摘要：Orthogonal frequency division multiplexing (OFDM) is a main multicarrier modulation that used in recent years because it has high spectral efficiency but, OFDM suffers from high sidelobes. In this letter, we propose a new method for sidelobe suppression of OFDM modulation that based on the previously introduced Constellation Expansion (CE) method. CE is one of the methods for reduction of OFDM sidelobes that has a good performance. In CE, no side information needs to be transmitted and it doesn’t involve complex optimization problem but, it has an increment in the bit error rate (BER) and peak to average power ratio (PAPR) parameters. CE method uses the iterative algorithm and in this algorithm, the different sequences of symbols of extended constellation are randomly selected and examined to achieve a sequence with desired sidelobe power. If the number of subcarriers is large, we have to test a very large number of sequences to obtain the proper one. Here, we present an algorithm for symbol by symbol construction of appropriate sequence in extended constellation that called Modified Sequence CE (MS-CE). Simulation results show that the MS-CE has a sidelobe reduction performance better than CE with much lower computations. Moreover, MS-CE does not have significant impacts on the system parameters such as BER and PAPR.
关键词：OFDM; sidelobe suppression; constellation expansion; power spectrum
