QAM调制与解调的全数字实现

论述了适用于数字微波系统的全数字正交幅度调制解调方式，并根据星座图的形状指出了16QAM。64QAM(星座图为矩形)与32QAM，128QAM(星座图为十字形)在调制与解调方法上的区别，最后用ADS(Advanced Design System)对16QAM，32QAM，64QAM，128QAM全数字调制与解调过程进行仿真，并给出了64QAM在加性高斯白噪声条件下的误码率。实验证明，全数字正交幅度调制解调易于实现，且性能良好。     

方形16QAM光信号生成方案的研究

基于16QAM光信号调制方式抗噪声性能好、频带利用率高以及在高频谱效率下信噪比要求较低的优点,16QAM光信号传输成为现代相干光通信网络研究的热点。常见的16QAM光信号星座图有方形星座图、星形星座图、环形星座图等,文章主要研究方形16QAM光信号调制方式的生成方案,并总结方形16QAM信号生成方案的优缺点。     

基于Saleh模型的DRSS信道建模与仿真

对DRSS信道URE链路进行建模仿真,采用Saleh模型描述DRSS信道URE链路中HPA的非线性特性。通过仿真8PSK、方型16QAM、星型16QAM调制信号并经过DRSS URE非线性信道后的非线性ISI特性、频率特性、星座图和误码特性,分析了信道非线性特性对通信系统性能的影响。     

基于星座图的QAM信号调制方式识别

给出了利用信号星座图的QAM信号调制方式识别技术。在对QAM信号进行分析的基础上。重点讨论了信号载频、码元速率盲估计方法以及信道盲均衡方法。仿真结果表明，利用这种方法，可以精确地估计QAM信号的载频和码元速率，成功地将信号星座图恢复出来，并通过信号星座图完成信号的识别。     

用信号空间分析的方法比较不同结构的QAM性能

本文用信号空间分析的方法,对不同结构的QAM信号的星座图结构、调制解调的方法以及各种性能进行了分析比较,得出了不同结构的QAM信号各自适用的环境,并通过仿真进一步验证了分析结果。     

高阶数据调制比特软输出的递归计算方法

该文设计了一种通过把低阶PAM(QAM)星座图递归排列形成高阶调制的星座图,这种星座图与原信号的关系仍为Gray映射,即相邻两星座点的映射比特序列仅相差1bit。另外高阶调制的比特软输出计算比较复杂,对每一种阶数的调制需要各自的公式计算。研究结果表明高阶调制的比特软输出可以通过低阶调制递归计算得出。只需计算二进制调制方式,就可计算出任意的高阶调制的比特软输出。从而可降低复杂度。仿真表明上述方法简化了高阶调制软信息的计算。     

自由空间光通信中相干OFDM系统性能分析

结合正交频分复用（OFDM）技术和相干探测的优势,研究了相干OFDM自由空间光通信（FSO）系统的误码性能,考虑了OFDM映射方式以及映射阶数对系统误码性能的影响。在Gamma-Gamma大气湍流信道下,分别从平均信噪比和所需平均接受光功率的角度考虑了系统在弱、中和强湍流三种情况下的误码性能。在此基础上,推导了系统误符号率的闭合表达式。仿真结果表明,相干探测下OFDM FSO系统可以较好地克服大气湍流效应,在弱、中湍流情况下,QAM映射方式下系统的误码性能明显优于PSK方式,在强湍流下这种优势不明显,此外随着映射阶数的增加,系统误符号率增加,因此在实际应用中可以通过降低映射阶数来提高系统误码性能。     

移动通讯中MQAM调制方式的优化选择——瑞利衰落信道中MQAM传输误码性能的分析

该文分析了在含有高斯白噪声的Rayleigh衰落信道中,矩形星座图MQAM、圆形星座图MQAM的传输误码性能,给出相应的误码率计算公式,并进行计算机数值分析,为在移动通信中MQAM调制方案的选择提供一个理论分析依据。     

十字形QAM信号的盲均衡技术研究

提出两种适用于十字形正交幅度调制QAM(Quadrature amplitude modulation)信号的盲均衡算法:改进的常十字模算法(MCXA)和基于判决引导的改进的常十字模算法(DD-MCXA).MCXA在CXA基础上重构了代价函数,在其代价函数中增加了星座图匹配误差(CME)函数,CXA部分提供了全局收敛,CME部分用来减少剩余误差和加快收敛速度.DD-MCXA在保持CXA部分提供良好的最初收敛的优点的同时,自动削弱了CXA部分在局部收敛区域的误差影响,从而进一步提高了均衡性能.通过对户外无线微波信道模型的仿真实验,验证了这两种算法良好的均衡性能.     

