Self Organizing strategies for enhanced ICIC (eICIC)

Small cells have been identified as an effective solution for coping with the important traffic increase that is expected in the coming years. But this solution is accompanied by additional interference that needs to be mitigated. The enhanced Inter Cell Interference Coordination (eICIC) feature has been introduced to address the interference problem. eICIC involves two parameters which need to be optimized, namely the Cell Range Extension (CRE) of the small cells and the ABS ratio (ABSr) which defines a mute ratio for the macro cell to reduce the interference it produces. In this paper we propose self-optimizing algorithms for the eICIC. The CRE is adjusted by means of load balancing algorithm. The ABSr parameter is optimized by maximizing a proportional fair utility of user throughputs. The convergence of the algorithms is proven using stochastic approximation theorems. Numerical simulations illustrate the important performance gain brought about by the different algorithms.Comment: Submitted to WiOpt 201

Distributed Enhanced Inter-Cell Interference Coordination (eICIC) in LTE-Advanced HetNets: A Potential Game Approach

International audienceIn this paper we propose a distributed algorithm for jointly optimizing almost blank subframe (ABS) and cell selection bias (CSB) patterns in Long Term Evolution-Advanced (LTE-A) heterogeneous networks (HetNets). We formulate the optimization problem as an exact potential game, where a Nash equilibrium point is guaranteed to be achieved within finite number of plays. Through simulations, we are able to demonstrate the fast convergence of the algorithm, an increase in average user rate, and a tremendous improvement on the service fairness of the users

Hierarchical Radio Resource Optimization for Heterogeneous Networks with Enhanced Inter-cell Interference Coordination (eICIC)

Interference is a major performance bottleneck in Heterogeneous Network (HetNet) due to its multi-tier topological structure. We propose almost blank resource block (ABRB) for interference control in HetNet. When an ABRB is scheduled in a macro BS, a resource block (RB) with blank payload is transmitted and this eliminates the interference from this macro BS to the pico BSs. We study a two timescale hierarchical radio resource management (RRM) scheme for HetNet with dynamic ABRB control. The long term controls, such as dynamic ABRB, are adaptive to the large scale fading at a RRM server for co-Tier and cross-Tier interference control. The short term control (user scheduling) is adaptive to the local channel state information within each BS to exploit the multi-user diversity. The two timescale optimization problem is challenging due to the exponentially large solution space. We exploit the sparsity in the interference graph of the HetNet topology and derive structural properties for the optimal ABRB control. Based on that, we propose a two timescale alternative optimization solution for the user scheduling and ABRB control. The solution has low complexity and is asymptotically optimal at high SNR. Simulations show that the proposed solution has significant gain over various baselines.Comment: 14 pages, 8 figure

Joint Optimization on Inter-cell Interference Management and User Attachment in LTE-A HetNets

International audienceTo optimize the network utility in 3GPP Long Term Evolution-Advanced (LTE-A) heterogeneous networks (HetNets), it is necessary to jointly consider inter-cell interference mitigation and user attachment. Based on potential game formulation, we optimize almost blank subframe (ABS) and/or cell selection bias (CSB) settings for both macrocells and picocells in a distributed manner. We demonstrate the need of joint ABS and CSB optimization via simulation case studies. Extensive simulations confirm that joint ABS and CSB optimizations can lead to a 20% improvement in spectral efficiency and a 46% improvement in energy efficiency while increasing the fairness of the achieved rates of users

이동 셀이 포함된 이종 셀룰러 네트워크에서 자원할당에 관한 연구

학위논문 (석사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 이용환.Due to the popularity of smart phones and wireless services, demand for high traffic has become a heavy burden in wireless cellular communication system. Deployment of small cells has been proposed as one of feasible solutions to support increasing traffic demand. However, it may need to resolve technical issues including the management of frequent handovers, cross-tier and inter-cell interference. In this thesis, we consider the employment of small moving cells (SMCs) in a heterogeneous cellular network to improve transmission performance of the whole network. An SMC can provide services for a small number of users moving together with a mobility of up to a few hundred Km/hour. For ease of interference management and in consideration of SMC mobility, the macro cell shares the resource with SMCs in an orthogonal manner. To maximally utilize the resource, the macro cell adjusts the amount of resource for the SMCs in response to the change of SMC operational environments and utilizes the rest of the resource for itself. It can also allocate resource to each SMC in an orthogonal manner. Exploiting that the peak-to-average load ratio (PALR) is much larger than one, SMCs can maximally utilize the resource without inter-cell interference. Finally, the proposed resource allocation scheme is verified by computer simulation.Contents Abstract i Contents iii List of Figures iv List of Tables v 1. Introduction 1 2. System model 3 2.1 Heterogeneous cellular network with small moving cells 3 2.2 Signal-to-interference plus noise ratio (SINR) 4 2.3 FA Size 5 2.4 Traffic load 6 3. Resource allocation for SMCs 9 3.1 Previous works 9 3.2 Proposed resource allocation 12 3.2.1 Resource allocation based on the mean FA size 13 3.2.2 Resource allocation based on the peak FA size 15 3.3 Resource adjustment for SMCs 16 3.4 Overhead 17 4. Performance evaluation 19 5. Conclusions 26 References 27 1. 초 록 30Maste

