Joint precoding and power allocation for multiuser transmission in MIMO relay networks

This paper proposes a joint precoding and power allocation strategy to maximize the sum rate of multiuser multiple‐input multiple‐output (MIMO) relay networks. A two‐hop relay link working on amplify‐and‐forward (AF) mode is considered. Precoding and power allocation are designed jointly at the base station (BS). It is assumed that there are no direct links between the BS and users. Under individual power constraints at the BS and relay station, precoders designed based on zero forcing, minimum mean‐square error and maximum ratio transmission are derived, respectively. Optimal power allocation strategies for these precoders are given separately. To demonstrate the performance of the proposed strategies, we simulate the uncoded bit error rate performance of the underlined system. We also show the difference of the sum rate of the system with the optimal power allocation strategies and with average power transmission. The simulation results show the advantages of the proposed joint precoding and power allocation strategies as expected. Copyright © 2011 John Wiley & Sons, Ltd.     

Precoder Distribution and Adaptive Codebook in Wideband Precoding

Based on wideband precoding (WBP) in the multiple‐input multiple‐output orthogonal frequency division multiplexing system, an adaptive nonuniform codebook is presented in this paper. The relationship between the precoder distribution and spatial correlation is analyzed at first. A closed‐form expression based on overlapped isosceles triangles is proposed as an approximation of the precoder distribution. Then, the adaptive codebook design is derived with the approximate distribution to minimize quantization errors. The capacity and bit error rate performance demonstrate that the adaptive codebook with WBP outperforms the conventional fixed uniform codebook.     

认知无线信道及其可达速率域的研究

认知无线信道是基于认知无线电理论的一种新的无线通信网络模型。到目前为止,已经有一些针对认知无线信道的可达速率域和速率域外界的结果给出,但是还不能得到认知信道的确切的容量域。文中主要研究了认知无线信道模型,以及实现其可达容量域所用到的编码方法,并给出了一些速率域的结果。     

Precoding with interference suppression sequence scheme for OFDM-based cognitive radio systems

Orthogonal frequency division multiplexing(OFDM)is considered to be one of the promising schemes for cognitive radios(CR)systems,due to its flexibility in spectrum shaping.However,the traditional way of spectrum-notching failed to suppress out-of-band leakage enough,resulting in interference with licensed users(LUs).A novel spectrum shaping scheme is proposed in this article,where a precoder with interference suppression sequence(ISS)is for the first time introduced for shaping the spectrum of OFDM signals in OFDM-based CR systems.The precoder matrix together with ISS matrix is obtained by minimizing the power of out-of-band interference,which results in the sufficient interference suppression of OFDM signal to LUs.Analysis and simulation results show that the proposed scheme can significantly suppress the interference power to LUs at a little cost of precoding efficiency.Meanwhile,the peak-to-average-power-ratio(PAPR)is invariable and the bit-error-rate(BER)performance over Rayleigh fading channel is improved.     

室内可见光通信中的线性均衡与判决反馈均衡

信道均衡是光通信的关键技术之一。信道均衡能有效地克服信息传输中的多径干扰和消除码间串扰,适合于数据传输。本文针对室内可见光通信系统中由信道失真引起的严重的码间串扰（ISI）情况,研究迫零均衡（ZFE）、最小均方误差（MMSE）均衡、判决反馈均衡（DFE）3种均衡技术,并利用计算机仿真对3种均衡技术的性能进行评估。仿真结果表明,判决反馈均衡器具有明显的优越性。     

一种改进的SLNR多用户MIMO预编码方法

MU-MIMO系统中,基站在相同的时间与频率资源上与多个用户进行通信,导致不同用户之间存在同信道干扰。SLNR预编码方法将联合优化的问题转化成若干个独立优化问题,在系统性能与复杂度之间取到很好的折中。提出了一种改进的SLNR预编码方法,该方法在泄漏信号的基础上,考虑干扰信号的影响,对预编码向量进行迭代优化。仿真结果表明,与SLNR方法相比,该方法在理想CSI和非理想CSI情况下都可以进一步提高系统的吞吐量。     

IMT—Advanced协作多点传输技术——信道互异性校准

文章以协作多点传输技术为背景,基于信道互异性模型,介绍了3类较为典型的校准算法：基于硬件检测的自校准方法、基于天线自检测反馈的自校准方法、基于校准天线检测反馈的互校准方法。以此为基础,文章分析和研究了各校准算法的特性,评估和仿真了各校准算法协作多点传输技术在各类联合预编码算法下的系统性能,同时预测了校准算法未来的研究进程及可能面临的挑战。     

多天线广播信道模型安全性分析

在无线广播网络中,信道的广播特性会导致通信特别容易被窃听,通信中的防窃听问题就变得更加重要。根据多天线（MIMO）高斯广播信道模型（MGBC-CM）,并结合了MIMO块对角化预编码思想,建立了一种多天线广播信道可靠安全模型。基站在向用户发送数据之前先进行块对角化预编码,这样不仅可以消除用户之间数据的相互干扰,而且更重要的是还可以有效防止用户数据被窃听。仿真结果表明,该模型具有很好的保密性和安全性。     

基于块对角化的格基规约GMD矢量预编码

研究了对多用户多输入多输出下行链路进行块对角化后,使用格基规约算法的几何均值分解矢量预编码的实现方法。根据块对角化思想将多用户多天线信道分解为等价并行子信道,基于等价子信道给出了单个用户的几何均值分解矢量预编码的传输方案,通过使用格基规约算法分别结合连续干扰消除和垂直分层空时编码两种方法,求解矢量预编码中的扰动矢量。仿真表明,提出的方法误码率性能优于块对角化矢量预编码算法2 dB以上,而且能在不降低系统性能的前提下降低计算复杂度。     

采用线性迫零接收机的多天线多用户分集性能分析

采用线性迫零接收机的多天线系统中,同时传输的多个数据流,其信噪比并不相互独立,这使得分析多用户分集的性能非常困难。该文通过分布假设检验和最大似然参数估计方法,采用伽马分布逼近所有数据流信噪比最大、最小值以及均值的概率分布,并基于此进一步分析了多天线多用户分集的系统性能。仿真结果表明,前述逼近的准确度较高,该文的分析方法能够较好地衡量多用户分集增益的大小。