多天线系统中的多用户分集方案的性能分析及比较

在多天线多用户无线通信系统中,可以利用用户之间彼此独立的随机衰落信道的特点,结合随机波束成型技术,或者空间分集技术,或者天线选择技术,获得多用户分集增益。然而不同多用户分集方案的系统性能不尽相同。该文分析了在多输入单输出(MISO)信道中目前几种典型的多用户分集方案的性能,给出系统吞吐率的定量表达式,并综合比较了不同用户数和不同天线数对各种多用户分集方案性能的影响,为实际多天线多用户系统设计提供了有益的参考。     

多天线认知系统中最优协作用户数的选择研究

针对非理想控制信道传输错误对认知系统中多天线多用户协作频谱感知性能影响的问题,提出一种使得认知系统误检概率最小的最优协作用户数选择方案,并推导给出其闭式表达式。该方案首先根据单根天线错误检测概率最小的原则推导出认知用户单根天线最优的判决门限。然后利用“K秩”准则对多天线进行合并,根据认知用户错误检测概率最小的原则推导出最优的“K”值。最后根据认知系统误检概率最小的原则推导出最优的协作感知用户数。通过仿真验证了该方案理论的正确性,并分析给出了控制信道错误概率对认知系统检测性能的影响。相比于传统的协作检测算法,本方案具有更好的检测性能。      

利用有向图实现多用户下行多天线系统的用户选择

在多用户下行多天线系统中,基站可利用信道状态信息将独立的数据流同时发送到多个用户以得到更高的信道容量.由于在实际系统中基站很难实时得到各用户的完全信道状态信息,可以基于有限的信道反馈量进行用户选择来提高系统的和速率.提出了一种部分信道状态信息下利用有向图实现多用户下行多天线系统用户选择的算法.该算法将用户选择的问题变成了在有向图中寻找闭合环的问题,可以大幅度降低用户选择的复杂度;克服了常规的随机波束成形算法只有在用户数非常多的时候才能有效工作的弱点,在用户数少或中等的时候能得到比其更好的性能.因此该算法更适合在实际系统中应用.     

多用户MIMO下行收发联合波束成形

针对随机波束成形(RBF)只有在包含大量用户的系统中才能获得较好性能的局限性,提出了一种新的收发联合波束成形方案,用于多用户多入多出(MIMO)下行链路传输。该方案有效地结合了RBF与接收天线合并技术。分析及仿真结果表明,即使在用户数为中等甚至较小时仍然能获得较高的和速率性能。由于每个用户的反馈开销没变,从而使获得同样和速率时系统的总反馈开销明显减少。仿真结果还显示,所提方案的和速率性能不仅优于原RBF,也比RBF结合最大比合并或者等增益合并的性能有明显改善,同时还保持了最优的随用户数变化的增长速度。     

大规模MIMO中继系统中多用户物理层安全传输方案

研究大规模多输入多输出中继网络中的多用户物理层安全传输方案.系统模型中假设窃听节点与源节点和中继节点间都有直接链路,窃听节点可以接收到源节点和中继发送的信号.在不能获得窃听者信道状态信息的情况下,大规模MIMO中继采用简单的最大比合并/最大比发射信号处理方案,并配合中继零空间人工噪声和目的端的协作干扰实现多用户的信息安全传输.对保密速率及其在中继天线数无限增长时的渐近值进行了理论分析,并进行仿真.仿真结果显示系统的保密和速率随中继天线数的增长而增长,最终趋于理论渐近上界值.仿真结果也表明即使窃听节点具有多用户间干扰消除能力,并能同时拦截源节点和中继发送的信号,采用本文的方案仍然能获得可观保密速率.     

