Peak-to-average Power Ratio Reduction in Multi-antenna OFDM Via Multiple Signal Representation

Modern digital communication systems take advantage of the combined application of orthogonal frequency-division multiplexing (OFDM) and multi-antenna (or multiple-input/multiple-output (MIMO)) systems, often denoted as MIMO OFDM. OFDM is a very popular approach to equalize the temporal intersymbol interferences caused by frequency-selective channels. Using MIMO systems, it is possible to increase the channel capacity while keeping the transmission bandwidth and the transmit power. One of the most serious drawbacks of OFDM are high peaks of the transmit signal. Processing such a transmit signal with a nonlinear power amplifier at the transmitter front-end causes signal clipping, which in turn generates out-of-band radiation. In order to avoid the disturbance of adjacent transmission channels, this out-of-band radiation has to be strictly avoided. Considering multi-antenna transmitters, the issue of out-ofband radiation gets even more serious. For this reason, a transmitter-sided algorithmic control of the signal peaks, also known as peak-to-average power ratio (PAR) reduction algorithm, is desirable.PAR reduction algorithms for single-antenna transmitters are well known in literature. However, there is a particular need for PAR reduction schemes, especially designed for MIMO systems. In this thesis, the schemes based on multiple signal representation, which are selected mapping (SLM) and partial transmit sequences (PTS), are extended to multi-antenna systems. In this context, we pursue the goal to exploit the multiple transmit antennas to achieve further gains in PAR reduction performance. Interestingly, based on the analysis of the multi-antenna extensions, further improvements on the respective single-antenna schemes can be derived. The analysis of the particular PAR reduction schemes and their extensions include further aspects, whose contributions are summarized as follows.