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  • 1.
    Abari, Farzad Foroughi
    Blekinge Institute of Technology, School of Engineering, Department of Signal Processing.
    Optimization of Audio Processing algorithms (Reverb) on ARMv6 family of processors2008Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Audio processing algorithms are increasingly used in cell phones and today’s customers are placing more demands on cell phones. Feature phones, once the advent of mobile phone technology, nowadays do more than just providing the user with MP3 play back or advanced audio effects. These features have become an integral part of medium as well as low-end phones. On the other hand, there is also an endeavor to include as improved quality as possible into products to compete in market and satisfy users’ needs. Tackling the above requirements has been partly satisfied by the advance in hardware design and manufacturing technology. However, as new hardware emerges into market the need for competence to write efficient software and exploit the new features thoroughly and effectively arises. Even though compilers are also keeping up with the new tide space for hand optimized code still exist. Wrapped in the above goal, an effort was made in this thesis to partly cover the competence requirement at Multimedia Section (part of Ericsson Mobile Platforms) to develope optimized code for new processors. Forging persistently ahead with new products, EMP has always incorporated the latest technology into its products among which ARMv6 family of processors has the main central processing role in a number of upcoming products. To fully exploit latest features provided by ARMv6, it was required to probe its new instruction set among which new media processing instructions are of outmost importance. In order to execute DSP-intensive algorithms (e.g. Audio Processing algorithms) efficiently, the implementation should be done in low-level code applying available instruction set. Meanwhile, ARMv6 comes with a number of new features in comparison with its predecessors. SIMD (Single Instruction Multiple Data) and VFP (Vector Floating Point) are the most prominent media processing improvements in ARMv6. Aligned with thesis goals and guidelines, Reverb algorithm which is among one of the most complicated audio features on a hand-held devices was probed. Consequently, its kernel parts were identified and implementation was done both in fixed-point and floating-point using the available resources on hardware. Besides execution time and amount of code memory for each part were measured and provided in tables and charts for comparison purposes. Conclusions were finally drawn based on developed code’s efficiency over ARM compiler’s as well as existing code already developed and tailored to ARMv5 processors. The main criteria for optimization was the execution time. Moreover, quantization effect due to limited precision fixed-point arithmetic was formulated and its effect on quality was elaborated. The outcomes, clearly indicate that hand optimization of kernel parts are superior to Compiler optimized alternative both from the point of code memory as well as execution time. The results also confirmed the presumption that hand optimized code using new instruction set can improve efficiency by an average 25%-50% depending on the algorithm structure and its interaction with other parts of audio effect. Despite its many draw backs, fixed-point implementation remains yet to be the dominant implementation for majority of DSP algorithms on low-power devices.

  • 2.
    Abelsson, Sara
    Blekinge Institute of Technology, School of Engineering, Department of Signal Processing.
    Propagation Measurements at 3.5 GHz for WiMAX2007Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    Propagation measurements at the frequency 3.5 GHz for the WiMAX technology have been conducted. The purpose of these measurements is that a coverage analysis should be accomplished. The mathematical software package MATLAB has been used to analyze the collected data from the measurement campaign. Path loss models have also been used and a comparison between these models and the collected data has been performed. An analysis prediction tool from an application called WRAP has also been used in the comparison with the collected data. In this thesis, diff

  • 3.
    Adapa, Nagaswaroopa
    et al.
    Blekinge Institute of Technology, School of Engineering.
    Bollu, Sravya
    Blekinge Institute of Technology, School of Engineering.
    Performance analysis of different adapative algorithms based on acoustic echo cancellation2013Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    In modern telecommunication systems like hands-free and teleconferencing systems, the problem arise during conversation is the creation of an acoustic echo. This problem degrades the quality of the information signal. All speech processing equipments like noise cancelling headphones and hearing aids should be able to filter different kinds of interfering signals and produce a clear sound to the listener. Currently, echo cancellation is a most interesting and challenging task in any communication system. Echo is the delayed and degraded version of original signal which travels back to its source after several reflections. Eliminating this effect without affecting the original quality of the speech is a challenge of research in present days. Echo cancellation in voice communication is a process of removing the echo to improve the clarity and quality of the voice signals. In our thesis we mainly focused on the acoustic echo cancellation in a closed room using adaptive filters. The Acoustic echo cancellation with adaptive filtering technique will more accurately enhance the speech quality in hands free communication systems. The main aim of using adaptive algorithms for echo cancellation is to achieve higher ERLE at higher rate of convergence with low complexity. The adaptive algorithms NLMS, APA and RLS are implemented using MATLAB. These algorithms are tested with the simulation of echo occurring environment by using constant room dimensions , microphone and source positions. The performance of the NLMS, APA and RLS are evaluated in terms ERLE and misalignment. The results show that RLS algorithm achieve good performance with more computational complexity comparing with the NLMS and APA algorithms. The NLMS algorithm has very low computational complexity comparing to RLS and APA algorithms. The results are taken for both input signal as speech signal and noise separately and plotted in the results section.

  • 4.
    ADHIKARLA, VAMSI KIRAN
    Blekinge Institute of Technology, School of Engineering.
    3D VIDEO FORMAT CONVERSION2011Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    The main aim of this thesis work is to find/implement various methods that convert Conventional Stereoscopic 3D Video (CSV) to Multiview video (MVV). The work investigates different methods that can produce multiple views given a stereoscopic pair from a frame of a particular video sequence and continues with the process of selecting the best among investigated methods that has optimum quality and speed. In contrast to the existing algorithms, this work disregards the physical depth but instead focus on pixel value correspondence. The intermediate view generation in this work is not considered as a geometrical problem, but a morphing problem. Different morphing algorithms (mesh, field and thin plate spline morphing techniques) are considered for conversion. Performance of each morphing algorithm is in turn compared using different correspondence matching techniqes. The investigated methods aim to produce arbitrary number of novel synthesized camera views from a sparse view set. Mesh morphing algorithm is found to be a better candidate in terms of signal to noise ratio, but requires accurate correspondences at edges of an object in a particular scene and also needs more execution time to generate more number of views. A new approach to field morphing has been introduced in this thesis work, which performs better in terms of execution time and also found to produce intermediate views with reasonable signal to noise ratio. This approach is observed to bring good trade off between speed and accuracy. This conversion has an advantage it can be used as a decompression mechanism that can produce multiple views required for an Autostereoscopic 3D display from a stereoscopic left and right pair. This approach also brings the benefit of backward compatibility as present standards for CSV may be used to provide multiview 3D video to high fidelity Autostereoscopic 3D displays of the future. This work has applications in free view point television, video conferencing systems etc.,

  • 5. Adolfsson, Stefan
    On Automatic Detection of Burn-through Using a Parametric Model1995Report (Other academic)
  • 6. Adolfsson, Stefan
    Quality Monitoring in Pulsed GMA Welding Using Modern Signal Processing Methods1995Licentiate thesis, comprehensive summary (Other academic)
  • 7. Adolfsson, Stefan
    Quility Monitoring in Robotised Short Circuiting GMA Welding1997Report (Other academic)
    Abstract [en]

    This paper addresses the problem of automatic monitoring the weld quality produced by robotised short arc welding. A simple statistical change detection algorithm for the weld quality, recursive Sequential Probability Ratio Test (SPRT), is used. The algorithm may equivalently be viewed as a cumulative sum (CUSUM) - type test. The test statistics is based upon the variance of the amplitude of the weld voltage. The performance of the algorithm is evaluated using experimental data. The results obtained from the algorithm indicate that it is possible to detect changes in the weld quality automatically and on-line.