人工噪声辅助的多用户安全传输方法

针对传统人工噪声辅助的安全传输方法无法适用于发射天线数等于接收天线数的多用户(Multiuser, MU)多输入多输出(Multiple-Input Multiple-Output, MIMO)系统的问题,提出了一种人工噪声辅助的多用户安全传输新方法。通过合理设计人工噪声与预编码矩阵,该方法可在同时满足所有用户传输需求的基础上,显著提升发射天线数等于接收天线数的MU-MIMO系统的安全性。同时,针对提出的方法进行了检测算法与平均保密速率的推导与分析。理论分析与仿真结果表明,所提方法可有效提升无线通信系统的安全性,在信噪比为20 dB时,该方法较传统方法的平均保密速率提升达到120%。     

基于天线波束成形的OFDMA系统的自适应资源分配

对正交频分复用接入系统在多用户多天线传输情况下的自适应资源分配策略进行了研究,提出了一种基于天线波束成形的,包括动态子载波分配、自适应调制、比特加载的无线资源分配方案.算法的优化设计目标是在满足总的恒定传输比特数和误比特率性能要求的情况下,使得系统总的发射功率最小.仿真结果表明,由于多天线阵列增益和多用户分集增益,系统整体性能得到了明显的优化.     

窃听多天线的多用户调度安全性能分析

物理层安全作为一种密钥缺省的安全方案,逐渐成为信息安全和无线通信两个领域的交叉热点,其主要利用物理层传输资源保证合法接收者正常通信,同时抑制窃听信道通信。针对这一特点,提出了基于无线通信网络中窃听用户多天线、发送端多用户调度,合法接收端选择最好用户的模型,这时窃听用户进行随机选择,分析这种情况下主信道信噪比、窃听信道信噪比、安全传输速率以及窃听用户天线数目对系统安全性能的影响。仿真结果表明,窃听信道多天线时中断概率增加,即降低了系统的安全性能,但增加发送端用户数目、降低窃听信道信噪比、增加主信道信噪比可以显著提高系统的安全速率。同时证明,这种方案同随机选择发送用户相比较,切实提高了系统的安全性能。     

多用户MIMO系统在有限反馈下结合预编码与调度算法的研究

捅要：研究了多用户多输入多输出（MIMO）系统在有限反馈下的一种结合单位预编码与用户调度算法的方案。在该系统中每一用户都具有多个接收天线,该方案具有较大的多用户分集增益和较小的计算复杂度,从而能够减少系统中的用户间干扰。每个用户独立地决定自己的天线合并矢量,并将最优波束矢量以及对应的估计信干噪比通过有限反馈信道反馈给基站,此时基站获取了相应的用户信道信息和用户间干扰信息。基于接收到的反馈信息,基站从预定义的码本中选取和速率最大的最优子集进行系统预编码,然后依照预编码矩阵调度欧氏距离最小的用户且用户个数不超过发送天线的数目。仿真结果显示该方案有效地改善了系统速率,特别是在用户数目较多或者信道环境较好的情况下。     

面向大规模MIMO下行多用户迫零预编码的交替训练研究

为解决频分双工大规模MIMO的信道获取开销问题,针对服务质量保障与基站采用迫零（ZF）预编码的典型场景,引入对信干噪比（SINR）的监督机制,设计多用户逐根天线交替训练方案。进而考虑交替训练引入的时间开销,设计基于天线分组的多用户交替训练方案。然后推导了2种方案的平均训练长度、传输成功率以及平均有效和频谱效率闭合表达式。理论与仿真揭示了发射功率、SINR阈值、用户数、分组长度与信道误差水平等参数的影响,并证明相比全训练与部分训练,所提方案可显著降低导频开销,提升传输成功率。     

信道估计误差场景MIMO ARQ系统中的模式切换

该文研究了多输入多输出(MIMO)系统自适应模式切换问题,综合考虑了实际系统中4个影响模式切换的因素:信道估计误差,系统丢包率限制,自动请求重传技术,离散的发送速率及实际的编解码性能。论文推导了复用和分集模式的吞吐率表达式,提出了吞吐率最大化的MIMO模式切换方法。仿真表明该文提出的自适应模式切换方法能明显提升系统的性能,所考虑的4个因素会对两种传输模式性能以及切换点产生影响。     

