Rui Dinis - Academia.edu (original) (raw)

Papers by Rui Dinis

Research paper thumbnail of Two-Step Multiuser Equalization for Hybrid mmWave Massive MIMO GFDM Systems

Electronics, 2020

Although millimeter-wave (mmWave) and massive multiple input multiple output (mMIMO) can be consi... more 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 app...

Research paper thumbnail of A Survey of Candidate Waveforms for beyond 5G Systems

Electronics

The 5G and beyond future wireless networks aim to support a large variety of services with increa... more The 5G and beyond future wireless networks aim to support a large variety of services with increasing demand in terms of data rate and throughput while providing a higher degree of reliability, keeping the overall system complexity affordable. One of the key aspects regarding the physical layer architecture of such systems is the definition of the waveform to be used in the air interface. Such waveforms must be studied and compared in order to choose the most suitable and capable of providing the 5G and beyond services requirements, with flexible resource allocation in time and frequency domains, while providing high spectral and power efficiencies. In this paper, several beyond 5G waveforms candidates are presented, along with their transceiver architectures. Additionally, the associated advantages and disadvantages regarding the use of these transmission techniques are discussed. They are compared in a similar downlink transmission scenario where three main key performance indicat...

Research paper thumbnail of A Low Complexity Channel Estimation and Detection for Massive MIMO Using SC-FDE

Telecom

5G Communications will support millimeter waves (mm-Wave), alongside the conventional centimeter ... more 5G Communications will support millimeter waves (mm-Wave), alongside the conventional centimeter waves, which will enable much higher throughputs and facilitate the employment of hundreds or thousands of antenna elements, commonly referred to as massive Multiple Input–Multiple Output (MIMO) systems. This article proposes and studies an efficient low complexity receiver that jointly performs channel estimation based on superimposed pilots, and data detection, optimized for massive MIMO (m-MIMO). Superimposed pilots suppress the overheads associated with channel estimation based on conventional pilot symbols, which tends to be more demanding in the case of m-MIMO, leading to a reduction in spectral efficiency. On the other hand, MIMO systems tend to be associated with an increase of complexity and increase of signal processing, with an exponential increase with the number of transmit and receive antennas. A reduction of complexity is obtained with the use of the two proposed algorithm...

Research paper thumbnail of A Physical Layer Security Technique for NOMA Systems with MIMO SC-FDE Schemes

Electronics

Current wireless communication systems employ Multi-Input, Multi-Output (MIMO) techniques to incr... more Current wireless communication systems employ Multi-Input, Multi-Output (MIMO) techniques to increase spectral efficiency, at the cost of higher hardware complexity. Most of these systems continue to employ traditional Orthogonal Multiple Access (OMA) schemes, which are suboptimal when compared to Non-Orthogonal Multiple Access (NOMA) schemes. By combining NOMA with MIMO, it is possible to achieve higher spectral efficiencies. However, security in NOMA-MIMO systems remains a problem. In this paper, we study the physical layer security issues of a power based NOMA-MIMO system with a Singular Value Decomposition (SVD) scheme, employed along with Single Carrier with Frequency Domain Equalization (SC-FDE) techniques. We consider a scenario where there is an unintended eavesdropper attempting to listen to the messages being exchanged. It is shown that the higher the channel estimate correlation between transmitter and receiver, the higher the secrecy rate, particularly for a scenario whe...

Research paper thumbnail of Reduced Complexity Detection in MIMO Systems with SC-FDE Modulations and Iterative DFE Receivers

Journal of Sensor and Actuator Networks

Research paper thumbnail of On the Physical Layer Security Characteristics for MIMO-SVD Techniques for SC-FDE Schemes

Sensors

Multi-Input, Multi-Output (MIMO) techniques are seeing widespread usage in wireless communication... more Multi-Input, Multi-Output (MIMO) techniques are seeing widespread usage in wireless communication systems due to their large capacity gains. On the other hand, security is a concern of any wireless system, which can make schemes that implement physical layer security key in assuring secure communications. In this paper, we study the physical layer security issues of MIMO with Singular Value Decomposition (SVD) schemes, employed along with Single-Carrier with Frequency-Domain Equalization (SC-FDE) techniques. More concretely. the security potential against an unintended eavesdropper is analysed, and it is shown that the higher the distance between the eavesdropper and the transmitter or receiver, the higher the secrecy rate. In addition, in a scenario where there is Line of Sight (LOS) between all users, it is shown that the secrecy rate can be even higher than in the previous scenario. Therefore, MIMO-SVD schemes combined with SC-FDE can be an efficient option for highly secure MIMO...

