441 research outputs found
Perturbation-based Distributed Beamforming for Wireless Relay Networks
This paper deals with distributed beamforming techniques for wireless
networks with half-duplex amplify-and-forward relays. Existing schemes optimize
the beamforming weights based on the assumption that channel state information
(CSI) is available at the relays. We propose to use adaptive beamforming based
on deterministic perturbations and limited feedback (1-bit) from the
destination to the relays in order to avoid CSI at the relays. Two scalable
perturbation schemes are considered and practical implementation aspects are
addressed. Simulation results confirm that the proposed techniques closely
approach optimum performance and have satisfactory tracking properties in
time-varying environments.Comment: 5 pages, 5 figures; accepted at IEEE GLOBECOM 2008, New Orleans, LA,
Nov 30 - Dec 4, 200
A scalable architecture for distributed receive beamforming: analysis and experimental demonstration
We propose, analyze and demonstrate an architecture for scalable cooperative
reception. In a cluster of N + 1 receive nodes, one node is designated as the
final receiver, and the N other nodes act as amplify-and-forward relays which
adapt their phases such that the relayed signals add up constructively at the
designated receiver. This yields received SNR scaling linearly with N, while
avoiding the linear increase in overhead incurred by a direct approach in which
received signals are separately quantized and transmitted for centralized
processing. By transforming the task of long-distance distributed receive
beamforming into one of local distributed transmit beamforming, we can leverage
a scalable one-bit feedback algorithm for phase synchronization. We show that
time division between the long-distance and local links eliminates the need for
explicit frequency synchronization. We provide an analytical framework, whose
results closely match Monte Carlo simulations, to evaluate the impact of phase
noise due to relaying delay on the performance of the one-bit feedback
algorithm. Experimental results from our prototype implementation on
software-defined radios demonstrate the expected gains in received signal
strength despite significant oscillator drift, and are consistent with results
from our analytical framework.Comment: submitted to IEEE Transactions on Wireless Communication
Study of Robust Distributed Beamforming Based on Cross-Correlation and Subspace Projection Techniques
In this work, we present a novel robust distributed beamforming (RDB)
approach to mitigate the effects of channel errors on wireless networks
equipped with relays based on the exploitation of the cross-correlation between
the received data from the relays at the destination and the system output. The
proposed RDB method, denoted cross-correlation and subspace projection (CCSP)
RDB, considers a total relay transmit power constraint in the system and the
objective of maximizing the output signal-to-interference-plus-noise ratio
(SINR). The relay nodes are equipped with an amplify-and-forward (AF) protocol
and we assume that the channel state information (CSI) is imperfectly known at
the relays and there is no direct link between the sources and the destination.
The CCSP does not require any costly optimization procedure and simulations
show an excellent performance as compared to previously reported algorithms.Comment: 3 figures, 7 pages. arXiv admin note: text overlap with
arXiv:1707.00953
Study of Opportunistic Cooperation Techniques using Jamming and Relays for Physical-Layer Security in Buffer-aided Relay Networks
In this paper, we investigate opportunistic relay and jammer cooperation
schemes in multiple-input multiple-output (MIMO) buffer-aided relay networks.
The network consists of one source, an arbitrary number of relay nodes,
legitimate users and eavesdroppers, with the constraints of physical layer
security. We propose an algorithm to select a set of relay nodes to enhance the
legitimate users' transmission and another set of relay nodes to perform
jamming of the eavesdroppers. With Inter-Relay interference (IRI) taken into
account, interference cancellation can be implemented to assist the
transmission of the legitimate users. Secondly, IRI can also be used to further
increase the level of harm of the jamming signal to the eavesdroppers. By
exploiting the fact that the jamming signal can be stored at the relay nodes,
we also propose a hybrid algorithm to set a signal-to-interference and noise
ratio (SINR) threshold at the node to determine the type of signal stored at
the relay node. With this separation, the signals with high SINR are delivered
to the users as conventional relay systems and the low SINR performance signals
are stored as potential jamming signals. Simulation results show that the
proposed techniques obtain a significant improvement in secrecy rate over
previously reported algorithms.Comment: 8 pages, 3 figure
Robust Cooperative Relay Beamforming
In this paper, the robust distributed relay beamforming problem is solved
using the worst case approach, where the problem solution has been involved
because of the effect of uncertainty of channel knowledge on the quality of
service (QoS) constraints. It is shown that the original robust design, which
is a non-convex semi-infinite problem (SIP), can be relaxed and reformed to a
semi-definite problem (SDP). Monte-Carlo simulations are presented to verify
the performance improvement of our proposed robust problem over existing robust
and non-robust problems in terms of transmit power and symbol error
probability.Comment: IEEE Wireless Communications Letter
Energy-Efficient Deterministic Adaptive Beamforming Algorithms for Distributed Sensor/Relay Networks
In this study, energy-efficient deterministic adaptive beamforming algorithms
are proposed for distributed sensor/relay networks. Specifically, DBSA, D-QESA,
D-QESA-E, and a hybrid algorithm, hybrid-QESA, that combines the benefits of
both deterministic and random adaptive beamforming algorithms, are proposed.
