一种基于GMD分解的混合预编码算法

提出了毫米波大规模MIMO系统中一种利用几何均值分解(GMD)设计模拟和数字预编码矩阵的算法.首先根据初始模拟预编码矩阵列向量相互正交,利用GMD分解计算出模拟预编码矩阵后,取其元素相位构成的矩阵为最终的模拟预编码矩阵,然后设计数字预编码矩阵.仿真结果表明,频谱效率和误码率较正交匹配追踪(OMP)算法分别有大约3dB和2.5dB的增益.     

干扰距离最远的多用户多天线干扰对齐算法

针对多用户多天线中小区边缘用户同频干扰问题,提出了一种基于干扰距离最远准则的多用户MIMO干扰对齐优化算法,通过对等效干扰信道进行SVD分解,选择与等效干扰信道矩阵距离最大的特征子信道作为传输预编码矩阵,并分析了算法复杂度以及空间相关性对性能的影响,仿真结果显示系统频谱效率较原始算法在8天线下有31.57％的提高.     

基于IAFS算法的毫米波大规模MIMO混合预编码方法

毫米波大规模多输入多输出系统可以通过部分连接混合预编码方法克服其信号路径损耗带来的不利影响,具有硬件实现复杂度低、能量效率高的优点,当输入的数据流数与射频链路数相等时,可以采用基于串行干扰消除的混合预编码方法。当输入的数据流数与射频链路数不相等时,提出了一种基于改进人工鱼群（IAFS）算法的混合预编码方法。其核心思想是基于频谱效率最优化准则和部分连接结构的特点,将针对模拟预编码矩阵变量的频谱效率优化问题转化为基于矢量变量的频谱效率最优化问题,利用IAFS算法进行寻优求解完成预编码矩阵设计。仿真结果表明,所提方法在低信噪比条件下具有较好的频谱效率与能量效率性能,有望在现实场景中得到应用。     

基于字典学习的毫米波大规模MIMO系统混合预编码

针对毫米波大规模多输入多输出(MIMO)系统混合预编码方案设计的难题,采用字典学习的思想,提出了一种高精度混合预编码方案.该方案首先对全数字预编码矩阵的各列采用稀疏表示;进而按列将字典原子从稀疏表示中分离出来,通过对误差矩阵采用奇异值分解(SVD)来更新对应的字典原子,直到所有字典原子更新,以形成新的字典矩阵;最后,利用更新后的字典矩阵稀疏重构全数字预编码矩阵,以得到模拟预编码矩阵和数字预编码矩阵.仿真结果表明,相较于基于正交匹配追踪(OMP)的混合预编码方案,所提方案在提升系统频谱效率和降低误码率方面具有明显的优势.     

基于不完美硬件系统的双智能反射面辅助波束赋形设计

在发射端具有不完美硬件的多输入多输出（Multiple Input Multiple Output,MIMO）系统中，存在失真噪声和干扰噪声，这导致用户侧接收信号受损，系统频谱效率低下。为解决此问题，考虑使用双智能反射面（Intelligent Reflecting Surface,IRS）辅助，联合优化基站波束赋形矩阵和两个IRS的反射相移矩阵，最大化多用户和速率。目标函数是变量高度耦合、复杂的非凸优化问题，分别使用交替优化方法、半正定松弛（Semi-Definite Relaxation,SDR）算法和奇异值分解归一化的方法求解。仿真结果表明，在发射端具有不完美硬件的MIMO系统中，与单IRS辅助和无IRS方案相比，使用双IRS辅助通信能够获得更好的系统频谱效率。     

不完全非负矩阵分解的加速算法

非负矩阵分解(NMF)已成为数据分析与处理的一种日益流行的方法.当数据矩阵不完全时,可用加权非负矩阵分解(WNMF)来分解矩阵.但是在WNMF算法中,对于给定的搜索方向,步长的选取一般来说不是最优的.本文研究了不完全非负矩阵分解(INMF)问题,提出了加速算法(AINMF).首先,将INMF问题转化为交替地求解两个非负...     

