Introduction on DAB/DAB+
DAB, DAB+ and T-DMB European digital radio and mobile television standards share the same transmission system. It based on OFDM modulation and uses 1.5MHz of spectrum in VHF television band 3 (or L-band in SHF). A transmitter is broadcasting a set of programs, called a multiplex. The system has been designed for mobile use and is robust up to 300km/h.
With the development of the mmbTools by CRC and opendigitalradio, it is now possible to run a full transmission infrastructure on a laptop running linux and using a USRP as RF hardware (with gnuradio) or any other similar device.
The transmission chain can be divided in 4:
- The encoding: encoding the sound to MPEG-2 Layer II for DAB, MPEG-4 HE-AACv2 for DAB+ or video in MPEG-4 H.264 for T-DMB.
- The Multiplexer: gather different streams, produce necessary signalling and output a single 2Mbit/s stream in ETI format (Ensemble Transport Interface).
- The Modulator: take the ETI stream and produce the complex baseband OFDM signal ready for upconvert at the desired radio frequency.
- The RF transmission performed by the USRP using appropriate RF daughterboards (Basic TX or modified RFX400).
However thank to the modular approach from these tools it is possible to interface it with other implementations. If there's no other software OFDM DAB modulator implementation at the moment, for the encoding it is possible to re-use Toolame that is an implementation of MPEG-2 Layer II.
How to get started
Let's say you want to learn about DAB transmission and set up a laboratory transmitter that you can use to experiment, gain better understanding, test ideas, evaluate receivers or do measurements.
A will need:
- Some linux system knowledge.
- A recent PC running Debian stable: http://debian.org
- A USRP (B200, USRP1, B100, USRP2, are tested to work. The others should be fine too, no guarantees.)
- To read documentation:
- Read http://en.wikipedia.org/wiki/Digital_audio_broadcasting.
- Have a look at ETSI EN 300 401 to understand DAB better.
- Maybe also ETSI ETS 300 799 defines the ETI interface between multiplexer and modulator.
- Read the pages about the ODR-mmbTools listed below.
- To install the required tools on the debian PC. The Installer scripts will simplify this a lot.
- Have a look at the example mux and mod configurations in the respective doc/ folders and in mmbtools-aux.
- And of course, a DAB receiver.
Good luck, and don't transmit without a licence !
Other users and developers are reachable on the crc-mmbtools google group: https://groups.google.com/forum/#!forum/crc-mmbtools
The ODR-mmbTools comprise the following tools:
- ODR-DabMux Ensemble Multiplexer
- ODR-DabMod COFDM Modulator
They work with
- Toolame DAB encoder
- Fdk-aac-dabplus DAB+ encoder
- CRC-dabplus DAB+ encoder (not open source)
New ideas: Ideas_for_projects