Field Experiments on Open-Loop Precoding MIMO Using Testbed Targeted at IMT-Advanced System

This paper presents field experiments on open-loop precoding multiple input multiple output (MIMO) using a testbed targeting International Mobile Telecommunication - Advanced (IMT-Advanced) systems. Open-loop MIMO is realized by applying Rotational OFDM (R-OFDM) to MIMO transmission. MIMO R-OFDM is more robust with respect to correlated channels than conventional open-loop MIMO-OFDM as was shown by the authors in a previous study. MIMO R-OFDM is implemented in a testbed targeting IMT-Advanced systems and is evaluated in a mobile environment. The antenna spacings are changed, i.e. the correlation coefficients between two antennas are changed, then the validity of MIMO R-OFDM is evaluated. The results of the field experiment reveal that MIMO R-OFDM is effective when the transmitter antenna spacings are decreased. The maximum cumulative distribution function (CDF) gain of MIMO R-OFDM with respect to conventional MIMO-OFDM is 6 % when the antenna spacing of the transmitter is same as the wave length of the carrier. In addition, it was also found that the rotational angle should be determined based not only on modulation order and coding rate, but also on the correlation coefficients between transmitter and receiver antennas.