Application of 4G wireless transmission technology in vehicle monitoring

    Current status of 4G application in vehicle monitoring

　　Vehicle monitoring is an important benchmark technology for the Internet of Vehicles. Baidu Encyclopedia defines the Internet of Vehicles as follows: The Internet of Vehicles is a large system network based on the in-vehicle network, inter-vehicle network and in-vehicle mobile Internet. According to the agreed communication protocol and data interaction standard, it conducts wireless communication and information exchange between vehicles and X (X: vehicles, roads, pedestrians and the Internet, etc.). It is an integrated network that can realize intelligent traffic management, intelligent dynamic information services and intelligent vehicle control. It is a typical application of Internet of Things technology in the field of transportation systems. As a carrier system for data transmission, the wireless mobile Internet transmits all application data from the vehicle monitoring system and transmits it back to the management center in a timely and effective manner. Through the background system, audio, video, pictures, satellite positioning, vehicle speed, fuel consumption, door status, temperature, humidity, and even face capture, headcount and other data are comprehensively analyzed and effectively presented, providing a series of operation, monitoring, management and command functions for managers to use, improving management efficiency, and ultimately achieving management requirements for people, vehicles and objects.

　　In the early days of vehicle-mounted monitoring, apart from satellite positioning technology, large-scale transmission of video images was not involved. There are two reasons: First, it is expensive to use the operator's wireless network for data transmission. It can be found on the Internet that around May 2007, when WAP was fully switched to GPRS Internet access, 50 yuan only included 50 megabytes of traffic. For vehicle-mounted monitoring videos that require hundreds of megabytes of storage space per hour, if real-time transmission is required, it is undoubtedly a drop in the bucket; second, the bandwidth of early wireless technology is less than 100kbps, which is difficult to provide effective bandwidth support for vehicle-mounted monitoring videos that require high bandwidth. It only brings new development inspiration to everyone as a prototype of vehicle-mounted monitoring that does not have market benefits.

　　Secondly, based on the issuance of 3G licenses in December 2008, 3G wireless technology has developed rapidly in China. The three major domestic operators have deployed their respective 3G networks on a large scale (China Mobile TD-SCDMA, about 520,000 base stations as of July 2014, C114 China Communication Network data), (China Unicom WCDMA, about 430,000 base stations as of November 2014, C114 China Communication Network data), (China Telecom EVDO, about 200,000 base stations as of February 2012, Communication World Network data). Thanks to the large-scale deployment of 3G networks, vehicle monitoring has been developed to a great extent. However, due to the insufficient 3G bandwidth (the best performance WCDMA standard, under a single base station, the uplink shared bandwidth is 5.76Mbps, and the actual application test, the average is only 128~256Kbps), and affected by other network factors, the industry adopts the mainstream vehicle monitoring solution of low bit rate and non-real-time return of audio and video images in emergency situations, and a large amount of audio and video recordings are stored in the device hard disk.

　　Furthermore, on December 4, 2013, the Ministry of Industry and Information Technology officially issued 4G TD-LTE licenses to the three major operators. It has been more than a year since then. China Mobile's TD-LTE base stations have exceeded 700,000 in the country, more than 500 4G mobile phones, dozens of MiFi 4G terminals, and 4G module products for industries (such as vehicle monitoring) have been marketed and tested. Some people compare 3G to a highway and 4G to magnetic levitation. The theoretical value of the uplink and downlink speeds is 50/100. The author has also conducted actual tests on the 4G speed (test location: 1KM west of Beijing Fengtai Stadium, 4G signal strength -70～-115dBm test software Speedtest, test phone iPhone6 ​​plus, phone format TD-LTE).

　　Test results: The average downlink rate is 17.678Mbps, the average uplink rate is 2.614Mbps, when the signal is -70dBm , the uplink rate can reach 7.78Mbps. See the red box in Figure 1, when 4G is turned off and 3G (TD-SCDMA) is used for testing, the downlink rate is 1.06Mbps and the uplink rate is only 130Kbps.

