Design of Multiuser Downlink Linear MIMO Precoding Systems With Quantized Feedback

We treat the problem of sum-rate maximization via scheduling and linear precoding in multiuser (MU) multiple-input–multiple-output (MIMO) systems with quantized feedback. We formulate the optimal quantized linear precoder design problem and provide the numerical procedure for finding the solution. We also provide a simple scheduling scheme that exploits the MU diversity gain. With the aim of sum-rate maximization, we further address the quantization codebook design based on the capacity measure by introducing a new distance metric. It is demonstrated that, with or without scheduling, the proposed optimal linear precoding scheme achieves significant gain over the conventional linear precoder designs with similar feedback overhead, such as the zero-forcing precoder. Moreover, although the proposed quantization codebook design improves the performance of other existing MU-MIMO precoding schemes, the performance gain offered by it is typically much higher when it is coupled with the proposed linear precoding design.      

Low complexity LMMSE turbo equalization for combined error control coded and linearly precoded OFDM

The turbo equalization approach is studied for Orthogonal Frequency Division Multiplexing （OFDM） system with combined error control coding and linear precoding. While previous literatures employed linear precodcr of small size for complexity reasons, this paper proposes to use a linear precoder of size larger than or equal to the maximum length of the equivalent discrete-time channel in order to achieve full frequency diversity and reduce complexities of the error control coder/decoder. Also a low complexity Linear Minimum Mean Square Error （LMMSE） turbo equalizer is derived for the receiver. Through simulation and performance analysis, it is shown that the performance of the proposed scheme over frequency selective fading channel reaches the matched filter bound; compared with the same coded OFDM without linear precoding, the proposed scheme shows an Signal-to-Noise Ratio （SNR） improvement of at least 6dB at a bit error rate of 10 6 over a multipath channel with exponential power delay profile. Convergence behavior of the proposed scheme with turbo equalization using various type of linear precoder/transformer, various interleaver size and error control coder of various constraint length is also investigated.     

New Design for Linear Precoding over STBC in the Presence of Channel Correlation

In order to account for spatial correlation in a multiple input multiple output (MIMO) channel using precoding over space-time block codes (STBC), an approach was proposed for the design of a linear precoder (H. Sampath and A. Paulraj, 2002). This approach works well for orthogonal STBC but fails in the case of non-orthogonal STBC. Based on a min-max problem formulation, a new design of the linear precoder is proposed in this paper. Simulation results in the case of quasi-orthogonal STBC (ABBA) are presented in order to show the gain over the conventional design approach and the non-precoded system     

Nonredundant Precoding-Assisted Blind Channel Estimation for Single-Carrier Space–Time Block-Coded Transmission With Frequency-Domain Equalization

Relying on nonredundant diagonal precoding and independent and identically distributed (i.i.d.) source assumption, this paper proposes a blind channel estimation scheme for single-carrier frequency-domain equalization-based space-time block coded systems. The proposed method exploits the precoding-induced linear signal structure in the conjugate cross correlation between the two temporal block received signals as well as the circulant channel matrix property and can yield exact solutions whenever the channel noise is circularly Gaussian and the receive data statistic is perfectly obtained. The channel estimation formulation builds on rearranging the set of linear equations relating the entries of conjugate cross-correlation matrix and products of channel impulse responses into one with a distinctive block-circulant with circulant-block (BCCB) structure. This allows a simple identifiability condition depending on precoder parameters alone and also provides a natural yet effective optimal precoder design framework for improving solution accuracy when imperfect data estimation occurs. We consider two models of data mismatch, from both deterministic and statistical points of view, and propose the associated design criteria. The optimization problems are formulated to take advantage of the BCCB system matrix property and are solved analytically. The proposed optimal precoder aims to optimize solution robustness against deterministic error perturbation and also minimize the mean-square error when the data mismatch is modeled as a white noise. Pairwise error probability analysis is conducted for investigating the equalization performance. Numerical examples are used to illustrate the performance of the proposed method     

多用户MIMO系统广播信道的连续块对角化预编码算法

针对块对角化(BD)算法无法满足各个用户的需要、串行优化(SO)算法排序复杂、容量较低的问题,提出了一种连续块对角化(SBD)算法.该算法按照各用户的信道条件、服务质量(QoS)需求给用户定义不同的优先级,并按优先级次序进行块对角化,后续用户在对高优先级用户及同优先级用户不干扰的条件下采用块对角化法抵消共信道干扰(CC...     

