Time Division Multiplexing

Time Division Multiplexing Technology TDM (Time Division Multiplexing)

Time division multiplexing takes channel transmission time as the division object, and realizes multiplexing by assigning non-overlapping time segments to multiple channels. Time division multiplexing divides the time used for transmission into several time slices, and each user is assigned a time slice. Time division multiplexing communication is that each signal occupies different time slices on the same channel to communicate. It can be known from the sampling theory that an important function of sampling is to turn a time-continuous signal into a time-discrete signal, and the limited time it occupies on the channel provides conditions for the transmission of multiple signals along the same channel. Specifically, the time is divided into some uniform time slices, and the transmission time of each signal is allocated in different time slices by means of synchronization (fixed allocation) or statistics (dynamic allocation), so as to achieve mutual separation and non-interference. Purpose.

As of September 2011, the most widely used time division multiplexing is the T1 carrier of the Bell system. T1 carrier is to multiplex 24 audio channels on one communication line. Before each audio signal is sent to the multiplexer, it must pass through a pulse code modulation encoder. The encoder samples 8000 times per second. For each of the 24 signals, a byte is inserted into the frame in turn. The length of each byte is 8 bits, of which 7 bits are data bits and 1 bit is used for channel control. Each frame consists of 24×8=192 bits, and 1 bit is added as the start flag bit of the frame, so each frame has a total of 193 bits. Since it takes 125us to send one frame, 8000 frames can be sent in one second. So the T1 carrier data transfer rate is:

193bit×8000=1544000bps=1544Kbps=1.544Mbps