Inter-cell Interference Modeling in LTE Systems

Traditionally, inter-cell interference in wireless cellular systems has been modeled as a zero-mean random variable with variance equal to the average power of the interference. While this model is appropriate for code division multiple access-type systems, in orthogonal frequency division multiple access-based systems, such as long term evolution (LTE), it does not hold anymore. This paper considers the problem of interference modeling for the downlink of LTE systems. It is shown, through analytical and numerical studies, that the interference can be deemed as a gaussian random variate with random variance (i.e., the variance depends on the strength of the interference itself), thus implying that it is actually a non-gaussian random variate.     

3GPP LTE小区间干扰协调方案研究

随着3G移动通信系统逐步成熟,3GPP已经开始了对其长期演进(LTE)系统的研究和标准化工作。由于使用了新的物理层技术,使得小区间干扰抑制成为一个热点问题。针对该问题,介绍了目前小区间干扰协调/躲避研究方面的现状,对几种具有代表性的方案进行了研究,最后对各方案进行了系统级计算机仿真分析。     

抑制LTE系统小区间干扰的软频率复用改进方案

为提高系统性能,LTE系统可通过频率复用因子（Frequency Reuse Factor,FRF）为 3的软频率复用（Soft Frequency Reuse,SFR）方案来有效抑制小区间的同频干扰,但在小 区峰值速率和系统容量方面仍有改善空间,由此介绍一种FRF为7的SFR方案,并结合与之相 适应的资源调度策略,可较大地提高小区边缘用户的峰值速率,使系统容量得以提升。     

OFDM系统的小区间干扰抑制技术研究

本文着重针对小区干扰消除技术对系统设计的要求进行了分析,提出了一种基于编码块分割的预定义频率资源块分配方法,以支持对多种带宽业务的小区间干扰消除.另外还提出了一种将小区间干扰协调和干扰消除合并使用的混合方法,可以在适应各种带宽业务的同时,实现系统频谱效率的最大化.     

LTE/LTE-Advanced异构网干扰消除技术研究

异构网是解决实际网络部署中覆盖和容量的有效途径,本文重点介绍3GPP中异构网小区间干扰消除技术的研究。     

LTE-A增强型小区间干扰协调技术标准化研究

异构网络通过改变网络拓扑结构达到更高频谱利用率、更大系统吞吐量,并能改善边缘用户性能,成为LTE-Advanced关注的主要技术之一。本文主要介绍了无线异构网络中的节点,对造成小区间干扰问题的成因做了重点阐述,并针对3GPP标准化组织关于LTE-A系统增强型小区间干扰协调方案的标准化进度做了总结。     

基于高斯混合模型的下行小区间干扰分布

在正交频分多址接入(Orthogonal Frequency Division Multiple Access, OFDMA)蜂窝网络中,小区间干扰的统计特性与网络性能密切相关。下行小区间干扰的累积分布函数(Cumulative Distribution Function, CDF)还没有一个闭合表达式。该文提出一种参数可显式计算的高斯混合模型对下行小区间干扰分布进行近似。进一步,利用高斯混合模型将下行小区间干扰的累积分布函数近似表示为若干个误差函数的加权和。仿真验证了高斯混合模型的准确性,并且表明基于高斯混合模型的累积分布函数能很好地近似下行小区间干扰的累积分布函数。     

Loading Schemes for Downlink OFDMA Systems

In this paper we study the subcarrier and bit allocation strategies for downlink OFDMA system.Our opti-mization objective is to find optimum subcarrier and bit assignment minimizing the total transmitted power with the con-straints on BER and data rate for all users.We divide this problem into three steps:resource allocation,subcarrier assign-ment and single-user power and bit allocation.For the first two steps we propose new algorithms.Various loading schemesconstitute by combining these algorithms as well as algorithms proposed in Ref.[6].Simulation results demonstrate thatour proposed suboptimal loading scheme can achieve performance closer to the near optimal algorithm in Ref.[8]withmuch lower complexity than schemes in Ref.[6].     

