Experiments on coherent adaptive antenna array diversity forwideband DS-CDMA mobile radio

In wideband direct sequence code division multiple access (W-CDMA), employing an adaptive antenna array is a very promising technique to reduce severe multiple access interference (MAI) from high rate users. A four-antenna pilot symbol-assisted coherent adaptive antenna array diversity (PSA-CAAAD) receiver comprising an adaptive antenna array based on a minimum mean squared error (MMSE) criterion and a RAKE combiner is implemented in preliminary laboratory and field experiments. There are two important design concepts of the PSA-CAAAD receiver. The first is that the adaptive antenna array forms an antenna beam for each resolved propagation path and tracks only slow changes in the directions of arrival (DOAs) and average powers of the desired and interfering user signals. The second is that the RAKE combiner tracks the instantaneous changes in channel conditions and coherently combines the signals of the desired user propagating along the resolved paths to maximize the instantaneous signal-to-interference plus background noise power ratio (SINR). This paper presents, both by laboratory and field experiments, the effectiveness of PSA-CAAAD receiver as a powerful means to reduce severe MAI from high rate users, and that it is more effective than using a space diversity receiver with the same number of antennas in the W-CDMA reverse link     

基于恒模算法的天线阵多载波码分多址系统空频盲多用户检测

多载波码分多址(MC-CDMA)可以对抗频率选择性,天线阵可以提高系统的性能.本文首先提出一种基于恒模算法的天线阵MC-CDMA系统空频盲自适应多用户检测,该算法具有MN维权向量,结构相对复杂;进而提出一种空频联合约束恒模算法的盲自适应多用户检测,可以保证算法具有鲁棒性,收敛于期望用户,该算法具有M N权向量,结构简单.仿真表明,本文提出的算法比传统的基于波束成形的两步算法具有更好的误码率性能.     

满足高精度测量的GNSS自适干扰抑制算法

日益复杂的电磁环境严重干扰了全球卫星导航系统（Global Navigation Satellite System,GNSS）的正常有效运行.多天线空域自适应处理能够有效抑制电磁干扰,但是空域自适应处理算法可能会引入卫星信号载波相位误差.此外,多天线组成的阵列本身存在各种不理想因素也会引入误差,这些对高精度测量系统来说是不可容忍的.为此,本文首先分析了GNSS中常用的空域自适应处理算法在抑制干扰的同时对载波相位测量的影响,在此基础上提出了一种不需要阵列流形信息的盲波束形成算法——二次解重扩算法.其核心思想是在解重扩（De-spread Re-spread,DR）算法的基础上增加频率精估计环节,并根据精估后的载波频率重新构造本地参考信号与接收数据进行相关,从而最小化波束形成权矢量与卫星信号的导向矢量之间的误差,减小了空域抗干扰对卫星信号载波相位的影响.     

A Multiuser Detection Receiver Using Blind Antenna Array and Adaptive Parallel Interference Cancellation

In this paper, the problem of multiuser detection for synchronous code division multiple access systems in both additive white Gaussian noise and multipath channels is addressed. A new multiuser detection receiver that uses an adaptive blind array along with an adaptive parallel interference canceler is proposed. The replacement of a conventional antenna array with a two-dimensional RAKE receiver is also considered for frequency selective Rayleigh fading channels. By using a constrained optimization criterion along with the gradient-projection algorithm, a blind algorithm for the adaptation of the array response vector is proposed. The new algorithm is superior to a few typical blind algorithms in the literature in terms of both performance and computational complexity. The proposed receiver has the ability to cancel very strong multiple access interference coming from the same direction as the desired signal. Simulation results are presented to show the excellent performance of the proposed combination scheme in comparison to that of using either a multiuser detection or adaptive antenna arrays in a severe near-far situation.     

