Time-Switching Quantum Relay-Assisted Free-Space Optical Communication

This paper develops a comprehensive analytical framework for a time-switching decode-and-forward quantum relay-assisted free-space optical communication system. In the proposed architecture, a batteryless relay harvests optical energy during a dedicated fraction of each transmission block and forwards quantum coherent states during the remaining time, enabling self-sustainable quantum relaying. Both hops are subject to Gamma-Gamma distributed atmospheric turbulence and additive Gaussian detection noise, while the relay and destination implement Helstrom-optimal quantum measurements that achieve the minimum symbol detection error. The framework unifies the effects of energy harvesting, turbulence-induced fading, and quantum-limited detection within a single performance model. Closed-form analytical expressions are derived for binary phase-shift keying modulation using the Helstrom bound, enabling tractable evaluation of the end-to-end error probability and the effective rate. The analysis establishes that the effective rate exhibits a strictly unimodal dependence on the harvesting fraction, yielding a unique optimal operating point that maximizes throughput under energy and noise constraints. Numerical results validate the theoretical findings and quantify the impact of turbulence severity, detection noise, and harvesting efficiency, demonstrating substantial performance gains over conventional non-harvesting quantum relays and providing new insights for energy-autonomous quantum optical networks.This paper develops a comprehensive analytical framework for a time-switching decode-and-forward quantum relay-assisted free-space optical communication system. In the proposed architecture, a batteryless relay harvests optical energy during a dedicated fraction of each transmission block and forwards quantum coherent states during the remaining time, enabling self-sustainable quantum relaying. Both hops are subject to Gamma-Gamma distributed atmospheric turbulence and additive Gaussian detection noise, while the relay and destination implement Helstrom-optimal quantum measurements that achieve the minimum symbol detection error. The framework unifies the effects of energy harvesting, turbulence-induced fading, and quantum-limited detection within a single performance model. Closed-form analytical expressions are derived for binary phase-shift keying modulation using the Helstrom bound, enabling tractable evaluation of the end-to-end error probability and the effective rate. The analysis establishes that the effective rate exhibits a strictly unimodal dependence on the harvesting fraction, yielding a unique optimal operating point that maximizes throughput under energy and noise constraints. Numerical results validate the theoretical findings and quantify the impact of turbulence severity, detection noise, and harvesting efficiency, demonstrating substantial performance gains over conventional non-harvesting quantum relays and providing new insights for energy-autonomous quantum optical networks.

International Conference on Quantum Communications, Networking, and Computing (QCNC)Apr 6, 20260 citations

Time-Switching Energy-Harvesting Quantum Relay-Assisted FSO Communication with Displaced Squeezed Signaling

Nizar Khalfet, Francisco A. Monteiro, Ioannis Krikidis

This paper investigates a quantum relay-assisted free-space optical (FSO) communication system in which a decode-and-forward relay is powered by time-switching optical energy harvesting and forwards the decoded information using displaced squeezed signaling (DSS). To obtain a physically con sistent description of turbulence-induced loss for non-classical signaling, each hop is modeled as a pure-loss bosonic chan nel whose random transmissivity follows a truncated Gamma Gamma law, i.e., the Gamma-Gamma irradiance conditioned on the physically admissible range of a transmittance. Under this channel, coherent states remain pure, whereas squeezed states are mapped to mixed Gaussian states. Under Helstrom-optimal detection, the average error of the coherent hop is derived in exact Laplace-series form. For the DSS hop, we derive the output states, a closed-form Gaussian fidelity with rigorous two sided bounds on the Helstrom error, and prove the existence of a loss-aware optimal photon partition. Furthermore, we prove that optimized squeezing preserves both the turbulence-induced diversity order and the leading asymptotic constant of coherent relaying, so that its benefit is a finite-photon-budget effect, and that an interior throughput-optimal harvesting fraction exists. A covariance-preserving benchmark with an exact series representation yields an analytical upper bound on the achievable throughput whose absolute gap vanishes as the relay photon budget grows. Numerical results based on the exact mixed-state Helstrom error quantify the benefit of squeezing and the regime in which it is useful.This paper investigates a quantum relay-assisted free-space optical (FSO) communication system in which a decode-and-forward relay is powered by time-switching optical energy harvesting and forwards the decoded information using displaced squeezed signaling (DSS). To obtain a physically con sistent description of turbulence-induced loss for non-classical signaling, each hop is modeled as a pure-loss bosonic chan nel whose random transmissivity follows a truncated Gamma Gamma law, i.e., the Gamma-Gamma irradiance conditioned on the physically admissible range of a transmittance. Under this channel, coherent states remain pure, whereas squeezed states are mapped to mixed Gaussian states. Under Helstrom-optimal detection, the average error of the coherent hop is derived in exact Laplace-series form. For the DSS hop, we derive the output states, a closed-form Gaussian fidelity with rigorous two sided bounds on the Helstrom error, and prove the existence of a loss-aware optimal photon partition. Furthermore, we prove that optimized squeezing preserves both the turbulence-induced diversity order and the leading asymptotic constant of coherent relaying, so that its benefit is a finite-photon-budget effect, and that an interior throughput-optimal harvesting fraction exists. A covariance-preserving benchmark with an exact series representation yields an analytical upper bound on the achievable throughput whose absolute gap vanishes as the relay photon budget grows. Numerical results based on the exact mixed-state Helstrom error quantify the benefit of squeezing and the regime in which it is useful.

