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1.INTRODUCTIONBody-worn cameras (BWCs) are small cameras which can be worn by people to record video or audio1. They are employed first by police forces1. BWCs can serve both law enforcement and public accountability function2, more and more countries begin to try the cameras now3. They have experienced rapid development in current ten years. It is forecasted that the global BWCs market would grow to more than 1.5 billion U.S. dollars in 20254. Currently BWCs have been popularized to different industries, such as health, retail, even to campus security. China is one of the earliest countries to use BWCs. Generally speaking, the development of BWC in China can be divided into three stages5. The start-up stage is from 2008 to 2010. BWC is mainly used by police. Only hardware terminal is used without docking station and audio/video management platform. In 2011, The primary industry standard is published by Ministry of Public Security of the People’s Republic of China6. The standard normalizes the function and performance requirement. Docking station and audio/video management platform are not specified until the upgrade version is released in 20157. Relying on the newly proposed system, the overall solution of BWCs is promoted and applied in all kinds of police, for example, public security police1, traffic police8, etc. Since 2016, they have reached the third regulated development stage. Driven by documents related to BWCs issued by a lot of national ministries and commissions, BWCs are thoroughly popularized in public security, and they are also quickly spreading to various industries, such as transport9, maritime affairs10, etc. The research and development of different categories of BWCs needs different technologies. It is mainly related to chips and various sensors. Ordinary BWC can use chips of Ambarella11, Hisilicon12 or other providers. These chips have the basic ability of codec function of video and audio. Transmission BWC prefers chips with additional communication ability, especially 4G/5G, Wi-Fi, etc., so that the BWC can support real-time services. The chips of Qualcom13, MediaTek14, or UNISOC15 can meet the requirements. In addition, the management platform must be combined with transmission BWC to play its unique role. To the best of our knowledge, this is the first work to review BWCs in China from the perspective of technology. Though several comprehensive papers2, 6 or books on BWCs have been published, the focus they put is very different. The remainder of the paper is organized as follows. Section 2 sketches the system of BWC. Then the functions and specifications of BWC are investigated in Section 3. At the same time, different categories of BWCs are listed and compared in terms of service. Section 4 discusses the docking station. The logical components and networking capability of the management platform are detailed in Section 5. Since transmission BWC is the huge trend, the abundant services of it are expounded separately in Section 6. Section 7 concludes the paper followed by a technology expectation of future development in BWC. 2.BODY-WORN CAMERA SYSTEMIn the initial stage, BWC is used alone7. To utilize the video/audio files recorded by the terminals, such as download, replay, query etc., docking station and management platforms are stipulated to make up the BWC system8. The architecture is illustrated in Figure 1. BWCs are responsible for data, such as video, audio, or photos recording. Because BWC is first used by police, BWC is more commonly known as law enforcement recorder in China. The system platform consists of the docking station and the management platform. It is responsible for data uploading, storage and process. The data interface between the BWC and the docking station, docking station and the platform has been standardized to make equipment of different providers compatible. 3.BODY-WORN CAMERAS SPECIFICATIONS3.1General architecture and functionBased on the requirements of standard8 and the products used in various industries, a general architecture is proposed in Figure 2. Buttons, interfaces and SIM/TF card/slot are arranged along the sides. Power, video/audio, and importance label buttons are required by the standard. Importance label button is designed to label the video/audio files as import after pressed by the police if necessary. The labeled files should be saved for ever. Menu button enables users to operate the menus of software. Other buttons differ greatly. For example, PTT (push to talk) makes the BWC can connect an intercom, or can push to talk with the BWC itself. TF card is the storage card for BWCs. SIM card is only required for the transmission one to facilitate 4G/5G communication. Infrared lamp is required by the standard so that BWC can be used at night. Other lamps, such as the white lamp and the radium lamp, are used to fill light and aim at the target object, respectively. Clip is peculiar to BWC to support its portability and wearability. There are various clips, such as shoulder clip, chest clip, etc. On the main board are modules with diverse functions. Chips are very important for DSP and CPU, codec etc. Image sensor is used for video. G-Sensor is used for data protection when BWC gets severe hits or drops. Light sensor cooperates with infrared module to star/close infrared ray (IR) due to the image brightness changes. MIC, receiver/speaker are modules for voice. Battery is often protected by iron sheets to power BWC. GPS/BDS/WIFI/BT/Antenna module is only used for transmission BWC. The embedded software running on corresponding hardware to facilitate the functions. 3.2Specifications and parametersThe specifications have been required clearly in law enforcement industry10, including general requirement, basic function. This also has significant reference sense to other industries. Some fundamental quantified parameters are summarized in Table 1. Table 1.Basic performance parameters for BWC.
