• Journal of the Korea Society of Computer and Information
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• v.21 no.1
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• pp.49-57
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• 2016

In this paper we propose the resource allocation scheme for the overlaid macro-femtocell networks, which considers the type of handovers such as the inter-macrocell, macrocell-to-femtocell, femtocell-to-macrocell, or inter-femtocell in order to guarantee Quality of Service (QoS) and expand the accommodation capacity. Our proposed scheme takes into account the movement of mobile terminals, the QoS degradation, or the load control which trigger handovers in the overlaid networks, before it allocates resources dynamically. Moreover it considers QoS requirements of realtime or non-realtime mobile multimedia services such as video communication, Video on Demand (VoD) and dataa services. Simulation results show that our scheme provides better performances than the conventional one with respect to the outage probability, data transmission throughput and handover failure rate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.10
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• pp.1236-1239
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• 2016

In this paper, we propose a new incentive mechanism for hybrid access in cognitive femtocell networks. The purpose of the proposed incentive mechanism is to guarantee the QoS of macro user equipments (MUEs) and to increase femtocell capacity. MUEs channel condition report triggers bidding procedure by neighbor femtocell base stations (FBS). Macro base station (MBS) can offer some subchannels as rewards to encourage FBSs to reliably support its MUEs. Simulation results validate the effectiveness of our proposed scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.4
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• pp.1535-1554
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• 2016

This paper proposes a novel channel assignment scheme called multi-cluster based dynamic channel assignment (MC-DCA) to improve system performance for the downlink of dense femtocell networks (DFNs) based on orthogonal frequency division multiple access (OFDMA) and frequency division duplexing (FDD). In order to dynamically assign channels for femtocell access points (FAPs), the MC-DCA scheme uses a heuristic method that consists of two steps: one is a multiple cluster assignment step to group FAPs using graph coloring algorithm with some extensions, while the other is a dynamic subchannel assignment step to allocate subchannels for maximizing the system capacity. Through simulations, we first find optimum parameters of the multiple FAP clustering to maximize the system capacity and then evaluate system performance in terms of the mean FAP capacity, unsatisfied femtocell user equipment (FUE) probability, and mean FAP power consumption for data transmission based on a given FUE traffic load. As a result, the MC-DCA scheme outperforms other schemes in two different DFN environments for commercial and office buildings.

• Journal of Internet Computing and Services
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• v.19 no.1
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• pp.11-17
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• 2018

In this paper, we propose a novel frequency reuse method using the fractional frequency reuse (FFR) for enterprise femtocell networks (EFNs) in which a lot of femtocell base stations (fBSs) are deployed in a buinding, e.g., business companies, department stores, etc, and evaluate the system performance for the downlink of EFNs. First, we introduce the concept of the split reuse method to allocate the frequency bandwidth with considering the interference between the macrocell and femtocell. Then, we propose the resource allocation with the FFR for fBSs of EFNs to reduce the interference and increase the system capacity. Through simulations, we show that the proposed FFR method outperforms a traditional resource allocation method with frequency reuse factor 4 in terms of the mean fUE capacity, total EFN capacity, and outage probability.

• International journal of advanced smart convergence
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• v.1 no.1
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• pp.19-26
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• 2012

The deployment of mobile femtocellular networks can enhance the service quality for the users inside the vehicles. The deployment of mobile femtocells generates a lot of handover calls. Also, numbers of group handover scenarios are found in mobile femtocellular network deployment. The ability to seamlessly switch between the femtocells and the macrocell networks is a key concern for femtocell network deployment. However, until now there is no effective and complete handover scheme for the mobile femtocell network deployment. Also handover between the backhaul networks is a major concern for the mobile femtocellular network deployment. In this paper, we propose handover control between the access networks for the individual handover cases. Call flows for the handover between the backhaul networks of the macrocell-to-macrocell case are proposed in this paper. We also propose the link switching for the FSO based backhaul networks. The proposed resource allocation scheme ensures the negligible handover call dropping probability as well as higher bandwidth utilization.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.10 no.1
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• pp.16-22
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• 2017

In this paper, we first introduce a mobile data traffic offload method called Local IP Access (LIPA) with femtocell networks. Then, we evaluate the traffic transmission time and probability of mobile data traffic that is transmitted to the core network (CN) when mobile devices transmit the mobile data traffic to indoor devices in three different scenarios, i.e., conventional systems, femtocell based systems, and femtocell and LIPA based systems. Through performance results, it is shown that the next generation mobile network with the femtocell and LIPA not only decrease the density of the mobile data traffic in CNs but also reduce the total transmission time of the mobile data traffic in indoor environments. That is, for the traffic transmission time, the conventional systems and femtocell based systems have 3 and 4 times higher than the femtocell and LIPA based systems, respectively, when the Internet delay is 10ms while 14 and 26 times higher than that, respectively, when the Internet delay is 100ms.