基于星座图聚类分析调制识别的改进算法

通过分析聚类分析在星座图中的应用,得出星座图聚类分析对高阶QAM短突发信号的类内调制识别不适用的结论,从而提出了星座图聚类调制识别法在短突发信号的改进方法。将星座点在坐标轴上投影,利用投影点进行聚类分析,可以提高星座聚类算法在高阶QAM短突发信号调制识别中的性能。仿真结果表明,在短突发信号的条件下,该方法具有良好的识别效果。     

一种新的非2的整数幂阶的QAM调制设计

 本文提出了一种新的具有普遍适用性的调制阶数非2的整数幂的正交幅度调制(Quadrature Amplitude Modulation,QAM)设计方法,通过建立特定个连续星座点与特定长度比特序列的映射关系,实现了码速率分辨率更高的QAM调制解调,丰富了自适应调制中QAM的选择,缩小待选QAM调制的性能间隔.本文以28QAM为例说明其设计方法.     

BER computation of 4/M-QAM hierarchical constellations

Hierarchical constellations offer a different degree of protection to the transmitted messages according to their relative importance. As such they found interesting application in digital video broadcasting systems as well as wireless multimedia services. Although a great deal of attention has been devoted in the literature to the study of the bit error rate (BER) performance of uniform quadrature amplitude modulation (QAM) constellations, very few results were published on the BER performance of hierarchical QAM constellations. Indeed the only available expressions "leading-term" approximate BER expressions for 4/16-QAM and 4/64-QAM. We obtain exact and generic expressions in M for the BER of the 4/M-QAM (square and rectangular) constellations over additive white Gaussian noise (AWGN) and fading channels. 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. Because of their generic nature, these new expressions readily allow numerical evaluation for various cases of practical interest. In particular numerical results show that the leading-term approximation gives significantly optimistic BER values at low carrier-to-noise ratio (CNR) in particular over Rayleigh fading channels but is quite accurate in the high CNR region     

Link22数据链调制方式性能分析

Link22工作频段的频率资源是有限的,为了提高信息速率,Link22使用了环形星座的QAM（正交调幅）及8PSK的调制方式。在加性高斯白噪声环境下,8PSK调制方式的误符号率计算方法已相当成熟,而环形星座的QAM调制方式的误符号率只有边界较为松疏的计算公式。文中采取将QAM环形星座上的星座点分解成两个相互正交的非均匀的PAM（脉冲振幅调制）信号的方法,计算出Link22在加性高斯白噪声环境下的16QAM环形星座误符号率。计算结果与相关资料相比具有很好的一致性,表明此分析方法是正确可行的。此方法也适于Link22的32QAM及64QAM的调制方式。     

Fourth power phase estimation with alternative two-dimensionalodd-bit constellations

It is well established that the fourth power phase estimator does not perform well for QAM cross (i.e., odd-bit) constellations. In this paper, new two-dimensional rectangular constellations are presented that give much improved performance, at a reasonably low increase in required constellation energy. For example, the 128B-COB constellation reduces the variance by an order of magnitude, while increasing the constellation's average energy by only 0.28 dB and the peak to average energy ratio by 1.25 dB, relative to 128-QAM     

Blind carrier phase acquisition for QAM constellations

A constant need for ever-increasing throughputs through fixed bandwidths, fueled by several high-speed applications (such as digital TV), has pushed system designers toward more throughput-efficient modulation schemes. Because of their relatively good performance, large quadrature amplitude modulation (QAM) constellations are being used in many of these applications. One of the problems associated with the use of large QAM constellations is that of carrier acquisition, which, for efficiency reasons, must often be done without the use of a preamble. The problem is further complicated for cross constellations, for which the high signal-to-noise ratio (SNR) corner points used by some simple carrier phase estimators are not available. We derive simple algorithms for carrier phase acquisition that can be used for both square and cross constellations, and compare their performance to those of the maximum-likelihood (ML), the fourth-power estimator, and a modified fourth-power estimator, obtained by considering a reduced constellation. The introduced algorithms convert the problem of carrier phase estimation into one of estimating the mode of an underlying distribution. An expression for this underlying distribution is also obtained. The results obtained indicate that the introduced algorithms significantly outperform the fourth-power estimator for moderate to high SNRs, especially when cross constellations are used     

