Downlink Multiuser MIMO-OFDM Systems
Multiple input multiple output (MIMO) techniques for wireless communication systems have attracted in the last years huge research activity due to the possibility of improving the link performance by increasing the channel capacity and decreasing the bit-error rate (BER). 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 field, the combination of MIMO transmission and OFDM (orthogonal frequency division multiplexing) can be considered as an essential part of fulfilling the requirements of future generations of wireless systems. However, single-user scenarios have reached a state of maturity. By contrast multiple 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. Furthermore, the use of multiple antennas both at the transmit and the receive front-ends introduces a correlation effect between the antennas due to their proximity producing interference. In consequence, the BER increases and the channel capacity decreases. The goal of the present contribution is to analyze the system performance under different spatial antennas distributions for Multiuser MIMO-OFDM systems in correlated and non-correlated fading channels. The performed joint optimization of the number of activated MIMO layers and the number of transmitted bits per subcarrier along with the appropriate allocation of the transmit power shows that not necessarily all user-specific MIMO layers per subcarrier have to be activated in order to minimize the overall BER under the constraint of a given fixed data throughput.
KeywordsMultiple-Input Multiple-Output System Orthogonal Frequency Division Multiplexing Singular-value Decomposition Bit Allocation Power Allocation Wireless Transmission
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