The Federal Communications Commission is starting to plan for cellular networks that can send users gigantic streams of data, but there are technical challenges to be solved and years of work ahead.

A Notice of Inquiry issued unanimously by the commission on Friday identifies frequencies of 24GHz and above as being able to provide gigabit or even 10Gbps speed. This would be a major change because today’s cellular networks use frequencies from 600MHz to 3GHz, with so-called “beachfront spectrum” under 1GHz being the most desirable because it can be used to deliver data over long distances. AT&T and Verizon Wireless control the most beachfront spectrum.

"It was long assumed that higher spectrum frequencies—like those above 24 GHz—could not support mobile services due to technological and practical limitations," the FCC said in a press release. "New technologies are challenging that assumption and promise to facilitate next generation mobile service—what some call '5G'—with the potential to dramatically increase wireless broadband speeds."

Rather than replacing today’s lower-spectrum systems, networks with frequencies of 24GHz and above could complement them by providing much higher data rates over short distances—perhaps very short. A new Wi-Fi standard that uses 60GHz can deliver up to 7Gbps but only if the transmitter and receiver are in the same room, for example.

The FCC’s notice talks about frequencies as high as 90GHz. Anything over 30GHz is classified as “millimeter wave frequencies,” which are blocked by walls. Indoor coverage is going to be tough.

“[W]hatever licensing regimes we adopt should take into account the fact that signals from carriers’ outdoor base stations will rarely be able to penetrate into the interiors of buildings, where around 75 percent of cellular data usage occurs today,” the FCC wrote. “Reaching such spaces will almost certainly require the deployment of indoor base stations.”

The FCC is asking experts for input on technical and licensing questions. The FCC wants to examine potential ways “mobile services can avoid interfering with each other” and with existing technologies that share the same frequency bands or operate in adjacent ones. The FCC said it intends to adopt licensing schemes that minimize the potential of interference while giving carriers what they need to boost data speeds.

Carriers holding exclusive licenses to spectrum are the norm today, but the FCC said it’s possible that carriers could share higher-frequency spectrum by using “dynamic beamforming capabilities” that distribute signals on different paths so as not to interfere with one another. Licenses could also be granted for smaller geographic areas than usual to minimize the amount of unserved real estate.

Another question is how much contiguous spectrum will be needed by operators in order to deliver high data rates.

“Nokia’s studies suggest the need for 2 gigahertz of contiguous spectrum to achieve maximum data throughputs of 10Gbps and at least 100Mbps at the cell edge with a maximum latency of no more than 1 millisecond,” Nokia said. “Samsung has demonstrated 500 megahertz systems in the 28GHz band with data rates ranging from 260Mbps to 1Gbps. We also seek comment on whether technology will allow licensees to effectively aggregate smaller, non-contiguous blocks of spectrum for use in providing mobile services, possibly reducing the need for large blocks of contiguous spectrum.”

Although millimeter waves require line-of-sight access to receivers, creative strategies might expand their use. Field trials conducted “at New York University and the University of Texas with funding from the US Army and Samsung… found that 39GHz mobile base stations can sustain 100 percent coverage in cells with a 200-meter radius in high-density urban areas,” the FCC said. “Receivers equipped with highly directional, steerable antennas were able to capture and combine as many as 14 links with rooftop-mounted transmitters despite obstructions in propagation paths, i.e., the receivers were able to ‘see’ multiple reflected signals from places where lines of sight to base stations were blocked. Samsung has conducted similar trials at 28 and 38 GHz, respectively, in Suwon, Korea, and Austin, Texas.”

While these higher frequencies may end up being used in 5G networks that replace today’s 4G ones, “[t]he truth is that 5G wireless technologies are likely to use many spectrum bands and may or may not include these millimeter wave frequencies,” Commissioner Michael O’Rielly wrote in a statement on the FCC’s decision.

5G commercial offerings could reach consumers within six years, Commissioner Ajit Pai wrote.

The FCC said it does not plan to require use of a specific technology or 5G standard. Instead, the commission said it intends to “let innovation and market competition drive the direction of technological development, and to put in place regulations that can accommodate future technological advances.”