下载掌阅APP，畅读海量书库
立即打开
1.Wireless Innovation Lab of Yunnan University，School of Information Science and Engineering，Yunnan University，Kunming，Yunnan，China
2.Yunnan Provincial Industry and Information Technology Commission，Kunming，Yunnan，China
*huangming＠ynu.edu.cn；yangjingjing＠ynu.edu.cn
Abstract： As the demand for refined spectrum management grows，the need for accurate and reliable radio monitoring data increases accordingly.In this context，the calibration of radio monitoring stations has become a routine work for efficient spectrum management.In this paper，an on line measurement and calibration method in Open Air Test Site（OATS）is described，followed by experimental verification.The results show that on line measurement and calibration is very important for improving the accuracy and reliability of radio monitoring data and thus provides effective technical support for spectrum management and audit.
Keywords： measurement；calibration；spectrum audit；radio monitoring
Radio spectrum is a scarce，non renewable and limited wireless information and communication technology（ICT）infrastructure resource.With the fast advance of the mobile Internet，the requirement for radio spectrum is increasing exponentially ［1］ .At the same time，radio spectrum audit measurement reports in many parts of the world have shown that there is a great under utilization of this resource ［2，3］ .Therefore，how to manage spectrum efficiently，how to allocate spectrum rationally and how to improve spectrum utilization are critical questions for ICT development.Then，refined management and spectrum audit are introduced into spectrum management field ［4，5，6］ .And analysis and evaluation of existing spectrum utilization efficiency is the basic work，which leads to high demand for accuracy and reliability of radio monitoring data.
The accurate and reliable spectrum measurements will give a true picture of the spectrum available，or that could be made available.Nevertheless，due to the aging of electronic components，and the influence of the temperature，humidity and other external environments，radio monitoring stations will cause measurement errors after prolonged work.For refined spectrum management and further spectrum audit，regular calibration has become a particular important aspect in operations，administration and maintenance（OAM）of radio monitoring stations ［7］ .Thus it puts forward higher requirement to on line measurement and calibration for radio monitoring stations.
In 2012，D.Z.Chen et al.reported the spectrum occupancy measurement campaign conducted in the frequency range of 20－3000MHz based on radio monitoring stations in Yunnan Province of China ［3］ ，and showed that the ambient noise had a great influence on spectrum occupancy measurement，so its calibration was a key issue in radio monitoring.Next，in 2015，we carried out a research project to assess state of the art of construction in radio monitoring technical facilities deployed in borderlands of China.And we found problems in daily OAM that the lack of calibration for radio monitoring stations and the incompleteness of fundamental parameters data，such as antenna factor，feeder loss，receiver indicators，etc..Consequently，it is urgent to collect and manage the technical parameters data of radio monitoring stations for regular measurement and calibration.
In this paper，we focus on the receiving capability of fixed radio monitoring stations，to explore an on line measurement and calibration method in Open Air Test Site（OATS） ［8］ ，and present the experimental verification in Honghe Hani and Yi Autonomous Prefecture of China.
Fig.1 is the block diagram for on line measurement and calibration of radio monitoring stations in OATS，which consists of transmitting antenna，monitoring antenna and the calibration system.The principle of on line measurement and calibration of fixed radio monitoring stations is that assuming the measured spatial electric field strength at monitoring antenna and standard antenna are the same，then the receiving capability of fixed radio monitoring stations can be calibrated by the spatial electric field strength measured at standard antenna.
Fig.1 The block diagram for on-line measurement and calibration
To be specific，supposing that the antenna factor of monitoring antenna is k 1 ，the feeder loss is L r1 ，and the received power of the receiver is P r1 （dBm），then the spatial electric field strength at monitoring antenna E 1 （dBμV）can be obtained
Similarly，the spatial electric field strength at standard antenna E 2 （dBμV）is
where k 2 is antenna factor of standard antenna，L r2 is the feeder loss，and P r2 （dBm）is the received power of the spectrum analyzer.Due to the fact that both monitoring antenna and standard antenna are in the far-field region，and the distance between transmitting antenna and standard antenna is equal to the one between transmitting antenna and monitoring antenna，so
In order toconfirm the above method，we conducted an experiment in Honghe Hani and Yi Autonomous Prefecture in Yunnan Province of China.The experimental scenario can be seen from Fig.2，where the monitoring antenna，the standard antenna and the transmitting antenna form an isosceles triangle，while the transmitting antenna is just located at the vertex of the isosceles triangle.Here，a rod antenna is connected with a Rohde＆Schwarz microwave signal generator working in the frequency range of 10MHz to 40GHz.The monitoring antenna and the EM550 receiver are main equipment of the radio monitoring station.And the standard antenna is connected to the Tektronix'H500 handheld spectrum analyzer with the frequency range from 10KHz to 6.2GHz via the feeder.The standard antenna is the TRILOG Broadband Antenna 30MHz－3000MHz which is a Logarithmic Periodic Broadband Antenna.The main parameters of standard antenna are listed in Table I.
