Hanqing Lou

LDGM codes for joint source-channel coding of correlated sources

A system based on the use of systematic linear codes with low-density generator matrix (LDGM codes) for joint source-channel coding of multiterminal correlated binary sources is proposed. The encoding structure and different decoding possibilities are investigated and evaluated. For the case of binary sources and AWGN channels, the resulting performance is close to the theoretical limits.

Rate-compatible low-density generator matrix codes

We propose a family of rate-compatible codes based on the concatenation of two linear codes with low-density generator matrix, which are a special class of LDPC codes with low encoding complexity. The proposed scheme is characterized by its simplicity of construction, and does not require optimization of the puncturing pattern.

Quantum error-correction using codes with low-density generator matrix

We propose the use of linear codes with low-density generator matrix in the context of quantum error correction. The proposed codes allow greater flexibility and are easier to design than existing sparse-graph quantum codes, while leading to better performance.

Low-density generator matrix codes for indoor and markov channels

We propose a modified algorithm for decoding of linear codes with low-density generator matrix (LDGM codes) over finite-state binary Markov channels. In order to avoid error floors, a serial concatenation of two LDGM codes is utilized. The hidden Markov model representing the channel is incorporated into the graph corresponding to the code, and the message passing algorithm is modified accordingly. The proposed scheme clearly outperforms systems in which the channel statistics are not exploited in the decoding process, allowing reliable communication at rates which are above the capacity of a memoryless channel with the same stationary bit error probability as the Markov channel. The proposed technique can be successfully applied for real wireless channels that can be modeled with hidden Markov models, such as indoor channels. In this case, the hidden Markov model representing the wireless channel can be estimated jointly with the decoding process

Random Labeling: A New Approach to Achieve Capacity in MIMO Quasi-Static Fading Channels

We introduce a layered scheme based on multilevel codes and random labeling of the MIMO constellation that attains constellation-constrained outage capacity in quasi-static fading channels. The proposed approach has the desirable features of using binary codes, not requiring demapper iterations and not applying constellation-expanding linear transformations in the complex field

Capacity Approaching Layered MIMO Schemes for Quasi-Static Fading Cheannels

We focus in the design of layered transmission schemes that can approach outage capacity in quasi-static fading channels in the high spectral efficiency regime without demapper iterations. We introduce a necessary and sufficient condition for layered schemes to achieve outage capacity in quasi-static fading channels, and we use it to search for high performance layered architectures. The transmission schemes considered in the analysis are based on multilevel codes and bit-interleaved coded modulation. Multi-dimensional random labeling is shown to satisfy the proposed criterion and, therefore, its performance is very close to outage capacity

LDGM coded space-time trellis codes from differential encoding

In this letter, we investigate the concatenation of a low density generator matrix (LDGM) outer code and a recursive space time trellis (RSTTC) inner code based on differential encoding. We provide guidelines for the design of the LDGM outer code and observe that previous schemes based on parity check outer codes are particular cases of the proposed framework

Guidelines for Channel Code Design in Quasi-Static Fading Channels

In this paper, we provide guidelines for the design of good binary error correcting codes in quasi-static fading channels, using established design rules in AWGN channels as a starting point. The proposed analysis is based on the Gaussian assumption of demodulator log-likelihood ratios. This assumption allows to decouple the influence of the convergence threshold, slope in the BER waterfall region and error-floor of the channel code, so that these parameters can be analyzed separately. Our analysis evidences that, contrary to what happens in AWGN channels, the design of good low rate codes in quasi-static fading channels is much simpler than those of standard rates (.3 to .8 ).

Improving the performance of LDGM codes over indoor channels by exploiting the channel statistics

We propose a scheme for improving the decoding of linear codes with low-density generator matrix (LDGM codes) over indoor-like channels. The key idea is to model the channel of interest as a hidden Markov model, which is estimated and exploited in the decoding process. No a priori knowledge about the hidden Markov model is assumed at the decoder site. The proposed system clearly outperforms systems in which the channel statistics are not considered in the decoding process.

Decoding of linear codes with low-density generator matrix over finite-state binary markov channels

We propose a modified algorithm for decoding of linear codes with low-density generator matrix (LDGM codes) over finite-state binary Markov channels. Simulation results show that the proposed scheme outperforms regular LDPC codes and achieves a performance close to that of turbo codes with much less encoding/decoding complexity