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arxiv: 2604.19388 · v1 · submitted 2026-04-21 · 📡 eess.SP

Recognition: unknown

Blockage-Aware and Shadowing Aware RIS Assisted Joint Communication and Positioning for Urban Non Terrestrial Networks

Muhammad Khalil , Ke Wang , Jinho Choi
Authors on Pith no claims yet

Pith reviewed 2026-05-10 02:00 UTC · model grok-4.3

classification 📡 eess.SP
keywords Reconfigurable Intelligent SurfacesLEO SatelliteJoint Communication and PositioningBlockage AwarenessShadowing TrackingPosition Error BoundNon-Terrestrial NetworksUrban Environments
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The pith

A terrestrial RIS uses direct and reflected delays to jointly support reliable satellite communication and user positioning in cities with blockages.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper develops a blockage-aware RIS framework for urban LEO satellite downlinks that reinforces weak direct links and adds a reflected path to make positioning observable through time delays. It reduces positioning to two dimensions using the direct-path delay and the RIS excess delay, then folds the resulting position error bound together with received SNR into a single utility function. A three-mode policy switches the RIS among communication-focused, balanced, and positioning-focused operation according to whether the direct link is blocked, while a Kalman filter tracks spatially correlated shadowing across blocks to keep codeword selection stable. The approach matters because future non-terrestrial networks must deliver both data and location services without dense ground infrastructure, and the framework shows how RIS hardware can serve both goals at once with low online complexity.

Core claim

A terrestrial RIS both strengthens the blockage-sensitive satellite-user link and supplies an extra reflected path whose excess delay, together with the direct-path delay, supports a reduced two-dimensional position error bound. These quantities are combined into a unified utility that trades SNR against positioning accuracy. A blockage-aware three-mode policy adapts RIS operation to the direct-link condition, and a state-space model with scalar Kalman filter tracks shadowing to produce robust codebook-based phase selection. Numerical evaluation shows the resulting controllable SNR-PEB tradeoff, improved positioning accuracy at competitive SNR, stabilized codeword selection, and rising joint

What carries the argument

The blockage-aware three-mode policy that selects among communication-oriented, balanced, and positioning-oriented RIS configurations according to direct-link condition, combined with a scalar Kalman filter that tracks shadowing estimates for robust codeword selection.

If this is right

  • The framework yields a controllable tradeoff between received SNR and position error bound.
  • Positioning accuracy improves while SNR remains competitive with the direct link.
  • Codeword selection remains stable when shadowing is tracked by the Kalman filter.
  • Joint success probability rises with larger RIS size and finer phase resolution, though returns diminish at high complexity.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Similar delay-based joint designs could be tested in terrestrial base-station scenarios where direct paths are also obstructed.
  • The low-complexity Kalman tracking step suggests that existing RIS codebooks could be augmented with lightweight state estimation without redesigning the entire control loop.
  • Optimal RIS size and phase resolution may be chosen once per deployment region rather than adapted continuously if shadowing statistics are stationary.

Load-bearing premise

That user position can be recovered accurately from only the direct-path delay and the RIS-assisted excess delay inside a simple two-dimensional model even when urban multipath and blockages are present.

What would settle it

Field measurements in a real urban setting where the observed position error exceeds the predicted bound once additional multipath components beyond the modeled direct and RIS paths become significant.

Figures

Figures reproduced from arXiv: 2604.19388 by Jinho Choi, Ke Wang, Muhammad Khalil.

Figure 1
Figure 1. Figure 1: System model of the considered RIS-assisted LEO NTN. A weak direct satellite–user path coexists with an RIS-assisted [PITH_FULL_IMAGE:figures/full_fig_p005_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Spatial variation of the average PEB versus the user x-position for different RIS selection strategies. The inset enlarges [PITH_FULL_IMAGE:figures/full_fig_p025_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Communication–positioning tradeoff in terms of average SNR and average PEB as the weighting parameter [PITH_FULL_IMAGE:figures/full_fig_p026_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Switching stability of the proposed RIS controller versus the shadowing-estimation noise. The robust and non-robust [PITH_FULL_IMAGE:figures/full_fig_p027_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Selection probability of the three RIS codeword families versus the direct-link blockage factor [PITH_FULL_IMAGE:figures/full_fig_p028_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: 3D decision map of the proposed RIS operating mode as a function of the user x-position and the direct-link blockage [PITH_FULL_IMAGE:figures/full_fig_p028_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: 3D surface of the joint success probability [PITH_FULL_IMAGE:figures/full_fig_p029_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Spatial validation of the proposed RIS-assisted framework. (a) Spatial variation of the received SNR over the considered [PITH_FULL_IMAGE:figures/full_fig_p030_8.png] view at source ↗
read the original abstract

