Bandwidth and power-coded modulation schemes are very desirable for many applications in high-data-rate transmission over a given allocated bandwidth. The goal is to design such coded modulation system for a given throughput with the lowest possible signal-to-noise ratio for not only a channel with additive White Gaussian noise, but those channels that are impaired by fading, a typical channel in wireless communications and even satellite communications where mobiles may use Omni directional antennas.
Bit-interleaved coded modulation (BICM) is a technique that allows relatively simple design of bandwidth-efficient coded modulation systems by concatenating a code, an interleaver, and a modulation mapper. One of the most popular codes to be used in BICM is the low-density parity-check (LDPC) code, and one of the most promising recent methods of designing LDPC codes is via protographs. Protograph methods allow the design of LDPC codes that are modular, easy to encode, and have excellent performance. Unfortunately, past attempts to use protograph LDPC codes in the context of BICM have not been very successful, in the sense that the design methods have been very restrictive and it has not been possible to produce a code with an arbitrary desirable rate and desirable modulation.
This invention addresses this question via a family of protograph-based LDPC codes, and combining them with a simple and efficient mapping to high-level modulation schemes. A method also was produced to calculate their iterative decoding threshold, a useful parameter when designing any capacity approaching LDPC code. In the context of Rayleigh fading, this invention presents the calculation of the threshold of protograph-based BICM.
A protograph-based LDPC code is an LDPC code that can be constructed from a small proto-matrix with a few nonzero entries. Protograph codes can achieve very good thresholds with low encoder complexity as well as fast decoding. In this invention, two families of protograph codes were studied: AR4JA protograph codes (a CCSDS standard proposed by JPL/Caltech) and a recently proposed protograph code by the same inventors. The codes were mapped to high-order modulations. The protograph-based LDPC coded BICM using AR4JA protograph codes with 16QAM in AWGN channel was previously studied by JPL/Caltech; the advantage of the new design process is that it is modular and easy to apply to other protographs and modulations. The effectiveness of this method is demonstrated via the calculation of the iterative decoding thresholds in Rayleigh faded channels. All coded modulation schemes under study in this invention are operating within a gap of 0.6 dB or less to their capacity limits.
This work was done by Dariush Divsalar of Caltech, and Thuy V. Nguyen and Aria Nosratinia of the University of Texas in Dallas for NASA’s Jet Propulsion Laboratory. NPO-48265
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Refer to NPO-48265.