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1.	Eklund, Johan, 1966-, et al. (författare) Tuning SCTP failover for carrier grade telephony signaling 2010 Ingår i: Computer Networks. - : Elsevier BV. - 1389-1286 .- 1872-7069. ; 54:1, s. 133-149 Tidskriftsartikel (refereegranskat)abstract The Stream Control Transmission Protocol (SCTP) has not only been selected as the signaling transport protocol of choice in IETF SIGTRAN, the architecture that bridges circuit-switched and IP-based mobile core networks, but also plays a pivotal role in SAE/LTE, the next-generation UMTS/HSPA networks. To meet the redundancy requirements of telecom signaling traffic, SCTP includes a failover mechanism that enables rerouting of traffic from an unreachable network path to a backup path. However, the recommendations provided by IETF on how to configure the SCTP failover mechanism to meet telecom signaling requirements are kept quite general and leave much of the tuning to the telecom equipment vendor and/or operator. Several works by us and others have been carried out to study the effect of different SCTP parameters on the failover performance. The main contribution of this paper is that it gives a coherent treatment of how to configure the SCTP failover mechanism for carrier-grade telephony signaling, and provides practically usable configuration recommendations. The paper also discusses an alternate or complementary way of optimizing the SCTP failover mechanism by relaxing the exponential backoff that foregoes a retransmission timeout in SCTP. Some results showing significantly reduced failover times by use of this mechanism, with only marginal deteriorating effects on a signaling network, are discussed and analyzed in the paper. (C) 2009 Elsevier B.V. All rights reserved.
2.	Zhang, Kewei, et al. (författare) Protecting GNSS Open Service-Navigation Message Authentication against Distance-Decreasing Attacks Annan publikation (övrigt vetenskapligt/konstnärligt)abstract As the security of global navigation satellite systems (GNSS) for civilian usage is increasingly important, navigation message authentication (NMA) significantly improves resilience to spoofing attacks. However, not all attacks can be effectively countered: a strong variant of replay/relay attacks, distance-decreasing (DD) attacks, can shorten pseudorange measurements, without manipulating the cryptographically protected navigation message, thus manipulating the position, velocity, and time solution undetected. First, we discuss how DD attacks can tamper with GNSS signals, demonstrating the attack effectiveness on a recorded Galileo signal. DD attacks might introduce bit errors to the forged signals, but the adversary can keep this error rate very low with proper attack parameter settings. Then, based on our mathematical model of the prompt correlator output of the tracking phase at the victim receiver, we find that the correlator output distribution changes in the presence of DD attacks. This leads us to apply hypothesis testing to detect DD attacks, notably a Goodness of Fit (GoF) test and a generalized likelihood ratio test (GLRT), depending on the victim’s knowledge on the DD attacks. Monte Carlo simulations are used to evaluate the detection probability and the receiver operating characteristic (ROC) curves for two tests, for different adversary configuration and noise settings. Then, we evaluate the effectiveness of the GoF and GLRT tests with a synthesized DD signal. Both tests can detect DD attacks with similar performance in high signal-to-noise ratio (SNR) environments. The GLRT detection probability is approximately 20% higher than that of the GoF test in low SNR environments.
3.	Alayon Glazunov, Andres, et al. (författare) On the Physical Limitations of the Interaction of a Spherical Aperture and a Random Field 2011 Ingår i: IEEE Transactions on Antennas and Propagation. - : IEEE. - 0018-926X .- 1558-2221. ; 59:1, s. 119-128 Tidskriftsartikel (refereegranskat)abstract This paper derives physical limitations on the interactions of antennas exciting TM or TE modes (but not both) and wireless propagation channels. The derivation is based on the spherical vector wave expansion of the electromagnetic field outside a sphere circumscribing the antennas. The result is an extension of the seminal work of Chu on the classical limitations on maximum antenna gain and radiation Q. Rather than maximizing antenna gain in a single direction we obtain physical limitations on the antenna gain pattern, which is directly translated to more condensed parameters, i.e., the instantaneous effective gain G(i) and the mean effective gain G(e) if instantaneous realizations or correlation statistics of the expansion coefficients of the electromagnetic field are known, spectively. The obtained limitations are on the maximum of G(i)/Q and G(e)/Q, which establish a trade-off between link gain and Q.
4.	Khanzadi, M Reza, 1983, et al. (författare) Calculation of the Performance of Communication Systems from Measured Oscillator Phase Noise 2014 Ingår i: IEEE Transactions on Circuits and Systems I: Regular Papers. - 1549-8328 .- 1558-0806. ; 61:5, s. 1553-1565 Tidskriftsartikel (refereegranskat)abstract Oscillator phase noise (PN) is one of the major problems that affect the performance of communication systems. In this paper, a direct connection between oscillator measurements, in terms of measured single-side band PN spectrum, and the optimal communication system performance, in terms of the resulting error vector magnitude (EVM) due to PN, is mathematically derived and analyzed. First, a statistical model of the PN, considering the effect of white and colored noise sources, is derived. Then, we utilize this model to derive the modified Bayesian Cramer-Rao bound on PN estimation, and use it to find an EVM bound for the system performance. Based on our analysis, it is found that the influence from different noise regions strongly depends on the communication bandwidth, i.e., the symbol rate. For high symbol rate communication systems, cumulative PN that appears near carrier is of relatively low importance compared to the white PN far from carrier. Our results also show that 1/f^3 noise is more predictable compared to 1/f^2 noise and in a fair comparison it affects the performance less.
5.	Khanzadi, M Reza, 1983 (författare) Modeling and Estimation of Phase Noise in Oscillators with Colored Noise Sources 2013 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract The continuous increase in demand for higher data rates due to applications with massive number of users motivates the design of faster and more spectrum efficient communication systems. In theory, the current communication systems must be able to operate close to Shannon capacity bounds. However, the real systems perform below capacity limits, mainly due to channel estimation error and hardware impairments that have been neglected by idealistic or simplistic assumptions on the imperfections. Oscillator phase noise is one of the hardware impairments that is becoming a limiting factor in high data rate digital communication systems. Phase noise severely limits the performance of systems that employ dense constellations. Moreover, the level of phase noise (at a given off-set frequency) increases with carrier frequency which means that the problem of phase noise may be even more severe in systems with high carrier frequency.The focus of this thesis is on finding accurate statistical models of phase noise, as well as the design of efficient algorithms to mitigate the effect of this phenomenon on the performance of modern communication systems. First we derive the statistics of phase noise with white and colored noise sources in free-running and phase-locked-loop-stabilized oscillators. We investigate the relation between real oscillator phase noise measurements and the performance of communication systems by means of the proposed model. Our findings can be used by hardware and frequency generator designers to better understand the effect of phase noise with different sources on the system performance and optimize their design criteria respectively. Then, we study the design of algorithms for estimation of phase noise with colored noise sources. A soft-input maximum a posteriori phase noise estimator and a modified soft-input extended Kalman smoother are proposed. The performance of the proposed algorithms is compared against that of those studied in the literature, in terms of mean square error of phase noise estimation, and symbol error rate of the considered communication system. The comparisons show that considerable performance gains can be achieved by designing estimators that employ correct knowledge of the phase noise statistics. The performance improvement is more significant in low-SNR or low-pilot density scenarios.
6.	Nopchinda, Dhecha, 1991 (författare) mm-Wave Data Transmission and Measurement Techniques: A Holistic Approach 2019 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract The ever-increasing demand on data services places unprecedented technical requirements on networks capacity. With wireless systems having significant roles in broadband delivery, innovative approaches to their development are imperative. By leveraging new spectral resources available at millimeter-wave (mm-wave) frequencies, future systems can utilize new signal structures and new system architectures in order to achieve long-term sustainable solutions. This thesis proposes the holistic development of efficient and cost-effective techniques and systems which make high-speed data transmission at mm-wave feasible. In this paradigm, system designs, signal processing, and measurement techniques work toward a single goal; to achieve satisfactory system level key performance indicators (KPIs). Two intimately-related objectives are simultaneously addressed: the realization of efficient mm-wave data transmission and the development of measurement techniques to enable and assist the design and evaluation of mm-wave circuits. The standard approach to increase spectral efficiency is to increase the modulation order at the cost of higher transmission power. To improve upon this, a signal structure called spectrally efficient frequency division multiplexing (SEFDM) is utilized. SEFDM adds an additional dimension of continuously tunable spectral efficiency enhancement. Two new variants of SEFDM are implemented and experimentally demonstrated, where both variants are shown to outperform standard signals. A low-cost low-complexity mm-wave transmitter architecture is proposed and experimentally demonstrated. A simple phase retarder predistorter and a frequency multiplier are utilized to successfully generate spectrally efficient mm-wave signals while simultaneously mitigating various issues found in conventional mm-wave systems. A measurement technique to characterize circuits and components under antenna array mutual coupling effects is proposed and demonstrated. With minimal setup requirement, the technique effectively and conveniently maps prescribed transmission scenarios to the measurement environment and offers evaluations of the components in terms of relevant KPIs in addition to conventional metrics. Finally, a technique to estimate transmission and reflection coefficients is proposed and demonstrated. In one variant, the technique enables the coefficients to be estimated using wideband modulated signals, suitable for implementation in measurements performed under real usage scenarios. In another variant, the technique enhances the precision of noisy S-parameter measurements, suitable for characterizations of wideband mm-wave components.
