Dynamic spectrum allocation for cell range extension in tiered Macro-Pico heterogeneous networks

Heterogeneous networks are employed in the next generation communication systems to enhance the area spectral efficiency (ASE), where cell range extension (CRE) is a promising technique to improve the cell edge performance and utilize the low power node (LPN) resources more effectively. In this paper we propose a dynamic spectrum allocation scheme for Macro-Pico scenario to mitigate both the co-tier and cross-tier interferences. The available system spectrum is divided into different parts by four steps, i.e. user set partition, service request collection, cross-tier occupation and CRE occupation decision, while the service request of each user is taken into consideration. During the process implementation, the reference signal receiving power (RSRP) threshold is derived by mathematical means to judge cell edge macro users when a predefined ratio is given. Simulation results show that the proposed scheme reaches almost the same cell edge performance with the best existing option, meanwhile provides higher overall system throughput and better spectral efficiency. Therefore, much better balance is achieved.     

异构网络中小区间联合干扰协调算法研究

研究了如何在LTE-Advanced系统异构网络中通过有效的增强型小区间干扰协调提高系统总吞吐量问题。通过分析网络中存在的干扰,建立数学模型,提出了一种基于减少发射功率几乎空白子帧的小区间联合干扰协调算法,利用优化方法研究系统总吞吐量和减少发射功率几乎空白子帧之间的关系,实现了最大化系统吞吐量,同时解决宏基站分配多少资源给微微小区,以及用户的接入选择问题。仿真结果表明,所提方法和对比方法相比,系统总吞吐量有19.8%提升,可以达到算法上限的97.4%,适用于对系统总吞吐量要求较高,而边缘用户性能要求较低的场景。     

Semi‐distributed dynamic inter‐cell interference coordination scheme for interference avoidance in heterogeneous networks

Inter‐cell interference (ICI) is a major problem in heterogeneous networks, such as two‐tier femtocell (FC) networks, because it leads to poor cell‐edge throughput and system capacity. Dynamic ICI coordination (ICIC) schemes, which do not require prior frequency planning, must be employed for interference avoidance in such networks. In contrast to existing dynamic ICIC schemes that focus on homogeneous network scenarios, we propose a novel semi‐distributed dynamic ICIC scheme to mitigate interference in heterogeneous network scenarios. With the goal of maximizing the utility of individual users, two separate algorithms, namely the FC base station (FBS)‐level algorithm and FC management system (FMS)‐level algorithm, are employed to restrict resource usage by dominant interference‐creating cells. The distributed functionality of the FBS‐level algorithm and low computational complexity of the FMS‐level algorithm are the main advantages of the proposed scheme. Simulation results demonstrate improvement in cell‐edge performance with no impact on system capacity or user fairness, which confirms the effectiveness of the proposed scheme compared to static and semi‐static ICIC schemes.     

异构网中载波聚合系统的成员载波选择和干扰协同

为了解决下一代演进移动通信系统在异构网场景由于低功率基站在高功率基站覆盖区域的随意分布而导致的小区间干扰问题及容量速率限制,提出了一种载波聚合系统的成员载波选择和干扰协同方法。该方法基于修正的载波公平比例准则,动态地在小区间协同选择成员载波。为了进一步提高低功率节点的系统容量,设计了新的基于调和平均数的用户小区选择准则及算法。仿真结果表明,与频率复用因子为1的系统相比,设计的方法由于静默了部分高功率节点用户成员载波,从而使低功率节点用户获得更多的选择机会,可提高低功率节点小区的容量。     

基于信漏噪比的异构网络载波干扰协调技术

针对异构网络存在小区间干扰的问题,提出了一种基于频域载波聚合的干扰协调管理机制。该机制将所有小区的用户分为中心用户和边缘用户,采用可降低干扰的信漏噪比(SLNR)准则,动态调度用户和选择小区载波,并将每种小区载波选择方案对应一种调度用户分组的机制,即对小区的中心用户和边缘用户采用不同优先级,以此有效避免小区间的干扰,其中优先级采用比例公平和SLNR准则。仿真结果表明,由于在系统目标最大化时实现了频率复用增益和干扰消除增益间实现最佳的平衡,可有效取得系统流量的分流和总吞吐量的提升。     

面向智能配电的异构融合通信网络动态负载均衡

随着经济的发展,人们对信息的需求也就越来越多,电网公司也在不断发展起来.通过建立面向智能配电的网络动态模型,分析了模型的具体内容及其业务上的划分,另外,还分析了负载均衡的相关问题.同时,为了更好地研究智能配电的相关系统,需要对模型的仿真效果进行分析.本文主要从模型及业务划分、均衡分析、仿真分析三个方面加以展开.     

