Fighting the Crowd

Wireless alternatives on the rise in many overcrowded urban areas

• By Ray Shilling
• Jul 16, 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. In many cases, a wire-line network connection (RJ-45 port) is not available at all locations required in the facility. So, wireless alternatives are increasingly being considered 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 installed today that functions well can fail dramatically next week or next year as a result of multiple products installed nearby operating in the same RF band.

Part 1 and 2 of this series provided important technical background on selecting the right unlicensed ISM band, as well as factors to consider in choosing a manufacturer and selecting the right product platform and architecture.

Hiring an Integrator
Now that you have designed a robust, fault-tolerant wireless network, the next task is to select the right integrator to install the system.

In many cases, the company that performed the design of the integrated solution is the same one conducting the installation. In fact, this is the preferred situation and will usually yield the best overall results. Because of the variables involved in the design and deployment of a wireless Ethernet network, hiring two separate firms to perform these tasks can result in differences in opinion, which can cause possible network performance issues. Considering the complexities and uncertainties associated with wireless networking in urban environments, having a single point of responsibility can be in the best interest of the project owner and, in many cases, the hired design-build contractor, as well.

When selecting the right firm for the job, be sure to look for the following principal qualifications.

Network design and configuration. Any well-designed wireless network is built upon solid fundamentals of local and wide-area networking principles. In pre-qualifying the company, there are a variety of networking certifications to look for that provide a baseline to work from, including several of the most widely issued versions from industry icons Cisco, Novell and Microsoft.

RF engineering and radio/antenna deployment. The FCC is the primary governing body in the United States for wireless technologies. However, while the FCC regulates products that can be legally produced and sold in the United States, it does not provide an industry standard wireless testing or professional certification process. Fortunately, there are numerous short courses offered by manufacturers to provide general wireless technology overview training, as well as vendor-specific installation guidelines and configuration procedures.

Perhaps the most important aspect of the selection process is to look for companies with experience in installing wireless networks. Keep in mind that since much of this technology is new, many integrators may be performing the installation for the first time. Finding an experienced integrator may not be easy. Certainly, if you do find a good team, be sure to allow them some latitude to solve problems that may arise during the installation. After all, they will be the first line of defense in ensuring the network is built well, stays online and is up to date.

Tools of the Trade
Installing a single RF data transmission link is usually fairly straightforward. However, as the project scale and number of wireless-enabled devices increase, it becomes more important to understand the RF environment specific to the jobsite.

The primary site survey tool for this is a spectrum analyzer or RF scanner. There are a wide variety of spectrum analyzers available in the market today. Costs range from $6,500 for a decent, used unit to more than $25,000 for a top-of-the-line model. Clearly, it represents a financial commitment from the integrator to plunge into this line of work. The most expensive units also are the most complex, and require training to operate effectively.

However, if the integrator or installer plans to spend much time analyzing or designing wireless networks, a site survey tool is essential. The good news is there is a new class of basic RF scanners being introduced that provide a reduced set of features but are more manageable in price.

In this line of work, all you need to get started is a good spectrum analyzer. Stick to the basics without all the bells and whistles. For U.S. integrators, a spectrum analyzer should cover all three principal and ISM bands at 900 MHz (range: 915 MHz +/- 13 MHz); 2.4 GHz (range: 2.45 GHz +/- 50 MHz); and 5.8 GHz (range: 5.8 GHz +/- 75 MHz).

Often during site surveys, workers may need to zoom in to look at specific detail. The ability to scale on demand is especially important if you have multiple fixed frequency discrete channels operating concurrently on the project site or need to review the performance of a frequency hopping solution.

Tips on locating and orienting system components. Once a basic design is complete, during the installation process it is critical to fine-tune the radio location, cabling and connectors, and antennae geometry and alignment. Determining where to locate, orient and align the wireless equipment is perhaps as much an art as it is a science.

Directional Versus Omni-Directional
The single important factor for interference avoidance is to deploy a directional antenna for RF transmission. When using a directional antenna, the RF transmit energy is focused primarily in the direction of a specific target. Equally important, the receive antenna is tuned to pick up signals preferentially from only the direction of the matching radio transceiver and not from other deleterious sources. This represents a double bonus in protecting against interference.

Since RF energy disperses at a geometric rate—proportional to the inverse square of the distance between sources—a pronounced reduction in RF noise can be achieved by increasing the physical separation between antennae output sources competing for the same spectrum. This is a simple, but often overlooked element in designing the overall system topology.

Another useful tip is to experiment with antenna polarity. Stretch out a Slinky toy between you and a colleague across a tabletop. Now, shake the spring laterally—the wave travels left to right and back again between end points. Next, suspend the spring 2 feet above the table and provide a vertical pulse down the spring, and the wave travels up and down the length of the spring. This is the basic concept of wave polarity.

Similarly, due to its geometry and dipole element configuration, Yagi- and pole-type antennae produce polarized electromagnetic radiation. Therefore, if you install a send-and-receive antenna with the same dipole orientation, then the ability of the antennae pair to communicate will improve, and the overall system performance will be enhanced. Polarity provides a good measure of RF interference resistance because the energy of a vertically polarized RF transmission will not impinge greatly upon a horizontal one.

This property of the basic physics of RF transmission can be used to your advantage. If a neighbor’s wireless system primarily uses vertically polarized antennae, simply installing an antenna with horizontal polarity and improve RF interference avoidance.

Frequency Selection for Adjacent Channels
When installing multiple devices in close proximity, use a multiple channel, fixed-frequency, direct-sequence architecture, including a maximum in spectral separation in the available ISM band. For example, if wireless connection “A” is deployed, transmitting at 5.725 GHz, then an adjacent wireless system “B,” designed to run in the same ISM band, should be programmed to operate at 5.850 GHz (the opposite end of the 5.8 GHz ISM band).

As the operating frequency increases, it becomes more critical to minimize the number of connectors and length of cabling the RF signal must pass during send-and-receive phases. For 900 MHz solutions, you can run 25, 50 or even 100 feet of high-quality RF cable between the radio transceiver and antenna. However, in the case of 5.8 GHz system design, be sure to locate the antenna as close as possible to the radio transceiver. At 900 MHz, losses of 0.08 dB per foot of cable are typical, whereas this number increases dramatically to 0.4 dB per foot for 5.8 GHz systems.

The use of notch filters to refine and restrict the RF energy received by an antennae array can be deployed to improve RF interference resistance. As the name implies, a notch filter will completely filter out a specific notch of a particular RF frequency or band. For example, some older paging systems (uni-directional, broadcast-only beepers—not two-way pagers used today), operate at a high-power output in the 929 to 931 MHz range. Therefore, operating systems in the 900 MHz band may require adding a notch filter if performance is poor. Often, this is only discovered once the integrator is attempting to install the devices in question. However, since notch filters can be fairly expensive, and often provide mixed results unless the analysis of the RF environment is accurate, they should be viewed as a final measure to attempt to troubleshoot the wireless network.

Note: This is the third of a four-part series that explores factors to consider when deploying a wireless security device under challenging conditions.