DSpace Collection: Thesis - Electrical Engineering

Cooperative MIMO System for WiMAX Technology

Mon, 15 Apr 2013 07:54:26 GMT

Title: Cooperative MIMO System for WiMAX Technology

Authors: Samuel, Medhn

Abstract: Multipath fading is one of the primary factors that degrade the performance of wireless networks. One of the most powerful techniques to combat the effect of fading is by using multiple antennas that provides space diversity and spatial multiplexing; this technique is called Multiple-Input Multiple-Output (MIMO). Cooperative diversity, an alternative form of realizing MIMO, has been recently proposed to realize the diversity advantage in a distributed manner. Cooperative diversity exploits the broadcast nature of wireless transmission and creates a virtual antenna array through cooperating nodes. Although, prior research in cooperative diversity considers users equipped with single antenna, in practical scenarios users may be able to accommodate multiple antennas due to the recent advances in semiconductor industry. Hence, the primary purpose of this thesis is to model, and by using simulation, investigates the end-to-end performance of a cooperative diversity system employing multi-antenna at cooperating nodes; the intention is to simultaneously exploit the diversity gain offered by the cooperative diversity and multiple antennas. One contribution of this work is, we propose a cooperative MIMO system where the cooperation uses amplify-and-forward (AF) relaying strategy and the MIMO is based on Vertical Bell-Labs Layered Space Time architecture (VBLAST). The proposed system is to be used for WiMAX technology. Complexity of the cooperative MIMO system is also analyzed considering Maximum Ratio Combining (MRC) and Equal Gain Combining (EGC) schemes for Zero Forcing (ZF), Minimum Mean Square Error (MMSE) and Maximum Likelihood (ML) detection techniques. Simulation results show that cooperative MIMO system achieves significantly better symbol error rate (SER) performance than conventional cooperative diversity and MIMO systems with comparable complexity. As an example, for SER of 10-3, cooperative MIMO system using MMSE detection has 10 dB SNR gain over systems that employ cooperative diversity or MIMO only.

DSP BASED IMPELEMENTATION OF FIELD-WEAKENING ON SYNCHRONOUS MOTOR FOR HIGH SPEED OPERATION

Mon, 15 Apr 2013 07:47:38 GMT

Title: DSP BASED IMPELEMENTATION OF FIELD-WEAKENING ON SYNCHRONOUS MOTOR FOR HIGH SPEED OPERATION

Authors: HENOK, BEREHANU

Abstract: Permanent magnet motors have high efficiency and torque density compared to induction and conventional synchronous motors in general. However, in applications requiring wide speed range, the air-gap field, which is produced by the permanent magnets, can’t be controlled directly to control the back-emf of the motor for field weakening operation. In conventional synchronous machines the excitation current can be controlled to control the field and hence the speed. This thesis presents development of field weakening control for Permanent Magnet Synchronous Motor (PMSM) using demagnetizing component of stator current. The control is implemented using Texas Instruments’ TMS320LF2401A Digital Signal Processor (DSP). The control method presented relies on the field orientated control (FOC) together with a field-weakening operation. The field-weakening operation is required to extend the speed in the constant power range of operation, where there is no more voltage adjustment possible to increase the speed. The field oriented control of the motors has been modeled, simulated using MATLAB and Some of the modules of field oriented control are tested practically and results are given in this thesis. The results demonstrate that the speed of the PMSM can be extended in the constant power range for applications requiring wide speed range like in electric vehicle.

Noise Robust Speaker Verification using SVM based GMM Supervector

Tue, 05 Mar 2013 06:04:34 GMT

Title: Noise Robust Speaker Verification using SVM based GMM Supervector

Authors: Bezawit, Wubishet

Abstract: This thesis shows research performed on the topic of text-independent speaker verification using support vector machine (SVM) based Gaussian mixture model (GMM) supervector classifier in the presence of environmental noise conditions. The basis is to use model based approaches to make the verification task noise robust. In this report, two model based approaches are applied. In the first approach, speaker model adaptation is implemented based on the noise condition observed during verification. In the second approach, multi-condition training is adopted in which multiple speaker models are trained using multiple noisy speech samples. In both approaches a range of signal to noise ratios are considered. The system is implemented in MATLAB. In addition, LibSVM toolbox is used as SVM trainer. The report gives an overview of speaker verification system. Methods and algorithms for speaker modeling are explained. The performance of the system in clean and environmental noise conditions is tested for both target trials and impostor trials. For clean training conditions, on average, results show that using GMM-SVM classifier improves the classification accuracy of Gaussian mixture model universal background model (GMM-UBM) classifier in terms of EER by 4.39% and 2.77% for babble and white noise, respectively. For test utterance corrupted by additive noise, test results show that multi-condition based noise compensation approach achieve from 1.34 % to 4.8 % improvement for GMM-UBM classifier and from 0.5 % to 3.08 % improvement for GMM-SVM classifier when compared with the corresponding standard classifiers. Experiments are performed using utterances of speakers from the free audio book collection found on the online digital library LibriVox. Results obtained are presented in terms of detection error tradeoff (DET) curve and equal error rate (EER).

Analysis and Evaluation of Diversity-Multiplexing Tradeoff for Multiple-Antenna systems in Ultra Wideband (UWB-MAS) and Rake Receiver

Thu, 21 Feb 2013 08:44:22 GMT

Title: Analysis and Evaluation of Diversity-Multiplexing Tradeoff for Multiple-Antenna systems in Ultra Wideband (UWB-MAS) and Rake Receiver

Authors: Gebremariam, Hailu

Abstract: Ultra wide-band (UWB) systems have recently attracted much research interest owing to their appealing features in short-range wireless communications. These features include high data rates, low power consumption, multiple access communications, and precise positioning capabilities.On the other hand, multiple antenna systems (MAS) and space-time coding (STC) techniques, such as space time block coding (STBC) are well known for their great potential to play a significant role in the design of the next- generation broadband wireless communications. Multiple-Input Multiple-Output (MIMO) system extends the link reliability (spatial diversity (SD)) and increase throughput,(spatial multiplexing (SM)).However, there is a fundamental tradeoﬀ(DMT) between how much of each type of gain in any coding scheme can extract. In this thesis the approach for multi-antenna system is to obtain tradeoff between SD and SM gains for UWB technology. Atheoretical analysis is conducted to enlighten the DMTfor UWB-MAS (UWB- MISO/SIMO) and therefore; performance enhancements provided by the proposed scheme compared to the classic single link scheme is evaluatedat ﬁnite signal-to-noise ratios (SNRs).The tradeoff curves provide a characterization of achievable SD and SM for a given space-time code at SNR’s encountered in practice. A Rake receiver is employed that captures energy from sequences transmitted from N transmit antennas at M receive antennas in a subset of the resolvable multipath components. Exact diversity gain expressions are determined for orthogonal space–time block codes (OSTBC). It is shown that the asymptotical diversity gain has an infinite valueeven with single-antenna systems and the multi-antenna techniques can be very beneficial in the practical range of signal-to-noise ratios. Comparisons are also provided with DMT results in the literature and found thatcodes that are not optimal over the Rayleigh fading channels are also not optimal over the UWB channels.