Orthogonal Frequency Division Multiplexing With Index Modulation Research Articles

Orthogonal Subblock Division Multiple Access for OFDM-IM-Based Multi-User VLC Systems

In this paper, we propose and experimentally demonstrate an orthogonal subblock division multiple access (OSDMA) scheme for orthogonal frequency division multiplexing with index modulation (OFDM-IM)-based multi-user visible light communication (MU-VLC) systems, where both single-mode index modulation (SM-IM) and dual-mode index modulation (DM-IM) are considered. In order to overcome the low-pass frequency response and the light-emitting diodes (LED) nonlinearity issues of practical MU-VLC systems, OSDMA is employed together with discrete Fourier transform spreading (DFT-S) and interleaving. The feasibility and superiority of the proposed scheme have been successfully verified via both simulations and hardware experiments. More specifically, we evaluate and compare the peak-to-average power ratio (PAPR) performance and the bit error rate (BER) performance of OFDM-SM-IM, DFT-S-OFDM-SM-IM, OFDM-DM-IM and DFT-S-OFDM-DM-IM without and with interleaving. Experimental results show that remarkable distance extensions can be achieved by employing DFT spreading and interleaving for both SM-IM and DM-IM in a two-user OSDMA-VLC system.

향상된 디더 신호 설계를 통한 OFDM-IM에서의 PAPR 감소 방법

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) 시스템은 기존의 OFDM 시스템에 색인 변조 (index modulation) 개념을 추가하여 데이터 전송율을 높인 새로운 통신 방식이다. 하지만 OFDM과 마찬가지로 OFDM-IM은 높은 peak-to-average power ratio (PAPR)을 가지고 있다. 따라서 OFDM-IM에서 디더 (dither) 신호를 비활성화 부반송파에 삽입하여 PAPR을 줄여주는 시도가 있었다. 본 논문에서는 이러한 디더 신호를 더 효과적으로 설계하여 PAPR 감소 성능을 향상시켰다.

Group‐indexed orthogonal frequency division multiplexing index modulation aided performance trade off

In this study, a novel group-indexed orthogonal frequency division multiplexing index modulation (OFDM-IM) scheme is proposed to achieve a tradeoff between spectral efficiency (SE) and bit-error-rate (BER) performance. In the proposed scheme, the total subcarriers in a group are divided into subgroups, and additional bits are transmitted by subgroup indexing, unlike the conventional OFDM-IM scheme, which uses index bits to select active subcarriers. With the proposed scheme, the additional degree of freedom provided by the number of active subgroups selected provides a tradeoff between spectral efficiency and BER performance. Decoding is performed in steps to reduce computional complexity in the decoder design. Simulaton results show that the number of active subgroups selected influences the proposed scheme's performance in terms of energy efficiency, spectral efficiency, and BER performance.

DFT-spread OFDM with quadrature index modulation for practical VLC systems.

In this paper, we for the first time propose and investigate a novel discrete Fourier transform-spread-orthogonal frequency division multiplexing with quadrature index modulation (DFT-S-OFDM-QIM) scheme for practical visible light communication (VLC) systems. By performing subcarrier index modulation on both the in-phase and quadrature components of each subcarrier, OFDM-QIM achieves a higher spectral efficiency than conventional OFDM with index modulation (OFDM-IM). Moreover, the peak-to-average power ratio (PAPR) of OFDM-QIM can be substantially reduced by applying DFT spreading, and hence DFT-S-OFDM-QIM exhibits high tolerance against light-emitting diode (LED) nonlinearity. The superiority of the proposed DFT-S-OFDM-QIM scheme over other benchmark schemes has been successfully verified by both simulation and experimental results.

