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arXiv 2024年

作者： Deb, Souvik Ghosh, Sasthi C. Advanced Computing & Microelectronics Unit Indian Statistical Institute West Bengal Kolkata700108 India

The channel estimation (CE) overhead for unstructured multipath-rich channels increases linearly with the number of reflective elements of reconfigurable intelligent surface (RIS). This results in a significant portion of the channel coherence time being spent on CE, reducing data communication time. Furthermore, due to the mobility of the user equipment (UE) and the time consumed during CE, the estimated channel state information (CSI) may become outdated during actual data communication. In recent studies, the timing for CE has been primarily determined based on the coherence time interval, which is dependent on the velocity of the UE. However, the effect of the current channel condition and pathloss of the UEs can also be utilized to control the duration between successive CE to reduce the overhead while still maintaining the quality of service. Furthermore, for muti-user systems, the appropriate coherence time intervals of different users may be different depending on their velocities. Therefore CE carried out ignoring the difference in coherence time of different UEs may result in the estimated CSI being detrimentally outdated for some users. In contrast, others may not have sufficient time for data communication. To this end, based on the throughput analysis on outdated CSI, an algorithm has been designed to dynamically predict the next time instant for CE after the current CSI acquisition. In the first step, optimal RIS phase shifts to maximise channel gain is computed. Based on this and the amount of degradation of SINR due to outdated CSI, transmit powers are allocated for the UEs and finally the next time instant for CE is predicted such that the aggregated throughput is maximized. Simulation results confirm that our proposed algorithm outperforms the coherence time-based strategies. © 2024, CC BY.

关键词： Channel estimation

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Non-optimal is Good! Resource Allocation in Presence of Dynamic Obstacles in D2D Networks

Non-optimal is Good! Resource Allocation in Presence of Dyna...

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Conference on Local Computer Networks (LCN)

作者： Rathindra Nath Dutta Sasthi C. Ghosh Advanced Computing and Microelectronics Unit Indian Statistical Institute Kolkata India

To cope with high bandwidth demands of modern applications, device-to-device (D2D) communications using millimeter-wave (mmWave) signals are being harnessed. The major challenge of mmWave signals is that they require a strict, obstacle-free line-of-sight communication. Static obstacles are easier to avoid; dynamic obstacles pose the main hurdle, their movement not being known. In this work, we propose a way to learn link blockages due to dynamic obstacles, using the link activation history. For this, one might have to explore non-optimal link activations. This ensures that all links are tried a sufficient number of times, ensuring adequate knowledge about link failures, thus creating an exploration-exploitation dilemma. To this end, we propose a systematic way of exploring such non-optimal channel allocations, so that the number of link failures is minimized. Given the hardness of this problem, we devise a greedy solution, and show its effectiveness over existing strategies through simulations.

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Joint Base Station and Reflector Placement in an urban mmWave Network

Joint Base Station and Reflector Placement in an urban mmWav...

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Communications and Networking (MeditCom), IEEE International Mediterranean Conference on

作者： Rathindra Nath Dutta Subhojit Sarkar Sasthi C. Ghosh Advanced Computing and Microelectronics Unit Indian Statistical Institute Kolkata India

Millimeter-wave (mmWave) technology is expected to be the backbone of future communication networks. However, for all its benefits, mmWave communication comes with its fair share of challenges. In this context, the obstacle free strict line-of-sight (LOS) requirement is one of the primary hurdles that has to be crossed. One way to deal with this problem is to densely deploy small range base stations, called gNBs, to overcome outage due to obstacles. Reflectors have been proposed to augment the transmission environment, and reflect mmWaves bypassing the obstacles. Evidently, they can be used to increase the coverage area that do not have LOS with the available gNBs. We argue that considering the placement of gNBs and reflectors independently may lead to suboptimal solution. In this paper, we consider an urban deployment scenario, and attempt to maximally cover it by jointly placing the gNBs and reflectors. Given the hardness of the joint problem, we first develop a set cover based greedy solution and also provide a linear programming (LP) relaxation based solution. With extensive simulations, we show that with fixed number of available gNBs and reflectors to be placed, both our joint placement solutions can achieve a larger coverage compared to an existing approach.

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Energy Efficient Resource Allocation for D2D Communications using Reinforcement Learning

Energy Efficient Resource Allocation for D2D Communications ...

