Abstract: Near-end crosstalk between identical discrete multi-tone modems is reduced by aligning the frames of all modems at a central office to each other, aligning the frames transmitted by subscribers' modems with the frames received by those modems, and including a cyclic prefix between the central office and the most distant subscriber to be served. By making adjacent DMT carrier frequencies be orthogonal to each other, the aforementioned modifications will reduce both Near End Cross-Talk and Leakage-Excited Cross-Talk. These benefits apply to modems at both the central office and subscriber ends of the communication path.

Abstract: An apparatus for reducing intermodulation distortion in a low current drain automatic gain control system includes a multiplier (1500) and an AGC digital signal processor (1100).

Abstract: It is an object of the present invention to provide an input circuit of a TV tuner without causing unnecessary attenuation within a VHF high band bandwidth and without worsening performance such as NF, input sensitivity, and S/N when receiving a VHF high band signal. The input circuit of a TV tuner is provided with a parallel resonance circuit and an input tuning circuit connected to an output of the resonance circuit, a varactor diode is provided in parallel with the parallel resonance circuit, and a resonance frequency of a parallel connecting circuit connecting in parallel the parallel resonance circuit with the varactor diode in a nonconductive state is set to a frequency of an FM broadcasting band. Further, a capacitance value of a capacitor is set such that a resonance frequency of a parallel connecting circuit connecting in parallel a second inductor in a conductive state of the varactor diode with the parallel resonance circuit constitutes a frequency higher than the VHF high band bandwidth.

Abstract: Briefly, in accordance with an embodiment of the invention, a method and circuit to reduce intermodulation distortion is provided, wherein the method includes receiving a baseband signal and an interferer signal located in a frequency band and attenuating the interferer signal to reduce intermodulation distortion in the frequency band, wherein the attenuating occurs prior to anti-alias filtering of the baseband signal.

Abstract: A digital FM demodulator employs a baseband phase lock loop (BBPLL), which is particularly effective for long range reception, for combining and demodulating a pair of signals represented by the mathematical expression A(t)ej&thgr;(t) to result in an approximation of d&thgr;/dt. This approximation is then subjected to an inverse of the linear approximation of the frequency response of the BBPLL that produces a very accurate &thgr;. This is conveniently achieved with a IIR filter whose transfer function happens to be the same as the inverse of the linear approximation of the frequency response of the BBPLL. The derivative is then taken of &thgr; to produce a very accurate d&thgr;/dt, the desired result for the output of an FM demodulator. To aid operation of the BBPLL, the incoming digital intermediate frequency is upsampled by a combination of sample and hold and FIR filtering prior to being processed by the BBPLL.

Abstract: An apparatus for reducing intermodulation distortion in a low current drain automatic gain control system includes a multiplier (1500) and an AGC digital signal processor (1100).

Abstract: A modulating module includes a modulator unit having a harmonically distorted modulator output adapted to be modulated by an input signal and containing a fundamental frequency component and harmonic frequency components, a power amplifier connected to the modulator unit, and a filter unit connected to the power amplifier for filtering the modulator output so as to permit only one predetermined harmonic frequency component to pass therethrough. In addition, a mixer device of a frequency shifting module includes a mixer unit adapted to receive an input signal with an input frequency, and a local oscillator connected to the mixer unit for generating an oscillator output with a local frequency. The mixer device mixes the input signal with a predetermined harmonic order of the oscillator output to result in an output signal with an intermediate frequency.

Abstract: A system and method for canceling DC offset for Mobile Station Modems having direct conversion architectures. The present invention is a fast acquiring DC offset cancellation block that provides rapid and accurate DC offset estimates and cancellation techniques to support direct conversion architectures. The fast acquiring DC offset cancellation block combines four mechanisms to rapidly acquire and remove a DC offset estimate after power up, temperature changes, receiver frequency changes, and gain setting changes by increasing high pass loop bandwidth and adjusting DC offset levels at baseband. After removing the DC offset in large portions, the high pass loop bandwidth is decreased to fine tune the previous estimate and to remove any small variation in DC offset due to receiver self-mixing products.

Abstract: Methods, systems, and apparatuses for down-converting an electromagnetic (EM) signal by aliasing the EM signal, and applications thereof are described herein. Reducing or eliminating DC offset voltages and re-radiation generated when down-converting an electromagnetic (EM) signal is also described herein. Down-converting a signal and improving receiver dynamic range is also described herein.

