Chung G. Kang

Korea University | KU · Department of Electrical Engineering

Enhanced licensed-assisted access (eLAA) is an operational mode that allows the use of unlicensed band to support long-term evolution (LTE) service via carrier aggregation technology. The extension of additional bandwidth is beneficial to meet the demands of the growing mobile traffic. In the uplink eLAA, which is prone to unexpected interference f...

In "Licensed-Assisted Access using LTE (LAA)" standard, carrier sensing via Listen-Before-Talk (LBT) procedure is a vital feature for fair sharing with the Wi-Fi systems. Furthermore, it has been designed to support frequency reuse-1 operation among all cells by the virtue of licensed spectrum. As opposed to the two existing channel access schemes...

A fundamental performance trade-off of multicell multiuser multiple-input multiple-output (MU-MIMO) systems is explored for achieving intercell and intracell interference-free conditions. In particular, we analyze the three-dimensional diversity-multiplexing-nulling trade-off (DMNT) among the diversity order (i.e., the slope of the error performanc...

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 sche...

In multiple measurement vectors (MMV) problems, the sparsity structure, i.e., the support of the measurement vectors, remains constant for multiple instants. For machine type communication (MTC) context, this sparsity structure may remain constant over all symbols in a frame, which can be termed as frame-wise sparsity. Instead of employing symbol-b...

This paper presents a compressive sensing (CS)-based one-shot random access (RA) scheme for massive and delay-intolerant machine-type communication (MTC). Furthermore, an iterative order recursive least square (IORLS)-based orthogonal matching pursuit (OMP) decoding algorithm is employed for high accuracy and low decoding complexity. By employing I...

In this paper, the system-level performance is evaluated for the feedback scheme on the pre-coding matrix index (PMI) and channel quality indication (CQI), which are required for user selection in the multi-user MIMO system. Our analysis demonstrates that the number of users, the number of selected users, and codebook size are the key factors that...

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 messa...

This paper proposes a distributed coordination framework with opportunistic scheduling among multiple users as opposed to the existing works on the multiple-cell cooperative beamforming problem that deals with a single active user in each cell. In this cross-layer design framework that deals with the beamforming in the physical layer and multiuser...

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...

While maintaining a quality of cellular link subject to underlay device-to-device (D2D) communication in the cellular system, it obvious that a performance of proximity-based service over D2D link would be varying with the location of its transmitter. We consider an open-loop fractional power control for the uplink cellular link while limiting the...

Heterogeneous network (HetNet) with the various types of cells, e.g., with the different cell size and transmit power, has been introduced to improve the cell coverage and areal capacity in cellular mobile communication system. In this paper, we consider a practical situation in which all cells share the same wireless resource while some of them ha...

Since mobile traffic has been increased tremendously due to popularization of high-end mobile devices, many mobile carriers and smartphone manufacturers have put their best effort on solving the capacity problem. Small cell is introduced as an idea for the solution, and various mobile carriers have installed small cells to provide more bandwidth to...

For interference alignment (IA) with no channel extension, determining the existence of IA solution for general system parameters is still an open problem. This same problem also exists in interference alignment and cancellation (IAC), which combines IA with interference cancellation in the receivers, involving a new receiver architecture associate...

This paper deals with a cross-layer design that combines link adaptation in the physical layer with random network coding for layered video multicasting in a cellular system. The objective is to design the optimum signal-to-noise ratio (SNR) threshold for adaptive modulation and coding (AMC) that can satisfy the target frame loss rate (FLS) under a...

By investigating the technical issues in the existing cell selection and scheduling scheme under some of carrier aggregation (CA) deployment scenarios discussed in LTE-Advanced system, we propose a distributed inter-cell cooperation scheme for joint scheduling that can improve the average system throughput when 6 different sectors are formed by dep...

This paper proposes a distributed coordination framework with opportunistic scheduling among the multiple users as opposed to the existing works on the multi-cell cooperative beamforming problem subject to a single active user in each cell. This framework deals with the best throughput trade-off between throughput gain by interference nulling, and...

One of the important processes in device-to-device communication is the discovery of proximate devices. In order to perform precise discovery of devices, the distance information among all the device pairs should be gathered by each device sending a discovery signal in turn and the other devices receiving the signal. However, periodic discovery sig...

Stochastic geometry analysis has been adopted to compute the analytical system performance under a scenario of dense relay station deployment for the relay-enhanced cellular network. Our numerical results show that the system throughput can be consistently increased with the larger number of relay stations, especially when the radio resource is pro...

In this paper, we consider an interference-limited dual-hop relay system, in which the overall system performance is governed not by an additive white Gaussian noise (AWGN), but by co-channel interference (CCI), due to aggressive frequency reuse for high spectrum utilization. We consider that the received signal-to-interference power ratio (SIR) at...

