Degradation and performance issues of MIMO/OFDM in the presence of motion

Abstract

Different degrees of channel knowledge at the transmitter lead to different transmission strategies with disparate performance in a multiple-input multiple-output (MIMO), orthogonal frequency-division multiplexing (OFDM) system. While in a frequency-division duplex (FDD) scheme instantaneous channel knowledge requires the feedback of channel state information (CSI) from the receiver, which, depending on system parameters, might be prohibitive, in a time-division duplex (TDD) system, channel estimates obtained during reception can be made use of during transmission. Thereby, the basic problem is obsolescence of CSI over a frame interval. Applying transmission strategies that adapt to the channel as much as the available CSI allows, the performance of a TDD MIMO/OFDM system is compared and discussed for four degrees of CSI: the theoretical case of perfect instantaneous CSI; perfect CSI that becomes outdated during the transmission of a frame; partial CSI, where partial refers to knowledge of the transmit correlation matrix of the channel; the case of no CSI. To this end, a channel model is introduced that permits the simulation of channel variations due to mobility for different spatial and temporal spreads.