7.	Wang, Chao, et al. (författare) On the Degrees of Freedom of Parallel Relay Networks 2010 Ingår i: 2010 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE GLOBECOM 2010. - 1930-529X. - 9781424456383 - 9781424456369 Konferensbidrag (refereegranskat)abstract We study the degrees of freedom (DOF) of a single-antenna M-user time-varying parallel relay network, where the communications between M pairs of unconnected sources and destinations are provided by a large number of half-duplex decode-and-forward (DF) relays. Unlike the conventional relaying strategy which demands all the relays to simultaneously assist the sources, we divide the relays into two clusters and permit them to take turns forwarding the source messages. With appropriate interference alignment design, it is proved that the M-user time-varying relay network has M DOF, provided that the number of relays is infinitely large.
8.	Stigwall, Johan, 1977, et al. (författare) Photonic GHz to THz tunable signal generation by chirped-pulse mixing 2006 Ingår i: 2006 European ISIS Workshop, Emerging Optical Broadband Technologies, Boppard am Rhein, Germany, May 29 - June 1, 2006. Konferensbidrag (refereegranskat)abstract Frequency-tunable generation of pulsed tones in the millimeter to sub-millimeter range was demonstrated by mixing of two chromatically dispersing femtosecond laser pulses split up in time by an adjustable differential group delay (DGD) and a polarizer. The signal frequency was set by adjusting the amount of DGD and the amount of dispersion, and was here tuned from below 1 GHz to 0.9 THz. Time-domain measurements were conducted using a sampling oscilloscope for the lower frequencies and an auto-correlator for the higher frequencies. Near 100% modulation depth was obtained, and the signal phase was very stable, being locked to the pulses from the femtosecond laser. The line-width of the mm-wave waveform was found to be transform-limited if the signal chirp induced by higher order dispersion was compensated for. Suggested applications for this system are for instance THz spectroscopy, characterization of high performance photo-diodes and real-time dispersion measurements.
9.	ur Réhman, Shafiq, 1978- (författare) Expressing emotions through vibration for perception and control 2010 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract This thesis addresses a challenging problem: “how to let the visually impaired ‘see’ others emotions”. We, human beings, are heavily dependent on facial expressions to express ourselves. A smile shows that the person you are talking to is pleased, amused, relieved etc. People use emotional information from facial expressions to switch between conversation topics and to determine attitudes of individuals. Missing emotional information from facial expressions and head gestures makes the visually impaired extremely difficult to interact with others in social events. To enhance the visually impaired’s social interactive ability, in this thesis we have been working on the scientific topic of ‘expressing human emotions through vibrotactile patterns’. It is quite challenging to deliver human emotions through touch since our touch channel is very limited. We first investigated how to render emotions through a vibrator. We developed a real time “lipless” tracking system to extract dynamic emotions from the mouth and employed mobile phones as a platform for the visually impaired to perceive primary emotion types. Later on, we extended the system to render more general dynamic media signals: for example, render live football games through vibration in the mobile for improving mobile user communication and entertainment experience. To display more natural emotions (i.e. emotion type plus emotion intensity), we developed the technology to enable the visually impaired to directly interpret human emotions. This was achieved by use of machine vision techniques and vibrotactile display. The display is comprised of a ‘vibration actuators matrix’ mounted on the back of a chair and the actuators are sequentially activated to provide dynamic emotional information. The research focus has been on finding a global, analytical, and semantic representation for facial expressions to replace state of the art facial action coding systems (FACS) approach. We proposed to use the manifold of facial expressions to characterize dynamic emotions. The basic emotional expressions with increasing intensity become curves on the manifold extended from the center. The blends of emotions lie between those curves, which could be defined analytically by the positions of the main curves. The manifold is the “Braille Code” of emotions. The developed methodology and technology has been extended for building assistive wheelchair systems to aid a specific group of disabled people, cerebral palsy or stroke patients (i.e. lacking fine motor control skills), who don’t have ability to access and control the wheelchair with conventional means, such as joystick or chin stick. The solution is to extract the manifold of the head or the tongue gestures for controlling the wheelchair. The manifold is rendered by a 2D vibration array to provide user of the wheelchair with action information from gestures and system status information, which is very important in enhancing usability of such an assistive system. Current research work not only provides a foundation stone for vibrotactile rendering system based on object localization but also a concrete step to a new dimension of human-machine interaction.
10.	Pérez-Penichet, Carlos, et al. (författare) Poster abstract : Augmenting WSNs with interoperable 802.15.4 sensor tags 2017 Ingår i: SenSys 2017 - Proceedings of the 15th ACM Conference on Embedded Networked Sensor Systems. - New York, NY, USA : Association for Computing Machinery, Inc. - 9781450354592 Konferensbidrag (refereegranskat)abstract The sensing capabilities of most sensor networks are fixed at the time of deployment. Adding new sensing capabilities to such networks is a costly and cumbersome process. We present Passive Sensor Tags, battery-free sensing devices that could be used to extend the sensing capabilities of an existing network. Sensor tags feature our new 802.15.4 receiver design which is suitable for micro-power operation, making battery-free tags possible. Because our tags can both transmit and receive 802.15.4 frames there is no need for any modification to the deployed hardware. We present preliminary measurements of transmission and reception range.
11.	Grabowski, Alexander, 1993 (författare) VCSEL Equivalent Circuits and Silicon Photonics Integration 2022 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract The vertical-cavity surface-emitting laser (VCSEL) is a light source of great importance for numerous industrial and consumer products. The main application areas are datacom and sensing. The datacom industry uses GaAs-based VCSELs for optical interconnects, the short-reach fiber optical communication links used to transfer large amounts of data at high rates between units within data centers and supercomputers. In the area of sensing, VCSELs are largely used in consumer products such as smart phones (e.g. face ID and camera auto focus), computer mice, and automobiles (e.g. gesture recognition and LIDAR for autonomous driving). In this work, an advanced physics-based equivalent circuit model for datacom VCSELs has been developed. The model lends itself to co-design and co-optimization with driver and receiver ICs, thereby enabling higher data rate transceivers with bandwidth limited VCSELs and photodiodes. The model also facilitates an understanding of how each physical process within the VCSEL affects the VCSEL static and dynamic performance. It has been applied to study the impact of carrier transport and capture on VCSEL dynamics. The work also includes micro-transfer-printing of GaAs-based single-mode VCSELs on silicon nitride photonic integrated circuits (PICs). Such PICs are increasingly used for e.g. compact and highly functional bio-photonic sensors. Transfer printing of VCSELs enables the much-needed on-PIC integration of power efficient light sources. The bottom-emitting VCSELs are printed above grating couplers on the PIC and optical feedback is used to control the polarization for efficient coupling to the silicon nitride waveguide. Wavelength tuning, as required by the bio-sensing application, is achieved by direct current modulation.
12.	Yanggratoke, Rerngvit, 1983- (författare) Data-driven Performance Prediction and Resource Allocation for Cloud Services 2016 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Cloud services, which provide online entertainment, enterprise resource management, tax filing, etc., are becoming essential for consumers, businesses, and governments. The key functionalities of such services are provided by backend systems in data centers. This thesis focuses on three fundamental problems related to management of backend systems. We address these problems using data-driven approaches: triggering dynamic allocation by changes in the environment, obtaining configuration parameters from measurements, and learning from observations. The first problem relates to resource allocation for large clouds with potentially hundreds of thousands of machines and services. We developed and evaluated a generic gossip protocol for distributed resource allocation. Extensive simulation studies suggest that the quality of the allocation is independent of the system size for the management objectives considered.The second problem focuses on performance modeling of a distributed key-value store, and we study specifically the Spotify backend for streaming music. We developed analytical models for system capacity under different data allocation policies and for response time distribution. We evaluated the models by comparing model predictions with measurements from our lab testbed and from the Spotify operational environment. We found the prediction error to be below 12% for all investigated scenarios.The third problem relates to real-time prediction of service metrics, which we address through statistical learning. Service metrics are learned from observing device and network statistics. We performed experiments on a server cluster running video streaming and key-value store services. We showed that feature set reduction significantly improves the prediction accuracy, while simultaneously reducing model computation time. Finally, we designed and implemented a real-time analytics engine, which produces model predictions through online learning.
