3,913 research outputs found
Robust Location-Aided Beam Alignment in Millimeter Wave Massive MIMO
Location-aided beam alignment has been proposed recently as a potential
approach for fast link establishment in millimeter wave (mmWave) massive MIMO
(mMIMO) communications. However, due to mobility and other imperfections in the
estimation process, the spatial information obtained at the base station (BS)
and the user (UE) is likely to be noisy, degrading beam alignment performance.
In this paper, we introduce a robust beam alignment framework in order to
exhibit resilience with respect to this problem. We first recast beam alignment
as a decentralized coordination problem where BS and UE seek coordination on
the basis of correlated yet individual position information. We formulate the
optimum beam alignment solution as the solution of a Bayesian team decision
problem. We then propose a suite of algorithms to approach optimality with
reduced complexity. The effectiveness of the robust beam alignment procedure,
compared with classical designs, is then verified on simulation settings with
varying location information accuracies.Comment: 24 pages, 7 figures. The short version of this paper has been
accepted to IEEE Globecom 201
Antenna arrays for the downlink of FDD wideband CDMA communication systems
The main subject of this thesis is the investigation of antenna array techniques for improving
the performance of the downlink of wideband code division multiple access (WCDMA) mobile
communication systems. These communication systems operate in frequency division duplex
(FDD) mode and the antenna arrays are employed in the base station. A number of diversity,
beamforming and hybrid techniques are analysed and their bit error ratio (BER) versus signalto-
noise ratio (SNR) performance is calculated as a function of the eigenvalues of the mean
channel correlation matrix, where this is applicable. Also, their BER versus SNR performance
is evaluated by means of computer simulations in various channel environments and using
different numbers of transmit antenna elements in the base station. The simulation results
of the techniques, along with other characteristics, are compared to examine the relationship
among their performance in various channel environments and investigate which technique is
most suitable for each channel environment.
Next, a combination of the channel correlation matrix eigenvalue decomposition and space-time
processing is proposed as a possible open loop approach to the downlink data signal transmission.
It decomposes the channel into M components in the form of eigenvectors (M is the
number of transmit antennas in the base station), and attempts to minimise the transmit power
that is needed to achieve a target BER at the mobile receiver by employing the optimum number
of these eigenvectors. The lower transmit power and the directional transmission by means
of eigenvectors are expected to lower interference levels to non-desired users (especially to
those users who are not physically close to the direction(s) of transmission). Theoretical and
simulation results suggest that this approach performs better than other presented open loop
techniques, while the performance gain depends on M and the channel environment.
In simulations it is usually assumed that the base and mobile station have access to perfect
estimates of all needed parameters (e.g. channel coecients). However, in practical systems
they make use of pilot and/or feedback signals to obtain estimates of these parameters, which
result in noisy estimates. The impact of the noisy estimates on the performance of various
techniques is investigated by computer simulations, and the results suggest that there is typically
some performance loss. The loss depends on the parameter that is estimated from pilot signals,
and may be a function of M, SNR and/or the channel environment.
In certain beamforming techniques the base station operates the transmit antenna array in an
open loop fashion by estimating the downlink weight vector from the directional information
of the uplink channel. Nevertheless, in FDD systems this results in performance loss due to
the separation between the uplink and downlink carrier frequencies (`FDD gap'). This loss is
quantified and the results show that it is a function of M and the FDD gap. Also, a very simple
technique for compensating this loss is proposed, and results obtained after its application suggest
that it eliminates most of the loss. Comparison of the proposed technique with an existing
compensation technique suggests that, even though the latter is more complex than the former,
it yields very little additional improvement
AirSync: Enabling Distributed Multiuser MIMO with Full Spatial Multiplexing
The enormous success of advanced wireless devices is pushing the demand for
higher wireless data rates. Denser spectrum reuse through the deployment of
more access points per square mile has the potential to successfully meet the
increasing demand for more bandwidth. In theory, the best approach to density
increase is via distributed multiuser MIMO, where several access points are
connected to a central server and operate as a large distributed multi-antenna
access point, ensuring that all transmitted signal power serves the purpose of
data transmission, rather than creating "interference." In practice, while
enterprise networks offer a natural setup in which distributed MIMO might be
possible, there are serious implementation difficulties, the primary one being
the need to eliminate phase and timing offsets between the jointly coordinated
access points.
