Kolloquium Informationstechnik

Bit-Interleaved Coded Modulation with Iterative Detection/Decoding (BICM-ID) has been recognized as being a bandwidth efficient coded modulation and transmission scheme. D.Zhao et al. proposed a yet very simple, close Shannon-limit achieving BICM-ID system. It uses very simple codes, irregular repetition and single parity check codes, combined with Extended Mapping (EM). With this structure, turbo cliff happens at a value range of Signal-to-Noise power Ratio (SNR), 1 s 2dB to the Shannon limit. Even having known that the key role played towards the optimal design of the proposed code is the degree allocation for variable nodes, in the original technique described above, though, the irregular allocation to the node degrees were determined only empirically. Another fundamental drawback of the original technique is that it still suffers from error floor. This is simply because the demapper EXtrinsic Information Transfer (EXIT) curve does not reach the top-right (1,1) Mutual Information (MI) point. This talk shows that the problem of the optimal degree allocation for the proposed BICM-ID technique can be solved by using Linear Programming (LP). Furthermore, this talk introduces the use of partial accumulator, combined with the original system. With this technique, we can lift up the right-most point of the demapper curve to the (1.1) MI point, and thereby the convergence tunnel opens until (1,1) MI point. Based on those two optimization techniques, this talk further investigates a technique to identify optimal labeling pattern for EM, so that we can flexibly change the shape of the demapper EXIT curve. This talk introduces EXIT-constraint Binary Switching Algorithm (EBSA) and unbalanced labeling. It is shown through EXIT analysis that using EBSA and unbalanced labeling, demapper and decoder EXIT curves closely match, and thereby, it can achieve near-capacity performance. Simulation results using proposed techniques are also given in this talk. Using the proposed optimization techniques, threshold SNR only 0.5dB away from the Shannon limit even though its required complexity is very low; the complexity is at the same level as a turbo code with only memory-2 constituency codes.

Since, as noted above, EBSA jointly optimize the code and mapping rule.  We apply this technique to IDMA where entire available bandwidth expansion factor is used for coding, hence no spreading is used.   The design of such "reverse L-shaped EXIT matching" (because of very low operation point in SNR) is made possible by EBSA, where  the demapper and the code EXIT curves are exactly matched, and BER threshold happens at the designed threshold.  Furthermore, we applied it to soft interference cancellation case.  In this case, EBSA optimization was performed assuming all the multiuser interference is canceled, with which global soft cancellation and internal each-user's iterations are combined.  The system works very nicely, and the users can achieve very close performance to the multiple rate region bound.  At the final stage, the presentation makes technical comparison with the publication:
K. Kusume, G. Bauch, W. Utschick, “IDMA Vs. CDMA: Detectors, Performance and Complexity”, Global Telecommunications Conference, 2009. GLOBECOM 2009,
which uses combination of spreading and error correction code, and soft MMSE is used before error correction.  On the contrary, in our design, all the bandwidth is allocated to BICM-ID, and no MMSE needed.  Since our designed BICM-ID using EBSA is very powerful, exact matching is still possible for very low rate code (exhibiting "reverse L EXIT shape", and hence MMSE is not needed. Henceforth, our technique is much better in terms of power efficiency (lower SNR threshold) and spectrum efficiency (it can accommodate more users given the SNR operation point).

Keywords: BICM-ID, Single Parity Check Code, Irregular Repetition Code, Extended Mapping, Optimization, Partial Accumulator, EXIT based Binary Switching Algorithm, Interleaver Division Multiple Access.
 

Harald Rohde received his Ph.D. in experimental quantum physics at the University of Innsbruck, Austria in 2001. Since then he worked for Siemens ICN, Siemens CT and lately for Nokia Siemens Networks, all in Munich, Germany. He worked in multiple fields on optical communication technologies, ranging from long haul technologies to in house communications. He authored or co-authored some 60 publications and has some 60 patents pending or granted in the field of optical communication. Currently his main research focus lies in the field of coherent optical access systems.

 

 

Dr. Nobuhiko Miki, NTT DOCOMO
Investigation on picocell deployments on heterogeneous network
 

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Prof. Dr.-Ing. Robert Fischer, Universität Ulm
Entzerrungsverfahren für Kanäle mit mehreren Ein- und Ausgängen: der Weg von der Gram–Schmidt–Orthogonalisierung über Sortierung und Quantisierung hin zu Lattice–Reduktion
 

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