Analisis sistem OFDM, FDE dan Pre-FDE dengan Cyclic Prefix dan metode Overlap-cut = Analysis of OFDM, FDE and Pre-FDE system with cyclic prefis and overlap-cut method

Pakpahan, Beatrice Dina (2017) Analisis sistem OFDM, FDE dan Pre-FDE dengan Cyclic Prefix dan metode Overlap-cut = Analysis of OFDM, FDE and Pre-FDE system with cyclic prefis and overlap-cut method. Bachelor thesis, Universitas Pelita Harapan.

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Abstract

This research is driven by the problem of using cyclic prefix in the transmission system that is usually used in OFDM. The purpose of this research is to find another method that can improve the performance of the system, but not using more bandwidth like adding the cyclic prefix in the system. The method is called the overlap-cut method, which will process an overlap version of data blocksThe overlap section in the left and right will be removed in the receiver system. The research uses MATLAB for simulating the transmission technique in multipath channel with 20 taps. The experiment shows that the overlap-cut method cannot be applied in OFDM system because the OFDM receiver works in the frequency domain so the overlap-cut method that cuts the effect of the cyclic convolution in the edge of the data cannot be done. However, the overlap-cut method can be used in the FDE system because the FDE system performs the equalization in the frequency domain then returns the signal to the time domain in the receiver. The result shows that the BER of the FDE system with the overlap-cut method is only slightly different from the OFDM system with a cyclic prefix. The OFDM system with the length of cyclic prefix of 50 bits shows the best BER when Eb/No 18 dB and the probability of bit error is 1.10-3 bit, while the FDE system with the length of overlap-cut method 50 bits shows the best BER when Eb/No 18 dB and the probability of bit error is 2.10-3 bit. The result indicates that the preFDE system has a better BER than OFDM and FDE assuming perfect knowledge of the channel coefficients. Pre-FDE system shows the best BER with the length of the cyclic prefix 50 bits when EB/No 10 dB and the probability of bit error is 2.10-6 bit. The research shows the BER of OFDM, FDE, and Pre-FDE system for different length of cyclic prefix in a multipath channel with 20 taps. The result shows that using cyclic prefix and overlap-cut improves the performance of the system so it decreases the BER and the best BER is achieved when the length of the cyclic prefix and overlap-cut are the same or longer than the multipath channel. / Penelitian ini dilatarbelakangi oleh permasalahan penggunaan cyclic prefix di sistem transmisi yang biasa dipakai oleh sistem OFDM. Penelitian bertujuan untuk menemukan metode selain penyisipan cyclic prefix yang dapat memperbaiki sistem, tanpa membuang bandwidth seperti pada transmisi sistem yang menggunakan cyclic prefix. Metode yang diterapkan adalah metode overlap-cut yang akan memproses data yang overlap ke blok data sebelum dan setelah blok data yang ingin diterima.. Data yang overlap akan dibuang kemudian oleh receiver. Penelitian ini menggunakan MATLAB untuk menyimulasikan sistem teknik transmisi yang diamati dengan multipath channel 20 tap. Percobaan menunjukkan bahwa metode overlap-cut nyatanya tidak dapat diterapkan di sistem OFDM karena penerima OFDM bekerja pada domain frekuensi, sehingga metode overlap-cut yang membuang efek tepian dari cyclical convolution tak dapat diterapkan. Namun, metode overlap-cut dapat diterapkan dengan baik pada sistem FDE yang melakukan equalization pada domain frekuensi kemudian mengembalikan sinyal ke time domain di receiver. Hasil si mulasi menunjukkan bahwa BER FDE dengan overlap-cut hanya berbeda sedikit dari sistem OFDM dengan cyclic prefix. Sistem OFDM dengan cyclic prefix sepanjang 50 bit menunjukkan BER terbaik saat Eb/No 18 dB dan probabilitas bit yang error adalah 1.10-3 sedangkan, FDE menggunakan overlap-cut sepanjang 50 bit menunjukkan BER terbaik saat Eb/No 18 dB dan probabilitas bit yang error adalah 2.10-3 bit. Juga ditemukan bahwa sistem Pre-FDE dapat menunjukkan BER yang jauh lebih baik daripada sistem OFDM dan FDE dengan asumsi koefisien kanal diketahui sempurna. Sistem Pre-FDE menunjukkan BER terbaik dengan cyclic prefix 50 bit saat Eb/No 10 dB dan probabilitas bit yang error adalah 2.10-6 bit. Hasil penelitian menampilkan kinerja BER sistem OFDM , FDE, dan Pre-FDE untuk panjang cyclic prefix yang berubah-ubah pada kondisi multipath channel 20 tap. Selain itu, hasil penelitian juga menampilkan kinerja BER di sistem FDE untuk panjang overlap-cut yang berubah-ubah pada kondisi multipath channel 20 tap. Hasil penelitian menunjukkan bahwa penggunaan cyclic prefix dan overlap-cut meningkatkan kinerja sistem sehingga BER menurun dan kinerja sistem yang maksimal didapatkan ketika panjang cyclic prefix dan overlapcut sepanjang multipath channel atau lebih.

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