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{{ProjektInfoBox
{{ProjektInfoBox
|name        = VGAtoBaseband
|name        = VGAtoIQBaseband
|status      = experimental
|status      = stable
|image      =  
|image      =  
|description = use the VGA port to generate I/Q baseband signals
|description = use the VGA port to generate I/Q baseband signals
|author      = [[Benutzer:siro|siro]]
|author      = [[Benutzer:siro|siro]]
|username    =  
|username    = siro
|version    = 0.1
|version    = 0.2
|update      =  
|update      =  
|platform    = Evil Hack
|platform    = Linux
|license    = GPL
|license    = mixed
|download    = [https://www.das-labor.org/trac/browser/host-apps/VGAtoIQBaseband]
|download    = [https://www.das-labor.org/trac/browser/host-apps/VGAtoIQBaseband]
}} __NOTOC__
}} __NOTOC__
== Description ==
This software provides an highspeed, easy to use DAC interface using the VGA compatibel CRTC in your graphics card. It reads from stdin and generates appropriate analog signals on the VGA connector. Those signals could for example be used to feed a rf-modulator.
This software is intended to be used with [[SDRT]] or [[SDRT2]].


== Requirements ==
== Requirements ==
Zeile 22: Zeile 26:
* GL_ARB_pixel_buffer_object for efficient CPU to GPU transfers
* GL_ARB_pixel_buffer_object for efficient CPU to GPU transfers


=== Linux ===
== What it does ==
* Mesa 9.0 (other drivers are untested)
[[Datei:Vgatoiqbaseband.png]]
* X-server


=== Windows ===
== Software ==
* Windows XP doesnt work
The current version runs on any symbolrate, recommended are 5MSymbols/s or more.<br>
* other OS are untested


== Software ==
Every symbol is a complex number, that contains an I (real) and Q (imag) value.<br>
This software generates analog I/Q Signals that can be feed into a rf-modulator.
By default the signal is lowpass filtered using convolutional sinc function. Low pass filtering can be disable using -n argument.
The current version is only working with 8Mhz * 8/7 symbolrate = 9,1428 MSymbols/s. A symbols contains an I and Q value.
The I/Q values are read from stdin. The software accepts BYTE, SHORT and FLOAT as input values.
It is possible to use fragment shader to low-pass filter the signal, simply pass the -filter argument.
The real part (I) is assigned to the RED and the imag part (Q) to the GREEN channel, while the BLUE channel is set to 0.5f.
The I/Q values are feed using a unix fifo / a file. 8 byte form two 32bit floats, that equals a complex number.
The values have to be between 0.0f and 1.0f.
The complex value is assigned to the RED and GREEN channel, while the BLUE channel is set to 0.5f.
8bit and 10bit VGA Graphic cards are supported.
8bit and 10bit VGA Graphic cards are supported.
<br>
<br>
vgatobaseband uses the first VGA output found. If none found it uses the first output that is active.
The VGA output has to be configured first using xrandr, arandr, ....<br>The coordinates are saved, a new modeline is added and set.
<br>
All baseband signals contains positive as well as negative numbers. If your signal range covers -1.0f to 1.0f you have to convert them.<br>
newval = (float2)(oldval.i/2 + 0.5f, oldval.q/2 + 0.5f)
The ''newval'' is now in range 0.0f to 1.0f and can be used with this programm.
<br>
Due to most GPU only having 8bit DACs the floats are converted into a range from -127 to 127 (using the blue channel as differential reference).
== Arguments ==
./vgatoiqbaseband [ARGS]
reads data from stdin
ARGS could be:
-n              disable fragmentshader
--nofilter      disable fragmentshader
-v              be verbose
--verbose        same as -v
-display DISPLAY Specify the X server to connect to. If not specified, the value of the DISPLAY environment variable is used.
-direct          force direct rendering
-t              generates test patterns
--testpattern    same as -t
-d <x>          convolutional depth
                  default: 17
-f <c>          same as --freq (float)
--freq <c>      set convolutional filter cut-of frequency to c Mhz (c is float)
                  default: 3.81 Mhz
-h              same as --help
--help          print help message
-z <x>          4 for float, 2 for ushort, 1 for uchar
--datasize <x>  same as -z
only if compiled with libXrandr support:
-cutofright <n>  cutof n rightmost pixels (hsync)
                  default:  1
-cutofbottom <m> cutof m bottommost pixels (vsync)
                  default:  2
-pclk <x>        use a pixelclock of x Mhz
                  default: 64
=== Examples ===
Set the VGA position first:
xrandr --output VGA-0 --right-of LVDS --auto
adjust ''VGA-0'' and ''LVDS'' according to your system.
cat inputfile.raw > ./vgatoiqbaseband -v
This will read from the file inputfile.raw .<br>
./vgatoiqbaseband -v -t
This will generate test paterns.