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Conference on Local Computer Networks (LCN)

作者： Rathindra Nath Dutta Sasthi C. Ghosh Advanced Computing and Microelectronics Unit Indian Statistical Institute Kolkata India

The millimeter-wave (mmWave) device-to-device (D2D) communication is already being employed to satisfy the high datarate demand of the internet-of-things nodes. Using mmWave signals has its own challenges as it suffers from high penetration losses. Therefore, presence of dynamic obstacles further complicates the already hard problem of allocation of channel resources to the demanding nodes. In this work, we have proposed a reinforcement learning (RL) based framework to jointly allocate the frequency channels as well as assign the transmit-powers to the demanding D2D pairs in order to maximize the energy-efficiency in presence of dynamic obstacles. We justify our choice of reward function through a formal proof and also ensure the convergence of the algorithm. Through extensive simulations, we show that our proposed RL framework not only converges, but also outperforms an existing approach.

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Obstacle Aware Link Selection for Stable Multicast D2D Communications 3rd

Obstacle Aware Link Selection for Stable Multicast D2D Comm...

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3rd International Conference on Computer and Communication Engineering, CCCE 2023

作者： Dutta, Rathindra Nath Ghosh, Sasthi C. Advanced Computing and Microelectronics Unit Indian Statistical Institute Kolkata India

ISBN: (纸本)9783031352980

The rapid growth of multimedia applications requiring high bandwidth has paved the way for millimeter-wave (mmWave) device-to-device (D2D) communications. In many modern applications, such as video streaming, same data packets need to be delivered to a group of users. Multicasting these packets has a clear advantage over repeated unicast. Establishing a stable multicast route for mmWave D2D communications is a challenging task as presence of obstacles can easily break a link. In this work we devise a mechanism for constructing a stable route for D2D multicast communications in presence of static as well as dynamic obstacles. This requires some knowledge about the blockage probabilities due to the obstacles. We then present a way of learning these blockage probabilities using the Dempster-Shafer evidential theory framework. We show the effectiveness of our proposed scheme over an existing approach through extensive simulations. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.

关键词： Multicasting

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LazyUAV: A Minimal Displacement Coverage Strategy for Multi-UAV mmWave Networks

LazyUAV: A Minimal Displacement Coverage Strategy for Multi-...

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Communications and Networking (MeditCom), IEEE International Mediterranean Conference on

作者： Subhojit Sarkar Rathindra Nath Dutta Sasthi C. Ghosh Advanced Computing and Microelectronics Unit Indian Statistical Institute Kolkata India

Unmanned Aerial Vehicles (UAVs) are a potential platform for deploying millimeter wave (mmWave) base stations. Their high spatial flexibility makes them an attractive choice for the deployment in disaster management scenarios, and for offloading in crowded areas. Apart from the stringent propagation requirements of mmWaves, one challenge that has to be addressed is the limited power onboard a UAV, which is used to hover and move the device, and of course, to transmit data. In this paper, we deal with the deployment of UAVs with an aim to minimising their displacement in subsequent time. We take into consideration user mobility, and propose LazyUAV, a Set-Cover based geometric approach to minimise UAV displacement, while maintaining maximal coverage. Via extensive simulations, we demonstrate the effectiveness of our approach.

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Optimized QAOA ansatz circuit design for two-body Hamiltonian problems

Optimized QAOA ansatz circuit design for two-body Hamiltonia...

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International Conference on VLSI Design

作者： Ritajit Majumdar Dhiraj Madan Debasmita Bhoumik Dhinakaran Vinayagamurthy Shesha Raghunathan Susmita Sur-Kolay IBM Quantum IBM India Research Lab Advanced Computing & Microelectronics Unit Indian Statistical Institute

Quantum Approximate Optimization Algorithm (QAOA) is a prospective candidate for providing quantum advantage in finding approximate solutions to optimization problems using near-term quantum devices. In this paper, the goal is to reduce the number of CNOT gates and the depth of quantum ansatz circuits for QAOA. First, we present a generalized QAOA formulation for any Hamiltonian that involves upto two-body interactions, as a graph. The circuit realization of the depth-p QAOA requires $2mp$ CNOT gates where the graph for the Hamiltonian has n vertices and m edges. Presently, a CNOT gate is one of the primary sources of error. We propose a graph-theoretic algorithm which can eliminate $n-1$ CNOTs from the QAOA ansatz while retaining functional equivalence with the original circuit. This improves upon previously proposed Depth First Search (DFS) method by restricting the increase in depth of the circuit, which was a drawback of the method, by $\simeq 84.8\%$ for Erdős-Renyi graphs. Finally, if the underlying connectivity (hardware coupling map) and the initial qubit placement for a hardware are known, then we present how to extend the greedy heuristic method in order to obtain a functionally equivalent circuit with $\simeq 5\%$; fewer SWAP gates for Erdős-Renyi graphs.

