General Dynamics Government Systems Corporation

Gte Government Systems Corporation

Sheldon Norman Salinger

Neil E Furukawa

Douglas G Forster

The presence of interfering continuous-wave signals are automatically detected in the demodulated output of a quadrature amplitude modulation data communications receiver. The transmitter is re-tuned in order to avoid the detected interferer. Statistical information concerning the received signal is accumulated at a receiver and is analyzed to determine whether a reduction in the received bit-error-rate is due to the presence of an interferer. If an inteferer is determined to be present within the signal transmission bandwidth, then the potentially available transmission band is spectrum analyzed to find a new portion of that band in which the signal can be transmitted free of the interferer. The results of the statistical analysis and the spectral analysis are conveyed back to the transmitter which then readjusts the transmission parameters and forwards the new parameters to the receiver. The system resumes operation in the new transmission band with no interference and with the bit-error-rate restored to its required level.

Interference detection and avoidance technique

A method and apparatus are described for adaptively predistorting a signal before it is transmitted by a transmitter in order to compensate for nonlinearities which are introduced. Statistical information regarding the received signal is accumulated at a receiver, and is preferably transmitted back to the transmitter for processing. The processing includes a constellation analysis to determine the distortion characteristics of the signal, which may include bias, gain imbalance, lock and quad angle errors, and nonlinear distortions including AM-AM and AM-PM conversion effects, with all of these phenomena occurring anywhere in the transmitter-channel-receiverchain. From analysis of the statistics of the distortions in the received signal constellation, adjustments are made in the transmitter and/or receiver parameters. The positions of the signal symbols in the transmitted constellation are thereby correctively predistorted to compensate for and ameliorate the distortions in the received signal, thereby improving the fidelity of the said received signal.

Adaptive predistortion system

A method and apparatus are described for adaptively pre-emphasizing signals transmitted over a stable but occasionally varying transmission medium such as a very-high-speed digital subscriber line (VDSL) signal, before it is transmitted by a transmitter, in order to compensate for frequency distortion that is introduced by the VDSL transmission line. At system start up, or whenever the parameters or configuration of the line are changed, the the line termination transceivers at both ends of the transmission line exchange calibration signals to measure the attenuation-versus-frequency curves of the line in both directions. Thereafter, whenever the signal transmission band is to be changed in either direction, the transmitter for that direction uses the measured attenuation curve for the line to calculate and design a set of filter coefficients for an adjustable pre-emphasis filter. The pre-emphasis filter filters the transmitted signal, attenuating most heavily those frequencies that are least attenuated by the transmission line, so that the net frequency response of the pre-emphasis filter plus transmission line is flat, thereby eliminating frequency distortion.

Adaptive pre-emphasis technique

An improved digital bi-directional communications transceiver in which the upstream and downstream portions of the frequency spectrum are allocated different bandwidths and positioned at different locations on the frequency spectrum in response to transmission line conditions and impairments such as system provisioning, background noise, radio frequency interference (RFI), crosstalk and reflected signals. The movement of the upstream and downstream carrier frequencies are elastic in that they may be adjusted in near real-time involving methods for determining the signal quality parameter(SQP) of the received signal. The SQP is used to estimate the bit error rate (BER) margin on the received data and also takes into account the total signal to interference ratio (SIR), where the interference includes crosstalk, RFI, and residual echo from the neighboring upstream or downstream channel. Because the carrier frequencies of the upstream and downstream channels are being dynamically allocated, it is necessary to implement a robust carrier acquisition, recovery and lock algorithm. The robust carrier algorithms allow carrier recovery of the transmitted upstream and downstream signals independent of the particular modulation or symbol rate.

Method and apparatus for variably allocating upstream and downstream

A cellular radiotelephone (24) engages in a call over a bidirectional channel (32) involving a cellsite base station (68) within a cellular network (22). Upon receipt of a notice (46), a geographical location computer (20) is activated and transmits a call locate instruction identifying the bidirectional channel (32) to a plurality of dual channel receivers (56, 58, 60, and 61). The dual channel receivers (56, 58, 60, and 61) are then tuned to the bidirectional channel (32) and receive the forward (78) and reverse (82) location signals over forward and reverse directions of the bidirectional channel (32). A probable location of the cellular radiotelephone (24) is determined by measuring phase differences of the forward (78) and reverse (82) location signals at each of the dual channel receivers (56, 58, 60, and 61).

Geographical location system and method for locating radiotelephone

An improved digital bidirectional communications transceiver in which the upstream and downstream portions of the frequency spectrum are allocated in response to transmission line conditions and impairments such as background noise, radio frequency interference (RFI), crosstalk and reflected signals. The movement of the upstream and downstream carrier frequencies are elastic in that they may be adjusted in near real-time involving methods for determining the signal quality parameter(SQP) of the received signal. The SQP is used to estimate the bit error rate (BER) margin on the received data and also takes into account the total signal to interference ratio (SIR), where the interference includes crosstalk, RFI, and residual echo from the neighboring upstream or downstream channel. Because the carrier frequencies of the upstream and downstream channels are being dynamically allocated, it is necessary to implement a robust carrier acquisition, recovery and lock algorithm. The robust carrier algorithms allow carrier recovery of the transmitted upstream and downstream signals independent of the particular modulation or symbol rate.

Growing community of inventors

Los Altos, CA, United States of America

Sheldon Norman Salinger