13.	Lian, Mengke, et al. (författare) What Can Machine Learning Teach Us about Communications 2018 Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. ; 15 January 2019 Konferensbidrag (refereegranskat)abstract Rapid improvements in machine learning over the past decade are beginning to have far-reaching effects. For communications, engineers with limited domain expertise can now use off-the-shelf learning packages to design high-performance systems based on simulations. Prior to the current revolution in machine learning, the majority of communication engineers were quite aware that system parameters (such as filter coefficients) could be learned using stochastic gradient descent. It was not at all clear, however, that more complicated parts of the system architecture could be learned as well. In this paper, we discuss the application of machine-learning techniques to two communications problems and focus on what can be learned from the resulting systems. We were pleasantly surprised that the observed gains in one example have a simple explanation that only became clear in hindsight. In essence, deep learning discovered a simple and effective strategy that had not been considered earlier.
14.	Jang, Jeong Keun, et al. (författare) Area-efficient scheduling scheme based FFT processor for various OFDM systems 2018 Ingår i: 2018 IEEE ASIA PACIFIC CONFERENCE ON CIRCUITS AND SYSTEMS (APCCAS 2018). - : IEEE. - 9781538682401 ; , s. 338-341 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract This paper presents an area-efficient fast Fouriertransform (FFT) processor for orthogonal frequency-division multiplexing systems based on multi-path delay commutator architecture. This paper proposes a data scheduling scheme to reduce the number of complex constant multipliers. The proposed mixed-radix multi-path delay commutator FFT processor can support 128-, 256-, and 512-point FFT sizes. The proposed processor was synthesized using the Samsung 65-nm CMOS standard cell library. The proposed processor with eight parallel data paths can achieve a high throughput rate of up to 2.64 GSample/s at 330 MHz.
15.	Alhashimi, Anas, 1978- (författare) The application of auto regressive spectrum modeling for identification of the intercepted radar signal frequency modulation 2012 Ingår i: Inventi Impact - Telecom. - Bhopal, India : Inventi Journals Pvt.Ltd.. - 2249-1414 .- 2230-8172. ; 2012:3 Tidskriftsartikel (refereegranskat)abstract In the Electronic Warfare receivers, it is important to know the type of modulation of the intercepted Radar signals (MOP modulation on pulse). This information can be very helpful in identifying the type of Radar present and to take the appropriate actions against it. In this paper, a new signal processing method is presented to identify the FM (Frequency Modulation) pattern from the received Radar pulses. The proposed processing method based on Auto Regressive Spectrum Modelling used for digital modulation classification [1]. This model uses the instantaneous frequency and instantaneous bandwidth as obtained from the roots of the autoregressive polynomial. The instantaneous frequency and instantaneous bandwidth together were used to identify the type of modulation in the Radar pulse. Another feature derived from the instantaneous frequency is the frequency rate of change. The frequency rate of change was used to extract the pattern of the frequency change. Results show that this method works properly even for low signal to noise ratios.
16.	Gaspar Sánchez, José Manuel, et al. (författare) Edge computing for cyber-physical systems : A Systematic Mapping Study Emphasizing Trustworthiness 2022 Ingår i: ACM Transactions on Cyber-Physical Systems. - : Association for Computing Machinery (ACM). - 2378-962X .- 2378-9638. ; 6:3, s. 1-28 Tidskriftsartikel (refereegranskat)abstract Edge computing is projected to have profound implications in the coming decades, proposed to provide solutions for applications such as augmented reality, predictive functionalities, and collaborative Cyber-Physical Systems (CPS). For such applications, edge computing addresses the new computational needs, as well as privacy, availability, and real-time constraints, by providing local high-performance computing capabilities to deal with the limitations and constraints of cloud and embedded systems. Edge computing is today driven by strong market forces stemming from IT/cloud, telecom, and networking - with corresponding multiple interpretations of ”edge computing” (e.g. device edge, network edge, distributed cloud, etc.). Considering the strong drivers for edge-computing and the relative novelty of the field, it becomes important to understand the specific requirements and characteristics of edge-based CPS, and to ensure that research is guided adequately, e.g. avoiding specific gaps.Our interests lie in the applications of edge computing as part of CPS, where several properties (or attributes) of trustworthiness, including safety, security, and predictability/availability are of particular concern, each facing challenges for the introduction of edge-based CPS. We present the results of a systematic mapping study, a kind of systematic literature survey, investigating the use of edge computing for CPS with a special emphasis on trustworthiness. The main contributions of this study are a detailed description of the current research efforts in edge-based CPS and the identification and discussion of trends and research gaps. The results show that the main body of research in edge-based CPS only to a very limited extent consider key attributes of system trustworthiness, despite many efforts referring to critical CPS and applications like intelligent transportation. More research and industrial efforts will be needed on aspects of trustworthiness of future edge-based CPS including their experimental evaluation. Such research needs to consider the multiple interrelated attributes of trustworthiness including safety, security, and predictability, and new methodologies and architectures to address them. It is further important to provide bridges and collaboration between edge computing and CPS disciplines.
17.	Cheng, Hei Victor (författare) Aspects of Power Allocation in Massive MIMO 2016 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract The past decades have seen a rapid growth of mobile data trac, both in terms of connected devices and data rate. To satisfy the ever growing data trac demand in wireless communication systems, the current cellular systems have to be redesigned to increase both spectral eciency and energy eciency. Massive MIMO (Multiple-Input-Multiple-Output) is one solution that satisfy both requirements. In massive MIMO systems, hundreds of antennas are employed at the base station to provide service to many users at the same time and frequency. This enables the system to serve the users with uniformly good quality of service simultaneously, with low-cost hardware and without using extra bandwidth and energy. To achieve this, proper resource allocation is needed. Among the available resources, transmit power is one of the most important degree of freedom to control the spectral eciency and energy eciency. Due to the use of excessive number of antennas and low-end hardware at the base station, new aspects of power allocation compared to current systems arises. In the rst part of the thesis, a new uplink power allocation schemes that based on long term channel statistics is proposed. Since quality of the channel estimates is crucial in massive MIMO, in addition to data power allocation, joint power allocation that includes the pilot power as additional variable should be considered. Therefore a new framework for power allocation that matches practical systems is developed, as the methods developed in the literature cannot be applied directly to massive MIMO systems. Simulation results conrm the advantages brought by the the proposed new framework. In the second part of the thesis, we investigate the eects of using low-end ampliers at the base stations. The non-linear behavior of power consumption in these ampliers changes the power consumption model at the base station, thereby changes the power allocation. Two dierent scenarios are investigated and both results show that a certain number of antennas can be turned o in low load scenarios.
18.	Do, Hieu, et al. (författare) An Achievable Rate Region for the Gaussian Z-interference Channel with Conferencing 2009 Ingår i: 2009 47TH ANNUAL ALLERTON CONFERENCE ON COMMUNICATION, CONTROL, AND COMPUTING, VOLS 1 AND 2. - NEW YORK : IEEE. ; , s. 75-81 Konferensbidrag (refereegranskat)abstract This paper presents an achievable rate region for a 2-user Gaussian Z-interference channel with a noiseless and bidirectional digital communication link between the receivers. The region is achieved by utilizing the rate-splitting encoding technique, and the decode-and-forward and compress-and-forward strategies. In the very strong interference regime, the capacity region is achieved. In the weak interference regime, the asymptotic sum rate is characterized and shown to be possibly unbounded, which is in contrast to a recent result by Yu and Zhou for a similar scenario, however, with a unidirectional communication link between the receivers.
