高阶QAM信号的盲载波相位估计

针对高阶QAM信号的盲载波相位估计问题进行了研究。首先对现有的各种盲载波相位估计算法的性能进行了分析总结,比较了在各种信噪比条件下,各种算法的优劣。在此基础上,提出了用于相位捕获的PL_DD算法,该算法估计性能好、效率高,运算复杂度也是在可接受的范围内,是一种高效相位估计算法。     

Blind phase recovery for QAM communication systems

In this paper, a novel phase estimator that can be employed for both square and cross Quadrature Amplitude Modulation (QAM) based digital transmission is presented. It does not need gain control and requires only the knowledge of the type of the transmitted symbol constellation, i.e., square or cross. It is based on the evaluation of the fourth power of the received data and the measurement of the orientation of the concentration ellipses of the bivariate Gaussian distribution having the same second-order moments. The analytical evaluation of the estimation error as well as of the asymptotic variance is provided. Experimental results outline the good performance of the estimator described here, which is superior to that of well-known phase estimation methods. Finally, it is outlined how the eccentricity of the concentration ellipses can be used to devise a test for detecting the constellation type.     

对高阶QAM信号盲载波相位捕获算法的一种改进方法

现有高阶QAM信号的载波相位捕获算法存在着估计精度不高的缺点,它使信号在捕获阶段不能被高质量的解调。为了克服这个问题,提出了利用现有的捕获算法估计得出一个粗略相位值,然后设定一个恰当的范围进行最大似然的迭代搜索,经过一定次数的迭代处理之后估计的精度大大提高。文中还对这种改进方法进行了简化,在保证估计性能基本不变的前提下,极大地降低了运算量。     

Joint blind equalization, carrier recovery and timing recovery forhigh-order QAM signal constellations

Two existing blind equalization tap update recursions for 64-point and greater QAM (quadrature amplitude modulation) signal constellations are studied, along with existing and novel carrier and timing recovery techniques. It is determined that the superior tap update recursion is the one known as the constant modulus algorithm. Carrier recovery requires a modified second-order decision-directed digital phase-locked loop. An all-digital implementation of band-edge timing recovery is used. With 14.4 kb/s outbound transmission using CCITT V.33 trellis-coded 128-QAM signals having 12.5% excess bandwidth, a prototype blind retrain procedure is developed to demonstrate the feasibility of the techniques for high-speed multipoint modems. A WE DSP32-based real-time digital signal processor was employed to test the retrain over a set of severely impaired channels. For each channel in the set, the retrain succeeded at least 90% of the time     

Performance analysis of blind carrier phase estimators for generalQAM constellations

Large quadrature amplitude modulation (QAM) constellations are currently used in throughput efficient high-speed communication applications such as digital TV. For such large signal constellations, carrier-phase synchronization is a crucial problem because for efficiency reasons, the carrier acquisition must often be performed blindly, without the use of training or pilot sequences. The goal of the paper is to provide thorough performance analysis of the blind carrier phase estimators that have been proposed in the literature and to assess their relative merits     

Minimisation of carrier frequency acquisition time in QAM systems

Two recent carrier recovery loops for high-order quadrature amplitude modulation (QAM) and optimisation of their parameters for minimum frequency acquisition times are analysed. All variations on the parameters were analysed and optimised to obtain optimal loop bandwidths and damping factors, for given signal-to-noise ratios. Simulation results show that after optimisation, the average acquisition time for 64-QAM is kept below 1000 symbols over the entire range of initial frequency offsets from 0 to 1/8 the symbol rate. This number increases to 3200 symbols for 256-QAM.     

Burst demodulation of QAM with unknown carrier phase

A new algorithm for the burst demodulation of QAM with unknown carrier phase is presented. This algorithm utilises sequence detection and the Viterbi algorithm and does not require estimation of the carrier frequency and phase. Its applications can be widely found in broadband wireless access and other systems that use burst transmission     

Full constellation phase detector for carrier recovery in high-order QAM systems

A full constellation phase detector that improves carrier acquisition performance in high-order quadrature amplitude modulation (QAM) is proposed. The weighting function of the phase detector is mathematically derived, and simulated phase detector characteristics are presented for 256QAM. The results of an experimental evaluation are also reported, which show that the carrier recovery loop based on the proposed phase detector has a large frequency acquisition range and low phase tracking error in high-order QAM.     

