Network video surveillance systems are widely used in production management, security protection, and many other applications because they provide direct, convenient, and detailed visual information.

A typical video surveillance system works as follows: one or more cameras are installed at important locations to capture the monitoring scene. The video signal is then transmitted through a transmission network, such as cable, wireless, optical fiber, or Ethernet, to a designated monitoring center. The media data can also be stored on storage devices. According to different requirements, other detection devices can also be installed on site as auxiliary equipment for the monitoring system.

Application Scenarios of Wireless Surveillance

1. Small-Scale Civil Applications

At present, wireless surveillance systems in the civil market are mostly used in small-scale areas such as offices, factories, and industrial parks. These systems are mainly based on WLAN or Wi-Fi networks.

In existing buildings, if a wired surveillance system is used, it may damage the original building structure because trenching, slotting, and cable laying may be required. Therefore, traditional wired monitoring is not always convenient.

Wireless networking is much simpler. In some cases, only a wireless router is needed for transmission, and there are no additional network fees. For small areas that require video monitoring, wireless transmission can be a practical solution.

However, this method also has limitations. In a completely open area without obstacles, the transmission distance may reach around 200 meters. In nearby building groups, video transmission can also be achieved, but the transmission quality may be affected and still needs improvement.

2. Self-Built Wireless Network Applications

For large-scale, long-distance, and fixed-point monitoring applications, wireless surveillance is often a suitable solution. Typical scenarios include:

• Forest fire prevention
• Remote mountain areas
• Oil fields
• Scenic areas
• Electric power systems
• Water conservancy projects
• Environmental protection monitoring

In these applications, traditional wired surveillance systems can be expensive and difficult to maintain due to large coverage areas, remote locations, and wiring difficulties. Therefore, wireless monitoring methods such as microwave transmission are often recommended.

The cost of building a wireless network is generally affected by transmission distance and the number of base stations. There are also initial construction costs and later maintenance costs. However, a self-built wireless network can provide guaranteed bandwidth and better image quality, making it suitable for remote monitoring applications.

Some industry professionals believe that industry-level self-built wireless networks should be considered public infrastructure and may be more reasonably funded by government investment.

3. Using Operator Networks

Mobile operators such as China Mobile, China Telecom, and China Unicom provide wireless transmission networks, such as 2.75G and 3G. These networks can be used in different wireless surveillance scenarios, including:

• Bus video monitoring
• Taxi monitoring
• Subway monitoring
• High-speed railway monitoring

This type of application usually rents the operator’s network. Its main advantage is wide coverage. As long as the operator’s network is available, the system can be used.

However, monthly rental fees must be paid to the operator, and the current cost can be relatively high. In addition, bandwidth and transmission speed still need further improvement.

Wireless Transmission Technologies

At present, wireless image transmission has not yet formed a fully standardized industrial development model. Different systems may use different technical methods. Below are some common access technologies used for wireless image transmission.

CDMA Technology

CDMA, or Code Division Multiple Access, allows users to send and receive data in an end-to-end packet transfer mode without using circuit-switched network resources. It provides an efficient and low-cost wireless packet data service.

CDMA mobile transmission technology has several advantages, including:

• Good confidentiality
• Strong anti-interference capability
• Resistance to multipath fading
• Flexible system capacity configuration
• Low network construction cost

For security systems, a low transmission frame rate is usually used to ensure image clarity. This is because image quality above CIF level is generally required for investigation and evidence collection.

However, CDMA has a major limitation: insufficient bandwidth. Its downlink bandwidth is about 153K, while uplink bandwidth is only around 70K–80K. Therefore, smooth video transmission is basically difficult to achieve.

In many cases, only a few frames can be transmitted, similar to image snapshots, and the image size is small. This cannot meet the requirements of real-time mobile video surveillance.

GPRS Technology

GPRS is a wireless packet switching technology based on the GSM system. It supports point-to-point and point-to-multipoint services and transmits data in packet form.

The main advantages of GPRS are always-on connection and traffic-based billing. Users can access the internet at any time without dialing and can stay connected to the network continuously.

However, like CDMA, GPRS also suffers from insufficient bandwidth. It cannot meet the requirements of high-quality real-time video surveillance.

Wi-Fi Technology

Wi-Fi is a short-range wireless technology with a coverage range of up to about 100 meters. Wi-Fi technology and products are already very mature.

Wi-Fi provides fast transmission speed. The bandwidth of 802.11b can reach 11 Mbit/s, while 802.11a and 802.11g can reach 54 Mbit/s.

However, Wi-Fi is mainly suitable for line-of-sight and directional transmission. It is difficult to support mobile transmission effectively, which limits its application in video surveillance systems.

