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

Mody Sy, Raymond Knopp

TL;DR

The paper tackles ultra-reliable, low-latency communication for short packets with unknown CSI by introducing block-wise joint estimation–detection (JED) receivers for BICM that operate over sliding symbol windows. It develops novel soft-likelihood metrics that couple LS-based channel estimation with block-wise detection (M ≈ 4) for SIMO and MIMO channels, applicable to Polar and LDPC coding with QPSK modulation. Numerical results show substantial gains over conventional symbol-by-symbol receivers, with gains up to around 3.5–3.75 dB in LOS and noticeable improvements in Rayleigh channels, bringing performance close to perfect CSI under realistic short-block conditions. The work also analyzes complexity and practical considerations such as DMRS density and power boosting, outlining limitations and future directions for higher-order modulations and scalable receiver design in 5G/6G URLLC scenarios.

Abstract

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.

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

TL;DR

The paper tackles ultra-reliable, low-latency communication for short packets with unknown CSI by introducing block-wise joint estimation–detection (JED) receivers for BICM that operate over sliding symbol windows. It develops novel soft-likelihood metrics that couple LS-based channel estimation with block-wise detection (M ≈ 4) for SIMO and MIMO channels, applicable to Polar and LDPC coding with QPSK modulation. Numerical results show substantial gains over conventional symbol-by-symbol receivers, with gains up to around 3.5–3.75 dB in LOS and noticeable improvements in Rayleigh channels, bringing performance close to perfect CSI under realistic short-block conditions. The work also analyzes complexity and practical considerations such as DMRS density and power boosting, outlining limitations and future directions for higher-order modulations and scalable receiver design in 5G/6G URLLC scenarios.

Abstract

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.
Paper Structure (20 sections, 8 theorems, 49 equations, 7 figures)

This paper contains 20 sections, 8 theorems, 49 equations, 7 figures.

Table of Contents

  1. Introduction
  2. General Framework
  3. Bit-Interleaved Polar-coded Modulation (BIPCM)
  4. Bit-Interleaved LDPC-coded Modulation (BILCM)
  5. Modulation and Resource Mapping
  6. Receiver Design
  7. SIMO Non-Coherent Fading Channel
  8. Perfect Channel State Information
  9. Unknown Channel State information
  10. Joint Estimation and Detection
  11. MIMO Rayleigh Block Fading Channel
  12. Numerical Results
  13. Performance Analysis
  14. SIMO Non Coherent Fading channel
  15. MIMO Rayleigh Block Fading Channel
  16. ...and 5 more sections

Key Result

Proposition 1

[A novel soft-likelihood metric for SIMO.] Neglecting multiplicative terms independent of the transmitted message, the likelihood function can be expressed as follows: where $\mathbf L_{\mathsf x} = \mathrm {N}_0+ 2(1-\alpha) \left\|\mathbf x \right\|^2$, $\mathbf \beta_x = \frac{2(1-\alpha)}{\mathrm {N}_0(\mathrm {N}_0 +2(1-\alpha) \left\|\mathbf x \right\|^2)}$ and $\operatorname{I_0}(\cdot)$ i

Figures (7)

  • Figure 1: Bit-Interleaved Polar/LDPC coded Modulation ( SIMO BIPCM/ SIMO BILCM) : Transmitter end.
  • Figure 2: Block Error Rate, 48 bits(TBs+CRC), NR POLAR BICM (CRC-aided successive-cancellation list decoder, List length=8), NR LDPC BICM (belief propagation decoder, iteration=30) QPSK modulation, 1 OFDM symbol, 4 PRBs, 48 REs (32 data, 4 DMRS), ($1\times4$) SIMO, vs outer (MC) and inner (RCUs) bounds, DMRS power Boosting via a scaling factor $\beta$.
  • Figure 3: LLR distribution characteristics via histograms at SNR = 0 dB.
  • Figure 4: Average Time Complexity of the proposed SIMO JED metrics vs Conventional metrics.
  • Figure 5: Block Error Rate, 48 bits(TBs+CRC), NR POLAR BICM (CRC-aided successive-cancellation list decoder, List length=8), NR LDPC BICM (belief propagation decoder, iteration=30) QPSK modulation, 1 OFDM symbol, 4 PRBs, 48 REs (32 data, 16 DMRS), ($4\times4$) MIMO.
  • ...and 2 more figures

Theorems & Definitions (10)

  • Proposition 1
  • Remark 1
  • Corollary 1
  • Proposition 2
  • Proposition 3
  • Remark 2
  • Lemma 1
  • Lemma 2
  • Theorem 1
  • Theorem 2