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1、英文文献The Application of one point Multiple Access Spread Spectrum Communication SystemLiu Jiangang, Nanyang City, Henan Province Electric Power Industry Bureau【ABSTRACT】Spread Spectrum Digital Microwave communication as a communication, because their excellent performance have been widely used. The a
2、rticle in Nanyang City Power Industry Bureau one point Multiple Access Spread Spectrum Communication System as an example. briefed the spread spectrum communications, the basic concept and characteristics of the power system communication applications.KEYWORDS ：one point multiple access; Spread-spec
3、trum communication; Attenuation Nanyang City in the outskirts of Central cloth 35 to 11 kv substation farm terminals, their operation management rights belong to the Council East, Rural Power Company west (the eastern suburb of agricultural management companies - four, the western suburbs of Rural P
4、ower Company Management 7), Scheduling of the various stations of the means of communication to the original M-150 radio and telephone posts. 2002 With the transformation of rural network, the remote station equipment into operation and communication channels to put a higher demand .As PUC Dispatch
5、Communication Building to the east and west of farmers - the difference between a company linked to fiber, Therefore, if 11 substations and the establishment of a transfer Link Building links Point may be the data and voice were sent to two rural power companies dispatch room, Rural Network scheduli
6、ng for the implementation of automation to create the necessary conditions.Given the status and power grid substation level, nature, taking into account the carrier and optical-fiber communications to conduct multiple forwarding, increasing the instability factor, considering the cost and conditions
7、 of the urban construction, Finally decided to adopt wireless spread-spectrum technology to establish that 11 farm terminal substation communication system. This paper describes the spread spectrum technology and the current system of the building.1. The basic concept of spread-spectrum communicatio
8、n.Spread Spectrum Communications basic characteristics, is used to transmit information to the signal bandwidth (W) is far greater than the practical information required minimum (effective) bandwidth ( F) , as the ratio of processing gain GP .GP = W/F As we all know, the ordinary AM, FM, or pulse c
9、ode modulation communications, GP values in the area more than 10 times, collectively, the narrow-band communication, and spread-spectrum communications GP values as high as hundreds or even thousands of times, can be called broadband communications. Due to the spread-spectrum signal, it is very low
10、 power transmitters, transmission space mostly drowned in the noise, it is difficult to intercepted by the other receiver, only spreading codes with the same (or random PN code) receiver, Gain can be dealt with, and despreading resume the original signal. 2. The technology superiority of spread-spec
11、trum communication .Strong anti-interference, bit error rate is low.As noted above, the spread spectrum communication system due to the expansion of the transmitter signal spectrum, the receiver despreading reduction signal produced spreading gain, thereby greatly enhancing its interference toleranc
