Imperfect channel state information in MIMO-transmission

A specially favorable MIMO-based concept for future mobile radio systems consists in the application of joint detection (JD) in the uplink and joint transmission (JT) in the downlink. By this, all the computationally complex signal processing is shifted to the base station (BS), resulting in low complexity mobile stations (MS). Both JD and JT require channel knowledge at the BS which, if time division duplexing is applied, can be obtained by training signal based channel estimation in the uplink. Unfortunately, channel estimates are never perfect, which leads to performance degradations if these channel estimates instead of perfect channel knowledge are used for JD or JT. A novel analytical analysis of these performance degradations is presented.