  • 8. Adolfsson, Stefan
    et al.
    Bahrami, Ali
    Bolmsjö, Gunnar
    Claesson, Ingvar
    Automatic quality monitoring in robotised GMA welding using a repeated sequential probability ratio test method1997In: International Journal for the Joining of Materials, ISSN 0905-6866, Vol. 9, no 1, 2-8 p.Article in journal (Refereed)
  • 9. Adolfsson, Stefan
    et al.
    Bahrami, Ali
    Claesson, Ingvar
    A Sequential Probability Ratio Test Method for Quality Monitoring in Robotised GMA Welding1997Conference paper (Refereed)
    Abstract [en]

    This paper deals with the problem of automatic monitoring the weld quality when welding with Gas Metal Arc (GMA) in short circuiting mode. Experiments with two different types of T-joints are performed in order to provoke optimal and non-optimal welding conditions. During the experiments, voltage and current are measured from the welding process. A simple statistical change detection algorithm for the weld quality, the repeated Sequential Probability Ratio Test (SPRT), is used. The algorithm can equivalently be viewed as a cumulative sum (CUSUM) - type test. The test statistics is based upon the fluctuations of amplitude in the weld voltage. It is shown that the fluctuations of the weld voltage amplitude decreases when the welding process is not operating under optimal condition. The results obtained from the experiments indicate that it is possible to detect changes in the weld quality automatically and on-line.

  • 10. Adolfsson, Stefan
    et al.
    Bahrami, Ali
    Claesson, Ingvar
    Quality Monitoring in Robotised Welding using Sequential Probability Ratio test1996Conference paper (Refereed)
    Abstract [en]

    This paper addresses the problem of automatic monitoring the weld quality produced by robotised short arc welding. A simple statistical change detection algorithm for the weld quality, recursive sequential probability ratio test (SPRT), is used. The algorithm may equivalently be viewed as a cumulative sum (CUSUM) type test. The test statistics is based upon the variance of the amplitude of the weld voltage. It is shown that the variance of the weld voltage amplitude decreases when the welding process is not operating under optimal condition. The performance of the algorithm is evaluated using experimental data. The results obtained from the algorithm indicate that it is possible to detect changes in the weld quality automatically and on-line

  • 11. Adolfsson, Stefan
    et al.
    Bahrami, Ali
    Claesson, Ingvar
    Bolmsjö, Gunnar
    On-line quality monitoring in short: circuit gas metal arc welding1999In: Welding Journal, ISSN 0043-2296, Vol. 78, no 2, 59S-73S p.Article in journal (Refereed)
    Abstract [en]

    This paper addresses the problems involved in the automatic monitoring of the weld quality produced by robotized short-arc welding. A simple statistical change detection algorithm for the weld quality, the repeated Sequential Probability Ratio Test (SPRT), was used. The algorithm may similarly be viewed as a cumulative sum (CUSUM) type test, and is well-suited to detecting sudden minor changes in the monitored test statistic. The test statistic is based on the variance of the weld voltage, wherein it will be shown that the variance decreases when the welding process is not operating under optimal conditions. The performance of the algorithm is assessed through the use of experimental data. The results obtained from the algorithm show that it is possible to detect changes in weld quality automatically and on-line.

  • 12. Adolfsson, Stefan
    et al.
    Ericson, Klas
    Grennberg, Anders
    Automatic Detection of Burn-through in GMA Welding Using a Parametric Model1996In: Mechanical Systems & Signal Processing, ISSN 0888-3270 , Vol. 10, no 5, 633-651 p.Article in journal (Refereed)
    Abstract [en]

    This paper addresses the problem of automatic detection of burn-through in weld joints. Gas metal are (GMA) welding with pulsed current is used, and welding voltage and current are recorded. As short-circuitings are common between the welding electrode and the work piece during burn-through, a short-circuit detector is developed to detect these events. To detect another specific characteristic of burn-through-a broadband long-lasting voltage component-this detector is combined with a square-law detector. This second detector is based on a non-linear modification of an autoregressive model with extra input (ARX-model) of the welding process. The results obtained from this compound detector indicate that it is possible to detect burn-through in the welds automatically. The work also indicates that it is possible to design an on-line monitoring system for robotic GMA welding.

  • 13. Adolfsson, Stefan
    et al.
    Ericson, Klas
    Gustavsson, Jan-Olof
    Ågren, Björn
    Quality Monitoring for Pulsed Arc Welding1994Conference paper (Refereed)
  • 14. Adolfsson, Stefan
    et al.
    Ericson, Klas
    Ågren, Björn
    On Automatic Detection of Burn-through in GMA Welding: Weld Voltage Analysis1995Report (Other academic)
  • 15.
    Afaq, Muhammad
    et al.
    Blekinge Institute of Technology, School of Engineering.
    Faheem, Sahibzada Muhammad
    Blekinge Institute of Technology, School of Engineering.
    Performance Analysis of Selected Cooperative Relaying Techniques2010Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Recently, cooperative communication has gained significant interest due to the fact that it exploits spatial diversity and provides capacity/performance gain over conventional single- input single-output (SISO) systems. A mobile node with single antenna can cooperate with a nearby mobile node having single antenna in multi-user environment to create the effect of virtual multiple antenna system. Hence, reducing the complexity associated with actual multiple antenna systems. Despite the small size and power constraints, a mobile node can still benefit from spatial diversity by employing cooperation, thus saving transmission power and increasing the coverage range of the network. In this thesis, we have selected some of relaying protocols, namely, amplify-and-forward, decode-and-forward, detect-and-forward, and selective detect-and-forward that are studied and implemented for two different relaying geometries, i.e. equidistant and collinear. Results are studied and compared with each other to show the performance of each protocol in terms of average symbol error probabilities. The considered system model has three nodes, i.e. source, relay, destination. Communicating nodes are considered to be half-duplex with single antenna for transmission and reception. The source, when communicating with the destination, broadcasts the information, which is heard by the nearby relay. The relay then uses one of the cooperation protocols. Finally, the relayed signal reaches the destination, where it is detected by maximal ratio combiner (MRC) and combined with the direct transmission for possible diversity gains. The transmission path or the channel is modeled as a frequency non-selective Rayleigh fading in the presence additive white Gaussian noise (AWGN). The effect of path loss has been observed on cooperation for collinear arrangement with exponential decay up to four. Considering equidistant arrangement, decode-and-forward shows good performance at high signal-to-noise ratio (SNR) while amplify-and-forward is very promising for very low SNR. A selective relaying scheme called selective detect-and- forward is also presented which outperforms its fixed counterparts for a wide range of SNR.

