Wireless devices: Be a nosy neighbor

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Sunday, April 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 (see the March issue of Security Systems News for part one) explores the factors to consider when deploying a wireless security device under these increasingly challenging conditions.

PART 2: Installing and Maintaining the System
Tips on locating/orienting system components to mitigate interference Since RF energy disperses at a geometric rate (proportional to the inverse square of the distance between sources), the most pronounced reduction in RF noise can be realized by increasing the distance between radio transceivers competing for the same spectrum. This is a very simple, but often-overlooked element in designing the overall system topology.
Secondly, as discussed in last month's Part I, the single most important factor is to deploy a directional antenna for your RF transmission. The transmission RF energy is focused and sent only in the direction of your specific target; and, the antenna is tuned to receive signals preferentially from the direction of your matching radio and not from other sources, a double bonus in protecting against interference.
Another often-overlooked factor is the polarity of the antenna. Stretch out a Slinky between you and a colleague suspended in mid-air; now shake the spring laterally - the wave travels left to right and back again between end-points. Next, provide a vertical pulse down the spring, the wave travels up and down the length of the spring. This of course is the basic concept of wave polarity.
Similarly, due to their geometry and dipole element configuration, Yagi- and pole-type antennae produce polarized electromagnetic radiation. Therefore, if you install your send and receive antennae with the same dipole orientation, then the ability of the antennae pair to communicate will improve and your overall system performance will be enhanced.
This quirk of RF transmission physics can be used to your advantage: If your neighbor's wireless system is using primarily vertically polarized antennae, simply installing your antennae with horizontal polarity can improve your RF interference avoidance.
Key tools of the trade: RF spectrum analyzers Installing a single RF data transmission link is usually fairly straightforward. However, as the project scale and number of wireless-enabled devices increases, it becomes more important to understand the RF environment specific to your job site.
The primary site survey tool for this purpose is the spectrum analyzer. There are a wide variety of spectrum analyzers available in the market today. Unfortunately, the best of these are fairly pricey, often topping $10,000, and require training and can have a steep learning curve to operate effectively. The good news is that there is a new class of basic RF scanners now being introduced, providing a reduced set of features, but also a much more manageable price tag ($500 to $1,500).

Maintenance requirements Unlike other environmental factors such as temperature, humidity, rainfall and wind speed that are generally fairly predictable, the public-band RF characteristics in an urban setting are constantly changing. It is not uncommon to test a given area with a spectrum analyzer one month, only to return the next month to find a completely different RF landscape.
Therefore, if the wireless system you are installing is mission-critical and cannot be down for any significant length of time, be sure to evaluate and plan for the costs associated with maintaining the system; i.e., the total cost of ownership.
The more complex the system, the more important it will be to have real-time access to a wireless network expert with the right tools and training for the job. For example, mesh networks, while powerful and flexible can be more of a challenge to maintain than simple hub-and-spoke multipoint or point-to-point backhaul systems.
Finally, include in the project budget a few spares of critical components to have on hand in the event of an outage. Be sure to also include items such as lightning arrestors, cabling and connectors that might become damaged during storms or power surges.

Defending the RF spectrum at your location As discussed in Part I, in the United States the FCC is the regulatory body responsible for managing unlicensed spectrum (ISM bands). The hard truth is that if your neighbor has installed an FCC-approved radio transceiver that is transmitting RF energy into your property and interfering with your wireless devices, there is very little recourse available to you. However, if they have installed illegal power amplifiers, and you can measure and document this overpowered signal, you do have the right to file a petition with the FCC to have these disconnected and the offender fined.

Protecting your investment/ future-proofing your network The most sophisticated wireless network designers today very carefully manage the unlicensed spectrum in their domain. Because of the rapid growth in the introduction of new Ethernet based products, they realize that at any time they may be called upon to add new network products while maintaining the current systems already in place.
For example, installing a high-powered frequency-hopping product can consume the entire ISM band at your property; thereby preventing you from installing a new wireless product down the road. Manage your spectrum wisely now, and you will be able to install next-generation products without rendering your current investment obsolete.

New wireless networking technologies, but will these help? In the past several years, tremendous advances have been made in the field of wireless wide area networking. For example, WiMAX and 4G cellular networks will provide homes, businesses and mobile users with a broadband alternative to the current DSL and Cable offerings. However, these technologies are in licensed bands, have limited upload speeds, required monthly subscriptions, and so are not easily applicable to the requirements of wireless security devices. Therefore, it appears that for the foreseeable future most wireless security and surveillance products are very likely to be limited to the unlicensed ISM bands.
Shannon's Theorem defines the maximal amount of data that can be carried by a given RF channel. For example, a 1MHz-wide slice of spectrum (say between 900-901 MHz) can be modulated to transmit approximately 800,000 bits of data per second. This is the current state of the art, and in order to improve upon this, design engineers will have to devise new technologies not yet conceived to squeeze more data through a fixed amount of spectrum.
Until this happens, our unlicensed ISM bands will become increasingly crowded. Therefore, like any finite resource on our planet, we must all be disciplined and only design and implement systems that are efficient in their use of this limited spectrum and hence play well with others.

Ray Shilling is the vice president of sales and marketing at AvaLAN Wireless. He can be reached at rshilling@avalanwireless.com.