MC92314 Datasheet, PDF (10/100 Pages) Motorola, Inc – DVB-T Single Chip Demodulator Application Note

System Overview
Freescale Semiconductor, Inc.
• Divide the whole available bandwidth into a large number of subchannels with different
frequencies (Frequency Division Multiplex).
• each subchannel is independent form all others (Orthogonality).
• To combat the echoes in the terrestrial channel a guard interval is used to absorb them.
• A certain amount of redundancy is added to the bits at the transmitter side, allowing powerful
error correction techniques in the receiver.
In principle the whole available bandwidth is divided into a large number N (e.g. 2048) of
separate narrowband subchannels (the OFDM subcarriers). Data transmission on each
subcarrier frequency is independent from and in parallel with the other subcarriers, leading to a
very low datarate on each subcarrier compared to the overall transmission capacity. The splitting
into the subchannels including the modulation onto the subcarriers can be done very efficiently
by performing an Inverse Fast Fourier Transform (FFT) to the data to be transmitted. In turn the
receiver must do a FFT to obtain the original information. Following the usual terms of digital
n _{signal processing the region before the IFFT in the transmitter and after the FFT in the receiver}
tio ^{is called ‘frequency domain’ and in contrast to it the signal after the IFFT (in the transmitter) until}
before the FFT (in the receiver) is associated with the ‘time domain’.
a _{All these steps together allow the realisation of a robust transmission scheme specially adapted}
rm _{to the terrestrial channel. Advances in silicon technology enable the implementation of the}
fo ^{advanced signal processing algorithms necessary at costs suitable to the consumer electronics}
industry.
In _{Additional information on the OFDM system can be obtained from Reference [1-2] and}
ry ^{Reference [1-3].}
ina ^{1.4 Overview of the DVB-T System}
After thorough investigation of the requirements the standard for digital terrestrial television was
lim ^{finalised in 1996 (see Reference [1-1]). In line with the standards for the satellite system (DVB-}
S) and the cable system (DVB-C) it specifies all the transmission parameters for the
Pre ^{broadcasting of services via terrestrial (e.g. UHF) channels.}
1.4.1 Modulation Scheme
The standard covers the Orthogonal Frequency Division Multiplex (OFDM) scheme, using
OFDM symbol lengths of either 2048 (2K) or 8192 (8K) complex-valued samples. The integrated
circuit covered in this document can deal only with the 2K-system, so the 8K system is not
covered here.
Figure 1-2 gives a block diagram of the complete DVB-T transmission system, the blocks marked
with thick lines are unique to the terrestrial system, whereas the other blocks are identical to the
satellite standard DVB-S. In this diagram also the basic parameters of the transmission
parameters are given, for a more detailed description see Reference [1-1]
MOTOROLA
1-4
Single Chip DVB-T Demodulator - Rev. 1.3 (11/30/98)
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