Abstract: 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.

Abstract: 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.

Abstract: 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).

Abstract: 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.