Therefore each user gets their own bandwidth or range of frequencies. In other words, all user can use the channel at the same time, but with their own bandwidths. On the sending point, all signals are combined into a single signal by using a multiplexer, that signal crosses the channel and at the reception point demultiplex these signals by using a demultiplexer. It separates these signals to their own frequencies. The figure shows how three voice-grade telephone channels are multiplexed using FDM.
When many channels are multiplexed together, first the voice channels are raised in frequency, each by a different amount then they can be combined with some gaps guard bands between the channels. Even though there are gaps between the channels, there is some overlapping between adjacent channels, because the filters do not have sharp edges. This overlapping means non-thermal noise between the two channels.
Example: 1. Radio broadcasting AM and FM provides multiple signals or stations of different frequencies with the inter-channel separation to prevent interference. Frequency Division multiplexing can be applied to fiber optics called Wavelength Division Multiplexing. This scheme is a variation of frequency division multiplexing.
Actually, WDM is a scheme of combining two or multiple fibres at a prism and each of its energy in a different band or variety of signals passed through the prism or grating, and transmit it to a single shared fiber optic media, at the destination point they have split again with the help of prism.
WDM is more popular than FDM because the bandwidth of a single fiber is about 25, GHz or more than that, and also the great potential for multiplexing many channels together over long-haul routes.
Technology allows demultiplexing signal at the receivers end. The signal that is received by the user on the telephone is multiplexed — the data that is not designed for this node is transmitted with frequency over Hz, so it cannot be heard by the human ear. There are multiple types of FDM existing for different purposes. Wave division multiplexing is using same basic principle as the FDM, while having fiber-optic cable as a media.
Bandwidth is the total capacity of a channel to transmit data. In FDM, the full bandwidth is divided among users. Therefore, each user gets their own bandwidth or range of frequencies. In other words, all users can use the channel at the same time, but they have their own bandwidths or frequency ranges for data transmission. On the sending side, all signals are combined into a single signal using a multiplexer. Then the signal crosses the channel.
At the reception, there is a demultiplexer. It separates the composite signal to separate the signals. A drawback of this multiplexing technique is that, since all the signals are transmitted simultaneously, there is a possibility of crosstalk. In short, FDM divides the bandwidth and provides frequencies to users. It does not divide time between users. In TDM, users can get full channel bandwidth to send signals but for a fixed time slot.
It scales the time between users. It scales the time among the users. Assume that there are three users as u1, u2 and u3 and the fixed time slot is t0. First, u1 will get the entire frequency bandwidth for t0 time.
When u1 transmit data, the other users cannot transmit data. After that time slot is over, u2 can transmit data for a t0 time. When u2 transmit data, the other users cannot transmit data. Then, u3 transmits data for t0 time. In brief, TDM divides time not the bandwidth among users. They can only transmit signals within the available time slot. As only, one signal transmits at a time, the crosstalk in TDM is minimum. Fiber Optic communication use WDM.
The concept of WDM relates to Physics. When a white light beam goes through a prism, it separates into individual colored light beams by the prism. Each light beam has different wavelengths.
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