面向大规模MIMO的分块空间调制技术研究

广义空间调制（Generalized Spatial Modulation,GSM）是一种基于多输入多输出（Multiple-Input Multiple-Output, MIMO）系统的高效的数字调制技术,在传统调制符号之外同时通过激活天线模式组合发送信息比特。针对大规模MIMO系统中发送天线数量过多导致的激活天线模式组合的数量过多的问题,提出了一种分块空间调制算法,将每个发送天线子块的激活模式组合构成完整的激活天线模式组合,可有效降低大规模MIMO系统中发送端的调制复杂度。在接收端使用球形译码方法实现逐个子块的天线激活模式组合的解调,可以大幅降低接收端的计算复杂度。仿真分析表明,提出的球形译码算法可以在大幅降低计算复杂度的情况下,实现接近最大似然（Maximum Likelihood,ML）接收机算法的误比特率（Bit Error Rate,BER）性能,且可实现接收端检测性能和计算复杂度之间的最佳折衷。     

一种新的低复杂度空间调制信号检测算法

空间调制技术(SM)作为一种新颖的多天线传输方案,近年来受到业界的广泛注意。它将输入信息比特分为两部分,一部分用于激活天线,另一部分用于信号调制,来共同承载发送信息。由于SM系统的最大似然(ML)最优检测算法需要穷举搜索激活天线序号和发送的数字调制符号的所有可能情况,它的检测复杂度很高。为此,人们相继提出了一些简化算法。与这些算法思路不同,本文从传统ML最优表达式出发,引入极坐标得到关于星座点幅度和相角的ML等价表达式,同时根据星座点相角的分布特性对相角进行近似,得到了一种新的次最优检测算法。新算法的检测性能比其他次优算法更接近ML,而且计算复杂度低。最后本文通过计算机仿真,验证了新算法的有效性。      

具有天线选择与中继选择的空间调制技术

针对空间调制(SM)技术存在的缺欠,提出了具有天线选择和中继选择的空间调制系统方案。首先在多输入多输出(MIMO)信道模型下,通过对发送端天线选择,将拥有最佳信道状态的天线选出进行SM,打破SM技术对发送端天线数的限制,并提升采用高阶调制的SM分集性能。然后进一步将此思想引入协作通信网络,结合传感器网络的分级观念,提出采用中继选择和空间调制的中继传输协议,并通过仿真观察系统分集性能的改善。仿真结果表明,上述中继传输协议不仅能提升系统性能,而且使系统配置更加灵活。     

广义空间调制系统的稀疏检测算法

空间调制技术作为一种新颖的多天线传输技术,这些年来受到业界的广泛关注,从单一激活天线的空间调制已扩展到多根激活天线的广义空间调制,进一步提高了频带效率。但是,采用多根激活天线发送也给系统的解调带来了困难。由于多激活天线的使用,最大似然（ML）检测算法的计算复杂度将随着激活天线数的增加呈指数增加,是一个NP-hard问题。针对上述问题,本文利用空间调制信号本身固有的稀疏特性,提出了一种次最优检测算法,新算法可以在保证检测性能的前提下,大大降低算法的计算量。不仅如此,由于稀疏性的引入,新算法还可以应用到发送天线数大于接收天线数的情况,计算机仿真试验验证了其有效性。      

低复杂度空间调制MPSK信号的最优检测

针对MQAM信号,已有低复杂度的最优检测算法,但是针对MPSK信号还没有类似的最优检测算法发表,因此从二维矢量量化的ML解调角度出发,利用MPSK星座图的特性,给出了与调制符号阶数无关的ML简化算法,避免了ML联合检测算法中对调制符号空间的搜索,极大地降低了算法复杂度。新算法不仅与ML最优检测算法具有完全相同的性能,而且具有较低的复杂度,有较好的理论和实际意义。该算法在天线技术和绿色通信技术中有较好的实际应用意义。     

正交空间调制的低复杂度检测算法

针对正交空间调制(QSM)系统中激活天线数的不确定性、最大似然(ML)检测算法复杂度极高的缺点,提出了一种低复杂度检测算法.首先,该算法基于压缩感知(CS)信号重构理论,对系统模型进行重构,使固定激活天线系统中的低复杂度算法可以在新的系统模型中使用;然后,借鉴正交匹配追踪(OMP)算法的思想,选出一个激活天线备选集;最后,通过ML算法搜索备选集,选出激活天线和调制符号.仿真结果显示,相比ML检测算法,所提算法在性能丢失较小的情况下,降低了约90％的复杂度.     

