Signal detection through circular convolution reconstruction for OFDM system in fast varying channel

A signal detection algorithm is proposed for the orthogonal frequency division multiplexing （OFDM） sys- tem in the presence of fast time-varying channel. The channel is represented by a piece-wise linear variant model with normalized Doppler frequency of less than 0.2. The channel parameters are extracted through ISI/ICI （inter-symbol in- terference/inter-carrier interference） cancellation and circular convolution reconstruction. Meanwhile, an improved OFDM symbol detection algorithm is also proposed based on circular convolution reconstruction. The channel state in- formation in the OFDM symbol duration can be obtained accurately from the adjacent two block pilots in a linear model. The simulation results show that the proposed method can not only track the channel variation, but also promise better performance gain in the OFDM symbol detection. Furthermore, the bit error ratio （BER） is close to the perform- ance with the perfect channel state information.

Carrier Frequency Offset Compensation for an Interleaved OFDMA Uplink

This paper reports an investigation of the carrier frequency offset （CFO） compensation in the uplink of the orthogonal frequency division multiple access （OFDMA） system with interleaved subcarrier assignment. The presence of CFOs between the transmitters and the uplink receiver will destroy the orthogonality among the different subcarriers, resulting in inter-carrier interference and multiuser interference. This paper proposes a pseudoinverse CFO compensation method based on the signal structure. The proposed method can compensate the CFOs of all users simultaneously and isolate the signals from all users at the same time. Compared with the existing CFO compensation methods, the new method provides a considerable signal-to-noise ratio gain on the bit error rate performance and has a relatively low implementation complexity.