1,723,850 research outputs found
Outage analysis and optimization for wireless multiuser relay networks
No full textIn this thesis, we propose a suite of schemes for wireless multiuser relay networks, where multiple source nodes (SNs) and relay nodes (RNs) share the spectral resources and hence we take into the account the co-channel interference (CCI). Our objective is to deal with both the channel fading and CCI in order to improve the attainable outage performance.Firstly, we consider the opportunistic relay selection (ORS) design in the scenario, where multiple RNs are available for assisting the transmission of a single SN, while CCI is imposed by other SNs in the network. We design the single-user-detection-aided (SUD-aided) and multi-user-detection based successive interference-cancellation-aided (MUD-SIC-aided) systems, where multiple-user detection (MUD) receivers using successive interference cancellation (SIC) at the destination node (DN) are adopted to combat co-channel interference. In SUD-aided system, we employ single-user detection (SUD) at the RNs and MUD SIC at the DN. In MUD-SIC-aided system, we employ MUD-SIC at both the RNs and DN. We present the outage analysis of both systems based on an outage-optimised ORS scheme, implying that the proposed ORS scheme provides the best outage performance. We show that the traditional ORS scheme proposed for SUD receivers based on the highest SNR criterion is not outage-optimal, when employing MUD-SIC in the presence of CCI. Hence, we propose a novel ORS scheme based on a best-effort detection (BED) criterion that outperforms the traditional ORS scheme. Furthermore, considering the effects of the outdated channel state information (CSI), an improved BED-ORS is proposed for enhancing the robustness towards CSI imperfections.Then, we study the scenario, where multiple SNs are coordinated to share a RN. In this case, network coding (NC) may be invoked at the RN, which treats the CCI from other SNs as useful messages and superimposes them to reduce the time slots required for relaying, therefore achieving higher spectral efficiency. However, NC systems may not always be beneficial in cooperative communications, where the detrimental interference of the undesired SNs, often referred to as network coding noise (NC noise), may outweigh the benefits of NC. In previous works, the outage performance was only evaluated numerically for several case studies. Against this background, we propose a systematically analytical framework for evaluating the outage performance for a multi-unicast NC-aided network, where each DN extracts the information of the desired SN from the NC signal forwarded by the RN. As our main contribution, we present the outage analysis of this system in the presence of NC noise and the closed-form analytical outage probability expressions are derived for an arbitrary number of SN-DN pairs. We show that if NC is employed, the quality of the worst SN-DN link may dominate the outage performance of every SNs.We then consider a two-hop network, where multiple SNs transmit to a DN with the aid of a RN and we assume the direct link between the SNs and the DN is weak. In this scenario, we show that the NC-aided relaying is not preferred and hence the buffer-aided relaying (BAR) is advocated for improving the uplink. The RN is equipped with a buffer, which is capable of storing multiple frames received from the SNs. During each time slot, the proposed protocol activates either the SNRN hop or the RN-DN hop, depending on the channel quality of each hop and the buffer state at the RN. In order to optimise the hop selection for the network, we design a hop quality metric (HQM) and propose a multi-user buffer-aided-relaying uplink (MU-BR-UL) protocol. The benefits of the proposed protocol is analysed in terms of the end-to-end outage probability and the end-to-end transmission delay. Then, the optimal power allocation is proposed for minimizing the end-to-end outage probability under the total power constraint. Furthermore, the impact of the buffer size, the number of users and the relay position on the achievable outage performance are characterized. The results indicate that the outage performance is significantly improved when the proposed power allocation is utilized in the MU-BR-UL protocol.Finally, we consider a new family of networks, in which the SNs and RNs have energy harvesting (EH) capability, which allows the nodes to harvest energy from the environments and convert it to electrical energy for wireless transmissions. The EH removes the constraints of relying on a battery for constant power supply, but also demands novel energy usage policy (EUP) design for effectively utilizing the random power supply gleaned from the EH system. We start with the point-to-point (P2P) network and by effectively exploiting the statistics of the energy arrival rates, we propose novel search algorithms for designing the EUP, which achieve a significantly better outage performance than the state-of-the-art designs reported in the literature. Based on the proposed methods in P2P network, we design novel EUPs for space-division-multiple-access (SDMA) and SDMA-based relay sharing networks. We show that the proposed EUPs significantly outperforms the state-of-the-art benchmarks in terms of outage performance
