Abdul Wakeel

• A major drawback of MIMO-OFDM systems is its high Peak-to-Average Ratio (PAR). The signal is clipped when the peak values are higher than the linear operation range of non-linear devices. In order to avoid clipping the signal above a certain threshold, measure must be taken to limit all peaks crossing the threshold value. In this thesis, we therefore investigate and address the PAR problem of different MIMO-OFDM scenarios and provide countermeasures to limit the peak excursions in MIMO-OFDM systems. First, we extend the Tone-Reservation algorithm for PAR reduction of MIMO-OFDM systems. For a point-to-point scenario, a spiky function is generated on the weakest eigenchannel not suited for data transmission. This spiky function is then iteratively used for PAR reduction of the transmit signal. For a multi-user broadcast scenario, the spiky function is generated on a small percent of tones reserved on all spatial dimensions, in the conventional manner. This spiky function is then used to limit the peak excursions of the transmit signal. Second, we introduce a novel Least-Squares iterative PAR reduction algorithm for MIMO-OFDM scenarios. For a P2P scenario, the weakest eigenchannel is used to approximate the peak excursions on the remaining spatial dimensions in a least-squares fashion. This model function is then added to the transmit signal for PAR reduction. The algorithm is thoroughly investigated in terms of the capacity loss and the mean power increase due to the modeled function. Moreover, for a broadcast scenario, we consider that one user is inactive and the channel associated to it is not used. This inactive channel is then used to approximate and model the peak excursions on the remaining spatial dimensions in the similar fashion. In a further part of this thesis, we consider PAR reduction using Trellis Shaping for single antenna systems. We concatenate an optimized irregular LDPC code with Trellis Shaping for PAR reduction.