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  • Wireless application range and transmission technology decomposition

        Network video surveillance system with its intuitive, easy to use, informative information is widely used in the production management, security and other occasions, the general process of video surveillance system are: to put in some important places one or several network cameras monitoring the site , and then video signals through a transmission network ( cable , wireless , optical, or Ethernet ) , the designated monitoring center spread , and through the storage device , the media storage to the storage medium , but also can be installed in the field depending on the needs and route other detection devices as an auxiliary device monitoring system.
        Wireless Monitoring Applications
        1 small civilian applications
        Currently in the civilian areas of application of wireless monitoring system , mostly in the office , factory and other small-scale used to WLAN, WiFi network approach based. In these buildings have been built , if wired monitor , there may be damage to the original building , need trenching , embedding , etc., it is not easy to traditional wired monitoring. According to World Albert Chen Hongxu introduced that way distribution network as simple as a wireless router , can be transmitted , and no additional network costs , in some areas they need to use a smaller monitor the occasion, the use of such methods to transmit video , would be a better way .
        However, the scope of application of this approach is limited in fully accessible open spaces , its transmission distance up to 200 meters . The buildings are in close proximity in the video transmission can be achieved , but relatively speaking , the transmission quality will be affected , but also need to be improved .
        2 , self-built wireless network applications
        In the forest fire monitoring applications , remote mountainous , oil, scenic , electricity, water, environmental protection and other large-scale , long-distance fixed- point , the use of wireless monitoring is a better solution. In such applications , due to a wide range of geographic remoteness, difficult wiring constraints and other factors, if the traditional wired monitoring methods will line laying and maintenance costs are very high , it is often recommended that the use of wireless monitoring, such as a microwave .
        Construction costs are normally subject to a wireless network of its proximity and the number of constraints from the base station , but also a one-time investment in pre- and post- maintenance costs , but the bandwidth is guaranteed , better image quality , which can meet the requirements of remote monitoring . Therefore, insiders say , the industry self-built wireless network Yingzhu public infrastructure facilities by the government to invest more reasonable .
        3 , the use of the operator´s network
        Mobile, Telecom, China Unicom and other operators , will provide some wireless transmission network , such as 2.75G, 3G and so on. Can be used in various applications require wireless monitoring applications, such as vehicle monitoring bus , taxi monitoring, high-speed rail subway surveillance applications. Such applications typically hire operator´s network , which is characterized by a very wide range of space , as long as the operator of the network area can be used. But the need to pay a monthly rental fee certain operators , and the current price is more expensive bandwidth and transmission rate also needs to be further improved.
        Wireless transmission technology decomposition
        Currently wireless image transmission has not yet formed a typical industrial development model, technology is also various ways to achieve the same , the following number of related access technology for wireless image transmission for a brief introduction.
        CDMA technology
        That code division multiple access CDMA technology, which allows users to send and receive data at end packet transfer mode , without the need for the use of circuit-switched mode network resources ; thus providing an efficient, low-cost wireless packet data services . CDMA mobile wireless network transmission technology with confidentiality, and strong anti-jamming capability , anti-multipath weakness, system capacity and flexible configuration , network construction and low cost. For security systems, generally use low transmission frame rate to ensure transmission clarity , because only CIF image clarity than before to meet the needs of the investigation and evidence collection . However , CDMA transmission defect exists insufficient bandwidth , downlink bandwidth of 153K, the upstream bandwidth of 70K ~ 80K, so smooth video transmission is basically impossible. Because the image is only a few frames , only to capture the form of transport , and for the small screen size , and therefore can not meet the needs of real-time mobile video surveillance images .
        GPRS technology
        GPRS is a GSM -based wireless packet switching technology systems , point to point and multipoint support services to "grouping" in the form of data transfer. The main advantage of GPRS always online and by traffic billing, no dial-up access to the Internet at any time , keep in touch with the network resource utilization is high. But with CDMA , as it exists the problem of insufficient bandwidth , unable to meet the needs of high-quality real-time video surveillance .
        Wi-Fi technology
        Wi-Fi is of short- range wireless technology , covering the range up to 100 meters , Wi-Fi technology and products so far , has been quite mature. Wi-Fi wireless fidelity technology, its transmission speed , 802.11b bandwidth up to 11Mbit / s, while the 802.11a and 802.11g is more up to 54Mbit / s. But only do pass, as the transmission, directional transmission , it is difficult to support mobile transmission , thus limiting its application in video surveillance systems, but due to poor security, are very vulnerable to attack from the outside world.
