Sueng Jae Bae

Interference Analysis for Femtocell Deployment in OFDMA Systems Based on Fractional Frequency Reuse

In OFDMA systems adopting fractional frequency reuse, we can allocate orthogonal bandwidth to femtocells, which mitigates throughput degradation of macrocell users. In this paper, we discuss the optimal power allocation for femtocells with different orthogonal subbands, based on analysis of macrocell interferences.

Dynamic power control mechanism for interference coordination of device-to-device communication in cellular networks

Device-to-device (D2D) communication in cellular networks can bring about interference between user equipments (UEs) in cellular and D2D communications, which may decrease performance of cellular networks. In this paper, we propose dynamic power control mechanism to reduce interference and improve performance of cellular systems. The proposed mechanism excludes cellular communication UE with same resource, base station, and areas of adjacent cells from the coverage area of D2D communication UE by adjusting transmit power of the D2D communication UE. By simulations, we show that the proposed dynamic power control mechanism can improve performance of the entire communication systems.

Handover triggering mechanism based on IEEE 802.21 in heterogeneous networks with LTE and WLAN

As the demands for various multimedia services requiring high capacity increase, shortage of wireless resources becomes a serious problem in cellular networks. In order to reduce the heavy load and increase overall capacity of cellular networks, internetworking between WLANs and cellular networks has being considered. However, in the internetworking of cellular networks and WLANs, since performance of overall networks is closely related with the execution timing of vertical handover, an efficient vertical handover triggering mechanism is required. Thus, in this paper, we propose a data rate based vertical handover triggering mechanism (DR-HTM) based on IEEE 802.21 Media Independent Handover (MIH) standard in order to maximize capacity of both WLANs and cellular networks. In DR-HTM, whenever a mobile node discovers WLAN, it obtains achievable data rate of the WLAN by using remote MIH services. Based on the information, the mobile node determines execution of vertical handover. To evaluate the performance of the DR-HTM, we have performed intensive simulations for handover triggering mechanisms based on data rate and RSS. From the results, we can find that loads of cellular networks are effectively shared with WLANs and capacity of overall networks can be maximized by using DR-HTM.

Relay Selection and Resource Allocation Schemes for Effective Utilization of Relay Zones in Relay-Based Cellular Networks

In relay-based cellular networks, total system throughput and cell-edge user throughput are affected by relay selection (RS) and resource allocation (RA) schemes. In this letter, we propose an RS scheme and two RA schemes (optimal and heuristic) for relay-based cellular networks. Via simulation, we show that the proposed RS and RA schemes improve total throughput of relay-based cellular networks while maintaining cell-edge user throughput comparable to existing schemes.

Delay-aware call admission control algorithm in 3GPP LTE system

Long Term Evolution (LTE) has being standardized by the 3rd Generation Partnership Project (3GPP) as the evolution of WCDMA. Different from the conventional mobile communication technologies that deliver voice traffic through circuit switched networks, in LTE, all kinds of traffic are transferred through packet switched networks based on Internet Protocol (IP). In order to provide Quality of Service (QoS) in packet switched networks, Radio Resource Management (RRM) is very important. Especially, Call Admission Control (CAC), which is a part of RRM, plays an important role in RRM because it can prevent network congestion and guarantee certain level of QoS for on-going calls by accepting or rejecting service requests. In this paper, we propose delay-aware CAC algorithm in order to provide QoS for various kinds of services in LTE system. Delay-aware CAC algorithm utilizes statistical datas for packet delay and PRB utilization in order to guarantee packet delay requirements for on-going calls. In order to evaluate performance of delay-aware CAC algorithm, we perform simulations under various environments. The simulation results show that the delay-aware CAC algorithm can satisfy packet delay requirements for various service types defined in LTE specification.

