Wireless has become so common today, that it is taken for granted. Cellular phone technology has almost replaced the traditional landline for many families. Cell phones are so prevalent and widely used that the movie theaters must remind patrons to turn them off, so that they do not disturb others in the theater. Wireless Internet is available at most hotels and coffee shops, the airport and even some trains. Cities have jumped on the bandwagon by providing wireless Internet service for homes, businesses and apartments within the city.
The popularity of wireless has far exceeded the expectations of its capabilities in just the last 10 years. Wireless products have become available for many applications that, not long ago, were hardwired only. It is becoming an integral part of our everyday lives.
The security market has used wireless keypads, sensors, radios and video transmitters/receivers for years. In short, wireless applications have exploded, while the cost has imploded. Today, any time there is an application that requires flexibility of movement, wireless is the first and often the only approach considered. Future applications of wireless are limited only by our imagination.
Wireless in Security Applications
Wireless applications are everywhere, they are relatively inexpensive, they allow tremendous flexibility and they almost always provide the desired results. Why then is anything hard-wired?
There are some issues with wireless that must be understood and incorporated into any electronic application, especially when used in security. The basic issues of wireless technology applications:
* Power is necessary for wireless to operate; and
* Reception can be a problem with wireless.
Power and Reception Issues
When designing or installing wireless security applications, it is important to remember that the wireless product requires electrical power. The power can be the standard 120 Volt (V) Alternating Current (AC) available in the electrical wall outlet, a battery, a solar panel, a low-voltage transformer or power supply. Most security applications will require low-voltage, solar or standard 120VAC power. Since wireless transmitters require power, the wireless applications are not totally without wires.
Another issue is reception. Recently, I purchased a wireless device that transmits a radio signal via Frequency Modulation (FM) to a car radio. The wireless device allows me to listen to songs on my vehicle's radio when reception would be impossible from a radio station while I am on long trips in sparsely populated parts of the country.
The reason that FM signaling was developed was to address and correct the signal loss and fade issues associated with AM radio signals. We have become accustomed to signal loss when using cell phones, in fact, there are commercials that advertise a person checking reception by saying “Can you hear me now?”
Loss of reception can occur for several reasons. For electronic security applications, the typical issues are: weather; signal blockage/loss; interference; and power level.
The weather impacts wireless in several ways. The level of humidity can negatively impact signals. Most people have noticed what is called “rain fade” on their television when using a satellite TV antenna. The picture quality degrades, becoming more and more grainy, until the signal is totally lost. Weather – or more accurately, seasonal – changes, can impair wireless signals through the growth of vegetation, which can block or shield RF signals, especially “line-of-sight” signals, such as microwave transmissions.
A tree in the path of a high frequency wireless signal may not cause a problem in the winter, when the tree is bare of leaves, but when summer comes and the tree is full, the signal can be blocked. The negative impact of vegetation on a signal will increase as the frequency of that signal goes higher.
Unintentional Interference
There are other blockage issues to consider when using wireless in security applications. For example, a microwave transmitter can be set up to send closed circuit television (CCTV) video from one location to another location many miles away. Signal blockage can occur with the construction of a new structure that is in the signal's path. This problem is exacerbated when there are changes of elevation along the wireless signal path. Any RF signal at high frequencies will require an unobscured line-of-sight. If there is a rise in elevation along the signal path, a structure can be built that is not very tall and still block the path. This type of interference is unintentional.
Another example of unintentional interference occurred in the early development of garage door opener technology. The early garage door openers would open the owner's garage door and, often times, the neighbor's garage door. Some people have experienced or have heard of someone whose garage door electronically opened by someone other than the owner. This is because a frequency was generated that was close enough to the garage door frequency that the opener accepted the signal. One way to minimize the problem is for the garage door opener manufacturer to incorporate a dipswitch in the transmitter and receiver for the garage door opener to set a “unique” code. Because the power level of the garage door opener is fairly low and a code is added, the amount of interference of garage door openers across a large metropolitan area is minimized.
Sometimes you can take advantage of interference. TV stations, for example, transmit microwave signals from vehicles with mobile microwave transmitters back to the TV station for remote broadcast. These vehicles often have one or more microwave dish/dishes mounted to an extendable arm or pole. Quite often, a TV station engineer faces RF interference issues, so the operator must direct the microwave antenna's line-of-sight signal directly at a source of interference, such as a metallic- or mirror-finished glass building to bounce the microwave signal back to the TV station-receiving antenna.
Intentional Interference
There are security concerns in reference to intentional interference, which blocks reception of the signal. Transmitting a high-power signal at the same frequency that is being used for the security wireless application can cause intentional signal blockage. (This problem is fairly unlikely for most commercial security applications.) Wireless security system manufacturers can incorporate different technologies to avoid the jamming or intentional interference problem by using what is referred to as “spread spectrum” technology, which enables the message or signal to be sent on one frequency and the next message to be sent on a different frequency.
