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Achieving Low Latency at Low Outage: Multilevel Coding for mmWave Channels

Mine Gokce Dogan, Jaimin Shah, Martina Cardone, Christina Fragouli, Wei Mao, Hosein Nikopour, Rath Vannithamby

TL;DR

This work tackles URLLC in mmWave networks by addressing blockage-induced outages through proactive, space-time symmetric Multilevel Diversity Coding (MDC). By modeling the network as a $1$-$2$-$1$ topology with $H$ edge-disjoint paths and a Poisson blockage process lasting $L$ time slots, the authors derive the channel PMF and design a hierarchical coding scheme that allocates reliability across $HT$ descriptions transmitted over $H$ paths and $T$ time slots. They introduce an optimization over packet fractions $f_i$ to maximize a rate objective while enforcing graceful degradation via a regularization term, and propose a low-complexity variant (MC-RC) that uses a subset of codes to reduce complexity. Numerical results show that MC and MC-RC achieve favorable rate-outage-delay trade-offs, providing graceful degradation for prioritised data streams and outperforming single-code baselines like EC-RO, thereby enabling low-latency, reliable mmWave communications under time-correlated blockages.

Abstract

Millimeter-wave (mmWave) spectrum is expected to support data-intensive applications that require ultra-reliable low-latency communications (URLLC). However, mmWave links are highly sensitive to blockage, which may lead to disruptions in the communication. Traditional techniques that build resilience against such blockages (among which are interleaving and feedback mechanisms) incur delays that are too large to effectively support URLLC. This calls for novel techniques that ensure resilient URLLC. In this paper, we propose to deploy multilevel codes over space and over time. These codes offer several benefits, such as they allow to control what information is received and they provide different reliability guarantees for different information streams based on their priority. We also show that deploying these codes leads to attractive trade-offs between rate, delay, and outage probability. A practically-relevant aspect of the proposed technique is that it offers resilience while incurring a low operational complexity.

Achieving Low Latency at Low Outage: Multilevel Coding for mmWave Channels

TL;DR

This work tackles URLLC in mmWave networks by addressing blockage-induced outages through proactive, space-time symmetric Multilevel Diversity Coding (MDC). By modeling the network as a -- topology with edge-disjoint paths and a Poisson blockage process lasting time slots, the authors derive the channel PMF and design a hierarchical coding scheme that allocates reliability across descriptions transmitted over paths and time slots. They introduce an optimization over packet fractions to maximize a rate objective while enforcing graceful degradation via a regularization term, and propose a low-complexity variant (MC-RC) that uses a subset of codes to reduce complexity. Numerical results show that MC and MC-RC achieve favorable rate-outage-delay trade-offs, providing graceful degradation for prioritised data streams and outperforming single-code baselines like EC-RO, thereby enabling low-latency, reliable mmWave communications under time-correlated blockages.

Abstract

Millimeter-wave (mmWave) spectrum is expected to support data-intensive applications that require ultra-reliable low-latency communications (URLLC). However, mmWave links are highly sensitive to blockage, which may lead to disruptions in the communication. Traditional techniques that build resilience against such blockages (among which are interleaving and feedback mechanisms) incur delays that are too large to effectively support URLLC. This calls for novel techniques that ensure resilient URLLC. In this paper, we propose to deploy multilevel codes over space and over time. These codes offer several benefits, such as they allow to control what information is received and they provide different reliability guarantees for different information streams based on their priority. We also show that deploying these codes leads to attractive trade-offs between rate, delay, and outage probability. A practically-relevant aspect of the proposed technique is that it offers resilience while incurring a low operational complexity.
Paper Structure (12 sections, 2 theorems, 18 equations, 7 figures)

This paper contains 12 sections, 2 theorems, 18 equations, 7 figures.

Table of Contents

  1. Introduction
  2. System Model and Background
  3. Channel Analysis
  4. Proposed Coding Schemes
  5. Selection of the Packet Fractions
  6. Low-complexity Coding Scheme
  7. Performance Evaluation
  8. Conclusions
  9. Related Work
  10. Proof of Proposition \ref{['prop:pmf']}
  11. Proof of Proposition \ref{['prop:asymptotic']}
  12. Numerical Analysis of Channel

Key Result

Proposition 1

Consider a 1-2-1 network with $H$ edge-disjoint paths. Let $T$ denote the code duration and $L$ denote the blockage duration in time slots, such that $L \geq T$. Then, $P_{X_j}$, $j\in[1:H]$ is given by: $\bullet$ The probability $P_{X_j}(0) = P(X_j=0)$ is where $\varepsilon_j$ is defined in eq:eps_alpha. $\bullet$ For $0 < r \leq T$, the probability $P_{X_j}(r) = P(X_j=r)$ is

Figures (7)

  • Figure 1: Blockage model illustration over a single LoS link.
  • Figure 2: An example network with $N=3$ relays.
  • Figure 3: $3$-level symmetric multilevel code setting.
  • Figure 4: Symmetric multilevel code design for $H\!=\!2$ and $T\!=\!3$.
  • Figure 5: Performance of the coding schemes over the network in Fig. \ref{['fig:example_network1']} with $H=3$ edge-disjoint paths.
  • ...and 2 more figures

Theorems & Definitions (7)

  • Definition 1
  • Definition 2
  • Proposition 1
  • Remark 1
  • Proposition 2
  • Definition 3
  • Remark 2