  • 16.
    Aftab, Adnan
    et al.
    Blekinge Institute of Technology, School of Computing.
    Mufti, Muhammad Nabeel
    Blekinge Institute of Technology, School of Computing.
    Spectrum sensing through implementation of USRP22011Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Scarcity of the wireless spectrum has led to the development of new techniques for better utilization of the wireless spectrum. Demand for high data rates and better voice quality is resulting in the development of new wireless standard making wireless spectrum limited than ever. In this era of wireless communication, service providers and telecom operators are faced with a dilemma where they need a large sum of the wireless spectrum to meet the ever increasing quality of service requirements of consumers. This has led to the development of spectrum sensing techniques to find the unused spectrum in the available frequency band. The results presented in this thesis will help out in developing clear understanding of spectrum sensing techniques. Comparison of different spectrum sensing approaches. The experiments carried out using USRP2 and GNU radio will help the reader to understand the concept of underutilized frequency band and its importance in Cognitive Radios.

  • 17.
    Ahmed, Ishtiaque
    Blekinge Institute of Technology, School of Engineering, Department of Telecommunication Systems.
    Study of the Local Backprojection Algorithm for Image Formation in Ultra Wideband Synthetic Aperture Radar2008Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    The purpose of this thesis project is to study and evaluate a UWB Synthetic Aperture Radar (SAR) data image formation algorithm, that was previously less familiar and, that has recently got much attention in this field. Certain properties of it made it acquire a status in radar signal processing branch. This is a fast time-domain algorithm named Local Backprojection (LBP). The LBP algorithm has been implemented for SAR image formation. The algorithm has been simulated in MATLAB using standard values of pertinent parameters. Later, an evaluation of the LBP algorithm has been performed and all the comments, estimation and judgment have been done on the basis of the resulting images. The LBP has also been compared with the basic time-domain algorithm Global Backprojection (GBP) with respect to the SAR images. The specialty of LBP algorithm is in its reduced computational load than in GBP. LBP is a two stage algorithm — it forms the beam first for a particular subimage and, in a later stage, forms the image of that subimage area. The signal data collected from the target is processed and backprojected locally for every subimage individually. This is the reason of naming it Local backprojection. After the formation of all subimages, these are arranged and combined coherently to form the full SAR image.

  • 18.
    Ahmed, Mamun
    Blekinge Institute of Technology, School of Engineering.
    Adaptive Sub band GSC Beam forming using Linear Microphone-Array for Noise Reduction/Speech Enhancement.2012Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    This project presents the description, design and the implementation of a 4-channel microphone array that is an adaptive sub-band generalized side lobe canceller (GSC) beam former uses for video conferencing, hands-free telephony etc, in a noisy environment for speech enhancement as well as noise suppression. The side lobe canceller evaluated with both Least Mean Square (LMS) and Normalized Least Mean Square (NLMS) adaptation. A testing structure is presented; which involves a linear 4-microphone array connected to collect the data. Tests were done using one target signal source and one noise source. In each microphone’s, data were collected via fractional time delay filtering then it is divided into sub-bands and applied GSC to each of the subsequent sub-bands. The overall Signal to Noise Ratio (SNR) improvement is determined from the main signal and noise input and output powers, with signal-only and noise-only as the input to the GSC. The NLMS algorithm significantly improves the speech quality with noise suppression levels up to 13 dB while LMS algorithm is giving up to 10 dB. All of the processing for this thesis is implemented on a computer using MATLAB and validated by considering different SNR measure under various types of blocking matrix, different step sizes, different noise locations and variable SNR with noise.

  • 19.
    Ahmed, Sabbir
    Blekinge Institute of Technology, School of Engineering, Department of Signal Processing.
    Performance of Multi-Channel Medium Access Control Protocol incorporating Opportunistic Cooperative Diversity over Rayleigh Fading Channel2006Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    This thesis paper proposes a Medium Access Control (MAC) protocol for wireless networks, termed as CD-MMAC that utilizes multiple channels and incorporates opportunistic cooperative diversity dynamically to improve its performance. The IEEE 802.11b standard protocol allows the use of multiple channels available at the physical layer but its MAC protocol is designed only for a single channel. The proposed protocol utilizes multiple channels by using single interface and incorporates opportunistic cooperative diversity by using cross-layer MAC. The new protocol leverages the multi-rate capability of IEEE 802.11b and allows wireless nodes far away from destination node to transmit at a higher rate by using intermediate nodes as a relays. The protocol improves network throughput and packet delivery ratio significantly and reduces packet delay. The performance improvement is further evaluated by simulation and analysis.

  • 20. Aibinu, A.M.
    et al.
    Iqbal, Muhammad Imran
    Nilsson, M.
    Salami, M.J.E.
    A New Method of Correcting Uneven Illumination Problem in Fundus Images2007Conference paper (Refereed)
    Abstract [en]

    Recent advancements in signal and image processing have reduced the time of diagnoses, effort and pressure on the screeners by providing auto diagnostic tools for different diseases. The success rate of these tools greatly depend on the quality of acquired images. Bad image quality can significantly reduce the specificity and the sensitivity which in turn forces screeners back to their tedious job of manual diagnoses. In acquired fundus images, some areas appear to be brighter than the other, that is areas close to the center of the image are always well illuminated, hence appear very bright while areas far from the center are poorly illuminated hence appears to be very dark. Several techniques including the simple thresholding, Naka Rushton (NR) filtering technique and histogram equalization (HE) method have been suggested by various researchers to overcome this problem. However, each of these methods has limitations at their own and hence the need to develop a more robust technique that will provide better performance with greater flexibility. A new method of compensating uneven (irregular) illumination in fundus images termed global-local adaptive histogram equalization using partially-overlapped windows (GLAPOW) is proposed in this paper. The developed algorithm has been tested and the results obtained show superior performance when compared to other known techniques for uneven illumination correction.

  • 21. Aibinu, A.M.
    et al.
    Iqbal, Muhammad Imran
    Nilsson, M.
    Salami, M.J.E.
    Automatic Diagnosis of Diabetic Retinopathy from Fundus Images Using Digital Signal and Image Processing Techniques2007Conference paper (Refereed)
    Abstract [en]

    Automatic diagnosis and display of diabetic retinopathy from images of retina using the techniques of digital signal and image processing is presented in this paper. The acquired images undergo pre-processing to equalize uneven illumination associated with the acquired fundus images. This stage also removes noise present in the image. Segmentation stage clusters the image into two distinct classes while the abnormalities detection stage was used to distinguish between candidate lesions and other information. Methods of diagnosis of red spots, bleeding and detection of vein-artery crossover points have also been developed in this work using the color information, shape, size, object length to breadth ration as contained in the acquired digital fundus image. Furthermore, two graphical user interfaces (GUIs) have also been developed during this work; the first is for the collection of lesion data information and was used by the ophthalmologist in marking images for database while the second GUI is for automatic diagnosing and displaying of the result in a user friendly manner. The algorithm was tested with a separate set of 25 fundus images. From this, the result obtained for microaneurysms and haemorrhages diagnosis shows the appropriateness of the method.

