Hyung Yun Kong

Bio: Hyung Yun Kong is an academic researcher from University of Ulsan. The author has contributed to research in topics: Relay & Rayleigh fading. The author has an hindex of 16, co-authored 164 publications receiving 974 citations.

Energy efficient cooperative LEACH protocol for wireless sensor networks

Abstract: We develop a low complexity cooperative diversity protocol for low energy adaptive clustering hierarchy (LEACH) based wireless sensor networks. A cross layer approach is used to obtain spatial diversity in the physical layer. In this paper, a simple modification in clustering algorithm of the LEACH protocol is proposed to exploit virtual multiple-input multiple-output (MIMO) based user cooperation. In lieu of selecting a single cluster-head at network layer, we proposed M cluster-heads in each cluster to obtain a diversity order of M in long distance communication. Due to the broadcast nature of wireless transmission, cluster-heads are able to receive data from sensor nodes at the same time. This fact ensures the synchronization required to implement a virtual MIMO based space time block code (STBC) in cluster-head to sink node transmission. An analytical method to evaluate the energy consumption based on BER curve is presented. Analysis and simulation results show that proposed cooperative LEACH protocol can save a huge amount of energy over LEACH protocol with same data rate, bit error rate, delay and bandwidth requirements. Moreover, this proposal can achieve higher order diversity with improved spectral efficiency compared to other virtual MIMO based protocols.

Exact outage probability of cognitive two-way relaying scheme with opportunistic relay selection under interference constraint

Abstract: In this study, the authors analyse the outage performance of a cognitive two-way relaying system under an interference constraint. In the proposed protocol, the best relay which is chosen by an opportunistic relay selection strategy, combines the received packets using XOR operation and then forwards the combined packet to two secondary sources. The authors derive an exact closed-form expression of outage probability over flat and block Rayleigh fading channels. Various Monte-Carlo simulations are presented to verify the theoretical analyses and to compare the performance of the proposed protocol with that of the two-way relaying protocol without network coding.

LLR-Based Decode-and-Forward Protocol for Relay Networks and Closed-Form BER Expressions

Abstract: Decode-and-forward cooperative communications protocol (DFP) allows single-antenna users in wireless medium to obtain the powerful benefits of multi-antenna systems without physical antenna arrays. So far, only signal-to-noise ratio (SNR) or square amplitude of path gain has been used to evaluate the reliability of received signals for relays to decide whether to forward the decoded data so as to prevent unsuccessful detection at the relays. In this paper, we propose using log-likelihood ratio (LLR) as an alternative to SNR in the conventional DFP. Closed-form BER expressions for different versions of DFP are also derived and verified by Monte-Carlo simulations. A variety of numerical results reveal the significant superiority of LLR-based DFP to SNR-based DFP regardless of threshold level and relay position under flat Rayleigh fading channel plus additive white Gaussian noise (AWGN).

Ergodic and outage capacity of interference temperature-limited cognitive radio multi-input multi-output channel

Abstract: In this study, we consider a cognitive radio multi-input multi-output (CR-MIMO) system in which the cognitive radio (CR) users are allowed to access the spectrum of the licensed primary users, provided that interference power received at the primary receiver is less than a certain threshold. The authors investigate the effect of the MIMO diversity on such multi-constraint CR-MIMO systems. They consider peak interference power constraint at the primary receiver and peak transmit power constraint at the CR transmitter. In MIMO systems, the allowable transmit power is distributed over the transmit-antennas. The power allocation problem of such CR systems is studied under both sum power and interference constraints. The authors show that the equal power allocation does not improve the ergodic capacity but improves the outage capacity over the single-input single-output (SISO) system. Transmit antenna selection (TAS) which is a special case of power allocation is also investigated. The authors show that, under the peak interference and transmit power constraint, selecting a single transmit-antenna and allocating all the power to the selected best antenna achieves the same performance as the optimal power allocation (OPA). The authors evaluate ergodic capacity and outage capacity for both power allocation- and antenna selection-based schemes. The closed-form expressions of the outage probabilities are also derived. Results show that both OPA and TAS significantly improves the capacities over the SISO system.

