arXiv subjects

Mody Sy

Publications and source records attributed to Mody Sy.

5 recordsLinked to original sources

arXiv2025

Demystifying 5G Polar and LDPC Codes: A Comprehensive Review and Foundations

Understanding how 5G networks correct errors is no trivial matter. At the heart of the process lie two sophisticated families of codes: LDPC and polar codes. This paper opens the black box, not only by explaining how these codes are designed, but also by showing how they are encoded and decoded in practice. To map where research currently stands, we present a detailed survey of the literature supplemented with insights that are often buried deep within technical standards. These foundations are not just historical footnotes: they are strong candidates for powering error correction in 6G and beyond. In bringing clarity to these building blocks, we aim to help engineers and researchers navigate what is both a complex and increasingly vital part of wireless communication.

cs.IT↗

arXiv2024

Enhanced BICM Receivers for Ultra-Reliable Low-Latency Short Packet Communications

This paper presents enhanced receiver metrics for joint estimation-detection in short blocklength transmissions, addressing scenarios with unknown channel state information and low or sparse training resource density. We show that it is possible to enhance the performance and sensitivity through block-wise joint estimation-detection compared to standard receivers. The performance analysis makes use of a full 5G transmitter and receiver chains for both Polar and LDPC coded transmissions paired with QPSK modulation scheme. We consider transmissions where reference signals are interleaved with coded data and both are transmitted over a small number of OFDM symbols so that near-perfect channel estimation cannot be achieved. Unlike conventional symbol-by-symbol detection in BICM systems, where the observation for a given coded bit is confined to the symbol in which it is conveyed,the proposed method performs block-wise joint detection over a sliding window of adjacent symbols to fundamentally leverages their statistical dependencies. Accordingly, the LLR for a particular coded bit incorporates information from all symbols within the detection window, rather than being constrained to its host symbol alone. Performance evaluation spans SIMO and SU-MIMO configurations, emphasizing the efficacy of the estimation-detection strategy in realistic base station receiver scenarios. Our findings demonstrate that when the detection windows used in the metric units are on the order of four modulated symbols, the proposed receivers remarkably outperform the conventional ones and can be used to achieve detection performance that is close to that of coherent receivers with perfect CSI.

cs.IT↗

arXiv2024

Low-Complexity Block-Based Decoding Algorithms for Short Block Channels

This paper presents low-complexity block-based encoding and decoding algorithms for short block length channels. In terms of the precise use-case, we are primarily concerned with the baseline 3GPP Short block transmissions in which payloads are encoded by Reed-Muller codes and paired with orthogonal DMRS. In contemporary communication systems, the short block decoding often employs the utilization of DMRS-based least squares channel estimation, followed by maximum likelihood decoding. However, this methodology can incur substantial computational complexity when processing long bit length codes. We propose an innovative approach to tackle this challenge by introducing the principle of block/segment encoding using First-Order RM Codes which is amenable to low-cost decoding through block-based fast Hadamard transforms. The Block-based FHT has demonstrated to be cost-efficient with regards to decoding time, as it evolves from quadric to quasi-linear complexity with a manageable decline in performance. Additionally, by incorporating an adaptive DMRS/data power adjustment technique, we can bridge/reduce the performance gap and attain high sensitivity, leading to a good trade-off between performance and complexity to efficiently handle small payloads.

cs.IT↗

arXiv2024

Novel Joint Estimation and Decoding Metrics for Short-Block length Transmission Systems

This paper presents Bit-Interleaved Coded Modulation metrics for joint estimation detection using training or reference signal transmission strategies for short to long block length channels. We show that it is possible to enhance the performance and sensitivity through joint detection-estimation compared to standard receivers, especially when the channel state information is unknown and the density of the training dimensions is low. The performance analysis makes use of a full 5G transmitter and receiver chains for both Polar and LDPC coded transmissions paired with BPSK/QPSK modulation schemes. We consider transmissions where reference signals are interleaved with data and both are transmitted over a small number of OFDM symbols so that near-perfect channel estimation cannot be achieved. This is particularly adapted to mini-slot transmissions for ultra-reliable, low-latency communications (URLLC) or for short packet random access use cases. We characterize the performance for up to eight receiving antennas in order to determine the performance gain offered by the proposed BICM detection in realistic base station receiver scenarios. Our findings demonstrate that when the detection windows used in the metric units is on the order of four modulated symbols the proposed BICM metrics can be used to achieve detection performance that is close to that of a coherent receiver with perfect channel state information for both polar and LDPC coded configurations. Furthermore, we show that for transmissions with low DMRS density, a good trade-off can be achieved in terms of additional coding gain and improved channel estimation quality by adaptive DMRS power adjustment.

cs.IT↗

arXiv2024

Enhanced Low-Complexity Receiver Design for Short Block Transmission Systems

This paper presents a comprehensive analysis and performance enhancement of short block length channel detection incorporating training information. The current communication systems' short block length channel detection typically consists of least squares channel estimation followed by quasi-coherent detection. By investigating the receiver structure, specifically the estimator-correlator, we show that the non-coherent term, often disregarded in conventional detection metrics, results in significant losses in performance and sensitivity in typical operating regimes of 5G and 6G systems. A comparison with the fully non-coherent receiver in multi-antenna configurations reveals substantial losses in low spectral efficiency operating areas. Additionally, we demonstrate that by employing an adaptive DMRS-data power adjustment, it is possible to reduce the performance loss gap, which is amenable to a more sensitive quasi-coherent receiver. However, both of the aforementioned ML detection strategies can result in substantial computational complexity when processing long bit-length codes. We propose an approach to tackle this challenge by introducing the principle of block or segment coding using First-Order RM Codes, which is amenable to low-cost decoding through block-based fast Hadamard transforms. The Block-based FHT has demonstrated to be cost-efficient with regards to decoding time, as it evolves from quadric to quasi-linear complexity with a manageable decline in performance. Additionally, by incorporating an adaptive DMRS-data power adjustment technique, we are able to bridge/reduce the performance gap with respect to the conventional maximum likelihood receiver and attain high sensitivity, leading to a good trade-off between performance and complexity to efficiently handle small payloads.

cs.IT↗