Fig.2 The experimental scenario
Table 1 Main parameters of standard antenna
续表
The steps are given as follows：
（i）Set the transmit power of the signal generator to 20dBm，and respectively record the received power of the spectrum analyzer P r2 and the received voltage of the receiver，i.e.，U r1 .
（ii）Reduce the transmit power of the signal generator gradually，record the received voltage of the receiver U r1 and the received power of the spectrum analyzer P r2 until U r1 is higher than the displayed ambient noise 6dB.The measured U r1 ，P r2 are given in Table II.
At this time，U r1 －6dB is the displayed ambient noise of the receiver，i.e.N r1 .Since the ambient noise of the receiver is uncertain，we assume that the actual ambient noise is P n1 and
where x expresses the uncertainty of the ambient noise of the receiver.And the received power of the receiver P r1 can be obtained
There by the spatial electric field strength E 1 at monitoring antenna can be written as
The parameters of standard antenna are known，so we can calculate the spatial electric field strength E 2 at standard antenna by（2）.Since（3），we obtain
In our experiment，feeder loss of standard antenna L r2 ＝0.2dB，and the antenna factor of standard antenna k 2 is given in Table I.Therefore，the receiving capability of fixed radio monitoring station can be defined as：
here，the unit of P r2 is dBm and the unit of U r1 is dBμV.
Table 2 Measurement results of the receiver
According to the measured U r1 ，P r2 and the antenna factor of standard antenna k 2 ，k 1 ＋L r1 ＋x can be calculated，as shown in Fig.3（c）.If the antenna factor k 1 and the feeder loss L r1 are known，we can get the actual ambient noise which is denoted as U r1 －6dB＋x.Because of the incompleteness of fundamental parameters data，here we assume that L r1 ＝－5dB.Then for a supposed relation between k 1 and frequency，we calculate the variation of actual ambient noise with frequency，as implied by the solid line in Fig.3（d）.As can be seen，the actual ambient noise is always greater than the ambient noise displayed by the receiver.From Fig.3（c）it is clear that when the frequency is 30MHz，k 1 ＋L r1 ＋x＝17.2dB；when the frequency is 3000MHz，k 1 ＋L r1 ＋x＝66.8dB.That is，the receiving capability of fixed radio monitoring station working at 3000MHz deteriorates 49.6dB than working at 30MHz，which is close to the theoretical result of40dB（i.e.20log3000－20log30）calculated by free space propagation model or 52.3dB（i.e.26.16log3000－26.16log30）calculated based on Okumura Hata propagation model.The results reveal that the method of on line measurement and calibration is feasible for evaluating the receiving capability of radio monitoring stations.
Fig.3 （a）Received power versus frequency（b）Antenna factor k 2 of the standard antenna（c）Receiving capability（d）The relation between ambient noise and frequency And the inset shows the supposed relation between k 1 and frequency
Data traffic of mobile Internet is increasing at an explosive rate，which has led to the demand for radio spectrum increasing rapidly as well.Currently，spectrum utilization efficiency is a major pillar towards the realization of a successful national broadband policy.Therefore，to ensure the reliability，stability and accuracy of radio monitoring data，regular calibration for fixed radio monitoring stations is very necessary.The proposed method in this paper can be used for on line measurement and calibration of radio monitoring stations in OATS，which is the key work for refined spectrum management and spectrum audit.Further discussion of on lines measurement and calibration can be found in ［7］ .
Our work was funded by the Ministry of Industry and Information Technology of the People's Re public of China and the National Natural Science Foundation of China（Grant Nos.61261002，61461052，11564044），and was supported by Yunnan Provincial Industry and Information Technology Commission.
［1］Cisco Visual Networking Index：GlobalMobile Data Traffic Forecast Update，2015－2020 White Paper［Online］.Available：http：／／www.cisco.com／c／en／us／solutions／collateral／serviceprovider／visual networking index vni／white＿paper＿c11－520862.html.
［2］L.Mfupe，F.Mekuria and M.Mzyece，Geo location white space spectrum databases：Models and design of South Africa's first dynamic spectrum access coexistence manager，KSII Transactions on Internet and Information Systems，2014，8（8）：3810－3836.
［3］D.Chen，J.Yang，J.Wu，et al.，Spectrum occupancy analysis based on radio monitoring network，IEEE International Conference on Communications in China.IEEE，2012：739－744.
［4］Q.Liu，L.Q.Wen，Research on spectrum audit in foreign countries and spectrum audit methods for China，Modern Science＆Technology of Telecommunications，2015，2：50－54.
［5］M.J.Marcus，The Challenge of balancing private sector and government spectrum use，IEEE Wireless Communications，2014，21（3）：8－9.
［6］J.Obuchowski，M.Greczyn，The opportunity of private sector sharing of government spectrum，IEEE Wireless Communications，2014，21（4）：5－7.
［7］J.Yang，M.Huang，Q.Lu，State of the art and Investment Demand of Radio Spectrum Management Technical Facilities in Borderlands of China，Yunnan University Press，2015.
本文发表在国际会议URSI AP－RASC 2016（P1334－1336，Seoul，Korea，Aug.21－25，2016.），发表时有删改。