 Figure 1 Speed ​​test comparison table

　　From the above test data, we can see that the increased speed and huge bandwidth of 4G wireless technology will provide guarantee for the vehicle monitoring to transmit high-quality and smooth video images, and even 720P and 1080P high-definition images can be transmitted back to the center. 4G wireless technology provides managers with richer, more comprehensive and complete comprehensive data, improves management efficiency and ultimately reduces management costs.

　　With the issuance of 4G (TD-LTE) licenses, 4G networks are officially commercialized (FDD-LTE experimental networks are being built in full swing, and the three major operators will obtain licenses and conduct hybrid networking). At the same time, mainstream vehicle monitoring manufacturers in the market have also launched their own 4G vehicle monitoring products, providing more functions, so that vehicle mobile monitoring systems, driven by 4G technology, will open up a new era in the vehicle field and gain a broader development space.

　　According to the data currently fed back by manufacturers, when the 4G signal coverage strength is -70 to -80dBm (3 to 4 signal grids), the average vehicle speed is 60 to 80KM/H, and 4-channel video is transmitted simultaneously (D1 resolution, 25fps frame rate, 512kbps bit stream/channel), accompanied by 1-channel voice, real-time satellite positioning, etc., the monitoring center can get a good remote real-time monitoring experience. Under the 3G (WCDMA, EVDO) network, only 1 channel of image, CIF resolution, 10 to 12fps frame rate, 128kbps bit stream can be transmitted simultaneously. This shows the huge gap in transmission rate between 3G and 4G wireless technologies (see Figure 2).

Figure 2 Wireless Technology Development MAP

　　Introduction to 4G Wireless Transmission Technology

　　4G includes two technologies: TDD-LTE and FDD-LTE. LTE (Long Term Evolution) is a global standard developed by the 3GPP organization and approved by the International Telecommunication Union. The two modes are essentially only slightly different, with a similarity of 90%. Among them, LTE-TDD, also known as TD-LTE (Time Division Long Term Evolution) in China, uses unpaired spectrum. TDD time division duplexing (Time Division Duplexing) is one of the duplexing technologies used in mobile communication technology, corresponding to FDD frequency division duplexing.

Figure 3 Control mechanisms of two 4G standards

　　As shown in Figure 3, FDD receives and transmits on two separate symmetrical frequency channels, using a protection band to separate the receiving and transmitting channels. FDD must use paired frequencies and rely on frequencies to distinguish between uplink and downlink. When supporting symmetrical services, it fully utilizes the uplink and downlink spectrum, but when supporting asymmetrical services, the FDD spectrum utilization rate will be greatly reduced. In this mode, uplink data and downlink data are on the same symmetrical frequency and need to be transmitted simultaneously. The advantage is that the frequency bandwidth is large and the data transmission speed is fast. However, if an asymmetrical service is encountered, the downlink data is much larger than the uplink, and the uplink data frequency channel will be occupied, which ultimately leads to low transmission efficiency.

　　TDD uses time to separate the receiving and transmitting channels. In a TDD mobile communication system, receiving and transmitting use different time slots of the same frequency carrier as the carrier of the channel. The resources in one direction are discontinuous in time, and the time resources are allocated in two directions. The base station sends signals to the mobile station in a certain time period, and the mobile station sends signals to the base station in another time period. The base station and the mobile station must work in coordination to work smoothly. Since the uplink and downlink data of this technology do not need to be transmitted together at the same time, it can be dynamically allocated according to the size of the uplink and downlink data, which is more efficient in frequency channel utilization.

　　To sum up, TD-LTE saves resources and is suitable for coverage in hot spots in cities, while FDD has fast speed and is suitable for wide-area coverage in areas such as the outskirts of cities.

