Incremental Relaying for Cooperative Relaying Systems with NOMA

Hongwu Liu,Kyung Sup Kwak 한국통신학회 2018 한국통신학회 학술대회논문집 Vol.2018 No.1

Decode-and-Forward Relaying for Cooperative NOMA Systems With Direct Links

Liu, Hongwu,Ding, Zhiguo,Kim, Kyeong Jin,Kwak, Kyung Sup,Poor, H. Vincent IEEE 2018 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.17 No.12

<P>This paper investigates a cooperative non-orthogonal multiple access system, in which a base station communicates with two far users with the aid of a decode-and-forward (DF) relay. Three cooperative relaying schemes, namely, the fixed relaying (FR), the selective DF with coordinated direct and relay transmission (SDF-CDRT), and the incremental-selective DF (ISDF) relaying are proposed to enhance the outage performance for the two far users by utilizing both the direct and relay links. Taking into account the received signal-to-noise ratio (SNR) events at the relay, the SDF-CDRT scheme adaptively forms an orthogonal transmission branch with respect to the direct link or keeps silent to reduce error propagation. Besides considering the relay detection results, the ISDF scheme further exploits the limited feedback of the received SNR events from two users, so that error propagation can be avoided and unnecessary relaying can be reduced. Analytical expressions for the outage probabilities and average throughputs of the paired users are derived in closed-form for the three cooperative relaying schemes. Asymptotic expressions for the outage probabilities are derived in the high SNR region. It is shown that the FR and SDF-CDRT schemes achieve a diversity order of one for both users, while the ISDF scheme achieves a diversity order of two for both users. The superior system performance achieved by the proposed schemes over those of the existing methods is verified by Monte Carlo simulations.</P>

Opportunistic relaying for low-altitude UAV swarm secure communications with multiple eavesdroppers

Liu, Hongwu,Yoo, Sang-Jo,Kwak, Kyung Sup Editorial Department of Journal of Communications 2018 Journal of communications and networks Vol.20 No.5

<P>In this study, we investigate the secrecy outage performance achieved by opportunistic relaying for a low-altitude unmanned aerial vehicle (UAV) swarm secure communication system in the presence of multiple UAV-eavesdroppers. In the primary channel, multiple UAV-transmitters are connected to a ground station via the ground-to-air (G2A) wireless backhaul and a UAV-transmitter and UAV-relay are selected to transmit the source signal to a far ground destination under air-to-air and air-to-ground Nakagami-m fading links. In the eavesdropping channel, maximum ratio combining is applied across multiple UAV-eavesdroppers for intercepting the legitimate transmissions from both the selected UAV-transmitter and UAV-relay. The backhaul reliability and eavesdropping probability are introduced to reflect the practical constraints on the G2A wireless backhaul and UAV-eavesdropper cooperation, respectively. The closed-form expression for the secrecy outage probability is derived in terms of the UAV cooperation, backhaul reliability, eavesdropping probability, and Nakagami-m fading parameters. In the high signal-to-noise ratio region, the asymptotic secrecy outage probability is also derived. It is shown that the secrecy diversity gain achieved by opportunistic relaying is jointly determined by the UAV cooperation and shape factors of Nakagami-m fading links in the primary channel. The analytical secrecy outage metrics achieved by opportunistic relaying are verified by Monte Carlo simulation results.</P>

Sequential Optimization for Subcarrier Pairing and Power Allocation in CP-SC Cognitive Relay Systems

( Hongwu Liu ),( Jaijin Jung ),( Kyung Sup Kwak ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.5

A sequential optimization algorithm (SOA) for resource allocation in a cyclic-prefixed single-carrier cognitive relay system is proposed in this study. Both subcarrier pairing (SP) and power allocation are performed subject to a primary user interference constraint to minimize the mean squared error of frequency-domain equalization at the secondary destination receiver. Under uniform power allocation at the secondary source and optimal power allocation at the secondary relay, the ordered SP is proven to be asymptotically optimal in maximizing the matched filter bound on the signal-to-interference-plus-noise ratio. SOA implements the ordered SP before power allocation optimization by decoupling the ordered SP from the power allocation. Simulation results show that SOA can optimize resource allocation efficiently by significantly reducing complexity.

Distributed Linear Dispersion Coding For Two-Way CP-SC Relay Systems

Hongwu Liu,Kyung Sup Kwak 한국통신학회 2012 한국통신학회 학술대회논문집 Vol.2012 No.6

Massive MIMO Relay Systems with Multipair Wireless Information and Power Transfer

Liu, Hongwu,Chang, Kyung Hi,Kwak, Kyung Sup Hindawi Limited 2017 Mobile information systems Vol.2017 No.-

<P>This paper investigates destination-aided simultaneous wireless information and power transfer (SWIPT) for a decode-and-forward relay network, in which massive multiple-input multiple-output antennas are deployed at relay to assist communications among multiple source-destination pairs. During relaying, energy signals are emitted from multiple destinations when multiple sources are sending their information signals to relay. With power splitting and unlimited antennas at relay, asymptotic expression of harvested energy is derived. The analysis reveals that asymptotic harvested energy is independent of fast fading effect of wireless channels; meanwhile transmission powers of each source and destination can be scaled down inversely proportional to the number of relay antennas. To significantly reduce energy leakage interference and multipair interference, zero-forcing processing and maximum-ratio combing/maximum-ratio transmission are employed at relay. Fundamental trade-off between harvested energy and achievable sum rate is quantified. It is shown that asymptotic sum rate is neither convex nor concave with respect to power splitting and destination transmission power. Thus, a one-dimensional embedded bisection algorithm is proposed to jointly determine the optimal power splitting and destination transmission power. It shows that destination-aided SWIPT are beneficial for harvesting energy and increasing sum rate. The significant sum rate improvements of the proposed schemes are verified by numerical results.</P>

