Digital Signal Processing Reference
In-Depth Information
DAB-transmitter in a neighbouring cell
(same frequency)
Next
DAB-transmitter
Mobile receiver
Illustration 276:
Multipath reception and synchronized reception with DAB
Coded OFDM (COFDM) and Digital Audio Broadcasting (DAB)
Digital Audio Broadcasting DAB is a joint development of several European countries.
Characteristic of DAB are its different transmission modes facilitating adaptation to
audio, text, images and mobile TV according to demand. For that reason DAB is not only
an improvement over its predecessor, FM broadcasting, but part of a completely new
transmission system for digital data - with a strong emphasis on radio and TV.
1536 sinusoidal carriers are transmitted at a distance of 1 kHz (mode I). For the duration
of each symbol length T
S
of 1.246 ms each carrier can take on four different discrete phase
states (4-DPSK). This is the equivalent of 2 bits (2
2
= 4). Within a DAB time frame of 76
symbols (94.7 ms) 76
1536 = 233,472 bits can be transmitted. The result is 2.4 Mbit,
i.e. the transmission rate with DAB is 2.4 Mbit/s.
∗
2
∗
Illustration 276 shows multipath and digitalized reception in mobile telephony. The
resulting problems such as interferences (fading) etc could not be solved by means of
analog methods. DAB has largely been able to solve these problems using a unique com-
bination of protective measures. Therefore DAB is referred to as COFDM (Coded
Orthogonal Frequency Division Multiplex).
