Monitoring transmission: Comment on wireless mode

Monitoring transmission: Comment on wireless mode

The monitoring system usually adopts different transmission methods according to different users, system scale, coverage area, signal transmission distance, information capacity and other requirements for system functions and quality indicators.

Wireless way of monitoring transmission

At present, wireless image transmission has not yet formed a typical industrial development mode, and the technical methods implemented are also different. The following is a brief introduction to some relevant receiving technologies that can be used for wireless image transmission.

CDMA technology

CDMA is code division multiple access technology, which allows users to send and receive data in an end-to-end packet transfer mode without using network resources in the circuit switching mode; thus providing an efficient and small wireless packet data service. The mobile transmission technology of CDMA wireless network has the advantages of good confidentiality, strong anti-interference ability, anti-multipath fading, flexible system capacity configuration, and low network construction cost. For security systems, low transmission frame rates are generally used to ensure transmission resolution, because only image sizes above CIF can meet the needs of investigation and evidence collection. However, CDMA transmission has the defect of insufficient bandwidth. Its downlink bandwidth is 153K and its uplink bandwidth is 70K~80K, so it is basically impossible to transmit smooth video. Since the image has only a few frames, it can only be transmitted in the form of a snapshot, and the screen size is small, so it cannot meet the needs of real-time moving image video surveillance.

GPRS technology

GPRS is a wireless packet switching technology based on the GSM system, which supports point-to-point and point-to-multipoint services, and transmits data in the form of “packets”. The main advantage of GPRS is that it is always online and billed according to traffic, without repeating it at any time, but like CDMA, it has enough problems to meet the real-time video surveillance needs.

Wi-Fi technology

Wi-Fi is a short-range wireless technology with a coverage range of up to 100 meters. The technology and products of Wi-Fi have just been mature. Wi-Fi wireless fidelity technology, its transmission speed is fast, the bandwidth of 802.11b can reach but can only achieve through-view transmission, directional transmission, it is difficult to support mobile transmission, which limits its application in video surveillance systems, and because of security Sex is relatively early, and it is very vulnerable to external attacks.

WiMax technology

WiMax is a wireless metropolitan area network technology based on the IEEE802.16 standard. It can provide high-speed Internet-oriented connections and is suitable for accessing the network under static and semi-static conditions. Its transmission distance can reach 60Mbps. In terms of security, WiMAX provides an encryption mechanism, defines an encryption sublayer in the media access layer (MAC), and uses digital certificate authentication to ensure that the information transmitted within the wireless network is securely protected. WiMAX is a point-to-multipoint broadband wireless access technology. It adopts new serial technologies such as dynamic adaptive modulation, flexible system resource parameters and multi-carrier modulation, as well as higher rate transmission capabilities (up to 70Mbit/s). 100Mbit/s) and better QoS and security control, the coverage can reach 1-3 miles, mainly positioned in the mobile wireless metropolitan area network environment, and 802.16e to obtain sufficient global unified frequency has certain defects, and construction costs And equipment prices are higher.

COFDM technology

The practical function of COFDM is a multi-carrier digital communication modulation technology used for military radio transmission in the early days, and it is also a variety of complete mobile reception and transmission technologies. The value is mainly to break through the limit of the viewing distance, good immunity to noise and interference itself, and can diffract and penetrate obstructions. It can separate multiple digital signals at the same time, and can operate safely around interfering signals. It can continuously monitor the sudden changes of the communication characteristics on the transmission medium, the ability of its communication path to transmit data will change over time, and COFDM can dynamically adapt to it, and cut off the corresponding magnetic field at the same time to ensure continuous success Communication. Like other OFDM-based technologies, while COFDM inherits the advantages of OFDM, it also has general deficiencies in the existing OFDM technology. The orthogonal characteristics between the two deteriorate, and only 1% frequency deviation will reduce the signal-to-noise ratio by 30dB. The power peak-to-average ratio (PAPR) is large, resulting in a decrease in the power efficiency of the RF amplifier, and the peak-to-average ratio will increase the requirements for the RF amplifier, resulting in a decrease in the power efficiency of the RF signal amplifier. Load algorithm and adaptive modulation technology will increase system complexity. The use of load algorithm and adaptive modulation technology will increase the complexity of the inverter and receiver, and when the terminal moving speed is higher than 30 kilometers per hour, the adaptive modulation technology is not very suitable.