  • 22. Aibinu, A.M.
    et al.
    Iqbal, Muhammad Imran
    Shafie, A.A.
    Salami, M.J.E.
    Nilsson, Mikael
    Vascular intersection detection in retina fundus images using a new hybrid approach2010In: Computers in Biology and Medicine, ISSN 0010-4825, E-ISSN 1879-0534, Vol. 40, no 1, 81-89 p.Article in journal (Refereed)
    Abstract [en]

    The use of vascular intersection aberration as one of the signs when monitoring and diagnosing diabetic retinopathy from retina fundus images (FIs) has been widely reported in the literature. In this paper, a new hybrid approach called the combined cross-point number (CCN) method able to detect the vascular bifurcation and intersection points in FIs is proposed. The CCN method makes use of two vascular intersection detection techniques, namely the modified cross-point number (MCN) method and the simple cross-point number (SCN) method. Our proposed approach was tested on images obtained from two different and publicly available fundus image databases. The results show a very high precision, accuracy, sensitivity and low false rate in detecting both bifurcation and crossover points compared with both the MCN and the SCN methods.

  • 23.
    Aida, Horaniet
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Telecommunication Systems.
    Isabel, Llorente
    Blekinge Institute of Technology, School of Engineering, Department of Telecommunication Systems.
    Formation of High Resolution Images in SAR using GNSS2009Independent thesis Basic level (degree of Bachelor)Student thesis
    Abstract [en]

    The aim of this thesis is to investigate the possibility to form high resolution Synthetic Aperture Radar (SAR) images using the Global Navigation Satellite System (GNSS) Galileo, GPS and Glonas, In particular the thesis study the GPS signal and evaluate its properties for bistatic case. The report is based on the fact that Galileo and GPS are both positioning systems with similar characteristics. The difference is mainly that Galileo System uses a larger number of satellites and a different modulation scheme to improve the efficiency of the system, resulting in a better accuracy. On the topic of GNSS SAR, the report will be described with modes, resolution, geometry and algorithms. It is also explained the Space Surface Bi-static Radar and within two particular cases: parallel and non parallel paths

  • 24.
    Ajayi, Taiwo Seun
    Blekinge Institute of Technology, School of Engineering, Department of Telecommunication Systems.
    Mobile Satellite Communications: Channel Characterization and Simulation2007Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    Abstract: The channel characterization of a mobile satellite communication which is an important and fast growing arm of wireless communication plays an important role in the transmission of information through a propagation medium from the transmitter to the receiver with minimum barest error rate putting into consideration the channel impairments of different geographical locations like urban, suburban, rural and hilly. The information transmitted from satellite to mobile terminals suffers amplitude attenuation and phase variation which is caused by multipath fading and signal shadowing effects of the environment. These channel impairments are commonly described by three fading phenomena which are Rayleigh fading, Racian fading and Log-normal fading which characterizes signal propagation in different environments. They are mixed in different proportions by different researchers to form a model to describe a particular channel. In the thesis, the general overview of mobile satellite is conducted including the classification of satellite by orbits, the channel impairments, the advantages of mobile satellite communication over terrestrial. Some of the major existing statistical models used in describing different type of channels are looked into and the best out of them which is Lutz model [6] is implemented. By simulating the Lutz model which described all possible type of environments into two states which represent non-shadowed or LOS and shadowed or NLOS conditions, shows that the BER is predominantly affected by shadowing factor.

  • 25.
    Akbar, Mohamed Kazaludeen
    Blekinge Institute of Technology, Faculty of Engineering, Department of Applied Signal Processing.
    Performance Evaluation and Comparison of Coherent and Incoherent Receivers under Atmospheric Turbulence2014Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Optical free space communication system faces the major challenge because of the atmospheric condition. Signals receive in the ground station using two different types of receivers (Coherent detection and Intensity Modulation and Direct Detection (IM/DD)). Coherent detection uses PIN photo detector in the receiver end to attain the more sensitivity of the receiver. It receives the input data as a carrier signal and the local oscillator signal is mixed with the received signal and down convert the carrier signal to an intermediate frequency signal. The Intensity Modulation direct detection uses the Avalanche photo detector in the receiver end to attain the more sensitivity. This detection receives the input signal as a carrier signal and it is directly demodulated at the receiver back into the original signal. Signals receive in the ground station from the aircraft will be affected by the various types of noise like shot noise, thermal noise, etc. The occurrence of noises in the coherent detection is not exactly same as the IM/DD. Some noise get varies according to the electrical circuit noise produced in the receiver side. By deriving the signal-to-noise ratio, the background noise occur in the desired signal can be calculated. One of the main goals would be to derive a Probability Density Function (PDF) of the Signal-to-Noise Ratio (SNR) of the each type of receiver to check the efficiency of the receivers. Transmitting the optical signal from aircraft will face some data loss problem due to atmospheric turbulence disturbances, to identify the loss arises in the transmitting signal will be done by using the probability error method. Bit Error Rate (BER) derivation will take place to calculate and to identify the data loss occurs in the received signal. The project deals with measuring the efficiency and sensitivity among those two optical receivers and to check the robustness between those receivers against scintillations (power fades and surges) effects. In this work performance of the coherent receiver and IM/DD receiver using APD is compared with the different system characteristics. Sensitivity and performance of both the receivers are calculated with the same fading vector. Signal to noise ratio and bit error rate are theoretically derived and numerically analyzed in the case of atmospheric turbulence. Numerical results predict the performance of both the receivers.

  • 26.
    Akbar, Zeeshan
    et al.
    Blekinge Institute of Technology, School of Computing.
    Ali, Asar
    Blekinge Institute of Technology, School of Computing.
    Evaluation of AODV and DSR Routing Protocols of Wireless Sensor Networks for Monitoring Applications2009Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Deployment of sensor networks are increasing either manually or randomly to monitor physical environments in different applications such as military, agriculture, medical transport, industry etc. In monitoring of physical environments, the most important application of wireless sensor network is monitoring of critical conditions. The most important in monitoring application like critical condition is the sensing of information during emergency state from the physical environment where the network of sensors is deployed. In order to respond within a fraction of seconds in case of critical conditions like explosions, fire and leaking of toxic gases, there must be a system which should be fast enough. A big challenge to sensor networks is a fast, reliable and fault tolerant channel during emergency conditions to sink (base station) that receives the events. The main focus of this thesis is to discuss and evaluate the performance of two different routing protocols like Ad hoc On Demand Distance Vector (AODV) and Dynamic Source Routing (DSR) for monitoring of critical conditions with the help of important metrics like throughput and end-to-end delay in different scenarios. On the basis of results derived from simulation a conclusion is drawn on the comparison between these two different routing protocols with parameters like end-to-end delay and throughput.

