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arxiv: 2605.14272 · v1 · submitted 2026-05-14 · 💻 cs.IT · math.IT

Recognition: no theorem link

Joint Transmit and Receive Antenna Orientation Design for Secure MIMO Communications

Ailing Zheng , Qingqing Wu , Xingxiang Peng , Qiaoyan Peng , Ziyuan Zheng , Yuxuan Chen , Wen Chen
Authors on Pith no claims yet

Pith reviewed 2026-05-15 02:12 UTC · model grok-4.3

classification 💻 cs.IT math.IT
keywords rotatable antennaphysical layer securityMIMOsecrecy rate maximizationbeamformingartificial noisealternating optimization
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The pith

Dynamically optimizing rotatable antenna orientations in MIMO systems enhances secrecy rates by reshaping channels to favor legitimate users over eavesdroppers.

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

This paper explores using rotatable antennas at both ends of a MIMO link to improve physical layer security against an eavesdropper. The authors formulate an optimization problem to maximize the secrecy rate by jointly tuning transmit beamforming, artificial noise, and the angles of the rotatable antennas. They develop an alternating optimization method that solves the non-convex problem efficiently, first analyzing a simpler SISO case and then extending to MIMO using an MMSE reformulation and Riemannian optimization for the orientations. Simulations demonstrate fast convergence and notable secrecy rate improvements compared to fixed antenna orientations.

Core claim

By jointly optimizing the transmit beamforming, artificial noise covariance, and the orientations of rotatable antennas at transmitter and receiver, the effective MIMO channels can be reshaped to increase the secrecy rate, with the optimization handled via alternating updates derived from the minimum mean-square error framework and Riemannian Frank-Wolfe method.

What carries the argument

The alternating optimization algorithm that alternates between closed-form solutions for beamforming and AN covariance and Riemannian Frank-Wolfe updates for antenna orientations.

If this is right

  • Significant secrecy rate gains are achieved in simulations compared to fixed-orientation schemes.
  • The scheme converges rapidly.
  • It extends to multi-receiver secure transmission scenarios.
  • The approach works for both SISO and general MIMO cases.

Where Pith is reading between the lines

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

  • If hardware for rotatable antennas becomes common in 6G, this could reduce reliance on traditional encryption by enhancing physical layer security.
  • The method might be adapted for scenarios with imperfect channel knowledge by incorporating robust optimization.
  • Testing in real-world environments with mobility could reveal practical limitations not captured in simulations.

Load-bearing premise

The design assumes the transmitter has perfect knowledge of the channel matrices to both the legitimate receiver and the eavesdropper.

What would settle it

If simulations or real measurements show that the secrecy rate with optimized orientations is no higher than with fixed orientations when using the same power and noise settings, the claimed gains would be falsified.

Figures

Figures reproduced from arXiv: 2605.14272 by Ailing Zheng, Qiaoyan Peng, Qingqing Wu, Wen Chen, Xingxiang Peng, Yuxuan Chen, Ziyuan Zheng.

Figure 1
Figure 1. Figure 1: Illustration of the RA-aided secure MIMO communication [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: SISO secrecy-oriented RA rotation under the unconstrained [PITH_FULL_IMAGE:figures/full_fig_p006_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Convergence behavior of the proposed algorithm under single [PITH_FULL_IMAGE:figures/full_fig_p010_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: SR versus the number of transmit antennas. [PITH_FULL_IMAGE:figures/full_fig_p010_4.png] view at source ↗
Figure 6
Figure 6. Figure 6: depicts the SR versus the antenna directivity factor 0. 0 0. 5 1 . 0 1 . 5 2. 0 2. 5 3. 0 3. 5 4. 0 1 0 1 5 20 25 3 0 S R ( b p s / H z ) Directivity factor, Proposed algorithm, M = 9 Proposed algorithm, M = 4 Discrete-orientation baseline Proposed algorithm, Q = 9 FOA Isotropic-antenna baseline Different Leg antennas 1 2% 9% 3 5% 55% p [PITH_FULL_IMAGE:figures/full_fig_p011_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: SR versus the maximum transmit power. p under different schemes. It is observed that the SR of the directional-antenna-based schemes generally increases with p. Among all considered schemes, the proposed algorithm with M = 9 achieves the best performance, followed by the proposed algorithm with M = 4. In contrast, the pro￾posed algorithm with Q = 9 suffers from noticeable perfor￾mance degradation, since mo… view at source ↗
Figure 8
Figure 8. Figure 8: SR versus the number of receivers. In particular, in the low transmit-power region, increasing the number of data streams yields only limited performance improvement. By contrast, in the high transmit-power region, the performance gain brought by additional data streams becomes much more pronounced. This indicates that, under the same antenna configuration, increasing the number of data streams can effecti… view at source ↗
read the original abstract

Physical layer security (PLS) is a promising paradigm for safeguarding 6G wireless networks by exploiting the inherent characteristics of wireless channels. However, the efficiency of conventional PLS is often limited by fixed orientation antennas. This paper investigates a rotatable antenna (RA)-aided secure multiple-input multiple-output (MIMO) communication system, where both the transmitter and the receiver are equipped with RAs in the presence of an eavesdropper. By dynamically optimizing the orientations of RAs, we can proactively reshape the effective MIMO channels to enhance legitimate transmission while simultaneously suppressing information leakage to the eavesdropper. We formulate a secrecy rate maximization problem by jointly optimizing the transmit beamforming, artificial noise (AN) covariance matrix, and the transmit/receive RA orientations, subject to the transmit power budget and antenna orientation constraints. To tackle the resulting highly coupled and non-convex problem, we first study a simplified single-input single-output (SISO) case to reveal the structure of the optimal RA orientation. For the general MIMO case, we develop an alternating optimization algorithm by reformulating the original problem through the minimum mean-square error framework. In particular, the transmit beamforming and AN covariance matrix are derived in semi-closed forms, while the RA orientations are updated via the Riemannian Frank-Wolfe method. The proposed design is further extended to the multi-receiver secure transmission scenario. Simulation results show that the proposed scheme converges rapidly and achieves significant secrecy rate gains over the conventional fixed-orientation scheme.

