A study on frequency synchronization methods for MC-CDMA systems

This work proposes novel frequency synchronization methods for time-domain spread multi-carrier CDMA (MC-CDMA) systems in which data and pilot symbols are spread in the time domain and code-multiplexed. In MC-CDMA systems, a wide continuous swath of bandwidth is divided into narrowband subcarriers. Therefore, precise compensation of carrier frequency offset is important. Moreover, in next generation mobile communication systems, we have to consider large carrier frequency offset because use of the microwave band is expected. Most OFDM-based systems, including MC-CDMA systems, use a frequency synchronization method that employs autocorrelation between guard interval and the tail part of the following OFDM symbol. However, the frequency offset acquisition range of the GI method is limited to one half of the sub-carrier spacing. Our proposal, a novel frequency synchronization approach called the "acquisition range extension method", offers a wider acquisition range through the utilization of code-multiplexed pilot symbols. Moreover, we propose the "2-step combined method", which offers both wide acquisition range and accurate synchronization by combining the acquisition range extension method and the guard interval method.