星地链路中基于毫米波大规模MIMO的混合预编码算法研究

为了提升星地链路通信系统频谱效率,针对毫米波(millimeter Wave, mmWave)大规模多输入多输出(Massive Multiple Input Multiple Output, Massive MIMO)系统,在正交匹配追踪(Orthogonal Matching Pursuit, OMP)算法的基础上,提出了一种改进的OMP (Improved-OMP)混合预编码算法。针对星地链路间通信的特定场景,引入了基于扩展的Saleh-Valenzuela (S-V)信道模型;针对OMP算法中求解模拟预编码矩阵时存在迭代次数过多的问题,在结合多步长思想的基础上,从天线阵列响应集合中选取与射频链路(Radio Frequency Chains, RF Chains)相等的前多列作为模拟预编码矩阵;为了克服OMP算法中的伪逆运算复杂度较高的问题,结合矩阵分解和H9lder不等式简化了数字预编码的求解。仿真结果表明,在理想的信道状态信道条件下,当RF Chains的数量和数据流的数量之间的差距较小时,Improved-OMP算法可以获得更优的性能。Improved-OMP方案有效地降...     

基于特征分解的高频地波雷达电离层杂波抑制

针对高频地波雷达中的电离层杂波,利用特征分解法在阵元-脉冲域和脉冲-距离域对它进行联合处理,并对特征分解法在脉冲-距离域和阵元-脉冲域分别进行了如下改进:在脉冲-距离域采用循环重构数据协方差矩阵,而在阵元-脉冲域则按扫频周期分段正交分解.OSMAR2003系统的实测数据表明:这种处理方法对抑制电离层杂波是有效的.     

基于奇异值分解的MIMO-OFDM系统角域MAP信道估计算法

最大后验概率信道估计算法应用于多输入多输出-正交频分复用(MIMOOFDM)系统时需要大规模的矩阵求逆和乘积运算,且系统数据传输效率随发送天线数的增加明显降低.为克服这些问题,提出了一种基于奇异值分解的角域最大后验概率信道估计算法.该算法通过期望最大化把(MIMO)信道估计问题简化为一系列独立的单输入单输出(SISO)问题,并使用奇异值分解避免了大规模矩阵求逆和乘积运算;通过多个OFDM符号联合估计信道提高了系统数据传输效率及算法的估计性能.仿真实验验证了此算法的有效性.     

一种高阶矩量法迭代求解的预处理技术

频域高阶矩量法越来越多地用于求解目标散射问题.但高阶矩量法得到的矩阵方程中,系数矩阵条件数较差,并且一般为非对角占优阵,通常用计算效率较低的直接方法求解.本文针对叠层高阶基函数的特点,提出了一种函数空间域分解的加性Schwarz预处理技术.通过数值计算,给出了最优分解方案,并数值验证了预处理技术的有效性.     

互耦条件下基于4阶累积量的双基地MIMO雷达角度估计

发射和接收阵列的互耦效应将使得双基地多输入多输出(MIMO)雷达的角度估计算法性能下降。针对阵列互耦效应和高斯色噪声并存情况,该文提出一种基于4阶累积量组合矩阵构造的收发角度估计方法。该方法首先根据收发互耦矩阵的Kronecker乘积特点,并结合互耦矩阵带状、对称的Toeplitz变换性质,充分利用所有的接收数据,构造出多组发射和接收4阶累积量矩阵,通过组合收发累积量矩阵进一步构造出4阶块累积量矩阵,并利用矩阵的奇异值分解,提取出发射和接收旋转不变因子。理论和仿真结果表明:在强互耦效应情况下,所提算法能够有效估计出高斯色噪声背景下目标的收发角度,并实现自动配对。在强互耦情况下,所提算法的估计性能优于其他算法。     

Capacity and performance of lattice reduction aided linear processing with lattice encoding and decoding in limited feedback systems

Linear processing for multi-input multi-output (MIMO) antenna systems is preferred to non-linear ones for computational efficiency. Using channel state information (CSI) at the receiver, channel matrix can be decomposed via singular value decomposition (SVD), and if the transmitter can be fed back with the right-unitary-matrix of the SVD from the receiver, the maximum channel-capacity can be achieved with linear processing in point-to-point wireless MIMO communications. However, if the transmitter receives no-feedback, the optimal linear detector at the receiver is the minimum-mean-squareerror- estimator, of which capacity is far below the channelcapacity. In practice, reducing the amount of feedback information to achieve a "reasonably close channel-capacity" is an important issue in point-to-point wireless communications. In this paper, we propose a limited feedback system employing linear processing, which achieves near-channel-capacity. The feedback information is only an integer matrix, which is much less than that of the right-unitary-matrix of the SVD. Key ideas of the proposed scheme are the lattice reduction and modulo operation. Moreover, the amount of feedback information can be further reduced to a binary matrix using multi-level/multi-stage encode and decode. Under the turbo channel code the proposed scheme shows excellent performance at high data rates. We compare our simulation results with Shannon capacity limits for ergodic MIMO channels.     

