Bum-Gon Choi

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.

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.

A femtocell power control scheme to mitigate interference using listening TDD frame

Due to the rapid growth of indoor wireless communications, many of the telecommunication industries recently are interested in femtocell. Femtocell is low power and low cost indoor base-station to cover indoor traffics. Before using femtocell in current wireless environments, interference problem between macrocell and femtocell should be solved since the interference affects the performance of both macrocell and femtocell. In order to reduce the interference, in this paper, we suggest a new time-division-duplex (TDD) frame structure called listening-TDD frame (LTDDF) for femtocells. In LTDDF, femtocell has both downlink and uplink periods during downlink period in macrocell. The uplink period in macrocell is used as listening period in femtocell that is used to overhear signals from surrounding macrocell users to obtain their channel quality information (CQI). Based on the CQI of macrocell users, femtocell base-station adaptively adjusts its transmission power. Thus, LTDDF can effectively reduce interference on macrocell users. By simulations, we evaluate the performance of LTDDF in terms of capacity of macrocell and femtocell in both downlink and uplink.

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-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.

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.

Mode selection scheme considering transmission power for improving performance of device-to-device communication in cellular networks

Device-to-device (D2D) communication (D2D-comm) which enables direct communications between mobile devices is considered as one of new approaches to extend capacity of cellular systems. Since radio resource sharing of conventional cellular systems is essential for D2D-comm to maximize the capacity, resource usage mode for D2D-comm should be carefully determined. In this paper, we propose a mode selection scheme which selects proper resource usage mode of each D2D pair by considering transmission power of D2D-comm user equipments (DUEs). The proposed scheme makes each D2D pair to select resource usage mode which is expected to achieve highest data rate based on its average signal-to-interference plus noise ratio (SINR) and expected amount of available radio resources. From simulations, we show that the proposed scheme can improve throughput of cellular systems with capability of D2D-comm.

Performance analysis of FlashLinQ with various yielding threshold values

Recently, Qualcomm Inc. has introduced MAC and PHY specifications, called FlashLinQ (FLQ), for device-to-device (D2D) communication. In FLQ, each D2D pair accesses to wireless medium through comparing signal to interference ratios (SIRs) and two predefined thresholds. In previous work for FLQ, only identical thresholds are considered for performance evaluation. Since performance of FLQ is mainly affected by the thresholds, they should be adjusted to optimize the network performance. In this paper, we evaluate performance of FLQ with various thresholds.

Delay-aware packet scheduling algorithm for multiple traffic classes in 3GPP LTE system

In wireless mobile environments, large bandwidth and high quality of service (QoS) are recently required to support the increased demand for multimedia services. Long term evolution (LTE) is one of the promising solutions for the next generation broadband wireless access systems. In order to support high data rate with low latency, LTE simplifies network architecture and uses orthogonal frequency division multiple access (OFDMA) for downlink transmission technology. Packet scheduling algorithm is one of the important features to support QoS in LTE system. In this paper, we propose delay-aware packet scheduling (DAPS) algorithm considering QoS requirements of delays for various traffic classes, channel conditions, and fairness. To reflect delay experience at scheduling instance, DAPS algorithm observes how queue waiting time of head-of-line (HOL) packet is closed to allowed maximum packet delay. As a result, DAPS increases the number of transmitted packets with satisfying the required delay. Comprehensive simulation results show that DAPS algorithm yields better delay performance compared with two existing PF and M-LWDF algorithms.

Radio Resource Management Scheme for Relieving Interference to MUEs in Relay-Based Cellular Networks

Relay nodes (RNs) have been recently introduced as a cost-effective solution to achieve ubiquitous high data rates in cellular networks. By providing a two-hop link between evolved nodeB (eNB) and user equipment (UE), RNs can improve the UEs signal-to-interference-plus-noise ratio (SINR) and throughput. A typical relay-based cellular network is comprised of macro UEs (MUEs) that are served directly by eNB and relay UEs (RUEs) that are served via RNs. The performance of the entire network is degraded if the interference between RNs and MUEs is not carefully managed. In this paper, we propose a radio resource management scheme that effectively exploits the advantages of RNs without causing severe interference to MUEs, which yields a better overall network and cell-edge user throughput. To improve channel quality of MUEs located nearby RNs, the proposed scheme determines a specific set of subchannels to be used by each RN. Second, the proposed scheme assigns subchannels to UEs and RNs considering channel quality, average UE data rate, and the number of required subchannels at RNs. For resource allocation, we formulate a binary integer linear programming (BILP) problem and propose a novel heuristic algorithm to reduce its computational complexity. Our simulation results show that the heuristic algorithm achieves similar performance with the BILP. In addition, we discuss a detailed procedure for control signal exchange and data transmission and analyze the lower bound of SINR gain of MUEs obtained from the proposed scheme. It has been shown that the proposed scheme improves the overall network throughput and the cell-edge user throughput compared with existing schemes.