Frequency division multiplexing

When the transmission capacity of a physical channel is higher than the demand for one signal, the channel can be shared by multiple signals, for example, the trunk line of a telephone system often has thousands of signals transmitted in a single fiber. Multiplexing is a technology to solve how to use a channel to transmit multiple signals at the same time. Its purpose is to make full use of the frequency band or time resources of the channel and improve the utilization rate of the channel.There are two common methods of signal multiplexing: Frequency division multiplexing (FDM) and Time division multiplexing (TDM). Time division multiplexing is commonly used for the multiplexing of digital signals and will be discussed in Chapter 10. Frequency division multiplexing is mainly used for the multiplexing of analog signals, but it can also be used for digital signals. This section will discuss the principles and applications of FDM.
Frequency division multiplexing is a multiplexing method that divides channels according to frequency. In FDM, the bandwidth of the channel is divided into multiple non-overlapping frequency bands (subchannels), and each signal occupies one of the subchannels, and there must be unused frequency bands (protection bands) between the channels to prevent signal overlap. At the receiving end, the appropriate bandpass filter is used to separate the multiple signals, so as to recover the required signals.
The diagram below shows the block diagram of the frequency division multiplexing system. At the transmitting end, each baseband voice signal is first passed through a low-pass filter (LPF) in order to limit the maximum frequency of each signal. Then, each signal is modulated to a different carrier frequency, so that each signal is moved to its own frequency band range, and then synthesized into the channel for transmission. At the receiving end, a series of band-pass filters with different center frequencies are used to separate the modulated signals, and the corresponding baseband signals are recovered after they are demodulated.
In order to prevent mutual interference between adjacent signals, carrier frequencies f_c1,f_c2, f_cn should be reasonably selected to leave a certain protection band between each modulated signal spectrum.

The above is Shenzhen HDV Phoelectron Technology Ltd. to bring you about “frequency division multiplexing” knowledge explanation, hope to help you, and Shenzhen HDV Phoelectron Technology Ltd. in addition to ONU series, transceiver series, OLT series, but also produce module series, such as: Communication optical module, optical communication module, network optical module, communication optical module, optical fiber module, Ethernet optical fiber module, etc., can provide the corresponding quality service for different users’ needs, welcome your visit.