扩展空间调制技术的低复杂度检测算法

针对发射天线数可变的扩展空间调制技术(Extended Spatial Modulation,ESM)提出了相应的低复杂度检测算法。传统的空间调制技术(Spatial Modulation,SM)将信息调制在发射的天线上,但是在一个符号周期内活跃的天线数为常数。而ESM允许在不同符号周期以不同数目的发射天线进行组合,不仅能够承载更多信息,同时对发射的天线也有了更多优选的空间,但是传统的检测算法在发射天线数固定时才能正常使用,针对ESM的特殊情况提出了阈值法检测天线,并通过数值实验给出了性能分析。     

广义空间调制MIMO系统的优化检测算法

针对大规模多输入输出（multiple-input multiple-output,MIMO）系统中采用广义空间调制（generalized spatial modulation,GSM）时信号检测复杂度过高的问题,提出一种新型天线分组激活方案.该方案首先需将发送天线分组激活,得到天线索引备选集,然后把天线组合符号按质量因子大小进行排序,最后遵循可信度判断准则进行量化判决检测,以此得到最佳的检测结果.相较于传统算法,所提出的检测算法避免了对信号空间的遍历搜索,在大规模天线系统下的性能更加优异.计算和仿真结果表明,本文提出的算法具有复杂度低、误码率低的特点,在采用广义空间调制的通信系统中具有较高的工程应用价值.     

采用相位判决的低复杂度广义空间调制检测算法

针对广义空间调制(GSM)系统中信号检测复杂度过高的问题,提出了一种基于相位判决的低复杂度检测算法.首先根据一种排序准则对天线组合进行排序,然后将排序后的天线组合中的符号向量依次通过基于相位判决的迫零(ZF)均衡器进行检测,最终得到星座调制符号和激活天线组合.分析和仿真结果表明,该检测算法可以有效缩小接收端的搜索范围,在提供与最大似然(ML)检测算法相近的误比特率(BER)性能的同时,计算复杂度降低了98％.     

接近最优的编码MIMO系统的发送天线子集选择算法

多天线无线系统可提供更大的信道容量和更好的抗衰落能力,发送端利用反馈的部分信道状态信息进行发送天线子集选择能够进一步提高信道容量。该文提出了一种MIMO系统的快速的、动态的天线子集选择算法,其提供的信道容量高于已有的静态算法,且接近于最优天线选择算法,而无需计算所有可能的天线子集组合的信道容量,因而具有更低的复杂度。将本文算法与比特交织编码调制(BICM)技术相结合,对各天线速率进行适配,提出了空时自适应比特交织编码调制(ST-ABICM)方案。仿真结果证实了该方案性能的优越性。     

Improved generalized spatial modulation via antenna selection

When a high spectral efficiency is needed, the cost of Euclidean distance‐based antenna selection for spatial modulation (EDAS‐SM) in terms of hardware, size, and computational complexity is significantly increased because of the large transmit antenna array required. In comparison, generalized spatial modulation (GSM) can match the spectral efficiency of EDAS‐SM, while using significantly fewer transmit antenna elements. However, the error performance of GSM is naturally limited because of the use of a predetermined and fixed set of transmit antenna combinations. By exploiting knowledge of the channel, the optimal set of transmit antenna combinations can be selected by maximizing the minimum Euclidean distance between transmit vectors. In this paper, an adaptive scheme for selection of the optimal set of transmit antenna combinations is proposed to improve the reliability of GSM. The computational overhead of the said scheme is relatively high; hence, a low‐complexity suboptimal scheme for selection of the set of transmit antenna combinations is further proposed. The improved GSM schemes address the spectral efficiency limitation of EDAS‐SM, while demonstrating superior error performance.     

Non-orthogonal multiple access protocol for overlay cognitive radio networks using spatial modulation and antenna selection

In this paper we propose a novel spectrum sharing protocol for overlay cognitive radio networks using non-orthogonal multiple access (NOMA), spatial modulation (SM) and antenna selection (AS). The proposed protocol allows a secondary transmitter (ST) to transmit simultaneously to both a primary receiver (PR) and a secondary receiver (SR) using SM. The usage of NOMA and SM will increase the spectral efficiency for both PR and SR with reduced detection complexity than the case without NOMA in which the detectors are required to jointly detect both SM symbols at each receiver. The application of AS at ST with regards to PR provides higher quality transmission for PR without affecting the performance of SR. The performance of the proposed protocol is investigated by derivations of upper bounds on the average symbol error probabilities at PR and SR and by Monte Carlo simulations. Analytical and simulation results show that the proposed protocol offers efficient spectrum utilization over spectrum sharing protocols proposed recently that uses SM – to convey the primary data to PR through the amplitude phase modulation technique and the secondary data to SR through the index of the active antenna.     