　　The difference between 4G and 3G and their respective advantages

　　3G is called the third generation of mobile communication technology. There are three international standards: CDMA2000, WCDMA, and TD-SCDMA. In May 2008, it was officially promulgated by the International Telecommunication Union. Europe mainly adopts the WCDMA standard, the United States mainly adopts CDMA2000, and China Unicom (WCDMA), China Telecom (CDMA2000), and China Mobile (TD-SCDMA) operate in China. Car monitoring currently mainly adopts two technologies: WCDMA and CDMA2000. There are even technical solutions that support dual-card or more than dual-card packaging in the market products, which effectively improves the bandwidth of audio, video, image positioning data return. TD-SCDMA is basically not adopted because of its low speed (up to 128Kbps uplink) and cannot meet the video return requirements.

　　As the fourth generation of mobile communication technology, 4G wireless technology has made a significant technological leap compared with 3G in a series of core technologies such as access mode and multiple access scheme, modulation and coding technology, high-performance receiver, smart antenna technology, MIMO technology, software radio technology, IP-based core network, and multi-user detection technology. In addition, WCDMA can be smoothly upgraded to FDD-LTE network through long-term evolution. The other two 3G technologies cannot evolve to 4G in the long term.

　　Several major advantages of 4G

　　Fast speed: The theoretical uplink and downlink speeds of TD-LTE and FDD-LTE both reach an astonishing 50/100Mbps.

　　High bandwidth: Each channel has a wide spectrum and high bandwidth. If calculated as 100M, it is 20 times that of the WCDMA network.

　　Good communication quality: Improved communication quality with large number of users and large amount of data.

　　Low cost: The system deployment cost is low, resulting in a reduction in future user communication costs.

　　As can be seen in Figure 4, the increase in wireless mobile communication speed has laid a solid foundation for the multiplication of massive data transmission in the fields of urban passenger transport (buses, taxis, etc.), long-distance transportation, and urban integrated management (such as urban management, traffic police, etc.), and even interactive high-definition video (720P, 1080P, 2K, 4K). It is also the driving force for operators to deploy more 4G high-speed wireless networks in the next few years and provide richer wireless application bearer links.

　　Discussion on the technical application of 4G in the field of vehicle monitoring

　　At present, the mainstream products in the vehicle monitoring market are standard definition (D1) solutions. Under the 4G network, since the transmission of video is supported by higher bandwidth (the aforementioned test case shows that at a signal strength of -80dBm, an astonishing 7Mbps uplink rate is achieved). Based on actual tests and user experience, the recommended configuration is usually single-channel video: 1Mbps bit rate, 25fps frame rate, D1 resolution, and medium-to-high video quality. Of course, the configuration parameters can also be adjusted according to actual conditions.

　　According to China Mobile's 4G network construction plan: TD-LTE network construction is divided into three phases, the first and second phases are urban coverage, the third phase is to expand the capacity of urban hot spots, and the connection and coverage of remote areas. Then, according to the actual needs of the vehicle monitoring system, it is necessary to deeply test the network coverage of the driving area, for example: in each network signal coverage with obvious differences (signal difference -5dBm), conduct 4G network rate test (you can use more professional mobile test tools, such as Speedtest), and save important parameters such as signal strength and uplink rate at that time. At the same time, according to the test data, adjust the video parameters and record them, cooperate with the remote management center to conduct real-time video return effect test, the center conducts real-time monitoring, and video storage (recommended DV recorders and other external video recording solutions are more appropriate, and the actual video playback quality, fluency, etc. can be observed). When problems such as stuttering, mosaics, and black screens are found, the configuration needs to be readjusted and tested again. The recommended speed for urban roads is 40 to 60km. The test plan is recommended to be repeated 2 to 3 times to obtain more ideal audio and video configuration parameters to meet the system's reliable operation requirements in 90% of environments. For long-distance passenger and freight transport vehicle monitoring systems, following-vehicle testing is not allowed in most cases. It is recommended to remotely query the video data to obtain the 4G signal strength along the way (with characters superimposed on the video screen). Of course, if there is an independent signal strength recording solution and the system configuration is optimized through user feedback, it will eventually be able to provide clear and smooth video to meet user application needs.

