Xiang Xiangjun: Promoting the development of smart grid by advancing optical fiber communication technology

The development of smart grids has increasingly become an international consensus, and China’s smart grid construction is also in full swing. Recently, China has built an advanced and reliable fiber-optic communication network for electric power. The development of sensor networks is also progressing day by day. The integration of the two will further promote the development of smart grids characterized by real-time monitoring of signals and high-speed processing of data.

Prof. Xiangjun Xiang is Associate Dean of the School of Electronic Engineering of Beijing University of Posts and Telecommunications, Director of the Optoelectronics and Optical Information Research Center and Ph.D. Supervisor. He also serves as a senior member of the China Communications Society, Institute of Electronics, and Optical Society. He has been engaged in front-line research and teaching for many years. He has extensive experience in optical communications and optical sensors. Today we are fortunate enough to ask Prof. Que to answer questions about fiber optic communications.

1. A strong smart grid requires a highly reliable, high-bandwidth communications network. Optical fiber communication has the advantages of high bandwidth, strong anti-jamming capability, superior cost performance and Other incomparable communication technologies, and has become the first choice for smart grid communication network construction. As an institution specializing in information and communications, what is the latest research progress in the application of optical fiber communication technology in the field of smart grids at Beijing University of Posts and Telecommunications?

Zang Xiangjun: This question can be elaborated from two aspects. On the one hand, it is the research achievements of the University of Posts and Telecommunications in optical communication, and on the other is the application of some of the achievements of optical communication in smart electricity networks.

As we all know, the core network and the access network are two major parts of optical communications. The two are interdependent, promote each other, and coordinate development. At present, the systems with single optical carriers in the DWDM (Dense Wavelength Division Multiplexing) system in the core network with the rates of 10G and 40G have already been commercialized, and the next major push in the industry is the single-carrier 100G DWDM system. It is worth mentioning that 40G related technologies and markets have been firmly occupied by China. Based on this consideration, foreign equipment manufacturers have directly developed 100G DWDM systems, and they are already commercially available. From this perspective, the current domestic 100GDWDM system may be somewhat behind the level of foreign developed countries. Fortunately, no matter from the scientific research workers, mainstream equipment manufacturers and our government departments, the sense of crisis in this area is very strong. Many subjects have been set up in this direction, and considerable human and financial resources have been invested. Achievements.

As far as the University of Posts and Telecommunications is concerned, research results in optical communication are mainly manifested in the fields of telecommunication core networks and access networks. The research results in this area mainly refer to undertaking some major projects of the Ministry of Science and Technology, conquering a number of key technologies, and proposing relevant standards. Many of these technologies and standards have been adopted by domestic operators and even international telecommunications organizations for the application of results. A relatively good response has been achieved. The field of access network has recently achieved almost the same level of scientific research results as the international advanced research, mainly to adapt to the next generation of optical access network based on the new modulation format of the PON architecture and some of the key technologies and algorithms, these results are accelerated The layout of NG-PON2 (40G or 100G) has important guiding value.

I also have a national 863 project and I have achieved some results. Of course, the commercial operations of these achievements also need to be jointly promoted by operators and suppliers. However, at the academic level, these achievements have, to a certain extent, promoted the development of domestic optical fiber communication technologies. In terms of access networks, GPON (Gigabit-Capable PON) and EPON (Ethernet Passive Optical Network) are currently in commercial use. With the extension of the access network distance and the significant increase in bandwidth requirements, GPON and EPON are also facing a large margin. The expansion of the upgrade, this upgrade may have a substantial change in the implementation mechanism. The upgraded access network is generally referred to as next generation access network NGPON (next generation). Access rates within 10G are NGPON1; 10G, 40G, 100G, and even access to T (Trillion byte) levels are generally referred to as NGPON2. Now that the University of Posts and Telecommunications has achieved some results based on 100G research, research on Tbit access has also begun.

Application of some of the results of optical communications on smart grids: With the successful development of fiber-optic composite voltage cables in 2009, in the overall construction of smart grids, optical fiber to the home is becoming a trend. At present, PON has been recognized as a power consumption information acquisition technology. It not only has the characteristics of security and reliability, but also can provide up to several tens of G of access bandwidth, which can create conditions for power grid companies to develop richer broadband services in the future. The application of optical communication technology of the University of Posts and Telecommunications in the smart grid application is not very rich, which will also be the focus of our next work. We will fully utilize the advantages of the University of Posts and Telecommunications in access networks based on our strengths in the field of telecommunications, and actively promote the application of smart grid-related technologies.

