Decoding Meteor-M2: QPSK, Viterbi, Reed Solomon and JPEG from IQ coefficients to images, analysis o…
Channel: FOSDEM
Date: 08/02/2019

Decoding Meteor-M2: QPSK, Viterbi, Reed Solomon and JPEG from IQ coefficients to images, analysis of digital weather satellite transmissions
by Jean-Michel Friedt

At: FOSDEM 2019
https://video.fosdem.org/2019/AW1.120/sdr_meteorm2n.webm


A low cost, digital video broadcast-terrestrial (DVB-T) receiver is used to collect radiofrequency signals emitted from the low Earth orbiting Russian satellite Meteor-M2. The QPSK encoded signal is analyzed all the way from extracting bit values, to recovering the JPEG encoded image transmitted from the satellite. This investigation is an opportunity to experimentally assess all the layers of digital communication widely used from Deep Space communication to daily mobile phone communication, including Viterbi encoding, Reed Solomon error correction, and JPEG image display. Few members of the audience might have any interest in the details of Meteor M2 weather satellite transmissions. However, tackling the reception of this digital weather satellite opens the opportunity to address most if not all the layers of the OSI model, from the physical layer by collecting the radiofrequency signal using a cost-effective DVB-T receiver acting as a general purpose software defined radio signal source, to the data link layer with the various error correction schemes implemented to address the corruption introduced by the noisy radiofrequency communication channel (Viterbi, Reed Solomon) and the network layer with the frame encoding including telemetry and, of course, the payload as a digital picture. The latter is encoded in JPEG format, adding more abstractions with the lossy compression to be reverted to display greyscale images representative of the atmosphere and ground reflectivity in the various wavelengths monitored by Meteor M2. This decoding path matches most recent space-borne signal transmissions, as documented by the Consultative Committee for Space Data Systems (CCSDS [1]), and despite extensive documentation available online, a practical demonstration of the various decoding steps helps understanding the many documents over which the information is spread. 

[1] https://public.ccsds.org/Publications/BlueBooks.aspx 

Room: AW1.120
Scheduled start: 2019-02-03 16:00:00+01