共查询到19条相似文献,搜索用时 482 毫秒
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为克服正交频分复用(OFDM)系统中因时变多径衰落信道破坏子载波的正交性引起载波间干扰(ICI),从而导致系统性能下降的问题,提出了一种基于最小均方误差(MMSE)估计和迭代算法相结合的迭代干扰抵消算法.为了消除一般MMSE均衡方法将载波间干扰当作加性高斯白噪声(AWGN)所带来的误差,该算法先使用MMSE方法对传输信号进行初值估计,再通过迭代干扰抵消和MMSE均衡相结合,来消除由时变信道所带来的载波间干扰.多次仿真表明,在时变多径衰落信道中使用本算法能够有效地消除载波间干扰,使系统性能得到很好的改善. 相似文献
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针对分集合并通信系统在复杂度与性能之间一直存在矛盾的问题,提出了一种将切换检测合并(SEC)与最大比合并(MRC)相结合的新的混合合并方式,并对各分支为独立同分布(i.i.d.)的瑞利衰落情况进行了研究,给出了中断概率(OP)、平均输出信噪比(SNR)的闭合表达式,以及误码率(BER)的有限区间积分形式表达式。最后将这种SEC/MRC合并方式与MRC及广义选择合并(GSC)进行了比较,结果表明,SEC/MRC合并方式在减少信道接收机数量、降低系统复杂度的情况下,仍能达到很好的性能,具有良好的实际应用价值。 相似文献
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滤波器组多载波系统的干扰分析和性能验证 总被引:1,自引:0,他引:1
分析了多普勒频偏以及多径时延对滤波器组多载波(FBMC)系统的影响,给出了多普勒频偏以及多径时延造成干扰的闭合定量分析式,该分析式对正交频分复用(OFDM)系统同样适用,并据此对无线多径衰落信道场景中的FBMC系统与传统OFDM系统性能进行了对比.研究结果表明,FBMC系统对多普勒频偏的抵抗性优于OFDM系统,但是系统性能会随信道多径时延的增大而降低.在多径时延相对较小的快衰落信道中,符号间干扰并非影响系统性能的主要因素,FBMC系统可以利用简单的频域均衡获得足够好的性能,仿真结果验证了这一点. 相似文献
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针对正交频分复用(OFDM)系统中由于信道快时变导致的子载波间干扰(ICI),基于基扩展模型,提出了一种时变信道下OFDM系统联合迭代信道估计与符号检测算法.该算法将基于基扩展模型的最小均方误差信道估计算法与一种类似于串行干扰抵消的符号检测方式相结合,并利用插值和滤波过程进一步消除噪声影响,进而通过联合迭代获得较为精确的符号检测结果.同时,利用带状矩阵近似降低算法的计算复杂度,在复杂度与算法性能之间取得比较好的折中.理论分析和仿真结果表明,在快时变信道条件下,这种新的联合迭代信道估计与符号检测算法可有效地提高系统性能. 相似文献
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本文在涵盖了从弱湍流到强湍流的所有信道条件,能够表征现有大多数湍流信道的M分布模型下,采用QPSK调制方式研究了多跳相干OFDM FSO系统的性能。系统在中继辅助链路的发射机和接收机之间使用DF中继协议。考虑大气湍流、路径损耗以及瞄准误差对大气信道衰落模型的联合作用,分别推导出系统的中断概率和误符号率的Meijer G形式的闭合表达式。通过仿真分析了中继链路长度、中继节点数以及子载波个数等关键因素对系统的中断性能和误符号率性能的影响。本研究为中继系统的实际应用奠定了理论基础。 相似文献
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文章在分析无线激光通信(FSO)存在两种主要的大气信道问题的基础上,针对激光大气信道问题尤其是在复杂湍流环境下的频率选择性衰落问题和多径效应问题,提出了基于正交频分复用(OFDM)的湍流效应抑制方法,构建了FSO-OFDM系统,研究了该系统的基带模型以及信号的多载波调制与解调方法。分析了无线激光通信中存在复杂湍流环境下的大气信道问题,讨论了大气湍流影响下的平面波激光通信系统模型,建立了大气湍流影响下对数正态湍流通道的高斯光束空间光通信系统模型,推导了光波强度的概率密度函数,研究了利用信噪比概率密度函数分析各种大气湍流效应对系统性能影响的方法;设计了无线光通信系统的OFDM多载波调制方案,构建了FSO-OFDM系统基带模式模型,并基于该模型研究了其信号的调制与解调原理。最后,采用MATLAB编程实现FSO-OFDM系统,对多径干扰下的FSO通信系统进行仿真实验,进行了不同保护间隔下的误码率特性实验,验证了FSO-OFDM系统具有很强的抗多径干扰和频谱选择性衰落能力以及良好的BER性能,可有效解决码间干扰大、链路不可靠的问题,具有非常广泛的应用前景和使用价值。 相似文献
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H. Gharavi F. Chin K. Ban R. Wyatt-Millington 《Journal of research of the National Institute of Standards and Technology》2003,108(4):299-321
The cdma2000 system is an evolutionary enhancement of the IS-95 standards which support 3G services defined by the International Telecommunications Union (ITU). cdma2000 comes in two phases: 1XRTT and 3XRTT (1X and 3X indicates the number of 1.25 MHz wide radio carrier channels used and RTT stands for Radio Transmission Technology). The cdma2000 1XRTT, which operates within a 1.25 MHz bandwidth, can be utilized in existing IS-95 CDMA channels as it uses the same bandwidth, while 3XRTT requires the commitment of 5 MHz bandwidth to support higher data rates. This paper describes a software model implementation of the cdma2000 reverse link and its application for evaluating the effect of rake receiver design parameters on the