2. We have learned that in information and communication, optical communication and wireless communication have their own advantages and disadvantages. The integrated application of the two may be a future development trend. Can you talk about your optical communication and Wireless communication convergence view?

Xiang Xiangjun: The integration of optical communications and wireless communications is the future development trend. We all know that the most important feature of fiber is stable, high-speed, long-distance and undisturbed. The most important feature of wireless is convenient use and flexible access. How to balance the advantages of both is always the focus of technical personnel research. This demand has become more pressing with new services such as wireless video calls. With multimedia wireless access, large capacity demands such as P2P file transfer have increased, and previous capacity has been unable to meet new demands. In view of this situation, operators have adopted a series of measures, such as the introduction of 4G communication technologies, but they still cannot avoid the problem of “limited wireless carrier frequency bandwidth”. This is a fundamental limitation. In addition, increasing the frequency of the wireless carrier frequency to 40 GHz or 60 GHz can significantly increase the wireless access bandwidth, but the wireless carrier coverage in this band is limited. Therefore, the combination of optical fiber and wireless has become a necessity: by adopting high carrier frequency wireless access in a small range, and then effectively extending the access range through low-cost optical fiber access, while avoiding the disadvantages of wireless high carrier frequency coverage. It also played the advantage of wireless smart, killing two birds with one stone.

This fusion system has been successfully developed in our laboratory demonstration system. Through this system, we can easily use the wireless access to enjoy Blu-ray DVD, that is, to use 60GHz wireless to bring the bitstream of Blu-ray DVD, and then to any destination via fiber, the wireless access rate can reach Gbit per second, the rate is very high . This technology can be applied to smart grids, and in the future it can also be used to monitor the relevant information of power transmission and distribution networks in real time, and even real-time monitoring video of all grid lines at high speed.

3, we understand that, compared with optical communication networks, optical sensor networks can use sensors to achieve a wide range of multi-point, multi-parameter monitoring. Can you tell us how multiple sensors make use of existing fiber-optic LAN technologies to form sensor networks? What is the significance of building a fully functional sensor network for grid intelligence?

Zhai Xiangjun: This issue is very important. This involves not only the networking mode after the smart grid, but also one of the important foundations for the realization of the “Internet of Things”. As far as the technology itself is concerned, it is also very important, because it is too close to the real life, especially with the advent of the smart age, the importance of the sensor will be further manifested.

To answer the first question, fiber-optic sensor networks collect information through sensors and transmit relevant data to the data center through optical fibers. Then rely on the data center data processing system to perform off-line or real-time processing of data collected by front-end sensors. This performs follow-up work, such as monitoring or monitoring, and if the sensor is placed on a transmission line, the status of the transmission line can be detected. For an actual sensor network, it mainly involves several aspects, one is the front-end acquisition system, the second is the intermediate transmission part, and finally the back-end processing part. In the transmission part, digital signals and analog signals may coexist, and different processing schemes are required at the data processing terminal. In addition, how to deploy and network a sensor network and how to integrate it with existing networks is also worthy of attention. At present, our research focuses mainly on the sensor itself. Due to the relatively large number of factors involved in the network, the work behind it is gradually unfolding.

Regarding the second question (What is the significance of building a fully-featured sensor network for grid intelligence), a full-featured sensor network involves many aspects. It may involve both fiber-optic sensor networks and wireless sensor networks. Is a fusion network of the two, as mentioned earlier, both have their own advantages. If this network is more complete, it will greatly promote the development of smart grid. At present, fiber-optic sensor networks used in smart grids (I'm still somewhat unprofessional, but as far as I know) can be mainly divided into two categories. One is for monitoring along the line, and more uses distributed fiber-optic sensor networks; Classes are used to monitor power grid equipment. Small-scale electrical equipment uses single-point sensing (this wireless or fiber-optic sensing is available). Large-scale electrical equipment uses distributed fiber-optic sensor networks.