Reconfigurable intelligent surfaces (RISs) have recently attracted interest for non-terrestrial networks (NTNs), especially for improving satellite communication performance. However, RIS-assisted urban NTN designs that jointly support reliable communication and user positioning under blockage, while maintaining low online complexity, remain limited. This paper proposes a blockage-aware and shadowing-aware RIS-assisted framework for joint communication and positioning in an urban low-Earth-orbit (LEO) satellite downlink. A terrestrial RIS is used both to reinforce the blockage-sensitive satellite--user link and to create an additional reflected path that enhances delay-domain positioning observability. We develop a reduced two-dimensional positioning model based on the direct-path delay and the RIS-assisted excess delay, and combine the resulting position error bound (PEB) with the received signal-to-noise ratio (SNR) into a unified utility. A blockage-aware three-mode policy then adapts RIS operation among communication-oriented, balanced, and positioning-oriented modes according to the direct-link condition. To improve robustness, spatially correlated RIS--user shadowing is tracked across coherence blocks using a state-space model and a scalar Kalman filter, and the filtered estimate is used in a robust codebook-based RIS selection strategy with low online complexity. Numerical results show that the proposed framework provides a controllable SNR--PEB tradeoff, improves positioning accuracy while maintaining competitive SNR, stabilizes codeword selection under shadowing uncertainty, and increases joint success probability with RIS size and phase resolution, with diminishing returns at high hardware complexity.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The paper proposes a blockage-aware and shadowing-aware RIS-assisted framework for joint communication and positioning in urban LEO satellite downlink. It develops a reduced two-dimensional positioning model based on direct-path delay and RIS-assisted excess delay to compute the position error bound (PEB), combines PEB with received SNR into a unified utility function, employs a blockage-aware three-mode policy to adapt RIS operation among communication-oriented, balanced, and positioning-oriented modes, tracks spatially correlated RIS-user shadowing via a state-space model and scalar Kalman filter, and applies a robust codebook-based RIS selection strategy. Numerical results are claimed to demonstrate a controllable SNR-PEB tradeoff, improved positioning accuracy with competitive SNR, stabilized codeword selection under shadowing uncertainty, and increased joint success probability that grows with RIS size and phase resolution but shows diminishing returns at high hardware complexity.

Significance. If the modeling assumptions hold, the work provides a low-online-complexity adaptive framework that integrates communication reliability and positioning in blockage-prone urban NTNs by leveraging RIS for both link reinforcement and delay-domain observability, with explicit handling of shadowing via Kalman filtering and mode switching. Strengths include the policy's adaptation to observable link conditions and the codebook approach that avoids high-complexity optimization per coherence block.

major comments (1)
  1. [§III] §III: The reduced two-dimensional positioning model, which derives user position and PEB solely from the direct-path delay and the RIS-assisted excess delay, is load-bearing for the utility function, the three-mode policy, and all numerical claims of SNR-PEB controllability and joint success probability. In urban environments, additional specular and diffuse multipath from building façades and ground reflections can bias the delay estimates away from the assumed two-path geometry, rendering the reported PEB optimistic and the claimed performance gains unverified under realistic propagation conditions.
minor comments (2)
  1. [Abstract] The abstract and numerical-results section should explicitly define the complexity metric (e.g., number of RIS elements, phase bits, or online flops) when stating 'diminishing returns at high hardware complexity'.
  2. Ensure consistent notation for the utility function and mode-switching thresholds across sections; the free parameters listed in the model (mode thresholds, Kalman parameters) should be tabulated with their chosen values for reproducibility.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive and insightful review of our manuscript. We address the major comment regarding the positioning model below, providing a point-by-point response while maintaining the integrity of our contributions.

read point-by-point responses

  1. Referee: [§III] §III: The reduced two-dimensional positioning model, which derives user position and PEB solely from the direct-path delay and the RIS-assisted excess delay, is load-bearing for the utility function, the three-mode policy, and all numerical claims of SNR-PEB controllability and joint success probability. In urban environments, additional specular and diffuse multipath from building façades and ground reflections can bias the delay estimates away from the assumed two-path geometry, rendering the reported PEB optimistic and the claimed performance gains unverified under realistic propagation conditions.

    Authors: We acknowledge that the reduced two-dimensional model relies on a two-path geometry (direct path plus RIS-assisted excess delay) and that additional multipath components in urban settings can introduce bias in delay estimates, potentially making the PEB optimistic. This modeling choice was made to obtain a tractable closed-form PEB expression that enables the unified utility function, the blockage-aware three-mode policy, and low-complexity codebook selection. The framework prioritizes the controllable direct and RIS-reflected paths, which are the dominant contributors under the blockage conditions targeted by the policy. We will revise the manuscript by adding a dedicated paragraph in Section III that explicitly discusses the two-path assumption, notes the potential for optimistic PEB under unmodeled multipath, and states that the reported numerical results hold under this idealized propagation model. We will also add a forward-looking remark on extending the positioning estimator to incorporate multipath mitigation techniques. This constitutes a partial revision that clarifies assumptions without altering the core framework or requiring new simulations. revision: partial

Circularity Check

0 steps flagged

No significant circularity; derivation remains self-contained

full rationale

The paper introduces a reduced two-dimensional positioning model from the direct-path delay and RIS-assisted excess delay, derives the PEB from that geometry, and forms a utility by combining the resulting PEB with the independently observed SNR. The three-mode policy is conditioned on observable direct-link status, and shadowing is tracked via a standard scalar Kalman filter on a state-space model. None of these steps reduce to a fitted parameter renamed as prediction, a self-definitional loop, or a load-bearing self-citation; the numerical evaluations are presented as forward simulations under the stated model rather than tautological outputs.

Axiom & Free-Parameter Ledger

2 free parameters · 1 axioms · 0 invented entities

Based solely on abstract; detailed parameters and assumptions not specified. The framework relies on standard wireless modeling assumptions plus introduced policy and filtering elements.

free parameters (2)
  • mode switching thresholds
    Threshold values on direct-link condition used to select among communication-oriented, balanced, and positioning-oriented modes.
  • Kalman filter parameters
    State transition matrix and process/measurement noise covariances for tracking spatially correlated shadowing.
axioms (1)
  • domain assumption Reduced two-dimensional positioning model using direct-path delay and RIS-assisted excess delay is sufficient for urban scenarios
    Invoked to develop the positioning model and combine with SNR into unified utility.

pith-pipeline@v0.9.0 · 5564 in / 1454 out tokens · 51492 ms · 2026-05-10T02:00:04.213822+00:00 · methodology

discussion (0)

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Reference graph

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