26-06-2013, 12:53 PM
Implementation of Time Division Multiplexing system using matlab
Learning Objectives
To be familiar with concept of time division multiplexing with the use of MATLAB.
THEORY
Time-division multiplexing (TDM) is a type of digital or (rarely) analog multiplexing in which two or more signals or bit streams are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel. The time domain is divided into several recurrent timeslots of fixed length, one for each sub-channel. A sample byte or data block of sub-channel 1 is transmitted during timeslot 1, sub-channel 2 during timeslot 2, etc. One TDM frame consists of one timeslot per sub-channel plus a synchronization channel and sometimes error correction channel before the synchronization. After the last sub-channel, error correction, and synchronization, the cycle starts all over again with a new frame, starting with the second sample, byte or data block from sub-channel 1, etc.
For multiple signals to share one medium, the medium must somehow be divided, giving each signal a portion of the total bandwidth.
The current techniques that can accomplish this include Frequency division multiplexing (FDM)
Time division multiplexing (TDM)-Synchronous vs Statistical1 Wavelength division multiplexing (WDM), Code division multiplexing (CDM).
Time Division Multiplexing:
Sharing of the signal is accomplished by dividing available transmission time on a medium among users.
Digital signaling is used exclusively. Time division multiplexing comes in two basic forms:
1. Synchronous time division multiplexing, and
2. Statistical, or asynchronous time division multiplexing.
Synchronous Time Division Multiplexing:
The original time division multiplexing, the multiplexor accepts input from attached devices in a round-robin fashion and transmits the data in a never ending pattern.
T-1 and ISDN telephone lines are common examples of synchronous time division multiplexing. If one device generates data at a faster rate than other devices, then the multiplexor must either
sample the incoming data stream from that device more often than it samples the other devices, or buffer the faster incoming stream.
If a device has nothing to transmit, the multiplexor must still insert a piece of data from that device into the multiplexed stream. So that the receiver may stay synchronized with the incoming data stream, the transmitting multiplexor can insert alternating 1s and 0s into the data stream.
Statistical Time Division Multiplexing:
A statistical multiplexor transmits only the data from active workstations (or why works when you don’t have to). If a workstation is not active, no space is wasted on the multiplexed stream. A statistical multiplexor accepts the incoming data streams and creates a frame containing only the data to be transmitted.
To identify each piece of data, an address is included. If the data is of variable size, a length is also included. More precisely, the transmitted frame contains a collection of data groups.