Research On Resource Allocation Algorithm In OFDMA Downlink Systems

With the continuously requirements of wireless communication system performance, it has become one of the hottest topics in the field of wireless communication that how to use the limited radio resources efficiently to meet the increasing demand of users. Recent years, the widespread application of high data rate wireless data services and requirement of ubiquitous coverage has triggered booming energy consumption, so it is important to improve the system efficiency of wireless network and reduce energy consumption for green operation. OFDMA (Orthogonal Frequency Division Multiple Access) technology can combat the frequency selective fading caused by multi-path effects, and improve the spectral efficiency of the system. OFDMA has become one of the key technologies of the next generation mobile communication standard. Therefore, the wireless resource allocation in OFDMA systems is researched in this thesis.To reduce signaling overhead and computation overload in the subcarrier-based resource allocation algorithm, the correlation among adjacent subcarriers can be considered in OFDMA system. By properly grouping a set of consecutive subcarriers into a chunk, the chunk can be allocated in the unit of chunk. Most of the existing chunk-based resource allocation algorithm based on the idea that users in good channel conditions have privileges in obtaining resources, which would make the user in terrible channel conditions obtain less even nothing and resulting in serious unfair among users. In this thesis, chunk-based resource allocation algorithm is introduced that maximize overall system throughput on condition that the total transmit power is limited and user data rate is proportional, and integer nature of the number of bit per subcarrier is considered. The idea of the proposed algorithm is described, we compare the performance of the proposed algorithm with subcarrier-based Jang algorithm on condition that the user data rate is not proportional, subcarrier-based Shen algorithm on condition that the user data rate is proportional, chunk-based Zhu algorithm on condition that the user data rate is not proportional by simulation.Then from the perspective of system energy efficiency, this thesis uses ant colony algorithm to solve power-limited and rate-limited resource allocation problem based on optimization of energy efficiency. The idea of using ant colony system (Ant Colony System, ACS) algorithm to solve power-limited resource allocation problem based on optimization of energy efficiency and using ant system(Ant System, AS) to solve rate-limited resource allocation problem based on optimization of energy efficiency is proposed. The basic idea of ACS and AS is to mimic the behavior of ants find the shortest path from the nest to the food source through communicating with pheromone. ACS overcomes the disadvantage of slow convergence rate in solution construction process. The system model and process of the proposed algorithm are described, firstly, we compare the performance of the proposed power-limited resource allocation problem based on optimization of energy efficiency algorithm with Jang algorithm and WOERA algorithm by simulation, secondly, we compare the performance of the proposed rate-limited resource allocation problem based on optimization of energy efficiency algorithm with BAH algorithm by simulation.