Hello,
We are a startup company designing a communication system for a flying drone.
Our raw idea is to put a LimeSDR on the drone, and another LimeSDR on the ground, and create a RF link as a general datalink, so we can send information both ways (telemetry, control commands, video, etc).
We are aiming at a reliable, low latency link at 100km distance, free line of sight, with at least 10Mbps datarate.
QUESTION 1: Is this doable? What products should we be looking at? (LimeSDR? Power amplifiers? Omnidirectional antennas?)
QUESTION 2: We will need help from an expert SDR freelancer to program this RF part, pick up optimized parts, etc. This is a paid job.
This is only a small part of the broader startup project.
Than you very much,
Luis Ródenas
10Mbps at 100km range sounds, well, interesting! I’m not in a position to advise and this does sound like a pretty involved project. However, it might help if you could say something about the system you plan to use, frequency band and therefore the associated constraints. I suspect that achieving a 10M link over 100km will be non-trivial and perhaps not possible without some sort of commercial spectrum licence. So before you can even start to think about amplifiers and antennas you need to know the target band, waveform and constraints such as channel bandwidth, EIRP and duty cycle etc.
Thank you Andrew for your answer.
If you are not able to work on this, could you please point us to somebody who could be interested?
For us this looks like quite standard usage scenario of LimeSDR, so maybe do you know of any other projects or resources we can look at for stablishing a datalink between 2 LimeSDRs?
More details:
We tested a datalink between two Silvus SC4240EP units (STREAMCASTER RADIOS - Silvus Technologies), working on 2.4GHz at maximum power (4W native, 8W effective with beamforming they say), and we got 20Mbps at 80km distance. No idea what waveform, channel bandwidth, etc was used because Silvus unit adapts automatically.
Our goal is to achieve something similar at a much lower cost using SDR, 5 Mbps would be enough for us. We would like to test first on open bands (430MHz, 1.2GHz, 2,3GHz…), planing to move to licensed commercial bands later on. This will be tested on a very remote location.
We plan to use LimeSDR mini or XTRX, with LNPA, connected to a Rpi5 or Jetson. We are also considering if we should instead use DVB-T for video and another different link for data, trying to understand the pros and cons of each solution. These are the kind of questions we need help with (apart from selecting optimized parts and program the SDRs).
That’s impressive. I was forgetting that the US permits much higher power levels on 2.4GHz. Seemingly up to ~4W EIRP.
I’d suggest looking into what’s legally possible with those bands. License exempt does not mean a wild west where anything goes. For example, I’d be surprised if operation at 430MHz permitted RF channel bandwidths anything like needed to sustain 10Mbps.
That probably doesn’t help much if you’re in violation of wireless regulations and at these sort of power levels and ranges, plus airborne use, it likely increases risk of getting into trouble.
You may find someone on here who could help, but it seems like more generally you want an experienced wireless engineer to guide you in the right direction. Sorry I can’t be of more help.
We are aiming at a reliable, low latency link at 100km distance, free line of sight, with at least 10Mbps datarate.
QUESTION 1: Is this doable? What products should we be looking at? (LimeSDR? Power amplifiers? Omnidirectional antennas?)
Depends. Doing 10Mbps at 100km will take a very large power amplifier. This requires alot of power with an omni antenna or a large amount of power with a sector or directional antenna. Drones don’t ususlly have this amount of power available. Does the waveform need to have a low-probability of detection, does the waveform need to work while jamming is active? If the data link is used to ‘drive’ the drone, then about 500Kbps using H.265 encoder and about a half second of latency should work and brings the CSWaP of the radio down.
QUESTION 2: We will need help from an expert SDR freelancer to program this RF part, pick up optimized parts, etc. This is a paid job.
As far as the power goes, I have gotten very strong clear reception at 50km with Omnidirectional antennas using only 4 watts from the near by mountain top to my house.
No, it was not that high. I was testing some with some OFDM data, but I am not sure what the bandwidth was - it was a few years ago and I was doing a lot of testing. At ground level all it takes is a small hill to block the transmission.
You need a COFDM waveform like the Silvus along with serious power amplifiers (4 watts atleast), filters (Ideally SAW) etc. The Silvus for long ranges uses Defence/ Licensed L and S band frequencies generally and using such a clean part of the spectrum helps a lot. Look at DVB-T/S for the video encoding.
