Urban Air Mobility Will Not Succeed Without a Dedicated 5G Network
April 17, 2019
By Brian L. Hinman
Clover Aviation, Inc.
As CEO of the newly-formed Clover Aviation, my primary goal is to address the exciting new Urban Air Mobility opportunity, developing an aircraft that will define the standard of air travel for decades to come. The near-term operations of these aircraft will obviously fly under existing air traffic rules. In the long-term, however, how should air traffic control work to address this new category of air travel, and what will the network of the future need to look like in order to carry this traffic? How should the rules change to govern a mixture of piloted and autonomous aircraft, some carrying cargo, some carrying passengers, and densified by a factor of a thousand?
The problems are complex, to be sure, and the FAA has segregated the work for future passenger aircraft traffic control, called “NextGen,” from the future air traffic control system for drones, called “UTM” (Unmanned Aircraft System Traffic Management). The work on NextGen began in 2007, with the goal of completion by 2025. Almost in parallel, the dramatic growth of the drone market gave rise to the concept of UTM, with work initiated in 2015, including participation from NASA, as well as a number of private entities. The Global UTM Association (GUTMA), for example, includes over 50 commercial enterprises, such as DJI, Intel, General Electric, Leonardo, and Sony. As an indication of where things are going, the “Airbus UTM” initiative boldly states, “We design, develop, and build the critical infrastructure necessary to allow new aircraft, including air taxis and delivery drones, to safely enter and share the skies of our future.”
During my earlier career in telecom, my work focused on developing teleconferencing technologies, and later, on the infrastructure side of broadband delivery — the “plumbing” so to speak — developing the technologies to connect homes and businesses to the internet. Being the network plumbing guy, I’ve been thinking carefully about the capacity, reliability, cost, and time necessary to build a communication network robust enough to seamlessly direct all the aircraft that will be in our skies over the next 50 years. Historically, the US has led the world in setting standards for aviation — we have again a unique opportunity to lead the way, and we should think judiciously through the complex issues from both a technical and a public policy perspective.
As the FAA has described, a pair of 25-year-old narrowband communication channels established for ADS-B (Automatic Dependent Surveillance — Broadcast) are the logical foundation for NextGen. Sadly, neither of the two ADS-B communication channels can support the future needs of piloted passenger aircraft, let alone thousands of new autonomous passenger aircraft and unmanned drones: the internationally adopted frequency of 1090MHz, transmitting “Mode-S extended squitter” data with a bandwidth of 50kHz, provides only enough capacity for the ground station to process messages from 300 aircraft within the area.
The other allocated ADS-B frequency is 978MHz, called the UAT (Universal Access Transceiver), adopted by the FAA for aircraft flying below 18kft MSL. While the UAT operates on 1.3MHz of bandwidth, much of this is consumed with the transmission of weather data. Envisioning a future with thousands of aircraft flying within a dense metro area, both piloted and autonomous, the entire aeronautical band from 960 to 1164MHz is simply unable to handle the future traffic control demands. This unfortunate fact is widely acknowledged within the FAA and NASA.
Identifying the future need for air traffic control spectrum, the ITU World Radiocommunications Conference (WRC) in 2012 allocated the band from 5030–5091MHz for future ground-to-aircraft and potentially satellite-to-aircraft communication links. At the time of the allocation, it was recognized that using large portions of the band would not be possible in many areas, due to the ongoing use of Microwave Landing Systems (MLS) in the band, especially by the military. In 2017, mirroring the ITU action, the FCC allocated the band for UTM purposes within the United States.
Concerns about capacity and interference in the 5030–5091MHz band have already been voiced by the aviation industry. In advance of an FCC rule making, the Aerospace Industry Association (AIA) petitioned the FCCin early 2018, requesting the adoption of rules covering mission-critical command and control messages for unmanned aircraftin the 5030–5091 MHz band. Less critical data, such a video feed, should be excluded, per the AIA petition. Though high-bandwidth video seems integral to cloud-controlled intelligent autonomous flight, the AIA recognizes the inability of the band to support the full requirements of UTM, particularly when required to share the spectrum with the legacy MLS service. While the FCC has yet to set rules for the 5030–5091MHz band, NASA is already testingthese types of narrowband radios for unmanned aircraft command and control. Thus, while government agencies are working on solutions that address a portion of our future UTM and NextGen networking needs, a holistic solution has yet to be articulated.
