إن معدل البيانات والقدرات و التغطية و الكفاءة الطيفية في نظم الاتصالات اللاسلكية يمكن أن تتعزز مع الناقل متعدد الحوامل والهوائي المتعدد، وبالتالي يتعزز الأداء العام لمنظومات الاتصالات اللاسلكية بشكل كبير من خلال الجمع بين تقنيات أنظمة تساعد تقنية الهوائيات متعددة المداخل والمخارج في ، تجميع تقسيم ترددي متعامد و أنظمة الهوائيات متعددة المداخل والمخارج زيادة سرعة تدفق البيانات وحيث أن تقنية تجميع تقسيم ترددي متعامد تعمل على نشر القناة الترددية انتقائية التلاشى على العديد من الرموز في هذه الأطروحة، سيتم تقييم الاداء بالاعتماد على مستوى الوصلة ومستوى النظام، حيث يتمثل قياس الأداء في مقدار حصيلة البيانات ، ونصف قطر الخلية وقوة الإشارة بالنسبة إلى التداخل الضوضاء، كما يعتمد على معيار القدرة المستخدمة آخذا في الإعتبار نوع التضميين والترميز .في هذه الأطروحة تبدأ السيناريوهات من الوصلة وتمتد الي مستوى النظام في تقنية التطور طويل الأمد. لتحقيق ما ورد أعلاه: من خلال تحليل المعادلات وبرنامج المحاكاة لحساب صافي البيانات عند حافة الخلية وتغطية الخلية والسعة على الوصلة الهابطة، ثم بعد تنفيذ برنامج المحاكاه، لاحظنا الهوائيات المتعددة الإرسال تؤثر على سرعة وصول النقل وأخذا في الاعتبار أسلوب التضمين فعند الزيادة في عدد الهوائيات فان صافي البيانات تزداد أيضا ولكن يجب أن تكون متناسبة مع احتمالية الخطأ وكذلك تتحسن التغطية مع نقصان رتبة التضمين المستخدم. ان مستوى النظام مع حركة المرور المختلفة الإنتاجية للنظم وقدرة الشبكة تتحدد بواسطة عدد كتل الموارد ، حيث ان عدد هذه الكتل تعتمد على معدل سرعة بيانات الخدمة ومعدل سرعة البيانات لكل كتلة. تنتهي هذه الأطروحة بخاتمة وملخص للنتائج وكذلك بعض التوصيات وبعض المواضيع لدراسات مستقبلية كإمتداد لما تم في هذه الأطروحة. Abstract In wireless communication systems the data rate, capacity, coverage, and spectral efficiency; can be enhanced with multi-carrier transmission and multi-antenna, then the overall wireless communication system performance is greatly enhanced by combining OFDM and MIMO schemes, MIMO helps in increasing the throughput where as OFDM spreading out the frequency selective fading channel over many symbols. In this thesis evaluating performance of the system depends on both link and system levels, where the measure of performance is represented in the throughput, cell radius and the effective signal to interference plus noise ratio (SINR). It also depends on the employed capacity criterion and it takes into account the impact of adaptive modulation and coding. The worked scenarios start from a link level extending to a system level in 3GPP LTE. To achieve the above a number of tasks followed by observations are carried out. They start by analysis of the equations and a Matlab program is written to calculate the cell edge throughput, cell coverage and DL capacity. After the programs implementation, the multi antenna transmission effect is noted on the arrival throughput when taking into account the modulation technique. When increasing the order of the antenna and the throughput is also increased, but it must be traded off with the probability of error; Coverage has also improved by decreasing the order of the modulation technique. For the system level with different traffic, the overall throughput of the system and the capacity of the network are determined by the number of resource blocks (RBs). These RBs depend on the bit rate of the service and bit rate for each RB. The adopted scenarios in this thesis start from link to system, where the features are represented in a flexible base station and user configurations, channel modeling with path loss, user mobility, also at different transmitter and receiver (MIMO). The approaches are useful in single user and multi-user MIMO, then all of the above can be standardized by metrics: capacity, throughput, spectral efficiency, user QoS etc. Finally thesis conclusion and some future work as an extension of this work are presented.
هبه مدحت الزقلعى (2014)

Abstract Voice over IP (VoIP) uses the Internet Protocol (IP) to transmit voice as packets over an IP network, like the Internet, Intranets and Local Area Networks (LAN). Here the voice signal is digitized, compressed and converted to IP packets and then transmitted over the IP network. However, at the receiving end, some packets may be missed in its way due to network congestion. This packets loss degrades the quality of speech at the receiving end of a voice transmission system in the IP network. Since the voice transmission is a real time process, the receiver cannot request for retransmission of the missing packets. High speed networks provide real time variable bit rate service with packet loss requirements. The burstiness of the correlated traffic makes dynamic buffer management highly desirable to satisfy the Quality of Service (QoS) requirements. This thesis presents an algorithm to improve and optimize the Adaptive Buffer Allocation Scheme to deal with input traffic based on loss of consecutive packets in data streams and buffer occupancy levels. Buffer is designed to allow the input traffic to be partitioned into different priority classes, and based on the input traffic behavior it controls the threshold dynamically. This scheme allows input packets to enter into buffer if its occupancy level is less than the threshold value for priority of that packet. The threshold is dynamically varied in runtime based on packet loss behavior. The performance evaluation is carried out using simulation and is carried out for two and multiple priority classes of the input traffic "real time and non real time classes". The simulation results show that the Modified Adaptive Partial Buffer Sharing (ADPBS) has better performance than Adaptive Partial Buffer Sharing under the same traffic conditions.
اسماء احمد الكيش (2010)

Abstract The conflict that took place in Libya in 2011, up to the present moment, has greatly affected the electrical power network and resulted in the rise of the voltage instability problem. This was due to loss of the some major transmission lines and certain generation units. Owing to the fact that the southern region of the Libyan network has no generation units, voltage drop phenomena has become a common problem as a result of the long transmission distance, which is approximately 750km. A proposed solution in order to solve this problem is via the utilization of small mobile generation units at the network weak points. This thesis revolves around discussing the voltage instability problem within the Libyan Network and how it can be enhanced when small and mobile generation units are connected to the network weak points. It will also establish and identify where the most weakened buses and regions are so that the mobile units should be connected for the attainment of optimized solution. Moreover, this solution was proposed as it can solve not only the voltage instability problem, but it will also solve the inadequacy in generation issue by circulating additional power within the network. Hence, reduce the load shedding phenomena. Furthermore, the thesis also includes future recommendations to improve and enhance the Libyan network by the addition of new 220kV and 400kV transmission lines that will enable the network to cope with the load growth in the future
ربيع محمد عمر (2014)