Why is multiplexing technology used in fiber optic communications?

In a data communication system or computer network system, the bandwidth or capacity of transmission often exceeds the need to transmit a single signal, and in order to effectively use the communication line, it is desirable to transmit multiple signals on one channel at the same time, which is the so-called multiplexing technology (multiplexii1g). The use of multiplexing technology can combine multiple signals to transmit on a physical channel, which can greatly save the installation and maintenance costs of cables when transmitting over long distances. Frequency Division Multiplexing (FDM) and Time Division Multiplexing (TDM) are two of the most commonly used multiplexing techniques.

The bandwidth of light is very wide, so it is necessary to use multiplexing technology.

Time-division multiplexing and wavelength division multiplexing, generally the baseband signal rate is low, and the channel is wasted, so time-division multiplexing is required; On the basis of time-division multiplexing, dense wavelength division multiplexing can be used to achieve a speed of several t/s

The main multiplexing techniques used are wavelength multiplexing and time multiplexing. Wavelength multiplexing is used for backbone networks and metro networks, wavelength multiplexing can increase the capacity of a single optical fiber several times, time multiplexing is now mainly used in the uplink of optical fiber access, this multiplexing can transmit more user information in one optical fiber, when the rate will be reduced.

The multiplexing technology used in optical fiber transmission is the technology of combining multiple low-speed channels into a high-speed channel, which can effectively improve the utilization rate of data links, so that a high-speed backbone link can provide services for a plurality of low-speed access links at the same time, that is, the network trunk can carry a large number of voice and data transmission at the same time.

1. Frequency division multiplexing.

It is to divide the total bandwidth used for transmission channels into several sub-bands (or sub-channels), and each sub-channel transmits one signal. Frequency division multiplexing requires that the total frequency width is greater than the sum of the frequencies of each sub-channel, and at the same time, in order to ensure that the signals transmitted in each sub-channel do not interfere with each other, an isolation band should be set up between the sub-channels, so as to ensure that the signals of each channel do not interfere with each other (one of the conditions).

2. Time-division multiplexing.

It is to divide the time provided to the entire channel to transmit information into several time slices (referred to as time slots), and assign these time slots to each signal source, and each signal occupies the channel in its own time slot for data transmission. Time-division multiplexing technology.

The characteristics are that the time slots are planned and allocated in advance and are fixed, so it is sometimes called synchronous time division multiplexing.

Its superior rubber point is a fixed time slot distribution, which is convenient for adjustment and control, and is suitable for the transmission of digital information; The disadvantage is that when a signal source has no data transmission, the channel corresponding to it will be idle, and other busy channels cannot occupy this free channel, so the utilization rate of the line will be reduced.

3. Code division multiplexing.

It is a multiplexing method that relies on different codes to distinguish each original signal, and is mainly combined with various multiple access technologies to produce various access technologies, including wireless and wired access. For example, in a multi-access cellular system, communication objects are distinguished by channels, and a channel only accommodates one user for talking, and many users who are talking at the same time are distinguished by each other by channels, which is multiple access.

The mobile communication system is a multi-channel system that works simultaneously, with the characteristics of broadcasting and large area coverage. Establish a wireless channel between users in the radio wave coverage area of the mobile communication environment.

Connection is a wireless multiple access mode, and the segment is not in the multiple access technology.

The main differences between multiplexed Fibre Channel and dedicated Fibre Channel nucleus hail:

Difference 1: The technology is different.

The dedicated method means that the two sides of the protection are directly connected by the fiber core, and a single fiber line is used in the center. The multiplexing method uses digital PCM multiplexing technology, and Liyanshi carries the existing Fibre Channel and microwave channels to protect the relay.

information.

Distinguish. Second, the laying method is different.

The dedicated mode requires a dedicated Fibre Channel for relay protection. The multiplexing mode uses the 64Kbit S digital interface to directly access the existing digital user network system through the PCM terminal equipment or the 2M interface, without laying optical cables, and the coarse volt transmission distance is also greatly improved, which can be extended to every communication point of the digital user network.

Distinguish. 3. The scope of protection is different.

Dedicated mode light receiving transceiver.

The working distance is limited and the cost of laying optical cables, and the communication distance is generally within 80km. The multiplexing method is mainly used for the protection of long-distance transmission lines.

The multiplexing technology used in optical fiber transmission is the technology of combining multiple low-speed channels into a high-speed channel, which can effectively improve the utilization rate of data links, so that a high-speed backbone link can provide services for a plurality of low-speed access links at the same time, that is, the network trunk can carry a large number of voice and data transmission at the same time.

Frequency Division Multiplexing (FDM) and Time Division Multiplexing (TDM) are two of the most commonly used multiplexing techniques. Frequency Division Multiplexing (FDM) Frequency division multiplexing divides channels by spectrum, with multiple baseband signals being modulated across different spectrums. Therefore they do not overlap in the spectrum, i.e. orthogonal in frequency but overlap in time and can be transmitted within a channel at the same time.