system performance under various multipath fading conditions. The cdma2000 models were developed at the National Institute of Standards and Technology (NIST), using SPW (Signal Processing Worksystem) commercial software tools. The model has been developed in a generic manner that includes all the reverse link six radio configurations and their corresponding data rates, according to cdma2000 specifications. After briefly reviewing the traffic channel characteristics of the cdma2000 reverse link (subscriber to base station), the paper discusses the rake receiver implementation including an ideal rake receiver. It then evaluates the performance of each receiver for a Spreading Rate 3 (3XRTT) operation, which is considered as a true “3G” cdma2000 technology. These evaluations are based on the vehicular IMT-2000 (International Mobile Telecommunication 2000) channel model using the link budget defined in cdma2000 specifications for the reverse link. 相似文献
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文章提出了一种基于极坐标格式算法(Polar Format Algorithm,PFA)进行聚束多子阵合成孔径声呐成像的改进方法,建立了非“停-走-停”条件下的斜视成像模型,推导了信号由时域到波数域的解析表达式,给出了信号处理流程。该方法首先使用场景中心点的精确距离史对平台运动误差进行补偿,并通过极坐标算法处理得到粗聚焦的图像。其次,为了解决非场景中心点的残余空变相位误差的补偿问题,对粗聚焦图像进行分块自聚焦处理,使场景边缘点的聚焦效果得到改善。最后,经过子图拼接及几何校正后得到完整的精聚焦图像。仿真及分析结果表明,该方法提高了方位向性能指标,同时也能准确补偿平台运动误差,可以很好地应用于多子阵声呐成像。该方法在大运动误差、大斜视情况下仍具有较好的鲁棒性。 相似文献
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The extended particle filter (EPF) assisted by the Takagi-Sugeno (T-S) fuzzy logic adaptive system (FLAS) is used to design the ultra-tightly coupled GPS/INS (inertial navigation system) integrated navigation, which can maneuver the vehicle environment and the GPS outages scenario. The traditional integrated navigation designs adopt a loosely or tightly coupled architecture, for which the GPS receiver may lose the lock due to the interference/jamming scenarios, high dynamic environments, and the periods of partial GPS shading. An ultra-tight GPS/INS architecture involves the integration of I (in-phase) and Q (quadrature) components from the correlator of a GPS receiver with the INS data. The EPF is a particle filter (PF) which uses the extended Kalman filter (EKF) to generate the proposal distribution. The PF depends mostly on the number of particles in order to achieve a better performance during the high dynamic environments and GPS outages. The T-S FLAS is one of these approaches that can prevent the divergence problem of the filter when the precise knowledge on the system models is not available. The results show that the proposed fuzzy adaptive EPF (FAEPF) can effectively improve the navigation estimation accuracy and reduce the computational load as compared with the EPF and the unscented Kalman filter (UKF). 相似文献
