209 research outputs found
A Robust Beamformer Based on Weighted Sparse Constraint
Applying a sparse constraint on the beam pattern has been suggested to
suppress the sidelobe level of a minimum variance distortionless response
(MVDR) beamformer. In this letter, we introduce a weighted sparse constraint in
the beamformer design to provide a lower sidelobe level and deeper nulls for
interference avoidance, as compared with a conventional MVDR beamformer. The
proposed beamformer also shows improved robustness against the mismatch between
the steering angle and the direction of arrival (DOA) of the desired signal,
caused by imperfect estimation of DOA.Comment: 4 pages, 2 figure
Optimal decentralized spectral resource allocation for OFDMA downlink of femto networks via adaptive gradient vector step size approach
For the orthogonal frequency division multiple access (OFDMA) downlink of a femto network, the resource allocation scheme would aim to maximize the area spectral efficiency (ASE) subject to constraints on the radio resources per transmission interval accessible by each femtocell. An optimal resource allocation scheme for completely decentralized femtocell deployments leads to a nonlinear optimization problem because the cost function of the optimization problem is nonlinear. In this paper, an adaptive gradient vector step size approach is proposed for finding the optimal solution of the optimization problem. Computer numerical simulation results show that our proposed method is more efficient than existing exhaustive search methods
Decentralized spectral resource allocation for OFDMA downlink of coexisting macro/femto networks using filled function method
For an orthogonal frequency division multiple access (OFDMA) downlink of a spectrally coexisting macro and femto network, a resource allocation scheme would aim to maximize the area spectral efficiency (ASE) subject to constraints on the radio resources per transmission interval accessible by each femtocell. An optimal resource allocation scheme for completely decentralized deployments leads however to a nonconvex optimization problem. In this paper, a filled function method is employed to find the global maximum of the optimization problem. Simulation results show that our proposed method is efficient and effective
Power-Efficient Ultra-Wideband Waveform Design Considering Radio Channel Effects
This paper presents a power-efficient mask-constrained ultra-wideband (UWB)
waveform design with radio channel effects taken into consideration. Based on a
finite impulse response (FIR) filter, we develop a convex optimization model
with respect to the autocorrelation of the filter coefficients to optimize the
transmitted signal power spectrum, subject to a regulatory emission mask. To
improve power efficiency, effects of transmitter radio frequency (RF)
components are included in the optimization of the transmitter-output waveform,
and radio propagation effects are considered for optimizing at the receiver.
Optimum coefficients of the FIR filter are obtained through spectral
factorization of their autocorrelations. Simulation results show that the
proposed method is able to maximize the transmitted UWB signal power under mask
constraints set by regulatory authorities, while mitigating the power loss
caused by channel attenuations.Comment: 14 pages, 2 figures, 1 tabl
Optimization Rotor Hole to Reduce Force in Cold Pressing Rotor into Crankshaft
Assembling rotor with crankshaft of a hermetic reciprocating compressor is, normally, heating of the rotor and then putting it into crankshaft. This assembly method allows larger magnitude of interference between rotor and crankshaft. Tolerance band of crankshaft could be relaxed and facilitate the process, however, the process requires heating equipment and higher energy consumption, obviously, this will increase the manufacturing cost of the compressor. In this situation, using cold pressing rotor into crankshaft can avoid the disadvantage mentioned above effectively, moreover, easily mount the rotor at the accurate location. Using of the original design of the rotor and crankshaft cold press will lead large force which may damage the crankshaft. This article presents an analysis about a geometric proposal for the rotor hole that guarantees to withstand sufficient torque, while cold press force is under the crankshaft yield strength
On Providing Downlink Services in Collocated Spectrum-Sharing Macro and Femto Networks
Femtocells have been considered by the wireless industry as a cost-effective
solution not only to improve indoor service providing, but also to unload
traffic from already overburdened macro networks. Due to spectrum availability
and network infrastructure considerations, a macro network may have to share
spectrum with overlaid femtocells. In spectrum-sharing macro and femto
networks, inter-cell interference caused by different transmission powers of
macrocell base stations (MBS) and femtocell access points (FAP), in conjunction
with potentially densely deployed femtocells, may create dead spots where
reliable services cannot be guaranteed to either macro or femto users. In this
paper, based on a thorough analysis of downlink (DL) outage probabilities (OP)
of collocated spectrum-sharing orthogonal frequency division multiple access
(OFDMA) based macro and femto networks, we devise a decentralized strategy for
an FAP to self-regulate its transmission power level and usage of radio
resources depending on its distance from the closest MBS. Simulation results
show that the derived closed-form lower bounds of DL OPs are tight, and the
proposed decentralized femtocell self-regulation strategy is able to guarantee
reliable DL services in targeted macro and femto service areas while providing
superior spatial reuse, for even a large number of spectrum-sharing femtocells
deployed per cell site
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