On Differential Modulation in Downlink Multiuser MIMO Systems
For MU-MIMO system designers, this work offers low-complexity transceiver designs that avoid channel estimation, but the results are incremental and lack concrete performance numbers.
The paper proposes downlink precoding combined with differential modulation to shift complexity from receivers to transmitter in MU-MIMO systems, and a spreading-based scheme that requires no channel knowledge at either end. Simulations show good performance with low complexity.
In this paper, we consider a space time block coded multiuser multiple-input multiple-output (MU-MIMO) system with downlink transmission. Specifically, we propose to use downlink precoding combined with differential modulation (DM) to shift the complexity from the receivers to the transmitter. The block diagonalization (BD) precoding scheme is used to cancel co-channel interference (CCI) in addition to exploiting its advantage of enhancing diversity. Since the BD scheme requires channel knowledge at the transmitter, we propose to use downlink spreading along with DM, which does not require channel knowledge neither at the transmitter nor at the receivers. The orthogonal spreading (OS) scheme is employed in order to separate the data streams of different users. As a space time block code, we use the Alamouti code that can be encoded/decoded using DM thereby eliminating the need for channel knowledge at the receiver. The proposed schemes yield low complexity transceivers while providing good performance. Monte Carlo simulation results demonstrate the effectiveness of the proposed schemes.