快时变多用户MIMO-OFDM系统中复杂度可调的子载波分组预编码技术

在时变多用户MIMO-OFDM系统中,所有子载波整体预编码方案的性能优于单个子载波单独预编码方案。然而前者的复杂度是基站发射天线数 与子载波总数 乘积的函数,显著高于后者,特别 时,复杂度极高。为了解决这个问题,我们提出了一种基于最大化信泄噪比的复杂度可调的分组子载波（grouped-subcarrier maximum signal-to-leakage-and-noise ratio,GS-Max-SLNR）预编码方案。此外,我们推导了组间干扰公式,该公式在给定多普勒频移和信噪比的条件下,可以根据需要选取合适的分组数。理论建模和仿真表明,通过选取合适的分组数目,提出的GS-Max-SLNR能够实现复杂度和性能的良好折中。     

基于准正交空时码的最优线性预编码矩阵设计

为了充分利用信道信息改善应用准正交空时分组码的MIMO系统的性能,该文提出了将预编码矩阵和准正交空时分组码相结合的发射机制。信息在经过准正交空时分组码编码后,要经过线性预编码矩阵进行处理,才可以从发射天线发送。文中的预编码矩阵设计利用了MIMO信道的非零均值矩阵和相关矩阵,并采用成对差错概率作为其最优设计准则。仿真结果表明,相对于未经过预编码矩阵的系统,新系统的误码率性能有明显改善。     

Adaptive precoding and power allocation in distributed antenna systems with limited feedback

This paper introduces the limited feedback precoding into the distributed antenna system and proposes to adapt the predetermined orthogonal space time block codes to the available channel state information at the transmitter. The optimal representation of precoding information, namely the precoder, with least bits therefore becomes the key problem. Inspired by the characteristics of the distributed antenna system, we focus our work on the precoder construction, adaptable in response to the large and small scale fading, such that the symbol error probability is significantly reduced over that of a fixed, non‐adaptive, independent and identically distributed precoder codebook design. Furthermore, a suboptimal power‐loading strategy is presented by minimizing the derived tight upper bound on the average pairwise error probability of the precoded orthogonal space time block codes, which approaches the optimal performance asymptotically without additional channel knowledge other than the available feedback information. We prove that the proposed precoded orthogonal space time transmission scheme can achieve full diversity order. In particular, the robustness of our proposed transmission scheme to channel estimation error and feedback delay is respectively investigated in some detail, and numerical results show that it obviously improves the link reliability and obtains substantial gains even with few bits of feedback in comparison with conventional antenna selection scheme. Copyright © 2013 John Wiley & Sons, Ltd.     

Efficient QR-Based Multi-Mode Precoding for Limited Feedback Multi-User MIMO Systems

This paper proposes QR-based criteria for efficient selection of multi-mode precoders in multi-user multiple-input multiple-output (MU-MIMO) precoded systems with a limited feedback. In particular, a MU-MIMO QR based precoding scheme is developed which takes advantage of the overall precoder design among users in conjunction with QR detection. A selection criterion is developed to identify the precoder that yields the maximum free distance. Efficient mode selection and tree search strategies are adopted to reduce the complexity associated with the identification of the optimum precoder. To further improve the detection performance in correlated channels, an efficient QR-based MMSE V-BLAST detector is proposed. Computer simulations confirm that the proposed QR-based precoding scheme attains the performance of existing schemes with a significantly lower complexity level.     

