Subject: Priniciples of Communication Engineering

Difficulty : Medium

Marks : 05

• Multiplexing is a process of simultaneously transmitting two or more individual signals over a single communication channel. D
• Due to multiplexing it is possible to increase number of communication channels so that more information can be transmitted.
• In FDM available B.W of communication channel is shared among the signals to be transmitted. Here many signals are transmitted with each signal occupying a different frequency slot with common bandwidth.
• Each signal to be transmitted modulates a different carrier. The modulated signals are then added together to form a composite signal which is transmitted over a single channel. Guard bands are introduced in order to avoid interference between adjacent channels.
• fig. 1 shows FDM transmitter. The signals which are to be multiplexed will each modulate a separate carrier.

• The type of modulation can be AM, SSB, FM or PM. Modulated signals are then added together to form complex signal which is transmitted over a single channel.

• Block diagram of FDM receiver is shown in fig.2. The composite signal is applied to group of BPF's of FDM receiver.

• Each BPF has a centre frequency correspondence to one of the carriers.
• BPF's have an adequate BW to pass all the channel information without any distortion.
• Each filter will pass only its channel and reject all the other channels. The channel de-modulator then removes the carrier and recovers the original signal back.

Fig. FDM Transmitter

Fig. FDM Receiver