For domestic power systems, the introduction of distributed fiber optic temperature sensing technology has just begun. For example, if we can monitor the temperature and pressure of power system cables, towers, and other facilities in real time, last year's snow disaster in the South will be able to provide timely risks and reduce the country’s economic losses. Our laboratory has long been devoted to the research of distributed optical fiber sensing, enabling three-in-one transmission of light, electricity, and sensors, and real-time online temperature measurement and pressure measurement. Its measurement accuracy has reached the world's advanced level, and a set of data terminal processing systems can be simultaneously real-time. Handle the data collected by nearly a thousand sensor heads at the same time.

4. With the continuous advancement of smart grid construction, the scale of fiber-to-the-home deployment will continue to expand, and the number of online optical cables will increase dramatically. In the large-scale, multi-user unit environment, how to maintain these optical cables is an urgent need to solve the problem. Do you have experience or research to share with us in fiber optic cable monitoring and maintenance?

Zhai Xiangjun: Before answering this question, first of all, I will mainly talk about the maintenance of fiber breaks in optical cables. It is necessary to simply distinguish the basic situation of optical cable applications. We know that there are mainly two kinds of application scenarios for optical fiber cables. One is the long-distance transmission cable used in the core network, and the other is the optical cable used in the passive optical network (PON). For the optical fiber cables in the core network, or long-distance optical cables, the current monitoring method mainly uses OTDR (Optical Time Domain Reflectometry) to detect the reflection points according to the principle of light resistance or reflection. If there is a problem on a certain line, the location of the problem can be determined by the optical signal delay and other variables, and then the professionals can fix it. For the access network, from the OLT (Optical Line Terminal) to the ONU (Optical Network Unit), also known as the feeder cable, the OTDR method can be used to locate and repair the broken part of the optical fiber. From the ONU to the user, the optical cable, which is also referred to as the wiring part, may be replaced directly without taking care of the cost.

However, with the upgrading of optical access networks (100G and even 1T access), on the one hand, the effective length of both the feeder and the wiring will be greatly extended. On the other hand, the split ratio will be 1:1000 or even higher. The split ratio gradually shifts, which means that there will be 1000 or more optical fibers in the splitter. This development trend presents new challenges for the future maintenance of fiber optic cable access networks. On the one hand, the fiber optic cable in the wiring part may be long-distance. If the broken wire is replaced by another method, the cost may increase significantly, and the repair may be more preferable. On the other hand, from the perspective of network management, it is hoped that the broken part can be automatically discovered, especially in developed countries such as Europe and the United States, where human costs are high, rather than human resources. We know that the OTDR is a good method for determining the location of the fault, but the use of the OTDR in such a large PON, that is, integration of the OTDR with the PON, is still faced with many difficulties.

Because the OTDR on the OLT is difficult to distinguish many optical fibers behind the SPLITER (split beam splitter), the current "propositional composition" has been focused on by some telecom operators. We will do our utmost to solve the problem and strive to achieve all the fiber or cable in the PON. Intelligent maintenance of fractures makes a contribution.

5. The FTTH pilot project for urban power is in full swing. In your opinion, if a series of related technologies such as power optical fiber communications and wireless communications are extended to rural areas and an intelligent rural power grid system is established, how can this be done? Promote deployment?

Xiang Xiangjun: Power fiber to the home is a very good concept and architecture. Its appeal is to receive the fiber directly at the same time, and this will greatly change the status quo of Internet access in the vast rural areas, and it will be even more commendable in China where rural areas lack electricity. We can achieve the greatest possible access to optical fibers while laying power lines, laying the foundation for future Internet access and even demand-side response. This is, of course, a follow-up statement, which also proves the necessity of powering fiber to the home from a certain perspective. This technology is likely to form the situation of “encircling the cities in the countryside” in the future, laying a solid foundation for the smart grid.

I think that when the State Grid Corporation promotes fiber-to-the-home in rural areas, it should pay attention to the difference between rural areas and cities, and at the same time make full use of fiber-to-the-home technical advantages and policy advantages in rural areas, especially in remote areas. We will vigorously promote the use of fiber-to-the-home power to complete the cost investment in a one-off manner, which will lay the foundation for the full deployment of smart grids in rural areas in the future.