I. Overview

Smart grid is to ensure safe and stable operation of power system came into being. Itis with the power system security and stability control systems, SCADAsystems are collectively known as the people security and stability ofpower systems of the three pillars. Oursmart grid after decades of ups and downs of the construction has begunto take shape, via satellite, microwave, carrier, cable and other meansof communication, build and become interchange communications network. As wireless communication technology, wireless communication system characteristics change dramatically. Viewof the wireless communication network is not dependent on power grids,and strong resistance to natural disasters, but also has the bandwidth,transmission distance, non-line transmission, etc., is very suitable tomake up the current means of communication, single, incomplete coverageof the defects . Here'sto a brief application of wireless communication transmission systemcharacteristics and advantages and disadvantages, and to analyze itsprospects in the power system.

Second, the wireless technology introduces

(A) the concept of wireless communication technology

Currently,wireless communications and application of information science andtechnology has become the most active research areas. The general by the wireless base stations, wireless terminals and application management server and other components.

(B) Development of wireless communication technology

Wirelesscommunication technology in accordance with the transmission distancecan be roughly divided into the following four techniques, namelyIEEE802.15-based wireless personal area network (WPAN), based on theIEEE802.11 wireless LAN (WLAN), wireless metropolitan area network basedon IEEE802.16 ( WMAN) and wireless wide area network based on IEEE802.20 (WWAN).

Overall,the long-range wireless access technology will be represented by: GSM,GPRS, 3G; short-range wireless access technology, includingrepresentatives: WLAN, UWB and so on. Mobility can also be divided in accordance with mobile access and fixed access. Fixedwireless access technology which are: 3.5GHz wireless access (MMDS),Local Multipoint Distribution Service (LMDS), 802.16d; mobile wirelessaccess technology include: Based on the 802.15 WPAN, 802.11-based WLAN,802.16 e, WiMAX, based on 802.20 WWAN. In accordance with the bandwidth of the wireless access can be divided into narrowband and broadband wireless access. Broadbandwireless access technology in which representatives of 3G, LMDS, WiMAX;narrow-band wireless access technology, representatives of first-andsecond-generation cellular mobile communication system.

1. Major wireless communication technology

Froma technical development trend can be seen to OFDM + MIMO wirelesscommunication technology as the core of the future of wirelesscommunications will become the mainstream of development direction. At present, the technology-based wireless communication technology are: B3G, WiMAX, Wi-Fi, WMN 4 kinds of technology.

2. Other wireless communication technology

Inaddition to the mainstream of wireless communication technology, thecurrent existing wireless communication technology also includes: IrDA,Bluetooth, RFID, UWB, cluster communications, and short-rangecommunications technology LMDS, MMDS, point to point microwave,satellite communications, and other long-distance communication technology.

(1)IrDA: Infrared Data Association, is the point to point data transferprotocol, communication distance is generally between 0-1m, the fastesttransfer rate up to 16Mbps, the communication medium for the wavelengtharound 900 nm near-infrared.

(2) Bluetooth:Bluetooth work in the global open 2.4GHzISM band, using frequencyhopping spread spectrum technology, communications media for the2.402GHz to 2.480GHz electromagnetic waves.

(3) RFID: Radio Frequency Identification, or RFID, commonly known as RFID. Itis a non-contact automatic identification technology, radio frequencysignal through the automatic target recognition and access to relevantdata. By the RFID tags, reader and antenna composed of three basic elements.

(4) UWB: Ultra Wideband, or UWB. UWBcommunication is also known as carrier-free baseband communications,nearly all digital communication systems, the required RF and microwavedevices rarely, it can reduce system complexity and reduce costs.

