查看更多>>摘要：A backward wave oscillator with parallel multiple beams and multi-pin slow-wave structure(SWS)operating at the frequency above 500 GHz is studied.Both the cold-cavity dispersion characteristics and CST Particle Studio simulation results reveal that there are obvious mode competition problems in this kind of terahertz source.Considering that the structure of the multi-pin SWS is similar to that of two-dimensional photonic crystals,we introduce the defects of photonic crystal with the property of filtering into the SWS to suppress high-order modes.Furthermore,a detailed study of the effect of suppressing higher-order modes is carried out in the process of changing location and arrangement pattern of the point defects.The stable,single-mode operation of the terahertz source is realized.The simulation results show that the ratio of the output peak power of the higher-order modes to that of the fundamental mode is less than 1.9％.Also,the source can provide the output peak power of 44.8 mW at the frequency of 502.2 GHz in the case of low beam voltage of 4.7 kV.
查看更多>>摘要：A high-efficiency polarization-rotating transmitarray antenna(TA)using wideband elements is pro-posed for millimeter-wave applications.The polarization-rotating element consists of three metallic layers and two substrates.Orthogonal polarizers are employed on the top and bottom of the element.And the split ring with a parasitic stub on the middle layer is symmetric about the diagonal,performing the polarization rotation and phase compensation simultaneously.A parasitic stub is designed to decrease transmission loss and broaden the bandwidth.The periodicity of the element is only 1/4 wavelength at 30 GHz.A prototype TA with 28 × 28 elements is designed,fabricated,and measured.The measured peak gain reaches 27.5 dBi at 37.8 GHz.The 1-dB gain drop bandwidth is 30.8-40 GHz(26.0％).The aperture efficiency reaches as high as 71％at 31.5 GHz.Within the bandwidth of 26.5-38.8 GHz(37.7％),the aperture efficiency is higher than 50％.The proposed polarization-rotating TA features wide bandwidth and high effi-ciency,demonstrating great application potential for 5G millimeter-wave communication.
查看更多>>摘要：This paper considers downlink multiuser multiple-input-multiple-output system with parallel spatial modulation scheme,in which base station transmitter antennas are separated into K groups corresponding to K user terminals.Generalized spatial modulation is employed,in which a subset(more than single antenna)of transmit antenna array are activated and the activating pattern corresponds to specific spatial symbol.Different from existing precoding-based algorithms,we develop a two-stage detection scheme at each user terminal:In the pre-processing stage,a minimax algorithm is proposed to identify the indices of active antennas,where the key idea is that the mini-mum output energy of the detector is maximized;A constrained minimum output energy algorithm is proposed in the post-processing stage to mitigate multiuser interference and extract temporal symbols.Compared with existing precoding-based algorithms,the complexity is significantly reduced.Moreover,the proposed algorithm is semi-blind,in which only a small subset of channel state information is required to identify active antennas as well as eliminate multiuser interference.Simulation results demonstrate that the proposed algorithm is near-far resistant and the spec-tral efficiency is extensively increased compared to the conventional spatial modulation scheme.
查看更多>>摘要：A compact filtering antenna system with wide-angle scanning is proposed for vehicle to infrastructure(V2I)communication which would handle complex communication scenarios.In this work,a wide beam filtering an-tenna is realized by using some inductive resistance structures such as metal pins and pillars,and capacitive struc-tures such as slots,parasitical patches to produce the radiation nulls at two sides of the operating frequency band and improve the impedance matching in the passband.Meanwhile,the wide beam capability is also realized by the above structure.Furthermore,two H-and E-plane linear arrays are designed for the beam scanning capability with filtering characteristics based on the proposed antenna.To verify the proposed design concept,a prototype is fabri-cated and measured.The measurement and simulation agree well,demonstrating an excellent filtering characteristic with the operating frequency band from 3.18 to 3.45 GHz(about 8.1％),the high total efficiency of about 88％,and 3-dB-beamwidth of more than 100° and 120° in the above two arrays,respectively.Additionally,the proposed arrays can realize the beam scanning up to the coverage of 112° and 120° with a lower gain reduction and a good filtering characteristic,respectively.
