TDD场景下小基站蜂窝网络上下行交叉干扰建模及性能分析

针对小基站网络立体分布特性,提出了一种TDD制式下小基站蜂窝网络三维随机几何模型并进行了性能分析。首先,本文根据3-D PPP模型下小基站的空间分布特性推导了TDD制式下小基站网络上下行覆盖概率的数学表达式。接下来,基于覆盖概率的表达式和网络频谱效率的定义,分别推导了上下行交叉干扰场景下,小基站网络上下行频谱效率的一般表达式。仿真结果在验证了本文模型的合理性的同时还说明,随着下行小区占比和功率控制因子的增大,网络的频谱效率都呈下降趋势。除此之外,室内环境也会对网络的覆盖性能产生影响。      

复合衰落信道下分布式MIMO系统中断概率及信道容量分析

针对分布式MIMO系统中断概率和信道容量这2大性能指标,在复合衰落信道模型下,当上行链路采用最大比发送—选择合并,下行链路采用选择发送—最大比合并时,利用Lognormal分布对复杂Gamma-Lognormal分布的近似,推导得到当移动台位置给定时,系统中断概率和信道容量的闭合表达式,证明了系统性能指标与移动台分布之间存在密切的联系;随后依照实际通信环境,提出一种考虑存在小区热点的移动台非均匀分布模型,然后推导得到考虑该分布模型后的系统平均中断概率和平均信道容量闭合表达式;最后通过计算机仿真,证明了所提近似处理的精确性以及各项理论分析的合理性。     

分布式天线系统中的系统上行中断概率分析

中断概率是无线通信系统的一个重要指标。该文针对分布式天线系统中的系统中断概率问题进行了研究。首先,建立了包含路径损耗、阴影衰落和瑞利衰落的复合信道模型;然后,在该信道模型下推导出给定移动台位置时的信噪比;接着,基于选择合并策略,分析出给定移动台位置时系统上行传输的中断概率表达式;最后,考虑到小区内移动台任意分布特点,文章给出系统上行中断概率闭合理论表达式。仿真结果表明,所提的系统上行中断概率理论表达式与仿真结果十分吻合。     

联合传输机制下的三维超密集网络性能分析

超密集网络（Ultra-dense Networks,UDN）作为一项新兴技术，通过密集部署微基站大幅提升了网络容量，近年来受到了广泛关注。但随着二维平面基站数量逐渐饱和，基站部署逐渐向三维（3D）立体化发展。因此，针对中央商务区（Central Business District,CBD）等未来移动通信典型应用场景，基于随机几何理论对写字楼中基站与用户的分布进行建模与分析。该场景下，考虑到实际部署情况，用户只会接收到其上方基站的信号，而忽略低楼层基站的影响。针对这一特点，基于联合传输（Joint Transmission,JT）方案的覆盖性能，推导出用户的覆盖率和遍历容量解析表达式。结果表明，覆盖率和遍历容量都随协作簇的变大而增加，收益呈递减状态。     

双向多中继协同通信系统的性能分析

针对频率非选择性瑞利衰落信道,研究了双向多中继协同通信模型的系统性能。首先,基于模型的信号传输过程分析了系统的信道容量;然后,根据接收信噪比的累积分布函数推导了系统中断概率的闭合上界表达式;进一步在MPSK调制方式下,通过计算在高信噪比条件下的矩母函数,推导了平均误码率的闭合表达式。仿真结果验证了理论推导的正确性,并且表明双向多中继模型的中断概率和平均误码率两项性能指标都优于双向单中继模型。     

3G LTE空间信道模型的三维修正及容量分析

空间信道模型SCM(Spatial Channel Model)是3GPP用于LTE系统仿真的MIMO二维信道模型。本文在SCM模型的基础上,综合考虑基站端和移动台端电波的离开角和到达角的三维特性,给出了三维MIMO信道模型的信道参数描述,提升了信道建模的准确度,并推导出该信道模型下包含极化特性的MIMO信道系数表达式。同时探究了天线间距、水平角扩展、俯仰角扩展等对MIMO信道空时相关性的影响。研究结果显示,随着俯仰角扩展从0°到60°增大,散射环境越来越强,信号在空间的色散度越高,不同天线单元接收到的信号之间的相关性越小,信道容量将会越大。     

