Martha Cecilia Paredes | Escuela Politécnica Nacional (original) (raw)

Papers by Martha Cecilia Paredes

2022 IEEE Sixth Ecuador Technical Chapters Meeting (ETCM)

Revista de Investigación en Tecnologías de la Información

In the Quito historical center, due to its narrow streets, vehicular congestion is very frequent.... more In the Quito historical center, due to its narrow streets, vehicular congestion is very frequent. Intelligent vehicles can be used, which have fully automatic driving, but need to interact with each other. The manner in which smart vehicles interact is through vehicle networks, which require the installation of an infrastructure called RSU (Road Side Unit) that uses the IEEE 802.11p standard and the RSU allows sending vehicle information to more distant places. However, installing RSUs requires an economic investment, so, as an alternative, it can be combined with an already deployed infrastructure such as the LTE (Long Term Evolution) cellular network, forming a heterogeneous network (HetNet). This paper seeks to analyze the behavior of the platooning HetNet through the analysis of physical and technical parameters of two network scenarios within of the Quito historical center.

2019 IEEE 90th Vehicular Technology Conference (VTC2019-Fall)

Most of the classic fading variables can be obtained through Nakagami-m distribution and the sum ... more Most of the classic fading variables can be obtained through Nakagami-m distribution and the sum of them has a pivotal role in the analytical performance evaluation of many practical wireless applications. However, the exact probability density function (PDF) of this sum of fading variables could be difficult to obtain. In this paper, we investigate the performance of the Maximum Likelihood Estimation to find a simple accurate approximation to the probability density function of the sum of Nakagami-m random variables. This approach provides expressions that can be used straightforwardly in the performance analysis of a number of wireless communication systems including multibranch receivers such as Maximal Ratio Combining and Equal Gain Combining, for which we present the application of the proposed framework. Numerical simulations show that our proposed method outperforms the well- known approach based on moment-matching method in terms of accuracy and simplicity. Moreover, the easiness of our proposal makes it suitable to be incorporated in network simulators to model and configure several wireless environments without additional computational complexity.

2019 IEEE Fourth Ecuador Technical Chapters Meeting (ETCM)

This paper studies the effect of two Peak to Average Power Ratio (PAPR) reduction methods over th... more This paper studies the effect of two Peak to Average Power Ratio (PAPR) reduction methods over the capacity of Orthogonal Frequency Division Multiplexing (OFDM) systems. These two methods are the Active Constellation Extension-Projection Onto Convex Sets (ACE-POCS) and Branch-and-Bound Constellation Extension (BBCE). Both methods modify the constellation points of some transmitted symbols to reduce the PAPR, so the channel capacity could be affected due to the unequal power allocation. In this work, the capacity is obtained through simulations of an uncoded OFDM system over a Rayleigh fading channel. Our results show that the ACE-POCS method obtains a capacity similar to the ergodic capacity of the Rayleigh fading channel. On the other hand, the capacity using the BBCE method is less than the ACE-POCS but with a higher reduction in the PAPR. Additionally, we compare the channel capacity using these two PAPR reduction schemes with an upper bound obtained with the water-filling algorithm, which maximizes the capacity by changing the power of the sub-carriers. Finally, we found that the PAPR of the OFDM signal obtained when the water-filling algorithm is applied shows a small variation compared to the OFDM signal without PAPR reduction.

arXiv (Cornell University), May 5, 2020

2019 IEEE Fourth Ecuador Technical Chapters Meeting (ETCM), 2019

This paper presents an analysis of the Orthogonal Frequency Division Mutiple Access (OFDMA) and S... more This paper presents an analysis of the Orthogonal Frequency Division Mutiple Access (OFDMA) and Single Carrier Frequency Division Multiple Access (SCFDMA) signals with high Peak to-Average Power Ratio (PAPR). The large envelope variations of the transmitted signals is the main drawback, which degrades the performance of the wireless systems and increases the power consumption of the transmitter.Two different PAPR reduction techniques, Clipping and Filtering (CAF) and Selective Mapping (SLM) are evaluated by using the complementary cumulative distribution function (CCDF) of the PAPR for both access schemes. Simulation results show that CAF is very effective for both OFDMA and SC-FDMA in reducing PAPR levels.

