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This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska- Curie ETN TeamUp5G, grant agreement No. 813391. R. Oliveira was also supported by the projects InfoCent-IoT (PTDC/EEI-TEL/30433/2017) and UIDB/EEA/50008/2020. This letter investigates the influence of the number of repetitions adopted in the NB-IoT standard to increase cellular coverage. We characterize the SINR in both uplink and downlink channels of ultra-dense networks, which is then used to derive the coverage probability and the NB-IoT’s capacity. The performance results show the effectiveness of the number of repetitions to reduce the block error rate for different densities of transmitters. authorsversion published

MASSIVE5G (SAICT‐45‐2017‐02) To circumvent the prohibitive complexity of linear minimum mean square error detection in a massive multiple-input multiple-output system, several iterative methods have been proposed. However, they can still be too complex and/or lead to non-negligible performance degradation. In this letter, a Chebyshev acceleration technique is proposed to overcome the limitations of iterative methods, accelerating the convergence rates and enhancing the performance. The Chebyshev acceleration method employs a new vector combination, which combines the spectral radius of the iteration matrix with the receiver signal, and also the optimal parameters of Chebyshev acceleration have also been defined. A detector based on iterative algorithms requires pre-processing and initialisation, which enhance the convergence, performance, and complexity. To influence the initialisation, the stair matrix has been proposed as the first start of iterative methods. The performance results show that the proposed technique outperforms state-of-the-art methods in terms of error rate performance, while significantly reducing the computational complexity. publishersversion published

This work was supported by Fundacao para a Ciencia e Tecnologia/Ministerio da Ciencia Tecnologia e Ensino Superior (FCT/MCTES) through National Funds and When Applicable Co-Funded EU Funds under Project UIDB/50008/2020. The Media Broadcast industry has evolved from Serial Digital Interface (SDI) based infrastructures to IP networks. While IP based video broadcast is well established in the data plane, the use of IP networks to transport media flows still poses challenges in terms of resource management and orchestration. SDN based orchestration architectures have emerged in the industry that use SDN to route the media flows of a broadcast service across the provider IP network. Several approaches to multimedia flow routing in IP based SDN networks have been proposed in the context of streaming applications over the Internet. These range from model based linear optimization solutions that have high complexity to simple shortest path based routing heuristics with either static or dynamic link costs. More recently model-free optimization methods such as Deep Reinforcement Learning (DRL) have been proposed for routing and Traffic Engineering of multimedia flows in SDN networks. The media broadcast scenario however has specific requirements, with services like Master Control Room operation and Live broadcasting of events, and it has been rarely addressed in the literature. In this work we propose a DRL based routing method for this scenario and compare it to static and dynamic link cost algorithms based on Dijkstra shortest paths. This is to our knowledge the first work to follow this approach in the context of Media Broadcast services in IP infrastructures. The algorithm is designed considering the specifications and capabilities of one of the leading SDN orchestrators in the market and considers the more common Service Level Agreement requirements in the industry. Three different DRL algorithms are implemented and compared and we evaluate them using a real service provider network topology. The results indicate that DRL based routing is applicable in real production scenarios and that it achieves considerable performance gains when compared to the static and dynamic link cost shortest path algorithms commonly used today. publishersversion published

Algebra has made the tasks of modelling routing algorithms and proving their correct operation very clear. However, traditional models are only concerned with the convergence to a stable routing solution not covering distributed hop-by-hop forwarding on multiple paths (within a flow or separately per flow). This paper addresses this challenge. Currently, loop-free distributed multipath forwarding is only proven if a strict decrease in the preference of a path occurs with every added link. This is very rigid for multipath routing, limiting the amount of equal preferred paths. In this work we prove that correct distributed forwarding behaviour is possible, without the strict decrease in preference, if the possible pairs of policy values applied to the directed edges connecting two nodes obey to a particular condition. If this is not true, correct behaviour is still possible if the policies applied to links forming circuits in the network graph are constrained according to two other conditions. Modern technologies are bringing the possibility to build new routing protocols using network programmability while distributed operation is still needed in many scenarios due to scaling issues. We show how our results can be relevant in this setting and serve as a tool in the design process and/or for formal protocol verification. authorsversion epub_ahead_of_print

