While installing Wi-fi solutions, a user may come up with a few impediments; specifically w.r.t the range and reception. It is very important to be aware of these impediments and see how they could affect the installation, before going in for a wireless solution.
Walls
The first thing to do is to check the construction of the walls. In theory, Wi-Fi signals are capable of passing through walls and other obstacles relatively easily. However, in reality, some walls are thicker or use reinforced concrete and may block some of the signals. Materials such as drywall, plywood, other kinds of wood and glass can be easily penetrated by wireless signals. However, materials such as brick, plaster, cement, metal, stone, and double-glazed glass may cause problems. The following facts should therefore be kept in mind:
- Metal bodies absorb Wi-Fi signals. Therefore, wireless surveillance solutions do not guarantee connectivity between floors of buildings and between thick reinforced concrete walls
- If the walls are made of non-porous materials, your wireless connection may have a shorter range or a slower speed
- Elevators block Wi-Fi signals to a great extent. When placing an IP camera; make sure the elevator does not come between the camera and the Wireless Access Point
- Tinted glass panes carry metal constituents. So if you have tinted glasses anywhere between WAP and the camera, you can expect a drop in signal strength.
Interference
The other thing to check for is potential interference with the Wi-Fi network’s frequency range. The 802.11 wireless standards communicate in the 2.4, 3.6 and 5 GHz frequency bands.
Interference can slow down a network significantly and reduce its range as well. The two most common sources of wireless network interference are wireless telephones and microwave ovens. Existing previously installed 802.11 networks can also cause interference.
Potential sources of interference in the 2.4GHz ISM band:
- Microwave ovens
- 2.4GHz cordless phones, DSSS and FHSS
- Fluorescent bulbs
- 2.4GHz video cameras
- Elevator motors
- Cauterizing devices
- Plasma cutters
- Bluetooth radios
- Nearby 802.11, 802.11b or 802.11g WLANs
- Wireless Internet Service Providers (WISPs)
Potential sources of interference in the 5GHz UNII bands include the following:
- 5GHz cordless phones
- Radar
- Perimeter sensors
- Digital satellite
- Nearby 802.11a or 802.11n WLANs
- Outdoor wireless 5GHz bridges
A basic wireless surveillance set-up normally consists of the wireless IP cameras, the Wireless Access Point (WAP) and the Network Video Recorder (NVR) or the media server. In addition to the above, keep the following points in mind while installing a wireless surveillance solution:
- Keep the antennas straight pointing to the sky unless told to do otherwise
- A long hallway or corridor will most likely need an indoor semi-directional antenna for coverage as opposed to an omni-directional antenna. Do check the manufacturer’s recommendations. Anytime a type of antenna that is not recommended by the manufacturer is added, do keep in mind that the signal may be getting a boost beyond the legal limits of the country.
- Weather events such as rain, snow, and even wind can wreak havoc with wireless signals
- A high concentration of human bodies can attenuate the RF signal due to absorption
- Trees are notorious for absorbing signal energy
- Wireless Access Point (WAP)
- Do not keep the Access Point device at a low level on the floor. If possible, try placing the WAP at a location equidistant from all the walls of the room. In other words, keep it in the middle of the room or desired area of coverage
- As far as possible, keep the WAP above all sources of obstruction. Even if it means overruling the earlier point. For example, in an office environment, keep the WAP above the height of all the cubicles. We would recommend it to be mounted close to the ceiling
- Try not to place the WAP near sources of heat or under the sun
- Do not operate multiple WAPs in close proximity (<100mts apart). Especially if the same SSID is used on both.
- Wireless IP Camera
- Once again, do not place the wireless IP Cameras at a low level. It is best placed high on the wall or nearer to the roof (to avoid all kinds of obstacles like furniture, cubicles, etc.)
- Try not to place the cameras near sources of heat or under the sun
- Do not keep the cameras too close to the WAP (<2mts). The camera radio may automatically turn down its transmit output power which may result in connection loss
- Do not keep the cameras too close to each other (<2mts). This will cause signal interference between them.
Conclusion
A careful and thorough evaluation of your security requirements will help a great deal in identifying the prudence of using a wireless surveillance system.