A Newton method for a simultaneous reconstruction of an interface and a buried obstacle from far-field data
No full textThis paper is concerned with the inverse problem of scattering of time-harmonic acoustic waves from a penetrable and a buried obstacle. By introducing a related transmission scattering problem, a Newton iteration method is proposed to simultaneously reconstruct both the penetrable interface and the buried obstacle inside from far-field data. The main feature of our method is that we do not need to know the type of boundary conditions on the buried obstacle. In particular, the boundary condition on the buried obstacle can also be determined simultaneously by the method. Finally, numerical examples using multi-frequency data are carried out to illustrate the effectiveness of our method
An Approximate Factorization Method for Inverse Acoustic Scattering with Phaseless Total-Field Data
No full textFMM-Yukawa: An Adaptive Fast Multipole Method for Screened Coulomb Interactions
Get PDF1 online resource (PDF, 19 pages, includes illustrations)Huang, Jingfang; Jia, Jun; Zhang, Bo. (2009). FMM-Yukawa: An Adaptive Fast Multipole Method for Screened Coulomb Interactions. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/180140
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Uniqueness in inverse acoustic and electromagnetic scattering with phaseless near-field data at a fixed frequency
No full textThis paper is concerned with uniqueness results in inverse acoustic and electromagnetic scattering problems with phaseless total-field data at a fixed frequency. We use superpositions of two point sources as the incident fields at a fixed frequency and measure the modulus of the acoustic total-field (called phaseless acoustic near-field data) on two spheres containing the scatterers generated by such incident fields on the two spheres. Based on this idea, we prove that the impenetrable bounded obstacle or the index of refraction of an inhomogeneous medium can be uniquely determined from the phaseless acoustic near-field data at a fixed frequency. Moreover, the idea is also applied to the electromagnetic case, and it is proved that the impenetrable bounded obstacle or the index of refraction of an inhomogeneous medium can be uniquely determined by the phaseless electric near-field data at a fixed frequency, that is, the modulus of the tangential component with the orientations eϕ and eθ, respectively, of the electric total-field measured on a sphere enclosing the scatters and generated by superpositions of two electric dipoles at a fixed frequency located on the measurement sphere and another bigger sphere with the polarization vectors eϕ and eθ, respectively. As far as we know, this is the first uniqueness result for three-dimensional inverse electromagnetic scattering with phaseless near-field data
A Novel Integral Equation for Scattering by Locally Rough Surfaces and Application to the Inverse Problem: The Neumann Case
No full textThis paper is concerned with direct and inverse scattering by a locally perturbed infinite plane (called a locally rough surface in this paper) on which a Neumann boundary condition is imposed. A novel integral equation formulation is proposed for the direct scattering problem which is defined on a bounded curve (consisting of a bounded part of the infinite plane containing the local perturbation and the lower part of a circle) with two corners and some closed smooth artificial curve. It is a nontrivial extension of our previous work on direct and inverse scattering by a locally rough surface from the Dirichlet boundary condition to the Neumann boundary condition [SIAM J. Appl. Math., 73 (2013), pp. 1811--1829]. For the Dirichlet boundary condition, the integral equation obtained is uniquely solvable in the space of bounded continuous functions on the bounded curve, and it can be solved efficiently by using the Nyström method with a graded mesh. However, the Neumann condition case leads to an integral equation which is solvable in the space of squarely integrable functions on the bounded curve rather than in the space of bounded continuous functions, making the integral equation very difficult to solve numerically with the classic and efficient Nyström method. In this paper, we make use of the recursively compressed inverse preconditioning method developed by Helsing to solve the integral equation which is efficient and capable of dealing with large wave numbers. For the inverse problem, it is proved that the locally rough surface is uniquely determined from a knowledge of the far-field pattern corresponding to incident plane waves. Moreover, based on the novel integral equation formulation, a Newton iteration method is developed to reconstruct the locally rough surface from a knowledge of multiple frequency far-field data. Numerical examples are also provided to illustrate that the reconstruction algorithm is stable and accurate even for the case of multiple-scale profiles
Opportunistic relay selection for co-operative relaying in cochannel interference contaminated networks
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