基于SMI－CMA联合自适应算法的性能分析

恒模算法(CMA)被广泛地应用到盲自适应波束形成中，除了传输信号波形具有恒定的包络外．CMA不需要先验知识。基于SMI—CMA算法的恒模(CM)阵列级联的结构，由SMI算法决定CMA的初始权向量．系统可以分离多个同信道信源，在干扰信号较强时，仍有稳定的SINR输出，具有较好的收敛速度。仿真结果也证明了SMI—CMA算法具有较强的稳健型和较快的收敛速度。     

An adaptive array for interference rejection

An adaptive array that rejects undesired or interfering signals is presented. The array pattern is controlled by an adaptive feedback system based on a steepest descent minimization of mean-square error. Error is defined as the difference between the array output and a locally generated reference signal. Minimization of mean-square error is closely related to maximization of signal-to-noise ratio (SNR). A two-element adaptive array has been built, and its experimental performance is discussed. Typical patterns for various desired and interfering signals are shown, as well as measured transient response. Finally, some experiments showing the array behavior with modulated signals are described. The results show that such an antenna system is capable of automatically rejecting interfering signals, subject only to certain basic constraints. No a priori information about the angles of arrival of the signals is required, Detailed knowledge of the waveforms of the desired and interfering signals is also not needed, although the spectral characteristics of the desired signal must be known.     

Blind space-time multiuser channel estimation in time-varying DS-CDMA systems

A multistep linear prediction (MSLP) approach is presented for blind channel estimation for short-code direct sequence code division multiple access signals in time-varying multipath channels using a receiver antenna array. The time-varying channel is assumed to be described by a complex exponential basis expansion model. First, a recently proposed MSLP approach to blind channel estimation for time-varying single-input multiple-output (SIMO) systems is extended to time-varying multiple-input multiple-output (MIMO) systems to define a "signal" subspace. Second, the knowledge of the spreading code of a desired user is exploited in conjunction with the signal subspace to estimate the time-varying channel of the desired user up to an unknown time-invariant scale factor. Equalization/detection for the desired user can be then carried out if the information sequence is differentially encoded/decoded. Sufficient conditions for channel identifiability are investigated. Three illustrative simulation examples are provided.     

Subspace blind adaptive detection for multiuser CDMA

Direct adaptive realizations of the linear minimum mean-square error (MMSE) receiver for direct-sequence code-division multiple access possess the attractive feature of not requiring any explicit information of interference parameters such as timing, amplitudes, or spreading sequences; however, they need a training sequence for the desired user. Previously, a new blind adaptive receiver was proposed based on an anchored least mean-squared (LMS) algorithm that requires only the spreading code and symbol timing of the desired user but obviates the need for a training sequence. In this work, it is analytically demonstrated that the blind LMS algorithm always provides (nominally) faster convergence than the training driven LMS-MMSE receiver of but at the cost of increased tap-weight fluctuations or misadjustment. Second, the property that the optimal MMSE or minimum-output energy filter coefficients lies in the signal subspace is exploited to propose a new efficient blind adaptive receiver requiring fewer adaptive coefficients. Improved detector characteristics (superior convergence rates and steady-state signal-to-interference-plus-noise ratios) is indicated by analysis and supported by simulation     

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.     

A Blind Adaptive QR-Based Lattice Multi-Channel Filter for Cellular Base-Station TDMA Transceivers with Antenna Arrays

A new adaptive algorithm for blind interference rejection and multipath mitigation is studied and applied to antenna array processing in TDMA cellular communication systems. It is shown how the estimation of multiple signals from different sources by means of a multi-sensor receiver can be formulated as a multi-channel deconvolution problem. The proposed method is based on High-Order Statistics (HOS) processing of the baseband vector samples at the antenna array output. The similarity between the cumulant-based solution and the standard multi-variable Least Squares solution is exploited to derive an efficient adaptive algorithm based on the vector lattice architecture. The algorithm is numerically stable, considerably less complex than other existing multi-channel methods using HOS processing and exhibits rapid convergence with respect to blind array processing algorithms using simple gradient-based minimization procedures.     

