非正交多址接入系统中关于迫零波束的用户配对

为了满足人们对移动通信越来越多的要求,第五代通信系统(5G)的研究日益受到人们的重视。为了增加系统的容量,非正交多址接入(NOMA)技术作为一种新的多址接入技术很有可能运用到5G中。由于接收端运用串行干扰消除技术,可以将多个信号结合在一起传送。因此将NOMA与多输入多输出技术结合在一起,采用迫零算法设计波束。每个波束可以有多个用户,主要讨论用户的配对选择问题。为了提高系统的效果,利用迫零算法波束的特点,提出了用户的配对选择算法。仿真结果证明,该算法有很好的效果。     

一种低复杂度非正交多址接入功率分配算法

功率分配是非正交多址系统(NOMA)资源分配中的一个重要研究问题。最优迭代注水功率分配算法能提高系统性能,但是算法复杂度较高。提出一种低复杂度的功率分配算法,首先对子载波采用注水原理得到总的复用功率,然后在单个子载波上叠加用户间采用分数阶功率分配方法进行功率再分配。通过仿真分析,与最优迭代注水功率分配算法相比,该算法在性能损失不超过3%的情况下,大幅减低了计算复杂度。     

非正交多址系统中基于公平性改善的双层挤压迭代功率分配方法

为了解决下行非正交多址系统中多用户通信的公平性问题,提出了基于公平性改善的双层挤压迭代功率分配方法。研究内容包括：首先,设计基于用户信道增益差的用户信道分裂过程,方便动态调整功率挤压时的挤压程度;其次,从强用户到弱用户进行内层功率挤压迭代,根据信道分裂情况设置挤压因子与附加挤压因子,使信道分裂处的弱用户对强用户挤压程度更强;第三,对内层挤压功率进行外层迭代的再分配与再挤压,可保持总功率不变的情况下,进一步提升功率分配的公平性。仿真结果表明,对比信道分裂下与信道未分裂下的公平性指数,其性能提升了25%;对比仅进行挤压因子与附加挤压因子调整,而未进行内外层迭代次数调整的情况,公平性指数性能提升了53.71%,同时,所提算法比注水算法达到的公平性指数明显改善,在公平性提升方面达到了较好的效果。     

NOMA中基于非规则码片映射的稀疏多用户检测算法

针对非正交多址接入系统灵活性不高的问题,基于码片映射码分多址（Chip Mapping-CDMA,CM-CDMA）系统,设计了一种非规则结构的码片映射矩阵。根据不同场景需求,该映射矩阵可为各用户分配不同数量的传输码片,提高了系统灵活性。同时分析了非规则映射矩阵的引入满足压缩感知RIP条件,并对该系统模型进行了验证。仿真结果表明,该系统能够利用压缩感知理论可靠地检测出活跃用户和数据,过载率可达300%,有效提升了频谱利用率。     

基于非正交多址的认知MIMO网络次用户系统容量优化

针对未来移动通信系统对大容量、高频谱利用率的需求,提出基于非正交多址（NOMA）技术的认知多输入多输出（MIMO）网络次用户系统容量优化方法。首先对发送信号进行预编码,随后按照信道质量增益对认知用户进行分簇,再对分簇之后的用户进行功率分配,最后将得到的NP-hard型多簇目标函数转化为求各子簇的容量;同时兼顾认知用户服务质量（QoS）及满足串行干扰消除（SIC）的条件,利用Lagrange函数结合Karush-Kuhn-Tucker （KKT）条件求解出分簇之后的最优功率分配系数,且该系数是0到1之间的常数。仿真结果表明,所提方法优于平均功率分配方法,并且在信道质量较差时,相比基于正交多址（OMA）技术的认知MIMO,显著提高了次用户系统容量。     

Design issues of uplink media access control (MAC) protocols for multimedia traffic over DS-CDMA systems

We propose an efficient uplink media access control (MAC) protocol for a variable spreading gain interference-limited wideband CDMA system. It can, with high spectral efficiency, support both real-time traffic like speech and video and also nonreal-time data traffic based on packet transmission. The schemes for power allocation, joint scheduling, and transmission rate adaptation for nonreal time data traffic are designed as integrated parts of the MAC, working together to improve the system performance in terms of capacity and delay. With these associated resource management mechanisms, the performances of the MAC protocol with two different channel-allocation methods for real-time traffic are numerically compared. One is demanding channel allocation, and the other is reserve channel allocation, in which a certain bandwidth is reserved for concurrent real-time traffic.     