Rigorous convergence analyses are provided for all our proposed algorithms and
convergence to the global optimal solution is shown for all our proposed
algorithms. Through extensive numerical simulations, we demonstrate that
superior performance is achieved by our proposed DBSA and D-QESA over random
adaptive beamforming algorithms for static channels. Surprisingly, D-QESA is
also more robust against random node removal than random adaptive beamforming
algorithms. For time-varying channels, hybrid-QESA indeed achieves the best
performance since it combines the benefits of both types of adaptive
beamforming algorithms. In summary, our proposed deterministic algorithms
demonstrate superior performance both in terms of convergence time and
robustness against channel and network uncertainties.Comment: Submitted for possible journal publicatio
Multi-User Flexible Coordinated Beamforming using Lattice Reduction for Massive MIMO Systems
The application of precoding algorithms in multi-user massive multiple-input
multiple-output (MU-Massive-MIMO) systems is restricted by the dimensionality
constraint that the number of transmit antennas has to be greater than or equal
to the total number of receive antennas. In this paper, a lattice reduction
(LR)-aided flexible coordinated beamforming (LR-FlexCoBF) algorithm is proposed
to overcome the dimensionality constraint in overloaded MU-Massive-MIMO
systems. A random user selection scheme is integrated with the proposed
LR-FlexCoBF to extend its application to MU-Massive-MIMO systems with arbitary
overloading levels. Simulation results show that significant improvements in
terms of bit error rate (BER) and sum-rate performances can be achieved by the
proposed LR-FlexCoBF precoding algorithm.Comment: 5 figures, Eusipc
Coordinate Tomlinson-Harashima Precoding Design for Overloaded Multi-user MIMO Systems
Tomlinson-Harashima precoding (THP) is a nonlinear processing technique
employed at the transmit side to implement the concept of dirty paper coding
(DPC). The perform of THP, however, is restricted by the dimensionality
constraint that the number of transmit antennas has to be greater or equal to
the total number of receive antennas. In this paper, we propose an iterative
coordinate THP algorithm for the scenarios in which the total number of receive
antennas is larger than the number of transmit antennas. The proposed algorithm
is implemented on two types of THP structures, the decentralized THP (dTHP)
with diagonal weighted filters at the receivers of the users, and the
centralized THP (cTHP) with diagonal weighted filter at the transmitter.
Simulation results show that a much better bit error rate (BER) and sum-rate
performances can be achieved by the proposed iterative coordinate THP compared
to the previous linear art.Comment: 3 figures, 6 pages, ISWCS 2014. arXiv admin note: text overlap with
arXiv:1401.475
Distributed Transmit Beamforming using Feedback Control
A simple feedback control algorithm is presented for distributed beamforming
in a wireless network. A network of wireless sensors that seek to cooperatively
transmit a common message signal to a Base Station (BS) is considered. In this
case, it is well-known that substantial energy efficiencies are possible by
using distributed beamforming. The feedback algorithm is shown to achieve the
carrier phase coherence required for beamforming in a scalable and distributed
manner. In the proposed algorithm, each sensor independently makes a random
adjustment to its carrier phase. Assuming that the BS is able to broadcast one
bit of feedback each timeslot about the change in received signal to noise
ratio (SNR), the sensors are able to keep the favorable phase adjustments and
discard the unfavorable ones, asymptotically achieving perfect phase coherence.
A novel analytical model is derived that accurately predicts the convergence
rate. The analytical model is used to optimize the algorithm for fast
convergence and to establish the scalability of the algorithm
Study of Efficient Robust Adaptive Beamforming Algorithms Based on Shrinkage Techniques
This paper proposes low-complexity robust adaptive beamforming (RAB)
techniques based on shrinkage methods. We firstly briefly review a
Low-Complexity Shrinkage-Based Mismatch Estimation (LOCSME) batch algorithm to
estimate the desired signal steering vector mismatch, in which the
interference-plus-noise covariance (INC) matrix is also estimated with a
recursive matrix shrinkage method. Then we develop low complexity adaptive
robust version of the conjugate gradient (CG) algorithm to both estimate the
steering vector mismatch and update the beamforming weights. A computational
complexity study of the proposed and existing algorithms is carried out.
Simulations are conducted in local scattering scenarios and comparisons to
existing RAB techniques are provided.Comment: 9 pages, 2 figures. arXiv admin note: text overlap with
arXiv:1505.0678
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