20 research outputs found
Low-Complexity Channel Estimation in OFDM MU-MIMO Next Generation Cellular Networks
No full textWe consider downlink communications between a Base Station (BS) and various mobile stations, equipped with multiple antennas, based on Orthogonal Frequency Division Multiplexing (OFDM). Transmission is compliant with the Long Term Evolution (LTE) standard operating in Frequency Division Duplex (FDD) mode. Since ideal feedback of channel state information to the BS may be cumbersome, we consider two suboptimal channel estimation algorithms, denoted as Resource Block (RB) and Resource Block Group (RBG). Both approaches approximate the channel as constant over multiples of the fundamental LTE block, known as Physical Resource Block (PRB). Our results show that RB and RBG incur a limited performance loss, yet guaranteeing significant saving in the amount of feedback information
An Experimental Performance Assessment of Temporal Convolutional Networks for Microphone Virtualization in a Car Cabin
No full text: In this paper, the experimental results on microphone virtualization in realistic automotive scenarios are presented. A Temporal Convolutional Network (TCN) was designed in order to estimate the acoustic signal at the driver's ear positions based on the knowledge of monitoring microphone signals at different positions-a technique known as virtual microphone. An experimental setup was implemented on a popular B-segment car to acquire the acoustic field within the cabin while running on smooth asphalt at variable speeds. In order to test the potentiality of the TCN, microphone signals were recorded in two different scenarios, either with or without the front passenger. Our experimental results show that, when training is performed in both scenarios, the adopted TCN is able to robustly adapt to different conditions and guarantee a good average performance. Furthermore, an investigation on the parameters of the Neural Network (NN) that guarantee the sufficient accuracy of the estimation of the virtual microphone signals while maintaining a low computational complexity is presented
Performance Analysis of Feedback MIMO ANC in Experimental Automotive Environment
No full textIn this paper, a performance analysis of FeedBack (FB) Active Noise Cancellation (ANC) systems for automotive applications is presented. Since the performance of FB ANC systems is strongly impaired by the delay induced by the physical distance between microphones and loudspeakers, an experimental setup representative of a car seat headrest has been developed. In this setup, the loudspeaker-microphone distance is on the order of few centimeters. An experimentally acquired band-limited noise source is obtained from an idling car. Noise reduction is performed by using a Filtered-x Least Mean Square (FxLMS) algorithm. Two 2×2 Multiple Input - Multiple Output (MIMO) schemes are considered—standard one and Filtered-Error (FE) based. Our experimental results show that the proposed MIMO systems enable improved performance and are able to control the perceived noise at two listening positions in a realistic automotive application
ANC: A Low-Cost Implementation Perspective
No full textIn the present work, we describe a low-cost implementation of an
Active Noise Cancellation (ANC) system. The most interesting feature of our implementation is the use of general-purpose hardware, without the need of expensive and hard-to-program Digital Signal Processing (DSP) devices. In particular, the reference signals, collected with accelerometers properly placed on noise-generating parts and the error feedback signals are collected by means of an USB interface. All signal processing, aimed at primary path estimation and anti-noise audio
signal generation, is performed using Simulink running on a
commercial mini PC. The Exponential Sine Sweep (ESS) method is
adopted for the measurement of the secondary path from the
cancellation loudspeakers to the error microphones. An adaptive
Filtered-X Least Mean Square (LMS) algorithm determines the anti-noise audio signal to be emitted. The system has been
tested on a commercial agricultural tractor cabin mounted over
electromagnetic shakers to emulate realistic operating conditions. Two error microphones are attached to the headrest, close to the driver’s ears. The resulting ANC system relies on the use of very small buffers (for audio/accelerometric data), with a latency comparable to that of more complex and expensive specific DSP systems used in this kind of applications. In terms of acoustic performance, a significant reduction of annoying peaks in the 200-500 Hz range and a broadband noise reduction at lower frequencies are observed, thus improving the overall sound quality experience. In conclusion, the implementation of an effective ANC system, employing common audio devices and a
relatively simple Simulink program, was obtained. This paves the way to straightforward experimentation (in Matlab/Simulink) of new ANC processing algorithms, allowing direct testing of simulation-based solutions, without the need of porting them to a proprietary DSP-based platform
Experimental Results on Observation Filter Estimation for Microphone Virtualization
No full textActive Noise Control (ANC) systems exploit the superposition principle to generate a quiet acoustic zone around a confined area affected by a disturbance signal detected by a monitoring microphone. In automotive applications, the problem of noise within the car cabin has become a hot research topic. Nowadays, most of the commercial solutions generate a silence zone around the position of the monitoring microphone only. Especially for the automotive environment, to weaken disturbance signal at a different position with respect to the monitoring microphone is fundamental. The estimation of the acoustic channel between the monitoring microphone and the physical region in which the noise cancellation is targeted, referred to as observation filter, is necessary. This approach is usually known as microphone virtualization, or Virtual Microphone Technique (VMT) since the audio signal detected by the virtual microphone (e.g., targeting driver’s ears) has to be retrieved starting from the monitoring ones. In this paper, a performance comparison between adaptive and fixed approaches to the estimation of the observation filter is presented. The disturbance signals are acquired in an experimental measurement campaign on a realistic car interior. Eight microphones are employed to acquire four different driving scenarios at various pace of the car. Experimental results show that, due the insufficient spectral coherence between the monitoring and virtual microphones, system performance is physically limited. A specific road and car pace scenario typically exhibits significant robustness to road mismatch. In the low frequency regime, both estimation approaches perform well. However, the fixed one guarantees improved broadband performance
Active Control of the Acoustic Field in a Vehicle Cabin
No full textIn this thesis, a thorough investigation on acoustic noise control systems for realistic automotive scenarios is presented. The thesis is organized in two parts dealing with the main topics treated: Active Noise Control (ANC) systems and Virtual Microphone Technique (VMT), respectively.