partially supported by the projects CoSHARE (LISBOA-01-0145-FEDER0307095 - PTDC/EEI-TEL/30709/2017), and UIDB/50008/2020. In this paper, we derive the outage probability in directional millimeter-wave communications, capturing the effect of beamforming. In the proposed scenario, multiple transmitters are spatially distributed according to a spatial Poisson Point Process, which can cause interference to a pair of transmitter/receiver communicating nodes. The analysis considers a general distance-based path loss with Rayleigh and Rician fading channels and a sectored antenna model. Assuming that nodes are uniformly distributed over a circular or annular area centered at the receiver, we derive the outage probability due to the aggregate interference caused by multiple transmitters. The outage probability is based on the Signal-to-interference-plus-noise ratio (SINR) derived for the transmitter/receiver pair. Several simulations confirm the effectiveness of the derived results for different wireless channels and beamwidth values, highlighting the effect of directional communications on the outage probability. authorsversion published

This work was supported in part by the European Regional Development Fund (FEDER), through the Competitiveness and Internationalization Operational Program of the Portugal 2020 Framework, in part by the Regional OP Centro under Grant POCI-01-0145-FEDER-030588, in part by the Regional OP Lisboa under Grant Lisboa-01-0145-FEDER-03058, in part by the FCT/MEC through national funds of MASSIVE5G Project under Grant SAICT-45-2017-02 and PES3N Project under Grant 2018-SAICT-45-2017-POCI-01-0145-FEDER-030629, in part by the UID/EEE/50008/2019 Project, and in part by the FCT Ph.D. under Grant SFRH/BD/108522/2015. Massive multi-input-multi-output (m-MIMO) schemes require low-complexity implementations at both the transmitter and the receiver side, especially for systems operation at millimeter wave (mmWave) bands. In this paper, we consider the use of offset constellations in m-MIMO systems operating at mmWave frequencies. These signals are designed to have either an almost constant envelope or be decomposed as the sum of constant-envelope signals, making them compatible with strongly nonlinear power amplifiers, which can have low-implementation complexity and high amplification efficient, making them particularly interesting for mmWave communications. We design and evaluate low-complexity frequency-domain receivers for offset signals. It is shown that the proposed receivers can have excellent performance/complexity trade-offs in m-MIMO scenarios, making them particularly interesting for future wireless systems operating at mmWave bands. publishersversion published

This paper derives the distribution of the residual self-interference (SI) power in an analog post-mixer canceler adopted in a wireless in-band full-duplex communication system. We focus on the amount of uncanceled SI power due to SI channel estimation errors. Closed form expressions are provided for the distribution of the residual SI power when Rician and Rayleigh fading SI channels are considered. Moreover, the distribution of the residual SI power is derived for low and high channel gain dynamics, by considering the cases when the SI channel gain is time-invariant and time-variant. While for time-invariant channels the residual SI power is exponentially distributed, for time-variant channels the exponential distribution is not a valid assumption. Instead, the distribution of the residual SI power can be approximated by a product distribution. Several Monte Carlo simulation results show the influence of the channel dynamics on the distribution of the residual SI power. Finally, the accuracy of the theoretical approach is assessed through the comparison of numerical and simulated results, which confirm its effectiveness. published

partially supported by the projects CoSHARE (LISBOA-01-0145-FEDER0307095 - PTDC/EEI-TEL/30709/2017), and UIDB/50008/2020. In this paper, we characterize the aggregate interference power in directional millimeter-wave communications, capturing the effect of beamforming. The analysis considers a general distance-based path loss with Rayleigh and Rician fading channels and a sectored antenna model. Moreover, the nodes are uniformly distributed over a circular or annular area centered at the receiver. The main contribution of the paper is the derivation of the moment generating function (MGF) of the aggregate interference power. The MGF is adopted in a moment-based approximation to a Gamma distribution and used as a model of the aggregate interference power. Several simulations confirm the effectiveness of the proposed approximation for different scenarios, highlighting the effect of directional communications on the aggregate interference power. authorsversion published