== Libraries ==
== Libraries ==
* libglut
* libglu
* libgl
* libpthread
''You may also use''
* libxrandr
* libX11
'''Debian packages:'''
* freeglut3-dev
* freeglut3-dev
* libglu1-mesa-dev
* libglu1-mesa-dev
* libgl1-mesa-dev
* libgl1-mesa-dev
* libxrandr-dev
== OFDM Bandwidth ==
OFDM useful carriers to total carriers ratio: 1705 / 2048 = 0.832
{| {{Prettytable}}
! DAC clock [Mhz]!! Msymbols/s!! carrier ratio !! 3dB Bandwidth Mhz
|-
|64
|9.14285
|0.832
|7.61
|-
|56
|8.000
|0.832
|6.66
|-
|48
|6.8571
|0.832
|5.71
|}
== Phase shift ==
As phase-shifting OFDM symbols results in malformed spektrum, the horizontal sync is padded with blanking pixel to make sure the sync has the same size as all other symbols.
== Interpolation Filter ==
The convolutional filter is critical in this application. Using OFDM 8 Mhz bandwidth the I and Q channel maximum frequency is 3.81 Mhz. The DAC sampling rate is 9.142 MSPS which is enough to reconstruct all frequencies, but due to the low sampling rate the baseband signal contains aliasing artefakts.
To remove those artefakts a si-filter is neccessary, including an interpolation DAC, which is running at much higher sampling rate.<br>
This is done by the fragment shader, implemented in shader.cpp.
The GPU has to fetch, multiply, add and store at least ''' <sampling rate> * <conv_depth> ''' pixels
{| {{Prettytable}}
! DAC clock [MSps]!! GPU !! Driver !! max Kernel_size
|-
|64
|RV710
|Mesa 9.0.2
|7
|-
|64
|RV710
|fglrx 8.97.2
|17
|-
|64
|RV910
|fglrx 12.104
|33
|-
|recommended
|
|
|27 or more
|}
A hardware low-pass filter is required to remove remaining aliasing effects.
== Screen size ==
On fglrx the default screen size is 1600x1600. To increase this limit generate an xorg.conf using 'aticonfig --initial' and add this line:
[...]
Section "Screen"
        Identifier "aticonfig-Screen[0]-0"
        Device    "aticonfig-Device[0]-0"
        Monitor    "aticonfig-Monitor[0]-0"
        DefaultDepth    24
        SubSection "Display"
                Viewport  0 0
                Virtual  3600 1600
                Depth    24
        EndSubSection
EndSection
The line containing "Virtual" is critical.
This should be no problem on Mesa as the default screen size is 8196x8196.
== TODO ==
** You may use a custom edid, see here for more details [[HackingVGAforFun]].
== Links ==
* http://software.intel.com/en-us/articles/custom-resolutions-on-intel-graphics
* http://bk.gnarf.org/creativity/vgasig/
* http://www.sevenforums.com/tutorials/7947-force-dvi-hdmi-resolutions-refresh-rates-4.html
[[Category:HowTo]]
[[Category:Software]]

Aktuelle Version vom 7. November 2013, 09:13 Uhr

         
VGAtoIQBaseband

Release status: stable [box doku]

Description use the VGA port to generate I/Q baseband signals
Author(s)  siro (siro)
Last Version  0.2 ()
Platform  Linux
License  mixed
Download  [1]




Description[Bearbeiten | Quelltext bearbeiten]

This software provides an highspeed, easy to use DAC interface using the VGA compatibel CRTC in your graphics card. It reads from stdin and generates appropriate analog signals on the VGA connector. Those signals could for example be used to feed a rf-modulator. This software is intended to be used with SDRT or SDRT2.

Requirements[Bearbeiten | Quelltext bearbeiten]

  • PC with VGA adapter
  • OpenGL with Direct Redering
  • Vsync enabled
  • Software-defined Radio Transmitter that generates I/Q Signals
  • GL_ARB_fragment_program to use the low-pass filter
  • GL_ARB_pixel_buffer_object for efficient CPU to GPU transfers

What it does[Bearbeiten | Quelltext bearbeiten]

Vgatoiqbaseband.png

Software[Bearbeiten | Quelltext bearbeiten]

The current version runs on any symbolrate, recommended are 5MSymbols/s or more.