Power Splitting-Based SWIPT With Decode-and-Forward Full-Duplex Relaying

Liu, Hongwu,Kim, Kyeong Jin,Kwak, Kyung Sup,Vincent Poor, H. IEEE 2016 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.15 No.11

<P>This paper investigates simultaneous wireless information and power transfer (SWIPT) for a decode-and-forward (DF) full-duplex relay (FDR) network. A battery group consisting of two batteries is applied to utilize the relay-harvested energy for FDR transmission. The virtual harvest-use model and the harvest-use-store model are considered, respectively. By switching between two batteries for charging and discharging with the aid of power splitting (PS), concurrent source and relay transmissions can overcome spectral efficiency loss compared with half-duplex relay (HDR)-assisted PS-SWIPT. The outage probability for the virtual harvest-use model is presented in an exact integral form and the optimal PS (OPS) ratio that maximizes the end-to-end signal-to-interference-plus-noise ratio (e-SINR) is characterized in closed form via the cubic formula. The fundamental tradeoff between the e-SINR and recycled self-power is quantified. The OPS ratios and the corresponding outage probabilities in noise-limited and interference-limited environments are also derived. In the harvest-use-store model, a greedy switching (GS) policy is implemented with energy accumulation across transmission blocks. The OPS ratio of the GS policy is presented and the corresponding outage probability is derived by modeling the relay's energy levels as a Markov chain with a two-stage state transition. Numerical results verify the performance improvement of the proposed scheme over HDR-assisted PS-SWIPT in terms of outage probability and average throughput.</P>

Secrecy Performance of Finite-Sized Cooperative Full-Duplex Relay Systems With Unreliable Backhauls

Hongwu Liu,Kyeong Jin Kim,Tsiftsis, Theodoros A.,Kyung Sup Kwak,Poor, H. Vincent Institute of Electrical and Electronics Engineers 2017 IEEE transactions on signal processing Vol.65 No.23

<P>This paper investigates secrecy performance of finitesized cooperative full-duplex relay (FDR) systems with unreliable wireless backhaul connections across multiple transmitters under Nakagami-m fading. Closed-form expressions for the secrecy outage probability and probability of nonzero achievable secrecy rate are derived in terms of self-interference (SI), transmitter cooperation, and backhaul reliability. It is shown that transmitter cooperation can effectively enhance the secrecy performance, while the asymptotic limits on the secrecy outage probability and probability of nonzero achievable secrecy rate are exclusively determined by backhaul reliability. With the aid of transmitter cooperation, the burden of SI cancelation can be alleviated for the FDR system in achieving the smallest allowed secrecy outage probability. Compared to that of a half-duplex relay (HDR) system, the FDR system achieves a lower secrecy outage probability with well suppressed SI. The analysis shows that the secrecy outage probability achieved by the FDR system converges to that of the HDR system under perfect backhaul as the target secrecy rate becomes small. The secrecy performance metrics of the considered system are verified by simulations for various backhaul scenarios.</P>

QoS-Constrained Relay Control for Full-Duplex Relaying With SWIPT

Liu, Hongwu,Kim, Kyeong Jin,Kwak, Kyung Sup,Poor, H. Vincent IEEE 2017 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.16 No.5

<P>This study investigates relay control for simultaneous wireless information and power transfer in full-duplex relay networks under Nakagami-m fading channels. Unlike previous work, harvest-transmit (HT) and general harvest-transmit-store (HTS) models are respectively considered to maximize average throughput subject to quality of service (QoS) constraints. The end-to-end outage probability of the network in an HT model is presented in an exact integral-form. To prevent outage performance degradation in an HT model, time switching (TS) is designed to maximize average throughput subject to QoS constraints of minimizing outage probability and maintaining a target outage probability, respectively. The optimal TS factors subject to QoS constraints are presented for an HT model. In general, in an HTS model, energy scheduling is performed across different transmission blocks and TS is performed within each block. Compared with the block-based HTS model without TS, the proposed general HTS model can greatly improve outage performance via greedy search (GS). By modeling the relay's energy levels as a Markov chain with a two-stage state transition, the outage probability for the GS implementation of the general HTS model is derived. To demonstrate the practical significance of QoS-constrained relay control, numerical results are presented showing that the proposed relay control achieves substantial improvement of outage performance and successful rate.</P>

Efficiency Analysis of Gear System Based on Gear Surface Micro-topography

Wei Liu,Yimin Shao,Hongwu Li,Yan Cheng,Jin Xu 제어로봇시스템학회 2018 제어로봇시스템학회 국제학술대회 논문집 Vol.2018 No.10

In order to accurately calculate the gear transmission efficiency, a new efficiency evaluation method is proposed considering the 3D micro-topography of the tooth surface. Firstly, a digital microsystem is used to obtain the surface micro-topography of gears. The roughnesses of the gears at different meshing positions are then calculated according to the tooth surface micro-topography parameters and the gear meshing principle. Subsequently, the calculated roughnesses are substituted into the gear system dynamic model with the ROMAX software employed, and the distribution of friction coefficient and efficiencies of gear system can be simulated at different input torques and roughnesses. The simulation results show that the greater the surface roughness, the lower the efficiency of gear transmission. Conversely, the greater the torque, the greater the efficiency of the gear transmission. Finally, to further validate the effectiveness of the proposed method, efficiency experiments at same working conditions are carried out and a sound comparative analysis of previous studies is launched. The results show that the proposed method is effective with an error of less than 2%.