Research paper thumbnail of A Survey on Massive MIMO Systems in Presence of Channel and Hardware Impairments

Sensors

Massive multiple input multiple output (MIMO) technology is one of the promising technologies for... more Massive multiple input multiple output (MIMO) technology is one of the promising technologies for fifth generation (5G) cellular communications. In this technology, each cell has a base station (BS) with a large number of antennas, allowing the simultaneous use of the same resources (e.g., frequency and/or time slots) by multiple users of a cell. Therefore, massive MIMO systems can bring very high spectral and power efficiencies. However, this technology faces some important issues that need to be addressed. One of these issues is the performance degradation due to hardware impairments, since low-cost RF chains need to be employed. Another issue is the channel estimation and channel aging effects, especially in fast mobility environments. In this paper we will perform a comprehensive study on these two issues considering two of the most promising candidate waveforms for massive MIMO systems: Orthogonal frequency division multiplexing (OFDM) and single-carrier frequency domain proces...

Research paper thumbnail of Receiver Design to Employ Simultaneous Wireless Information and Power Transmission for Joint CFO and Channel Estimation

Research paper thumbnail of A Novel Reservation-based MAC Scheme for Distributed Cognitive Radio Networks

IEEE Transactions on Vehicular Technology, 2016

Research paper thumbnail of Robust Frequency-Domain Receivers for a Transmission Technique with Directivity at the Constellation Level

2014 IEEE 80th Vehicular Technology Conference (VTC2014-Fall), 2014

It was shown recently that we can decompose multilevel constellations as the sum of constant-enve... more It was shown recently that we can decompose multilevel constellations as the sum of constant-envelope components which can be amplified and transmitted by separate antennas, allowing power-efficient transmitters, together with directivity at the constellation level without changing on the radiation pattern associated to the set of antennas. However, errors in the direction estimates can lead to substantial performance performance degradation since the constellations seen at the receiver can be substantially distorted. In this paper we present an improved receiver that is designed taking into account constellation distortion effects inherent to errors in direction estimates. It is shown that these "smart" receivers, optimized taking into account the apparent constellation at the receiver side can substantially outperform conventional receivers that assume that assume undistorted constellations.

Research paper thumbnail of Optimum Asymptotic Performance for Nonlinearly Amplified OFDM Signals

2013 IEEE 77th Vehicular Technology Conference (VTC Spring), 2013

Research paper thumbnail of Robust detection for the uplink of broadband wireless systems with strong ACI levels

Research paper thumbnail of An FFT-based acquisition scheme for DS-CDM a systems

Research paper thumbnail of Frequency-Domain Multiuser Detection for Highly Overloaded DS-CDMA Systems

Research paper thumbnail of Using Exome Sequencing to Reveal Mutations in TREM2 Presenting as a Frontotemporal Dementia–like Syndrome Without Bone Involvement

Research paper thumbnail of Massive MIMO Techniques for 5G and Beyond—Opportunities and Challenges

Electronics

Telecommunications have grown to be a pillar to a functional society and the urge for reliable an... more 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.

Research paper thumbnail of Frequency-Domain Equalization in OFDM and Single-Carrier Modulation

Encyclopedia of Wireless Networks

Research paper thumbnail of Joint Channel Estimation and Synchronization Techniques for Time-Interleaved Block-Windowed Burst OFDM

Applied Sciences, 2021

From a conceptual perspective, 5G technology promises to deliver low latency, high data rate and ... more From a conceptual perspective, 5G technology promises to deliver low latency, high data rate and more reliable connections for the next generations of communication systems. To face these demands, modulation schemes based on Orthogonal Frequency Domain Multiplexing (OFDM) can accommodate these requirements for wireless systems. On the other hand, several hybrid OFDM-based systems such as the Time-Interleaved Block Windowed Burst Orthogonal Frequency Division Multiplexing (TIBWB-OFDM) are capable of achieving even better spectral confinement and power efficiency. This paper addresses to the implementation of the TIBWB-OFDM system in a more realistic and practical wireless link scenarios by addressing the challenges of proper and reliable channel estimation and frame synchronization. We propose to incorporate a preamble formed by optimum correlation training sequences, such as the Zadoff-Chu (ZC) sequences. The added ZC preamble sequence is used to jointly estimate the frame beginning...

