Clemens Stierstorfer

(Gray) Mappings for Bit-Interleaved Coded Modulation

Mappings for square quadrature amplitude modulation (QAM) are investigated in terms of the achievable capacity in bit-interleaved coded modulation (BICM). In G. Caire et al. (1998) it is conjectured that Gray labelings maximize this capacity. However, Gray mappings are not unique and it can be shown that the conjecture cannot hold in general for QAM constellation sizes larger than 16. Based on the bit level capacities of mappings, structures determining capacity are analyzed. Construction guidelines leading to capacity maximizing Gray mappings are presented.

Polar-Coded Modulation

A framework is proposed that allows for a joint description and optimization of both binary polar coding and 2m-ary digital pulse-amplitude modulation (PAM) schemes. For the latter, the multilevel coding (MLC) approach as well as bit-interleaved coded modulation (BICM) are considered. The conceptual equivalence of polar coding and multilevel coding is covered in detail. Based on an alternative characterization of the channel polarization phenomenon, rules for the optimum choice of the labeling in coded modulation schemes employing polar codes are developed. Simulation results regarding the error performance of the proposed schemes on the AWGN channel are included.

Precoding for point-to-multipoint transmission over MIMO ISI channels

Tomlinson-Harashima type precoding for point-to-multipoint transmission over linear dispersive channels which suffer from intersymbol interference and multiuser interference is reviewed. The tasks of the matrix filters at the joint transmitter, their calculation by spectral factorization, and the necessity of an optimized processing order are discussed. The performance of precoding is covered by numerical simulations.

Multilevel polar-coded modulation

A framework is proposed that allows for a joint description and optimization of both binary polar coding and the multilevel coding (MLC) approach for 2m-ary digital pulse-amplitude modulation (PAM). The conceptual equivalence of polar coding and multilevel coding is pointed out in detail. Based on a novel characterization of the channel polarization phenomenon, rules for the optimal choice of the bit labeling in this coded modulation scheme employing polar codes are developed. Simulation results for the AWGN channel are included.

Rate loading in OFDM based on bit-level capacities

A new bit allocation algorithm for uncoded transmission over parallel, independent channels (e.g., multicarrier transmission) is proposed. In contrast to state-of-the-art loading algorithms it is based on bit-level capacities and aims at the maximization of the so-called parallel decoding capacity. The algorithm can be implemented very efficiently and requires significantly lower complexity than existing approaches. Numerical results show a performance in terms of the bit-error ratio comparable to established bit-loading algorithms.

Single- and multicarrier transmission in up- and downlink scenarios with intersymbol interference: a comparison

Up- and downlink transmission over multiple-input/multiple-output (MIMO) channels where the trans- mission paths exhibit intersymbol interference (ISI) are studied. Equalisation schemes for multipoint-to-point scenarios (multiple access problem, uplink) and precoding schemes for point-to-multipoint scenarios (broadcast channel (BC), downlink) are investigated. In particular, singlecarrier modulation employing decision-feedback equalisation (DFE)/precoding, multicarrier (MC) modulation employing BLAST/precoding per carrier and frequency-division multiplexing (FDM) in disjoint frequency bands are considered. The rate regions, that is the region of admissible rates of the users, for these approaches are given and compared. It is shown, that despite single- and multicarrier transmission can achieve the same sum rate, in each case MIMO OFDM offers the largest rate region. The results are illustrated via numerical examples. Copyright

Comparison of code design requirements for single- and multi-carrier transmission over frequency-selective MIMO channel

Point-to-point transmission over multiple-input/multiple-output channels with intersymbol interference is considered. Two different equalization strategies - single-carrier transmission with spatial/temporal decision-feedback equalization and multicarrier transmission with V-BLAST in each carrier - and the respective requirements on channel coding are studied and compared. Via capacity arguments, it is shown that bit-inter-leaved coded modulation is not well suited for the situations at hand. This holds in particular if channel coding is used in combination with rate loading, i.e., non-uniform rate distribution over the carriers. Approaches to overcome this problem are discussed