预编码的反馈方式的仿真

本文主要对预编码的反馈方式进行研究。首先介绍了预编码技术,然后分别对离散傅里叶变换码本反馈法和格拉斯曼码本反馈方式进行介绍和分析。最后在Mat lab上对系统误码率进行仿真,比较不同反馈方式对于预编码性能的影响。格拉斯曼码本反馈法的性能好于离散傅里叶变换码本的性能,但是格拉斯曼码本反馈更复杂。     

LTE中基于发送分集的预编码

MIMO技术是LTE中采用的关键技术之一,本文研究的基于发送分集的预编码技术就是MIMO技术中的一种方案。本文对LTE中使用的2发射天线和4发射天线的基于发送分集的预编码方案进行了推导,并对其性能进行了仿真,将其与空时分组码方案进行了性能比较。推导结果表明LTE中基于发送分集的预编码方案与2根发射天线的空时分组码的编码原理相同。仿真结果表明在两根发射天线情况下,空时分组码的误码率性能和预编码方案相同;在4发射天线的情况下,空时分组码的误码率低于预编码方案,但预编码方案的传码率要高于空时分组码。     

基于发射端获知部分信道状态信息MIMO系统线性预编码的设计

在现实通信系统中,由于各种原因在发送端获知很难获得完全的信道状态信息,只能获得部分信道状态信息,这样接收端的检测就非常复杂。在MIMO系统中,为了提高系统的性能和降低接收端算法的复杂度,可以通过把正交空时分组与线性预编码结合。本文提出了一种在MIMO非相关信道中,在部分信道状态信息的条件下,把正交空时分组码与线性预编码结合的方案。仿真结果表明,提高了MIMO系统的性能,降低系统误码率,获得了很好的性能增益。     

一种有限字符输入的线性预编码设计算法

针对有限字符输入下多输入多输出(MIMO)信道的互信息最大化问题,该文提出一种复杂度低的线性预编码算法。该算法根据水银/注水理论,融合基于均匀旋转的空时-线性星座预编码(Space-Time Linear Constellation Precoding,ST-LCP)矩阵的预编码方法和最大化最小输出向量信号间距的方法,从两者中选择互信息更高者用于预编码。然后,在基于均匀旋转的ST-LCP矩阵的预编码方法中,把MIMO信道的奇异值矩阵作为功率分配矩阵,并提出局部搜索和矩阵加幂两种改进措施。最后,利用有限字符集的对称性,进一步降低了互信息的计算复杂度。该算法在各种信道和信噪比条件下均能逼近互信息的理论最大值,并且减少甚至避免了搜索,计算复杂度大大下降。仿真结果验证了该算法的有效性。     

一种MIMO时变信道下的低反馈量有限反馈预编码方法

本文提出了一种新颖的适用于MIMO时变信道环境的有限反馈预编码方法.该方法利用子空间跟踪算法自适应跟踪时变信道的发射预编码矩阵,同时结合Jacobi迭代算法有效降低了有限反馈预编码的反馈量.通过计算机仿真,该方法在ARI时变信道模型,以及更实际的Jake's时变信道模型下的跟踪性能得到很好的验证.在更低的反馈量下,该方法可以获得比传统的存在反馈延时的Grassmannian预编码方法更好的系统容量性能,而且该方法在相同的反馈量下,无论是收敛性能还是误码率性能都明显优于将Jacobi迭代算法直接应用于时变信道跟踪的预编码方法.     

两种闭环准正交空时分组码的设计

针对准正交空时分组码(QOSTBC)存在自干扰的特性,提出了两种基于部分反馈的闭环QOSTBC的设计方法,这两种反馈方法可以减小QOSTBC的自干扰,提高QOSTBC的误码性能。仿真和分析结果表明提出的方法在相同反馈信息下的性能优于天线混淆(TAS)准正交空时分组码,在系统性能相差不大(不超过0.5dB)的情况下所需的反馈信息远小于信道正交化空时分组码(CO-STBC),而且提出的方法具有较低的设备复杂性和较好的鲁棒性。     

基于信道状态的MIMO预编码算法

针对多输入多输出（MIMO）的应用需要,研究了一种利用发端信道状态信息（CSIT）进行预编码,增强系统性能的方法。该方法在发送端采用线性预编码器对CSIT进行预编码,合理分配不同天线的发射功率以提高系统性能;分别在低、高信噪比条件下,对进行预编码前后的容量比值差值进行了仿真分析。分析结果表明：进行预编码后,MIMO系统容量明显改善,以上研究结果对MIMO的工程应用有良好的参考意义。     

预编码的反馈方式研究

本文主要对预编码的两种反馈方式进行研究.首先介绍了预编码技术,然后分别对1bit反馈法、随机矢量量化码本反馈法进行介绍和分析,比较不同反馈方式对于预编码性能的影响.1bit反馈法的系统性能可以接近完全信道信息反馈的系统性能,并能大大减少反馈数据量.     

