Lars Oberhofer
← All work

Data off a landing aircraft

Earlier work · BSc thesis with Volocopter · 2021 – 2022

Earlier work / Wi-Fi 6E / Field tests

How much data can reach the ground before the aircraft takes off again?

An air taxi has a short stop between flights to hand over its onboard data. For my bachelor’s thesis I investigated a Wi-Fi 6E link for that handover: how distance, altitude and reflections change it, and what the new 6 GHz band adds to 2.4 and 5 GHz.

Lars kneels in a field at dusk with a laptop on a red case; a router with six antennas and a small test rig stand on the grass beside him
A field test, with the router and the test rig on the grass.

I built the radio test setup, simulated the antennas and took the link outdoors, with the radios carried by drones.

The specific results belong to Volocopter and are not published here.

My workWorking student, Digital Platform, and my BSc thesis in Electrical Engineering at the University of Twente

When and where2021 – 2022, Volocopter, Bruchsal

Decision / Bench

In autumn 2021, the 6 GHz band was open in Germany on paper only.

Germany had opened the lower part of the band, 5945 to 6425 MHz, in July 2021. When I started that autumn, I could get neither a driver nor hardware to use it with a German country code.

The radio card takes its allowed channels from the country code that nearby access points broadcast, so setting it to the US by hand changed nothing.

The workaround suggested on Intel’s community forum was a room where the card hears only one access point, configured for the US. Mine was a cellar.

Intel’s Linux driver for the AX210 needs PCIe, and the Raspberry Pi 4 has no PCIe slot to put the card in. So the setup moved to a Raspberry Pi Compute Module 4 on a carrier board with a PCIe slot, and I patched its kernel.

pi@raspberrypi:~ $ iwconfig wlp1s0
wlp1s0  IEEE 802.11  ESSID:"Volocopter6G"
        Mode:Managed  Frequency:6.535 GHz
        Bit Rate=490 Mb/s   Tx-Power=22 dBm
        …
        Link Quality=70/70  Signal level=-30 dBm
Transcribed from a photo of the screen: the card on a 6 GHz channel, 6535 MHz, which is above the part of the band Germany had opened; the card was on the US setting. 490 Mb/s is the negotiated link rate, not a measurement of data actually transferred.
A tiled cellar floor with a monitor, a router with antennas, a small circuit board, cables, a keyboard and a laptop
The cellar, where the radio heard only the one access point set to the US.
A Raspberry Pi Compute Module carrier board with a radio card in its PCIe slot and two antennas
The Compute Module’s carrier board, with the radio in its PCIe slot. It became the portable test rig.

Method / Simulation and field

From simulated antennas to a link in the air.

I simulated 4×4 MIMO antennas in Ansys HFSS: where they radiate, how strongly, and how the elements affect each other.

The link analysis compared modulation schemes from QPSK to 1024-QAM: how much each radio symbol carries, and how noise affects the error rate. A Rician fading model stood in for the ground-to-air channel.

In the field, the link was measured against altitude, distance and reflections, with the radios carried by drones.

Radios
Intel AX210 on Raspberry Pi Compute Module 4 carriers
Bands
2.4, 5 and 6 GHz compared
Simulation
Ansys HFSS · 4×4 MIMO
Results
Volocopter’s; not published here
Three simulated three-dimensional antenna radiation patterns in red, yellow and green on polar axes
Radiation patterns simulated in Ansys HFSS for the antenna study.
A router with antennas, a small rig and a laptop on a red case on a meadow, with hills behind
The field setup, ready for a test.

Sources: my thesis notes from 2021 and 2022, a photo of the radio’s screen, and the project photographs. The thesis results belong to Volocopter and are not published.