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Projeto de investigação
Coordinated Spectrum Sharing for Opportunistic Access
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Publicações
Wireless IoT – Avaliação de desempenho da camada MAC
Publication . Silva, Tiago Chagas da; Oliveira, Rodolfo
With the increase of connected devices, the internet of things has gained increasing importance. Nowadays it is essential to have a technology that supports the growing use of IoT
devices and information sharing. LoRa was developed to fulfill those requirements, being a protocol designed for low-cost devices that achieves long-range information transmission and low
energy consumption. Currently, LoRa is used in a variety of applications, including agriculture
and health. LoRa is used to improve the efficiency of various businesses. In order to guarantee
robustness in the communications, it is essential to obtain a high performance at the Medium
Access Control sublayer, since it is the layer responsible for controlling the medium access of a
potentially large number of nodes.
The objective of this dissertation is to develop a simulator that allows the study of the
performance of the communications supported by the LoRa protocol in several scenarios. The
simulator should be as realistic as possible, guaranteeing the occurrence of collisions between the
nodes, as well as specifying different levels of load on the network, including different sizes of
messages exchanged.
In this work the Matlab software was adopted to evaluate the simulator’s performance.
The various versions of the developed scripts were tested and validated theoretically, allowing to
verify the accuracy of the results obtained by simulation through the comparison with the theoretical models.
Analytical performance evaluation of massive MIMO techniques for SC-FDE modulations
Publication . Fernandes, Daniel; Cercas, Francisco; Dinis, Rui; DEE - Departamento de Engenharia Electrotécnica e de Computadores; DEE2010-A1 Telecomunicações; MDPI - Multidisciplinary Digital Publishing Institute
In the Fifth Generation of telecommunications networks (5G), it is possible to use massive Multiple Input Multiple Output (MIMO) systems, which require efficient receivers capable of reaching good performance values. MIMO systems can also be extended to massive MIMO (mMIMO) systems, while maintaining their, sometimes exceptional, performance. However, we must be aware that this implies an increase in the receiver complexity. Therefore, the use of mMIMO in 5G and future generations of mobile receivers will only be feasible if they use very efficient algorithms, so as to maintain their excellent performance, while coping with increasing and critical user demands. Having this in mind, this paper presents and compares three types of receivers used in MIMO systems, for further use with mMIMO systems, which use Single-Carrier with Frequency-Domain Equalization (SC-FDE), Iterative Block Decision Feedback Equalization (IB-DFE) and Maximum Ratio Combining (MRC) techniques. This paper presents and compares the theoretical and simulated performance values for these receivers in terms of their Bit Error Rate (BER) and correlation factor. While one of the receivers studied in this paper achieves a BER performance nearly matching the Matched Filter Bound (MFB), the other receivers (IB-DFE and MRC) are more than 1 dB away from MFB. The results obtained in this paper can help the development of ongoing research involving hybrid analog/digital receivers for 5G and future generations of mobile communications.
Recolha Oportunística de Energia em Sistemas de Comunicação Sem Fios
Publication . Pisco, Guilherme Fernandes; Oliveira, Rodolfo
O presente trabalho tem como objetivo apresentar um estudo comparativo entre a potência
medida em três tecnologias sem fios, sendo elas o Wifi, o GSM e o DECT e identificar outros
fatores que possam afetar essa potência, nomeadamente a localização tridimensional do emissor
e do recetor. A medição da potência pretende identificar de uma forma prática qual a energia que
poderá ser recolhida e armazenada num cenário de Energy Harvesting a partir do espectro RF.
No decorrer do trabalho foram realizadas medições de potência nos canais utilizados por cada
tecnologia, com a utilização de um analisador espectral sweep-tuned, para várias configurações
do cenário de medição.
Os resultados relativos às medições de potência são reportados na forma de várias imagens
espectrais e em tabelas, onde são apresentadas as várias potências calculadas para cada cenário
de medição, assim como uma análise estatística onde são calculados a variância, o desvio padrão
e a incerteza recorrendo à distribuição normal t-student com um grau de incerteza de 95%. Este
estudo permite concluir que em média a tecnologia onde se poderá recolher mais energia é o
GSM. Tal como era esperado, é também possível concluir que a localização tridimensional do
emissor e do recetor e a distância entre eles poderá influenciar significativamente a quantidade de
energia que poderá ser recolhida.
Residual Self-Interference Estimation in In-Band Full-Duplex Wireless Systems
Publication . Irio, Luís; Abusabah, Ayman T.; Oliveira, Rodolfo; DEE - Departamento de Engenharia Electrotécnica e de Computadores; DEE2010-A1 Telecomunicações
In this paper, we present a novel method to estimate the distribution of the residual self-interference (SI) power of an in-band Full-duplex (IBFDX) system. Considering the residual SI distribution caused by the uncanceled SI in a post-mixer scheme due to a single propagation tap, we propose a framework capable of estimating the residual SI distribution. The estimator relies on the computation of two estimated parameters, which takes advantage of using the method of moments of the residual SI distribution in a straightforward manner. Additionally, we assess the accuracy of the proposed estimators, considering different sample set lengths adopted in the estimation process. The results testify the quality of the estimation method and its ability to achieve high accuracy, even for a reduced number of samples. This work is of practical importance, particularly when the residual self-interference is mainly due to a line-of-sight component, where the proposed technique can use a small set of samples to predict the residual interference in an accurate way.
In-Band Full-duplex Residual Self-interference Approximation in Multi-tap Delay Fading Channels
Publication . Abusabah, Ayman T.; Irio, Luís; Oliveira, Rodolfo; DEE - Departamento de Engenharia Electrotécnica e de Computadores; DEE2010-A1 Telecomunicações
Residual self-interference (SI) is primarily a key challenge when designing In-Band Full-duplex (IBFDX) wireless systems. Channel estimation errors are one of the major causes of the residual SI. The SI channel is composed by multiple fading taps which makes the characterization of the residual SI more challenging as multiple copies of the transmitted signal, with variable delays and gains, are eventually aggregated at the receiver. In this paper, we derive an approximation for the distribution of the residual SI power in multi-tap delay fading channels. In particular, we show that under specific conditions the multi-tap fading channel can be represented by a summation of non-identical independent gamma distributions. In a further step, we approximate the summation of the gamma distributions using the Welch-Satterthwaite equation, obtaining a closed form expression for the distribution of the residual SI power. The accuracy of the theoretical approach is evaluated through simulation results. The similarity comparison between simulated data and the proposed model indicates a high accuracy of the adopted approximation when considering low fading uncertainty associated to the taps and low estimation errors. On the other hand, the accuracy of the approximation slightly decreases for higher uncertainty fading scenarios and for higher estimation errors. However, as a final remark, we highlight that the results computed with the model are close to the simulated ones and for most of the applications the model's error can be negligible.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
9471 - RIDTI
Número da atribuição
PTDC/EEI-TEL/30709/2017