THE STUDY OF AN M-ARY MC-CDMA SYSTEM BASED ON CYCLIC SPREADING CODES & PRE-EQUALIZATION

A novel fast despreading scheme for M-ary Multi-Carrier Code-Division Multiple Access (MC-CDMA) system is proposed based on cyclic spreading codes and pre-equalizer. In the transmitter, the M spreading codes of each user are generated by circularly shifting the prototype spreading code. A feedback pre-equalizer is employed to process the M-ary MCCDMA signal before transmitted. The received signal is multiplied by the Inverse Discrete Fourier Transform (IDFT) result of the mirror image code of the prototype spreading code, and then demodulated by Orthogonal Frequency-Division Multiplexing (OFDM) demodulator. Compared with the conventional M-ary MC-CDMA receiver, the proposed scheme increases bandwidth efficiency, meanwhile, it achieves M-ary despread spectrum and multi-carrier demodulation, which reduces computation complexity remarkably.     

Hybrid Beamforming for Massive MIMO Using Rectangular Antenna Array Model in 5G Wireless Networks

Fifth and future generation (5G and B5G) wireless networks aim to serve users with higher data rates and lower latency. Data traffic due to the rapid growth in communication has motivated the study of Multiple Input Multiple Output (MIMO) systems. They utilize multiple antennas in both transmitter and receiver sides. It is necessary to improve the existing technology to achieve fast and reliable communication. In this research work, a rectangular array antenna based hybrid beamforming in a massive MIMO model has been proposed to improve the spectral efficiency of the system. Thus channel capacity with small RF chains is used. To achieve the high signal strength in the main lobe, Chebyshev tapering has been used to suppress the side lobes signals. In this manner, the proposed Hybrid Beamforming for Massive Output MIMO has been realized with a small complexity and higher spectral efficiency. In this research work, the spectral efficiency of both proposed Hybrid and fully-digital beamforming with a different number of RF chains for a various number of antennas at the transmitter, the receiver side has been analyzed. From the simulation results, it has been observed that the proposed rectangular array antenna based Hybrid beamforming in a massive MIMO system reduces the computational complexity up to 99% as compared with conventional fully digital beamforming to achieve the same spectral efficiencies, which is a productive model for 5G wireless networks.

     

THE STUDY OF AN M-ARY MC-CDMA SYSTEM BASED ON CYCLIC SPREADING CODES ＆ PRE-EQUALIZATION

A novel fast despreading scheme for M-ary Multi-Carrier Code-Division Multiple Access (MC-CDMA) system is proposed based on cyclic spreading codes and pre-equalizer. In the transmitter, the M spreading codes of each user are generated by circularly shifting the prototype spreading code. A feedback pre-equalizer is employed to process the M-ary MCCDMA signal before transmitted. The received signal is multiplied by the Inverse Discrete Fourier Transform (IDFT) result of the mirror image code of the prototype spreading code, and then demodulated by Orthogonal Frequency-Division Multiplexing (OFDM) demodulator. Compared with the conventional M-ary MC-CDMA receiver, the proposed scheme increases bandwidth efficiency, meanwhile, it achieves M-ary despread spectrum and multi-carrier demodulation, which reduces computation complexity remarkably.     