The message can also be broken up into pieces of data referred to as a packet. One piece can be sent on one frequency and another packet on a different frequency, and so on. No matter how the data is spread over the frequency spectrum, the receiver and transmitter must be in synchronization to ensure proper reassembly of the data. Synchronization allows the total data stream to be recombined into a usable recognizable signal.
Assigning Frequencies
The power radiated by the transmitter will affect the maximum distance the receiver can be placed from the transmitter to receive a valid signal. The Federal Communication Commission (FCC) controls the power levels and frequencies used by all RF devices in the United States .
The requirement for an FCC license depends on the frequencies used and the transmitted power. Many security products and wireless LANs on the market fall into one of several frequencies. 5.8 billion Hertz (GHZ) is one of the common frequencies, while other frequencies include 2.4 GHZ and 433 million Hertz (MHZ). The 5.8 GHZ, 2.4 GHZ and 433 MHZ security RF wireless products can be legally used, in many cases, without an FCC license.
If a product's literature does not indicate whether an FCC license is required, it is important to verify that requirement before purchase. Deciding between products that require an FCC license and do not, primarily depends on the distance needed between the transmitter and receiver. Longer distances require more power and may require an FCC license.
Signal Degradation
Some caution is needed when applying the distances advertised for a given product vs. what can be expected in real-life. The wireless manufacturer provides the distance their product will transmit in their literature. This distance is under ideal conditions in unobstructed “clear air.” The assumption is that there are no obstructions, a clear line-of-sight, low humidity and no signal loss or interference due to reflections.
There are many reasons that a signal might be degraded. The connection between the antenna and the receiver and/or the transmitter might not be tight or it has become corroded. The transmitter and receiver electronics can degrade over time. Metal objects and building construction can degrade and reflect the signal. The reflected signals can interact with the actual desired signal, causing a signal loss at the receiver.
Interference can also come from power lines, pumps, transformers and motors that produce radiated electromagnetic interference (EMI). It is important to verify that the equipment will provide the needed distance in your particular application.
Antennas
The antenna used can also impact the operation of a wireless system. There are two basic types of antennas: directional and omni-directional. A directional antenna receives or transmits in a single direction, thus requiring a line-of-sight, while the omni-directional antenna will transmit or receive from any direction.
To help clarify the difference, consider this example: A security control center operator cannot dispatch response instructions to the security officer in a remote building several miles away. The remote building is in a low spot in the terrain, but the officers can hear the control center radio from the remote building's parking lot. To solve the problem, a directional antenna is placed on the roof of the remote building pointed toward the security control center-transmitting antenna. To relay the radio signal inside the remote building, an omni-directional antenna is placed inside.
The two antennas can be connected together via coax or a bi-directional amplifier can be added between the two antennas. If only coax is used, the approach is a passive antenna system. If an amplifier is used, it is best to incorporate a notch filter to pass only the radio frequencies used by the company and an FCC license may be required, depending upon power levels transmitted.
Configuring the System
Wireless security equipment is available in two basic configurations. One form uses a separate transmitter and receiver. When a wireless application is required to operate on an existing security product, such as a badge reader for access control, the security product is connected to a separate transmitter. In this example, to allow the access control capability to operate in a wireless application, a transmitter and a receiver are necessary. The transmitter is connected to the reader, enabling badge data to be sent wirelessly to the receiver located at the access control panel.
The other approach has a transmitter that is an integral part of the actual security product, with the receiver separated or incorporated into another security product. For example, there are many wireless CCTV cameras that have a built-in transmitter. The receiver could be physically separate and send the CCTV video signal to a switcher or directly to a video monitor. A combined wireless camera/transmitter and a monitor/receiver are often sold for covert security applications.
Benefits Abound
Wireless options in security systems are endless. Any link in the security system can be changed from hardwire to wireless. The primary reason for incorporating wireless technology is convenience, flexibility and cost. In this article we are considering wireless communication to be provided by RF technology. If a CCTV camera needs to be mounted in an existing parking lot, wireless can be a very cost effective and an easy-to-install solution. Otherwise, the parking lot must be dug up or tunneled under to allow wires to be installed to obtain the video signal from the camera.
If temporary CCTV cameras, badge readers, motion detectors, etc., need to be installed, wireless technology adds placement flexibility, ease of installation and rapid deployment. In situations where esthetics and access for limited physical wiring exists, wireless is an excellent choice.
Wireless applications allow links to exist in any security system to provide conductivity where a hard-wired link is cumbersome, cost-prohibitive or impractical. Many hard-wired systems will become hybrid security systems (hardwire and wireless), as it expands. The expansion will often require wireless technology for the system enhancements where hardwiring a security application is not the best solution.
Robert Pearson is a registered professional engineer and has been an instructor at George Washington University teaching "Integrated Security Systems" and "Corporate Security Management.” His book, A Manager's Guide to Evaluating and Selecting System Solutions , has been published. He oversees design, project management and maintenance of security systems for multiple sites.