OFDM with Double Spatial Modulation for Improving the Reliability of Wireless Communication

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) has recently attracted numerous research interests, which enhances the spectral efficiency and the reliability of wireless communication by well transplanting the core idea of spatial modulation (SM) into the OFDM system such as the index of subcarrier. Due to that double spatial modulation (DSM) improves the spectral efficiency and the uncoded bit error rate (BER) as compared with SM, in this paper, a new design of OFDM with DSM (OFDM-DSM) is further investigated. Specifically, the design of the OFDM-DSM system is elaborately introduced. Based on the maximum-likelihood (ML) detector, the average bit error probability is presented. Finally, compared to conventional schemes such as OFDM, OFDM-IM, simulation results show that the OFDM-DSM system has better BER performance than other schemes over Rayleigh distribution and additive white Gaussian noise (AWGN) in wireless communication network.

Performance analysis of OFDM-IM scheme under STO and CFO

In this letter, performance analysis of orthogonal frequency division multiplexing with index modulation (OFDM-IM) is presented in term of bit error rate (BERs). The analysis considers its performance under two impairments, symbol time offset (STO) and carrier frequency offset (CFO) in frequency-selective fading channel. As orthogonal multicarrier system, OFDM-IM is subject to both inter-symbol interference (ISI) and inter-carrier interference (ICI) in a frequency-selective fading channel. OFDM-IM is a new multicarrier communication system, where the active subcarriers indices are used to carry additional bits of information. In general, in the previous existing works, OFDM-IM are evaluated only for near-ideal communication scenarios by only incorporating the CFO factor. In this work, the OFDM-IM performance is investigated and compared with conventional OFDM in the presence of two impairments, STO and CFO. Simulation results show that OFDM-IM outperforms the conventional OFDM with the presence of STO and CFO, especially at high SNR areas.

Protection scheme of subcarrier index in OFDM with index modulation aided by LDPC coding

The receiver of OFDM with Index Modulation (OFDM-IM) usually adopts a Log Likelihood Ratio (LLR) detection algorithm based on the activation state of subcarriers. However, the LLR detection algorithm will cause detection errors in subcarrier activation pattern (SAP) or get illegal SAP. Consequently, further errors occur in demodulation, increasing the bit error rate (BER). To solve this problem, we propose the protection scheme of subcarrier index aided by LDPC coding, which reduces the SAP detection errors by encoding the index information bits. On the receiver, the LDPC Coding Aided (LA) detection algorithm is designed, and the formula of LLR of index information bits is derived in detail. Monte Carlo simulation is carried out over multi-path fading channel by MATLAB software. The results show that under the condition that the spectrum efficiency is not lower than the classical OFDM-IM scheme, the proposed protection scheme can obtain a gain of about 5~9 dB when the BER is 10-4, effectively improving the BER performance of OFDM-IM scheme.

Toward Spectral and Energy Efficient 5G Networks Using Relayed OFDM With Index Modulation

Next generation wireless networks are expected to provide much higher data throughput and reliable connections for a far larger number of wireless service subscribers and machine-type nodes, which results in increasingly stringent requirements of spectral efficiency (SE) and energy efficiency (EE). Orthogonal frequency-division multiplexing with index modulation (OFDM-IM) stands out as a promising solution to satisfy the SE requirement with a reasonable increase in system complexity. However, the EE of OFDM-IM is still required to be enhanced. Moreover, diversity gain is difficult to harvest from the frequency domain without affecting the SE for OFDM-IM systems, which hinders further reliability enhancement. In this regard, relay-assisted OFDM-IM, as a promising joint paradigm to achieve both high SE and EE, was proposed and has been studied since last year. The objectives of this study are to summarize the recent achievements of this joint paradigm, articulate its pros and cons, and reveal the corresponding challenges and future work. More importantly, we provide a full picture and insights into the implementation of this new paradigm in next generation networks.

