Ju-Yeop Kim

Design and implementation of a simulator based on a cross-layer protocol between MAC and PHY layers in a WiBro Compatible.IEEE 802.16e OFDMA system

In this article we propose cross-layer design frameworks for 802.16e OFDMA systems that are compatible with WiBro based on various kinds of cross-layer protocols for performance improvement: a cross-layer adaptation framework and a design example of primitives for cross-layer operation between its MAC and PHY layers. In addition, we provide a simulation framework for cross-layer analysis between the MAC and PHY layers in 802.16e systems. Through this cross-layer simulator, we show that average cell throughput can be improved by 25-60 percent by applying careful cross-layer adaptation schemes.

A Joint Power and Subchannel Allocation Scheme Maximizing System Capacity in Indoor Dense Mobile Communication Systems

Indoor mobile communication systems (or simply indoor systems) are expected to yield significant improvement of capacity and coverage at low cost on mobile communication systems. However, the indoor system will likely be in dense environments, in which many cells exist in a small region, and a great portion of the coverage of a cell is overlapped by that of other cells. In dense environments, the systems are exposed to strong intercell interference, which is critical to system performance and should be mitigated by a novel radio resource management (RRM) scheme. In this paper, we first derive the characteristics of an optimal allocation of power and subchannel in dense environments. We prove that a special form of power allocation, which is called binary power allocation, in which only one transmitter transmits a signal for each subchannel, performs better than power allocation by conventional schemes. Then, we propose an efficient scheme for jointly allocating power and a subchannel based on the binary power allocation. Simulation and numerical results show that the proposed scheme can achieve larger system capacity than conventional schemes.

Enhanced adaptive modulation and coding schemes based on multiple channel reportings for wireless multicast systems

This paper shows various schemes to change Mod- ulation and Coding Schemes(MCS) adaptively for multicasting. Applying Adaptive Modulation and Coding(AMC) scheme to multicasting will show better performance in view of spectrum efficiency aspect than fixing MCS level. Since there exist mul- tiple receivers for a data in multicasting, there is much more difficulty in determining the overall MCS level which satisfies all the receivers. Based on the channel quality information of the receivers, the source can determine the overall MCS level by three schemes; minimum MCS algorithm, average MCS algorithm, and weighted average MCS algorithm. Here, a tradeoff between spectrum efficiency and robustness exists: minimum MCS algorithm chooses robustness that guarantees low error rate to all the receivers, while average MCS algorithm chooses spectrum efficiency to improve throughput performance. A compromise between spectrum efficiency and robustness can be made by introducing weights to averaging MCS. Depending on the parameters related to the weights, more robustness or spec- trum efficiency can be achieved. This paper presents numerical analysis showing the performance of the proposed schemes and a conventional scheme. Also simulation is presented to verify the numerical analysis results and shows the performance of weighted MCS algorithm.

Resource Allocation Scheme for Minimizing Power Consumption in OFDM Multicast Systems

This letter introduces a resource allocation scheme in orthogonal frequency division multiplexing(OFDM) multicast systems which focuses on minimizing power consumption. By allocating the resource optimally, the number of OFDM symbols that each mobile station(MS) receives can be minimized, resulting in the reduced power consumption of MSs. A heuristic algorithm for allocating resources suboptimally with low complexity is also proposed, and is shown to achieve almost optimal performance.

A joint power and subchannel allocation scheme maximizing system capacity in dense femtocell downlink systems

Femtocell system is expected to bring significant improvement of system performance with low cost. However, when a number of femto BSs are installed by users without cell-planning, the femtocell system will be in dense environment, in which many femto co-cells exist in a small region and a great portion of the femto cell is overlapped by other femto cells. Femtocell system in dense environment is exposed to strong inter-cell interference problem which is critical to system capacity. In this paper, we derive a joint power and subchannel allocation scheme in dense environment. The simulation and numerical results show that our proposed scheme simply finds a better solution compared to the conventional scheme in dense environment.