이동셀이 포함된 이종 셀룰러 네트워크에서 자원 관리 연구

학위논문 (석사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 이용환.Deployment of small cells has received a great attention as one of feasible technologies to support explosively increasing traffic demands in cellular communication systems. However, it may involve technical issues, including the management of handovers and cross-tier interference near the cell boundary. In this thesis, we consider deployment of small moving cells (SMCs) in a heterogeneous cellular communication system that employs fixed small cells such as femto- and pico-cells. SMCs can have mobility while providing services for a small number of users in a very short transmission range. We assume that SMCs can make communications among them through a side-haul link for their cooperative operation and make communications with the macro cell through a wireless back-haul. We also assume that the macro cell and SMCs orthogonally share resource to avoid cross-tier interference. We consider resource management for SMCs to maximize the transmission performance by exploiting the mobility of SMCs. For ease of implementation, we consider the resource allocation by coordination among SMCs without involvement of the macro cell. Exploiting that the peak-to-average load ratio (PALR) is larger than 1, we can minimize the resource utilization for SMCs, while allowing them to utilize the resource orthogonal to each other. Thus, the proposed scheme can make SMCs operate without experiencing inter-cell interference. It also virtually reduce the PALR of cells, which is one of major concerns for resource saving operation. Finally, the performance of the proposed scheme is verified by computer simulation.Abstract i Contents iii List of Figures iv List of Tables v 1. Introduction 1 2. System model 4 2.1. Resource allocation for SMCs 4 2.2. Resource structure 6 2.3. Signal-to-interference plus noise ratio 8 2.4. Traffic load 10 3. Previous works 13 3.1. Conventional resource management 13 3.2. Dynamic radio resource allocation 16 4. Proposed resource management 17 4.1. FA size 17 4.2. Resource management 18 4.3. Cooperative resource allocation 20 5. Performance evaluation 23 6. Conclusions 31 References 33 1. 초 록 37Maste

A Game Theoretic Distributed Algorithm for FeICIC Optimization in LTE-A HetNets

International audienceIn order to obtain good network performance in Long Term Evolution-Advanced (LTE-A) heterogeneous networks (HetNets), enhanced inter-cell interference coordination (eICIC) and further enhanced inter-cell interference coordination (FeICIC) have been proposed by LTE standardization bodies to address the entangled inter-cell interference and the user association problems. We propose distributed algorithms based on the exact potential game framework for both eICIC and FeICIC optimizations. We demonstrate via simulations a 64% gain on energy efficiency (EE) achieved by eICIC and another 17% gain on EE achieved by FeICIC. We also show that FeICIC can bring other significant gains in terms of cell-edge throughput, spectral efficiency (SE) and fairness among user throughputs. Moreover, we propose a downlink scheduler based on a cake-cutting algorithm that can further improve the performance of the optimization algorithms compared to conventional schedulers

