Iterative Channel Estimation for MIMO-OFDM System in Fast Time-Varying Channels

( Lihua Yang ),( Longxiang Yang ),( Yan Liang ) 한국인터넷정보학회 2016 KSII Transactions on Internet and Information Syst Vol.10 No.9

A practical iterative channel estimation technique is proposed for the multiple-input-multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system in the high-speed mobile environment, such as high speed railway scenario. In the iterative algorithm, the Kalman filter and data detection are jointed to estimate the time-varying channel, where the detection error is considered as part of the noise in the Kalman recursion in each iteration to reduce the effect of the detection error propagation. Moreover, the employed Kalman filter is from the canonical state space model, which does not include the parameters of the autoregressive (AR) model, so the proposed method does not need to estimate the parameters of AR model, whose accuracy affects the convergence speed. Simulation results show that the proposed method is robust to the fast time-varying channel, and it can obtain more gains compared with the available methods.

Sum rate and Energy Efficiency of Massive MIMO Downlink with Channel Aging in Time Varying Ricean Fading Channel

( Lihua Yang ),( Longxiang Yang ),( Hongbo Zhu ),( Yan Liang ) 한국인터넷정보학회 2018 KSII Transactions on Internet and Information Syst Vol.12 No.3

Achievable sum rate and energy efficiency (EE) are investigated for the massive multiple-input multiple-output (Massive MIMO) downlink with channel aging in the time varying Ricean fading channel. Specifically, the expression of the achievable sum rate of the system for the maximum ratio transmission (MRT) precoder with aged channel state information (CSI) in the time varying Ricean fading channel is first presented. Based on the expression, the effect of both channel aging and the Ricean factor on the power scaling law are studied. It is found that the transmit power of base station (BS) is scaled down by 1/√M (where M is the number of the BS antennas) when the Ricean factor K is equal to zero (i.e., time varying Rayleigh fading channel), indicating that aged CSI does not affect the power scaling law. However, the transmit power of the BS is scaled down by for the time varying Ricean fading channel (where K≠0) indicating that the Ricean factor affects the power scaling law and sum rate, and channel aging only leads to a reduction of the sum rate. Second, the EE of the system is analyzed based on the general power consumption model. Both the theoretical analysis and the simulations show that the channel aging could degrade the sum rate and the EE of the system, and it does not affect the power scaling law.

Joint Relay Selection and Power Alloca-tion for Two-way Relay Channels with Asymmetric Traffic Requirements

( Sijia Lou ),( Longxiang Yang ) 한국인터넷정보학회 2013 KSII Transactions on Internet and Information Syst Vol.7 No.8

This paper studiesrelay selection and power allocationfor amplify-and-forward (AF)based two-way relay networks (TWRN)with asymmetric traffic requirements (ATR).A joint relay selection and power allocation algorithm is proposed to decrease the outage probability of TWRN with ATR.In this algorithm,two sources exchange information with the help of the relay during two time slots. We first calculatethe optimal power al-location parameters based on instantaneous channel state information (CSI), and then de-rivea tight lower bound of outage probability. Furthermore,weproposea simplified relay selection criterion,which can be easilycalculated as harmonic mean of instantaneous channel gains, according tothe outage probability expressions. Simulationresults verifiedthe theoretical analyses we presented. It is shown that theoutage probability of ouralgo-rithm improves3-4dBcomparing with that of otherexisting algorithms,and the lower bound is tight comparing with actual valuefor the entiresignal-to-noise ratio (SNR) re-gion.

Virtual Resource Allocation in Virtualized Small Cell Networks with Physical-Layer Network Coding Aided Self-Backhauls

( Yulun Cheng ),( Longxiang Yang ),( Hongbo Zhu ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.8

Virtualized small cell network is a promising architecture which can realize efficient utilization of the network resource. However, conventional full duplex self-backhauls lead to residual self-interference, which limits the network performance. To handle this issue, this paper proposes a virtual resource allocation, in which the residual self-interference is fully exploited by employing a physical-layer network coding (PNC) aided self-backhaul scheme. We formulate the features of PNC as time slot and information rate constraints, and based on that, the virtual resource allocation is formulated as a mixed combinatorial optimization problem. To solve the problem efficiently, it is decomposed into two sub problems, and a two-phase iteration algorithm is developed accordingly. In the algorithm, the first sub problem is approximated and transferred into a convex problem by utilizing the upper bound of the PNC rate constraint. On the basis of that, the convexity of the second sub problem is also proved. Simulation results show the advantages of the proposed scheme over conventional solution in both the profits of self-backhauls and utility of the network resource.

Opportunistic Multiple Relay Selection for Two-Way Relay Networks with Outdated Channel State Information

( Sijia Lou ),( Longxiang Yang ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.2

Outdated Channel State Information (CSI) was proved to have negative effect on performance in two-way relay networks. The diversity order of widely used opportunistic relay selection (ORS) was degraded to unity in networks with outdated CSI. This paper proposed a multiple relay selection scheme for amplify-and-forward (AF) based two-way relay networks (TWRN) with outdated CSI. In this scheme, two sources exchange information through more than one relays. We firstly select N best relays out of all candidate relays with respect to signal-noise ratio (SNR). Then, the ratios of the SNRs on the rest of the candidate relays to that of the Nth highest SNR are tested against a normalized threshold μ∈[0, 1], and only those relays passing this test are selected in addition to the N best relays. Expressions of outage probability, average bit error rate (BER) and ergodic channel capacity were obtained in closed-form for the proposed scheme. Numerical results and Simulations verified our theoretical analyses, and showed that the proposed scheme had significant gains comparing with conventional ORS.