一种多输入多输出系统中有限反馈预编码的自适应跟踪测度

该文提出一种新的适用于无线相关信道中有限反馈预编码多输入多输出系统的预编码矩阵自适应跟踪测度。由于该测度在统计意义下对信道的相关性与预编码矩阵变化的关系具有更优化的描述,所以基于该测度的方案在保持较低反馈信息量的前提下,能够进一步改善预编码系统性能。文中给出优化自适应跟踪测度的理论推导。系统仿真分别针对无线信道的频域相关和时域相关,并结合空间分集和空间复用两类系统结构予以讨论,并验证了理论分析结果。另外,由于该测度方案算法复杂度更低,所以更具工程实用价值。     

一种基于OSTBC空时码跨层安全通信方案

随着无线通信的发展,无线通信的广播特性使得无线网络缺乏物理边界,没有物理连接的无线通信对于外来的窃听者来说是开放的,在物理层解决通信安全问题已成为必需。物理层安全方法与传统加密方法跨层组合能在不大幅增加系统的额外开销的同时,提高系统的安全性能。文中重点介绍多进制调制方式下,基于正交空时码跨层增强技术变形码集设计。通过仿真,验证了该方案可以使无线通信可靠性接近1。     

Limited feedback unitary precoding for orthogonal space-time block codes

Orthogonal space-time block codes (OSTBCs) are a class of easily decoded space-time codes that achieve full diversity order in Rayleigh fading channels. OSTBCs exist only for certain numbers of transmit antennas and do not provide array gain like diversity techniques that exploit transmit channel information. When channel state information is available at the transmitter, though, precoding the space-time codeword can be used to support different numbers of transmit antennas and to improve array gain. Unfortunately, transmitters in many wireless systems have no knowledge about current channel conditions. This motivates limited feedback precoding methods such as channel quantization or antenna subset selection. This paper investigates a limited feedback approach that uses a codebook of precoding matrices known a priori to both the transmitter and receiver. The receiver chooses a matrix from the codebook based on current channel conditions and conveys the optimal codebook matrix to the transmitter over an error-free, zero-delay feedback channel. A criterion for choosing the optimal precoding matrix in the codebook is proposed that relates directly to minimizing the probability of symbol error of the precoded system. Low average distortion codebooks are derived based on the optimal codeword selection criterion. The resulting design is found to relate to the famous applied mathematics problem of subspace packing in the Grassmann manifold. Codebooks designed by this method are proven to provide full diversity order in Rayleigh fading channels. Monte Carlo simulations show that limited feedback precoding performs better than antenna subset selection.     

Optimized non-unitary linear precoding for orthogonal space-time block codes

This letter proposes a novel optimized non-unitary linear precoding design for orthogonal space-time block codes (OSTBCs). We dig out the transmission potentials by the analysis from eigen-space point of view according to the unique structure of OSTBCs. The proposed precoding form is proved to be theoretically optimized. Compared with the classical unitary Grassmannian codebook design, in the sense of restriction on the time average power of transmit signal, the proposed non-unitary codebook further improves the overall performance of practical systems. The new constraint on codebook size to guarantee full diversity order is given and proved. The advantages of our proposed design are verified in the numerical simulations.     

Channel estimation for space-time orthogonal block codes

Channel estimation is one of the key components of space-time systems design. The transmission of pilot symbols, referred to as training, is often used to aid channel acquisition. In this paper, a class of generalized training schemes that allow the superposition of training and data symbols is considered. First, the Cramer-Rao lower bound (CRLB) is derived as a function of the power allocation matrices that characterize different training schemes. Then, equivalent training schemes are obtained, and the behavior of the CRLB is analyzed under different power constraints. It is shown that for certain training schemes, superimposing data with training symbols increases CRLB, and concentrating training power reduces CRLB. On the other hand, once the channel is acquired, uniformly superimposed power allocation maximizes the mutual information and, hence, the capacity.     