12、e . Under the spreading gain, or even negative in the signal-to-noise ratio conditions, can also signal from the noise drowned out Extraction, in the current business communications systems, spread spectrum communication is only able to work in a negative signal-to-noise ratio under the conditions o
13、f communication. Anti-multi-path interference capability, increase the reliability of the system. Spread-spectrum systems as used in the PN has a good correlation, correlation is very weak. different paths to the transmission signal can easily be separated and may in time and re-alignment phase, for
14、mation of several superimposed signal power, thereby improving the systems performance to receive increased reliability of the system. Easy to use the same frequency, improving the wireless spectrum utilization.Wireless spectrum is very valuable, although long-wave microwave have to be exploited, an
15、d still can not meet the needs of the community. To this end, countries around the world are designed spectrum management, users can only use the frequency applications, rely on the channel to prevent the division between the channel interference. Due to the use of spread-spectrum communication rela
16、ted receive this high-tech, low signal output power ( a W, as a general-100 mW), and will work in the channel noise and thermal noise in the background, easy to duplicate in the same area using the same frequency, can now all share the same narrow-band frequency communications resources.Spread spect
17、rum communication is digital communications, particularly for digital voice and data transmission while, spread spectrum communication with their own encryption, only in the same PN code communication between users, is good for hiding and confidential in nature, facilitating communications business
18、. Easy to use spread-spectrum CDMA communications, voice compression and many other new technologies, more applicable to computer networks and digitization of voice, image information transmission. Communication is the most digital circuits, equipment, highly integrated, easy installation, easy main
19、tenance, but also very compact and reliable. The average failure rate no time was very long. We have decided to adopt the spread-spectrum communication technology construction of 11 farm terminal substation communications system, Due to the spread-spectrum communication by the line-of-sight transmis
20、sion distance restrictions, has become unstoppable system design premise. If the PUC scheduling Building and 11 substations have stopped, and the problem becomes more complicated, use spread spectrum system on the feasibility greatly reduced. Therefore, we look at the city Aerial topographical map,
21、initially identified has not stopped to consider systems design, and requests the companies used this equipment Spread Spectrum 11 points transmission routing of the measured and the results have been satisfactory.Then spread spectrum wireless equipment market supply of cash, Initially, we selected
22、a series of Spread Spectrum Comlink third generation products. Because most of the point-to-point mode, Merit function of the spread-spectrum equipment in a point-to-multipoint application environments encountered many problems : First is the issue of frequency resources. Even a minimum of 64 kbit /
23、 s data rate radio, space also occupied bandwidth 5 MHz, Because 32 of the PN code isolation is only about 15 dBm, the project had to use frequency division multiple access 35 db to get around the theoretical isolation. 11 stations will use 11 frequency, frequency greater waste of resources. Comlink
