High Accuracy Tailored Cyclic Delay Diversity in MIMO-OFDMA System with Frequency-Domain User Scheduling

Based on multi-carrier techniques, the orthogonal frequency division multiplexing access (OFDMA) scheme can support multiple user access through sub-carrier allocation. The performance of OFDMA depends on the frequency selectivity of the wireless fading channel. In order to increase the frequency selectivity, a cyclic delay diversity scheme is introduced, where multiple antennas are used to create an artificial fading channel. Using a predetermined fixed cyclic delay, the original scheme is not ensured to be optimal in various circumstances. This paper presents a multi-degree cyclic delay diversity scheme where the delay values can be tailored by each individual user with the aid of feedback channel. With sub-channel-wise channel dependent user scheduling, each sub-channel will be occupied by the user who can achieve the best performance with its reported cyclic delay values. In addition, for further performance enhancement, a new transmitter structure is proposed to provide high accuracy delay control. Computer simulation results verify the effectiveness of the proposed method.