19.	Haque, Muhammad Fahim Ul (författare) Pulse-Width Modulated RF Transmitters 2017 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract The market for wireless portable devices has grown signicantly over the recent years.Wireless devices with ever-increased functionality require high rate data transmissionand reduced costs. High data rate is achieved through communication standards such asLTE and WLAN, which generate signals with high peak-to-average-power ratio (PAPR),hence requiring a power amplier (PA) that can handle a large dynamic range signal. Tokeep the costs low, modern CMOS processes allow the integration of the digital, analogand radio functions on to a single chip. However, the design of PAs with large dynamicrange and high eciency is challenging due to the low voltage headroom.To prolong the battery life, the PAs have to be power-ecient as they consume a sizablepercentage of the total power. For LTE and WLAN, traditional transmitters operatethe PA at back-o power, below their peak efficiency, whereas pulse-width modulation(PWM) transmitters use the PA at their peak power, resulting in a higher efficiency.PWM transmitters can use both linear and SMPAs where the latter are more power efficient and easy to implement in nanometer CMOS. The PWM transmitters have a higher efficiency but suffer from image and aliasing distortion, resulting in a lower dynamic range,amplitude and phase resolution.This thesis studies several new transmitter architectures to improve the dynamicrange, amplitude and phase resolution of PWM transmitters with relaxed filtering requirements.The architectures are suited for fully integrated CMOS solutions, in particular forportable applications.The first transmitter (MAF-PWMT) eliminates aliasing and image distortions whileallowing the use of SMPAs by combining RF-PWM and band-limited PWM. The transmittercan be implemented using all-digital techniques and exhibits an improved linearity and spectral performance. The approach is validated using a Class-D PA based transmitter where an improvement of 10.2 dB in the dynamic range compared to a PWM transmitter for a 1.4 MHz of LTE signal is achieved.The second transmitter (AC-PWMT) compensates for aliasing distortion by combining PWM and outphasing. It can be used with switch-mode PAs (SMPAs) or linear PAs at peak power. The proposed transmitter shows better linearity, improved spectral performanceand increased dynamic range as it does not suffer from AM-AM distortion of the PAs and aliasing distortion due to digital PWM. The idea is validated using push-pull PAs and the proposed transmitter shows an improvement of 9 dB in the dynamic rangeas compared to a PWM transmitter using digital pulse-width modulation for a 1.4 MHzLTE signal.The third transmitter (MD-PWMT) is an all-digital implementation of the second transmitter. The PWM is implemented using a Field Programmable Gate Array(FPGA) core, and outphasing is implemented as pulse-position modulation using FPGA transceivers, which drive two class-D PAs. The digital implementation offers the exibility to adapt the transmitter for multi-standard and multi-band signals. From the measurement results, an improvement of 5 dB in the dynamic range is observed as compared to an all-digital PWM transmitter for a 1.4 MHz LTE signal.The fourth transmitter (EP-PWMT) improves the phase linearity of an all-digital PWM transmitter using PWM and asymmetric outphasing. The transmitter uses PWM to encode the amplitude, and outphasing for enhanced phase control thus doubling the phase resolution. The measurement setup uses Class-D PAs to amplify a 1.4 MHz LTEup-link signal. An improvement of 2.8 dB in the adjacent channel leakage ratio is observed whereas the EVM is reduced by 3.3 % as compared to an all-digital PWM transmitter.The fifth transmitter (CRF-ML-PWMT) combines multilevel and RF-PWM, whereas the sixth transmitter (CRF-MP-PMWT) combines multiphase PWM and RF-PWM. Both transmitters have smaller chip area as compared to the conventional multiphase and multilevel PWM transmitters, as a combiner is not required. The proposed transmitters also show better dynamic range and improved amplitude resolution as compared to conventional RF-PWM transmitters.The solutions presented in this thesis aims to enhance the performance and simplify the digital implementation of PWM-based RF transmitters.
20.	Mollén, Christopher, 1987- (författare) High-End Performance with Low-End Hardware : Analysis of Massive MIMO Base Station Transceivers 2017 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Massive MIMO (multiple-input–multiple-output) is a multi-antenna technology for cellular wireless communication, where the base station uses a large number of individually controllable antennas to multiplex users spatially. This technology can provide a high spectral efficiency. One of its main challenges is the immense hardware complexity and cost of all the radio chains in the base station. To make massive MIMO commercially viable, inexpensive, low-complexity hardware with low linearity has to be used, which inherently leads to more signal distortion. This thesis investigates how the degenerated linearity of some of the main components—power amplifiers, analog-to-digital converters (ADCs) and low-noise amplifiers—affects the performance of the system, with respect to data rate, power consumption and out-of-band radiation. The main results are: Spatial processing can reduce PAR (peak-to-average ratio) of the transmit signals in the downlink to as low as 0B; this, however, does not necessarily reduce power consumption. In environments with isotropic fading, one-bit ADCs lead to a reduction in effective signal-to-interference-and-noise ratio (SINR) of 4dB in the uplink and four-bit ADCs give a performance close to that of an unquantized system. An analytical expression for the radiation pattern of the distortion from nonlinear power amplifiers is derived. It shows how the distortion is beamformed to some extent, that its gain never is greater than that of the desired signal, and that the gain of the distortion is reduced with a higher number of served users and a higher number of channel taps. Nonlinear low-noise amplifiers give rise to distortion that partly combines coherently and limits the possible SINR. It is concluded that spatial processing with a large number of antennas reduces the impact of hardware distortion in most cases. As long as proper attention is paid to the few sources of coherent distortion, the hardware complexity can be reduced in massive MIMO base stations to overcome the hardware challenge and make massive MIMO commercial reality.
21.	Ranisch, Robert, et al. (författare) Ethics of digital contact tracing apps for the Covid-19 pandemic response 2020 Rapport (övrigt vetenskapligt/konstnärligt)abstract There is a growing interest in contact tracing apps (CT apps) for pandemic man- agement. These apps raise significant moral concerns. It is therefore crucial to consider ethical requirements before and while implementing such apps. Public trust is of major importance for population uptake of contact tracing apps. Hasty, ill-prepared or badly communicated implementations of CT apps will likely under- mine public trust, and as such, risk impeding general effectiveness. In response to these demands, to meet ethical requirements and find a basis for justified trust, this background introduces an ethical framework for a responsible design and implementation of CT apps. However, even prudently chosen measures of digital contact tracing carry moral costs, which makes it necessary address different trade-offs. This background paper aims to inform developers, researchers and decision-makers be- fore and throughout the process of implementing contact tracing apps.
22.	Brunnstrom, Kjell, 1960-, et al. (författare) Statistical quality of experience analysis: on planning the sample size and statistical significance testing 2018 Ingår i: Journal of Electronic Imaging (JEI). - SPIE/IS&T : IS&T - the Society for Imaging Science and Technology. - 1017-9909 .- 1560-229X. ; 27:5, s. 053013-1-053013-11 Tidskriftsartikel (refereegranskat)abstract This paper analyzes how an experimenter can balance errors in subjective video quality tests betweenthe statistical power of finding an effect if it is there and not claiming that an effect is there if the effect is not there,i.e., balancing Type I and Type II errors. The risk of committing Type I errors increases with the number ofcomparisons that are performed in statistical tests. We will show that when controlling for this and at thesame time keeping the power of the experiment at a reasonably high level, it is unlikely that the number oftest subjects that are normally used and recommended by the International Telecommunication Union (ITU),i.e., 15 is sufficient but the number used by the Video Quality Experts Group (VQEG), i.e., 24 is more likelyto be sufficient. Examples will also be given for the influence of Type I error on the statistical significance ofcomparing objective metrics by correlation. We also present a comparison between parametric and nonparametricstatistics. The comparison targets the question whether we would reach different conclusions on the statisticaldifference between the video quality ratings of different video clips in a subjective test, based on thecomparison between the student T-test and the Mann–Whitney U-test. We found that there was hardly a differencewhen few comparisons are compensated for, i.e., then almost the same conclusions are reached. Whenthe number of comparisons is increased, then larger and larger differences between the two methods arerevealed. In these cases, the parametric T-test gives clearly more significant cases, than the nonparametrictest, which makes it more important to investigate whether the assumptions are met for performing a certaintest.
