| 1. |
- Alvarado, Alex, 1982, et al.
(författare)
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Correcting Suboptimal Metrics in Iterative Decoders
- 2009
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Ingår i: IEEE International Conference on Communications. - 1550-3607. - 9781424434350
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Konferensbidrag (refereegranskat)abstract
- In this paper the issue of improving the performance of iterative decoders based on sub-optimal calculation of the messages exchanged during iterations (L-values) is addressed. It is well known in the literature that a simple---yet very effective---way to improve the performance of suboptimal iterative decoders is based on applying a scaling factor to the L-values. In this paper, starting with a theoretical model based on the so-called consistency condition of a random variable, we propose a methodology for correcting the L-values that relies only on the distribution of the soft information exchanged in the iterative process. This methodology gives a clear explanation of why the well-known linear scaling factor provides a very good performance. Additionally, the proposed methodology allows us to avoid the exhaustive search required otherwise. Numerical simulations show that for turbo codes the scaling factors found closely follow the optimum values, which translates to a close-to-optimal BER performance. Moreover, for LDPC codes, the proposed methodology produces a better BER performance compared with the known method in the literature.
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| 2. |
- Alvarado, Alex, 1982, et al.
(författare)
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Unequal Error Protection in BICM with QAM Constellations: Interleaver and Code Design
- 2009
-
Ingår i: IEEE International Conference on Communications. - 1550-3607. - 9781424434350
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Konferensbidrag (refereegranskat)abstract
- In this paper we present a general methodology for the interleaver and code design for QAM-based BICM transmissions. We develop analytical bounds on the bit error rate and we use them to predict the performance of BICM when unequal error protection (UEP) is introduced by the constellation labeling. Based on these bounds, the optimum design of interleaver and code is presented. The improvements obtained reached 2~dB for the analyzed cases, and are obtained without complexity increase. Although previous works noted the influence of the interleaver design and the UEP, to the best of our knowledge, this paper is the first to analyze formally this problem for BICM transmissions.
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| 3. |
- Huang, Jinliang, et al.
(författare)
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Discrete rate spectral efficiency improvement by scheme switching for MIMO systems
- 2008
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Ingår i: IEEE International Conference on Communications. - 1550-3607 .- 1938-1883. ; , s. 3998-4002
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Tidskriftsartikel (refereegranskat)abstract
- Adaptive modulation scheme has been widely used in multiple-input multiple-output (MIMO) systems to enhance spectral efficiency while maintaining the bit error rate (BER) under a target level. We consider two MIMO schemes, orthogonal space-time block codes (OSTBC) and spatial multiplexing with zero-forcing receiver (SM-ZF), that apply adaptive modulation scheme and derive closed-form expressions of the average spectral efficiency and BER. Based on the closed-form expression of spectral efficiency, a low complexity switching method is utilized to obtain high spectral efficiency gain over an adaptive system using a single scheme.
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| 4. |
- Osseiran, Afif, et al.
(författare)
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Capacity Evaluation of Fixed Beams in a WCDMA System using channel estimation based on P-CPICH
- 2006
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Ingår i: IEEE International Conference on Communications. - New York : IEEE. - 1550-3607 .- 1938-1883. - 1424403553 ; 11, s. 4900-4905
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Tidskriftsartikel (refereegranskat)abstract
- A fixed multi-beam system that uses the Primary- Common PIlot CHannel (P-CPICH) as a phase reference for channel estimation and demodulation in WCDMA is evaluated in a dynamic radio network simulator. The impact of the angular spread on the downlink system performance is analyzed. Furthermore, a scrambling code allocation strategy and an adaptive load-dependent power tuning algorithm for the P-CPICH are proposed. Extensive simulation studies are carried out to evaluate the capacity gains of 3 sector sites where each site is equipped with 1, 2 or 4 beams in a typical urban radio channel. Moreover an alternative antenna configuration consisting of 6 sector sites where each sector is equipped with 2 beams is evaluated.
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