Terahertz(THz) communication is being considered as a potential solution to mitigate the demand for high bandwidth. The characteristic of THz band is relatively different from present wireless channel and imposes tech...Terahertz(THz) communication is being considered as a potential solution to mitigate the demand for high bandwidth. The characteristic of THz band is relatively different from present wireless channel and imposes technical challenges in the design and development of communication systems. Due to the high path loss in THz band,wireless THz communication can be used for relatively short distances. Even,for a distance of few meters( > 5 m),the absorption coefficient is very high and hence the performance of the system is poor. The use of multiple antennas for wireless communication systems has gained overwhelming interest during the last two decades.Multiple Input Multiple Output( MIMO) Spatial diversity technique has been exploited in this paper to improve the performance in terahertz band. The results show that the Bit Error Rate( BER) is considerably improved for short distance( < 5 m) with MIMO. However,as the distance increases,the improvement in the error performance is not significant even with increase in the order of diversity. This is because,as distance increases,in some frequency bands the signal gets absorbed by water vapor and results in poor transmission. Adaptive modulation scheme is implemented to avoid these error prone frequencies. Adaptive modulation with receiver diversity is proposed in this work and has improved the BER performance of the channel for distance greater than 5 m.展开更多
This paper propose a novel noncoherent chaotic com- munication scheme named multiple-input multiple-output correlation-delay-shill- keying （MIMO-CDSK）. In this scheme, multiple antennas are employed to strengthen th...This paper propose a novel noncoherent chaotic com- munication scheme named multiple-input multiple-output correlation-delay-shill- keying （MIMO-CDSK）. In this scheme, multiple antennas are employed to strengthen the robustness in transmission, and to get more diversity gain. The bit error rate （BER） of the MIMO-CDSK is studied analytically in AWGN channel model and multipath fading channel model. The theory and simulation results show that, the performance gain can be obtained with multiple antennas allocated in the transmitter and receiver. Moreover, it is observed that MIMO-CDSK system can effectively reduce the multipath interference.展开更多
A least square （IS） parametric channel estimation method in broadband mt/ltiple input multiple output （MIMO） orthogonal frequency division multiplexing （OFDM） systems is proposed. The mean square error （MSE） p...A least square （IS） parametric channel estimation method in broadband mt/ltiple input multiple output （MIMO） orthogonal frequency division multiplexing （OFDM） systems is proposed. The mean square error （MSE） performance using optimal training pilots is also given, which proves the method can improve the estimation precision greatly in sparse channel.. Since such method needs the multi-path time delays information of the channel, the probabilistic data association （PDA） method is employed to estimate the time delay of each path. Simulation results show that both the bit error rate （BER） and the MSE performance of the proposed method are better than the traditional LS channel estimation method.展开更多
This paper presents the concepts of completely connected network,mean path length and cluster for analysis performance of wireless multihop network,where matrix are used to express topology of network and use a new al...This paper presents the concepts of completely connected network,mean path length and cluster for analysis performance of wireless multihop network,where matrix are used to express topology of network and use a new algorithm to compute the number of cluster in the network.Multiple-input/multiple-output(MIMO) communication promises performance enhancement over conventional single-input/single-output(SISO) technology for the same radiated power,if leveraged in multihop network,MIMO may be able to provide significant network performance improvement in network robustness and in power consumption,this paper analyzes three types of multihop networks employing SISO, MIMO with maximum ratio combining(MRC) and MIMO with maximum ratio transmission(MRT) as link model respectively,and get that using MIMO link model can increase robust,decrease mean path length by simulation.展开更多
