Impact of channel sounder phase noise on directional channel estimation by space-alternating generalised expectation maximisation

Multi-input multi-output (MIMO) radio channel sounders commonly employ time-division multiplexing (TDM) technique to switch between transmit and receive antennas. The TDM method offers single-input single-output sounders the MIMO capability in a cost-effective manner. However, the TDM approach leads to errors in MIMO channel measurements because of phase noise in local oscillators. Phase noise varies in the short term during the switching sequence for a MIMO channel sample. The high-resolution space-alternating generalised expectation maximisation (SAGE) algorithm has been efficiently applied for the estimation of the channel parameters. The impact of phase noise on the directional channel parameters, which are estimated by the SAGE algorithm, has been studied. Although the previous studies have investigated long-term random walk noise, we concentrate on the short-term noise which affects consecutive MIMO channel matrix measurements. It has been shown that errors in direction of arrival and direction of departure estimation because of the short-term phase noise can be effectively decreased by time domain filtering of the impulse responses prior to the SAGE processing