In addition, Wi-Fi has relatively weak security and can be vulnerable to external attacks if not properly protected.

WiMAX Technology

WiMAX is a wireless metropolitan area network technology based on the IEEE 802.16 standard. It can provide high-speed internet-oriented connections and is suitable for fixed or semi-fixed network access.

Its transmission rate can reach up to 60 Mbps. In terms of security, WiMAX provides encryption mechanisms. An encryption sublayer is defined in the Media Access Control layer, also known as MAC. Through digital certificate authentication, WiMAX can help protect information transmitted within the wireless network.

WiMAX is a point-to-multipoint broadband wireless access technology. It adopts a series of advanced technologies, including:

• Dynamic adaptive modulation
• Flexible system resource parameters
• Multi-carrier modulation

It offers relatively high transmission capacity, which can reach around 70 Mbit/s to 100 Mbit/s, as well as good QoS and security control. Its coverage range can reach about 1–3 miles.

WiMAX is mainly positioned for mobile wireless metropolitan area network environments. However, obtaining globally unified frequency resources for 802.16e remains difficult, and the construction cost and equipment price are relatively high.

COFDM Technology

COFDM image transmission technology offers high spectrum utilization and strong resistance to multipath delay spread.

It is a multi-carrier digital communication modulation technology that was originally used in military wireless transmission. It is also a relatively mature technology for mobile receiving and transmission.

The practical value of COFDM lies in its ability to break through line-of-sight limitations. It has strong resistance to noise and interference and can diffract and penetrate obstacles.

COFDM can separate multiple digital signals at the same time and can operate safely around interfering signals. It can continuously monitor sudden changes in the communication characteristics of the transmission medium. Since the data transmission capability of the communication path may change over time, COFDM can dynamically adapt by switching corresponding carriers on and off to ensure continuous and successful communication.

Like other OFDM-based technologies, COFDM inherits the advantages of OFDM, but it also has some common limitations.

First, it is sensitive to frequency offset and phase noise. Frequency offset and phase noise can damage the orthogonality between subcarriers. Even a 1% frequency offset may cause the signal-to-noise ratio to drop by 30 dB.

Second, COFDM has a high peak-to-average power ratio, also known as PAPR. This leads to lower power efficiency in RF amplifiers. A high PAPR increases the requirements for RF amplifiers and reduces the power efficiency of RF signal amplification.

Third, loading algorithms and adaptive modulation technologies increase system complexity. They make both transmitters and receivers more complicated. In addition, when the terminal moving speed is higher than 30 km/h, adaptive modulation technology may become less suitable.

MiWAVE Technology

The MiWAVE system adopts 4G core technology. It inherits the advantages of COFDM while avoiding some of its shortcomings.

For uplink air interface technology, MiWAVE uses DFT-S-GMC, which is an orthogonal frequency division multiple access technology based on Discrete Fourier Transform spreading.

By using DFT for frequency-domain spreading, MiWAVE reduces the peak-to-average power ratio of the transmission signal, making it more suitable for uplink transmission.

At the same time, DFT-S-GMC uses Inverse Filter Bank Transform, also known as IFBT, to achieve frequency division multiplexing and frequency division multiple access.

The bandwidth of each DFT-S-GMC sub-band is relatively large compared with carrier frequency offset and Doppler shift. There is also a certain frequency-domain guard interval between sub-bands. In addition, each sub-band has steep out-of-band attenuation.

These features make GMC more robust against multi-user interference caused by carrier frequency offset and timing errors. Compared with traditional OFDM air interface technology, it provides better performance.

For downlink air interface technology, MiWAVE uses OFDMA. Compared with traditional FDMA, OFDMA improves spectrum utilization. In addition, OFDMA uses two-dimensional resource scheduling in both time and frequency domains. This provides fine data rate granularity and supports multimedia applications with different quality-of-service requirements.

Conclusion

In wireless image monitoring systems, access technology is the core factor that determines system performance and application scenarios.

Different access technologies have different performance characteristics from the beginning of their development. Therefore, it is not appropriate to simply judge them as good or bad. In actual applications, the most suitable transmission method should be selected according to the specific monitoring scenario and application requirements in order to achieve the best cost performance.

As the real-time requirements of wireless image monitoring continue to increase, broadband access technology has become an inevitable trend. Narrowband access technologies will gradually fade from mainstream applications.

At the same time, wireless image transmission technology is moving toward more diversified applications. It is no longer limited to simple image transmission. While real-time monitoring is being performed, large amounts of monitoring data and interactive data also place new requirements on surveillance transmission networks.In the future, wireless image monitoring transmission technologies with excellent transmission performance and the ability to support multiple applications will become an important choice for modern security surveillance systems.