실제 전파 환경을 반영한 이동통신 시스템의 최적화 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2016. 8. 김성철.The 4th generation cellular systems, such as LTE (Long-Term Evolution) or LTEAdvanced, significantly improve the speed and the quality of data service as compared to the previous generation systems. In this situation, many applications generating a huge amount of mobile traffic (e.g., high definition (HD) video streaming or cloudbased storage services) have been widely spread. For this reason, the amount of mobile data traffic keeps increasing and sometimes even exceeds the capacity of the system. In order to accommodate explosively increasing mobile data traffic, service providers try to enhance the spatial reuse of wireless resources by deploying more base stations (BSs). Furthermore, small-sized BSs, such as pico and femto BSs, draw much attention as an economical and easy to deploy solution for relieving the load of macro BSs. In this dissertation, I investigate several strategies for optimizing the utilization of cellular systems. Especially, load balancing algorithms, which forcibly redirect users associated with a congested BS thereby experiencing low service quality to nearby BSs, are proposed. As a first step, I propose methods for predicting the service quality (or equivalently the long-term average throughput) of each individual user when multiple users share the same BS. During developing these algorithms, the time-varying characteristic of wireless channel due to multi-path propagation environment is considered to reflect real propagation environments. To this end, the fluctuation phenomenon of the received signal strength is expressed by a random variable, and then, two types of user throughput estimation schemes are developed. The proposed algorithms can be easily implemented in a practical system, and prediction errors are less than 10% for almost every case. Based on the proposed throughput estimation methods, I deal with a user association problem in multi-cell environments. At first, a centralized user association algorithm is developed, where a central node collects all the channel information between every BS and every user and then assigns an optimal base station to each individual user. However, transferring a lot of information to the central node requires excessive uplink feedback and backhaul usage. In addition, such overheads are increased with the density of BSs. For this reason, I propose a decentralized version of user association algorithm, where users themselves choose an optimal BS by considering not only their service quality but also network-wide utilization. The proposed decentralized algorithm especially can be compatible with heterogeneous cellular networks, where there are abundant BSs in the vicinity of each user. Finally, I study an inter-tier interference management problem between macro and small cell BSs in heterogeneous cellular networks. As the name indicates, small cell BSs are designed to consume much less power as compared to conventional macro BSs. For this reason, users associated with small cell BSs experience severe interference from macro BSs. To mitigate inter-tier interference, the eICIC (enhanced Inter Cell Interference Coordination) method was proposed. In this scheme, macro BSs periodically mute data transmission in order to guarantee the signal quality of users at the small cell BSs. In this dissertation, I try to optimize both user association and inter-tier interference management problems. As a result, users change their association and the system alters data transmission strategies in order to optimize network-wide utilization.Chapter 1 INTRODUCTION 1 Chapter 2 USER THROUGHPUT ESTIMATION FOR THE PF SCHEDULING ALGORITHM 5 2.1 Motivation 5 2.2 System Model 6 2.3 Throughput Estimation for a Single Antenna Scenario under the Rayleigh Fading Environment 9 2.4 Throughput Estimation for General Cases 13 2.4.1 Single User MIMO Scheduling Scenario 13 2.4.2 Multiuser MIMO Scheduling Scenario 14 2.5 Implementation Issues 15 2.6 Performance Evaluation and Discussion 16 2.6.1 Simulation Setup 16 2.6.2 Single Antenna Scenario 17 2.6.3 Multiple Antenna Scenario 20 Chapter 3 DYNAMIC USER ASSOCIATION IN MULTI-CELL CELLULAR NETWORKS 24 3.1 Motivation 24 3.2 System Model 25 3.3 Problem Formulation 27 3.3.1 Objective and Optimal Algorithm 27 3.3.2 User Association Problem 29 3.4 Centralized Dynamic User Association Algorithm 31 3.5 Performance Evaluation and Discussion 34 3.5.1 Simulation Setup 34 3.5.2 Throughput Estimation Error in Multi-cell Environments 36 3.5.3 Load Balancing Effect 37 Chapter 4 DECENTRALIZED USER ASSOCIATION METHOD IN HETEROGENEOUS CELLULAR NETWORKS 40 4.1 Motivation 40 4.2 System Model 41 4.3 Problem Formulation 43 4.4 Decentralized User Association Algorithm 44 4.4.1 Overview 44 4.4.2 User Scheduling and Throughput Estimation 46 4.4.3 Broadcast Signal Design 46 4.5 Fully Decentralized Algorithm 52 4.6 Performance Evaluation and Discussion 53 4.6.1 Simulation Setup 53 4.6.2 Unbalanced Traffic Intensity 54 4.6.3 Equal Traffic Intensity 59 4.6.4 Dynamic Scenarios 64 Chapter 5 JOINT OPTIMIZATION OF USER ASSOCIATION & INTER-TIER INTERFERENCE MANAGEMENT IN HETEROGENEOUS CELLULAR NETWORKS 68 5.1 Motivation 68 5.2 System Model 69 5.3 Problem Formulation 70 5.4 Joint Optimization Algorithm 72 5.5 Performance Evaluation and Discussion 74 5.5.1 Simulation Setup 74 5.5.2 Simulation Results 74 Chapter 6 CONCLUSION 80 Appendix 82 Appendix A Proof of Proposition 5.1 82 Appendix B Proof of Proposition 5.3 83 Abstract (In Korean) 93Docto