Most of the time, video surveillance systems use hardwired solutions to transmit video and control signals—copper or fiber for traditional CCTV or standard network infrastructure for networked, digital systems. However, it’s worthwhile to consider using wireless video transmission under certain circumstances.
- If a long distance separates the camera location from the control site. In this situation, trenching and cable installation may be cost prohibitive, right of way may be unavailable, and a leased line may incur too many recurring expenses.
- If your cable route is limited. In historical buildings it may be virtually impossible to provide an affordable and workable cable route.
- If you need a flexible deployment. For museums or exhibition halls, cameras must periodically be relocated to suit changing needs.
- If you require covert installation. Small, battery-operated, wireless covert units can be deployed quickly and easily.
- If you need a mobile solution. Mobile cameras can improve incident response by allowing the incident command center to monitor first-responder activities and provide accurate assessment of the situation.
Transmission Capacities and Security
Analog. Virtually all wireless video surveillance transceivers operate in the unlicensed part of the radio spectrum. Under the provisions of FCC regulations (47CFR parts 15 and 18), the industrial, scientific and medical (ISM) bands are a part of the unlicensed radio spectrum set aside for anybody to use without a license. One can easily find analog wireless video transceivers operating in the 5.8GHz, 2.4 GHz and 900 MHz ISM bands. There are a few wireless video devices operating in the 1.2 GHz amateur band, and some lower-power, short-range consumer products operating in the UHF band.
These analog video transceivers do not offer any special measures to secure the transmitted video signal. The full-frame, real-time NTSC video signal is sent via either FM or AM modulation, and the transmitted signal is received with the right receiver. Since these wireless video links operate in the unlicensed public access band, it is extremely easy and affordable for criminals to put together a wireless video receiver with an external antenna and a signal booster to intercept the unencrypted video signals.
To safeguard these transmissions, a pair of encoder and decoder video encryption units can be used to apply a line cut and rotate scrambling technique. An encryption key produces a random sequence of line cut positions. The encoder selects a cut point in the NTSC video signal, cuts the signal into two segments, and presents the last segment to the output first, followed by the first segment. At the receiving end, the decoder reverses the process to rebuild the video signal.
WLAN. In the digital video world, the network infrastructure is standards based, with virtually all wireless local area network (WLAN) devices complying with IEEE802.11a, IEEE802.11b or IEEE802.11g with a bandwidth of up to 54Mbps. These devices operate in 2.4GHz and 5.8GHz.
Due to challenges like latency, bandwidth availability, wireless link quality, high bandwidth demand and variability of video applications, the quality of video over WLAN is still poor when multiple cameras are sharing the same access point. The traditional priority and buffering technique cannot provide the proper quality of service needed to deliver streaming video over WLAN. A wireless network may suffer from sudden and severe drops in bandwidth, resulting in stuttering and frozen video. Hopefully the Wireless Metropolitan Area Network (Wi-Max) standard expected in the near future will boost the allowable bandwidth to 280Mbps at the access point up to a distance of 20km, eliminating or mitigating some of the video quality issues.
WLAN devices have built-in security measures to protect the transmitted information. There are two encryption standards in use: