Browsing by Author "Gidey, Tesfay"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    Magnetic Field Decay Due to Gravitational Radiation in Neutron Star
    (Addis Ababa University, 11/3/2017) Gidey, Tesfay; Reshid, Remudin (PhD)
    In this thesis, magnetic _eld decay due to gravitational radiation in neutron star (NS) is theoretically studied. By considering the inuence of the \dynamo mechanism"on the generation of a strong magnetic _eld in NS. A NS formed as a large star die in a type II supernova, and their magnetic _elds during formation is 1012 Gauss and 1015 Gauss for both magnetars and pulars, respectively. But their magnetic _eld is decreased. Thus, this study focuses on by how much does the magnetic _eld decay using the mathematical calculation of decay law equation. Based on our _ndings, we have two results. The _rst result shows that, the magnetic _eld of a rotating NS depends only on the decaying time since the moment of inertia is constant. The second result also shows, the magnetic _eld of a rotating NS depends on the decaying time and rotational frequency since moment of inertia varies as a function of rotational frequency. The variation in moment of inertia causes to the variation in braking index as a function of rotational frequency. Thus, the quadrapole magnetic _eld is decaying for positive _ and increased for negative _ , respectively.
  • No Thumbnail Available
    Item
    Magnetic Field Decay Due to Gravitational Radiation in Neutron Star
    (Addis Ababa University, 2017-11-03) Gidey, Tesfay; Reshid, Remudin (PhD)
    In this thesis, magnetic _eld decay due to gravitational radiation in neutron star (NS) is theoretically studied. By considering the inuence of the \dynamo mechanism"on the generation of a strong magnetic _eld in NS. A NS formed as a large star die in a type II supernova, and their magnetic _elds during formation is 1012 Gauss and 1015 Gauss for both magnetars and pulars, respectively. But their magnetic _eld is decreased. Thus, this study focuses on by how much does the magnetic _eld decay using the mathematical calculation of decay law equation. Based on our _ndings, we have two results. The _rst result shows that, the magnetic _eld of a rotating NS depends only on the decaying time since the moment of inertia is constant. The second result also shows, the magnetic _eld of a rotating NS depends on the decaying time and rotational frequency since moment of inertia varies as a function of rotational frequency. The variation in moment of inertia causes to the variation in braking index as a function of rotational frequency. Thus, the quadrapole magnetic _eld is decaying for positive _ and increased for negative _ , respectively.
  • No Thumbnail Available
    Item
    Performance Analysis and Investigation of Digital Symbol Detection Techniques for Single and Multi-carrier Modulations
    (Addis Ababa University, 2017-10) Gidey, Tesfay; Dereje, Hailemariam (PhD)
    During symbol transmission we may use single carrier or multi-carrier modulation. In case of single carrier transmission all users share the same transmission medium and this causes the problem of Inter Symbol Interference (ISI) which leads to error in reception. In case of multicarrier transmission there is Multiple Access Interference (MAI). In several digital communication problems, the received signal is given by a linear combination of the data symbols corrupted by channel effects. So the received symbol may be affected by transmission channel noise, interference, distortion, bit synchronization problems, attenuation, and wireless multipath-fading. Therefore efficient demodulation and symbol detection strategies are very necessary. This thesis work on symbol detection is done as per the request of Information Networks Security Agency (INSA) of Ethiopia. The industry wants to implement advanced digital receiver for local use. So the industry main aim is to review, investigate, and implement efficient symbol detection algorithms. In this paper we have considered a class of single carrier and multi-carrier symbol detection algorithms and compare their performance in terms of Bit Error Rate (BER) and Signal to Noise Ratio (SNR) of various modulation type and order. M-ary PSK and M-ary QAM have been simulated with optimum and sub-optimum detectors like Maximum-Likelihood (ML), Minimum Mean Square Error (MMSE) and Zero Forcing (ZF) detector. From our findings, for the single carrier single user case for additive White Gaussian Noise (AWGN) channel the BER at 15dB is 10 , which is acceptable. Again for the case of Rayleigh Fading channel at 35dB still we have a BER of 10 -3 . In the case of multicarrier multi user (MCCDMA) detection over Rayleigh fading channel, we have been shown how the three different detectors behave in performance and complexity analysis. Finally, it can be seen that the most complex and the best performing detector, is the Maximum Likelihood detector.