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The convergence of expectation-maximization (EM)-based algorithms typically requires continuity of the likelihood function with respect to all the unknown parameters (optimization variables). The requirement is not met when parameters…

Signal Processing · Electrical Eng. & Systems 2024-04-18 Geethu Joseph

We consider the problem of channel estimation and joint active and passive beamforming for reconfigurable intelligent surface (RIS) assisted millimeter wave (mmWave) multiple-input multiple-output (MIMO) orthogonal frequency division…

Signal Processing · Electrical Eng. & Systems 2022-10-05 Xi Zheng , Jun Fang , Hongwei Wang , Peilan Wang , Hongbin Li

In this paper, we propose a unified approach to harness quantum conformal methods for multi-output distributions, with a particular emphasis on two experimental paradigms: (i) a standard 2-qubit circuit scenario producing a four-dimensional…

Quantum Physics · Physics 2025-01-22 Emre Tasar

We study distributed similarity estimation of quantum channels (DSEC), a primitive for cross-platform verification where two remote quantum devices are compared by estimating the inner product of their Choi states. We show that the optimal…

Quantum Physics · Physics 2026-01-19 Congcong Zheng , Kun Wang , Xutao Yu , Ping Xu , Zaichen Zhang

In quantum communication via noisy channels, the error probability scales exponentially with the length of the channel. We present a scheme of a quantum repeater that overcomes this limitation. The central idea is to connect a string of…

Quantum Physics · Physics 2007-05-23 H. -J. Briegel , W. Dür , J. I. Cirac , P. Zoller

The performance of the information reconciliation phase is crucial for quantum key distribution (QKD). Reverse reconciliation (RR) is typically preferred over direct reconciliation (DR) because it yields higher secure key rates. However, a…

Information Theory · Computer Science 2025-02-13 Marco Origlia , Marco Secondini

This letter proposes a novel hybrid key distribution architecture that jointly exploits quantum key distribution (QKD) and Kirchhoff-law-Johnson-noise (KLJN) statistical-physical key exchange. In the proposed system, an optical BB84-type…

Quantum Physics · Physics 2026-05-18 Ertugrul Basar

The Quantum Key Distribution protocol can encode a single quantum state and implements an information-theoretically secure key distribution protocol in communication. In the actual QKD experimental system, there are usually two encoding…

Quantum Physics · Physics 2020-08-26 Gao Feifei , Li Zhihui , Liu Chengji , Han Duo

We study the joint channel estimation and data detection (JED) problem in a cell-free massive multiple-input multiple-output (CF-mMIMO) network, where access points (APs) communicate with a central processing unit (CPU) over fronthaul…

Signal Processing · Electrical Eng. & Systems 2025-06-24 Sajjad Nassirpour , Toan-Van Nguyen , Hien Q. Ngo , Le-Nam Tran , Tharmalingam Ratnarajah , Duy H. N. Nguyen

In massive multiple-input multiple-output (MIMO) systems, hybrid analog-digital beamforming is an essential technique for exploiting the potential array gain without using a dedicated radio frequency chain for each antenna. However, due to…

Information Theory · Computer Science 2022-06-09 Kai Kang , Qiyu Hu , Yunlong Cai , Guanding Yu , Jakob Hoydis , Yonina C. Eldar

In this work, we propose variations of a Gaussian mixture model (GMM) based channel estimator that was recently proven to be asymptotically optimal in the minimum mean square error (MMSE) sense. We account for the need of low computational…

Information Theory · Computer Science 2023-06-06 Benedikt Fesl , Michael Joham , Sha Hu , Michael Koller , Nurettin Turan , Wolfgang Utschick

In this paper, we consider the parameter estimation problem over sensor networks in the presence of quantized data and directed communication links. We propose a two-stage algorithm aiming at achieving the centralized sample mean estimate…

Systems and Control · Computer Science 2015-07-27 Shanying Zhu , Yeng Chai Soh , Lihua Xie

Quantitative magnetic resonance imaging (qMRI) derives tissue-specific parameters -- such as the apparent transverse relaxation rate R2*, the longitudinal relaxation rate R1 and the magnetisation transfer saturation -- that can be compared…

Image and Video Processing · Electrical Eng. & Systems 2021-05-10 Yaël Balbastre , Mikael Brudfors , Michela Azzarito , Christian Lambert , Martina F. Callaghan , John Ashburner

We present a quantum code-division multiple-access (q-CDMA) framework for multiuser continuous-variable quantum key distribution (CV-QKD) over a shared quantum channel. The proposed architecture employs chaotic phase shifters to encode and…

Quantum Physics · Physics 2026-03-16 Shahnoor Ali , Neel Kanth Kundu , Sourav Chatterjee

We propose to use neural networks to estimate the rates of coherent and incoherent processes in quantum systems from continuous measurement records. In particular, we adapt an image recognition algorithm to recognize the patterns in…

Quantum Physics · Physics 2017-11-15 Eliska Greplova , Christian Kraglund Andersen , Klaus Mølmer

Quantum error correction (QEC) is an essential concept for any quantum information processing device. Typically, QEC is designed with minimal assumptions about the noise process; this generic assumption exacts a high cost in efficiency and…

Quantum Physics · Physics 2007-06-26 Andrew S. Fletcher

We experimentally demonstrate adaptive reconciliation for continuous-variable quantum key distribution over a turbulent free-space optical channel. Additionally, we propose a method for optimising the reconciliation efficiency, increasing…

Continuous phase modulation (CPM) has extensive applications in wireless communications due to its high spectral and power efficiency. However, its nonlinear characteristics pose significant challenges for detection in frequency selective…

Information Theory · Computer Science 2024-08-15 Zilong Liu , Yi Song , Qinghua Guo , Peng Sun , Kexian Gong , Zhongyong Wang

Joint-channel carrier-phase estimation can improve the performance of multichannel optical communication systems. In the case of pilot-aided estimation, the pilots are distributed over a two-dimensional channel--time symbol block that is…

Signal Processing · Electrical Eng. & Systems 2024-01-25 Arni F. Alfredsson , Erik Agrell , Magnus Karlsson , Henk Wymeersch

This paper proposes maximum (quasi)likelihood estimation for high dimensional factor models with regime switching in the loadings. The model parameters are estimated jointly by the EM (expectation maximization) algorithm, which in the…

Econometrics · Economics 2023-04-11 Giovanni Urga , Fa Wang