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Whitening and Interleaving Operations for Modems

IP.com Disclosure Number: IPCOM000046418D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Maddens, F: AUTHOR

Abstract

In a modem transmitter the data bit flow is split into fixed length groups of bits, each group of bits being used to define a symbol selected within a two-dimensional constellation of symbols and the components of the selected symbol are used to modulate quadrature component carriers. In a number of cases, the conversion from a group of bits to a symbol involves a convolutional encoding of predetermined bits of each group of bits, and then the encoded bits and the remaining non-encoded bits are used to address a ROM (read-only memory) providing the corresponding symbol coordinates. This symbol is then used to modulate carriers using, for instance, the DSB-QC techniques, before being transmitted over a transmission line toward the receiver.

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Whitening and Interleaving Operations for Modems

In a modem transmitter the data bit flow is split into fixed length groups of bits, each group of bits being used to define a symbol selected within a two- dimensional constellation of symbols and the components of the selected symbol are used to modulate quadrature component carriers. In a number of cases, the conversion from a group of bits to a symbol involves a convolutional encoding of predetermined bits of each group of bits, and then the encoded bits and the remaining non-encoded bits are used to address a ROM (read-only memory) providing the corresponding symbol coordinates. This symbol is then used to modulate carriers using, for instance, the DSB-QC techniques, before being transmitted over a transmission line toward the receiver. On the receiving side, the received signal is sampled and coded before being demodulated, equalized and decoded to recover the original bit configurations.

The equalizing operations color any input white noise which, in turn, degrades the decoding performance. A solution to this problem is provided by spreading successive equalizer output symbols in the time domain to whiten the noise at the decoder input. A correlative operation needs thus to be performed on the transmitting side by interleaving originally consecutive symbols.

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