Outage Probability Analysis for D2D-Enabled Heterogeneous Cellular Networks with Exclusion Zone:A Stochastic Geometry Approach

Interference management is one of the most important issues in the device-to-device(D2D)-enabled heterogeneous cellular networks(HetCNets)due to the coexistence of massive cellular and D2D devices in which D2D devices reuse the cellular spectrum.To alleviate the interference,an efficient interference management way is to set exclusion zones around the cellular receivers.In this paper,we adopt a stochastic geometry approach to analyze the outage probabilities of cellular and D2D users in the D2D-enabled HetCNets.The main difficulties contain three aspects:1)how to model the location randomness of base stations,cellular and D2D users in practical networks;2)how to capture the randomness and interrelation of cellular and D2D transmissions due to the existence of random exclusion zones;3)how to characterize the different types of interference and their impacts on the outage probabilities of cellular and D2D users.We then run extensive Monte-Carlo simulations which manifest that our theoretical model is very accurate.

A Tractable Approach to Analyzing the Physical-Layer Security in K-Tier Heterogeneous Cellular Networks

This study proposes a tractable approach to analyze the physical-layer security in the downlink of a multi-tier heterogeneous cellular network. This method is based on stochastic geometry, has low computational complexity, and uses the two-dimensional Poisson point process to model the locations of K-tier base stations and receivers, including those of legitimate users and eavesdroppers. Then, the achievable secrecy rates for an arbitrary user are determined and the upper and lower bounds of secrecy coverage probability derived on the condition that cross-tier interference is the main contributor to aggregate interference. Finally, our analysis results reveal the innate connections between information-theoretic security and the spatial densities of legitimate and malicious nodes.

Uplink Performance Analysis in Multi-Tier Heterogeneous Cellular Networks with Power Control and Biased User Association

A K-tier uplink heterogeneous cellular network is modelled and analysed by accounting for both truncated channel inversion power control and biased user association. Each user has a maximum transmit power constraint and transmits data when it has sufficient transmit power to perform channel inversion. With biased user association, each user is associated with a base station(BS) that provides the maximum received power weighted by a bias factor, but not their nearest BS. Stochastic geometry is used to evaluate the performances of the proposed system model in terms of the outage probability and ergodic rate for each tier as functions of the biased and power control parameters. Simulations validate our analytical derivations. Numerical results show that there exists a trade-off introduced by the power cut-off threshold and the maximum user transmit power constraint. When the maximum user transmit power becomes a binding constraint, the overall performance is independent of BS densities. In addition, we have shown that it is beneficial for the outage and rate performances by optimizing different network parameters such as the power cut-off threshold as well as the biased factors.

Physical Layer Security of Multi-hop Aided Downlink MIMO heterogeneous Cellular Networks

This study investigates physical layer security in downlink multipleinput multiple-output(MIMO) multi-hop heterogeneous cellular networks(MHCNs),in which communication between mobile users and base stations(BSs) is established by a single or multiple hops,to address the problem of insufficient security performance of MIMO heterogeneous cellular networks.First,two-dimensional homogeneous Poisson point processes(HPPPs) are utilized to model the locations of K-tier BSs in MIMO MHCNs and receivers,including those of legitimate users and eavesdroppers.Second,based on the channel gain distribution and the statistics property of HPPP,the achievable ergodic rates of the main and eavesdropper channels in direct and ad hoc links are derived,respectively.Third,the secrecy coverage probability and the achievable ergodic secrecy throughput of downlink MIMO MHCNs are explored,and their expressions are derived.Lastly,the correctness of the theoretical derivation is verified through Monte Carlo simulations.

