Dynamic Resource Allocation in Packet-Oriented Multi-Cell OFDMA Systems

Over the last decade, the scope of cellular networks has been shifted from low bit rate voice delivery to high bit rate multimedia services. Consequently, cellular systems have evolved from the circuit switched to the packet oriented system architecture, and an integration with the Internet has taken place. The perpetual need for higher data rates in such systems has caused the development of efficient transmission and medium access techniques. The currently most popular one among them is orthogonal frequency division multiple access (OFDMA). In general, OFDMA systems split the overall system bandwidth into a number of low data rate sub-channels. Each high data rate stream arriving at the transmitter is split into several low data rate streams that are transmitted in parallel over a sub-set of the available sub-channels, where distinct subsets can be assigned to different active terminals. Lately, it has been shown that the system’s transmission capacity and quality can be significantly improved, if the sub-channels and the available transmission power are dynamically allocated among the terminals according to their instantaneously experienced channel quality. These performance gains, however, come at the cost of significant signaling overhead and increased system complexity. Moreover, the dynamic mechanisms have originally been developed for systems that differ from packet-oriented cellular systems in three major points: the packet nature of the traffic, the quality and quantity of the required control signaling data, and the particular interference situation of cellular systems. This thesis faces the challenges that arise from these three differences when deploying the dynamic mechanisms in the downlink of packet-oriented cellular OFDMA based systems. In particular, mathematical optimization problems are developed in order to determine the potential of the individual dynamic approaches. It is shown that by dynamically assigning the transmission resources, the system’s throughput performance, its inter-terminal fairness, as well as the transmission reliability can be significantly improved, if data and control channel resources are assigned dynamically. Furthermore, a high potential to increase the system performance is observed, if neighboring cells jointly optimize their resource utilization, instead of applying legacy interference mitigation techniques. In order to cope with the real world equipment’s limited computational power, which makes optimally solving the mathematical optimization problems in real-time impossible, individual heuristic algorithms are developed to sub-optimally solve them: a combined data channel packet scheduling/resource allocation algorithm, a control channel dynamic power allocation algorithm, a control channel dynamic coding algorithm, and an inter-cell power coordination algorithm. In summary, this thesis demonstrates the potential of using dynamic mechanisms in packet-oriented cellular OFDMA based networks and presents means to efficiently deploy them in real world systems.