On the impact of multi-antenna RF transceivers’ amplitude and phase mismatches on transmit

Transmit Maximum-Ratio Combining (transmit MRC) is a popu-lar antenna diversity technique that provides both spatial diversity and array gain in downlink Multiple-Input Single-Output (MISO) links. These gains, however, critically depend on the availability of the downlink Channel State Information (CSI). In time-division duplexing systems, channel reciprocity has been commonly put forth to justify the convenient use of the CSI already acquired from the uplink, in the calculation of the transmit-MRC weights. Recent work has questioned this practice, based on the non-reciprocity of multi-antenna RF transceivers, due to significant amplitude and phase mismatches across the antennas. Furthermore, expensive digital calibration solutions have been proposed to enforce the reci-procity of the multi-antenna RF transceivers. Both the impact of multi-antenna amplitude and phase mismatches and the perfor-mance of the proposed calibration approaches have only been as-sessed via simulations. In this contribution, we propose an alterna-tive statistical analysis of the impact of these mismatches on trans-mit MRC. This analysis allows a faster and more reliable charac-terization as well as provides insight into the relative importance of these mismatches. Consequently, sufficient matching require-ments can be extracted for the multi-antenna RF transceivers, for which simpler and cheaper calibration solutions can be devised. 1