23.	Chen, Kairang, 1986- (författare) Energy-Efficient Data Converters for Low-Power Sensors 2016 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Wireless sensor networks (WSNs) are employed in many applications, such as for monitoring bio-potential signals and environmental information. These applications require high-resolution (> 12-bit) analog-to-digital converters (ADCs) at low-sampling rates (several kS/s). Such sensor nodes are usually powered by batteries or energy-harvesting sources hence low power consumption is primary for such ADCs. Normally, tens or hundreds of autonomously powered sensor nodes are utilized to capture and transmit data to the central processor. Hence it is profitable to fabricate the relevant electronics, such as the ADCs, in a low-cost standard complementary metal-oxide-semiconductor (CMOS) process. The two-stage pipelined successive approximation register (SAR) ADC has shown to be an energy-efficient architecture for high resolution. This thesis further studies and explores the design limitations of the pipelined SAR ADC for high-resolution and low-speed applications.The first work is a 15-bit, 1 kS/s two-stage pipelined SAR ADC that has been implemented in 0.35-μm CMOS process. The use of aggressive gain reduction in the residue amplifier combined with a suitable capacitive array digital-to-analog converter (DAC) topology in the second-stage simplifies the design of the operational transconductance amplifier (OTA) while eliminating excessive capacitive load and consequent power consumption. A comprehensive power consumption analysis of the entire ADC is performed to determine the number of bits in each stage of the pipeline. Choice of a segmented capacitive array DAC and attenuation capacitorbased DAC for the first and second stages respectively enable significant reduction in power consumption and area. Fabricated in a low-cost 0.35-μm CMOS process, the prototype ADC achieves a peak signal-to-noise-and-distortion ratio (SNDR) of 78.9 dB corresponding to an effective number of bits (ENOB) of 12.8-bit at a sampling frequency of 1 kS/s and provides a Schreier figure-of-merit (FoM) of 157.6 dB. Without any form of calibration, the ADC maintains an ENOB > 12.1-bit up to the Nyquist bandwidth of 500 Hz while consuming 6.7 μW. Core area of the ADC is 0.679 mm2.The second work is a 14-bit, tunable bandwidth two-stage pipelined SAR ADC which is suitable for low-power, cost-effective sensor readout circuits. To overcome the high open-loop DC gain requirement of the OTA in the gain-stage, a 3-stage capacitive charge pump (CCP) is utilized to achieve the gain-stage instead of using the switch capacitor (SC) amplifier. Unity-gain OTAs have been used as the analog buffers to prevent the charge sharing between the CCP stages. The detailed design considerations are given in this work. The prototype ADC, designed and fabricated in a low-cost 0.35-μm CMOS process, achieves a peak SNDR of 75.6 dB at a sampling rate of 20 kS/s and 76.1 dB at 200 kS/s while consuming 7.68 μW and 96 μW, respectively. The corresponding Schreier FoM are 166.7 dB and 166.3 dB. Since the bandwidth of CCP is tunable, the ADC maintains a SNDR > 75 dB upto 260 kHz. The core area occupied by the ADC is 0.589 mm2.As the low-power sensors might be active only for very short time triggered by an external pulse to acquire the data, the third work is a 14-bit asynchronous two-stage pipelined SAR ADC which has been designed and simulated in 0.18-μm CMOS process. A self-synchronous loop based on an edge detector is utilized to generate an internal clock with variable phase. A tunable delay element enables to allocate the available time for the switch capacitor DACs and the gain-stage. Three separate asynchronous clock generators are implemented to create the control signals for two sub-ADCs and the gain-stage between. Aiming to reduce the power consumption of the gain-stage, simple source followers as the analog buffers are implemented in the 3-stage CCP gain-stage. Post-layout simulation results show that the ADC achieves a SNDR of 83.5 dB while consuming 2.39 μW with a sampling rate of 10 kS/s. The corresponding Schreier FoM is 176.7 dB.
24.	del Aguila Pla, Pol, 1990-, et al. (författare) Clock synchronization over networks - Identifiability of the sawtooth model Annan publikation (övrigt vetenskapligt/konstnärligt)abstract In this paper, we analyze the two-node joint clocksynchronization and ranging problem. We focus on the case of nodes that employ time-to-digital converters to determine the range between them precisely. This specific design leads to a sawtooth model for the captured signal, which has not been studied in detail before from an estimation theory standpoint. In the study of this model, we recover the basic conclusion of a well-known article by Freris, Graham, and Kumar in clock synchronization. Additionally, we discover a surprising identifiability result on the sawtooth signal model: noise improves the theoretical condition of the estimation of the phase and offset parameters. To complete our study, we provide performance references for joint clock synchronization and ranging. In particular, we present the Cramér-Rao lower bounds that correspond to a linearization of our model, as well as a simulation study on the practical performance of basic estimation strategies under realistic parameters. With these performance references, we enable further research in estimation strategies using the sawtooth model and pave the path towards industrial use.
25.	Gustavsson, Ulf, 1975 (författare) From Noise-Shaped Coding to Energy Efficiency - One bit at the time 2011 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Three parameters that drive the research and development of future RF transmitter technologies for high speed wireless communication today are energy efficiency, flexibility and reduction of the physical footprint. This thesis treats the use of single-bit quantization in conjunction with a method called Noise-Shaped Coding (NSC), as an enabler for these parameters, foremost in terms of energy efficiency.The first part of the thesis provides a short introduction to the common Radio Frequency Power Amplifier (RFPA) power efficiency enhancement techniques. The pulsed RF transmitter is introduced in which the RFPA is used as a switch, modulated by a single-bit quantized signal which allows it to operate solely at its two most efficient states.The second part of the thesis provides an introduction to the concept of NSC and the underlying idea of how high signal quality can be achieved with one bit quantization of the signal amplitude. A particular method of implementing NSC, namely the ΣΔ-modulator, is introduced and some common methods for design and analysis are discussed. An optimization-based approach to ΣΔ-modulator design is proposed and benchmarked against conventional methods in terms of its ability to shape the power spectral density of the quantization noise according to a given reconstruction filter response, minimizing the reconstructed error metric.The third and final part of the thesis focuses specifically on the application of ΣΔ-modulation in a pulsed RF transmitter context. The concepts of band-pass and baseband ΣΔ-modulation are introduced. A few important challenges related to the use of ΣΔ-modulation in a pulsed RF-transmitter context are identified. A ΣΔ-modulator topology which handles a complex input signal is investigated in great detail and advantages compared to conventional methods for using ΣΔ-modulation are unveiled by means of theoretical analysis and simulations. A method for suppressing the quantization noise within a frequency band surrounding the modulated RF carrier, enabling the use of more wideband reconstruction filter and moderate pulse-rates, is also presented. A detailed theoretical analysis reveals how optimized Noise-Shaped Coding, as provided by the optimization method introduced in the second part, can be deployed in order to improve the system performance. Finally, the method is validated by experimental measurements on two different high efficiency RFPAs at 1 and 3.5 GHz respectively, showing promising results.
26.	Jonsson, Fredrik, et al. (författare) A Voltage Controlled Oscillator with Automatic Amplitude Control in SiGe Technology 2001 Ingår i: 19th Norchip. ; , s. 28-33, s. 28-33 Konferensbidrag (refereegranskat)
27.	Mao, Yadong, et al. (författare) Decentralized Training of 3D Lane Detection with Automatic Labeling Using HD Maps 2023 Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. ; 2023-June Konferensbidrag (refereegranskat)abstract To have competent 3D lane detection for real-world driving, a massive amount of data from all over the world is needed, but data collection and manual annotation are costly and time-consuming. The diversity of data collected by developmental cars might still be limited compared to the data collected by a large fleet of customer cars. Federated learning enables training models on edge without transferring data out of devices. However, training supervised learning tasks at the edge is directly tied to having access to high-quality labels, which is limited at the edge. In this paper, we propose a fully automatic method to generate 3D lane labels at the edge using a pre-recorded HD map to enable the federated training of the 3D lane detection model. As a reference, a semi-automatic method is applied for creating a 3D-lane dataset used as ground truth. Our experimental results show that the model can achieve comparable performance when training on the same dataset in both a centralized and a decentralized manner. And the models trained on semi-automatic labeled datasets slightly outperform those trained on fully-automatically labeled datasets. This study shows that a well-performing 3D lane detection model can be trained in a supervised and fully decentralized manner, and most importantly, data privacy at the edge is guaranteed.
28.	Panigrahi, Smruti Ranjan, 1983-, et al. (författare) A Study of Delay and Doppler Spreads at 24 GHz ISM band 2020 Ingår i: 2020 16th International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781728197227 ; , s. 1-6 Konferensbidrag (refereegranskat)abstract This article investigates the wide-band channel characteristics at 24 GHz ISM band in a mobile radio environment. The mobility in the test environment is achieved by attaching the transmit antenna to a KUKA robot's arm. The radio measurements were carried out inside the robotics lab at the University of Gävle, Sweden. The radio channel measurements were carried out at various situations, e.g., line of sight (LOS), non-line of sight (NLOS), regular lab environment, reflective environment, and different velocities of the robot's arm. The influence of these situations on the power delay profile, Doppler spectral density, root mean square (RMS) delay spread, RMS Doppler spread, coherence bandwidth and coherence time, has been studied.