一种联合迫零和独立信道预编码OFDM系统

提出了一种联合迫零和独立信道预编码OFDM系统。该系统用发送端迫零顸编码和哈达玛矩阵预编码对发送数据进行联合预处理,简化了接收端,提高了系统的分集增益,仿真结果表明该方法提高了系统的误码率性能。     

多用户MIMO系统基于消息块预编码的可信通信技术

针对多用户MIMO窃听信道,提出了在未知非法接收者任何信息的前提下,实现可信通信的基于消息块的人为干扰和预编码算法,并且在实现可信通信"可信性"的同时,考虑了"有效性"和"效率"问题。人为干扰仅干扰非法接收者,而不对合法接收者产生任何影响。预编码算法是已有的用于消除多用户干扰的"迫零"方式与基于SVD分解的线性预编码方式的结合。与基于单消息符号的预编码方式相比,提高了可信通信的效率。仿真结果表明,其进一步降低了非法接收者的SINR,并提高了多用户MIMO系统的通信容量。     

Modified precoding strategy over MIMO double-correlated channels

Double-correlated channels commonly occur due to insufficient scattering around both the transmitting and receiving antennas. In this article, the authors propose a linear precoding strategy with a modified system model over double-correlated channels. In this system model, an inner decorrelation strategy is added combined with precoding. First, a linear precoder that achieves minimum bit error rate (MBER) is proposed and analyzed based on the modified system model. The simulation results show that the bit error rate (BER) performance can be improved by decorrelation. Second, the influence of double correlation on multiple input and multiple output (MIMO) capacity is analyzed and simulated.     

Interpolation Based Unitary Precoding for Spatial Multiplexing MIMO-OFDM With Limited Feedback

Spatial multiplexing with linear precoding is a simple technique for achieving high spectral efficiency in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. Linear precoding requires channel state information for each OFDM subcarrier, which can be achieved using feedback. To reduce the amount of feedback, this paper proposes a limited feedback architecture that combines precoder quantization with a special matrix interpolator. In the proposed system, the receiver sends information about a fraction of the precoding matrices to the transmitter and the transmitter reconstructs the precoding matrices for all the subcarriers. A new interpolator is proposed inspired by spherical interpolation that respects the orthogonal columns of the precoding matrices and the performance invariance to right multiplication by a unitary matrix. The interpolator is parameterized by a set of unitary matrices; a construction of a suitable set is briefly described. Simulations illustrate the performance of limited feedback precoding with coding, estimation or prediction error, and time variation for bit error rate (BER), mutual information, and mean squared error (MSE)     

On the MMSE‐based multiuser millimeter wave MIMO hybrid precoding design

A hybrid MMSE‐based precoder and combiner design with low complexity is studied in this paper for both the downlink and uplink multiuser millimeter wave MIMO systems. At first, according to the underlying channel knowledge, the phases of the RF precoder and combiner are manipulated by using the MMSE criterion. On the basis of the MMSE‐based analog precoder design, the MMSE‐based digital baseband precoder can be readily derived. Thus, this method combines the advantage of using the MMSE precoding and phase extraction technique to obtain a reasonable solution. The proposed hybrid precoding design will be examined in both the uplink and downlink multiuser MIMO systems. Numerical results are presented to show that the proposed MMSE‐based hybrid precoding design is capable of attaining superior performance in terms of both the spectral efficiency and energy efficiency over the existing designs. Moreover, we will show that the MMSE‐based design can be readily extended to the multiuser millimeter wave MISO systems when only statistical channel state information is available.     