Generalization of Index-Modulation: Breaking the Conventional Limits on Spectral and Energy Efficiencies

In the context of orthogonal frequency-division multiplexing with index modulation (OFDM-IM), this paper first presents an improved index modulation (IIM) technique to address the well-known low spectral efficiency problem of IM techniques in general and OFDM-IM in particular. OFDM-IIM is realized by deriving the minimum required number of subcarriers per group, and the minimum number of active subcarriers in each group, of the conventional OFDM-IM technique. It is proven that OFDM-IIM can deliver higher spectral and energy efficiencies than classical OFDM and OFDM-IM. The gains come at the expense of increased detection complexity. Therefore, a proposal of OFDM with generalized IM (OFDM-GIM) technique is presented, where a variable number of subcarriers per group are allowed to be activated. Two variants of OFDM-GIM are designed based on the activation pattern of the subcarriers: the first achieves superior spectral efficiency with reduced detection complexity as compared to OFDM-IIM, and the second is tailored for low data rate communications with higher energy efficiency requirements. Besides optimal maximum likelihood detection, a less-complex sub-optimal detector is proposed. A closed-form expression for the bit error rate (BER) of OFDM-IIM and the two variants of OFDM-GIM is derived, considering transmissions over Nakagami fading channels and multiple-antenna reception. Finally, OFDM-IIM and OFDM-GIM are compared with state-of-the-art techniques to validate their superiority in terms of BER, achievable rate, and energy efficiency.

SCMA System Design With Index Modulation via Codebook Assignment

Sparse code multiple access (SCMA) is a promising non-orthogonal multiple access (NOMA) scheme for massive machine-type communications for 5G-and-beyond communication systems. Innovative use of orthogonal frequency division multiplexing with index modulation (OFDM-IM) takes advantage of using tone indices in data transmission. In this study, we propose a novel multiplexing and multiple access scheme, namely SCMA based on OFDM-IM (SCMA-IM). SCMA-IM method can be implemented in uplink NOMA systems in an efficient way with similar computational complexity as SCMA. In this method constellation differences and diversity are obtained via SCMA codebooks (CBs) and the employment of CBs is transferred to index modulation (IM). Performance improvement is achieved via CBs so that the number of data bits carried by indices increases more than one bit with different constellations, and also with the number of CBs assigned. In order to determine the indices used in IM, the receiver structure is simplified by the message passing algorithm and log-likelihood ratio detection process used in SCMA receivers without indexing the receiver. Thus, a new NOMA scheme is obtained by coding with IM. Bit error rate performance of the system is studied for 150% and 200% overloading factors.

Power Allocation for Relayed OFDM With Index Modulation Assisted by Artificial Neural Network

In this letter, we propose a power allocation scheme for relayed orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems. The proposed power allocation scheme replies on artificial neural network (ANN) and deep learning to allocate transmit power among various subcarriers at the source and relay nodes. The objective of the power allocation scheme is to minimize the overall transmit power under a set of constraints. Without loss of generality, we assume all subcarriers at source and relay nodes are independently distributed with different statistical distribution parameters. The relay node adopts the fixed-gain amplify-and-forward (FG AF) relaying protocol. We employ the adaptive moment estimation method (Adam) to implement back-propagation learning and simulate the proposed power allocation scheme. The analytical and simulation results show that the proposed power allocation scheme is able to provide comparable performance as the optimal solution but with lower complexity.

LDPC Decoding With Low Complexity for OFDM Index Modulation

In this paper, the posterior probabilities of the low-density parity check (LDPC) coded bits are derived for the orthogonal frequency division multiplexing index modulation (OFDM-IM) system to reduce the implementation complexity of LDPC decoding without performance loss. Specifically, the complexity of LDPC decoding is reduced by decomposing the posterior probability of the coded bit into multiple likelihood probabilities, each of which is obtained for each subcarrier of the corresponding OFDM-IM subblock. The results of the complexity analysis indicate that the proposed approach significantly reduces the implementation complexity of LDPC decoding for OFDM-IM compared to the conventional approach. Furthermore, the simulation results confirm that the proposed approach provides the same bit error rate performance as the conventional approach.

