阵列处理器中改进几乎空白子帧算法的并行化实现

两层异构网络中出现的小区间干扰协调是当前异构网络干扰问题研究的热点。针对软件实现增强小区调度几乎空白子帧(ABS)的干扰方案存在处理数据量大、速度慢的缺点,基于可重构阵列结构提出了一种动态ABS干扰协调的并行化硬件实现方案。该算法在增强小区内根据用户数动态分配ABS比例,以改善小区边缘用户的信道容量,通过流水线的方式使用多个轻核处理元(PE)实现并行计算以提高运算效率。测试结果表明,使用12个PE同时调度实现算法的映射,运行1983个周期,其性能比单个PE提升77.03%,该算法的并行计算能力得到显著提升,宏基站用户的吞吐量可以达到4.76 Mbit/s.     

一种基于过渡区的小区间干扰协调方法

文章提出了一种基于过渡区的小区间干扰协调方法,通过小区的网络规划、时频资源划分和上行链路发射功率规划三个部分,详细阐述了该方案的实现。该方案能有效提高整个网络的平均用户吞吐量和小区边缘用户的吞吐量。     

LTE-A系统时域小区间干扰协诟技术标准化研究

异构网络被LTE-A系统视为一种提升单位区域频谱效率的关键技术而得到广泛关注。然而,异构网络会带来严重的小区间干扰,小区间干扰协调因此成为3GPP标准化进程研究的重点。首先总结了异构网络及小区间干扰协调技术,然后介绍了目前3GPP中讨论的小区覆盖扩展（CRE：CellRange Extension）和基于几乎空白子帧（ABS：Almost Blank Subframe）的时域小区间干扰协调技术。最后,基于动态系统级仿真平台,评估了CRE和ABS技术方案系统性能。     

一种抑制小区间干扰的比例公平调度算法

针对LTE-Advanced系统中小区间干扰及用户公平性问题,提出了基于多小区联合预编码和静态功率控制的比例公平(MCPPC-PF)调度算法。通过干扰空间迫零和静态控制发射功率的方法抑制小区间干扰,并结合比例公平(PF)调度算法,提高用户的公平性。仿真结果表明,与传统算法相比,MCPPC-PF算法提升系统容量的同时还提高了用户的公平性;与基于多小区联合预编码和静态功率控制的最大化吞吐量调度算法相比,MCPPC-PF算法在系统容量损失了4.6%的情况下,边缘用户容量提高了约45%。     

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。     

基于功率控制的LTE系统下行ICIC算法研究

在LTE系统中,小区的边缘用户会同时受到邻区同频用户的干扰,需要一种小区间的干扰协调技术（ICIC）来解决这个问题。分析传统ICIC算法的不足,提出一种优化的算法,通过计算边缘用户在单个干扰用户和多个干扰用户情况下的容量,得出邻区基站较为精确的发射功率控制量。参考3GPP标准案例仿真模型,对该算法进行了仿真,仿真结果表明与传统ICIC算法的相比,该算法可以明显提高边缘用户的吞吐量。     

TD-LTE系统干扰分析与交叉时隙干扰协调算法及仿真

LTE系统子载波之间完善的正交性使小区内干扰几乎可以忽略,而小区间干扰则是系统干扰的最重要的来源[1]。小区间干扰中由于不同小区帧结构不一致而形成的交叉时隙干扰对系统的影响十分严重。针对上下行同时服务的TDD系统,文章设计了一种基于无线资源管理的交叉时隙干扰协调技术,用于降低小区间干扰。无线资源管理广泛的被研究用于降低干扰、增加小区边缘用户性能和提高小区覆盖。通过文中的算法分析研究与仿真,有效降低TD-LTE系统干扰,改善了系统性能。     

基于Q学习异构网络干扰协调算法

在LTE-A中采用异构网络能提高用户的性能,但是由于小区间使用相同的频谱资源,产生了小区间干扰,影响了用户性能,从而需要采用小区间干扰协调技术来控制小区间干扰(ICI)。虽然现有的小区间干扰协调技术可以降低小区间干扰,但是存在Macro用户性能影响较大的问题。为此,提出了基于Q学习的ETPS算法,在不影响Macro用户性能的前提下,降低小区间干扰。仿真结果表明,QL-ETPS算法较传统固定ABS/RP-ABS子帧配置方案性能更优,可以在尽量不影响Macro基站用户的前提下,提高Pico基站边缘用户的吞吐量。     

5G超密集组网的必然性和挑战性分析

针对5G用户体验速率和海量设备连接需求,给出提升5G网络容量的三种方法。分析超密集组网在网络建设、成本、信号质量、网络容量上的优势,论证超密集组网是5G的必然选择。然后解析超密集组网遇到的干扰挑战,最后从三个维度给出应对挑战的措施:通过自组织网络最佳化覆盖与容量、利用CRE(小区覆盖扩展)和ABS(几乎空白子帧)技术协调宏微小区间干扰、利用网络多输入多输出技术协调管理小小区基站。     

