Broadband access scheme based on power line

0 Introduction
Modern telecommunications is moving towards broadband, integration and personal development, the explosive development of the Internet has changed people's way of life, people no longer content to call, watch TV, but there are many new two-way interactive business, such as: E-mail, video-on-demand, home shopping, distance teaching, remote diagnostics, Conference TV, High-speed data fax and so on. These types of business are many, and require high quality, high-speed transmission, which gives the entire telecommunications network, computer networks, "The last kilometer," the bottleneck of communication constraints posed a huge challenge. Optical fiber to the Home (FTTH) is the future of the user network is the inevitable direction of development, however, because the cost of optical fiber user network is too high, for a long time in the future, most users will still not be able to fully use optical fiber, so in recent years there have been a variety of transitional broadband access network technology, so far, there is still no perfect solution, Each program has its own advantages, and each has its own shortcomings.
1 Current main access network technology
In many scenarios, ADSL technology using the original telephone lines, without modification can transmit high-speed data (downlink 12.5-8mb/s, uplink 16-640kb/s), the local Dslam after reuse and ATM network adaptation, is a traditional carrier development network special fancy of the program, But ADSL provides the bandwidth is not too high, the actual use of the opening rate is not high, affecting its large area of promotion.
Hfc+calbe Modem program, make full use of a wide range of coaxial cable, can provide higher bandwidth, high-speed data and analog TV cable, multi-channel, cheap. However, both theoretically and practically, this scheme can not get rid of the noise to the data and language of the serious interference of the shadow, to ensure the system's QoS, but also to carry out the transformation of the coaxial two-way network.
The use of pure IP technology, 10m/100m Ethernet directly into the family of the scheme is not low three new access scheme, high bandwidth, seamless connection, real high-speed Internet access, but the current IP phone is not mature enough, optical path utilization is not high, the reliability of optical transmission is not too high.
Atm-pon technology is a promising development direction, can truly achieve voice, data, video business integration, but at present, Apon is not mature, the price is also high.
2 Broadband access scheme based on power line
In many of the transitional programmes, how to build a comprehensive, economic, reliable, effective communication network, not only to meet the current broadband services, but also for the future, support the growing number of users, greater bandwidth and new business, to avoid unnecessary duplication of investment, is an important topic.
Electricity is one of the most popular and essential networks in every network nowadays. If the electricity and information can be combined to make full use of the integrated business of voice, video, data and so on, it is the most convenient, concise and economical to develop and make use of power line resources all over the tens of thousands of households to form the information exchange terminals and realize broadband access based on the electric network. It is of great significance to improve the economic benefit of the power system or widen the channel of people's access to information and reduce the cost of communication.
(1) Breakthrough of new technology
Since the 1990s, with the development of communication technology, power line carrier technology has made a great breakthrough. North Telecom (Nortel Telecom) and the United Kingdom Joint Public Utility (Norweb) announced in October 1997 that its newly developed DPL technology (digital distribution line carrier technology) implemented remote communication on the distribution network, In order to convert the Low-voltage power line into the ready-made channel of the information superhighway, the low voltage network transmits the modulated Internet data rate over 1mb/s, which is 10 times times faster than ISDN, and is 20 times times faster than the high-speed modem connected with the ordinary telephone line. Since then, many of the world's well-known communications companies have been researching and developing DPL technology, aimed at increasing its communication rate, at present, the world's leading companies in the United States Intellon Company has developed in the power line data transmission rate of up to 14mb/s communication system. There is no difficulty in transmitting audio, video on demand and real-time TV at such a rate, so DPL technology has aroused wide concern.
The DPL technology uses improved Internet Protocol (IP) and complex dedicated electronic devices to transmit MHz high-frequency digital communication signals on low-voltage power grids while monitoring pulse signals and other forms of interference that cause information distortion. Data transmission is not as easy to be disturbed as voice communication, as it is packaged and transmitted, rather than transmitted as a continuous stream of signals. In addition, IP can be guaranteed to be affected by the noise of the package can be transmitted again. At the same time, due to the use of digital duplex equipment and the application of modulation process, the available communication bandwidth has been increased to 100 times times.
At present, the DPL technology is to modulate the distribution cable system so that it can transmit two or even multiple signals at the same time without any mutual loss. The frequencies of these signals are wide, ranging from ultra-low frequency (e.g. 50/60hz) to UHF (e.g. 500/600mhz). The modulation of the technique is achieved by installing a three-outlet directional coupling modulation unit (CU) at the corresponding network interconnection point, the CU consists of a network outlet (NP) with interconnected high-pass and Low-pass filters, a communication distribution outlet (CDP), and a frequency-division direction coupler for a Power distribution outlet (EDP).
The use of a certain amount of CU on a low-voltage grid constitutes the so-called high-frequency modulated Power network (HFCPN). A typical HFCPN is characterized by high stability and strong tolerance to noise. The goal of DPL technology is to convert a low-voltage power grid into a local area network (LAN) that transmits high-speed data information through HFCPN, with the aim of making access to the Internet as convenient as using a telephone.
(2) Broadband access scheme based on power line
DPL technology can provide users with end-to-end data Services, data from local substations through the Low-voltage distribution network directly to the user home or small and medium-sized companies. Thus, from the communication point of view, the DPL technology is to transform the low voltage distribution network to the carrier information LAN (LAN).
