AUSTIN, Texas – AT&T outlined a vision for “5G” networks using millimeter wave technology at this year’s Texas Wireless Summit. The carrier also demonstrated its 5G network technology with Ericsson.
Arunabha Ghosh, director of wireless communications at AT&T Labs, said mm wave spectrum is plentiful but can be difficult to use. He said that due to noise limitations, power amplifiers are less efficient in mm wave networks than they are in lower bands. The solution, he said, is to place cell sites very close together.
“If you want to use 500 megahertz of spectrum and deliver 100 megabits per second, you have to have the sites like 200 meters apart maximum, 100 meters for autonomous vehicles,” he said. “A city block in Austin is 200-250 meters. You are talking about several small cells deployed every block to support this 100 megabits per second that we need.”
A dense network of small cells will require more fiber, Ghosh said, adding that in some desirable small cell locations fiber might be just a few feet away, but still be very hard to access. He also noted that highways will need to support connected cars, and fiber is often unavailable alongside highways.
Ghosh said that 5G networks also will require new network architectures. He said mm wave offers large amounts of bandwidth and many of the envisioned use cases will have high variability in the number of users. Therefore AT&T is looking at architectures that use the same frequencies for access and over-the-air backhaul.
AT&T also foresees multihub networks. He said there are at least two possible ways to design multihub networks. One would be true mesh networks that could let each node determine the route of the packet, but Ghosh said that in this scenario the worst case quality of service might be insufficient for some critical applications. Another approach would be to use the uplink and downlink to create a more hierarchical system.
Transitions will need to be much faster in mm wave networks than they are in current networks, he said, and for mm wave networks, blocking is actually a blessing because the distances between access points are so short. But when blocking occurs, traditional handovers will not be fast enough to keep users connected.
“When you have blocking in mm wave the transition periods are much faster,” Ghosh said. “Once a base station starts to fade, you can do a handover in the networks we are used to. But not in mm wave … very fast switching is needed.”
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