As outdoor small cells are deployed in higher density for LTE and 5G, wireless backhaul will commonly be used to provide the base station connectivity. Due to the high number of links that result in lot of spectrum usage, as well as the required short link lengths, the millimeter wave bands are being considered as ideal spectrum for this small cell backhaul application. However, there’s still a lot of debate and questions around which of the bands to use. Like most wireless network cases, there is no a clear black and white answer for this scenario—one that can also vary significantly by region. A good approach is to look at the suitability and characteristics of both V-Band (60 GHz) and E-Band (70/80 GHz), as they relate to small cell backhaul.
V-Band (60 GHz)—60 GHz has 5+ GHz of spectrum available in most countries, so there is plenty of room for a lot of high capacity services. Although there is high oxygen absorption in this band, this reduces inter-system interference, and is still very suitable for links in the 300 to 500 meter range. 60 GHz has also been very attractive for many component suppliers that are producing high volume 60 GHz parts to support the WiGig standard. When these commodity parts can be reused for small cell backhaul systems, it can result in very cost effective radios.
The focus on V-Band from WiGig, has resulted in a great deal of R&D work on electronically steerable antennas. Electronically steerable antennas have many benefits that can be leveraged to reduce Total Cost of Ownership, as discussed in my previous paper, Antenna Steering for 5G Backhaul. 60 GHz also allows for small antennas (six in or 15 cm) in most countries, which is ideal for inconspicuous, low profile street- level deployments. 60 GHz is an unlicensed band in most jurisdictions, and is also open for many uses beyond telecom. Because it is unlicensed, there is no process to acquire part of the spectrum for exclusive use in a certain geographical area—a real concern for some operators, as they may face interference. While this currently is not an issue due to light use of the band, the beamwidths are very narrow and oxygen absorption limits the interference range. Because of this, interference could become a deployment hurdle in the future.
E-Band (70/80 GHz)—In E-Band, there is 10+ GHz spectrum available in most countries, also making it very suitable for high density and high capacity wireless backhaul applications. The oxygen absorption in the E-Band is much lower compared to the V-band, but it faces higher fade from rain. This can be engineered into the link though, and E-band is very suitable for small cell links of 300-500 meters. The 70/80 GHz band is a licensed or lightly licensed band in most countries, and is restricted to backhaul applications. The fees are typically quite low, especially on a per-MHz basis, so it is very economical for backhaul deployments. What’s more, because it is more regulated, it does not face any of the interference concerns that may rise in the V-Band spectrum. As the band has primarily been limited to backhaul, there are much lower volumes on the components, and there has not been much development on (electronically) steerable antennas in E-Band. E-Band also permits small antennas suitable for street level deployments, with the exception of the United States, where there is currently a 12” limitation, although the FCC is publicly considering changing this regulation through their recent NPRM (Notice of Proposed Rule Making) process.
Both the E-band and V-Band spectrum are very suitable for small cell deployment. The V-Band is promising in that there may be very low cost and electronically steerable-antenna solutions in the future, but those advantages must be weighed against the potential for interference in this band.
Reader Interactions