大规模MIMO系统中基于二对角矩阵分解的低复杂度检测算法

在大规模多输入多输出(MIMO)系统的上行链路检测算法中,最小均方误差(MMSE)算法是接近最优的,但算法涉及到大矩阵求逆运算,计算复杂度仍然较高。近年提出的基于诺依曼级数近似的检测算法降低了复杂度但性能有一定的损失。为了降低复杂度的同时逼近MMSE算法性能,该文提出基于二对角矩阵分解的诺依曼级数(Neumann Series)近似,即将大矩阵分解为以两条主对角线上元素组成的矩阵与空心矩阵之和。理论分析与仿真结果表明所提算法检测性能逼近MMSE检测算法,且其复杂度从O(K3)降低到O(K2),这里K是用户的数目。     

大规模MIMO系统混合线性迭代信号检测算法

针对大规模多输入多输出(MIMO)系统中线性最小均方误差(MMSE)信号检测算法复杂的高维矩阵求逆难以用于实际工程的问题,文章基于矩阵分块思想并结合Neumann级数展开算法,提出了一种低复杂度的混合迭代算法.利用MMSE算法中加权矩阵逆矩阵的Neumann级数二阶展开作为其分块矩阵求逆的迭代初始值,可以有效提高算法收...     

基于Kaczmarz迭代的大规模MIMO系统低复杂度软输出信号检测

大规模MIMO系统上行链路中,最小均方误差（MMSE）算法能获得接近最优的线性检测性能,但是涉及复杂度较高的矩阵求逆运算.本文基于Kaczmarz迭代提出一种低复杂度软输出信号检测算法,在算法实现中避免了矩阵求逆运算,将实现复杂度由O（K³）降为O（K²）.同时,引入了最优松弛参数进一步加快算法收敛,最后给出了两种用于信道译码的LLR的近似计算方法.仿真结果表明：所提出的Kaczmarz迭代软输出信号检测算法经过两到三次简单的迭代即可较快地收敛,并达到接近MMSE检测算法的误码率性能的水平,其性能与复杂度均优于基于矩阵近似求逆的一类检测算法.     

基于切比雪夫-迹迭代的大规模MIMO系统软输出信号检测

在多用户大规模多输入多输出(MIMO)系统信号检测算法中,最小均方误差(MMSE)算法可取得近似最优性能,但MMSE算法中高维矩阵求逆的复杂度过高,导致在实际应用中难以快速有效地实现.同时,对于高阶正交幅度调制(HQAM),如果符号向比特的解映射采用硬判决,将会导致后续信道译码的性能明显下降.因此,该文针对采用格雷编码的HQAM的多用户大规模MIMO系统,提出一种基于切比雪夫-迹迭代(CTI)的低复杂度软输出信号检测算法.该算法不但有效地规避了信号检测所需的高维矩阵求逆,同时,利用格雷编码的调制信号的比特翻转特性和二叉树结构,给出了一种融合三叉链表搜索的比特对数似然比(LLR)简化计算方法.仿真结果表明,该文所提的软输出信号检测算法最多需要3次迭代就能收敛并可取得接近MMSE算法的性能,在复杂度和性能之间取得了很好的折中.     

用于大规模MIMO系统的改进CG检测算法

针对大规模多输入多输出(Multiple-Input Multiple-Output,MIMO)系统中近似最优线性最小均方误差(Minimum Mean Square Error,MMSE)算法复杂度过高问题,提出了RC-CG(Region Constellation-Conjugate Gradient)低复杂度近似最优信号检测算法。该算法首先利用共轭梯度(Conjugate Gradient,CG)迭代算法避免MMSE信号检测算法的高维度矩阵求逆,降低计算复杂度;其次引入二分查找算法对星座图进行区域分块,优化迭代初始解,使算法在保证原来检测性能的基础上加快收敛速度。仿真结果表明,该算法不仅可以达到近似MMSE算法的检测性能,而且适用于高阶调制,算法复杂度从O(K3)降低到O(K2)。     

基于LDPC编码的MIM0系统迭代接收机研究

研究了基于LDPC编码无线MIMO通信系统中的软输出最小均方误差干扰抵消迭代(MMSE PIC)检测算法.针对初次迭代检测时PIC输出的后验比特对数似然比(LLR)不可靠的问题,利用MMSE滤波器输出的高斯近似表示,给出了基于后验概率估计的迭代干扰抵消检测算法,以提高检测器输出的编码比特对数似然比的可靠性.仿真结果表明:改进的检测算法优于现有算法.     

