As the lines between unlicensed and licensed spectrum blur in carrier strategies, bands of both types are increasingly valued and therefore contested. This is clear in the acceleration of spectrum-related developments in the US so far this year, starting with the record sums raised for the non-beachfront AWS-3 licences, and now seen in a series of disputes over the next frequencies to become available for licence-exempt use, including extended 5GHz, 3.5GHz, and the spaces in the 600MHz broadcast bands.
In the licence-exempt spectrum, there are many interested parties, not just wireless service providers. The car industry is pitched against the broadband business, for instance, as Congress seeks to pass a reworked ‘WiFi Innovation Act’, which would pave the way to open up the higher end of the 5GHz band (5850-5925GHz) for unlicensed broadband technologies like WiFi. However, the 5.9GHz band is already the home of ITS (intelligent transportation systems) for car safety.
The Act has been introduced this week in the Senate and is supported by a companion bill in the House of Representatives. The legislation, originally proposed last summer, has been modified but has the same goal – to get the FCC to test the feasibility of opening up this new bandwidth for WiFi. However, car makers are concerned about possible interference with vehicle safety systems, which are seeing rapid uptake.
Senator Marco Rubio, one of the proposers of the Senate bill, said: “America’s policies must adapt to the colossal technological advancements that are defining the twenty-first century and transforming the very nature of the American economy. The WiFi Innovation Act would bolster innovation, spur economic development, and increase connectivity by providing more spectrum to the public.”
His bill would require the FCC to conduct testing “that would provide more spectrum to the public,” though he added “we are ultimately putting the resource to better use and recognizing the future needs and important work being done in intelligent transportation.”
He was backed by many industry groups such as the Wireless Innovation Alliance, which includes Dell, Google and Microsoft, and the TIA, whose members include Apple, Cisco and VMware. The latter said in a statement: “The US is in vital need of more spectrum in order to meet unprecedented and growing demand for video, data, Wii connectivity and more. The Innovation Act identifies meaningful steps to help alleviate the spectrum crunch that threatens the advancement of global communications.”
However, in its own hyperbole, the equivalent body in the car safety space – ITS America – The High Tech Transportation Association – trumped better broadband access with saving lives, saying: “We are on the cusp of a revolution in vehicle safety that will save thousands of lives each year and dramatically reduce the nearly $1 trillion cost of traffic crashes and congestion to families, communities and the nation’s economy.”
It said that there was already ongoing collaborative work, involving experts from the automotive, WiFi and intelligent transportation systems (ITS) industries, to investigate possible spectrum sharing technologies which would allow WiFi to coexist in the 5.9GHz band, “without delaying time-critical communications needed to prevent crashes”. It argues that “this collaborative process should continue without Congressionally-imposed deadlines, restrictive parameters or political pressure that creates regulatory uncertainty and could delay bringing these life-saving crash prevention technologies to consumers.”
Another thorny debate in the US concerns the licence-exempt guard bands in the 600MHz spectrum. The FCC is proposing rule changes for unlicensed operations in the television bands, the repurposed 600MHz band, 600MHz guard bands and duplex gap, and Channel 37. The attempt to increase licence-exempt wireless use of these bands, without interfering with the primary users, will affect the frequencies which continue to be held by broadcasters after next year’s incentive auction, and those which will pass to mobile operators.
Qualcomm, no fan of unlicensed spectrum, has been vocal in claiming that this use of the guard bands would cause harmful interference to mobile services, in violation of FCC rules and the Spectrum Act. It is reiterating many of its claims now in response to the FCC’s Notice of Proposed Rulemaking (NPRM). “This harmful interference will occur when a white space device is within 19 meters (or 62 feet) of a 600MHz cellular device, using the FCC’s proposed parameters,” Qualcomm said in its latest filing. “Nothing has changed.” It added that one proposed protection radius, of seven meters, was not “a viable, reasonable or defensible interference protection radius … devices using WiFi and LTE are much closer than that all the time and virtually everywhere – at work, at home and in public places. So, the NPRM’s own analysis and Qualcomm’s extensive technical studies both confirm that the proposed rules for unlicensed devices in the duplex gap and guard bands are untenable.”