24、 and Spread Spectrum products in the same frequency to achieve a point-to-multipoint communications. Second antenna erection problems, point-to-point equipment for the main radio station, the main station need to set up a number of terminal antennas, the vast majority of domestic engineering compani
25、es used by the U.S. Conifer 24 dBi parabolic semi-cast magnesium grid directional antenna. vertical polarization - 1 m wide, it is difficult to top the layout and avoid flap flap and the mutual interference, Although the project can be set up to take stratified, or through cooperation and on the roa
26、d to one or more omnidirectional antenna launch, However, as construction of a road and the signal attenuation, transmission result is not satisfactory. In addition, the RF cable laying, The application of network management software such factors we have also decided to adopt the final 1:00 Comlink
27、Multiple Access Spread Spectrum products. Its system configuration, as shown in Figure 2:3. Routing AnalysisCombining visual distance access and use the radio and antenna gain, cable attenuation and environmental factors, and testing the design is reasonable, determine the attenuation affluent chann
28、el capacity. Spread spectrum microwave link attenuation depends on the reliability margin.Attenuation margin calculation formula : FG= GSG + GANT - LGL - LPL FGAttenuation margin ； GSGSystem Gain (dB）； GANTAntenna Gain (dBi）； LGLConnectors and cables attenuation (dB)； LpL Channel attenuation (dB）。 G
29、ain spread spectrum radio system : GSG = +27 - (-97) = 124 (dBm)； Antenna Gain : master-use 2.4 GHz, 12 dBi Omni-Directional Antenna, stop-use 2.4 GHz, 24 dBi parabolic directional antennas; Connector and cable attenuation : cable attenuation of about 3 dB, as a joint dB attenuation, LGL = 3 + 1 = 4
30、 (dB); Channel attenuation to the farthest distance from the building scheduling substation (27 km) as an example : LPL = 92.4 + + 20lg27 20lg2.4 = 128 (dB); Therefore attenuation cushion : FG = 124 + 12 + 24-2 4-128 = 24 (dB). Calculated from the amount of affluent link can be seen, the program has
31、 larger reserves and thus the rational design of the program, According to the measured and the results showed the channel can ensure quality and reliability. 4. Operation of the system.System since May 2003 has been put into operation more than two years, each station to transmit information, there
32、 are two phones, 600 or 1200 Porter remote information operations, clear voice station, Channel stability, without error, System not had any serious interruptions and failures, equipment operating normally. Thus, the spread spectrum link to the design and equipment selection has been very good to me
33、et the voice and remote automated information transmission, Network for the safe and stable operation to provide a reliable guarantee.5. Concluding remarks .Spread-spectrum technology in the initial stages of development, it has become a theory and a major technological breakthrough, Later in the de
34、velopment process is the improvement and hardware performance improved. Development to the present, spread-spectrum technology and the theory has been almost perfect, mainly from the point of view of overall performance, and other new technology applications. Therefore, the application has been driv
35、en by the development of spread-spectrum technology is a powerful driving force, the future wireless communication systems, such as mobile communications, Wireless LAN, global personal communications, spread spectrum technology will certainly play an important role. Although fiber technology in the
