Avoiding Effects of OFDM Adjacent Channel Interference by Using Combinations of Modulation Schemes
GRIN Verlag, 2009 - 88 pages
Master's Thesis from the year 2008 in the subject Engineering - Communication Technology, grade: erfolgreich bestanden, Keio University (Graduate school of Science and Technology - School of Science for Open and Environmental Systems), language: English, abstract: Non-orthogonality among adjacent OFDM channels creates OFDM adjacent channel interference and it heavily affects the entire system's performance. Conventional methods to avoid OFDM adjacent channel interference are not only insufficient but also are wasting a lot of frequency resources. In this research, a method using combinations of modulation schemes is proposed to avoid effects of OFDM adjacent channel interference. It can be obtained by modulating the sub-carriers at the outer sides of an OFDM channel with lower order modulation schemes (such as BPSK or QPSK), while modulating the sub-carriers at the inner side of the OFDM channel with higher order modulation schemes (such as 16QAM or 64QAM). Intensive simulations have been carried out to evaluate the performance of the proposed method. The simulation results have shown an increase in the OFDM system's resistance against adjacent channel interference while still maintain the bandwidth efficiency.
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16QAM and totally 16QAM modulation scheme 16QAM OFDM system 32 inner sub-carriers 32 outer sub-carriers 64QAM OFDM adjacent channel inter adjacent channel interference bandwidth efficiency BER performance better than 16QAM bit error ratio blue line shows BPSK or QPSK channel estimation CIR is equal convolution code Digital Terrestrial Television Eb/No value entire 64 sub-carriers equal to 0dB ference with conventional Figure frequency channel Going from left Guard-band horizontal axis shows interference with conventional ISM bands Keio University Mbps modulated with 16QAM modulated with QPSK modulation order Near-far problem Nyquist ISI criterion OFDM symbol outer sub-carriers 16 parameters pass-band phase shift keying power is getting proposed modulation methods Rayleigh fading saturated throughput value shows the BER shows the throughput signal power simulated 16QAM OFDM simulated 64QAM sub carriers sub-carriers 16 sub-carriers sub-carriers are modulated system under adjacent Throughput performance totally 32 outer transfer function transmitted vertical axis shows wireless