MIMO系统中一种新颖的联合信道估计与检测算法

本文基于EM(Expectation-Maximum)算法,提出了一种简单而有效的联合信道估计与检测接收机结构。接收机中通过采用非穷尽列表形式的后验概率检测算法,避免了传统干扰抵消结构中各天线发送信号间的残余干扰对后验概率计算的影响。并进一步针对常用的非穷尽列表形式后验概率检测算法存在的列表冗余度大的问题,提出了自适应长度的列表球形译码算法(ASLSD,Adaptive Size List Sphere Decoding)。该算法通过更新检测半径和设置停止条件,使检测列表长度可随信噪比和迭代次数自适应变化。而且通过将列表操作与LSD(List Sphere Decoding)算法相结合,避免了符号序列在不同半径下的重复检测和排序操作。仿真表明,在复杂度方面,该算法需搜索的路径数远小于LSD算法。在算法性能方面,以3次迭代10~(-4)误码率为例,该算法与PIC算法相比可以获得近2dB的性能增益,因而具有更优的性能与复杂度的折衷。     

MIMO系统中一种自适应的迭代检测译码算法

针对常用的非穷尽列表形式后验概率检测算法直接采用恒定且较大的列表长度,导致列表冗余度大的问题,该文提出了一种自适应长度的列表球形译码算法（Adaptive Size List Sphere Decoding,ASLSD）。在算法中通过更新检测半径和设置停止条件,使检测列表长度可随信噪比和迭代次数自适应变化。而且通过将列表操作与LSD（List Sphere Decoding）检测相结合,避免了符号序列在不同半径下的重复检测。仿真表明,在较小性能损失的前提下,该算法可以大大减小所需检测列表的长度,进而有效降低接收机的复杂度。     

MIMO系统中一种自适应的迭代检测译码算法

针对常用的非穷尽列表形式后验概率检测算法直接采用恒定且较大的列表长度,导致列表冗余度大的问题,该文提出了一种自适应长度的列表球形译码算法(Adaptive Size List Sphere Decoding, ASLSD)。在算法中通过更新检测半径和设置停止条件,使检测列表长度可随信噪比和迭代次数自适应变化。而且通过将列表操作与LSD (List Sphere Decoding)检测相结合,避免了符号序列在不同半径下的重复检测。仿真表明,在较小性能损失的前提下,该算法可以大大减小所需检测列表的长度,进而有效降低接收机的复杂度。     

基于SSCANL译码器的联合迭代检测译码算法

为了提升基于极化码的稀疏码多址接入（sparse code multiple access,SCMA）系统接收机性能,提出了基于简化软消除列表（simplify soft cancellation list,SSCANL）译码器的循环冗余校验（cyclic redundancy check,CRC）辅助联合迭代检测译码接收机方案。该方案中极化码译码器使用SSCANL译码算法,采用译码节点删除技术对软消除列表（soft cancellation list,SCANL）算法所需要的L次软消除译码（soft cancellation, SCAN）进行简化,通过近似删除冻结位节点,简化节点间软信息更新计算过程,从而降低译码算法的计算复杂度。仿真结果表明,SSCANL算法可获得与SCANL算法一致的性能,其计算复杂度与SCANL算法相比有所降低,码率越低,算法复杂度降低效果越好;且基于SSCANL译码器的CRC 辅助联合迭代检测译码接收机方案相较基于SCAN译码器的联合迭代检测译码（joint iterative detection and decoding based on SCAN decoder, JIDD-SCAN）方案、基于SCAN译码器的CRC辅助联合迭代检测译码（CRC aided joint iterative detection and decoding based on SCAN decoder,C-JIDD-SCAN）方案,在误码率为10^-4时,性能分别提升了约0.65 dB、0.59 dB。     