多小区Massive MIMO系统中低复杂度MMSE线性检测算法研究

文章针对多小区Massive MIMO上行链路系统中MMSE线性检测中涉及大矩阵求逆具有高复杂度的问题,提出了一种低复杂度的MMSE检测算法。首先考虑已知目标小区的信道状态信息而其他小区信道状态信息未知条件下,通过求解干扰项与噪声之和的均值与方差,将多小区信道模型转化为单小区信道模型,再利用MMSE算法进行检测。为了降低求逆矩阵的复杂度,将大矩阵分解为对角矩阵和空心矩阵之和,再利用诺依洛曼级数近似将其展开,并优化展开项因子来增加算法收敛速度。仿真结果表明,所提出的改进算法在性能损失很少的情况下复杂度从O(K~3)降低到O(K~2),其中K为本小区中的用户数。     

基于LDPC编码的MIM0系统迭代接收机研究

研究了基于LDPC编码无线MIMO通信系统中的软输出最小均方误差干扰抵消迭代(MMSE PIC)检测算法.针对初次迭代检测时PIC输出的后验比特对数似然比(LLR)不可靠的问题,利用MMSE滤波器输出的高斯近似表示,给出了基于后验概率估计的迭代干扰抵消检测算法,以提高检测器输出的编码比特对数似然比的可靠性.仿真结果表明...     

大规模MIMO系统中块高斯-赛德尔检测算法

最小均方误差(Minimum Mean Square Error,MMSE)检测算法,虽然能在大规模多输入多输出系统中获得接近最优的线性检测性能,但是涉及高维矩阵求逆运算,难以在实际应用中快速有效地实现.提出了块高斯-赛德尔(Block Gauss-Seidel,BGS)低复杂度信号检测算法,将MMSE检测器的滤波矩阵先进行分块预处理,构造分裂矩阵,再通过迭代求解发送信号向量估计值,以提高算法检测性能.仿真结果表明,BGS迭代算法在调制方式为64QAM、用户侧的天线数量设置为16、基站侧的天线数量设置为256时,迭代2次后就能快速接近MMSE检测性能.在设置近似初始值后,BGS算法的性能得到了进一步的改善.当调制方式为256QAM时,设置近似初始值的BGS算法在迭代2次后就能逼近MMSE算法的误码率(Bit Error Ratio,BER)性能曲线,此时算法的复杂度仍然保持在O(K2).     

MMSE信道估计下的软输出MMSE MIMO检测算法

信道编码的MIMO无线通信系统中,MIMO信号检测器需要输出编码比特的对数似然比,以获得更好的误码率性能.现有的软输出MMSE MIMO检测算法基于理想信道估计得到,在实际信道估计下会导致性能损失.本文针对MMSEMIMO信道估计,基于MMSE信道估计的统计特性,推导了考虑信道估计误差影响的新的软输出MMSE MIMO检测算法.仿真结果表明,相对于现有的软输出MMSE MIMO检测算法,所提出的算法可以显著降低由于信道估计误差导致的残留误码平层,而增加的计算复杂度可以忽略不计;同时,所提算法对信道估计误差方差的相对误差不敏感,具有实际应用的价值.     

Joint Iterative Multiuser and Narrowband Interference Suppression in Coded Asynchronous DS-CDMA Channels

Multiuser interference suppression in coded direct sequence code division multiple access (DS-CDMA) uplink channels is significantly impacted by the application of the turbo processing concept. This paradigm essentially involves the iterative exchange of soft information between a multiuser demodulator and a bank of single-user decoders, to their mutual benefit. The present work proposes a joint iterative minimum mean square error (MMSE) multiuser and narrowband interference suppressor for coded asynchronous DS-CDMA channels. Since the parameters of the narrowband interference are unknown a priori, the first iteration in this scheme is effectively just MMSE multiuser interference suppression. The outputs of all users' soft decoders (available at the end of each iteration) are fed back to subtract their (estimated) cumulative contribution from the received signal vector. The residue comprises the narrowband interference embedded in wideband noise, so that the former can be piecewise interpolated over chip intervals of appropriate duration, and then subtracted from the received signal, to provide a narrowband-interference-free input signal for the next iteration. The soft-decoded feedback estimates of the interferers' signals are used in each iteration also to perform soft MMSE multiuser interference suppression, in conjunction with subtractive interference cancellation. This scheme performs well at both low and high received signal powers, and displays the successive cancellation property across iterations, exhibiting good near-far resistance. Introducing multisensor arrays at the receiver relaxes the limitations imposed by the inherent suboptimality of MMSE multiuser demodulation, insofar as it enhances interuser separation, now in the spatial sense. Simulations indicate that the performance of the proposed technique surpasses that of all existing suboptimal algorithms in this context.     

