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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 Corresponding author：Ming Huang（huangming＠ynu.edu.cn）
Abstract： This paper provides an overview of radio spectrum monitoring in China.Firstly research background，the motivation are described and then train of thought，the prototype system，the accomplishments are presented.Current radio spectrum monitoring systems are man machine communication systems，which are unable to detect and process the radio interference automatically.In order to realize intelligent radio monitoring and spectrum management，we proposed a Internet of Things based spectrum sensing approach using information system architecture，and implemented a pilot program，then some very interesting results were obtained.
Radio monitoring is the basis of spectrum management.The radio wave is invisible，intangible and susceptible to radio interference.Spectrum monitoring helps spectrum regulators to plan and use frequencies，avoid incompatible usage，and identify sources of harmful interference.It is a growing problem due to the growing number of spectrum uses.As early as 1820s，the United States made the radio spectrum frequency allocation chart of 0～60MHz，began to construct spectrum monitoring system ［1，2］ ，and enacted the Radio Act of 1927.China began large scale construction of monitoring stations in 1990s.Through twenty years of development，a national spectrum monitoring system has been built，which plays a critical role in performing all the routine or special monitoring tasks and basically meets monitoring requirements in the frequency range of 20MHz～3000MHz band ［3］ .Incumbent spectrum monitoring systems comply with the International Telecommunication Union（ITU）guidelines in design and construction ［4］ ，which are typical man machine communication systems，without capabilities of automatic locating，detecting and processing the radio interfer ence.Radio Monitoring Transfer Protocol（RMTP）is applied among multiple monitoring facilities from different manufacturers to achieve interoperability，but the application layer protocol has not been defined ［5］ .
In June 2013 Executive Memorandum on Expanding America's Leadership in Wireless Innovation，President Obama directed the National Telecommunications and Information Administration（NTIA）to design and conduct a pilot program to monitor spectrum usage in real-time in selected communities throughout the U.S..Afterwards，NTIA invested a Spectrum Monitoring Pilot Program ［6］ .In China，the Central Leading Group for Internet Security and Informatization was established in February 2014，which is chaired by President Xi Jinping.This initiative enhanced the security of cyberspace into national strategies in China.To better serve and integrate into the National Cyberspace Security Strategy，Bureau of Radio Regulation of the Ministry of Industry and Information Technology conducted a research project in March2015 to assess state of the art of construction in radio monitoring equipments deployed in borderlands of China.We undertook the project and found problems of existing systems，then proposed solutions ［5］ .
This paper provides high level descriptions of the project in China，and describes a real-time spectrum monitoring system based on Internet of Things（IoT）and cloud computing（or big data）．The intelligence solutions were reflected in the State Radio Management Plan（2016～2020）of China ［3］ .And a prototype system was constructed in Honghe Hani and Yi Autonomous Prefecture of China.
The national spectrum monitoring system，which is combined withfixed，remote，unmanned and mobile monitoring stations and transportable，portable radio monitoring equipments，is the strong technical support to fulfill spectrum management functions in China ［5］ .Existing problems of current spectrum monitoring systems include ［5，7，8］ ：（1）mainly consisting of large and expensive monitoring equipments，with which to build large scale spectrum monitoring systems would be high cost and inefficient；（2）not information systems but communication systems，and complying with RMTP just for data transmission，in which facilities transfer monitoring data originally without processing；and（3）little effort to dig large amounts of spectrum data acquired by monitoring equipments for all benefits，especially to utilize the time and location dimensions of the radio frequency.
To solve the above problems，experts have come up with many solutions.In 2012，D.Z.Chen et al.proposed a radio monitoring approach based on spectrum sensing in real-time in specific areas ［9］ .Subsequently，the approach was implemented and the project won Yunnan Provincial Science and Technology Progress Award in China.In 2015，L.Yang et al.discussed how to design a platform which can store，manage，retrieve and analyze radio coverage data based on B／S model by using database and Baidu map JavaScript API technology and combining with the characteristics of radiomonitoring equipments ［10］ .Although China has put forward the concept of grid monitoring for almost 10 year，there is no report on the implementation of radio spectrum monitoring systems based on IoT and cloud computing（or big data）.
In 2015，M.Cotton et al.provided an overview of the Spectrum Monitoring Pilot Program in the U.S.and described the development of a federated Measured Spectrum Occupancy Database architecture and progress in RF sensor R＆D ［7］ .In the same year，T.Cooklev et al.in response to the U.S.NTIA's Notice of Inquiry，presented a permanent cloud based system of systems for spectrum monitoring.The main conclusion is that spectrum monitoring system must be integrated spectrum management and spectrum monitoring on a large scale，but such a system does not currently exist.They describe the interface to the cloud as an importantenabler and propose a solution that allows ontology descriptions to be used for both spectrum management and monitoring ［8］ .
The expected spectrum monitoring system is a real-time and intelligent one，which is a machine machine infrastructure to acquire and amass monitoring data automatically and make them intuitively available to regulators in real-time，for dynamic，intelligent and efficient spectrum management.
With this aim，we proposed a cloud based IoT approach to spectrum monitoring withdeploying spectrum sensors and presented a unified cloud computing platform for refined spectrum management.Figure 1 is the system architecture.And Figure 2 is the schematic of cloud computing platform.The system achieves the integration and unity of cloud，network and terminals.Among them，“cloud”refers to cloud computing and big data infrastructure to provide computing resources，i.e.，cloud computing platform in Figure 1；“network”not only includes 3G，4G，Internet，VPN，but also extends to IoT，for network bearing，directly providing communication services，i.e.，transport layer；“terminals”means data sources，such as sensors，i.e.，perceptual layer.The perceptual layer is at the most fronted of information collection，esp.an overwhelming flow of data in either structured or unstructured format，which plays a fundamental role in the IoT.
