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authorMatthias P. Braendli <matthias.braendli@mpb.li>2014-02-07 09:24:39 +0100
committerMatthias P. Braendli <matthias.braendli@mpb.li>2014-02-07 09:24:39 +0100
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-README for the SFN patch
-========================
-
-Concept
--------
-
-Each modulator receives ETI frames with absolute timestamps. These timestamps
-are composed of two parts:
-- The TIST field as defined in the ETI standard, giving an offset after the
- pulse per second signal;
-- A time information transmitted using the MNSC, representing the precise time
- when the frame must be transmitted, with one-second resolution.
-
-When CRC-DABMUX is called with -s, the TIST is defined in each frame. The
-Time is always encoded in the MNSC.
-
-In a SFN setup, it is not possible to rely on a modulator to slow down the
-Ensemble multiplexer. CRC-DABMUX takes an additional parameter -r to output one
-ETI frame every 24ms. This output parameter only adds a simul:// output.
-
-The ETI stream must then be made available to several transmission sites. For
-this, the eti_tcp server can be used.
-The eti_tcp server listens on the port specified on the command line.
-An example invocation is:
-./mux-throttled.sh -s -m 1 | ./eti_tcp/eti_tcp.py 54001
-
-Each modulator then receives the ETI stream through a TCP connection. Each frame
-contains the complete timestamp, to which an per-modulator offset is added.
-The sum is then given to the USRP. The offset can be specified in two ways:
-
-using -o delay:
-Adds a constant delay specified on the command line (see 1st example).
-
-using -O delayfile
-Adds the delay specified in the given file. The file must contains a single
-line containing a floating point number. This file is read each 50 frames, and
-the modulator delay is updated.
-
-In both cases, the units are seconds.
-
-Example modulator invocation (for a B100 USRP supporting 2048Msps and with a
-fixed delay of 2.3 seconds)
-nc localhost 54001 | ./moduhd-2048.sh -o 2.3
-
-Example modulator invocation (for an USRP requiring resampling and with a delay
-specified in a separate file "moddelay")
-nc localhost 54001 | ./moduhd-resample.sh -O moddelay -G 5
-
-It is also possible to set daugherboard gain using -G. Furthermore, the transmission
-frequency is set on the command line, as seen in the examples in moduhd-XXX.sh.
-
-CRC-DABMOD uses the UHD library to output modulated samples to the USRP device.
-When started, it defines the USRP time using the local time and the PPS signal.
-It is therefore important to synchronise computer time using NTPd.
-
-When a frame arrives with a timestamp that is in the past, the frame is dropped.
-If the timestamp is too far in the future, the output module waits a short
-delay.
-
-Synchonisation can be verified by using an oscilloscope and a receiver. It is
-very easy to see if the null symbols align.
-
-
-Hardware requirements
----------------------
-
-The following hardware is required to test the SFN patch to the CRC mmbTools:
-- Two USRPs ;
-- One or two computers with the mmbTools installed ;
-- A network connection between the two computers ;
-- A 10MHz refclk source ;
-- A 1PPS source synchronised to the 10MHz ;
-- An oscilloscope to check synchronisation.
-
-The lab setup used in the experiments :
-http://pic.mpb.li/IMAG0411.jpg
-
-In this example, one USRP B100 and one USRP2 are used. Modulation is done on two
-different computers, but it also works with a single computer. In that case, the
-device string for the -u option for CRC-DABMOD must specify the device. (e.g.
--u "type=b100", -u "type=usrp2" or -u "serial=ABC123")
-
-The HP33120A generator at the bottom is used to generate the 10MHz REFCLK (sine,
-2Vpp). It's sync output is used as 10MHz IN for the Agilent 33250A generator.
-The Agilent is set to a square wave, 1Hz. Its sync output is then wired to the
-PPS input of the USRPs.
-
-List of changes made
---------------------
-To CRC-DABMUX:
-- Throttled output option instanciates a simul output
-- Set TIST and use MNSC to transmit time
-- Command line arguments handling
-
-Files:
-Modified Eti.h and DabMux.cpp
-
-To CRC-DABMOD:
-- Added multithreaded UHD Output module
-- Added normalisation for UHD (we must divide output samples by
- 32768.0)
-- Command line arguments handling
-- Changed the flowgraph to be able to chose between outputs
-- Added decoding of time in MNSC
-- Added delay control for the modulator using -o and -O
-- Initially set the timezone to UTC, because the MNSC is in UTC
-
-Files:
-Added OutputUHDThreaded.{cpp,h}, TimestampDecoder.{cpp,h}; Modified DabMod.cpp,
-DabModulator.h, Eti.h, EtiReader.{cpp,h}; Changed some .h files to include
-<stdio.h> because of compilation issues; Corrected OutputMemory char* name().
-
-
-Future elements to be changed
------------------------------
-- Communicate delay and buffer information between multiplexer and modulators,
- to have a better control about delays.
-- Handle UHD asynchronous messages in another thread, and use this information
- for monitoring
-
-Repository:
-http://hg.mpb.li/mmbtools-sfn/
-
-2012-07-11
-Matthias P. Braendli
-matthias@mpb.li
-