During this investigation, Traveling Salesman Problem or TSP is applied in a Wireless Sensor Netw... more During this investigation, Traveling Salesman Problem or TSP is applied in a Wireless Sensor Network (WSN), through a free simulator named Castalia and programming codes on JAVA and GNU/Linux Scripting in order to implement two methods for solving the TSP. First method, consist of Minimum Spanning Tree (MST) with the 2-opt algorithm and the second one is Branch and Bound (B&B) method related to the Held-Karp lower bound. Likewise, the Prim, Boruvka and Kruskal algorithms will be compared in order to determine, which of them solves the MST problem in less time, through the simulator which defines two scenarios for three models of motas: TelosB, Imote2, and Zolertia. Finally, some parameters will be also compared, such as throughput and energy consumption for each scenario, node model and solving method of the TSP, and conclude what is the best method that could be applied to a WSN.

Proceedings of the 24th International ACM Conference on Modeling, Analysis and Simulation of Wireless and Mobile Systems, 2021

The Third Generation Partnership Project (3GPP) has recently announced its Release 16, which intr... more The Third Generation Partnership Project (3GPP) has recently announced its Release 16, which introduces advanced functionalities to support the cellular vehicle to everything (C-V2X) technology. C-V2X allows direct communication between vehicles through the sidelink operation. This appears as an option to DSRC technologies; both are key wireless technologies that play a vital role in implementing and deploying advanced driving applications. This paper presents a thorough review of the available open-source frameworks intended for the performance evaluation of C-V2X protocols and V2X applications. For this, we consider validated OMNeT++-based simulation libraries and frameworks: SimuLTE, OpenCV2X, Artery-C, 5G-Sim-V2I/N, and Simu5G. We focus on the different frameworks' support regarding advanced V2X communications on 5G mobile networks.

IEEE Journal on Selected Areas in Communications, 2018

2016 8th IEEE Latin-American Conference on Communications (LATINCOM), 2016

Orthogonal Frequency Division Multiplexing (OFDM) has become the popular modulation technique in ... more Orthogonal Frequency Division Multiplexing (OFDM) has become the popular modulation technique in high speed wireless communications. It has several advantages over other techniques, such as high data rate, strong immunity to multipath and high spectral efficiency. However, it could have high peaks in the transmitted signal; this is the well-known Peak-to-Average Power Ratio (PAPR) problem. It is very important to deal with PAPR reduction in OFDM systems to avoid signal degradation. Currently, the PAPR problem is an active area of research and in this paper we discuss about the PAPR problem and the main metrics that are used to measure the PAPR in any OFDM system. Moreover their advantages and disadvantages have been enumerated in order to provide the readers the actual situation of the metric to cuantizate the PAPR problem.

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Revista de Investigación en Tecnologías de la Información

Electronics

Network simulators are used for the research and development of several types of networks. Howeve... more Network simulators are used for the research and development of several types of networks. However, one of the limitations of these simulators is the usage of simplified theoretical models of the Packet Error Rate (PER) at the Physical Layer (PHY) of the IEEE 802.11 family of wireless standards. Although the simplified PHY model can significantly reduce the simulation time, the resulting PER can differ considerably from other more realistic results. In this work, we first study several PER theoretical models. Then, we propose a curve fitting algorithm, which is able to obtain a fast and accurate approximation of other PER models. The curve fitting algorithm uses simulated data as input and outputs the coefficients of a simple model that offers a very accurate approximation of the original PER. Finally, we implemented this approximation in the ns-3 network simulator, thus obtaining high realism since now we can select several theoretical PER models or even a more realistic scenario w...

The provided code simulates the physical layer of the IEEE 802.11p standard.<br> It is writ... more The provided code simulates the physical layer of the IEEE 802.11p standard.<br> It is written in Matlab. The goal is to simplify the simulation of the <br> 802.11p standard but maintaining control over of process. Therefore, it can<br> be easily modified to test techniques in the different steps of wireless transmission.<br> The main folder contains two subfolders: 1. All the code files needed to simulate a wireless transmission using 802.11p<br> are located in the folder src. To execute the code, you must run the Selec_grap.m file that presents three<br> options:<br> Simulated PHY graph<br> Graph of the theoretical models<br> Graphic comparison of PHY and theoretical models Necessary datasets are included so that Selec_grap.m runs without any<br> inconvenience. <br> If you want to re-simulate the physical layer, you must first run the file <br> simulation_802_11_p.m and then proceed to run Selec_grap.m 2. The ...

