arxiv: 2604.20676 · v1 · submitted 2026-04-22 · 📡 eess.SP

Recognition: unknown

Tri-Hybrid Beamforming Design for ISAC Systems with Reconfigurable Antennas

Jiangong Chen , Xia Lei , Yuchen Zhang , Kaitao Meng , Christos Masouros

Authors on Pith no claims yet

Pith reviewed 2026-05-09 23:25 UTC · model grok-4.3

classification 📡 eess.SP

keywords Integrated Sensing and CommunicationReconfigurable AntennasHybrid BeamformingBeamforming OptimizationSpectrum EfficiencySensing SCNRAlternating Optimization

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The pith

Reconfigurable antennas with triple-hybrid beamforming nearly double spectrum efficiency in ISAC systems.

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

The paper develops a decoupled triple-hybrid beamforming framework for integrated sensing and communication systems that use reconfigurable antennas. It alternately optimizes digital, analog, and electromagnetic beamformers to maximize the communication rate and sensing signal-to-clutter-plus-noise ratio in both single-user single-target and multi-user multi-target settings. Fractional objectives are converted to fraction-free forms and solved with closed-form or low-complexity iterative updates. The design delivers substantial gains over conventional omnidirectional and directional antennas.

Core claim

By incorporating reconfigurable antennas into ISAC systems, the proposed Tri-HBF architecture decouples and alternately optimizes the digital beamformer, analog beamformer, and EM beamformer to jointly maximize communication rate and sensing SCNR. For SUST scenarios closed-form solutions are derived for all variables; for MUMT scenarios a low-complexity per-antenna iterative method replaces semidefinite relaxation in the EM subproblem. Simulations show the scheme achieves nearly 100 percent higher spectrum efficiency and 62.5 percent lower antenna overhead than benchmarks using fixed omnidirectional or directional antennas.

What carries the argument

The Tri-HBF framework, which performs alternating optimization across digital, analog, and electromagnetic beamformers to maximize the joint rate-SCNR objective.

If this is right

Closed-form updates for most variables enable low-complexity implementation in single-user single-target cases.
The per-antenna iterative method for the EM subproblem in multi-user multi-target cases reduces computational cost compared with semidefinite relaxation.
The design maintains performance close to fully digital beamforming while using fewer antennas and simpler hardware.
Both communication rate and sensing SCNR improve simultaneously without separate hardware chains.

Where Pith is reading between the lines

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

Reconfigurable antennas could reduce the physical size and cost of ISAC arrays in compact devices such as vehicles or drones.
The framework may extend to time-varying channels if paired with tracking algorithms that update the EM configuration at each coherence interval.
Energy efficiency gains are likely when the reduced antenna count lowers RF chain power draw.
Real-world validation would require measuring actual reconfiguration latency against the assumed negligible overhead.

Load-bearing premise

Reconfigurable antennas can be dynamically controlled in real time with negligible additional overhead or performance loss, and alternating optimization reliably reaches high-quality solutions for the joint rate-SCNR objective.

What would settle it

A hardware prototype or simulation that accounts for realistic reconfiguration delays, power consumption, and channel estimation errors and shows the performance gains over conventional antennas disappear.

Figures

Figures reproduced from arXiv: 2604.20676 by Christos Masouros, Jiangong Chen, Kaitao Meng, Xia Lei, Yuchen Zhang.

**Figure 2.** Figure 2: Objective Value versus transmit power: (a) SUST; (b) [PITH_FULL_IMAGE:figures/full_fig_p010_2.png] view at source ↗

**Figure 4.** Figure 4: CPU time comparisons : (a) SUST; (b) 2-CUs 2-targets s [PITH_FULL_IMAGE:figures/full_fig_p010_4.png] view at source ↗

**Figure 5.** Figure 5: Trade-off relationship: (a) SUST; (b) 2-CUs 2-targe [PITH_FULL_IMAGE:figures/full_fig_p010_5.png] view at source ↗

**Figure 6.** Figure 6: Radiation pattern comparisons where NCU = 2, NTar = 2, and NRF = 4. (circle: CU, square: target, cross: scatterers). reduced computational cost. Compared with the above RAbased Tri-HBF schemes, the OA/CosA HBF schemes incur the shortest running time, since no EM beamforming optimization is required [PITH_FULL_IMAGE:figures/full_fig_p011_6.png] view at source ↗