In this paper we propose AirSync, a novel scheme which provides not only time
but also phase synchronization, thus enabling distributed MIMO with full
spatial multiplexing gains. AirSync locks the phase of all access points using
a common reference broadcasted over the air in conjunction with a Kalman filter
which closely tracks the phase drift. We have implemented AirSync as a digital
circuit in the FPGA of the WARP radio platform. Our experimental testbed,
comprised of two access points and two clients, shows that AirSync is able to
achieve phase synchronization within a few degrees, and allows the system to
nearly achieve the theoretical optimal multiplexing gain. We also discuss MAC
and higher layer aspects of a practical deployment. To the best of our
knowledge, AirSync offers the first ever realization of the full multiuser MIMO
gain, namely the ability to increase the number of wireless clients linearly
with the number of jointly coordinated access points, without reducing the per
client rate.Comment: Submitted to Transactions on Networkin
AoA-aware Probabilistic Indoor Location Fingerprinting using Channel State Information
With expeditious development of wireless communications, location
fingerprinting (LF) has nurtured considerable indoor location based services
(ILBSs) in the field of Internet of Things (IoT). For most pattern-matching
based LF solutions, previous works either appeal to the simple received signal
strength (RSS), which suffers from dramatic performance degradation due to
sophisticated environmental dynamics, or rely on the fine-grained physical
layer channel state information (CSI), whose intricate structure leads to an
increased computational complexity. Meanwhile, the harsh indoor environment can
also breed similar radio signatures among certain predefined reference points
(RPs), which may be randomly distributed in the area of interest, thus mightily
tampering the location mapping accuracy. To work out these dilemmas, during the
offline site survey, we first adopt autoregressive (AR) modeling entropy of CSI
amplitude as location fingerprint, which shares the structural simplicity of
RSS while reserving the most location-specific statistical channel information.
Moreover, an additional angle of arrival (AoA) fingerprint can be accurately
retrieved from CSI phase through an enhanced subspace based algorithm, which
serves to further eliminate the error-prone RP candidates. In the online phase,
by exploiting both CSI amplitude and phase information, a novel bivariate
kernel regression scheme is proposed to precisely infer the target's location.
Results from extensive indoor experiments validate the superior localization
performance of our proposed system over previous approaches
Distributed space time block coding and application in cooperative cognitive relay networks
The design and analysis of various distributed space time block coding
schemes for cooperative relay networks is considered in this thesis.
Rayleigh frequency flat and selective fading channels are assumed to
model the links in the networks, and interference suppression techniques
together with an orthogonal frequency division multiplexing (OFDM)
type transmission approach are employed to mitigate synchronization
errors at the destination node induced by the different delays through
the relay nodes.
Closed-loop space time block coding is first considered in the context
of decode-and-forward (regenerative) networks. In particular, quasi orthogonal
and extended orthogonal coding techniques are employed for
transmission from four relay nodes and parallel interference cancellation
detection is exploited to mitigate synchronization errors. Availability
of a direct link between the source and destination nodes is studied.
Outer coding is then added to gain further improvement in end-to-end
performance and amplify-and-forward (non regenerative) type networks
together with distributed space time coding are considered to reduce
relay node complexity. A novel detection scheme is then proposed
for decode-and-forward and amplify-and-forward networks with closed-loop
extended orthogonal coding and closed-loop quasi-orthogonal coding
which reduce the computational complexity of the parallel interference cancellation. The near-optimum detector is presented for relay
nodes with single or dual antennas. End-to-end bit error rate simulations
confirm the potential of the approach and its ability to mitigate
synchronization errors
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