Sistem pembahagian frequensi ortogon (OFDM) telah dilaksanakan secara meluas dalam sistem komunikasi berkelajuan tinggi tanpa wayar. Hal ini demikian kerana kelebihan OFDM yang mempunyai keteguhan terhadap perambatan berbilang, kecekapan spectrum yang tinggi dan mudah dilaksanakan. Namun, nisbah kuasa puncak ke purata (PAPR) yang tinggi merupakan kelemahan utama dalam OFDM. Nilai PAPR yang tinggi akan mendorong kepada penyebaran spectrum dan kemerosotan prestasi kadar ralat bit (BER). Oleh kerana terdapat pelbagai teknik pengurangan PAPR, kriteria bagi pemilihan teknik pengurangan PAPR telah diperkenalkan. Pemetaan dipilih (SLM) merupakan teknik pengurangan PAPR yang terbaik. Hal ini demikian kerana ia menghasilkan nilai PAPR yang terendah, fleksibel dengan sebarang nombor subpembawa dan tiada penyelewengan dalam isyarat yang dihasilkan. Dalam tesis ini, terdapat dua kaedah baru yang telah dicadangkan untuk pengurangan PAPR iaitu Pengedaran semula Kaedah Statistik (SRM) dan SLM digabungkan bersama SRM. SRM adalah perubahan ciri-ciri statistik dalam OFDM simbol daripada taburan Rayleigh ke taburan Gaussian. Operasi matematik iaitu punca kuasa telah diaplikasikan ke atas isyarat keluaran OFDM. Kesan SRM dapat dilihat melalui perubahan nilai puncak dan kuasa purata dan sekaligus mengurangkan nilai PAPR. Bagi 64 QAM OFDM dengan 128 subpembawa, pengurangan PAPR ialah 4.671 dB. Manakala, nilai pengurangan PAPR meningkat kepada 7.205 dB selepas SRM diaplikasikan. Perbezaaan nilai PAPR sebanyak 2.534 dB ini membuktikan bahawa SRM memberi kesan yang terbaik dalam pengurangan PAPR.
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Orthogonal Frequency Division Multiplexing (OFDM) has widely implemented in high speed wireless communications due to its advantages which are its robustness against multi path propagation, has higher spectral efficiency, simple equalizer and it is simple to be implemented. However, the high amplitudes which exceed mean value several time results in high peak to average power ratio (PAPR) and it is the main disadvantages of OFDM. This high PAPR will lead to spectral spreading and degradation of bit error rate (BER) performance. There are variety of techniques are available for PAPR reduction. So, the criteria for selection of PAPR reduction technique had been introduced. Selected mapping (SLM) has been choosing as the best PAPR reduction technique in this project due to the lowest PAPR result, little redundancy, flexible to work with an arbitrary number of subcarriers and distortion less scheme for reducing PAPR. In this thesis, there are two new methods had been proposed in order to further reduction of PAPR which are Statistical Redistribution Method (SRM) and SLM combines with SRM. SRM is a change of statistical characteristics of OFDM symbol from Rayleigh distribution into Gaussian distribution. The mathematical operation which is surd had been applied on the OFDM output signals. The effects of SRM can be seen in the change of the peak and average power values and this is lead to reduction in PAPR value. For the 64 QAM OFDM systems with 128 subcarriers, the reduction of PAPR is 4.671 dB. While after applying SRM on SLM, the PAPR reduce by 7.205 dB. The different value between SLM before and after applying SRM is 2.534 dB. This shows that SRM provide the best performance in term of PAPR reduction.
Peak to average power ratio (papr) reduction using selected mapping (slm) in orthogonal frequency division multiplexing system (ofdm) / Siti Nur Elyani Abd Rahman