Loral Aerospace Corp.

Lockheed Martin Aerospace Corporation

John Kaufmann

A signal conditioner comprising several embodiments of transversal (FIR) filters that utilize symbol addressed multiplier lookup tables. In particular, five embodiments in accordance with the principles of the present invention are described. The present invention generates a predistorted waveform within the transversal filter that provides for compensation for the effects of nonlinear amplifiers and intersymbol interference. The present invention may be employed to digitally generate an arbitrary baseband waveform that represents a limited alphabet of symbols. The present invention dramatically simplifies the implementation of FIR filters where the application of the FIR filter is to provide a transversal filter function for waveforms that represent symbols. The degree of simplification is related to the number of bits that define the size of the symbol alphabet as compared to the number of bits required to adequately represent a digital sample of the waveform. Typically 2, 3 or 4 bits represent the alphabet of communication symbols, whereas waveforms require as a minimum 8 bits of quantization. A second aspect of the present invention comprises combining the function of generating arbitrary waveforms with the symbol addressed lookup tables that are part of the FIR filter. The waveform is precompensated to minimize the effect of intersymbol interference and is prewarped to compensate for transmitter nonlinearities.

Signal conditioner with symbol addressed lookup table producing values

A programmable PCM/TDM demultiplexer including an FA function unit including Frame Alignment Logic (FAL) hardware controlled by a Programmable Frame Alignment Controller (PFAC), and accompanied by a DECommutation and dejustification (DEC) function unit including Output Logic Hardware (OLH) controlled by a Programmable Decommutator Sequencer (PDS) controlled in turn by a Programmable Decommutator Sequencer Controller (PDSC).

Programmable PCM/TDM demultiplexer

Adaptive equalizers and processing methods wherein data required to implement an adaptation algorithm is sampled at a rate that is significantly lower than the symbol rate. The adaptation algorithm is processed at this reduced rate, in that updated tap coefficients, sample timing errors and symbol clock error signals are computed at this reduced rate. An advantage of the adaptive equalizer and processing method of the present invention is that the adaptation algorithm may be implemented in equipment that operates at a clock rate that is much less then the symbol rate. In particular, the adaptation algorithm may be computed using software that is resident in inexpensive general purpose digital processor, such as a personal computer, for example. A benefit of the adaptive equalizer and processing method of the present invention is that more sophisticated and more effective adaptation algorithms are practical when compared to adaptive equalizers using algorithms that are constrained to operate at higher symbol rates.

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Palo Alto, CA, United States of America

John Kaufmann