        WiMax technology
        WiMax is based on the IEEE802.16 standard for wireless metropolitan area network technology to provide high-speed Internet connection -oriented , suitable for stationary and semi- stationary state to access the network , the transmission rate of up to 60Mbps. In terms of security , WiMAX provides encryption mechanism in the media access layer (MAC) sub-layer encryption is defined , by using a digital certificate authentication mode transmission within the wireless network to ensure that information is security. WiMAX is a multipoint broadband wireless access technology , has taken a dynamic adaptive modulation and flexible system resource parameters and multi-carrier modulation and a series of new technologies, and both a higher rate of transmission capacity ( up to 70Mbit / s ? 100Mbit / s) and better QoS and security control , the coverage can reach 1-3 miles , mainly located in the mobile wireless metropolitan area network environment , however 802.16e sufficient globally harmonized frequency there is a certain degree of difficulty , and the construction costs and higher equipment prices .
        COFDM technology
        COFDM video transmission technology with high spectrum efficiency and combat multipath delay spread characteristics, is an early military radio transmissions multicarrier modulation technique used in digital communications , but also a more complete mobile reception and transmission technology. COFDM practical value mainly to break the line of sight restrictions on noise and interference have a good immune system, and can penetrate diffraction and obstruction . It can simultaneously separate a plurality of digital signals and the interference signal can be around the safe operation . It is possible to constantly monitor a sudden change in the communication characteristics of the transmission medium , changes in the data transmission capacity of the communication path will occur over time and with COFDM can dynamically adapt and corresponding carrier on and off , in order to ensure continued successful communication . Like other OFDM -based technologies , COFDM inherits the advantages of OFDM , but also inevitably exist OFDM technology is generally inadequate . Frequency offset and phase noise sensitive , and the deterioration of the phase noise offset orthogonality between subcarriers will each only 1 percent of the offset signal to noise ratio will decrease 30dB. Peak and mean power ratio (PAPR) , leading to lower power efficiency of the RF amplifier to increase the peak to mean ratio of the RF amplifier requirements , resulting in reduced efficiency of the power amplifier RF signal . Load algorithm and adaptive modulation techniques will increase the system complexity. Load algorithm and adaptive modulation techniques are used to increase the complexity of the transmitter and receiver , and when the terminal moves above 30 kilometers per hour speed , adaptive modulation technique is not very fit .
        MiWAVE Technology
        MiWAVE core system using 4G technology , inherits the advantages of COFDM and abandon inadequacies of COFDM .
        Uplink air interface technology uses DFT-S-GMC, which is based on the discrete Fourier transform spread orthogonal frequency division multiple access , spread-spectrum frequency domain using DFT , thereby reducing the PAPR of a transmission signal for uplink transmission . While using the DFT-S-GMC inverse transform filter bank (IFBT), to implement frequency division multiplexing and frequency division multiple access . DFT-S-GMC each sub-band broadband relative to the carrier frequency offset and Doppler frequency shift is large. While between each sub-band having a guard interval in the frequency domain , in addition to the spectrum of each sub-band having a steep band attenuation , these characteristics make the carrier frequency offset between the GMC and the timing error caused by the multi-user interference robustness of a strong resistance, compared to traditional OFDM air interface for better technical performance , MiWAVE downlink OFDMA air interface technology than the traditional FDMA improve the spectrum utilization. In addition, using OFDMA , two-dimensional frequency resource scheduling , to provide a fine granularity of data rates to support multimedia applications with different quality of service requirements.
        Epilogue
        In summary, the access technology as the core technology of wireless video surveillance transmission determines the performance and application monitoring system , a variety of access technologies that exist at the beginning of the performance difference between its birth , and not simply to distinguish the pros and cons . In practical applications , face different scenarios , select the transmission mode to meet the application requirements , in order to achieve the best value for money. However, with real-time requirements of wireless video surveillance continues to improve broadband access technology has become an inevitable trend , narrowband access technology will gradually fade out of sight. Meanwhile, the wireless video transmission technology tend to be more diverse applications , are no longer limited to simple image transfer applications ; while real-time monitoring of a large number of monitoring data and interactive data transmission also monitor the transmission network will also propose a new requirements, with excellent transmission performance , to meet a variety of applications for wireless video surveillance transmission technology will be the preferred future security monitoring.