基于MUSIC和LMS算法的智能天线设计

基于来渡方向估计和自适应波束成形的智能天线系统,用多重信号分类(MUSIC)算法实现来波方向估计,辨识天线阵列上接收信号的各个方向,使用最小均方误差(LUS)的自适应算法控制天线的主辩方向,实现对期望信号的跟踪,同时实现对干扰信号的零陷处理.文中使用Matlab编程进行计算机仿真,通过仿真结果,MUSIC算法可以识别天线接收端的信号的入射方向,LMS算法可以实现对干扰信号的抑制.     

一种智能天线降维频域波束形成算法的研究

本文提出一种智能天线降维的频域自适应波束形成（RFD—ABF）算法,该算法先对接收信号进行FFT,然后再带通滤波,最后通过LMS算法实现了频域的自适应波束形成。此算法可以有效降低信号的维数,消除干扰信号,大大降低计算量和存储量,通过对此算法收敛速度和有效抑制干扰的仿真,验证了智能天线降维频域波束形成算法的可行性,为智能天线技术在第三代移动通信系统应用提供理论基础。     

TD-SCDMA系统中智能天线的重复迭代自适应算法

提出一种用于TD-SCDMA系统的重复迭代自适应智能天线算法。通过在自适应算法中把阵列输入信号和作为参考信号的训练序列重复使用,可以在短训练序列情况下实现较好的收敛,提高通信系统的传输效率。对LMS算法中全训练序列重复迭代和滑动窗口重复迭代算法进行了仿真,结果表明,在有限训练序列时本算法比传统LMS算法更好地逼近最佳解。     

WCDMA-TDD中的重复迭代自适应智能天线算法

提出一种用于WCDMA-TDD系统的重复迭代自适应智能天线算法.通过在自适应算法中把阵列输入信号和作为参考信号的训练序列重复使用,可以在短训练序列情况下实现较好的收敛,提高通信系统的传输效率.对LMS算法中全训练序列重复迭代和滑动窗口重复迭代算法进行了仿真,结果表明,在有限训练序列时该算法比传统LMS算法更好地逼近最佳解.     

一种基于自适应阵列天线的波束赋形算法

自适应阵列天线中的数字波束赋形(DBF)技术是智能天线数字信号处理部分的核心.提出了一种可用于自适应阵列波束赋形的SMI-LMS算法--由SMI(采样协方差矩阵求逆)算法决定LMS(最小均方)算法的初始权向量.该算法充分结合了SMI算法收敛速度快和LMS算法稳态误差小的优点,能在较强干扰环境下,确保权向量的快速收敛和跟踪速度.与传统的LMS算法相比,SMI-LMS算法具有良好的收敛性能、较快的跟踪速度和较小的输出误差,并可以有效改善自适应方向图的副瓣性能.仿真结果验证了该结论.     

两种新的抑制高频雷达中Es层干扰的自适应算法

提出了两种新的抑制Es层杂波的自适应对消算法,分别是频域瞬时值LMS算法和归一化频域瞬时值LMS算法。频域瞬时值LMS算法是利用辅助天线输出的Es层杂波瞬时值来估计主天线当前输出中的Es层杂波成分,可以更大程度上抑制Es层杂波。而归一化频域瞬时值LMS算法则是在频域瞬时值LMS算法的基础上增加归一化的过程,可以大大缩短自适应过程的收敛时间。     

基于LS-LMS的智能天线自适应干扰抑制方法

针对基于训练序列的智能天线自适应干扰抑制系统,提出了一种最小二乘(Least squares,LS)-最小均方(Least mean squares,LMS)智能天线自适应干扰抑制方法,该方法首先利用小快拍数LS方法为LMS方法提供初始加权矢量,然后用LMS算法更新加权矢量.对LS、LMS和LS-LMS三种算法复杂度分析比较得知新方法的计算量较小,在快拍数较大或阵元与快拍数均较大时都能有效地提高计算效率.仿真实验表明,新方法性能优于LMS算法,具有较快的收敛速度,且收敛速度与干扰环境无关.     

TD-SCDMA系统中一种软件集成智能天线算法

给出了一种采用信干噪比准则的、集成了预多波束天线与LMS自适应天线的软件天线方案,该方案采用开关合并方法,把软件天线输出接到最大输出信噪比的算法输出,实现算法分集.在TD-SCDMA动态模型上对提出的方法进行了仿真,结果表明,采用集成软件天线方案的误码率性能要优于单纯的预多波束天线或LMS自适应智能天线.仿真过程考虑了用户来波方向和用户到基站距离的动态变化,以及功率控制算法和系统同步过程的影响.     

