LTE-A上行链路中的串行干扰消除检测算法研究

文中介绍LTE-A上行链路中串行干扰消除算法的实现方式。根据串行干扰消除算法容易引起误差传播的缺陷,提出一种改进的干扰消除算法,该方法利用译码反馈信息代替硬判决反馈信息,逐层去除干扰,对每层重构新的数据流进行检测,以降低层间的误差传播。最后,通过MATLAB仿真,表明本文提出的改进后的串行干扰消除算法比原始的串行干扰消除方法效果更好。     

频率选择性MIMO衰落信道中基于导频的软均衡算法

MIMO无线传输技术的有效应用有赖于高效的空时干扰抑制策略.针对频率选择性衰落MIMO信道特点,本文提出一种联合判决反馈干扰抵消和粒子滤波的软均衡方案.首先利用导频,确定了各发送信号最强径与接收天线之间的对应关系以及基于信干噪比的判决反馈干扰抵消顺序;其次,依据后验估计准则,充分利用径强度及接收信号结构信息,构造了接收信号的重要性分布函数,采用粒子滤波算法对感兴趣用户信号实施最优判决并进行干扰抵消.仿真结果表明:相比于其他均衡方法,本算法可以有效抑制均衡误差的传播,同时具有较低的计算复杂度.     

上行链路MC-CDMA系统并行干扰抵消接收机的改进

介绍了上行链路MC-CDMA系统的一种初级采用线性MMSE检测的PIC多用户接收机。为了减小初级判决不精确带来的误差传播,提出了一种新的基于部分并行干扰抵消的多级PIC接收机结构,他是通过每级乘以一个不同的部分相消因子实现的。在不考虑信道估计误差的情况下,仿真了上行信道不同用户数、不同部分相消因子对改进的接收机性能的影响。仿真结果表明改进的接收机具有更好的误码率性能。     

MIMO系统中一种改进的迭代串行干扰消除算法

多输入多输出(MIMO)系统中,串行干扰消除(SIC)算法复杂度相对较低,但干扰消除时存在差错传播问题。针对独立编码的垂直分层空时(V-BLAST)系统,提出一种联合译码的SIC算法,将译码完成的码字反馈给解调器,从接收信号中消除。引入一种码字排序准则,利用软信息对码字排序,优先对高可靠性码字译码。通过码字排序和联合译码提高检测符号的准确性,减少差错传播。仿真结果表明,与已存在的接收方法相比,该算法能有效地抑制差错传播,大幅提升误码率性能。      

MC-CDMA系统中的PPIC多用户接收机研究

研究了上行链路MC-CDMA系统中的部分干扰抵消多用户接收机方案,提出了初级采用线性MMSE检测的多级PIC多用户接收机。为了减小初级判决不精确带来的误差传播,每级乘以一个不同的部分相消因子以实现部分消除。在不考虑信道估计误差的情况下,仿真了不同用户数下该方案与传统解相关和最小均方误差多用户检测的性能比较。仿真结果表明提出的PPIC接收机具有更好的误码率性能。     

一种比较决策多用户检测器的研究

以多速率码分多址(CDMA)传输为出发点，以满足不同用户信号的信干比(SIR)检测要求为目标，给出了在具有决策反馈的并行干扰抵消(PIC)检测框架下，通过实施基于概率数据关联(PDA)预估计软判决和并行干扰抵消硬判决的两种决策比较，进而选择最佳判决的方法，有效地抑制了由于信号估计不准确而造成的错误干扰抵消及相应的判决错误。文中给出了仿真结果，并分别就单一的软、硬判决及比较决策的检测性能进行了分析和比较。     

适用于迫整接收机的排序格基规约算法

针对单用户多输入多输出（MIMO）无线信号传输系统,本文采用一种低复杂度高性能的线性接收机结构—迫整接收机（Integer-Forcing）,并在此基础上提出一种利用成对列变换依次减小格基的模长的格基规约（Lattice Reduction）算法—排序格基规约。迫整接收机利用整数域的闭环特性以及最大化每层信干噪比（SINR）的优化技术,可以用较低的复杂度获得较好的性能。鉴于最大化各层信干噪比等价于格理论中的最短独立向量组（SIVP）问题,本文提出的排序格基规约算法以较小的正交性能损失作为代价,有效的降低了解决该问题的复杂度,特别适合中大规模的MIMO系统。仿真实验和分析表明,不仅在格基模长性能上优于经典的LLL算法,而且具有更快的运算速度;同时,基于排序格基规约的迫整接收机显示出优于大部分线性接收机,且接近最大似然（ML）接收机的误比特率（BER）性能。      

