Mobility Load Balancing in Cellular System with Multicriteria Handoff Algorithm

Efficient traffic load balancing algorithm is very important to serve more mobile users in the cellular networks. This paper is based on mobility load balancing handoff algorithm using fuzzy logic. The rank of the serving and the neighboring Base Transceiver Stations (BTSs) are calculated every half second with the help of measurement report from the two-ray propagation model. This algorithm is able to balance load of the BTS by handing off some ongoing calls on BTS’s edge of highly loaded BTS to move to overlapping underloaded BTS, such that the coverage area of loaded BTS virtually shrunk towards BTS center of a loaded sector. In case of low load scenarios, the coverage area of a BTS is presumed to be virtually widened to cover up to the partial serving area of neighboring BTS. This helps a highly loaded neighboring BTS or failed BTS due to power or transmission. Simulation shows that new call blocking and handoff blocking using the proposed algorithm are enhanced notably

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

Radio resource management for OFDMA systems under practical considerations.

Orthogonal frequency division multiple access (OFDMA) is used on the downlink of broadband wireless access (BWA) networks such as Worldwide Interoperability for Microwave Access (WiMAX) and Long Term Evolution (LTE) as it is able to offer substantial advantages such as combating channel impairments and supporting higher data rates. Also, by dynamically allocating subcarriers to users, frequency domain diversity as well as multiuser diversity can be effectively exploited so that performance can be greatly improved. The main focus of this thesis is on the development of practical resource allocation schemes for the OFDMA downlink. Imperfect Channel State Information (CSI), the limited capacity of the dedicated link used for CSI feedback, and the presence of a Connection Admission Control (CAC) unit are issues that are considered in this thesis to develop practical schemes. The design of efficient resource allocation schemes heavily depends on the CSI reported from the users to the transmitter. When the CSI is imperfect, a performance degradation is realized. It is therefore necessary to account for the imperfectness of the CSI when assigning radio resources to users. The first part of this thesis considers resource allocation strategies for OFDMA systems, where the transmitter only knows the statistical knowledge of the CSI (SCSI). The approach used shows that resources can be optimally allocated to achieve a performance that is comparable to that achieved when instantaneous CSI (ICSI) is available. The results presented show that the performance difference between the SCSI and ICSI based resource allocation schemes depends on the number of active users present in the cell, the Quality of Service (QoS) constraint, and the signal-to- noise ratio (SNR) per subcarrier. In practical systems only SCSI or CSI that is correlated to a certain extent with the true channel state can be used to perform resource allocation. An approach to quantifying the performance degradation for both cases is presented for the case where only a discrete number of modulation and coding levels are available for adaptive modulation and coding (AMC). Using the CSI estimates and the channel statistics, the approach can be used to perform resource allocation for both cases. It is shown that when a CAC unit is considered, CSI that is correlated with its present state leads to significantly higher values of the system throughput even under high user mobility. Motivated by the comparison between the correlated and statistical based resource allocation schemes, a strategy is then proposed which leads to a good tradeoff between overhead consumption and fairness as well as throughput when the presence of a CAC unit is considered. In OFDMA networks, the design of efficient CAC schemes also relies on the user CSI. The presence of a CAC unit needs to be considered when designing practical resource allocation schemes for BWA networks that support multiple service classes as it can guarantee fairness amongst them. In this thesis, a novel mechanism for CAC is developed which is based on the user channel gains and the cost of each service. This scheme divides the available bandwidth in accordance with a complete partitioning structure which allocates each service class an amount of non-overlapping bandwidth resource. In summary, the research results presented in this thesis contribute to the development of practical radio resource management schemes for BWA networks