Yulong Wang

Dynamic Resource Allocation with Threshold in OFDMA-based Relay Networks

In this paper, we investigate resource allocation issue in OFDMA-based decode-and-forward cooperative networks and propose joint subcarrier and power allocation schemes. The optimal solution of this combinable allocation has high computational complexity, so we divide our solution into two steps. The first step is to distribute subcarriers to relays and destination under the assumption of equal power distribution. Here, we propose Proportional Allocation (PA) strategy to achieve tradeoff between total throughput and fairness. To further improve the system performance, we introduce threshold into PA strategy, named Proportional Allocation with Threshold (PA-T), where subcarriers with bad performance are prevented from transmitting. Next, water-filling method is adopted to distribute the power to cooperative links in order to fully utilize the limited power. Simulation results show that system performance of the proposed schemes is significantly enhanced compared with an existing resource allocation scheme. Besides, the resource allocation schemes with water-filling method notably outperform schemes with equal power allocation.

Performance Evaluation of Frequency Planning in a Novel Cellular Architecture Based on Sector Relay

To avoid inter-cell interference effectively and to improve the performance of cell-edge users, a novel cellular architecture, termed Cellular Architecture Based on Sector Relay (CASR), is proposed in this paper, and two frequency planning schemes based on CASR are investigated. In CASR, fixed relays equipped with directional antennas are located at the vertex of the hexagonal cell for sectorization, thus each relay can be shared by three cells. The two frequency planning schemes are designed for different situations, one of which focuses more on the performance of cell one-hop users and the other one focuses on the performance balance between one-hop users and two-hop users. Interference analysis and performance evaluation are implemented for both one-hop users and two-hop users. System-level simulation in multi-cell and multi-user environment shows that compared with the existing cellular relay cell architecture, the proposed CASR combined with the two frequency planning schemes yield higher cell spectral efficiency. Moreover, the performance of cell-edge users is significantly improved.

Device-to-Device Dynamic Clustering Algorithm in Multicast Communication

Device-to-Device (D2D) communications make high-speed multicast services possible since the multicast receivers with poor downlink channel conditions can be retransmitted by devices nearby via D2D links. In this paper, we consider how to efficiently use D2D communications to help enhance the quality of wireless multicast services in cellular networks. To achieve this, a dynamic D2D retransmission scheme with maximized utility is proposed, which can adaptively select the retransmission algorithm according to the state of the network load. Through both analysis and simulations, we show that our algorithms achieve a significant gain in terms of utility, and reduce the burden of the base station (BS).

Iterative Cooperation DV-Hop Localization Algorithm in Wireless Sensor Networks

According to the comprehensive analysis of the traditional DV-Hop, we propose an Iterative Cooperation DV-Hop localization (ICDV-Hop) algorithm, which improves the localization performance through adopting hop count threshold, collinearity test and new beacon nomination. The proposed algorithm selects the optimal beacon nodes for high localization accuracy by employing the hop count threshold to limit the distances between nodes and using collinearity degree to restrict topology relations between nodes. When the localization error of the located node is under the error threshold, it is nominated as new beacon to help the remaining unknown nodes to re-locate themselves, namely to expand localization coverage by iterative cooperation. Simulation results demonstrate that ICDV-Hop algorithm is more effective to improve the localization accuracy and coverage. Moreover, it is more reliable and robust compared to the traditional DV-Hop, especially when the ratio of beacon nodes is low and the network topology is sparse.

Location-Aware Relay Selection Scheme in Opportunistic Relay Communications

In this paper, we propose a location-aware relay selection (LARS) scheme based on geographical information in the distributed opportunistic relay (OR) communication system. The scheme aims to limit the contention among potential relays through dividing the whole relay selection region into some small nonoverlapping contending torus zones. If a relay lies in the specified contending zone and its local channels are better than the source-destination channel, it becomes a contending relay and will transmit a FLAG packet to signal the presence when its own timer expires. If no relay is selected in the previous contending zone, the current contending torus zone will be extended. The contention is an iterative course until the relay selection process completes. Performance analysis and simulation results show that the LARS scheme leads to a remarkable improvement in collision probability. Meanwhile the outage performance and consuming time of LARS scheme are closed to those of original OR scheme.

