Method and apparatus for adaptive iterative decision feedback control coding in modems
View Patent ↗A modem employing feedback control coding to dynamically control signal-to-noise ratios and to identify errored codewords for retransmission. The receive path components of the modem include a signal-to-noise estimator, a feedback controller and a dynamic demapper. The signal-to-noise estimator repeatedly determines a difference between a target signal-to-noise ratio (SNR) and actual SNR in communications received from an opposing modem. A feedback controller responds to each determination by the signal-to-noise controller to send to the opposing modem a set of modified transmit control parameters for reducing the difference between the target and actual SNRs. The dynamic demapper dynamically alters constellation size or power spectral density for demapping communications received from the opposing modem responsive to a change in transmission parameters thereof resulting from the modified set of transmit control parameters.
1. A method for communication between a pair of modems coupled to opposing ends of a wire line communication medium for multi-tone modulated X-DSL communications thereon, and the method comprising:
detecting errored forward error correction (FEC) codewords during decoding of received FEC encoded data on the first of the pair of modems;
sending indicia identifying the errored FEC codewords detected in the detecting act from the first to a second of the pair of modems;
finding, on the second of the pair of modems, buffered data associated with the errored FEC codewords identified by the indicia received from the first of the pair of modems in the sending act; and
re-transmitting corresponding FEC codewords associated with the buffered data found in the finding act from the second to the first of the pair of modems responsive to the indicia received from the first of the pair of modems in the sending act and wherein the detecting and sending acts further comprises:
iteratively determining a signal to noise ratio (SNR) of a received data on the first of the pair of modems;
characterizing a type of noise as transient or stationary based on a duration thereof;
initiating a changeover in transmit control parameters including at least one FEC encoding parameter of the corresponding codewords including: FEC codeword size and FEC code rate responsive to a stationary type noise characterization in the characterizing act; and
avoiding a changeover in transmit control parameters responsive to a transient type noise characterization in the characterizing act.