Browsing by Author "Girma, Dereje"
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Item 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.Item Performance Analysis of Space Time Coding on Mimo and Cooperative Diversity System(Addis Ababa University, 2011-07) Girma, Dereje; Hailemariam, Dereje (PhD)In a wireless network, users can relay information to exploit cooperative diversity, thereby increasing reliability. The uses of multiple transmit and receive antennas (MIMO) can help to exploit transmit and receive diversity respectively. This thesis discusses the application of a technique called space time block coding (STBC) on a system based on the joint use of cooperative diversity and MIMO schemes, which we hope intuitively that the system performance can be increased further. A source node, equipped with two transmits antennas, first encodes incoming data using STBC and then broadcasts the resulting code to relay and destination nodes. Then, the two relay nodes, each equipped with single antenna, either amplify-and-forward (AF) or decode-and-forward (DF) the received codes to the destination. The destination node combines (e.g., using maximum ratio combining (MRC)) signals received from the source’s and relay’s antennas and decodes the combined signal in order to recover the original data. As the signals from the source and relay are received through different paths, which are assumed to be spatially independent, spatial diversity can be exploited. Compared with point-to-point transmission system and simple Alamouti STBC system with no relays, AF based STBC system obtains one additional benefit, achieving spatial diversity offered by the relays. Moreover, the STBC-based DF cooperative system has two additional benefits. First, it achieves the spatial diversity offered by the relay channel and secondly, it has the ability to introduce the characteristics of STBC into the relay system. In addition, the system model and performance evaluation of these systems in various channel conditions and modulations (using simulation) will be addressed.