1. Preface
Today, when human society is about to enter an information society, the development of telecommunications networks and computer networks has greatly changed the lifestyle of people in the whole society, and the changes in people's lifestyles have in turn put forward higher requirements on the service capabilities of computer networks and telecommunications networks.
Since the 1990s, with the rise of the Internet and the popularity of personal computers, the number of Internet users and data services represented by IP have shown explosive growth, and a large number of new business demands have emerged, such as video conferencing, e-commerce, VOD video on demand, etc. These new service requirements put new requirements on network bandwidth. Due to the advancement of OA and DWDM technologies, as well as the emergence of ATM technology, MPLS technology, and Tbps-level routers, it provides timely means for the upgrade of transmission networks and switching networks, and the bandwidth bottleneck has fallen on the access network.
With the emergence and development of different systems based on different transmission media and their various solutions, such as twisted pair wire (xDSL, HomePNA), digital power lines, wireless (WLL), coaxial cable (HFC, CableModem) and optical fiber (OAN) systems, access network broadband has achieved unprecedented development.
The development of access network broadband has in turn promoted the generation and development of new business needs. Remote monitoring is one of them.
2. Remote monitoring and image compression methods
In the past, only banking and financial institutions, cultural and museum enterprises and institutions had this business need. Most of them were based on traditional access methods, using DDN, V.90Modem, ISDN and other access methods to remote centralized monitoring of the computer room in the communication room of banking and financial institutions and telecom operators.
Now with the broadbandization of the access network, remote monitoring is no longer an unattainable business for families. It will flourish as a new access network business with the development of the broadband access network, bringing people a new family experience.
As the main monitoring content of remote monitoring, images need to focus on solutions due to their large amount of data. If the image problem is solved, other data such as home anti-theft, recording of entry and exit personnel will also be solved.
1. Image compression method
At present, there are many methods of image compression encoding and development, and classic encoding methods such as Huffman encoding, arithmetic encoding, prediction encoding, transform domain encoding, etc. Considering that the visual perception characteristics of people are inconsistent with the information distribution in the statistical sense, the so-called "perceptual entropy" theory was introduced. At the same time, with the in-depth development of mathematical theories, such as wavelet transformation and related disciplines, modern encoding methods, also known as analysis and synthesis methods were produced. Based on the above two encoding methods, various international standards for image compression encoding formulated according to different application purposes have been successively introduced.
In summary, there are mainly H.261, H.263, H.264 suggestions, JPEG standards, MPEG-1, MPEG-2, MPEG-4 standards, etc. MPEG standards include MPEG-7, MPEG-21, etc. MPEG-1/2/4 is a system-level standard. They not only have video encoding, but also audio encoding and system-level protocol content, including multiplexing and synchronization time bases. H.261 and H.263 are just video encoding standards and must be matched with other relevant international standards and suggestions.
H.261 is mainly used for videophone/conference television, H.263 is mainly used to simulate videophone/video conference on telephone lines, while JPEG is mainly used to transmit high-resolution still image and low-resolution image transmission. H.262, the same series as H.261/3, and MPEG are jointly used as the draft ISO/IEC13818 standard. This draft standard is mainly used for digital storage, video broadcasting and communications. The storage medium can be directly connected to the decoder, or connected through communication means such as bus, local area network (LAN), or telecommunications links.
The MPEG-1 standard is used to encode moving images and their accompanying sounds on digital memory banks, with a digital rate of 1.5Mbps. MPEG-1 has made significant improvements based on H.261 to meet the requirements of random access and high compression ratio. Its image scanning format is SIF (SourceInputFormat) format and is used as the standard for VCD discs.
The title of MPEG-2 is "General encoding of moving images and related sound information", which can be understood as further expansion and improvement based on MPEG-1. At present, MPEG-2 has been recognized by the world, and it is the basic standard for digitization of sound and image signals and has been widely used. The concept of "scalability" is introduced to realize hierarchical video compression encoding. Including main-level ITU-RBT.601/D1 format, HDTV-level advanced widescreen/narrow screen format, etc.
The MPEG-4 (ISO/IEC14496) standard passed in 1998 is not a substitute for MPEG-2. It focuses on different application fields, and has a very low digital rate (can be less than 64kbps) moving image encoding technology. Its encoding method is based on model methods, morphological methods and fractal methods, which are different from MPEG-1/2 and have excellent fault tolerance. It has been widely used in digital monitoring systems (DVR, etc.).