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This paper presents the exact average bit error rate (BER) analysis of the free-space optical system employing subcarrier intensity modulation (SIM) with Gray-coded quadrature amplitude modulation (QAM). The intensity fluctuations of the received optical signal are caused by the path loss, atmospheric turbulence and pointing errors. The exact closed-form analytical expressions for the average BER are derived assuming the SIM-QAM with arbitrary constellation size in the presence of the Gamma–Gamma scintillation. The simple approximate average BER expressions are also provided, considering only the dominant term in the finite summations of obtained expressions. Derived expressions are reduced to the special case when optical signal transmission is affected only by the atmospheric turbulence. Numerical results are presented in order to illustrate usefulness of the derived expressions and also to give insights into the effects of different modulation, channel and receiver parameters on the average BER performance. The results show that the misalignment between the transmitter laser and receiver detector has the strong effect on the average BER value, especially in the range of the high values of the average electrical signal-to-noise ratio. 相似文献
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针对传统水声滤波器组多载波(Filter Bank Multi-Carrier,FBMC)通信接收端需经过信道估计和均衡才可恢复出发送符号,系统复杂度高且信道估计精度不佳等问题。文章将深度神经网络融入到水声多载波通信当中,提出一种基于深度神经网络的水声FBMC信号检测方法。在训练阶段通过大量的数据迭代、调试超参数和优化算法来改善深度神经网络参数,使其具有预期的估计效果。利用训练完成的深度神经网络模型取代传统FBMC通信系统接收端的信道估计、均衡等模块,自适应地学习水声信道状态信息,同时避免了固有的虚部干扰影响。在测试阶段直接将频域序列作为网络的输入来预测发送的二进制序列,仿真结果表明所提出的基于深度神经网络的FBMC信号检测方法相比传统信道估计算法有更好的误码率性能。 相似文献
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带有高压贮液器的热泵系统不同充灌量下的实验研究 总被引:1,自引:0,他引:1
高压贮液器是制冷、空调、热泵系统中的常用部件,但其对系统性能的影响在相关系统性能分析时却常被忽视。通过实验讨论了在充灌量过少、适量、过量的情况下,高压贮液器对系统工况和性能的影响与制约,并给出了充灌量过少、适量、过量的简易判别标准。 相似文献
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滤波器相位的非线性引起的信号失真是超短基线接收机系统中必须要解决的问题之一。采用常规滤波器与全通网络级联的方法设计了一种相位均衡器,解决了仅使用常规滤波器带来的非线性相位问题,使超短基线接收机在带宽内保持线性相位。给出了全通网络的原理、电路结构推导,分析了该网络中各参量对相位的影响。在设计实例中,相位均衡技术应用到实际硬件电路中进行测试,并结合试验数据及仿真结果对系统的性能进行评估。测试结果证明了相位均衡器可以实现相位的均衡校正功能,在水声接收机领域中有良好的应用前景。 相似文献
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Aasif Bashir Dar 《Journal of Modern Optics》2017,64(6):555-566
Various dispersion compensation units are presented and evaluated in this paper. These dispersion compensation units include dispersion compensation fiber (DCF), DCF merged with fiber Bragg grating (FBG) (joint technique), and linear, square root, and cube root chirped tanh apodized FBG. For the performance evaluation 10 Gb/s NRZ transmission system over 100-km-long single-mode fiber is used. The three chirped FBGs are optimized individually to yield pulse width reduction percentage (PWRP) of 86.66, 79.96, 62.42% for linear, square root, and cube root, respectively. The DCF and Joint technique both provide a remarkable PWRP of 94.45 and 96.96%, respectively. The performance of optimized linear chirped tanh apodized FBG and DCF is compared for long-haul transmission system on the basis of quality factor of received signal. For both the systems maximum transmission distance is calculated such that quality factor is ≥ 6 at the receiver and result shows that performance of FBG is comparable to that of DCF with advantages of very low cost, small size and reduced nonlinear effects. 相似文献