QSM-IDM – A novel quadrature spatial modulation based on interleaving division multiplexing for multiple antenna system

Quadrature Spatial Modulation (QSM) is a high spectral efficiency Multiple-Input Multiple Output (MIMO) technique used to improve the spectral efficiency of wireless communication systems. The main concept of QSM is to extend the spatial constellation of the conventional Spatial Modulation (SM) in both the in-phase and quadrature components of the data symbol. In this paper, because QSM-based on Interleaving Division Multiplexing (IDM) has not been introduced in the literature as a multiple antenna system, we introduced a novel scheme, called QSM system based on Interleaving Division Multiplexing (QSM-IDM). The antenna sets are also applied to a spreader, before being used to assign an antenna number for information transmission. Analysis and simulations for a flat fading channel show that the proposed QSM-IDM method significantly outperforms the original QSM system with the same data rate, while maintaining a relatively acceptable complexity. The obtained simulation results show that the conducted analysis yields significant improvements for the accuracy of the proposed scheme, with satisfactory complexity.     

车联网中基于NOMA-MEC的卸载策略研究

随着车联网(IoV)的迅猛发展,请求进行任务卸载的汽车终端用户也逐渐增长,而基于移动边缘计算(MEC)的通信网络能够有效地解决任务卸载在上行传输时延较高的挑战,但是该网络模型同时也面临着信道资源不足的问题。该文引入的非正交多址(NOMA)技术相较于正交多址(OMA)能够在相同的信道资源条件下为更多的用户提供任务卸载,同时考虑到任务卸载过程中多方面的影响因子,提出了混合NOMA-MEC卸载策略。该文设计了一种基于深度学习网络(DQN)的博弈算法,帮助车辆用户进行信道选择,并通过神经网络多次迭代学习,为用户提供最优的功率分配策略。仿真结果表明,该文所提出的混合NOMA-MEC卸载策略能够有效地优化多用户卸载的时延以及能耗,最大限度保证用户效益。     

Interleaved coding and sequential transmission scheme for packet‐level forward error correction over burst loss channels

Burst packet loss is a common problem over wired and wireless networks and leads to a significant reduction in the performance of packet‐level forward error correction (FEC) schemes used to recover packet losses during transmission. Traditional FEC interleaving methods adopt the sequential coding‐interleaved transmission (SCIT) process to encode the FEC packets sequentially and reorder the packet transmission sequence. Consequently, the burst loss effect can be mitigated at the expense of an increased end‐to‐end delay. Alternatively, the reversed interleaving scheme, namely, interleaved coding‐sequential transmission (ICST), performs FEC coding in an interleaved manner and transmits the packets sequentially based on their generation order in the application. In this study, the analytical FEC model is constructed to evaluate the performance of the SCIT and ICST schemes. From the analysis results, it can be observed that the interleaving delay of ICST FEC is reduced by transmitting the source packets immediately as they arrive from the application. Accordingly, an Enhanced ICST scheme is further proposed to trade the saved interleaving time for a greater interleaving capacity, and the corresponding packet loss rate can be minimized under a given delay constraint. The simulation results show that the Enhanced ICST scheme achieves a lower packet loss rate and a higher peak signal‐to‐noise‐ratio than the traditional SCIT and ICST schemes for video streaming applications.     

Efficient channel utilization for real-time video in OVSF-CDMA systems with QoS assurance

In this paper, the utilization of real-time video service in the downlink of an orthogonal variable spreading factor code division multiple access (OVSF-CDMA) system is studied. By modeling the video traffic and wireless channel as a joint Markov modulated process, and properly partitioning the states of the Markov process, an adaptive rate allocation scheme is proposed for real-time video transmission with quality of service provisioning while achieving high channel utilization. The scheme is applicable for packet switching and frame-by-frame real-time video transmission, and incorporates both the physical layer and network layer characteristics. For QoS provisions, the closed form expressions of packet delay and loss probability are derived based on the Markov model. Analytical and simulation results demonstrate that the proposed scheme can significantly improve the channel utilization over the commonly used effective bandwidth approach.     