3.3Categories of Body-worn camerasThe product positioning and function of BWC decide the industries it applies to. With the progress of technology in BWC, more and more new industries require new types of BWC. The application in the fresh industries drives the evolution of services and platform continuously. Table 2 lists the key technology factors for BWC. Table 2.Key technology factors for BWC.
The ordinary BWC can merely record locally. Some BWCs are equipped with GPS/BEIDOU and WIFI/2G/3G abilities at most. This makes them able to report some positioning information to the platform via 2G/3G. But they cannot transmit real-time video stream. Other ordinary BWCs equipped with WIFI can only communicate in limited areas. Due to these factors, there is no more practical and beneficial business produced. Ordinary BWCs with WIFI/2G/3G do not attract more attention and are not used widely. The introduction of technology of mobile communication, especially 4G and 5G, to BWC spawns a new type of transmission BWC. Transmission BWC can communicate in real time without geographical restrictions. It also can make use of AI technology. The main functions have expanded from recording video/audio to command and dispatching. Transmission BWC and ordinary BWC have become two mainstreams. In Section 6, the business of the transmission BWC will be introduced in detail. Applied to different industries, varied types of BWCs come into being after the specific features of the industry are combined. Table 3 lists some new types emerged in recent years. In China, law enforcement BWC leads the development of BWC. It complements IPCs of Skynet of the Ministry of Public Security. Many specifications and business of BWC are created for public security law enforcement and then popularized to other industries. Law enforcement BWC requires that no frame can be lost to meet the evidence requirement. Transmission BWC is mainly utilized to command and dispatch. It is stipulated that policeman must wear BWC when on duty. Service BWC is much smaller than traditional BWC. Job/duty BWC aims at the non-law enforcement industry and crossover BWC aims at reducing the wearing burden of video and audio electronics. Care BWC integrates some functions of medical instruments, for example, physiological index test and warning, to monitor the change of physical and mental health state in law enforcement. Table 3.Different categories of BWC in China.
4.DOCKING STATION4.1Categories of docking stationsFor the off-line data collect, a docking station is the bridge between BWC and management platform. Files recorded by BWC can only be collected and transmitted to the platform by a docking station. Docking station can be set in multiple types. The most general type is vertical-type16. The docking station can stand on the floor, with slots at the middle position, touch screen (optional) at the top position, and wheels installed at the bottom. The structure of docking station is shown in Figure 3. All the hardware resources are settled in the resource hosting module. The module can coordinate all modules to fulfill the basic functions. Power supply module makes it possible to use the alternating current or powered by UPS in the case of electricity blackout. The peripherals and interfaces module integrate some peripheral equipment, such as serial port, network port and so on. Storage module provides data storage medium. BWC must be connected by the mini-USB or type-C to the docking station. Software environment and computation module support the software to realize the functions mentioned above. The selection of combination of CPU and operation system is limited, relying on the compatibility and maturity of them. Table 4 lists some combinations. Table 4.CPU and operating system for docking station.
4.2Specifications and parametersThe functions of docking station are stipulated from the following aspects: general requirement, basic function, extended function, performance, EMC, environmental adaptability, availability and reliability. The fundamental qualified requirements are given in Table 5. Software can enrich the docking station more distinctive functions and features. The upload of large volume data depends on the network. The duration and upper bounds of transmission can be configured. Since the docking station is normally in unmanned guard, automatic maintenance is very essential. Table 5.Basic performance parameters for docking station.
