Modified CMA based blind multiuser equaliser with decision directed scheme

A modified constant modulus (CM) algorithm based blind multiuser equaliser with a decision directed (DD) scheme is developed that does not require any mutual decorrelation and is suitable for downlink direct sequence code division multiple access systems. The performance of the proposed time domain adaptive equaliser is evaluated with respect to usual parameters and is found to perform better than the concurrent CM algorithm and DD scheme.     

A modified constrained constant modulus approach to blind adaptivemultiuser detection

An alternative blind adaptive multiuser detection is investigated based on modified constrained constant modulus (CM) criterion. It is shown that the performance of a CM-based receiver is limited by the received power of the desired user. In this paper, we show that the limitation can be avoided using the noncanonical constraint CM criterion and that in the presence of channel noise the modified CM criterion function is strictly convex by properly selecting some constant. With analyzing the extrema of the cost function, we point out how to select the constant. Moreover, a simple stochastic gradient algorithm for implementing our scheme is presented, and the convergence properties of the algorithm are analyzed. Simulation examples are given to demonstrate the performance of the proposed scheme     

A Technique for Frequency Synchronization in Multi-Band OFDM in Realistic UWB Channel

This paper presents a highly accurate frequency offset estimation algorithm for multi-band orthogonal frequency division multiplexing (MB-OFDM) systems effective for realistic ultra-wideband (UWB) environment. The proposed algorithm derives its estimates based on phase differences in the received subcarrier signals of several successive OFDM symbols in the preamble. We consider different carrier frequency offsets and different channel responses in different bands to keep the analysis and simulation compatible for practical multi-band UWB scenario. Performance of the proposed algorithm is studied by means of bit error rate (BER) performance of MB-OFDM system. In order to compare the variance of the synchronizer to that of the theoretical optimum, we derive the Cramer–Rao lower bound (CRLB) of the estimation error variance and compare it with the simulated error variance both in additive white Gaussian noise and UWB channel model (CM) environments, CM1–CM4. Next, we modify the estimation algorithm by proposing a multi-band averaging frequency offset synchronization (MBAFS) scheme. We establish superior BER performance with MBAFS compared to our first scheme. We calculate modified CRLB for MBAFS and compare it with simulation results for CM1–CM4. Both analysis and simulation show that MBAFS algorithm can estimate the carrier frequency offset effectively and precisely in UWB fading channels for MB-OFDM applications. We also analyze the computational complexity of both the proposed algorithms in order to verify their feasibility of implementation in practical UWB receiver design.     

基于延迟锁相环的到达时间估计算法

超宽带脉冲信号具有高时间分辨能力,能达到厘米级的定位精度。目前,脉冲超宽带测距定位系统中普遍采用基于能量检测的非相关到达时间(TOA)估计算法的性能通常受限于阈值门限和估计偏差。该文在原先锁相环方案基础之上引入延时迟支路和衰减因子,提出了一种易于实现的基于延迟锁相环的TOA估计算法。通过在迟支路中设置不同的衰减因子,仿真结果表明,在IEEE802.15.4a4种信道模型CM1~CM4中,新算法均能有效提升测距定位精度,即缩短了首达路径与锁相环稳态锁定点之间的时差,其估计偏差最低可降至原有方案的1/10。     

Maximum likelihood separation of constant modulus signals

In this correspondence, we derive a Newton scoring algorithm for the maximum likelihood separation and direction-of-arrival (DOA) estimation of constant modulus (CM) signals using a sensor array. We present a rapidly converging scheme for the joint estimation of the signals and their directions based on their CM property. We discuss initialization and show that the complexity is moderate     

Blind estimation of space?time coded systems using the finite alphabet?constant modulus algorithm

Space-time coding introduces spatial and temporal correlations into signals transmitted from multiple antennas in order to provide diversity and coding gain at the receiver. In the field of blindly estimating space-time coded signals impinging on an antenna array, an effective scheme for jointly exploring the constant modulus (CM) and the finite alphabet (FA) constraints is presented. The CM constraints are explored algebraically, whereas the FA constraints are explored via an iterative algorithm considering the constraints imposed by the space-time coded signals. This leads to our novel FACM algorithm that offers a wide range of trade-offs between performance and complexity while it lends itself to an amenable (step-by-step) algorithmic implementation as well as an amenable algorithmic complexity     

简化的复数非圆信号广义线性盲均衡算法

为了提高复数非圆信号的盲均衡性能,本文深入分析广义线性滤波理论,利用常模准则的简便性和稳健性,针对低阶复数非圆信号构造了简化的广义线性盲均衡器,并提出了一种简化的广义线性递归最小二乘常模盲均衡算法。简化的广义线性盲均衡器直接利用接收信号的实部和虚部作为均衡器输入,从而得到接收信号完整的实部和虚部的二阶统计量信息。新算法将标准的广义线性均衡算法的复数运算变成实数运算,有效地降低了标准广义线性均衡器的复杂度。仿真实验结果表明,与传统常模盲均衡算法相比,新算法在不提高计算复杂度的基础上,能够有效降低剩余码间干扰和误码率。      

