Embedded Wireless Video Monitoring System Based on H.264

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1 Introduction

For Image Monitoring Systems, users often put forward some special requirements for the use of the environment, they want to be able to monitor objects that are far away from each other, these objects may be the power grids in the mountains, the wells in the wasteland, or other important equipment that are unattended or inaccessible to people. On the other hand, they want to get clear images, at the same time, they have high real-time requirements for image transmission, which is obvious. The traditional PC-based image acquisition card is difficult to meet this requirement [1].

In the past, many video surveillance systems use MPEG-4 standards, while the new generation of video compression standards H. 264 is a video image coding and transmission technology for wireless networks and the Internet. Compared with the MPEG-4 standard, in addition to enhancing the network adaptability, it greatly improves the compression coding efficiency, higher subjective and objective quality can be achieved at the same bit rate.

Code Division Multiple Access wireless network features wide coverage, high efficiency, and low cost. The data transmission rate of the Code Division Multiple Access Network is up to 150 kb/s. The embedded wireless video positioning and monitoring system developed here is a data transmission system built Based on H.264 video compression technology, Code Division Multiple Access wireless network technology, and embedded system features.

In this paper, a design scheme of hi3510 system is proposed, and the hardware and software of the system are discussed in detail to complete the video signal acquisition, compression and transmission functions.

2 system architecture

The system consists of wireless or wired Internet monitoring users, central servers, and embedded monitoring terminals. The system architecture is shown in 1. A wireless terminal user or wired Internet user sends a user request command to the central server, first accesses the Internet through the Code Division Multiple Access Gateway, and then arrives at the central server. After receiving the USER command, the central server parses the command and sends the control command to the monitoring terminal through a wireless network. After the monitoring terminal receives the monitoring task from the central server, it uses the image acquisition module to take on-site images, and will pass through H. 264 the compressed image data is sent back to the central server through the code division multiple access module according to the RTP communication protocol. For wireless users, the central server then sends monitoring videos or images to users over the wireless network, while the Internet user center server directly uses
The Internet provides network users with video or image monitoring. The central server must first handle data packet errors, verification errors, packet loss, and packet duplication during data transmission. That is, the request packet loss retransmission and timeout mechanisms are added to the communication protocol; second, the central server also needs to monitor the quality of Code Division Multiple Access transmission data and provide feedback to control the speed at which code division multiple access sends data under different signal quality. Finally, the server also provides users with Web browsing, hard disk storage, download, and other functions of the monitoring system. The system adopts a dual-C/S architecture and has excellent scalability. Multiple monitoring terminals are installed in different locations to achieve real-time monitoring of different targets.

Figure 1. architecture of the Monitoring System

3 monitoring terminal design

The monitoring terminal system is built based on the high-performance communication media processor Code Division Multiple Access of Huawei haisi. Hi3510 is a high-performance communication media processor based on arm9-based, DSP dual processor core and hardware acceleration engine. It is highly integrated, programmable, and supports MPEG-4 AVC/H.264 protocol. Build the corresponding hardware and software environments around hi3510, so that you can easily design the monitoring terminal.

3.1 monitoring terminal hardware design

To run a system correctly, the hardware should at least include the CPU, memory and solid state memory, the internal bus of the system, and peripheral interfaces. hi3510 processor systems meet these conditions well. The specific hardware system structure is shown in figure 2.

Figure 2. hi3510 processor mechanism Diagram

Hi3510 uses the ARM926EJ-S kernel, the Harvard structure of 32-bit RISC processor, the built-in MMU, clock speed can reach 240 MHz, can run well embedded linux2.6, it not only keeps the embedded system small, low-power, and portable, but also makes full use of the complete memory, file, and thread management functions of the Linux system, this greatly facilitates Program Development and implementation of multi-task functions in the program.

H.264 is a video image encoding and transmission technology for wireless networks and the Internet. Its Related Research has become a cutting-edge topic in information science and technology. H.264 has excellent performance such as high compression ratio, good network adaptability, and certain robustness. However, its high computing capacity and long coding time limit its wide application. Hi3510 chip is a H.264 hardware-encoded SoC chip. hi3510 uses the arm9-+ DSP + hardware engine mode to conveniently provide H.264 compressed video streams and obtain a good compression ratio.

The Code Division Multiple Access Communication module uses Shenzhen yitian technology company ETPro-309 ai cdma modem, its built-in SIM card, its internal core chip is Qualcomm msm6025. The module consists of a modulation and demodulation system based on the Code Division Multiple Access Service Standard is95 and is2000, and has a built-in TCP/IP protocol stack. The at command can be used to directly communicate with it. The code division multiple access module is connected to the core processor using UART.