Meanwhile, in the commercial world of drones and UTM, stakeholders such as the GSMA, Qualcomm and Ericsson have proposed the use of 5G technology as the platform for future air traffic control. While 5G-NR(5G New Radio) is the most advanced wireless technology ever conceived, I’m personally skeptical that 5G networks built for terrestrial mobile applications will address the needs for UTM, for a variety of reasons:
· mm-wave frequencies, to be used for initial 5G deployments, will not allow long-distance communications in rain conditions, around building, or through trees.
· 5G base stations will be positioned for optimal coverage of foot traffic in major cities, not for airborne traffic.
· Terrestrial antennas are designed for “downtilt” to provide gain to mobile devices, while aviation applications will require “uptilt.”
· Aviation applications cannot afford the loss of messages that may occur during mobile traffic overload conditions.
· Terrestrial 5G networks will not accommodate the degree of Doppler shift that occurs with high-velocity aircraft; and
· Mobile spectrum licenses specifically prohibit ground-to-air applications.
The best and only solution, I believe, will be a dedicated 5G aviation network, addressing the needs of both UTM and NextGen, and operating on frequencies with adequate propagation characteristics.
At my prior company, Mimosa Networks, we were huge advocates for sharing the old satellite C-band, extending from 3.7 to 4.2GHz, for fixed terrestrial networks, and I’ve posted several articleson this topic over the years. As we noted then, not all spectrum is created equal, and this “mid-band” spectrum provides an excellent trade-off between large bandwidth and good propagation characteristics. This is especially critical for UTM applications. Within the next decade, there may be a thousand or more unmanned and manned aircraft within range of a single 5G cell, each consuming an average of 100kbps of bandwidth. Building an aviation network with 500Mbps+ capacity per cell, with clear reception at distances of 10 miles in heavy rain conditions, creates a platform that will scale for decades to come, addressing the full range of UTM and NextGen needs.
Unfortunately for others who want access to the band, the major mobile operators recognize the value of this mid-band spectrum, and absent any changes, the current likely outcome will result in half of the 500MHz being “recovered” from the satellite operators and sold to the highest bidders at auction, for exclusive use, potentially raising at least $10B for the US Treasury. This would be considered another win for the FCC, though arguably a loss for consumers, who ultimately foot the bill when carriers spend billions on exclusively-licensed mobile spectrum, and certainly a loss for the future viability of UTM.
Given that the timing of the FCC mid-band spectrum initiative coincides with the FAA’s need to build a new network for air traffic control, one that will accommodate the full scope of UTM and NextGen requirements, I make this appeal to my friends at the FCC:
When recovering 250MHz of the C-band, why not set aside 50MHz for a future 5G aviation network?
Given the spectral efficiency of 5G-NR, the loss of 50MHz will not significantly harm the mobile operators, nor have much impact on the auction outcome; yet the failure to set aside this critical spectrum for UTM could irreversibly hamper the growth of UAM for the foreseeable future.
As the worldwide leaders in both spectrum policy and aviation policy, allocating dedicated spectrum for a government-funded 5G network in the United States sets the precedent for all other countries to follow suit. A dialogue among the FAA, NASA and the FCC is of course critically important for the future of UTM, as current decisions about the C-band will irreversibly limit solutions for future air traffic control. And while worldwide adoption would require formal action at the ITU WRC, the push to develop the next-gen transportation network is clearly an initiative that all developed countries can rally around. The next scheduled WRC will be in the fall of 2019, and then again in 2023 — a short four years to achieve broader consensus around the appropriate standards and spectrum requirements to secure the future of UTM.