软判决技术在MIMO系统中的应用

随着移动无线通信技术的迅猛发展,MIMO成为在5G及其未来通信中的关键性技术。本文重点讨论了软判决技术在MIMO系统中的应用,并利用Matlab软件对MIMO系统进行建模分析;接收机分别采用软判决和硬判决技术对接收信号进行检测,通过仿真证明了软判决相对于硬判决具有更好的抗噪性能。     

低复杂度的分组检测空时接收机

V-BLAST接收机是提高无线通信系统传输数率的有效技术,但由于该算法存在大量的求伪逆、迫零和排序,算法的复杂度高,限制了它在实际中的应用;线性迫零(ZF)接收机和最小均方误差(MMSE)接收机复杂度低,但性能差。该文提出了一种分组检测空时接收机,组内采用串行干扰抵消接收,与V-BLAST接收机相比,降低了算法的复杂度。仿真结果表明：所提出的基于MMSE准则下的分组检测空时接收机的性能明显好于基于迫零准则的 V-BLAST接收机。     

一种基于SIC的NOMA下行链路信号检测方法

面对频谱效率和系统容量等方面出现的新需求,传统的多址方式已经不能满足需要,业内提出一种新的多址方式NOMA。NOMA具有频谱利用率高、系统容量大等优点,但是其传统的下行链路串行干扰消除检测技术中的检测算法是基于硬判决的,检测性能差。介绍了NOMA链路实现的基本原理,并提出一种改进的串行干扰消除检测方法,即直接计算比特的软信息来完成软判决,恢复干扰信号后再做消除。最后通过仿真分析验证,该算法可以提高串行干扰消除检测的检测性能。     

Performance of successive interference cancellation inconvolutionally coded multicarrier DS/CDMA systems

This article presents a successive interference cancellation (SIC) scheme for a multicarrier (MC) asynchronous DS/CDMA system, wherein the output of a convolutional encoder modulates bandlimited spreading waveforms at different subcarrier frequencies. In every subband, the SIC receiver successively detects the interferers' signals and subtracts them from that of the user-of-interest. The SIC receiver employs maximal-ratio combining (SIC-MRC) for detection of the desired user, and feeds a soft decision Viterbi decoder. A comparison is made among SIC-MRC, matched filter detection with MRC (MF-MRC), and N-tap minimum mean-squared error (MMSE) receivers with optimal tap coefficients, assuming a slowly varying, frequency selective, Rayleigh fading channel, where N is the processing gain. Analysis and simulation results show that the SIC-MRC can obtain performance close to that of N-tap MMSE receivers, and both of them have better ability to suppress multiple-access interference (MAI) than does MF-MRC. Finally, with timing or phase tracking errors, the results show that SIC-MRC can still retain a performance advantage over MF-MRC     

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.      

Equal BER performance in linear successive interferencecancellation for CDMA systems

In this contribution, we calculate the received power distribution required to obtain equal bit-error rate (BER) performance for all links in a code-division multiple-access system employing a linear successive interference cancellation (SIC) receiver at the base station for an additive white Gaussian noise channel. We show that the variance of the decision statistic of the linear SIC receiver can be formulated in a nonrecursive manner that allows calculation of the power profile necessary to obtain equal signal-to-noise-plus-interference ratios for all received signals when cancellation order is determined based on average power. When equal BER performance is required, this formulation allows capacity limits to be determined for a required signal-to-interference-plus-noise ratio (SINR) or an SINR limitation to be calculated for a given capacity. We also show that the power profiles required are significantly larger than those obtained when perfect cancellation is assumed, highlighting the inadequacy of such an assumption     

Soft-decision multistage multiuser interference cancellation

Successive interference cancellation (SIC) refers to a family of low-complexity multiuser detection methods for direct-sequence code-division multiple-access systems. The performance of multistage SIC depends on the decision function used in the interference cancellation iterations, e.g., hard, soft, or linear decision functions. Due to error propagation, multistage SIC with hard data bit decisions may perform more poorly than multistage SIC with linear or soft decision functions. We propose and analyze a family of generalized unit-clipper bit decision functions that better combine linear and hard decisions. Performance within 0.4 dB of the single-user bound can be obtained. We then make robust the above soft-decision SIC to time-delay errors as large as half a PN chip and evaluate its performance.     

