509 research outputs found
A Tutorial on the Optimization of Amplify-and-Forward MIMO Relay Systems
The remarkable promise of multiple-input multiple-output (MIMO) wireless channels has motivated an intense research activity to characterize the theoretical and practical issues associated with the design of transmit (source) and receive (destination) processing matrices under different operating conditions. This activity was primarily focused on point-to-point (single-hop) communications but more recently there has been an extensive work on two-hop or multi-hop settings in which single or multiple relays are used to deliver the information from the source to the destination. The aim of this tutorial is to provide an up-to-date overview of the fundamental results and practical implementation issues of designing amplify-and-forward MIMO relay systems
Power Allocation in Two-Hop Amplify-and-Forward MIMO Relay Systems with QoS requirements
The problem of minimizing the total power consumption while satisfying
different quality-of-service (QoS) requirements in a two-hop multiple-input
multiple-output network with a single non-regenerative relay is considered. As
shown by Y. Rong in [1], the optimal processing matrices for both linear and
non-linear transceiver architectures lead to the diagonalization of the
source-relay-destination channel so that the power minimization problem reduces
to properly allocating the available power over the established links.
Unfortunately, finding the solution of this problem is numerically difficult as
it is not in a convex form. To overcome this difficulty, existing solutions
rely on the computation of upper- and lower-bounds that are hard to obtain or
require the relaxation of the QoS constraints. In this work, a novel approach
is devised for both linear and non-linear transceiver architectures, which
allows to closely approximate the solutions of the non-convex power allocation
problems with those of convex ones easy to compute in closed-form by means of
multi-step procedures of reduced complexity. Computer simulations are used to
assess the performance of the proposed approach and to make comparisons with
alternatives
Reconfigurable Intelligent Surfaces for Energy Efficiency in Wireless Communication
The adoption of a Reconfigurable Intelligent Surface (RIS) for downlink
multi-user communication from a multi-antenna base station is investigated in
this paper. We develop energy-efficient designs for both the transmit power
allocation and the phase shifts of the surface reflecting elements, subject to
individual link budget guarantees for the mobile users. This leads to
non-convex design optimization problems for which to tackle we propose two
computationally affordable approaches, capitalizing on alternating
maximization, gradient descent search, and sequential fractional programming.
Specifically, one algorithm employs gradient descent for obtaining the RIS
phase coefficients, and fractional programming for optimal transmit power
allocation. Instead, the second algorithm employs sequential fractional
programming for the optimization of the RIS phase shifts. In addition, a
realistic power consumption model for RIS-based systems is presented, and the
performance of the proposed methods is analyzed in a realistic outdoor
environment. In particular, our results show that the proposed RIS-based
resource allocation methods are able to provide up to higher energy
efficiency, in comparison with the use of regular multi-antenna
amplify-and-forward relaying.Comment: Accepted by IEEE TWC; additional materials on the topic are included
in the 2018 conference publications at ICASSP
(https://ieeexplore.ieee.org/abstract/document/8461496) and GLOBECOM 2018
(arXiv:1809.05397
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