Neung-Hyung Lee

Virtual extension of cell IDs in a femtocell environment

In this paper, we solve a cell identification problem in a femtocell environment. In the densely deployed area, the number of Physical Cell Identifiers (PCIs) for femtocells may not be sufficient. The scarcity of PCIs results in identification ambiguity due to duplicated PCIs in a certain area, which may result in handover failure. Using time synchronization between femtocells and macro cells, we propose a scheme to efficiently identify cells in a femtocell environment. Our scheme can increase the number of cell identifiers up to 1024 times using even coarse local time synchronization, without changing the existing physical layer specification. Since time synchronization occurs locally, we can apply the proposed scheme to asynchronous as well as synchronous wireless systems. We verify the proposed scheme via simulations.

Uplink QoS Scheduling for LTE System

In this paper, we propose a QoS uplink scheduling algorithm for LTE collaborating with delay estimation. Unlike downlink scheduling, uplink scheduling cannot incorporate packet delay information due to specification constraints of LTE. The limited information results in difficulty ensuring a QoS when conventional scheduling algorithms are employed. Using a delay estimation tailored to LTE, we have shown that the uplink performance of the proposed QoS scheduling scheme can be improved more than 11% even with a simple estimation via simulations.

Cell ID extension in femtocell environments

In this paper, we solve a cell identification problem in a femtocell environment. Wireless communication standards specify physical cell identifiers (PCIs) for user entities (UEs) to discriminate data from different cells and for networks to identify cells. However, in the densely deployed area, the number of PCIs for femtocells may not be sufficient. The scarcity of PCIs results in identification ambiguity due to duplicated PCIs in a certain area, which may result in handover failure. Using time synchronization between femtocells and macro-cells, we propose a scheme to efficiently identify cells in a femtocell environment. The proposed scheme defines the virtual cell identifier (vID) of a femtocell as the system frame number offset of the femtocell with respect to a macro-cell and differentiates femtocells with combinations of vIDs and PCIs. Our scheme can increase the number of cell identifiers up to 1024 times using even coarse local time synchronization without changing the existing physical layer specification. The improvement in cell identification resolution reduces redundant message transactions, resulting in network performance enhancement. Since our scheme demands only local time synchronization between adjacent cells, it can be applied to asynchronous as well as synchronous wireless systems. We verify the proposed scheme via simulations in various environments.

Extended proportional fair scheduling for statistical QoS guarantee in wireless networks

Opportunistic scheduling provides the capability of resource management in wireless networks by taking advantage of multiuser diversity and by allowing delay variation in delivering data packets. It generally aims to maximize system throughput or guarantee fairness and quality of service (QoS) requirements. In this paper, we develop an extended proportional fair (PF) scheduling policy that can statistically guarantee three kinds of QoS. The scheduling policy is derived by solving the optimization problems in an ideal system according to QoS constraints. We prove that the practical version of the scheduling policy is optimal in opportunistic scheduling systems. As each scheduling policy has some parameters, we also consider practical parameter adaptation algorithms that require low implementation complexity and show their convergences mathematically. Through simulations, we confirm that our proposed schedulers show good fairness performance in addition to guaranteeing each users QoS requirements.

Mobility-aware time delay compensation algorithm for mobile OFDM systems

Fourth generation mobile telecommunication systems adopt Orthogonal Frequency Division Multiplexing (OFDM) to promise wideband wireless services. However, the OFDM system intrinsically needs a mechanism to compensate transmission delay due to different distance from MS to BS, referred to as ranging. In this paper, we propose an efficient periodic ranging algorithm with adaptive period. The algorithm varies the ranging period based on the estimated MS velocity. Simulation results show that the proposed algorithm even with coarse mobility estimation outperforms fixed periodic ranging.