The patent's assignee for patent number 8526547 is
News editors obtained the following quote from the background information supplied by the inventors: "Conventional systems and methods for the combination of binary error correcting codes (such as turbo codes) and multi-level signal sets (such as QAM) typically operate as depicted in FIG. 1. Input data is encoded, for example using Turbo Encoding. The encoded output is interleaved and mapped m bits at a time to a QAM constellation using a QAM constellation mapping which is typically a Gray mapping. The result is transmitted over a channel. At the receiver, the QAM de-mapping is performed, followed by turbo decoding.
"In these schemes, Turbo decoding is achieved in two stages. First, the probability values corresponding to the bits are extracted by adding up the probability of the corresponding constellation points. Then, these bit probability values are passed to a conventional Turbo-decoder for iterative decoding. The complexity of these methods grows with the size of the constellation due to the step required in extracting the probability values. In addition, the extra interleaving stage required between the binary encoder and the constellation (to reduce the dependency between the adjacent bits mapped to the same constellation) adds to the overall system complexity. It is well known that the coding gain of these schemes drops as the spectral efficiency increases.
"Disadvantageously, noise in the QAM may result in multiple bit errors which may not be correctable. For example, in a constellation with 1024 points, capable of representing ten bits per symbol, an error in the mapping may result in up to all ten bits being in error. Most current systems map similar bit sequences to constellation points which are close to each other to mitigate this problem somewhat. Gray Mapping is an example of this.
"Notwithstanding Gray mapping, the error rates achieved with such systems are still significantly less than the limit said to be theoretically achievable by Shannon's coding theorem. As QAM size increases, the coding loss becomes significant."
As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "One broad aspect of the invention provides a method of encoding a stream of data elements. The method involves splitting the stream of data elements into a first stream and a second stream; encoding the first stream to produce a first encoded stream; performing a constellation mapping using a combination of the first encoded stream and a third stream which is based on the second stream.
"In some embodiments, the constellation mapping performs a Gray mapping in mapping the third stream.
"In some embodiments, the third stream is identical to the second stream.
"In some embodiments, the method further involves encoding the second stream to produce the third stream using relatively weak encoding compared to that used in encoding the first stream to produce the third stream.
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