Modulation-Mode Assignment in SVD-Aided Downlink Multiuser MIMO-OFDM Systems

Multicarrier transmission such as OFDM (orthogonal frequency división multiplexing) is an established technique for radio transmission systems and it can be considered as a promising approach for next generation wireless systems. However, in order to comply with the demand on increasing available data rates in particular in wireless technologies, systems with múltiple transmit and receive antennas, also called MIMO (multiple-input multiple-output) systems, have become indispensable for future generations of wireless systems. Due to the strongly increasing demand in high-data rate transmission systems, frequency non-selective MIMO links have reached a state of maturity and frequency selective MIMO links are in the focus of interest. In this fleld, the combination of MIMO transmission and OFDM can be considered as an essential part of fulfllling the requirements of future generations of wireless systems. However, single-user scenarios have reached a state of maturity. By contrast múltiple users' scenarios require substantial further research, where in comparison to ZF (zero-forcing) multiuser transmission techniques, the individual user's channel characteristics are taken into consideration in this contribution. The performed joint optimization of the number of activated MIMO layers and the number of transmitted bits per subcarrier shows that not necessarily all user-speciflc MIMO layers per subcarrier have to be activated in order to minimize the overall BER under the constraint of a given flxed data throughput. Keywords—Multiple-input multiple-output system, orthogonal frequency división multiplexing, singular-value decomposition, bit allocation, wireless transmission.