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Sudhanshu Arya,Yeonghae Kim(김영해),Yeon Ho Chung(정연호) 한국통신학회 2022 한국통신학회 학술대회논문집 Vol.2022 No.2
In this paper, we propose a novel game theoretic approach that permit to maximize the performance of an interference-limited photon-counting multiuser memoryless Poisson channel with asymptotically low transmit power considered. We consider a conflicting situation where multiple users share the same spectrum and attempt to maximize their throughput. The received signal is characterized by a photon-counting receiver. We consider the transmission at an asymptotically low-power regime. We present the Nash equilibrium beamformer. We show that, selfish but cooperative users can achieve maximum sum-rate performance.
Non-Line-of-Sight Ultraviolet Communication With Receiver Diversity in Atmospheric Turbulence
Arya, Sudhanshu,Chung, Yeon Ho IEEE 2018 IEEE Photonics Technology Letters Vol.30 No.10
<P>In this letter, we propose spatial diversity reception of non-line-of-sight (NLOS) ultraviolet (UV) communication in turbulent atmospheric channel. The turbulent atmospheric channel causes fluctuation in the received signal intensity of a UV system, resulting in power loss and subsequent performance degradation at the receiver. To mitigate this adverse effect, we present the spatial diversity reception in the form of dual-branch switch and stay combining (SSC) at the receiver. That is, one branch is only connected to the receiver at any instant using appropriate switching logic. The channels are assumed to be exponentially correlated in space, while irradiance fluctuation due to turbulence is modeled by a Gamma–Gamma distribution with parameters directly related to the attributes of the NLOS UV link. Analytic expressions for both the outage probability and the average symbol error probability are derived using the SSC diversity technique with the correlated receivers.</P>
ARYA SUDHANSHU,Chung Yeon Ho 한국통신학회 2023 ICT Express Vol.9 No.6
By leveraging the characteristics of both quantum encoding and classical data channel, we present a unique and novel multiuser optical communication system that utilizes fascinating properties of the structured light for information transmission. Specifically, we propose an indoor orbital angular momentum (OAM) multiuser multiple-input multiple-output (MIMO) optical communication system, where the quantum encoding is performed and the multiuser transmission is then analyzed from the context of the classical data channel. In the proposed system, as the OAM beam propagates, its angular spread is analyzed. In addition, we show that the variance of the beam divergence increases with the increasing OAM index mode on the basis of the derived MIMO channel impulse response for OAM carrying Laguerre–Gaussian beams. Comparative studies reveal that the proposed system significantly outperforms the conventional non-orthogonal multiple access (NOMA) applied with MIMO.
ARYA SUDHANSHU,정연호,정완영,김종진,김남호 한국통신학회 2021 ICT Express Vol.7 No.3
In this paper, we address the problem of joint transmit beamforming and power control for a multiuser multiple-input single-output (MISO) indoor optical downlink channel. We adopt a shot-noise limited Poisson channel with transmitting signals subject to average and peak transmits power constraints. To minimize the total transmit power, we formulate an optimal downlink beamforming problem using convex optimization method via second-order cone programming techniques. In our approach, the total transmit power is optimized subject to the signal-to-interference-plus-noise ratio (SINR). The results verify performance improvements of the proposed technique as compared to conventional multiuser MISO indoor optical systems.