　　Bottlenecks and solutions of 4G in vehicle monitoring applications

　　Since 4G licenses were issued just over a year ago, network construction is far from meeting market needs. The main bottleneck of vehicle monitoring is uneven signal coverage. The real-time video and data transmission is good in some areas, but it is impossible to transmit in real time in areas with poor or no signal. Secondly, the charges are expensive. In the traffic rate policies given by major operators, the traffic provided in the packages is far from meeting the requirements of real-time video and data transmission. For video data of 10GB, the cost is too expensive.

　　Through in-depth research and development of technology, and in continuous practice, we have found that the use of a comprehensive solution that supports multiple networks and combines static and dynamic networks, such as: combining the operator's 4G/3G network with the parking lot's self-built Wi-Fi network, combining the real-time return of driving dynamics data with the scheduled and fixed-point data return to the station, combining the return of emergency status data on the way with the automatic data upload to the station, combining the real-time return of standard-definition video on the way with the real-time return of high-definition video to the station, and integrating a series of technologies into on-board monitoring, effectively solves the problem of poor 4G signal coverage and expensive charges.

　　In 2013, as the person in charge of product and system solutions, I had the honor to participate in the construction of the on-board monitoring system of urban buses in Yuhuan, Zhejiang. The system adopted a comprehensive wireless technology solution of 3G/4G+Wi-Fi (see Figure 5):

Figure 5: Bus monitoring system in Yuhuan, Zhejiang

　　During the driving of the vehicle, the 4G/3G network is used to transmit the vehicle monitoring data in real time, and the video data is saved in the vehicle monitoring equipment (video recording scheme: 4 cameras per vehicle, each with D1 resolution, 512kbps bit rate, 25fps frame rate, and 10 hours of work per day). At the same time, a Wi-Fi system is deployed in the bus parking lot. After the vehicle returns to the station, the video data is automatically uploaded to the back-end vehicle monitoring platform system via Wi-Fi. The centralized storage scheme reduces the risk of important clues being unable to be queried due to data loss; at the same time, the vehicle automatically uploads data when it returns to the station, and no longer requires ultra-large capacity storage space. It can be replaced with a low-capacity SD flash memory card (currently commercially available products, the capacity also reaches 64G) for storage. First, it changes the irreversible damage of the mechanical hard disk caused by the bumpy road of the vehicle, and second, the use of SD flash memory cards reduces the terminal storage investment. This comprehensive wireless vehicle monitoring solution greatly reduces the construction cost and management cost (personnel and time) for the Yuhuan bus management system, and ultimately wins high recognition from users.

　　The future of 4G wireless technology in vehicle monitoring applications

　　The current 4G (TD-LTE, FDD-LTE), in a strict sense, should be called 3.9G (LTE: Long Term Evolution), and LTE-Advanced is the 4G technology recognized by the International Telecommunication Union. At present, the three major domestic operators are actively deploying 4G networks. As a new technology with high speed, high bandwidth, low tariff and low investment, and as an international standard for sustainable development, its future prospects are very broad. At the same time, manufacturers with R&D capabilities have been paying close attention to the development of 4G technology since 2004 and actively carrying out R&D work. From upstream chip manufacturers, module manufacturers to downstream terminal product manufacturers, they have successively launched related products in 2013. In the field of vehicle-mounted monitoring, mainstream manufacturers have also launched a series of products with modular multi-mode wireless technology, which have been commercially applied on a large scale and accumulated rich experience in 4G network applications (see Figure 6).

Figure 6 Applications supported by different networks

　　Vehicle security monitoring is an industry driven by the application side. Communication technology and vehicle security monitoring technology are constantly influencing, promoting, promoting and integrating each other (especially with the continuous development of video technology and the "content" occupying the commanding heights of application). Both of them regard the user's good application experience as the core driving force of their technological development. In the near future, the ultimate goal of the Internet of Vehicles will be truly realized. Let us look forward to it and be excited about it!