The unlicensed V-band has been getting a lot of attention of late. The initial focus was on using it for residential broadband, but now the interest has turned to in-building wireless backbones. One of the great advantages of the V-band is that it has an enormous amount of spectrum (14 GHz in the U.S.) and can achieve very high spectral reuse with beamforming technology. The weakness of the band is that the range is limited (largely because of oxygen absorption), and it has trouble with foliage and rain, none of which are a problem when operating indoors, but obstructions are always a problem.
The list of in-building obstructions includes people, walls, furniture, and equipment. One way to mitigate this problem is to mount the radios just below the ceiling, which eliminates everything except for the walls. Common building materials include sheetrock (aka drywall), wood, glass, brick, stone, metal, and concrete. Sheetrock is found in all modern office buildings, but the others will also be present in most cases. A sheetrock wall is fairly transparent to 60 GHz signals and usually consists of two ½ inch pieces of gypsum separated by an air gap of about 4 inches. That gap is often filled with soundproofing material, but these substances are not dense and are easily penetrated. Places where you might run into metal include elevator shafts that are usually in the center of the building. Glass can be divided into interior single-pane glass that is easily penetrated and exterior dual-pane glass with a metallic coating that is almost totally impenetrable to 60 GHz signals. The latter is actually a good thing as it prevents interior RF from escaping the work area, and exterior RF from entering the work area.
So, what is to be done when designing an in-building wireless backbone when obstructions are present?
There are two ways to deal with obstructions. Option #1 is to use a system that can route around an obstruction. This is best done using a dual counter-rotating wireless ring configuration such as the Airvine WaveTunnel system described below.
In this scenario, the WaveTunnel nodes can be positioned to pick up traffic from locally attached Wi-Fi 6/6E AP’s, while at the same time relaying traffic from neighbor nodes. If the network is laid out properly it can pass traffic around a serious obstruction, such as an elevator shaft. The relaying of the signal also overcomes signal attenuation, which enables the system to cover a lot of area at a very low cost.
If it’s not possible to route around an obstruction, then the only other alternative is to blast right through it with a system that has the link budget to handle the extra attenuation (option #2).
A lot of work has been done over the years to categorize V-band signals as they pass-through different building materials. Testing at Airvine has produced the following data (attenuation numbers are in dB/cm).
Certain building materials are easy to pass-through such as sheetrock, plywood, and single pane glass, and others are far more problematic. In our testing, nothing was more challenging than concrete (cavity cinder block) which provided 11.3 dB of attenuation per centimeter or about 45 dB per block.
WaveTunnel technology has the link budget to allow RF signals to pass-through a variety of wall materials when the option to route around them does not exist. The extra link budget is made possible by operating indoors where the range is limited (as is the Free Space Path Loss), and by developing a very high-gain beamforming antenna (approaching 30 dBi). The narrower the beam (pencil width) the higher the gain, and the higher the gain the more easily it can BLAST THROUGH WALLS!
For more on Airvine technology and the All-Wireless Enterprise please visit us at www.airvine.com.