29.	Seyedhosseinzadeh, Neda, et al. (författare) A 100–140 GHz SiGe-BiCMOS sub-harmonic down-converter mixer 2017 Ingår i: 2017 12th European Microwave Integrated Circuits Conference (EuMIC). - 9782874870484 ; 2017-January Konferensbidrag (refereegranskat)abstract This paper demonstrates a wideband, subharmonic down converting mixer using a commercial 130-nm SiGe-BiCMOS technology. The mixer adopts a frequency doubling LO-stage, a differential switched-transconductance RF-stage, on-chip LO and RF baluns, and two emitter-follower buffer-stages. The measured results exhibit a maximum conversion gain up to 2.6 dB over the frequency range of 100 to 140 GHz with a LO power of 5 dBm. The mixer achieves an input referred 1-dB compression point of −7.2 dBm, with a DC power of 46.3 mW, including 26.7 mW for buffer-stages. It demonstrates also up to 12 GHz 3-dB IF bandwidth, which to the authors' best knowledge, is the highest obtained among active sub-harmonic mixers operating above 100 GHz. The chip occupies 0.4 mm2, including pads.
30.	Åkerberg, Johan, et al. (författare) Design challenges and objectives in industrial wireless sensor networks 2017 Ingår i: Industrial Wireless Sensor Networks: Applications, Protocols, and Standards. - Boca Raton : CRC Press. - 9781466500525 - 9781466500518 ; , s. 79-100 Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract In recent years the advances in wireless sensor networks have grown exponentially and WSNs have been deployed in diverse application areas such as agriculture, disaster management, intelligent transport systems, and industrial automation. In industrial automation, wireless sensor networks have so far mostly been considered within building automation, factory automation, and process automation in order to save cost in cable reduction and maintenance but also improved flexibility [14]. Recently, wireless sensor networks for smart grid applications have been discussed. Several market forecasts have recently predicted exponential growths in the sensor market over the next few years, resulting in a multi-billion dollar market in the near future. For instance, ABI research [18] predicts that in 2015 around 645 million IEEE 802.15.4 chipsets will be shipped and that the worldwide market for automation systems in process industries will grow to roughly $150 billion.
31.	Liu, Yang, et al. (författare) A Study Towards Enhanced Reliability Performance of Remote Control and Monitoring Application Over Commercial Wireless Communication Networks 2006 Ingår i: 2006 International Conference on Wireless Communications, Networking and Mobile Computing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1424405173 - 1424405173 ; , s. 1-4 Konferensbidrag (refereegranskat)abstract Remote control and monitoring systems provide many useful operating advantages in industrial automation and demand highly reliable and secure communication means. Their widespread use is, however, limited because of the high cost of current communications in use making them economically infeasible. Hence, there is a need to develop new low cost communication and control concepts by making such solutions economically feasible. In this paper, we present a scheme for implementing reliable wireless communication links for application of remote control and monitoring system based on current available commercial wireless communication networks, e.g. GPRS/EDGE/UMTS. The reliability enhancement over wireless networks has been proposed and its performance has been studied. This paper examines the proposed solution by means of both analytical and numerical evaluation, and has shown that the demanded reliability performance can be met by using only commercial wireless communication networks.
32.	Homem, Irvin, 1985- (författare) Advancing Automation in Digital Forensic Investigations 2018 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Digital Forensics is used to aid traditional preventive security mechanisms when they fail to curtail sophisticated and stealthy cybercrime events. The Digital Forensic Investigation process is largely manual in nature, or at best quasi-automated, requiring a highly skilled labour force and involving a sizeable time investment. Industry standard tools are evidence-centric, automate only a few precursory tasks (E.g. Parsing and Indexing) and have limited capabilities of integration from multiple evidence sources. Furthermore, these tools are always human-driven.These challenges are exacerbated in the increasingly computerized and highly networked environment of today. Volumes of digital evidence to be collected and analyzed have increased, and so has the diversity of digital evidence sources involved in a typical case. This further handicaps digital forensics practitioners, labs and law enforcement agencies, causing delays in investigations and legal systems due to backlogs of cases. Improved efficiency of the digital investigation process is needed, in terms of increasing the speed and reducing the human effort expended. This study aims at achieving this time and effort reduction, by advancing automation within the digital forensic investigation process.Using a Design Science research approach, artifacts are designed and developed to address these practical problems. Summarily, the requirements, and architecture of a system for automating digital investigations in highly networked environments are designed. The architecture initially focuses on automation of the identification and acquisition of digital evidence, while later versions focus on full automation and self-organization of devices for all phases of the digital investigation process. Part of the remote evidence acquisition capability of this system architecture is implemented as a proof of concept. The speed and reliability of capturing digital evidence from remote mobile devices over a client-server paradigm is evaluated. A method for the uniform representation and integration of multiple diverse evidence sources for enabling automated correlation, simple reasoning and querying is developed and tested. This method is aimed at automating the analysis phase of digital investigations. Machine Learning (ML)-based triage methods are developed and tested to evaluate the feasibility and performance of using such techniques to automate the identification of priority digital evidence fragments. Models from these ML methods are evaluated in identifying network protocols within DNS tunneled network traffic. A large dataset is also created for future research in ML-based triage for identifying suspicious processes for memory forensics.From an ex ante evaluation, the designed system architecture enables individual devices to participate in the entire digital investigation process, contributing their processing power towards alleviating the burden on the human analyst. Experiments show that remote evidence acquisition of mobile devices over networks is feasible, however a single-TCP-connection paradigm scales poorly. A proof of concept experiment demonstrates the viability of the automated integration, correlation and reasoning over multiple diverse evidence sources using semantic web technologies. Experimentation also shows that ML-based triage methods can enable prioritization of certain digital evidence sources, for acquisition or analysis, with up to 95% accuracy.The artifacts developed in this study provide concrete ways to enhance automation in the digital forensic investigation process to increase the investigation speed and reduce the amount of costly human intervention needed.
33.	Selén, Yngve, et al. (författare) RAKE Receiver for Channels with a Sparse Impulse Response 2007 Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276 .- 1558-2248. ; 6:9, s. 3175-3180 Tidskriftsartikel (refereegranskat)abstract We derive the optimal receiver for RAKE diversity combining on channels with a sparse impulse response. The receiver is based on the Bayesian philosophy and thus it requires the knowledge of certain a priori parameters. However, we also derive an empirical Bayesian version of our receiver, which does not require any a priori knowledge, nor the choice of any user parameters. We show that both versions of our detector can outperform a classical training-based maximum-ratio-combining detector.
34.	Ahsin, Tafzeel Ur Rehman, et al. (författare) Constellation Selection in Network Coded Distributive Antenna System 2009 Ingår i: GLOBECOM 2009 - 2009 IEEE Global Telecommunications Conference. - : IEEE. - 9781424441471 ; , s. 342-346 Konferensbidrag (refereegranskat)abstract Relays can improve wireless links by providing an extra path to the direct path which together form a virtual multiple antenna system. Network Coded-Distributive Antenna System (NC-DAS) and Plain-Distributive Antenna System (P-DAS) are examples of realizations of such scenario. Although the asymptotic diversity gain for both the schemes is comparable, the network coded scheme can further take advantage of the redundancy and the extra dimension provided by the relay link. This extra signal dimension can be very useful when multilevel modulation is employed as it gives the possibility for a better spread of the modulation signal points within the augmented signal space. This article presents a simple and effective Constellation Selection (CS) scheme for all the three links within the NC-DAS system. This selection procedure improves the bit error probability in both AWGN and Rayleigh fading channels. Two different detections schemes are considered in the paper. Joint detection where the both users are decoded simultaneously and detection with successive cancelation where the strongest user is detected first followed by cancelation and maximum ratio combining. Analytical expressions for the error probability supported by simulation results are presented. The obtained results show that constellation selection provides good performance gain as compared to the case of same constellation.
35.	Bao, Husileng, 1991, et al. (författare) Wideband mm-wave Spectrum-Efficient Transmitter Using Low-Pass Sigma–Delta-Over-Fiber Architecture 2023 Ingår i: IEEE Microwave and Wireless Technology Letters. - 2771-9588 .- 2771-957X. ; 33:10, s. 1505-1508 Tidskriftsartikel (refereegranskat)abstract The millimeter-wave band offers large bandwidth and promises high data rates for wireless communication systems. This work proposes a millimeter-wave radio-over-fiber architecture suitable for wideband mm-wave communication, using a lowpass sigma-delta modulation approach. The central unit generates baseband sigma-delta bitstreams, in-phase/quadrature (I/Q) components, which are transported to a remote radio head (RRH) using a standard QSFP28 optical interconnect link connection. In the RRH, the baseband I/Q signals are upconverted to the millimeter-wave band, amplified, and transmitted through an antenna. The performance of the resulting sigma-delta-over-fiber transmitter architecture is experimentally verified at 28 GHz, demonstrating a state-of-the-art symbol rate up to 1.5 Gsym/s. Furthermore, in over-the-air measurements, the architecture is shown to support 1 Gsym/s with 5.9% error vector magnitude for 64/256/1024 quadrature amplitude modulation cases over a 5 m wireless distance. The results demonstrate the feasibility of the proposed architecture for the realization of wideband millimeterwave distributed antenna systems.
