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Turbo Codes Promise Better Wireless Transmission

Posted by timothy on from the squashing-things-down dept.

captain igor writes "IEEE is running a story about two French professors that have created a new class of encoding, called 'Turbo Codes,' that will allow engineers to pass almost twice as much data through a given communications channel, or equivalently, the same amount of data at half the power. The new codes allow the Shannon Limit (the theoretical maximum capacity of a channel) to be approached to, currently, within .5 dB. Scientists hope that this breakthrough will revolutionize wireless communications, especially with the coming reclamation of large swaths of the EM spectrum." As the article points out, such codes are in use now, but seem poised for much wider implementation.

4 of 212 comments (clear)

  1. It gets better by s20451 · · Score: 4, Interesting

    Briefly, the big problem in data communication is achieving the Shannon limit, which is the maximum theoretical data rate at which information can be transmitted with arbitrarily low probability of error. Shannon proved his result in 1948, but until the Turbo guys, nobody knew how to achieve it.

    The main problem is that optimal decoding of any non-trivial code is NP-hard, which has been known for about 30 years now (i.e., the only known algorithm has exponential complexity in the code length). The Turbo breakthrough was to show that a suboptimal decoder with O(n) complexity for code length n could nonetheless achieve excellent results. This is the so-called "Turbo principle".

    There is an even "newer" class of codes called Low-Density Parity-Check Codes that can beat turbo codes. Turbo codes have a small gap to the Shannon limit, and these new codes can potentially eliminate the gap. Small gains are a big deal; the rule of thumb is that 1 dB of gain is equal to a million dollars of annual revenue for a wireless provider.

    The twist is that these LDPC codes were actually proposed in a 1963 PhD thesis, but were disregarded as beyond the computational abilities of the time. They were only "rediscovered" in 1996, after the Turbo code furore.

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    1. Re:It gets better by GuyZero · · Score: 4, Interesting

      The twist is that these LDPC codes were actually proposed in a 1963 PhD thesis, but were disregarded as beyond the computational abilities of the time. They were only "rediscovered" in 1996, after the Turbo code furore.

      The article also mentions that the latency associated with turbo codes is too high for most voice applications and that LDPC codes, while more computationally intensive, have a low latency. (At least, that's what I remember from the article).

      I thought it was funny that their sponsor, Alcatel or whoever, never patented it in Asia so NTT has been using turbo codes in Japan for years, free.

  2. Re:TURBO! by nosphalot · · Score: 4, Interesting
    Actually, turbo is an appropriate name for the way these codes work. If I remember correctly, its been 4 years since it was explained to me, as the data leaves the encoder, some of it gets routed back into the first stage to act as a hint for encoding the next stage of data. So the data exhaust, helps compress the data intake, much like a mechanical turbo.

  3. LDPC codes by auburnate · · Score: 5, Interesting

    Lots of /.ers have been quick to point out that turbo codes have been around since 1993. However, the IEEE article points out that LDPC ( low density parity check) codes were invented in the early 1960s. Researchers have gotten the LDPC codes to outperform the turbo codes, and to top it off, the LDPC patents have all expired, meaning no royalty fees like turbo codes. My first slashdot post ... be gentle!!!