Digital Signal Processing Reference
In-Depth Information
bandwidth such as television with normally up to 8 MHz bandwidth,
which are 'crying out' for reliable digital transmission methods. Using a
multi-carrier method is one reliable approach to this. The information is
transmitted digitally not via one carrier but via many - in some cases thou-
sands of subcarriers with multiple error protection and data interleaving.
These methods, which have been known since the seventies, are:
•
Coded Orthogonal frequency division multiplexing (COFDM)
•
Discrete multitone (DMT)
They are used in
•
Digital Audio Broadcasting (DAB)
•
Digital Video Broadcasting (DVB-T)
•
Asymmetrical Digital Subscriber Line (ADSL)
•
Transmission of data signals via power lines
•
ISDB-T
•
DMB-T
In this Section, the background, characteristics and generation of multi-
carrier modulation methods such as coded orthogonal frequency division
multiplexing (COFDM) or discrete multitone (DMT) are described.
The concept of multi-carrier modulation goes back to investigations in
the Bell Laboratories in the U.S. [CHANG] and to ideas in France in the
seventies. In those days, however, chips which were fast enough to imple-
ment these ideas were nowhere in sight. It wasn't until many years later, at
the beginning of the nineties, that the concept was turned into reality and
applied for the first time in Digital Audio Broadcasting (DAB). Although
DAB cannot really be called an absolute marketing success, this is cer-
tainly not due to the technology but rather the inappropriate marketing (or
complete lack of it) and this, in principle, is attributable to industry and
politics. The technology itself is first class. Even today, it is difficult to
convince the consumer in many fields that this product or the other is bet-
ter. It is certainly correct to leave many decisions to the consumer but he or
she must then have knowledge of the new possibilities and underlying
principles or even be able to purchase the new type of product. In the case
of DAB, this has only been possible since 2001 (availability of DAB re-
ceivers) which is unfortunate for this excellent method of transmitting au-
dio virtually in CD quality via terrestrial channels. The situation is differ-
ent in the case of ADSL in telecommunications where ADSL is
increasingly accepted and demanded for Internet access because of its
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