Performance Improvement of Multi-UserMC-CDMA system Using Discrete Hartly Transform Mapper

Future wireless communication systems must be able to accommodate a large number of users and simultaneously to provide the high data rates at the required quality of service. In this paper a method is proposed to perform the N-Discrete Hartley Transform (N-DHT) mapper, which are equivalent to 4-Quadrature Amplitude Modulation (QAM), 16-QAM, 64-QAM, 256-QAM, … etc. in spectral efficiency. The N-DHT mapper is chosen in the Multi Carrier Code Division Multiple Access (MC-CDMA) structure to serve as a data mapper instead of the conventional data mapping techniques like QPSK and QAM schemes. The proposed system is simulated using MATLAB and compared with conventional MC-CDMA for Additive White Gaussian Noise, flat, and multi-path selective fading channels. Simulation results are provided to demonstrate that the proposed system improves the BER performance and reduce the constellation energy as compared with the conventional syste

New OFDM schemes based on orthogonal transforms for mobile communications systems :

PhD ThesisIn this thesis, two new orthogonal frequency division multiplexing (OFDM) systems are presented. The first scheme proposes a new OFDM system transceiver based on the C-transform, which is termed C-OFDM. Over multipath channels, the C-OFDM achieves 10 dB signal-to-noise ratio (SNR) gain at 10−4 bit-error-rate (BER), in comparison to the OFDM that based on the is discrete cosine transform (DCT-OFDM) and the conventional OFDM schemes. It also reduces the peak-to-average power ratio (PAPR) of the OFDM signal by about 1 dB and in some cases up to 3 dB. In the second scheme, a new fast, orthogonal X-transform is produced. The proposed X-transform is then used in a new OFDM named X-OFDM to greatly reduce the complexity, the PAPR and the BER. The proposed scheme achieves around 15 dB SNR gain in comparison to the conventional OFDM at 10−4 BER and reduces the average PAPR (over 105 OFDM symbol) by about 6 dB for N =1024 subcarriers. Furthermore, in this study, the X-transform is utilized to produce a new Alamouti space-time OFDM (ST-OFDM). The proposed ST-X-OFDM scheme reduces the transmitter complexity and achieves important SNR gain over the conventional ST-OFDM systems. The BER performance of the proposed schemes in the presence of solid-state power amplifiers (SSPAs) is also investigated analytically and by simulation. It shows that the X-OFDM is resilient to the SSPAs nonlinear distortion whereas the C-OFDM may lead to BER impairment in the presence of the SSPA. Furthermore, a coding technique to mitigate the sensitivity of the COFDM scheme to the SSPA is also proposed in this study. In this research, mathematical models for the proposed C-OFDM, XOFDM and ST-X-OFDM, which tightly match the simulation results over a diverse range of transmission scenarios and mapping schemes, are also derived. In addition, the BER performance of the proposed COFDM and X-OFDM schemes in the presence of the carrier frequency offset (CFO), with and without frequency synchronization algorithm, are also investigated. The proposed C-OFDM and X-OFDM schemes are more sensitive to the CFO than the conventional schemes. However, when frequency synchronization algorithm is used, both the proposed schemes retain their significant BER improvement in comparison to the conventional schemes.Ministry of Higher Education and Scientific Research (MOHSR), Iraq and to the Iraqi cultural attach- London for supporting me financially during my study in England