MC92314 Datasheet, PDF (13/100 Pages) Motorola, Inc – DVB-T Single Chip Demodulator Application Note

Freescale Semiconductor, Inc.
System Overview
• 3 Bit soft-decision input in suited to the output of the OFDM block.
• Code rate ¹/₂ and depunctured rates of ²/₃, ³/₄, ⁵/₆, and ⁷/₈.
• Automatic or manual rate selection.
• Programmable internal synchronizer.
• Provision for external synchronization.
• Survivor depth 96
• No internal APLL needed, clock is provided by the OFDM block.
• Signal quality output data.
1.4.4.2 Convolutional Deinterleaver
n ^{To achieve the optimal performance of any concatenated coding scheme there must be an}
tio ^{interleaver in the transmitter between the inner and outer encoder. This interleaver distributes}
the bytes in a pseudo random order before feeding them into the inner encoder. In turn the
a deinterleaver in the receiver rearranges the original order, spreading error bursts provoked by
overloading the inner decoder due to bad channel conditions.
rm _{In case of the DVB system the interleaving scheme uses a Convolutional 12x17 Forney}
fo _{Interleaver: Every 204 bytes of data are interleaved (reordered) at the transmitter and}
In ^{deinterleaved in the receiver using a Convolutional Deinterleaver with I=12 branches and M=17}
byte storage cells as defined by the DVB Specifications.
ry _{1.4.4.3 Reed-Solomon Decoder}
a _{The FEC block contains a complete Reed-Solomon decoder as specified by DVB for digital}
in _{receiver applications (204, 188) of GF(256), that means input blocks with 188 byte in length,}
added redundancy of 16 checkbytes leading to 204 bytes output block length. The block will
lim accept data from the Viterbi decoder and deliver an MPEG-2 transport stream to the Set-Top Box
e ^{core demultiplexer.}
Pr 1.4.4.4 Energy Dispersal Removal (Descrambling)
The MPEG-2 data (excluding Sync Bytes) are randomised for Energy Dispersal in the
transmitter. This block reverses the process and re-inverts the inverted Sync Byte prior to
delivering the data to the MPEG-2 Transport Demultiplexer. It is the last step in the frontend
processing chain.
The main features of the deinterleaver, RS decoder and descrambling block are given below:
• 37 MBit/s typical input and output data rates
• optimized Frame Synchronizer performance for DVB parameters
• DVB compliant 12x17 Forney Deinterleaver
• Reed-Solomon (204,188,8) decoder as specified by DVB
• DVB Descrambler for Energy Dispersal & inverted Sync Byte removal
Single Chip DVB-T Demodulator - Rev. 1.3 (11/30/98)
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