Funding Information: V. CONCLUSIONS This work proposed four classification models based on LSTM RNNs to classify SIP dialogs. The detection probability was evaluated based on experimental data. To detect abnormal SIP dialogs, we have adopted classification features computed from the output of the LSTM RNN model and two different classification schemes were proposed. A semi-supervised scheme is shown to reach higher performance, achieving a detection probability of 99.45%, thus confirming the effective utility of the proposed methodology to detect abnormal SIP sequences in a short period of time. ACKNOWLEDGEMENTS This work was funded by Fundac¸ão para a Ciência e Tecnologia, under the projects InfoCent-IoT (PTDC/EEI-TEL/30433/2017), CoSHARE (PTDC/EEI-TEL/30709/2017), and RFSense (UIDB/50008/2020). The detection of abnormal sequences of SIP messages in real-time is crucial to avoid SIP signaling-based attacks. In this paper, we propose a deep learning approach to detect signaling patterns of multimedia sessions established with the Session Initiation Protocol (SIP). The approach is based on a recurrent neural network (RNN). We study the performance of different Long Short-term Memory (LSTM) RNN architectures, which are trained using a SIP signaling dataset of trustworthy SIP dialogs captured by a SIP server. The trained RNNs are then used to detect the SIP dialogs in real-time. After characterizing the dataset adopted for the training, validation, and testing, we present the experimental results obtained for the different RNN architectures, showing that the classification probability of trustworthy SIP dialogs exceeds 93% in the test stage. Finally, we present two methodologies to detect abnormal SIP dialogs, i.e., not contained in the trustworthy training dataset. After a detailed analysis of the skewness and kurtosis computed with the numerical RNN outputs, we show that they can be used as classification features. The first method is based on a K-means unsupervised classifier, while the second one is based on a semi-supervised threshold-based classifier. Experimental results show that the threshold-based classifier achieves 99.45% of detection probability, showing the effective utility of the proposed methodology to detect abnormal SIP sequences in a short period of time. authorsversion published

Funding Information: This work was funded by Fundac¸ão para a Ciência e Tecnologia, under the projects InfoCent-IoT (PTDC/EEI-TEL/30433/2017), CoSHARE (PTDC/EEI-TEL/30709/2017), and Grant UIDB/50008/2020. This work presents an effective tool to predict the future trajectories of vehicles when its current and previous locations are known. We propose a Long Short-Term Memory (LSTM) Recurrent Neural Network (RNN) prediction scheme due to its adequacy to learn from sequential data. To fully learn the vehicles' mobility patterns, during the training process we use a dataset that contains real traces of 442 taxis running in the city of Porto, Portugal, during a full year. From experimental results, we observe that the prediction process is improved when more information about prior vehicle mobility is available. Moreover, the computation time is evaluated for a distinct number of prior locations considered in the prediction process. The results exhibit a prediction performance higher than 89%, showing the effectiveness of the proposed LSTM network. authorsversion published

POCI-01-0145-FEDER-030588 SAICT-45-2017-02 Cell free (CF) massive multiple input multiple output (mMIMO) has been suggested as a key solution to meet the high data rate demands of future wireless communications. Studying the performance of these systems in practical scenarios such as in the presence of hardware impairments is of vital importance. In this paper, we study the effect of power amplifier non-linearity on the uplink and downlink sum-rate of CF mMIMO systems. We derive closed form expressions for the uplink and downlink achievable sum-rates of orthogonal frequency division multiplexing (OFDM) based CF mMIMO systems. Our results show that in the uplink the sum-rate does not increase unlimitedly as the number of access points (AP) increases, being upper bounded, contrarily to the ideal linear case. In fact, the rate of each user is limited by the distortion signal of its power amplifier. However, in the downlink, the sum-rate of the system with non-linear power amplifiers is not bounded and increases unlimitedly with the number of APs. Our results also indicate that for the same signal to distortion ratio (SDR) at the power amplifier output or the same normalized saturation level of the power amplifiers, the relative downlink sum-rate degradation is lower than the relative uplink sum-rate degradation (both with respect to their corresponding values in the ideal linear case). In fact, our results confirm that the user side power amplifier non-linearity has higher impact on the system performance than the power amplifier non-linearity on the AP antennas. publishersversion published

InfoCent-IoT (POCI-01-0145- FEDER-030433. 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. published

InfoCent-IoT (POCI-01-0145- FEDER-030433). 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. published

This article is focused on implementing simultaneous wireless information and power transmission as a physical layer security measure by using artificial noise. A series of high energy precoded symbols is simultaneously transmitted along with the information symbols over a Rayleigh frequency selective fading channel. The high energy precoded symbols act as an artificial noise for the eavesdroppers. The energy symbols are precoded on the basis of a legitimate user&rsquo, s channel matrix to form a null space vector, which eliminates the interference of energy symbols at the information symbol receiver antennas, while allowing the rectenna to harvest energy from the superimposed information and energy symbols. We analyze the secrecy rate and error rate performance at the receiver under different circumstances, and we show that the performance of the legitimate user can be improved by using the iterative block decision feedback equalization method at the receiver.

