Sensores passivos em suporte de cortiça

Mestrado em Engenharia Eletrónica e TelecomunicaçõesÉ do conhecimento dos entendidos em vinhos, que a temperatura a que estes possam estar sujeitos afecta significativamente a qualidade dos mesmos. Nesse sentido, seria útil ter acesso a um histórico de temperatura, para que este possa ser lido e o cliente possa realizar uma compra com a qual fique satisfeito. Esta dissertação propõe construir uma antena RFID numa rolha, que servirá na base para que no futuro se incorpore o sensor de temperatura e toda a tecnologia adjacente. Tendo em conta o objectivo, a primeira parte do trabalho desenvolvido passou pela caracterização electromagnética da cortiça. Estudou-se diversos métodos, e depois com o conhecimento suficiente, desenvolveu-se um método baseado em linhas microstrip, pois era aquele se perspectivava dar resultados satisfatórios, e ao mesmo tempo seria possível de implementar, tendo em conta os recursos disponíveis. Na segunda parte simulou-se e construiu-se diversas antenas RFID com substrato de cortiça, finalizando-se com uma antena na própria rolha de cortiça.It's well known for the skilled people in wine, that the temperature at which they may be subjected significantly affect their quality. Therefore, it would be useful to have access to a temperature historic, so that it can be read and the customer can make a purchase with which it satisfied. This dissertation proposes to build a RFID antenna in cork stopper, which will serve as the basis for that in future can be incorporated the temperature sensor and all adjacent technology. Having regard to the objective, the first part of the work started by the electromagnetic cork characterization. It was studied various methods, and then with enough knowledge, it was developed a method based on microstrip lines, because it was hoped satisfactory results, and it would be possible to implement, given the available resources. In the second part was simulated and built various RFID antennas with substrate cork, ending up with an antenna in cork stopper

Hybrid multi-user equalizer for massive MIMO millimeter-wave dynamic subconnected architecture

This paper proposes a hybrid multi-user equalizer for the uplink of broadband millimeterwave massive multiple input/multiple output (MIMO) systems with dynamic subarray antennas. Hybrid subconnected architectures are more suitable for practical applications since the number of required phase shifters is lower than in fully connected architectures. We consider a set of only analog precoded users transmitting to a base station and sharing the same radio resources. At the receiver end, the hybrid multi-user equalizer is designed by minimizing the sum of the mean square error (MSE) of all subcarriers, considering a two-step approach. In the first step, the digital part is iteratively computed as a function of the analog part. It is considered that the digital equalizers are computed on a per subcarrier basis, while the analog equalizer is constant over the subcarriers and the digital iterations due to hardware constraints. In the second step, the analog equalizer with dynamic antenna mapping is derived to connect the best set of antennas to each radio frequency (RF) chain. For each subset of antennas, one antenna and a quantized phase shifter are selected at a time, taking into account all previously selected antennas. The results show that the proposed hybrid dynamic two-step equalizer achieves a performance close to the fully connected counterpart, although it is less complex in terms of hardware and signal processing requirements.publishe

Iterative analog-digital multi-user equalizer for wideband millimeter wave massive MIMO systems

Most of the previous work on hybrid transmit and receive beamforming focused on narrowband channels. Because the millimeter wave channels are expected to be wideband, it is crucial to propose efficient solutions for frequency-selective channels. In this regard, this paper proposes an iterative analog-digital multi-user equalizer scheme for the uplink of wideband millimeter-wave massive multiple-input-multiple-output (MIMO) systems. By iterative equalizer we mean that both analog and digital parts are updated using as input the estimates obtained at the previous iteration. The proposed iterative analog-digital multi-user equalizer is designed by minimizing the sum of the mean square error of the data estimates over the subcarriers. We assume that the analog part is fixed for all subcarriers while the digital part is computed on a per subcarrier basis. Due to the complexity of the resulting optimization problem, a sequential approach is proposed to compute the analog phase shifters values for each radio frequency (RF) chain. We also derive an accurate, semi-analytical approach for obtaining the bit error rate (BER) of the proposed hybrid system. The proposed solution is compared with other hybrid equalizer schemes, recently designed for wideband millimeter-wave (mmWave) massive MIMO systems. The simulation results show that the performance of the developed analog-digital multi-user equalizer is close to full-digital counterpart and outperforms the previous hybrid approach.publishe

