Soft decision threshold control in a signal receiver using soft decision error correction

A method of adjusting soft decision thresholds in a signal receiver, wherein the signal receiver receives an input signal representative of encoded data, wherein the signal receiver detects the input signal using a plurality of soft decision thresholds to produce a plurality of soft decision detection signals each including a data stream of binary values, and wherein the signal receiver decodes the encoded data represented by the plurality of soft decision detection signals to produce decoded data, the method comprising:

• determining a bit error rate (BER) for the decoded data;
• determining a bit value average for at least one of the soft decision thresholds, wherein the bit value average represents the average number of ones per a sample of bits or the average number of zeros per a sample of bits occurring in the bit stream of the soft decision detection signal detected using the at least one of the soft decision detection thresholds;
• and
• adjusting the at least one of the soft decision thresholds in response to the determined bit value average and in response to the determined BER.

An optical communication system comprising:

• an optical signal transmitter comprising an encoder for encoding a binary data stream and a modulator for modulating the encoded binary data stream to produce an encoded optical signal;
• an optical signal receiver for receiving the encoded optical signal, the optical signal receiver comprising:
• a demodulator for demodulating the encoded optical signal to provide an input signal representative of the encoded data stream;
• a soft decision detector configured to receive the input signal and to produce at least one soft decision output signal representative of the encoded data stream using soft information, wherein the soft decision detector is configured to compare the input signal to a plurality of soft decision thresholds to produce a plurality of soft decision detection signals representing the encoded data stream, each of the soft decision detection signals including a bit stream of binary values;
• a soft decision FEC decoder configured to decode the encoded data stream represented by the soft decision output signal to produce decoded data;
• and
• a decision threshold control unit configured to adjust at least one of the soft decision thresholds in the soft decision detector in response to at least one bit value average and in response to a bit error rate (BER) determined for the decoded data, wherein the at least one bit value average is determined for the at least one of the soft decision thresholds and represents the average numbers of ones per a sample of bits or the average number of zeros per a sample of bits occurring in the bit stream of the soft decision detection signal detected using the at least one of the soft decision thresholds.

A soft decision threshold control system configured to adjust soft decision thresholds in an optical signal receiver, wherein the optical signal receiver receives an input signal representative of encoded data, wherein the optical signal receiver detects the input signal using a plurality of soft decision thresholds to produce a plurality of soft decision detection signals each including a data stream of binary values, and wherein the optical signal receiver decodes the encoded data represented by the plurality of soft decision detection signals to produce decoded data, the system comprising:

• a circuit configured to determine a bit error rate (BER) for the decoded data;
• a circuit configured to determine a bit value average for at least one of the soft decision thresholds, wherein the bit value average represents the average number of ones per a sample of bits or the average number of zeros per a sample of bits occurring in the bit stream of the soft decision detection signal detected using the at least one of the soft decision detection thresholds;
• and
• a circuit configured to adjust the at least one of the soft decision thresholds in response to the determined bit value average and in response to the determined BER.