Low Complexity Iterative ICI Cancellation and Equalization for OFDM Systems Over Doubly Selective Channels

In this paper, a low complexity iterative intercarrier interference (ICI) cancellation and equalization technique is proposed for use in OFDM systems over doubly selective channels. In the iterative parallel interference cancellation/minimum mean square error (PIC/MMSE) detector has a high complexity and a restriction on the structure which can not remove the ICI in the initial stage. Therefore, an error propagation occurs due to the ICI regenerated by the incorrect output of soft-input soft-output (SISO) decoder. In order to reduce the error propagation, an MMSE detector based on the successive interference cancellation (SIC) is used in the initial stage. The low complexity MMSE detector is also derived to minimize the error propagation by quantifying the decision error before SISO decoding. In the first iteration, simulation results show that the proposed scheme outperforms the conventional PIC/MMSE scheme by about 3 dB at bit error rate $({rm BER})=1times 10^{-3}$ while maintaining the equivalent computational complexity. In the subsequent iteration, it is possible to cancel the ICI out in the received signals by the aid of soft log-likelihood ratio (LLR) fed from the SISO decoder. Converting the LLR to the decision error probability, the error covariance matrix is obtained more accurately. As a result, the error propagation can be effectively reduced by dealing with only the dominant components, when considering decision errors. Finally, simulation results show that the proposed scheme outperforms the conventional PIC/MMSE scheme.      

Multi‐group linear turbo equalization with intercell interference cancellation for MC‐CDMA cellular systems

In this paper, we investigate multi‐group linear turbo equalization using single antenna interference cancellation (SAIC) techniques to mitigate the intercell interference for multi‐carrier code division multiple access (MC‐CDMA) cellular systems. It is important for the mobile station to mitigate the intercell interference as the performance of the users close to cell edge is mainly degraded by the intercell interference. The complexity of the proposed iterative detector and receiver is low as the one‐tap minimum mean square error (MMSE) equalizer is employed for mitigating the intracell interference, while a simple group interference canceller is used for suppressing the intercell interference. Simulation results show that the proposed iterative detector and receiver can mitigate the intercell interference effectively through iterations for both uncoded and coded signals. Copyright © 2009 John Wiley & Sons, Ltd.     

Multicell uplink spectral efficiency of coded DS-CDMA with randomsignatures

A simple multicell uplink communication model is suggested and analyzed for optimally coded randomly spread direct sequence code-division multiple access (DS-CDMA). The model adheres to Wyner's (1994) infinite linear cell-array model, according to which only adjacent-cell interference is present, and characterized by a single parameter 0⩽α⩽1. The discussion is confined to asymptotic analysis where both the number of users and the processing gain go to infinity, while their ratio goes to some finite constant. Single cell-site processing is assumed and four multiuser detection strategies are considered: the matched-filter detector, “optimum” detection with adjacent-cell interference treated as Gaussian noise, the linear minimum mean square error (MMSE) detector and a detector that performs MMSE-based successive interference cancellation for intracell users with linear MMSE processing of adjacent-cell interference. Spectral efficiency is evaluated under three power allocation policies: equal received powers (for all users), equal rates, and a maximal spectral efficiency policy. Comparative results demonstrate how performance is affected by the introduction of intercell interference, and what is the penalty associated with the randomly spread coded DS-CDMA strategy. Finally, the effect of intercell time-sharing protocols as suggested by Shamai and Wyner (1997) is also examined, and a significant system performance enhancement is observed     

