Time-varying multicarrier and single-carrier modulation systems

The modulation system is an important part in all communication networks including wireline and wireless networks. Orthogonal frequency-division multiplexing/orthogonal frequency-division multiple access (OFDM/OFDMA) and single-carrier frequency-division multiple access (SCFDMA) are representatives of multicarrier and single-carrier 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 time-varying symbol block or time-varying subcarrier number into the modulation systems to improve the system performance. The author call the new modulation system time-varying OFDM (TVOFDM), time-varying OFDMA (TV-OFDMA) for multicarrier modulation, and time-varying SCFDMA(TV-SCFDMA) for single-carrier modulation. Here, peak-to-average 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 time-varying modulation schemes can clearly reduce the PAPR values for both multicarrier and single-carrier modulation systems.