Coordination of the multiple base stations by user and beam scheduling can be considered as a promising means of mitigating the inter-cell interference in future cellular networks. Due to the complexity of joint user and beam scheduling problem, its optimal performance has never been revealed yet. In this paper, we investigate its sub-optimal perfo...

We consider a ship ad-hoc network (SANET) that extends the service coverage for data communication with the multi-hop connectivity among the ships. In this paper, we propose two means of transmission rate control to maximize the system throughput subject to the reservation-based random access that is is inherent to the ad-hoc self-organizing TDMA (...

We consider the device-to-device (D2D) communication underlaying multi-cell interference system, in which the cellular downlink (DL) resource is reused by K cells and two D2D transmission links within each cell. In this paper, we propose an interference alignment (IA) scheme that can effectively reduce both the inter-cell interference and intra-cel...

In this letter, a Scalable Transmission Control (STC) scheme is proposed as a new framework of radio resource allocation when Scalable Video Coding (SVC) is used for the Enhanced Multicast & Broadcast Service (E-MBS) in Mobile WiMAX network. We present a marginal utility-based suboptimal solution to the STC problem and demonstrate that the overall...

In this paper, we present a resource management framework for scalable transmission control, which optimizes resource allocation for scalable video coding (SVC)-based mobile IPTV service. In particular, it includes a scenario without any bandwidth constraint, in which total resource consumption for mobile IPTV service must be minimized so as to sup...

Two different mechanisms affecting the device instability and mobility degradation at graphene MOSFET on SiO2 substrate and their time constant, 40μsec and ~ 370μsec, have been identified. Oxygen/H2O reaction at the surface of graphene was identified as a major source of device hysteresis causing mobility degradation and device instability.

The feasibility condition for interference alignment (IA) with no channel extension has not been known yet. In this paper, for the first time, we explore the feasibility of interference alignment and cancellation (IAC) which has been proposed for IA with no channel extension. We investigate IAC for the Gaussian interference multiple access channel...

Characteristics of new reconfigurable graphene device with Metal/ Ferroelectric (PVDF-TrFE)/Graphene (MFG) stack is presented. Key features include programming speed

The Jianghan plain is the first large-scale offloading basin of the Yangtze River after the formation of the Three Gorges. Its sediment deposits should reflect that the Yangtze River used to flow through. Ti-augite, a characteristic rock of Panxi area, where the formational conditions is unique in the Yangtze River basin, can be used as a tracing m...

In this paper, we propose a scalable transmission control (STC) scheme as a new framework of radio resource allocation for mobile IPTV service, especially when scalable video coding (SVC) is used for all programs channels in Mobile WiMAX network. We present a suboptimal solution to the STC problem and demonstrate that the overall service coverage c...

This letter proposes a new retransmission structure with multiple retransmission codebooks for a linear precoding-based closed-loop multiple-input multiple-output (CL-MIMO) system. While conventional codebooks are defined only for the initial transmission in CL-MIMO systems, we propose a multiple codebook structure in which a different codebook is...

As various types of wireless systems are characterized by its own individual reliability and transmission cost in the multi-band maritime communication network, a means of selecting a least-cost system is required for transmitting the shipment information within a pre-specified time constraint. In this paper, a simple decision criterion for a least...

In this paper, we consider a cooperative beam-forming problem for MISO interference networks, modeling the downlink capacity that is significantly limited by inter-cell interference (ICI). It is yet a critical issue to improve the performance of cell-edge users who suffer from strong ICI. We propose a cooperative beamforming scheme that combines re...

Quaternary eolian deposits largely distribute in the Harbin area. The dust has been proved to be composed of dust carried by wind. The samples were taken from the representative local loess deposit,fluvial sediments at the Songhua River drainage, Horqin Sandy Land and the loess deposits at Changchun and Songyuan. Heavy mineral analysis was carried...

This letter provides a tight upper bound on the bit error rate (BER) over the Nakagami-m fading channel for the dual carrier modulation (DCM) scheme, which is adopted by the multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) system. Its tightness is verified with the existing result for Rayleigh fading channel, i.e...

In this paper, we consider the BER analysis of constellation rearrangement (CoRe), which is not subject to the Gray-encoding constraint for the first transmission. This type of CoRe can be applied in a parallel transmission system such as cooperative relay networks. Furthermore, it allows us to construct the accumulate constellation, which obtained...

We provide a BER analysis of the well-known rotation code, which has been applied to various transmission schemes, such as coordinate-interleaved design (CID) for space-time block codes and trans-modulation or constellation rearrangement for a cooperative relay system. An upper bound on the BER of the rotation code under a fading channel is derived...

