During the past several years, wireless and IP video surveillance have practically become synonymous with one another. However, as many security professionals have painfully learned, wireless is as much an art as it is a science. A properly engineered wireless network can be the difference between a successful video surveillance deployment and a never-ending nightmare of support and maintenance.

This article will highlight some of the basic fundamentals to consider when designing a wireless system including: which network topology to choose, which frequency(s) to choose, Timed Division Duplex (TDD) vs. Frequency Division Duplex (FDD), and calculating your application’s bandwidth needs. Also, see the sidebar to learn how solar power can be applied to surveillance applications.

This material is intended to show you how to select the most well suited radio system to support your specific application. Make no mistake; this is not the be all and end all of wireless. The objective is to help you understand which questions to ask your customers, your vendors and yourself so you can select the perfect network design the first time, every time.

3 Wireless Network Topologies

There are three main network topologies for a wireless network: Point-to-Point (PTP), Point-to-Multipoint (PtMP) and Mesh. Often, in larger networks, some combination of these three topologies is used to achieve the most robust and reliable solution.

A PTP network is the simplest of the three. As the term suggests, there are only two locations in the network. Location A transmits and receives data to and from location B. PTP networks can be used in smaller networks with a single camera or small cluster of cameras at the remote end. They can also be used in larger networks to aggregate large amounts of video traffic from a PtMP or Mesh network since PTP bridges are capable of providing much more bandwidth (more on bandwidth later). PTP networks operate in a large number of licensed and unlicensed frequency bands. The unlicensed frequency bands of 900MHz, 2.4GHz, 5GHz, 24GHz, and 60GHz along with the licensed frequency bands of 6GHz, 11GHz, 18GHz, 23GHz, and 80GHz are the most commercially available.

A PtMP network is a one in which a central point (commonly referred to as hub, access point or base station) broadcasts and receives signals to multiple remote locations. A PtMP network is an efficient and cost-effective way for several remote locations to transmit data back to a central location. These networks are common in applications such as connecting buildings on a campus or connecting several remote cameras in a city. Most PtMP systems in the United States operate in the unlicensed frequency bands of 900MHz, 2.4GHz, or 5GHz and in the licensed frequency bands of 3.65GHz and 4.9GHz.

A Mesh network is undoubtedly the most complex of the three network topologies. Also known as “Multipoint-to-Multipoint,” Mesh networks consist of three or more radios, all of which transmit and receive data to and from each other. This allows any radio on the network to act as a hub or base station. Mesh networks are designed to be self-healing and fully redundant so they are well suited for mission-critical applications. This makes Mesh a very popular solution for water-treatment facilities, utility companies and public safety/first responders such as police, fire, and EMS. Most Mesh networks in the U.S. operate in the unlicensed frequency bands of 900MHz, 2.4GHz and 5GHz, and in the licensed frequency band of 4.9GHz.

What to Watch for in Site Surveys

The first and most important step in any successful wireless deployment is performing a wireless site survey. Just as in a video surveillance site survey: Identify the customer’s wants/needs, locate power, measure cable runs, identify mounting structures, etc. However, with a wireless survey there are two additional and critical steps you must take to ensure successful deployment. First, verify line of sight (LOS) between all locations. Second, perform a frequency spectrum analysis.

Verifying LOS for short distances (less than one mile) can be as easy as climbing up to where you will mount the antenna and confirming visual LOS to the other location(s). However, in applications such as a citywide video surveillance deployment in which the wireless signal may be traveling several miles, additional steps need to be taken to verify LOS. A vital step in confirming LOS is accounting for the Fresnel (fray-NEL) zone.

As a radio wave is transmitted away from the antenna, it expands. At the midway point between the two antennas, the radio signal will be at its largest diameter. You can usually tolerate some obstruction of the Fresnel zone; however, the maximum allowable obstruction is 40%, while the recommended obstruction is 20% or less. Remember that the Fresnel zone is three dimensional. If you are transmitting between two buildings, you not only need to take into consideration obstacles that are on the ground, but also the distance between the two buildings.

Understanding and accounting for the Fresnel zone will enable you to determine the necessary antenna heights to ensure a clear LOS. There are many free calculators available that will help you determine the Fresnel zone for your application (search “Fresnel zone calculator”).

Performing a spectrum analysis is necessary to verify which RF bands and channels are being used in the area so you can avoid RF interference. Today it is safe to assume that there will be other RF radios in your area. Not knowing which frequencies are being used could mean the difference between a one-day install and weeks of troubleshooting. Spectrum analyzer options can range from an app on your phone to a rugged device costing tens of thousands of dollars (like most things, you get what you pay for).

For short range applications (less than a mile), you can usually get away with using a lower cost spectrum analyzer. If you are designing a network that spans several miles, however, it is well worth the investment of either renting a good spectrum analyzer yourself or hiring a third party. A spectrum analysis will identify other RF bands and channels in use in the area and ultimately be one of the deciding factors on which radio system and frequency you will choose for your solution.

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