In a frequency-division multiplexing system, the signals M1(T) and M2(T) at the transmitter end are ,...Mn(t) ,... each carrier F1(T) and F2(T) through their respective low-pass filtersfn(t) is modulated, and then the corresponding sideband is filtered out by each bandpass filter (carrier** usually uses single-sideband modulation), and after adding, it forms a frequency-division multiplex signal. At the receiving end, the bandpass filter of each channel separates the signal from each channel and ,... with the carriers f1(t) and f2(t) of each channel respectivelyfn(t) multiplies to achieve coherent demodulation, which can recover each signal and realize frequency-division multi-channel communication. In order to construct large-capacity frequency division multiplexing equipment, the spectrum of the modern large-capacity carrier series is composed of various basic groups according to the modular structure.

According to the International Telegraph Advisory Committee (CCITT), the base group is divided into pregroup, base group, supergroup, and main group. The front group, also known as the 3-way group. It consists of 3 channels after frequency conversion.

The carrier frequency of each channel frequency conversion is 12, 16, 20 kHz respectively. Take the upper sideband and get a front group signal with a spectrum of 12 24 kHz. The base group, also known as the 12-way group.

It consists of 4 front groups after frequency conversion. The carrier frequencies of each pre-group conversion are 84, 96, 108, 120 kHz, respectively. Remove the sidebands to obtain a base group signal with a spectrum of 60 108 kHz.

The base group can also be composed of 12 channels after a frequency conversion. Supergroup, also known as 60 road group. It is composed of 5 base groups after frequency conversion.

The carrier frequencies of each base group are 420,468,516,564,612 kHz, respectively. Removing the sidebands, a superior signal with a spectrum of 312 552 kHz is obtained. The main group, also known as the 300-way group.

It is composed of 5 supergroups after frequency conversion. The carrier frequencies of each supergroup frequency conversion are 1364, 1612, 1860, 2108, 2356 kHz respectively. Removing the sidebands, the main group signal with a spectrum of 812 2044 kHz is obtained.

The 3 main groups can form a super-main group of 900 channels. 4 super-master groups can form a giant group of 3600 roads. The advantages of frequency division multiplexing are that the channel multiplexing rate is high, the number of multiplexing channels is allowed, and the shunting is also very convenient.

Therefore, frequency division multiplexing has become the most important multiplexing method in modern analog communication, and has been widely used in analog telemetry, wired communication, microwave relay communication and satellite communication.

Multiplexing technology is a technology that combines multiple low-channel channels into a high-speed channel, which can effectively improve the utilization rate of data links, so that a high-speed backbone link can provide services for multiple low-speed access links at the same time, that is, the network trunk can carry a large number of voice and data transmission at the same time. Time division multiplexing is to use the channel transmission time as the segmentation object, and the method of assigning non-overlapping time slices to multiple channels is realized, so time division multiplexing is more suitable for the transmission of digital signals. It is further divided into synchronous time division multiplexing and statistical time division multiplexing.

WDM is the frequency division multiplexing of light, which uses diffraction gratings in optical systems to synthesize and decompose multiple light wave signals of different frequencies.

Commonly used ones are frequency-division multiplexing, time-division multiplexing, and code-division multiplexing.

The use of Fibre Channel is divided into dedicated and multiplexed modes, and the dedicated mode refers to the direct connection of the two sides of protection with the fiber core, and the separate occupation of a pair of fiber cores. The multiplexing mode refers to the method of reconnecting multiple signals on a pair of optical fiber cores through a photoelectric conversion interface device and communication PCM. Each signal occupies 2M or 64K bandwidth.

Answer] :d The so-called wavelength division multiplexing is to divide the entire wavelength frequency band into several wavelength ranges, and each signal occupies a wavelength range for transmission. It belongs to special frequency division multiplexing.

The blind plexing method of multiplexing keys used in optical fiber communication is wavelength division multiplexing. The T1 system has a total of 24 voice channels, and each time slot transmits 8 bits (7 bits of coding plus 1 bit of signaling), so it shares 193 bits (192 bits plus 1 bit of frame synchronization). 8000 frames per second are transmitted, so the PCM primary group T1 data rate = 8000 193b s, where the data rate per voice channel is 64 kb s.

Also pay attention to e2, t2, e3, t3 rate questions, which are common concept questions.

1. Ordinary optical fiber, that is, single-mode optical fiber, is mainly composed of fiber core, cladding and coating layer, the fiber core is made of highly transparent materials, and the refractive index of the cladding layer is slightly smaller than that of the fiber core, thus causing a kind of optical waveguide ant hunger effect, so that most of the electromagnetic field is bound in the fiber core for transmission, and the role of the coating layer is to protect the optical fiber from water vapor erosion and mechanical abrasion, and at the same time increase the flexibility of the optical fiber.

2. Multiplexed optical fiber, i.e., multi-mode optical fiber, refers to the light that can transmit multiple modes. However, the inter-mode dispersion is large, which limits the frequency muffle of the transmitted digital signal, and it will be more serious with the increase of distance.

3. Single-mode optical fiber can only transmit single-mode signals, while multi-mode optical fibers can transmit multi-mode signals, and the disadvantage of multi-mode is inter-mode dispersion. Single-mode fiber can only transmit single-mode signals, while multimode fiber can transmit multi-mode signals.