A blind adaptive scheme is proposed for joint maximum likelihood （ML） channel estimation and data detection of singleinput multiple-output （SIMO） systems. The joint ML optimisation over channel and data is decompo...A blind adaptive scheme is proposed for joint maximum likelihood （ML） channel estimation and data detection of singleinput multiple-output （SIMO） systems. The joint ML optimisation over channel and data is decomposed into an iterative optimisation loop. An efficient global optimisation algorithm called the repeated weighted boosting search is employed at the upper level to optimally identify the unknown SIMO channel model, and the Viterbi algorithm is used at the lower level to produce the maximum likelihood sequence estimation of the unknown data sequence. A simulation example is used to demonstrate the effectiveness of this joint ML optimisation scheme for blind adaptive SIMO systems.展开更多
In this paper, we propose a downlink transmission and receiving scheme for interleave-division multiple access （IDMA） system based on time-division duplexing （TDD） mode and time-reversal （TR） technique. The prop...In this paper, we propose a downlink transmission and receiving scheme for interleave-division multiple access （IDMA） system based on time-division duplexing （TDD） mode and time-reversal （TR） technique. The proposed scheme uses the time-reversed version of the channel impulse responses （CIR） obtained from the transmitted signal at base uplink to pre-process the station. By exploiting the weak correlations of fading channels for different user ends （UE）, it is helpful to alleviate the multi-user interference （MUI） and co-channel interference （CCI）. Moreover, the application of the TR technique in a multiple input-single output （MISO） configuration can reduce the delay spread of the channel impulse response, and mitigate inter-symbol interference （ISI）. The UE can be simplified by canceling the iteration operation. Thus the data detection of the proposed scheme is rather simple as compared with the traditional IDMA, the complexity and computational load of UE is decreased substantially, and the proposed scheme provides a great deal of privacy and security to mobile users.展开更多
针对智能反射面(IRS, intelligent reflecting surface)辅助的多输入单输出(MISO, multiple input singleoutput)无线携能通信(SWIPT, simultaneous wireless information and power transfer)系统,考虑基站最大发射功率、IRS反射相移...针对智能反射面(IRS, intelligent reflecting surface)辅助的多输入单输出(MISO, multiple input singleoutput)无线携能通信(SWIPT, simultaneous wireless information and power transfer)系统,考虑基站最大发射功率、IRS反射相移矩阵的单位膜约束和能量接收器的最小能量约束,以最大化信息传输速率为目标,联合优化了基站处的波束成形向量和智能反射面的反射波束成形向量。为解决非凸优化问题,提出了一种基于深度强化学习的深度确定性策略梯度(DDPG, deep deterministic policy gradient)算法。仿真结果表明,DDPG算法的平均奖励与学习率有关,在选取合适的学习率的条件下,DDPG算法能获得与传统优化算法相近的平均互信息,但运行时间明显低于传统的非凸优化算法,即使增加天线数和反射单元数,DDPG算法依然可以在较短的时间内收敛。这说明DDPG算法能有效地提高计算效率,更适合实时性要求较高的通信业务。展开更多
近年来,电网换相换流器型高压直流输电(line commutated converter based on high voltage direct current,LCC-HVDC)系统的稳定性问题得到广泛关注,多位专家学者建议采用谐波状态空间(harmonic state space,HSS)等线性周期时变建模方...近年来,电网换相换流器型高压直流输电(line commutated converter based on high voltage direct current,LCC-HVDC)系统的稳定性问题得到广泛关注,多位专家学者建议采用谐波状态空间(harmonic state space,HSS)等线性周期时变建模方法对其分析。然而,HSS不可避免地提高了建模的复杂度与维数,在面对大规模交直流系统时具有局限性。同时,LCC-HVDC包含多类型谐波耦合,各部分耦合对稳定性的影响大小尚未得到充分论证。为此,文中以HSS为底层理论建立LCC-HVDC的耦合阻抗矩阵,揭示高压直流输电系统内部的谐波耦合机理。进一步,通过多频电路等效思想,提出三相系统多维阻抗的降维方法,将耦合阻抗矩阵无损降维成单入单出阻抗,以此分析不同次数的谐波耦合对阻抗特性与稳定性的影响。结果表明,考虑到13次谐波截断可以有效提升高压直流输电系统阻抗模型精度,但对稳定性分析结果的影响小于忽略工况变化、简化逆变侧带来的误差。展开更多
文摘Terahertz(THz) communication is being considered as a potential solution to mitigate the demand for high bandwidth. The characteristic of THz band is relatively different from present wireless channel and imposes technical challenges in the design and development of communication systems. Due to the high path loss in THz band,wireless THz communication can be used for relatively short distances. Even,for a distance of few meters( > 5 m),the absorption coefficient is very high and hence the performance of the system is poor. The use of multiple antennas for wireless communication systems has gained overwhelming interest during the last two decades.Multiple Input Multiple Output( MIMO) Spatial diversity technique has been exploited in this paper to improve the performance in terahertz band. The results show that the Bit Error Rate( BER) is considerably improved for short distance( < 5 m) with MIMO. However,as the distance increases,the improvement in the error performance is not significant even with increase in the order of diversity. This is because,as distance increases,in some frequency bands the signal gets absorbed by water vapor and results in poor transmission. Adaptive modulation scheme is implemented to avoid these error prone frequencies. Adaptive modulation with receiver diversity is proposed in this work and has improved the BER performance of the channel for distance greater than 5 m.