**Figure 7.** Figure 7: Objective value versus NRF where NCU = 2 and NTar = 2. 4 9 16 25 36 Number of Antenna 0 10 20 30 40 50 60 70 80 Objective Value Reduce 30 Antennas Reduce 10 Antennas [PITH_FULL_IMAGE:figures/full_fig_p012_7.png] view at source ↗

**Figure 8.** Figure 8: Objective value versus NT where NRF = 4, NCU = 2 and NTar = 2. model and discrete pattern selection model, are introduced and optimized in both SUST and MUMT scenarios. Compared with the conventional hybrid and fully digital schemes with non-RA, the proposed schemes achieve superior performance in terms of objective value, communication and sensing tradeoff, beam pattern focusing, and hardware overhead re… view at source ↗

read the original abstract

Integrated Sensing and Communication (ISAC) systems require efficient beamforming architectures to jointly support communication and sensing functionalities. To reduce hardware overhead, Hybrid Beamforming (HBF) has been widely studied and shown to achieve performance close to fully digital beamforming under practical hardware constraints. As a promising evolution, Reconfigurable Antenna (RA) technologies have recently emerged to further enhance beamforming Degrees of Freedom (DoFs) by dynamically reconfiguring antenna Electromagnetic(EM) characteristics, yet their integration into ISAC systems remains largely unexplored. In this paper, we investigate an RA-assisted ISAC system and develop a decoupled Triple-Hybrid Beamforming (Tri-HBF) framework that alternatively optimizes digital, analog, and EM beamformers to maximize the communication rate and sensing Signal-to-Clutter-plus-NoiseRatio (SCNR). For both Single-user Single-target (SUST) and Multiple-user Multiple-target (MUMT) scenarios, we first transform the original fractional objectives into fraction-free ones via methods tailored to their respective structures. The resulting problems are then solved via alternating optimization over different variable blocks. Closed-form updates are derived for all variables except the EM beamforming subproblem in the MUMT scenario. To further reduce the complexity introduced by Semidefinite Relaxation (SDR) in EM beamforming, we propose a low-complexity iterative approach across antennas with closed-form updates. Simulation results demonstrate that the proposed scheme significantly outperforms benchmark designs with conventional omnidirectional and directional antennas, achievingalmost 100% improvement in spectrum efficiency and 62.5% reduction in antenna overhead, thereby unveiling the

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.

Desk Editor's Note private letter to a colleague

The Tri-HBF framework adds reconfigurable antennas to ISAC beamforming with clear sim gains, but the alternating optimization has no convergence analysis so the numbers are hard to trust.

read the letter

The main point is a new decoupled Tri-HBF scheme that treats reconfigurable antenna EM states as a third optimization block alongside digital and analog beamformers for joint rate and SCNR maximization in ISAC. They handle both single-user single-target and multi-user multi-target cases by rewriting the fractional objectives into more tractable forms and then running block coordinate descent, with closed forms for most updates and a low-complexity per-antenna iteration after SDR for the hardest EM subproblem. The simulations report nearly double spectrum efficiency and a 62.5 percent drop in required antennas versus fixed omnidirectional or directional baselines, which is a concrete engineering result if the numbers hold up. That extension of hybrid beamforming to include dynamic EM reconfiguration is the actual novelty here, and it fits squarely in the ISAC hardware literature without overclaiming broader impact. The soft spot is the lack of any convergence guarantee or initialization study for the non-convex joint problem. Different starting points can easily produce different local solutions when beamformers, quadratic SCNR terms, and discrete RA states are all coupled, so the reported gains could be sensitive to how the iterations are seeded. The abstract also gives no simulation parameters or channel models, which makes it difficult to judge how representative the results are. This is aimed at researchers working on practical ISAC transceiver design and reconfigurable antenna hardware. Readers already familiar with hybrid beamforming and alternating optimization will get the most out of it. I would send it to peer review because the core idea and the claimed performance delta are worth expert scrutiny on the algorithm details and simulation setup, even if revisions are needed to strengthen the analysis side.

Referee Report

2 major / 2 minor

Summary. The paper proposes a Tri-Hybrid Beamforming (Tri-HBF) design for reconfigurable antenna (RA)-assisted ISAC systems. It develops a decoupled alternating optimization framework over digital, analog, and electromagnetic (EM) beamformers to jointly maximize the communication rate and sensing SCNR. For SUST and MUMT scenarios, fractional objectives are transformed into fraction-free forms, solved via block coordinate descent with closed-form updates except for the MUMT EM subproblem (addressed via SDR followed by a low-complexity per-antenna iteration). Simulations claim nearly 100% spectral efficiency improvement and 62.5% antenna overhead reduction versus benchmarks using conventional omnidirectional and directional antennas.