Low Complexity Iterative-QR (IQR) Precoder Design Based on Structure Blocks for Massive MIMO System

Massive multiple-input multiple-output (MIMO) technology is a promising technique having a high spectral efficiency for future wireless systems. Counterintuitively, the practical issues of transmitted signals are being attenuated by fading, propagation limitations, and implement non-linear precoding are solved by enlarging system dimensions. However, the computational complexity of precoding grows with the system dimensions. The existence block diagonalization (BD) precoding, which completely pre-cancels the multiuser interference is very complicated to implement with the use of a large number of BS antennas, since it considers full multiplexing order. Motivated by the high performance of the BD and generalized for the case when the users have multiple antennas, we propose a structure blocks based on iterative QR decompositions (IQRDs) to compute the precoding scheme. The proposed BLIQR-based precoder designed partitioned the channel matrix into capable square-wise blocks matrix and the IQRDs are applied to the blocks channel matrix. The channel matrix is partitioned such that it can fulfill the multiplexing order for the use in Massive MIMO. The computational complexity of the proposed design is effectively reduced and the sum-rate performance is improved, especially in large number of BS antennas. The performance of the proposed scheme achieves a good trade-off between throughput and computational complexity.     

Hybrid Analog and Digital Precoding Based on Adaptive Method in P2P Massive MIMO

To achieve a far higher capacity in massive multi-input multi-output, the hybrid analog and digital precoding has been studied recently. In this paper, we consider the downlink single user communication system and propose an efficient matrix adaptive gradient descent algorithm to design the radio frequency precoder and combiner, and use the singular value decomposition method to obtain the digital precoder and combiner. Simulation results show that the proposed method can approach the performance of the conventional full digital precoding with a fast convergence rate.     

毫米波大规模MIMO系统中抑制IQ不平衡的广义线性混合预编码方案

毫米波大规模MIMO（Multiple-Input Multiple-Output）系统的混合预编码在基于理想硬件假设的前提下获得了广泛的研究。然而,在毫米波频段难以避免的硬件非理想特性会导致射频失真的产生,并严重制约系统的性能。本文考虑了毫米波大规模MIMO系统发射机同相和正交（In-phase and Quadrature-phase, IQ）支路不平衡问题,设计了一种基于广义线性实值信号模型的混合预编码方案以抑制IQ不平衡对系统性能的不利影响。该方案利用复-实变换将含有IQ不平衡引起的共轭干扰的接收信号模型转化为广义线性实值信号模型,基于正交匹配追踪（Orthogonal Matching Pursuit, OMP）算法,分别在复数域和实数域迭代设计模拟预编码器和数字预编码器。仿真结果表明,该方案能有效地提高频谱效率和误码性能。      

Joint coding-precoding with low-complexity turbo-decoding

We combine error-control coding with linear precoding (LP) for flat-fading channels, as well as for wireless orthogonal frequency-division multiplexing transmissions through frequency-selective fading channels. The performance is analyzed and compared with the corresponding error-control-coded system without precoding. By wedding LP with conventional error-control coding, the diversity order becomes equal to the error-control code's minimum Hamming distance times the precoder size. We also derive a low-complexity turbo-decoding algorithm for joint coded-precoded transmissions. We analyze the decoding complexity and compare it with an error-control-coded system without LP. Extensive simulations with convolutional and turbo codes for HiperLan/2 channels support the analysis and demonstrate superior performance of the proposed system.     

基于毫米波大规模MIMO系统的混合预编码设计

大规模多输入多输出（MIMO）被认为是未来5G的关键技术之一。毫米波因其足够大的频谱带宽近来备受关注。针对部分连接结构、单用户下行链路毫米波大规模MIMO系统，提出了一种新型的混合预编码设计。利用分层设计思想，首先设计模拟预编码器，提出一种模拟预编码器算法；然后通过注水算法获得最佳数字预编码器；最后，将起始最优化问题转化为在每根天线功率分配约束下单个RF链路连接天线子阵列最优化问题，再根据迭代方法获得最佳混合预编码器。仿真结果表明，最佳混合预编码器性能接近纯数字预编码器的性能。     

Stabilized precoder for indoor radio communications

A low complexity, stabilized precoder for broadband indoor radio is presented, which uses radial root reduction for stability, and so avoids the use of a module operator. Simulations show that the stabilized precoder has comparable performance to Tomlinson-Harashima (1971) precoding with perfect automatic gain control (AGC), and is immune to AGC fluctuations which degrade the performance of TH precoding