Energy-Efficient Index Modulation With In-Phase/Quadrature Format in the Generalized Fading Channel

Dual-mode (DM) or multi-mode (MM) index modulation (IM) techniques with the in-phase/quadrature (IQ) format have been investigated for improving the performance of the orthogonal frequency division multiplexing with IM (OFDM-IM) system in the frequency-selective Rayleigh fading channel. However, all subcarriers in these schemes must be activated so that the energy efficiency (EE) of the system inevitably decreases. In this paper, we propose a novel modulation scheme named quadrature tri-mode index modulation (QTM-IM) technique to achieve a trade-off between the spectral efficiency (SE) and EE. The proposed QTM-IM can also be flexibly extended into multi-mode form called MM with enhanced IQ (MM-EIQ). The multi-mode $M$ -ary pulse amplitude modulation (PAM) constellations containing the origin point are designed to map the information bits into the active subcarriers. On the other hand, the theoretical analysis of IM-based schemes over the Rician fading channel has been conducted since most previous papers only considered the Rayleigh fading channel. At the receiver, three kinds of detectors with different algorithm complexities are employed for signal demodulation. Finally, the computer simulation results demonstrate the enhancement of the proposed schemes. More specially, (i) QTM-IM achieves 4dB signal-to-noise ratio (SNR) gain at the BER level of 10−5 compared with quadrature DM (QDM) scheme with the same SE in the Rician fading channel and (ii) MM-EIQ harvests 0.89 bits/s/Hz SE gain and almost doubles the EE compared with MM-IQ scheme without any SNR loss over the Rayleigh fading channel.

A SLM Scheme for PAPR Reduction in Polar Coded OFDM-IM Systems Without Using Side Information

In the present article, we propose a novel selected mapping (SLM) scheme based on a Polar coding technique for peak to average power ratio (PAPR) reduction in orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems. The proposed scheme by utilizing random frozen bits in polar codes generates different number of candidate sequences. Then the candidate sequence with the smallest PAPR is selected for transmission. The proposed scheme can be considered as one block in an OFDM-IM system that performs both PAPR reduction and error correction. For a fair comparison, the performance of an OFDM-IM system based on the proposed scheme is compared with a system that carries out the same operations with two separate blocks where a Polar encoder is cascaded with the one for PAPR reduction (such as conventional SLM or PTS), and a Polar coded OFDM-IM system without any PAPR reduction scheme. Moreover, based on our proposed SLM scheme, a novel receiver without using side information (SI) is proposed. This SI free receiver is based on the successive cancellation list (SCL) polar decoding scheme. Simulation results show that as the Polar code can bring both error correction and PAPR reduction capabilities by using our proposed scheme. Also, the proposed SI free receiver can achieve similar bit error rate (BER) performance as that of the ideal case in both additive Gaussian white noise (AWGN) and frequency selective channels.

Orthogonal frequency division multiplexing with power distribution index modulation

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a promising multicarrier transmission technique that exploits both conventional modulation and the indices of active subcarriers for data transmission. In this Letter, the authors propose OFDM with power distribution index modulation (OFDM-PIM) where a unique power distribution technique is applied to index modulated subcarriers. Furthermore, we propose OFDM with in-phase/quadrature PIM (OFDM-I/Q-PIM) which performs the same power distribution process on the real and imaginary parts of the data symbols, independently. Average bit error performances of OFDM-PIM and OFDM-I/Q-PIM are obtained and the superiority of the proposed schemes over reference schemes is demonstrated via extensive computer simulations.

ABC Algorithm-Based Subblocks Set Design for OFDM With All Index Modulation

In this letter, we propose a low complexity artificial bee colony (ABC) algorithm based subblocks set design to maximize the diversity gain of orthogonal frequency division multiplexing with all index modulation (OFDM-AIM), which is inspired by OFDM with index modulation (OFDM-IM). Unlike the conventional OFDM-IM, where constellation points of the M-ary signals are fixed, ABC aided OFDM-AIM (ABC-OFDM-AIM) scheme has flexible subcarrier constellation points to enhance the diversity gain, which ensures better BER performance. Also, a parallel ABC (PABC) algorithm, which has a more powerful search strategy than the ABC algorithm, is proposed (PABC-OFDM-AIM) to further enhance the diversity gain of the OFDM-AIM. Performances of the proposed schemes have been tested according to the average bit error probability (ABEP), search complexity, and BER performance criteria. Simulation results show that the proposed schemes outperform other OFDM-IM based schemes, especially in the improvement of BER.