Irreversible Adsorption and Reduction of p-Nitrothio-Phenol Monolayers on Gold: Electrochemical in Situ Surface Enhanced Raman Spectroscopy

Abstract The redox behavior of p-nitrothiophenol (p-NTP) monolayers on gold was studied by electrochemical in situ surface enhanced Raman spectroscopy (SERS). The chemical adsorption of p-NTP on gold through Au-S bonding was confirmed by the comparison between the Raman spectra of parent molecules and that of the monolayer. The irreversible reduction of p-NTP monolayers to p-aminothiophenol (p-ATP) monolayers was evidenced by the observed potential dependent spectral changes. The present results demonstrated the potential of SERS in investigating the adsorbate-substrate interaction and in monitoring surface reactions at a monolayer scale.

Outage Analysis of Opportunistic Cooperative Multi-Antenna Multicast Based on Space-Time Coding

Two Opportunistic Multi-antenna Relay Selection (OMRS) strategies are proposed and analyzed in Decode-and-Forward (DF) relay networks for cooperative multicast using space time codes, assuming multiple antennas are available at the relay nodes. These two strategies select the best relay based on (i) maximizing the average SNR and (ii) maximizing the minimum SNR respectively. The closed-form expressions of multicast outage probability for the two strategies are studied over Rayleigh fading channel. Simulations are provided to verify the correctness of the theoretical analysis. Our multicast outage probability results reveal that OMRS based on maximizing the minimum SNR is outage-optimal among multi-antenna relay selection schemes and approaches the space time codes scheme. Moreover, it can be found that compared with previous single-antenna Opportunistic Relaying (OR) scheme, OMRS brings remarkable performance improvement obtained from maximum ratio combining (MRC) and space-time coding, which proves that multiple antennas at the relays could provide more array gain and diversity gain.

Gold nanoparticles assembly as the model system in studying mechanisms of surface enhanced raman scattering

Abstract Colloidal gold nanoparticles were immobilized on to a solid surface through a bifunctional self-assembled monolayer, forming a sandwiched structure in the form of [gold nanoparticulate film]/[self-assembled monolayer]/[solid surface]. Thus prepared model system was used to study the mechanisms of surface enhanced Raman scattering(SERS). A preliminary result is given in this paper on particle size and potential dependencies of surface enhancement of Raman scattering.

Optimization of Relay Transmission Schemes with Interference Cancellation in Wireless Systems

In this paper, new transmission schemes are proposed to deal with the CCI (co-channel interference) in wireless relay transmission. We first introduce an optimal decoding process to fully utilize the information forwarded by relay. Then based on conventional transmission schemes, two modified transmission schemes and a novel adaptive scheme are proposed. Furthermore, we derive the outage probabilities and throughput for all the proposed schemes in closed form. Numerical simulations are presented to validate the analytical results and it shows that the adaptive scheme improves the spectral efficiency significantly compared to others in most condition.

A Wireless Resources Allocation Method for D2MD Communication under IMT-A System

A wireless resources allocation method for Device-to-Multi-Device (D2MD) communication under the control of base station is proposed. In the premise of ensuring quality of services (QoS) of all D2MD groups, the method can allocate wireless resources for D2MD groups through three steps: mode selection, spectrum allocation and power control. Simulation results show that the method can select the high-spectrum-efficiency mode which reuses the spectrum of cellular users for most D2MD communications, and does not affect cellular communications, the interference to cellular uplink of proposed suboptimal LCH algorithm which allocates cellular spectrums for D2MD groups to reuse can achieve the same level as the optimal algorithm, in addition, the calculating complexity is lower therefore shortening the response time of the base station.