超密集分簇网络中基于马尔可夫模型的移动性能建模与分析

第五代移动通信(5G)系统中,大规模MIMO天线和超密集部署网络是实现高吞吐量的两种主要方法。在超密集部署网络中,将小蜂窝的基站按照地域位置和信号强度等条件进行分簇,簇内所有的小蜂窝共用同一控制平面,实现了业务和控制的分离。基于此场景,提出了基于马尔可夫模型对移动终端在超密集分簇网络下的移动状态进行建模,推导出系统吞吐量、阻塞概率等系统性能的闭式表达式。仿真结果表明超密集分簇网络可以有效地减少移动终端不必要的切换次数,并提高系统吞吐量。     

IRS辅助的星地融合认知网络中断性能分析

分析了智能反射面（IRS）辅助的星地融合认知网络系统的中断性能。首先,针对卫星采用点波束技术服务地球站,而基站通过智能反射面扩大通信范围,并采用非正交多址接入（NOMA）技术服务多用户场景,在系统采用认知无线电技术来实现卫星主网络与地面次级网络之间频谱共享的情况下,建立以地面用户平均信干噪比最大化为目标的优化问题;其次,基于角度域的信道状态信息提出了一种低复杂度的IRS相移设计方案,从而得到智能反射面相移矩阵;接着,分别推导出地面用户在固定和移动2种情况下的中断概率闭合表达式。为了进一步分析系统性能,推导了高信噪比条件下系统的中断概率近似表达式。最后,计算机仿真验证了中断概率表达式的正确性,并分析了主要参数对系统性能的影响。     

自适应RBF神经网络在CDMA移动通信上行链路功率控制中的应用研究

提出了一种自适应RBF神经网络功率控制方案。详细研究了该网络在DS-CDMA通信中，进行上行链路闭环功率控制(基于信扰比(SIR))的应用理论，给出了该网络参数的计算方法。最后用计算机仿真法模拟出该控制器的运行性能。结果表明基于SIR的自适应RBF神经网络功率控制器能自适应地调整移动台的发射功率，使基站接收信号的信扰比始终非常接近于一个常数，且有比定步长功率控制更小的SIR跟踪误差，从而可以降低接收信号的中断概率、提高信道容量。     

多层高度的无人机-地面异构网络的覆盖性能

针对分布在不同高度的多层无人机-地面异构网络,采用泊松点过程对网络中的无人机基站与地面蜂窝基站的空间位置进行了建模,基于视距传输概率与最大平均接收信号强度关联机制推导了关联概率、条件覆盖概率与总体覆盖概率的理论表达式,并对不同高度分布下多层无人机-地面异构网络的总体覆盖概率进行了仿真验证与分析.仿真结果验证了推导的理论...     

Analysis of the decoupled uplink downlink technique for varying path loss exponent in multi-tier HetNet

In this paper, the impact of varying path loss exponent (PLE) on user association probability, decoupled uplink coverage probability as well as decoupled uplink average spectral efficiency in downlink uplink decoupled (DUDe) multi-tier heterogeneous networks, is investigated. We investigate the effect of the difference in path loss exponents in both macro and small cell environments over uplink network performance. It is assumed that the mobile user connected to the macro base station experience different path loss exponent as compared to when connected to small base station. It is observed that the difference of path loss exponents in both cases has significant effect on the user association probability, decoupled uplink coverage probability as well as decoupled uplink average spectral efficiency. Moreover, in order to further support key findings and make sound comparison between coupled and DUDe performance in varying PLE environment, generalized analytical expressions for coupled association probabilities, along with coupled uplink coverage probability and coupled uplink average spectral efficiency have been derived. The analytical results evaluated in this paper are compared with the computer simulation and found in good agreement. Our analysis shows that decoupling technique performs suboptimal for cases where the environments around macro and small base stations are different with respect to each other. The work explained in this paper highlights the limitation of applying DUDe technique in realistic conditions where the PLEs of cellular tiers are not exactly equal to one another.