Abstract: A method is provided to automatically identify noise events in a channel of a communication system comprising the steps of: receiving an input signal from the channel; determining the mean energy of the input signal; determining the recent energy of the input signal; identifying a beginning of the noise event when the recent energy is greater than the product of the mean energy and a predefined first threshold; identifying an end of a noise event when the recent energy is less that the product of the mean energy and a predefined second threshold; and providing for output the beginning of the noise event and the end of the noise event. Other systems and methods are disclosed.

Abstract: There is described a method and apparatus for separating two independently modulated co-channel interfering fm carriers. The method involves generating a numerator signal being a function of generating a numerator function and a denominator function, the numerator and denominator functions being themselves functions of the ratio of the interfering carrier to the wanted carrier and of the instantaneous difference between the frequency of the wanted carrier and the interfering carrier, and performing a division process between said denominator function and said numerator function to generate a quotient function and using said quotient function to condition an output circuit.

Abstract: In a communications receiver (100) with a front stage (110) for receiving a transmitted RF input signal and a mixer stage (130) for mixing the RF input signal with an oscillator signal (OS) to provide an intermediate frequency (IF) signal, wherein the front stage (110) and the mixer stage (130) are coupled by an interconnecting section (130), intermodulation (IM) effects are reduced by (a) creating a forward (F) current through the section (120) by forward current means (R1, R3, R5, R4, C3, C1, C3, PD1, switch 140), (b) creating a reverse (R) current through the section (120) by reverse current means, (c) selectively coupling forward (F) and reverse (R) current means to the section (120) by selector means (140), to reduce the amplitude of the signal (RF OUT), which is applied to the mixer stage (130), and (d) operating the mixer stage in its linear operating range.

Abstract: A radio frequency receiver includes an amplifier and a detector that produces a bias control signal indicating the level of the signal environment in which the receiver is currently operating. A bias generator sets the bias level of the amplifier according to the bias control signal, where the bias level tends to increase as the signal level increases. Further, the receiver, includes a first circuit adapted to receive a radio frequency input signal, the circuit having an adjustable bias level, a bias control having more than one level of control for generating a bias control signal based upon a base-band signal for controlling the first circuit and generating an output signal; and an alternative bypass switch across the first circuit so as to send a DC signal corresponding to the total power generated by said feedback means.

Abstract: During the time when a radio mobile station is in communication with a base station at a certain frequency, when the frequency is being switched to another frequency and the reception level is being measured, AD data applied to a despreading/demodulating circuit (6) is set to “0” by an A/D output mask control portion (16). Thus, a noise component irrelevant to demodulation is prevented from being input to the despreading/demodulating circuit (6) after a local oscillation signal is output from a PLL synthesizer (4) until a stable baseband signal is output from a mixer circuit (3), so that stable demodulation is ensured.

Abstract: A waveform reconstruction circuit receives an rf signal from an antenna, digitizes it, and then generates an undistorted reconstructed waveform. The reconstructed waveform can then be conventionally mixed and demodulated to extract useful signal information with enhanced receiver fidelity and sensitivity.

Abstract: A sensor front end for an electronic radar sensor is disclosed that provides for a lower parts count while providing technical functionality by using multifunction parts, i.e., parts that are used both in transmitting and receiving. The sensor front end includes a continuous wave signal source that functions as a signal source when the front end is transmitting a signal and as a local oscillator when the front end is receiving a signal. The sensor front end also includes a tri-mode mixer that functions as a phase-modulator and transmit switch when the front end is transmitting a signal and as a mixer/down-converter when the front end is receiving a signal. The sensor front end further includes a common aperture antenna that acts as both a transmitting antenna for transmitting a sensor signal and for receiving a reflected signal from a object.

Abstract: An enhancer that is added to a receiver to increase the dynamic range thereof. The enhancer comprises a downconverter for converting a received signal to an intermediate frequency of the receiver, and a coupler for sending the downconverted signal to the receiver. The dynamic range of the enhancer is greater than the dynamic range of the receiver such that the receiver can now receive strong signals via the enhancer. The downconverter may comprise a local oscillator that is operative to generate a local oscillator signal and a mixer operative to mix the received signal with the local oscillator signal in order to downconvert the received signal to the intermediate frequency of the receiver. In this respect, the enhancer may be an add-on device which is plugged directly into the antenna port of the receiver and immediately increases the dynamic range thereof.