Broadband multicarrier communication receiver based on analog to digital conversion in the frequency domain

This paper introduces a multicarrier communication receiver for broadband applications based on analog to digital conversion (ADC) of the received signal in the frequency domain. The samples of the spectrum of the received signal are used in the digital receiver to estimate the transmitted symbols through a matched filter operation in the discrete frequency domain. The proposed receiver is aimed at the reception of high information rates in a multicarrier signal with very large bandwidth. Thus, the receiver architecture provides a solution to some of the challenging problems found in the implementation of conventional wideband multicarrier receivers based on time-domain ADC, since It efficiently parallelizes the A/D conversion reducing the sampling speed requirements. We show that the sampling rate requirements are relaxed as the number of frequency samples is increased, which introduces a trade-off between complexity and sampling rate. The new receiver possesses additional advantages, including scalability with increasing frequency samples, the possibility of optimally allocating the available number of bits for the ATD conversion across the frequency domain samples which potentially reduces the distortion introduced by the high-speed ADC, narrowband interference suppression that can be directly carried out in the frequency domain, and inherent robustness to frequency offset which makes it an attractive solution when compared with traditional multicarrier receivers. We also investigate how the proposed receiver responds to common multicarrier communication receiver problems such as phase noise and channel frequency selectivity.     

Rateless coded Orthogonal Frequency Division Multiplexing system design based on intercarrier interference self‐cancelation

In this paper, we consider a rateless coded Orthogonal Frequency Division Multiplexing (OFDM) system under a quasistatic fading channel. During each transmission round, transmitter keeps transmitting to the receiver using Raptor code until the receiver feeds back an acknowledgement (ACK). On the other hand, frequency offset between the transmitter and receiver ruins the orthogonality of OFDM subcarriers and cause intercarrier interference (ICI). We resort to ICI self‐cancelation precoding to combat ICI, wherein the data symbol vectors are multiplied with some precoding matrix before transmission. To improve the system robustness, we jointly optimize the precoding matrix and the degree profile of Raptor code, with only statistical channel state information (CSI) being assumed at the transmitter. The optimization problem is formulated based on the extrinsic information transfer (EXIT) analysis of the decoding process at the receiver. The advantage of the proposed design is that the instant CSI is not required at the transmitter, which reduces the system overhead. Simulation results verify that the proposed scheme with the optimized precoding matrix and degree profile can effectively combat ICI and achieve good performance both in bit error ratio (BER) and average transmission rate.     

一种多输入多输出变换域通信系统的设计及其抗干扰性能研究

传统多输入多输出技术可以提高信道容量,但不能解决信号抗干扰问题;而变换域通信系统已经被证明是一种良好的抗干扰通信系统。通过引入变换域处理技术,提出了一种多输入多输出变换域通信系统(MIMO-TDCS),旨在突破传统MIMO系统的应用瓶颈。对其收发信机模型和抗干扰机制作了简要介绍,并通过仿真窄带干扰下的误码率性能,表明MIMO-TDCS是一种可靠的抗干扰通信手段。     

Feasibility of Analog Realization of a Sliding-Mode Observer: Application to Data Transmission

One of the main contributions of this paper is to highlight the feasibility of analog realization of a chaotic observer-based communication system. The system is composed of a chaotic Colpitts oscillator considered as transmitter and a sliding-mode observer used as receiver. The method used in this realization is based on the synchronization of two chaotic systems (transmitter-receiver). Moreover, another originality of this work is the application of a sliding-mode observer to a Colpitts oscillator, which has a totally different structure with respect to it. Nevertheless, the proposed structure of the observer is designed particularly for this type of oscillator. Only one of the states of the transmitter (chosen according to theoretical criteria) is sent to the receiver which is designed to reconstruct all of the states of the transmitter knowing only the transmitted state. In order to show an application of this work, a message signal is injected into the transmitter using the so-called inclusion method. The message is then recovered by the receiver once all of the transmitter states are reconstructed. Thus, the so-called left inversion problem is resolved experimentally. The whole system (transmitter-observer) is realized using simple and standard analog components, and practical results close to simulations are obtained.     

LSTBC+OFDM分层方法的一种改进

基于OFDMA(Orthogonal Frequency-Division Multiple Access)中不同用户的子载波选择矩阵相互正交,提出了频率选择性衰落信道下分层结构的空时分组编码LSTBC(Layered Space-Time Block Code)的一种改进的分层方法.发射端采用分层结构的空时分组编码结合OFDM技术,在接收端提出了利用OFDM中子载波选择矩阵进行分组干扰抑制,然后对LSTBC的每层进行空时分组码的传统解码.相对于基于奇异值分解的分组干扰抑制方法,该方法只需要一根接收天线,降低了系统接收机设计的复杂度.仿真结果验证该方法的有效性.