A blind equalization with the sign algorithm for broadband access

This paper presents an optimal reduced constellation point of sign reduced constellation algorithm (SRCA) for square and nonsquare carrierless amplitude and phase (CAP)/QAM signal constellations. Convergence characteristics of the SRCA algorithm are analyzed and compared to those of the RCA algorithm     

Square m-QAM相干光通信载波相位估计性能研究

基于前馈载波相位估计算法,研究了square 16-QAM调制相干光纤通信系统的载波相位估计性能,进一步证明了当存在相位噪声时square m-QAM调制并非QAM调制最佳星座图的原因。仿真计算结果显示,由于square 16-QAM调制星座图中星点之间相位距离分布不均匀,引起载波相位估计中出现连续相位跳变,导致载波估计性能劣化,系统误码率增大约2～3倍。     

Multidimensional constellations. I. Introduction, figures of merit,and generalized cross constellations

The authors discuss the major attributes desired in signal constellations, such as signal-to-noise ratio (SNR) efficiency, simplicity of mapping bits to points and vice versa, compatibility with coded modulation schemes, and compatibility with quadrature amplitude modulation (QAM). The capability of supporting a so-called opportunistic secondary channel, often used for internal control signaling, is considered. The gain in SNR efficiency of a multidimensional constellation (lattice code) consisting of the points from a lattice Λ within a region R compared to a cubic constellation is shown to be approximately separable into the coding gain of Λ and the shape gain of R, for large constellations. Similarly, the expansion of the associated constituent 2-D constellation is shown to be approximately separable into a constellation expansion ratio (CER) coding component CER_c(Λ) and a shaping component CER _s(R). The N sphere is the region R with the best shape gain, but N also has large constellation expansion. Bounds for the best possible shape gain versus CER_s(R) or peak-to-average-power ratio (PAR) are given. Generalized cross constellations are discussed. These constellations yield a modest shape gain with very low CER_s(R) or PAR, are easily implemented, are well suited for use with coded QAM modems, and can be readily adapted to support an opportunistic secondary channel     

Constellation labeling for linear encoders

This paper investigates optimal constellation labeling in the context of the edge profile. A constellation's edge profile lists the minimum-distance edge for each binary symbol error. The paper introduces the symmetric-ultracomposite (SU) labeling structure and shows that this structure provides undominated edge profiles for 2ⁿ-PSK, 2 ⁿ-PAM, and 2²ⁿ-point square QAM. The SU structure is a generalization of the commonly used reflected binary Gray code. With the proper choice of basis vectors, SU labeling can support either set-partition or Gray-code labeling of 2ⁿ-PSK, 2ⁿ-PAM, and 2²ⁿ-point square QAM. Notably, there are Gray-code and set-partition labelings that do not have the SU structure. These labelings yield inferior edge profiles. The SU structure does not apply to cross constellations. However, for any standard cross constellation with 32 or more points, a quasi-SU labeling structure can approximate the SU structure. With the correct choice of basis, quasi-SU labelings produce quasi-Gray labelings. However, the quasi-SU structure cannot support set-partition labeling. In fact, the quasi-SU structure provides a better edge profile than standard set-partition labeling. Thus, for cross constellations there is a choice between edge profile optimality and the group structure provided by set-partitioning. Here, the correct choice depends on whether the encoder trellis has parallel branches     

Comparison of Asymmetrically Clipped Optical OFDM and DC-Biased Optical OFDM in AWGN

We present theoretical and simulation results for the performance of asymmetrically-clipped optical OFDM (ACO-OFDM) and DC-biased optical OFDM (DCO-OFDM) in AWGN for intensity-modulated direct-detection systems. Constellations from 4 QAM to 1024 QAM are considered. For DCO-OFDM, the optimum bias depends on the constellation size which limits its performance in adaptive systems. ACO-OFDM requires less optical power for a given data rate than DCO-OFDM for all but the largest constellations and is better suited to adaptive systems as the same structure is optimum for all constellations.