On the Phase Sequences and Permutation Functions in the SLM Scheme for OFDM-IM Systems

Abstract

In orthogonal frequency division multiplexing with index modulation (OFDM-IM), the active subcarriers can convey information bits by modulated symbols as well as their indices. OFDM-IM has attracted a great deal of attention from researchers by virtue of high energy efficiency. Unfortunately, OFDM-IM has inherited large peak-to-average power ratio (PAPR) of the classical OFDM signal, but there are few works dealing with it. Selected mapping (SLM) is a promising PAPR reduction technique that is distortionless, has good PAPR reducing capability, and can be easily adapted in OFDM-IM systems. In SLM for OFDM-IM systems, the phase sequences rotate the OFDM-IM block in the frequency domain before the inverse fast Fourier transform (IFFT) is applied. Also, in the recent work, permutation procedure in the frequency domain has been proposed before multiplication of phase sequences in SLM, which is newly introduced in OFDM-IM regime. Unfortunately, the theoretical investigation on the efficiency of the permutation in SLM is insufficient. In this paper, we investigate the phase sequence set (PSS) and permutation functions in the SLM scheme for OFDM-IM systems; First, the efficiency of the permutation is analyzed as a function of the number of active subcarriers. Second, the optimal conditions for the PSS and permutation functions are derived, which is verified through simulations. INDEX TERMS Index modulation (IM), orthogonal frequency division multiplexing (OFDM), peak-toaverage power ratio (PAPR), permutation, phase sequence, selected mapping (SLM).

Precoded Filterbank Multicarrier Index Modulation With Non-Orthogonal Subcarrier Spacing

“…The popular PAPR reduction techniques developed for OFDM have been studied in the context of OFDM-IM. For example, selective mapping (SLM) has been investigated for OFDM-IM in [39], [40]. Active constellation extension (ACE) of OFDM has also been extended to the OFDM-IM by exploiting inactive subcarriers in [41].…”

Overview on PAPR reduction techniques in OFDM-IM

“…However, if the ratio is high, it would be better to remove the permutation procedure. Furthermore, to guarantee the performance of PAPR reduction, optimal conditions for PSs and permutation procedure have to be taken into account (Kim, 2020). The block diagram shown in Figure 5 shows the permutation used in OFDM-IM system.…”

Peak‐to‐average power ratio of selective mapping technology involving a phase generation mechanism based on polar codes for orthogonal frequency division multiplexing with index modulation systems

“…However, the subcarrier selection mechanism, number of active subcarriers, and data they transmit all effect the peak‐to‐average power ratio (PAPR) of OFDM‐IM signals. A high PAPR may cause the high‐power amplifier of transmitters to generate distortion and hence increase the complexity of the analog‐to‐digital conversion process 12–15 . Therefore, reducing the PAPR in OFDM‐IM technology has been a popular research topic.…”

“…Selective mapping (SLM) is a popular technology used to reduce the PAPR 13–15 . It multiplies the input signal by various randomly generated phase sequences to generate candidate signals.…”

“…Although SLM considerably improves PAPR performance, the mechanism of generating phase sequences with an optimal PAPR could be improved and requires further research. Kim 14 attempted to improve the PAPR performance in OFDM‐IM system by investigating the effects of the SLM sequencing mechanism of active subcarriers and mechanism through which phase sequences are generated. Simulation results indicated that when the numbers of subcarriers were 32 and 64, the number of active subcarriers was 2; a random arrangement of the active subcarriers led to higher PAPR performance compared with conventional SLM.…”