Research paper thumbnail of IB-DFE SIC based receiver structure for IA-precoded MC-CDMA systems

2014 22nd European Signal Processing Conference (EUSIPCO), 2014

Interference alignment (IA) is a promising technique that allows high capacity gains in interferi... more Interference alignment (IA) is a promising technique that allows high capacity gains in interfering channels. On the other hand, iterative frequency-domain detection receivers based on the IB-DFE concept (Iterative Block Decision Feedback Equalization) can efficiently exploit the inherent space-frequency diversity of the MIMO MC-CDMA systems. In this paper we design a joint iterative IA precoding at the transmitter with IB-DFE successive interference cancellation (SIC) based receiver structure for MC-CDMA systems. The receiver is designed in two steps: first a linear filter is used to mitigate the inter-user aligned interference, and then an iterative frequency-domain receiver is designed to efficiently separate the spatial streams in the presence of residual inter-user aligned interference at the output of the filter. Our scheme achieves the maximum degrees of freedom provided by the IA precoding, while allowing an almost optimum space-diversity gain, with performance close to the ...

Research paper thumbnail of Joint Channel and Information Estimation on Symbol Decomposition-Based Secure Point-to-Point Communications

Energy efficiency and physical layer security are important features in future wireless communica... more Energy efficiency and physical layer security are important features in future wireless communication networks. A secure point to point communication is established by using a symbol decomposition method where higher order modulation symbols are decomposed into bits or smaller symbols as separate components and then transmitted to the receiver through multiple amplifiers on the same channel. One of the main challenges in symbol decomposition is accurate channel knowledge for the case of non-static transmitter and receiver position, which necessitates employing a robust and accurate channel estimation with this technique. To improve the accuracy of the channel estimate, an iterative block decision feedback equalizer (IB-DFE) is used at the receiver for joint channel and information estimation. In this paper, we study the symbol decomposition method along with the channel estimation technique and analyze the performance of the system model by using bit error rate parameter and results...

Research paper thumbnail of Two-Step Multiuser Equalization for Hybrid mmWave Massive MIMO GFDM Systems

Electronics, 2020

Although millimeter-wave (mmWave) and massive multiple input multiple output (mMIMO) can be consi... more 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 app...

Research paper thumbnail of A Survey of Candidate Waveforms for beyond 5G Systems

Electronics

The 5G and beyond future wireless networks aim to support a large variety of services with increa... more The 5G and beyond future wireless networks aim to support a large variety of services with increasing demand in terms of data rate and throughput while providing a higher degree of reliability, keeping the overall system complexity affordable. One of the key aspects regarding the physical layer architecture of such systems is the definition of the waveform to be used in the air interface. Such waveforms must be studied and compared in order to choose the most suitable and capable of providing the 5G and beyond services requirements, with flexible resource allocation in time and frequency domains, while providing high spectral and power efficiencies. In this paper, several beyond 5G waveforms candidates are presented, along with their transceiver architectures. Additionally, the associated advantages and disadvantages regarding the use of these transmission techniques are discussed. They are compared in a similar downlink transmission scenario where three main key performance indicat...

Research paper thumbnail of A Low Complexity Channel Estimation and Detection for Massive MIMO Using SC-FDE

Telecom

5G Communications will support millimeter waves (mm-Wave), alongside the conventional centimeter ... more 5G Communications will support millimeter waves (mm-Wave), alongside the conventional centimeter waves, which will enable much higher throughputs and facilitate the employment of hundreds or thousands of antenna elements, commonly referred to as massive Multiple Input–Multiple Output (MIMO) systems. This article proposes and studies an efficient low complexity receiver that jointly performs channel estimation based on superimposed pilots, and data detection, optimized for massive MIMO (m-MIMO). Superimposed pilots suppress the overheads associated with channel estimation based on conventional pilot symbols, which tends to be more demanding in the case of m-MIMO, leading to a reduction in spectral efficiency. On the other hand, MIMO systems tend to be associated with an increase of complexity and increase of signal processing, with an exponential increase with the number of transmit and receive antennas. A reduction of complexity is obtained with the use of the two proposed algorithm...