Multiuser equalizer for hybrid massive MIMO mmWave CE-OFDM systems

This paper considers a multiuser broadband uplink massive multiple input multiple output (MIMO) millimeter-wave (mmWave) system. The constant envelope orthogonal frequency division multiplexing (CE-OFDM) is adopted as a modulation technique to allow an efficient power amplification, fundamental for mmWave based systems. Furthermore, a hybrid architecture is considered at the user terminals (UTs) and base station (BS) to reduce the high cost and power consumption required by a full-digital architecture, which has a radio frequency (RF) chain per antenna. Both the design of the UT’s precoder and base station equalizer are considered in this work. With the aim of maximizing the beamforming gain between each UT and the BS, the precoder analog coefficients are computed as a function of the average angles of departure (AoD), which are assumed to be known at the UTs. At the BS, the analog part is derived by assuming a system with no multi-user interference. Then, a per carrier basis nonlinear/iterative multi-user equalizer, based on the iterative block decision feedback equalization (IB-DFE) principle is designed, to explicitly remove both the multi-user and residual inter carrier interferences, not tackled in the analog part. The equalizer design metric is the sum of the mean square error (MSE) of all subcarriers, whose minimization is shown to be equivalent to the minimization of a weighted error between the hybrid and the full digital equalizer matrices. The results show that the proposed hybrid multi-user equalizer has a performance close to the fully digital counterpart.publishe

Two-step multiuser equalization for hybrid mmWave massive MIMO GFDM systems

Although millimeter-wave (mmWave) and massive multiple input multiple output (mMIMO) can be considered as promising technologies for future mobile communications (beyond 5G or 6G), some hardware limitations limit their applicability. The hybrid analog-digital architecture has been introduced as a possible solution to avoid such issues. In this paper, we propose a two-step hybrid multi-user (MU) equalizer combined with low complexity hybrid precoder for wideband mmWave mMIMO systems, as well as a semi-analytical approach to evaluate its performance. The new digital non-orthogonal multi carrier modulation scheme generalized frequency division multiplexing (GFDM) is considered owing to its efficient performance in terms of achieving higher spectral efficiency, better control of out-of-band (OOB) emissions, and lower peak to average power ratio (PAPR) when compared with the orthogonal frequency division multiplexing (OFDM) access technique. First, a low complexity analog precoder is applied on the transmitter side. Then, at the base station (BS), the analog coefficients of the hybrid equalizer are obtained by minimizing the mean square error (MSE) between the hybrid approach and the full digital counterpart. For the digital part, zero-forcing (ZF) is used to cancel the MU interference not mitigated by the analog part. The performance results show that the performance gap of the proposed hybrid scheme to the full digital counterpart reduces as the number of radio frequency (RF) chains increases. Moreover, the theoretical curves almost overlap with the simulated ones, which show that the semi-analytical approach is quite accurate.publishe

Iterative Equalization and Interference Alignment for Multiuser MIMO HetNets with Imperfect CSI

In this paper we consider a scenario, where several small-cells work under the same coverage area and spectrum of a macrocell. The signals stemming from the small-cell (macrocell) users if not carefully dealt with will generate harmful interference into the macrocell (small-cell). To tackle this problem interference alignment and iterative equalization techniques are considered. By using IA all interference generated by the small-cell (macrocell) users is aligned along a low dimensional subspace, at the macrocell (small-cells). This reduces considerably the amount of resources allocated, to enable the coexistence of the two systems. However, perfect IA requires the availability of error-free channel state information (CSI) at the transmitters. Due to CSI errors one can have substantial performance degradation due to imperfect alignments. Since in this work the IA precoders are based on imperfect CSI, an efficient iterative space-frequency equalization is designed at the receiver side to cope with the residual aligned interference.The results demonstrate that iterative equalization is robust to imperfect CSI and removes efficiently the interference generated by the poorly aligned interference. Close to matched filter bound performance is achieved, with a very few number of iterations

Técnicas híbridas de pré-codificação e equalização para sistemas sem fios baseados na banda das ondas milimétricas e MIMO massivo