Arya, Sudhanshu,Chung, Yeon Ho Elsevier 2019 OPTICS COMMUNICATIONS - Vol.450 No.-
<P><B>Abstract</B></P> <P>Spectrum sensing is a fundamental component in multi-user free space optical communication systems. In order to avoid interference among the users, it is required to periodically sense the optical frequency spectrum to detect if the channel is occupied by active transceiver pairs. Spectrum sensing allows the user to continuously sense the optical spectrum within their operating range to detect the channels. In this paper, we propose a generic novel blind spectrum sensing scheme for an unknown optical signal over strong atmospheric turbulence channel. By generic, we mean that the proposed scheme is applicable to all optical wavelengths, i.e. ultraviolet (UV), visible light, and infrared. The proposed blind spectrum sensing scheme is based on the estimated signal-to-noise ratio (SNR) and the noise power, for which we have derived expressions from a statistical ratio of the received signal. The atmospheric turbulence is the main reason behind the signal fading in free space optical links as it causes fluctuations in the received signal intensity. To mitigate this adverse effect, the proposed scheme is equipped with a spatial diversity scheme in the form of switch-and-stay combining. We use Gamma–Gamma distribution to model both small-scale and large-scale turbulence fadings. From the estimated SNR and noise power expressions, we formulate the novel closed-form expressions for the probabilities of detection and false alarm mathematically. Numerical and simulation results based on randomly generated optical signals are presented to verify the effectiveness of the proposed scheme.</P>
Spectrum sensing for free space optical communications in strong atmospheric turbulence channel
Arya, Sudhanshu,Chung, Yeon Ho Elsevier 2019 OPTICS COMMUNICATIONS - Vol.445 No.-
<P><B>Abstract</B></P> <P>One of the primary challenges in multi-user optical wireless communications (OWC) is to periodically sense the optical frequency spectrum at the receiver to detect whether the channel is occupied by other transceiver pairs in order to avoid interference. Spectrum sensing enables the user to continuously sense the channel prior to its access to the channel. In this paper, we propose the spectrum sensing of an unknown optical signal over strong atmospheric turbulence channel. The turbulent atmospheric channel causes fluctuations in the received signal intensity, resulting in power loss at the receiver. To mitigate this adverse effect, we present an energy detection based optical spectrum sensing scheme with the spatial diversity reception in the form of a square-law selection diversity. The intensity fluctuations are modeled by a negative exponential distribution. The analytical closed-form expressions for the probability of detection and the probability of false alarm are derived. Based on the derived expressions, we obtain the performance analysis as a function of the system parameters. It is also found that sensing capability is boosted with the square-law diversity scheme.</P>
Optical Array Selection Transmit Diversity Scheme for Ground-to-UAV Optical Links
Yeonghae Kim,Sudhanshu Arya,Yeon Ho Chung 한국통신학회 2021 한국통신학회 학술대회논문집 Vol.2021 No.11
Recently, unmanned aerial vehicles (UAVs) have emerged as a promising solution in establishing optical wireless communication (OWC) links. Despite providing huge unlimited bandwidth, the quality of the data transmission is negatively affected by the pointing error and turbulence-induced fading. In view of minimizing the bit error rate (BER) and combating the fading, we propose a power-efficient transmission scheme that utilizes the maximal selection transmit diversity (MSTD) for UAV enabled OWC link with a strict power budget imposed. The model considers the joint effect of the atmospheric turbulence and pointing error. Results demonstrate the superiority of the MSTD in combating the turbulence-induced fading and minimizing the BER. We further discuss the impact of different turbulence strengths on the performance. It is shown that, even for a channel with strong turbulence strength, the application of the MSTD improves the performance significantly. For instance, it is depicted that, at a signal-to-noise ratio of 20 dB, utilizing MSTD can decrease the BER by an order of 10.
Yeonghae Kim(김영해),Sudhanshu Arya,Yeon Ho Chung(정연호) 한국통신학회 2022 한국통신학회 학술대회논문집 Vol.2022 No.2
In this paper, we present a unique and novel transmission technique for ground-to-UAV communication link. In particular, we propose frequency-shift keying sub-carrier intensity modulation (FSK-SIM) equipped with switch-and-stay combining (SSC) diversity technique. We consider a realistic scenario with gamma-gamma distributed turbulence-induced fading over correlated optical channel. We analyze the impact of correlation on the performance of the ground-to-UAV link. We obtain the closed-form expression of the average bit error rate (BER).