Subblocks Set Design Aided Orthogonal Frequency Division Multiplexing With All Index Modulation

Abstract

In recent years, OFDM with index modulation (OFDM-IM) has become a potential technique due to its improvement of diversity gain. In typical OFDM-IM schemes, incoming information bits are divided into two parts, symbols bits, and index bits. However, the symbol bits conveyed by each OFDM symbol suffer from low diversity order, which has a negative impact on diversity gain. In this paper, we propose the scheme called OFDM with all index modulation (OFDM-AIM), which replaces the PSK/QAM constellation modulator with subblock modulator and simplifies the structure. With such an arrangement, the subblocks of OFDM-AIM become flexible, which contributes to achieving the higher diversity order of the system. Moreover, we study the effects of Euclidean distance and diversity order based on the unconditional pair error probability, which gives the guideline to design a legitimate subblocks set. Then the algorithm to build the subblocks set with higher diversity order is proposed, which can achieve better diversity gain. Theoretical and simulated results show that the OFDM-AIM scheme is capable of achieving better BER performance than other index modulated OFDM schemes.INDEX TERMS OFDM-IM, diversity order, diversity gain, all index modulation, Euclidean distance, subblocks set design, pairwise error probability.

Subblock design aided orthogonal frequency division multiplexing with all index modulation using search algorithm

“…It worth noticing that OFDM‐AIM with ML detector can achieve better BER performance compared with OFDM‐IM and CI‐OFDM‐IM schemes 22 . However, the computational complexity of OFDM‐AIM is , which is much higher than of OFDM‐IM and CI‐OFDM‐IM.…”

“…It is worth noting that in Algorithm 1 the subblock realizations with highest diversity orders among each other can be added into initial set S as Reference 22 due to their high diversity gains. Therefore, the initial set S contains x 1 = [ x 1 x 1 x 1 x 1 ] T , , where x 1 , x 2 , … , x M are M different constellation points.…”

“…However, the structures of typical index modulated OFDM schemes limited the way to enhance the diversity gain due to the symbol bits. In Reference 22, OFDM with all index modulation (OFDM‐AIM) was proposed, which conveyed all information bits via the index of the legitimate subblock realizations inside a designed look‐up table and could be regarded as a more flexible codebook. With such arrangement, the subblock realizations with better diversity order can be formed in order to enhance the diversity gain.…”

Encrypted subblock design aided OFDM with all index modulation

“…It can be seen that the bits conveyed by active subcarriers are the same as the traditional OFDM scheme created by the QAM/PSK modulator. Note that the bits conveyed by the index of SAPs have better BER performance under Rayleigh fading channel [27]. As a result, the whole BER performance of OFDM‐IM is better than OFDM scheme.…”

“…However, for basic structure of OFDM‐IM and other enhanced versions, the diversity gain is hard to fully achieve due to the existence of symbol bits. In [27], OFDM with all index modulation (OFDM‐AIM) is proposed where index bits are fully used to convey all the information bits. For each subblock, all the pairwise error probability events can achieve high diversity orders by subblocks set design, which directly enhances the diversity gain compared to classical OFDM‐IM.…”