LTE小区间干扰控制技术研究及进程

干扰问题对系统的性能有着直接而且重要的影响,因此成为每个系统都要考虑的重要问题。随着OFDMA与SC-FDMA技术在LTE系统中的应用,主要干扰源体现为小区间干扰。文章结合3GPP相关提案,按照时间顺序介绍了LTE小区间干扰控制技术进程,并对相关典型提案进行了研究和总结。     

蜂窝系统上行小区间干扰链路统计分析

在同频复用网络中,小区间干扰已成为限制系统性能提升的关键因素之一。该文对单个干扰小区产生的上行小区间干扰链路进行统计建模,通过分析路损的矩生成函数和累积量生成函数,得出了干扰链路路损分布函数的近似表达式。进一步地,根据得出的统计模型分析系统参数设置对干扰路损分布的影响。研究发现,阴影衰落的标准差越大,上行干扰路损分布越接近高斯分布。另外,传播模型参数中的衰减指数也对路损分布有较大的影响。     

基于软频率复用规划的LTE小区间干扰抑制

主要分析了LTE系统的小区间干扰（ICI）协调技术和ICI消除技术。针对传统软频率复用规划的不足提出了改进方案,并且通过迭代ICI消除技术,达到更好的干扰抑制效果。     

LTE-Advanced系统部署Pico后的小区间干扰协调技术

Pico在LTE-Advanced系统设计中受到了广泛的关注。本文首先对Pico的部署场景及其产生的干扰进行了详细的分析。然后,针对上述干扰情况提出了几种可行的干扰解决方案并重点介绍了三种增强型小区间干扰协调技术。最后,通过系统级仿真来评估这三种增强型小区间干扰协调技术在系统性能方面的影响并给出了使用建议。     

LTE小区间干扰抑制技术分析

LTE系统采用更灵活的频率复用策略,任何一个小区都有可能使用所有的频谱资源,因此小区间的干扰不可避免。本文从干扰协调和干扰消除两方面介绍了LTE小区间干扰抑制的最新研究成果,对学术界及3GPP标准提案中的主流算法进行了综合评述。最后,结合LTE标准的演进,分析了LTE系统小区间干扰抑制技术的发展趋势。     

基于HII的LTE上行干扰协调研究

为了改善传统软频率复用方案在面对小区边缘业务激增时会导致系统吞吐量的下降,提出了一种基于高干扰指示的LTE上行软频率复用方案。首先根据服务基站与最强干扰临小区的RSRP差值将用户分为边缘用户和中心用户,然后利用传统软频率复用方案给用户分配资源。当存在小区边缘用户未分配资源时,再根据从X2接口传来的高干扰指示信息来‘借用’干扰不敏感的邻小区边缘带宽资源去分配给这些用户。通过系统级仿真结果表明,与传统软频率复用方案相比,该方案在面对小区边缘业务量激增时,有效改善了小区边缘吞吐量和系统吞吐量。     

Interference Cancellation with Space Diversity for Downlink MC-CDMA Systems

Modern wireless communications require an efficient spectrum usage and high channel capacity and throughput. Multiple-input and multiple-output (MIMO), Linear equalizers, multi-user detection and multicarrier code-division multiple access (MC-CDMA) are possible solutions to achieve spectral efficiency, high channel capacity, eliminate multiple access interference (MAI), eliminate Inter symbol interference (ISI) and robustness against frequency selective fading. In this paper, we combine all these techniques and investigate BER performance. We propose a low complexity receiver structure for Single-input Multiple-output (SIMO) downlink MC-CDMA systems. It employs an interference cancellation scheme to suppress the interference caused by the multipath fading channel. Also, the proposed scheme is developed for MIMO MC-CDMA system. The performance analysis of Downlink MIMO MC-CDMA systems with V-BLAST over frequency selective fading channel is investigated under various number of transmit and receive antennas. The simulation results show proposed SIMO equalization with parallel interference cancellation scheme is effective in reducing the ISI and the MAI. It improves the performance significantly and the simulation results show that MIMO MC-CDMA with V-BLAST multi-user detection provides high data rate and the BER significant improvement.     

