Abstract:

Multi-user signal synchronization and separation for the interleaved orthogonal frequency division multiplexing (OFDMA) uplink are investigated. In interleaved OFDMA uplink, each user’s signal has a special periodic structure within an OFDMA block. Firstly, by utilizing the signal structure characteristic and subspace-based method, multi-users’ carrier frequency offsets can be obtained. Next, minimum mean square error (MMSE) filters are applied to the received signal to recover single user signal wave thus implementing user separation and frequency synchronization at the same time. Finally, based on the recovered single user training signal, each user’ timing offset can be estimated. The generalized chirp-like ( GCL ) sequence has the ideal periodic auto-correlation function, optimum periodic cross-correlation function and low peak-average power ratio (PAPR). Therefore, GCL sequences are used as training sequences to estimate each user’ timing offset. Simulation results show the proposed scheme is effective in multi-path fading channels.

Key words: orthogonal frequency division multiplexing, generalized chirp like sequence, carrier frequency offset estimation, multi-user signal separation