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 / 1 minor

Summary. The paper investigates a rotatable antenna (RA)-aided secure MIMO system in which both the transmitter and legitimate receiver employ RAs in the presence of an eavesdropper. It formulates a secrecy-rate maximization problem that jointly optimizes transmit beamforming, artificial-noise covariance, and the RA orientations at both ends, subject to power and orientation constraints. A SISO case is analyzed to reveal the structure of the optimal orientation; the general MIMO case is solved via an alternating optimization that reformulates the objective through the MMSE framework, yielding semi-closed-form expressions for beamforming and AN covariance together with Riemannian Frank-Wolfe updates for the orientations. The algorithm is extended to the multi-receiver setting, and numerical results are presented to illustrate rapid convergence and secrecy-rate gains relative to fixed-orientation baselines.

Significance. If the reported gains hold, the work demonstrates that dynamic RA orientation supplies a useful additional degree of freedom for physical-layer security, allowing the effective MIMO channels to be reshaped so that legitimate singular values are strengthened while leakage is suppressed. The algorithmic approach (MMSE reformulation plus Riemannian optimization) is standard yet applied here in a novel RA context, and the explicit SISO structural result plus the multi-receiver extension are clear contributions. The significance is limited by the idealized channel-knowledge assumptions underlying the simulation claims.

major comments (1)
  1. [Numerical Results] The secrecy-rate objective and the alternating optimization (MMSE reformulation for beamforming/AN and Riemannian Frank-Wolfe for orientations) are evaluated under the assumption of perfect knowledge of all channel matrices, including the eavesdropper channels H_e and G_e. No robustness term, worst-case formulation, or Monte-Carlo evaluation over CSI estimation error appears in the problem statement or numerical section; because the reported dB gains rely on precise AN null-space alignment and orientation-driven channel reshaping, this assumption is load-bearing for the central simulation claim.
minor comments (1)
  1. [Abstract] The abstract states that beamforming and AN covariance are derived in 'semi-closed forms,' yet the precise expressions and the conditions under which they hold are not summarized; adding a short statement of the final closed-form expressions would improve readability.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive feedback and for recognizing the algorithmic contributions and the value of the SISO structural result. We address the single major comment below.

read point-by-point responses

  1. Referee: [Numerical Results] The secrecy-rate objective and the alternating optimization (MMSE reformulation for beamforming/AN and Riemannian Frank-Wolfe for orientations) are evaluated under the assumption of perfect knowledge of all channel matrices, including the eavesdropper channels H_e and G_e. No robustness term, worst-case formulation, or Monte-Carlo evaluation over CSI estimation error appears in the problem statement or numerical section; because the reported dB gains rely on precise AN null-space alignment and orientation-driven channel reshaping, this assumption is load-bearing for the central simulation claim.

    Authors: We agree that the presented results rely on perfect CSI of all links, including the eavesdropper channels. This is the standard modeling choice in the PLS literature when the goal is to characterize the fundamental gains obtainable from a new degree of freedom (here, RA orientation). The MMSE reformulation and Riemannian updates are derived under this assumption, and the numerical gains illustrate the potential improvement when perfect alignment is possible. In the revised manuscript we will (i) explicitly restate the perfect-CSI assumption in Section II and in the caption of the numerical results, (ii) add a short paragraph in the conclusions discussing the sensitivity of the scheme to CSI errors and noting that robust or worst-case extensions constitute a natural follow-up direction, and (iii) include a brief Monte-Carlo experiment under additive Gaussian CSI error to illustrate graceful degradation. These changes clarify the scope of the claims without requiring a complete reformulation of the optimization problem. revision: yes

Circularity Check

0 steps flagged

No circularity: derivation relies on external MMSE framework and standard alternating optimization

full rationale

The paper formulates a standard secrecy-rate maximization objective and solves it via an alternating algorithm that reformulates the problem through the minimum mean-square error (MMSE) framework, which is an established external technique. Beamforming and AN covariance are derived in semi-closed form, and RA orientations use the Riemannian Frank-Wolfe method; none of these steps reduce by construction to a fitted parameter, self-definition, or self-citation chain. The SISO case is used only to reveal structure, not to force the MIMO result. Simulations report empirical gains under perfect CSI, but the derivation itself remains self-contained against external benchmarks and does not rename or smuggle in prior results as new predictions.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The paper relies on standard MIMO channel models and the secrecy-rate expression as an objective; no new free parameters, ad-hoc axioms, or invented entities are introduced in the abstract. The optimization is performed under power and orientation constraints that are conventional.

axioms (1)
  • domain assumption Perfect channel state information of legitimate and eavesdropper links is available at the transmitter.
    Required to evaluate the secrecy-rate objective exactly; stated implicitly by the formulation of the optimization problem.

pith-pipeline@v0.9.0 · 5579 in / 1393 out tokens · 28074 ms · 2026-05-15T02:12:48.765137+00:00 · methodology

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