On Energy Efficient Design for Dynamic CoMP Transmission in K-Tier Heterogeneous Cellular Networks

Motivated by the objective of pursuing revenue, improvement in coverage and reduction in energy cost for wireless communication networks have been of great significance for mobile operators. Therefore, heterogeneous cellular networks(HCNs) and Coordinated Multipoint(Co MP) transmission are considered as promising solutions to enhance the performances of wireless communication systems. This paper analyzed the K-tier HCNs with a dynamic downlink Co MP scheme, in which the flexible clusters of cooperative stations are determined by a connecting threshold θ. Using stochastic geometry, the coverage probability(CP) and energy efficiency(EE) of a K-tier HCN operating under this scheme are derived, based on which the trade-off between CP and EE is discovered and discussed. Simulation results show the validity of our derivations. The proposed schememay significantly reduce energy consumption sacrificing a small amount of CP, and outperforms the fixed scheme as well. The CP-EE trade-off are also revealed, whichsuggests suitable trade-off points between CP and EE that will deliver the maximum economic profitability. Tendencies discovered in this paper may provide the operators with opportunities for further optimization in pursuit of economic profitability.

Resource Allocation and User Association for HTTP Adaptive Streaming in Heterogeneous Cellular Networks with Small Cells

Video streaming,especially hypertext transfer protocol based(HTTP) adaptive streaming(HAS) of video,has been expected to be a dominant application over mobile networks in the near future,which brings huge challenge for the mobile networks.Although some works have been done for video streaming delivery in heterogeneous cellular networks,most of them focus on the video streaming scheduling or the caching strategy design.The problem of joint user association and rate allocation to maximize the system utility while satisfying the requirement of the quality of experience of users is largely ignored.In this paper,the problem of joint user association and rate allocation for HTTP adaptive streaming in heterogeneous cellular networks is studied,we model the optimization problem as a mixed integer programming problem.And to reduce the computational complexity,an optimal rate allocation using the Lagrangian dual method under the assumption of knowing user association for BSs is first solved.Then we use the many-to-one matching model to analyze the user association problem,and the joint user association and rate allocation based on the distributed greedy matching algorithm is proposed.Finally,extensive simulation results are illustrated to demonstrate the performance of the proposed scheme.

Energy Efficiency Optimization for Heterogeneous Cellular Networks Modeled by Matérn Hard-Core Point Process

The Poisson point process(PPP) has been widely used in wireless network modeling and performance analysis due to the independence between its nodes. Therefore, it may not be a suitable model for many of the exclusive networks between the nodes. This paper analyzes the energy efficiency(EE) and optimizes the two-tier heterogeneous cellular networks(Het Nets). Considering the mutual exclusion between macro base stations(MBSs) distribution, the deployment of MBSs is modeled by the Matérn hard-core point process(MHCPP), and the deployment of pico base stations(PBSs) is modeled by the PPP. We adopt a simple approximation method to study the signal to interference ratio(SIR) distribution in two-tier MHCPP-PPP networks and then derive the coverage probabilities, the average data rates and the energy efficiency of Het Nets. Finally, an optimization algorithm is proposed to improve the EE of Het Nets by controlling the transmit power of PBSs. The simulation results show that the EE of a system can be effectively improved by selecting the appropriate transmit power for the PBSs. In addition, two-tier MHCPP-PPP Het Nets have higher energy efficiency than two-tier PPP-PPP Het Nets.

Deep reinforcement learning-based resource allocation for D2D communications in heterogeneous cellular networks

Device-to-Device(D2D)communication-enabled Heterogeneous Cellular Networks(HCNs)have been a promising technology for satisfying the growing demands of smart mobile devices in fifth-generation mobile networks.The introduction of Millimeter Wave(mm-wave)communications into D2D-enabled HCNs allows higher system capacity and user data rates to be achieved.However,interference among cellular and D2D links remains severe due to spectrum sharing.In this paper,to guarantee user Quality of Service(QoS)requirements and effectively manage the interference among users,we focus on investigating the joint optimization problem of mode selection and channel allocation in D2D-enabled HCNs with mm-wave and cellular bands.The optimization problem is formulated as the maximization of the system sum-rate under QoS constraints of both cellular and D2D users in HCNs.To solve it,a distributed multiagent deep Q-network algorithm is proposed,where the reward function is redefined according to the optimization objective.In addition,to reduce signaling overhead,a partial information sharing strategy that does not observe global information is proposed for D2D agents to select the optimal mode and channel through learning.Simulation results illustrate that the proposed joint optimization algorithm possesses good convergence and achieves better system performance compared with other existing schemes.

