Compressed-Sensing-Aided Space-Time Frequency Index Modulation

Abstract

Abstract-In space-time shift keying (STSK), the information is conveyed by both the spatial and time dimensions, which can be used to strike a trade-off between the diversity and multiplexing gains. On the other hand, orthogonal frequency division multiplexing (OFDM) relying on index modulation (IM) conveys information not only by the conventional signal constellations as in classical OFDM, but also by the indices of the subcarriers. In this paper, we combine the benefits of STSK and IM in order to strike a flexible trade-off between the throughput and bit-error performance by transmitting extra information bits in each subcarrier block, whilst increasing the diversity order. In order to further improve this trade-off, as well as to decrease the complexity of the detector, compressed sensing (CS) is combined with the proposed STSK-aided IM system. We first present the Maximum LikeLihood (ML) detection, which forms the best-case bound on the proposed system's performance. Then we propose a pair of reduced-complexity detection algorithms capable of approaching the ML detector's performance. Furthermore, in order to attain a near capacityperformance, we propose a soft-input soft-output (SISO) decoder that is capable of exchanging soft-information with a channel decoder through iterative decoding.

Optimal Mapper for OFDM With Index Modulation: A Spectro-Computational Analysis

“…• We derive the general OFDM-IM mapper lower-bound Ω(k log 2 M + log 2 N k + k) and show it becomes the same of the classic OFDM mapper under the optimal configuration (i.e., g = 1, k = N/2, M = 2). This formally proves that enabling all OFDM-IM waveforms is not computationally intractable, as previously conjectured [9], [14]; • Based on the upper and lower bound we identify, we show that the optimal OFDM-IM mapper must run in exact Θ(N ) asymptotic complexity. An implementation running above this complexity (i.e.…”

“…This stems from the fact that the number of index modulated bits P 1 approaches N − log 2 √ N as N → ∞ (Lemma 2). Therefore, although the number of waveforms of the optimal OFDM-IM setup grows exponentially on N , the CC of the IM mapping problem is not intractable (i.e., Ω(2 N )) as previously conjectured [9], [14]. .…”

“…The computational complexity of the OFDM-IM mapper under the optimal SE configuration has been conjectured as an "impossible task" [9], [14]. This belief comes from the fact that the number of mappable OFDM-IM waveforms , which becomes exponential if the optimal SE configuration is allowed.…”

“…Thus, setting g = 1 (i.e., deactivating SP) means maximizing the SE efficiency. SP has represented the state of the art approach to balance SE and CC across the family of IM-based multi-carrier waveforms [8], [9], [12]- [14], [16]- [31].…”

A Spatial Time-Frequency Hopping Index Modulated Scheme in Turbulence-free Optical Wireless Communication Channels

“…combine OFDM-IM and space-time shift keying (STSK) with the complexity reduction determined by compressed sensing [14], an idea further explored in [15] for multi-dimensional IM. These systems trade-off final performance against reduced resources consumption.…”