The technology of ANC allows to increase the driver's/passenger's comfort and safety exploiting the principle of mitigating the disturbing acoustic noise by the superposition of a secondary sound wave of equal amplitude but opposite phase. Performance analyses of both FeedForwrd (FF) and FeedBack (FB) ANC systems, in experimental scenarios, are presented. Since, environmental vibration noises within a car cabin are time-varying, most of the ANC solutions are adaptive. However, in this work, an effective fixed FB ANC system is proposed. Various ANC schemes are considered and compared with each other. In order to find the best possible ANC configuration which optimizes the performance in terms of disturbing noise attenuation, a thorough research of \gls{KPI}, system parameters and experimental setups design, is carried out.
In the second part of this thesis, VMT, based on the estimation of specific acoustic channels, is investigated with the aim of generating a quiet acoustic zone around a confined area, e.g., the driver's ears. Performance analysis and comparison of various estimation approaches is presented. Several measurement campaigns were performed in order to acquire a sufficient duration and number of microphone signals in a significant variety of driving scenarios and employed cars. To do this, different experimental setups were designed and their performance compared. Design guidelines are given to obtain good trade-off between accuracy performance and equipment costs. Finally, a preliminary analysis with an innovative approach based on Neural Networks (NNs) to improve the current state of the art in microphone virtualization is proposed
Kilpailijakartoitus ja mielikuvatutkimus Metropolia liiketaloudelle
No full textTämän opinnäytetyön toimeksiantaja oli Metropolia Ammattikorkeakoulu. Tutkimuksen tarkoituksena oli selvittää, millaisia mielikuvia opinto-ohjaajilla on eri ammattikorkeakoulujen liiketalouden ohjelmista ja viestinnästä sekä kuinka Metropolia voisi viestinnällään erottautua muista ammattikorkeakouluista. Vastausten avulla pyrin myös selvittämään, millainen imago Metropolialla on opinto-ohjaajien silmissä.
Tutkimuksen kysely lähetettiin pääosin Etelä-Suomen alueella sijaitsevien lukioiden opinto-ohjaajille, koska he ovat suuressa osassa välittämässä tietoa ja kertomassa eri vaihtoehdoista ammattikorkeakouluihin hakeville opiskelijoille. Työssäni pyrittiin myös saamaan selkeitä vastauksia, kuinka ammattikorkeakoulujen tulisi kehittää koulutusohjelmiensa viestintää.
Opinnäytetyön teoreettisen viitekehyksen muodostavat imago, kilpailijaseuranta ja mielikuva. Tutkimus suoritettiin kvantitatiivistä tutkimusmenetelmää käyttäen. Tutkimuslomakke lähetettiin opinto-ohjaajille internetin välityksellä e-lomakekyselynä. Kyselylomakkeen kysymykset olivat pääosin strukturoituja eli vastaajille oli annettu luettelo valmiiksi annetuilla vaihtoehdoilla. Kyselylomake meni 160 opinto-ohjaajalle, joista 48 vastasi. Näin ollen vastausprosentiksi muodostui 33,3 prosenttia.
Tutkimustuloksista voidaan päätellä, että Metropolian liiketalouden ohjelma sekä viestintä koetaan varsin positiiviseksi, vaikka se ei juurikaan pahimmistaan kilpailijoista Haaga-Heliasta ja Laureasta erotu. Tutkimustulosten selvisi, että Metropolia voisi erottautua pahimmista kilpailijoistaan yhteisöllisyytensä kehittämisellä ja sen painottamisella
viestinnässä.The purpose of this study was to measure the kinds of images study advisors have of the business administration programs of different universities of applied sciences and how they communicate about themselves and their programs. The author also wanted to discover how Metropolia could differentiate from other universities of applied sciences. The results were used to figure out what kind of image Metropolia has in the eyes of study advisors.
A questionnaire was sent mainly to upper secondary schools’ study advisors who are located in southern Finland, because they provide information to upper secondary students concerning where to apply after they are graduated from upper secondary school. In this study the author also aimed to get clear answers about how universities of applied sciences should develop communications of their training programs.
The theoretical basis for this thesis is based on imago, business intelligence and image. Quantitative research methodology was used. A questionnaire was sent to study advisors via internet via an e-form. The questions were mainly structured, which means that respondents were given a list with already given options. The questionnaire was sent to 160 study advisors and 48 of them answered. Thus the response rate was 33,3 percent.
It can be concluded from the results that Metropolia’s business administration program is perceived very positively, though it does not differ from its most important competitors Haaga-Helia and Laurea. The research results indicate that Metropolia could differentiate from its most important competitors by developing its communications and by highlighting
its sense of community
Corrigendum: Dissection of DLBCL microenvironment provides a gene expression-based predictor of survival applicable to formalin-fixed paraffin-embedded tissue (Annals of Oncology (2018) 29 (2363-2370) DOI: 10.1093/annonc/mdy450)
No full textThe affiliations of authors T. Venesio and A. Sapino were originally incorrect. These have now been corrected as per the author listing above