Dynamic spectrum allocation in heterogeneous wireless networks under interference constraints across the cell coverage

In order to improve spectrum utilization, dynamic spectrum allocation (DSA) schemes with interference management have been widely investigated, and a special interest is in the current heterogeneous wireless network (HWN) environment. In the previous work, the approach that guarantees quality of service for the cell‐boundary user is extensively used in the DSA scheme. However, such approach gives a pessimistic result. In this paper, we design a DSA scheme for the HWN system, which adopts relatively accurate interference constraints. First, considering that users may randomly locate over the cell, we propose interference constraints across the cell coverage, in which the interference experienced at a point is controlled below the level suffered when using fixed spectrum allocation in only a single network, and the proportion of the cell area where interference is controlled reaches the required area coverage probability. Then under the interference constraints, we formulate the downlink DSA scheme as a combinatorial optimization problem. As the problem is NP‐hard, to reduce the computational complexity, we propose two greedy heuristic algorithms for its solution. Simulation results show that the DSA scheme could improve the total spectrum utility for operators and increase the satisfaction rate of spectrum demands for base stations. Copyright © 2013 John Wiley & Sons, Ltd.     

基于先进小区干扰协调技术的异构网络联合资源分配

高发射功率的宏基站与低发射功率的小基站之间的资源分配策略直接影响着异构蜂窝网络的性能。这是一个联合资源优化问题,即用户的基站接入选择、宏基站预留给小基站的资源数量和基站的调度策略。针对这一问题,利用块并列下降方法,提出了一组新颖的资源优化算法。所提出的解决方案能分布式实现,并兼容先进长期演进技术( LTE-A )协议中的先进小区间干扰协调技术( eICIC)。大量的动态系统级仿真结果表明系统性能和用户间公平性都得到了显著提升。     

A measurement‐based study of handover improvement through range expansion and interference coordination

Although the range expansion and inter‐cell interference coordination (ICIC) have been shown to successfully enhance the capacity and load balancing in the Heterogeneous Network, their impacts on the handover (HO) performance are not fully understood in existing studies. In this paper, a novel measurement‐based approach is adopted to investigate these issues, where the real measured data of the reference signal received power in a macro–pico co‐channel deployment are collected. Then the mobility performance in terms of the HO failure rate and ping‐pong rate is simulated with various ICIC schemes in the same reality environment. This has been made possible by modeling the possible HO failure events based on evaluating the downlink received signal‐to‐interference‐plus‐noise ratio from reference signal received power. The simulation results indicate that range expansion together with ICIC can have positive or negative influences on macro‐to‐pico, pico‐to‐macro, pico‐to‐pico and macro‐to‐macro HOs in the Heterogeneous Network. The existing static ICIC or mobility‐based ICIC cannot handle the intra‐layer (pico‐to‐pico and macro‐to‐macro) interference, thus limiting their abilities to improve the mobility performance. Motivated by this, a dynamic‐ICIC‐aided HO procedure is proposed. The proposed HO enhancement method is more flexible and effective in mitigating both the inter‐layer and intra‐layer interference, outperforming the existing methods significantly. 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.     

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。     

SMDP-based sleep policy for base stations in heterogeneous cellular networks

A dense heterogeneous cellular network can effectively increase the system capacity and enhance the network coverage. It is a key technology for the new generation of the mobile communication system. The dense deployment of small base stations not only improves the quality of network service, but also brings about a significant increase in network energy consumption. This paper mainly studies the energy efficiency optimization of the Macro-Femto heterogeneous cellular network. Considering the dynamic random changes of the access users in the network, the sleep process of the Femto Base Stations (FBSs) is modeled as a Semi-Markov Decision Process (SMDP) model in order to save the network energy consumption. And further, this paper gives the dynamic sleep algorithm of the FBS based on the value iteration. The simulation results show that the proposed SMDP-based adaptive sleep strategy of the FBS can effectively reduce the network energy consumption.     

