584 research outputs found
Weighted Fair Multicast Multigroup Beamforming under Per-antenna Power Constraints
A multi-antenna transmitter that conveys independent sets of common data to
distinct groups of users is considered. This model is known as physical layer
multicasting to multiple co-channel groups. In this context, the practical
constraint of a maximum permitted power level radiated by each antenna is
addressed. The per-antenna power constrained system is optimized in a maximum
fairness sense with respect to predetermined quality of service weights. In
other words, the worst scaled user is boosted by maximizing its weighted
signal-to-interference plus noise ratio. A detailed solution to tackle the
weighted max-min fair multigroup multicast problem under per-antenna power
constraints is therefore derived. The implications of the novel constraints are
investigated via prominent applications and paradigms. What is more, robust
per-antenna constrained multigroup multicast beamforming solutions are
proposed. Finally, an extensive performance evaluation quantifies the gains of
the proposed algorithm over existing solutions and exhibits its accuracy over
per-antenna power constrained systems.Comment: Under review in IEEE Transactions in Signal Processin
Multicast Multigroup Beamforming under Per-antenna Power Constraints
Linear precoding exploits the spatial degrees of freedom offered by
multi-antenna transmitters to serve multiple users over the same frequency
resources. The present work focuses on simultaneously serving multiple groups
of users, each with its own channel, by transmitting a stream of common symbols
to each group. This scenario is known as physical layer multicasting to
multiple co-channel groups. Extending the current state of the art in
multigroup multicasting, the practical constraint of a maximum permitted power
level radiated by each antenna is tackled herein. The considered per antenna
power constrained system is optimized in a maximum fairness sense. In other
words, the optimization aims at favoring the worst user by maximizing the
minimum rate. This Max-Min Fair criterion is imperative in multicast systems,
where the performance of all the receivers listening to the same multicast is
dictated by the worst rate in the group. An analytic framework to tackle the
Max-Min Fair multigroup multicasting scenario under per antenna power
constraints is therefore derived. Numerical results display the accuracy of the
proposed solution and provide insights to the performance of a per antenna
power constrained system.Comment: Presented in IEEE ICC 2014, Sydney, AUS. arXiv admin note:
substantial text overlap with arXiv:1406.755
Multicast Multigroup Beamforming for Per-antenna Power Constrained Large-scale Arrays
Large in the number of transmit elements, multi-antenna arrays with
per-element limitations are in the focus of the present work. In this context,
physical layer multigroup multicasting under per-antenna power constrains, is
investigated herein. To address this complex optimization problem
low-complexity alternatives to semi-definite relaxation are proposed. The goal
is to optimize the per-antenna power constrained transmitter in a maximum
fairness sense, which is formulated as a non-convex quadratically constrained
quadratic problem. Therefore, the recently developed tool of feasible point
pursuit and successive convex approximation is extended to account for
practical per-antenna power constraints. Interestingly, the novel iterative
method exhibits not only superior performance in terms of approaching the
relaxed upper bound but also a significant complexity reduction, as the
dimensions of the optimization variables increase. Consequently, multicast
multigroup beamforming for large-scale array transmitters with per-antenna
dedicated amplifiers is rendered computationally efficient and accurate. A
preliminary performance evaluation in large-scale systems for which the
semi-definite relaxation constantly yields non rank-1 solutions is presented.Comment: submitted to IEEE SPAWC 2015. arXiv admin note: substantial text
overlap with arXiv:1406.755
Secure Satellite Communication Systems Design with Individual Secrecy Rate Constraints
In this paper, we study multibeam satellite secure communication through
physical (PHY) layer security techniques, i.e., joint power control and
beamforming. By first assuming that the Channel State Information (CSI) is
available and the beamforming weights are fixed, a novel secure satellite
system design is investigated to minimize the transmit power with individual
secrecy rate constraints. An iterative algorithm is proposed to obtain an
optimized power allocation strategy. Moreover, sub-optimal beamforming weights
are obtained by completely eliminating the co-channel interference and nulling
the eavesdroppers' signal simultaneously. In order to obtain jointly optimized
power allocation and beamforming strategy in some practical cases, e.g., with
certain estimation errors of the CSI, we further evaluate the impact of the
eavesdropper's CSI on the secure multibeam satellite system design. The
convergence of the iterative algorithm is proven under justifiable assumptions.
The performance is evaluated by taking into account the impact of the number of
antenna elements, number of beams, individual secrecy rate requirement, and
CSI. The proposed novel secure multibeam satellite system design can achieve
optimized power allocation to ensure the minimum individual secrecy rate
requirement. The results show that the joint beamforming scheme is more
favorable than fixed beamforming scheme, especially in the cases of a larger
number of satellite antenna elements and higher secrecy rate requirement.
Finally, we compare the results under the current satellite air-interface in
DVB-S2 and the results under Gaussian inputs.Comment: 34 pages, 10 figures, 1 table, submitted to "Transactions on
Information Forensics and Security
Codebook Based Hybrid Precoding for Millimeter Wave Multiuser Systems
In millimeter wave (mmWave) systems, antenna architecture limitations make it
difficult to apply conventional fully digital precoding techniques but call for
low cost analog radio-frequency (RF) and digital baseband hybrid precoding
methods. This paper investigates joint RF-baseband hybrid precoding for the
downlink of multiuser multi-antenna mmWave systems with a limited number of RF
chains. Two performance measures, maximizing the spectral efficiency and the
energy efficiency of the system, are considered. We propose a codebook based RF
precoding design and obtain the channel state information via a beam sweep
procedure. Via the codebook based design, the original system is transformed
into a virtual multiuser downlink system with the RF chain constraint.
Consequently, we are able to simplify the complicated hybrid precoding
optimization problems to joint codeword selection and precoder design (JWSPD)
problems. Then, we propose efficient methods to address the JWSPD problems and
jointly optimize the RF and baseband precoders under the two performance
measures. Finally, extensive numerical results are provided to validate the
effectiveness of the proposed hybrid precoders.Comment: 35 pages, 9 figures, to appear in Trans. on Signal Process, 201
Multi-user spatial diversity techniques for wireless communication systems
Multiple antennas at the transmitter and receiver, formally known as multiple-input
multiple-output (MIMO) systems have the potential to either increase the data rates
through spatial multiplexing or enhance the quality of services through exploitation
of diversity. In this thesis, the problem of downlink spatial multiplexing, where a
base station (BS) serves multiple users simultaneously in the same frequency band is
addressed. Spatial multiplexing techniques have the potential to make huge saving
in the bandwidth utilization. We propose spatial diversity techniques with and without
the assumption of perfect channel state information (CSI) at the transmitter.
We start with proposing improvement to signal-to-leakage ratio (SLR) maximization
based spatial multiplexing techniques for both fiat fading and frequency selective
channels. [Continues.
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