Dynamic Spectrum Control-Assisted Secure and Efficient Transmission Scheme in Heterogeneous Cellular Networks

Heterogeneous cellular networks(HCNs)are envisioned as a promising architecture to provide seamless wireless coverage and increase network capacity.However,the densified multi-tier network architecture introduces excessive intra-and cross-tier interference and makes HCNs vulnerable to eavesdropping attacks.In this article,a dynamic spectrum control(DSC)-assisted transmission scheme is proposed for HCNs to strengthen network security and increase the network capacity.Specifically,the proposed DSC-assisted transmission scheme leverages the idea of block cryptography to generate sequence families,which represent the transmission decisions,by performing iterative and orthogonal sequence transformations.Based on the sequence families,multiple users can dynamically occupy different frequency slots for data transmission simultaneously.In addition,the collision probability of the data transmission is analyzed,which results in closed-form expressions of the reliable transmission probability and the secrecy probability.Then,the upper and lower bounds of network capacity are further derived with given requirements on the reliable and secure transmission probabilities.Simulation results demonstrate that the proposed DSC-assisted scheme can outperform the benchmark scheme in terms of security performance.Finally,the impacts of key factors in the proposed DSC-assisted scheme on the network capacity and security are evaluated and discussed.

Dual-Threshold Based Secure On-Off Transmission Scheme for Dense HCNs with Imperfect CSI

In this paper, we propose a dual-threshold based secure On-Off transmission scheme, where signals are transmitted only if the channel condition can guarantee secure and reliable communication. First, we present a dynamic access strategy to increase access efficiency, which provides an access region for the intended user. Then, we propose an emission control policy to transmit signals according to the current channel condition, which declines the influence of channel estimation errors and guarantees qualities of communication links. Furthermore, we give a comprehensive performance analysis for the proposed scheme in terms of connection outage probability(COP) and secrecy outage probability(SOP), and present a dual-threshold optimization model to further support the performance. Numerical results verify that the secure On-Off transmission scheme can increase the system secure energy efficiency and guarantee reliable and secure communication.

Hybrid millimeter wave heterogeneous networks with spatially correlated user equipment

In this paper,we analyze a hybrid Heterogeneous Cellular Network(HCNet)framework by deploying millimeter Wave(mmWave)small cells with coexisting traditional sub-6GHz macro cells to achieve improved coverage and high data rate.We consider randomly-deployed macro base stations throughout the network whereas mmWave Small Base Stations(SBSs)are deployed in the areas with high User Equipment(UE)density.Such user centric deployment of mmWave SBSs inevitably incurs correlation between UE and SBSs.For a realistic scenario where the UEs are distributed according to Poisson cluster process and directional beamforming with line-of-sight and non-line-of-sight transmissions is adopted for mmWave communication.By using tools from stochastic geometry,we develop an analytical framework to analyze various performance metrics in the downlink hybrid HCNets under biased received power association.For UE clustering we considered Thomas cluster process and derive expressions for the association probability,coverage probability,area spectral efficiency,and energy efficiency.We also provide Monte Carlo simulation results to validate the accuracy of the derived expressions.Furthermore,we analyze the impact of mmWave operating frequency,antenna gain,small cell biasing,and BSs density to get useful engineering insights into the performance of hybrid mmWave HCNets.Our results show that network performance is significantly improved by deploying millimeter wave SBS instead of microwave BS in hot spots.

