For orthogonal frequency division multiplexing (OFDM) systems, the frequency synchronization and channel estimation are always tightly coupled with timing synchronization. In this paper, we investigate the effects of timing offset on the performance of a recently proposed subspace based joint carrier frequency offset (CFO) and channel estimation scheme. It is found that this scheme is highly sensitive to timing offsets. An improved timing robust scheme is then proposed. In the proposed CFO estimation scheme, the orthogonality loss between two subspaces due to timing offset is restored by exploiting a reduced null-subspace. The missing taps in the original channel estimate are recovered by using an upper bound of the channel length instead of the actual value. The effectiveness of the proposed scheme is verified by simulations.
['Jianwu Chen', 'Yik-Chung Wu', 'Tung-Sang Ng']
Timing Robust Joint Carrier Frequency Offset and Channel Estimation for OFDM Systems