An underwater acoustic communication scheme using time delay and multiple frequency modula-tion technique is presented in this paper. 研究了一种采用脉冲时延差和多频码元组合编码的水声通信技术。
While single frequency tones worked on certain phone routes, the most common signaling on the then long distance network used Multi-Frequency tones. 而某些单频音调闪耀电话线最常见的则长途信令网采用多频音调。
