Digital Audio Broadcasting
Design of VLSI-Components for Digital Audio Broadcasting
Analog radio transmission services are in widespread use since the beginning of the century. Especially for mobile reception ("car radio'') the quality of the received audio programme suffers because of noise and signal drop-outs.
Therefore, during the years 1992-95 a digital transmission scheme for radio broadcasting has been defined which will resolve most of the problems inherient to the currently used analog transmission methods. This Digital Audio Broadcasting (DAB) scheme, as defined by the European Telecomunication Standard (ETS 300 401) will provide CD audio quality even for mobile receivers. DAB-based radio broadcasting will officially start in the year 1997 in Germany.
The poor quality of the mobile analog reception is caused by two effects. First, the received signal is disturbed by noise originating e.g. from other transmitters, electrical machines, car ignition, etc. Second, the transmitted signal interferes with itself because of multi-path signal propagation (due to reflections of the signal at buildings etc). Moreover, a moving receiver leads to changes of the interference and noise pattern over time ("fading'' multi-path effects).
These problems are solved by DAB by incorperating the following schemes (among others):
- Forward Error-Correction (FEC) based on convolutional codes
- Orthogonal Frequency Divison Multiplexing (OFDM) and
- Redistribution of the data bits over some time interval (time interleaving)
The use of these methods will provide a high qualtity of service but it also leads to a very significant amount of digital signal processing at the receiver site. The mature digital CMOS VLSI technologies allow to implement DAB receivers in a cost-effective manor.
Our work - The first full-rate DAB Viterbi decoder
In a close co-operation with industry we are developing VLSI-components for the digital signal processing section of DAB receivers. During the last year we have developed a key component of the DAB receiver, the Viterbi Decoder. The Viterbi Decoder performs the error-correction of the received noise-disturbed signal.