Blind multiuser detection: a subspace approach

A new multiuser detection scheme based on signal subspace estimation is proposed. It is shown that under this scheme, both the decorrelating detector and the linear minimum-mean-square-error (MMSE) detector can be obtained blindly, i.e., they can be estimated from the received signal with the prior knowledge of only the signature waveform and timing of the user of interest. The consistency and asymptotic variance of the estimates of the two linear detectors are examined. A blind adaptive implementation based on a signal subspace tracking algorithm is also developed. It is seen that compared with the previous minimum-output-energy blind adaptive multiuser detector, the proposed subspace-based blind adaptive detector offers lower computational complexity, better performance, and robustness against signature waveform mismatch. Two extensions are made within the framework of signal subspace estimation. First, a blind adaptive method is developed for estimating the effective user signature waveform in the multipath channel. Secondly, a multiuser detection scheme using spatial diversity in the form of an antenna array is considered. A blind adaptive technique for estimating the array response for diversity combining is proposed. It is seen that under the proposed subspace approach, blind adaptive channel estimation and blind adaptive array response estimation can be integrated with blind adaptive multiuser detection, with little attendant increase in complexity     

Blind adaptation of antenna arrays using a simple algorithm basedon small frequency offsets

With the development of wireless and personal communication systems, there is considerable interest in using antenna array technology to improve the system capacity in both present and future generation wireless systems. A novel and simple algorithm is proposed for blind adaptive extraction of a binary phase-shift keying (BPSK) signal in the presence of interference by cyclostationary signal processing using an antenna array. The algorithm operates in an interference-limited system in which the desired and interfering signals have identical symbol rates, but are modulated on slightly different carrier frequencies. Compared to existing blind algorithms which also exploit the cyclostationarity of the received signal, the new algorithm provides a simpler and faster converging means to estimate the channel phase for diversity combining. Analytical and simulation results are presented and performances are compared with direct matrix inversion (DMI) and existing blind algorithms. Based on the proposed algorithm and the result obtained by Gardner, Schell and Murphy (1992), a time-division multiple-access (TDMA) system with the new channel assignment scheme called cyclic TDMA (CTDMA) is proposed. The simulation results also show that the proposed algorithm is relatively simple and very promising in applications to indoor wireless communication where interference rejection and increased spectrum efficiency are the objectives. Analysis and simulation results are presented to confirm the interference rejection capabilities. The robustness of existing and proposed algorithms to the perturbation of cyclostationarity is also discussed     

Experimental investigations of a new adaptive dual-antenna array for handset applications

This paper presents the design and implementation of a new adaptive dual-antenna array for mitigation of both interference and multipath effects in digital mobile communications at the handset level. This proposed system employs a nonlinear adaptive algorithm in the front end of the receiver to enhance the transmission quality in confined areas. The enhancement is blind since no priori knowledge of spatial signatures or training sequences is required. Furthermore, to obtain a compact antenna array system, a miniaturized shorting postmicrostrip antenna that operates in the 1.9 GHz PCS band is used as a radiating element. Using this microstrip antenna, a new experimental adaptive dual-antenna array prototype was designed and implemented. To examine the expected performance of this approach, experimental measurements were carried out and the measured performances indicate that gain improvement of 7 dB can be achieved by using this approach.     

Adaptive array processing for multipath fading mitigation viaexploitation of filter banks

We propose subband adaptive array processing for mitigation of both intersymbol interference (ISI) and cochannel interference (CCI) in digital mobile communications. Subband adaptive array processing employs filter banks in a front end to an adaptive array receiver. By decomposing the signals into a set of subband signals, the analysis filters enhance the correlation of multipath rays in each subband. This enhancement is blind in the sense that no a priori knowledge of the temporal characteristics or spatial signatures of arriving signals is required. With the increased coherence, the desired signal can be effectively equalized by subsequent spatial processing. Further, the CCI signals and their multipaths can be suppressed with fewer degrees of freedom. The effects of quadrature mirror filter and discrete Fourier transform filter banks on multipath correlation are delineated     

衰落信道中的DS/CDMA系统盲差分自适应接收机

在本文中，我们针对标准MMSE自适应接收机在频率非选择性衰落信道中的相位滑动和失锁问题，提出了一种无需进行训练和信道参数估计的盲差分自适应接收机。为自适应地实现该接收机，我们同时提出了一种基于正交分解的盲平均随机梯度（Orthogonal Decomposition-based Blind Aver-aged stochastic Gradient，简称ODBAG）算法。仿真结果表明，这种以ODBAG算法实现的盲差分自适应接收机在瑞利（Rayleigh）衰落信道中，误码率性能比传统匹配滤波器（Matched Filter，简写为MF）接收机有显著的提高，并接近改进的MMSE自适应接收机的性能。     

