一种基于LLR软判决的LTE解映射简化算法

针对目前LTE解映射算法复杂度高的缺陷,提出了一种基于LLR软判决的LTE解映射简化算法SLLR。该算法旨在通过使用对数似然比进行软判决,以简化指数计算与对数计算为主,降低LTE解映射过程中计算的复杂度。通过对标准算法与简化算法的QAM调制方式产生的误码率、误块率进行仿真和比较,结果表明该SLLR简化算法性能良好,适用于LTE通信系统。     

一种基于FPGA的简化LLR算法研究

高阶调制方式结合软信息解调的前向纠错编码技术是解决无线通信频谱资源拥挤的有效方法。在传统软信息对数似然比计算方法的基础上,结合mQAM调制技术的正交格雷码映射星座图的特性,提出了一种更简单的计算mQAM软信息方案。在硬件实现上不需要使用乘法器,和传统的LLR计算相比大大节省了FPGA资源,仿真结果表明所提出的LLR简化算法,在(2,1,7)卷积编码下的误码性能接近理想的简化LLR计算结果。     

概率整形对数似然比计算方法

概率整形技术可改变星座点概率分布从而提升传输性能,其传输重要环节之一的对数似然比计算采用log-map算法复杂度太高,难以进行硬件实现。针对上述问题,提出了一种简化的概率整形对数似然比计算方法。首先对16QAM同相或正交分量任一方向进行log-map算法简化处理,主要依据为指数累和运算的对数计算表达式,起主导作用的是求和项中的最大值。其次,依据映射符号和对应的比特顺序使用前述化简式逐个比特进行分解,概率使用玻尔兹曼分布代入计算。然后,依据浮点数值超出-1～1范围表示对数似然比软判决为比特0或1的概率足够大的规则再次进行简化。最后,将同相分量与正交分量方向的对数似然比合并构成16QAM对数似然比简化计算方法。简化算法在降低实现复杂度的基础上保持了较高的解调性能,相比log-map算法性能只退化0.1 dB,相同BER条件下比均匀分布SNR低约3.1 dB。     

Improved LDPC Algorithm Based on 16QAM Modulation System

对QAM调制系统进行分析,提出了一种简化状态软输入软输出APP算法.它基于LDPC和积算法思想,与其他简化状态SISO算法相比,具有更为一般的形式.该算法在解调输出时有效利用映射点之间的欧氏距离,计算出每一个编码比特的似然值,从而简化运算复杂度,并且利用判决反馈减小简化状态网格的Euclid距离损失.仿真表明,该方案能够有效利用QAM解调中的软输出,在高斯信道下,简化的译码算法比原有LDPC方案提高了0.25 dB增益.     

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。     

一种基于16QAM调制系统的LDPC改进算法

对QAM调制系统进行分析,提出了一种简化状态软输入软输出APP算法。它基于LDPC和积算法思想,与其他简化状态SISO算法相比,具有更为一般的形式。该算法在解调输出时有效利用映射点之间的欧氏距离,计算出每一个编码比特的似然值,从而简化运算复杂度,并且利用判决反馈减小简化状态网格的Euclid距离损失。仿真表明,该方案能够有效利用QAM解调中的软输出,在高斯信道下,简化的译码算法比原有LDPC方案提高了0.25 dB增益。     

高阶QAM调制MIMO系统高斯逼近简化算法

针对多输入多输出(MIMO)高阶正交幅度调制(QAM)系统检测算法使用传统的高斯逼近算法检测复杂度高的问题,研究了其简化算法.MIMO系统高斯逼近算法通过采用树形搜索的办法,对符号后验概率影响大的符号序列加以保留,其算法复杂度与保留符号序列数目成线性,且与调制阶数成指数关系.针对高阶调制QAM符号的特点,用多级映射的方法来进行高斯逼近,新方法结合树形搜索算法的思想,通过将高阶调制QAM符号拆分成多个4-QAM符号,从而可以每次两个比特的计算序列权重,其算法复杂度与调制阶数成线性关系,从而使得高阶调制系统的检测复杂度大大降低.仿真结果表明,多级映射高斯逼近算法能取得接近传统高斯逼近算法的性能.     

一种基于折线逼近的对数似然比简化算法

针对16QAM信号的对数似然比计算,该文提出一种新颖的折线逼近简化算法,采用分段的折线逼近16QAM信号的对数似然比曲线,进而使用简单的线性运算替代原标准LLR算法中复杂的非线性运算,仿真结果表明,该算法可以理想地逼近标准LLR算法的计算结果,在BITCM系统中应用不会带来系统的性能折损。     

HSDPA中QAM软解调算法实现和性能分析

正交幅度调制(QAM)方式可以提高系统的频谱利用率,因此受到高速通信体制的广泛青睐,3GPP在HS-DPA中也引入了16QAM和64QAM.为了提高QAM系统性能,解调时一般采用软判决译码方式,对数似然比(Log Likelihood Ratio,LLR)软判决准则就是为计算QAM信号软判决译码度量值发展而来的.本文在介绍LLR求取原理的基础上,引入了简单的LLR求取算法,并进行了相关仿真工作.     

