15 research outputs found
Dual-Polarized Reconfigurable Intelligent Surface Assisted Broad Beamforming
A reconfigurable intelligent surface (RIS) consists of a large number of
low-cost elements that can control the propagation environment seen from a
transmitter by intelligently applying phase shifts to impinging signals before
reflection. This paper studies an RIS-assisted communication system where a
transmitter wants to transmit a common signal to many users residing in a wide
angular area. To cover this sector uniformly, the RIS needs to radiate a broad
beam with a spatially flat array factor, instead of a narrow beam as normally
considered. To achieve this, we propose to use a dual-polarized RIS consisting
of elements with orthogonal polarizations and show that the RIS can produce a
broad beam if the phase shift configuration vectors in the two polarizations
form a so-called Golay complementary sequence pair. By utilizing their
properties, we also present a method for constructing configuration for large
RISs from smaller ones, while preserving the broad radiation pattern of the
smaller RIS. The numerical results corroborate the mathematical analyses and
highlight the greatly improved coverage properties.Comment: This letter has been accepted for publication in IEEE Communications
Letter
Asymptotic Analysis of SU-MIMO Channels With Transmitter Noise and Mismatched Joint Decoding
Hardware impairments in radio-frequency components of a wireless system cause
unavoidable distortions to transmission that are not captured by the
conventional linear channel model. In this paper, a 'binoisy' single-user
multiple-input multiple-output (SU-MIMO) relation is considered where the
additional distortions are modeled via an additive noise term at the transmit
side. Through this extended SU-MIMO channel model, the effects of transceiver
hardware impairments on the achievable rate of multi-antenna point-to-point
systems are studied. Channel input distributions encompassing practical
discrete modulation schemes, such as, QAM and PSK, as well as Gaussian
signaling are covered. In addition, the impact of mismatched detection and
decoding when the receiver has insufficient information about the
non-idealities is investigated. The numerical results show that for realistic
system parameters, the effects of transmit-side noise and mismatched decoding
become significant only at high modulation orders.Comment: 16 pages, 7 figure
On the Optimal Precoding for MIMO Gaussian Wire-Tap Channels
We consider the problem of finding secrecy rate of a multiple-input
multiple-output (MIMO) wire-tap channel. A transmitter, a legitimate receiver,
and an eavesdropper are all equipped with multiple antennas. The channel states
from the transmitter to the legitimate user and to the eavesdropper are assumed
to be known at the transmitter. In this contribution, we address the problem of
finding the optimal precoder/transmit covariance matrix maximizing the secrecy
rate of the given wiretap channel. The problem formulation is shown to be
equivalent to a difference of convex functions programming problem and an
efficient algorithm for addressing this problem is developed.Comment: Published in Proceedings of the Tenth International Symposium on
Wireless Communication Systems (ISWCS 2013), Ilmenau, Germany, August 201
Large-system analysis of correlated MIMO multiple access channels with arbitrary signaling in the presence of interference
Presence of multiple antennas on both sides of a communication channel
promises significant improvements in system throughput and power efficiency. In
effect, a new class of large multiple-input multiple-output (MIMO)
communication systems has recently emerged and attracted both scientific and
industrial attention. To analyze these systems in realistic scenarios, one has
to include such aspects as co-channel interference, multiple access and spatial
correlation. In this paper, we study the properties of correlated MIMO
multiple-access channels in the presence of external interference. Using the
replica method from statistical physics, we derive the ergodic sum-rate of the
communication for arbitrary signal constellations when the numbers of antennas
at both ends of the channel grow large. Based on these asymptotic expressions,
we also address the problem of sum-rate maximization using statistical channel
information and linear precoding. The numerical results demonstrate that when
the interfering terminals use discrete constellations, the resulting
interference becomes easier to handle compared to Gaussian signals. Thus, it
may be possible to accommodate more interfering transmitter-receiver pairs
within the same area as compared to the case of Gaussian signals. In addition,
we demonstrate numerically for the Gaussian and QPSK signaling schemes that it
is possible to design precoder matrices that significantly improve the
achievable rates at low-to-mid range of signal-to-noise ratios when compared to
isotropic precoding.Comment: To appear in IEEE Transactions on Wireless Communication