What are the methods of using the different frequencies of carrier signals to achieve circuit multip

Frequency division multiplexing (TDM) is a method that uses the different frequencies of carrier signals to achieve circuit multiplexing.

Frequency-division multiplexing (FDM) refers to a multiplexing technology in which the carrier bandwidth is divided into a variety of sub-channels of different frequency bands, and each sub-channel can transmit a signal in parallel. FDM is commonly used in broadband networks where analog transmissions are made. In a communications system, the bandwidth provided by a channel is often much wider than the bandwidth required to transmit a signal.

If it is very wasteful for a channel to transmit only one signal, in order to be able to make full use of the bandwidth of the channel, the method of frequency division multiplexing can be used. In a frequency division multiplexing system, the available frequency bands of the channel are divided into several non-overlapping frequency bands, and each signal is transmitted in one of the frequency bands, so that they can be filtered out separately by a filter and then demodulated and received separately.

Principle of Frequency Division Utilization:

If the available bandwidth of a physical channel exceeds the bandwidth required for a single original signal (such as CH1, CH2, and CH3 in the schematic), the total bandwidth of the physical channel can be split into several and transmit a single signal bandwidth.

identical (or slightly wider) sub-channels; One signal is then transmitted on each sub-channel to enable the simultaneous transmission of multiple signals in the same channel. Before the multi-channel original signal is multiplexed by frequency division, the spectrum of each signal should be moved to different segments of the physical channel spectrum through spectrum transfer technology, so that the bandwidth of each signal does not overlap with each other (the transferred signal is shown in the middle 3-channel signal waveform in the figure); Each signal is then modulated with different frequencies, and each signal is transmitted on a channel of a certain bandwidth centered on its carrier frequency. In order to prevent mutual interference, it is necessary to isolate each channel with anti-interference protection measures.

If the carriers are different, the digital FFT can be used to separate the different signals, and if the analog is used, the frequency selection network can be used.

As follows:

1. In bilateral band coherent demodulation, the influence of phase error on demodulation performance: the amplitude of the demodulated output signal will decrease.

2. In single-sideband coherent demodulation, the influence of phase error on demodulation performance: not only will the amplitude decrease, but also produce an orthogonal interference signal, and the buried wheel will distort the waveform of the baseband signal.

Introduce. Carrier synchronization, also known as carrier recovery, is to generate a local bridge oscillation at the same frequency and phase with the carrier of the received signal in the receiving equipment, and supply the desensitized liquid family modulator for coherent solution call.

When the received signal contains discrete carrier-frequency components, the signal carrier needs to be separated from the signal as a local coherent carrier at the receiving end. The frequency of the locally coherent carrier thus separated must be the same as that of the received signal, but in order to achieve the same phase, it may be necessary to make appropriate adjustments to the phase of the separated carrier.

The periodic signal spectrum is characterized by:

1. Discreteness: The spectral lines are discrete.

2. Harmonics. Sexuality: Spectral lines appear only at frequencies that are integer multiples of the fundamental frequency.

3. Convergence: The general trend of harmonic amplitude decreases with the increase of harmonic times.

When the pulse width of the signal.

When the signal period becomes larger, the interval between adjacent spectral lines becomes smaller and the spectrum becomes denser. If the period grows indefinitely, then the spacing of adjacent lines will approach zero, and the discrete spectrum of the periodic signal will be filtered to the continuum of the non-periodic signal.

In addition, the amplitude of each frequency point spectrum line in the spectrum is also related to the pulse width, and when the signal pulse width is unchanged, the larger the signal period, the smaller the amplitude of the frequency point spectrum line, and vice versa.

There are several ways to use the different frequencies of carrier signals to realize circuit multiplexing:

1.Frequency division multiplexing (FDM): Transmits different information on different frequencies, and these frequencies are assigned to different users or channels, and multiplexing is achieved through spectrum segmentation.

2.Time Division Multiplexing (TDM): Transmits different information at the same frequency in different time periods, and these time periods are allocated to different users or channels, and multiple transmissions are achieved through time splitting.

3.Wavelength division multiplexing (WDM): In the same optical fiber transmission channel, different wavelengths of light are used to transmit different information to achieve multiplexing.

4.Code division multiplexing (CDMA): Each user uses a different code sequence to complete the signal differentiation, so that multiple users can transmit information on the same frequency band to achieve multi-channel transmission nuclear return.

5.Space division multiplexing (SDM): Using the spatial distribution of multiple antennas, multiple signals are sent to multiple receiving points at the same time to improve the throughput of the system.

These methods are mostly used in the field of communication, which realizes efficient information transmission and improves communication efficiency and spectrum utilization.