Third, the advantages and disadvantages of wireless technology

(A) WLAN Technical Analysis

Wi-Fi technology and products are already quite mature, and mass production. Thetechnology for wireless local area network, as an extension of wirednetworks, broadband applications for the particular location, althoughthe Wi-Fi technology is widely used, but still there is a certainsecurity, security risk, Wi-Fi uses a radio frequency (RF ) technology to send and receive data through the air. Becausewireless networks use radio waves to transfer data signals, it is veryvulnerable to attacks from outside hackers can compare easily withinrange of radio waves to steal data or even access to unprotectedintranet.

(B) WiMAX Technical Analysis

WiMAXis an advanced technology, introduced relatively late, there is a smallfrequency reuse, using low, but only recently completed thestandardization of the technology needed to promote large-scale practicetest. Prospects from the applicationperspective, the technology can meet online in a wide range requirementsmay include outdoor and indoor coverage, the signal can cover a largearea, even if a small number of base stations to cover the whole citycan be achieved. WiMAX technology because of itsadvanced and ultra-long transmission distance, has been optimistic aboutthe industry, the future development direction of mobile technology andprovides an excellent last-mile Internet access service.

(C) WMN Technical Analysis

WMNtechnology is being studied in research on different aspects ofcontinuous integration in the characteristics of fusion of varioustechnologies, and has no a mature product line to support large-scaleapplication of the technology. Fromprospect to see, WMN, not only in the emerging wireless broadband accessnetwork has a broad application space, in other areas such as combineddata, image acquisition module can be monitored on the target object ordata collection, and widely applied to environmental monitoring, industry, transportation and other fields. Constantlyupdated as other technologies improve, WMN better integration with it,complementary, which can exceed and play their respective advantages.

(D) 3G Technical Analysis

Proposed 3G standards in 1996, completed in 2000, including a complete upper-layer protocols, including standard-setting work. 3Gnetwork deployment already has considerable experience, there is acomplete theory of networking, including network link budget, the budgetpropagation model and computer simulation. Fromthe commercial prospects, at present, 3G in some areas have beenlarge-scale commercial applications, such as many European countries,Japan, Korea and so has built a 3G network. 3Gtechnology has entered a practical stage to, there are many countriesand regions are under construction or will be building 3G networks.

(E) LMDS Technical Analysis

LocalMultipoint Distribution Service System is to provide multipoint LMDSfixed broadband wireless access communication technology, frequency20GHZ over their work, the use of millimeter wave transmission, can beprovided within a certain number of duplex voice, data, Internet and video services, is a very good broadband fixed wireless access solutions. In the best case, the distance of up to 8 km; However, due to rainfall reasons, usually limited to 1.5 km distance.

Themain works by sector or base station equipment to ATM backbone networkfor the RF modulated base band signal transmission of information out inits coverage area to receive the many CPE ATM and RF the signal tobaseband signal, without the need for the Eachuser specifically laying fiber or copper cases, the realization oftwo-way symmetrical high-bandwidth wireless data transmission.

(F) MMDS Technical Analysis

Themain drawback of MMDS is blocking the signal quality problems and theimpact of vulnerability to climate change, available bandwidth is alsonot wide enough, no more than 200MHz. Secondly, MMDS very strict requirements on the transmission path. Modulationof the MMDS technology is primarily used in the phase shift keying PSK(including BPSK, DQPSK, QPSK, etc.) and quadrature amplitude modulationQAM modulation techniques, can not do non-sight transmission, in thepresent complex are difficult to promote the use of the urbanenvironment. In addition, MMDS is no uniform international standards, the manufacturers of equipment compatibility problems.

(G) of the cluster communication technology

Digitaltrunking system has many advantages, it has greatly improved spectrumefficiency can further improve the user capacity of the cluster system;it increases the signal capacity of resistance to channel fading, thewireless transmission quality changed for the better; the use of anumber of mature encryption theory and practical skills, so the digital system, the secrecy has greatly improved.

Digitaltrunking mobile communications system can provide operational services,digital voice signal, that in addition, users can transfer digitalimage information. The net transfer of a unified digital signal, thus greatly enhancing the cluster network services.