Abstract: A switching amplifier generates noise at its switching frequency and harmonics thereof. The noise at these harmonics, for an audio amplifier, will be generated with significant amplitude in the AM band. Thus, an AM tuner will experience interference problems if the tuner frequency is sufficiently close to one of these harmonics. To avoid this problem the switching frequency of the switching amplifier is chosen based on the tuner frequency. Thus, the switching frequency is chosen to avoid having harmonics at or too near the chosen tuner frequency. The switching amplifier is disabled when the tuner is in seek or scan mode. Instead of using the tuner frequency to determine what switching frequency should be used to avoid interference, the interference can be detected directly to cause a change in the switching frequency and thus remove the interference.

Abstract: A system and method for performing extended space-time processing. An improved symbol decision is generated of a desired sub-channel of the signal vector by first generating a baseline decision for the sub-channel. A contribution of a strongest sub-channel is subtracted from the signal vector to generate a modified signal vector. The modified signal vector is multiplied by a unitary matrix generated from a QR decomposition of another channel matrix. Channel interference of the remaining sub-channels of the modified signal vector is cancelled from a remaining sub-channel.

Abstract: A distortion reduction system uses upstream signal information from carrier frequencies in a signal to be amplified, to determine at least one frequency for the distortion generated by an amplifier amplifying the signal. A sample of an output is taken, and a distortion detection circuitry is used to detect the amplitude of the distortion at least at the one frequency. In response to the amplitude of the distortion at the one frequency, the processing circuitry provides gain and/or phase control signal(s) to adjust the relative phase and/or gain between combining distortion products to reduce the amplitude of the distortion.

Abstract: In a process for the transfer of data between a base station and a transponder by means of an electromagnetic carrier wave, on which data bits are modulated by means of amplitude modulation, the duration of a modulation interval of a data bit is determined and compared with a reference value, a correction value is calculated from the deviation of the actual value of the duration of the modulation interval from the reference value, and the actual values of the duration of the modulation intervals of the following data bits are corrected with the correction time. As a result of the correction, the duration of the modulation intervals may be reduced and the data transfer rate increased or the transfer rate may be adapted to the transfer conditions.

Abstract: A predistortion linearizer has

Abstract: Pre-amplification software-based linearization of a signal that is subsequently distorted by a nonlinear amplifier to produce a signal having reduced intermodulation distortion. The predistortion that reduces the intermodulation distortion is obtained by processing the original signal using an algorithm that is based on the characteristics of the nonlinear amplifier. Exemplary processing apparatus comprises circuitry that digitizing an input signal. A software linearizer processes the digitized signal to produce a pre-distorted RF signal. Circuitry is provided that converts the pre-distorted RF signal to an analog signal. A nonlinear amplifier amplifies the pre-distorted analog signal to produce an output signal corresponding to the input signal that has reduced intermodulation distortion. An exemplary processing method comprises the following steps. An input signal is digitized.

Abstract: A method and apparatus for acquiring time synchronization to a received signal are described. First, a burst of data which includes a known sequence is received. This received signal is processed using a plurality of different synchronization techniques. Each synchronization technique can be paired with a corresponding channel estimation technique, which pairing is predetermined to be optimized for particular channel conditions. A processor or model validation unit selects the channel estimate associated with the channel conditions currently being experienced by the radio signal.

Abstract: A post-amplification linearization technique for processing a signal distorted by a nonlinear amplifier. The post-amplification linearization technique is implemented using a linearizer and linearization method and involves processing the distorted signal using nonlinear processing to reduce intermodulation distortion. The nonlinear processing reduces the intermodulation distortion by applying an integral transformation to the nonlinear amplifier characteristic.

Abstract: A weaker signal receiving system inclusive of stronger nearby-sourced interference signal cancellation capability. Stronger interference signal cancellation is accomplished by actively canceling or subtracting from the received signal an intermediate signal in which the weaker signal has been attenuated but the stronger signal remains. Attenuation of the weaker signal in this intermediate signal is accomplished in a feedback loop arrangement by an amplitude-responsive signal processing element embodied from for example a ferrite material such as yttrium iron garnet disposed in a physical wave propagating and wave amplitude sensitive film. The cancellation or subtracting is accomplished using received signals and without need for a direct output sample of the stronger signal at its source. Military aircraft use of the disclosed system in the microwave and other spectral regions with transmission mode as opposed to reflection mode signal amplitude discrimination by the ferrite device is included.