Hi3510 support ITU-R bt.656/601 video input interface, camera interface to accept ITU Standard image data, can not directly receive CCD camera output analog video signal, therefore, we only need to add a saa7114 video decoding chip to build the hardware system.

3.2 monitoring terminal software design

The core of the control terminal software is the embedded Linux operating system. All functions are implemented based on the Linux operating system. It consists of three layers: the bootloader Service Program and the basic peripheral driver, which completes system loading and ARM core processor Initialization Configuration, the second layer is mainly the driver of the camera module and code division multiple access module, and the last layer is the system application.

The Linux kernel adopts a modular design. Many modules can be loaded or detached independently. Therefore, miniaturization is to re-compile the Linux kernel, carefully select the functional modules required by the embedded device during compilation, and delete unnecessary functions. Only the serial port driver, saa7114 video decoding chip driver, and dial-up network applications are required. The PPP and TCP/IP network protocols are also supported. You can delete all others, reduce the number of cores required for system operation to less than 1 MB. Code Division Multiple Access dialing is performed by running the PPP program. In Linux, the PPP package is specially written to solve the modem dial-up Internet access problem and is open source code. The PPP dialing script program calls the pppd and chat applications and uses the AT command to perform modem operations.

The application monitors USER commands. After receiving the commands, it calls the camera module to collect images and then uses the code division multiple access module to send image data. Once initialized, the terminal establishes a TCP connection with the central server. During the operation, the terminal maintains a TCP connection with the central server. The central server can actively request image data at any time. Therefore, application Systems with high requirements on interactivity and real-time performance can achieve better responses. The software process of the monitoring terminal is shown in step 3.

Figure 3. monitoring terminal software flowchart

4. RTP-based H.264 Video Stream Transmission Control

Because H.264 has many advantages, the H.264 Video Stream Transmission Control Based on RTP is designed. RTP supports real-time data transmission, including timestamps, serial numbers, load type identifiers, and source identifiers. timestamps reflect the sampling time of the first byte data in RTP data frames, the sampling time increases linearly monotonically. The receiver reconstructs the time sequence of the received data based on the time stamp of the received data frame, so that the media stream can be correctly played back. The serial number is used for data transmission loss detection and frame sequence reconstruction. The load type identifier indicates the encoding format of the RTP frame data load. The source identifier indicates the source of the data received by the receiving method. The above functions are implemented through the RTP frame header.

The RTP data protocol runs on datagram-oriented UDP. It can only provide connectionless and unreliable services. Frame loss or errors will reduce the quality of images or sounds. The RTCP control protocol must be used together with the RTP data protocol. RTP itself does not provide reliable guarantees for data packet transmission in order, nor does it provide traffic control and congestion control, these are all done by RTCP.

H.264 video streams are respectively mounted with RTP headers, UDP headers, and IP headers, and IP packets are then transmitted to the receiving end over the Internet. After receiving the IP packet, the receiving end extracts the RTP Header and Video Stream Data in the reverse order. Based on the serial number in the RTP Header and the video stream data is cached by the receiving end for decoding and output by the decoder. RTP feedback control is mainly implemented through the RTCP receiver report. by extracting the feedback from the receiver Report SR in RTCP, the available bandwidth of the network is estimated, and then the encoding parameters are dynamically adjusted based on the available bandwidth, the RTP Transmission Bit rate is lower than the available bandwidth of the network to ensure transmission reliability. [3]

Figure 4. RTP transmission Feedback Control Model

5. Central Design

The main function implemented by the server software is to receive and H.264 Software decodes the monitoring data sent from the embedded terminal, and save and transmit the obtained images to end users. A static IP address must be applied for when the control center host logs on to the Internet through broadband access. After the host logs on to the Internet, it can run the server software. The server program design mainly includes network communication, data receiving, H.264 Software Decoding, image storage, and instant re-display. The whole process is software system development and will not be discussed in detail in this article.

6 conclusion

This design is proposed in the application background that the city or remote mobile devices need to monitor. For example, the city armed police vehicles, the application of this system will provide assurance for the early warning command. The author's innovation point is to design a wireless video monitoring system that combines embedded technology, video compression coding technology, wireless communication technology, network technology, monitoring technology, and many other technologies, embedded Technology and Linux real-time multi-task operating system, based on Code Division Multiple Access wireless data transmission, H. 264 video screen compression and RTP real-time transmission control make the system extremely useful.

References
[1] sun Hongwei, based on the S3C2440 remote image wireless monitoring system design, micro-computer information, 2006, 4-2, 90-92.
[2] hith semiconductor Co., Ltd., hi3510 Media Processing Software Development Guide, 2006
[3] Tao guidong, research on QoS Assurance for Video Stream Transmission Based on RTP protocol H.264, Journal of armored Engineering College, 264