Computer Engineering

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Browsing Computer Engineering by Author "Abdo, Mohammed (PhD)"

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    Adaptive Antenna Array Algorithms and Their Impact on Code Division Multiple Access Systems (CDMA).
    (Addis Ababa University, 2004-03) Hadgu, Dereje; Abdo, Mohammed (PhD)
    In mobile communications there is a need to increase the channel capacity. The increasing demand for mobile communication services without a corresponding increase in RF spectrum allocation (channel capacity) motivates the need for new techniques to improve spectrum utilization. The CDMA and adaptive antenna array are two approaches that shows real promise for increasing spectrum efficiency. This research focuses on the application of adaptive arrays to the Code Division Multiple Access (CDMA) cellular systems. The adaptive antenna has an intelligent control unit, so the antenna can follow the user, direct the radiation pattern towards the desired user, adapt to varying channel conditions and minimize the interference. Therefore there can be several users in the same channel in the same cell. The driving force of this intelligent control unit are special kinds of algorithms and we are going to investigate the performance of these different adaptive array algorithms in the CDMA systems. Four each blind adaptive array algorithms are developed, and their performance under different test situations (e. g. AWGN (Additive White Gaussian Noise) channel, and multipath environment) is studied. A MATLAB test bed is created to show their performance on these two test situations and an optimum one can be selected.
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    Design and Simulation of Multiband Microstrip Patch Antenna for Mobile Communications
    (Addis Ababa University, 2006-09) Mammo, Daniel; Abdo, Mohammed (PhD)
    In this thesis work a single band microstrip patch antenna having a narrow operating bandwidth around the GSM900 band is designed. Theoretical analysis and design was performed by the Finite Difference Time Domain (FDTD) method based on the electromagnetic field solver Empire software. To achieve the multiband antenna that can operate well in the: GSM (Global systems for mobile communication, 890-960 MHz), DCS (Digital cellular systems, 1710-1880 MHz), PCS (Personal Communication services, 1850-1990MHz), and UMTS (Universal Mobile Telecommunications Systems, 1920-2170MHz) bands. One needs to fine-tune the microstrip element to get dual band (GSM900 and GSM1800 bands) operation and to get a third or more operating band, one need to apply a shorted parasitic patch that is electromagnetically coupled to the main radiator. The multiband antenna posses 14-dB around the GSM 900 band of operation and greater than 8-dB return loss with bandwidths enough to cover the intended higher operating bands. As the proposed antenna can achieve such wide operating bandwidth with relatively low profile, it is very suitable for multi-band mobile communication handsets.
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    Evaluation of Various Routing Protocols for Mobile Ad-Hoc Networks (Manets
    (Addis Ababa University, 2004-09) Awash, Etsegenet; Abdo, Mohammed (PhD)
    Mobile Ad-hoc NETwork (MANET), which is a concept of mobile communication without a fixed communication infrastructure, is one of the current emerging technologies gaining much attention from both researchers and users. Because there is no as such a fixed responsible device router, each computing node is to act as a router and should be willing to forward other’s packets. Routing in mobile computing is a difficult task as we have a very dynamic network topology. Another problem is, the nodes in ad-hoc network are usually laptops and personal digital assistants and are often very limited in resources such as CPU capacity, storage capacity, battery power and bandwidth. This means, any routing protocol running on a mobile node should try to minimize routing or control packets and also be reactive. A research work group established by IETF, has set a number of requirements to be met by an ad-hoc routing protocol. According to these requirements, a number of routing protocols have been proposed broadly into two main categories, proactive and reactive. In this thesis, a detailed discussion of routing protocols from both proactive and reactive group is presented followed by simulation work using a discrete event Network Simulator called NS-2. Because these groups of routing protocols fail to satisfy all the requirements of MANET under all conditions such as high mobility, big network size and large number of traffic sources, a new scheme of hybrid routing protocol is proposed. This new routing protocol, called ZRP, is to x take advantages from both proactive and reactive group of protocols. It alleviates scalability problem of other routing protocols by classifying the network into manageable sizes called zones. ZRP combines two different routing schemes in one protocol. IntrAzone routing uses a proactive protocol to maintain up-to-date routing information to all nodes within its routing zone. By contrast intErzone route discovery is based on a reactive route request and reply scheme. Simulation results of this thesis work shows that ZRP performs well under all conditions especially when we have large network size.
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    Implementation of Energy-Efficient Routing Protocols for Mobile Ad hoc Networks (MANET
    (Addis Ababa University, 2004-08) Girma, Dereje; Abdo, Mohammed (PhD)
    The nodes in a mobile ad hoc network also form its routing infrastructure. Previous research shows that the idle power consumption in the nodes is significant, as the network interfaces on them is always on in order to maintain the routing fabric. As mobile nodes are dependent on battery power, there is a need for protocols that minimize energy consumption. In this thesis, the Dynamic Source Routing protocol used for on-demand routing in an ad hoc network is modified to reduce the power consumption in nodes by adaptively putting their interfaces to sleep. In an ad hoc network, it is impossible to predict accurately when it is all right for a node to put its network interface to sleep, using only its own information. In the approach presented, the time slot during which the interface is on is alternated with a time slot during which the interface is put to sleep. The duration of the on period depends only on indigenously available information about the number of packets the interface receives during this time slot. In the absence of any network activity in the on slots, the sleep period is linearly increased up to a maximum. The report explains all the factors that can affect the performance of the modified routing protocol and its influence on the energy consumption in the network. The penalty of increase in delay and packet loss is unavoidable and the levels of the factors are identified to minimize the penalty. The modified protocol is implemented in the Ns-2 network simulator. A linear equation is used to model the energy consumption for each node in the network. Simulations are conducted to test the modified protocol and the factors varied to study their impact. The results are compared with those obtained from the simulations using the unmodified DSR protocol. The results show average energy savings per-packet of up to 25% with an average of 2-3ms per-packet increase in the delay. The packet loss is comparable to the unmodified DSR protocol.
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    Performance Evaluation on Transmitter Detection Techniques for Cognitive Radio
    (Addis Ababa University, 2010-10) Gared, Fikreselam; Abdo, Mohammed (PhD)
    Wireless communications and the utilization of the radio frequency spectrum have witnessed a tremendous boom during the past few decades. Given the limitations of the natural frequency spectrum, it becomes obvious that the current static frequency allocation schemes cannot accommodate the requirements of an increasing number of higher data rate devices. Cognitive Radio has come after several studies indicating that most of the allocated radio spectrum is idle most of the time. As a result, spectrum regulation around the world is in progress to allow unlicensed access in a non-interfering way. Cognitive radio is a candidate technology for more efficient spectrum utilization systems based on opportunistic spectrum sharing. But to avoid interference, effective detection of primary users is a major issue of cognitive radio. In this thesis work, various literature reviews on cognitive radio and detection theory by different authors which help to understand necessary theoretical background for thesis work have been made. Performance of energy detector, replica correlation detector and cooperative detector has been evaluated using different performance metrics and the performance of energy detector has been enhanced. To evaluate the performance of the detection techniques MATLAB software has been used for simulation. The results of performance evaluation for the detectors have shown that the replica correlation detector (delivers Pm of less than 1%) is better than energy detector (delivers Pm of less than 10% but greater than 1%) under both AWGN and Rayleigh fading channel. But due to fading, single node detection is unreliable and results in a high probability of missed detection and lower probability of correct detection. Thus, Rayleigh fading degrades the performance of single node energy and replica correlation detectors. It has been shown that cooperative detection helps to reduce the fading effect of single node detection and it is concluded that cooperative spectrum detection outperforms single user energy detection and replica correlation detector. Thus, the OR fusion rule of cooperative detection delivers better performance. In this paper, noise uncertainty has been shown to introduce considerable amount of degradation in the detection performance of energy and replica correlation ii detectors. It has been also shown that cooperative detection helps to reduce the effect of noise uncertainty factor in the overall detection performance of cognitive radio. Finally, this work proposes a new enhanced energy detector algorithm method. Its performance has been compared with standard squared law energy detector algorithm. The Simulation results indicate that the new energy detector algorithm method has better performance than square law energy detector. The enhanced energy detector delivers probability of detection 12% better than square law energy detector. Keyword: cognitive radio, hypothesis test and spectrum detector (energy, replica correlation and cooperative detector)
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    Quantum Detection- Optimal Quantum Receiver Performance Analysis For Free Air Channel
    (Addis Ababa University, 2004-02) Oumer, Abdulrezak; Abdo, Mohammed (PhD)
    T h e f u n d ame n t a l p e r f o rma n c e l imi t s o f o p t i c a l c ommu n i c a t i o n s s y s t ems o p e r a t i n g o v e r t h e f r e e - s p a c e c h a n n e l wi l l b e e x ami n e d u s i n g q u a n t um d e t e c t i o n p r i n c i p l e . T h e p e r f o rma n c e o f t h e o p t imum q u a n t um r e c e i v e r f o r On /O F F k e y i n g a n d B i n a r y P h a s e - s h i f t k e y i n g Op t i c a l mo d u l a t i o n f o rma t i n t e rms o f q u a n t um me a s u r eme n t s t a t e s wh o s e p e r f o rma n c e i s o p t imi z e d v i a g e n e r a l i z e d r o t a t i o n i n H i l b e r t s p a c e i s f i r s t e x ami n e d a s a p u r e - s t a t e ( n o - n o i s e ) p r o b l em. T h e p e r f o rma n c e o f q u a n t um r e c e i v e r f o r M- a r r a y p u l s e - p o s i t i o n mo d u l a t i o n ( P PM) , wh i c h r e q u i r e s a p r o d u c t s t a t e r e p r e s e n t a t i o n , a n d (M- 1 ) d ime n s i o n a l r o t a t i o n a l A l g o r i t hm wi l l b e e v a l u a t e d wi t h t h e d e v e l o pme n t o f a n e f f i c i e n t r o t a t i o n a l a l g o r i t hm a n d a c omp u t e r p r o g r amme f o r c a r r y i n g o u t t h e r e q u i r e d n ume r i c a l o p t imi z a t i o n i s d e s c r i b e d a n d a p p l i e d . P e r f o rma n c e c omp a r i s o n s s h ows s u b s t a n t i a l imp r o v eme n t wh e n q u a n t um d e t e c t i o n p r i n c i p l e i s emp l o y e d . A s a f u r t h e r a p p l i c a t i o n o f t h e q u a n t um d e t e c t i o n p r i n c i p l e , t h e R e a l i z a t i o n o f q u a n t um d e t e c t i o n O p a r a t o r F o r M- a r r a y P h a s e s h i f t o p t i c a l mo d u l a t i o n f o rma t i s a l s o p r e s e n t e d .