基于软判决的MMSE-OSIC接收机

串行干扰相消接收机是广泛应用于多输入多输出系统中的一种接收端信号处理与检测技术。在串行干扰相消接收机中,先检测的层的判决准确性会对后续层的检测产生影响。检测过程中产生的判决误差,将对后续层的检测引入残留干扰,进而影响后续层检测的正确性,造成差错传播。本文提出一种基于软判决的最小均方误差检测带排序串行干扰相消接收机,可以有效减轻基于硬判决方法的带排序串行干扰相消接收机的差错传播问题。在重构干扰信号时,该接收机使用根据软判决信息得到的符号期望,替代硬判决方法,能够有效降低干扰相消时各层之间由判决误差引起的残留干扰;该接收机还可以精确估计残留干扰的功率以及各层数据流的后处理信干噪比,改善了基于硬判决方法的串行干扰相消接收机存在的各层后处理信干噪比估计值偏大的问题。可靠性更高的软判决结果有效降低了残留干扰,更精确的各层后处理信干噪比抑制了残留干扰对后续数据流检测的影响,提高了判决结果和排序过程的准确性。仿真结果证明,基于软判决的最小均方误差检测带排序串行干扰相消接收机可以有效避免差错传播的产生,因而获得较大的性能提升。      

Weighted interference cancellation detector for convolutionallycoded CDMA system

Weighted interference cancellation is proposed to improve the post-decoding interference cancellation detector in a convolutionally coded CDMA system. A weight determination method is presented in which the estimated information bit error probability from the soft-output Viterbi algorithm is used. Simulation results show that the proposed scheme outperforms the previous post-decoding interference cancellation detector     

Iterative Group-Blind Multiuser Detection and Decoding With Signal Rank Estimation for Coded CDMA Systems

In this paper, a turbo receiver structure is proposed for the uplink of coded code-division multiple-access (CDMA) systems in the presence of unknown users. The proposed receiver consists of two stages following each other. The first stage performs soft interference cancellation and group-blind linear minimum mean square error (MMSE) filtering, and the second stage performs channel decoding. The proposed group-blind linear MMSE filter suppresses the residual multiple-access interference (MAI) from known users based on the spreading sequences and the channel characteristics of these users while suppressing the interference from other unknown users using a subspace-based blind method. The proposed receiver is suitable for suppressing intercell interference in heavily loaded CDMA systems. Since the knowledge of the number of unknown users is crucial for the proposed receiver structure, a novel estimator is also proposed to estimate the number of unknown users in the system by exploiting the statistical properties of the received signal. Simulation results demonstrate that the proposed estimator can provide the number of unknown users with high accuracy; in addition, the proposed group-blind receiver integrated with the new estimator can significantly outperform the conventional turbo multiuser detector in the presence of unknown users.      

On the Equivalence of Turbo Multiuser Detector using MMSE with <Emphasis Type="Italic">A-Priori</Emphasis> Information and Soft Interference Cancellation Followed by MMSE Filtering

This letter derives a turbo multiuser detector with linear minimum mean squared error (MMSE) filtering using a-priori information in order to reduce the computational complexity. The equivalence of the turbo multiuser detector developed in this letter and the one based on soft interference cancellation followed by a linear MMSE filtering is established.     

Downlink transmission of broadband OFCDM systems-part IV: soft decision

In this paper, the performance of turbo-coded orthogonal frequency and code-division multiplexing (OFCDM) systems is investigated with soft multicode interference (MCI) cancellation and minimum mean-square error (MMSE) detection for downlink transmission in future high-speed wireless communications. To regenerate the soft interference signal, the conventional turbo decoding algorithm must be modified to provide log-likelihood ratio (LLR) values for all coded bits. Based on the LLR outputs of turbo decoder, two soft-decision functions are proposed, called LLR-soft-decision and Gaussian-soft-decision functions. The Gaussian assumptions used for deriving these two soft functions are verified by simulation results, and simple methods are proposed to estimate parameters used in the soft functions in practical systems. By means of computer simulations, the performance of soft MCI cancellation is studied extensively and compared with that of hard ones. It is shown that in a highly frequency-selective channel, soft MCI cancellation and MMSE detection can significantly improve the performance of turbo-coded OFCDM systems. Two iterations in turbo decoding are sufficient for both hard and soft-decision functions. The proposed soft-decision functions outperform the hard-decision function with various channel conditions and system parameters, such as the channel correlation, the quality of channel estimation, the number of iterations in turbo decoding and the frequency-domain spreading factor (N/sub F/). Furthermore, the Gaussian-soft-decision function provides better performance than the LLR-soft-decision function. Finally, although frequency diversity gain is saturated for large channel correlation when N/sub F/ is large as in , the gain increases further with increasing N/sub F/ for small channel correlation even when N/sub F/ is large.