LTE-A系统异构网络时域小区间干扰协调技术标准化研究

微微蜂窝（Picocell）是一种有效提高特定区域吞吐量和单位区域频谱效率的新兴技术。然而,宏蜂窝与Picocell重叠覆盖的特点使系统干扰结构更加复杂,因此在实际部署中,需要采用有效的小区间干扰协调技术以降低干扰。文章重点介绍了小区覆盖扩展（CRE）技术、以及基于几乎空白子帧（ABS）和目前3GPP重点关注的 reduced power ABS时域小区间干扰协调技术方案。     

Distributed optimization of enhanced intercell interference coordination and resource allocation in heterogeneous networks

In two‐tier heterogeneous networks (HetNets), the cross‐tier interference caused by spectrum sharing between macrocell and small cells poses obstacle to ideal overall network performance. Both enhanced intercell interference coordination (eICIC) at the macrocell base station (MBS) and resource allocation (RA) at small cell base station (SBS) have been considered as efficient approaches to mitigate the cross‐tier interference. In this paper, we propose a distributed optimization framework to jointly optimize the eICIC and RA schemes at different tiers. In specific, an enhanced almost blank subframe (ABS) scheme is performed by the MBS to encourage SBSs to adopt hybrid access policy and admit the offloaded macrocell users (MUs) so as to guarantee their QoS requirements. To model the intricate interaction between two tiers, we formulate the joint optimization problem as a one‐leader multiple‐follower Stackelberg game. We prove the existence of Stackelberg equilibrium (SE) and obtain the optimal strategies for both tiers. Numerical results are presented to show that the proposed framework with hybrid access policy converges to a unique SE and utilities for both tiers is maximized, which creates a win‐win situation.     

Pricing framework for almost blank subframe scheme in two‐tier heterogeneous networks

As a part of enhanced inter‐cell interference coordination (eICIC), almost blank subframe (ABS) is an efficient technique to mitigate the cross‐tier interference of two‐tier heterogeneous networks (HetNets) and enhance overall network performance. However, in small cells with closed subscriber group (CSG) mode, how to motivate small cell base stations (SBSs) to adopt ABS schemes is still one of technical challenges due to the selfish nature of SBSs. In this paper, we propose a pricing framework with ABS scheme that benefit both the macrocell and small cell tier. Within the proposed framework, each SBS with closed access policy performs ABS scheme by muting a portion of the whole frame in time domain, and then dedicating this interference‐free subframe to macrocell users (MUs) for exclusive use. In return, the macrocell base station (MBS) announces the price for these ABSs and offers a certain amount of revenue to each SBS according to the length of its ABS. Furthermore, we extend the small cell performance analysis to the scenario of hybrid access policy, which allow neighboring MUs to access small cells. To investigate the interaction between two tiers, we formulate the proposed framework as a one‐leader multiple‐follower Stackelberg game, which regards the MBS and SBSs as leader and followers, respectively. On the basis of the theoretical analysis, we prove that a unique Stackelberg equilibrium (SE) exists and obtain the optimal strategies for both tiers. Numerical results evaluate the utility performance of both tiers when SE is achieved and verify the validity of the proposed framework.     

异构网络跨层协作传输技术研究

提出了一种分层协作框架,在此框架下采用结合协作预编码的跨层协作传输技术以解决异构网络严重的层间干扰,特别是小区范围扩展区域的干扰问题。所提出的协作传输策略基于OFDMA下行传输系统并支持宏基站和低功率基站在资源块级别的协作传输。仿真结果表明在使用小区范围扩展的异构网络中,基于分层协作框架的协作传输技术在系统吞吐量性能方面优于现有eICIC技术。     

Feedback‐based multi‐layered STBC system for MIMO multi‐cellular networks with cochannel interference

A feedback‐based multi‐layered STBC (MLSTBC) system, which is adapted to cochannel interference, is proposed. This system can adjust its transmitter configuration so that the largest throughput for the given SINR is obtained, also, it can use joint beamforming and power control to minimize cochannel interference so that the throughput requirement is satisfied. We propose an iterative algorithm to realize joint beamforming and power control for the feedback‐based MLSTBC system, and in this algorithm, we derive the required SINR and the corresponding transmitter configuration for attaining the throughput requirement. Some properties and simulation results are presented, they show that the proposed algorithm helps the feedback‐based MLSTBC system increase the probability of the success in meeting the throughput requirement, also they show that the feedback‐based MLSTBC system results in larger throughput than MLSTBC (with fixed transmitter configuration), STBC, and V‐BLAST. Copyright © 2010 John Wiley & Sons, Ltd.     

Design and analysis of energy efficient inter-tier interference coordination in heterogeneous networks

Wireless Networks - Inter-tier interference coordination has been a vital design problem to ensure the edge-user service quality in heterogeneous networks. In this regard, the almost blank subframe...     