LTE-A系统一种降低复杂度的软球形检测算法

软球形译码算法虽然能接近ML(最大似然)算法的误码性能,但其计算复杂度很高。文章提出了一种降低计算复杂度的SSD(软球形译码)算法,该算法在QR(正交三角)分解算法的反向迭代上三角矩阵R中引入减弱噪声部分以缩小初始搜索半径,然后利用最小距离准则对搜索树进行有效地删减,缩小树搜索空间。MATLAB仿真结果表明,该算法在获得接近传统SSD性能的条件下,能够很大程度地降低系统的计算复杂度。     

V-BLAST系统中一种近似最佳列表检测算法

针对V-BLAST系统,提出一种近似最佳列表检测算法。该列表检测算法通过调节列表维数参数在检测性能和计算复杂度之间实现了较好的折衷。此外,给出了一种不同于OSIC算法的检测排序方法,进一步提高了检测性能。仿真和复杂度比较结果表明,在不相关和空间相关性较强的信道下,该列表检测算法均显著优于OSIC算法,甚至接近ML算法的性能,实现了性能和复杂度较好的折衷,是一种实用的选择。      

一种低复杂度的降低MIMO—OFDM峰平比的CARI方法

天线旋转取反算法(CARI)是降低MIMO-OFDM系统峰平功率比(PAPR)的一种性能较优的算法,不足之处是其迭代次数很大。CARI的次最优算法逐次次最优天线旋转取反(SS-CARI)算法虽然可以减小迭代次数,但性能损失又比较大。针对这一问题,提出了一种用滑动窗搜索旋转取反组合的次最优CARI方法,利用滑动窗搜索局部最优的旋转取反组合,既可以避免整体的遍历搜索大大减小CARI算法的计算复杂度,又可以改善SS-CARI的PAPR减小性能。仿真结果表明,该方法能够在系统复杂度与PAPR降低性能上取得很好的折衷。     

Turbo-MIMO系统中一种基于部分后验概率的软检测算法

迭代树搜索(ITS)是一种有效的基于M-算法的软MIMO检测方案。然而ITS会遇到某些比特的对数似然比(LLR)无法确定的情况,虽可采用赋常数值方法(称为clipping)解决,但这会影响系统性能。为此,该文提出一种新的基于M-算法的软检测方案。该方案在树的每一级递推计算部分符号序列的后验概率,并基于此近似计算从第1级到该级的所有比特LLR,再采用M-算法保留部分符号序列延伸至下一级。该算法可确保每比特都可计算LLR,且能得到可靠性高的LLR值。考虑到某些比特LLR会多次计算,文中给出了算法的低复杂度实现。另外,该文还给出了一种计算符号序列后验概率的简单方法。最后,仿真结果表明所提算法相比ITS具有更好的性能,并使性能与复杂度达到较好的折中。     

基于空间交替广义最大似然的低复杂度列表检测

针对V-BLAST系统,提出了一种低复杂度的空间交替广义最大似然（SAGL）列表检测算法。该算法的子检测器由简化最大似然（SML）检测器和连续干扰抵消（SIC）检测器组成。传统SIC算法每次只能对单一符号进行检测,而所提算法则利用相邻符号进行联合滑动检测,可以获得更高的分集增益。此外,所提SAGL算法对检测结果进行迭代修正来进一步提升检测性能。分析与仿真结果表明,与传统列表检测算法相比,所提SAGL列表检测算法以少许复杂度的增加为代价显著提升了检测性能。     

基于提前终止迭代的概率近似消息传递检测算法

大规模多输入多输出技术作为第5代通信系统的关键技术,可有效提高频谱利用率。基站端采用消息传递检测(MPD)算法可以实现良好的检测性能。但是由于MPD算法的计算复杂度随调制阶数和用户天线数的增加而增加,而概率近似消息传递检测(PA-MPD)算法可以减少MPD算法的计算复杂度。为了进一步降低PA-MPD算法的复杂度,该文在PA-MPD算法的基础上引入了提前终止迭代策略,提出了一种改进的概率近似消息传递检测算法(IPA-MPD)。首先确定不同用户的符号概率在迭代过程中的收敛速率,然后根据收敛率来判断用户的符号概率是否达到最佳收敛,最后对符号概率到达最佳收敛的用户终止算法迭代。仿真结果表明,在不同单天线用户配置下IPA-MPD算法的计算复杂度可降低为PA-MPD算法的52%～77%,且不损失算法的检测性能。     