HSDPA中QAM软解调算法实现和性能分析

正交幅度调制（QAM）方式可以提高系统的频谱利用率,因此受到高速通信体制的广泛青睐,3GPP在HS-DPA中也引入了16QAM和64QAM。为了提高QAM系统性能,解调时一般采用软判决译码方式,对数似然比（Log Likelihood Ratio,LLR）软判决准则就是为计算QAM信号软判决译码度量值发展而来的。本文在介绍LLR求取原理的基础上,引入了简单的LLR求取算法,并进行了相关仿真工作。     

Coded QAM using a binary convolutional code

As an alternative to trellis coding, a binary convolutional code is considered for use with such nonbinary modulation schemes as quadrature amplitude modulation (QAM). A Gray code is used to map the encoder output to the M-ary QAM constellation. The focus is on the design of 16-ary coded QAM with a rate 3/4 punctured convolutional code of a constraint length 7. A quantized binary metric generation method is proposed and shown to be suboptimum as compared to the direct use of a M-ary unquantized metric. Impressive coding gains and bandwidth efficiency are shown in comparison with uncoded systems     

General Log‐Likelihood Ratio Expression and Its Implementation Algorithm for Gray‐Coded QAM Signals

A simple and general bit log‐likelihood ratio (LLR) expression is provided for Gray‐coded rectangular quadrature amplitude modulation (R‐QAM) signals. The characteristics of Gray code mapping such as symmetries and repeated formats of the bit assignment in a symbol among bit groups are applied effectively for the simplification of the LLR expression. In order to reduce the complexity of the max‐log‐MAP algorithm for LLR calculation, we replace the mathematical max or min function of the conventional LLR expression with simple arithmetic functions. In addition, we propose an implementation algorithm of this expression. Because the proposed expression is very simple and constructive with some parameters reflecting the characteristic of the Gray code mapping result, it can easily be implemented, providing an efficient symbol de‐mapping structure for various wireless applications.     

Near-capacity coding in multicarrier modulation systems

We apply irregular low-density parity-check (LDPC) codes to the design of multilevel coded quadrature amplitude modulation (QAM) schemes for application in discrete multitone systems in frequency-selective channels. A combined Gray/Ungerboeck scheme is used to label each QAM constellation. The Gray-labeled bits are protected using an irregular LDPC code with iterative soft-decision decoding, while other bits are protected using a high-rate Reed-Solomon code with hard-decision decoding (or are left uncoded). The rate of the LDPC code is selected by analyzing the capacity of the channel seen by the Gray-labeled bits and is made adaptive by selective concatenation with an inner repetition code. Using a practical bit-loading algorithm, we apply this coding scheme to an ensemble of frequency-selective channels with Gaussian noise. Over a large number of channel realizations, this coding scheme provides an average effective coding gain of more than 7.5 dB at a bit-error rate of 10/sup -7/ and a block length of approximately 10/sup 5/ b. This represents a gap of approximately 2.3 dB from the Shannon limit of the additive white Gaussian noise channel, which could be closed to within 0.8-1.2 dB using constellation shaping.     

On the general BER expression of one- and two-dimensional amplitude modulations

Quadrature amplitude modulation (QAM) is an attractive technique to achieve high rate transmission without increasing the bandwidth. A great deal of attention has been devoted to the study of bit error rate (BER) performance of QAM, and approximate expressions for the bit error probability of QAM have been developed in many places in the literature. However, the exact and general BER expression of QAM with an arbitrary constellation size has not been derived yet. We provide an exact and general closed-form expression of the BER for one-dimensional and two-dimensional amplitude modulations, i.e., PAM and QAM, under an additive white Gaussian noise (AWGN) channel when Gray code bit mapping is employed. The provided BER expressions offer a convenient way to evaluate the performance of PAM and QAM systems for various cases of practical interest. Moreover, simple approximations can be found from our expressions, which are the same as the well-known approximations, if only the dominant terms are considered.     

Monitoring Data Management Information System for Securities Market

The quadrature amplitude modulation (QAM) is the basic technology on high speed broadband communication physical level symbol mapping. Systems requiring lower signal to noise ratio to achieve the same error probability are more power-efficient. The usage of high order modulation is limited due to its low power efficiency compared to lower order modulation. This paper combines the characteristics of Gray code symbol mapping for QAM constellation to design a soft decision algorithm based on signal diversity (div-log-MAP). The bottle-neck of the low power efficiency is overcome and highest power efficiency can be realized. The performance of div-log-MAP can beyond the performance of log maximum a posteriori probability algorithm. At the same time, the proposed algorithm is a more effective method to utilize high order QAM modulation on high speed broadband communication.     

Constellation mappings for two-dimensional signaling of nonuniform sources

The design of two-dimensional constellation mappings for the transmission of binary nonuniform memoryless sources over additive white Gaussian noise channels using standard M-ary PSK and QAM modulation schemes is investigated. The main application of this problem is the incorporation of an adaptive mapping assignment in modem devices that employ fixed PSK/QAM modulation schemes for the transmission of heterogenous data (such as multimedia information) containing various levels of nonuniformity. In general, the optimal mapping depends on both the probability distribution of the input signals and the signal-to-noise ratio (SNR) in the channel, in addition to the geometry of the signal constellation. We show that constellation mappings which follow the objective of minimizing the average symbol energy and, given this, maximizing the decoding probability of the most likely signals, can yield symbol-error-rate and bit-error-rate performance that is substantially better than Gray encoding maps. Gains as high as 3.5 dB in SNR E/sub b//N/sub 0/ are obtained for highly nonuniform sources. Finally, we note that the mappings techniques result in nonzero mean constellations and briefly consider their performances when they are converted to zero mean constellations by shifting. In this case, we observe that the shifted zero-mean Gray map outperforms our shifted maps for small- to medium-sized constellations (M/spl les/32), but not for larger sizes.     

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.