Thursday, May 22, 2008


Time-Division Multiplexing
Time-Division Multiplexing (TDM) is a type of digital or 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.

Time-division multiplexing (TDM) is a method of putting multiple data streams in a single signal by separating the signal into many segments, each having a very short duration. Each individual data stream is reassembled at the receiving end based on the timing.

Time division multiplexing (TDM) and has many applications, including wireline telephone systems and some cellular telephone systems. The main reason to use TDM is to take advantage of existing transmission lines.

TIME DIVISION MULTIPLEXING (TDM) allows multiple conversations to take place by the sharing of medium or channel in time. A channel is allocated a the whole of the line bandwidth for a specific period of time. This means that each subscriber is allocated a time slot.

Frequency-Division Multiplexing
Frequency-division multiplexing (FDM) is a form of signal multiplexing where multiple baseband signals are modulated on different frequency carrier waves and added together to create a composite signal
In many communication systems, a single, large frequency band is assigned to the system and is shared among a group of users. Examples of this type of system include:

1. A microwave transmission line connecting two sites over a long distance.
2. AM or FM radio broadcast bands, which are divided among many channels or stations. The stations are selected with the radio dial.

The deriving of two or more simultaneous, continuous channels from a transmission medium by assigning a separate portion of the available frequency spectrum to each of the individual channels. (188)

The simultaneous transmission of multiple separate signals through a shared medium at the transmitter, the separate signals into separable frequency bands, and adding those results linearly either before transmission or within the medium. All the signals may be amplified, conducted, translated in frequency and routed toward a destination as a single signal, resulting in economies which are the motivation for multiplexing.

Difference No. 1
TDM: Total available time is divided into several user
FDM: total frequency bands are divided into several users

Difference No. 2
FDM:A multiplex system for transmitting two or more signals over a common path by using a different frequency band for each signal.
TDM: Transmission of two or more signals on the same path, but at different times.

Difference No. 3
TDM:TDM imply partitioning the bandwidth ofthe channel connecting two nodes into finite set of time slots
FDM:The signals multiplexed come from different sources/transmitters.

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