In this paper, we analyze the outage performance of relay-enhanced cellular systems in an interference-limited environment, where the co-channel interference (CCI) is a crucial factor that governs the overall system performance as compared to an AWGN (additive white Gaussian noise). Furthermore, the relay station and destination are subject to the...

Graphene and its derivatives (graphite, CNT) have very high conductivity and critical current density higher than 108 A/cm2, which can be utilized in interconnect applications. Theoretically, a doped graphene is predicted to have better performance than Cu as an interconnect conductor. However, the feasibility of graphene interconnect has not been...

Seamless vertical handover is a key requirement in heterogeneous wireless networks where different networks are integrated. In this paper, we introduce an enhanced information server (EIS) to accelerate vertical handover procedures in IEEE 802.21 media independent handover (MIH) networks. Based on the EIS, we propose an improved vertical handover p...

In this paper, we consider a dual carrier modulation (DCM) which is employed in multi-band orthogonal frequency multiplexing (OFDM) ultra wide-band (UWB) system. DCM transforms two QPSK symbols to two 16-QAM symbols with different bit-to-symbol mappings. We find that the basic idea of DCM is the same as that of the rotation code. More specifically,...

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...

Various types of cooperative relaying (CR) schemes exhibit different levels of throughput and outage performance because of their inherent trade-off between diversity gain and opportunity cost; in other words, the overhead that is associated with cooperation. This article attempts to answer whether cooperative communication is beneficial or not fro...

Orthogonal frequency division multiplexing (OFDM) transmission scheme is a type of a multichannel system, which is similar to the Filtered Multi-Tone (FMT) transmission scheme in the sense that it employs multiple subcarriers. OFDM scheme places a guard band at outer subcarriers, called virtual carriers (VCs), around the frequency band to reduce th...

The cellular CDMA system is virtually interference-free due to its interference-averaging capability with a wide spreading bandwidth. As long as its spreading factor is sufficiently large, the cellular CDMA system can be robust against co-channel interference, even when the same frequency channels are assigned to all neighbor cell sites, that is, f...

This chapter addresses signal detection techniques for spatially multiplexed (SM) MIMO systems. It first discusses hard-decision detection techniques such as linear signal detection, ordered successive interference cancellation (OSIC) signal detection, maximum likelihood (ML) signal detection, sphere decoding (SD) method, QRM-MLD Method, and lattic...

This chapter addresses transmission techniques that exploit the channel state information (CSI) on the transmitter side. The CSI can be completely or partially known on the transmitter side. Sometimes, only statistical information on the channel state may be available. Exploitation of such channel information allows for increasing the channel capac...

This chapter deals with the channel models for the single-input and single-output (SISO) system that employs a single transmit antenna and a single receive antenna in the different environments. The short-term fading SISO channel models are considered for two different channel environments: indoor and outdoor channels. The chapter discusses the use...

In an OFDM system, the transmitter modulates the message bit sequence into PSK/QAM symbols, performs IFFT on the symbols to convert them into time-domain signals, and sends them out through a (wireless) channel. In general, the channel can be estimated by using a preamble or pilot symbols known to both transmitter and receiver, which employ various...

This chapter focuses on the space-time coding (STC) techniques that are used for achieving the antenna diversity gain. It provides a mathematical description of space-time coded systems. Based on the mathematical model, a pairwise error probability is derived. A space-time code design criterion is described by using a pairwise error probability. Th...

Compared to a conventional single antenna system, the channel capacity of a multiple antenna system with NT transmit and NR receive antennas can be increased by the factor of min (NT , NR), without using additional transmit power or spectral bandwidth. Multiple antenna techniques can be broadly classified into two categories: diversity techniques a...

In the multi-user communication system, multiple antennas allow the independent users to transmit their own data stream in the uplink (many-to-one) at the same time or the base station to transmit the multiple user data streams to be decoded by each user in the downlink (one-to-many). This is attributed to the increase in degrees of freedom with mu...

This chapter first presents an overview of a statistical channel model for MIMO system. Then, it describes a correlation-based I-METRA channel model and a ray-based 3GPP spatial channel model (SCM) as specific methods of implementing the MIMO channel. While the correlation-based channel model can be implemented with a spatial correlation matrix for...

This chapter analyzes the effects of symbol time offset (STO) and carrier frequency offset (CFO), and then discusses the synchronization techniques to handle the potential STO and CFO problems in OFDM systems. Like STO estimation, CFO estimation can also be performed either in the time or the frequency domain. The chapter investigates the effect of...