Millimeter wave communications (mmWave) and massive MIMO will be two of the keys enabling technologies for future wireless communication systems. The combination of these technologies will allow to achieve multi Gb/s needed to meet the quality of service requirements. In this research work we design solutions for mmWave massive MIMO systems, where a set of users equipped with a large number of antennas transmit data to a receiver also equipped with a massive number of antennas. Since we consider a large number of antennas, we cannot use one dedicated RF chain per antenna, due to power consumption and hardware costs. The solution is the use of a hybrid architecture, where the number of RF chains is lower than the number of antennas. In such architecture the processing is distributed by the analog and digital domains (contrary to the conventional fully digital systems). Thus, the conventional fully digital approaches cannot be used in this hybrid architecture where an additional analog filter must be computed and we have additional hardware constraints. Therefore, this research work explores the design of beamforming and equalization techniques assuming massive antenna terminals for mmWave based systems, and to cope with the hardware limitations inherent to this type of systems, three hybrid analog-digital architectures are considered: the fully connected, and the subconnected with fixed or dynamic subarray antennas. A major advantage of the exploration of mmWave bands is to allow larger bandwidths, which lead to larger number of subcarriers for multicarrier based systems. Therefore, the orthogonal frequency division multiplexing (OFDM) technique, which is very efficient to mitigate the effects of inter-symbol interference (ISI) in frequency selective channels, results in a signal with higher amplitude fluctuations, making the large peak-to-average power ratio (PAPR) a problem that should be taken into account for mmWave mMIMO systems. A high PAPR results in strong nonlinear distortions caused by the power amplifier, degrading system performance. To solve the PAPR problem, constant envelope modulations which present a PAPR equal to 0 dB, such as the constant envelope OFDM (CE-OFDM), can be used. Therefore, this research work explores the design of an equalization technique for hybrid analog-digital systems using the CE-OFDM as modulation technique. Additionally, there is significant interest in the design of nonlinear equalizers, that have been considered to efficiently separate the spatial streams and mitigate the inter-carrier-interference (ICI) problem in the current MIMO systems, and that can be extremely efficient in a mMIMO scenario. Iterative block decision feedback equalization (IB-DFE) approach is one of the most promising nonlinear equalization schemes. Therefore, this work explores the IB-DFE principles for the hybrid analog-digital systems. The first part of the thesis is focused on the development of efficient precoding/beamforming and equalization algorithms for a narrowband channel. In the first phase, a single-user scenario is assumed to separate the spatial streams and later the developed solution is extended for multiuser scenarios, to reduce the inter-user interference. The second part of the thesis is focused on the development of algorithms for a wideband channel, which have to be different from the narrowband case due to specificities of analog-digital architectures. The CEOFDM is also exploited as a mean for solving the PAPR problem. These algorithms are accompanied with numerical results to evaluate their performance. The numerical results show that the proposed algorithms for analog-digital architectures, based on iterative procedures, are very efficient to remove the multiuser/inter-symbol interference. The performance obtained with these algorithms almost achieve the optimal performance of conventional fully digital architectures with a very few iterations. Therefore, they are interesting for practical mmWave massive MIMO based systems, since it ensures good performance at a low cost.As comunicações na banda das ondas milimétricas e a utilização de terminais equipados com um número elevado de antenas serão duas das tecnologias chave que possibilitarão os futuros sistemas de comunicação sem fios. A combinação destas tecnologias permitirá atingir os multi Gb/s necessários para atender aos requisitos de qualidade de serviço. Uma vez que consideramos um número elevado de antenas, não podemos usar uma cadeia de radiofrequência por antena, devido ao consumo de potência e custos de hardware. A solução é o uso de arquiteturas híbridas, onde o número de cadeias de radiofrequência é menor que o número de antenas. Em tal arquitetura, o processamento é distribuído entre os domínios analógico e digital (contrariamente aos sistemas convencionais completamente digitais). Logo, as abordagens usadas nos sistemas convencionais completamente digitais não podem ser usadas nestas arquiteturas híbridas, onde um filtro analógico tem que ser calculado, para além de outras restrições de hardware adicionais. Portanto, este trabalho de investigação explora o projeto de técnicas de formação de feixe e equalização, assumindo terminais com um número elevado de antenas na banda das ondas milimétricas. Uma das principais vantagens da exploração da banda das ondas milimétricas é permitir maiores larguras de banda, o que leva a um maior número de subportadoras para sistemas multiportadora. Portanto, a técnica orthogonal frequency division multiplexing (OFDM), que é bastante eficiente para mitigar os efeitos da interferência entre símbolos em canais seletivos na frequência, resulta num sinal com maiores flutuações em amplitude, tornando o elevado peak-toaverage power ratio (PAPR) um problema que deve ser tido em conta para sistemas na banda das ondas milimétricas com um número elevado de antenas. O alto PAPR resulta em fortes distorções não lineares causadas pelos amplificadores de potência, degradando o desempenho do sistema. Para resolver o problema do PAPR, podem ser usadas modulações de envolvente contante que apresentam um PAPR igual a 0 dB, tal como a constant envelope OFDM (CEOFDM). Portanto, este trabalho de investigação explora o projeto de uma técnica de equalização, especificamente para sistemas híbridos usando o CE-OFDM como técnica de modulação. Adicionalmente, há um interesse significativo no projeto de equalizadores não lineares que têm sido considerados para eficientemente separar os dados de forma espacial, e mitigar o problema da interferência entre portadoras nos atuais sistemas multi-antenas, e que podem ser especialmente eficientes num cenário com um elevado número de antenas. O iterative block decision feedback equalization (IB-DFE) é um dos equalizadores não lineares mais promissores. Portanto, este trabalho explora os princípios do IB-DFE em sistemas híbridos. A primeira parte da tese foca no desenvolvimento de algoritmos eficientes para precodificação/formação de feixe e equalização, para um canal de banda estreita. Numa primeira fase são assumidos cenários de um utilizador, para separar os fluxos de dados espaciais, tendo sido depois esta solução estendida para cenários de múltiplos utilizadores, para reduzir a interferência entre estes. A segunda parte da tese foca no desenvolvimento de algoritmos para um canal de banda larga, que tem de ser diferente do caso de banda estreita, devido às especificidades das arquiteturas analógico-digitais. O CE-OFDM é também explorado como um meio para resolver o problema do PAPR. Estes algoritmos são acompanhados com resultados numéricos para avaliar os seus desempenhos. Os resultados numéricos mostram que os algoritmos propostos para as arquiteturas analógico-digitais, baseados em processos iterativos, são bastante eficientes para remover a interferência entre utilizadores e entre símbolos. Os desempenhos obtidos com estes algoritmos quase alcançam o desempenho ótimo das arquiteturas convencionais completamente digitais, apenas com algumas iterações. Portanto, são interessantes para sistemas práticos baseados em terminais com um número elevado de antenas na faixa das ondas milimétricas, uma vez que asseguram um bom desempenho a baixo custo.Programa Doutoral em Engenharia Eletrotécnic

