Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
1999-07-09
2003-11-04
Bayard, Emmanuel (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
Reexamination Certificate
active
06643332
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to encoding and decoding of digital communication systems. More particularly, the present invention relates to multi-level encoding and decoding digital bits using the same or an identical encoder and decoder.
2. The Prior Art
Generally, communication systems include both a digital signal transmission and receiving system. The transmission portion of the digital signal transmission and receiving system includes an encoder, possibly a puncturing or zero-tailing module, and a modulator, providing a modulated signal at a communication channel. Similarly, a receiving portion of the digital signal transmission and receiving system includes a demodulator, possibly a depuncturing or block decoder module if punctured or zero-tailed, respectively, during encoding, and a decoder.
The modulated signal includes an in-phase component and a quadrature component. When the modulated signal is received, after conversion from an analog to a digital signal, each bit is demodulated into the in-phase and quadrature signal components by the demodulator using sine and cosine functions. The decoder may comprise a Viterbi decoder, which may be used to decode these convolutional codes.
In satellite broadcasting, severe location-dependent fades can occur due to rain attenuation. If a single trellis coded modulation (TCM) scheme is used, then those locations with severe attenuation will loose the incoming signal, as shown in
FIG. 1
a
. On the other hand, by using different TCM schemes, the digital signal can be encoded in such a way that information at a lower rate is received under severe attenuation. Receivers in locations with less adverse atmospheric conditions can receive information at higher rates, as shown in
FIG. 1
b
. This is known as graceful degradation. However, to achieve an efficient system design, different constellations may need to be used in multiplexing TCM schemes. Thus, a control mechanism to switch seemlessly between different rates and constellations is required. This leads to a reduced throughput, due to overhead information, as well as a more complex receiver structure to process different signal constellations and to synchronize properly.
What is needed is a method which would work over the same constellation without degrading the signal under adverse atmospheric conditions; thereby, eliminating the overhead associated with multiplexing control and/or rate switching.
BRIEF DESCRIPTION OF THE INVENTION
The purpose of the present invention is to provide a method and apparatus for encoding and decoding digital signals which would allow the system to compensate for atmospheric degradation using a multilevel, j, encoding/decoding system where each level uses either the same or an identical encoder/decoder. This would allow for higher bandwidth efficiency and would simplify the structure of the receiver.
The encoding method includes the steps of: choosing a component code rate, r
j
, for each substream, splitting the data stream into a plurality, j, of data substreams, sending each substream through an identical encoder; possibly puncturing or zero-tailing each data substream, combining the substreams into symbols of n output length, applying a 2
j
symbol generator that provides an output of a plurality of modulator values, applying these modulator values to a modulator for transmission over the channel. The multi-stage decoding method includes the steps of: receiving the multi-level encoded, modulated signal, pre-processing the data including depuncturing or block decoding if the data was punctured or zero-tailed respectively during encoding, sending the data through an identical decoder, saving the first-level information bits in a buffer, and repeating the process of pre-processing, decoding, storing, and delivering the data for j-stages. Additionally, using a nonstandard partitioning scheme, encoded data can be mapped into disjoint regions of X-dimensional space, creating independent variables that can be identified and eliminated from decoding schemes.
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Fossorier Marc
Lin Shu
Morelos-Zaragoza Robert
Bayard Emmanuel
LSI Logic Corporation
Maiorana P.C. Christopher P.
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