Abstract: A system and method for quickly detecting and remedying an interference incident caused by one of a plurality of mobile terminals in communication with a transponded satellite. The method makes use of a time line constructed from communications of each of the mobile terminals. The time line forms a real time, sequential record of events wherein various mobile terminals have made contact with the transponded satellite. The method extrapolates from the time line which one of the mobile terminals has caused an interfering event by determining which mobile terminal accessed the communication system just prior to the interference event arising.

Abstract: A method of, and receiver for, countering distortions in radio channels due to intersymbol interference (ISI) and other non-linearities in a radio link, comprises a first equaliser (48) using a training sequence for equalising one type of distortion, say that due to ISI, and a second equaliser (50) coupled to recieve the equalising output of the first equaliser and using another training sequence for equalising another type of distortion. The first and second equalisers may be fractionally spaced equalisers.

Abstract: Systems and methods can be used to maintain operation of a receiver co-located with a transmitter in a communication device and susceptible to interference therefrom by anticipating the intervals during which the transmitter is active (i.e., transmitting) and then desensitizing the receiver during that interval. Although the receiver may operate in a reduced capacity due to periodic desensitization, the adverse effects of interference generated by the transmitter can be avoided. For example, interference from the transmitter can cause variables, such as the gain applied by an automatic gain control module at the receiver input, to deviate from a normal operating or steady state value, which must then be recovered when the interference from the transmitter ceases.

Abstract: Electrical circuit (300, 500, 800, 900) has an input (301, 501, 801, 802, 901, 902) and an output (311, 502, OUT, I-OUT, Q-OUT). The circuit samples an input signal coupled to the input having a certain input frequency and converts the input signal into a certain output frequency at the output, the output frequency being lower than the input frequency. It comprises a first sampler circuit (302, 510, 803, 910) coupled to the input, a second sampler circuit (303, 520, 804, 920) coupled to the input, a buffering component (309, 509, 809, 903, 904) coupled to the output and buffer switching means (305-307, 514, 515, 811-818, 914, 915, 924, 925, 934, 935, 944, 945, 954, 955, 964, 965, 974, 975, 984, 985). The buffer switching means are arranged to respond to a buffering command (fs/N, A, B) by coupling said first sampler circuit and said second sampler circuit to said buffering component.

Abstract: A radio frequency tuner is provided for selecting channels from a cable distribution network or other reception system. The tuner has one or more stages whose performance, such as signal to noise plus intermodulation, and gain are functions of the stage power consumption. A comparator compares the tuner performance, such as bit error rate, with a predetermined performance. When the tuner performance exceeds the predetermined performance, a power consumption control circuit reduces the power consumption of one or more of the stages so as to reduce the tuner power consumption while maintaining acceptable tuner performance. As an alternative, the control circuit may have an input which allows the power consumption to be preset in accordance with the tuner application. The control circuit also controls a variable gain arrangement to compensate for changes in gain resulting from changes in power consumption.

Abstract: A system and method in which a dual image-reject mixer arrangement receives an RF signal having at least one channel. The dual image-reject mixer arrangement generates first and second signals corresponding to each channel of the RF signal. Each first and second signal includes a desired signal, an image frequency signal and an intermodulation signal. A feed-forward arrangement receives the first and second signals corresponding to each channel and outputs a third signal that is formed by constructively combining the desired signals corresponding to each channel and substantially cancelling the intermodulation signals corresponding to each channel. An in-phase and quadrature hybrid network receives the third signal and outputs an in-phase baseband signal and a quadrature baseband signal corresponding to each channel of the RF signal.

Abstract: The invention concerns generally the technology of reducing frequency offset in a radio receiver. Especially the invention concerns receivers where a channel estimator is used for correcting the base band signal. The objects of the invention are achieved by monitoring the phase of the channel estimation output and generating a complex phasor on the basis of successive phase values. The received baseband signal is then multiplied by the generated complex phasor for compensating the frequency offset. The frequency compensation can be made before or after said channel estimation thus producing a feedback compensation or feedforward compensation. The feedback compensation can be implemented by compensating the baseband signal either prior to the despreading or after the despreading.

Abstract: A wireless control system for use in system having a plurality of periodic noise sources includes an antenna; an RF receiver connected to the antenna for receiving RF noise from an external periodic noise source; a phase synchronization circuit connected to the RF receiver for generating a clock signal that is in phase with the external periodic noise; and a noise source control circuit connected to the phase synchronization circuit for receiving the clock signal and controlling a periodic noise source, whereby the periodic noise sources in the system are synchronized to emit their periodic noise in phase with each other.