• Journal of Communications and Networks
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• v.15 no.3
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• pp.312-320
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• 2013

Home evolved Node-B (HeNB), also called a femtocell or a femto base station, is introduced to provide high data rate to indoor users. However, two main problems arise in femtocell networks: (1) Small coverage area of HeNB, which results in limited cell-splitting gain and ping-pong handover (HO) problems and (2) high inter-femtocell interference because HeNBs may be densely deployed in a small region. In this study, an efficient cooperation mechanism called an HeNB-aided virtual-HO (HaVHO) scheme is proposed to expand the coverage area of femtocells and to reduce inter-femtocell interference. The cooperation among neighbor HeNBs is exploited in HaVHO by enabling an HeNB to relay the data of its neighbor HeNB without an HO. The HaVHO procedure is compatible with the existing long term evolution specification, and the information exchange overhead in HaVHO is relatively low. To estimate the signal to interference plus noise ratio improvement, the area average channel state metric is proposed, and the amount of user throughput enhancement by HaVHO is derived. System-level simulation shows that HaVHO has a better performance than the other four schemes, such as lesser radio link failure, lesser ping-pong handover, lesser short-stay handover, and higher user throughput.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.11
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• pp.2597-2615
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• 2013

This paper proposes a dynamic downlink load control scheme that jointly employs dynamic load threshold management and virtual coverage management schemes to reduce the degree of performance degradation due to traffic overload in two-tier femtocell networks. With the proposed scheme, the downlink load in a serving macrocell is controlled with a load threshold which is adjusted dynamically depending on the varying downlink load conditions of neighboring macrocells. In addition, traffic overloading is alleviated by virtually adjusting the coverage of the overloaded serving macrocell, based on the adjusted load threshold of the serving macrocell. Simulation results show that the proposed scheme improves the performance of two-tier femtocell networks in terms of the outage probability and sum throughput. This improvement is significantly increased with appropriate values of load thresholds and with an intermediate-level adjustment of the virtual coverage area (i.e., handover hysteresis margin: HOM). Furthermore, the proposed scheme outperforms both a previously proposed load control scheme with a static load threshold and the LTE system without a HOM adjustment.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.7
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• pp.2530-2547
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• 2015

In the recent years, femtocell technology has received a considerable attention due to the ability to provide an efficient indoor wireless coverage as well as enhanced capacity. However, under the spectrum sharing between femtocell user equipment (FUEs) and the owner of spectrum macrocell user equipment (MUEs), both may experience higher uplink interference to each other. This paper proposes a novel distributed power control algorithm for the interference management in two-tier femtocell networks. Due to the assignment of licensed radio frequency to the outdoor macrocell users, the access priority of MUEs should be higher than FUEs. In addition, the quality of service (QoS) of MUEs that is expressed in the target signal-to-interference-plus-noise ratio (SINR) must always be achieved. On the other hand, we consider an efficient QoS provisioning cost function for the low-tier FUEs. The proposed algorithm requires only local information and converges even in cases where the frontiers of available power serve the target SINRs impossible. The advantage of the algorithm is the ability to implement in a distributed manner. Simulation results show that the proposed algorithm based on our cost function provides effective resource allocation and substantial power saving as compared to the traditional algorithms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.10
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• pp.865-873
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• 2013

In the cellular networks adopting femtocells, the macrocell users can suffer from severe interference by the femtocells. In this paper, we propose a distributed transmission power control scheme for femtocells to protect macrocell users. With the proposed scheme, when a macrocell user experiences outage due to severe interference, it informs the interfering femtocell base station (BS) of the outage occurrence, via the macrocell BS. Then, the femtocell BS reduces the transmission power to protect the macrocell user. The proposed scheme does not require too much control information among the macrocell BS, the macrocell users, and the femtocell BS. Moreover, the computational complexity in femtocell BS is very low. By using simulation, we show that the performance of the proposed scheme is good enough to use in practice, in spite of its simplicity.