SPC05-1: Coded Modulation for ISI Channels with LDPC Codes

We propose a simple PAM-based coded modulation scheme that combines low-density parity-check (LDPC) codes and classical maximum-distance separable (MDS) codes. To approach the capacity of an ISI-constrained channel, the code is employed in conjunction with spectral shaping, Tomlinson-Harashima preceding and decision- feedback equalization (DFE). The scheme performs within 2-2.5 dB of un-shaped channel capacity (the sphere-bound) at a BER of 10 ^-12, even with regular LDPC codes of modest block lengths (1000-2000 bits). For further improvement, we consider signal sets on dense multi-dimensional lattices. With codes over the well-known Schlafli, Gosset, Barnes-Wall, and Leech lattices, the constructions reduce the gap to the sphere-bound. We consider the practical application of the proposed schemes to 10G- base-T, an emerging Ethernet standard over twisted-pairs at 10 Gbit/sec. A simple 1-dimensional scheme improves upon recent proposals by 0.5 dB at a BER of 10 ^-11, using a (3,6)-regular code of 2000 bits.