A Wireless World

Consider band options before jumping into wireless solution

• By Ray Shilling
• Apr 03, 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 analog-based products to a digital Ethernet platform. Unfortunately, in many cases, a wire-line network connection is not available at all locations required in the facility. So wireless alternatives are increasingly becoming more prevalent to deploy Ethernet devices.

With the dramatic increase in the use of wireless technologies in the past five years, unlicensed radio spectrum is becoming increasingly overcrowded in many urban areas. A wireless system that’s installed today and functions well can fail dramatically next week, next month or next year, simply as a result of multiple products operating at the same radio frequency.

Before You Begin
When deciding to go wireless, it’s imperative that you know all the facts before getting started.

Licensed versus un-licensed RF spectrum. It is now widely accepted that RF communication technologies provide robust, cost-effective and easy-to-install solutions to deploy wireless data transmission across a wide variety of geographic and weather conditions.

Globally, the ITU radio communication sector is a standards subcommittee of the International Telecommunication Union relating to radio communication. Its role is to regulate allocation of radio frequencies and, in doing so mitigate the interference between powerful RF devices in various countries. ITU also has responsibility for regulating orbital positions of RF satellites, as well as publishing international engineering standard documents.

In the United States, the Federal Communication Commission defines the rules and regulations for the use of domestic data telecommunications using RF spectrum. FCC has devised a simple, two-pronged approach to assign and regulate RF spectrum: licensed versus unlicensed.

As the term implies, licensed spectrum requires licensure from the governing body, and the spectrum is typically very expensive to acquire. Telecommunication giants, such as AT&T, Verizon, Sprint, British Telecom and T-Mobile, pay billions of dollars worldwide to license an exclusive slice of the RF spectrum at the appropriate frequency for the devices being supported. For example, by paying for the 1,850-1,910 MHz spectrum in the Dallas area, Verizon can advertise that a GSM cell phone has a high probability of success of working in Dallas when cell phone users need to make a call.

For this reason, licensed spectrum has become a hot commodity, with many companies bidding on parts of the spectrum at auctions as it becomes available. Once secured, the telecom firms vigorously defend RF real estate to protect the quality of service provided to customers. In the United States, with millions of dollars in annual leasing fees at stake, FCC is strongly motivated by telecom giants to ensure the spectrum is not encroached upon by others not paying the license fees. Violation of licensed spectrum can exact heavy fines.

By contrast, unlicensed RF spectrum defines the portion of the spectrum that does not require the user to obtain a license from the FCC to operate the device. However, the FCC does require manufacturers submit products to rigorous testing to receive FCC approval in a specific, unlicensed band. And, any modifications made to radio products by an end user typically voids the manufacturer’s FCC approval and can subject the user to legal action. Such modifications often include installing a product with uncertified antennas and use of external power amplifiers to increase radio transmitter output.

There also is a modest amount of spectrum reserved for public safety and homeland security that can be characterized as regulated, unlicensed spectrum in that it can be used without license, but only by qualified police and municipal users.

Unlicensed ISM bands in the United States. In the United States, the industrial, scientific and medical radio bands were originally reserved by the FCC for non-commercial use of industry-specific electromagnetic fields. Today, these guidelines have been expanded and now permit manufacturers to build commercial products using the unlicensed spectrum, as long as FCC guidelines and certification processes are followed.

So, 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 band saturation and cause RF interference among devices.

Finding an Appropriate Spectrum
Determining the appropriate spectrum utilization for maximum RF interference avoidance in this crowded, wireless world is difficult, and certain factors should be considered.

The preferred spectral architecture is a fixed-frequency, non-overlapping channel model, where the RF band is divided into smaller subsections or channels. Under this model, each non-overlapping channel supports its own discrete communication 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. Frequency hopping systems 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.

When selecting a wireless product, be sure also to specify a system with a channelized radio transceiver that uses adaptive frequency agility. AFA is a useful feature in crowded RF environments because it provides the wireless system with the ability to sense an increase in 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.

Directional versus Omni-directional Antennae
Omni-directional antennae transmit and receive RF energy equally in all directions with 360-degree performance. This can have advantages in applications that require area coverage, for instance short-range indoor systems at a coffee shop with multiple laptop clients accessing the same Wi-Fi access point. This network topology also is applicable when client devices must be mobile, for example a security guard driving around the parking lot of a shopping mall facility.

However, for the majority of security applications, the installed Ethernet device—such as an IP camera, gate access controller or biometric scanner—is fixed. Furthermore, outdoor installations typically require longer transmission distances and higher noise immunity than indoor counterparts.

In this case, it is advisable to deploy directional (Yagi or panel-type) antenna in the radio system for three reasons: the RF output energy is highly concentrated and focused on the target receiver; the system will have enhanced listening ability and will experience less interference from other RF sources due to the improved amplification gain and directionality of the antenna, and with omni-directional antennae, directional antennae do not pollute RF noise in all directions.

An omni-directional antenna is like a grenade; it blows up spreading shrapnel in all directions and strafing everything around it—whether you intended to or not. By contrast, the directional antenna is analogous to an RF rifle—focused specifically to hit the desired target (the receiving radio) with little or no collateral damage along the way.

The secret to being a good wireless citizen is to deploy systems that produce as little RF leakage as possible into your neighbor’s property. In doing so, you are more likely to be able to encourage them to do the same on your behalf—lending the situation to the ultimate case of do unto others as you would have them do unto you.

This means following many of the guidelines discussed in the series. Some best practices to consider include the use of radio transceivers with a fixed-frequency, non-overlapping channel architecture, avoid frequency hopping technologies that consume the entire ISM band, deploy systems with adaptive frequency agility that can self heal in the event of new sources of RF interference introduced in the future and use directional antennae to focus RF energy at the target to avoid undesirable RF pollution.