5.9 GHz – POTs and PANs

FCC Proposes New WiFi Spectrum

On December 17 the FCC issued a Notice of Proposed Rulemaking for the 5.9 GHz spectrum band that would create new public spectrum that can be used for WiFi or other purposes. The 5.9 GHz spectrum band was previously assigned in 2013 to support DSRC (Dedicated Short Range Communications), a technology to communicate between cars, and between cars and infrastructure. The spectrum band covered by the order is 75 megahertz wide. The FCC suggests that the lower 45 megahertz be made available to anybody as new public spectrum. They’ve assigned the highest 20 megahertz for a newer smart car technology called C-V2X. The FCC tentatively kept the remaining bandwidth for the older DSRC technology, dependent upon the users of that technology convincing the agency that it’s viable – otherwise, it also converts to C-V2X usage.

DSRC technology has been around for twenty years. The goal of the technology is to allow cars to communicate with each other and to communicate with infrastructure like toll booths or traffic measuring sensors. One of the biggest benefits touted for DSRC is increased safety so that cars will know what’s going on around them, such as when a car ahead is braking suddenly.

For the new technology, the V2X stands for vehicle-to-everything. Earlier this year Ford broke from the rest of the industry and dropped research in DSRC communications in favor of C-V2X. Ford says they will introduce C-V2X into their whole fleet in 2022. Ford touts the technology as enabling cars to ‘see around corners’ due to the ability to gather data from other cars in the neighborhood. They believe the new technology will improve safety, reduce accidents, allow things like safely forming convoys of vehicles on open highways, and act as an important step towards autonomous cars. C-V2X uses the 3GPP standard and provides an easy interface between 5G and vehicles.

This decision was not without controversy. The Department of Transportation strenuously opposed the reduction of spectrum assigned for vehicle purposes. The DOT painted the picture of the spectrum providing a huge benefit for traffic safety in the future, while the FCC argued that the auto industry has done a poor job of developing applications to use the spectrum.

This is an NPRM, meaning that there will be a cycle of public comments before the FCC votes on the order. I think we can expect major filings by the transportation industry describing reasons why taking away most of this spectrum is a bad idea. On the day of the FCC vote, Elaine Chao, the Secretary of Transportation said that the FCC is valuing Netflix over public safety – so this could yet become an ugly fight.

Perhaps the biggest news from the announcement is the big slice of the spectrum that will be repositioned for public use – a decision praised by the WiFi Alliance. The FCC proposes to make this public spectrum that is open to everybody, not just specifically for WiFi. The order anticipates that 5G carriers might use the spectrum for cellular offload. If the cellular carriers heavily use the spectrum in urban areas, then the DOT might be right and this might be a giveaway of 5G spectrum without an auction.

There is no guarantee that the cellular carriers will heavily use the spectrum. Recall a few years ago there was the opportunity for the cellular carriers to dip into the existing WiFi spectrum using LTE-U to offload busy cellular networks. The carriers used LTE-U much less than anticipated by the WiFi industry, which had warned that cellular offload could overwhelm WiFi. It turns out the cellular carriers don’t like spectrum where they have to deal with unpredictable interference.

Even if the cellular carriers use the spectrum for cellular offload in urban areas, the new public block ought to be mostly empty in rural America. That will create an additional spectrum band to help boost point-to-multipoint radios.

Regardless of how the new spectrum might be used outdoors, it ought to provide a boost to indoor WiFi. The spectrum sits just a little higher than the current 5.4 GHz WiFi band and should significantly boost home WiFi speeds and volume capability. The new spectrum will provide an opportunity to reduce interference with existing WiFi networks by providing more channels for spread home use.

This particular docket shows why spectrum decisions at the FCC are so difficult. Every potential use for this mid-range spectrum creates significant public good. How do you weigh safer driving against better 5G or against better rural broadband?

The Death of 2.4 GHz WiFi?

It’s been apparent for a few years that the 2.4 GHz band of WiFi is getting more crowded. The very thing that has made the spectrum so useful – the fact that it allows multiple users to share the spectrum at the same time – is now starting to make the spectrum unusable in a lot of situations.

Earlier this year Apple and Cisco issued a joint paper on best network practices for enterprises and said that “the use of the 2.4 GHz band is not considered suitable for use for any business and/or mission critical enterprise applications.” They recommend that businesses avoid the spectrum and instead use the 5 GHz spectrum band.

There are a number of problems with the spectrum. In 2014 the Wi-Fi Alliance said there were over 10 billion WiFi-enabled devices in the world with 2.3 billion new devices shipping each year. And big plans to use WiFi to connect IoT devices means that the number of new devices is going to continue to grow rapidly.

And while most of the devices sold today can work with both the 2.4 GHz and the 5 GHz spectrum, a huge percentage of devices are set to default to several channels of the 2.4 GHz spectrum. This is done so that the devices will work with older WiFi routers, but it ends up creating a huge pile of demand in only part of the spectrum. Many devices can be reset to other channels or to 5 GHz, but the average user doesn’t know how to make the change.

There is no doubt that the spectrum can get full. I was in St. Petersburg, Florida this past weekend and at one point I saw over twenty WiFi networks, all contending for the spectrum. The standard allows that each user on each of these networks will get a little slice of available bandwidth, which leads to the degradation of everyone using it in a local neighborhood. And in addition to those many networks I am sure there were many other devices trying to use the spectrum. The WiFi spectrum band is also filled with uses by Bluetooth devices, signals from video cameras and is one of the primary bands of interference emitted by microwave ovens.

We are an increasingly wireless society. It was only a decade or so ago where people were still wiring new homes with Category 5 cable so that the whole house could get broadband. But we’ve basically dropped the wires in favor of connecting everything through a few channels of WiFi. For those that in crowded areas like apartments, dorms, or within businesses, the sheer number of WiFi devices within a small area can be overwhelming.

I’m not sure there is any really good long-term solution. Right now there is a lot less contention in the 5 GHz band, but one can imagine that in less than a decade that it will also be just as full as the 2.5 GHz spectrum today. We just started using the 5 GHz spectrum in our home network and saw a noticeable improvement. But soon everybody will be using it as much as the 2.4 GHz spectrum. Certainly the FCC can put bandaids on WiFi by opening up new swaths of spectrum for public use. But each new band of spectrum used is going to quickly get filled.

The FCC is very aware of the issues with 2.4 GHz spectrum and several of the Commissioners are pushing for the use of 5.9 GHz spectrum as a new option for public spectrum. But this spectrum which has been called dedicated short-range communications service (DSRC) was set aside in 1999 for use by smart vehicles to communicate with each other to avoid collisions. Until recently the spectrum has barely been used, but with the rapid growth of driverless cars we are finally going to see a big demand for the spectrum – and one that we don’t want to muck up with other devices. I, for one, do not want my self-driving car to have to be competing for spectrum with smartphones and IoT sensors in order to make sure I don’t hit another car.

The FCC has a big challenge in front of them now because as busy as WiFi is today it could be vastly more in demand decades from now. At some point we may have to face the fact that there is just not enough spectrum that can be used openly by everybody – but when that happens we could stop seeing the amazing growth of technologies and developments that have been enabled by free public spectrum.

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