Research paper thumbnail of A Physical Layer Security Technique for NOMA Systems with MIMO SC-FDE Schemes

Electronics

Current wireless communication systems employ Multi-Input, Multi-Output (MIMO) techniques to incr... more Current wireless communication systems employ Multi-Input, Multi-Output (MIMO) techniques to increase spectral efficiency, at the cost of higher hardware complexity. Most of these systems continue to employ traditional Orthogonal Multiple Access (OMA) schemes, which are suboptimal when compared to Non-Orthogonal Multiple Access (NOMA) schemes. By combining NOMA with MIMO, it is possible to achieve higher spectral efficiencies. However, security in NOMA-MIMO systems remains a problem. In this paper, we study the physical layer security issues of a power based NOMA-MIMO system with a Singular Value Decomposition (SVD) scheme, employed along with Single Carrier with Frequency Domain Equalization (SC-FDE) techniques. We consider a scenario where there is an unintended eavesdropper attempting to listen to the messages being exchanged. It is shown that the higher the channel estimate correlation between transmitter and receiver, the higher the secrecy rate, particularly for a scenario whe...

Research paper thumbnail of Reduced Complexity Detection in MIMO Systems with SC-FDE Modulations and Iterative DFE Receivers

Journal of Sensor and Actuator Networks

Research paper thumbnail of On the Physical Layer Security Characteristics for MIMO-SVD Techniques for SC-FDE Schemes

Sensors

Multi-Input, Multi-Output (MIMO) techniques are seeing widespread usage in wireless communication... more Multi-Input, Multi-Output (MIMO) techniques are seeing widespread usage in wireless communication systems due to their large capacity gains. On the other hand, security is a concern of any wireless system, which can make schemes that implement physical layer security key in assuring secure communications. In this paper, we study the physical layer security issues of MIMO with Singular Value Decomposition (SVD) schemes, employed along with Single-Carrier with Frequency-Domain Equalization (SC-FDE) techniques. More concretely. the security potential against an unintended eavesdropper is analysed, and it is shown that the higher the distance between the eavesdropper and the transmitter or receiver, the higher the secrecy rate. In addition, in a scenario where there is Line of Sight (LOS) between all users, it is shown that the secrecy rate can be even higher than in the previous scenario. Therefore, MIMO-SVD schemes combined with SC-FDE can be an efficient option for highly secure MIMO...

Research paper thumbnail of A Survey on Massive MIMO Systems in Presence of Channel and Hardware Impairments

Sensors

Massive multiple input multiple output (MIMO) technology is one of the promising technologies for... more Massive multiple input multiple output (MIMO) technology is one of the promising technologies for fifth generation (5G) cellular communications. In this technology, each cell has a base station (BS) with a large number of antennas, allowing the simultaneous use of the same resources (e.g., frequency and/or time slots) by multiple users of a cell. Therefore, massive MIMO systems can bring very high spectral and power efficiencies. However, this technology faces some important issues that need to be addressed. One of these issues is the performance degradation due to hardware impairments, since low-cost RF chains need to be employed. Another issue is the channel estimation and channel aging effects, especially in fast mobility environments. In this paper we will perform a comprehensive study on these two issues considering two of the most promising candidate waveforms for massive MIMO systems: Orthogonal frequency division multiplexing (OFDM) and single-carrier frequency domain proces...

Research paper thumbnail of Receiver Design to Employ Simultaneous Wireless Information and Power Transmission for Joint CFO and Channel Estimation

Research paper thumbnail of A Novel Reservation-based MAC Scheme for Distributed Cognitive Radio Networks

IEEE Transactions on Vehicular Technology, 2016

Research paper thumbnail of Robust Frequency-Domain Receivers for a Transmission Technique with Directivity at the Constellation Level

2014 IEEE 80th Vehicular Technology Conference (VTC2014-Fall), 2014

It was shown recently that we can decompose multilevel constellations as the sum of constant-enve... more It was shown recently that we can decompose multilevel constellations as the sum of constant-envelope components which can be amplified and transmitted by separate antennas, allowing power-efficient transmitters, together with directivity at the constellation level without changing on the radiation pattern associated to the set of antennas. However, errors in the direction estimates can lead to substantial performance performance degradation since the constellations seen at the receiver can be substantially distorted. In this paper we present an improved receiver that is designed taking into account constellation distortion effects inherent to errors in direction estimates. It is shown that these "smart" receivers, optimized taking into account the apparent constellation at the receiver side can substantially outperform conventional receivers that assume that assume undistorted constellations.