忆阻耦合异构忆阻细胞神经网络的多稳态与相位同步研究

忆阻具有天然的可塑性,可实现与生物神经元和突触所具有的相似或相同机制的硅基神经元和纳米突触。将忆阻用作突触耦合两个异构的忆阻细胞神经网络,该文构建了一个忆阻耦合异构忆阻细胞神经网络。该耦合网络含有一个与忆阻突触初值条件和子网初值条件相关的空间平衡点集,可呈现出复杂的动力学演化。利用数值仿真方法,揭示了耦合网络依赖于初值条件而存在的稳定点、周期、混沌、超混沌以及无界振荡等多稳态行为。此外,在忆阻突触的调控下,两个异构子网可达成相位同步。最后,基于STM32单片机硬件平台完成了电路实验验证。

基于改进NaSch模型的网联异质交通流特性分析

为研究智能网联环境下异质交通流演变规律,设计典型场景驾驶模拟实验,采集传统车辆(human driven vehicle,HDV)与智能网联车辆(connected vehicle,CV)驾驶行为特征指标,对异质交通流关键参数进行分析和标定;构建考虑HDV与CV驾驶行为差异的异质交通流元胞自动机模型;并基于改进的NaSch模型进行仿真实验,解析智能网联环境下交通流基本图,分析异质交通流特性。研究结果表明:较于HDV,CV驾驶员捕捉道路信息和反应时间提升约11.4%;自由流状态下,CV车速比HDV车速提升了7.4%,且同一车速下安全跟驰距离缩短了18.2%;随着CV所占比例由20%增至80%,交通流基本图显示交通流平均车速显著提升,交通流率增加,时空轨迹图显示局部拥堵状况明显改善。

D2D通信复用异构蜂窝网络中分布式路由资源分配方法

由于设备到设备(Device-To-Device,D2D)通信复用异构蜂窝网络环境的复杂性和动态性,难以实现高效、均衡的路由资源利用,文章提出D2D通信复用异构蜂窝网络中分布式路由资源分配方法。采用分布式系统模型构建D2D通信复用异构蜂窝网络的拓扑结构,基于邻居节点信息交换实现D2D设备发现,并引入自适应的会话建立策略建立通信链路,采用贪婪算法为D2D用户分配子信道,实现路由资源的均衡分配。实验结果表明,设计方法在提升D2D用户之间数据传输速率方面具有较好的性能,适用于D2D通信复用异构蜂窝网络中的路由资源分配。

Load-balance cell association for improving network capacity in heterogeneous cellular networks

Heterogeneous cellular networks improve the spectrum efficiency and coverage of wireless communication networks by deploying low power base station （BS） overlapping the conventional macro cell. But due to the disparity between the transmit powers of the macro BS and the low power BS, cell association strategy developed for the conventional homogeneous networks may lead to a highly unbalanced traffic loading with most of the traffic concentrated on the macro BS. In this paper, we propose a load-balance cell association scheme for heterogeneous cellular network aiming to maximize the network capacity. By relaxing the association constraints, we can get the upper bound of optimal solution and convert the primal problem into a convex optimization problem. Furthermore we propose a Lagrange multipliers based distributed algorithm by using Lagrange dual theory to solve the convex optimization, which converges to an optimal solution with a theoretical performance guarantee. With the proposed algorithm, mobile terminals （MTs） need to jointly consider their traffic type, received signal-to-interference-noise-ratios （SINRs） from BSs, and the load of BSs when they choose server BS. Simulation results show that the load balance between macro and pico BS is achieved and network capacity is improved significantly by our proposed cell association algorithm.