一种用于数字QAM解调芯片中的盲均衡器实现

设计了一种用于数字QAM解调芯片中的自适应盲均衡器。该均衡器采用常模算法（CMA）和判决引导最小均方算法（DD-LMS）,结合判决反馈结构（DFE）,即采用前向滤波和反馈滤波两级滤波器组,该方案提高了信道的自适应性能和降低了均衡器的阶数。通过对算法的简化和电路结构的优化,减少了硬件资源,降低了电路的面积和功耗。     

Blind carrier phase tracking with guaranteed global convergence

Conventional blind carrier recovery algorithms have been observed to show unstable behaviors for large constellation modulation schemes such as 64-QAM or 256-QAM. We propose a new carrier tracking approach that has guaranteed global convergence. First, we show that the carrier tracking problem is equivalent to a blind source separation problem, which involves the separation of a linear unitary mixture of two independent components that are the real and imaginary parts of the emitted signal. Then, by using a blind source separation procedure, we derive a new and robust carrier tracking algorithm with guaranteed global convergence. Some numerical simulations are provided to illustrate the effectiveness of the proposed method     

Optimal blind nonlinear least-squares carrier phase and frequency offset estimation for general QAM modulations

This paper introduces a family of blind feedforward nonlinear least-squares (NLS) estimators for joint estimation of the carrier phase and frequency offset of general quadrature amplitude modulated (QAM) transmissions. As an extension of the Viterbi and Viterbi (1983) estimator, a constellation-dependent optimal matched nonlinear estimator is derived such that its asymptotic (large sample) variance is minimized. A class of conventional monomial estimators is also proposed. The asymptotic performance of these estimators is established in closed-form expression and compared with the Cramer-Rao lower bound. A practical implementation of the optimal matched estimator, which is a computationally efficient approximation of the latter and exhibits negligible performance loss, is also derived. Finally, computer simulations are presented to corroborate the theoretical performance analysis and indicate that the proposed optimal matched nonlinear estimator improves significantly the performance of the classic fourth-power estimator.     

一种QAM信号的盲信噪比估计算法

本文首先推导了QAM信号信噪比估计的克拉米罗下限,然后以两个统计量比值与信噪比关系的研究为基础,提出了一种QAM信号的盲信噪比估计算法.虽然高阶QAM信号的信噪比估计需要较多的观察数据才能得到准确的信噪比估计值,但是本算法不需要额外的存储器来存储这些数据;并且该算法具有非常低的运算复杂度.文章还以多种QAM信号为例进行了具体的分析和计算机仿真,分析和仿真的结果表明在合适的观察数据长度下,该算法对文中测试的各种QAM信号都能进行有效估计.     

适用于圆形高阶QAM信号的盲均衡算法

针对现有盲均衡算法大多仅适用于方形或十字形QAM信号的问题,本文提出了一种适用于圆形高阶QAM信号的混合盲均衡算法。该算法首先对区域多模盲均衡算法进行改进,提出了新的区域划分方法并将其与改进的多模盲均衡算法相结合,构造了新的误差模型使之与圆形星座匹配程度大大提高;然后将其与判决引导算法和数据重用技术有机结合,构成低稳态误差的快速混合盲均衡算法。与其他同类型盲均衡算法相比,本文算法对于圆形星座高阶QAM信号尤为有效,不仅降低了稳态误差,且大幅度减少了收敛所需符号数。仿真结果验证了该算法的有效性。      

ML-oriented NDA carrier synchronization for general rotationallysymmetric signal constellations