2017 IEEE Second Ecuador Technical Chapters Meeting (ETCM), 2017

In wireless communication systems, antenna diversity is an important technique to tackle deep fad... more In wireless communication systems, antenna diversity is an important technique to tackle deep fading. Diversity techniques mitigate the effects of fading by generating several copies of the signal transferred over M different theoretically independent channels. In this paper we review the most significant metrics used in the performance analysis of diversity combining techniques over Nakagami-m fading channels. These well-known metrics are Signal-to-Noise Ratio (SNR), Outage Probability (OP), Bit Error Rate (BER), Level Crossing Rate (LRC) and Average Fade Duration (AFD). In addition, we summarize how they are obtained from the first and second-order statistics of the resulting combined signal. The goal of this paper is to provide an straightforward guide on these metrics to ease the comparison studies among wireless communication systems. Moreover, we provide handy hints and references of the situation of this research area.

This paper investigates the impact on the achievable secrecy performance of multiple-input multip... more This paper investigates the impact on the achievable secrecy performance of multiple-input multiple-output systems by dealing with realistic propagation conditions. Specifically, we focus on the κ-μ shadowing fading model, which has proven to be more accurate in characterizing mm-wave scenarios than traditional Rice and Rayleigh ones. By considering transmit antenna selection and maximal ratio combining at the receiver ends, we study two different scenarios, namely: (i) the transmitter has knowledge of the channel state information (CSI) of the eavesdropper link, and (ii) the transmitter does not know eavesdropper’s CSI. Based on these assumptions, we derive novel analytical expressions for the secrecy outage probability (SOP) and the average secrecy capacity (ASC) to assess the secrecy performance in passive and active eavesdropping scenarios, respectively. Moreover, we develop analytical asymptotic expressions of the SOP and ASC at high signal-to-noise ratio regime. Some useful in...

2019 IEEE Fourth Ecuador Technical Chapters Meeting (ETCM), 2019

This paper proposes a neural network-based scheme for Peak-to-Average Power Ratio (PAPR) reductio... more This paper proposes a neural network-based scheme for Peak-to-Average Power Ratio (PAPR) reduction which also replaces the Inverse Fast Fourier Transform (IFFT) block of an Orthogonal Frequency Division Multiplexing (OFDM) transmitter. The scheme is composed by one neural network per subcarrier, which are implemented only in the transmitter. The training inputs of each neural network are frequency-domain OFDM symbols and the outputs are time-domain PAPR reduced OFDM symbols obtained using a Branch-and-Bound Constellation Extension (BBCE) scheme. The results show that our scheme achieves a PAPR reduction and Bit Error Rate (BER) similar to constellation shaping techniques but with reduced complexity.

2021 IEEE Fifth Ecuador Technical Chapters Meeting (ETCM), 2021

In this paper, we explore the effect of practical channel conditions on the achievable secrecy of... more In this paper, we explore the effect of practical channel conditions on the achievable secrecy of reconfigurable intelligent surface (RIS)-aided multiple-input single-output (MISO) wireless communications with the existence of both the legitimate (Bob) and the eavesdropper (Eve) nodes. Specifically, by considering beamforming at the source (Alice), we study the practical scenario where Alice has Bob's channel state information (CSI); however, she doesn't know Eve's CSI. (i.e., passive eavesdropping case). To this end, we first derive approximate expressions for modeling the RIS cascaded channel applying the Maximum Likelihood (ML) algorithm. This approach allows for incorporating relevant factors into RIS's channel modeling, including phase shift noise, correlation between RIS elements, and coexistence or not of the direct links at both the legitimate and eavesdropper nodes. Based on these findings, we obtain a closed-form solution of the outage secrecy probability for the underlying system. Finally, some valuable insights on how various channel features and the number of RIS elements affect the secrecy behavior are also presented.

