ODR-DabMod

About ODR-DabMod

ODR-DabMod is the DAB OFDM modulator initially developed by Communication Research Center (CRC) from Canada, and subsequently forked by Opendigitalradio.

CRC have stopped releasing new versions. The development is now pursued by opendigitalradio on GitHub with releases available as git tags. The git master branch always points to the latest release, the next branch is where development happens.

The main communication channel is the CRC-mmbTools Google Group mailing list

Original CRC version CRC-DabMod description and source code archived on the MMBTools website

Description

ODR-DabMod takes an Ensemble Transport Interface (ETI) stream as input and outputs a complex baseband stream of interlaced I/Q samples with a default sampling frequency of 2.048MHz. It can also directly drive SDR devices through Ettus' UHD driver, SoapySDR and LimeSuite.

Some devices require resampling to another sampling rate, which increases CPU requirements and can be done internally by ODR-DabMod.

Build information

If you run debian, have a look at the Installer scripts

Prerequisites

You will need boost at least version 1.54. The one from your distribution is probably fine, and if you have installed GNURadio or UHD, you will already have it.

You need uhd and/or soapy (including drivers for your SDR device), don't forget to also install the -dev package from your distribution.

You need a recent (4.0.4 or later) version of ZeroMQ, preferably installed from your distribution's repository. Also don't forget the -dev package.

Building odr-dabmod

First get it via the package or git repository:

git clone https://github.com/Opendigitalradio/ODR-DabMod
cd ODR-DabMod

Build and install according to the instructions in the README.

to update to latest upstream:

git pull

and do the bootstrap configure make again.

Usage

There are two ways of using ODR-DabMod: with a configuration file, and a smaller set of features is available through command line arguments. Use the -h option to see all options:

odr-dabmod -h

For the configuration file, start with the example configuration inside the doc folder: doc/example.ini

This example file describes and explains all supported settings.

Several settings can be modified while the modulator is running by enabling the remotecontrol, see doc/README-RC.md for more details.

Once you have defined a configuration file (let's call it modulator.ini), you can call:

odr-dabmod modulator.ini

See also DAB hardware

Additional information concerning the options

-c, or dac_clk_rate: Pre-correction for the CIC filter in the USRP:

This filter is used on the FPGA for up-sampling to 128MHz. This pre-correction filter is only enabled when the -c option is used. You should use -c128000000 for the old USRP1 device only.

-g, or gainmode: Gain computation mode

The gainmode option controls how ODR-Dabmod computes the OFDM symbol gain.

mode 0 (FIX) uses a fixed factor and is really not recommended. It is more useful on an academic perspective for people trying to understand the DAB modulation.

mode 1 (MAX) is the normalization of every OFDM symbol. No overshoot, no truncating, but varying output power (around 3dB) which might not be the best for some power amplifier.

mode 2 (VAR) uses the method specified in ETSI 300 798. This method normalizes to 4 times the standard deviation for an approximation of the RMS power. So around 6/100000 samples will be truncated and will introduce some really minor distortion. But this mode also maximizes the output power. This is the gain mode recommended for real world operation as it is based on a DAB standard; the only difference is that ODR-Dabmod uses a better resolution with 16 bits in place of 8 bits.

(Additional info taken from google groups discussion, originally written by Pascal Charest, CRC)

• CRC-DabMod usage