5.9 GHz spectrum and transportation technology, explained

November 23, 2020

Tyson Fisher


The Federal Communications Commission recently made most of the 5.9 GHz spectrum available for unlicensed use, after it was reserved only for smart vehicle technology since 1999. What exactly does all this mean?

On Nov. 18, the FCC announced that it will make the lower 45 megahertz (5.850-5.895 GHz) of the 5.9 GHz spectrum available to unlicensed uses like Wi-Fi, with the upper 30 megahertz (5.895-5.925 GHz) reserved for enhanced vehicle safety using cellular vehicle-to-everything tech, better known as C-V2X.

What is the 5.9 GHz spectrum?

Whenever we broadcast anything, it needs a way to get from point A to point B. When delivering goods, the mode of transportation is a truck. When delivering information, the mode of transportation is the airwaves.

Radio frequency is broken down into spectrums from 30 Hz to 300 GHz. Spectrums are further broken down into sections called bands. Governments regulate those bands and spectrums by allocating them for specific uses. For example, the 30-300 MHz spectrum is used for radio and television broadcasts. The extremely high frequency of 30-300 GHz is for stuff like radio astronomy and directed-energy weapons. The point of regulating frequencies is to make sure no band or spectrum is congested to the point of rendering it useless.

Currently, most Wi-Fi devices communicate using the 2.4 GHz or 5 GHz bands. The lower bands deliver farther, whereas the higher band travels faster. That’s why there will need to be more transmitters for 5G cellphones, for example.

For the past two decades, the entire 5.9 GHz spectrum (5.850-5.925) was reserved for intelligent transportation systems like C-V2X. Meaning, only devices for transportation-related purposes have been allowed access to that spectrum. Now, most of the bands in that spectrum are accessible to devices like wireless internet routers.

Some say this is disastrous for future autonomous and safety technology for vehicles. On the other hand, others say the transportation industries have been hoarding the spectrum for too long.

The case for 5.9 GHz spectrum for transport only

Immediately after the FCC announced the reallocation of the 5.9 GHz spectrum, transportation stakeholders heavily criticized the move.

The American Association of State Highway and Transportation Officials released the following statement:

“AASHTO is disappointed that the FCC has abandoned the 5.9 GHz safety band, despite the unified voice of state DOTs and the broader transportation industry. The leaders of all 50 state departments of transportation, the District of Columbia and Puerto Rico are unanimous in their support for preserving the 5.9 GHz wireless spectrum for transportation-only usage. Without the full 5.9 GHz spectrum available to use for connected vehicle technologies it will be significantly more difficult to eliminate the kinds of fatal vehicle crashes that contribute to more than 37,000 fatalities on America’s roadways each year, as well as the safe deployment of connected and automated vehicles.”

The Intelligent Transportation Society of America said, “Today’s move will, in effect, likely render the entire band useless for safety. We are evaluating all possible options to preserve public safety and significantly reduce the tragic deaths of nearly 37,000 people who die on our roadways every year.”

Essentially, stakeholders are claiming they need all of that space. Getting rid of any of that allocated space, let alone most of it, could drastically slow down and jam up vehicle technology.

If traffic safety is at stake, why did the FCC reallocate the 5.9 GHz spectrum to mostly Wi-Fi users?

According to the FCC, vehicle technology under which the spectrum was reserved “has not been meaningfully deployed.” For the most part, stakeholders are not using the spectrum. In other words, you snooze, you lose.

However, stakeholders are arguing that it takes years and sometimes decades to develop new, groundbreaking technology like C-V2X. They need that space to develop the tech, and they will certainly need all of it to deploy such technology. Stakeholders are basically calling the FCC impatient, and saying that impatience can be detrimental to safety.

Internet traffic congestion solution?

Just as many people are applauding the FCC’s move, especially wireless communications stakeholders and consumers.

As mentioned above, wireless devices are communicating mostly through the 2.4 GHz and 5 GHz spectrum of bands. Back in the earlier part of the 21st century, and certainly in 1999, that was not much of an issue. Cellphones and the internet in general were not nearly as prevalent as they are today.

Considering wireless technology was not as cheap and accessible 20 years ago, not as many people had devices taking up space on those bands. Since the turn of the century, technology has advanced exponentially. Today, nearly everyone has a cellphone. In fact, most people in the U.S. probably use multiple Wi-Fi devices daily. With the number of people and devices using the 2.4 GHz and 5 GHz bands having increased by an order of magnitude, space is running out.

Consumers complain about the lag time on wireless devices. Documents take too long to download. Signals drop. Internet browsers keep crashing. With everyone scrambling to use the same frequencies at the same time, there’s not enough space for information to freely travel.

In fact, think of the 5.9 GHz spectrum as a highway.

Above, I mentioned that information travels through the airwaves like goods travel on trucks. If information is the goods and airwaves are the trucks, think of these bands as highways. Only some vehicles were traveling on two major highways: 2.4 GHz and 5 GHz. Traffic was very light. A third highway, 5.9 GHz, was for only vehicle research and future self-driving cars.

As more people began to own vehicles, traffic on 2.4 GHz and 5 GHz increasingly became more congested. A trip to deliver goods and people that once took 30 minutes can now take up to an hour or more. Meanwhile, 5.9 GHz is mostly empty. However, those who have access to 5.9 GHz keep telling the public that they will inevitably use all of it and so will everyone else someday.

After a certain amount of time, motorists on 2.4 GHz and 5GHz got fed up with the congestion despite the fact there was a completely unused highway available. The government eventually opened up most of that highway to the public. Now, goods and people are travelling faster and more smoothly.

That highway analogy is the argument for the reallocation of the 5.9 GHz spectrum. Wireless devices need more space, and the 5.9 GHz spectrum has been mostly unused since 1999.

Although the effect on consumer products is clear, what effect the reallocation of space will have on vehicle technology is not. Transportation Secretary Elaine Chao claims the decision will lead to “thousands more deaths annually on-road and millions more injuries than would be the case otherwise.” Others say transportation industries will adapt, as they always have. Fingers crossed that Chao is wrong on this one.  LL

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Tyson Fisher

Tyson Fisher joined Land Line Magazine in March 2014. An award-winning journalist and tireless researcher, his news reports, features and blogs bring depth to our editorial content, backed with solid detail. Tyson is a lifelong Kansas Citian.