Patent ID: 7026963

Claim:
A fast look-ahead path modulation apparatus using criteria, such as states, paths and modulation characteristics for modulation in a look-ahead path calculation process, comprising: a data word modulator, which converts a received data word to more than one corresponding available codewords, and output a digital sum value (DSV) and a weight of each available codeword; a codeword memory, which stores more than one survival codewords and corresponding DSVs after a selection process, and updates the contents of the codeword memory after an optimal codeword is produced and outputted; a DSV calculator comprising: an available path DSV calculator for calculating each available path DSV based on the DSV and the weight of each available codeword; and an available path absolute DSV summer for receiving each available path DSV and calculating an available path absolute DSV sum; a survival path selector, which selects the available path absolute DSV sum based on a first set of selecting criteria, and determines each survival codeword among the received available codewords; and an optimal path selector, which selects a foremost codeword of each received survival path and the corresponding available path absolute DSV sum based on a second set of selecting criteria, and decides an optimal modulation codeword to output, wherein when the survival path selector decides each survival codeword, a survival state signal is generated and sent to the data word modulator for the next data word modulation to process and to the available path DSV calculator for storing the survival path DSV corresponding to each survival codeword into the codeword memory, and then updating the available path DSV calculator and the survival path absolute DSV summer, wherein when the content of the codeword memory accumulates to a designed look-ahead length, the codeword memory sends the foremost codeword corresponding to the each survival path to the optimal path selector where the optimal modulation codeword is selected based on the sum of each survival path absolute DSV, and the codeword memory sends the sum of the survival path absolute DSV corresponding to the foremost codeword of the each survival path to the available path absolute DSV summer.