Spectrum‐efficiency enhancement in small cell networks with biasing cell association and eICIC: An analytical framework

Load balancing and interference management play crucial roles in small cell network (SCN) capacity and spectrum efficiency (SE) enhancement. By performing load balancing between macrocell and small cells, biasing cell association has attracted great attentions since it is proposed. Additionally, enhanced intercell interference coordination (eICIC) technology is also developed as an efficient interference mitigation method for the biasing cell association‐based SCNs. In this paper, we develop an SE enhancement framework with joint consideration of the eICIC factor and biasing factor. Using the stochastic geometry theory, the network is modeled by spatial Poisson point process. We firstly derive the downlink average rate, which is performed at a typical user. Secondly, the eICIC factor‐related network SE is analyzed by proving the existence of optimal eICIC factor, which maximizes the network SE. For the intractability of the closed‐form expression of optimal eICIC factor, a bisection search‐based algorithm is developed then. At last, numerical results confirm our analysis and show the proposed algorithm performance. Copyright © 2014 John Wiley & Sons, Ltd.     

Efficient coordination of almost blank subframes with coupling macro cells in heterogeneous networks

Heterogeneous networking is an inevitable trend in mobile communication systems, where macrocells and small cells coexist to provide the service of wireless access. The technique of enhanced inter‐cell interference coordination (eICIC) is popularly used to mitigate signal interference among cells. A number of subframes are picked as almost blank subframes (ABSs), during which a macro‐cell base station suspends data transmissions to improve signal quality of small cells that it covers. Since the throughput of macro cells drops to zero in an ABS, how to decide the number of ABSs (ie, the ABS ratio) and their positions (ie, the ABS placement) is critical. Many studies implicitly consider that every small cell resides in only one macro cell and they manage ABSs for each individual macro cell accordingly. In practice, some macro cells may cover the same small cells (called coupling macrocells) which makes the management of their ABSs depend on each other. To address this issue, the paper proposes an efficient coordination of ABS with coupling macro cells (ECO) algorithm. It divides the network into component subnetworks depending on whether macro cells are coupling or not. Then, ECO computes the ABS ratios for the macro cells in each component subnetwork based on multiple factors, including data rate, traffic demand, and quality of service (QoS) support. Moreover, ECO jointly places the ABSs of coupling macro cells to shorten packet latency. Experimental results show that the ECO algorithm not only increases the network throughput but also reduces the loss rate of real‐time data.     

Energy‐Efficient Power Allocation for Cognitive Radio Networks with Joint Overlay and Underlay Spectrum Access Mechanism

Traditional designs of cognitive radio (CR) focus on maximizing system throughput. In this paper, we study the joint overlay and underlay power allocation problem for orthogonal frequency‐division multiple access–based CR. Instead of maximizing system throughput, we aim to maximize system energy efficiency (EE), measured by a “bit per Joule” metric, while maintaining the minimal rate requirement of a given CR system, under the total power constraint of a secondary user and interference constraints of primary users. The formulated energy‐efficient power allocation (EEPA) problem is nonconvex; to make it solvable, we first transform the original problem into a convex optimization problem via fractional programming, and then the Lagrange dual decomposition method is used to solve the equivalent convex optimization problem. Finally, an optimal EEPA allocation scheme is proposed. Numerical results show that the proposed method can achieve better EE performance.     

TD-LTE与TD-SCDMA系统共存子帧配比兼容分析研究

对于当前TD-LTE与TD-SCDMA系统邻频共存的情况,由于两者皆为TDD系统,所以TD-LTE必须与TD-SCDMA系统的子帧配比兼容以避免系统间干扰;给出了两者共存时兼容的子帧配比,研究了此子帧配比下TD-LTE的两种特殊时隙配比方案SSP5与SSP6,并从下行资源利用情况、单小区下行峰值吞吐量、基站可规避干扰距离等方面将两方案做了对比分析,指出SSP6能够更好地利用系统的下行资源,有利于提升系统容量。     

A distributed implementation of mobility load balancing with power control and cell reselection in 4G network

We consider a self‐organizing network (SON) capability of mobility load balancing in a 4G network, which determines the transmission power level for individual base stations and cell reselection for individual mobile stations such that the network‐wide load is minimized while satisfying the minimum signal‐to‐noise and interference ratio (SINR) requirement of individual users. Both centralized and distributed schemes are proposed. The centralized scheme is based on the greedy algorithm, serving as a performance bound to the distributed scheme. The distributed scheme is to solve the system‐wide optimization problem in the flat network model, i.e. no central control node. Furthermore, it requires relatively low inter‐cell exchange information among neighboring cells over an inter‐cell channel, e.g. X2 interface in the LTE network. The proposed design objective is to minimize the number of mobile users that do not satisfy the specified average throughput, while distributing the user traffic load as uniformly as possible among the neighboring cells. Our simulation results for a uniform user distribution demonstrate that the proposed scheme can achieve up to almost 80% of a load balancing gain that has been achieved by a greedy algorithm in the centralized optimization. Copyright © 2014 John Wiley & Sons, Ltd.