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The modulation system is an important part in all communication networks including wireline and wireless networks. Orthogonal frequencydivision multiplexing/orthogonal frequencydivision multiple access (OFDM/OFDMA) and singlecarrier frequencydivision multiple access (SCFDMA) are representatives of multicarrier and singlecarrier modulations, which are widely used in different communication standards, like WiMAX and Long Term Evolution (LTE). However, all existed modulation systems use the fixed symbol block length or fixed subcarrier number. In the adaptive OFDM system the subcarrier number is still fixed, and just the symbol constellation mapping schemes are adaptively selected based on the subchannel quality. In this study, the author introduce a new concept, namely timevarying symbol block or timevarying subcarrier number into the modulation systems to improve the system performance. The author call the new modulation system timevarying OFDM (TVOFDM), timevarying OFDMA (TVOFDMA) for multicarrier modulation, and timevarying SCFDMA(TVSCFDMA) for singlecarrier modulation. Here, peaktoaverage power ratio (PAPR) is used as criteria to change the symbol block length timely. The algorithm for determination of the symbol block length is presented. The simulation results show that the timevarying modulation schemes can clearly reduce the PAPR values for both multicarrier and singlecarrier modulation systems.
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