参数资料
型号: L64781
厂商: LSI CORP
元件分类: 消费家电
英文描述: SPECIALTY CONSUMER CIRCUIT, PQFP100
封装: PLASTIC, QFP-100
文件页数: 94/164页
文件大小: 2003K
代理商: L64781
Channel Estimation and Equalization
2-15
2.13 Channel Estimation and Equalization
The output from the common phase-error (CPE) correction block is a
sequence of complex numbers, each describing the signal received on
one of the COFDM carriers. The numbers correspond to values, chosen
from points of the current constellation, which were used to modulate
each carrier at the modulator. Each carrier is received with unknown
amplitude and phase due to the combined effects of:
The channel through which the RF signal has passed (which, in
general, is frequency selective)
Any minor error in the FFT timing window
The purpose of the channel estimation and equalization block is to
correct these effects so that the complex numbers at its output would, if
plotted on an Argand diagram, correspond to points of the transmitted
constellation (for example, QPSK, 16-QAM, or 64-QAM) except for any
superimposed noise or interference.
2.14 Viterbi Metric Assignment and Quantization
The Viterbi metric assignment and quantization block takes in a
sequence of complex numbers, each describing the signal received on
one of the COFDM carriers, after equalization. These are the received
complex numbers chosen at the modulator for the current constellation
points, according to the coded bits to be sent. This block forms Viterbi
metrics (“soft decisions”) for each received bit. The block quantizes these
metrics and passes them on, after reordering in the deinterleaver stages,
to the associated Viterbi convolutional decoder. The use of “soft” rather
than “hard” decisions is vital to obtaining the rugged properties of
COFDM.
2.15 Inner Symbol Deinterleaver
From each received constellation point, the Viterbi metric assignment
block extracts up to six soft decisions. The symbol deinterleaver accepts
one COFDM symbol’s worth of soft decisions and reorders them
l64781.book Page 15 Friday, January 19, 2001 1:28 PM
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