2022 IEEE Sixth Ecuador Technical Chapters Meeting (ETCM)

Revista de Investigación en Tecnologías de la Información

In the Quito historical center, due to its narrow streets, vehicular congestion is very frequent.... more In the Quito historical center, due to its narrow streets, vehicular congestion is very frequent. Intelligent vehicles can be used, which have fully automatic driving, but need to interact with each other. The manner in which smart vehicles interact is through vehicle networks, which require the installation of an infrastructure called RSU (Road Side Unit) that uses the IEEE 802.11p standard and the RSU allows sending vehicle information to more distant places. However, installing RSUs requires an economic investment, so, as an alternative, it can be combined with an already deployed infrastructure such as the LTE (Long Term Evolution) cellular network, forming a heterogeneous network (HetNet). This paper seeks to analyze the behavior of the platooning HetNet through the analysis of physical and technical parameters of two network scenarios within of the Quito historical center.

2019 IEEE 90th Vehicular Technology Conference (VTC2019-Fall)

Most of the classic fading variables can be obtained through Nakagami-m distribution and the sum ... more Most of the classic fading variables can be obtained through Nakagami-m distribution and the sum of them has a pivotal role in the analytical performance evaluation of many practical wireless applications. However, the exact probability density function (PDF) of this sum of fading variables could be difficult to obtain. In this paper, we investigate the performance of the Maximum Likelihood Estimation to find a simple accurate approximation to the probability density function of the sum of Nakagami-m random variables. This approach provides expressions that can be used straightforwardly in the performance analysis of a number of wireless communication systems including multibranch receivers such as Maximal Ratio Combining and Equal Gain Combining, for which we present the application of the proposed framework. Numerical simulations show that our proposed method outperforms the well- known approach based on moment-matching method in terms of accuracy and simplicity. Moreover, the easiness of our proposal makes it suitable to be incorporated in network simulators to model and configure several wireless environments without additional computational complexity.

2019 IEEE Fourth Ecuador Technical Chapters Meeting (ETCM)

This paper studies the effect of two Peak to Average Power Ratio (PAPR) reduction methods over th... more This paper studies the effect of two Peak to Average Power Ratio (PAPR) reduction methods over the capacity of Orthogonal Frequency Division Multiplexing (OFDM) systems. These two methods are the Active Constellation Extension-Projection Onto Convex Sets (ACE-POCS) and Branch-and-Bound Constellation Extension (BBCE). Both methods modify the constellation points of some transmitted symbols to reduce the PAPR, so the channel capacity could be affected due to the unequal power allocation. In this work, the capacity is obtained through simulations of an uncoded OFDM system over a Rayleigh fading channel. Our results show that the ACE-POCS method obtains a capacity similar to the ergodic capacity of the Rayleigh fading channel. On the other hand, the capacity using the BBCE method is less than the ACE-POCS but with a higher reduction in the PAPR. Additionally, we compare the channel capacity using these two PAPR reduction schemes with an upper bound obtained with the water-filling algorithm, which maximizes the capacity by changing the power of the sub-carriers. Finally, we found that the PAPR of the OFDM signal obtained when the water-filling algorithm is applied shows a small variation compared to the OFDM signal without PAPR reduction.

arXiv (Cornell University), May 5, 2020

2019 IEEE Fourth Ecuador Technical Chapters Meeting (ETCM), 2019

This paper presents an analysis of the Orthogonal Frequency Division Mutiple Access (OFDMA) and S... more This paper presents an analysis of the Orthogonal Frequency Division Mutiple Access (OFDMA) and Single Carrier Frequency Division Multiple Access (SCFDMA) signals with high Peak to-Average Power Ratio (PAPR). The large envelope variations of the transmitted signals is the main drawback, which degrades the performance of the wireless systems and increases the power consumption of the transmitter.Two different PAPR reduction techniques, Clipping and Filtering (CAF) and Selective Mapping (SLM) are evaluated by using the complementary cumulative distribution function (CCDF) of the PAPR for both access schemes. Simulation results show that CAF is very effective for both OFDMA and SC-FDMA in reducing PAPR levels.

