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The frequency-selective channel-estimation problem in multi-input-multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems is investigated from the perspective of compressed sensing (CS). By minimizing the mutual coherence of the measurement matrix in CS theory, two pilot allocation methods for the CS-based channel estimation in MIMO-OFDM systems are proposed. Simulation results show that using the pilot patterns designed by the two proposed methods gives a much better performance than using other pilot patterns in terms of the mean square error of the channel estimate as well as the bit error rate of the system. Moreover, the optimal pilot patterns obtained by the proposed second method based on genetic algorithm and shift mechanism could offer a larger performance gain than those by the first method based on minimizing the largest element in the mutual coherence set possessed by pilot patterns for all multiple antenna ports.Index Terms-Channel estimation, compressed sensing (CS), multi-input-multi-output orthogonal frequency division multiplexing (MIMO-OFDM), mutual coherence, pilot allocation.

Considering tip relief, a finite element model of a spur gear pair in mesh is established by ANSYS software. Time-varying mesh stiffness under different amounts of tip relief is calculated based on the finite element model. Then, a finite element model of a geared rotor system is developed by MATLAB software considering the effects of time-varying mesh stiffness and constant load torque. Emphasis is given to the effects of tip relief on the lateral–torsional coupling vibration responses of the system. The results show that as the amount of tip relief increases, the saltation of time-varying mesh stiffness reduces at the position of approach action and transition mesh region from the single tooth to double tooth. A number of primary resonances and some super-harmonic of gears 1 and 2 are excited by time-varying mesh stiffness in amplitude frequency responses. As the amount of tip relief increases, some super-harmonic responses change due to the variation in the higher frequency components of time-varying mesh stiffness. After tip relief, the vibration and meshing force decrease obviously at lower mesh frequency range except at some resonance frequencies; however, tip relief is not effective in reducing the vibration at higher mesh frequency range. The amplitude fluctuation of the vibration acceleration reduces evidently after considering tip relief, which is not remarkable with the increase of meshing frequency.

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An ad hoc wireless network permits wireless mobile nodes to communicate without prior infrastructure. Due to the limited range of each wireless node, communication sessions between two nodes are usually established through a number of intermediate nodes. Unfortunately, some of these intermediate nodes might be malicious, forming a threat to the security or confidentiality of exchanged data. While data encryption can protect the content exchanged between nodes, analysis of communication patterns may reveal valuable information about end users and their relationships. Using anonymous paths for communication provides security and privacy against traffic analysis. To establish these anonymous paths, all nodes build a global view of the network by exchanging routing information. In dynamic ad hoc networks, building this global view is not an option. In this paper, we propose and analyze a distributed route construction algorithm for use in the establishment of anonymous routing paths in ad hoc wireless networks.

resistance of the mushroom shaped gate is reduced by a factor of 7 over conventional ones. 19 02c -k 0 0002 0 2 0 'DS, '

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This paper addresses the sparse channel estimation problem in multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems from the perspective of distributed compressed sensing (DCS). It is focused on deterministic pilot allocation of MIMO-OFDM systems to improve the performance of DCS-based channel estimation. By transforming the problem of DCS-based channel estimation to a problem of reconstructing block-sparse signals, a class of mutual coherence-related criteria is first proposed for optimizing pilot locations. By employing the proposed criteria, a genetic algorithm-based method of optimizing the pilot locations is then presented. Simulation results show that the DCS-based MIMO channel estimation with optimized pilot locations can improve the spectrum efficiency by nearly 36% and the bit error rate (BER) performance by 1.5dB, as compared with the least square (LS) channel estimation with equidistant pilot locations. Moreover, the DCS-based MIMO channel estimation yields a 4.7% improvement in spectrum efficiency under the same BER performance over the CS-based channel estimation. Index Terms-MIMO-OFDM, channel estimation, distributed compressed sensing, mutual coherence, block-sparse signals, pilot allocation.