5G fixed wireless access in millimeter waves seen in the U.S. as the first phase of commercial 5G
5G fixed wireless access has emerged, particularly in the United States, as the likely first phase of commercial 5G services. This presents operators with the opportunity to offer 5G services as 3GPP continues to standardize the technological aspects of 5G, while gaining better insight into the characteristics of mobile 5G, especially as it relates to tapping into high capacity millimeter wave spectrum. Another key factor underpinning the interest in fixed wireless 5G relates to the business case in that a gigabit per second signal can be delivered without the costly and time consuming process of running fiber to every home, apartment or business, effectively addressing the lingering last mile problem with fiber.
AT&T and AT&T Labs have a big presence in Austin, Texas, where the telco offers gigabit-speed home and business fiber broadband, as well as its 5G Evolution service, which uses three channel carrier aggregation, multiple-input, multiple-output (MIMO) and 256 QAM to double the speeds of its regular LTE speeds and is only available on Samsung Galaxy S8 and S8+ devices. In addition to these mobile-related initiatives, AT&T is using Austin as a testbed for its 5G fixed wireless access services.
In partnership with Ericsson and Intel, AT&T last year used millimeter wave spectrum in the 15 GHz and 28 GHz bands, to test enterprise 5G applications at one of Intel’s local offices. That trial pushed more than a gigabit per second in support of enterprise apps including internet access, virtual private network connections, 4K video streaming, delivery of DirecTV and VoIP. The field trial extended lab testing in several frequency bands and involving not only Ericsson, but also Samsung and Nokia.
Wolter, AT&T Labs AVP of of radio technology and strategy, said the trial at Intel’s office had a range of about 250 meters. “The enterprise customer then had the device, which terminated the 28 GHz 5G signal, then we distributed that to multiple users via Wi-Fi. We gave it a workout as to what an enterprise would need from that kind of a system and let the employees of the enterprise use it. We are, in fact, continuing that work, but what we’ve done now is to extend that to a friendly user trial that involves residential and small business users.”
That trial, also in Austin, uses Ericsson’s 5G RAN (radio access network) and Intel’s 5G Mobile Trial Platform. Ericsson AIR 6468 is billed by the Swedish infrastructure giant as “the industry’s first 5G NR-capable radio; it has 64 transmit and 64 receive antennas for massive MIMO and multi-user MIMO, as well as advanced beamforming enabled by a “split cloud RAN architecture,” and is meant to support LTE and evolve to the coming 5G standard. Intel’s Mobile Trial Platform, the second generation of which was unveiled at Mobile World Congress earlier this year, features a 28 GHz radio frequency front end and 4×4 and 8×8 millimeter wave arrays. This trial extends functionality from an enterprise setting to include residential and small business and delivers DirecTV NOW over a fixed wireless signal.
“What we’ve been looking at there,” Wolter said, “is adding additional base stations, antennas, as well as additional customers. We started out with small business users and here we’re putting the device in the customer’s premise behind a window pointing out towards our base stations.” In addition to “generally putting the technology through its paces,” Wolter said the operator is studying millimeter wave propagation characteristics in both line-of-sight and non-line-of-sight conditions.
“As to the number of devices that can be served,” he continued, “that’s going to depend on the ability of the software. What is gets down to eventually is what does the traffic load look like, what is the demand? When you talk about capacity, you have to start getting into those questions and simulate the system, including all the scheduling behavior to see what that all looks like. That one is a little tough to answer as we’re a little early in the day.”
He explained that for this expanded 5G fixed wireless access trial, “We’ve run fiber from our lab out to two telephone poles we have a little less than a mile from the building we’re using. We have the baseband units in our lab. What’s out at these poles are the radio heads. One of our apartments is behind probably 20 meters of foliage between the antennas and the window this unit is in. As you would, given the beamforming capability, it has actually found a bounced signal that is stronger than the main signal. It is getting around some of the limitation so foliage by bouncing around that. Others are direct line of sight.”
Another major factor, particularly given modern construction techniques, is window attenuation, Wolter said. “You can’t just say, ‘I’ll put this 5G modem in the closet and connect my internet.’ That’s not going to work. Right now everything is mounted in a window facing the base station.” Reflective window coatings are a major hindrance; Wolter said AT&T had to replace infrared reflective glass with more traditional dual pane glass. “That’s going to be a concern that people have to think about if you’re trying to do any kind of indoor deployment. The equipment is not ready to do that just yet.” And, while Wolter said AT&T has verified beamforming, beam tracking, beam acquisition, higher throughput and lower latency– “all the things you’d hope to find in a millimeter wave system,”–but, at the end of the day, “Everything is dependent on environment.”
According to materials provided by AT&T, use cases for 5G fixed wireless access could include a customer going to a dentist’s office and using connectivity “that allows customers to do things like immerse in augmented or virtual reality as they pass the time…A hometown retail shop can utilize the enhanced reliability to enable an all mobile checkout experience.”
