信號在通道中傳送的過程中，當傳輸速率增加以傳送更多資訊時，會造成符元間的干擾（ISI）及雜訊（AWGN），這將會增加接收機在判讀0與1的錯誤率。利用最大可能性（Maximum-Likelihood）方法來降低ISI及雜訊對信號的影響。由於ISI效應會使得代表該位元（bit）的符元（symbols）波形延伸至左右鄰居，而其效果是波與波的相加，這將使得每個接收到的符元包含著過去數個位元的訊息（information），若是能妥善地利用這個特性來移除ISI的干擾，將可改進對整體的效能。 本論文中採用A* 解碼搜尋最佳解，因A* 解碼已被証明可找到最佳解，並可以有效移除在搜尋中無價值的節點，故無須作全區搜尋，且當訊雜比大時，會有效減少搜尋的節點數而快速找到一最佳解。論文中還探討二位元信號在經過線性區塊碼（linear block codes）編碼及未經編碼的情況下，會採用不同的演算法，前者是採用一整個區塊序列（sequence）做最佳搜尋，後者是用序列前後位元做加權後所得估計值來進行判斷。 Signals will cause ISI and AWGN and increase the error rate of deciding 0 and 1 on the process of transmitted in channel, when one increases transmitting rate to transmit more information. Maximum-likelihood method is used in the thesis to degrade the effect of ISI and noise on signals. ISI effect will extend the waves of symbols to neighboring waves, and it will cause adding of waves. It will make each symbol contain the information of few past bits, and it is very helpful for the performance if one can use the property adequately to degrade the effect of ISI. A* decoding method is used in the thesis to search the optimum solution, because it’s proven to be able to get the optimum solution, and remove the useless nodes on the process of searching. It doesn’t need to search globally, and it’s able to find the solution efficiently when signal-to-noise ratio is large enough. Binary signals encoded by linear block codes or not and the corresponding algorithms is discussed in the thesis. The former uses the whole block sequence to do the optimum search, and the later uses the evaluated values gotten by weighting the neighbor bits of the sequence to make the decision. The difference of performance using A* decoding method on whether encoding by linear block codes or not is also discussed in the thesis.