查看更多>>摘要：An optical space time pulse position modulation(OSTPPM)scheme is proposed to satisfy the com-munication requirement of high transmission rate and better reliability.For the OSTPPM scheme,an improved threshold judgment-based orthogonal matching pursuit(IT-OMP)algorithm with low-complexity and near optimal performance is proposed.The average bit error rate of OSTPPM-IT-OMP scheme is investigated over the exponen-tial Weibull channel,and its analytical expression is verified via Monte Carlo simulation.With the same simulation parameters,the signal to noise ratio of(4,4,2)-OSTPPM-IT-OMP is respectively 3.75 dB and 8.5 dB better than that of spatial pulse position modulation(SPPM)scheme and generalized spatial pulse position modulation(GSPPM)scheme at a bit error rate of 1 x 10-3.With the same transmission bits per symbol,the computational complexity of(3,4,2)-OSTPPM-IT-OMP scheme is reduced by 90.47％and 75.4％compared with(16,4,2)-SPPM and(5,4,2)-GSPPM schemes,respectively.
查看更多>>摘要：To further improve the performance of passive intelligent reflecting surface(IRS)-assisted communica-tion systems and mitigate the serious path loss due to"double-fading"of IRS-assisted links,an active IRS-aided simultaneous wireless information and power transfer(SWIPT)system is investigated.This paper jointly optimizes the transmit beamforming at the base station(BS)and the phase shifts at the active IRS in order to maximize the power collected by the energy harvesting receiver under both perfect and imperfect channel state information(CSI)states,subject to the signal-to-interference-noise ratio constraint of the information decoding receiver,and the power constraints of the BS/IRS.Under perfect CSI,the alternating optimization algorithm is utilized for obtaining the transmit beamforming at the BS and the phase shifts at the active IRS.For each subproblem,we first transform non-convex objective function and constraints into convex ones by performing a first-order Taylor expansion.Then,each subproblem is solved by using the interior point method.Given that obtaining perfect CSI is impractical,two robust beamforming designs are proposed for imperfect CSI case.Under the bounded CSI error model,we first transform the non-convex optimization problem into two semidefinite programming subproblems,and then solve each subproblem based on S-procedure and sequential rank-one constraint relaxation(SROCR)techniques.Under the stochastic CSI error model,the alternating optimization method is applied in an iterative manner based on Bernstein-type inequality and SROCR technique.Simulation results show that both robust and non-robust schemes for active IRS-assisted SWIPT systems can achieve extremely superior performance over conventional passive IRS-assisted systems under the same overall power budget.
查看更多>>摘要：The asynchronous time-sensitive networking(TSN)based on IEEE 802.1Qcr is expected to be a prom-ising solution for the asynchronous transmissions of safety-critical flows without the support of clock synchronization.When the asynchronous traffic shaping(ATS)mechanism is adopted to meet the deadline requirements for transmissions of safety-critical flow,it is necessary to formally verify the real-time properties and corresponding network performance.However,it is still unclear how to build an efficient formal model to evaluate different frame selection methods dur-ing the ATS scheduling process,which originate from the dominations of priority or eligibility time.In this paper,we present a formal modeling framework to compare the impacts of different frame selection on transmission sequence under the ATS mechanism.According to the priority level(pATS)or eligibility time(eATS)for flows,two transmission selection methods in ATS are modeled and compared.Then,we verify the real-time properties of ATS.The result shows that the shaping-for-free property can be satisfied with the pATS method but can not be fulfilled with the eATS method.Besides,the timing analysis results illustrate that the eATS method can provide more fairness than the pATS method for the transmission of low-priority flows in TSN networks.
查看更多>>摘要：This paper investigates the performance of a new generalized frequency division multiplexing(GFDM)parallel relay free space optical(FSO)communication system using multi-input multi-output(MIMO)orthogonal space-time block codes(OSTBC)scheme.Under the M distribution atmospheric turbulence,taking into account the triple effects of irradiance,pointing errors and path loss,the mathematical expression of system symbol error rate is derived with the help of Meijer G-function.The symbol error performance of GFDM is compared with on-off keying,Gaussian minimum shift keying,polarization shift keying and orthogonal frequency division multiplexing(OFDM)modulation methods.The effects of the MIMO-OSTBC parallel relay scheme on the GFDM system including filter roll down coefficient,the number of transmitting and receiving antennas,the number of relays,normalized beamwidth and jitter variance are analyzed,and the numerical results are verified by Monte Carlo simulation.This work provides a good foundation for engineering applications.
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