Diversity performance of precoded orthogonal space-time block codes using limited feedback

Orthogonal space-time block codes (OSTBCs) are simple space-time codes that can be used for open-loop transmit diversity systems. OSTBCs, however, can only be designed for certain numbers of transmit antennas. Channel-dependent linear precoders have been proposed to overcome this deficiency, but it is not clear what conditions the precoder design must satisfy to guarantee full diversity order. In this letter, we show necessary and sufficient conditions for linear precoded OSTBCs to provide full diversity order. We show that limited feedback precoding can achieve full diversity order using fewer bits than limited feedback beamforming. We also present a simplified version of antenna subset selection for OSTBCs that can provide full diversity order with low complexity and only a small amount of feedback.     

A systematic design of high-rate complex orthogonal space-time block codes

In this letter, a systematic design method to generate high-rate space-time block codes from complex orthogonal designs for any number of transmit antennas is proposed. The resulting designs have the best known rates. Two constructions with rates 2/3 and 5/8 are further illustrated for 6 and 7 transmit antennas, respectively.     

Automatic design of orthogonal or near-orthogonal linear dispersive space-time block codes

This paper considers a wireless multiple-input multiple-output (MIMO) communication system in a frequency-nonselective scenario with spatially uncorrelated Rayleigh fading channel coefficients and investigates the design of linear dispersive (LD) space-time block codes. Efficient LD codes are obtained by optimizing the constituent weight matrices so that an upper bound on the union bound of the codeword error probability is minimized. Interestingly, the proposed design procedure automatically generates LD codes that either correspond to, or are close to, the well-known class of orthogonal space-time block (OSTB) codes. A theoretical analysis confirms this by proving that OSTB codes are indeed optimal, when the setup under study permits their existence. Simulation results demonstrate the excellent performance of the designed codes. In particular, the importance of the codes' near-orthogonal property is illustrated by showing that low-complexity linear equalizer techniques can be used for decoding purposes while incurring a relatively moderate performance loss compared with optimal maximum-likelihood (ML) decoding.     

Performance of concatenated channel codes and orthogonal space-time block codes

In this paper we analyze the performance of an important class of MIMO systems that of orthogonal space-time block codes concatenated with channel coding. This system configuration has an attractive combination of simplicity and performance. We study this system under spatially independent fading as well as correlated fading that may arise from the proximity of transmit or receive antennas or unfavorable scattering conditions. We consider the effects of time correlation and present a general analysis for the case where both spatial and temporal correlations exist in the system. We present simulation results for a variety of channel codes, including convolutional codes, turbo codes, trellis coded modulation (TCM), and multiple trellis coded modulation (MTCM), under quasi-static and block-fading Rayleigh as well as Rician fading. Simulations verify the validity of our analysis.     

Bit-error probability for orthogonal space-time block codes with differential detection

Explicit closed-form expressions of the bit-error probabilities are obtained for space-time block codes based on generalized orthogonal designs with differential encoding and differential detection using 2/sup b/-ary phase-shift keying mapping. The frequency-nonselective, block-wise constant Rayleigh fading channel is considered here. The results are applicable to any number of transmit and receive antennas, where the number of transmit antennas is dictated by the available coding schemes.     

Closed-form blind MIMO channel estimation for orthogonal space-time block codes

In this paper, a new computationally simple approach to blind decoding of orthogonal space-time block codes (OSTBCs) is proposed. Using specific properties of OSTBCs, the authors' approach estimates the channel matrix in a closed form and in a fully blind fashion. This channel estimate is then used in the maximum-likelihood (ML) receiver to decode the information symbols. The proposed estimation technique provides consistent channel estimates, and, as a result, the performance of the authors' blind ML receiver approaches that of the coherent ML receiver, which exploits the exact channel state information (CSI). Simulation results demonstrate the performance improvements achieved by the proposed blind decoding algorithm relative to the popular differential space-time modulation scheme.     

Extending orthogonal block codes with partial feedback

During the last few years a number of space-time block codes have been proposed for use in multiple transmit antennas systems. We propose a method to extend any space-time code constructed for m transmit antennas to m p transmit antennas through group-coherent codes (GCCs). GCCs make use of very limited feedback from the receiver (as low as 1 bit). In particular the scheme can be used to extend any orthogonal code (e.g., Alamouti code) to more than two antennas while preserving low decoding complexity, full diversity benefits, and full data rate.