  • 27.
    Akhter, Habiba
    Blekinge Institute of Technology, School of Engineering, Department of Electrical Engineering.
    Apodization Method in UWB SAR Imaging2014In: 2014 1ST INTERNATIONAL CONFERENCE ON ELECTRICAL ENGINEERING AND INFORMATION & COMMUNICATION TECHNOLOGY (ICEEICT 2014), IEEE Computer Society Digital Library, 2014Conference paper (Refereed)
    Abstract [en]

    Synthetic Aperture Radar (SAR) image processing involves a two dimensional (2-D) Fourier Transform (FT) and the spectrum shape introduces high intensity sidelobes. These sidelobes may severely distort the image. Apodization technique can decrease the sidelobes level while preserving the image resolution. However, in Ultra wideband (UWB) SAR imaging, we have to reduce both orthogonal and non-orthogonal sidelobes. In this paper, a new linear window function has been presented based on analysis of different linear and non-linear apodization techniques. This new linear method controls both orthogonal and non-orthogonal sidelobes better than other conventional window functions. This method has been applied and verified with a real SAR image.

  • 28.
    Akhter, Habiba
    Blekinge Institute of Technology, School of Engineering.
    Evaluation of weighting functions for Sidelobe control in UWB SAR image processing2013Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Ultra wideband (UWB) Synthetic Aperture Radar (SAR) holds huge possibilities for both terrestrial and celestial object sensing with excellent details which assists in science and technology. SAR systems associated with large antenna beamwidth, large signal bandwidth and low frequency operating in the VHF/UHF region is becoming gradually more popular because of their rising number of application in the areas of ground-penetrating radar (GPR) and foliage penetration radar (FOPEN). Apodization techniques in UWB SAR imaging have attracted significant interest in recent years for sidelobe suppression in SAR images. This technique is split into two groups: linear apodization and non-linear apodization. Linear apodization technique means to apply amplitude weighting functions in frequency domain prior to the final inverse Fourier transform requisite to appropriately focus on the SAR images. Both linear and non linear techniques can be used to suppress sidelobes level. Frequently used linear weighting functions are Hanning, Hamming and Blackman. Linear techniques can control the sidelobes level but image resolution reduces simultaneously. But non-linear techniques like Spatially Variant Apodization (SVA), Complex Duel Apodization and Dual-Apodization can suppress sidelobes and preserve the spatial resolution concurrently. However for these methods, it can be hard to understand how the output signal relates to input signal and also the phase information of image is lost. In this thesis paper, the main focus is, on apodization techniques to propose a new weighting function for sidelobe apodization and investigate it on real SAR images. In this thesis, we also study Impulse response (IPR) function for UWB SAR image processing. A two dimensional sinc function is used as an impulse response function for narrow band (NB) SAR system. This function can be obtained from a two dimensional Fourier Transform of a SAR image. This rectangular estimation is reasonable for narrow band and narrowbeam SAR. But for large bandwidth and wide integration angles, this approximation for the UWB SAR spectrum is not valid. It can provide erroneous SAR image quality measurements. To obtain precise image quality measurement, SAR image need to be generated for a range of different integration angle as UWB SAR systems are related with large integration angle to maintain azimuth focusing. So, in this work the choices of optimum windows have been investigated at different integration angles in order to see if there are large differences between NB SAR Apodization and UWB SAR Apodization.

  • 29.
    Akinwande, Gbenga Segun
    Blekinge Institute of Technology, School of Computing.
    Signaling Over Protocols Gateways in Next-Generation Networks2009Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    In this thesis, I examined various signalling both in wired and mobile networks, with more emphasis on SIGTRAN. The SIGTRAN is the protocol suite applicable in the current new generation and next-generation networks, most especially as it enables service provider to be able to interpolate both wireline and wireless services within the same architecture. This concept is an important component in today’s Triple-play communication, and hence this thesis has provided a broad view on Signalling and Protocol Gateways in Traditional and Next Generations Networks. Signal flow in a typical new generation network was examined by carrying out discrete event simulation of UMTS network using OPNET modeller 14.5. Through both Packet-Switching (PS) and Circuit-Switching (CS) signalling, I was able to examine the QoS on a UMTS. Precisely, I looked at throughput on UMTS network by implementing WFQ and MDRR scheduling schemes.

  • 30.
    Alam, Md. Jobayer
    et al.
    Blekinge Institute of Technology, School of Engineering.
    Sujan, Shaha Mohammed Goni Abed
    Blekinge Institute of Technology, School of Engineering.
    Low Complexity Channel Estimation for OFDM Systems Based on LS and MMSE Estimators’2010Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    In this paper we investigate the block-type pilot channel estimation for orthogonal frequency-division multiplexing (OFDM) systems. The estimation is based on the minimum mean square error (MMSE) estimator and the least square (LS) estimator. We derive the MMSE and LS estimators’ architecture and investigate their performances. We prove that the MMSE estimator performance is better but computational complexity is high, contrary the LS estimator has low complexity but poor performance. For reducing complexity we proposed two different solutions which are the Simplified Least Square (SLS) estimator and the modified MMSE estimator. We evaluate estimator’s performance on basis of mean square error and symbol error rate for 16 QAM systems. We also evaluate estimator’s computational complexity.

  • 31.
    ALAM, MD. SHAMSER
    Blekinge Institute of Technology, School of Engineering.
    On sphere detection for OFDM based MIMO systems2010Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    The mobile wireless communication systems has been growing fast and continuously over the past two decades. Therefore, in order to fulfill the demand for this rapid growth, the standardization bodies along with wireless researchers and mobile operators around the world have been constantly working on new technical specifications.An important problem in modern communication is known as NP complete problem in the Maximum Likelihood (ML) detection of signals transmitting over Multiple Input Multiple Output channel of the OFDM transceiver system. Development of the Sphere Decoder (SD) as a result of the rapid advancement in signal processing techniques provides ML detection for MIMO channels at polynomial time complexity average case. There are weaknesses in the existing SDs. The sphere decoder performance is very sensitive for the most current proposals in order to choose the search radius parameter. At high spectral efficiencies SNR is low or as the problem dimension is high and the complexity coefficient can become very large too. Digital communications of detecting a vector of symbols has importance as, is encountered in several different applications. These symbols are as the finite alphabet and transmitted over a multiple-input multiple-output (MIMO) channel with Gaussian noise. There are no limitation to the detection of symbols spatially multiplexed over a multiple-antenna channel and the multi user detection problem. Efficient algorithms are considered for the detection problems and have recognized well. The algorithm of sphere decoder, orders has optimal performance considering the error probability and this has proved extremely efficient in terms of computational complexity for moderately sized problems in case of signal to noise ratio. At high SNR the algorithm has a polynomial average complexity and it is understood the algorithm has an exponential worst case complexity. The efficiency of the algorithm is ordered the exponential rate derivation of growth. Complexity is positive for the finite SNR and small in the high SNR. To achieve the sphere decoding solution applying Schnorr-Euchner by Maximum likelihood method , Depth-first Stack-based Sequential decoding is used. This thesis focuses on the receiver part of the transceiver system and takes a good look at the near optimal algorithm for sphere detection of a vector of symbols transmitted over MIMO channel. The analysis and algorithms are general in nature.