quant-pharXiv:2610.39091Oct 30, 20260 citations

Performance Analysis of Coherent-State Quantum Optical Wireless Communication Over Turbulent Channels With Pointing Errors

Jyothisri Kodela, Hemanta Kumar Sahu

This paper investigates the performance of coherent-state quantum optical wireless communication systems operating over atmospheric turbulence channels with pointing errors (PEs). The average error probability (AEP) and average achievable rate (AAR) are analyzed for on–off keying (OOK) and binary phase-shift keying (BPSK) signaling under photon-counting (PC), homodyne, and optimal Helstrom detection. The proposed framework jointly incorporates deterministic path loss, atmospheric turbulence, and PEs, and accommodates multiple statistical channel models, including Gamma-Gamma (GG), doubly inverted Gamma-Gamma (IGGG), and Fisher-Snedecor $F$ distributions, within a unified analytical formulation. Closed-form expressions for AEP and AAR are derived via direct probability density function (PDF)-based integration of the conditional error probability, along with high-photon-number asymptotic approximations that provide insight into performance scaling behavior. Numerical results validate the analytical expressions and demonstrate the impact of PEs on system performance. The analysis further enables systematic comparison between classical and optimal quantum detection schemes and quantifies the achievable performance gains under different channel conditions. These results provide useful design insights for modulation and receiver selection in turbulent free-space optical (FSO) communication systems.This paper investigates the performance of coherent-state quantum optical wireless communication systems operating over atmospheric turbulence channels with pointing errors (PEs). The average error probability (AEP) and average achievable rate (AAR) are analyzed for on–off keying (OOK) and binary phase-shift keying (BPSK) signaling under photon-counting (PC), homodyne, and optimal Helstrom detection. The proposed framework jointly incorporates deterministic path loss, atmospheric turbulence, and PEs, and accommodates multiple statistical channel models, including Gamma-Gamma (GG), doubly inverted Gamma-Gamma (IGGG), and Fisher-Snedecor $F$ distributions, within a unified analytical formulation. Closed-form expressions for AEP and AAR are derived via direct probability density function (PDF)-based integration of the conditional error probability, along with high-photon-number asymptotic approximations that provide insight into performance scaling behavior. Numerical results validate the analytical expressions and demonstrate the impact of PEs on system performance. The analysis further enables systematic comparison between classical and optimal quantum detection schemes and quantifies the achievable performance gains under different channel conditions. These results provide useful design insights for modulation and receiver selection in turbulent free-space optical (FSO) communication systems.

IEEE Open Journal of the Communications SocietyJan 1, 20260 citations

Quantum Relay-Assisted Free-Space Optical Communication

Manav R. Bhatnagar, M. K. Arti, Kushagra Bhatnagar

Relay-based quantum communication utilizes intermediate nodes to extend the transmission distance of quantum signals and mitigate the masking effect caused by obstacles or turbulence in free-space optical (FSO) channels. In this study, we investigate a three-node quantum communication system, where Alice, the transmitter, sends quantum-encoded binary information to Bob, the ultimate receiver, via an intermediate relay node, Charlie. By introducing Charlie, the end-to-end transmission is divided into two shorter FSO links, improving signal stability and reliability in the presence of severe atmospheric turbulence and noise. This work proposes a quantum relaying method specifically designed for FSO links and examines the impact of two-hop relaying in terms of the probability of error. The Helstrom error bound is derived to assess the system's detection limits, while density operator calculations are performed to characterize the quantum relaying setup. In addition, a closed-form expression is obtained for key system performance metrics. The findings offer valuable insights into optimizing quantum relaying strategies for long-distance quantum communication over FSO channels.Relay-based quantum communication utilizes intermediate nodes to extend the transmission distance of quantum signals and mitigate the masking effect caused by obstacles or turbulence in free-space optical (FSO) channels. In this study, we investigate a three-node quantum communication system, where Alice, the transmitter, sends quantum-encoded binary information to Bob, the ultimate receiver, via an intermediate relay node, Charlie. By introducing Charlie, the end-to-end transmission is divided into two shorter FSO links, improving signal stability and reliability in the presence of severe atmospheric turbulence and noise. This work proposes a quantum relaying method specifically designed for FSO links and examines the impact of two-hop relaying in terms of the probability of error. The Helstrom error bound is derived to assess the system's detection limits, while density operator calculations are performed to characterize the quantum relaying setup. In addition, a closed-form expression is obtained for key system performance metrics. The findings offer valuable insights into optimizing quantum relaying strategies for long-distance quantum communication over FSO channels.

