基于低分辨率模数转换的全双工大规模MIMO中继系统频谱效率分析

为了降低由于大规模基站天线阵列模数转换(analog-to-digital converters, ADCs)所造成的巨大硬件损耗,同时有效地提高系统的能量和频谱效率,基于迫零传输/迫零接收(zero-forcing transmitting/ zero-forcing receiving, ZFT/ZFR)预处理方案,文章提出了低分辨率模数转换的多用户全双工大规模多入多出(massive multiple-input multiple-output, massive MIMO)中继系统,基站采用放大转发(amplify-and-forward, AF)协议,并对系统频谱效率进行了分析。文章首先获得了任一用户对频谱效率的闭式表达式,然后分别对三种不同功率缩放方案下系统的频谱效率进行了渐近分析。研究结果表明,当基站天线数量足够大时,三种不同的功率缩放方案对系统的环路干扰和量化误差有不同的影响,且当信源功率固定、基站的传输功率与发送天线数量成反比时,系统能够有效地抑制系统的环路干扰和量化误差,这对低分辨率全双工massive MIMO 中继系统的部署具有一定的指导意义。      

基于迫零波束成形技术的大规模MIMO混合中继系统性能分析

文章基于迫零波束成形技术及不完备信道状态信息,研究了大规模双向多输入多输出中继网络的系统频谱效率和系统能量效率。首先,在中继站的天线数量M足够大时获取用户端信干噪比的一般表达式,得到系统频谱效率与能量效率的一般表达式。其次,获取了功率缩放方案下系统频谱效率与能量效率的渐进值。对于非零信干噪比,当中继站及每个用户终端的发射功率均降低为原来的M分之一,系统能量效率将大幅度提升。     

基于迫零方式下带有硬件损害的大规模MIMO全双工中继系统

该文考虑一个大规模MIMO全双工中继系统,该系统下多个单天线的源节点和多个单天线的目的节点通过一个在接收端和发送端分别配置${N_{{\mathop{\rm rx}\nolimits} }}$和${N_{{\mathop{\rm tx}\nolimits} }}$根天线的中继进行通信。在非完美信道状态信息(CSI)和硬件损害的情况下,中继端在译码转发(DF)的方式下使用迫零(ZF)方法去处理接收信号和发送信号,并获得了闭合形式的接收速率表达式。根据这些表达式,可以得到各种功率收缩规律,发现随着中继端接收天线数量和发送天线数量以一定比例趋近于无穷大时,源节点的能量、中继端的能量和导频的能量可以以一定条件收缩来维持系统性能。     

基于混合精度模数转换器的大规模MIMO-OFDM系统性能分析

该文对在接收端使用混合精度的模数转换器且采用迫零接收算法的大规模MIMO-OFDM系统的上行链路的频谱效率和能量效率进行了研究。采用加性量化噪声模型来对系统的性能进行分析,推导出整个系统的频谱效率和能量效率的近似闭式表达式,并通过仿真证明了表达式的正确性。研究结果表明,系统的频谱效率和每个用户的发送功率,接收端天线数目和接收端量化精度有关。数值和仿真结果还表明可以通过增加基站端的天线数量来补偿由低精度模数转换器带来的性能损失。     

基于大规模天线的多用户 MISO 下行链路频谱效率分析简

在大规模天线时分双工通信系统中,分析了多用户MISO下行链路的频谱效率。假定用户数固定且基站天线数M无限增大,通过理论推导分析发现,当基站发送功率减小到单天线基站的1/M时,随着M的增加系统频谱效率趋于一个恒值;并且简单的预处理即可消除用户间干扰和快衰落的影响。虽然多小区系统会受导频污染的影响,致使小区间干扰不能被完全消除,但是降低后的发送功率可使系统由干扰受限转变为噪声受限。采用迫零单位预编码与采用最大比发送单位预编码的系统频谱效率极限表达式相同。最后给出采用空时分组码的多用户下行链路的频谱效率下限值,并通过仿真分析证实了以上结论的正确性。     

多天线无线数据通信系统中多用户分集的研究

研究当接收天线不少于发送天线时多输入多输出(MIMO)系统的多用户分集能力。首先从理论上分析了发送天线个数等于1和2时最大似然接收和迫零接收系统的平均吞吐量和调度增益,以及仿真分析了发送天线个数大于2时系统性能。理论分析和仿真表明：在多用户的MIMO系统中,接收的平均信噪比、用户个数、收发天线个数、接收机的结构等对于多用户分集有很大的影响。当发送天线个数为1时,接收天线较少(1,2,3)和平均信噪比为．10dB时调度增益很大,但调度增益随着天线个数和发送功率增大急剧下降。和最大似然接收相比,迫零接收具有更大的多用户分集增益,因此迫零接收机的吞吐量可以很容易超过最大似然接收机。     