CMA-Based Channel Estimation for Space-Time Block Coding Transmission Systems

In this paper, we present channel estimation methods for space-time block coding (STBC) transmissions using constant modulus algorithm (CMA). The channel estimates are directly calculated from the convergence value of the CMA. Two algorithms using the channel-vector-based and channel-gain-based constant modulus (CM) criteria are proposed. An approximation of the CM cost function is introduced to allow the use of the recursive least-square (RLS) technique in designing fast RLS-CMA's. Performance of the proposed schemes is evaluated and compared with others using simulation. Illustrative results show that the proposed scheme outperforms the cross-correlated method and can approach the performance of the training-based method.     

一种基于恒模算法的多用户盲波束形成新方法

提出了一种适用于多用户的盲波束形成新方法.该方法基于最小二乘恒模算法,当最小二乘恒模算法收敛于某一信号后,我们导出了算法的权向量与其它用户波达方向的关系,进而在不同用户的波达方向上形成初始增益,从而实现对所有用户的波束形成.文中给出了算法的并行和串行实现方案.     

Estimation and choice of neighbors in spatial-interaction models of images

Some aspects of statistical inference for a class of spatial-interaction models for finite images are presented: primarily the simultaneous autoregressive (SAR) models and conditional Markov (CM) models. Each of these models is characterized by a set of neighbors, a set of coefficients, and a noise sequence of specified characteristics. We are concerned with two problems: the estimation of the unknown parameters in both SAR and CM models and the choice of an appropriate model from a class of such competing models. Assuming Gaussian-distributed variables, we discuss maximum likelihood (ML) estimation methods. In general, the ML scheme leads to nonlinear optimization problems. To avoid excessive computation, an iterative scheme is given for SAR models, which gives approximate ML estimates in the Gaussian case and reasonably good estimates in some non-Gaussian situations as well. Likewise, for CM models, an easily computable consistent estimate is given. The asymptotic mean-squared error (mse) of this estimate for a four-neighbor CM model is shown tn be substantially less than the mse of the popular coding estimate. Asymptotically consistent decision rules are given for choosing an appropriate SAR or CM model. The usefulness of the estimation scheme and the decision rule for the choice of neighbors is illustrated by using synthetic patterns. Synthetic patterns obeying known SAR and CM models are generated, and the models corresponding to true and several competing neighbor sets are fitted. The estimation scheme yields estimates close to the parameters of the true models, and the decision rule for the choice of neighbors picks up the true model from the class of competing models.     

An Adaptive Timing Synchronization Scheme for Multi-Band Orthogonal Frequency Division Multiplexing Based Ultra-Wideband Communication Systems

This article deals with a new energy based adaptive timing synchronization scheme (ATS) which estimates the symbol timing information within two (2) OFDM symbols and updates the information with different frequency bands (adaptive in sense) in a multi-band orthogonal frequency division multiplexing (MB-OFDM) based system. The new approach provides significant improvement in system performance for high delay spread ultra-wideband (UWB) channel model (CM) environments where fast and low-complexity timing synchronization is a critical issue. This paper also addresses a crucial aspect of UWB channel which is frequency dependent delay characteristics. This effect contributes to different dispersion and timing shift of an UWB signal for different frequency bands. In this work, the wideband channel delay characteristics are studied and delay parameters are found considerably different over frequency bands 3.1–4.6 GHz. Based on this observation, the ATS which estimates and maintains the timing delays of each band separately is presented. The performance of ATS algorithm is measured by mean-squared error (MSE), synchronization probability, signal to interference ratio (SIR) reduction due to synchronization errors and bit error rate (BER) through the computer simulation for several UWB CM environments CM2–CM4. Each of these UWB CMs is simulated for 100,000 noisy channel realizations for both coded and uncoded MB-OFDM system. It is shown that ATS gives signal-to-noise ratio (SNR) improvement of 1.1 dB at BER of 1 × 10⁻³, 1.2 dB at BER of 2 × 10⁻⁴, and 0.7 dB at BER of 2 × 10⁻⁴ for CM4, CM3, and CM2 respectively for coded MB-OFDM system over a non-adaptive synchronization scheme [Yak et al., Proceedings of IEEE PIMRC, Berlin, Germany, vol 1, pp 471–475, September 11–14, 2005].     

