The IQ File sink, tried to create the IQ
file even if it was instructed by the user not to
store IQ data. Despite the fact that no data were
written, it could trigger however errors in case
the destination file could not be opened,
eg. due to permissions.
The problem was that the base class tried to
open the file at its contructor. This commit
deals with this issue and the file is created
only if the user specifies that wants the IQ
data to be stored.
This commit adds a hierarchical block that performs Doppler
compensation and resampling.
Rather than using directly the available Doppler correction blocks,
based on the user parameters of the incoming sampling rate and the
desired target sampling rate, it applies proper decimation on the signal
so the frequency shift to be applied to a smaller sampling rate,
reducing significantly the CPU resources required. At the previous
architecture (gr-satnogs 1.x.x) we used seperate blocks for the doppler
correction and the LO digital shift, operating at the device sampling rate.
These two blocks, performing almost the same operation, contributed to a
30% CPU usage of the overall application. Now the LO is compensated by
the Doppler correction block, taking into account at the same time the
Doppler drift.
After the digital LO shift, the Doppler corrected signal is passed through
an Polyphase Arbitrary Resampler, to match exactly the sampling rate
requested by the user.
Add a IEEE 802.15.4 like decoder, which supports
the IEEE 802.15.4 standard but also a large variety
of ICs based on this framing scheme. Such framings
are quite common in many Cubesat missions.
The decoder has been tested an works well with at least
the Reaktor Hello World satellite
* Removed obsolete blocks
* Created a new CRC class with static methods. This will make easier the
integration of new CRC schemes. The old way was rather too C-styled
* Blocks removed are now covered from decoders available supporting the
new decoder architecture
* The quadrature demodulation filter block, had as primary goal to
reduce the false alarms and the performance of the DUV decoder. Now the
new DUV decoder, uses a shift register approach, likewise the AX.25
decoder, therefore it is not needed anymore.
TODO:
* Use the shift register likewise the AX.25 to get rid off the
quadrature demodulation filter. This will significantly increase the
number of decoded frames
The decoders produce a PMT message containing several information about
the decoded frame. While this is very convenient for handling data
inside the flowgraph, it is not for third party applications. The JSON
converter block is responsible to serialize all the information
contained in a PMT originating from a decoded frame.
For simple demonstration some metadata were added on the AX.25 decoder.
These metadata are still a WIP and they subjected to changes.
To simplify the logic and allow an easy and more efficient way to add
new decoders, the new architecture uses only one decoder block.
This block takes as input a void* stream and produces PDUs with their
metadata. To do so, the block accepts a decoder object. Every decoder
should implement the virtual class decoder(). This class provides the
necessary API and an arbitrary number of decoders can be supported. The
decoding status is reported to the frame_decoder block through the
decoder_status_t structure.
* Introduce the hysteresis option, in order the CW demodulator to adjust
properly the plateau length based on the WPM and any filtering that can
be used before
* Instead for a frame per word, now the CW decoder waits for 10 long
spaces before it commits a frame. With this way many words are placed on
the same frame telemetry decoding is easier
Seems that there is a probleb with general blocks and the history, so
the filter cannot act as valve. However, it produces zeros, in the
presence of noise.
This is an attempt to cut the signal free period after the quadrature
demodulation block. The idea seems that works, but there still an issue
with the samples not passing correctly from the valve.
The CW encoder is a debug block that can be used to check the
performance of the CW decoder of gr-satnogs module under different RF
conditions. It can also serve as a perfect debug tool for sattelite
missions.
CW decoding using match filtering is pretty much useless in LEO.
The information about the tone frequency is very rare and carrier
oscillations during the satellite pass reduce significantly the
performance.
The new next CW decoder is based on the autocorrelation of the received
signal.
Manolis Surligas
nickoe
Thanos Gkiolias
Nikos Karamolegkos
George Vardakis
Kostis Triantayllakis
Kostis Triantafyllakis