Dmitry Artemasov

Gennady Shutkov, Dmitry Artemasov, Alexey Frolov et al.

We consider the design of low-density parity-check (LDPC) codes for a given iterative decoder. Despite tools such as direct simulation, density evolution (DE), and EXIT-chart analysis, selecting a parity-check matrix remains a difficult combinatorial optimization problem. Existing approaches often rely on population-based search, random mutations, genetic algorithms, or related heuristics, which require careful parameter tuning and may be computationally expensive. Recent gradient descent (GD)-based methods optimize relaxed parity-check matrices by differentiating through decoder simulations. However, such decoder-in-the-loop strategies rely on noisy Monte Carlo estimates, require line search over soft matrix representations, and remain costly for long LDPC codes. Moreover, although optimization is performed in a relaxed domain, the loss is typically evaluated only at integer-valued parity-check matrices. In this work, we focus on the design of long protograph-based LDPC codes and propose a deterministic GD-based framework that operates directly on a relaxed protograph representation. Each protograph entry is interpreted as the probability that the corresponding element is equal to one. The loss function is based on DE bit error rate (BER) performance and can be evaluated directly for relaxed protographs. To justify this relaxation, we associate the relaxed representation with an ensemble of binary protographs and show that the proposed relaxed DE gives the ensemble-averaged DE performance. The resulting optimization procedure is fully autonomous and uses standard GD methods. Owing to deterministic DE evaluation and informative gradients, the proposed approach provides fast and reliable convergence. Numerical experiments for the min-sum decoder show that the optimized protographs outperform 5G LDPC codes with the same protograph dimensions.

Rostislav Gusev, Nikita Aleksandrov, Artem Solomkin et al.

Forward error correction is essential for reliable communication over noisy channels. Attention-based model-free neural decoders have shown strong performance for short codes, but their scalability to longer codes is limited by the quadratic memory and computational cost of attention. In this paper, we introduce the Mamba message-passing decoder (MMPD), an attention-free syndrome-based neural decoder for binary linear codes. MMPD retains the Tanner-graph structure of a message-passing decoder by performing local pairwise aggregation along variable-check edges. To enable efficient long-range information propagation, these local updates are combined with bidirectional Mamba state-space blocks. By avoiding dense attention matrices, MMPD scales more favorably for long codes in both memory and computation. Experiments on the (1056, 880) LDPC code show that MMPD achieves a 0.45 dB gain over the state-of-the-art CrossMPT decoder at a specified target bit error rate, while reducing memory consumption by a factor of 1.5. This reduction factor increases substantially for longer codes, demonstrating the applicability of MMPD to scalable neural decoding of practical long codes.

Irina Kopnina, Dmitry Artemasov, Sergey Matveev

Accurate channel state information (CSI) prediction is crucial for next-generation multiple-input multiple-output (MIMO) communication systems. Classical prediction methods often become inefficient for high-dimensional and rapidly time-varying channels. To improve prediction efficiency, it is essential to exploit the inherent low-rank tensor structure of the MIMO channel. Motivated by this observation, we propose a dynamic mode decomposition (DMD)-based prediction framework operating on the low-dimensional core tensors obtained via a Tucker decomposition. The proposed method predicts reduced-order channel cores, significantly lowering computational complexity. Simulation results demonstrate that the proposed approach preserves the dominant channel dynamics and achieves high prediction accuracy.