基于5G无线通信的稀疏码多址接入系统的FPGA实现

在理解无线通信多址接入的基础之上,提出了一种低复杂度的基于5G无线通信的稀疏码多址接入系统的FPGA实现方案,利用可综合的Verilog语言在Quartus II及Model Sim平台下完成了电路的设计综合仿真及FPGA验证,结果证明该设计实现功能完备,可以实际应用。     

A novel channel-adaptive uplink access control protocol for nomadic computing

We consider the uplink access control problem in a mobile nomadic computing system, which is based on a cellular phone network in that a user can use the mobile device to transmit voice or file data. This resource management problem is important because an efficient solution to uplink access control is critical for supporting a large user population with a reasonable level of quality of service (QoS). While there are a number of recently proposed protocols for uplink access control, these protocols possess a common drawback in that they do not adapt well to the burst error properties, which are inevitable in using wireless communication channels. We propose a novel TDMA-based uplink access protocol, which employs a channel state dependent allocation strategy. Our protocol is motivated by two observations: (1) when channel state is bad, the throughput is low due to the large amount of FEC (forward error correction) or excessive ARQ (automatic repeated request) that is needed and (2) because of item 1, much of the mobile device's energy is wasted. The proposed protocol works closely with the underlying physical layer in that, through observing the channel state information (CSI) of each mobile device, the MAC protocol first segregates a set of users with good CSI from requests gathered in the request contention phase of an uplink frame. The protocol then judiciously allocates channel bandwidth to contending users based on their channel conditions. Simulation results indicate that the proposed protocol considerably outperforms five state-of-the-art protocols in terms of packet loss, delay, and throughput.     

Channel-aware multi-user uplink transmission scheme for SIMO-OFDM systems

The problem of medium access control(MAC) in wireless single-input multiple-output-orthogonal frequency division multiplexing(SIMO-OFDM) systems is addressed. Traditional random access protocols have low overheads and inferior performance. Centralized methods have superior performance and high overheads. To achieve the tradeoff between overhead and performance,we propose a channelaware uplink transmission(CaUT) scheme for SIMO-OFDM systems. In CaUT,users transmit requestto-send(RTS) at some subcarriers whos...     

A verifiable trust evaluation mechanism for ultra-reliable applications in 5G and beyond networks

With the development of Internet of Thing (IoT) joint 5G and Beyond Networks, Mobile Edge Users (MEUs) can act as mobile data collectors to collect data for various applications. However, some malicious MEUs reporting false or malicious data can cause serious harm to applications, especially for ultra-reliable applications. A novel Verifiable Trust Evaluation joint UAV (VTE-UAV) mechanism is proposed to select trustworthy MEUs to conduct the task for ultra-reliable applications. The VTE-UAV strategy adopts two novel trust evaluation methods, one is the aggregation-based MEU trust evaluation mechanism, when malicious evaluation objects are in the minority, the mechanism takes most evaluation results as baseline data. The other is an active trust acquisition mechanism, it takes the data obtained by Unmanned Aerial Vehicles (UAVs) as baseline data to actively validate the authenticity of the data. Through these two cross evaluation strategies, we obtain more accurate trust evaluation results. Finally, this paper transforms the trust evaluation optimization problem into the optimization of the accuracy of trust evaluation with reducing the cloud payment and the dispatch cost of UAVs. Extensive experiments have verified the validity of the VTE-UAV strategy. Compared with the previous strategies, the VTE-UAV improves the cloud recruitment performance by 7.74%-25.91%, increases the accuracy of trust evaluation of IoT devices by 2.24%-11.72%, and reduces the cloud payment and the cost of UAVs by 3.11%-10.20% and 58.23%, respectively.     

