Peak factor in orthogonal multicarrier modulation with variable levels

Abstract

Usually in multicarrier modulation (MCM) the level of the modulated signal is constant and does not depend on the specific vector of information symbols which are actually transmitted. In such a case the value of peak factor (PF) for an MCM signal composed of N carriers is 10log10N [dB]. The author proposes a method for reducing the PF, where for each vector of information symbols, for which the maximum of the instantaneous envelope power exceeds some given threshold value, the amplitudes of all carriers are uniformly reduced to obtain equality between the maximum of the instantaneous envelope power and the threshold. Moreover, for each vector of symbols, for which the maximum of the instantaneous envelope power is lower than the threshold, the amplitudes of all carriers are uniformly increased to obtain equality. Thus the PF of the whole modulation is reduced without reducing the net bit rate. The price paid for reduction of the PF is an insignificant increase in bit error rate (BER).