Joint interference coordination approach in femtocell networks for QoS performance optimization

Future heterogeneous networks with dense cell deployment may cause high intercell interference. A number of interference coordination (IC) approaches have been proposed to reduce intercell interference. For dense small‐cell deployment with high intercell interference between cells, traditional forward link IC approaches intended to improve edge user throughput for best effort traffic (ie, file transfer protocol download), may not necessarily improve quality of service performance for delay‐sensitive traffic such as voice over long‐term evolution traffic. This study proposes a dynamic, centralized joint IC approach to improve forward link performance for delay‐sensitive traffic on densely deployed enterprise‐wide long‐term evolution femtocell networks. This approach uses a 2‐level scheme: central and femtocell. At the central level, the algorithm aims to maximize network utility (the utility‐based approach) and minimize network outage (the graphic‐based approach) by partitioning the network into clusters and conducting an exhaustive search for optimized resource allocation solutions among femtocells (femto access points) within each cluster. At the femtocell level, in contrast, the algorithm uses existing static approaches, such as conventional frequency reuse (ReUse3) or soft frequency reuse (SFR) to further improve user equipment quality of service performance. This combined approach uses utility‐ and graphic‐based SFR and ReUse3 (USFR/GSFR and UReUse3/GReUse3, respectively). The cell and edge user throughput of best effort traffic and the packet loss rate of voice over long‐term evolution traffic have been characterized and compared using both the proposed and traditional IC approaches.     

基于迭代联合传输的超密集网络动态干扰协调方案

鉴于超密集网络中急剧增长的小区和用户数量,研究了如何通过合理地选择联合传输用户来实现动态干扰协调,以此提高小区边缘用户频谱效率。通过动态协作簇划分和动态联合静默传输2种手段,将所有用户分类;再利用迭代优化算法进一步提高系统性能,同时解决了联合传输用户的数量选择问题。仿真结果表明,与传统的协作多点方案相比,所提方案在不损失小区平均频谱效率的前提下,在小区边缘频谱效率方面存在显著的性能增益。     

Energy-efficient data transmissions in heterogeneous ultra-dense networks using a hybrid metaheuristic optimization

The heterogeneous ultra-dense network (UDN) is a complex network environment where the small cells (SCs) are densely populated to acquire data transmission. The UDN is mainly adopted to deal with the explosive growth of mobile data and its consequential energy consumption issues. The UDN consists of mobile users, restricting the SCs from offering seamless services as the movement may disrupt the transmissions. To provide an effective solution, this paper introduces an energy-efficient framework that enables effective data transmissions irrespective of the users' mobility. The proposed model considers the clustered SC deployment where the four-tiered architecture is adopted. The architecture includes a macro base station (BS), microcells, picocells, and femtocells. The SCs are responsible for transferring the data received from the mobile users to the macro BS. The proposed model introduces the hybrid algorithm called the firefly oriented multiverse optimization (FF-MVO) algorithm to identify the most optimal path for data transmission. This algorithm works iteratively to identify the optimal path to reach the macro BS for each transmission from the user. The proposed model is simulated in the network simulator 3 (NS3) platform, and the results are evaluated with the existing models. The outcomes proved that the proposed algorithm is more optimal than the other models in finding the optimal path to result in energy-efficient transmissions. The proposed method achieved an average energy consumption of 0.24 J, an average energy efficiency of 10.965 bits/s/J and an average network throughput of 33.907 Gbps.     

Green cell association for multimedia transmission in cognitive heterogeneous networks

With the introduction of low‐powered pico/femto‐base stations and relay nodes into the macro‐cell, recent heterogeneous networks provide an attractive approach for future wireless communication. Although it may achieve better coverage and higher capacity, several problems remain unsolved before practical deployment. For example, how to select the proper cell from neighbor low‐powered cells and then occupy the radio resource without interference on macro‐users is both important and challenging, especially for rigorous multimedia applications. The traditional cell access algorithms and quality‐control parameters such as delay or throughput no longer suit well in this complex environment. An effective approach should be pursued. In this paper, we investigate this interesting cell association problem and propose a complete green resolution on the basis of thorough discussions about the multimedia transmission under these concerns. Cognitive radio is introduced to share spectrum between macro‐cell and low‐powered cells while securing the transmission of authorized macro‐users. We also bring forth the concept of ‘interference balance’ to better manage the overall interference and energy consumption in the network. Restless bandit model is formulated on the basis of channel state, data rate, interference control, and the carefully chosen intra‐refreshing rate for multimedia traffic. Then the cell association scheme is designed to be efficient and practical because of the simple index property of our model output. Simulation results have proven the performance of our proposed resolution compared with existing algorithms on interference constraint, multimedia distortion, and overall network energy consumption balance. Copyright © 2013 John Wiley & Sons, Ltd.     