GO-MC-CDMA上行链路ML多用户检测研究

正交分组多载波码分多址（GO-MC-CDMA）每个用户组是独立的MC-CDMA系统,合理选择组内载波数使得最大似然（ML）算法切实可行。分析了GO-MC-CDMA上行链路在考虑载波频偏（CFO）的情况下采用最大似然序列估计（MLSE）检测的系统性能;比较了不同用户数和不同数字调制方式对误比特率（BER）的影响。数值仿真结果表明：载波频偏在一定范围内时,采用ML多用户检测的GO-MC-CDMA系统具有较好的对抗载波频偏能力和优异的误比特率性能;用户数目和调制方式对误比特率影响较大。     

频分多址系统分布式强化学习功率控制方法

近年来,深度强化学习作为一种无模型的资源分配方法被用于解决无线网络中的同信道干扰问题。然而,基于常规经验回放策略的网络难以学习到有价值的经验,导致收敛速度较慢;而人工划定探索步长的方式没有考虑算法在每个训练周期上的学习情况,使得对环境的探索存在盲目性,限制了系统频谱效率的提升。对此,提出一种频分多址系统的分布式强化学习功率控制方法,采用优先经验回放策略,鼓励智能体从环境中学习更重要的数据,以加速学习过程;并且设计了一种适用于分布式强化学习、动态调整步长的探索策略,使智能体得以根据自身学习情况探索本地环境,减少人为设定步长带来的盲目性。实验结果表明,相比于现有算法,所提方法加快了收敛速度,提高了移动场景下的同信道干扰抑制能力,在大型网络中具有更高的性能。     

Multimedia flow segmentation access mechanism with adaptive cooperative uplink and downlink

Multimedia Tools and Applications - In order to improve the access efficiency of multimedia communication system and solve the problem of two-way link collaboration effectively, based on the...     

Friendly-jamming schemes to secure ultra-reliable and low-latency communications in 5G and beyond communications

The security vulnerabilities are becoming the major obstacle to prevent the wide adoption of ultra-reliable and low latency communications (URLLC) in 5G and beyond communications. Current security countermeasures based on cryptographic algorithms have a stringent requirement on the centralized key management as well as computational capabilities of end devices while it may not be feasible for URLLC in 5G and beyond communications. In contrast to cryptographic approaches, friendly jamming (FJ) as a promising physical layer security method can enhance wireless communications security while it has less resource requirement on end devices and it can be applied to the full distribution environment. In order to protect wireless communications, FJ signals are introduced to degrade the decoding ability of eavesdroppers who maliciously wiretap confidential information. This article presents a state-of-the-art survey on FJ schemes to enhance network security for IoT networks with consideration of various emerging wireless technologies and different types of networks. First, we present various secrecy performance metrics and introduce the FJ method. The interference caused by FJ signals on legitimate communication is the major challenge of using FJ schemes. In order to overcome this challenge, we next introduce the integration of FJ schemes with various communication technologies, including beamforming, multiple-input multiple-output, full duplex, and relay selection. In addition, we also integrate FJ schemes with different types of communication networks. Finally, a case study of FJ schemes is illustrated and future research directions of FJ schemes have been outlined.     

Design of a compact multiband circularly polarized antenna for global navigation satellite systems and 5G/B5G applications

Design of a multiband circularly polarized antenna is proposed in this article. The antenna has a simple and compact form factor by employing single‐feed stacked patch structure. It exhibits good performance at the global navigation satellite system (GNSS) frequency bands of L1, L2, and L5 and cellular communications frequency band of 2.3 GHz. The antenna has a 3‐dB axial ratio bandwidth of 1.1%, 1.0%, 4.1%, and 1.5% at the four operating bands of L1 (1.575 GHz), L2 (1.227 GHz), L5 (1.176 GHz), and 2.3 GHz. The antenna also achieves a gain of more than 2.2 dBiC and efficiency of more than 70% at the four frequencies. A detailed parametric study is carried out to investigate the importance of different structural elements on the antenna performance. Results are verified through close agreement of simulations and experimental measurements of the fabricated prototype. Good impedance matching, axial ratio bandwidth, and radiation characteristics at the four operating bands along with small profile and mechanically stable structure make this antenna a good candidate for current and future GNSS devices, mobile terminals, and small satellites for 5G/Beyond 5G (5G/B5G) applications.     