     

SBT (Sense Before Transmit) Based LTE Licenced Assisted Access for 5 GHz Unlicensed Spectrum

Utilization of unlicensed spectrum under licensed assisted access ensuring fair co-existence with Wi-Fi networks is a good solution to address immense usage of mobile data. Radio communication operation of LTE in unlicensed frequency band is referred as LTE-unlicensed (LTE-U) or LTE-licensed assisted access. In this paper, we consider a HGNW in which coverage area of Wireless-Fidelity (Wi-Fi)’s Access Point is integrated within the LTE-U small base station’s cellular network coverage area. To overcome the disadvantages of existing LTE-U technics like carrier sense adaptive transmission and listen before talk, we proposed a new methodology i.e., sense before transmit in this paper by adopting a transmit power control mechanisms using reciprocity theorem based on the channel state information to assign the secondary carriers in the uplink as well as in the downlink directions in the unlicensed spectrum to carry the traffic. In our proposal, LTE-U users are allowed to use the unlicensed spectrum provided that the interference produced at Wi-Fi users due to LTE-U activities is remained below a certain threshold. We evaluated the performance of proposed network model in terms of outage probability and achievable throughputs.

     

Coverage and Energy Modeling of HetNet Under Base Station On‐Off Model

Small cell networks, as an important evolution path for next‐generation cellular networks, have drawn much attention. Different from the traditional base stations (BSs) always‐on model, we proposed a BSs on‐off model, where a new, simple expression for the probabilities of active BSs in a heterogeneous network is derived. This model is more suitable for application in practical networks. Based on this, we develop an analytical framework for the performance evaluation of small cell networks, adopting stochastic geometry theory. We derive the system coverage probability; average energy efficiency (AEE) and average uplink power consumption (AUPC) for different association strategies; maximum biased received power (MaBRP); and minimum association distance (MiAD). It is analytically shown that MaBRP is beneficial for coverage but will have some loss in energy saving. On the contrary, MiAD is not advocated from the point of coverage but is more energy efficient. The simulation results show that the use of range expansion in MaBRP helps to save energy but that this is not so in MiAD. Furthermore, we can achieve an optimal AEE by establishing an appropriate density of small cells.     

Relay Placement for Coverage Extension in Cellular Wireless Networks Under Composite Fading Model

In relay-assisted cellular networks, mobile stations are connected to base station through two or more single-hop communication links, where the intermediate nodes act as relay stations (RSs). The focus of this paper is on two-hop relay assisted cellular networks, where optimal relay placement is a crucial issue for achieving maximum extension of the cell coverage. However, the location of RS has significant impact on signal-to-interference plus noise ratio (i.e., SINR) and outage probability experienced on the access and backhaul links. Moreover, the frequency re-use factor also has significant influence on the SINR. In this paper, we develop analytical models for computing the SINR and outage probability performance of a two-hop relay assisted cellular network for both downlink (DL) as well as uplink (UL) transmission scenarios, considering the impact of path loss, shadowing, Nakagami fading and co-channel interference. We then investigate optimal placement of RS while satisfying the required criterion on probability of correct decoding, initially by considering the DL scenario alone and then by considering both DL and UL scenarios jointly. Through extensive evaluations, we report the impact of realistic propagation models on outage probability, optimal relay position and the cell coverage radius. Further, the model can be used to find the impact of co-channel re-use factor on optimal relay positioning in two-hop cellular networks.     