(Viii) technical analysis point to point microwave communication

The advantages of microwave transmission in the following aspects: First, operators can reduce operating costs. Compared with leased lines, microwave systems as long as a year or so investment can be recovered. Second, the microwave transmission system deployment simple and fast. Comparedwith the traditional means of transmission, the advantages of rapiddeployment of new services more quickly to meet the needs of thedevelopment. Third, the currentdevelopment of microwave products for the future is guaranteed, for thenew business operators and new requirements can give good support. Thefuture, microwave transmission system will be upgraded to fullIP-platform, operators can fully support the future development.

(Ix) Analysis of satellite communication technology

Satellite population is not very dense in some areas to cope with terrestrial communications. Scatteredin these areas, but not intensive wide range of users, we can usesatellites as a user connected to a fixed wireline network accessfacilities. Terrestrial communication networkshave been constituted in the broadband multimedia network environment,the use of satellite broadband satellite access system is built betterand practical solutions, economical and reliable.

But,after all, is the use of satellite communications satellites ascommunications platforms, and its ground station building, rental costsare communication channels need to spend a lot of money, andcommunication resources for the satellite communications company,subject to its bandwidth limitations, making the transmission of largeamounts of data need to pay a very high price. Therefore,as everyday life and production is extremely uneconomical use; andsatellite communications as emergency communications, combatcommunications, are more suitable for overseas communications.

Fourth, comprehensive comparison of wireless technology

Various technologies in wireless communications become increasingly clear complementarity. Thiswas reflected in different access technologies with different coveragefor different regions, different technical characteristics, differentaccess rates. Solve the wide area 3G coverage andseamless roaming strong demand for mobility, WLAN resolve thelonger-distance high-speed data access, while UWB can achieveultra-high-speed wireless access at close range.

Firstof all, from the standardization point of view, the technology involvedin this report, only the technology is not mature WMN standard system,LMDS, MM-DS, the cluster has a variety of communication standards, butthere is no uniform international standards, the rest of the technologyare standardization work has been completed, and have carried out a trial network construction and building business networks.

Fromthe frequency point of view, Wi-Fi technology, WMN are using openspectrum, WiMAX technology, 3G technology and other technologies usinglicensed spectrum.

From thecoverage point of view, Wi-Fi technology, WMN technology is the wirelessLAN access technology, only covers 35m-100m; WiMAX technology, 3Gtechnology, LMDS technology, MMDS technology, cluster communications areMAN access technologies, coverage In the 1km-54kmrange, and satellite communications, point to point microwave belongsto WAN technology, typically used for communications backbone networkconstruction.

Transfer rate fromthe point of view, microwave and satellite communications are point topoint trunk transmission technology, different rates of change in thelarger situation, and the rest of the technology are access technology,3G technology is only the minimum access speed, only 384k, but M are dozens of other technologies or even hundreds of M's rate.

Fromthe modulation point of view, in which Wi-Fi technology, WiMAXtechnology, WMN, 3G technologies are using the latest modulationtechnique OFDM, the rest of the technology were not using OFDMmodulation.

Antenna technologyfrom the point of view, only 3G and WiMAX technology uses MIMOtechnology, and other techniques were not using MIMO technology; theenvironment from the transport point of view, only the WiMAX technologyand 3G technology to support non line of sight transmission, and theremaining technologies require line of sight transmission environment;from the point of view of network security and QoS mechanisms, WiMAXtechnology and 3G technology in this area have done quite good, perfect,all the rest there is a big problem.

V. Application and Prospect of wireless technology

Atpresent, the grid power system communication still has a high transferrate, high bandwidth, high reliability and other characteristics of theoptical fiber communication based, but with the power of the disasterresponse, distribution automation, demand for business intelligence andother proposed wireless Communicationwill be its rapid deployment, and other characteristics are not seekingto limit the ground in the power system communication applications. Therefore,the wireless communications power systems can be an importantsupplementary means of communication, in order to build an integratedpower system communication network to provide a very important part.