CDMA中的半盲恒模算法

该文研究了应用于CDMA上行链路多用户检测中的半盲恒模算法。它首先利用非盲算法消除所有小区内干扰用户的影响,接着再利用盲算法抵消剩余的干扰。通过仿真实验,将之与盲恒模算法及解相关算法相比较,可以看出在于扰用户增多时,本文提出的半盲恒模算法的性能明显优于另外两种算法。     

有限地平面上差分对共模噪声的分析

共模噪声是高速数字电路产生电磁干扰的主要原因,而共模电感又是共模噪声大小的决定因素。以多层板的微带线为模型,推导出在偏离地平面中心以及跨越不连续地平面的情况下,PCB上差分对共模电感的定量表达式,并对其共模噪声的特性进行了详细讨论。其结论可以帮助设计人员理解共模噪声产生机制,并针对具体电路走线定量分析,提前准确发现设计中潜在的问题。     

An Efficient Packet Detection Method with a Verification Mode in MB-OFDM UWB Systems

In this paper, we propose a novel packet detection method using a cross-correlation scheme with a verification mode in ultra wide-band (UWB) systems adopting multi-band OFDM (MB-OFDM) techniques. In the packet detection process, a cross-correlation scheme has the advantage of performing the acquisition of transmitted time-frequency code (TFC) for frequency hopping as well as packet detection with low hardware costs; however, it suffers from performance degradation caused by an imperfect decision process using a threshold value compared with an auto-correlation method. By using a verification mode, the proposed method improves detection performance of a cross-correlation technique considerably. This is because the verification mode can reduce a false alarm probability on packet detection by reconfirming whether or not the desired signal is received and can effectively reject temporal small correlation peaks due to the noise or sub-path signals having smaller energies. For the verification of proposed algorithm, we employ CM1 and CM4 channel models given in IEEE802.15.3a and compare the detection performance between conventional algorithms as well as the proposed one by using computer simulations. Experimental results show that the proposed scheme can reduce a packet detection error probability (PDER) to about 10⁻³ in CM1 channel and about 10⁻² in CM4 channel at SNR = 9 dB compared with conventional methods having more than 10⁻¹ PDER. From the experimental results, we can find that the proposed algorithm can compensate for performance degradation under high SNR condition caused by using a fixed single threshold value. We also estimate the power consumption of algorithms by utilizing both the total number of multiplications and additions employed in the algorithms and the consuming power of hardware elements under 0.13 um CMOS technology. Next, we discover that the proposed method can reduce computational complexity by a minimum of 24.5% compared with conventional cross-correlation algorithms. From the experimental and power estimation results, we can see that the proposed method is very useful for packet detection in UWB MB-OFDM systems, in which low-power implementation is an important issue.     

Convergence analysis of the least squares constant modulusalgorithm in interference cancellation applications

The convergence behavior of the least squares constant modulus (CM) algorithm in an adaptive beamforming application is examined. It is assumed that the desired signal and the interference are uncorrelated. The improvement in output signal-to-interference ratio (SIR) with each iteration of the algorithm is predicted for several different signal environments. Deterministic results are presented for an environment containing two complete sinusoids. Probabilistic results are presented for a CM desired signal with a CM interferer and with a Gaussian interferer. The asymptotic improvement in output SIR as the output SIR becomes high is also derived. The results of Monte Carlo simulations using sinusoidal, frequency modulation, and quadrature phase-shift keying signals are included to support the derivations     

探索CMTS+CM与EPON+EoC的和谐发展

本文从双向HFC接入网与CMTS＋CM业务开展和单向HFC与EPON＋EoC业务开展入手,介绍了各自的优点与不足,提出具备融合特征的三通道有线接入网概念。再对三通道有线接入网的频谱规划、结构形式、关键设备进行分析,描述了多种业务在三通道有线接入网上的应用和揭示了CMTS＋CM和EPON＋EoC的和谐发展方向。     

一种基于并联式恒模阵和DOA的同信道信号接收算法

提出一种基于并联式恒模阵和DOA的同信道信号接收算法。采用DOA算法获得信号的波达角，结合初始预测的方法对并联式恒模阵加以初始化，实现对同信道信号的接收和跟踪。它具有无需精确已知信号波达角的特点，克服了已有算法中需要阵列校正的缺陷，同时具有不会误收敛的优点。计算机仿真证实了算法的有效性。     

Blind Feedforward Symbol-Timing Estimation With PSK Signals: A Constant-Modulus Approach

In this letter, the problem of blind symbol-timing estimation with M-ary phase-shift keying (M-PSK) signals is considered. An estimator exploiting the constant modulus (CM) property of M-PSK constellations and the structure of the received signal when the convolution of the transmitter's signaling pulse and the receiver filter satisfies the Nyquist criterion is proposed. Since the derived estimator, termed the CM estimator, requires a maximization with respect to a continuous variable, a closed-form approximate CM (ACM) algorithm, suitable for digital implementation, is proposed. Computer simulation results show that with small excess bandwidth factors, the derived ACM algorithm outperforms previously proposed algorithms at moderate and high signal-to-noise ratios