Time Dispersion Characteristics of Cross-Polarized 2X2 MIMO Self-Interference Indoor Radio Channels

In full-duplex wireless communication systems, transmission signals travel through self-interference radio channels before they will be received by the local receivers. This paper studies time dispersion characteristics of these channels for an indoor cross-polarized 2x2 multiple-input-multiple-output antenna (MIMO) system. Four cross- polarized radio channels - excited by two transmit antennas and captured by two receive antennas perpendicularly polarized to the transmit antennas - were measured in an indoor spacious foyer (entrance hall) environment. By means of a vector network analyzer, one gigahertz of bandwidth, which occupies 2-to-3-GHz frequency band, was swept to sound these self-interference channels. The four vector network analyzer test ports were connected to two dually- polarized magnetoelectric dipole antennas that were utilized to observe the self-interference channels. Each of the dipole antennas possesses: Two radio-frequency ports, a hemispherical radiation pattern, and an excellent cross-polarization discrimination properties. The antennas were placed at two meter height and moved in track along the room circumference to measure the self-interference channels at 27 positions. The excellent cross-polarization isolation properties of the utilized antennas has allowed to capture a time- domain instantaneous channel dynamic that exceeds 120 dB - normalized with respect to the transmit power at the antennas' physical ports. This vast dynamic has used to analyze the channel with sliding sensitivity threshold. The channel measurement reports maximum excess delays up to 689 ns. Furthermore, time dispersion parameters and their associated values are discussed and reported in this paper based on the conducted self-interference channel measurements.