Cooperative communication with energy-harvesting relays under physical layer security

Abstract: In this study, the authors propose a cooperative transmission scheme with energy-harvesting (EH) relays under wiretapping of an eavesdropper. In this scheme, the relays harvest energy from radio-frequency (RF) signals of a source through power-splitting receivers, and process arrived signals by amplify-and-forward (EH-AF protocol) and decode-and-forward (EH-DF protocol) technologies. In the proposed protocols, a best relay is selected at the destination so that the end-to-end achievable secrecy rates are maximal. Exact and asymptotic secrecy outage probability expressions are used to evaluate the EH-AF and EH-DF protocols, respectively, and are confirmed by Monte Carlo simulations. The simulation results show that (i) the EH-DF protocol outperforms the EH-AF protocol, and both proposed protocols are improved when the number of cooperative relays and the distances of the relay–eavesdropper links increase and the relays move toward the destination, (ii) the secrecy performance of the EH-AF and EH-DF protocols is the best at optimal power-splitting ratios, which are obtained by the golden section search method, (iii) the energy conversion efficiency and the noise at RF-to-baseband conversion units seriously affect the proposed protocols, and finally, (iv) the theoretical analysis results fit those of the Monte Carlo simulations.

Table Of Integrals Series And Products

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Simultaneous Wireless Information and Power Transfer (SWIPT): Recent Advances and Future Challenges

Abstract: Initial efforts on wireless power transfer (WPT) have concentrated toward long-distance transmission and high power applications. Nonetheless, the lower achievable transmission efficiency and potential health concerns arising due to high power applications, have caused limitations in their further developments. Due to tremendous energy consumption growth with ever-increasing connected devices, alternative wireless information and power transfer techniques have been important not only for theoretical research but also for the operational costs saving and for the sustainable growth of wireless communications. In this regard, radio frequency energy harvesting (RF-EH) for a wireless communications system presents a new paradigm that allows wireless nodes to recharge their batteries from the RF signals instead of fixed power grids and the traditional energy sources. In this approach, the RF energy is harvested from ambient electromagnetic sources or from the sources that directionally transmit RF energy for EH purposes. Notable research activities and major advances have occurred over the last decade in this direction. Thus, this paper provides a comprehensive survey of the state-of-art techniques, based on advances and open issues presented by simultaneous wireless information and power transfer (SWIPT) and WPT assisted technologies. More specifically, in contrast to the existing works, this paper identifies and provides a detailed description of various potential emerging technologies for the fifth generation communications with SWIPT/WPT. Moreover, we provide some interesting research challenges and recommendations with the objective of stimulating future research in this emerging domain.

A Survey of Device-to-Device Communications: Research Issues and Challenges

Abstract: Device-to-Device (D2D) communication has emerged as a promising technology for optimizing spectral efficiency in future cellular networks. D2D takes advantage of the proximity of communicating devices for efficient utilization of available resources, improving data rates, reducing latency, and increasing system capacity. The research community is actively investigating the D2D paradigm to realize its full potential and enable its smooth integration into the future cellular system architecture. Existing surveys on this paradigm largely focus on interference and resource management. We review recently proposed solutions in over explored and under explored areas in D2D. These solutions include protocols, algorithms, and architectures in D2D. Furthermore, we provide new insights on open issues in these areas. Finally, we discuss potential future research directions.

Cognitive Radio: An Information-Theoretic Perspective

Abstract: Cognitive radios have been proposed as a means to implement efficient reuse of the licensed spectrum. The key feature of a cognitive radio is its ability to recognize the primary (licensed) user and adapt its communication strategy to minimize the interference that it generates. We consider a communication scenario in which the primary and the cognitive user wish to communicate to different receivers, subject to mutual interference. Modeling the cognitive radio as a transmitter with side-information about the primary transmission, we characterize the largest rate at which the cognitive radio can reliably communicate under the constraint that (i) no interference is created for the primary user, and (ii) the primary encoder-decoder pair is oblivious to the presence of the cognitive radio.

Mobility-Aware Edge Caching and Computing in Vehicle Networks: A Deep Reinforcement Learning

Abstract: This paper studies the joint communication, caching and computing design problem for achieving the operational excellence and the cost efficiency of the vehicular networks Moreover, the resource allocation policy is designed by considering the vehicle's mobility and the hard service deadline constraint These critical challenges have often been either neglected or addressed inadequately in the existing work on the vehicular networks because of their high complexity We develop a deep reinforcement learning with the multi-timescale framework to tackle these grand challenges in this paper Furthermore, we propose the mobility-aware reward estimation for the large timescale model to mitigate the complexity due to the large action space Numerical results are presented to illustrate the theoretical findings developed in the paper and to quantify the performance gains attained