LISBOA-01-0145-FEDER-0307095-PTDC/EEITEL/30709/2017 PTDC/EEI-TEL/30588/20 UIDB/50008/2020 In this paper, we provide an analytical performance assessment of downlink non-orthogonal multiple access (NOMA) systems over Nakagami-m fading channels in the presence of nonlinear high-power amplifiers (HPAs). By modeling the distortion of the HPA by a nonlinear polynomial model, we evaluate the performance the NOMA scheme in terms of outage probability (OP) and ergodic sum rate. Hence, we derive a new closed-form expression for the exact OP, taking into account the undesirable effects of HPA. Furthermore, to characterize the diversity order of the considered system, the asymptotic OP in the high signal-to-noise (SNR) regime is derived. Moreover, the ergodic sum rate is investigated, resulting in new upper and lower bounds. Our numerical results demonstrate that the performance loss in presence of nonlinear distortions is very substantial at high data rates. In particular, it is proved that in presence of HPA distortion, the ergodic sum rate cannot exceed a determined threshold which limits its performance compared to the ideal hardware case. Monte-Carlo simulations are conducted and their results agree well with the analytical results. publishersversion published

UIDB/EEA/50008/2020 One of the main concerns of telecommunications operators is related to network coverage. A weak coverage can lead to a performance decrease, not only in the user experience, when using the operators' services, such as multimedia streaming, but also in the overall Quality of Service. This paper presents a novel cloud-based framework of a semi-empirical propagation model that estimates the coverage in a precise way. The novelty of this model is that it is automatically calibrated by using drive test measurements, terrain morphology, buildings in the area, configurations of the network itself and key performance indicators, automatically extracted from the operator's network. Requirements and use cases are presented as motivations for this methodology. The results achieve an accuracy of about 5 dB, allowing operators to obtain accurate neighbour lists, optimise network planning and automate certain actions on the network by enabling the Self-Organising Network concept. The cloud implementation enables a fast and easy integration with other network management and monitoring tools, such as the Metric platform, optimising operators' resource usage recurring to elastic resources on-demand when needed. This implementation was integrated into the Metric platform, which is currently available to be used by several operators. publishersversion published

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 residual SI. Consequently, a deeper understanding of the impact of the channel effects on the residual SI becomes indispensable. In this paper, we investigate the influence of multiple taps on the residual SI power of IBFDX systems. We first formulate the effect of having independent taps on the residual SI power mathematically. The derivations take into account the amount of interference cancellation on each tap by considering phase and amplitude estimation coefficients. We conclude that the increase in the number of taps always leads to an additive effect of the residual power. Such findings are shown mathematically and also reported in different results obtained by simulation. Finally, we compare the distribution of the residual SI power with different known distributions, concluding that Weibull and Gamma distributions are the closest ones in terms of accuracy. In-Band Full-Duplex communication Residual self-interference Independent fading taps channel. authorsversion published

IF/00325/2015 This work was supported in part by CTS multi-annual funding project PEst-OE/EEI/UI0066/2014 (UNINOVA), IT UID/EEA/50008/2013 (plurianual founding and project GLANCES), EnAcoMIMOCo EXPL/EEI-TEL/2408/2013, project IT UID/EEA/50008/2013 - MM5G and Program Investigador FCT under Grant IF/00325/2015. It is well-known that massive multiple-input multiple-output (MIMO) systems have high potential for future wireless broadband systems. Requirements such as high spectral and power efficiency are also crucial in 5G. Based on a multi-amplifier structure it is possible to define a double layered structure where each amplification branch is connected to an antenna array to achieve both constellation and power directivies, assuring at same time similar performances to systems using transmitters with 2-dimensional antenna arrays. Thus, a different path can be followed to improve energy efficiency of power amplification where the usage of parallel amplification branches is combined with big arrays of antennas and multi-stream communication systems. These systems can be combined with single-carrier with frequency domain equalization (SC-FDE) schemes to improve the power efficiency in uplink due to the low envelope fluctuations. publishersversion published

partially supported by the FCT -Fundacao para a Ciencia e Tecnologia and Instituto de Telecomunicacoes under projects UID/EEA/50008/2019. PES3N POCI-01-0145-FEDER-030629. 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 communications. publishersversion published

This work was funded, in part, by the Russian Federation State Project "Science", Grant No. 8.13264.2018/8.9, by the framework of the Competitiveness Enhancement Program of the National Research Tomsk Polytechnic University, and by Fundacao para a Ciencia e Tecnologia and Instituto de Telecomunicacoes, under Project UID/EEA/50008/2013. In this paper, we present a few novel simultaneous wireless information and power transfer (SWIPT) schemes that can be effectively used in various 5G wireless network implementations. First, we study the possibility of integrating distributed energy beamforming with the data rate fairness beamforming in a cooperative communication system with multiple cooperative relays and multiple destination users communicating simultaneously. We show that the system exploits significant performance gain using such a joint energy and data rate fairness beamforming scheme. Further, we propose an enhanced version of the SWIPT scheme, the energy-efficient modulation-based non-orthogonal multiple access (M-NOMA) SWIPT scheme, and observe its system efficiency in terms of more harvested energy. Finally, we consider an energy-harvesting SWIPT scheme where the channel response is estimated using the energy-harvesting signal as pilots superimposed on the information signal. For such a scheme, we compute the optimum transmit power ratio between the pilot and information signals under varying SNR conditions and improve the accuracy of the decoding process at the reception. publishersversion published

This work was supported in part by the Framework of the Competitiveness Enhancement Program of the National Research Tomsk Polytechnic University, Russia, and in part by the Fundacao para a Ciencia e Tecnologia and the Instituto de Telecomunicacoes under Project UID/EEA/50008/2013. Radio-frequency energy harvesting (EH) is one of the enabling technologies for the next-generation wireless communication systems. EH techniques are specifically used to improve the energy efficiency of the system. Recently, the simultaneous wireless information and power transmission (SWIPT) protocol is adapted for EH. In this paper, we design a new receiver for joint carrier frequency offset (CFO) and channel estimation on single-carrier modulations with frequency-domain equalization along with SWIPT implementation for EH by using the pilot signal. The pilot signal is a highly energized signal, which is superimposed with the information signal. The superimposed signal is used not only to transmit power for EH purposes but also to estimate the CFO and channel conditions. The receiver is designed to accommodate the strong interference levels in the channel estimation and data detection. The proposed scheme offers a flexible design method and efficient resource utilization. We validate our analytical results using simulations. publishersversion published

Nr. 024539 (POCI-01-0247-FEDER-024539) under grant agreement No 783221 UID/EEA/00066/2019 Unmanned Aerial Vehicles (UAVs), although hardly a new technology, have recently gained a prominent role in many industries being widely used not only among enthusiastic consumers, but also in high demanding professional situations, and will have a massive societal impact over the coming years. However, the operation of UAVs is fraught with serious safety risks, such as collisions with dynamic obstacles (birds, other UAVs, or randomly thrown objects). These collision scenarios are complex to analyze in real-time, sometimes being computationally impossible to solve with existing State of the Art (SoA) algorithms, making the use of UAVs an operational hazard and therefore significantly reducing their commercial applicability in urban environments. In this work, a conceptual framework for both stand-alone and swarm (networked) UAVs is introduced, with a focus on the architectural requirements of the collision avoidance subsystem to achieve acceptable levels of safety and reliability. The SoA principles for collision avoidance against stationary objects are reviewed and a novel approach is described, using deep learning techniques to solve the computational intensive problem of real-time collision avoidance with dynamic objects. The proposed framework includes a web-interface allowing the full control of UAVs as remote clients with a supervisor cloud-based platform. The feasibility of the proposed approach was demonstrated through experimental tests using a UAV, developed from scratch using the proposed framework. Test flight results are presented for an autonomous UAV monitored from multiple countries across the world. publishersversion published

The demand for ubiquitous telecommunications services forces operators to have a special concern about signal quality and the coverage area they offer to their customers. This was usually checked by using suitable propagation models for Single Input Single Output (SISO) systems, which are no longer the case for new and future mobile generations, such as 5G and beyond. To guarantee good signal quality coverage, operators started to replace these models with Multiple Input Multiple Output (MIMO) ones. To achieve the best results, these models are usually calibrated with Drive Test (DT) measures, however, the DTs available for MIMO propagation models are sparse, in contrast to SISO ones. The main contribution presented in this paper is a methodology to extend the propagation models of SISO systems so they can be applied in MIMO sytems with Single-Carrier and Frequency-Domain Equalization (SC-FDE), while still using DTs acquired for SISO systems. This paper presents the impact on Bit Error Rate (BER) performance and its coverage area resulting from the application of our proposed method. We consider a MIMO SC-FDE system with an Iterative Block Decision Feedback Equalization (IB-DFE) receiver and we present the improvement expressions for the BER that we illustrate with some simulations.

Decentralized wireless networks are gaining increasing popularity as they do not need a fixed infrastructure. Simultaneously, multiple research initiatives have led to different findings at the PHY layer of the wireless communication systems, which include Multi-Packet Reception (MPR) techniques that enable a receiver to decode multiple packets that are transmitted simultaneously. However, the distributed nature of decentralized wireless networks demands different network control policies that should take into account the MPR capabilities to increase the network performance. This work studies the performance of a wireless network composed of multiple transmitters that are willing to transmit to a single receiver. This receiver has MPR capability and adopts an Energy-based Sensing (EBS) technique to enable uplink users&rsquo, transmissions without interfering with the ongoing transmissions from other transmitters. The first remark to be made is that the MPR technique performance depends on the channel propagation conditions and on the amount of time the receiver needs to detect the spectrum&rsquo, s occupancy state. However, it is shown that by increasing the number of samples needed to increase the sensing accuracy, the receiver may degrade its throughput, namely if the receiver is equipped with a single radio, that is sequentially used for sensing and transmitting (split-phase operation). The results presented in the paper show the impact of the channel propagation condition and EBS parameterization on wireless network throughput and the cases where the receiver MPR capture performance is greatly improved by the use of a spectrum sensing technique.

authorsversion published

IF/00325/2015 This work was funded by FCT/MEC through national funds and when applicable co-funded by FEDER - PT2020 partnership agreement under Projects UID/EEA/00066/2013, UID/EEA/50008/2013, as well as Programa Investigador FCT under Grant IF/00325/2015. This work revises existing solutions for a problem of target localization in wireless sensor networks (WSNs), utilizing integrated measurements, namely received signal strength (RSS) and angle of arrival (AoA). The problem of RSS/AoA-based target localization became very popular in the research community recently, owing to its great applicability potential and relatively low implementation cost. Therefore, here, a comprehensive study of the state-of-the-art (SoA) solutions and their detailed analysis is presented. The beginning of this work starts by considering the SoA approaches based on convex relaxation techniques (more computationally complex in general), and it goes through other (less computationally complex) approaches, as well, such as the ones based on the generalized trust region sub-problems framework and linear least squares. Furthermore, a detailed analysis of the computational complexity of each solution is reviewed. Furthermore, an extensive set of simulation results is presented. Finally, the main conclusions are summarized, and a set of future aspects and trends that might be interesting for future research in this area is identified. publishersversion published

The authors would like to thank the editor and the anonymous reviewers for their valuable comments and suggestions which improved the quality of the paper. This work was partially supported by Fundacao para a Ciencia e a Tecnologia under Project PEst-OE/EEI/UI0066/2014, Project UID/EEA/50008/2013, Project UID/EEA/50009/2013, and Program Investigador FCT under Grant IF/00325/2015. This work addresses the problem of tracking a signal-emitting mobile target in wireless sensor networks (WSNs) with navigated mobile sensors. The sensors are properly equipped to acquire received signal strength (RSS) and angle of arrival (AoA) measurements from the received signal, while the target transmit power is assumed not known. We start by showing how to linearize the highly non-linear measurement model. Then, by employing a Bayesian approach, we combine the linearized observation model with prior knowledge extracted from the state transition model. Based on the maximum a posteriori (MAP) principle and the Kalman filtering (KF) framework, we propose new MAP and KF algorithms, respectively. We also propose a simple and efficient mobile sensor navigation procedure, which allows us to further enhance the estimation accuracy of our algorithms with a reduced number of sensors. Model flaws, which result in imperfect knowledge about the path loss exponent (PLE) and the true mobile sensors’ locations, are taken into consideration. We have carried out an extensive simulation study, and our results confirm the superiority of the proposed algorithms, as well as the effectiveness of the proposed navigation routine. publishersversion published

