Method and apparatus for equalization and tracking of coded digital communications signals

A receiver for digital signals, comprising:

• a) a front end unit for receiving an analog signal having transmitted data bits which is encoded by an encoding operation with data redundancy, for down-converting said signal using a provided estimated carrier frequency, for filtering out of band signals and for generating a sequence of samples at a sampling rate using a provided estimated symbol rate;
• b) a synchronization unit for providing the estimated carrier frequency and the estimated symbol rate for the received signal;
• c) an equalizer and detector unit for receiving the output of the front end unit, for compensating for possibly time varying inter-symbol-interference, phase noise, carrier and symbol timing offsets, AM hum, filtering noise and interference, and for detecting the transmitted data bits by utilizing data redundancy within the signal and for generating delay-less symbol estimates â0(t), where t is the time-index of the symbol;
• and
• d) a back-end unit for performing a decoding operation matched to the encoding operation that has been performed on the signal and for restoring the transmitted data bits.

A digital communications system, comprising:

• a transmitter having an encoder and modulator for generating an encoded digital data stream, and
• a receiver for receiving said digital data stream having a front end unit for receiving an analog signal having transmitted data bits which is encoded by an encoding operation with data redundancy, for down-converting said signal using a provided estimated carrier frequency, for filtering out of band signals and for generating a sequence of samples at a sampling rate using a provided estimated symbol rate;
• a synchronization unit for providing the estimated carrier frequency and the estimated symbol rate for the received signal;
• an equalizer and detector unit for receiving the output of the front end unit, for compensating for possibly time varying inter-symbol-interference, phase noise, carrier and symbol timing offsets, AM hum, filtering noise and interference, and for detecting the transmitted data, which includes a forward filter for receiving the output of the front end unit, for performing a linear filtering operation using a filter with adjustable parameters and for generating an estimated symbol sequence at a the estimated symbol rate, a phase rotator for compensating for the effect of an estimated carrier phase offset of the received signal at the input of a symbol detector, the symbol detector for receiving the sum of the outputs of the forward filter and a backward filter, for detecting the transmitted data bits by utilizing data redundancy within the signal and for generating delay-less symbol estimates â0(t), where t is the time-index of the symbol, and optionally generating delayed symbol estimate âN(t), where N is a decision delay, the backward filter for performing a linear filtering operation on the outputs of the symbol detector â0(t), using adjustable parameters, and when the symbol detector generates delayed symbol estimates, to use âN(t), as input to a section of the backward filter which processes elements with delay larger than N, and a tracking and acquisition unit for adapting the parameters of said receiver, including the carrier phase of the phase rotator and the parameters of the forward filter and the backward filter, in order to track channel and signal impairment, using the outputs of the symbol detector, and a back end unit for performing a decoding operation matched to the encoding operation that has been performed on the signal and for restoring the transmitted data bits.