A resource allocation scheme for device-to-device communications using LTE-A uplink resources

Abstract Device-to-device (D2D) communications enabling devices to directly communicate with each other have been considered to overcome the shortage of available radio resource and reduce heavy traffic load on cellular base station. D2D communications operating on cellular networks can improve the efficiency of utilizing radio resource by reusing the resource of cellular networks. However, it can cause interference between cellular and D2D entities using the same resource, and the interference may degrade the performance of the entire system. D2D communications have been preferred to use uplink (UL) resources of cellular networks due to asymmetric UL and downlink (DL) service loads. In Long Term Evolution Advanced (LTE-A), single carrier frequency division multiple access (SC-FDMA) has adopted as UL transmission scheme in order to achieve low a high peak-to-average power ratio (PAPR). There are the exclusivity and the adjacency constraints in SC-FDMA. In order to enable D2D communications to efficiently reuse UL resources of the cellular networks, a radio resource allocation scheme with the constraints of SC-FDMA is proposed in this paper. The proposed scheme pairs up a cellular user equipment (CUE) and a D2D pair as a resource sharing pair (RSP) by controlling transmission power of D2D user equipments (DUEs), and allocates the contiguous subchannels to an RSP based on the well-known proportional fairness (PF) scheduling algorithm. The results of performance evaluation show that the proposed scheme can maintain throughputs of CUEs and alleviate the high PAPR problem of user equipments (UEs).

A Resource-Estimated Call Admission Control Algorithm in 3GPP LTE System

As the evolution of high speed downlink packet access (HSDPA), long-term evolution (LTE) has being standardized by the 3rd generation partnership project (3GPP). In the existing mobile communication networks, voice traffic is delivered through circuit-switched networks, but to the contrary in LTE, all kinds of traffic are transferred through packet-switched networks based on IP. In order to provide quality of service (QoS) in wireless networks, radio resource management (RRM) is very important. To reduce network congestion and guarantee certain level of QoS for on-going calls, call admission control (CAC), in part of RRM, accepts or rejects service requests. In this paper, we proposed resource-estimated CAC algorithm and evaluated the performance of the proposed CAC algorithm. The result shows that the proposed algorithm can maximize PRB utilization and guarantee certain level of QoS.

Mobility-based handover decision mechanism to relieve ping-pong effect in cellular networks

In order to guarantee quality of service (QoS) and seamless communications to nomadic users, it is important to prevent unnecessary handovers occurred during a short interval, so-called ping-pong effect. Considering mobility is one of the useful methods to relieve ping-pong effect in cellular networks since a mobile device can efficiently determine whether it should perform handover or not through the estimation of its moving direction or velocity. In this paper, we propose a mobility estimation method that estimates radial velocity of mobile device directed to the neighboring base stations based on the received signal strength (RSS). In addition, we propose an efficient handover decision mechanism based on the estimated mobility to relieve ping-pong effect. From performance evaluation based on simulations, we find that the proposed mobility estimation mechanism can accurately estimate mobility of moving devices and the proposed handover mechanism can effectively relieve ping-pong effect and reduce handover delay.

A resource allocation scheme for improving user fairness in device-to-device communication based on cellular networks

As one of solutions to radio resource shortage and heavy burden on base stations, device-to-device (D2D) communication which enables devices to directly communicate with each other has been considered. If D2D communication operates based on cellular networks, it can efficiently utilize radio resources by reusing the resources of cellular networks. However, the interference between cellular and D2D communication entities can be occurred when they share the same resource, and this may degrade entire system performance. In order to coordinate the interference, a resource allocation scheme which allocates resources to cellular mobile equipments (CMEs) and D2D pairs is proposed in this paper. The proposed scheme involves one CME and one D2D pair in a resource sharing pair (RSP) by considering interference between them, and allocates the resources to RSPs based on proportionally-fair (PF) scheduling algorithm. The proposed scheme can improve the overall performance of cellular network by improving fairness among user throughputs as maintaining total system capacity.

Self-configuration scheme to alleviate interference among APs in IEEE 802.11 WLAN

Wireless local area network (WLAN) is the one of the technologies which enable mobile users to connect to local area network through a wireless radio connection in industrial, scientific and medical (ISM) band. Since WLAN can support high data rate communications with low-cost, the use of WLAN is rapidly increasing. However, in congested region, such as shopping mall, airport, and so on, where a lot of WLAN access points (AP) becomes collocated, indiscriminate installation of APs causes high signal interference and heavy contention in overlapping region among APs. In order to solve these problems, we propose self-configurable cooperative RRM (CRRM) scheme for WLAN. The proposed CRRM scheme effectively reduces the overlapping regions by cooperatively coordinating channel assignments and adjusting transmission power of neighboring APs. From simulations for various scenarios, we verify that the proposed scheme can help to mitigate interference and reduce the contention between neighboring APs.