Subcarrier Requirement Analysis For Downlink OFDMA Cellular Network

OFDMA cellular mobile communication is an effective scheme. In the OFDMA cellular network, spectrum resources are divided into a set of narrow band subcarriers which are orthogonal to each other. When the user initiates a call, a group of subcarriers are allocated to meet the data rate requirement and then the call is allowed. The user is not interfered by the subcarrier in the same cell, but it is interfered by the users in the neighboring cell who are allocated the same subcarriers.In this thesis, OFDMA single-hop cellular network and OFDMA Multi-hop cellular network is researched respectively. Firstly, the inter-cell interference on downlink is analyzed, based on the key technologies such as OFDMA, relay, subcarrier allocation algorithm etc. The mean value, variance and cumulative distribution function are obtained based on the interference signal ratio(ISR). Secondly, using random subcarrier allocation, the number of subcarrier is determined according to the data rate requirement. From the relation between subcarrier requirement and ISR, the threshold of ISR and the probability distribution function of subcarrier requirement is ensured. Then the average subcarrier requirement is quantized. Finally, by the simulation, the effects of the parameters such as path loss, cell radius and data rate on the subcarrier requirement and system performance are analyzed, and the correctness of the theoretical calculation results is verified. During simulation, the number of subcarriers is compared in three cases using grouping subcarrier allocation, random subcarrier allocation and adaptive subcarrier allocation respectivelyIt is shown that the introduction of relay technology can improve the capacity of OFDMA cellular network. The study results are useful for the system performance improvement, network architecture design, resource planning and call admission of the OFDMA cellular network.