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    Enhancement of bit error rate in long term evaluation system over different channels based on hybrid transform
    (İstanbul Gelişim Üniversitesi Lisansüstü Eğitim Enstitüsü, 2024) Abuhameed, Sura Saadi Mohammed
    Long Term Evolution (LTE) technologies have significantly transformed wireless communication by offering rapid data transmission and extensive connectivity. However, the existence of deteriorating channels and interference can have a detrimental impact on the bit error rate (BER) performance of LTE systems, resulting in a reduction in data reliability. This study extensively examined LTE system by proposing a novel system structure based on the discrete cosine transform (DCT) and Walsh-Hadamard code (W-H) a QPSK mapper. The (DCT), known for its capacity to compress energy and represent information in the frequency domain, is proposed as a signal processing technique to mitigate the impact of multipath fading, interference, and other distortions induced by the channel. It's important to note that the suggested method doesn't need to use a cyclic prefix (CP), which means that the data rate is higher and the bandwidth is bigger. The main goal is to use the Walsh-Hadamard code as an orthogonal encoder to take advantage of its ability to fight the conflict between the symbols and the frames of the I/P data. By using both the (DCT) and the Walsh-Hadamard (W-H) approach, the system aims to enhance the (BER) performance of the entire system in comparison to alternative techniques. several simulation experiments are done to showcase the enhanced performance of the modified structures in various Doppler shift scenarios, particularly at maximum Doppler Frequencies (MDS) of 6, 60, and 180. This thesis begins with simulating LTE system scenarios to evaluate its performance in terms of (BER). A strategy called W-H-DCT-LTE was employed in the simulation scenarios, and its performance was compared to the standard Fast Fourier Transform- Long Term Evolution (FFT-LTE) method. The system was designed with the utilization of modulation schemes such as Quadrature Phase Shift Keying (QPSK) and WalshHadamard (W-H), using a subcarrier size of 1024. In addition, there are two communication channel models: Additive White Gaussian Noise (AWGN) and Rayleigh. These models are used with a 2x2 multiple-input/multiple-output configuration. We performed the system simulation on four users using the MATLAB program. The evaluation of the new structures for various channel types revealed a considerable improvement of approximately 2.5 dB in BER performance when compared to conventional LTE. When employing W-H-DCT in an LTE system, the signal-to-noise ratio (SNR) needed to achieve a (BER) of 10−4 with 1024 BPSK (5MDS) FFT-LTE is approximately 23 dB. However, when utilizing W-H-DCT-LTE, the required SNR drops to 12.8 dB. The proposed system significantly outperforms the three existing systems for this specific channel model.