SWIPT techniques for multiuser MIMO broadcast systems

In this paper, we present an approach to solve the nonconvex optimization problem that arises when designing the transmit covariance matrices in multiuser multiple-input multiple-output (MIMO) broadcast networks implementing simultaneous wireless information and power transfer (SWIPT). The MIMO SWIPT design is formulated as a nonconvex optimization problem in which system sum rate is optimized considering per-user harvesting constraints. Two different approaches are proposed. The first approach is based on a classical gradient-based method for constrained optimization. The second approach is based on difference of convex (DC) programming. The idea behind this approach is to obtain a convex function that approximates the nonconvex objective and, then, solve a series of convex subproblems that, eventually, will provide a (locally) optimum solution of the general nonconvex problem. The solution obtained from the proposed approach is compared to the classical block-diagonalization (BD) strategy, typically used to solve the nonconvex multiuser MIMO network by forcing no inter-user interference. Simulation results show that the proposed approach improves both the system sum rate and the power harvested by users simultaneously. In terms of computational time, the proposed DC programming outperforms the classical gradient methods.Peer ReviewedPostprint (author's final draft

Joint optimization of power and data transfer in multiuser MIMO systems

We present an approach to solve the nonconvex optimization problem that arises when designing the transmit covariance matrices in multiuser multiple-input multiple-output (MIMO) broadcast networks implementing simultaneous wireless information and power transfer (SWIPT). The MIMO SWIPT problem is formulated as a general multiobjective optimization problem, in which data rates and harvested powers are optimized simultaneously. Two different approaches are applied to reformulate the (nonconvex) multiobjective problem. In the first approach, the transmitter can control the specific amount of power to be harvested by power transfer whereas in the second approach the transmitter can only control the proportion of power to be harvested among the different harvesting users. We solve the resulting formulations using the majorization-minimization (MM) approach. The solution obtained from the MM approach is compared to the classical block-diagonalization (BD) strategy, typically used to solve the nonconvex multiuser MIMO network by forcing no interference among users. Simulation results show that the proposed approach improves over the BD approach both the system sum rate and the power harvested by users. Additionally, the computational times needed for convergence of the proposed methods are much lower than the ones required for classical gradient-based approaches.Peer ReviewedPostprint (author's final draft

User grouping and resource allocation in multiuser MIMO systems under SWIPT

This paper considers a broadcast multiple-input multiple-output (MIMO) network with multiple users and simultaneous wireless information and power transfer (SWIPT). In this scenario, it is assumed that some users are able to harvest power from radio frequency (RF) signals to recharge batteries through wireless power transfer from the transmitter, while others are served simultaneously with data transmission. The criterion driving the optimization and design of the system is based on the weighted sum rate for the users being served with data. At the same time, constraints stating minimum per-user harvested powers are included in the optimization problem. This paper derives the structure of the optimal transmit covariance matrices in the case where both types of users are present simultaneously in the network, particularizing the results to the cases where either only harvesting nodes or only information users are to be served. The trade-off between the achieved weighted sum rate and the powers harvested by the user terminals is analyzed and evaluated using the rate-power (R-P) region. Finally, we propose a two-stage user grouping mechanism that decides which users should be scheduled to receive information and which users should be configured to harvest energy from the RF signals in each particular scheduling period, this being one of the main contributions of this paper.Peer ReviewedPostprint (published version

Stochastic resource allocation with a backhaul constraint for the uplink

We propose a novel stochastic radio resource alloca- tion strategy for the uplink that achieves long-term fairness in terms of similar bitrates considering backhaul and air-interface capacity limitations. We focus on a single cell scenario based on WCDMA technology. We propose to use a maximin criteria to introduce fairness among the different users’ throughputs. An stochastic approximation is implemented to obtain an online algorithm where the Lagrange multipliers are estimated at each scheduling period. Our results show that the proposed scheme achieves higher fairness among the users and, in some cases, a higher sum-rate compared with the well-known proportional fair scheduler.Postprint (author's final draft

