查看更多>>摘要：With flexibility,convenience and mobil-ity,unmanned aerial vehicles(UAVS)can provide wire-less communication networks with lower costs,easier de-ployment,higher network scalability and larger coverage.This paper proposes the deep deterministic policy gradi-ent algorithm to jointly optimize the power allocation and flight trajectory of UAV with constrained effective en-ergy to maximize the downlink throughput to ground users.To validate the proposed algorithm,we compare with the random algorithm,Q-learning algorithm and deep Q network algorithm.The simulation results show that the proposed algorithm can effectively improve the communication quality and significantly extend the ser-vice time of UAV.In addition,the downlink throughput increases with the number of ground users.
查看更多>>摘要：Unmanned aerial vehicle(UAV)as a powerful tool has found its applicability in assisting mo-bile users to deal with computation-intensive and delay-sensitive applications(e.g.,edge computing,high-speed Internet access,and local caching).However,deployment of UAV-aided mobile services(UMS)faces challenges due to the UAV limitation in wireless coverage and energy storage.Aware of such physical limitations,a future UMS system should be intelligent enough to self-plan trajector-ies and best offer computational capabilities to mobile users.There are important issues regarding the UAV-user interaction,UAV-UAV cooperation for sustainable ser-vice provision,and dynamic UMS pricing.These network-ing and resource management issues are largely over-looked in the literature and this article presents intelli-gent solutions for cooperative UMS deployment and oper-ation.Mobile users'locations are generally private in-formation and changing over time.How to learn on-de-mand users'truthful location reporting is important for determining optimal UAV deployment in serving all the users fairly.After addressing the truthful UAV-user inter-action issue via game theory,we further study the UAV network sustainability for UMS provision by minimizing the energy consumption cost during deployment and seek-ing UAV-UAV cooperation.Finally,for profit-maximiz-ing purpose,we analyze the cooperative UAVs'deploy-ment,capacity allocation,and dynamic service pricing.
查看更多>>摘要：Unmanned aerial vehicles(UAVs)have recently been regarded as a promising technology in In-ternet of things(IoT).UAVs functioned as intermediate relay nodes are capable of establishing uninterrupted and high-quality communication links between remotely de-ployed IoT devices and the destination.Multiple UAVs are required to be deployed due to their limited onboard energy.We study a UAV pair-supported relaying in un-known IoT systems,which consists of transmitter and re-ceiver.Our goal is that transmitter gathers the data from each device then transfers the information to receiver,and receiver finally transmits the information to the des-tination,while meeting the constraint that the amount of information received from each device reaches a certain threshold.This is an optimization problem with highly coupled variables,such as trajectories of transmitter and receiver.On account of no prior knowledge of the envir-onment,a dueling double deep Q network(dueling DDQN)algorithm is proposed to solve the problem.Whether it is in the phase of transmitter's receiving in-formation or the phase of transmitter's forwarding in-formation to receiver,the effectiveness and superiority of the proposed algorithm is demonstrated by extensive sim-ulationsin in comparison to some base schemes under dif-ferent scenarios.
查看更多>>摘要：To improve the time-varying channel es-timation accuracy of orthogonal frequency division multi-plexing air-ground datalink in complex environment,this paper proposes a time-varying air-ground channel estima-tion algorithm based on the modulated learning networks,termed as MB-ChanEst-TV.The algorithm integrates the modulated convolutional neural networks(MCNN)with the bidirectional long short term memory(Bi-LSTM),where the MCNN subnetworks accomplish channel inter-polation in frequency domain and compress the network model while the Bi-LSTM subnetworks achieve channel prediction in time domain.Considering the unique char-acteristics of airframe shadowing for unmanned aircraft systems,we propose to combine the classical 2-ray chan-nel model with the tapped delay line model and present a more realistic channel impulse response samples genera-tion approach,whose code and dataset have been made publicly available.We demonstrate the effectiveness of our proposed approach on the generated dataset,where experimental results indicate that the MB-ChanEst-TV model outperforms existing state-of-the-art methods with a lower estimation error and better bit error ratio per-formance under different signal to noise ratio conditions.We also analyze the effect of roll angle of the aircraft and the duration percentage of the airframe shadow on the channel estimation.
查看更多>>摘要：Interference source localization with high accuracy and time efficiency is of crucial importance for protecting spectrum resources.Due to the flexibility of unmanned aerial vehicles(UAVs),exploiting UAVs to locate the interference source has attracted intensive re-search interests.The off-the-shelf UAV-based interfer-ence source localization schemes locate the interference sources by employing the UAV to keep searching until it arrives at the target.This obviously degrades time effi-ciency of localization.To balance the accuracy and the ef-ficiency of searching and localization,this paper proposes a multi-UAV-based cooperative framework alone with its detailed scheme,where search and remote localization are iteratively performed with a swarm of UAVs.For search-ing,a low-complexity Q-learning algorithm is proposed to decide the direction of flight in every time interval for each UAV.In the following remote localization phase,a fast Fourier transformation based location prediction al-gorithm is proposed to estimate the location of the inter-ference source by fusing the searching result of different UAVs in different time intervals.Numerical results re-veal that in the proposed scheme outperforms the state-of-the-art schemes,in terms of the accuracy,the robust-ness and time efficiency of localization.