36.	Bencheikh Lehocine, Chouaib, 1993, et al. (författare) Robust Analog Beamforming for Periodic Broadcast V2V Communication 2022 Ingår i: IEEE Transactions on Intelligent Transportation Systems. - 1524-9050 .- 1558-0016. ; 23:10, s. 18404-18422 Tidskriftsartikel (refereegranskat)abstract We generalize an existing low-cost analog signal processing concept that takes advantage of the periodicity of vehicle-to-vehicle broadcast service to the transmitter side. In particular, we propose to process multiple antennas using either an analog beamforming network (ABN) of phase shifters, or an antenna switching network (ASN) that periodically alternates between the available antennas, to transmit periodic messages to receivers that have an analog combining network (ACN) of phase shifters, which has been proposed in earlier work. To guarantee robustness, we aim to minimize the burst error probability for the worst receiving vehicular user, in a scenario of bad propagation condition that is modeled by a single dominant path between the communicating vehicles. In absence of any form of channel knowledge, we analytically derive the optimal parameters of both ABN and ASN. The ABN beamforming vector is found to be optimal for all users and not only for the worst receiving user. Further, we demonstrate that Alamouti scheme for the special case of two transmit antennas yields similar performance to ABN and ASN. At last, we show that the derived parameters of the two proposed transmission strategies are also optimal when hybrid ACN-maximal ratio combining is used at the receiver.
37.	Bencivenni, Carlo, 1986 (författare) Aperiodic Array Synthesis for Telecommunications 2017 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Arrays of antennas offer important advantages over single-element antennas and are thus a key part of most advanced communication systems. The majority of current arrays are based on a classical regular layout, which offer simple design criteria despite some limitations. Aperiodic arrays can reduce the number of elements and improve the performance, however their design is far more challenging. This thesis focuses on the synthesis of aperiodic arrays, advancing the state-of-the-art of phased arrays and pioneering the application to Multiple-Input Multiple-Output (MIMO) systems.In satellite communications (SATCOM), aperiodic sparse arrays have the potential for drastically reducing the costs of massive antennas. Most available synthesis methods are however either intractable, suboptimal or limited for such demanding scenarios. We propose a deterministic and efficient approach based on Compressive Sensing, capable of accounting for electromagnetic phenomena and complex specifications. Some of the key contributions include the extension to the design of multi-beam, modular, multi-element, reconfigurable and isophoric architectures.The same approach is successfully applied to the design of compact arrays for Point-to-Point (PtP) backhauling. The aperiodicity is used here instead to reduce the side lobes and meet the target radiation envelope with high aperture efficiency. A dense, column arranged, slotted waveguide isophoric array has been successfully designed, manufactured and measured.Line-of-Sight (LoS) MIMO can multiply the data rates of classical Single-Input Single-Output (SISO) backhauling systems, however it suffers from limited installation flexibility. We demonstrate how aperiodic arrays and their switched extensions can instead overcome this shortcoming. Since a small number of antennas are typically used, an exhaustive search is adopted for the synthesis.Massive Multi-User (MU) MIMO is envisioned as a key technology for future 5G systems. Despite the prevailing understanding, we show how the MIMO performance is affected by the array layout. To exploit this, we propose a new hybrid statistical-density tapered synthesis approach. Results show a significant improvement in minimum power budget, capacity and amplifier efficiency, especially for massive and/or crowded systems
38.	Chani Cahuana, Jessica, 1988, et al. (författare) Digital Predistortion Parameter Identification for RF Power Amplifiers Using Real-Valued Output Data 2017 Ingår i: IEEE Transactions on Circuits and Systems II: Express Briefs. - 1549-7747 .- 1558-3791. ; 64:10, s. 1227-1231 Tidskriftsartikel (refereegranskat)abstract This brief presents a novel digital predistortion (DPD) parameter identification technique that requires only the acquisition of either the in-phase (I) or the quadrature (Q) component of the power amplifier (PA) output signal. To this end, an approach that allows us to estimate the parameters of a model using only one of the IQ components of the model output is presented. Based on experimental results, it is shown that the proposed real-valued measurements based technique can offer similar linearization capabilities as its complex-valued counterparts. The experimental results also indicate that the proposed technique can be used in combination with other techniques that focus on reducing the speed of analog-to-digital converters (ADCs)
39.	Chen, Jingjing, 1982, et al. (författare) 10 Gbps 16QAM transmission over a 70/80 GHz (E-band) radio test-bed 2012 Ingår i: European Microwave Week 2012: "Space for Microwaves", EuMW 2012, Conference Proceedings - 7th European Microwave Integrated Circuits Conference, EuMIC 2012. - : IEEE. - 9782874870286 - 9781467323024 - 9782874870262 ; , s. 556-559 Konferensbidrag (refereegranskat)abstract A millimeter-wave radio test-bed is implemented which demonstrates 16QAM transmission over 70/80 GHz band for data rate up to 10 Gbps. Performance of the 16QAM transmitter and receiver is evaluated in a loop-back lab set-up. With the proposed 10 Gbps on single carrier system architecture, it is possible to achieve 40 Gbps over a 5 GHz bandwidth when combined with polarization and spatial multiplexing.
40.	Farhadi, Hamed, 1983 (författare) On the throughput of wireless interference networks with limited feedback 2011 Ingår i: IEEE International Symposium on Information Theory Proceedings (ISIT'11). - 2157-8095. - 9781457705960 ; , s. 762 - 766 Konferensbidrag (refereegranskat)abstract Considering a single-antenna M-user interference channel with symmetrically distributed channel gains, when the channel state information (CSI) is globally available, applying the ergodic interference alignment scheme, each transmitter-receiver pair achieves a rate proportional to ½ of a single user's interference-free achievable rate. This is substantially higher than the achievable rate of the conventional orthogonal transmission schemes such as TDMA. Since the rigid requirement on the CSI may be difficult to realize in practice, in this paper we investigate the performance of applying the ergodic interference alignment scheme when the estimation of each channel gain is made globally known through exploiting only a limited feedback signal from the associated receiver of that channel. Under a block fading environment, we provide a lower bound on the achievable average throughput of the network. Our results imply that the better performance of interference alignment over TDMA may still exist even without the assumption of perfect CSI. Also, the trade off between allocating feedback rate of each receiver to the desired channel or the interference channels at deferent SNR region investigated.
41.	Ghahfarokhi, Sohil Shahabi, et al. (författare) Impact of Moisture Content on RFID Antenna Performance for Wood-Log Monitoring 2011 Ingår i: RFMTC11. - Gävle, Sweden. Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract In recent years, the use of RFID technology has gained popularity in the timber industry for wood-log monitoring. Harvested wood-logs are stored for different time periods before being processed. As a result, the moisture content in the stored wood-logs varies compared to the freshly-cut wood and it must also be noted that the moisture content of freshly cut wood differs from one log to another. Apart from storage time period of wood-logs, the environmental factors such as temperature, rain, snow and sun also contributes to the variation in the moisture content of the wood-logs. This variation of the moisture content changes the dielectric constant of the wood and hence, influences the characteristics of the RFID antenna. In this paper the impact of variations in moisture content in wood and its effect on the performance of the RFID antenna are studied.
42.	Jia, Kelin, 1981- (författare) Electromagnetic noise generated in the electrified railway propulsion system 2011 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract The electromagnetic compatibility (EMC) problem in the railway propulsion system is a significant safety issue of high concern. The problems can be caused by any part of the propulsion system as well as any combination of the sub systems. Simulation is a fast economical way to understand the system and to predict the EMC performance. In this thesis, the propulsion system is studied partly from the rectifier to the motor. To simulate the rectifier, a two level pulse width modulation (PWM) controlled rectifier is built in Simulink. Time domain line current as well as frequency domain spectra is studied. The spectrum changing according to time variation is obtained. In order to study the high derivative of switching pulse in the insulated gate bipolar transistor (IGBT), a simple circuit is proposed to investigate it. The high frequency noise spectrum is given and the variation of the spectrum due to the reverse recovery time of the ant-parallel diode is also demonstrated. Transmission line theory is used to model the cable used to connect the inverter and motor. The method to extract the characteristic capacitance and inductance matrices of the cable system is presented. Decoupling these characteristic matrices is required for modeling the multiconductor transmission line (MTL) in PSpice. A simple way to decouple them is thus proposed here. Through the simulation studies, we analyze the oscillation and overvoltage in the cable. A fourth cable with optimized layout is also illustrated here to reduce the oscillation on the line. Furthermore, the relationship between the length of line and the noise frequency is studied. Shielding is another way to reduce the electromagnetic (EM) coupling of power lines. The method to model shielded cables in PSpice is given in this thesis. Based on the model we have investigated the shielding effect and analyzed the impact of different grounding conditions on the shielding performance.