Outage probability in Poisson‐cluster‐based LTE two‐tier femtocell networks

This paper analyzes two‐tier orthogonal frequency‐division multiplexing (OFDM)‐based cellular structure, when the traditional macrocell structure is extended with femtocells. The benefit of using femtocells is the capacity and coverage extension capability. To fulfill strict quality of service requirements in next‐generation mobile networks such as Long Term Evolution (LTE) or LTE‐Advanced, capacity and coverage enhancing becomes rather important. On the other hand, adding small cells such as femtocells next to macrocell modifies the interference pattern of the current region. Therefore, the number of small cells in a given area should be limited. In this paper, we provide an analytic framework to calculate the outage probability for a macrocell user in OFDM‐based femtocell networks when the deployed femto base stations are composing an independent Poisson cluster process such as Thomas cluster process. Cluster‐based femtocell modeling offers accurate network planning for mobile operators. In this cluster‐based realization, we give an interference characterization and consider the outage probability for a randomly deployed user when communication channel is infected with Rayleigh fading. Copyright © 2014 John Wiley & Sons, Ltd.     

采用部分频率复用的小小区网络建模与分析

小小区组网技术被认为是解决迅速增长的移动数据量需求的方法。然而,密集的小小区组网会导致严重的小区间干扰。传统的部分频率复用方法不能完全照搬用在部署不规则的小小区网络内,急需一种合理高效建模采用频率复用小小区网络的方法,对其性能进行评估。利用随机几何理论对小小区网络考虑部分频率复用场景进行建模,推导了考虑部分频率复用的小小区网络下行覆盖概率和网络吞吐量的表达式。数值仿真结果显示：部分频率复用技术可以提高小小区网络下行覆盖概率,但是会降低网络图吞吐量。在满足覆盖概率约束条件下,得到了使得网络吞吐量最大的频率复用因子的表达式。以上结果对未来采用频率复用技术的小小区组网的具体实施具有重要的指导意义。     

A Simple 3-D Geometric Channel Model for Macrocell Mobile Communications

One of the fundamental research areas in wireless communications is the development of realistic models that can efficiently and accurately describe the wireless propagation channel. Most of the proposed models disregard the three dimensional character of the signal spread or use techniques with excessive computational complexity. In this paper, we develop a simple 3-D geometric scattering model for the uplink of a macrocell mobile environment that provides the statistics of Angle-of-Arrival (AoA) of the multipath components. The model extends the 2-D geometrical-based single bounce macrocell (GBSBM) model. Explicit closed-form expressions are derived for the statistics of the AoA of the multipaths in the azimuth and elevation planes. Analysis of the results exhibits the advantages of our proposal compared to 2-D and 3-D ones published in the literature. Comparisons with experimental data confirm its validity. Interesting conclusions for the effective evaluation of mobile communication systems have been derived. Moreover, an application of the model to mobile location estimation has been developed and evaluated.     

NR覆盖增强方案及标准化进展

为提升5GNR网络的覆盖性能,研究并讨论覆盖瓶颈信道的相关覆盖增强方案,包括物理上行共享信道的重复传输增强、多时隙传输块处理、联合信道估计方案,物理上行控制信道的动态重复传输指示、解调参考信号绑定方案,以及随机接入中的Msg3信道的重复传输方案.基于上述增强方案,聚焦3GPP Release 17 NR覆盖增强的标准化...     

Performance of mobile networks with wireless channel unreliability and resource insufficiency

New closed-form formulas for the call complete probability and the probability density function (pdf) of the completed call holding time (CCHT) are developed under the concurrent impacts of the resource insufficiency as well as the wireless link unreliability in the wireless mobile networks performance evaluation. The results are obtained with the general scenario, i.e. general call holding time, general cell residence time and the generalized wireless channel model. The analysis result is validated by the simulation model under typical call holding time and cell residence time distributions, Gilbert-Elliott or Fritchman wireless channel model. The comparison indicates that the wireless networks performance will be greatly overestimated without taking into account the unreliable wireless link effect.