Iterative Joint Detection, Decoding, and Channel Estimation in Turbo-Coded MIMO-OFDM

An iterative receiver for a multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system is considered to jointly decode the transmitted bits and estimate the channel state. The receiver consists of a list detector, a turbo decoder, and a channel estimator that is based on the space-alternating generalized expectation-maximization (SAGE) algorithm. This paper proposes a way to improve the convergence of the iterative detection and decoding by using a priori information to also recalculate the candidate list, aside from the log-likelihood ratios (LLRs) of the coded bits. A new list parallel interference cancellation (PIC) detector is derived to approximate an a posteriori probability (APP) algorithm with reduced complexity and minimal losses of performance. Furthermore, the organization of spectrally efficient decision-directed (DD) SAGE channel estimation under a constrained number of detector-decoder iterations is optimized by computer simulations, and the SAGE algorithm itself is modified for nonconstant envelope constellations. The list recalculation is shown to improve convergence. It is also shown that the list PIC detector with good initialization outperforms the K-best list sphere detector (LSD) in the case of small list sizes, whereas the complexities of the algorithms are of the same order. Despite the low preamble density and fast-fading channel, the proposed iterative receiver shows robust performance.     

New List Sphere Decoding (LSD) and Iterative Synchronization Algorithms for MIMO-OFDM Detection With LDPC FEC

New sphere decoding and synchronization algorithms for multiple-input–multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems are proposed in this paper. In particular, an iterative list branch-and-bound (BB) algorithm based on the basic BB algorithm is described to obtain a candidate list to compute soft information that is used in the iterative detector. Furthermore, an improved algorithm that uses prior information from the preceding iteration to calculate the lower bound is proposed, and the candidate list is updated every iteration. To obtain a complete modem architecture, we propose an efficient expectation–maximization (EM)-based iterative algorithm for synchronization and channel estimation to interface with the proposed list-sphere-decoding detector, and we investigate the performance of the designed MIMO-OFDM modem on a realistic fading channel. The obtained performance results show that it is possible to practically design a performing MIMO-OFDM modem with high spectral efficiency, i.e., 8 bit/s/Hz with a 4 $times$ 4 16-QAM MIMO-OFDM system.      

Near-Optimum Iterative Multiuser Receiver for FEC Encoded DS-CDMA

The powerful iterative algorithm of Turbo code is employed in the proposed iterative multiuser receiver for the downlink of a forward error correction (FEC) coded direct-sequence code-division multiple access (DS-CDMA) environment. The receiver iterates between the 2 coding dimensions, namely the spreading codes and the FEC codes. The optimum iterative multiuser receiver uses the optimum decentralised single-user detector to generate the single-user extrinsic information for the single-user decoders. This paper suggests a near-optimum detector using a folded trellis preselection stage for the multiuser signal detection, in order to reduce the dominating complexity of the optimum decentralised detector. Simulation results show that performance is close to optimum. The effect of the single-user decoders' extrinsic information on the signal detection stage is also investigated and it is found that extrinsic information improves performance.     