延迟容忍网络自适应差错控制方法

根据延迟容忍网络的时延较大、误码率较高等特点,在现有的传输控制层和MAC层差错控制的基础上改进,结合IEEE 802.11 DCF机制的特点,提出一种基于MAC层丢包率的自适应差错控制方案.该方案能有效改善延迟容忍网络的传输时延,满足对时延要求比较敏感的业务的要求.     

两种异构CSMA/CA机制OSTS/BSTS无线传感网络公平性、实时性分析比较

IEEE802.15.4作为一种专为低速率无线个人区域网络(WPAN)而设计的低成本、低功耗、低速率的短距离无线通信新标准,为无线传感器网络提供了一种很好的解决方案。本文针对异构、非饱和无线网络,提出了两种新的CS-MA/CA机制:OSTS/BSTS机制;异构节点数据到达率不同,其各自获取的吞吐量不同,由此分析获得异构网络节点的公平性。OSTS/BSTS机制最大的特点是异构节点被赋予了公平的机会来访问信道,不存在优先权等级的问题。这两种机制采用两个半马尔可夫链模型来分别表达两组节点的访问过程,一个宏观马尔可夫链模型来表达信道状态转换过程,结合队列理论模型来分析异构节点的延时量、吞吐量、传输概率等特性,以获取网络实时性、公平性理论模型,并采用NS-2仿真工具对分析结果进行了仿真。     

Broadcast scheduling with MIMO links in multi-hop ad hoc networks

As the current medium access control protocols with Multiple Input Multiple Output (MIMO) links only bear point to point service, broadcast scheduling algorithm in ad hoc networks with MIMO links is proposed. The key to the proposed broadcast scheduling algorithm is the time slot scheduling algorithm which guarantees collision-free transmissions for every node and the mini- mum frame length. The proposed algorithm increases the simultaneous transmissions of MIMO links efficiently. Due to the interference null capacity of MIMO links, the interference node set of each node can decrease from two-hop neighbors to one-hop neighbors possibly. Simulation results show that our algorithm can greatly improve network capacity and decrease average packet delay.     

OFDMA系统保证服务质量的分组调度算法

在正交频分多址接入系统中采用正比公平算法可以兼顾吞吐量和公平性,有效地提高系统性能。结合正比公平算法,该文提出一种应用于正交频分多址接入系统保证服务质量的分组调度算法。为防止需求速率高但瞬时信道状况差的用户分配过多的子载波,算法使用了动态变化的权重因子。在一次调度过程中,剩余子载波的权重因子可以随着子载波的分配而更新。仿真结果证明,在满足实时业务服务质量的前提下,该算法比正比公平算法具有更好的公平性。     

A Real Time Transport Scheme for Wireless Multimedia Communications

In wireless communications systems, a mobile station is typically equipped with limited processing capability and buffer space for transmitting and receiving. The radio link is usually found to be noisy and its propagation delay is sometimes non-negligible as compared with the packet transmission delay. And because of the necessity of flow control and packet retransmission upon error, the delay and throughput performance cannot satisfy the need of a particular traffic type, i.e., real-time multimedia. This paper presents a scheme suitable for the above condition, called the Burst-oriented Transfer with Time-bounded Retransmission (BTTR). The present scheme uses a large transmission window for sending/receiving a burst of time-sensitive data and, within this window, another smaller observation window is repeatedly used for error status feedback via the backward channel. There is time limitation on each retransmission such that the burst of data can be received in a timely manner, however, with some degradation on the packet loss rate. An analysis is given in terms of the expectations of delay, throughput, and packet drop rate. A comparison with an error-free link protocol will also be given. The result shows that the proposed scheme can meet the delay and throughput requirement under reasonable packet drop rate.