OFDMA Interference Depression And Sub-Carrier Assignment

As an optimum version of the multicarrier transmission scheme, the Orthogonal Frequency Division Multiplexing (OFDM) transmission scheme is a promising candidate for achieving high data rate transmission in mobile environment. The series IEEE 802.16 have deployed this technology to accommodate the needs for fast access of subscribers. The research of this text is based on the OFDM technology.For accommodating more subscribers access and improving quality of the subscribers, the network needs improving radio resource management. One significant thing is to improve quality of the edge subscribers. This text focuses on the balance of the cell throughput and the edge user data rate. All methods will be simulated and analyzed by the tools of VC++ and Matlab.OFDM system assures the Orthogonality of sub carriers in the one cell, but do not promise the Orthogonality of sub carriers in the all cells. Therefore, sub carriers face serious interference from the sub carriers of the adjacent cells in the same frequency. We use soft frequency reuse scheme.In the proposed soft frequency reuse scheme, sub-carriers are divided into two groups in every cell. One group is called major sub-carriers group, and the other one is called minor sub-carriers group. The major sub-carrier can be used to cover the center of the cell area, while the minor sub-carrier is used only in the other part of the cell. This text focuses on the ratio between the center and the edge. After the simulation and analyses, we get the conclusion that if the radii of the whole cell if R, 0.8R is recommended for the center radii.In OFDMA system, another point is assignment of the sub-carrier. We research the assignment in the situation of single cell and multi cells. In the environment of multi cells, we study three schemes that are max throughput scheme, proportional fair scheme and fair rate scheme. In these three schemes, max throughput scheme focus on the cell throughput, and fair rate scheme focus on the fairness of the subscribers, and proportional fair scheme balances two sects.