Wireless devices: Be a good neighbor

SSN Staff  - 
Thursday, March 1, 2007

To take advantage of the powerful and ubiquitous TCP/IP communication platform, manufacturers of security products such as network video cameras, gate access controllers, biometric scanners, perimeter fencing systems and mobile covert monitoring solutions are gradually migrating their analog-based products to a digital Ethernet platform. Unfortunately, in many cases, a wire-line network connection is not available at all of the locations required in the facility. Therefore, wireless alternatives are increasingly being considered to deploy these Ethernet devices.
With the dramatic increase in the use of unlicensed wireless technologies over the past five years, unlicensed radio spectrum is becoming overcrowded in many urban areas. This two-part series explores the factors to consider when deploying a wireless security device under these increasingly challenging conditions.

PART 1: Designing the System
Licensed vs. Un-licensed RF Spectrum Radio Frequency (RF) communication technologies provide the most cost-effective and robust method to provide wireless data transmission across a wide variety of geographic and weather conditions.
In the United States, the Federal Communication Commission defines the rules and regulations for the use of domestic data telecommunications using RF spectrum. The FCC has devised a simple system to assign and regulate RF spectrum: licensed vs. unlicensed. As the term implies, "unlicensed" defines that portion of the RF spectrum that does not require the user to obtain a license from the FCC to operate the device. Licensed spectrum requires licensure and this spectrum is typically very expensive to acquire. There is also some spectrum reserved for Public Safety and Homeland Security that can be used by police and municipal users.
The FCC requires manufacturers to submit their radio products to rigorous testing to receive an FCC approval to sell them. Modifications to radio products by an end user typically voids the manufacturer's FCC approval and could subject the user to legal actions from the FCC. Modifications often include installing with uncertified antennae and use of external power amplifiers.
United States ISM Bands In the United States, the Industrial, Scientific and Medical (ISM) radio bands were originally reserved by the FCC for non-commercial use of RF electromagnetic fields for industrial, scientific and medical purposes. Today, manufacturers can build commercial products that use this un-licensed spectrum, as long as the FCC guidelines are followed.
Therefore, wireless RF transmission products are free to operate in these bands without regulation of the density of users in a specific band space or location. This of course can result in the saturation of the band and cause RF interference among devices.
The following unlicensed ISM bands are defined in the United States: 900 MHz band (902 - 928 MHz); 2.4 GHz band (2.400-2.4835 GHz); 5.8 GHz band (5.725-5.875 GHz).
Band Allocation, Frequency Agility and Antenna Selection To reduce the adverse impact of RF interference in the ISM bands, and to be a good wireless citizen to others around you, three important factors should be considered when selecting the right wireless network technology and product suite for the job:
1. The preferred spectral architecture is a fixed-frequency, non-overlapping channel model, whereby the RF band is divided into smaller subsections or "channels." Under this model, each non-overlapping channel supports its own discrete communications link. This channelized approach yields maximum data capacity of the band.
By contrast, products that employ a frequency-hopping technique, whereby the entire band is occupied by a single transmission device, should be avoided since they do not operate well with other manufacturers' products in the same band space and yield a much lower aggregate data capacity for the band as each hopping radio causes interference to all new and existing band users.
2. When selecting a wireless product, be sure to also specify a system with a channelized radio transceiver that uses Adaptive Frequency Agility (AFA). AFA is a very useful feature in crowded RF environments in that it provides the wireless system with the ability to sense an increase in the noise level and relocate to a quieter channel automatically as a result of interference in a specific channel within the band. AFA allows the radio to be perpetually self-healing as it adapts to other spectral users that may enter the band in the future.
3. Omni-directional antennae transmit and receive RF energy equally in all directions (360-degree performance). This can have advantages in applications that require area coverage, for instance short-range indoor systems with multiple laptop clients accessing the same access point (Wi-Fi).
However, outdoor installations require longer ranges and higher noise immunity than their indoor counterparts. Outdoor systems typically require directional antennae, higher RF output power and operation over wide temperature ranges. By using directional antenna in the radio system, the RF energy is focused the on a specific target and the system will have enhanced listening ability. When compared to using omni-directional antennae, directional antennae have the added "good neighbor" effect of not polluting in all directions with RF noise and it improves noise immunity as the radio will experience less interference from other RF sources outside of its main directional beam.
Ray Shilling is the vice president of sales and marketing at AvaLAN Wireless. He can be reached at rshilling@avalanwireless.com. In Part II of this series, he will examine the specific installation tips and hardware tools to best avoid your wireless network being compromised now or in the future.