Techniques for Meeting the Challenges of Wireless Video Installations
March 1, 2008
Ports and airports need to be protected by extensive video security systems; however, these facilities present complex cabling issues which can be incredibly burdensome in terms of higher costs and installation delays. These higher costs â€” often due to the extensive surface to be covered â€” have led many systems integrators and designers to consider wireless solutions, either optical or radio frequency. Although wireless solutions can significantly reduce installation costs, the design and installation of a wireless transmission system in a port or airport area involves a number of challenges that can be very trying for the products, designers and installers working on the project.
ENVIRONMENTAL FACTORS & CHALLENGESThe first element to consider is the environmental factor. Especially at industrial ports, environmental conditions are often extreme in both temperature and atmosphere, as well as in the vibrations and shocks that the products may suffer.
The air in ports is characterized by high salinity, which makes it extremely aggressive to radio and video products; therefore, it is essential to select equipment with adequate physical features. The IP classification, which identifies the waterproof degree of products’ outer protection, is the most commonly used method.
- IP65 â€” the product is splash-resistant.
- IP66 â€” the products is resistant to salt water intrusion.
- IP67 â€” the product can be immersed up to 1 m deep for limited periods
- IP68 â€” the product can be immersed up to 1 m deep for extended periods of time.
IP68 transmitters are superior compared with the others, because of their total resistance to penetration of both water and saline atmosphere into the equipment’s outdoor protection. This ensures a longer operating life of the system, since the electric and electronic circuits will not suffer from accelerated wear due to atmospheric aggressiveness. Therefore, it is recommended to use transmitters with IP68-rated protection and to place a bag of dehumidifying material inside the protection during installation to absorb any moisture which may have penetrated inside the transmitter.
For video equipment, the best solution is to use products equipped with anhydrous nitrogen-pressurized stainless-steel cases. In addition to ensuring total moisture resistance, pressurization prevents the saline atmosphere from damaging the cameras’ electrical and mechanical components.
EXOGENOUS INTERFERENCESPort and airport areas are also both characterized by a high density of RF devices. The problems related to exogenous interferences deriving from other transmitters are rather frequent.
The types of interferences that may occur are due mainly to:
- other transmitters operating on frequencies close to or coinciding
with those used (for example, Wi-Fi networks, Hiperlan data networks, and
analog radio links for various purposes including video-security);
- different devices whose operation creates interferences in the bands affected by the transmission (for example, radars or microwave ovens).
Interference is one of the most complex phenomena that need to be tackled in the area of radio transmission, and must be addressed simultaneously at different levels using the least busy channels, but also introducing redundancy into the system so that it may help automatic adjustment in case of unexpected and unpredictable interferences.
During preliminary inspections and installation, it is important to be able to evaluate any possible interferences due to other wireless networks existing in the area; a Wi-Fi device in listening mode or a spectrum analyzer may be used to identify them. Also, it is advisable to ask your customer about the existence of other radio devices in the area, their carrying frequency, their bandwidth and power. Careful planning can solve a large percentage of the problems related to interferences.
However, when operating on license-free bands, it is necessary to keep in mind that the absence of a wireless network on the day of testing does not mean that one may not be installed in the near future. Consequently, it’s important to introduce redundancy in the network and use dynamic equipment that’s able to identify new interferences and respond to minimize their effects. This approach usually requires the use of “smart” radio equipment, often of the mesh type, set to perform constant transmission channel analysis and to select in real time the best pathway within the network and/or channel most free of interference.
Another common source of interference in port and airport environments is radars. In particular, marine radars operate on two different bands: S radar band, ranging from 2 GHz to 4 GHz, and X radar band ranging from 8 GHz to 12 GHz. Most problems of interference with license-free radio devices are created by radars in the S band. With respect to radars, the problems should be addressed in the same way as indicated for unpredictable interferences. Creating a network is recommended, so that the equipment is able to modify the channel in use or the transmission pathway based on the current conditions of the RF spectrum.
ANTENNA ALIGNMENTAnother characteristic shared by ports and airports is the distances involved, which are sometimes extremely long. This requires the use of high-gain directional antennas. These antennas are often grids or parabolic devices able to cover distances between 2 and 20 Km. However, highly directional antennas are inherently difficult to align. Often the corresponding antenna cannot be clearly identified because the distance is too long, and therefore the alignment process requires a great deal of patience, some experience, and adequate instruments. It’s also very important that the antennas are easily accessible during installation so that they can be aligned properly.
The alignment procedure is usually based on the creation, on one side of the link, of a carrying signal that can be received on the other side. Once the signal is received, the vertical and horizontal orientation of the antenna can be modified by a few degrees to evaluate any signal increases or reductions due to a better or worse alignment.
Also, it is important to keep in mind that grid antennas â€” and especially parabolas â€” create a significant load under the influence of wind and, if they are not installed correctly, their alignment can be altered so badly on a windy day as to make a radio link totally unusable.
EFFECTS DUE TO PRECIPITATIONPrecipitation (rainfall or snowfall) and certain weather conditions (such as fog) may negatively impact the quality of radio connections, depending on the frequency used by the device. All devices operating on license-free bands (2.4 GHz and 5 GHz) are not affected by precipitation since the wavelength (12 cm for 2.4 GHz transmission and 5 cm for 5 GHz transmission) is significantly larger than the diameter of any rain drop. Devices operating on licensed bands above 10 GHz and laser optic devices, on the other hand, may be affected by precipitation in that the wavelength is close to, or even smaller than, the size of a raindrop’s diameter.
The opportunities offered by wireless projects within port and airport areas are clearly on the rise. However, we must realize that the learning curve of wireless technology is rather steep, and that â€” especially when tackling the first wireless project â€” crucial requirements are both training and utmost support from the supplier, at the design stage as well as at the time of system calibration and testing. Evaluate suppliers not only on the basis of technology and price, but also take into account the type of support and training they are able to provide to their customers.