Experimental Performance Evaluation of Frequency-Domain Linear MIMO Reception Using Null-Space Expansion Technique

This research focuses on multiple-input multiple-output signal separation in environments with changing channels, such as mobile communications. When separating signals by combining weights fixed in a packet, the orthogonality between interfering signals and combining weights is broken due to the movement of the receiver, resulting in interference leakage. To mitigate such degradation, a null-space expansion technique in the frequency-domain is employed, assuming that there are extra antennas at the receiver side. This technique improves channel time-varying immunity by using extra receiving antennas to form a null-space that suppresses interference between streams. In this paper, the performance advantage of the null-space expansion technique is revealed through in-lab and field measurement campaigns.