During this investigation, Traveling Salesman Problem or TSP is applied in a Wireless Sensor Netw... more During this investigation, Traveling Salesman Problem or TSP is applied in a Wireless Sensor Network (WSN), through a free simulator named Castalia and programming codes on JAVA and GNU/Linux Scripting in order to implement two methods for solving the TSP. First method, consist of Minimum Spanning Tree (MST) with the 2-opt algorithm and the second one is Branch and Bound (B&B) method related to the Held-Karp lower bound. Likewise, the Prim, Boruvka and Kruskal algorithms will be compared in order to determine, which of them solves the MST problem in less time, through the simulator which defines two scenarios for three models of motas: TelosB, Imote2, and Zolertia. Finally, some parameters will be also compared, such as throughput and energy consumption for each scenario, node model and solving method of the TSP, and conclude what is the best method that could be applied to a WSN.

Proceedings of the 24th International ACM Conference on Modeling, Analysis and Simulation of Wireless and Mobile Systems, 2021

The Third Generation Partnership Project (3GPP) has recently announced its Release 16, which intr... more The Third Generation Partnership Project (3GPP) has recently announced its Release 16, which introduces advanced functionalities to support the cellular vehicle to everything (C-V2X) technology. C-V2X allows direct communication between vehicles through the sidelink operation. This appears as an option to DSRC technologies; both are key wireless technologies that play a vital role in implementing and deploying advanced driving applications. This paper presents a thorough review of the available open-source frameworks intended for the performance evaluation of C-V2X protocols and V2X applications. For this, we consider validated OMNeT++-based simulation libraries and frameworks: SimuLTE, OpenCV2X, Artery-C, 5G-Sim-V2I/N, and Simu5G. We focus on the different frameworks' support regarding advanced V2X communications on 5G mobile networks.

IEEE Journal on Selected Areas in Communications, 2018

2016 8th IEEE Latin-American Conference on Communications (LATINCOM), 2016

Orthogonal Frequency Division Multiplexing (OFDM) has become the popular modulation technique in ... more Orthogonal Frequency Division Multiplexing (OFDM) has become the popular modulation technique in high speed wireless communications. It has several advantages over other techniques, such as high data rate, strong immunity to multipath and high spectral efficiency. However, it could have high peaks in the transmitted signal; this is the well-known Peak-to-Average Power Ratio (PAPR) problem. It is very important to deal with PAPR reduction in OFDM systems to avoid signal degradation. Currently, the PAPR problem is an active area of research and in this paper we discuss about the PAPR problem and the main metrics that are used to measure the PAPR in any OFDM system. Moreover their advantages and disadvantages have been enumerated in order to provide the readers the actual situation of the metric to cuantizate the PAPR problem.

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Revista de Investigación en Tecnologías de la Información

Electronics

Network simulators are used for the research and development of several types of networks. Howeve... more Network simulators are used for the research and development of several types of networks. However, one of the limitations of these simulators is the usage of simplified theoretical models of the Packet Error Rate (PER) at the Physical Layer (PHY) of the IEEE 802.11 family of wireless standards. Although the simplified PHY model can significantly reduce the simulation time, the resulting PER can differ considerably from other more realistic results. In this work, we first study several PER theoretical models. Then, we propose a curve fitting algorithm, which is able to obtain a fast and accurate approximation of other PER models. The curve fitting algorithm uses simulated data as input and outputs the coefficients of a simple model that offers a very accurate approximation of the original PER. Finally, we implemented this approximation in the ns-3 network simulator, thus obtaining high realism since now we can select several theoretical PER models or even a more realistic scenario w...

The provided code simulates the physical layer of the IEEE 802.11p standard.<br> It is writ... more The provided code simulates the physical layer of the IEEE 802.11p standard.<br> It is written in Matlab. The goal is to simplify the simulation of the <br> 802.11p standard but maintaining control over of process. Therefore, it can<br> be easily modified to test techniques in the different steps of wireless transmission.<br> The main folder contains two subfolders: 1. All the code files needed to simulate a wireless transmission using 802.11p<br> are located in the folder src. To execute the code, you must run the Selec_grap.m file that presents three<br> options:<br> Simulated PHY graph<br> Graph of the theoretical models<br> Graphic comparison of PHY and theoretical models Necessary datasets are included so that Selec_grap.m runs without any<br> inconvenience. <br> If you want to re-simulate the physical layer, you must first run the file <br> simulation_802_11_p.m and then proceed to run Selec_grap.m 2. The ...

