arXiv subjects

Or Elimelech

Publications and source records attributed to Or Elimelech.

4 recordsLinked to original sources

arXiv2025

On PIR and SPIR Over Gaussian MAC

This paper revisits the problems of Private Information Retrieval (PIR) and Symmetric PIR (SPIR). In PIR, a user retrieves a desired message from $N$ replicated, non-communicating databases, each storing the same $M$ messages, while preserving the privacy of the requested message index. SPIR extends this notion further by additionally protecting the privacy of the databases, ensuring that the user learns no information beyond the requested message. In this paper, we assume a block-fading Additive White Gaussian Noise Multiple Access Channel (AWGN MAC) linking the user and the databases. Previous work by Shmuel et al. presented a joint channel-PIR scheme utilizing the Compute and Forward (C\&F) protocol, demonstrating the potential of a joint PIR-channel coding scheme over a separated one, yet still lagging behind the channel capacity and requiring significant computational complexity. We propose an improved scheme that offers reduced computational complexity while improving the achievable rate for finite parameters, as well as its scaling laws. Specifically, the achievable rate outperforms the C\&F-based approach and scales with the number of databases $N$ and the power $P$ similarly to the channel capacity \textit{without the privacy constraint}. Furthermore, the analysis demonstrates that the improved rate exhibits only a finite gap from this unconstrained channel capacity -- $1$ $bit/sec/Hz$ as $N$ increases. Finally, we provide two SPIR schemes. The first is a modification for our PIR scheme to attain SPIR with no rate loss, which is accomplished by introducing shared common randomness among databases. The second is a novel joint channel-SPIR scheme that utilizes the channel and lattice codes characteristics to nontrivially achieve SPIR without requiring common randomness, at the price of a loss in the achievable rate.

cs.IT↗

arXiv2025

PIR Over Wireless Channels: Achieving Privacy With Public Responses

In this paper, we address the problem of Private Information Retrieval (PIR) over a public Additive White Gaussian Noise (AWGN) channel. In such a setup, the server's responses are visible to other servers. Thus, a curious server can listen to the other responses, compromising the user's privacy. Indeed, previous works on PIR over a shared medium assumed the servers cannot instantaneously listen to other responses. To address this gap, we present a novel randomized lattice -- PIR coding scheme that jointly codes for privacy, channel noise, and curious servers which may listen to other responses. We demonstrate that a positive PIR rate is achievable even in cases where the channel to the curious server is stronger than the channel to the user.

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arXiv2024

Correction to "Private Information Retrieval Over Gaussian MAC"

In the above article \cite{shmuel2021private}, the authors introduced a PIR scheme for the Additive White Gaussian Noise (AWGN) Multiple Access Channel (MAC), both with and without fading. The authors utilized the additive nature of the channel and leveraged the linear properties and structure of lattice codes to retrieve the desired message without the servers acquiring any knowledge about the retrieved message's index. Theorems 3 and 4 in \cite{shmuel2021private} contain an error arising from the incorrect usage of the modulo operator. Moreover, the proofs assume a one-to-one mapping function, $ϕ(\cdot)$, between a message $W_j\in\mathbb{F}_p^L$ and the elements of $\cC$, mistakenly suggesting that the user possesses all the required information in advance. % \st{However, this is not the case.} \textcolor{black}{To deal with that, we defined $ϕ(\cdot)$ as a one-to-one mapping function between a vector of $l$ information bits and a lattice point $λ\in\cC$}. Herein, we present the corrected versions of these theorems.

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arXiv2022

Perfectly Covert Communication Assisted by an Intelligent Reflecting Surface

This work investigates perfectly covert communication assisted by a passive Intelligent Reflecting Surface (IRS). In contrast to most existing IRS-assisted covert communication studies, which allow a nonzero detection leakage and optimize an epsilon-covertness constraint, we study the stricter regime in which the received signal component at the warden is completely canceled. We first derive a necessary and sufficient condition for perfect covertness and characterize its feasibility under Rayleigh fading. For the case of two reflecting elements, we provide a closed-form characterization of all feasible IRS phase configurations. For a general number of reflecting elements, we prove that the perfect-covertness condition is eventually satisfied almost surely as the number of IRS elements grows. To construct such configurations, we distinguish between the full Bob-aware design problem and the perfect-covertness feasibility subproblem, and formulate the latter as a warden-signal nulling problem. We then propose a gradient-based IRS phase-design algorithm with per-iteration computational complexity $O(N)$ and prove that, with random initialization, it converges to a global minimizer with probability one over the initialization set. The numerical results show that Bob-aware initialization preserves the legitimate link while driving Willie leakage to the numerical floor, and further evaluate multi-antenna Willie and imperfect-CSI settings. Finally, to address practical limitations such as imperfect channel state information and finite detector resolution, we introduce operational perfect covertness and derive a robust transmit-power condition that guarantees indistinguishability at the warden under bounded CSI uncertainty.

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