CAPACITY IMPROVEMENT OF MIMO-OFDMA SYSTEM USING ADAPTIVE RESOURCE ALLOCATION ALGORITHM

Abstract

The user demands for wireless communication are increasing but the existing networks are not able to fulfill the high data rate of future communication services. More bandwidth can support high data rate wireless access. Due to spectral limitations, it is very expensive to increase. Therefore, the available bandwidth is needed to use efficiently. Orthogonal Frequency Division Multiplexing (OFDM) has been explored as a promising air interface technology to utilize the bandwidth effectively. OFDM can be exploited as a multiple access technique, called Orthogonal Frequency Division Multiple Access (OFDMA) that can support both frequency and multiuser diversity. In order to serve the user population, one of the most sophisticated techniques, resource allocation technique, can be integrated into the OFDMA system. Multiple Input Multiple Output (MIMO) technology can increase the spectral efficiency because multiple data streams can be simultaneously transmitted over the channel. The combination of MIMO technology and OFDMA system can achieve both higher spectral efficiency and better Quality of Service (QoS) such as capacity, fairness, and Bit Error Rate (BER). In this paper, a MIMO-OFDMA system is developed for downlink transmission within one single cell. Two optimization methods such as subcarrier allocation and power allocation are used for resource allocation. To decompose the MIMO channel into parallel single channels, Eigen Value Decomposition (EVD) is used. Subcarrier selection is based on the priority of the user by using the dominant eigen channels. Water-filling algorithm is adapted for power distribution among users. The aim is to maximize the system capacity subject to constraints on total power and proportional fairness. The performance of the system is evaluated by comparing the static allocation method (equal subcarrier allocation with equal power) and two adaptive allocation methods (adaptive subcarrier allocation with equal power and adaptive subcarrier allocation with adaptive power).