During the 2020 challenge we will need to control our ‘rescue’ quadcopter in a farm shed up to 12 km from our ground station and establish a video and audio link to the farmer in the shed, without any dependence on the cell phone network. Quite a challenge! We think that this really pushes the limits of technology that is available to the hobbyist, community groups and small businesses.
Our general philosophy for the 2020 UAV Challenge is that we want to have redundancy in our networks to avoid a single point of failure during the mission and to take advantage of the opportunities of radio frequency diversity. By having two networks operating on different frequencies we should maximise the data rates available at higher frequencies (such as 2.4GHz) while exploiting the reliable range performance and better object penetration of lower frequencies (915MHz).
We have had some significant testing success with our communications for the 2020 UAV Challenge in the last few weeks, including a strong connection at 11.2km for all three of the radio types that we have tested: our Airborne Innovations and Microhard 2.4GHz network, our trusty RFD900Xs and some promising open source ‘New Packet Radios’.
Airborne Innovations and Microhard have generously supplied us with set of 2.4GHz pMDDL2450 based radios to potentially use in the competition. We recently tested this in a point-point link test at 11.2km. The representative air platform was on top of a hill connected to a Holybro Durandal to establish a representative MAVlink connection to a ground station. On the ground we used a video aerial systems super cannon and pepperbox antenna while the ‘air platform’ used MadMusroom antennae. We established a good telemetry and control link with very low packet loss and a fade margin of 12dB, which we are pretty happy with. These radios can be set up to mesh network, so they could be used like the RFD900x to link the rescue aircraft to the ground station via the communications relay aircraft. This set up has potential for telemetry, control, video and audio from the rescue aircraft, but we have more testing to do here.
The RFD900X radios are very capable and reliable for maintaining long range line of sight control and telemetry links with the UAV; their ability to mesh network also makes them very useful to use with a communications relay aircraft when we lose line of sight with the rescue aircraft. We used these successfully in 2016 and 2018. The big change for the 2020 challenge is the need to send video and audio from the rescue aircraft back to the ground station. We have been working on a new video encoder that can send video at very low frame rate over a low bandwidth over the RFD900X alongside the control and telemetry data. We are having some success here and it looks promising, so we have more testing to do with this setup.
The New Packet Radios are an open source design that uses the same STM32 radio module as the RFD900X but operates at around 433MHz. We think it would need a Ham (amateur radio) to operate it at the necessary power for the challenge. These radios showed good potential for a link with a good data rate between the ground station and the relay aircraft. Unfortunately these radios lack the small form factor to fit onto the rescue Quadcopter so it would only be useful for connecting the ground control station to the comms relay aircraft. For this reason, we have decided not to proceed further with testing these radios as part of our 2020 Challenge project.