Chung G. Kang

Mobile device-to-device (D2D) content delivery networking: A design and optimization framework

We consider a mobile content delivery network (mCDN) in which special mobile devices designated as caching servers (caching-server device: CSD) can provide mobile stations with popular contents on demand via device-to-device (D2D) communication links. On the assumption that mobile CSDs are randomly distributed by a Poisson point process (PPP), an optimization problem is formulated to determine the probability of storing the individual content in each server in a manner that minimizes the average caching failure rate. Further, we present a low-complexity search algorithm, optimum dual-solution searching algorithm (ODSA), for solving this optimization problem. We demonstrate that the proposed ODSA takes fewer iterations, on the order of O (log N) searches, for caching N contents in the system to find the optimal solution, as compared to the number of iterations in the conventional subgradient method, with an acceptable accuracy in practice. Furthermore, we identify the important characteristics of the optimal caching policies in the mobile environment that would serve as a useful aid in designing the mCDN.

Scheduling for virtual MIMO in Single Carrier FDMA (SC-FDMA) system

In this paper, we consider a joint frequency-domain scheduling and user-pairing problem for virtual MIMO in the single carrier frequency division multiple access (SC-FDMA) system, e.g., the uplink transmission for third generation partnership project-long term evolution (3GPP-LTE) standard. Due to the sub-carrier adjacency constraint inherent to SC-FDMA, its complexity becomes unmanageable. We propose a greedy heuristic algorithm for PF scheduling so as to deal with the complexity issue in this joint problem. It has been shown that its performance can reach up to 90% of its upper bound.

Interference mitigation and D2D parameter estimation for distributed‐control D2D underlay systems

Although centralised-control schemes for device-to-device (D2D) underlay communications can produce satisfactory results by efficiently managing the interference between cellular and D2D transmissions, they can become prohibitively complicated and may require a large amount of feedbacks from devices, because it is important to handle the inter-cell interference as well as the intra-cell interference. Such a burden can be alleviated by a distributed-control mechanism, in which a base station performs the resource management of its cellular devices and each D2D device selects its own resource without a small-scale control of the cellular network. This paper addresses interference issues in distributed-control D2D underlay systems and presents an interference mitigation technique based on frequency spreading, in order to meet the target outage probability. This paper also proposes a simple estimation scheme, which can be used for the mode selection and the determination of D2D transmission parameters. Copyright

Reconfigurable Wireless Power Transfer System for Multiple Receivers

We present a novel schematic using a 3-dB coupler to transmit radiofrequency (RF) power to two receivers selectively. Whereas previous multiple receiver supporting schemes used hardware-switched methods, our scheme uses a soft power-allocating method, which has the advantage of variable power allocation in real time to each receiver. Using our scheme, we can split the charging area and focus the RF power on the targeted areas. We present our soft power-allocating method in three main points. First, we propose a new power distribution hardware structure using a FPGA (field-programmable gate array) and a 3-dB coupler. It can reconfigure the transmitting power to two receivers selectively using accurate FPGA-controlled signals with the aid of software. Second, we propose a power control method in our platform. We can variably control the total power of transmitter using the DC bias of the drain input of the amplifier. Third, we provide the possibility of expansion in multiple systems by extending these two wireless power transfer systems. We believe that this method is a new approach to controlling power amplifier output softly to support multiple receivers.

Scalable Video Coding-based MIMO Broadcasting System With Optimal Power Control

This paper presents a scalable video coding (SVC)-based open-loop multi-input multioutput (MIMO) scheme for broadcast services such as LTE broadcast/evolved multimedia broadcast multicast service and terrestrial broadcast TV/ATSC 3.0. It intends to guarantee the minimum essential information (as a base layer) and obtain additional information for improving the video quality (as enhancement layers) when multiple transmit and receive antennas are employed. Two types of SVC-based open-loop MIMO broadcasting schemes are considered: 1) SVC-MIMO-time division multiplexing (TDM) and 2) SVC-MIMO-spatial multiplexing (SM). They provide differentiated video quality that depends on the average channel gain of individual users by employing different modulation and coding scheme (MCS) levels for unequal error protection of individual layers, i.e., a lower MCS level for the base layer and a higher MCS level for the enhancement layers. In particular, SVC-MIMO-SM extends the per-layer service coverage by performing a block-wise successive interference cancellation (SIC) from the base layer up to the highest enhancement layer in the receiver. As a result, the base layer can be decoded with the most robust MCS while the enhancement layers can be decoded with an SIC diversity gain. Furthermore, we formulate an optimal power allocation problem for the SVC-MIMO-SM scheme that can maximize the average system utility function while ensuring the target service coverage. Optimal solutions for different cases are derived by identifying the Karush–Kuhn–Tucker conditions for the given problem. Our numerical results demonstrate that the optimal power allocation provides more average system utility gain than SVC-MIMO-TDM and SVC-MIMO-SM without power control schemes, indicating the enhancement in the per-layer service coverage performance.