基金Supported by the National Natural Science Foundation of China(61373136,61401226,61304169)the Innovation Project for Graduate Education of Jiangsu Province(KYLX_0814)the Natural Science Foundation of Jiangsu Province(BK20130857)
文摘This paper propose a novel noncoherent chaotic com- munication scheme named multiple-input multiple-output correlation-delay-shill- keying （MIMO-CDSK）. In this scheme, multiple antennas are employed to strengthen the robustness in transmission, and to get more diversity gain. The bit error rate （BER） of the MIMO-CDSK is studied analytically in AWGN channel model and multipath fading channel model. The theory and simulation results show that, the performance gain can be obtained with multiple antennas allocated in the transmitter and receiver. Moreover, it is observed that MIMO-CDSK system can effectively reduce the multipath interference.
文摘A least square （IS） parametric channel estimation method in broadband mt/ltiple input multiple output （MIMO） orthogonal frequency division multiplexing （OFDM） systems is proposed. The mean square error （MSE） performance using optimal training pilots is also given, which proves the method can improve the estimation precision greatly in sparse channel.. Since such method needs the multi-path time delays information of the channel, the probabilistic data association （PDA） method is employed to estimate the time delay of each path. Simulation results show that both the bit error rate （BER） and the MSE performance of the proposed method are better than the traditional LS channel estimation method.
文摘This paper presents the concepts of completely connected network,mean path length and cluster for analysis performance of wireless multihop network,where matrix are used to express topology of network and use a new algorithm to compute the number of cluster in the network.Multiple-input/multiple-output(MIMO) communication promises performance enhancement over conventional single-input/single-output(SISO) technology for the same radiated power,if leveraged in multihop network,MIMO may be able to provide significant network performance improvement in network robustness and in power consumption,this paper analyzes three types of multihop networks employing SISO, MIMO with maximum ratio combining(MRC) and MIMO with maximum ratio transmission(MRT) as link model respectively,and get that using MIMO link model can increase robust,decrease mean path length by simulation.
文摘A blind adaptive scheme is proposed for joint maximum likelihood （ML） channel estimation and data detection of singleinput multiple-output （SIMO） systems. The joint ML optimisation over channel and data is decomposed into an iterative optimisation loop. An efficient global optimisation algorithm called the repeated weighted boosting search is employed at the upper level to optimally identify the unknown SIMO channel model, and the Viterbi algorithm is used at the lower level to produce the maximum likelihood sequence estimation of the unknown data sequence. A simulation example is used to demonstrate the effectiveness of this joint ML optimisation scheme for blind adaptive SIMO systems.
基金the Nature Science Founding of China under Grant. No. 60496313National Basic Research Program of China under Grant No. 2007CB310604.