Abstract: An electronic, programmable filter is disclosed which selectively removes interference, noise or distortion components from a frequency band without perturbing any of the other signals of the band. An input frequency band such as a television channel spectrum is initially demodulated to baseband and applied to the input of the filter. The baseband spectrum is combined in a complex mixer with a synthesized frequency signal that shifts the spectrum a characteristic amount, in the frequency domain, so as to position an interference component in the region about DC. Once shifted, the frequency components about DC are removed by DC canceler circuit and the resulting spectrum is mixed with a subsequent synthesized frequency signal which shifts the spectrum back to its original representation and baseband. The frequency signals are developed by a programmable frequency synthesizer which a user may program with an intelligence signal that defines the frequency location of an interference signal within the spectrum.

Abstract: A radio communications transceiver which operates to transmit radio signals via a transmit antenna and receive radio signals via a receive antenna, wherein said transmit and receive antennas are disposed to provide at least a substantial amount of radio signal isolation therebetween. The radio communications transceiver further includes a cancellation device comprising a first coupler coupled to the transmit antenna and arranged to extract a sample of the transmit signal, a second coupler coupled to the receiver antenna and arranged to extract a sample of the received signal, a correlator fed on first and second inputs with the transmit and the received signal samples respectively, the correlator operating to generate an error signal representative of a correlation of the transmit and received radio signals, which error signal is fed to a modulator which operates to modulate the transmit signal sample, consequent upon the error signal.

Abstract: There is provided a selective calling radio-receiver including (a) a demodulator demodulating a received selective calling radio signal, (b) a waveform-shaper shaping waveform of a demodulation signal transmitted from the demodulator, (c) a data-receiving signal generator generating a data-receiving signal which is in synchronization with the modulation signal having a waveform having been shaped by the waveform-shaper, and which has a plurality of pulses per a symbol term, (d) a data-receiver receiving the demodulation signal at every pulse of the data-receiving signal, (e) a sign discriminator discriminating a sign of received data at every symbol, based on data having been received in the data-receiver, and (f) a processor processing the received data a sign of which has been discriminated by the sign discriminator.

Abstract: There is provided an intermodulation (IMD) control device and method in a mobile communication system. In the IMD control device, an LNA performs low noise amplification on an input RF signal, a first switch is connected to the LNA in parallel, for switching according to a first control signal received for IMD control, a frequency converter down-converts the output of the LNA to an IF signal, an IF amplifier amplifies the IF signal, a second switch is connected in parallel to the IF amplifier, for switching according to a second IMD control signal received for IMD control, and a controller generates the IMD control signals at voltage levels determined according to an RSSI and an energy to noise ratio.

Abstract: A noise reducer generates a gate signal by detecting noise in a demodulated signal, and changes the lengths the gate pulses indicating the presence of noise according to the electric-field strength of a radio signal from which the demodulated signal has been obtained. The demodulated signal is modified during intervals indicated by the gate pulses, to reduce the noise. The amount of change of the gate-pulse lengths is preferably increased as the electric-field strength decreases. Noise can then be removed satisfactorily under even weak electric-field conditions.

Abstract: A crosstalk noise calculation method for calculating crosstalk noise among a plurality of wirings, includes calculating a crosstalk noise using a function in which the crosstalk noise becomes approximately constant when a predetermined wiring length is exceeded, so as to improve the design efficiency of the wirings by preventing an excessively strict checking from being performed.

Abstract: A demodulator with a cross polarization interference canceling function for canceling interference of cross polarization in the main polarization includes a demodulating unit for demodulating a baseband signal of the main polarization, a phase control unit which controls the phase of an interference signal, which is a baseband signal of cross polarization, based upon an error in the demodulated signal, and an interference cancellation unit which cancels an interference signal component from the demodulated signal of the main polarization.

Abstract: A waveform reconstruction circuit receives an rf signal from an antenna, digitizes it, and then generates an undistorted reconstructed waveform. The reconstructed waveform can then be conventionally mixed and demodulated to extract useful signal information with enhanced receiver fidelity and sensitivity.

