Multiplexing Technology (Frequency division multiplexing, time division multiplexing and Wavelength Division multiplexing) __ Phone number

Baseband signal is the digital signal 1 or 0 directly using two different voltage to express, and then sent to the line to transmit.

The wideband signal is a frequency division multiplexing analog signal which is modulated by the baseband signal.

The basic principle of multiplexing technology is: Before entering the same wired or wireless transmission medium, each signal is modulated into a modulated signal which is not confused with each other, then enters the transmission medium to transmit to the other side, and then uses the Demodulation (Anti-tune) technology to differentiate the signals. And make them return to the original signal, so as to achieve multiplexing purposes.

Commonly used multiplexing technology has frequency division multiplexing technology and Time division multiplexing technology.

Frequency division Multiplexing is the modulation of each signal to different frequency bands for transmission, mostly for analog communication. Frequency Division Multiplexing (Fdm,frequency Division multiplexing) is to divide the total bandwidth used for the transmission channel into several sub bands (or sub channels) and transmit 1 signals per sub channel. Frequency division multiplexing requires that the total frequency width is greater than the sum of each sub channel frequency, at the same time, in order to ensure that the signals transmitted in each sub channel are not interfered, we should set up the isolation zone between each sub channel, so as to ensure that each signal is not interfered (one condition). The characteristic of frequency division multiplexing is that all the signals transmitted by the Sub channel work in parallel, and the transmission time delay is not considered in each signal transmission, so the frequency division multiplexing technology has been widely used. In addition to frequency division Multiplexing (FDM) in traditional sense, frequency division multiplexing (OFDM) is a kind of orthogonal frequency division multiplexing. The schematic diagram of frequency division multiplexing is shown below:

Time Division Multiplexing (TDMA) technology is widely used in digital communication, which uses discrete pulses to form overlapping multi-channel signals. Time division multiplexing is suitable for the transmission of digital signals. Because the bit transmission rate of the channel exceeds the data transmission rate of each signal, the channel can be divided into several fragments by time to rotate to multiple signals. Each time slice is occupied by a multiplex signal, in the specified time, many digital signals can be transmitted according to the required transmission, which also realizes the transmission of multiple digital signals on a physical channel. Suppose that the data bit rate for each input is 9. 6KBIT/S, the maximum bit rate of the line is 76. 8 kbit/s, 8-channel signal can be transmitted.

In addition to frequency division and Time Division Multiplexing technology, there is also a wavelength division multiplexing technology. This is in the light wave frequency range, the different wavelength of light waves, at a certain interval arranged in a fiber transmission. The "Wavelength division multiplexing" technology used in optical fiber communication is now developing rapidly. Wavelength Division Multiplexing (WND) is the use of two or more different wavelengths of optical carrier signals (carrying various information) at the transmitter through the multiplexer (also known as the Wave-filter, multiplexer) converge and coupled to the transmission of the same fiber in the optical circuit; at the receiving end, the Multiplexer ( Also known as the splitter or the multiplexer, demultiplexer the wavelength of the optical carrier separation, and then the optical receiver for further processing to restore the original signal. This technique for simultaneously transmitting two or more different wavelengths of light signals in the same fiber is called wavelength division multiplexing

The difference between frequency division multiplexing and time division Multiplexing is as follows:
(1) on microcosmic, the signal of frequency division multiplexing is parallel, while the time division multiplexing is serial.

(2) Frequency division multiplexing is more suitable for analog signals, while time division multiplexing is more suitable for digital signals.

Frequency division multiplexing is to split the available bandwidth of the transmission medium into a "band", so that each input device is assigned to a "band". The maximum bandwidth allowed by the transmission medium constitutes a channel, so each "band" is a sub channel.

The characteristic of frequency division multiplexing is that the data of each user terminal is transmitted through the channel specially allocated to it, and no other user can use it when the user has no data transfer. Frequency division multiplexing is suitable for analog signal frequency division transmission, mainly used in telephone and cable television (CATV) system, in the data communication system and modulation and demodulation technology in conjunction with.