Due to their robustness against multipath fading channels and the ease of equalization, multicarrier modulation techniques have been widely used in communication systems. In particular, orthogonal frequency-division multiplexing (OFDM) has been the technology of choice for a large number of wired and wireless standards. However, OFDM has some limitations that make it unable to address many new communication requirements. Hence, the innovative multicarrier systems as well as general frequency division multiplexing (GFDM) have been candidate as alternate solutions for physical layer in the next wireless communication generation. GFDM is a multicarrier technique with circular pulse shaping that is designed in a way to address emerging applications in fifth generation (5G) networks such as Internet of things (IoT), machine-to-machine (M2M) communications and opportunistic use of spectrum. The same as other multicarrier systems, GFDM suffers from a high peak to average power ratio (PAPR). To address this problem, essential features of GFDM such as possibility of reducing the number of subcarriers and changing the parameters of the pulse shaping filter, are considered. However, there still is the need for reducing the peak values to the lowest level possible while keeping the performance at a satisfactory level. Clipping technique along with iterative nonlinear noise mitigation receiver and block diagonal precorder with discrete Fourier transform (DFT) blocks are two methods already discussed in the literature. However, the high computational complexity and adverse effect on bit error rate (BER) performance cause the inadequacy of these approaches. In this thesis more effective methods for GFDM PAPR reduction are proposed. The first method is a companding technique call polynomial based companding technique (PCT). In this technique, a polynomial-based compressing function is used at the transmitter side and an iterative algorithm is applied at the receiver as a dual transformation that is performed at the transmitter. Although the compressor function is the same as previously proposed method for OFDM, but expander algorithm is redesigned for general forms of multicarrier systems including GFDM. Simulation results reveal that there is a trade-off between computational complexity, PAPR reduction ability, and BER performance. The second proposed method is the calculation of a linear data-independent precoding by using Gradient optimization algorithm. This precoder can be determined as a block circulant matrix that can be used for both GFDM and generalized frequency division multiple access (GFDMA) systems . The proposed precoder has a desirable performance in PAPR reduction, BER and out of band radiation compared to other methods . The block circulant structure of precoder enables a low complexity implementation of combination of precoder and original system. This implementation also reduce the amount of memory requirement in multi-user system, GFDMA. Keys Words Multi-carrier communication system, GFDM, GFDMA, PAPR, BER, PCT, Linear precoder, Blockcirculant matrix.
