Browsing by Author "Ohta, C."
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Item Comparison of Interference Reduction Schemes by Femto Base Stations to Macro Cell Users(Institute of Electronics, Information and Communication Engineers (IEICE), 2010) Tanabe, Y.; Afolabi, A. S.; Ohta, C.; Tamaki, H.; Tanaka, Y.; Yamamoto, T.; Okada, Y.In 3GPP TR25.820, three kinds of approaches, access control, bandwidth control, and power control, to reduce interference from femtocell to macrocell are examined. Further, five types of configurations as combinations of these approaches are also discussed. The relative effectiveness among these configurations are, however, not clear since they are not compared in the same scenario enough. Therefore, at the beginning in this paper, under the simple scenario where one femto-cell exists in one macro-cell, we compare Shannon capacities of the following three configurations: 1) Open Access, Co-channel, and Fixed Power, 2) CSG (Closed Subscriber Group), Dedicated Channel, and Fixed Power, 3) CSG, Co-channel, and Adaptive Transmission Power. We also investigate conditions that transmission power control is effective.Item Fair Partitioning of the Downlink Resources of an OFDMA-based Multi-User Multi-Tier Cellular Network Using Fractional Frequency Reuse(Maruzen Co., Ltd/Maruzen Kabushikikaisha, 2012) Afolabi, A. S.; Munkhbat, E.; Takaki, Y.; Ohta, C.; Tamaki, H.; Tanaka, Y.; Yamamoto, T.; Okada, Y.Orthogonal Frequency Division Multiple Access (OFDMA) is a leading air interface candidate for future generation cellular networks. However, if deployed in a multi-user multi-tier cellular system, it is important to fairly share radio resources such as transmission power and sub-carriers among co-tier and cross-tier users. This paper focuses on a mathematical formulation of cell inner-zone radio resource partitioning variables and considers the case of an FFR-based macrocell underlaid with femtocell. By applying an exhaustive search procedure on the developed formulation, we determine the optimal radio resource partitioning parameter values from the perspectives of macrocell user fairness and femtocell throughput maximization.Item Fair Resource Partitioning Between Cell-edge and Cell-center of FFR-based Multi-tier Wireless Access Networks(Institute of Electrical and Electronics Engineers (IEEE), 2011) Afolabi, A. S.; Munkhbat, E.; Ohta, C.; Tamaki, H.This paper addresses the problem of fair radio resource partitioning between the cell-edge and cell-center regions in the context of the downlink of a SISO-OFDMA cellular system. Although, a plethora of studies concerning OFDMAbased radio resource allocation exists, it is, however, imperative to accord special attention to the proper design of network resource partitioning variables in order to ensure fairness in cell structures in which cell-wide reuse-1 is impracticable. This work focuses on the mathematical formulation of cell-edge/cell-center radio resource partitioning variables and considers the case of an FFR-based multi-layer cellular structure comprising of femtocell underlay. By way of exhaustive search procedure, we determined the optimal radio resource partitioning parameter values from the perspective of user fairness and throughput maximization.Item Macrocell Batch Resource Allocation for a Closed Access Femto-Macro Cellular Wireless Network(Institute of Electrical and Electronics Engineers (IEEE), 2011) Afolabi, A. S.; Ohta, C.; Tamaki, H.Femtocell is an emerging technology that promises increased network capacity and enhanced indoor coverage at a low capital and operational cost. However, macrocell network performance depreciates when macrocell users (mUEs) are located indoors with femtocell base stations (FBSs), and these users are not allowed access to the FBSs (closed access). This is a critical issue that needs to be addressed in order to successfully deploy femtocell tier over existing macrocell networks. This paper proposes a macrocell proportional fair-based batch resource allocation strategy that enables FBS to be aware of macrocell resource usage schedule. In this context, batch means multiple time-slots. The knowledge of macrocell resource usage schedule enables the FBS to effectively mitigate interference caused to mUEs in its neighborhood. We show by simulation results that our proposed cross-layer interference coordination approach significantly increases the total macrocell throughput through interference reductionItem Macrocell Batch Resource Allocation for a Co-Channel Macrocell/Femtocell Network(Institute of Electronics, Information and Communication Engineers (IEICE), 2010) Afolabi, A. S.; Ohta, C.; Tamaki, H.This research work proposes an interference mitigation strategy that adjusts the maximum transmit power of femtocell base stations so as to reduce the aggregate cross-tier interference received by nearby microcell users. Most of the existing research works considered resource allocation and interference avoidance separately but in this work, both are investigated together. A resource block allocation strategy which ensures that each user served by the microcell or femtocell base station receives a fair share of the resource blocks available in the serving cell is discussed in this work. In the case of femtocell, a non-linear optimisation model is developed to maximize the total cell throughput. The optimisation process comprises of two parts, channel allocation and power allocation which are treated separately. Simulation results show that the proposed scheme can increase considerably the average microcell throughput in an interference-prone multilayer wireless network as the case of macro-femto cellular networks.Item A Novel Co-Operative Channel Assignment Scheme for Indoor Base Stations(Global Science and Technology Forum (GSTF)., 2011) Afolabi, A. S.; Ohta, C.; Tamaki, H.Abstract—This paper presents a co-operation technique of channel assignment (CA) for indoor base stations (BSs). Indoor BSs are most of the time deployed by users in an ad-hoc manner which makes prior network planning by network operators impossible. If the same pool of radio resources (e.g channels) is used by close BSs, co-operation between these BSs is vital for resolving problems such as interference. In the proposed scheme, femtocell base station (FBS), which is a typical example of indoor BS, is considered. FBSs in close proximity exchange UE-assisted (User Equipment) measured reference power information, and based on individual position of each FBS, inter-BS interaction is used to form clusters. In each cluster, the cluster-head (CH) uses channel assignment tables to assign channel resources to cluster-members (CMs) in a distributed manner. This scheme helps to ensure that the interest of neighbor BSs is always considered whenever a BS makes use of the available network resources. Our simulation results show that co-operative CA using a cluster-based approach yields higher average user throughput than autonomous channel selection by individual BSs.