  • 32.
    Alam, Tahmid
    et al.
    Blekinge Institute of Technology, School of Engineering.
    Irshad, Sharmeen
    Blekinge Institute of Technology, School of Engineering.
    SW features in power systems for telecom equipment2013Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    This thesis report is a research effort with Ericsson’s devices and internal documents. In essence this thesis report contributes with a perspective to understand the power system of Radio Base Station and its features. The overall research aim is to understand the existing power system and its features and to propose new software and hardware features. A lot of investigations have been done with the Functional Specification and Requirement Specification documents for analysis of the present features. The main goal is to identify software features and their benefits to customer. After analysing the present features new features were proposed. For the proposal many steps were taken into consideration including cost and system information. Also some hardware changes have been required. With the new proposed features, the power system will perform better with different environments and also some of the proposals were improvements of the existing features. The proposed features are mostly focused on power saving and cost to benefit the customer.

  • 33. Alaves, Dimas
    et al.
    Machado, Renato
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    da Costa, Daniel Benevides
    Legg, Andrei Piccinini
    Uchoa-Filho, Bartolomeu F.
    A dynamic hybrid antenna/relay selection scheme for the multiple-access relay channel2014In: 2014 11TH INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATIONS SYSTEMS (ISWCS), IEEE , 2014, 594-599 p.Conference paper (Refereed)
    Abstract [en]

    We propose a dynamic hybrid antenna/relay selection scheme for multiple-access relay systems. The proposed scheme aims to boost the system throughput while keeping a good error performance. By using the channel state information, the destination node performs a dynamic selection between the signals provided by the multi-antenna relay, located in the inter-cell region, and the relay nodes geographically distributed over the cells. The multi-antenna relay and the single-antenna relay nodes employ the decode-remodulate-and-forward and amplify-and-forward protocols, respectively. Results reveal that the proposed scheme offers a good tradeoff between spectral efficiency and diversity gain, which is one of the main requirements for the next generation of wireless communications systems.

  • 34.
    Aldalaty, Khalid
    Blekinge Institute of Technology, School of Engineering.
    Mobile IP handover delay reduction using seamless handover architecture2009Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Seamless communication is becoming the main aspect for the next generation of the mobile and wireless networks. Roaming among multiple wireless access networks connected together through one IP core makes the mobility support for the internet is very critical and more important research topics nowadays. Mobile IP is one of the most successful solutions for the mobility support in the IP based networks, but it has poor performance in term of handover delay. Many improvements have been done to reduce the handover delay, which result in two new standards: the Hierarchical MIP (HMIP) and the Fast MIP (FMIP), but the delay still does not match the seamless handover requirements. Finally Seamless MIP (S-MIP) has been suggested by many work groups, which combine between an intelligent handover algorithm and a movement tracking scheme. In This thesis, we show the handover delay reduction approaches, specifically the Seamless Mobile IP. The thesis studies the effects of the S-MIP in the handover delay and the network performance as well. A simulation study takes place to compare between the standard MIP and the new suggested S-MIP protocol in term of handover delay, packet loss and bandwidth requirement. The thesis concludes with the analyzing of the simulation results, evaluating the S-MIP performance and finally gives some suggestions for the future work.

  • 35.
    Aleti, Mahesh
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Applied Signal Processing.
    Syed, Rahamatulla
    Blekinge Institute of Technology, Faculty of Engineering, Department of Applied Signal Processing.
    Chennupati, Rajendra Prasad
    Blekinge Institute of Technology, Faculty of Engineering, Department of Applied Signal Processing.
    Fuzzy Based power control system Using ANFIS and MIMO-OFDM Techniques in Cognitive Radio Networks2014Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Cognitive Radio technology is used for efficient utilization of the spectrum. There are two types of users, one is the Primary user (PU), and the second one is the Secondary user (SU). In those users, PU is having the license to use the spectrum. The SU does not have the license to use the spectrum. Cognitive Radio comprises of Spectrum sensing, Spectrum Management and Spectrum Mobility. In cognitive radio, optimal power control in spectrum sharing is main research issues. In the spectrum, sharing both PU and SU can access the spectrum simultaneously as long as there is no interference to PU’s of Quality of service (QOS). So we have to handle this interference to the PU and we have to improve the performance of the SU. For that power control is the main consternate to improve the performance of SU. In our thesis, we are divided into two parts, the first one is we used ANFIS (Adaptive Neuro Fuzzy Inference System) for optimizing power control in cognitive radio network Users (SU) by optimization of SNR & SINR at Primary User (PU) to maintain QOS of PU and improve the performance of SU and Channel capacity computation for various ISR tolerance levels at PU. In second part, we used implementation of MIMO (Multiple Input Multiple output)-OFDM (Orthogonal Frequency Division Multiplexing) transmission technique in CRN (Cognitive Radio networks) for it is use in emergency conditions where transmission requires reliability and high data rate. Then it is tested BER (Bit error rate) performance on MATLAB. Key words: Cognitive Radio, Power Control, the Fuzzy Interference System (FIS), ANFIS, “MIMO” (“Multiple Input Multiple Output”), “OFDM” (“Orthogonal Frequency Division Multiplexing”), AWGN, BER, SNR, Eb/N0

  • 36.
    Ali, Mohsin
    et al.
    Blekinge Institute of Technology, School of Engineering.
    Nasir, Muhammad Jamal
    Blekinge Institute of Technology, School of Engineering.
    Echo Cancellation using PMSAF and Compare the performance with NLMS and improved PNLMS under different Impulse responses2013Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    In the field of signal processing adaptive filtering is a major subject which has vast applications in speech processing e.g. speech coding, speech enhancement, echo cancellation and interference. Echo is the major problem in the communication systems. There are two major types of echoes hybrid and acoustic echoes. In order to remove these echoes the most important method for removing these echoes is through cancellation. Adaptive filters are used to estimate the replication of echoes and then subtracted from the infected signal. . We introduced subband filters to improve the performance of adaptive filter (time domain). Due to small adaptive filters in the subband filter banks, we can improve the reduction of complexity, computational and convergence level as compared with others. The major goal of this thesis is to present the echo cancellation using the multiband subband adaptive filtering and also compare the performance with NLMS and Improved PNLMS using different impulse responses. PMSAF algorithm behaves continuously better convergense rate with excitation signal (colored noise and speech signal) for both impulse responses (sparse and dispersive) as compared with IPNLMS and NLMS algorithms.

  • 37.
    Ali, Sajjad
    et al.
    Blekinge Institute of Technology, School of Computing.
    Ali, Asad
    Blekinge Institute of Technology, School of Computing.
    Performance Analysis of AODV, DSR and OLSR in MANET2010Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    A mobile ad hoc network (MANET) consists of mobile wireless nodes. The communication between these mobile nodes is carried out without any centralized control. MANET is a self organized and self configurable network where the mobile nodes move arbitrarily. The mobile nodes can receive and forward packets as a router. Routing is a critical issue in MANET and hence the focus of this thesis along with the performance analysis of routing protocols. We compared three routing protocols i.e. AODV, DSR and OLSR. Our simulation tool will be OPNET modeler. The performance of these routing protocols is analyzed by three metrics: delay, network load and throughput. All the three routing protocols are explained in a deep way with metrics. The comparison analysis will be carrying out about these protocols and in the last the conclusion will be presented, that which routing protocol is the best one for mobile ad hoc networks.