Abstract: An electronic, programmable filter is disclosed which selectively removes interference, noise or distortion components from a frequency band without perturbing any of the other signals of the band. An input frequency band such as a television channel spectrum is initially demodulated to baseband and applied to the input of the filter. The baseband spectrum is combined in a complex mixer with a synthesized frequency signal that shifts the spectrum a characteristic amount, in the frequency domain, so as to position an interference component in the region about DC. Once shifted, the frequency components about DC are removed by DC canceler circuit and the resulting spectrum is mixed with a subsequent synthesized frequency signal which shifts the spectrum back to its original representation and baseband. The frequency signals are developed by a programmable frequency synthesizer which a user may program with an intelligence signal that defines the frequency location of an interference signal within the spectrum.

Abstract: The invention is directed toward a simple and cost effective method of wirelessly transmitting digital information with an analog carrier signal. The method, referred to as Interrupt Modulation IM, will allow broadcasters to make the transition from an analog to a digital format while using existing analog equipment and conserving radio spectrum. Interrupt Modulation consists of allowing digital information to be transmitted to control a high speed analog special interrupter circuit which interrupts the circuit path of an unmodulated carrier signal such that the analog carrier is interrupted to directly correspond with the time length of the high segment of the digital pulse wave. Digital information is then transferred by the absence of the analog carrier signal. As modern high speed analog switches are capable of on/off operation at speeds of several megahertz, which is common in digital information computers, throughout rates of up to 100 megabits per second are obtainable.

Abstract: A method for detecting nonlinear distortion over communication channels. The method utilizes moment invariants in determining whether nonlinear distortion exists. The method is particularly applicable to detecting the presence of nonlinear distortion over telephone lines that are used for modem communications. The detection of the presence of nonlinear distortion is important in order that appropriate processing operations be performed which are required in the presence of such distortion. The particular processing operations that are performed in the presence of nonlinear distortion function to improve the reliability of data transfer especially at higher data rates. The nonlinearity distortion is detected by calculating high order moment invariants of the error magnitude present at the input to the slicer stage in the receiver. The method of the invention is effective, in part, because the probability density function of the noise is different, i.e.

Abstract: A method for reducing the level of an undesired signal, generated through a frequency converter device, by implementing a local oscillator (hereinafter "LO") leak cancellation circuit. A feedback correction loop, for a radio frequency (RF) transmitter or receiver, reduces an undesired local oscillator leak generated through a single input frequency converter device, such as a mixer, by a unique detection circuit. A unique nulling circuit is also implemented for a multiple input frequency converter device, such as a quadrature modulator.

Abstract: A reference signal source produces a substantially distortion free reference signal which is supplied to a demodulator that is arranged to demodulate the substantially distortion free reference signal. A calibration filter and an equalizer are included downstream of the demodulator. A controller sets the calibration filter to initially pass the reference signal to the equalizer without substantial change to the reference signal. The controller subsequently calibrates the calibration filter in accordance with the demodulator caused distortion reduced by the equalizer.

Abstract: A CATV transceiver is provided within an RF shield enclosure. The transceiver circuit includes a diplexer, having fixed value inductors, that is coupleable to a CATV cable plant to receive an RF input signal and to transmit an RF output signal. The RF receiver is coupled to the diplexer and includes a frequency up-converter, a first frequency down-converter and a second frequency down-converter. The up and first down-converters include voltage controlled oscillators that are responsive to a control signal generated from a single oscillator crystal. The second frequency down-converter operates to provide an output signal representative of the RF input signal within a predetermined output frequency pass-band. The RF transmitter is also coupled to the diplexer and provides for the transmission of the RF output signal in response to an input signal.

Abstract: This invention reduces near-end crosstalk between identical discrete multi-tone (DMT-type) modems by introducing the following modifications to modems at a central office or a subscriber premises. The modifications include: a mechanism for aligning the frames of all modems at the central office (CO), a mechanism for aligning the frames transmitted by the subscribers' modems with the frames received by those modems, and lengthening the DMT frame to include a cyclic prefix. The cyclic prefix to a frame has been made longer than twice the maximum round-trip delay, that is, the delay between the central office and the most distant subscriber to be served. By making adjacent DMT carrier frequencies be orthogonal to each other, the aforementioned modifications will reduce both Near End Cross-Talk (NEXT) and Leakage-Excited Cross-Talk (LEXT). These benefits apply to modems at both the central office (CO) and subscriber ends of the communication path (for example, a high capacity twisted-pair wire).

Abstract: The invention relates to a multi-face phased array antenna. To prevent crosstalk between the individual faces, each face comprises two cancellers, each of which cancels the crosstalk from an adjacent face. To this end, each canceller receives a reference signal from an adjacent face and is provided with a quadrature mixer and a vector modulator.