基于LMS算法的智能天线自适应波束形成研究

自适应波束形成是智能天线的核心技术,其主要思想是利用自适应算法调整阵列的权向量,将各阵元接收到的信号进行加权求和,把天线阵列形成的波束"导向"到一个方向上,使期望用户信号方向得到最大的增益,并相应地使干扰信号方向得到较低的增益,从而提高系统的性能。本文对智能天线中的自适应波束形成进行研究,运用MATLAB软件对固定步长和变步长LMS算法进行计算机仿真实验。仿真结果表明,基于LMS算法的自适应波束形成器能够形成符合要求的波束图,变步长的LMS算法均方误差收敛效果较好,收敛速度更快,具有较强的实用性。     

智能天线在多径信道中的性能仿真与分析

首先讨论了自适应阵列天线算法原理,然后通过对采用LMS算法的智能天线在多径信道中抗多径干扰性能的仿真,进一步分析了多径干扰对智能天线性能的影响。结果表明,智能天线阵列的抗多径干扰性能受信号空间分布、信号幅度等因素的影响。     

MBER Space-Time Decision Feedback Equalization Assisted Multiuser Detection for Multiple Antenna Aided SDMA Systems

This paper proposes a space-time decision feedback equalization (ST-DFE) assisted multiuser detection (MUD) scheme for multiple receiver antenna aided space division multiple access systems. A minimum bit error rate (MBER) design is invoked for the MUD, which is shown to be capable of improving the achievable bit error rate performance and enhancing the attainable system capacity over that of the standard minimum mean square error (MMSE) design. An adaptive implementation of the MBER ST-DFE assisted MUD is proposed using a stochastic gradient-based least bit error rate algorithm, which is demonstrated to consistently outperform the classical least mean square (LMS) algorithm, while achieving a lower computational complexity than the LMS algorithm for the binary signalling scheme. Our simulation results demonstrate that the MBER ST-DFE assisted MUD is more robust to channel estimation errors as well as to potential error propagation imposed by decision feedback errors, compared to the MMSE ST-DFE assisted MUD.     

Mitigation of Multipath Effects Based on a Robust Fractional Order Bidirectional Least Mean Square (FOBLMS) Beamforming Algorithm for GPS Receivers

Consideration on positioning and location services among the public has been increasing in the recent years with their applications in most of the anticipating milieus such as automobile navigation system etc. This insists for a development of high recitation global navigation satellite system such as global positioning system (GPS). Multipath effects, interference, signal jamming etc. are the major sources of error influencing the performance of the GPS receiver. Literature presents many of the multipath mitigation techniques. Among them, adaptive processing technology based beamforming algorithms appears a viable solution for multipath mitigation. The least mean square (LMS) beamforming algorithms were sensitive to dynamic environments thus affecting the accuracy of GPS. In this paper, an adaptive beamforming algorithm called fractional order bidirectional least mean square (FOBLMS) algorithm is proposed to mitigate the multipath effects and to conceal the jammer signal in a GPS receiver. The FOBLMS is an integration of the fractional calculus and bidirectional least mean square algorithm. The effectiveness of the proposed algorithm is validated using the bit error rate and experimentation gain results over the existing beamforming algorithms. Experimental results demonstrated that the performance of the proposed beamforming algorithm is better than LMS algorithm with maximal relative antenna gain of 28.92 dB, 32.84 dB for two and four element antenna arrays at ??60° and 10°, direction of arrivals respectively. The outcome of this work would be useful for developing a robust technique for multipath mitigation in GPS receivers.

     

Performance analysis of coded space‐time adaptive detection in DS/CDMA systems over Rayleigh fading channels

In this paper, we study the use of channel coding in a direct‐sequence code‐division multiple‐access (DS‐CDMA) system that employs space‐time adaptive minimum‐mean square‐error (MMSE) interference suppression over Rayleigh fading channels. It is shown that the employment of adaptive antenna arrays at the receiver can assist in attenuating multiuser interference and at the same time speeds‐up the convergence rate of the adaptive receiver. In this work, we assess the accuracy of the theoretical results developed for the uncoded and convolutionally coded space‐time multiuser detector when applied to the adaptive case. It is found that the use of antenna arrays brings the receiver performance very close to its multiuser counterpart. Using performance error bounds, we show that a user‐capacity gain of approximately 200% can easily be achieved for the space‐time adaptive detector when used with a rate 1/2 convolutional code (CC) and a practical channel interleaver. This capacity gain is only 10% less than the gain achieved for the more complicated multiuser‐based receiver. Finally, we perform a comparison between convolutional and turbo coding where we find that the latter outperforms the former at all practical bit‐error rates (BER). Copyright © 2006 John Wiley & Sons, Ltd.     

Adaptive DFE Multiuser Receiver for CDMA Systems using Two-Step LMS-Type Algorithm: An Equalization Approach

This paper presents an adaptive decision feedback equalizer (DFE) based multiuser receiver for code division multiple access (CDMA) systems over smoothly time-varying multipath fading channels using the two-step LMS-type algorithm. The frequency-selective fading channel is modeled as a tapped-delay-line filter with smoothly time-varying Rayleigh-distributed tap coefficients. The receiver uses an adaptive minimum mean square error (MMSE) multiuser channel estimator based on the reduced Kalman least mean square (RK-LMS) algorithm to predict these tap coefficients (Kohli and Mehra, Wireless Personal Communication 46:507–521, 2008). We propose the design of adaptive MMSE feedforward and feedback filters by using the estimated channel response. Unlike the previously available Kalman filtering algorithm based approach (Chen and Chen, IEEE Transactions on Signal Processing 49:1523–1532, 2001), the incorporation of RK-LMS algorithm reduces the computational complexity of multiuser receiver. The computer simulation results are presented to show the substantial improvement in its bit error rate performance over the conventional LMS algorithm based receiver. It can be inferred that the proposed multiuser receiver proves to be robust against the nonstationarity introduced due to channel variations, and it is also beneficial for the multiuser interference cancellation and data detection in CDMA systems.     