  • 38.
    allouh, mahmoud
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Electrical Engineering.
    Gomez, Carlos
    Blekinge Institute of Technology, School of Engineering, Department of Electrical Engineering.
    Shockwarner for a Smartphone2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 39.
    AL-MAMUN, ABDULLAH
    et al.
    Blekinge Institute of Technology, School of Engineering.
    ULLAH, MOHAMMAD RAFIQ
    Blekinge Institute of Technology, School of Engineering.
    Cognitive Radio for Short Range Systems based on Ultra-Wideband2011Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Cognitive Radio (CR) has been proposed as a promising and effective technology to improve radio spectrum utilization. It can change its transmitter parameters depending on the environment in which it operate based on interaction. In CR, a number of different methods of spectrum sensing are used to identify the presence of signal transmission. Among them, the multitaper method (MTM), has been investigated in this thesis paper at the same time with other sensing methods, recently seems to be the best choice for spectrum sensing CR because of its accurate identification and estimation, quick computation, and regularization. This thesis paper is examining how CR can be utilized in short range systems based on Ultra-Wideband (UWB). UWB is a promising technology in wireless communication use for high speed data transmission with low power utilization or long distance localization in both military, radar, sensor, data collection, tracking or commercial application. UWB has the ability to move between very low data rate or very high data rate, short range distance or long range distance applications. Impulse radio UWB (IR-UWB) shows some impressive characteristics in short-range communication systems with varieties of throughput option including high data rates. The strong synergy between the aims of CR and features of IR-UWB has been shown in this thesis. Our key objective is to understand how CR can be applied to UWB systems.

  • 40. Al-Qahtani, Fawaz S.
    et al.
    Duong, Quang Trung
    Gurung, Arun K.
    Bao, Vo Nguyen Quoc
    Selection Decode-and-Forward Relay Networks with Rectangular QAM in Nakagami-m Fading Channels2010Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate the average symbol error probability (SEP) of fixed decode-and-forward relay networks over independent but not identically distributed Nakagami-m fading channels. We have derived closed form expression of SEP for general rectangular quadrature amplitude modulation (QAM) under relay selection scheme where only the best relay forwards message from the source to the destination. The expressions are in terms of hypergeometric series which can be efficiently numerically evaluated. The numerical results are validated with Monte-Carlo simulations.

  • 41. Al-Qahtani, Fawaz S.
    et al.
    Duong, Quang Trung
    Blekinge Institute of Technology, School of Computing.
    Zhong, Caijun
    Qaraqe, Khaild A.
    Alnuweiri, Hussein
    Performance Analysis of Dual-Hop AF Systems with Interference in Nakagami-m Fading Channels2011In: IEEE Signal Processing Letters, ISSN 1070-9908, Vol. 18, no 8, 454-457 p.Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate the performance of dual-hop channel state information-assisted amplify-and-forward relaying systems over Nakagami-m fading channels in the presence of multiple interferers at the relay. Assuming integer fading parameter m, we derive closed-form expressions for the exact outage probability and accurate approximation for symbol error rate of the system. Furthermore, we look into the asymptotical high signal to noise ratio regime, and characterize the diversity order achieved by the system. All the analytical results are validated via Monte Carlo simulations.

  • 42. Alves, Dimas I.
    et al.
    Machado, Renato
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Legg, Andrei P.
    Uchoa-Filho, Bartolomeu F.
    Cooperative multiple-access scheme with antenna selection and incremental relaying2014In: 2014 INTERNATIONAL TELECOMMUNICATIONS SYMPOSIUM (ITS), São Paulo: IEEE , 2014Conference paper (Refereed)
    Abstract [en]

    A cooperative multiple-access scheme for wireless communications systems with antenna selection and incremental relaying is proposed. The scheme aims to improve the system throughput while preserving good performance in terms of bit error rate. The system consists of N nodes which send their information to both the destination node and the multiple-antenna relay station. Based on the channel state information, the destination node decides whether or not relaying will be performed. When the relaying is performed, the decode-remodulate-and-forward protocol is used with the best antenna. Results reveal that the proposed scheme achieves a good tradeoff between throughput and bit error rate, which makes suitable to be considered for multi-user networks.

  • 43. Alves, G.R.
    et al.
    Marques, M.A.
    Viegas, C
    Lobo, M.C. Costa
    Barral, R.G.
    Couto, R.J.
    Jaob, F.L.
    Ramos, C.A.
    Vilao, G.M.
    Gustavsson, Ingvar
    Using VISIR in a large undergraduate course: Preliminary assessment results2011Conference paper (Refereed)
    Abstract [en]

    The use of remote labs in undergraduate courses has been reported in literature several times since the mid 90's. Nevertheless, very few articles present results about the learning gains obtained by students using them, especially with a large number of students, thus suggesting a lack of data concerning their pedagogical effectiveness. This paper addresses such a gap by presenting some preliminary results concerning the use of a remote laboratory, known as VISIR, in a large undergraduate course on Applied Physics, with over 500 students enrolled.

  • 44. Alvesund, Carolin
    Att minska beroendet av motoriserade transporter: en fråga om att kunna och vilja!1998Report (Other academic)
    Abstract [en]

    The report includes (i) planning measures potential on reducing the dependency of motorized transports, (ii) the intrest of municipals and county administrative boads on reducing the dependency of motorized transports and (iii) legal potentials on reducing the dependency of motorized transports.

  • 45.
    Amerineni, Rajesh
    Blekinge Institute of Technology, School of Engineering.
    Multi Channel Sub Band Wiener Beamformer2012Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    With the recent advance in microphone array speech processing, achieving robustness of speaker localization becomes most significant aspect. At the same time considerable research growth is performed in developing the multiple microphone sensors equipped rooms are developed also called as smart rooms for real time applications. The accuracy of speaker localization is down casted by acoustic noise and room reverberations. In distributed meeting environment speaker localization is performed by far field microphone arrays with the help of beamforming. But far field Microphone performance is degraded by room reverberations and acoustic noise. In this master thesis, speaker localization with two adaptive beamforming techniques in distributed meeting application in reverberated environment with the help of far filed microphone arrays is design and implemented. The two beamforming methods examined are multichannel wiener beamformer and multichannel sub band wiener beamformer. These methods use wiener filtering technique for their implementation and they are implemented to capture the human voice using widely separated microphone arrays even when irregular disturbances are present. A smart room is developed with Image source model for generating reverberation in which beamformers are implemented. In sub band beamformer WOLA filter bank is designed. The sub band beamforming is further extended to steered response power with phase transform for speaker localization is achieved with the cross correlation but speech is heavily degraded by the noise which can be further studied to eliminated it. Finally the quality of the speech is tested using SNR and PESQ (Perceptual Evaluation of Speech Quality) and also the performance of the system with respect to reverberation time is calculated. The results show that the two implementations are acceptable in terms of PESQ score.

