Solving user-symbol specific phase offset problem for multiuser MIMO-OFDM fixed uplink

Previous works on carrier frequency offset (CFO) estimation for a multi-user multiple-input multiple-output orthogonal frequency division multiplexing (MU-MIMO-OFDM) uplink typically assume CFO being constant over multiple OFDM symbol periods. The assumption may not hold when an inexpensive global positioning system (GPS) receiver is used to generate a frequency reference. We propose a new channel estimation method designed for fixed MU-MIMO-OFDM uplink utilizing GPS receivers. The effectiveness of the proposed method is verified by 1) bit error probability simulation and 2) actual MU-MIMO-OFDM uplink packet transmission test in a lab involving 6 independent users in a UHF band.