Degrees of Freedom of Millimeter Wave Full-Duplex Systems With Partial CSIT

The degrees of freedom (DoF) of L-path poor scattering full-duplex (FD) systems is studied in which a FD base station having M transmit antennas and M receive antennas supports a set of half-duplex mobile stations (MSs). Assuming no self-interference, a hybrid scheduling is proposed achieving the optimal sum DoF with partial channel state information at the transmitter side as the number of MSs increases. In particular, the proposed scheme combines a zero-forcing beamforming for uplink and a random transmit beamforming for downlink with opportunistic scheduling. It is shown that the optimal sum DoF of 2M is asymptotically achievable as long as the number of MSs scales faster than snrmin(M-1,L)+M, where snr denotes the signal-to-noise ratio.

New D2D Peer Discovery Scheme Based on Spatial Correlation of Wireless Channel

Due to the increasing popularity of device-to-device (D2D) services, it is becoming increasingly important to find efficient means of identifying nearby users, i.e., by peer discovery. Herein, we propose a low-power peer discovery scheme, in which we exploit the tradeoff between the power consumption and the accuracy/scope of peer discovery. In our proposed scheme, the transmission of a proximity beacon is scheduled based on channel values, such that users in close proximity are likely to transmit beacons at similar time instants due to the spatially correlated wireless channel. As a result, users can find nearby peers accurately with a lower power consumption by shortening the reception period for the beacons. The performance of the proposed scheme, in terms of accuracy and power consumption, is derived. By means of simulation results, we show that nearby users can be found with lower power consumption than in conventional schemes, while achieving a high accuracy of peer discovery.

Size-dependent structural evolution of the biomineralized iron-core nanoparticles in ferritins

The structural identity of the biomineralized iron core nanoparticles in Helicobacter pylori ferritins (Hpfs) has been determined by employing soft x-ray absorption spectroscopy and soft x-ray magnetic circular dichroism. Valence states of Fe ions are nearly trivalent in all Hpfs, indicating that the amount of magnetite (Fe3O4) is negligible. With increasing filling of Fe ions, the local configurations of Fe3+ ions change from the mixture of the tetrahedral and octahedral symmetries to the octahedral symmetry. These results demonstrate that the biomineralization of the ferritin core changes from maghemite-like (γ-Fe2O3) formation to hematite-like (α-Fe2O3) formation with increasing Fe content.

Resource Allocation Scheme for Minimizing Power Consumption in OFDMA Systems

This paper proposes novel resource allocation schemes which minimize power consumption of Mobile Stations(MSs) in Orthogonal Frequency Division Multiple Access(OFDMA) systems. The conventional resource allocation schemes focus on maximizing throughput or mitigating inter cell interference. The proposed schemes allocate resource units assembled in an OFDM symbol to each MS for minimizing the total number of Orthogonal Frequency Division Multiplexing(OFDM) symbols that MSs receive. As a result, MSs can decode their own data with consuming less power for processing OFDM symbols. This paper introduces two schemes : Optimization Approached Scheme and Heuristic Approached Scheme. The simulation results in this paper show that the proposed schemes can contribute to reduce the power consumption of MSs and Heuristic Approached Scheme is more practical than Optimization Approached Scheme in view of computational time.

OFDM Resource Allocation Scheme for Minimizing Power Consumption in Multicast Systems

This paper introduces a resource allocation strategy which focuses on minimizing power consumption in orthogonal frequency division multiplexing (OFDM) systems. In case of multicasting systems, it is appropriate to allocate resource with power saving strategy, since the effect of frequency selective channel is ignorable. By this strategy, the number of OFDM symbols MSs receive is minimized. A great amount of power can be saved, because the radio frequency and baseband processes are the dominant factors of power consumption. This paper also proposes a heuristic algorithm for finding the suboptimal solution of resource allocation with low complexity. By this algorithm, resource allocation process requires O(n3) computations with little performance degradation. The numerical analysis and simulation results show that the performance of this algorithm is close to the optimum.