Summary. Frequency modulation Frequency modulation, the full name of "frequency modulation". A modulation method that makes the instantaneous frequency of the carrier wave change according to the change law of the desired transmitted signal. It is a modulation method that causes the instantaneous frequency of the modulated wave to change with the modulated signal.

Hello dear This adjustment method is called FSK - also known as frequency shift keying.

FSK is an earlier modulation method in the transmission of information from the base of the book, and its main advantages are: it is easy to implement, and the anti-noise and anti-attenuation performance is better. It has been widely used in medium and low-speed data transmission.

Frequency Modulation Frequency modulation, the full name of "Punch Pure Frequency Modulation". A modulation method that makes the instantaneous frequency of the carrier wave change according to the change law of the desired transmitted signal. It is a modulation method that makes the instantaneous frequency of the measured ant wave change with the signal buried in the tuning.

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It's all original, non-**, and I've been writing it for a long time

In fact, Ethernet is not all baseband transmission, and there are also specifications for frequency band transmission, such as the 100broad-f standard, but it is rare.

Different from wireless transmission, which is limited by antenna size and space transmission characteristics and must modulate the signal to the frequency band, the baseband transmission performance of copper cables is relatively good, so the baseband transmission can make better use of bandwidth, and the hardware implementation cost is far lower than that of frequency band transmission.

Far from it, the base in our commonly used 10base-t and 100base-tx represents the "baseband", the information you mentioned on the Internet is too old, and the best counterexample is optical communication! The same baseband signal, but can reach 10Gbps or even 40Gbps rate, of course, copper cable can not reach such a high rate, but through optimization, 1000Mbps can be barely reached (why reluctantly, look at the strict requirements of 1000base-tx for the cable and the upper limit of the transmission distance), so it proves that no one has stipulated that the frequency band of the baseband signal is very narrow!

The reason why the bandwidth of copper cables (twisted pairs) is less than that of fiber is due to the following contradiction:

1. The larger the diameter of the copper cable, the lower the cut-off frequency, so the higher the signal frequency, the smaller the required cable diameter;

2. Copper cables have a skin effect, that is, at high frequencies, the signal will tend to be transmitted in the part of the copper core close to the outer surface, so in order to reduce attenuation, the diameter of the cable must be increased.

Therefore, it is difficult to greatly improve the limit rate of copper cables.

The latter problem, the theoretical rate of 1000base-tx and 1000base-fx is the same, but in actual use, it is not good, for example, affected by cable quality, electromagnetic interference, and light quality, it is possible to deteriorate the signal and produce bit errors.

Hope mine, helped! Hehe.

The carrier wave is the medium through which the signal is carried. For example: radio waves.

The frequency range of the carrier wave is limited, and the low-speed signal (e.g., electrical signal, sound wave) must be modulated to the high-frequency part in order to be transmitted in the channel of the radio wave. Low-speed signals cannot propagate in the channel if they do not reach the frequency points used.

Therefore, the frequency of the carrier is higher than the frequency of the signal.

Upstairs is very good, to add, in wireless transmission, electromagnetic waves travel approximately at the speed of light, which has nothing to do with frequency, and the baud rate is related to the carrier frequency.

Typical spectrum of amplitude modulated waves: Symmetrical upper and lower sidebands (modulated signals) with the carrier wave as the center.

So there are: carrier 700MHz, sum frequency 700MHz 1khz, differential frequency 700MHz 1khz.

This method is FSK frequency keying modulation.

FSK (Frequency-Shift Keying) - Frequency shift keying uses the frequency change of the carrier wave to transmit digital information. It is a digital modulation technology that uses the discrete value characteristics of baseband digital signals to key the carrier frequency to transmit information. FSK (frequency-shift keying) is an earlier modulation method used in information transmission, and its main advantages are:

It is easy to implement, and the anti-noise and anti-attenuation performance is better. It has been widely used in medium and low-speed data transmission. The most common is a dual-frequency FSK system that carries binary 1s and 0s with two frequencies.

There are two classifications of technically FSKs, incoherent and coherent FSKs. In the incoherent FSK, the transfer between instantaneous frequencies is two discrete values named Mark and spatial frequencies, respectively. On the other hand, in coherent frequency shift keying or binary FSK, there is no discontinuity in the output signal.

In the digital era, computer communication is transmitted on data lines (** wires, network cables, optical fibers or wireless media), which is carried out by FSK modulation signals, that is, the binary data is converted into FSK signal transmission, and in turn the received FSK signal is demodulated into binary data, and it is converted into a binary language represented by high and low levels, which is a language that the computer can directly recognize.