TDD大规模MIMO系统中两种新的下行预编码方案

针对时分双工大规模MIMO系统,该文提出两种新的下行链路预编码方案,即新最大比合并(NMRC)和新迫零(NZF)方案,通过理论分析得到两种新预编码方案下目标用户和非目标用户的下行链路信干噪比和频谱效率的表达式,并与传统的迫零(ZF)和最大比合并(MRC)预编码的下行链路信干噪比、频谱效率和误码率性能进行比较.仿真结果表明,所提出的NMRC和NZF预编码与传统的MRC和ZF预编码相比,在不增加运算复杂度的前提下可以获得更好的性能,而且新的预编码方案在提高目标用户性能的同时,对其他非目标用户的性能也有一定的改善.     

一种基于预编码的异构网下行干扰协调方法

在通用移动通信系统（Universal Mobile Telecommunications System,UMTS）异构网络中,理论分析了宏基站对微微（Pico）小区边缘用户的下行干扰问题。在传统空白帧（ABS）方法的基础上,提出了一种干扰避免策略,其主要思想是通过联合时域ABS策略和空域基于码本限制的策略提高传统ABS策略的系统性能,即在ABS子帧上,宏基站并不是完全不发送数据,而是采用码本受限的预编码进行传输。限制的码本可以根据宏小区自身的负载动态进行更改,并通过广播传递给低功率节点（Low Power Node,LPN）,LPN根据得到的信息进行边缘用户的调度。仿真结果表明,提出的方法在最差5%用户吞吐率比ABS方法略有下降的情况下,使用户平均吞吐量得到了提升。     

TDD大规模MIMO系统中两种新的下行预编码方案

针对时分双工大规模MIMO系统,该文提出两种新的下行链路预编码方案,即新最大比合并(NMRC)和新迫零(NZF)方案,通过理论分析得到两种新预编码方案下目标用户和非目标用户的下行链路信干噪比和频谱效率的表达式,并与传统的迫零(ZF)和最大比合并(MRC)预编码的下行链路信干噪比、频谱效率和误码率性能进行比较。仿真结果表明,所提出的NMRC和NZF预编码与传统的MRC和ZF预编码相比,在不增加运算复杂度的前提下可以获得更好的性能,而且新的预编码方案在提高目标用户性能的同时,对其他非目标用户的性能也有一定的改善。     

Mobility-Aware Admission Control Schemes in the Downlink of Third-Generation Wireless Systems

In this paper, novel connection admission control (CAC) algorithms that take into account the effect of mobility of users both inside and outside the cell in the downlink of third-generation mobile systems are developed. First, the system capacity, including the other-cell interference, subject to feedback between cells is studied. Then, effective bandwidth expressions for calls are obtained as a function of both their location in the cell as well as their class of traffic (i.e., voice versus data). Next, this formulation is used to derive two mobility-aware admission control algorithms, i.e., a priority CAC, where calls are accepted not only upon resource availability, but also through acceptance ratios that reflect their levels of priority, and a squeezing CAC, where elastic calls may be squeezed to a minimum agreed value, giving way to admit more calls in the system and to secure further ongoing mobile users. Using Markovian analysis, several performance measures are obtained, namely the blocking probability, the dropping probability, both intracell and intercell, as well as the overall cell throughput. The authors eventually investigate the performance of our CAC and show how to extend the Erlang capacity bounds, i.e., the set of arrival rates such that the corresponding blocking/dropping probabilities are kept below predetermined thresholds     

LTE系统上行小区间干扰协调技术研究

为了进一步提升LTE上行系统中小区边缘用户的吞吐量,文章对现有的软频率复用方案予以改进,提出了一种同时基于优先级的频率协调和基于用户位置的功率调整的小区间干扰协调方案,并通过系统级仿真对该方案在LTE上行系统中的性能进行了评估。仿真结果表明,此方案可以在尽量避免对扇区平均性能和小区中心用户性能造成负面影响的前提下,大幅提升小区边缘用户性能。