Abstract: A bi-directional data communication system using inverse multiplexers for transmitting and receiving data at high-speeds using regular analog channels. The inverse multiplexer splits a high-speed digital signal into low-speed digital signals that are input to analog modems. The analog modems modulate the low-speed digital signals into low-speed analog signals for transmission over the analog channels to the public switched telephone network. At the remote end, the data carried by the analog channels is reverse inverse multiplexed into a high-speed digital signal by an inverse multiplexer operating in a reverse inverse multiplexing mode.

Abstract: A maximum likelihood decoding system includes a branch metric processor which calculates only one of four branch metrics associated with branches leading to two consecutive states S.sub.j and S.sub.+1, where j is even. The system determines the remaining three metrics by producing a second branch metric by manipulating the first branch metric using simple binary operations and assigns the first and second metrics to the second and first branches, respectively, leading to the odd state. The system next retrieves associated path metrics from a path metric memory which stores the information in locations accessed by addresses related to identifiers associated with the branch initial states. After the system selects a surviving path for each end state, it stores in a path memory location associated with the end state information identifying the previous state on the surviving path.