What is the difference between single carrier and dual carrier network?

400G  The opportunity of OTN technology is that PMC digi-g4 is the highest density single-chip 4 × 100gott processor in the industry, and its port power has been reduced by more than half, which has solved the implementation requirements of encryption transmission technology supporting SDN, and met the capacity, security and flexibility of 400g line card in packet optical transport platform (p-otp), ROADM / WDM and optimized data center interconnection platform Please. In today's optical network connection, it is very important to provide support for bearer network. Facing the evolution of 400g optical network, it can be a situation in the near future.

The replacement of 100g to 400g is not to replace 100g with 400g, but to use 400g in appropriate scenarios. 100g still has its own advantages in transmission performance, for example, the transmission distance is longer than 400g, so the global OTN market will maintain the coexistence of 100g and 400g for a long time.

G.654. E fiber with large effective area and low loss is considered to be the best choice to support the next generation ultra-high speed, long-distance and large capacity transmission, and has become a hot topic in the industry. With the emergence of new services such as cloud computing, big data and high-definition video, as well as the upcoming trial commercial deployment of 5g services, network bandwidth pressure is increasing, and operators put forward higher requirements for single fiber capacity. Compared with the existing 100g system, 400g technology has the advantages of large bandwidth, low delay and low power consumption. It is an irresistible trend to deploy 400g system to meet bandwidth requirements.

Three transmission schemes of 400g in OTN network:

2x200g transmission scheme, 4x100g transmission scheme and 1x400g transmission scheme

Compared with the above three transmission schemes, they have their own characteristics and application scenarios. At present, the most widely used is the first 2x200g transmission scheme. The carrier and reactive power modulation of 200km-500am are realized in DMN.

We take 2x200g transmission scheme as an example to introduce the key technologies of 400g system.

PM-16qam Technology

This is a high order mode modulation scheme. PM refers to separating an optical signal into two polarization directions, and then modulating the signal to these two polarization directions for transmission. It is equivalent to the data processing of "1 divided into 2", and the rate is reduced by half.

16QAM means that one symbol represents four digital bits, which is equivalent to processing data in one part into four, and the rate is reduced by 1 / 4.

Carrier double light source technology

Single carrier only uses one frequency point; multi carrier uses several frequency points to transmit information. If N frequencies transmit information to one user, the rate can be increased by N times.

The 400g dual carrier carries out signal processing through DSP. One 400g is divided into two 200g pm-16qam signals, and one 200g occupies 37.5 GHz spectrum. In this way, 400g only needs 75 GHz spectrum and achieves the spectrum efficiency of 5.33 bit / S / Hz.

Variable grid ROADM Technology

Flexible packaging and intelligent scheduling of optical signals on the line are realized.

Variable grid means that the channel spacing is configurable and supports intervals starting from 37.5 GHz in steps of 12.5 GHz.

The variable grid is compatible with 50 GHz and 100 GHz wavelength grids at fixed intervals.

The service board supports 12.5 GHz wavelength tuning, and the combining and splitting board supports 12.5 GHz variable grid configuration, which can be packaged flexibly according to the signal size.

The optical signal can be reconstructed by ROADM to realize the intelligent scheduling of optical signal.

What is the difference between single carrier and dual carrier network?

With 5g's commercial use and the continuous emergence of new services such as cloud computing and big data, the pressure of network bandwidth is increasing sharply. Compared with the earlier 25g / 100g, 400g has the advantages of large bandwidth, low delay and low power consumption. Therefore, the deployment of 400g optical transport network (OTN) is the general trend. At present, 400g has three transmission technologies: single carrier, dual carrier and four carrier, which can realize 400g optical transmission network (OTN). Apart from the difference of carrier number, what are the differences among these three transmission technologies?

Overview of single carrier 400G Technology

Single carrier 400g technology adopts high-order modulation format, and builds 400g channel based on 400g pm-16qam, pm-32qam and pm-64qam. It is suitable for short-range applications such as metropolitan area network (man), data center interconnection (DCI) and other short-range applications (applications that do not require long-distance transmission but require large band tolerance).