查看更多>>摘要：Space-air-ground integrated network is capable of providing seamless and ubiquitous services to cater for the increasing wireless communication demands of emerging applications.However,how to efficiently manage the heterogeneous resources and protect the pri-vacy of connected devices is a very challenging issue,es-pecially under the highly dynamic network topology and multiple trustless network operators.In this paper,we in-vestigate blockchain-empowered dynamic spectrum man-agement by reaping the advantages of blockchain and software defined network(SDN),where operators are in-centive to share their resources in a common resourced pool.We first propose a blockchain enabled spectrum management framework for space-air-ground integrated network,with inter-slice spectrum sharing and intra-slice spectrum allocation.Specifically,the inter-slice spectrum sharing is realized through a consortium blockchain formed by the upper-tier SDN controllers,and then a graph coloring based channel assignment algorithm is pro-posed to manage the intra-slice spectrum assignment.A bilateral confirmation protocol and a consensus mechan-ism are also proposed for the consortium blockchain.The simulation results prove that our proposed consensus al-gorithm takes less time than practical Byzantine fault tol-erance algorithm to reach a consensus,and the proposed channel assignment algorithm significantly improves the spectrum utilization and outperforms the baseline al-gorithm in both simulation and real-world scenarios.
查看更多>>摘要：The special position of terahertz wave in the electromagnetic spectrum makes it possess the charac-teristics of orientation,broadband,penetration and low energy,which promotes the extensive research of tera-hertz wave in the fields of communication,radar,imaging,sensing,security inspection and so on.The solid-state terahertz sources based on semiconductor devices have at-tracted extensive attention in the field of terahertz in-formation technology due to their characteristics such as being able to work at room temperature,being small in size,being easy to integrate and having good frequency stability.Terahertz planar Schottky diode is a kind of low parasitic semiconductor device.Its high cutoff frequency makes it work well in the terahertz range.The frequency multiplier based on planar Schottky diode is an import-ant part of terahertz solid state source.In this review,the development of Schottky diodes technology in recent years have been introduced,including the structures and preparation of Schottky diodes.In addition,the current situation and performance of different types of terahertz sources based on Schottky diodes are further introduced,and the future development trend is discussed.
查看更多>>摘要：Terahertz(THz)communications are considered as very promising for the sixth-generation(6G)ultra-dense wireless networks.However,THz sig-nals suffer from well-known severe path loss,which con-sequently shortens the coverage of THz communication systems.To deal with this issue,precoding technique is expected to be beneficial to extend the limited coverage by providing directional beams with ultra large number of antenna arrays.In this paper,we overview the state-of-the-art developments of THz precoding techniques such as reconfigurable intelligent surface based precoding,hybrid digital-analog precoding and delay-phase precoding.Based on the survey,we summarize several open issues remain-ing to be addressed,and discuss the prospects of a few potential research directions on THz precoding,such as one-bit precoding,precoding for hardware impairments and THz security precoding.This overview will be help-ful for researchers to study innovative solutions of THz precoding in the future 6G wireless communications.
LU XuyangVenkatesh SureshSaeidi HoomanSengupta Kaushik...
499-515页
查看更多>>摘要：Advances in 6G communication changes how machines and humans interact.The blossom of new applications demands significantly higher data bandwidth while preserving the mobility and sustainability of elec-tronic wireless communication systems.It also demands an integrable system that allows convenient interactions between communication units and signal processing units.A review of CMOS-based THz communication system solutions is presented,with a focus on novel systematic EM-circuit co-design philosophy.This review starts with a review of THz power generation,followed by the discus-sion of THz localization and THz beamforming for effi-cient high-throughput communication.
查看更多>>摘要：With the increasing number of users and emerging new applications,the demand for mobile data traffic is growing rapidly.The limited spectrum resources of the traditional microwave and millimeter-wave fre-quency bands can no longer support the future wireless communication systems with higher system capacity and data throughput.The terahertz(THz)frequency bands have abundant spectrum resources,which can provide sufficient bandwidth to expand channel capacity and in-crease transmission data rate.In addition,with the rapid development of silicon-based semiconductor technology,its characteristic size keeps decreasing,and the radio fre-quency performance of active devices is gradually ap-proaching the performance of Ⅲ-Ⅴ semiconductor techno-logy.The realization of THz communication systems based on low-cost,high-stability,and easy-to-integrate sil-icon-based process has become a feasible solution.This re-view summarizes the reported silicon-based THz commu-nication systems,as well as the key sub-circuit chips in these systems,including the local oscillator,power ampli-fier,low noise amplifier,on-chip antenna and transceiver chip,etc.
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