Media‐based single‐symbol generalized spatial modulation

Single‐symbol generalized spatial modulation (GSM) improves upon the limitation of spatial modulation (SM) by reducing the number of required transmit antennas to achieve high data rates. In this paper, we investigate the application of media‐based modulation (MBM) based on radio frequency mirrors to single‐symbol GSM, with the aim of improving error performance. The theoretical average bit error probability of the proposed scheme is derived, employing a lower bound approach and used to validate the Monte Carlo simulation results. Finally, the effect of optimal and suboptimal mirror activation pattern selection employing Euclidean distance and channel amplitude coupled with antenna correlation is investigated for the proposed media‐based single‐symbol GSM system. The Monte Carlo simulation results obtained demonstrate a significant improvement over the conventional SM, GSM, and media‐based SM (MB‐SM) schemes in terms of error performance and spectral efficiency.     

A simple low-complexity algorithm for generalized spatial modulation

Generalized spatial modulation (GSM) is an extension of spatial modulation which is significant for the next generation communication systems. Optimal detection process for the GSM is the maximum-likelihood (ML) detection which jointly detects the antenna combinations and transmitted symbols. However, the receiver is much more complicated than SM due to inter-antenna interference and/or increased number of combinations. Therefore, the computational complexity of the ML detection grows with the number of transmit antennas and the signal constellation size. In this letter, we introduce a novel and simple detection algorithm which uses sub-optimal method based on the least squares solution to detect likely antenna combinations. Once the antenna indices are detected, ML detection is utilized to identify the transmitted symbols. For obtaining near-ML performance while keeping lower complexity than ML detection, sphere decoding is applied. Our proposed algorithm reduces the search complexity while achieving a near optimum solution. Computer simulation results show that the proposed algorithm performs close to the optimal (ML) detection resulting in a significant reduction of computational complexity.     

Antenna Selection Schemes in Quadrature Spatial Modulation Systems

This paper presents antenna selection schemes for recently proposed quadrature spatial modulation (QSM) systems. The antenna selection strategy is based on Euclidean distance optimized antenna selection (EDAS). The symbol error rate (SER) performance of these schemes is compared with that of the corresponding algorithm associated with spatial modulation (SM) systems. It is shown through simulations that QSM systems using EDAS offer significant improvement in terms of SER performance over SM systems with EDAS. Their SER performance gains are seen to be about 2 dB–4 dB in E_s/N₀ values.     

Transmit Antenna Selection Schemes for Quadrature Spatial Modulation

The objective of this paper is to investigate the application of transmit antenna selection (TAS) to quadrature spatial modulation (QSM). The application of optimal Euclidean distance based antenna selection (EDAS) to QSM (EDAS-QSM) is first proposed. EDAS-QSM requires an exhaustive search, which imposes a significantly high computational complexity. In this regard, a reduced-complexity algorithm for the computation of EDAS-QSM is proposed. Finally, several low-complexity, sub-optimal TAS techniques for QSM are investigated. The decision metrics of these schemes are based on channel amplitude, antenna correlation, Euclidean distance or a combination thereof. Monte Carlo simulation results demonstrate the effectiveness of the proposed schemes, while the computational complexity of each is analysed. The trade-off between error performance and computational complexity is discussed for each of the schemes.     

Spatial modulation and physical layer network coding based bidirectional relay network with transmit antenna selection over Nakagami‐m fading channels

In this paper, a high data rate bidirectional relay network is proposed by combining the merits of spatial modulation (SM) and physical layer network coding. All nodes in the network are equipped with multiple antennas. Spatial modulation technique is used to reduce hardware complexity and interchannel interference by activating only one antenna at any time during transmission. In the proposed bidirectional relay network, transmit antennas are selected at the source nodes and relay node on the basis of the order statistics of channel power. It increases received signal power and provides a significant improvement in the outage performance. Also, the data rate of the proposed network is improved by physical layer network coding at the relay node. A closed form analytical expression for the outage probability of the network over Nakagami‐m fading channel is derived and validated by Monte Carlo simulations. In addition, asymptotic analysis is investigated at high signal‐to‐noise ratio region.The outage performance of the proposed network is compared with SM and physical layer network coding bidirectional relay network without transmit antenna selection and point‐to‐point SM. With approximate SNR≈1 dB difference between the two networks, the same data rate is achieved.