Time domain channel estimation method for uplink OFDMA system

Orthogonal Frequency Division Multiple Access (OFDMA) is considered as one of promising wireless access techniques which can accommodate multiple users flexibly and efficiently. In the uplink OFDMA system, it is required to estimate all users´ channel frequency responses (CFRs) simultaneously which are used in the equalization for the data information at the base station (BS). To realize this requirement, the Discrete Fourier Transform interpolation based channel estimation (DFTI-CE) method was proposed in which all users transmit one scattered pilot symbol to the BS at the same time. The DFTI-CE method can achieve higher estimation accuracy for all users´ CFRs only when the number of FFT points is equal to the number of data subcarriers which corresponds to the Nyquist rate. However the CFR estimation accuracy would be degraded in the actual OFDM system at the non-Nyquist rate in which null subcarriers (zero padding) are added at both ends of OFDM data subcarrier to reject the aliasing occurring at the output of digital to analogue (D/A) converter. To solve this problem, this paper proposes a time domain channel estimation (TD-CE) method which can achieve higher estimation accuracy even at the non-Nyquist rate. This paper presents various simulation results for the uplink OFDMA system in the time-varying fading channels to demonstrate the effectiveness of proposed estimation method.