Three-dimensional metaphorical objects in street advertising

This paper aims at unravelling the role of metaphor in three street marketing campaign advertisements. Each advertisement is the product of a creative process involving metaphorical mappings from an urban object (shelter, bench, ramp) onto a target domain (a billboard). The study draws on two approaches from the fields of cognitive linguistics (Forceville 2009) and industrial design (Cila 2013) in order to provide a qualitative analysis of metaphor and modality in the so-called three-dimensional metaphorical objects involved in each advertisement. A new version of the interaction mode (Cila 2013: 18) is proposed as an analytical mode for those threedimensional metaphorical entities whose real-word materialisation establishes new sets of sensory-motor interactional pathways with human beings. Results show how metaphors combine to yield the desired interactive effects through different patterns of modality. The paper concludes that this combination is a key campaign asset and calls for further work on the deliberate use of metaphor in creative processes.P1.1A2014-2. Department of English Studies (Universitat Jaume I). IULMA (Institut Interuniversitari de Llengües Modernes Aplicades de la Comunitat Valenciana

A stochastic approach for resource allocation with backhaul and energy harvesting constraints

We propose a novel stochastic radio-resource-allocation strategy that achieves long-term fairness considering backhaul and air-interface capacity limitations. The base station (BS) is powered only with a finite battery that is recharged by an energy harvester. The energy harvesting is also taken into account in the proposed resource-allocation strategy. The constrained scenario is often found in remote rural areas where the backhaul connection is limited, and the BSs are fed with solar panels of reduced size. Our results show that the proposed scheme achieves higher fairness among the users and provides greater worst user rate and sum rate if an average backhaul constraint is considered.Peer ReviewedPostprint (published version

Base station on/off strategies for wireless networks powered with energy harvesting sources

In this paper, we present a procedure for switching on and off base stations (BSs) that are powered with solar panels and have finite batteries. In the scenario under consideration it is considered that the BSs are placed at the same site with fully overlapped coverage areas and using different frequencies. We propose a decision strategy where we assume perfect knowledge of the traffic profile and a second approach where a robust Bayesian strategy is considered in order to account for possible error modeling in the traffic profile information.The research leading to these results has received funding from the European Commission in the framework of the FP7 Network of Excellence in Wireless COMmunications NEWCOM# (Grant agreement no. 318306) and project TUCAN3G (Grant agreement no. ICT-2011-601102), from the Spanish Ministry of Economy and Competitiveness (Ministerio de Economía y Competitividad) through the project TEC2011-29006-C03-02 (GRE3N-LINK-MAC), project TEC2013-41315-R (DISNET), and FPI grant BES-2012-052850, and from the Catalan Government (AGAUR) through the grant 2014 SGR 60.Peer ReviewedPostprint (author's final draft

Robustez en Multidimensional Scaling

En este trabajo se presenta, mediante un estudio de simulación, una solución del problema de Multidimensional Scaling (MDS), cuando los datos aparecen perturbados por un error aleatorio. En el estudio de simulación se plantea un diseño cuyos factores son los distintos estimadores robustos considerados, el tipo de error y la intensidad del mismo. Asimismo se estudia la adecuación de la solución propuesta y su comparación con algoritmos clásicos de resolución del problema de MDS tratado.In this paper we show, by means a simulation study, a method to solve the perturbational error Multidimensional Scaling (MDS) problem. We work with a factorial design in which it has been considered several robust estimators, and two types of random error with several intensities. Furthermore we study the fit of the obtained configuration and its comparison with other classical MDS methods

A real-time FPGA-based implementation of a high-performance MIMO-OFDM mobile WiMAX transmitter

The Multiple Input Multiple Output (MIMO)-Orthogonal Frequency Division Multiplexing (OFDM) is considered a key technology in modern wireless-access communication systems. The IEEE 802.16e standard, also denoted as mobile WiMAX, utilizes the MIMO-OFDM technology and it was one of the first initiatives towards the roadmap of fourth generation systems. This paper presents the PHY-layer design, implementation and validation of a high-performance real-time 2x2 MIMO mobile WiMAX transmitter that accounts for low-level deployment issues and signal impairments. The focus is mainly laid on the impact of the selected high bandwidth, which scales the implementation complexity of the baseband signal processing algorithms. The latter also requires an advanced pipelined memory architecture to timely address the datapath operations that involve high memory utilization. We present in this paper a first evaluation of the extracted results that demonstrate the performance of the system using a 2x2 MIMO channel emulation.Postprint (published version

Design, implementation and testing of a real-time mobile WiMAX testbed featuring MIMO technology

Postprint (author’s final draft