IEEE photonics journalApr 22, 20258 citations

Tesla Meets Helstrom: A Wireless-Powered Quantum Optical System

Ioannis Krikidis

This letter investigates a novel wireless-powered quantum optical communication system, in which a batteryless quantum transmitter harvests energy from a classical radio-frequency source to transmit quantum coherent states. The transmission employs M-ary phase shift keying (M-PSK) modulation over an optical channel impaired by thermal noise, and the fundamental detection performance is evaluated using the Helstrom bound. An optimization framework is proposed that jointly determines the optimal quantum measurement and the energy-harvesting time fraction to maximize the effective rate under a block time constraint. Analytical expressions are derived for special cases, while semidefinite programming techniques are employed for the general M-PSK scenario. Numerical results validate the unimodal nature of the effective rate function and demonstrate the impact of the optimal design parameters.This letter investigates a novel wireless-powered quantum optical communication system, in which a batteryless quantum transmitter harvests energy from a classical radio-frequency source to transmit quantum coherent states. The transmission employs M-ary phase shift keying (M-PSK) modulation over an optical channel impaired by thermal noise, and the fundamental detection performance is evaluated using the Helstrom bound. An optimization framework is proposed that jointly determines the optimal quantum measurement and the energy-harvesting time fraction to maximize the effective rate under a block time constraint. Analytical expressions are derived for special cases, while semidefinite programming techniques are employed for the general M-PSK scenario. Numerical results validate the unimodal nature of the effective rate function and demonstrate the impact of the optimal design parameters.

arXiv:2509.07421IEEE Wireless Communications LettersSep 11, 20254 citations

Quantum Communication in Weakly Turbulent Channels: Error Analysis and Capacity Bounds

Shri Ramtej Kondamuri, Neel Kanth Kundu, Amit Ghanshyala

In this letter, we analyze the average probability of error of quantum modulation schemes in weakly turbulent quantum communication channels utilizing coherent states. Atmospheric turbulence-induced fading is a significant challenge that degrades the performance of free-space quantum communication systems. We derive and present closed-form expressions for the average probability of error for various detection methods: classical (shot-noise limited) single-photon detection, coherent detection, and the optimal quantum hypothesis-testing (Helstrom) detection for binary quantum modulation schemes. Our analysis focuses on the transmission of classical data modulated by quantum coherent states over a log-normal turbulent channel. Additionally, we discuss the lower bounds of the average capacities for Helstrom detection, providing comprehensive insights into the achievable information rates in realistic atmospheric conditions. The derived expressions show excellent agreement with numerical Monte Carlo simulations across a broad range of average transmitted photon numbers, offering valuable guidelines for the design and optimization of quantum communication systems.In this letter, we analyze the average probability of error of quantum modulation schemes in weakly turbulent quantum communication channels utilizing coherent states. Atmospheric turbulence-induced fading is a significant challenge that degrades the performance of free-space quantum communication systems. We derive and present closed-form expressions for the average probability of error for various detection methods: classical (shot-noise limited) single-photon detection, coherent detection, and the optimal quantum hypothesis-testing (Helstrom) detection for binary quantum modulation schemes. Our analysis focuses on the transmission of classical data modulated by quantum coherent states over a log-normal turbulent channel. Additionally, we discuss the lower bounds of the average capacities for Helstrom detection, providing comprehensive insights into the achievable information rates in realistic atmospheric conditions. The derived expressions show excellent agreement with numerical Monte Carlo simulations across a broad range of average transmitted photon numbers, offering valuable guidelines for the design and optimization of quantum communication systems.

IEEE Wireless Communications LettersOct 23, 20245 citations

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distributions, within a unified analytical formulation. Closed-form expressions for AEP and AAR are derived via direct probability density function (PDF)-based integration of the conditional error probability, along with high-photon-number asymptotic approximations that provide insight into performance scaling behavior. Numerical results validate the analytical expressions and demonstrate the impact of PEs on system performance. The analysis further enables systematic comparison between classical and optimal quantum detection schemes and quantifies the achievable performance gains under different channel conditions. These results provide useful design insights for modulation and receiver selection in turbulent free-space optical (FSO) communication systems.