Super-Mode OFDM With Index Modulation

Orthogonal frequency division multiplexing (OFDM) with index modulation (OFDM-IM) appears as a promising multi-carrier waveform candidate for beyond 5G due to its attractive advantages such as operational flexibility and ease of implementation. However, OFDM-IM may not be a proper choice for 5G services such as enhanced mobile broadband (eMBB) since achieving high data rates is challenging because of its null subcarriers. One solution to enhance the spectral efficiency of OFDM-IM is the employment of multiple distinguishable constellations (modes) by also exploiting its null subcarriers for data transmission. This article proposes a novel IM technique called super-mode OFDM-IM (SuM-OFDM-IM), where mode activation patterns (MAPs) and subcarrier activation patterns (SAPs) are jointly selected and conventional data symbols are repetition coded over multiple subcarriers to achieve a diversity gain. For the proposed scheme, a low-complexity detector is designed, theoretical analyses are performed and a bit error rate (BER) upper bound is derived. The performance of the proposed system is also investigated through real-time experiments using a software-defined radio (SDR) based prototype. We show that SuM-OFDM-IM exhibits promising results in terms of spectral efficiency and error performance; thus, appears as a potential candidate for 5G and beyond communication systems.

Coded OFDM-IM with iterative detection☆

Coded Orthogonal frequency division multiplexing with index modulation (OFDM-IM) has been proposed, where channel coding and soft decision are employed to exploit the multipath diversity for the information conveyed by the constellation symbols. However, the performance of coded OFDM-IM is dependent on the detection performance of subcarrier activation pattern (SAP) and the diversity order of the SAPs requires further investigation. In this paper, a lower-bound of LLR detector is derived to show that the maximum achievable diversity order is the minimum Hamming distance between the SAPs for the LLR detector. Based on the analyses, iterative detection is proposed to improve the performance of coded OFDM-IM, where information-assisted LLR detector is proposed to improve the detection performance of SAP by using the soft information of the constellation symbols. Simulation results are provided to corroborate the diversity analyses and show the advantage of the coded OFDM-IM with iterative detection.

Q-Ary Multi-Mode OFDM With Index Modulation

In this letter, we propose a novel orthogonal frequency division multiplexing with index modulation (OFDM-IM) scheme, which we call Q -ary multi-mode OFDM-IM (Q -MM-OFDM-IM). In the proposed scheme, Q disjoint M-ary constellations are used repeatedly on each subcarrier, and a maximum-distance separable code is applied to the indices of these constellations to achieve the highest number of index symbols. A low-complexity subcarrier-wise detection is shown possible for the proposed scheme. Spectral efficiency (SE) and the error rate performance of the proposed scheme are further analyzed. It is shown that the proposed scheme exhibits a very flexible structure that is capable of encompassing conventional OFDM as a special case. It is also shown that the proposed scheme is capable of considerably outperforming the other OFDM-IM schemes and conventional OFDM in terms of error and SE performance while preserving a low-complexity structure.

Deep Convolutional Neural Network-Based Detector for Index Modulation

In this letter, a convolutional neural network-based detection framework is proposed for the wireless communication systems using orthogonal frequency-division multiplexing with index modulation (OFDM-IM). In the proposed framework, the received symbols are transformed to polar coordinates to help the neural network detect the indices of the activated subcarriers. We parallel the amplitude and the phase of the received symbols to form 2-dimensional matrices and use 2-dimensional convolutional layers to fully exploit the inherent information in the OFDM-IM symbols. After offline training, the proposed detector can be employed to implement online detection of the OFDM-IM symbols. Simulation results demonstrate that the proposed detector is capable of achieving near maximum likelihood detection performance with much lower complexity.