By contrast, arch-rival Broadcom, which is a powerhouse in WiFi as Qualcomm is in LTE, is positive about many aspects of the proposals. It submitted its own comments, as reported by IDG, that the FCC’s proposed band plan for duplex-gap operations (with a 40 mW power restriction on unlicensed devices) would adequately protect LTE downlink. “We have conducted extensive research on this question. Our work, supported by both mathematical analysis and real world testing, clearly indicates that the answer is ‘yes’,” said the filing. “Our analysis shows that unlicensed devices can easily coexist with licensees at powers well in excess of 40 mW, even when separated by 4MHz rather than the 5MHz separation contemplated in the NPRM for the duplex gap.”
For its part, Google – perhaps the greatest of the campaigners for more WiFi spectrum and for harnessing the white spaces in the TV bands – analyzed both chipmakers’ tests and concluded: “Broadcom’s analysis is vastly more realistic than Qualcomm’s. Google agrees that the touchstone of interference analysis should be how devices perform under reasonably foreseeable conditions. The interference analyses submitted by Broadcom reflect this standard, while those submitted by Qualcomm do not.”
Another US band where non-traditional wireless providers hope to be able to muscle in on the cellcos’ territory is 3.5GHz, which the FCC wants to redesignate as the ‘Citizens Broadband Radio Service’ (CBRS). The regulator has proposed a three-tiered spectrum sharing system in this band, with different levels of access priority for federal incumbents, licensed non-federal users and general access users. At the recent Spectrum 2025 conference, Preston Marshall, principal wireless architect at Google, said he thinks the FCC will finalize rulemaking on the band in the next few months.
He said there were no real concerns about interference with the current incumbent, the US Navy, which has radar systems in this spectrum, as it would be the top-tier licensee. The second tier would be for priority access licensees (PALs), probably wireless carriers. PAL users will be able to obtain one-year licences for 10MHz of spectrum as long as they guarantee not to interfere with the Navy users (they do not get protection from government users in return).
The third tier is for general authorized access (GAA) users, which could be MNOs, enterprises or unlicensed technology users. They have the same rights and obligations as PAL users in the second tier. Equipment that covers one part of the band has to work in all parts of the band for all users, so carrier equipment would have to work for GAA users.
With the cellular community eyeing parts of 3.5GHz as a potential global small cell band, and Google seeing opportunities for a new implementation of WiFi, this is one of the most interesting of the emerging spectrum options – one where licensed and unlicensed technologies may coexist; traditional and non-traditional service models develop; and where the nascent spectrum sharing ideas, which most agree are vital to avoid future shortages, can be tested in relatively uncluttered frequencies.
The FCC is defining the CBRS 3.5GHz band as 3550-3650 MHz, with possibly 50 MHz more being added to take it to an upper limit of 3700 MHz. Half of the spectrum will be set aside for GAA users. The 3GPP has defined Bands 42 (3400-3600MHz) and 43 (3600-3800MHz) for TD-LTE use, and Marshall said the current assumption is that the US system would be based on TD-LTE, especially as that technology is already in use in the 2.5GHz band at Sprint.
However, licensed spectrum carriers may be wary of operating in this very new way (though they are having to get used to shared and unlicensed bands quickly as the LTE-LAA debates show – see separate item). Google supports the FCC’s plan to have a centralized spectrum manager, or Spectrum Access System (SAS), to assign channels dynamically and support dynamic aggregation to assign the channels in real time. This kind of model has been championed by the search giant for years, to encourage more flexible spectrum allocation. It argues this would support large numbers of small service providers, even those which need bandwidth only at certain times of day, for instance, and so could not afford a full MVNO deal – and it would also provide better QoS levels for certain sensitive applications than a fully unlicensed free-for-all band. Carriers like AT&T have supported SAS as a way to manage the different tiers of licensees, but oppose the dynamic aspects, which would start to break down the habit of long term, static spectrum allocations on which the power of the cellcos rests.