  • 46.
    Ande, Santosh
    Blekinge Institute of Technology, School of Engineering.
    Stereo Echo Cancellation(SEC) employing Signal Decorrelation with emphasis on Affine Projection Algorithm(APA)2013Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Monophonic tele-conferencing systems employ acoustic echo cancellation (AEC) to reduce echoes that result from coupling between loudspeaker and microphone. Acoustic echo cancellation is simple to develope as there is a single channel. But future tele conferencing systems are expected to have multi channel communication which is necessary in hands-free multi user tele communication systems. Stereophonic echo cancellation (SEC), has been studied since the early 1990s, in hands-free tele communication applications such as tele conferencing, multi user desktop conferencing, and tele video gaming. To enhance the sound realism in order to increase the speech intelligibilty it is necessary to use two channel (stereo) audio systems. This requires SEC systems. In SEC there is a fundamental problem that the adaptive algorithm used can not identify correct echo path responses due to strong correlation between stereo signals and also the convergence is slow. In this case it is necessary to identify two echo paths for each channel thus there are four echo paths to identify which is very difficult. In this thesis, the problems with stereo echo cancellation is explained and echo cancellation with emphasis on two channel affine projection algorithm (APA) is studied. The signal de-correlation techniques are reviewed and compared. The idea behind signal decorrelation techniques is to introduce nonlinearity into each channel. This can be done by using half-wave rectifiers or time varying all-pass filters.Three methods were developed to reduce correlation between stereo signals. One, is to use two positive half-wave rectifiers on both channels considered as NLP1. Second, is to use positive and negative half-wave rectifiers on each channel (NLP2). Third, is to use time varying all-pass filters (TV-APF) on both channels with delays. Experiments were performed using MATLAB and observed echo return loss enhancement (ERLE) and misalignment(MIS) with different scenarios. The euclidean norm distance calculation has been used to find out MIS between filter coefficients and true echo path models. It is observed that NLP1 and NLP2 lack signal perception even though ERLE was good. The MIS falls down below 25dB with decorrelated stereo signals. The use of TV-APFs gives good echo cancellation and does not effect the signal perception, the ERLE in this case was 40.3231dB.

  • 47. Andrén, Linus
    Active suppression of vibration and noise in industrial applications2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Today, active control technology is about to emerge from the research labs into products in various areas. It has become an attractive method where passive techniques have low impact at low frequencies and adding active control to that part is often an attractive solution. The active control technique has been enabled by the rapid development of digital signal processors over the last decades. The focal point in this thesis is active vibration and noise suppression. Two different industrial applications have been subjected to active control to reduce unwanted disturbances. In cutting operations, active vibration suppression has been applied to both external turning and boring operations with successful results. Turning operations, and in particular boring operations, are typical examples of chatter prone machining. In order to implement active vibration control in boring operations a thourough investigation of the boring process has been made in the first two parts in this thesis. The following two parts of the thesis treat active vibration suppression in external turning operations and in boring operations. The second industrial application treats the noise in a fork-lift truck. In the final part of the thesis, active noise suppression has been implemented in the cabin of a fork-lift truck.

  • 48. Andrén, Linus
    et al.
    Håkansson, Lars
    Active Vibration Control of Boring Bar Vibrations2004Report (Other academic)
    Abstract [en]

    The boring operation is a cumbersome manufacturing process plagued by noise and vibration-related problems. A deep internal boring operation in a workpiece is a classic example of chatter-prone machining. The manufacturing industry today is facing tougher tolerances of product surfaces and a desire to process hard-to-cut materials; vibrations must thus be kept to a minimum. An increase in productivity is also interesting from a manufacturing point of view. Penetrating deep and narrow cavities require that the dimensions of the boring bar are long and slender. As a result, the boring bar is inclined to vibrate due to the limited dynamic stiffness. Vibration affects the surface finish, leads to severe noise in the workshop and may also reduce tool life. This report presents an active control solution based on a standard boring bar with an embedded piezo ceramic actuator; this is placed in the area of the peak modal strain energy of the boring bar bending mode to be controlled. An accelerometer is also included in the design; this is mounted as close as possible to the cutting tool. Embedding the electronic parts not only protects them from the harsh environment in a lathe but also enable the design to be used on a general lathe as long as the mounting arrangements are relatively similar. Three different algorithms have been tested in the control system. Since the excitation source of the original vibrations, i.e. the chip formation process cannot be observed directly, the algorithms must be constructed on the basis of a feedback approach. Experimental results from boring operations show that the vibration level can be reduced by 40 dB at the resonance frequency of a fundamental boring bar bending mode; several of its harmonics can also be reduced significantly.

  • 49. Andrén, Linus
    et al.
    Håkansson, Lars
    Brandt, Anders
    Claesson, Ingvar
    Identification of Dynamic Properties of Boring Bar Vibrations in a Continuous Boring Operation2004In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 18, no 4, 869-901 p.Article in journal (Refereed)
    Abstract [en]

    Vibrations in internal turning operations are usually a cumbersome part of the manufacturing process. This article focuses on the boring bar vibrations. Boring bar vibrations in alloyed steel, stainless steel and cast iron have been measured in both the cutting speed direction and the cutting depth direction with the aid of accelerometers. The dynamic response of a boring bar seem to be a time varying process that exhibits non-linear behaviour. The process is influenced by non-stationary parameters that are not under the control of the operator or experimenter. The vibrations are clearly dominated by the first resonance frequency in one of the two directions of the boring bar. The problem with force modulation in rotary machinery, which appears as side band terms in the spectrum, is also addressed. Furthermore, the resonance frequencies of the boring bar are correlated to an Euler-Bernoulli beam model.

  • 50. Andrén, Linus
    et al.
    Håkansson, Lars
    Brandt, Anders
    Claesson, Ingvar
    Identification of Motion of Cutting Tool Vibration in a Continuous Boring Operation: Correlation to structural Properties2004In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 18, no 4, 903-27 p.Article in journal (Refereed)
    Abstract [en]

    The internal turning operation has a history of being a cumbersome metal working process as vibration in boring operations is usually inevitable. In this article, the deflection shapes and/or mode shapes as well as the resonance frequencies of a boring bar have been put under scrutiny. Three methods have been used in order to investigate dynamic properties of a clamped boring bar: a theoretical Euler-Bernoulli beam model, an experimental modal analysis and an operating deflection shape analysis. \\ The results indicate a correlation between the shapes of the deflection shapes and/or mode shapes produced by the three different analysis methods. On the other hand, the orientation of the forced deflection shapes and/or mode shapes and the resonance frequencies demonstrates differences between the three methods. During continuous cutting, it is demonstrated that the bending motion of the first two resonance frequencies is to a large extent in the cutting speed direction.

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