PS20230 Datasheet, PDF (18/26 Pages) List of Unclassifed Manufacturers – COFDM demodulator with USB interface for PC-TV

PS20230
7.16MPEG Frame Aligner
The Viterbi decoded bit stream is aligned into 204-byte frames. A robust synchronization algorithm is
used to ensure correct lock and to prevent loss of lock due to noise impulses.
7.17 De-interleaver
Errors at the Viterbi output occur in bursts and the function of the de-interleaver is to spread these errors
over a number of 204-byte frames to give the Reed-Solomon decoder a better chance of correcting these.
The de-interleaver is a memory unit which implements the inverse of the convolutional interleaving
function introduced by the transmitter.
7.18Reed-Solomon Decoder
Every 188-byte transport packet is encoded by the transmitter into a 204-byte frame, using a truncated
version of a systematic (255,239) Reed-Solomon code. The corresponding (204,188) Reed-Solomon
decoder is capable of correcting up to eight byte errors in a 204-byte frame. It may also detect frames
with more than eight byte errors.
In addition to efficiently performing this decoding function, the Reed-Solomon decoder in PS20230 keeps
a count of the number of bit errors corrected over a programmable period and the number of
uncorrectable blocks. This information can be used to compute the post-Viterbi BER.
7.19 De-scrambler
The de-scrambler de-randomizes the Reed-Solomon decoded data by generating the exclusive-OR
of this with a pseudo -random bit sequence (PRBS). This outputs 188-byte MPEG transport packets.
The TEI bit of the packet header will be set if required to indicate uncorrectable packets.
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