3,658 research outputs found
Design and Analysis of Transmit Beamforming for Millimetre Wave Base Station Discovery
In this paper, we develop an analytical framework for the initial access
(a.k.a. Base Station (BS) discovery) in a millimeter-wave (mm-wave)
communication system and propose an effective strategy for transmitting the
Reference Signals (RSs) used for BS discovery. Specifically, by formulating the
problem of BS discovery at User Equipments (UEs) as hypothesis tests, we derive
a detector based on the Generalised Likelihood Ratio Test (GLRT) and
characterise the statistical behaviour of the detector. The theoretical results
obtained allow analysis of the impact of key system parameters on the
performance of BS discovery, and show that RS transmission with narrow beams
may not be helpful in improving the overall BS discovery performance due to the
cost of spatial scanning. Using the method of large deviations, we identify the
desirable beam pattern that minimises the average miss-discovery probability of
UEs within a targeted detectable region. We then propose to transmit the RS
with sequential scanning, using a pre-designed codebook with narrow and/or wide
beams to approximate the desirable patterns. The proposed design allows
flexible choices of the codebook sizes and the associated beam widths to better
approximate the desirable patterns. Numerical results demonstrate the
effectiveness of the proposed method.Comment: 30 pages, 13 figures, submitte
Phase only transmit beamforming for spectrum sharing microwave systems
This paper deals with the problem of phase-only transmit beamforming in spectrum sharing microwave systems. In contrast to sub-6 GHz schemes, general microwave systems require a large number of antennas due to its huge path loss. As a consequence, digital beamforming needs a large number of computational resources compared to analog beamforming, which only needs a single radio-frequency chain, results the less computational demanding solution. Analog schemes are usually composed by a phase shifter network whose elements transmit at a certain fixed power so that the system designer shall compute the phase values for each element given a set of directions. This approach leads to non-convex quadratic problems where the traditional semidefinite relaxation fails to deliver satisfactory outcomes. In order to solve this, we propose a nonsmooth method that behaves well in several scenarios. Numerical evaluations in different spectrum sharing scenarios, which show the performance of our method, are provided.Peer ReviewedPostprint (author's final draft
OAM multiple transmission using uniform circular arrays: numerical modeling and experimental verification with two digital television signals
In this work we present the outcomes of a radio-frequency OAM transmission
between two antenna arrays performed in a real-world context. The analysis is
supplemented by deep simulative investigations able to provide both a
preliminary overview of the experimental scenario and a posteriori validation
of the achieved results. As a first step, the far-field OAM communication link
is tested at various frequencies and the corresponding link budget is studied
by means of an angular scan generated by the rotation of the receiving system.
Then, on the same site, two digital television signals encoded as OAM modes
(=1 and =-1) are simultaneously transmitted at a common frequency
of 198.5 MHz with good mode insulation.Comment: 16 pages, 14 figure
Spatial Multiplexing of QPSK Signals with a Single Radio: Antenna Design and Over-the-Air Experiments
The paper describes the implementation and performance analysis of the first
fully-operational beam-space MIMO antenna for the spatial multiplexing of two
QPSK streams. The antenna is composed of a planar three-port radiator with two
varactor diodes terminating the passive ports. Pattern reconfiguration is used
to encode the MIMO information onto orthogonal virtual basis patterns in the
far-field. A measurement campaign was conducted to compare the performance of
the beam-space MIMO system with a conventional 2-by-?2 MIMO system under
realistic propagation conditions. Propagation measurements were conducted for
both systems and the mutual information and symbol error rates were estimated
from Monte-Carlo simulations over the measured channel matrices. The results
show the beam-space MIMO system and the conventional MIMO system exhibit
similar finite-constellation capacity and error performance in NLOS scenarios
when there is sufficient scattering in the channel. In comparison, in LOS
channels, the capacity performance is observed to depend on the relative
polarization of the receiving antennas.Comment: 31 pages, 23 figure
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