Approximate Minimum BER Power Allocation for MIMO Spatial Multiplexing Systems

Precoding for multiple-input multiple-output (MIMO) spatial multiplexing generally requires high feedback overhead and/or high-complexity processing. Simultaneous reduction in transmitter complexity and feedback overhead is proposed by imposing a diagonal structural constraint to precoding, i.e., power allocation. Minimum bit-error rate (MBER) is employed as the optimization criterion, and an approximate MBER (AMBER) power-allocation algorithm is proposed for a variety of receivers, including zero-forcing (ZF), successive interference cancellation (SIC), and ordered SIC (OSIC). While previously proposed precoding schemes either require ZF equalization for MBER, or use a minimum mean-squared error (MMSE) criterion, we provide a unified MBER solution to power allocation for ZF, SIC, and OSIC receiver structures. Improved error-rate performance is shown both analytically and by simulation. Simulation results also indicate that SIC and OSIC with AMBER power allocation offer superior performance over previously proposed MBER precoding with ZF equalization, as well as over MMSE precoding/decoding. Performance under noisy channels and power feedback is analyzed. A modified AMBER algorithm that mitigates error propagation in interference cancellation is developed. Compared with existing precoding methods, the proposed schemes significantly reduce both transmit processing complexity and feedback overhead, and improve error-rate performance     

时频双选信道OFDM系统的ICI消除与均衡

在正交频分复用（OFDM）系统中,因高速移动造成的多普勒效应导致子载波间正交性的破坏并产生载波间干扰（ICI）。为了消除ICI,本文通过分析ICI分布特性及带状矩阵特性,提出了低复杂度的迭代干扰抵消算法和基于最小均方误差准则的排序串行干扰抵消(MMSE-OSIC)算法。仿真结果表明,与传统子载波间干扰频域均衡算法相比,新算法在计算复杂度和性能之间取得了良好的平衡,且MMSE-OSIC算法可以利用时变信道的时间分集特性在高信噪比情况下有效地消除“地板效应”。      

Analysis of an adaptive SIC for near-far resistant DS-CDMA

A new multiuser detection scheme is proposed which employs adaptive minimum mean square error (MMSE) detection in combination with successive interference cancellation (SIC). Through theoretical analysis and numerical examples, it is shown that the proposed detector provides superior performance to existing ones in terms of asymptotic multiuser efficiency (AME) and bit error rate (BER)     

Space-Time Adaptive MMSE Multiuser Decision Feedback Detectors With Multiple-Feedback Interference Cancellation for CDMA Systems

In this paper, we propose a novel space-time minimum mean square error (MMSE) decision feedback (DF) detection scheme for direct-sequence code-division multiple access (DS-CDMA) systems with multiple receive antennas, which employs multiple-parallel-feedback (MPF) branches for interference cancellation. The proposed space-time receiver is then further combined with cascaded DF stages to mitigate the deleterious effects of error propagation for uncoded schemes. To adjust the parameters of the receiver, we also present modified adaptive stochastic gradient (SG) and recursive least squares (RLS) algorithms that automatically switch to the best-available interference cancellation feedback branch and jointly estimate the feedforward and feedback filters. The performance of the system with beamforming and diversity configurations is also considered. Simulation results for an uplink scenario with uncoded systems show that the proposed space-time MPF-DF detector outperforms existing schemes such as linear, parallel DF (P-DF), and successive DF (S-DF) receivers in terms of bit error rate (BER) and achieves a substantial capacity increase in terms of the number of users, compared with the existing schemes. We also derive the expressions for MMSE achieved by the analyzed DF structures, including the novel scheme, with imperfect and perfect feedback and expressions of signal-to-interference-plus-noise ratio (SINR) for the beamforming and diversity configurations with linear receivers.     

Hybrid SNR-Adaptive Multiuser Detectors for SDMA-OFDM Systems

Multiuser detection (MUD) and channel estimation techniques in space-division multiple-access aided orthogonal frequency-division multiplexing systems recently has received intensive interest in receiver design technologies. The maximum likelihood (ML) MUD that provides optimal performance has the cost of a dramatically increased computational complexity. The minimum mean-squared error (MMSE) MUD exhibits poor performance, although it achieves lower computational complexity. With almost the same complexity, an MMSE with successive interference cancellation (SIC) scheme achieves a better bit error rate performance than a linear MMSE multiuser detector. In this paper, hybrid ML-MMSE with SIC adaptive multiuser detection based on the joint channel estimation method is suggested for signal detection. The simulation results show that the proposed method achieves good performance close to the optimal ML performance at low SNR values and a low computational complexity at high SNR values.     

V-BLAST系统中一种简单的发射功率分配方案

采用发射功率分配方案可以有效地提高V-BLAST系统的性能。一方面,采用注水发射功率分配方案,可以有效地提高系统容量,另一方面,采用合理的发射功率分配方案,可以在固定数据速率时,改善误码率性能。本文针对第二种应用,给出了一种基于等信干噪比的发射功率分配方案,计算复杂度低,需要的反馈信令少,而且该功率分配方案与调制方式和检测算法无关。通过对MMSE串行干扰抵消和MMSE软干扰抵消检测算法仿真验证,其性能远好于不采用发射功率分配方案,同时接近基于拉格朗日极值法的功率分配方案性能。