Joint Detection and CFO Compensation in Asynchronous Multi-User MIMO OFDM Systems

It is well known that carrier frequency offsets caused by inaccuracies of local oscillators between transmitter and receiver stations destroy the orthogonality among OFDM subcarriers and induce additional intercarrier interference. In conjunction with MIMO transmission where different users interfere with each other, this effect strongly degrades the signal detection performance if it is not compensated beforehand. In the uplink of multi-user systems different CFOs between all mobile terminals occur whereas its correction is more difficult. In this paper we consider the uplink of a fully asynchronous system with different transmitter and receiver CFOs which appears in distributed MIMO systems with separate users and base stations. We describe a combined scheme for joint CFO correction and spatial layer detection in frequency domain. The detection performance is shown for some selected equaliser concepts. In this way we present interference cancellation algorithms with low and scalable complexity. Finally, numerical simulation results are provided to compare the detection performance.