Recommended gr-ais repo/branch/commit for GnuRadio 3.7.x (latest git) and UHD 3.7.1?

GNU Radio
1

Hi.

What is the recommended gr-ais repo/branch/commit that yields a working
gr-ais with GnuRadio 3.7.x (git commit
3831dd37c8df19e25fa258db4d393ee068889dae)
and the Ettus UHD 3.7.1

GitHub shows this fork network:

Right now I’m using bistromath/gr-ais commit
754c13ca4f1c3fb0d079d3a42002b0dade2268ff
(master HEAD, IIRC), but I’m not getting any !AIVDM output to the
terminal window.

Regards,
Andy

2

754C is correct. What hardware are you using? Are you sure you have a
line-of-sight view to ships?

3

Ettus X310.

No ship needed; I have a known good transponder connected through RF
cables and attenuators to the X310. :slight_smile:

I can send AIS text and safety messages on demand, and the transponder
will out its own position messages every 3 minutes since it is
stationary.

Regards,
Andy

4

On Fri, 2014-04-25 at 17:22 -0400, Andy W. wrote:
[snip]

    GitHub shows this fork network:
    https://github.com/bistromath/gr-ais/network

    Right now I'm using bistromath/gr-ais commit
    754c13ca4f1c3fb0d079d3a42002b0dade2268ff
    (master HEAD, IIRC), but I'm not getting *any* !AIVDM output
    to the terminal window.

Well, I’ve identified one problem.

The “unstuff” operation is being applied before the correlator for the
start flag of 01111110 (0x7e). The start flag, end flag, and preamble
are not subject to bit stuffing per ITU-R M.1371-4 Annex 2 Sections
3.2.2.1 through 3.2.2.4.

I suspect this causes a problem with proper detection of the start of
the message, as the unstuff, as I understand it, will change the start
flag from 01111110 to 0111110m, where m is the first bit of the message
payload.

Putting the unstuff operation after the correlators doesn’t fix
everything though. All potential message decodes still fail the CRC
check.

Bypassing the CRC check and inspecting the output !AIVDMs with gpsdecode
verifies they are junk. :frowning:

Regards,
Andy

5

Thanks for the report. Going to move this one offlist – have some stuff
for you to try.

–n