Q. Are wireless backhaul systems secure? If so, what means of encryption do they use?
A. Most if not all point-to-point (as well as WiFi) systems today employ some means of encryption for security. Most point-to-point wireless backhaul systems incorporate AES encryption.  AES (Advanced Encryption Services) come in 128, 192, and 256 bit strengths. Although AES 192 and 256 offer a higher strength against brute force attacks, manufacturers offering these are doing so primarily for marketing purposes. AES 128 encryption would take a single computer running constantly billions of years to crack based on today’s technology. Even millions of computers running in parallel would not be able to successfully crack any of the AES algorithms in our lifetime.

Q. How fast is wireless backhaul?
A. Unlicensed wireless backhaul systems that run in the 5.8 GHz band typically range in speed between 18 Mbps up to as high as 100 Mbps full-duplex. Some short-range systems are said to run close to Gigabit speeds. But these are limited to a few thousand feet and consume practically the entire 5.8 GHz license-free band to do so. Also, it is worth noting some manufacturers advertise their system’s over-the-air speed in one direction which is a misleading marketing ploy to look faster than the competition. The full-duplex Ethernet speed is the important specification and is usually about 40% of the over-the-air single direction link speed. For example, if a particular radio specifies a 130 Mbps over-the-air link rate, the net full-duplex Ethernet speed is going to be somewhere in the 50-52 Mbps range. The full-duplex speed is the all important measurement of performance. There are two factors that govern the speed. One is purely distance. The farther apart the transceivers are from one another, the more time it takes the data to travel back and forth–hence less net user speed. Another factor in conjunction with distance is signal strength. The lower the signal strength, the higher the probable error rate. To counter this, manufacturers provide for multiple over-the-air link rates. In the U.S., the FCC allows lower link rates to be transmitted at progressively higher transmit levels–up to four times greater than at the highest link rates. This increases the signal strength at longer distances, but reduces the overall throughput.

Q. Do I need line-of-sight between my wireless backhaul antennas?
A. This is a multi-part question. Microwave energy exhibits different characteristics at various wavelengths (frequencies). Unlicensed backhaul systems typically run in the 900MHz, 2.4-2.5 GHz, and 4.9-5.9 GHz ranges. Typically, systems in the 900 MHz range will run non-line-of-sight since this band can pass through trees and other obstacles. Likewise, systems in the 2.4 and 2.5 GHz range can, to a lesser degree, pass through trees. These systems are billed as near-line-of-sight. Systems of 4.9 GHz and up are generally considered line-of-sight systems and do not perform well when blocked by trees and buildings. However, all of these systems will work well in rain, sleet, and show–showing some attenuation, but not a complete dropout of the signal.

Q. I’ve heard the 4.9 GHz band is licensed for public safety use only. How do I know if we qualify to use this band?
A. The 4.9 GHz public safety band was created to allow government agencies a reserved band to aid in law-enforcement, fire and rescue, and homeland security functions. Qualifying agencies need only fill out an online form and submit it to the FCC for approval. In general, if a government entity is involved in police and/or fire and rescue, it qualifies.

Q. What unlicensed frequencies are available?
A. In general, unlicensed “bands” are located in the 900 MHz, 2.4 GHz, 5.3 GHz, 5.4 GHz, and 5.8 GHz spectrum in the U.S. In addition, there is also the 4.9 GHz band that is strictly reserved for public safety use only. The 5.3 and 5.4 bands are referred to as DFS (Dynamic Frequency Selection) bands since they must give priority to other uses such as radar. When they sense radar on the same frequency, the radio must automatically switch to another frequency.