The main hardware device of typical client is DPL coupling unit and Remote DPL Communication module. The DPL coupling unit separates the information data from the power frequency electricity and connects with the remote DPL Communication module through the cable. There are 3 communication interfaces at the other end of the remote DPL Communication module, the first interface is connected with the computer network card through the medium of twisted-pair, thin cable, and can realize the mutual conversion between the private networking protocol (such as IEEE 802.14 Protocol) and the common protocol (such as IP protocol) followed by the network port in the Low-voltage distribution network. So that the computer can use the Low-voltage distribution network to communicate without the addition of modules; In addition, the set-top box can be connected with the TV, the user can download VOD or MP3 program through the TV. The second interface is connected with the ordinary telephone through the audio cable, which realizes the switch between the IP voice packet and the standard voice signal, so that the ordinary telephone can realize duplex communication on the Low-voltage distribution network, so the telephone service of the IP communication mode is no longer limited to the current long-distance telephone service. The third interface provides a data channel for user automation information, in order to realize the remote automatic copy of the three tables and the remote control of the home intelligent equipment, and with the opening of the electric power market, the intelligent electric meter connected with the power information network can be used for electricity settlement and electricity control according to the real-time electricity price, so as to realize the automation management conveniently.
The main hardware equipment of substation is DPL coupling unit, local DPL communication module and IP switch equipment. Similar to the client side, the information data is separated from the power frequency by the DPL coupling unit and enters the DPL communication module through the cable. The local DPL Communication module converts the information from the special protocol of the Low-voltage distribution network into the IP protocol packet, and then enters the IP switch. The IP switch separates various kinds of information according to the IP address of the data, in which: the user automation information connects the user Automation information management system, the IP voice packet transforms the standard voice signal into the public telephone network through the gateway, the Internet information directly connects with the Internet network. The IP switch of the branch has the function of router and gateway, it transmits the data by detecting the IP address of the packet, and can manage the network. The IP switch also has a server that provides local information services. Information data from other power line coupling units of substations are connected with IP switches through their respective local communication modules, and the exchange of user automation information, voice information and Internet information with the outside world is realized through IP switch.
3 Key Technologies
DPL Communication module is the key equipment to realize this scheme, it not only has the function of modem to realize the transmission of high-speed information data on power line, but also has powerful communication interface to provide multimedia integrated service.
(1) Interface between carrier information network and computer networks
Since the information of the same side of the transformer does not necessarily need to be sent to the other side, the DPL communication module must have the function of the LAN data forwarding, that is, the function of the Network Bridge. In the Low-voltage distribution network, the user to the front end of the distance often a few kilometers, which makes the user end to the front-end signal transmission delay increase, which determines the user computer and front-end network communication can not use the common LAN protocol, but must adopt a dedicated network protocol, such as IEEE 802.14 protocol. This requires the DPL communication module to send the cable section of the use of IEEE 802.14 protocol data through the layer layer after the packet to submit the network layer, subsequently, the Ethernet protocol layer is packaged and forwarded to the computer network interface, and the data sent by the computer is forwarded to the Low-voltage distribution network after the corresponding inverse operation.
(2) interface between carrier information network and telephone network
The telephone signal transmitted on the Low-voltage distribution network is actually a voice packet based on IP technology. The DPL Communication module receives the standard voice signal, after digitized processing and compressing, then divides into the standard IP voice packet, transmits through the Low-voltage distribution network to the destination's other DPL communication module, carries on the reverse operation to the network packet, converts it to the standard voice signal. The client's DPL communication module is connected with the user's telephone and PC, and the DPL communication module of the substation is connected to the public telephone network and the Internet respectively, so the users of the Low-voltage distribution network can realize the communication of telephone to telephone, PC to PC, PC to telephone by the DPL communication module.
(3) Information over the transformer measures
Information over Transformer is a difficult point, although the new technology bidirectional power-frequency communication solves the problem of transmitting data directly across the transformer, the technology is only suitable for the lower frequency mode of modulating signal frequency 3-7 times, and for the MHz modulation signal discussed in this paper, the bypass capacitor is considered, The use of additional cables or the use of appropriate wireless devices, and other measures to solve. In addition, each transformer can be considered as a local information processing center, the processing of information directly connected to the broadband backbone or the telephone network, the Internet and Power information network, that is, the use of power carrier line to solve the "last kilometer" scheme.
(4) Other
For an Access TV network, the backbone should be a bandwidth backbone (SONET or ATM) first. Because the video compression standard MPEG-2 needs 4-6MB/S transmission rate, so the local access network must satisfy this transmission rate, when DPL technology will increase the transmission rate to this rate, only then can satisfy the request, then uses the set-top box to connect with the television in the client, then can watch the television program through the Low-voltage distribution network.
In addition, because the power carrier line is not shielded line, high-frequency signal radiation is also a problem that can not be neglected, such a defect, if properly resolved, will be based on the implementation of broadband access scheme is of great significance.
4 concluding remarks
The biggest advantage of broadband access based on power line is that it can make full use of the existing power grids, avoid duplication of investment and waste, especially in the distribution of more dispersed households and remote users. Another advantage is that the power grids within each user naturally constitute the local area network, which makes it simple and feasible to control the household intelligent equipment through the network.
With the continuous socialization of power system communication and the rapid development of new technology of powerline communication, it is believed that one day, broadband integrated service access based on Powerline will eventually become a reality.