Ultra-reliable secure data aggregation scheme with low latency for isolated terminals in 5G and beyond defined STINs

5G and beyond defined space-terrestrial integrated networks (STINs) have become an emerging research field, thanks to the rapid development of future generation communication technologies and satellite networks. Ultra-reliable low latency STINs utilizing 5G and beyond technologies put forward requirements for the trustworthiness of network terminals and the convenience of data aggregation. Some research work has been carried out in this field. However, the secure aggregation in STINs between isolated terminals that lack connection with base stations and data centers needs to be further studied. In this paper, a trustworthiness based secure data aggregation scheme with low latency for isolated terminals in 5G and beyond defined STINs is proposed. The trustworthiness of the isolated terminals is evaluated by the satellites and the data centers to increase the reliability of the aggregated data. A lightweight trusted special channel establishment method between an isolated terminal and a data center is presented. The security and performance analysis shows that the novel proposal is secure and efficient.     

基于5G网络无线接入安全技术措施研究

[目的/意义]在互联网技术不断发展的进程中,5G技术凸显出优势,但是该技术在具体应用中,往往面临着诸多安全问题的挑战。加强无线接入安全防护,可以提高网络的安全性,降低信息被盗、丢失等风险。所以,基于5G网络无线接入安全技术措施的研究,对于提高互联网应用的安全性,具有十分重要的现实意义。[方法/过程]基于5G网络安全架构,提出了5G网络无线接入安全需求,并以此为基础,提出了认证与授权、基于切片安全隔离技术、5G网络切片技术架构、5G网络切片自身安全技术、物理层安全保密通信技术等措施,并对这些技术措施的应用进行了介绍。[结果/结论]基于仿真实验数据的分析结果显示,认证与授权、基于切片安全隔离技术、5G网络切片技术架构、5G网络切片自身安全技术、物理层安全保密通信技术等措施的应用,可以有效地提高5G网络无线接入安全,降低网络被侵害的概率。     

SoftAir: A software defined networking architecture for 5G wireless systems

One of the main building blocks and major challenges for 5G cellular systems is the design of flexible network architectures which can be realized by the software defined networking paradigm. Existing commercial cellular systems rely on closed and inflexible hardware-based architectures both at the radio frontend and in the core network. These problems significantly delay the adoption and deployment of new standards, impose significant challenges in implementing and innovation of new techniques to maximize the network capacity and accordingly the coverage, and prevent provisioning of truly- differentiated services which are able to adapt to growing and uneven and highly variable traffic patterns. In this paper, a new software-defined architecture, called SoftAir, for next generation (5G) wireless systems, is introduced. Specifically, the novel ideas of network function cloudification and network virtualization are exploited to provide a scalable, flexible and resilient network architecture. Moreover, the essential enabling technologies to support and manage the proposed architecture are discussed in details, including fine-grained base station decomposition, seamless incorporation of Openflow, mobility- aware control traffic balancing, resource-efficient network virtualization, and distributed and collaborative traffic classification. Furthermore, the major benefits of SoftAir architecture with its enabling technologies are showcased by introducing software- defined traffic engineering solutions. The challenging issues for realizing SoftAir are also discussed in details.     

Embedded access points for trusted data and resources access in HPC systems

Biometric authentication systems represent a valid alternative to the conventional username–password based approach for user authentication. However, authentication systems composed of a biometric reader, a smartcard reader, and a networked workstation which perform user authentication via software algorithms have been found to be vulnerable in two areas: firstly in their communication channels between readers and workstation (communication attacks) and secondly through their processing algorithms and/or matching results overriding (replay attacks, confidentiality and integrity threats related to the stored information of the networked workstation). In this paper, a full hardware access point for HPC environments is proposed. The access point is composed of a fingerprint scanner, a smartcard reader, and a hardware core for fingerprint processing and matching. The hardware processing core can be described as a Handel-C algorithmic-like hardware programming language and prototyped via a Field Programmable Gate Array (FPGA) based board. The known indexes False Acceptance Rate (FAR) and False Rejection Rate (FRR) have been used to test the prototype authentication accuracy. Experimental trials conducted on several fingerprint DBs show that the hardware prototype achieves a working point with FAR=1.07% and FRR=8.33% on a proprietary DB which was acquired via a capacitive scanner, a working point with FAR=0.66% and FRR=6.13% on a proprietary DB which was acquired via an optical scanner, and a working point with FAR=1.52% and FRR=9.64% on the official FVC2002_DB2B database. In the best case scenario (depending on fingerprint image size), the execution time of the proposed recognizer is 183.32 ms.