WCDMA系统中空时2D-RAKE接收机性能分析

分析了在WCDMA系统的基站中采用含智能天线的空时2D-RAKE接收机的结构和性能.在建立了WCDMA信道、信号模型的基础上,给出了输出误码率的表达式.提出了一种新的利用两个连续时隙的导频符号估计出的信道参数进行加权最小二乘意义下二次曲线内插的信道参数估计方法(WLS).仿真结果表明:WLS算法能很好地跟踪多径衰落信道的变化,提出的空时2D RAKE接收机的误码性能大大改善,而且在移动台移动速度较高时仍能正常工作.     

Adaptive Minimum Symbol Error Rate Beamforming Assisted Detection for Quadrature Amplitude Modulation

We consider beamforming assisted detection for multiple antenna aided multiuser systems that employ the bandwidth efficient quadrature amplitude modulation scheme. A minimum symbol error rate (MSER) design is proposed for the beamforming assisted receiver, and it is shown that this MSER design provides significant performance enhancement, in terms of achievable symbol error rate, over the standard minimum mean square error (MMSE) design. A sample-by-sample adaptive algorithm, referred to as the least symbol error rate, is derived for adaptive implementation of the MSER beamforming solution. The proposed adaptive MSER scheme is evaluated in simulation using Rayleigh fading channels, in comparison with the adaptive MMSE benchmarker.     

A Stabilized Multichannel Fast RLS Algorithm for Adaptive Transmultiplexer Receivers

The transmultiplexer (TMUX) system has been studied for its application to multicarrier communications. The channel impairments including noise, interference, and distortion draw the need for adaptive reconstruction at the TMUX receiver. Among possible adaptive methods, the recursive least squares (RLS) algorithm is appealing for its good convergence rate and steady state performance. However, higher computational complexity due to the matrix operation is the drawback of utilizing RLS. A fast RLS algorithm used for adaptive signal reconstruction in the TMUX system is developed in this paper. By using the polyphase decomposition method, the adaptive receiver in the TMUX system can be formulated as a multichannel filtering problem, and the fast algorithm is obtained through the block Toeplitz matrix structure of received signals. In addition to the reduction of complexity, simulation results show that the adaptive TMUX receiver has a convergence rate close to that of the standard RLS algorithm and the performance approaches the minimum mean square error solution.     

Adaptive parallel interference cancellation for CDMA systems—A weight selection and filtering scheme

Parallel interference cancellation (PIC) is a well-known multiuser detection algorithm in direct-sequence code-division multiple-access (DS-CDMA) systems. It is typically implemented with a multi-stage architecture. One problem associated with the PIC is that unreliable interference cancellation may occur in the early stages and the system performance may be degraded. Thus, the partial PIC detector was developed to control the cancellation level by use of interference cancellation factors. Partial PIC can be implemented with an adaptive form, in which optimal weights are derived using the least mean square (LMS) algorithm. In this paper, we propose an algorithm improving the conventional adaptive partial PIC. The main idea is to reduce the number of active weights in the LMS algorithm, and to perform weight post-filtering such that the resultant excess mean square error can be reduced. We also analyze the performance of the proposed algorithm and derive the bit error rate of the second stage output. Simulation results verify that the proposed algorithm outperforms the conventional partial PIC, and derived analytical results are accurate.     

可见光通信中自适应空间调制研究

针对可见光通信中MIMO系统的信道干扰问题,采用自适应空间调制技术,即发送端任一时刻只有一个发光LED处于工作状态来传输数据,接收端采用最大似然算法恢复原始信号,同时为优化误码率性能,加入自适应Fischer算法,发送端能够根据信道状态信息对各个子载波分配不同的比特,降低误码率.实验结果表明:在传输速率和发送功率一定的情况下,结合Fischer算法的空间调制技术能有效降低系统误码率,改善可见光通信系统的通信性能.     

Performance evaluation of LMS-based adaptive suppression schemes in asynchronous CDMA

The objective of this paper is to evaluate the bit-error-rate performance of various adaptive structures in combating multi-user interference in an asynchronous code division multiple access (CDMA) system. In particular, two adaptive schemes, known as the N-tap filter and D-tap cyclical shifted bank filter, are considered. The least mean square (LMS) and predictive LMS (PLMS) algorithms are employed for the adaptation of tap weights. An analytical expression is developed for the numerical evaluation of the bit error probability. In addition, the bit error rate performances of the adaptive schemes are compared with those of the matched filter receiver. Results attest to the pratical usefulness of the LMS-based adaptive suppression schemes in combating multi-user interference in an asynchronous CDMA system.