5.MANAGEMENT PLATFORMWith the emergence of transmission BWC which has the real-time communication function, BWC is hoped to act as an intelligent terminal in the command and dispatching. The command and dispatching function needs the cooperation of BWC and management platform. Various services should be developed in the platform, such as the location on the map, two-way pronunciation, trunked intercom, or even the integration of video and audio to command and dispatch. 5.1Logical layer and module divisionManagement platform is designed according to the principle of open system interconnection reference model. The following diagram Figure 4 illustrates the logical layer and module division of the platform in China. The platform consists of five layers. The bottom layer is infrastructure, i.e., the network in which the platform deployed. Data layer is the second layer which is responsible for the operation of data collected by the BWC and docking station. The third layer is service layer. Basic service is provided in a modular fashion. Five “scenario-based” business centers are presented to users on the web page. The top layer is industry application. 5.2Networking capabilityNetworking capability is a key function of platform. Figure 5 presents a classic network in China (Platform is abbreviated as PF). In this figure, the management platform is viewed as a network element. Systems without background are the centers deployed independently. Systems with light background are the existing systems in each industry. Depending on the cascade capability provided by the network layer, the platforms can cascade in administrative divisions at different levels, from province to county. At each level, the platform can be deployed according to the distribution of law enforcement unit. In the middle part, live video stream can be transmitted to Internet by private protocol, i.e., RTSP, RTMP etc. Herein the “private” means that the protocol choice is up to manufactures. The top right corner is the public security scenario where the transmission can be enabled by GB/T 28181 protocol, a variant of SIP protocol. Under the dotted line demonstrates the access capability. Different intelligent terminals access the docking station to transmit the local video. The networking capability is still evolving quickly to meet the sophisticated application scenarios. 6.SERVICE REALIZATION FOR TRANSMISSION BWC AND PLATFORMTransmission BWC is the result of ordinary BWC continuous development and integration with mobile communication technology. User wishes can be used as a professional wearable broadband intelligent communication terminal. The BWC can support position location, voice and live video stream in addition to record and photograph. Collaboration with the platform, the entire system can upload video/audio files through wireless interface, especially can meet the requirements to command and dispatch. The following services are some basic functions required for transmission BWC and platform. 6.1Position locationIn China, Beidou navigation satellite system and GPS should be supported at least. The wearer can be found through the map presentation of position location. Normally, 2D map is used. 3D map is a future candidate because it can make information more intuitive. Historical track playback is demonstrated on the map. It can facilitate users to check the route patrolled in necessity later. A practical application is SOS function defined in some transmission BWC. If the SOS button is pressed, the position information of this BWC will be broadcast to other peers within the circle around the BWC with a defined radius. This makes it possible for the peers to rescue the seeker timely. 6.2IntercomIntercom of BWC uses digital voice. There are three kinds of intercom. The first is intercom between platform and a BWC. The second one is intercom between two BWCs. The third is intercom within a group. The intercom is often half duplex. 6.3Live video streamPosition service and intercom can be realized in 2G/3G BWC. But live video stream becomes feasible only when 4G/5G provides wider bandwidth. It is the basic factor for visualized law enforcement. Convergence of video network live-broadcasting and streaming media makes it possible to play the scene to the supervisors in command center in real time. Video stream can be played in multiple windows and gives more rich and visual information to the commander. It is helpful for the commander to make decisions more accurately. 6.4Integrated command and dispatchingThe integration of the services mentioned above brings more actual combat service. There are three scenarios for integrated command and dispatching. A commander in the command center, or on the cloud, or even with a mobile phone, can utilize a permanent or a temporary group to call a meeting or deploy work. The picture of the commander can be transmitted to each BWC in the group accompanied with voice. This is the first one. The second one is that when a supervisor in the command center finds a wearer is in danger via the live stream, he can dispatch the other peers near the dangerous people to aid at once. He can establish a temporary group and push the live stream of the people to the aider immediately and intercom with each other. The third one is that when SOS is activated by a wearer, the alarm is transmitted to the people on duty. The people can initiate the flow of scenario two to help the seeker. 7.CONCLUSIONFrom a technical point of view, the three stages and background of BWC development in China are investigated. The system is first introduced at a high level. Then each subsystem. The architecture is presented and the technical specifications are summarized. Especially, BWC is classified according to the main purposes and features. This motivates the evolution of the whole system further. Transmission BWC has become a hot point of research and development due to the fact that it can resolve some challenges of actual combat. At last, the abundant services and business of transmission BWC are analyzed systematically. ACKNOWLEDGMENTSThis work is financially supported by National Key Research and Development Program of China (No. 2018YFC0807500), Shenzhen Strategic Emerging Industries Program (No. F-2019-Z99-502115). REFERENCESLiu, J.,
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