In uplink orthogonal frequency division multiple access (OFDMA) systems, the amounts of carrier frequency offset (CFO) and symbol timing offset (STO) are different in each user. CFO and STO degrade the demodulation performance significantly. Thus, CFO and STO must be compensated for in OFDMA systems. However, since the amounts of CFO and STO are different in each user, CFO/STO compensation schemes proposed in orthogonal frequency division multiplexing (OFDM) systems cannot be used directly. In this paper, we propose a CFO/STO compensation scheme which uses time domain turbo equalization with soft cancellation. The proposed receiver can achieve CFO/STO compensation and channel equalization simultaneously by exploiting the path diversity gain. Furthermore, the extension of the processing duration of each symbol is considered to obtain a further path diversity gain. Simulation results show that the proposed receiver attains a bit error rate (BER) performance which is almost the same as that in the case without offset when the variance of offset among users is small.
['Yuusuke Miyauchi', 'Takahiko Saba']
WLC43-6: Turbo Equalization Combined Timing and Frequency Offsets Compensation in Uplink OFDMA Systems