Fig.1 The cloud-based IoT architecture
Fig.2 Cloud computing platform schematic
Cloud computing platform realizesthe structured（or unstructured）data extraction and concentration，analyzes and extracts data relations，conducts aggregation，then forms a unified whole data for further display.According to requirements of spectrum regulator，it mines the key data for different services effectively，establishes appropriate statistical analysis models，achieves scientific and advanced management，thus meet radio monitoring and spectrum management demands.
Spectrum sensors are typical simple and inexpensive devices to meet band specific monitoring requirements with signal processing capabilities.Combined with IoT，sensors deployed with different characteristics are revolutionary substitution to traditional monitoring equipments.
In this regard，we carried out researches on radio monitoring in specific areas based on spectrum sensing，and explored on design approach for antenna minimization of spectrum sensors ［11］ .A cooperative compressed spectrum sensing model was proposed ［12］ .Besides，a spectrum monitoring system based on spectrum sensing and LabVIEW to measure illegal broadcasting signals ［13－15］ was also developed.Sensor hardware and software were designed to detect well defined system transmissions in specific frequency band（s）.What is more，a real-time and intelligent spectrum monitoring prototype system with smart sensors has been built recently in China.Many interesting works have been developed.
Figure 3 is the prototype system framework.The system consists of spectrum sensing network，communication infrastructure，storage integration，intelligent monitoring data processing and smart visualization.Key parts are spectrum sensing network and big data processing platform（i.e.cloudbased intelligent processing platform）.
Fig.3 The prototype system framework
Spectrum sensors provide abilities such as automatical spectrum scanning，smart monitoring，intelligent signal processing，data storage，communication and firmware management.Each sensor hardware includes indoor unit and outdoor unit.The indoor unit is made up of signal processing module，routing module and power supply.The outdoor unit consists of spectrum sensing module，two monitoring antennas（one is an omnidirectional wide band antenna with a working frequency range of 20MHz to 6000 MHz，another one is a FM antenna）and surveillance camera，as shown in Figure 4.
Fig.4 The outdoor unit of spectrum sensor in prototype system
The data processing platform can deal with correlation analysis of spectrum，radio stations，monitoring data and other kinds of data acquired，so as to provide technical support to the management of radio frequency and stations and related foreign affairs.
We deployed 5 smart sensors within VPN in Hekou Yao Autonomous County of Honghe，bordering Vietnam.And arranged a data center，comprising the server and related network equipments，as part of the big data processing platform.Our prototype system topology is shown in Figure 5. It has been running steadily for more than 6 months，as well as intelligently mining many interesting stories behind vast amounts of spectrum monitoring data.
Fig.5 The prototype system topology
According to the Radio Regulation（RR）enacted by ITU，every country should control the use of the radio spectrum on its territory and within its geographical borders.However，the radio wave is propagated in free space and then likely to causing harmful interference to other countries.To simplify matters，international frequency coordination is developed in place，that is a technical and regulatory process which is intended to remove or mitigate radio interference between radio systems from different countries utilizing the same operational frequency，and to ensure rational，equitable，efficient use of the radio spectrum and satellite orbits around the world.There were 12 times sino vietnamese frequency coordination bilateral talks，and several bilateral agreements were formed.
Fig.6 A statistical result of the mobile communication signal smeasured at Hekou
Fig.7 A comparison of the total number of mobile commucation signals demodulated by five spectrum sensors deployed at the border town Hekou
In order to master the initiative in frequency coordination，we especially focused on radio frequency cross border coverage measurement in prototype system design.We divided 20MHz to 3000MHz frequency band into several sub bands，on the basis of42 kinds of radio services defined in the RR.Combined with monitoring data from spectrum sensors，we obtained intuitive spectrum occupancy of certain radio service between our country and the neighbouring country.Taking theGSM public mobile communication service as an example，Figure 6 and Figure 7 gave the statistical results of the usage of GSM.We were surprised to find that：（1）The average spectrum occupancy of radio frequency from China was 54.67％，that was only 9.34％more than the one from Vietnam；（2）At Yipin and Yaoshan，where the total number of Vietnam signals were even more than that within borders of China.So，it is quite necessary to carry out frequency coordination.
Currently，spectrum related technology is moving much faster than spectrum related regulation in the context of demand for spectrum growing at an accelerated rate.So that using modern information and communication technologies to upgrade incumbent radio spectrum monitoring systems for automatic monitoring and intelligent management is the trend.In this work，we proposed a cloud based IoT approach to spectrum monitoring and implemented the prototype system，where monitoring data can be real-time acquired automatically，be effectively managed，stored and intuitively available to spectrum regulators.Ideas and solutions presentedin this paper is an useful exploration.The prototype system provides effective technical support to radio regulation in borderlands，and promotes scientific decision making.
We want more people to join this effort to promote the standardization for intelligent spectrum monitoring systems and accelerate the development of radio monitoring industry in worldwide.
At present，we arecarrying out researches on computational intelligence and mining algorithms for spectrum data analytics，further work will be published later.
Our work was funded by the National Natural Science Foundation of China（Grant Nos.61261002，61461052，11564044），and was supported by the Ministry of Industry and Information Technology of the People's Republic of China.
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