SNR degradation due to timing and frequency synchronization errors for OFDMA systems with subband carrier allocation

Phase noise, frequency dispersion and time shifts are main challenges that concern OFDM systems. However, perfect synchronization between a transmitter and a receiver cannot be accomplished. These difficulties are dilated in an OFDMA system and consequently the performance degradation due to synchronization errors is increased. The receiver has the task to choose optimal sampling instants and to align the subcarrier frequencies of an OFDM symbol that contains signals from multiple users. In this study the effects of time and frequency synchronization errors are examined. The presented results refer to adjacent subcarrier permutation OFDMA systems where users are separated in bands of adjacent subcarriers. First an uplink OFDMA system model is presented and analytical relations explaining how synchronization errors cause both intercarrier and intersymbol interference are extracted. Then simulation results that quantify the SNR degradation due to synchronization errors are presented. The system used as a reference in this current study is the mobile WiMax with subband OFDMA allocation strategy and 1024 subcarriers.