Significance. If the performance claims hold under rigorous validation, the work offers a practical advance in ISAC beamforming by integrating RA to increase DoFs while cutting hardware costs, with the objective transformation and low-complexity EM iteration providing implementable tools. The decoupled structure and benchmark comparisons are clear strengths. However, the non-convex nature of the joint problem and lack of supporting analysis reduce the immediate impact on the field.

major comments (2)

[Optimization Framework (Sections III-IV)] The alternating optimization procedure for the non-convex joint rate-SCNR objective (involving products of beamformers and quadratic SCNR forms) lacks any convergence proof to a stationary point or analysis of sensitivity to initialization. This is load-bearing for the central performance claims, as different starting points can yield materially different local solutions in such problems.
[Simulation Results] The reported ~100% SE gain and 62.5% antenna overhead reduction rest on simulation results without disclosed details on Monte Carlo runs, initialization strategies, multi-start validation, or parameter settings. This undermines verification of whether the gains are robust rather than initialization-dependent.

minor comments (2)

[Abstract] The abstract ends abruptly mid-sentence ('thereby unveiling the').
[Throughout] Ensure all acronyms (e.g., SCNR, RA, HBF, DoFs) are defined on first use and used consistently.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments, which help improve the clarity and rigor of our work. We address each major comment below and indicate the revisions planned for the next manuscript version.

read point-by-point responses

Referee: [Optimization Framework (Sections III-IV)] The alternating optimization procedure for the non-convex joint rate-SCNR objective (involving products of beamformers and quadratic SCNR forms) lacks any convergence proof to a stationary point or analysis of sensitivity to initialization. This is load-bearing for the central performance claims, as different starting points can yield materially different local solutions in such problems.

Authors: We acknowledge that the joint optimization is non-convex and that the original manuscript does not provide a formal convergence proof to a stationary point. In the revised version, we will add an empirical convergence analysis in Section IV, including iteration plots demonstrating that the objective stabilizes within a modest number of iterations across SUST and MUMT cases. We will also include a sensitivity study reporting average and best-case performance over multiple random initializations (e.g., 10 starts per channel realization) to show that the reported gains remain consistent. While deriving a theoretical guarantee is beyond the current scope and left for future work, these additions will substantiate the reliability of the performance claims. revision: partial
Referee: [Simulation Results] The reported ~100% SE gain and 62.5% antenna overhead reduction rest on simulation results without disclosed details on Monte Carlo runs, initialization strategies, multi-start validation, or parameter settings. This undermines verification of whether the gains are robust rather than initialization-dependent.

Authors: We agree that the simulation details must be expanded for reproducibility and to confirm robustness. The revised manuscript will add a new subsection in the Simulation Results section specifying: 1000 independent Monte Carlo channel realizations, initialization methods (random phases for analog and EM beamformers, closed-form initialization for digital), multi-start validation using the best of 10 random starts per trial, and all relevant parameters (SNR values, antenna counts, RA states, clutter models). These additions will directly support the validity of the nearly 100% spectral efficiency improvement and 62.5% antenna overhead reduction relative to the benchmarks. revision: yes

Circularity Check

0 steps flagged

No significant circularity in derivation chain

full rationale

The paper transforms fractional rate and SCNR objectives into equivalent fraction-free forms using standard algebraic manipulations tailored to SUST and MUMT structures, then applies block coordinate descent with closed-form solutions for digital/analog variables and a low-complexity per-antenna iteration for the EM subproblem after SDR. These steps follow externally grounded optimization methods (fractional programming and alternating optimization) without reducing any prediction or result to a fitted parameter, self-definition, or load-bearing self-citation. Simulation-based performance claims against external benchmarks remain independent of the derivation inputs.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract-only review provides insufficient detail to enumerate specific free parameters, axioms, or invented entities; the method appears to rest on standard alternating optimization and SDR techniques common to the beamforming literature.

pith-pipeline@v0.9.0 · 5599 in / 1122 out tokens · 29368 ms · 2026-05-09T23:25:39.861898+00:00 · methodology

discussion (0)

Reference graph

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