文摘In this paper, we propose a downlink transmission and receiving scheme for interleave-division multiple access （IDMA） system based on time-division duplexing （TDD） mode and time-reversal （TR） technique. The proposed scheme uses the time-reversed version of the channel impulse responses （CIR） obtained from the transmitted signal at base uplink to pre-process the station. By exploiting the weak correlations of fading channels for different user ends （UE）, it is helpful to alleviate the multi-user interference （MUI） and co-channel interference （CCI）. Moreover, the application of the TR technique in a multiple input-single output （MISO） configuration can reduce the delay spread of the channel impulse response, and mitigate inter-symbol interference （ISI）. The UE can be simplified by canceling the iteration operation. Thus the data detection of the proposed scheme is rather simple as compared with the traditional IDMA, the complexity and computational load of UE is decreased substantially, and the proposed scheme provides a great deal of privacy and security to mobile users.
文摘针对智能反射面(IRS, intelligent reflecting surface)辅助的多输入单输出(MISO, multiple input singleoutput)无线携能通信(SWIPT, simultaneous wireless information and power transfer)系统,考虑基站最大发射功率、IRS反射相移矩阵的单位膜约束和能量接收器的最小能量约束,以最大化信息传输速率为目标,联合优化了基站处的波束成形向量和智能反射面的反射波束成形向量。为解决非凸优化问题,提出了一种基于深度强化学习的深度确定性策略梯度(DDPG, deep deterministic policy gradient)算法。仿真结果表明,DDPG算法的平均奖励与学习率有关,在选取合适的学习率的条件下,DDPG算法能获得与传统优化算法相近的平均互信息,但运行时间明显低于传统的非凸优化算法,即使增加天线数和反射单元数,DDPG算法依然可以在较短的时间内收敛。这说明DDPG算法能有效地提高计算效率,更适合实时性要求较高的通信业务。
文摘近年来,电网换相换流器型高压直流输电(line commutated converter based on high voltage direct current,LCC-HVDC)系统的稳定性问题得到广泛关注,多位专家学者建议采用谐波状态空间(harmonic state space,HSS)等线性周期时变建模方法对其分析。然而,HSS不可避免地提高了建模的复杂度与维数,在面对大规模交直流系统时具有局限性。同时,LCC-HVDC包含多类型谐波耦合,各部分耦合对稳定性的影响大小尚未得到充分论证。为此,文中以HSS为底层理论建立LCC-HVDC的耦合阻抗矩阵,揭示高压直流输电系统内部的谐波耦合机理。进一步,通过多频电路等效思想,提出三相系统多维阻抗的降维方法,将耦合阻抗矩阵无损降维成单入单出阻抗,以此分析不同次数的谐波耦合对阻抗特性与稳定性的影响。结果表明,考虑到13次谐波截断可以有效提升高压直流输电系统阻抗模型精度,但对稳定性分析结果的影响小于忽略工况变化、简化逆变侧带来的误差。
文摘现有工程运行数据显示,并网变流器(grid-connected converter,GCC)的动态特性与工作点密切相关。受新能源出力波动、负载投切等外部因素的影响,变流器工作点呈现随机时变特性。因此,分析整个工作区间中所有工作点的系统稳定性具有重要意义。传统阻抗/导纳分析方法可以有效分析GCC运行于特定工作点时的稳定性,但考虑系统所有可能工作点时则需重复分析,工作量大且难度较高。为解决这一难题,提出一种考虑工作点变量的多元建模方法。将工作点变量引入导纳模型,通过控制环路重构,建立GCC的多变量单输入单输出(single input single output,SISO)模型。所提模型直接包含工作点变量,因此可以有效分析变流器全工作区间动态特性。此外,综合考虑变流器最大传输限制和动态特性,提出一种基于安全运行域的稳定性分析方法,以实现多维工作区间中系统稳定性的直观表征。仿真和实验验证了所提多变量SISO模型和基于安全运行域的分析方法的正确性。所提模型和方法在分析电力电子装置运行极限、指导变流器设计和辅助功率器件发挥极限性能等工程场景中具有广泛应用潜力。