36、power system communication applications become increasingly common. But the county power communication network or higher cost-effective communications network, 1:00 Multiple Access microwave communications will continue to play an important role in spread spectrum technology and will enjoy even broa
37、der application of space.中文文献一点多址扩频通信系统的应用刘建刚 河南省南阳市电力工业局【摘要】扩频通信作为数字微波通信的一种，由于其本身具备的优良性能而得到广泛应用。该文以南阳市电力工业局一点多址扩频通信系统为例，简要介绍了扩频通信技术的基本概念、特点及其在电力系统通信中的应用。 关键词：一点多址；扩频通信；衰耗 在南阳市郊区环布着11座35 kv农用终端变电站，其运行管理权分属市局东、西郊农电公司（其中东郊农电公司管理4座，西郊农电公司管理7座），调度到各站的通信方式原为150 M无线电和邮电市话。2002年随着农网改造的进行，各站远动设备投入运行，对通信通道提出
38、了更高要求。由于市局调度通信大楼到东、西郊农电公司之间分别有光纤相连，故如果这11座变电站建立了和调通大楼的联系，则可将各站数据和话音分别送往两个农电公司调度室，从而为农网调度自动化的实施创造必要的条件。 鉴于电网现状和变电站的等级、性质，考虑到载波和光纤通信要经过多次转接，增加了不稳定因素，综合考虑成本及市区施工条件，最后决定采用无线扩频技术建立这11座农用终端变电站的通信系统。本文简要介绍了扩频技术及在此次系统建设中的应用。 1 .扩频通信技术的基本概念 扩频通信的基本特点，是其传输信息所用信号的带宽（W）远大于信息本身实际所需的最小（有效）带宽（F），其比值称为处理增益GP GP = W
39、/F 众所周知，在普通的调幅、调频或脉冲编码调制通信中，GP值一般都在十多倍范围内，统称“窄带通信”，而扩频通信的GP值高达几百甚至几千倍，可以称为“宽带通信”。 由于扩频后的信号，它的发射功率很低，传输时大多淹没在空间的噪声中，因此很难被其它接收机截获，只有具有相同扩频码（或称PN随机码）的接收机，才能获得处理增益，解扩并恢复出原发的信号。 2. 扩频通信技术的优越性 抗干扰性强，误码率低。如上所述，扩频通信系统由于在发送端扩展信号频谱，在接收端解扩还原信号，产生了扩频增益，从而大大地提高了抗干扰容限。根据扩频增益不同，甚至在负的信噪比条件下，也可以将信号从噪声的淹没中提取出来，在目前商用的
40、通信系统中，扩频通信是惟一能够工作于负信噪比条件下的通信方式。 抗多径干扰能力强，增加了系统的可靠性。由于扩频系统中采用的PN码具有很好的自相关性，互相关性很弱，不同路径传输来的信号能容易地被分开，并可在时间和相位上重新对齐，形成几路信号功率的叠加，从而改善了接收系统的性能增加了系统的可靠性。 易于同频使用，提高了无线频谱利用率。无线频谱十分宝贵，虽然从长波到微波都已得到开发利用，仍然满足不了社会的需求。为此，世界各地都设计了频谱管理机构， 用户只能使用申请获得的频率，依靠频道划分来防止信道之间发生干扰。 由于扩频通信采用了相关接收这一高技术，信号发送功率极低（ 1 W，一般为1100 mW）
41、，且可工作在信道噪声和热噪声背景中，易于在同一地区重复使用同一频率，也可以与现今各种窄带通信共享同一频率资源。 扩频通信是数字通信，特别适合数字话音和数据同时传输，扩频通信自身具有加密功能，只能在PN码相同的用户之间进行通信，隐蔽性好，保密性强，便于开展各种通信业务。扩频通信容易采用码分多址、语音压缩等多项新技术，更加适用于计算机网络以及数字化的话音、图像信息传输。 扩频通信绝大部分是数字电路，设备高度集成，安装简便，易于维护，也十分小巧可靠，平均无故障率时间也很长。 在我们决定采用扩频通信技术建设这11座农用终端变电站的通信系统之后，由于扩频通信的传输距离受到视距的限制，阻挡就成为系统的设计
42、前提。若市局调度大楼和11座变电站之间有阻挡，则问题就变得较为复杂，选用扩频系统的可行性就大打折扣。因此，我们查看了我市航测地形图，初步确定没有阻挡才考虑进行系统设计，并请有关公司用扩频设备对这11个点的传输路由进行了实测，结果令人满意。 根据当时市面上无线扩频设备现货供应情况，我们初步选定了Comlink扩频系列第三代产品。因为大多数在点对点方式下，功能优异的扩频设备在一点对多点的应用环境中遇到许多问题：首先是频率资源问题，即使最低64 kbit/s数据速率的电台，空间带宽也要占用5 MHz，由于32位PN码的码间隔离度只有15 dBm左右，所以工程上不得不采用频分多址，以获得35 db左右
43、的理论隔离度。11个站就要使用11个频点，频率资源浪费较大，而Comlink扩频产品可在同一频点实现一点对多点通信。其次是天线架设问题，点对点设备，对于主站的多个电台，需要在主站端架设多个天线，国内工程绝大多数采用美国Conifer公司24 dBi的半抛物面铸镁栅格定向天线，垂直极化面展宽1 m，很难在塔顶布置且避开侧瓣和后瓣的相互干扰，虽然工程上可以采取分层架设，或是通过合路器并至一个或多个全向天线发射，但由于施工及合路器的信号衰减等原因，传输效果并不理想。此外，射频电缆的铺设、网管软件的应用等因素也使我们最后决定采用Comlink一点多址扩频产品。其系统配置，如图2所示。 3. 路由分析
44、待添加的隐藏文字内容1结合可视通道距离、选用的电台、天线增益、电缆衰耗及环境因素，检验设计是否合理，确定通道的衰耗富裕量。扩频微波链路的可靠性取决于衰减裕量。 衰减裕量计算公式FG= GSG + GANT - LGL - LPL 式中 FG衰减裕量； GSG系统增益(dB）； GANT天线增益(dBi）； LGL接插件及电缆衰耗(dB)； LpL通道衰耗(dB）。 扩频电台系统增益：GSG = +27 - (-97) = 124 (dBm)； 天线增益：主站端选用2.4 GHz，12 dBi的全向天线，分站端选用2.4 GHz，24 dBi的抛物面定向天线； 连接头及电缆衰耗：电缆衰耗约为3
45、dB，接头衰耗为1 dB，LGL= 3 + 1 = 4 (dB)； 通道衰耗，以距离调度大楼最远的变电站（27 km）为例：LPL = 92.4 + 20lg2.4 + 20lg27 = 128(dB)； 因此衰减余量为：FG= 124 + 12 + 24 - 24 - 128 = 24 (dB)。 从计算出的链路富裕量可以看出，该方案有较大储备，因此本方案设计合理，并根据实测结果表明可保证通道的质量和可靠性。 4. 系统运行情况 系统自2003年5月投入运行至今已有两年多时间，每站传输信息有两路电话、600或1200波特的远动信息一路，各站话音清晰，通道稳定，无误码，系统未出现过严重中断和故
46、障，设备运行正常。因此，该扩频链路的设计及设备选型已很好地满足了话音及远动自动化信息的传输要求，为电网的安全稳定运行提供了可靠保证。 5 结束语 扩频技术在发展的初始阶段，就已经实现了理论和技术上的重大突破，在此后的发展过程中主要是硬件的改善和性能的提高。发展到现在，扩频技术理论和技术都已趋于完善，主要应从系统的角度考虑总体性能，且与其它新技术结合应用。因此，应用的驱动一直是扩频技术发展的强大动力，未来的无线通信系统，如移动通信、无线局域网、全球个人通信等，扩频技术必将发挥重要作用。 虽然光纤技术在电力系统通信中应用越来越普遍，但在县级电力通信网或者要求较高性价比的通信网中，一点多址微波通信仍将发挥重要作用，而扩频技术也必将获得更加广阔的应用空间。
