3
$\begingroup$

I've recently become extremely interested in tiny "picoballoons" which can float around the world multiple times in some cases.

I was extremely surprised to find DL7AD's picoballoon, which has a camera and can transmit images with SSDV over APRS. Check it out here

I'm interested in different possible methods of transmitting these images. SSDV seems to work well as an encoding method, but the APRS VHF network is limited to 1200 baud AX.25. Even with low quality images it takes a few minutes to transmit a single image.

I've thought about the possibility of using 9600 baud raw AX.25 with SSDV on either 2m or 70cm. Would it be feasible to transmit a raw image file instead of using SSDV? I'm aware SSDV provides built in error correction.

My main question is if there are other, possibly faster, alternatives to APRS SSDV that have been used.

$\endgroup$
16
  • $\begingroup$ two aspects: SSDV is a pretty "stupid" format. It uses an ancient still image codec (namely, JPEG) to send images independently. Instead, it could use a modern moving picture coded (a video codec), eliminating most of the transmitted data volume by not transmitting things that were there in the previous frame but might have moved, darkened, … in the view of the camera (which, for a drifting high-altitude balloon should be most of the picture). Check out the data rates that would be sufficient for the same (or better) quality of picture sequences with x265, for example. $\endgroup$ Commented Oct 9, 2022 at 18:20
  • $\begingroup$ So, a first step in modernizing this approach is to not go with SSDV, but with a modern video codec, like h265, or at least one of the long-established MPEG4 HEVC versions $\endgroup$ Commented Oct 9, 2022 at 18:22
  • $\begingroup$ second: AX.25 is really the worst case packet format for wireless communications. Seriously, if you're not bound to use a system that already uses it, avoid it at all cost. It's never been meant for wireless comms (it comes from the wired frame relay data world), and it ignores comms theory from 1942 onwards. Seriously. If your system does not start by using AX.25, it's better off. Then, you could move the error correction from the data/representation layer (i.e., the video) into the link/physical layer, where it actually belongs. $\endgroup$ Commented Oct 9, 2022 at 18:24
  • $\begingroup$ is if there are other, possibly faster, alternatives to APRS SSDV that have been used. yeah, sure. Many a 60€ quadcopter does better video than SSDV at the same bit rate. But it doesn't do that under ham licensing, but as unlicensed 2.4 GHz transmitter. So, here's your demo. $\endgroup$ Commented Oct 9, 2022 at 18:28
  • $\begingroup$ So now that we know that there's better, cheap, readily available wireless systems that can transmit a few images a second to a few images per minute, the question is, what are the interoperability and individual link requirements that you want to fulfill? $\endgroup$ Commented Oct 9, 2022 at 18:29

2 Answers 2

1
$\begingroup$

SSDV is commonly transmitted over LoRa (250kHz, SF6, CR4:6, which is good for around 15kbit/s of payload bandwidth) or less commonly Wenet / Horus FSK, which requires more power but achieves a net bandwidth of around 90kbit/s.

Both of those modes have a wide occupied bandwidth compared to 1200 baud packet, and so in most places they're only allowed on the 70cm and higher bands.

$\endgroup$
-1
$\begingroup$

Packet Compressed Sensing has been used. https://maqifrnswa.github.io/PCSI/

$\endgroup$
1
  • $\begingroup$ It would be good if you could add a bit more meat to this answer. $\endgroup$
    – David Hoelzer
    Commented Jun 10, 2023 at 13:07

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .