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  • 1.
    Andersen, Olav
    et al.
    Ericsson.
    Björsell, Niclas
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik. University of Gävle, Center for RF Measurement Technologies.
    Keskitalo, Niclas
    University of Gävle, Center for RF Measurement Technologies. University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    A Test-Bed Designed to Utilize Zhu’s General Sampling Theorem to Characterize Power Amplifiers2009In: Instrumentation and measurement technology conference 2009 I2MTC '09 IEEE, Singapore, 2009, p. 201-204Conference paper (Refereed)
    Abstract [en]

    Characterizing power amplifiers require test set-ups with performance superior to the power amplifiers. A commonly used method is to use an IQ-demodulator. However, problem arises due to imperfections in the demodulator such as IQ-imbalance; an alternative method is to use a direct down converter to intermediate frequency. The drawback then is the limited bandwidth. However, the required bandwidth of the ADC does not need to be exceptional. According to Zhu’s general sampling theorem is it enough to sample the output signal at the Nyquist rate of the input. However, even though the required sampling rate is reduced the demands on the analog bandwidth remains. Unfortunately, commercially available instruments such as vector signal analyzers can not be used for this purpose since their analog bandwidth is too small. In this paper a test-bed is designed to utilize the Zhu’s general sampling theorem. The RF front-end has frequency range of 500 MHz – 2.7 GHz and a bandwidth of 1 GHz. All performance data are verified with measurements.

  • 2.
    Andersson, Daniel
    et al.
    Radarbolaget.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Ottoson, Patrik
    Radarbolaget.
    Rönnow, Daniel
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Sandberg, Mats
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Radar Images of Leaks in Building Elements2015In: Energy Procedia, ISSN 1876-6102, Vol. 78, p. 1726-1731Article in journal (Refereed)
    Abstract [en]

    Through leakage in the building envelope there is a penetration of air, water vapor and particles. The degree of leakage of air can be quantified by existing methods. However, the location of adventitious openings is often not known. In order to overcome the limitations in existing methods, a non-contact and non-destructive method based on ultra-wide bandwidth radar technology is suggested. A test-bed is designed that can measure with different polarization to be able to detect flaws in different directions. Initial measurements shows promising results for further development of the method of using radar images to find leaks in building elements.

  • 3.
    Andersson, Rabé
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    The Energy Consumption and Robust Case Torque Control of a Rehabilitation Hip Exoskeleton2022In: Applied Sciences, E-ISSN 2076-3417, Vol. 12, no 21, article id 11104Article in journal (Refereed)
    Abstract [en]

    Gait disorders, muscle weakness, spinal cord injuries (SCIs) and other work-related disorders have increased the need for rehabilitation exoskeletons—specifically, for the hip because a huge percentage of mechanical power comes from the hip joint. However, realising a lightweight rehabilitation hip exoskeleton for mobility and at-home use with reliable control is challenging. The devices developed are restricted by a joint actuator and energy source design and tend to have various uncertainties. Thus, this study tested the robustness of four optimal controller cases in a simulation-based environment. We sought to determine whether the most robust optimal controller consumed less energy and demonstrated better performance in tracking the desired signal. The robustness of the optimal cases was tested with the hip torque signals of healthy subjects. The number of sit-to-stand (STS) instances and the walking distance at various speeds were calculated. The results showed that the most robust case controller was more energy efficient for STS, but not for walking activity. Furthermore, this study provides compelling evidence that various optimal controllers have different degrees of robustness and effects on energy consumption.

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  • 4.
    Andersson, Rabé
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    The MATLAB Simulation and the Linear Quadratic Regulator Torque Control of a Series Elastic Actuator for a Rehabilitation Hip Exoskeleton2022Conference paper (Refereed)
    Abstract [en]

    Almost the half of mechanical energy of a human gait cycle is generated by a hip joint. Therefore, this paper discusses a rehabilitation hip exoskeleton, starting with the modeling, simulation and ending with controlling its hip joints. A MATLAB based simulation environment with the use of Simscape Multibody toolbox was utilized to design and control the robotic hip exoskeleton. More details of adding a series elastic actuators (SEA) to the hip joints with the mathematical model are presented. However, the linearised mathematical model of the entire exoskeleton was found in simulation software which establish the basic need of controlling hip joints. The trajectory tracking is commonly used of controlling rehabilitation exoskeleton and to ensure a safe and reliable motion tracking methods, two desired torque signals were tested and analysed with the optimal linear quadratic regulator (LQR). The experiments with two torque signals–representing the sit-to-stand (STS) and the walking activity, demonstrated good performance of the motion gait tracking based on torque signals of a healthy person, which is carried out in the simulation environment. Furthermore, some studies in a human robot interaction are also mentioned in this paper.

  • 5.
    Andersson, Rabé
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    The Technical Challenges in Orthotic Exoskeleton Robots with Future Directions: a Review Paper2023Conference paper (Refereed)
    Abstract [en]

    The robotic wearable exoskeletons have been developed due to various advantages offered by these devices. These advantages are manifested by integrating the human and a robot into one system under the user's control, which motivated researchers to develop different exoskeletons through years. However, several advances in exoskeleton; still, dealing with the various technical challenges in designing these impressive devices is inevitably. This paper aims to introduce informative resources and quick guidance of various technical challenges as such information is critical for exoskeleton development. The constructive discussion is intended to encourage researchers, innovators and academia to be aware of these challenges. Finally, the contemporary research gaps with various challenges have been highlighted, which remain to be solved as well as some future directions in this field that will have far-reaching effects on developing exoskeletons.

  • 6.
    Andersson, Rabé
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Isaksson, Magnus
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Robots are a promising investment to fight pandemics2021In: 2021 8th International Conference on Signal Processing and Integrated Networks (SPIN), IEEE , 2021, p. 458-463Conference paper (Refereed)
    Abstract [en]

    Coronavirus caused pandemics as many viruses did through human history. The current pandemic causes overwhelmed healthcare system, locked down cities, and massive fatality among humans. Thus, different robots have been used since the COVID outbreak worldwide to reduce spreading infectious diseases and support frontline healthcare workers. This paper sets out the different robots implemented for hospital, non-hospital use, and possible use that can be deployed amidst the pandemic. A literature survey of versatile robots during COVID-19 is introduced. Roboticists contributed with wheeled and drone robots with various applications to assist medical care systems and society during the ongoing crisis. Pandemics are common throughout human history and difficult to avoid or prevent; thus, we intend to encourage societies, academia, engineers and innovators to invest more in robots that cannot catch the virus and consequently introduce beneficial solutions to fight such pandemic in the future.

  • 7.
    Barbé, Kurt
    et al.
    Vrije Universiteit Brussel, ELEC.
    Van Moer, Wendy
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Lauwers, L
    Vrije Universiteit Brussel.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    A Simple Nonparametric Preprocessing Technique to Correct for Nonstationary Effects in Measured Data2012In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 61, no 8, p. 2085-2094Article in journal (Refereed)
    Abstract [en]

    The general approach for modeling systems assumes that the measured signals are (weakly) stationary, i.e., the power spectrum is time invariant. However, the stationarity assumption is violated when: 1) transient effects due to experimental conditions are dominant; 2) data are missing due to, for instance, sensor failure; or 3) the amplitude of the excitation signals smoothly varies over time due to, for instance, actuator problems. Although different methods exist to deal with each of these nonstationary effects specifically, no unified approach is available. In this paper, a new and general technique is presented to handle nonstationary effects, based on processing overlapping subrecords of the measured data. The proposed method is a simple preprocessing step where the user does not need to specify which nonstationary effect is present, nor the time interval where the nonstationary effect appears. The merits of the proposed approach are demonstrated on an operational wireless system suffering from interrupted link effects.

  • 8.
    Bemani, Ali
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Aggregation Strategy on Federated Machine Learning Algorithm for Collaborative Predictive Maintenance2022In: Sensors, E-ISSN 1424-8220, Vol. 22, no 16, article id 6252Article in journal (Refereed)
    Abstract [en]

    Industry 4.0 lets the industry build compact, precise, and connected assets and also has made modern industrial assets a massive source of data that can be used in process optimization, defining product quality, and predictive maintenance (PM). Large amounts of data are collected from machines, processed, and analyzed by different machine learning (ML) algorithms to achieve effective PM. These machines, assumed as edge devices, transmit their data readings to the cloud for processing and modeling. Transmitting massive amounts of data between edge and cloud is costly, increases latency, and causes privacy concerns. To address this issue, efforts have been made to use edge computing in PM applications., reducing data transmission costs and increasing processing speed. Federated learning (FL) has been proposed a mechanism that provides the ability to create a model from distributed data in edge, fog, and cloud layers without violating privacy and offers new opportunities for a collaborative approach to PM applications. However, FL has challenges in confronting with asset management in the industry, especially in the PM applications, which need to be considered in order to be fully compatible with these applications. This study describes distributed ML for PM applications and proposes two federated algorithms: Federated support vector machine (FedSVM) with memory for anomaly detection and federated long-short term memory (FedLSTM) for remaining useful life (RUL) estimation that enables factories at the fog level to maximize their PM models’ accuracy without compromising their privacy. A global model at the cloud level has also been generated based on these algorithms. We have evaluated the approach using the Commercial Modular Aero-Propulsion System Simulation (CMAPSS) dataset to predict engines’ RUL Experimental results demonstrate the advantage of FedSVM and FedLSTM in terms of model accuracy, model convergence time, and network usage resources. 

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  • 9.
    Bemani, Ali
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Cyber-Physical Control of Indoor Multi-vehicle Testbed for Cooperative Driving2020In: 2020 IEEE Conference on Industrial Cyberphysical Systems (ICPS), IEEE , 2020, p. 371-377Conference paper (Refereed)
    Abstract [en]

    The system of connected vehicle to vehicle and vehicle to infrastructure can be considered as a wireless cyber-physical system of systems (Wireless CPSoS), which will be provided with the high ability of adaptive control on system of systems, cooperative scenarios to control of a Wireless CPSoSand adaptive wireless networked control system (WNCS). In this paper we present our multi-vehicle testbed based on the cyber-physical system that was designed for verification and validation of cooperative driving algorithm involving WNCStesting. Vehicles were developed as the physical prototype equipped with Raspberry-pi microprocessor and other sensing elements. This testbed consists of a fleet of 4 robot vehicles. An indoor positioning system (IPS) based on particle filter is purposed by using an inertial measurement unit (IMU) and iBeacon that is built upon Bluetooth Low Energy. Some typical cooperative driving scenarios can be implemented on this testbed under indoor laboratory. The method used to realize the objective statement was Model Predictive Control (MPC) with a state observer based on a Kalman Filter (KF). Because the wireless control systems can be severely affected by the imperfections of the wireless communication link. Our experimental testbed paves the way for testing and evaluating more intelligent cooperative driving scenario with the use new wireless technology and control system in the future.

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  • 10.
    Bemani, Ali
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Distributed Event Triggering Algorithm for Multi-Agent System over a Packet Dropping Network2021In: Sensors, E-ISSN 1424-8220, Vol. 21, no 14, article id 4835Article in journal (Refereed)
    Abstract [en]

    The availability of wireless networked control systems (WNCSs) has increased the interest in controlling multi-agent systems. Multiple feedback loops are closed over a shared communication network in such systems. An event triggering algorithm can significantly reduce network usage compared to the time triggering algorithm in WNCSs, however, the control performance is insecure in an industrial environment with a high probability of the packet dropping. This paper presents the design of a distributed event triggering algorithm in the state feedback controller for multi-agent systems, whose dynamics are subjected to the external interaction of other agents and under a random single packet drop scenario. Distributed event-based state estimation methods were applied in this work for designing a new event triggering algorithm for multi-agent systems while retaining satisfactory control performance, even in a high probability of packet drop condition. Simulation results for a multi-agent application show the main benefits and suitability of the proposed event triggering algorithm for multi-agent feedback control in WNCSs with packet drop imperfection.

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  • 11.
    Bemani, Ali
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Distributed Event-Triggered Control of Vehicular Networked System with Bursty Packet Drops2021In: 2021 7th International Conference on Event-Based Control, Communication, and Signal Processing (EBCCSP), Krakow, Poland: IEEE , 2021, p. 1-7Conference paper (Refereed)
    Abstract [en]

    This paper investigates the distributed event-triggered control of leader-follower consensus problem with harsh environmental conditions such as a high probability of burst packet drops occurs in the communication channels between the vehicles. The main objective in the vehicular platoons is to ensure that all follower vehicles are traveling at the same speed as the leader while maintaining a desired inter-vehicular distance with considering the minimum communication resource usage. To achieve the object, a novel distributed event-triggered communication strategy based on the estimation and prediction of self-states and other agents’ states in each vehicle is proposed which includes two parallel algorithms. The first one is based on comparing the state estimation and prediction of the vehicle itself, and the second one is based on comparing the state estimation and prediction of other vehicles which have interaction in their process with the active vehicle. Collision avoidance, speed convergence, and limited communication resource usage of each vehicle are simultaneously considered in the design of the event-triggered mechanism in a harsh packet drops environment. Numerical simulations are presented to show that the proposed event triggering algorithm under three scenarios of burst packet drops can converge the consensus problem of vehicular platooning.

  • 12.
    Bemani, Ali
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Low-Latency Collaborative Predictive Maintenance: Over-the-Air Federated Learning in Noisy Industrial Environments2023In: Sensors, E-ISSN 1424-8220, Vol. 23, no 18, article id 7840Article in journal (Refereed)
    Abstract [en]

    The emergence of Industry 4.0 has revolutionized the industrial sector, enabling the development of compact, precise, and interconnected assets. This transformation has not only generated vast amounts of data but also facilitated the migration of learning and optimization processes to edge devices. Consequently, modern industries can effectively leverage this paradigm through distributed learning to define product quality and implement predictive maintenance (PM) strategies. While computing speeds continue to advance rapidly, the latency in communication has emerged as a bottleneck for fast edge learning, particularly in time-sensitive applications such as PM. To address this issue, we explore Federated Learning (FL), a privacy-preserving framework. FL entails updating a global AI model on a parameter server (PS) through aggregation of locally trained models from edge devices. We propose an innovative approach: analog aggregation over-the-air of updates transmitted concurrently over wireless channels. This leverages the waveform-superposition property in multi-access channels, significantly reducing communication latency compared to conventional methods. However, it is vulnerable to performance degradation due to channel properties like noise and fading. In this study, we introduce a method to mitigate the impact of channel noise in FL over-the-air communication and computation (FLOACC). We integrate a novel tracking-based stochastic approximation scheme into a standard federated stochastic variance reduced gradient (FSVRG). This effectively averages out channel noise's influence, ensuring robust FLOACC performance without increasing transmission power gain. Numerical results confirm our approach's superior communication efficiency and scalability in various FL scenarios, especially when dealing with noisy channels. Simulation experiments also highlight significant enhancements in prediction accuracy and loss function reduction for analog aggregation in over-the-air FL scenarios.

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  • 13.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    AD and DA conversion2015In: Modern Measurements: Fundamentals and Applications / [ed] Ferrero, A., Petri, D., Carbone, P. and Catelani, M., Hoboken: John Wiley & Sons, 2015, p. 125-148Chapter in book (Refereed)
    Abstract [en]

    This chapter describes the conversion process and its limitations and discusses methods to reduce the impact of these limitations in various applications. The process of converting analog signals into digital signals can be divided into two parts. First, the signal will be measured at discrete time instants and then quantized into fixed amplitude levels. The key parameters to consider when selecting an analog-to-digital converter (ADC) or digital-to-analog converter (DAC) are the resolution of the quantizer in number of bits and the sampling rate of the sampler. The chapter discusses these two functions with a basic example. It introduces some commonly used sampling techniques for improving the performance of an existing ADC, such as oversampling, sigma-delta conversion, dithering, time-interleaved sampling, undersampling, harmonic sampling, time-equivalent sampling and post-correction methods. The theory behind signal reconstruction is discussed with respect to the sampling theorem.

  • 14.
    Björsell, Niclas
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Modeling analog to digital converters at radio frequency2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This work considers behavior modeling of analog to digital converters with applications in the radio frequency range, including the field of telecommunication as well as test and measurement instrumentation, where the conversion from analog to digital signals often is a bottleneck in performance. The models are intended to post-process output data from the converter and thereby improve the performance of the digital signal. By building a model of practical converters and the way in which they deviate from ideal, imperfections can be corrected using post-correction methods.

    Behavior modeling implies generation of a suitable stimulus, capturing the output data, and characterizing a model. The demands on the test setup are high for converters in the radio frequency range. The test-bed used in this thesis is composed of commercial state-of-the-art instruments and components designed for signal conditioning and signal capture. Further, in this thesis, different stimuli are evaluated, theoretically as well as experimentally.

    There are a large number of available model structures for dynamic nonlinear systems. In order to achieve a parameter efficient model structure, a Volterra model was used as a starting-point, which can describe any weak nonlinear system with fading memory, such as analog to digital converters. However, it requires a large number of coefficients; for this reason the Volterra model was reduced to a model structure with fewer parameters, by comparing the symmetry properties of the Volterra kernels with the symmetries from other models. An alternative method is the Kautz-Volterra model, which has the same general properties as the Volterra model, but with fewer parameters. This thesis gives experimental results of the Kautz-Volterra model, which will be interesting to apply in a post-correction algorithm in the future.

    To cover behavior not explained by the dynamic nonlinear model, a complementary piecewise linear model component is added. In this thesis, a closed form solution to the estimation problem for both these model components is given. By gradually correcting for each component the performance will improve step by step. In this thesis, the relation between a given component and the performance of the converter is given, as well as potential for improvement of an optimal post-correction.

  • 15.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Andersen, Olav
    Händel, Peter
    High Dynamic Range Test-Bed for Characterization of Analog-To-Digital Converters Up To 500 MSPS2005In: 10th Workshop on ADC modelling and testing, 2005, p. 601-604Conference paper (Refereed)
    Abstract [en]

    A measurement set-up of for the characterization of analog-to-digital converters (ADCs) is described. The measurement set-up characterizes ADCs up to 16 bits at 350 MHz (option for>500 MHz). Testing dynamic performance of high-speed ADCs is regarded as difficult and expensive. By using existing state-of-the-art instruments in combination with specially designed amplifiers and filters, a high performance, cost efficient test-bed has been built-up. Practical performance corresponds to ADC datasheet and exceeds the performance obtained if using commercial instruments only. Consequently, the measurement results represent the true performance of the ADC without impact from the test-bed. 1.

  • 16.
    Björsell, Niclas
    et al.
    Högskolan i Gävle-Sandviken.
    Blomqvist, Claes
    Högskolan i Gävle-Sandviken.
    Utveckling av nya system som ger möjlighet till flexibel behovsstyrning av luftflödena1998Report (Other academic)
  • 17.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik. University of Gävle, Center for RF Measurement Technologies.
    Daponte, Pasquale
    Department of Engineering, University of Sannio, Italy.
    De Vito, Luca
    Department of Engineering, University of Sannio, Italy.
    Rapuano, Sergio
    Department of Engineering, University of Sannio, Italy.
    Automatic signal recognition for a flexible spectrum management2009In: XIX IMEKO World Congress, 2009, p. 568-573Conference paper (Refereed)
    Abstract [en]

    The paper presents the prototype of an automatic digital modulation classifier, to be used for signal recognition in frequency bands managed in a flexible way. The prototype is based on a Data Acquisition System, consisting of an Analog-to-Digital converter embedded in an evaluation board, a frame grabber and a Personal Computer. The modulation classifier is able to recognize the most used digital modulations. An experimental validation of the realized prototype in a radio environment is also provided.

  • 18.
    Björsell, Niclas
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    De Vito, Luca
    University Sannio.
    Rapuano, Sergio
    University Sannio.
    A GNU radio-based signal detector for cognitive radio systems2011In: 2011 IEEE International Instrumentation and Measurement Technology Conference (I2MTC), New York: IEEE conference proceedings, 2011, p. 1045-1049Conference paper (Refereed)
    Abstract [en]

    This paper deals with the hardware and software architecture of a signal detector prototype. It is able to observe a wide band and to find, in such band, the empty or occupied channels. It is intended to be used either in telecommunication devices or in spectrum monitoring instruments working in the new scenarios of telecommunications, where a flexible and dynamic spectrum management will be introduced. The signal detector has been validated on simulated and emulated signals showing high detection percentages even with low signal to noise ratios.

  • 19.
    Björsell, Niclas
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    De Vito, Luca
    Department of Engineering, University of Sannio, Benevento, Italy.
    Rapuano, Sergio
    Department of Engineering, University of Sannio, Benevento, Italy.
    A waveform digitizer-based automatic modulation classifier for a flexible spectrum management2011In: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 44, no 6, p. 1007-1017Article in journal (Refereed)
    Abstract [en]

    The paper presents the development and validation of an automatic digital modulation classifier based on a waveform digitizer architecture. The proposed automatic digital modulation classifier can be used for signal recognition in the next generation telecommunication systems, characterized by a flexible and dynamic management of the radio spectrum. It has been implemented on a PC architecture, connected with two different types of waveform digitizers. The experimental validation has been carried out by means of actual telecommunication signals, even in presence of narrowband and wideband interference. (C) 2011 Elsevier Ltd. All rights reserved.

  • 20.
    Björsell, Niclas
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Hamid, Mohamed
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Kerttula, Jussi
    Aalto.
    Imadur, Rahman
    Ericsson AB.
    Initial Report on the tolerance of legacy systems to transmissions of secondary users based on legacy specifications2010Report (Other academic)
    Abstract [en]

    Secondary use of exclusively licensed but inefficiently used spectrum bands has been proposed as a solution to make more efficient use of spectrum resources. An important requirement for such secondary usage is to ensure that the primary services and systems performance are not degraded due to the presence of the secondary system. In this report three licensed primary systems are studied, namely digital video broadcasting, radar and aeronautical systems. In this initial report, the odelled tolerance limits for the primary users are investigated and verified by means of measurements for the case of DVB systems and literature review for the cases of Radar and Aeronautical systems. The impact of interference is evaluated as a functionof Desired to Undesired Power level (D/U) ratio for DVB systems, the pulse detection error for Aeronautical systems and the maximum interference-to-noise ratio (INR) for Radar systems. The main conclusions are that co-channel and adjacent channel interference need to be taken into account when assessing the tolerance limits for secondary systems in the TV bands. Also, non-continuous bursty-type users do not cause any higher interference compared to continuous data traffic users; thus, same tolerance limits can be used for both traffic behaviours.

     

    For aeronautical systems, spatial separation and transmit power of the secondary system determine the feasibility of secondary usage of the L-band. For other radar systems e.g. in S band and C band, the INR value, the spatial separation, the transmit power of the secondary system and the IF separation effects determine the possibilities for secondary users. For DVB systems, multiple interferers cause accumulative interference effects on the co-channels and adjacent channels, and the total amount of interference caused by multiple interferers should be kept below the desired signal level.

  • 21.
    Björsell, Niclas
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Hosseinzadeh Dadash, Amirhossein
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science, Electronics.
    Finite Horizon Degradation Control of Complex Interconnected Systems2021In: Proceedings of the 17th IFAC Symposium on Information Control Problems in Manufacturing Budapest, Hungary, June 7-9, 2021, Elsevier , 2021, p. 319-324Conference paper (Refereed)
    Abstract [en]

    In industrial production, it is of great importance to have high availability in its production equipment. Well-functioning maintenance is a significant factor for a high level of availability. This can be achieved by minimizing the number of reactive maintenance stops and optimizing scheduled maintenance. New methods for predictive maintenance provide a good opportunity for this, but most technologies that are available today are designed for individual sub-systems and they are rarely designed for a complex, interconnected machine. In the process industry, raw materials are rocessed into a finished product in a continuous flow through several subsystems and if one subsystem stops, the entire process flow stops. For these processes, it is more important to optimize the maintenance efforts for subsystems so maintenance can take place synchronized. This paper describes a method of supervised control that includes maintenance aspects; health parameters indicating deterioration are included in a MIMO controller. The method is verified in a simulation of a rolling mill with three rollers. The results show that it is possible to optimize the whole complex process including several subprocesses by using a health parameter as a control parameter and broadening the controllability of the system by dividing the workload in a way that all the subsystems reach the desired degradation level for maintenance in a desired optimum time. 

  • 22.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Händel, Peter
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    A Statistical Evaluation of ADC Histogram Tests with Arbitrary Stimuli Signal2005In: ADDA 2005, 2005, p. 259-264Conference paper (Refereed)
    Abstract [en]

    Histogram tests are a commonly used method for characterizing analogue to digital converters. However, different stimuli signals can be used in the histogram test. An overview of common input stimuli for the test is presented. Previous works have analysed the statistical properties of the resulting histograms for different stimuli signals, separately. In this paper, generally applicable results for asymptotically unbiased minimum variance estimator and Cramer-Rao lower bound are derived, irrespective of used input stimuli. Where available, the general expression is compared and found in accordance with signal-specific expressions.

  • 23.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Händel, Peter
    Signal Processing Lab., ACCESS Linnaeus Center, School of Electrical Engineering, Royal Institute of Technology, Stockholm, Sweden.
    Achievable ADC Performance by Postcorrection Utilizing Dynamic Modeling of the Integral Nonlinearity2008In: EURASIP Journal on Advances in Signal Processing, ISSN 1687-6172, E-ISSN 1687-6180, article id 497187Article in journal (Refereed)
    Abstract [en]

    There is a need for a universal dynamic model of analog to digital converters (ADC) aimed for post-correction. However, it is complicated to fully describe the properties of an ADC by a single model. An alternative is to split up the ADC model in different components, where each component has unique properties. In this paper, a model based on three components is used, and a performance analysis for each component is presented. Each component can be post-corrected individually and by the method that best suits the application. The purpose with post-correction of an ADC is to improve the performance. Hence, for each component, expressions for the potential improvement have been developed. The measures of performance are total harmonic distortion (THD) and signal to noise and distortion (SINAD) and to some extent spurious free dynamic range (SFDR).

  • 24.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Händel, Peter
    Analog-to-Digital Converters for High-Speed Applications2005In: GigaHz 2005, 2005, p. 151-154Conference paper (Refereed)
    Abstract [en]

    There is a rapid development of the performance of state-of-the-art analog to digital converters (ADC). Resolution and sampling rate are increasing continuously. Sampling rates in the high intermediate frequency (IF) range with sufficient dynamic range for communication applications were introduced about the turn of the millennium. Post-correction methods enable fast ADCs with modest linearity, and thereby weak dynamic performance, for high-speed applications.

    A post-correction procedure involves a characterization of the ADC non-linearity and then utilizing this information by processing the ADC output samples to remove the distortion. ADC characterization is usually performed by estimating ADC characteristics from measurements. Consequently, successful characterizations require both developed test methods and high performance test-beds.

    Characterization and testing ADCs are interesting in many different aspects. Not only that a proper characterization can be used for error compensation, testing is a major factor of cost for manufacturers, and shortening of the test cycle implies large savings. Testing ADCs is complicated, time consuming and demands high-performance instrumentation.

  • 25.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Händel, Peter
    Benefits with Truncated Gaussian Noise in ADC Histogram Tests2004In: IMEKO 04, 2004, p. 787-792Conference paper (Refereed)
  • 26.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Händel, Peter
    Royal Institute of Technology, Stockholm.
    Dynamic behavior models of analog to digital converters aimed for post-correction in wideband applications2006In: IMEKO Workshop on ADC and DAC Modelling and Testing, September 17-22, 2006, Rio de Janeiro, 2006, p. 5-Conference paper (Refereed)
    Abstract [en]

    In this paper a dynamic behavior model of analog to digital converters is proposed. The model is aimed for post correction in wideband applications. The suggested post correction method is a combination of look up tables and model based correction. The model consists of three components. The first is a component represented by a Hammerstein model; that is a static nonlinearity followed by a time invariant linear filter. The second component is a nonparametric model caused by significant deviation from the characterized integral nonlinearity and the output from the Hammerstein model. The third component contains of the remaining deviation and is considered as a random model error. Results from simulations verify that the examined ADC can be described by an ordinary Hammerstein model and a static look-up table.

  • 27.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Händel, Peter
    Signal Processing Laboratory, Royal Institute of Technology, Stockholm, Sweden.
    Histogram Tests for Wideband Applications2008In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 57, no 1, p. 70-75Article in journal (Refereed)
    Abstract [en]

    Characterization and testing of analog-to-digital converters (ADCs) are important in many different aspects. Histogram test is a common method to characterize the linearity features of an ADC. Two commonly used stimuli signals are sine waves and Gaussian noise. This paper presents a metrological comparison between Gaussian and sine wave histogram tests for wideband applications; that is we evaluate the performance in characterization of the ADC and the usability of post-correction. A post-correction procedure involves characterization of the ADC non-linearity and then use of this information by processing the ADC output samples to remove the distortion.

    The results show that the Gaussian histogram test gives reasonable accuracy to measure non-linearities. However, it does not result in a suitable model for post-correction in wideband applications. A single-tone sine wave histogram will be a better basis for post-correction. Best result can be obtained if the look-up table is trained with several single-tone sine waves in the frequency band.

  • 28.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Händel, Peter
    On Gaussian and Sine Wave Histogram Tests for Wideband Applications2005In: IMTC 2005, Ottawa, 2005, p. 677-682Conference paper (Refereed)
  • 29.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Händel, Peter
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Post-Correction of Under-Sampled Analog to Digital Converters2007In: IEEE Instrumentation and Measurement Technology Conference, 2007Conference paper (Refereed)
    Abstract [en]

    Applications with wide bandwidth and high center frequencies force the analog to digital converter (ADC) to be active in a working range with less dynamic performance in relation to lower frequency bands. However using under-sampling techniques in combination with post-correction methods enable a combination of high sampling rate, wide bandwidth and low distortion. In this paper the employed dynamic post-correction is a combination of look-up tables and model based correction. The results are mainly based on measurements on a 12 bit 210 MSPS ADC. The improvement in total harmonic distortion and spurious free dynamic range are acceptable over a wide frequency range and it is robust to variations in amplitude.

  • 30.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Händel, Peter
    Royal Institute of Technology, Signal Processing Laboratory, Stockholm, Sweden.
    Truncated Gaussian noise in ADC histogram tests2007In: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 40, no 1, p. 36-42Article in journal (Refereed)
    Abstract [en]

    One method to characterize analogue to digital converters (ADCs) is to use a histogram, where Gaussian noise may be used as stimulus signal. However, a Gaussian noise signal that excites all transition levels also generates input values outside working range of the ADC. Modern signal generators can generate arbitrary signals. Hence, excluding undesired values outside the ADC full scale can minimize test sequences. Truncating the signal to the working range gives further advantages, which are explored in this paper. The Cramér-Rao lower bound and a minimum variance estimator for histogram tests with an arbitrary stimulus are derived. These are applied for truncated Gaussian noise and the result is theoretically evaluated and compared to untruncated noise. It is shown that accuracy increases for a fixed sample length and that variation over transition levels decrease.

  • 31.
    Björsell, Niclas
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Händel, Peter
    Royal Institute of Technology, Signal Processing Lab, ACCESS Linnaeus Center.
    Jansson, Magnus
    Royal Institute of Technology,Signal Processing Lab, ACCESS Linnaeus Center.
    Medawar, Samer
    Royal Institute of Technology, Signal Processing Lab, ACCESS Linnaeus Center.
    Improved Estimate of Parametric Models for Analogue to Digital Converters by Using Weighted Integral Nonlinearity Data2010In: 17th Symposium IMEKO TC4 - Measurement of Electrical Quantities, 15th International Workshop on ADC Modelling and Testing, and 3rd Symposium IMEKO TC19: Environmental Measurements / [ed] Linus Michaeli, Jan Saliga, 2010, p. 597-600Conference paper (Refereed)
    Abstract [en]

    Error modelling has played a major role in generating post-corrections of analogue to digital converters (ADC). Benefits by using parametric models for post-correction are that they requires less memory and that they are easier to identify for arbitrary signals. However, the parameters are estimated in two steps; firstly, the integral nonlinearity (INL) is estimated and secondly, the model parameters. In this paper we propose a method to improve the performance in the second step, by utilizing information about the statistical properties of the first step.

  • 32.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Isaksson, Magnus
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Händel, Peter
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Rönnow, Daniel
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Kautz-Volterra modelling of an analogue-to-digital converter using a stepped three-tone excitation2007In: 12th IMEKO TC-4 International Workshop on ADC MODELLING AND TESTING, Iasi, Romania, September 2007, 2007, p. 107-112Conference paper (Refereed)
  • 33.
    Björsell, Niclas
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics. Royal Inst Technol, ACCESS Linnaeus Ctr, Stockholm, Sweden.
    Isaksson, Magnus
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics. Royal Inst Technol, ACCESS Linnaeus Ctr, Stockholm, Sweden.
    Händel, Peter
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics. Royal Inst Technol, ACCESS Linnaeus Ctr, Stockholm, Sweden.
    Rönnow, Daniel
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Kautz-Volterra modelling of analogue-to-digital converters2010In: Computer Standards & Interfaces, ISSN 0920-5489, E-ISSN 1872-7018, Vol. 32, no 3, p. 126-129Article in journal (Refereed)
    Abstract [en]

    In many test and measurement applications, the analogue-to-digital converter (ADC) is the limiting component. Using post-correction methods can improve the performance of the component as well as the over all measurement system. In this paper an ADC is characterised by a Kautz-Volterra (KV) model, which utilises a model-based post-correction of the ADC with general properties and a reasonable number of parameters. It is also shown that the inverse model has the same dynamic properties as the direct KV model. Results that are based on measurements on a high-speed 12-bit ADC, shows good results for a third order model.

  • 34.
    Björsell, Niclas
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Nader, Charles
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics. Signal Processing Lab, Royal Institute of Technology, Stockholm, Sweden.
    Händel, Peter
    Signal Processing Lab, Royal Institute of Technology, Stockholm, Sweden.
    Multi-tone design for out-of-band characterization of nonlinear RF modules using harmonic sampling2010In: 2010 IEEE International Instrumentation and Measurement Technology Conference, I2MTC 2010: Proceedings, Piscataway, NJ: IEEE Service Center , 2010, p. 620-623, article id 5488231Conference paper (Refereed)
    Abstract [en]

    In this paper we evaluate the generation of a multi-tone set for characterizing the behavior of nonlinear radio frequency (RF) modules in its out-of-band when harmonic sampling is used as digitizer. The purpose is to provide the reader with a tool to select proper frequencies and record length for a given application and test-bed. The method is based on simulations and the use of Sidon sequences. The proposed method is applicable to sparse discrete frequency multi-tones.

  • 35.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Rönnow, Daniel
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Händel, Peter
    Measuring Volterra kernels of analog to digital converters using a stepped three-tone scan2006In: Proceedings of the IEEE Instrumentation and Measurement Technology Conference, 2006. IMTC 2006, 2006, p. 1047-1050Conference paper (Refereed)
    Abstract [en]

    Volterra theory can be used to mathematically model nonlinear dynamic components such as analog-to-digital converter (ADC). This paper describes how frequency domain Volterra kernels of an ADC are determined from measurements. The elements of Volterra theory are given and practical issues are considered, such as methods for signal conditioning, finding the appropriate test signals scenario and suitable sampling frequency. The results show that for the used pipeline ADC, the frequency dependence is significantly stronger for second order difference products than for sum products and the linear frequency dependence was not as pronounced as that of the second order Volterra kernel.

  • 36.
    Björsell, Niclas
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik.
    Sucháneck, Petr
    Department of Measurement, Czech Technical University, Prague, Czech Republic.
    Händel, Peter
    Signal Processing Laboratory, Royal Institute of Technology, Stockholm, Sweden.
    Rönnow, Daniel
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik. WesternGeco, Asker, Sweden.
    Measuring Volterra kernels of analog to digital converters using a stepped three-tone scan2008In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 57, no 4, p. 666-671Article in journal (Refereed)
    Abstract [en]

    Volterra theory can be used to mathematically model nonlinear dynamic components such as analog-to-digital converter (ADC). This paper describes how frequency domain Volterra kernels of an ADC are determined from measurements. The elements of Volterra theory are given and practical issues are considered, such as methods for signal conditioning, finding the appropriate test signals scenario and suitable sampling frequency. The results show that for the used pipeline ADC, the frequency dependence is significantly stronger for second order difference products than for sum products and the linear frequency dependence was not as pronounced as that of the second order Volterra kernel. It is suggested that the Volterra kernels have the symmetry properties of a specific box model, namely a parallel Hammerstein systems.

  • 37.
    Björsell, Niclas
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Van Moer, Wendy
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Adding errors to reduce the PAPR and BER of OFDM-based transmissions2013In: 2013 IEEE International Instrumentation and Measurement Technology Conference (I2MTC 2013), New York: IEEE , 2013, p. 743-746Conference paper (Refereed)
    Abstract [en]

    When transmitting signals, one of the most important issues is to keep the transmission errors as low as possible. Or in other words, to obtain a reliable transmission link, the bit-error-rate (BER) should be kept within certain limits. However, the probability of transmission errors strongly depends on the signal-to-noise ratio (SNR) of the transmitted signals. Hence, the power amplifier plays a key role in the sender part: the more power, the higher the SNR, the lower the probability of transmission errors. Unfortunately, this is a too simple vision.

    One should take care to keep the peak-to-average power ratio (PAPR) of the transmitted signal low in order not to push the power amplifier into its nonlinear operation region. Classical techniques use clipping or backing-off the input signal to reduce the PAPR of the transmitted signal. However, these techniques have a negative influence on the SNR and hence on the BER.

    In this paper, we present a technique to reduce the PAPR of the transmitted signals and hence to reduce the BER, by introducing errors into Orthogonal Frequency Division Multiplexing (OFDM) signals in a controlled way. Channel coding will be used to compensate for the introduced errors.

    Download full text (pdf)
    fulltext
  • 38.
    Björsell, Niclas
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Van Moer, Wendy
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Measuring and Characterizing Nonlinear RF Systems: Faculty Course Development Award 20132017In: IEEE Instrumentation & Measurement Magazine, ISSN 1094-6969, E-ISSN 1941-0123, Vol. 20, no 4, p. 45-48Article in journal (Refereed)
  • 39.
    Fraile, F
    et al.
    Universidad Politécnica de Valencia.
    Nader, Charles
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Guerri, J. C.
    Universidad Politécnica de Valencia.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    On the reuse of DVB-T transmitter infrastructure for DVB-T22011Conference paper (Refereed)
    Abstract [en]

    The new DVB-T2 standard was specifically designed to allow the reuse of DVB-T infrastructure if required. This paper presents measurement results that verify the correct performance of a commercial DVB Power Amplifier with DVB-T2 waveforms. Furthermore, the paper includes configuration guidelines and performance evaluation of the Tone Reservation PAPR reduction algorithm included in the DVB-T2 standard. PAPR reduction is key technology when reusing DVB-T amplifiers for DVB-T2 transmissions without penalizing amplifier efficiency.

  • 40.
    Fraz, Hamza
    et al.
    Georgia Tech..
    Björsell, Niclas
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för elektronik. University of Gävle, Center for RF Measurement Technologies.
    Kenney, J. S.
    Georgia Tech..
    Sperlich, R.
    Texas Instruments.
    Prediction of Harmonic Distortion in ADCs using dynamic Integral Non-Linearity model2009In: Behavioral Modeling and Simulation Workshop, 2009. BMAS 2009. IEEE, 2009, p. 102-107Conference paper (Refereed)
    Abstract [en]

    This paper investigates the application of dynamic, Integral Non-Linearity (INL) model of Analog-to-Digital Converters (ADC) to predict the harmonic distortion in pipelined ADCs. The device used to validate the model is Texas Instruments' ADS6129; a 12-bit, 250 MSPS1 pipelined ADC. The performance of the model is measured using single tones in the first Nyquist zone, with an amplitude ranging between −1 dBFS2 and −46 dBFS. Total Harmonic Distortion (THD) and Spurious Free Dynamic Range (SFDR) are used as metrics to compare the performance of the model to the actual ADC. The results indicate that a model for High Code Frequency (HCF) INL is essential for correct prediction of distortion for input signals with small amplitudes. The results also suggest that dynamic INL models offer an effective method to model the distortion in ADCs until Nyquist frequency only. Beyond Nyquist frequency, the non-linear effects of Track and Hold (T/H) start manifesting and the INL model can no longer account for all the distortion seen at the output of ADCs.

  • 41.
    Gonzales Fuentes, Lee
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences. Vrije Universiteit Brussel.
    Barbe, Kurt
    Vrije Universiteit Brussel.
    Van Moer, Wendy
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics. Vrije Universiteit Brussel.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Cognitive radios: discriminant analysis finds the free space2012In: 2012 IEEE International Instrumentation and Measurement Technology Conference (I2MTC), New York: IEEE conference proceedings, 2012, p. 2242-2247Conference paper (Refereed)
    Abstract [en]

    Spectrum sensing is an essential pre-processing step for cognitive radio technology. This paper presents a novel method to detect the significant spectral components in measured nonflat spectra, and to estimate the magnitude of the spectral components. Furthermore, the probability that the spectral component was incorrectly classified is available. The algorithm is able to detect the presence or absence of signals in any kind of spectrum since no prior knowledge about the measured signal is needed. Hence, this method becomes a strong basis for a high-quality operation mode of cognitive radios. Simulation results prove the advantages of the presented technique.

  • 42.
    Gonzales-Fuentes, Lee
    et al.
    Vrije Universiteit Brussel.
    Barbe, Kurt
    Vrije Universiteit Brussel.
    Van Moer, Wendy
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics. Vrije Universiteit Brussel.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Cognitive Radios: Discriminant Analysis for Automatic Signal Detection in Measured Power Spectra2013In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 62, no 12, p. 3351-3360Article in journal (Refereed)
    Abstract [en]

    Signal detection of primary users for cognitive radios enables spectrum use agility. In normal operation conditions, the sensed spectrum is nonflat, i.e., the power spectrum is not constant. A novel method proposes the segmentation of the measured spectra into regions where the flatness condition is approximately valid. As a result, an automatic detection of the significant spectral components together with an estimate of the magnitude of the spectral component and a measure of the quality of classification becomes available. In this paper, we optimize the methodology for signal detection in cognitive radios such that the probability that a spectral component was incorrectly classified is iteratively reduced. Simulation and measurement results show the advantages of the presented technique in different types of spectra.

    Download full text (pdf)
    fulltext
  • 43.
    Hamid, Mohamed
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics. Communications Systems Lab (CoS), Royal Institute of Technology (KTH), Stockholm, Sweden .
    Barbe, Kurt
    Vrije Universiteit Brussel, ELEC.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics. Communications Systems Lab (CoS), Royal Institute of Technology (KTH), Stockholm, Sweden .
    Van Moer, Wendy
    Vrije Universiteit Brussel.
    Spectrum sensing through spectrum discriminator and maximum minimum eigenvalue detector: a comparative study2012In: 2012 IEEE International Instrumentation and Measurement Technology Conference (I2MTC), New York: IEEE conference proceedings, 2012, p. 2252-2256Conference paper (Refereed)
    Abstract [en]

    In this paper we present a new spectrum sensing technique for cognitive radios based on discriminant analysis called spectrum discriminator and compare it with the maximum minimum eigenvalue detector. The common feature between those two techniques is that neither prior knowledge about the system noise level nor the primary user signal, that might occupy the band under sensing, is required. Instead the system noise level will be derived from the received signal. The main difference between both techniques is that the spectrum discriminator is a non-parametric technique while the maximum minimum eigenvalue detector is a parametric technique. The comparative study between both has been done based on two performance metrics: the probability of false alarm and the probability of detection. For the spectrum discriminator an accuracy factor called noise uncertainty is defined as the level over which the noise energy may vary. Simulations are performed for different values of noise uncertainty for the spectrum discriminator and different values for the number of received samples and smoothing factor for the maximum minimum eigenvalue detector.

  • 44.
    Hamid, Mohamed
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    A Novel Approach for Energy Detector Sensing Time and Periodic Sensing Interval Optimization in Cognitive Radios2011In: Proceedings of the 4th International Conference on Cognitive Radio and Advanced Spectrum Management, New York: ACM Press, 2011Conference paper (Refereed)
    Abstract [en]

    In this paper a new approach of optimizing the sensing time and periodic sensing interval for energy detectors has been explored. This new approach is built upon maximizing the probability of right detection, captured opportunities and transmission efficiency. The probability of right detection is defined as the probability of having no false alarm and correct detection. Optimization of the sensing time relies on maximizing the summation of the probability of right detection and the transmission efficiency while optimization of periodic sensing interval subjects to maximizing the summation of transmission efficiency and the captured opportunities. The optimum sensing time and periodic sensing interval are dependent on each other, hence, iterative approach to optimize them is applied and convergence criterion is defined. The simulations show that both converged sensing time and periodic sensing interval increase with the increase of the channel utilization factor, moreover, the probability of false alarm, the probability of detection, the probability of right detection, the transmission efficiency and the captured opportunities have been taken as the detector performance metrics and evaluated for different values of channel utilization factor and signal-to-noise ratio.

  • 45.
    Hamid, Mohamed
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Frequency Hopping for Fair Radio Resources Allocation in TVWS2015In: ICWMC 2015: The Eleventh International Conference on Wireless and Mobile Communications / [ed] Carlos Becker Westphall, Iwona Pozniak-Koszalka, Eugen Borcoci & Dragana Krstic, 2015, p. 71-76Conference paper (Refereed)
    Abstract [en]

    Using frequency hopping for fair resources allocation in TV white spaces is proposed and evaluated in this paper. The degree of fairness is judged by the achieved throughput by different secondary users. The throughput of the secondary users is determined by their permissible transmission power and the interference from the TV and other secondary users. The permissible transmission power for secondary users in TV white spaces in different channels is investigated. The main concern of calculating the permissible secondary user transmission power is protecting the primary TV receivers from harmful interference. With the aid of SPLAT (RF Signal Propagation, Loss, And Terrain analysis tool), the received TV signal power in a study case of the surroundings of the city of Gävle is fetched. The interference from the TV transmission into the free channels is measured in six different locations. The simulated system is a deployed Wi-Fi access points in a building representing an office environment in an urban area. Moreover, the size of the hopping set and the number of APs influences are investigated.

  • 46.
    Hamid, Mohamed
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Geo-location Spectrum Opportunities Database in Downlink Radar Bands for OFDM Based Cognitive Radios2011Conference paper (Refereed)
    Abstract [en]

    In this paper a model to investigate the spectrum opportunities for cognitive radio networks in three radar frequency bands L, S and C at a specific location is introduced. We consider underlay unaware spectrum sharing model. The Secondary System we assume is an OFDM based system. The followed strategy is built upon defining a specific co or adjacent channel as a spectrum opportunity if -and only if- the interference generated by the secondary system occupying that channel  into the radar system is less than the permissible interference defined by the value of Interference to Noise ratio (INR) and the radar receiver inherited noise level. The simulation results show that for the same transmission parameters C band offer more spectrum opportunities than S band which is itself offers more spectrum opportunities than L band.

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    Geo-location Spectrum Opportunities Radar Bands
  • 47.
    Hamid, Mohamed
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Maximum Minimum Eigen Values Based Spectrum Scanner in GNU Radio2011In: RFMTC11, Gävle, 2011Conference paper (Other academic)
  • 48.
    Hamid, Mohamed
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Maximum Minimum Eigenvalues Based Spectrum Scanner for Cognitive Radios2012In: 2012 IEEE International Instrumentation and Measurement Technology Conference (I2MTC), New York: IEEE conference proceedings, 2012, p. 2248-2251Conference paper (Refereed)
    Abstract [en]

    In this paper we introduce a technique for spectrum scanning with the maximum minimum eigenvalue detection based spectrum sensing. The fundamental problem we address in this paper is the inability of using maximum minimum eigenvalue detection with filtering in time domain where the white noise becomes coloured. The solution we propose here is based on frequency domain rectangular filtering. By frequency domain rectangular filtering we take the spectral lines inside each sub-band and throw out the rest. After doing the frequency domain rectangular filtering, we generate the corresponding time domain signal and inject it to the maximum minimum eigenvalue detector. An experimental verification has been performed and the obtained results show that the technique is implementable with a performance better than the energy detector as a reference technique in terms of the probability of detection when both technique have the same probability of false alarm.

  • 49.
    Hamid, Mohamed
    et al.
    University of Agder, Kristiansand, Norway.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Radio Resource Allocation for Indoor Secondary Access in TV White Space2016In: International Journal On Advances in Telecommunications, ISSN 1942-2601, E-ISSN 1942-2601, Vol. 19, no 1-2, p. 25-34Article in journal (Refereed)
    Abstract [en]

    This paper considers fair radio resource assignment for secondary users operating in TV white space by means of frequency hopping. The achieved throughput for different secondary users is used to measure the degree of fairness. The permissible transmission power for secondary users is set to protect the TV transmission from excessive interference. Hence, there are different limits on the secondary transmission power when operating in different idle TV channels because different adjacent channels generates different amounts of interference based on the TV receiver transfer function in the frequency domain. Moreover, different free TV channels experience different amounts of interference due to the non-linearities in the TV transmission. A model for power assignment in each of the free TV channels is developed based on the received TV signal, TV receiver characteristics and secondary user location. For the sake of fair resource allocation, frequency hopping is proposed herein, and its performance is evaluated. In this study, three different TV transmitters located in three different cities in Sweden, namely, Gavle, Stockholm and Link ¨ oping, are ¨ exploited where the interference from the TV transmission into the free channels is measured. For the secondary system, the deployment of indoor WiFi access points in an office environment is considered and simulated. The main finding is that frequency hopping can provide fair radio resource distribution in terms of the obtainable throughput. Moreover, it is shown that the denser the area is, the higher the achievable secondary throughput due to the higher attenuation of the interfering signals.

  • 50.
    Hamid, Mohamed
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics. Communication Systems Department, KTH Royal Institute of Technology, Stockholm, Sweden.
    Björsell, Niclas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
    Ben Slimane, Slimane
    Communication Systems Department, KTH Royal Institute of Technology, Stockholm, Sweden.
    Signal Bandwidth Impact on Maximum-Minimum Eigenvalue Detection2015In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 19, no 3, p. 395-398, article id 7001062Article in journal (Refereed)
    Abstract [en]

    The impact of the signal bandwidth and observation bandwidth on the detection performance of the maximumminimum eigenvalue detector is studied in this letter. The considered signals are the Gaussian signals. The optimum ratio between the signal and the observation bandwidth is analytically proven to be 0.5 when reasonable values of the system dimensionality are used. The analytical proof is verified by simulations.

123 1 - 50 of 123
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