Junho Cho

Spatially Coupled Soft-Decision Error Correction for Future Lightwave Systems

In this paper, we discuss and present some recent advances in the field of error correcting codes and discuss their applicability for lightwave transmission systems. We introduce several classes of spatially coupled codes and discuss several design options for spatially coupled codes and show how rapidly decodable codes can be constructed by careful selection of the degree distribution. We confirm the good performance of some spatially coupled codes at very low bit error rates using an FPGA-based simulation. Finally, we compare all proposed schemes and show how spatially coupled Low-Density Parity-Check (LDPC) codes outperform conventional LDPC and polar codes with similar receiver complexity and memory requirements.

Analysis of soft-decision FEC on non-AWGN channels

Soft-decision forward error correction (SD-FEC) schemes are typically designed for additive white Gaussian noise (AWGN) channels. In a fiber-optic communication system, noise may be neither circularly symmetric nor Gaussian, thus violating an important assumption underlying SD-FEC design. This paper quantifies the impact of non-AWGN noise on SD-FEC performance for such optical channels. We use a conditionally bivariate Gaussian noise model (CBGN) to analyze the impact of correlations among the signals two quadrature components, and assess the effect of CBGN on SD-FEC performance using the density evolution of low-density parity-check (LDPC) codes. On a CBGN channel generating severely elliptic noise clouds, it is shown that more than 3 dB of coding gain are attainable by utilizing correlation information. Our analyses also give insights into potential improvements of the detection performance for fiber-optic transmission systems assisted by SD-FEC.

Construction of protographs for large-girth structured LDPC convolutional codes

In this paper, we present a method to construct girth-6 protographs that lead to the shortest constraint length in the convolutional structure. A stringent structural constraint is imposed on the protographs such that the decoder can be implemented efficiently. Then, given the structural constraint, it is shown that finding the aforementioned protographs is equivalent to solving a simple algebraic problem. Based on this mathematical formulation, girth-6 protographs are created without having to resort to a graph search. Using the girth-6 protographs, we derive good low-density parity-check (LDPC) convolutional codes by using periodic quasi-cyclic lifting. The performance of such constructed codes is compared with AR4JA-based LDPC convolutional codes.

Next Generation Error Correcting Codes for Lightwave Systems

In this paper, we discuss and present some recent advances in the field of error correcting codes and discuss their applicability for lightwave transmission systems. We compare polar codes and spatially coupled codes and present recent modifications of the latter.

Enhanced physical layer security of MIMO-SDM systems through information scrambling

Using as a security metric the bit error ratio after decoding that a wire-tapping eavesdropper can at best attain, we demonstrate that information scrambling significantly enhances the physical layer security in multiple-input-multiple-output space-division multiplexing (MIMO-SDM).