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DRAMS: Double-RIS Assisted Multihop Routing Scheme for Device-to-Device Communication

arXiv

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arXiv 2023年

作者： Sau, Lakshmikanta Mukherjee, Priyadarshi Ghosh, Sasthi C. The Advanced Computing & Microelectronics Unit Indian Statistical Institute Kolkata700108 India

Reconfigurable intelligent surfaces (RISs) is a promising solution for enhancing the performance of multihop wireless communication networks. In this paper, we propose a double-RIS assisted multihop routing scheme for a device-to-device (D2D) communication network. Specifically, the scheme is dependent on the already deployed RISs and users in the surroundings. Besides the RISs, the emphasis of this work is to make more use of the existing intermediate users (IUs), which can act as relays. Hence, the density of RIS deployment in the surroundings can be reduced, which leads to the avoidance of resource wastage. However, we cannot solely depend on the IUs because this implies complete dependence on their availability for relaying and as a result, the aspect of reliability in terms of delay-constrained information transfer cannot be guaranteed. Moreover, the IUs are considered capable of energy harvesting and as a result, they do not waste their own energy in the process of volunteering to act as a relay for other users. Numerical results demonstrate the advantage of the proposed scheme over some existing approaches and lastly, useful insights related to the scheme design are also drawn, where we characterize the maximum acceptable delay at each hop under different set-ups. © 2023, CC BY-NC-ND.

关键词： Energy harvesting

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DCSK-based Waveform Design for Self-sustainable RIS-aided Noncoherent SWIPT

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IEEE Transactions on Communications 2025年

作者： Mukherjee, Priyadarshi Psomas, Constantinos Krikidis, Ioannis Indian Statistical Institute Advanced Computing and Microelectronics Unit Kolkata India University of Cyprus Department of Electrical and Computer Engineering Nicosia1678 Cyprus

This paper investigates the problem of transmit waveform design in the context of a chaotic signal-based self-sustainable reconfigurable intelligent surface (RIS)-aided system for simultaneous wireless information and power transfer (SWIPT). Specifically, we propose a differential chaos shift keying (DCSK)-based RIS-aided point-to-point set-up, where the RIS is partitioned into two non-overlapping surfaces. The elements of the first sub-surface perform energy harvesting (EH), which in turn, provide the required power to the other sub-surface operating in the information transfer (IT) mode. In this framework, by considering a generalized frequency-selective Nakagami-m fading scenario as well as the nonlinearities of the EH process, we derive closed-form analytical expressions for both the bit error rate (BER) at the receiver and the harvested power at the RIS. Our analysis demonstrates, that both these performance metrics depend on the parameters of the wireless channel, the transmit waveform design, and the number of reflecting elements at the RIS, which switch between the IT and EH modes, depending on the application requirements. Moreover, we show that, having more reflecting elements in the IT mode is not always beneficial and also, for a given acceptable BER, we derive a lower bound on the number of RIS elements that need to be operated in the EH mode. Furthermore, for a fixed RIS configuration, we investigate a trade-off between the achievable BER and the harvested power at the RIS and accordingly, we propose appropriate transmit waveform designs. Finally, our numerical results illustrate the importance of our intelligent DCSK-based waveform design on the considered framework. © 1972-2012 IEEE.

关键词： Energy harvesting

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Modeling and Verification of Service Allocation Policies for Multi-Access Edge computing Using Probabilistic Model Checking

Modeling and Verification of Service Allocation Policies for...

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作者： Ray, Kaustabha Banerjee, Ansuman Advanced Computing and Microelectronics Unit Indian Statistical Institute Kolkata India

In recent times, Multi-Access Edge computing (MEC) has emerged as a new paradigm allowing low-latency access to services deployed on edge nodes offering computation, storage and communication facilities. Vendors deploy their services on MEC servers to improve performance and mitigate network latencies often encountered in accessing cloud services. An allocation policy determines how to allocate service requests from users to MEC servers. A number of proposals for binding user service requests to nearby edge servers enroute have been proposed in literature. However, none of these proposals, to the best of our knowledge, provide quantitative guarantees on performance metrics. Indeed, the evolving environment, along with a large allocation configuration space makes proving performance guarantees for such allocation policies a challenging task. Further, the implications of MEC server failures on allocation policies have been relatively unexplored. To address such issues, we propose a trace driven approach to derive a formal model of allocation policies and perform quantitative verification to produce probabilistic guarantees on performance metrics. We use the San Francisco taxi dataset, the LDNS availability dataset and allocation policies from recent literature to validate our approach. Experimental results demonstrate how our model can be utilized to quantitatively compare performance metrics of service allocation policies in MEC systems. © 2004-2012 IEEE.

关键词： Edge computing

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