Joint resource allocation with QoS provisioning in K-tier heterogeneous cellular networks

In this paper, the joint resource allocation （RA） problem with quality of service （QoS） provisioning in downlink heterogeneous cellular networks （HCN） is studied. To fully exploit the network capacity, the HCN is modeled as a K-tier cellular network where each tier＇s base stations （BSs） have different properties. However, deploying numbers of low power nodes （LPNs） which share the same frequency band with macrocell generates severe inter-cell interference. Enhancement of system capacity is restricted for inter-cell interference. Therefore, a feasible RA scheme has to be developed to fully exploit the resource efficiency. Under the constraint of inter-cell interference, we formulate the RA problem as a mixed integer programming problem. To solve the optimization problem we develop a two-stage solution. An integer subchannel assignment algorithm and Lagrangian-based power allocation algorithm are designed. In addition, the biasing factor is also considered and the caused influence on system capacity is evaluated. Simulation results show that the proposed algorithms achieve a good tradeoff between network capacity and interference. Moreover, the average network efficiency is highly improved and the outage probability is also decreased.

Price-Based Power Allocation in Two-Tier Spectrum Sharing Heterogeneous Cellular Networks

Attributable to the using of the same spec-trum resources,heterogeneous cellular networks have serious interference problems,which greatly restricts the performance of the network.In this paper,the price-based power allocation for femtocells underlaying a macrocell heterogeneous cellular network is investigated.By ex-ploiting interference pricing mechanism,we formulate the interference management problem as a Stackelberg game and make a joint utility optimization of macrocells and femtocells.Specially,the energy consumption of macrocell users and the transmission rate utility of femtocell users are considered in this utility optimization problem.In the game model,the macrocell base station is regarded as a leader,which coordinates the interference from femtocell users to the macrocell users by pricing the inter-ference.On the other hand,the femtocell base stations are modelled as followers.The femtocell users obtain their power allocation by pricing.After proving the existence of the Stackelberg equilibrium,the non-uniform and uniform pricing schemes are proposed, and distributed interference pricing algorithm is proposed to address uniform interference price problem. Simulation results demonstrate that the proposed schemes are effective on interference management and power allocation.

基于智能SDN面向5G的异构蜂窝网络架构

首次提出了智能SDN(软件定义网络)的概念和架构,解决了以往SDN系统缺乏智能化的问题。通过与蜂窝网的结合,提出了基于智能SDN面向5G的异构蜂窝网络总体架构,实现对无线接入网和有线核心网的统一管理。基于智能SDN的管理和协调,在无线接入部分提出控制和数据分离、上行和下行分离、无线资源动态适配等技术,提高频谱效率和能量效率;在核心网部分实现高效的内容分发以及快速的网络安全防护策略,增加数据吞吐率以及网络可扩展性。同时,通过无线接入网和核心网之间的资源共享和联合优化,提供网络功能虚拟化和个性化业务定制,实现智能SDN系统与异构蜂窝网络的深度融合。

基于微基站功率分配的异构蜂窝网络能效优化

针对异构蜂窝网络中微基站密集部署带来能耗不断攀升的问题,对二层异构蜂窝网络能量效率进行了分析,提出一种通过调整微基站发射功率来最大化网络能量效率的方法。首先,利用齐次泊松点过程对异构蜂窝网络进行建模,推导出各层基站的覆盖率;其次,根据能量效率定义,分别推导出网络总功耗和总吞吐量,并给出能量效率的闭式表达式;最后,分析了微基站发射功率对网络能量效率的影响,提出一种能够最大化能量效率的微基站功率优化算法。仿真结果表明,微基站的发射功率对异构蜂窝网络能量效率有显著影响,通过优化微基站发射功率能有效提升异构蜂窝网络能量效率。

基于干扰消除的异构蜂窝网络中断分析

在异构网络中,小小区可以为宏基站用户提供接入服务,并能够根据自身条件调节传输参数。该文研究在宏基站端干扰消除技术,来消除宏基站到小小区用户的干扰。该文分析了采用此种方案后异构网络下行链路的整体性能,推导了宏基站和小小区用户接收端信噪比的概率密度函数和分布函数。在此基础上,得到了系统整体中断概率的闭合表达式。理论推导和仿真结果表明,干扰消除方案能够有效提升异构蜂窝网络的整体性能。