As a new generation of multimedia encoding technology, H.264 is the successor of MPEG4/H.263.
H.264 is a new digital video encoding standard developed by the joint video group (JVT: jointvideoteam) of ITU-T's VCEG (Video Coding Expert Group) and ISO/IEC's MPEG (Mobile Image Coding Expert Group). It is both H.264 of ITU-T and the MPEG-4 of ISO/IEC. The draft collection began in January 1998, and the first draft was completed in September 1999. Its testing model TML-8 was formulated in May 2001. The JVT meeting in June 2002 passed the FCD board of H.264, and was officially finalized in March 2003.
H.264 is the same as the previous standard, and is also a hybrid encoding mode of DPCM plus transform encoding. However, it adopts a simple design of "regression to basics" and does not use many options to obtain much better compression performance than H.263++; it strengthens its adaptability to various channels, adopts a "network-friendly" structure and syntax, which is conducive to the processing of code errors and packet loss; the application target range is wide to meet the needs of different rates, different resolutions, and different transmission (storage) occasions; its basic system is open and does not require copyright.
Technically, there are multiple flashes in the H.264 standard, such as unified symbol coding, high-precision, multi-mode displacement estimation, integer transformation based on 4×4 blocks, layered encoding syntax, etc. These measures make the H.264 algorithm have a very high encoding efficiency, and can save a code rate of about 50% compared to H.263 under the same reconstructed image quality. H.264's code stream structure network is highly adaptable, increasing error recovery capabilities, and can adapt well to IP and wireless networks. It can be said that H.264 is currently the highest compression standard for video compression. And it has been applied in digital monitoring systems.
2. Implementation of image compression
Although different manufacturers adopt different image compression and encoding methods, from the above analysis, we can see that the MPEG standard is a dedicated universal encoding for moving images. Therefore, the use of MPEG standard for remote image monitoring has inherent advantages. In practical systems, when the network application environment changes greatly, the MPEG-4 standard with the strongest fault tolerance and strong adaptability is mostly used (MEPG-4Part2, MPEG-4Part10=H.264), which can be used to compress high-quality images and low-quality images. When the network application environment is good (greater than 2Mbps), the MPEG-2 standard can be used to achieve the purpose of transmitting high-quality images.
Specifically as a solution for image compression, the analog video signal output by the CCD camera is sent to the video capture card of the video server (IPEncoder) for video sampling and A/D conversion, and converting the analog video signal into a digital signal. Then it is sent to the calculation processing unit for MPEG compression, and finally the compressed digital video signal is sent to the network interface and transmitted to the remote end via the network.
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3. The implementation of remote monitoring based on broadband access network
1. Point-to-point implementation method based on ADSL/CableModem
The remote monitoring system structure based on ADSL/CableModem point-to-point method. If a household has a PC, a video capture card will be added to the PC to access 1-4 analog camera signals. The ADSL user transmission unit ATU-R can act as a network interface for video processing, and is connected to the ATU-C (ADSL transceiver unit) in the DSLAM digital user line access multiplexer in the ISP computer room via twisted pair cable. If the household does not have a PC, it can adopt the method of integrating the video capture card with the MPEG compression part to form a video server. Remote users use ADSL/CM/LAN/Modem and other access methods to connect to the Internet, and then find the PC or video server in the home based on the IP address of the residents' ADSL, extract the image signal compressed by MPEG, and conduct image observation and language communication for the elderly, children and patients in the home. It is just that the residents need to upstream the digital image to the Internet, so the rate will be limited by the upstream rate of ADSL (64k-640kbps). When working through CableModem, the situation is basically the same, except that ATU-R is replaced with CableModem, DSLAM is replaced with CMTS, and the uplink rate of HFC images can reach a maximum of 1.5Mbps, which will be higher than the maximum uplink rate of ADSL, but HFC has bandwidth sharing problems.
Since ADSL and CableModem are different depending on the service provider, the provided IP address may be dynamic, but the IP address will remain unchanged after each boot. Therefore, remote users can find the video server in the household based on this IP address, and can also send a method to inform the remote users of the IP address after the resident's home PC is turned on to achieve interconnection. If a special security control software is installed in the resident's PC and the RS232 upload signal of the home alarm host is received through the serial port, remote monitoring and control of the home security system can be realized at the same time (fortification/disarming, etc.).
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