Dissipation factor and permittivity estimation of dielectric substrates using a single microstrip line measurement

The knowledge of the dielectric properties of materials, for the design of several components and circuits at high frequencies, is mandatory. In this paper, we present a simple method for the estimation of the dissipation factor (loss tangent) of dielectric materials based on the reflection measurement of a single microstrip line, which is applied to some common known materials, such as FR-4 and Rogers RO3010 laminates. The obtained results match well with the data on the literature for the considered materials.info:eu-repo/semantics/publishedVersio

Effective PSCCH Searching for 5G-NR V2X Sidelink Communications

Cooperative Intelligent Transport Systems (C-ITS) are essential for increasing road safety and to make road transport more efficient, sustainable, and environmentally friendly. The implementation of C-ITS technology is only possible through the connectivity of Vehicle-to-Everything (V2X), which allows the interconnection of vehicles in a network and with road support infrastructure. However, real-time systems require efficient signal processing in order to respond within the necessary time. Some of this processing is related to searching the Physical Sidelink Control Channel (PSCCH), where a blind algorithm is commonly used. However, this algorithm is quite inefficient to searching the PSCCH, since all the processing should be completed several times before successful decoding it. Therefore, the aim of this paper is to design a more efficient algorithm to search/decode the PSCCH. In the proposed algorithm, we firstly compute all the correlations between the received signal and the Demodulation Reference Signal (DMRS), and the remaining conventional processing to decode the PSCCH is only performed over the subchannels with higher correlation, which leads to a strong complexity reduction. The proposed algorithm is evaluated and compared with the conventional blind algorithm. The results have shown a significant performance improvement in terms of runtime

RFID passive tag antenna for cork bottle stopper

In this paper we propose a possible design for a RFID tag antenna embedded into cork. The antenna is small and conformal and intended to be used into bottle stoppers for tracking and logging purposes of wine or other beverages. The proposed design is based on an inductive ring and an added resistance in order to modify the current distributions of the antenna. The resulting antenna has a relatively directive radiation pattern and despite the small efficiency it is able to operate with a commercial RFID reader at a reasonable distance. © 2014 IEEE