Collaborative Attributes and Resources for Single-Stage Virtual Network Mapping in Network Virtualization

Haotong Cao,Hongbo Zhu,Longxiang Yang 한국통신학회 2020 Journal of communications and networks Vol.22 No.1

Virtual network embedding (VNE) is the virtualized nodeand link resources allocation problem in network virtualization environment,aiming at achieving the simultaneous optimal node andlink mapping assignment per VN. Currently, a large number ofmapping algorithms for VNE exist in the academia. Existing algorithmsmostly focus on mapping each virtual network (VN) intwo ordered stages: First virtual node mapping stage and secondvirtual link mapping stage, leading to non-optimal VN mappingassignment. Though multiple one-stage algorithms exist, adoptingeither optimization theory or graph theory, they usually involvemuch more VN assignment calculation time. Hence, theseone-stage algorithms are not suitable for dynamic network scenario. Not to mention practical VNE application. Based on thebackground and our gained research results, we propose anotherheuristic mapping algorithm VNE-ARS, completing all nodes andlinks per VN in one single embedding stage. Each VN embeddingassignment can be completed in polynomial time, using ourVNE-ARS. Main network attributes and resources are collaborated,serving as the mapping criterion of our VNE-ARS. In orderto highlight our VNE-ARS strength, we conduct the evaluation experiments. We compare our VNE-ARS algorithm against existingmapping algorithms.

Improved Compressed Network Coding Scheme for Energy-Efficient Data Communication in Wireless Sensor Networks

( Ying Zhou ),( Lihua Yang ),( Longxiang Yang ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.6

An improved energy-efficient compressed network coding method is proposed for the data communication in the wireless sensor networks (WSNs). In the method, the compressed sensing and network coding are jointly used to improve the energy efficiency, and the two-hop neighbor information is employed to choose the next hop to further reduce the number of the transmissions. Moreover, a new packet format is designed to facilitate the intermediate node selection. To theoretically verify the efficiency of the proposed method, the expressions for the number of the transmissions and receptions are derived. Simulation results show that, the proposed method has higher energy efficiency compared with the available schemes, and it only requires a few packets to reconstruct measurements with reasonable quality.

Cell-Free Massive MIMO: Zero Forcing and Conjugate Beamforming Receivers

Yao Zhang,Haotong Cao,Meng Zhou,Longxiang Yang 한국통신학회 2019 Journal of communications and networks Vol.21 No.6

In this paper, the uplink performance of cell-free massivemulti-input multi-output (mMIMO) system with the zero-forcing(ZF) and conjugate beamforming (CB) receivers is investigated. Anovel tight approximate rate expression for the ZF receiver is derived,which provides us with a tool for easily quantifying the impactsof the multi-antenna access point (AP), estimation error, pilotcontamination, and power control scheme. Then, leveraging on thetrackable ZF rate expression and the pre-studied CB rate expression,two power control algorithms are proposed. In particular, thefirst algorithm elaborates on maximizing the total rate, subjectingto the quality-of-service (QoS) constraint and each user power constraint. This algorithm utilizes the sequential convex approximationmethod to solve the non-convex issues. In addition, the secondaims at maximizing the rate of one user, in which the remainingusers can meet their QoS constraints. It can be characterized as ageometry programming. Simulation results are provided to showthat the ZF receiver is superior to the CB receiver in terms of sumrate and our proposed algorithms work well in many respects.

Matrix-Diffusion-Controlled Coarsening of the γ′ Phase in Waspaloy

Haiping Wang,Dong Liu,Yongzhao Shi,Jianguo Wang,Yanhui Yang,Longxiang Wang,Weidong Qin 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.6

This paper discussed the coarsening behavior of the γ′ phase in Waspaloy during heat treatment at different aging timesunder the temperatures of 960 °C and 1000 °C. The morphology of γ′ phase is obtained by scanning electron microscopyand it is measured by the software Image Pro Plus 6.0 in a variety of aging conditions. The volume fraction of the γ′ phase isdecreasing with the increase of the temperature. The radius of the γ′ phase is subject to involve the coarsening process duringaging treatment, and the coarsening rate decreases with the extension of the aging time at certain temperature. Besides,the coarsening kinetics of γ′ phase in Waspaloy is adequately characterized by the Lifshitz–Slyozov–Wagner (LSW) theorymodel as the particle size distribution and coarsening behavior show excellent agreement with the LSW model. Accordingto the experimental results and LSW model, the coarsening rate coefficients were determined to be 27.23 nm3/s and58.67 nm3/s under the aging temperature of 960 °C and 1000 °C respectively. Meanwhile, on the basis of the experimentalstatistics analysis and the LSW model, the mathematical model of the coarsening behavior of the γ′ phase in Waspaloy wasdeveloped. Mathematical model developed in this paper can be used to evaluate the coarsening process of the γ′ phase duringthermal exposure. The interfacial energy between the γ′ phase and the γ matrix was determined to be 56.04 mJ/m2 and44.27 mJ/m2 at the temperature of 960 °C and 1000 °C respectively.