Research paper thumbnail of Optimum Asymptotic Performance for Nonlinearly Amplified OFDM Signals

2013 IEEE 77th Vehicular Technology Conference (VTC Spring), 2013

Research paper thumbnail of Robust detection for the uplink of broadband wireless systems with strong ACI levels

Research paper thumbnail of An FFT-based acquisition scheme for DS-CDM a systems

Research paper thumbnail of Frequency-Domain Multiuser Detection for Highly Overloaded DS-CDMA Systems

Research paper thumbnail of Using Exome Sequencing to Reveal Mutations in TREM2 Presenting as a Frontotemporal Dementia–like Syndrome Without Bone Involvement

Research paper thumbnail of Massive MIMO Techniques for 5G and Beyond—Opportunities and Challenges

Electronics

Telecommunications have grown to be a pillar to a functional society and the urge for reliable an... more 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.

Research paper thumbnail of Frequency-Domain Equalization in OFDM and Single-Carrier Modulation

Encyclopedia of Wireless Networks

Research paper thumbnail of Joint Channel Estimation and Synchronization Techniques for Time-Interleaved Block-Windowed Burst OFDM

Applied Sciences, 2021

From a conceptual perspective, 5G technology promises to deliver low latency, high data rate and ... more From a conceptual perspective, 5G technology promises to deliver low latency, high data rate and more reliable connections for the next generations of communication systems. To face these demands, modulation schemes based on Orthogonal Frequency Domain Multiplexing (OFDM) can accommodate these requirements for wireless systems. On the other hand, several hybrid OFDM-based systems such as the Time-Interleaved Block Windowed Burst Orthogonal Frequency Division Multiplexing (TIBWB-OFDM) are capable of achieving even better spectral confinement and power efficiency. This paper addresses to the implementation of the TIBWB-OFDM system in a more realistic and practical wireless link scenarios by addressing the challenges of proper and reliable channel estimation and frame synchronization. We propose to incorporate a preamble formed by optimum correlation training sequences, such as the Zadoff-Chu (ZC) sequences. The added ZC preamble sequence is used to jointly estimate the frame beginning...

Research paper thumbnail of IB-DFE SIC based receiver structure for IA-precoded MC-CDMA systems

2014 22nd European Signal Processing Conference (EUSIPCO), 2014

Interference alignment (IA) is a promising technique that allows high capacity gains in interferi... more Interference alignment (IA) is a promising technique that allows high capacity gains in interfering channels. On the other hand, iterative frequency-domain detection receivers based on the IB-DFE concept (Iterative Block Decision Feedback Equalization) can efficiently exploit the inherent space-frequency diversity of the MIMO MC-CDMA systems. In this paper we design a joint iterative IA precoding at the transmitter with IB-DFE successive interference cancellation (SIC) based receiver structure for MC-CDMA systems. The receiver is designed in two steps: first a linear filter is used to mitigate the inter-user aligned interference, and then an iterative frequency-domain receiver is designed to efficiently separate the spatial streams in the presence of residual inter-user aligned interference at the output of the filter. Our scheme achieves the maximum degrees of freedom provided by the IA precoding, while allowing an almost optimum space-diversity gain, with performance close to the ...

Research paper thumbnail of Joint Channel and Information Estimation on Symbol Decomposition-Based Secure Point-to-Point Communications

Energy efficiency and physical layer security are important features in future wireless communica... more Energy efficiency and physical layer security are important features in future wireless communication networks. A secure point to point communication is established by using a symbol decomposition method where higher order modulation symbols are decomposed into bits or smaller symbols as separate components and then transmitted to the receiver through multiple amplifiers on the same channel. One of the main challenges in symbol decomposition is accurate channel knowledge for the case of non-static transmitter and receiver position, which necessitates employing a robust and accurate channel estimation with this technique. To improve the accuracy of the channel estimate, an iterative block decision feedback equalizer (IB-DFE) is used at the receiver for joint channel and information estimation. In this paper, we study the symbol decomposition method along with the channel estimation technique and analyze the performance of the system model by using bit error rate parameter and results...