Do-hyung Park

Degrees of Freedom on the K-User MIMO Interference Channel with Constant Channel Coefficients for Downlink Communications

In this paper, we study degrees of freedom for the K-User multiple-input multiple-output (MIMO)-interference channel (IFC) with constant channel coefficients. In this channel, we investigate how many total number of transmit antennas, M1 + M2 + . . . + MK, are required in minimum to achieve di = 1, ∀i degrees of freedom when all receivers have N = 2 antennas, which is a downlink communication scenario. To answer this question, we propose a new interference alignment scheme based on intersection subspace property of the vector space. The proposed interference alignment scheme can be easily generalized regardless of the number of users. In addition, we investigate degrees of freedom for the partially connected MIMOIFC where some arbitrary interfering links are disconnected due to the large path loss or deep fades. In this channel model, we examine how these disconnected links are considered on designing the beamforming vectors for interference alignment.

Design of fine phosphor system for the improvement in the luminescent properties of the phosphor layer in the plasma display panel: Theoretical and experimental analysis

Improvement in the luminescent properties of plasma display panels via phosphor size control was theoretically and experimentally investigated. From theoretical analyses of photon extraction and plasma efficiency, fine phosphor system was designed, which was compared with experimental data. The denser microstructure of finer phosphor-based layer promoted photon extraction efficiency by higher reflectivity. Also, the finer phosphor increased vacuum-ultraviolet discharge space and corresponding plasma efficiency via decrease in layer thickness. Based on the results, the phosphor size control improved the panel efficiency by the synergistic effect of improvements in photon extraction and plasma efficiency.

A study on the optimal degree-of-freedoms of cellular networks: Opportunistic interference mitigation

We introduce an opportunistic interference mitigation (OIM) protocol for cellular networks, where a user scheduling strategy is utilized in uplink K-cell environments with time-invariant channel coefficients and base stations (BSs) having M receive antennas. In the OIM scheme, each BS opportunistically selects a set of users who generate the minimum interference to the other BSs. We consider two OIM protocols according to the number S of simultaneously transmitting users per cell. Then, their performance is analyzed in terms of degrees-of-freedom (DoFs). As our main result, it is shown that KS DoFs are achievable if and only if the total number N of users in a cell scales at least as SNR(K−1)S. These results indicate that there exists a trade-off between the achievable number of DoFs and the scaling parameter N by tuning the number S of selected users. By showing an upper bound on the DoFs, it is also shown that the OIM scheme with M selected users is DoF-optimal. Finally, numerical evaluation is performed.

19.4: Luminescence Characteristics of YAl3B4O12: Tb3+ Phosphor for PDP Application

Photoluminescence(PL) characteristics under vacuum ultraviolet(VUV) region of Tb3+ doped yttrium aluminium borate phosphor were investigated for Plasma Display panel(PDP) application. The single-phase green emitting Y1−xTbxAl3B4O12(YAB: Tb3+) powder phosphors were prepared with various Tb3+ ion concentration. As a result, the intensity around 147nm of excitation spectrum in YAB: Tb3+ decrease slightly with increase of Tb3+ ion concentration due to concentration quenching behavior, but on the contrary, the intensity of 172nm increase with increase of Tb3+ ion concentration due to attributing the 4f8 4f7 5d1 transition of Tb3+ [1]. However in the result of gas discharge chamber test which has the same gas mixture as real PDP, relative PL luminance of YAB: Tb3+ increase with increase of Tb3+ ion concentration due to effect of increasing absorption at 172nm. Besides, YAB: Tb3+ with high Tb3+ ion concentration (x=0.7) has higher VUV luminance saturation property than low Tb3+ ion concentration (x=0.4) since high Tb3+ ion concentration phosphor has more activators than lower one which can react with VUV photon in unit volume.

Ad hoc indoor peer-to-peer tracking using relative location estimation

We consider an ad hoc indoor device tracking problem where a user device has no knowledge of map and infrastructure. Since it does not have any information of reference points, the user device finds relative location of its target device. In fact, relative location, which can be described by direction and distance, is sufficient for the user device to track and approach the target device. However, indoor multipath environment and a single antenna of the device are obstacles to measuring direction using direction-of-arrival (DOA). Instead, if the user or the target device is moving, then, by fusing distance measurements and sensor information, the user device can estimate direction and thus calculate the relative location of the target. We show that the relative location can be calculated by trilateration in some cases. As a flexible and adaptable method, we also employ a simultaneous localization and mapping (SLAM)-based method using a particle filter (PF).We evaluate the ad hoc device tracking in some environments by simulation.