Abstract: A method and apparatus are provided for decoding a plurality of codewords from a received binary bitstream. A first decoding stage processes each of the codewords with a first iterative decoding algorithm based on forward error-correction information of the codewords. A second decoding stage processes selected ones of the codewords with a second iterative decoding algorithm, which is based on forward error-correction information in the selected ones of the codewords. Each codeword selected for the second decoding stage is selected in response to an exit from the decoding of that codeword without the production of a decoded codeword. The second iterative decoding algorithm is configured to enable a greater number of iterations of decoding per codeword than the first iterative decoding algorithm.

Abstract: A low-density parity-check (LDPC) decoder comprising a pre-processor, a core decoder, and a post-processor. The pre-processor is configured to transform a received log-likelihood-ratio (LLR) sequence into a form that enables the core decoder to toggle at a reduced rate during iterative decoding processing thereof. Upon stoppage of the decoding processing corresponding to the LLR sequence, the post-processor operates to apply a complementary transformation to the output of the core decoder, which recovers the corresponding codeword of the LDPC code. An example embodiment of the LDPC decoder operating in this manner may be able to beneficially reduce the power consumption therein by about 10%.

Abstract: An apparatus, comprising: circuitry configured, in response to receipt of input data, to transmit a stream of symbols of a constellation to a modulator for modulation onto a carrier wherein a frequency of occurrence of symbols in the stream is dependent upon a probability-amplitude distribution for symbols of the constellation, wherein the probability-amplitude distribution has a kurtosis less than a target value and a shape of the probability-amplitude distribution causes low-amplitude symbols to occur more frequently on average in the stream than high-amplitude symbols.

Abstract: An apparatus, comprising: circuitry configured, in response to receipt of input data, to transmit a stream of symbols of a constellation to a modulator for modulation onto a carrier wherein a frequency of occurrence of symbols in the stream is dependent upon a probability-amplitude distribution for symbols of the constellation, wherein the probability-amplitude distribution has a kurtosis less than a target value and a shape of the probability-amplitude distribution causes low-amplitude symbols to occur more frequently on average in the stream than high-amplitude symbols.

Abstract: An apparatus includes a digital signal processor to perform perturbation-based optical nonlinearity compensation of optical data signals of a communication stream. The digital signal processor includes first digital circuits to calculate multiplicative factors for corrections to the optical data signals from products of values of the optical data signals at a reduced set of times. The reduced set is a down-sampling of the sequence of consecutive symbol times of the communication stream. The digital signal processor also includes second digital circuits to calculate the multiplicative factors for corrections to the optical data signals at the consecutive symbol times by interpolating the multiplicative factors evaluated at the reduced set of times.

Abstract: In a method of demapping a tributary from a first frame into a second frame, the first frame has a plurality of tributary words and a synchronization word, and first and second counters are provided. The first counter is increased by a first value at each dock cycle of the second frame, and reading operations are performed according to the second counter. Synchronization information, generated according to the synchronization word, is used to change between first and second states. When in the first state, the second counter is synchronized to the first counter at each clock cycle of the second frame; and, when in the second state, the second counter is synchronized to the first counter at a predetermined instant of the second frame, the second counter increasing by a second value at each clock cycle of the second frame wherein the reading operation is performed.