Take 400G pm-16qam technology as an example. Among them, "PM" refers to separating a 400g (448gbit / s) optical signal into two polarization directions (x and Y directions), and then modulating the signal to these two polarization directions for transmission, as shown in the figure below. It is equivalent to processing the data in half. "QAM" refers to the process of separating X and Y signals. At this time, the rate is reduced by half, that is 224gbit / s. "16" means that X and Y signals are divided into four signals, and the rate is reduced from 224gbit / s to 56gbit / s. Some people will surely ask, why do we need to reduce the baud rate? Because from the current stage of circuit technology, 100Gbit / S is close to the limit of "electronic bottleneck". If we continue to increase the speed, a series of problems such as signal loss, power dissipation and electromagnetic interference are difficult to solve. Even if they are solved, they also need to pay a huge cost.

Advantages: compared with multi carrier light source technology, single carrier 400g technology is a relatively simple wavelength modulation solution with simpler structure, smaller size and relatively low power consumption. Moreover, it can provide network management. Because the single carrier 400g technology adopts a higher-order modulation format, it can improve the signal rate and spectrum efficiency by more than 300%, thus greatly expanding the network capacity to support more users. Moreover, it has a high degree of system integration, which can connect the individual subsystems into a complete system, so that they can work together with each other to obtain the best performance. In other words, single carrier is an economical and efficient solution.

Disadvantages: because single carrier adopts higher-order modulation format, it needs higher optical signal to noise ratio, which greatly shortens the transmission distance (less than 200 km). If the technology is not broken through, the application in long-distance transmission is not optimistic. At the same time, single carrier is easily affected by laser phase noise and fiber nonlinear effect.

Overview of 400G dual carrier technology

For the single carrier 400g technology, the dual carrier 400g adopts the 2 * 200g super channel technology scheme, which mainly constructs the 400g super channel through the modulation formats such as 8qam, 16QAM and QPSK, which is suitable for long-distance and complex man. Dual carrier 400g is mainly used for signal processing through DSP. One 400g optical signal is divided into two 200g signals, and one 200g occupies 37.5ghz spectrum. Thus, 400g only needs 75ghz spectrum, thus achieving a spectrum efficiency of 5.33bit/s/hz. The data baud rate of 400g (448 Gbit / s) signal processing is 448 ￣ 2 (dual carrier) ＋ 2 (PM) ＋ 4 (16QAM) = 28g baud.

Advantages: the spectrum efficiency of dual carrier 400g is improved by more than 165%. The system has high integration, small size and low power consumption. At present, the transmission technology has begun to be commercial, commonly used in 400g OTN. At the same time, compared with single carrier 400g, dual carrier 400g can transmit 500 km with a slightly longer transmission distance; when it is used with low loss optical fiber and EDFA, the transmission distance can reach more than 1000 km, which can basically meet the application requirements of long-distance transmission.

Disadvantages: Although the dual carrier 400g is used with low loss optical fiber and EDFA, the transmission distance can reach more than 1000 km, but it can not meet the ultra long distance transmission requirements of more than 2000 km.

Four carrier 400G Technology

Four carrier 400g technology means that four subcarriers (each carrying a 100g signal) use Nyquist WDM pdm-qpsk modulation method to create 400g channel, which is suitable for ultra long distance backbone network transmission.

Advantages: the technology of four carrier 400g is mature, and it has been used in commercial scale with low cost, and the transmission distance can reach 2000 km.

Under the condition of 400g spectrum compression chip, we can only solve the problem by introducing 400g spectrum chip and upgrading the system power consumption.

400g technology greatly improves the transmission bandwidth and distance of OTN network, making OTN network realize large bandwidth and long distance non relay transmission, which plays an important supporting role in the 5g commercial application of OTN network.

Challenges of 400G transmission

When 400g transmission technology is widely needed and developing rapidly, 400g transmission technology is also faced with diversified challenges. For example, with the gradual increase of modulation series, the decline of transmission distance requires high standard components. However, the current 100g transmission has gradually approached the transmission limit. Therefore, in the growing demand of multi subcarriers, the system's The complexity is doubling. Moreover, the spectrum efficiency and transmission distance become the main architecture contradiction of ultra-100g.