基于成对用户大规模MIMO中继系统的频谱效率性能分析

该文针对成对用户大规模MIMO中继系统,在中继采用最大比合并/最大比发射（MRC/MRT）预编码方案下,利用大数定律,推导出系统频谱效率的闭合表达式,显式的描述了频谱效率与中继天线数、该文针对成对用户大规模MIMO中继系统,在中继采用最大比合并/最大比发射（MRC/MRT）预编码方案下,利用大数定律,推导出系统频谱效率的闭合表达式,显式的描述了频谱效率与中继天线数、用户对个数以及信源用户和中继发射功率的关系。基于此,分析了当天线数增大时,在用户对个数固定不变和等比例增长两种情况下,频谱效率的渐进性能和所能获得的发射功率增益。结果表明,当用户数固定时,频谱效率将随天线数呈近似对数增长规律;当用户数随天线数等比例增长时,通过调整比例值,可满足平均每个用户的频谱效率达到任意指定值,且无需额外发射功率消耗。最后,通过数值仿真验证了所推导的频谱效率闭合表达式的精确性以及所有渐进性能的分析结果。      

基于联合用户分组及天线选择的大规模MIMO波束成形

大规模MIMO系统中,当小区用户数与基站天线数较大时,各用户的信道条件不尽相同,提出一种适用于大规模MIMO下行链路的基于联合用户分组及天线选择的迫零波束成形算法。将用户分成两组,选择信道条件较优的一组用户来接收信号,并为每一个发送数据流选择最优的基站天线组合进行通信,以较小的性能损失,换取大规模MIMO 射频电路的成本与功耗的大幅度降低。仿真结果证明,该算法能够较好地实现系统性能与硬件复杂度的折中。     

单中继多用户MIMO系统中继预编码新方案

针对单中继多用户多输入多输出(MIMO)通信系统中用户间干扰问题,提出了一种可以有效抑制用户间干扰的中继接收和预编码方案。该方案在中继端对信号进行迫零(ZF)接收,利用最大化信漏噪比(SLNR)准则设计中继端预编码向量,并针对难以获得最优解的情况,利用迭代解出次优解。仿真结果表明,与中继端ZF预编码相比,SLNR预编码更好地抑制了用户间干扰,相同和速率性能下,基站发送端功率比ZF预编码减少4 dB,具有实用价值。     

基于混合精度ADC的大规模MIMO中继系统物理层安全性能研究

研究多天线窃听者场景基于混合精度模数转换器(Analog-to-Digital Converter,ADC)大规模多输入多输出(Multiple Input Multiple Output,MIMO)中继系统,中继将接收到的信号放大转发,通过在基站采用最大比合并接收信号,推导出合法用户与窃听者的频谱效率表达式,最终得出...     

Energy efficiency optimization of one-way and two-way DF relaying considering circuit power

In this paper, the energy efficiency (EE) of a decode and forward (DF) relay system is studied, where two sources communicate through a half-duplex relay node in one-way and two-way relaying strategies. Both the circuitry power and the transmission power of all nodes are taken into consideration. In addition, three different coding schemes for two-way DF relaying strategy with two phases and two-way DF relaying with three phases are considered. The aim is to maximize the EE of the system for a constant spectral efficiency (SE). For this purpose, the transmission time and the transmission power of each node are optimized. Simulations are used to compare the EE–SE curve of different DF strategies with one-way and two-way amplify and forward (AF) strategies and direct transmission (DT), to find the best energy efficient strategy in different SE conditions. Analytical and simulation results demonstrate that in low SE conditions, DF relaying strategies are more energy efficient compared to that of AF strategies and DT. However, in high SE conditions, the EE of two-way AF relaying and DT strategy outperform some of the DF relaying strategies. In simulations, the impact of different circuitry power and different channel conditions on the EE–SE curves are also investigated.     

Energy‐efficient relay deployment in cellular systems using fractional frequency reuse and transmit antenna selection techniques

To cope with the steep surge in mobile traffic, network operators are now expanding their infrastructure for mobile access networks. However, since energy costs and greenhouse gas emissions are a large burden to network operators, they are making great efforts to improve the energy efficiency (EE) of their networks by promising techniques, including relaying and multiple‐input multiple‐output (MIMO). Relaying technique can considerably improve the EE when the interference between base stations (BSs) and relay stations (RSs) is effectively coordinated by an elaborate relay deployment using the fractional frequency reuse (FFR) technique. Also, MIMO techniques improve the radio channel quality through diversity gains, so the system capacity and the EE can be improved. Therefore, a combination of relaying/MIMO techniques can be considered to achieve the higher performance, particularly, if the system complexity and costs of using such techniques are low. Since the transmit antenna selection (TAS), one of MIMO techniques, can provide a sufficient transmit diversity gain and satisfy the requirements for low complexity and cost (thus, practical), the TAS is recommended for use with the relaying technique. In this paper, for an energy‐efficient relay deployment using FFR and TAS techniques, we derive the EE and the resource partitioning according to RS positions and the number of BS antennas by a mathematical analysis. Then, the optimal RS positions according to the number of antennas can be determined by an optimization approach. The numerical and simulation results indicate that the proposed analysis method can efficiently analyze the EE and locate the RSs.     