2017 IEEE Second Ecuador Technical Chapters Meeting (ETCM), 2017

In wireless communication systems, antenna diversity is an important technique to tackle deep fad... more In wireless communication systems, antenna diversity is an important technique to tackle deep fading. Diversity techniques mitigate the effects of fading by generating several copies of the signal transferred over M different theoretically independent channels. In this paper we review the most significant metrics used in the performance analysis of diversity combining techniques over Nakagami-m fading channels. These well-known metrics are Signal-to-Noise Ratio (SNR), Outage Probability (OP), Bit Error Rate (BER), Level Crossing Rate (LRC) and Average Fade Duration (AFD). In addition, we summarize how they are obtained from the first and second-order statistics of the resulting combined signal. The goal of this paper is to provide an straightforward guide on these metrics to ease the comparison studies among wireless communication systems. Moreover, we provide handy hints and references of the situation of this research area.

This paper investigates the impact on the achievable secrecy performance of multiple-input multip... more This paper investigates the impact on the achievable secrecy performance of multiple-input multiple-output systems by dealing with realistic propagation conditions. Specifically, we focus on the κ-μ shadowing fading model, which has proven to be more accurate in characterizing mm-wave scenarios than traditional Rice and Rayleigh ones. By considering transmit antenna selection and maximal ratio combining at the receiver ends, we study two different scenarios, namely: (i) the transmitter has knowledge of the channel state information (CSI) of the eavesdropper link, and (ii) the transmitter does not know eavesdropper’s CSI. Based on these assumptions, we derive novel analytical expressions for the secrecy outage probability (SOP) and the average secrecy capacity (ASC) to assess the secrecy performance in passive and active eavesdropping scenarios, respectively. Moreover, we develop analytical asymptotic expressions of the SOP and ASC at high signal-to-noise ratio regime. Some useful in...

2019 IEEE Fourth Ecuador Technical Chapters Meeting (ETCM), 2019

This paper proposes a neural network-based scheme for Peak-to-Average Power Ratio (PAPR) reductio... more This paper proposes a neural network-based scheme for Peak-to-Average Power Ratio (PAPR) reduction which also replaces the Inverse Fast Fourier Transform (IFFT) block of an Orthogonal Frequency Division Multiplexing (OFDM) transmitter. The scheme is composed by one neural network per subcarrier, which are implemented only in the transmitter. The training inputs of each neural network are frequency-domain OFDM symbols and the outputs are time-domain PAPR reduced OFDM symbols obtained using a Branch-and-Bound Constellation Extension (BBCE) scheme. The results show that our scheme achieves a PAPR reduction and Bit Error Rate (BER) similar to constellation shaping techniques but with reduced complexity.

2021 IEEE Fifth Ecuador Technical Chapters Meeting (ETCM), 2021

In this paper, we explore the effect of practical channel conditions on the achievable secrecy of... more In this paper, we explore the effect of practical channel conditions on the achievable secrecy of reconfigurable intelligent surface (RIS)-aided multiple-input single-output (MISO) wireless communications with the existence of both the legitimate (Bob) and the eavesdropper (Eve) nodes. Specifically, by considering beamforming at the source (Alice), we study the practical scenario where Alice has Bob's channel state information (CSI); however, she doesn't know Eve's CSI. (i.e., passive eavesdropping case). To this end, we first derive approximate expressions for modeling the RIS cascaded channel applying the Maximum Likelihood (ML) algorithm. This approach allows for incorporating relevant factors into RIS's channel modeling, including phase shift noise, correlation between RIS elements, and coexistence or not of the direct links at both the legitimate and eavesdropper nodes. Based on these findings, we obtain a closed-form solution of the outage secrecy probability for the underlying system. Finally, some valuable insights on how various channel features and the number of RIS elements affect the secrecy behavior are also presented.