Η αυξημένη ζήτηση για λήψη δεδομένων της πολυμεσικής Broadcast/Multicast υπηρεσίας από τους χρήστες των δικτύων κινητών επικοινωνιών τρίτης γενιάς, απαιτεί την κατανάλωση μεγάλων ποσών ισχύος για την εξυπηρέτησή τους, ενώ η διαθέσιμη ισχύς των δικτύων είναι περιορισμένη. Με στόχο, την αποδοτικότερη χρήση των ποσών ισχύος του συστήματος, και την εξυπηρέτηση με τον τρόπο αυτό περισσότερων χρηστών, αλλά με ταυτόχρονη διατήρηση της ποιότητας της υπηρεσίας, έχουν προταθεί κάποιες τεχνικές οι οποίες οδηγούν σε μείωση της εκπεμπόμενης ισχύος. Στην διπλωματική αυτή εργασία, αναλύονται αρχικά τα δίκτυα τρίτης γενιάς καθώς και η πολυμεσική Broadcast/Multicast υπηρεσία. Στη συνέχεια, περιγράφονται όλες οι τεχνικές που έχουν προταθεί, και με την χρήση κατάλληλου λογισμικού προσομοιώνεται μία από τις τεχνικές αυτές. Τα ποσοστά μείωσης ισχύος, που προκύπτουν ως αποτελέσματα της προσομοίωσης αυτής, αποδεικνύουν την σημαντική μείωση της εκπεμπόμενης ισχύος που μπορεί να επιτευχθεί με την χρήση της τεχνικής αυτής. / The increased demand for data download of the Multimedia Broadcast/Multicast service by the users of the mobile third generation networks, requires the consumption of large power amounts for their service, while the available power of the networks is limited. With the view of more efficient usage of the system power resources, and the service in this way of more users, but with the simultaneous maintenance of the quality of service, they have been proposed some techniques which lead to the reduction of the transmitted power. In this work, initially, the third generation networks and the Multimedia Broadcast/Multicast service are being analyzed. Afterwards, all the techniques that they have been proposed are being described, and with the usage of the appropriate software, one of these techniques is being simulated. The power reduction percentages, that they come of as a result of this simulation, prove the significant transmitted power reduction, which can be achieved with the usage of this technique.

Network coding refers to the implementation of coding methods to utilize network connections more efficiently. Network coding is commonly researched in the information theory field, but very little research is being done on the physical implementation thereof. One exception is COPE where network coding is implemented in wireless networks for unicast transmission sessions. In this dissertation, we discuss the physical arrangement of wireless nodes to form topologies suitable for the implementation of network coding. We implement linear network coding in wireless ad hoc networks for multicast transmission sessions. We calculate the areas in which each wireless node must be located for a specific network coding suitable topology to be formed. The identified topologies are simulated in OPNET Modeler and then implemented on a six node testbed, to analyse the effect of implementing network coding in these topologies. We provide results indicating the trade-off between reduced network load and higher end-to-end delay when our developed network coding algorithm is active in the respective topologies. The results indicate that the developed network coding scheme will produce better overall performance when implemented in sensor networks or highly congested ad hoc networks. / Thesis (M.Ing. (Computer and Electronical Engineering))--North-West University, Potchefstroom Campus, 2011.

Network coding refers to the implementation of coding methods to utilize network connections more efficiently. Network coding is commonly researched in the information theory field, but very little research is being done on the physical implementation thereof. One exception is COPE where network coding is implemented in wireless networks for unicast transmission sessions. In this dissertation, we discuss the physical arrangement of wireless nodes to form topologies suitable for the implementation of network coding. We implement linear network coding in wireless ad hoc networks for multicast transmission sessions. We calculate the areas in which each wireless node must be located for a specific network coding suitable topology to be formed. The identified topologies are simulated in OPNET Modeler and then implemented on a six node testbed, to analyse the effect of implementing network coding in these topologies. We provide results indicating the trade-off between reduced network load and higher end-to-end delay when our developed network coding algorithm is active in the respective topologies. The results indicate that the developed network coding scheme will produce better overall performance when implemented in sensor networks or highly congested ad hoc networks. / Thesis (M.Ing. (Computer and Electronical Engineering))--North-West University, Potchefstroom Campus, 2011.

Device-to-device (D2D) networking enables direct discovery and communication between cellular subscribers that are in proximity, thus bypassing the base stations (BSs). In principle, exploiting direct communication between nearby mobile devices will improve spectrum utilization, overall throughput, and energy consumption, while enabling new peer-to-peer and location-based applications and services. D2D-enabled broadband communication technology is also required by public safety networks that must function when cellular networks are not available. Integrating D2D into cellular networks, however, poses many challenges and risks to the long-standing cellular architecture, which is centered around the BSs. This dissertation identifies outstanding technical challenges in D2D-enabled cellular networks and addresses them with novel models and fundamental analysis. First, this dissertation develops a baseline hybrid network model consisting of both ad hoc nodes and cellular infrastructure. This model uses Poisson point processes to model the random and unpredictable locations of mobile users. It also captures key features of multicast D2D including multicast receiver heterogeneity and retransmissions while being tractable for analytical purpose. Several important multicast D2D metrics including coverage probability, mean number of covered receivers per multicast session, and multicast throughput are analytically characterized under the proposed model. Second, D2D mode selection which means that a potential D2D pair can switch between direct and cellular modes is incorporated into the hybrid network model. The extended model is applied to study spectrum sharing between cellular and D2D communications. Two spectrum sharing models, overlay and underlay, are investigated under a unified analytical framework. Analytical rate expressions are derived and applied to optimize the design of spectrum sharing. It is found that, from an overall mean-rate perspective, both overlay and underlay bring performance improvements (vs. pure cellular). Third, the single-antenna hybrid network model is extended to multi-antenna transmission to study the interplay between massive MIMO (multi-input multiple-output) and underlaid D2D networking. The spectral efficiency of such multi-antenna hybrid networks is investigated under both perfect and imperfect channel state information (CSI) assumptions. Compared to the case without D2D, there is a loss in cellular spectral efficiency due to D2D underlay. With perfect CSI, the loss can be completely overcome if the number of canceled D2D interfering signals is scaled appropriately. With imperfect CSI, in addition to pilot contamination, a new asymptotic underlay contamination effect arises. Finally, motivated by the fact that transmissions in D2D discovery are usually not or imperfectly synchronized, this dissertation studies the effect of asynchronous multicarrier transmission and proposes a tractable signal-to-interference-plus-noise ratio (SINR) model. The proposed model is used to analytically characterize system-level performance of asynchronous wireless networks. The loss from lack of synchronization is quantified, and several solutions are proposed and compared to mitigate the loss. / text