Abstract: A system and method for performing peak-to-average power ratio reduction in a transmitter using pulse amplitude modulation (PAM) encoding. Broadly, a transmitter is configured to perform active digital filtering to detect encoded data symbols that if uncorrected would lead to relatively high analog signal peaks in the data transmission. A prediction is made of the peak values that would be applied at the digital to analog converter (DAC) if the original output of the Tomlinson precoder was sent into the shaping filter. If the absolute value of the predicted peak value exceeds a threshold, a correction of a full 2L step is applied for one sample of the Tomlinson precoded stream. The correction step is applied in such a way as to reduce the resulting peak output. Two methods of predicting the peak values are presented. The first method segments the shaping filter into causal and non causal portions so that no extra delay is introduced.

Abstract: An improvement to system timing and synchronization in a digital transceiver allows the synchronization of a transceiver located at a central office to a network or system clock without the use of any additional transmitted bits or additional external circuitry. The system allows a transceiver to achieve timing and synchronization lock to a system master clock, such as a T1 or E1 clock, by operating on the two level input clock with a complex rotator to develop an error signal which allows a phase locked loop circuit to drive a frequency synthesizing device, which in turn drives a system clock. The system clock provides an input to a complex generator, which in turn develops a complex rotation function. The complex rotation function allows the transceiver clock to synchronize to the network master clock.

Abstract: An adaptive preceding system is implemented within a data communications system in order to precode data to track changes in a communications channel. The adaptive precoding system initializes a set of precoder values within a precoder filter of a transmitter during an initialization phase. The precoder filter is used to create a precoding signal that is combined with a transmission data signal in order to compensate for distortions on a communications channel. During a communications phase, a decision feedback equalizer generates equalizer coefficients that correspond to changes on the communications channel. The equalizer coefficients are periodically transmitted to a converter within the transmitter over a secondary channel. The converter determines a new set of precoder values that compensate for the changes in the communications channel and slowly updates the values in the precoder filter until they match the new set of precoder values.

Abstract: A system and method for demodulating digital information from a modulated signal that can be represented in a signal space diagram as an odd constellation of sample points. The system comprises filtering means for receiving the modulated signal that includes means for rotating the received sample points 45.degree. clockwise on the signal space diagram such that decision or neighborhood regions can be drawn having borders that are either parallel or perpendicular to the axes of the signal space diagram. As a result, a slicer can easily extract the symbol information from the rotated sample points with a minimum of computational complexity. Moreover, and perhaps most importantly, the rotation is accomplished through a one time modification of the tap coefficients used by the filtering means thus eliminating any additional processor real time required to perform the rotation.

Abstract: The present invention is drawn to a system and method for transmitting a data signal using digital subscriber loops in an expanded frequency band. According to the present invention, an encoder receives a data signal to be transmitted to a second modem. The encoder generates both an in-phase and a quadrature signal based on the data signal. Both the in-phase signal and the quadrature signals are then processed by a signal precoder in preparation for transmission across the channel. Next, the in-phase and quadrature signals are processed by digital filters to produce signals of limited bandwidth which can be transmitted across the channel. The coefficients of the digital filter are chosen such that the resulting filtered in-phase and quadrature signals are transmitted in an expanded bandwidth. The quadrature signal is filtered so as to be orthogonal to the in-phase signal. Thereafter the filtered signals are added and then converted to an analog signal which is transmitted to the second modem.