  Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is
a novel multicarrier scheme, which uses the indices of the active subcarriers
to transmit data. OFDM-IM also inherits the high peak-to-average power ratio
(PAPR) problem, which induces in-band distortion and out-of-band radiation when
OFDM-IM signal passes through high power amplifier (HPA). In this letter,
dither signals are added in the idle subcarriers to reduce the PAPR. Unlike the
previous work using single level dither signals, multilevel dither signals are
used by exploiting that the amplitudes of the active subcarriers are variously
distributed for different subblocks. As a result, the proposed scheme gives the
dither signals more freedom (a larger radius of dithering) in average.
Simulation results show that the proposed scheme can achieve better PAPR
reduction performance than the previous work.