MiWAVE technology

MiWAVE system adopts 4G core technology, inherits the advantages of COFDM, and replaces the shortcomings of COFDM. Uplink air interface technology uses DFT-S-GMC, that is, orthogonal frequency division multiple access using discrete Fourier transform spread spectrum, and DFT is used for frequency domain DFT-S-GMC uses spread spectrum, thereby reducing the peak-to-average ratio of the transmission signal, suitable for uplink Link transmission. At the same time, DFT-S-GMC adopts inverse filter bank transform (IFBT) to realize frequency division multiplexing and frequency division multiple access. At the same time, there is a certain frequency domain guard interval between each subband, and the frequency spectrum of each subband has a steep out-of-band attenuation. These characteristics have GMC. It is stubborn to interfere with multi-user interference caused by coaxial frequency offset and timing errors. It is better to use traditional OFDM air interface technology. MiWAVE downstream air interface technology OFDMA improves the spectrum utilization rate than traditional FDMA. OFDMA adopts time and frequency two-dimensional resource scheduling, which can provide fine data rate granularity to support multimedia applications with different service quality requirements.

Compared with the image transmission monitoring system using WiFi, WiMAX, COFDM, CDMA1X and other technologies, the MiWAVE system will have advantages. The MiWAVE system organically integrates the uplink DFT-S-GMC and the downlink OFDMA technology, and the ratio of the system that uses OFDMA for both the uplink and the downlink. It has small equipment power consumption, large coverage, low multi-user interference, and low base station signal detection algorithm complexity. Features. A single base station has a large coverage area, with a maximum coverage distance of up to 25km, which can realize long-distance data transmission. The number of base stations required for networking is small and the cost is low. The system has high bandwidth, high coefficient, single base station up to 60Mbps, flexible networking, supports a variety of topological structures, can network with the same frequency/different frequency, high spectrum utilization, supports 120km/h mobile communications, and supports high-speed vehicles use. Multimedia interactive services such as video, voice, and data image transmission can be realized. The service configuration is flexible. The ratio of uplink and downlink transmission bandwidth can be configured as needed, and the uplink and downlink quantum can be adjusted to support specific services. The all-IP-based emergency communication system can be connected to the IP backbone network and the Internet through multiple access methods such as satellite reception, microwave relay, and terrestrial fixed network access (ADSL, cable), which expands the scope of application and reduces the application of equipment And maintenance costs.

The MiWAVE system is based on the National Broadband Wireless Multimedia (BWM) standard and is compatible with the WiMAX standard framework. It adopts key technologies such as adaptive, automatic hybrid retransmission, broadband multi-carrier transmission, wireless resource scheduling, and wireless network structure design. The adaptive adaptive technology can adaptively adjust the transmission power, modulation and coding method and data frame length according to the channel state to overcome the time-varying characteristics of the channel to obtain the best communication effect; the automatic hybrid retransmission technology can well compensate the wireless The influence of time-varying and multipath fading of the mobile channel on signal transmission can effectively reduce the bit error rate of the system to ensure the quality of service; the wireless resource scheduling algorithm makes full use of the time-varying characteristics of the channel to obtain multi-user diversity gain and improve system performance. Corruption: A system designed with a basic architecture does not require a centralized control entity such as BSC. The MiWAVE base station combines the functions of traditional BS, BSC, and some functions of packet data services to make network deployment easier. The number of components required is reduced, the network becomes more reliable, flexible, easy to deploy, and operating costs are reduced.


Post time: Jan-15-2021