We point out that the nondecision-aided (NDA) carrier synchronizer, maximizing the low E_s/N_o limit of the likelihood function averaged over a general 2π/N-rotationally symmetric signal constellation, reduces to the familiar timing-aided Nth power synchronizer; this extends a result of D'Andrea, Mengali and Reggiannini (1988) where only M-PSK constellations have been considered. Whereas in the case of M-PSK the tracking error variance of this NDA ML synchronizer is known to converge to the Cramer-Rao bound (CRB) with increasing E_s/N_o. We show that for other rotationally symmetric constellations (such as QAM) the tracking error variance is substantially larger than the CRB     

A closed-form expression for the exact BER of generalized PAM and QAM constellations

We derive an explicit closed-form expression for the exact bit-error rate (BER) computation of generalized hierarchical M-ary pulse amplitude modulations over additive white Gaussian noise (AWGN) and fading channels. This expression can also be used to obtain the exact BER of generalized hierarchical quadrature amplitude modulations (square and rectangular). For the AWGN case, these expressions are in the form of a weighted sum of complementary error functions, and are solely dependent on the constellation size M, the carrier-to-noise ratio, and a constellation parameter which controls the relative message importance.     

适合高阶QAM的载波恢复算法

为解决DVB—C系统中多电平调制信号(如64，128，256QAM)的频偏捕获，描述了一种极性判决鉴相的算法，该算法可捕获高阶QAM信号的频偏达200kHz。对于一般的频偏较小的QAM信号可用传统的DD算法纠正。这样对收到的带有较大频偏和噪声、部分多径的基带信号就可先用极性判决捕获大频偏，稳定之后再用全星座判决纠正剩下的小频偏。     

快速QAM信号多模盲均衡算法

该文提出一种改进的QAM信号的多模盲均衡算法,其利用发送信号的实部(或虚部)信息构造代价函数。并且,提出了通过共轭梯度算法得到均衡器最优权的算法,该算法具有二次收敛性,与传统恒模算法和多模算法相比较,有非常快的收敛速度和非常少的计算量,并且均衡效果相当。最后,通过误码率和收敛速度分析该算法的可靠性和有效性,通过计算机仿真证明了该算法的有效性。     

一种QAM信号多普勒参数盲估计方法

在卫星移动通信中,卫星相对地面接收站的高速运动导致接收信号存在时变多普勒频率,给正交幅度调制(QAM)信号的载波同步带来了极大困难.现有的多普勒参数估计方法多利用导频等先验信息,适用于移相键控(PSK)信号.但在估计多普勒频率变化率时假设多普勒频率较小,不符合实际情况,且现有方法无法估计较大的多普勒频率,另外在非协作通信下先验信息难以获得.对此,本文提出了一种针对高阶QAM信号的多普勒参数盲估计方法.将信号盲去调制后,利用瞬时频率估计函数,可在较大的多普勒频率下估计出多普勒频率变化率;通过检测信号四倍频率处的循环频率,实现了多普勒频率盲估计;最后利用arg运算求出初相.详尽的Monte Carlo仿真分析了方法的估计性能,仿真结果表明,所提方法能有效实现QAM信号的多普勒参数盲估计.     

一种用于QAM接收机的符号定时盲恢复方法

以采样信号在频率户f=1/2T处频谱取最大值为准则,提出一种用于QAM接收机的定时相位迭代估计算法.该方法用数字差分滤波对采样信号进行处理,提高了信号中的定时分量,从而加快了算法的收敛速度.仿真结果表明,该方法缩短了QAM接收机符号同步建立时间,在低信噪比情况下的性能仍良好.     

QAM解调中载波相位估计算法研究

QAM在相干解调时,接收机需要提供一个与发射机调制载波同频同相的相干载波,以保证接收机以较低的错误概率恢复出发送信号,载波提取性能的好怀是评价接收机性能的重要标准。可见,为了保证信息的可靠传输,对载波频率偏移和相位偏移的估计方法的研究与改进具有重要意义,为此,研究了一种面向判决的载波相位估计算法,仿真结果表明效果较好。