Synchronization and packet separation in wireless ad hoc networks by known modulus algorithms

In mobile asynchronous ad hoc networks, multiple users may transmit packets at the same time. If a collision occurs, then in current systems both packets are lost and need to be retransmitted, reducing the overall throughput. To mitigate this, we consider to extend the receiver with a small antenna array, so that it can suppress interfering signals. To characterize the signal of interest, we propose to modulate it at the symbol rate by a known amplitude variation. This allows the corresponding multichannel receiver to estimate the beamformer weights that will suppress the interfering sources. We introduce "known modulus algorithms" to achieve this. We also derive synchronization algorithms to estimate the offset of the desired packet in an observation window, among interfering data packets. The algorithms are illustrated via simulations.     

Blind adaptive multiuser detection for DS/SSMA communications withgeneralized random spreading

A new spreading scheme and an accompanying blind adaptive receiver structure are proposed for direct-sequence spread-spectrum multiple-access communications in a slowly-varying, frequency-selective fading channel. Each user's spreading sequence is given by the Kronecker product of a long-period pseudonoise (PN) sequence, which is accurately modeled by a random sequence, and a short-length deterministic signature code. This spreading scheme bridges the gap between pure PN spreading and pure short-code spreading schemes. It is shown that with this spreading scheme, the channel response to the desired signal component is easily estimated without relying on the spectral decomposition of the signal correlation matrix. With the estimate of the channel response, the receiver suppresses interference based on the maximum signal-to-interference ratio criterion. The blind adaptive receiver requires only coarse timing information and a priori knowledge of the desired user's PN sequence for adaptation. Numerical results show that the adaptive receiver significantly suppresses interference by successfully estimating the channel response and the interference statistics with a low computational complexity. An extension to spatio-temporal processing using an array antenna is also discussed     

An efficient code-timing estimator for receiver diversity DS-CDMAsystems

We propose an efficient algorithm for estimating the code timing of direct-sequence code-division multiple-access (DS-CDMA) systems that consist of an arbitrary antenna array at the receiver and work in a flat-fading and near-far environment. The algorithm is an asymptotic (for large number of data samples) maximum-likelihood (ML) estimator that is derived by modeling the known training sequence as the desired signal and all other signals including the interfering signals and the additive noise as unknown colored Gaussian noise. The algorithm does not require the search over a parameter space and the code timing is obtained by rooting a second-order polynomial, which is computationally very efficient. Simulation results show that the algorithm is quite robust against the near-far problem and channel fading. It requires a shorter training sequence than the single-antenna-based estimators     

基于DOA估计的RLS-CMA算法

恒模算法被广泛地应用到盲自适应波束形成中,除了传输信号波形具有恒定的包络外,恒模算法不需要先验知识。提出一种基于来波方向估计的递推最小二乘恒模算法,基于恒模阵列级联的结构,由递推最小二乘算法决定恒模的初始权向量,同时通过对权向量多项式求根获得下一级的初始权向量,再利用最小二乘恒模迭代几步获得准确的结果。系统可以分离多个同信道信源,在干扰信号较强时,仍有稳定的信干比输出,并对阵列幅相差不敏感。计算机仿真证明了算法的正确性和有效性。     

Performance Analysis of Multicarrier DS-CDMA with Antenna Array in a Fading Channel

In this paper, an antenna array based base station receiver structure for multicarrier direct sequence code-division-multiple-access (Multicarrier DS-CDMA) system with binary phase shift keying (BPSK) modulation is proposed. One of the main advantages of the receiver structure is that the spatial diversity is obtained by combining signals at different array elements. Based on the detailed analysis of multiple access interference (MAI) and additive white Gaussian noise (AWGN) characteristics, the uplink bit error rate (BER) performance of the proposed antenna array Multicarrier DS-CDMA is provided. With regard to spatial domain combining, the optimum spatial combining (OSC) and suboptimum spatial combination (SOSC) weights is derived while the suboptimum set of weights is simplified in the sense that only the knowledge of array vector of desired user alone is sufficient for the combining. Simulation results verify the analysis, and it is shown that MAI is mitigated and subsequently the system performance is improved significantly by incorporating antenna array at the base station.