Prof. Dr. Paulo Montezuma

A Robust Bisection-Based Estimator for TOA-Based Target Localization in NLOS Environments

This letter addresses the problem of target localization in a 3-D space, utilizing combined measurements of received signal strength and angle of arrival (AoA). By using the spherical coordinate conversion and available AoA observations to establish new relationships between the measurements and the unknown target location, we derive a simple closed-form solution method. We then show that the proposed method has straightforward adaptation to the case where the target’s transmit power is also not known. Simulation results validate the outstanding performance of the proposed method.

10 August 2017 in IEEE Communications Letters

Journal Article

Slavisa Tomic

Massive MIMO Techniques for 5G and Beyond—Opportunities and Challenges

This letter addresses the problem of target localization in harsh indoor environments based on range measurements. To mitigate the non-line-of-sight (NLOS) bias, we propose a novel robust estimator by transforming the localization problem into a generalized trust region sub-problem framework. Although still non-convex in general, this class of problems can be readily solved exactly by means of bisection procedure. The new approach does not require to make any assumptions about the statistics of NLOS bias, nor to try to distinguish which links are NLOS and which are not. Unlike the existing algorithms, the computational complexity of the proposed algorithm is linear in the number of reference nodes. Our simulation results corroborate the effectiveness of the new algorithm in terms of NLOS bias mitigation and show that the performance of our estimator is highly competitive with the performance of the state-of-the-art algorithms. In fact, they show that the novel estimator outperforms slightly the existing ones in general, and that it always provides a feasible solution.

13 July 2021 in Electronics

Journal Article

David Borges

Distributed algorithm for target localization in wireless sensor networks using RSS and AoA measurements

Telecommunications have grown to be a pillar to a functional society and the urge for reliable and high throughput systems has become the main objective of researchers and engineers. State-of-the-art work considers massive Multiple-Input Multiple-Output (massive MIMO) as the key technology for 5G and beyond. Large spatial multiplexing and diversity gains are some of the major benefits together with an improved energy efficiency. Current works mostly assume the application of well-established techniques in a massive MIMO scenario, although there are still open challenges regarding hardware and computational complexities and energy efficiency. Fully digital, analog, and hybrid structures are analyzed and a multi-layer massive MIMO transmission technique is detailed. The purpose of this article is to describe the most acknowledged transmission techniques for massive MIMO systems and to analyze some of the most promising ones and identify existing problems and limitations.

1 June 2017 in Pervasive and Mobile Computing

Journal Article

Slavisa Tomic

Iterative Frequency-Domain Equalization for general constellations

1 April 2010

Conference Paper

Optimum and Sub-Optimum Receivers for OFDM Signals with Strong Nonlinear Distortion Effects

Nuno Souto

Joao Silva

IB-DFE (Iterative Block DFE) is a promising turbo equalization technique for SC-FDE schemes (Single-Carrier with Frequency Domain Equalization). However, typical IB-DFE implementations are tailored for a specific constellation (usually QPSK). In this paper we propose a general method for designing IB-DFE receivers for any constellation. Our approach relies on an analytical characterization of the mapping rule were the constellation symbols are written as a linear function of the transmitted bits. This method is then employed in both uniform and non-uniform QAM constellations.

1 August 2013 in IEEE Transactions on Communications

Journal Article

João Guerreiro