多用户MIMO网络的OFDM放大转发双向中继策略

在多用户MIMO通信网络中,该文提出一种新的放大转发双向中继策略,在第1时隙的多址传输中采用OFDMA,在第2时隙的广播传输中采用OFDM/SDMA,通过利用频率分集和空间分集提高了系统性能。针对双向中继传输的特点,采用两种方法在每个子载波上设计了中继波束形成矩阵,即信漏噪比(SLNR)准则和块对角化迫零(BDZF)准则。利用割集理论推导了该双向中继网络的容量域上界。仿真结论表明,所提出的双向中继策略在系统和速率性能上优于其他3种中继策略,并能逼近所推导的容量域上界。     

On the energy efficiency of MIMO cooperative relaying networks

Cooperative relaying techniques can greatly improve the capacity of the multiple input and multiple output (MIMO) wireless system. The transmit power allocation (TPA) strategies for various relaying protocols have become very important for improving the energy efficiency. This article proposes novel TPA schemes in the MIMO cooperative relaying system. Two different scenarios are considered. One is the hybrid decode-and-forward (HDF) protocol in which the zero-forcing (ZF) process is operated on relays, and the other is the decode-and-forward (DF) protocol with relay node and antenna selection strategies. The simulation results indicate that the proposed schemes can bring about significant capacity gain by exploiting the nature of the relay link. Additionally, the proposed TPA scheme in the HDF system can achieve the same capacity as the equal TPA with fewer relay nodes used. Finally, the capacity gain with the proposed schemes increases when the distribution range of relay nodes expands.     

非对称MIMO双向中继干扰信道的干扰对齐算法

针对非对称的多用户MIMO双向中继干扰信道,本文提出了一种简化的基于最大信干噪比的干扰对齐算法,给出了干扰对齐的可行性条件和干扰抑制方案,并分析了系统容量和自由度。本文算法的中继节点不必做复杂的信号处理,大大降低了整个系统的信号处理复杂度;同时,本文算法是基于最大信干噪比方案,与现有文献的中继迫零方案比较,大大提高了系统在中低信噪比时的容量;进一步,通过仿真验证表明,基于本文算法的K用户对双向中继干扰网络可以达到。      

Relaying Schemes Using Matrix Triangularization for MIMO Wireless Networks

Multiple input multiple output (MIMO) relay networks are wireless communication systems comprising of multiple nodes, each of which is equipped with multiple antennas. Information theories have shown that using multiple nodes to simultaneously relay a message can improve the capacity of source-to-destination communications. In this paper, we propose new relaying schemes for MIMO relay networks. The major concept behind the proposed schemes is to transform each of the MIMO relay channels into an equivalent triangular channel with positive real diagonal entries. By doing so, the resultant MIMO relay channel can simultaneously offer both distributed array gain (diversity gain obtained among relay nodes) and intranode array gain (diversity gain realized by multiple antennas of individual relay node) while maintaining the maximum spatial multiplexing gain (number of parallel data pipes). Based on this concept, three relaying schemes are derived that perform QR decomposition and phase control. Numerical results confirm that at least one of the proposed schemes outperforms the amplify-and-forward and the zero-forcing relaying schemes under various conditions. Moreover, we show that ratios of noise power level at relay and destination node have a great impact on capacities.     

Spectral efficient protocols for half-duplex fading relay channels

We study two-hop communication protocols where one or several relay terminals assist in the communication between two or more terminals. All terminals operate in half-duplex mode, hence the transmission of one information symbol from the source terminal to the destination terminal occupies two channel uses. This leads to a loss in spectral efficiency due to the pre-log factor one-half in corresponding capacity expressions. We propose two new half-duplex relaying protocols that avoid the pre-log factor one-half. Firstly, we consider a relaying protocol where a bidirectional connection between two terminals is established via one amplify-and-forward (AF) or decode-and-forward (DF) relay (two-way relaying). We also extend this protocol to a multi-user scenario, where multiple terminals communicate with multiple partner terminals via several orthogonalize-and-forward (OF) relay terminals, i.e., the relays orthogonalize the different two-way transmissions by a distributed zero-forcing algorithm. Secondly, we propose a relaying protocol where two relays, either AF or DF, alternately forward messages from a source terminal to a destination terminal (two-path relaying). It is shown that both protocols recover a significant portion of the half-duplex loss     

基于成对用户大规模MIMO两跳中继系统的最优能效设计

该文针对成对用户大规模MIMO中继系统,研究了最优能效准则下的系统参数设计。在中继采用最大比合并/最大比发射(MRC/MRT)预编码方案下,借助于大数定律,推导出能效函数关于用户发射功率、中继发射功率和中继天线数的解析表达式。根据能效函数性质,分别证明了全局最优发射向量和最优天线数的存在性和唯一性。为了求解最优发射功率,利用分数规划,将原优化问题转换为等价的减法形式,进而提出一种新的低复杂度迭代优化算法,并求得最优发射功率的闭合解。对于最优天线数,则利用Lambert W函数,得到了能效最大时的最优天线数闭合解。通过数值仿真,验证了所提功率优化算法以极少迭代次数取得了接近最优算法的性能,并验证了所给出的最优天线数闭合解的精确性。