Scheduling for virtual MIMO in single carrier FDMA (SC-FDMA) system

In this paper, we consider a joint frequency-domain scheduling and user-pairing problem for virtual MIMO in the single carrier frequency division multiple access (SC-FDMA) system, e.g., the uplink transmission for third generation partnership project-long term evolution (3GPP-LTE) standard. Due to the sub-carrier adjacency constraint inherent to SC-FDMA, its complexity becomes unmanageable. We propose a greedy heuristic algorithm for PF scheduling so as to deal with the complexity issue in this joint problem. It has been shown that its performance can reach up to 90% of its upper bound.

Optimization Framework and Parameter Determination for Proximity-Based Device Discovery in D2D Communication Systems

One of the most important processes in device-to-device communications of cellular devices is that of discovery, which determines the proximity of devices. When a discovery process is performed, there are several parameters to determine, including the discovery range, the discovery period, and the modulation and coding scheme of the discovery messages. In this paper, we address the relationships between these parameters and describe an optimization framework to determine them. In the proposed procedure, it is important to first optimize the discovery rate, which is defined as the number of discoverable devices per unit time. Once the discovery rate is maximized, the discovery period can be determined accordingly based on the device density and the target discovery range. Since the discovery rate is not affected by many of discovery parameters such as the discovery range, the device density, and the discovery period, it can be used as a performance metric for comparing discovery schemes with different discovery ranges or different discovery periods.

Modulation Scheme for Network-coded Bi-directional Relaying over an Asymmetric Channel

In this paper, we propose a modulation scheme for a network-coded bi-directional relaying (NBR) system over an asymmetric channel, which means that the qualities of the relay channel (the link between the BS and RS) and access channel (the link between the RS and MS) are not identical. The proposed scheme employs a dual constellation in such a way that the RS broadcasts the network-coded symbols modulated by two different constellations to the MS and BS over two consecutive transmission intervals. We derive an upper bound on the average bit error rate (BER) of the proposed scheme, and compare it with the hybrid constellation-based modulation scheme proposed for the asymmetric bi-directional link. Furthermore, we investigate the channel utilization of the existing bi-directional relaying schemes as well as the NBR system with the proposed dual constellation diversity-based modulation (DCD). From our simulation results, we show that the DCD gives better average BER performance about 3.5~4dB when is equal to , while maintaining the same spectral efficiency as the existing NBR schemes over the asymmetric bi-directional relaying channel.

Scheduling scheme of packet length-based group-wise transmission for integrated voice/data service in burst-switching DS/CDMA system

This paper proposes a new packet rate scheduling scheme for a non-real time data service over the uplink of a burst switching-based direct sequence code division multiple access (DS/CDMA) system to support the integrated voice/data service. We consider the most general form of optimization problem formulation to determine the optimal number of transmission-time groups along with their data rates, which minimize the average packet transmission delay. An ordered packet length-based group-wise transmission (OLGT) scheme is proposed as a simple heuristic solution approach to this problem and present some analytical results for performance comparison with other possible schemes.

System level simulation for 5G cellular communication systems

In 5G cellular communication systems, a new type of simulation methodology may be required due to the emergence of new services and applications, new environments and requirements, new performance indicators, and increased need for accurate end-to-end performance measurements of systems including wired and wireless sections. In this paper, we address the characteristics of 5G simulations compared with 4G simulations especially focusing on system level simulation. Considering the characteristics of 5G simulations, the requirements for 5G simulators can be derived. In order to fulfill the requirements, a system level simulator is currently being developed and some selected features of the simulator are presented.