This work was partially supported by Portuguese Foundation for Science and Technology under grants SFRH/ BPD/108232/2015 and Science 2008 Post-Doctoral Research grant, as well as projects UID/EEA/50008/2013 (Portuguese Telecommunications Institute) and PEst-OE/EEI/UI0066/2014 (UNINOVA), project PTDC/EEI-TEL/6308/2014-HAMLeT, GALNC EXPL/EEI-TEL/1582/2013 and Program Investigador FCT (IF/00325/2015). Energy efficient power amplification of multilevel constellations can be achieved by an amplification structure based on the constellation's decomposition as a sum of polar components, such as M BPSK (Bi-Phase Shift Keying), that are separately amplified. By doing this one can define highly efficient transmitters based on multiple amplifiers. However, amplifiers' imbalances might lead to substantial constellation distortion since phase and gain imbalances cause rotations and translations of the symbols associated to each amplification branch that are combined to generate the resulting constellation. Therefore, it becomes crucial the knowledge of the amplifiers' imbalances to overcome this problem at the receiver side. For that we propose and evaluate efficient two new methods for estimating amplifier imbalances. Simulation results demonstrate that the good performance attainable by the proposed estimate algorithms can be assured without significant increase in system and computational complexity. publishersversion published

UID/MULTI/04111/0213 UID/MULTI/04111/0216 PCIF/SSI/0102/2017 UID/EEA/50008/2019 PES3N POCI-01-0145-FEDER-030629 Grant IF/00325/2015 This work proposes a novel approach for tracking a moving target in non-line-of-sight (NLOS) environments based on range estimates extracted from received signal strength (RSS) and time of arrival (TOA) measurements. By exploiting the known architecture of reference points to act as an improper antenna array and the range estimates, angle of arrival (AOA) of the signal emitted by the target is first estimated at each reference point. We then show how to take advantage of these angle estimates to convert the problem into a more convenient, polar space, where a linearization of the measurement models is easily achieved. The derived linear model serves as the main building block on top of which prior knowledge acquired during the movement of the target is incorporated by adapting a Kalman filter (KF). The performance of the proposed approach was assessed through computer simulations, which confirmed its effectiveness in combating the negative effect of NLOS bias and superiority in comparison with its naive counterpart, which does not take prior knowledge into consideration. publishersversion published

This work was partially supported by the Portuguese Science and Technology Foundation (FCT/MEC) under the grant SFRH/BD/108525/2015. It is well known that the stochastic nature of the interference deeply impacts the performance of emerging and future wireless communication systems. In this work we consider an ad hoc network where the nodes move according to the Random Waypoint mobility model. Assuming a timevarying wireless channel due to slow and fast fading and, considering the dynamic path loss due to the mobility of the nodes, we start by characterizing the interference distribution caused to a receiver by the moving interferers located in a ring. For this purpose, we consider a receiver located at the center of the simulated region. Based on the distribution of the interference's power, we evaluate different methodologies to estimate the power of the interference in real-time. Results achieved with a Maximum Log-likelihood estimator (MLE) and a Probability Weighted Moments (PWM) estimator are compared. The accuracy of the results achieved with the proposed methodologies in several simulations show that they may used as an effective tool of interference power estimation in future wireless communication systems, exhibiting high accuracy even when the number of samples is low. publishersversion published

PES3N POCI-01-0145-FEDER-030629 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 where there is a Line-Of-Sight (LOS) between all users. Therefore, power based NOMA MIMO-SVD schemes, combined with SC-FDE, can be considered efficient options for highly secure MIMO communications. publishersversion published