In this paper, we consider the relay station (RS) selection schemes for an orthogonal amplify-and-forward relaying system with half-duplexing in a multi-cell environment. The selection schemes are to to maximize the instantaneous received SINR either when the channel gains for the other cells are fully known or not. We propose a sub-optimal RS sele...

It has been known that adaptive modulation and coding (AMC) at the physical layer can be combined with a truncated automatic repeat request (ARQ) at the data link layer so as to maximize the spectral efficiency under prescribed delay and error performance constraint. In this paper, we consider the same joint design approach when incremental redunda...

The gravel bed in Yichang is more than 100m thick and composed of 22 layers. It lies over Cretaceous red bed and covered with Middle Pleistocene plinthitic red earth. The authors analyzed the sedimentary facies of the gravel bed. The upper and middle fan subfacies of alluvial fan exist in Shanxiyao and Yunchi profiles from the bottom upward. There...

In this paper, we consider an optimal topology control problem that dynamically configures the path and capacity under the varying traffic load for constructing a multihop backbone network in the TDD-OFDMA system. In order to deal with the co-channel interference among the different relay stations, K orthogonal subzones of OFDMA data regions are sp...

This paper considers a design of signal constellations for trans-modulation (constellation rearrangement: CoRe) in a relay system with the multiple links in which the same signal is decoded-and-forwarded to the destination over N time slots, each assigned to the different relay node. Demonstrating that the minimal accumulated squared Euclidean dist...

A multihop relay (MR) and repeater are useful means for improving system throughput and coverage in a cellular mobile packet access system, as the carrier-to-interference ratio can be improved when deploying them in a heavily shadowed region. In this paper, we report on our investigation of bandwidth efficiency and the associated service outage per...

Seamless vertical handover is a key requirement in heterogeneous wireless networks where different networks are integrated. In this paper, we introduce an enhanced information server (EIS) in the IEEE 802.21 media independent handover (MIH) architecture. We also propose an improved vertical handover procedure in which the wireless channel condition...

In this paper, we consider a modulation scheme for a network-coded bi-directional relaying (CBR) scheme in which two different signals from mutually communicating nodes are network-coded in the relay node. It employs dual constellations as a useful means of dealing with its performance degradation in the CBR over asymmetric channel (i.e., the diffe...

In this paper, we evaluate the system-level performance of MIMO-based Mobile WiMAX system, a.k.a. Wave-2 system, especially taking the spatially correlated channel characteristics and channel estimation error into account in the different radio environments and propagation scenarios. Our simulation framework carefully follows the standard evaluatio...

This letter proposes a type of mutually cooperative relaying (MCR) scheme based on a spatially coordinate-interleaved orthogonal design (SCID), in which two cooperative users are spatially multiplexed without bandwidth expansion. It provides not only diversity gain (with order of two) as in the existing MCR scheme, but also additional coding gain....

While the conventional codebook is defined only for the initial transmission in the closed-loop MIMO system, this paper proposes a new retransmission structure with a sequence of multiple codebooks, rather than using a single identical codebook for every retransmission. The pre-coding matrices, in each codebook, are sequentially linked so that each...

In broadband wireless OFDMA systems where a set of subcarriers is shared among multiple users, the overall system throughput can be improved by a band AMC mode that selects subbands preferential to individual users. As long as channel qualities for the subbands of all users are known a priori, multiuser and frequency diversity gains can be simultan...

While the conventional codebook is defined only for the initial transmission in the closed-loop MIMO system, this paper proposes a new retransmission structure with a sequence of multiple codebooks, rather than using a single identical codebook for every retransmission. The pre-coding matrices in each codebook are sequentially linked so that each o...

In this paper, we present a packet scheduling algorithm for a non-real-time service, with soft QoS requirements, which allows for degrading the QoS level, e.g., typically the packet delay, whenever necessary, in mobile broadband wireless Internet access systems. This algorithm is designed to properly trade off system throughput and delay performanc...

In this letter, we propose a generalized version of the window-based pseudonoise (PN) acquisition scheme verifying one or more best hypotheses rather than the best one per search window. The false alarm probability, detection probability, and mean acquisition time (MAT) of the proposed scheme are derived by using the well-known flow graph approach...

Depending on the position of mobile stations in the multi-hop relay system, various types of cooperative relaying schemes show the different level of throughput and outage performance, due to their inherent trade-off between diversity gain and overhead associated with individual cooperation scheme. In order to improve both throughput and outage per...

In this paper, we evaluate the performance of OFDMA/TDD-based broadband mobile internet access system with the features of adaptive modulation & coding (AMC) and hybrid ARQ. We present a framework of system-level simulation and furthermore, intend to derive the insightful results towards understanding the performance of broadband mobile internet ac...