Entity

Time filter

Source Type

Addis Ababa, Ethiopia

Addis Ababa University is a state university in Addis Ababa, the capital of Ethiopia. Originally called the University College of Addis Ababa at its establishment in 1950, it was later renamed Haile Selassie I University in 1962 after the Ethiopian Emperor Haile Selassie I. The institution received its current name in 1975. Wikipedia.


Yohannes E.,Hawassa University | Hailemariam D.,Addis Ababa University
IEEE AFRICON Conference | Year: 2015

This paper presents joint adaptive modulation and multiple-input multiple-output (MIMO) system (JAMAMS) in Long Term Evolution (LTE) network that adapts both modulation type and MIMO scheme based on channel conditions. Specifically, four adaptive modulation-based MIMO techniques, namely, 1 × 2 MIMO with maximum ratio combining (MRC); 2 × 1 and 2 × 2 Alamouti techniques; and 2 × 2 Vertical Bell Labs Layered Space-Time Architecture (V-BLAST) are investigated. Bit error rate (BER) and spectral efficiency (SE) are used as performance metrics and Zero Forcing (ZF) detection is used in all the MIMO techniques. For each of the four techniques, first the signal-to-noise (SNR) thresholds for switching from one modulation order to the next (i.e., adaptive modulation) are determined. Then, based on comparison of the thresholds of the four schemes, a proposal is made when the system has to switch from one MIMO scheme to the other; and the resulting system is called JAMAMS. In the uplink scenario, as an example, adaptive modulation-based 2 × 2 Alamouti, 1 × 2 scheme with MRC, and 2 × 2 V-BLAST schemes have shown 'optimal' SE performance in the SNR ranges 4-19 dB, 19 dB-28 dB, and greater than 28 dB, respectively, while satisfying target BER constraint, BERth ≤ 10-2. Moreover, it is shown that JAMAMS has comparable computational complexity in comparison to fixed MIMO systems. © 2015 IEEE.


Medhn S.,Adigrat University | Hailemariam D.,Addis Ababa University
IEEE AFRICON Conference | Year: 2015

In this paper, we propose a cooperative Multiple-Input Multiple Output (MIMO) system where the cooperation uses amplify-and-forward (AF) relaying strategy and the MIMO is based on Vertical Bell-Labs Layered Space Time (V-BLAST) architecture. The idea is to simultaneously exploit the advantages offered by cooperative diversity and MIMO and the proposed system is intended for use in Worldwide Interoperability for Microwave Access (WiMAX) technology. Complexity of the cooperative MIMO (Co-MIMO) is also analyzed considering Maximum Ratio Combining (MRC) and Equal Gain Combining (EGC) schemes; Zero Forcing (ZF), Minimum Mean Square error (MMSE) and Maximum Likelihood (ML) detections; and V-BLAST transmission technique at transmitting node. Simulation results show that, at comparable complexity, Co-MIMO achieves significantly better symbol error rate (SER) performance than the conventional cooperative diversity or MIMO system only. As an example, at SER of 10-3, Co-MIMO system using MMSE detection has 10 dB signal-to-noise ratio (SNR) gain over systems that employ cooperative diversity or MIMO only. © 2015 IEEE.


Aschalew Y.,Bahir Dar University | Mamo M.,Addis Ababa University
IEEE AFRICON Conference | Year: 2015

In concentrated winding multi-phase permanent magnet machines, harmonic currents are intentionally injected to produce additional torque. However, harmonics result additional power losses, core temperature rise and reduction in efficiency. In this paper, analysis on the electrical power losses due to the harmonics in nine-phase permanent magnet synchronous motor is done. Analytical loss model and modified nine-phase machine, accounting for the power losses are derived. The analytical model is to generate the flux distribution in different regions of the machine and determine the losses as the result of the non-sinusoidal flux distribution. The modified model for nine-phase machine is presented to show an appropriate operating points which minimizes the total electrical loss (copper plus core loss). Comparison of power loss and efficiency in nine-phase machine with that of equivalent three phase machines is also explored. © 2015 IEEE.


Adane W.,Jimma University | Hailemariam D.,Addis Ababa University
IEEE AFRICON Conference | Year: 2015

This paper investigates orthogonal frequency division multiplexing (OFDM) based cooperative communication system for frequency flat and selective channel conditions. Carrier frequency offset (CFO) that creates inter-carrier interference (ICI) is one known problem in OFDM-based systems. The CFO problem becomes worse when OFDM is integrated into the cooperative systems as identical OFDM signal suffers from several offsets at different uncorrelated channels. To minimize the multiple CFO effects, a two step technique is proposed in this work. Firstly, a time-domain windowing is used at the transmitter to reduce the effect of frequency offset due to Doppler shift. Secondly, Maximum Likelihood (ML)-based CFO estimation is used in each of the receiving nodes to reduces the effect of synchronization errors. The performance of the time-domain windowing and the ML-based CFO estimation is investigated, separately and jointly. Then, comparison of these systems with inter-carrier interference (ICI) self-cancellation and data conjugate techniques is performed. The combined technique has a signal to noise ratio (SNR) advantage of 7dB for a sample standard bit error rate (BER) value of 10-3. © 2015 IEEE.


Kebede N.,Addis Ababa University
Eastern Mediterranean health journal = La revue de santé de la Méditerranée orientale = al-Majallah al-ihhīyah li-sharq al-mutawassi | Year: 2010

To determine the prevalence of human hydatidosis in Bahir Dar and the sex and age distribution and awareness, we used a questionnaire and retrospective analysis covering 5 years of the case reports at public health institutions in Bahir Dartown and the surrounding areas. We interviewed 244 individuals: 150 households, 32 abattoir workers, 30 butchers and 32 health professionals. None of the householders or butchers knew about cystic echinococcosis, nor did 25% of the health professionals; however, 100% of the abattoir workers and 75% of the health professionals recognized it. The householders owned on average 3 livestock and 1 dog and during holidays, ceremonies and other feasts, the community mostly practised backyard slaughter. Case book analysis between January 2002 and December 2006 showed that out of the total of 36,402 patients admitted for ultrasound examination, 24 hydatidosis cases were registered, giving a mean annual incidence rate of approximately 2.3 cases per 100,000 per year. Ultrasound was the most frequently used diagnostic method.

Discover hidden collaborations