of one or many signals. Subharmonic sampling may be used in analog to digital conversion of an IF signal to detect for distortion within a passband.

Abstract: A digital receiver for receiving an RF signal has a conventional RF to intermediate frequency (IF) converter. The IF signal, however, is amplified with a limit on its amplitude. In addition, a Receive Signal Strength Intensity (RSSI) signal is generated. The RSSI signal contains the envelope information of the modulated IF signal. The IF amplitude limited signal containing phase information, is then digitized and a complex baseband signal is produced. The complex baseband signal is then combined with the RSSI signal to restore the amplitude information of the modulated IF signal in the complex baseband signal. The restored complex baseband signal can be equalized with a conventional equalizer to remove intersymbol interference. A conventional symbol detector detects the symbol in this signal stream.

Abstract: A diversity combiner for a digital receiver receives a plurality of complex baseband signals (S.sub.1 (t), S.sub.2 (t)) each having an associated receive signal strength-intensity signal (RSSI.sub.1, RSSI.sub.2). The combiner differentially detects each of the complex baseband signals (S.sub.1 (t), S.sub.2 (t)) to produce a plurality of differential signals (RX.sub.1 (t), RX.sub.2 (t)) in accordance with:RX.sub.1 (t)=S.sub.1 (t).multidot.S.sub.1 *(t-T), andRX.sub.2 (t)=S.sub.2 (t).multidot.S.sub.2 *(t-T)where S.sub.x * is the complex conjugate of S.sub.x and T is a symbol delay. The differential signals (RX.sub.1 (t), RX.sub.2 (t) ) are processed to produce a selected differential signal R(t). The selected differential signal R(t) is converted to produce a plurality of converted signals D.sub.1 (t) and D.sub.2 (t) in accordance with:D.sub.1 (t)=R(t).multidot.e.sup.-j2.pi.fstD.sub.2 (t)=R(t).multidot.e.sup.+j2.pi.fstThe converted signals D.sub.1 (t) and D.sub.2 (t) are further processed to produce timing (.

Abstract: An automatic level control circuit for cellular telephone transmitters which is compatible with both existing analog cellular service and expected next generation digital TDMA service. The circuit automatically and dynamically changes modes to maintain communication when a mobile subscriber moves from one type of service to another. In a first mode of operation, which is compatible with existing analog cellular service, the circuit provides a closed loop negative feedback circuit which produces a control signal for continuously controlling the output power level of the transmitter amplifier. In a second mode of operation, which is compatible with proposed digital TDMA service, the circuit operates to alternately close the negative feedback loop during the periods when the transmitter is permitted to transmit (assigned TDMA frames) and open the loop during other periods when the transmitter is turned off. When the loop is opened, the invention temporarily stores the magnitude of the control signal.

Abstract: A technique for correcting the sampling time and carrier frequency error in a receiver for digitally modulated signals. Discrete-time, complex-valued samples of the incoming signal are fed to a pair of non-linear operators such as correlators. The first correlator provides a signal having a first phase component related to the symbol timing error and a second phase component related to the carrier frequency error. The second correlator provides a signal having a first phase component related to the symbol timing error and a second phase component related to the negative of the carrier frequency error. The phase components are then separated and detected to extract an estimate of the symbol timing error and the carrier frequency error. In the preferred embodiment, the complex-valued samples are frequency-shifted, before being fed to the correlators, so that the phase components of interest appear at zero frequency.

Abstract: A method and apparatus for generating a frequency offset estimate and a timing offset estimate from a base band signal. In an important application of the invention, a modulated carrier signal is transmitted over a transmission channel and then received and demodulated to generate the base band signal. The modulated carrier signal comprises data having a transmitted symbol frequency and phase, and a carrier signal modulated by the data. The invention simultaneously generates from the base band signal a frequency offset estimate representing the difference between the transmitted and received carrier signal frequency, and a timing offset estimate representing the difference between the transmitted symbol phase and the recovered symbol phase of the base band signal. In preferred embodiments, the base band signal is a digital signal sampled at a rate which exceeds the Nyquist rate. Typically, a sampling rate of more than two samples per symbol is adequate to meet this condition.

Abstract: A selection system in a space diversity system of a mobile receiver combines the ultra high frequency signals after they have been frequency shifted to an intermediate frequency. The system combines the intermediate frequency signals depending on the ratio of the magnitudes of these signals. If the ratio of the magnitude of the received signals is equal to or greater than a preset magnitude level, for example, 5 db, a control unit selects only the received signal having the largest magnitude. Otherwise, the control unit linearly combines both received signals Specifically, if the absolute value of the difference in received phase signals is less than 90.degree., the output of a phase detector causes the control unit to pass both received signals to a summer that linearly combines them prior to demodulation. Otherwise, the control unit inverts the phase of one of the received signals prior to passing both received signals to the summer.

Abstract: A receiver suitable for use in a radio-telephone system for recovering data from encoded, quadrature-modulated communication signals employs a feedback arrangement for suppressing cross-talk between the receiver's in-phase and quadrature channels to improve data recovery rates during decoding. The receiver converts in-coming analog communication signals into in-phase and quadrature digital signals, which may have cross-talk components. The receiver has an attenuator for subtracting feedback signals from the in-phase and quadrature digital signals to produce cross-talk-attenuated in-phase and quadrature digital signals, a decoder for decoding the cross-talk-attenuated in-phase and quadrature digital signals to generate first and second data output signals, and the above-mentioned feedback arrangement, which preferably employs a recoder and cross-correlation techniques, for generating the feedback signals.

Abstract: In a digital radio-telephone receiver, an open-loop arrangement for generating a received-signal-strength-indicating ("RSSI") value suitable for use in mobile assisted hand-off within a cellular telephone system. The receiver has an amplifier for amplifying a received signal with a gain controlled by a gain-control signal, and an automatic-gain-control circuit ("AGC") responsive to the amplitude of the amplifier output and coupled in a feedback-loop for applying an AGC signal to the amplifier as the gain-control signal. An RSSI value is generated by (i) opening the AGC feedback loop so that the AGC output signal is not applied to the amplifier, (ii) applying a ramp signal of increasing amplitude to the VGA while the AGC monitors the signal envelope, and (iii) when the signal envelope passes a pre-selected threshold, applying the then-occurring ramp-signal value to a calibrated look-up table to obtain the corresponding RSSI value stored therein.