1,366 research outputs found
In-situ Measurements of Blast Seismic Waves and Their Safety Distance
Empirical formulae and their applications are given after systematically analysing the seismic wave data as measured in various blasting operations. The computed results are ln close agreement with the field measured dat
is diophantine over with 32 unknowns
In 2016 J. Koenigsmann refined a celebrated theorem of J. Robinson by proving
that is diophantine over , i.e., there
is a polynomial such
that for any rational number we have where variables range over
, equivalently In this paper we prove further that we
may even take and require deg, which provides the
best record in this direction. Combining this with a result of Sun, we get that
there is no algorithm to decide for any whether where
variables range over .Comment: 13 pages. Correct few typo
Beamforming Designs and Performance Evaluations for Intelligent Reflecting Surface Enhanced Wireless Communication System with Hardware Impairments
Intelligent reflecting surface (IRS) can effectively control the wavefront of
the impinging signals, and has emerged as a promising way to improve the energy
and spectrum efficiency of wireless communication systems. Most existing
studies were conducted with an assumption that the hardware operations are
perfect without any impairment. However, both physical transceiver and IRS
suffer from non-negligible hardware impairments in practice, which will bring
some major challenges, e.g., increasing the difficulty and complexity of the
beamforming designs, and degrading the system performance. In this paper, by
taking hardware impairments into consideration, we make the transmit and
reflect beamforming designs and evaluate the system performance. First, we
utilize the linear minimum mean square error estimator to make the channel
estimations, and analyze the factors that affect estimation accuracy. Then, we
derive the optimal transmit beamforming vector, and propose a gradient descent
method-based algorithm to obtain a sub-optimal reflect beamforming solution.
Next, we analyze the asymptotic channel capacities by considering two types of
asymptotics with respect to the transmit power and the numbers of antennas and
reflecting elements. Finally, we analyze the power scaling law and the energy
efficiency. By comparing the performance of our proposed algorithm with the
upper bound on the performance of global optimal reflect beamforming solution,
the simulation results demonstrate that our proposed algorithm can offer an
outstanding performance with low computational complexity. The simulation
results also show that there is no need to cost a lot on expensive antennas to
achieve both high spectral efficiency and energy efficiency when the
communication system is assisted by an IRS and suffer from hardware
impairments.Comment: arXiv admin note: text overlap with arXiv:2004.09804,
arXiv:2004.0976
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