ESPS scheme for two‐tier interference suppression in a heterogeneous network with cooperative femtocells

The coexistence of a macrocell and a number of femtocells often leads to a two‐tier heterogeneous network, where the co‐tier interference (CotIN) and cross‐tier interference (CrotIN) both degrade users' quality of service. In order to suppress these interferences, we propose a precoding scheme in a heterogeneous network with cooperative femtocells, called CotIN elimination and CrotIN suppression with precoding criterion selection (ESPS) scheme. In this scheme, we first eliminate the CotINs of each user by applying the QR decomposition to channel matrix. Then the CrotINs of macrocell users and femtocell users are suppressed via the macrocell base station (MBS) and femtocell access points (FAPs) with precoding criterion selection, respectively. By using the ESPS scheme, spatial resources can be efficiently exploited. In addition, our ESPS scheme requires little information exchange between MBS and FAPs without iteration and thus significantly reduces the implementation complexity. Furthermore, the robustness is increased through introducing the information of channel uncertainty into the ESPS when channel estimation or quantization error exists. The performance analysis for the ESPS demonstrates that the ESPS is practical in the heterogeneous networks. Finally, simulation results show that the ESPS can decrease users' bit error rates and increase their transmission rates. Copyright © 2015 John Wiley & Sons, Ltd.     

Network planning for Type 1 and Type 1a relay nodes in LTE‐Advanced networks

In this paper, the planning problem of multiple evolved Node Bs (eNBs) and two types of relay nodes is defined base on linear programming. Type 1 relay nodes are placed in the center of eNB, and Type 1a relay nodes are deployed at cell edge. Three algorithms are proposed to investigate the Type 1a relay node placement and communication interference. All algorithms are designed on the basis of graph theory and analyzed in planning case and simulation results. The ultimate goal is to maximize the average throughput of all served users with minimum communication interference. Results showed that the proposed interference coordination algorithm not only provides the lowest construction cost with slightly fewer numbers of served users but also eliminates the communication interference with the highest average throughput. Most importantly, it achieves the best communication quality for next generation mobile networks. Copyright © 2015 John Wiley & Sons, Ltd.     

Self‐optimization of handover parameters for dynamic small‐cell networks

Seamless handover is an essential feature of cellular networks. For small‐cell networks, effective handover becomes particularly challenging. If some cells may be activated and deactivated dynamically, effective handover handling will become even more difficult. A key factor of good handover performance is “handover timing,” that is, making handover decision at a right time. If handover is executed too early or too late, users will experience temporary link disconnection, called radio link failure (RLF). Handover timing is controlled by handover parameters, which are set by the network. RLF prevention is directly related to the proper configuration of these parameters. In this paper, we propose a self‐optimization scheme that adjusts the handover parameters to minimize RLFs for dynamic small‐cell networks. Our scheme first detects the types of RLF and then adjusts the handover parameters according to the types of RLF. Unlike most existing schemes, our scheme adjusts both system common parameters and cell‐specific parameters together. In certain situations, such as when two adjacent cells do not have sufficient coverage overlap, RLFs may not be reduced to a satisfactory level by the handover parameter adjustment alone. To deal with such a case, our scheme adjusts the cell coverage in conjunction with the handover parameter optimization. The simulation results show that the proposed scheme can virtually eliminate RLFs. Copyright © 2013 John Wiley & Sons, Ltd.     

在工业网中EPON的DBA算法研究

EPON系统中,上行数据传输的动态带宽分配（DBA）算法是关键技术之一。针对EPON在工业网络通信中的应用,对现有的DBA算法进行了分析和改进,以保证监控和报警等特殊业务的实时送达,消除交叉轮询的带宽浪费,并对该算法进行了仿真实验。仿真结果表明,该算法的带宽利用率高,业务时延抖动低,并且在低负载时无轻载惩罚现象。