43.	Jia, Kelin, 1981-, et al. (författare) EMC assessment of the railway traction system by using PSpice 2010 Ingår i: 2010 Asia-Pacific Symposium on Electromagnetic Compatibility, APEMC 2010. - 9781424456215 ; , s. 598-601 Konferensbidrag (refereegranskat)abstract This paper describes how to analyze the EMC performance of the railway traction system by using PSpice. This analysis method is based on the accurate modelling of the IGBT and power diodes. The paper gives the analysis method as well as the modelling details of these power devices. An efficient way to predict the worst EMC performance is proposed, especially for high frequency EM noise. We have also studied the impact of the reverse-recovery time of a free wheeling diode on high frequency EM noise generation.
44.	Jia, Kelin, 1981-, et al. (författare) Modeling the traction system in PSpice for electromagnetic noise analysis 2011 Konferensbidrag (övrigt vetenskapligt/konstnärligt)
45.	Jia, Kelin, 1981-, et al. (författare) Optimal cable assembly for reducing conducted electromagnetic interference in the traction system 2012 Ingår i: IET Electrical Systems in Transportation. - : Institution of Engineering and Technology (IET). - 2042-9738. ; 2:1, s. 29-37 Tidskriftsartikel (refereegranskat)abstract The present work deals with a method of modelling a traction system in PSpice with the consideration for optimal cable arrangements for reducing conducted electromagnetic interference. Multiconductor transmission line (MTL) theory is adopted to model the cable which connects the pulse-width modulation (PWM) source inverter and the motor. A simple decoupling transformation method is proposed and used to transform the MTL into several single transmission line, which can be easily modelled in PSpice. The PWM controlled voltage source and induction motor are also included in this model. Thus, the full model for a traction system is realised in PSpice. From system simulation, the voltage oscillation in the cable is observed and the conducted electromagnetic noise in the system is studied. The relationship between the frequency of the noise and the length of feeding cables are also demonstrated in this work. In order to mitigate the high-frequency noise, a cable system with a fourth parallel earth conductor is proposed and the noise level is indeed reduced by this technique. This modelling procedure for traction system can be used for any specific application like the electrified railway traction system.
46.	Jia, Kelin, 1981-, et al. (författare) PSpice Modeling of Electrified Railway Propulsion Drive Rectifiers for Harmonic Analysis 2009 Ingår i: ITST. - New York : IEEE. ; , s. 113-116 Konferensbidrag (refereegranskat)abstract A method to construct the electrified railway propulsion drive rectifier in PSpice for EMC assessment is developed. The working mechanisms of a three level NPC PWM rectifier and its logical signal generator are elaborated. Besides that, the convergence problem of PSpice is explained and the proper parametric settings for simulation in this paper are given. At last, the noise spectra for two different loads are compared and the causes for this difference are discussed as well.
47.	Kang, Jeongwan, et al. (författare) Optimized Switching Between Sensing and Communication for mmWave MU-MISO Systems 2022 Ingår i: 2022 Ieee International Conference On Communications Workshops (Icc Workshops). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 498-503 Konferensbidrag (refereegranskat)abstract In this paper, we propose a scheme optimizing the per-user channel sensing duration in millimeter-wave (mmWave) multi-user multiple-input single-output (MU-MISO) systems. For each user, the BS predicts the effective rate to be achieved after pilot transmission. Then, the channel sensing duration of each user is optimized by ending the pilot transmission when the predicted rate is lower than the current rate. The robust regularized zero-forcing (RRZF) precoder and equal power allocation (EPA) are adopted to transmit sensing pilots and data. Numerical results show that the more severe the interference among users, the longer channel sensing duration is required. Moreover, the proposed scheme results in a higher sum rate compared to benchmark schemes.
48.	Katsikas, Georgios P., 1987- (författare) NFV Service Chains at the Speed of the Underlying Commodity Hardware 2018 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Link speeds in networks will in the near-future reach and exceed 100 Gbps. While available specialized hardware can accommodate these speeds, modern networks have adopted a new networking paradigm, also known as Network Functions Virtualization (NFV), that replaces expensive specialized hardware with open-source software running on commodity hardware. However, achieving high performance using commodity hardware is a hard problem mainly because of the processor-memory gap. This gap suggests that only the fastest memories of today’s commodity servers can achieve the desirable access latencies for high speed networks. Existing NFV systems realize chained network functions (also known as service chains) mostly using slower memories; this implies a need for multiple additional CPU cores or even multiple servers to achieve high speed packet processing. In contrast, this thesis combines four contributions to realize NFV service chains with dramatically higher performance and better efficiency than the state of the art.The first contribution is a framework that profiles NFV service chains to uncover reasons for performance degradation, while the second contribution leverages the profiler’s data to accelerate these service chains by combining multiplexing of system calls with scheduling strategies. The third contribution synthesizes input/output and processing service chain operations to increase the spatial locality of network traffic with respect to a system’s caches. The fourth contribution combines the profiler’s insights from the first contribution and the synthesis approach of the third contribution to realize NFV service chains at the speed of the underlying commodity hardware. To do so, stateless traffic classification operations are offloaded into available hardware (i.e., programmable switches and/or network cards) and a tag is associated with each traffic class. At the server side, input traffic classes are classified by the hardware based upon the values of these tags, which indicate the CPU core that should undertake their stateful processing, while ensuring zero inter-core communication.With commodity hardware, this thesis realizes Internet Service Provider-level service chains and deep packet inspection at a line-rate 40 Gbps and stateful service chains at the speed of a 100 GbE network card on a 16 core single server. This results in up to (i) 4.7x lower latency, (ii) 8.5x higher throughput, and (iii) 6.5x better efficiency than the state of the art. The techniques described in this thesis are crucial for realizing future high speed NFV deployments.
49.	Kylin, Carl, 1996 (författare) Over the air calibration of transmitter distortion for active antenna arrays 2024 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract Radar systems for air surveillance have long utilised large antenna arrays to generate high enough gain for a narrow enough transmitted beam. In most modern systems this is accomplished through the use of large active electronically steered antenna arrays. Calibrating a large active antenna array is a challenging endeavour. Distorting effects stemming from the amplifying circuitry can have a non-negligible effect on the transmitted signal, and the effects can vary across the array. In modern and future transmitter arrays, individually controlled antenna elements will be a feature. With such systems, distortion that varies over an array can be combatted. One challenge is how to collect data about what signal is being transmitted and in what way the actual signal differs from the desired transmitted signal. The work presented in this thesis studies aspects of characterising a model describing the distortion generated in an active antenna array using an over the air channel. Specifically, the first included article presents a method where signals collected using an over the air channel generated by targets of opportunity are used to estimate the parameters of a non-linearly parametrised model for a radar transmitter. In this article, the radar is assumed to transmit different signals on each antenna element. The second included article studies conditions for identifiability for the setup in the first article as well as for other similar setups. These works constitute the second part of this thesis. To put this work into context, the first part of this thesis presents an overview of the problems caused by distortion in a radar system. This is investigated under different modelling assumptions and for radars operating in a number of different modes.
50.	Liu, Edward, et al. (författare) A 25-40 GHz Three-Way Power Amplifier with No Load Modulation Achieving Broadband Deep Power Back-Off Efficiency Enhancement 2024 Ingår i: Digest of Papers - IEEE Radio Frequency Integrated Circuits Symposium. - 1529-2517. - 9798350359473 ; , s. 127-130 Konferensbidrag (refereegranskat)abstract This paper presents a millimeter-wave (mm-Wave) power amplifier (PA) topology that avoids the trade-off between bandwidth and load modulation. The proposed topology uses three PA paths and can achieve efficiency enhancement at power back-off without load modulation. With a 100 MHz 5G NR FR2 1-CC 64-QAM signal, this PA achieves average power and PAE of 6.45 - 12.61 dBm and 5.9 - 16.4% from 25 - 40 GHz, respectively. With a 200 MHz signal, average power and PAE are 5.58 - 11.1 dBm and 4.8 - 13.3%, respectively.

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