Maximum Multipath Routing Throughput in Multirate Wireless Mesh Networks

In this paper, we consider the problem of finding the maximum routing throughput between any pair of nodes in an arbitrary multirate wireless mesh network (WMN) using multiple paths. Multipath routing is an efficient technique to maximize routing throughput in WMN, however maximizing multipath routing throughput is a NP-complete problem due to the shared medium for electromagnetic wave transmission in wireless channel, inducing collision-free scheduling as part of the optimization problem. In this work, we first provide problem formulation that incorporates collision-free schedule, and then based on this formulation we design an algorithm with search pruning that jointly optimizes paths and transmission schedule. Though suboptimal, compared to the known optimal single path flow, we demonstrate that an efficient multipath routing scheme can increase the routing throughput by up to 100% for simple WMNs.Comment: This paper has been accepted for publication in IEEE 80th Vehicular Technology Conference, VTC-Fall 201

An Efficient Network Coding based Retransmission Algorithm for Wireless Multicasts

Retransmission based on packet acknowledgement (ACK/NAK) is a fundamental error control technique employed in IEEE 802.11-2007 unicast network. However the 802.11-2007 standard falls short of proposing a reliable MAC-level recovery protocol for multicast frames. In this paper we propose a latency and bandwidth efficient coding algorithm based on the principles of network coding for retransmitting lost packets in a singlehop wireless multicast network and demonstrate its effectiveness over previously proposed network coding based retransmission algorithms.Comment: 5 pages, 5 figure

V2O5-WO3 composite films and surface-coated LiCoO2 for enhanced Li-ion intercalation properties

We have investigated the enhanced Li-ion intercalation properties of two different materials, which are V2O5-WO3 composite and surface-coated LiCoO2. A simple and novel solution processing method is employed to prepare V2O5-WO3 composite films that demonstrate enhanced Li-ion intercalation properties for applications in Li-ion batteries or electrochromic displays. This solution processing method employs precursors that only contain the elements of V, W, O and H, which avoids impurity elements such as Na that has been commonly used in other solution methods (e.g. using precursors of sodium metavanadate and sodium tungstate solution). The V2O5-WO3 composite films show enhanced Li-ion intercalation properties compared to pure V2O5 and WO3 films. For example, at a high current density of 1.33 A/g, the V2O5-WO3 film with a V2O5/WO3 molar ratio of 10/1 exhibits the highest discharge capacities of 200 mA•h/g at the first cycle and 132 mA•h/g after 50 cycles, while pure V2O5 film delivers discharge capacities of 108 mA•h/g at the first cycle and 122 mA•h/g after 50 cycles. The enhanced capacity of the composite films is ascribed to the reduced crystallinity, increased porosity and thus the enhanced surface area. Both cyclic voltammogram and chronopotentiometric curves of the V2O5-WO3 film with a molar ratio of 10:1 are distinctively different from those of pure oxide films, suggesting a different Li-ion intercalation process in the V2O5-WO3 film with the molar ratio of 10:1. For surface-coated LiCoO2, a molten salt synthesis method is employed to prepare LiCoO2 powders with submicron size, and ultrathin conformal Al2O3 or ZnO layers are coated on LiCoO2 electrodes by utilizing atomic layer deposition. The Al2O3-coated LiCoO2 electrode exhibits improve cycling stability during the electrochemical measurements, while the ZnO-coated LiCoO2 electrode does not show an improved cycling performance. The Al2O3 coating can prevent the direct contact between LiCoO2 and the electrolyte, and thus suppress the cobalt dissolution and side reaction. Therefore, LiCoO2 with nanosized thin Al2O3 coating exhibits improved cycling performance. In contrast, the ZnO coating is not electrochemically stable, so the ZnO-coated LiCoO2 electrode exhibits a similar cycling performance with the bare LiCoO2 electrode

Lecture 07: Nonlinear Preconditioning Methods and Applications

We consider solving system of nonlinear algebraic equations arising from the discretization of partial differential equations. Inexact Newton is a popular technique for such problems. When the nonlinearities in the system are well-balanced, Newton\u27s method works well, but when a small number of nonlinear functions in the system are much more nonlinear than the others, Newton may converge slowly or even stagnate. In such a situation, we introduce some nonlinear preconditioners to balance the nonlinearities in the system. The preconditioners are often constructed using a combination of some domain decomposition methods and nonlinear elimination methods. For the nonlinearly preconditioned problem, we show that fast convergence can be restored. In this talk we first review the basic algorithms, and then discuss some recent progress in the applications of nonlinear preconditioners for some difficult problems arising in computational mechanics including both fluid dynamics and solid mechanics