Design of low-density parity-check codes for modulation and detection

Bell Labs., Crawford, NJ, USA
IEEE Transactions on Communications (Impact Factor: 1.75). 05/2004; DOI: 10.1109/TCOMM.2004.826370
Source: DBLP

ABSTRACT A coding and modulation technique is studied where the coded bits of an irregular low-density parity-check (LDPC) code are passed directly to a modulator. At the receiver, the variable nodes of the LDPC decoder graph are connected to detector nodes, and iterative decoding is accomplished by viewing the variable and detector nodes as one decoder. The code is optimized by performing a curve fitting on extrinsic information transfer charts. Design examples are given for additive white Gaussian noise channels, as well as multiple-input, multiple-output (MIMO) fading channels where the receiver, but not the transmitter, knows the channel. For the MIMO channels, the technique operates within 1.25 dB of capacity for various antenna configurations, and thereby outperforms a scheme employing a parallel concatenated (turbo) code by wide margins when there are more transmit than receive antennas.

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    ABSTRACT: In this paper, two-user Gaussian interference channel(GIC) is revisited with the objective of developing implementable (explicit) channel codes. Specifically, low density parity check (LDPC) codes are adopted for use over these channels, and their benefits are studied. Different scenarios on the level of interference are considered. In particular, for strong interference channel examples with binary phase shift keying (BPSK), it is demonstrated that rates better than those offered by single user codes with time sharing are achievable. Promising results are also observed with quadrature-shift-keying (QPSK). Under general interference a Han-Kobayashi coding based scheme is employed splitting the information into public and private parts, and utilizing appropriate iterative decoders at the receivers. Using QPSK modulation at the two transmitters, it is shown that rate points higher than those achievable by time sharing are obtained.
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    ABSTRACT: In this paper, we focus on the two-user Gaussian interference channel (GIC), and study the Han-Kobayashi (HK) coding/decoding strategy with the objective of designing low-density parity-check (LDPC) codes. A code optimization algorithm is proposed which adopts a random perturbation technique via tracking the average mutual information. The degree distribution optimization and convergence threshold computation are carried out for strong and weak interference channels, employing binary phase-shift keying (BPSK). Under strong interference, it is observed that optimized codes operate close to the capacity boundary. For the case of weak interference, it is shown that via the newly designed codes, a nontrivial rate pair is achievable, which is not attainable by single user codes with time-sharing. Performance of the designed LDPC codes are also studied for finite block lengths through simulations of specific codes picked from the optimized degree distributions.
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    ABSTRACT: In this work, we exploit the capacity approaching capability of low density parity check (LDPC) codes over wire-less relay channels. We consider the classical full-duplex relay channel model under both ergodic and non-ergodic scenarios, and propose two practical relaying schemes. By comparing with the theoretical information rate bounds, we show that the LDPC coded relay systems can approach the ergodic/outage information rates (i.e., constrained channel capacities) very closely. Specifically, we show that they can even outperform the existing turbo coded relay systems under appropriate code design. In addition, based on the measure of average mutual information, we analyze the convergence behavior of the proposed schemes which also demonstrates their great potential to perform near capacity over both ergodic and non-ergodic wireless relay channels.


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