Every symbol is a complex number, that contains an I (real) and Q (imag) value.
By default the signal is lowpass filtered using convolutional sinc function. Low pass filtering can be disable using -n argument. The I/Q values are read from stdin. The software accepts BYTE, SHORT and FLOAT as input values. The real part (I) is assigned to the RED and the imag part (Q) to the GREEN channel, while the BLUE channel is set to 0.5f. 8bit and 10bit VGA Graphic cards are supported.

vgatobaseband uses the first VGA output found. If none found it uses the first output that is active. The VGA output has to be configured first using xrandr, arandr, ....
The coordinates are saved, a new modeline is added and set.
All baseband signals contains positive as well as negative numbers. If your signal range covers -1.0f to 1.0f you have to convert them.

newval = (float2)(oldval.i/2 + 0.5f, oldval.q/2 + 0.5f)

The newval is now in range 0.0f to 1.0f and can be used with this programm.
Due to most GPU only having 8bit DACs the floats are converted into a range from -127 to 127 (using the blue channel as differential reference).

Arguments[Bearbeiten | Quelltext bearbeiten]

./vgatoiqbaseband [ARGS]

reads data from stdin

ARGS could be:

-n               disable fragmentshader
--nofilter       disable fragmentshader
-v               be verbose
--verbose        same as -v
-display DISPLAY Specify the X server to connect to. If not specified, the value of the DISPLAY environment variable is used. 
-direct          force direct rendering
-t               generates test patterns
--testpattern    same as -t
-d <x>           convolutional depth
                 default: 17
-f <c>           same as --freq (float)
--freq <c>       set convolutional filter cut-of frequency to c Mhz (c is float)
                 default: 3.81 Mhz
-h               same as --help
--help           print help message
-z <x>           4 for float, 2 for ushort, 1 for uchar
--datasize <x>   same as -z
only if compiled with libXrandr support:
-cutofright <n>  cutof n rightmost pixels (hsync)
                 default:  1
-cutofbottom <m> cutof m bottommost pixels (vsync)
                 default:  2
-pclk <x>        use a pixelclock of x Mhz
                 default: 64

Examples[Bearbeiten | Quelltext bearbeiten]

Set the VGA position first:

xrandr --output VGA-0 --right-of LVDS --auto

adjust VGA-0 and LVDS according to your system.

cat inputfile.raw > ./vgatoiqbaseband -v

This will read from the file inputfile.raw .

./vgatoiqbaseband -v -t

This will generate test paterns.

Libraries[Bearbeiten | Quelltext bearbeiten]

  • libglut
  • libglu
  • libgl
  • libpthread

You may also use

  • libxrandr
  • libX11

Debian packages:

  • freeglut3-dev
  • libglu1-mesa-dev
  • libgl1-mesa-dev
  • libxrandr-dev

OFDM Bandwidth[Bearbeiten | Quelltext bearbeiten]

OFDM useful carriers to total carriers ratio: 1705 / 2048 = 0.832

DAC clock [Mhz] Msymbols/s carrier ratio 3dB Bandwidth Mhz
64 9.14285 0.832 7.61
56 8.000 0.832 6.66
48 6.8571 0.832 5.71

Phase shift[Bearbeiten | Quelltext bearbeiten]

As phase-shifting OFDM symbols results in malformed spektrum, the horizontal sync is padded with blanking pixel to make sure the sync has the same size as all other symbols.

Interpolation Filter[Bearbeiten | Quelltext bearbeiten]

The convolutional filter is critical in this application. Using OFDM 8 Mhz bandwidth the I and Q channel maximum frequency is 3.81 Mhz. The DAC sampling rate is 9.142 MSPS which is enough to reconstruct all frequencies, but due to the low sampling rate the baseband signal contains aliasing artefakts. To remove those artefakts a si-filter is neccessary, including an interpolation DAC, which is running at much higher sampling rate.
This is done by the fragment shader, implemented in shader.cpp.

The GPU has to fetch, multiply, add and store at least <sampling rate> * <conv_depth> pixels

DAC clock [MSps] GPU Driver max Kernel_size
64 RV710 Mesa 9.0.2 7
64 RV710 fglrx 8.97.2 17
64 RV910 fglrx 12.104 33
recommended 27 or more

A hardware low-pass filter is required to remove remaining aliasing effects.

Screen size[Bearbeiten | Quelltext bearbeiten]

On fglrx the default screen size is 1600x1600. To increase this limit generate an xorg.conf using 'aticonfig --initial' and add this line:

[...]
Section "Screen"
       Identifier "aticonfig-Screen[0]-0"
       Device     "aticonfig-Device[0]-0"
       Monitor    "aticonfig-Monitor[0]-0"
       DefaultDepth     24
       SubSection "Display"
               Viewport   0 0
               Virtual   3600 1600
               Depth     24
       EndSubSection
EndSection

The line containing "Virtual" is critical. This should be no problem on Mesa as the default screen size is 8196x8196.

TODO[Bearbeiten | Quelltext bearbeiten]

Links[Bearbeiten | Quelltext bearbeiten]