大气光通信中迭代检测算法研究

基于对数正态(L-N)湍流信道模型,研究了LDPC编码大气光通信多输入多输出(FSO-MIMO)系统迭代检测算法。分析了内迭代与外迭代次数对系统性能及计算复杂度的影响,并针对PDA检测算法复杂度高的问题,提出了一种基于反馈阈值的M-PDA迭代检测算法。改进的算法利用译码输出的比特先验信息对发送比特进行分类,从而降低检测复杂度,并通过选取合适的阈值,可以获得更好的检测性能。仿真结果表明,实验时需要综合考虑计算复杂度和性能,选取合适的内外迭代次数,仿真条件下,误码率为10-5、反馈阈值为0.7时,可以获得0.15dB的性能增益。     

Iterative reduced-search decoding for coded partial-response channels

The full-complexity soft-input/soft-output (SISO) detector based on the BCJR algorithm for coded partial-response channels has a computational complexity growing exponentially with channel memory length. In this letter, we propose a low complexity soft-output channel detector based on the Chase decoding algorithm, which was previously applied to decode turbo product codes. At each iteration, the proposed detector forms a candidate list using all possible combinations of bit patterns in the weakest indices based on tentative hard estimates and a priori information fed back from the outer decoder. To demonstrate the performance/complexity tradeoff of the proposed detector, simulation results over rate-8/9 turbo-coded EPR4 and ME/sup 2/PR4 channels are presented, respectively. It is shown that the proposed detector can significantly reduce the computational complexity with only a small performance loss compared to the BCJR algorithm.     

Extending a Fixed-Complexity Sphere Decoder to Obtain Likelihood Information for Turbo-MIMO Systems

A list extension for a fixed-complexity sphere decoder (FSD) to perform iterative detection and decoding in turbo-multiple input-multiple output (MIMO) systems is proposed in this paper. The algorithm obtains a list of candidates that can be used to calculate likelihood information about the transmitted bits required by the outer decoder. The list FSD (LFSD) overcomes the two main problems of the list sphere decoder (LSD), namely, its variable complexity and the sequential nature of its tree search. It combines a search through a very small subset of the complete transmit constellation and a specific channel matrix ordering to approximate the soft- quality of the list of candidates obtained by the LSD. A simple method is proposed to generate that subset, extending the subset searched by the original FSD. Simulation results show that the LFSD can be used to approach the performance of the LSD while having a lower and fixed complexity, making the algorithm suitable for hardware implementation.      

MIMO系统中的迭代分组MAP检测算法

该文提出了在分组MAP检测器内部进行干扰信息更新和检测信息迭代反馈的检测算法。在MIMO系统基本的分组MAP检测算法基础上,利用先检测分组产生的后验信息替代先验信息提高干扰信号的估计精确度,进一步可以使用迭代反馈的方法在检测器内部进行反馈检测分组的后验信息,从而提高了检测信号的分集度。仿真结果表明在未编码系统中改进的分组检测方法能够显著地提高系统误码率性能,在编码系统中能够加快整个系统的收敛。     

多径信道下一种线性空时多用户检测方法

给出了用于DS/CDMA系统的线性空时多用户接收机的数学模型,分析了在多用户空时接收机中空域处理和时域匹配滤波的作用,引入SOR算法,并将其改进应用到多径信道下的线性空时多用户检测中。通过迭代避免了直接求逆运算,显著降低了运算复杂度。仿真表明:线性空时多用户接收机能够明显提高接收机性能,并且随着接收机天线数的增加性能明显提高。     

基于消息传递的大规模多用户MIMO低复杂度的检测算法

针对大规模多用户多输入多输出(MIMO)系统中基站端检测复杂度高的问题,提出了一种低复杂度、基于强制收敛的变量节点全信息高斯消息传播迭代检测(VFI-GMPID-FC)算法.首先对传统的GMPID算法进行改进,得到VFI-GMPID算法,VFI-GMPID算法的检测性能逼近最小均方误差检测(MMSE)算法,但复杂度要大大低于MMSE算法.然后结合强制收敛思想和VFI-GMPID,提出VFI-GMPID-FC算法,进一步降低算法复杂度,提升检测效率.最后通过仿真结果表明,所提算法在保证检测性能的同时,能有效地降低算法的复杂度.