Enhanced Orthogonal Frequency Division Multiplexing

Orthogonal Frequency Division Multiplexing (OFDM) has been used in all kinds of wide-band high-speed data transmission systems and is one of the promising techniques for future wireless communication systems, since it has high spectrum efficiency and its robustness to the frequency selective fading environments.However, OFDM is a multi-carrier systems, has a higher peak to average power ratio (PAPR), requiring a number of components such as amplifiers, A/D and D / A converter have a large linear dynamic range; otherwise, when the peak signal of the non-linear components get into the region, it will cause a inband distortion and out of band radiation, destructing the orthogonality of subcarriers, resulting in the rise of bit error rate. On the other hand, OFDM transform a frequency-selective fading channel into parallel flat-fading subchannels, thereby significantly reducing the receiver complexity in the equalization. However, this comes at a performance cost for the loss of multipath diversity. When the channel may undergo fading, reliable detection of the symbols carried by these faded subcarriers becomes much difficult.This dissertation study and works for above-mentioned shortcomings. Through the research and application in a variety of enhanced techniques, they can significantly reduce adverse impact caused by these shortcomings.This dissertation does research about an enhanced technique based on Selective Mapping OFDM (SLM-OFDM). By analyzing the shortcomings of the traditional algorithm, the author introduces a low-complexity SLM-OFDM technique; finally, the authors proposes new algorithm to further optimize the enhanced technique. The algorithm gives a criteria to advantages and disadvantages of different phase sequence set; meanwhile introduces a new phase sequence set which significantly improves the PAPR performance of SLM-OFDM.Vector OFDM is s alternative enhanced technique which improve BER performance significantly by employing diversity gain over multipath fading channel. In this dissertation, a theoretical analysis of diversity characteristics of vector OFDM is first given; based on the analytical result, its diversity gain is optimized. The simulation results corroborate the theoretical analysis.The last part of this dissertation is to study the enhanced technique based on DFT Spreaded OFDM (DFT-SOFDM). Owing to the characteristics of low PAPR, DFT-SOFDM has become an important candidate technique in the 3GPP LTE uplink transmission scheme. This section focuses on the equalization scheme of DFT-SOFDM based on interleaved subcarriers mapping mode (IFDMA); meantime, improving the BER performance significantly through the sphere decoding algorithm. Finally, the author proposes a joint transceiver optimization scheme to further promote the system performance. The technique not only further optimize the performance of IFDMA system, and ensure no change of the low PAPR.characteristic.