Secure Index and Data Symbol Modulation for OFDM-IM

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.

Orthogonal Frequency Division Multiplexing with Index Modulation (OFDM-IM) is an effective communication technology that utilizes subcarrier indices to transmit information in addition to the information traditionally modulated on active subcarriers. However, OFDM-IM suffers from high peak-to-average power ratio (PAPR), which can result in signal distortion and hence system performance degradation. One of the techniques used to alleviate the PAPR in OFDM-IM is the selected mapping (SLM) technique. The effectiveness of the SLM PAPR reduction technique is affected by OFDM-IM system parameters, such as the number of subcarriers and subcarrier activation ratio. This paper explores the impact of these OFDM-IM system parameters on the PAPR reduction performance of the SLM technique with different phase sequence settings. The obtained results provide an overview of the collective effect of both OFDM-IM and SLM parameters in different operation cases. The findings show that the amount of PAPR reduction is mainly affected by the number of subcarriers, and less affected by the subcarrier activation ratio. That is a greater PAPR reduction of up to 4.2 dB is achievable with relatively smaller number of subcarriers. The results show the limited effect of more complex phase vectors, hence suggesting simpler SLM parameter setting alternatives to achieve a target PAPR reduction performance. Finally, the results show the improvement in Bit Error Rate (BER) performance of OFDM-IM system employing the SLM with carefully selected PAPR reduction parameters.

Orthogonal frequency division multiplexing with index modulation (OFDM-IM), which transmits information bits via <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> -ary constellation symbols and indices of the active subcarriers, is a promising OFDM-based multicarrier transmission scheme. Recently, several new schemes have been proposed by utilizing the flexibility of the OFDM-IM to meet the diverse needs of 5G networks. Coordinate interleaved OFDM-IM (CI-OFDM-IM) that conveys the real and imaginary part of the data symbols over different subcarriers and OFDM with power distribution IM (OFDM-PIM) that transmits the data symbols over high and low power subcarriers, are two OFDM-IM based schemes with additional diversity gain and improved bit error rate (BER) performance. In this letter, we propose a novel transmission scheme named as coordinate interleaved OFDM with power distribution IM (CI-OFDM-PIM), which applies coordinate interleaving and power distribution in subcarriers to achieve a higher diversity gain. The average bit error probability (ABEP) for the CI-OFDM-PIM is derived and the superior error performance of the proposed scheme over benchmarks are shown via computer simulations.

Next generation of mobile networks is the key area of research with increasing demand for new applications and use cases. In order to satisfy the applications with high data rate, high reliability, and low latency, multicarrier transmission through index modulation (IM) has been considered as a promising candidate owing to its flexible structures. In general, existing IM schemes are only evaluated for ideal communication scenarios. In this work, error performance of three frequency domain IM schemes are investigated and compared in the presence of carrier frequency offset (CFO) and in-phase/quadrature (IQ) imbalance. Orthogonal frequency division multiplexing with IM (OFDM-IM), OFDM with generalized IM (OFDM-GIM), and OFDM with subcarrier number modulation (OFDM-SNM) are assessed. It is shown via computer based simulations that although OFDM-GIM and OFDM-SNM provide higher spectral efficiency compared with OFDM-IM, they are more sensitive against RF impairments. Among them, OFDM-IM provides the best error performance under CFO and IQ imbalance.

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is an extension of the traditional OFDM modulation scheme. Its key idea is to adopt the activated subcarrier index to carry extra information. In this paper, we propose a new optical multi-input multiple-output (MIMO) visible light communication (VLC) system based on OFDM-IM and generalized light-emitting diode (LED) index modulation (GLIM). The proposed scheme utilizes the subcarrier index selection to improve the system flexibility and adopts the LED index modulation to increase the spectral efficiency, which also avoids the Hermitian symmetry processing. Simulation results show that the proposed scheme achieves better bit error rate (BER) performance than the traditional GLIM scheme. Moreover, the proposed scheme can flexibly select the number of the active subcarriers according to the channel condition and ensure better system performance.

Jamming is a simple but efficient attack method that challenges communications while traditional physical-layer defence solutions are limited. Recently, index modulation (IM) is proposed to enable index transmission in addition to data symbol transmission, which gains resistance against jamming but with limited efficacy. This letter proposes a coding split and adjustment (CSA) framework for low-density parity-check (LDPC) coding assisted orthogonal frequency division multiplexing with IM (OFDM-IM) to enhance its anti-jamming capability. CSA splits the traditionally single system code rate into an index code rate and a data code rate, each independently adjusted based on jamming impacts to error performance. Simulation results verify that OFDM-IM with CSA exhibits superior error performance over traditional OFDM-IM and OFDM in three investigated jamming scenarios. Moreover, this letter reveals that the CSA assisted OFDM-IM can still recover signals while OFDM-IM and OFDM completely fail under high jamming power.

This paper is interested in studying the Peak to Average Power Ratio (PAPR) reduction in Orthogonal Frequency Division Multiplexing with Index Modulation (OFDM-IM) system transmitter. PAPR is a common issue in multicarrier transmission techniques which is the result of adding independent multicarrier signals of different peak values on the same phases. The reduction schemes have been diversly examined for classical OFDM and the majority of them can be directly extended to OFDM-IM while some require slight changes to suit the OFDM-IM characteristics. Selective Mapping (SLM), Partial Transmit Sequence (PTS), Tone Reservation (TR), and Peak Insertion (PI) are some examples on the reduction schemes that will be investigated throughout this paper. As for PI, to the best knowledge of the authors is for the first time implemented in OFDM-IM. The system parameters effects, number of total subcarriers(N), number of subblocks (n), the active subcarriers (k), and the activation ratio (r) are studied to gain the lowest PAPR amount possible that reached (1.2 dB) at specified system parameters.

In this paper, we propose an orthogonal frequency division multiplexing with index modulation (OFDM-IM) based on high-dimensional spherical codes. Unlike the traditional OFDM-IM system, which conveys the traditional M-ary constellation symbol on the active subcarriers, we use the adjacent subcarriers in the sub-block as a whole to be modulated based on high dimensional spherical code. Since the Euclidean distances between the constellation points increase by using high dimensional modulation, the performance of the OFDM-IM system is improved. We derive the general form of symbol error rate (SER) for the proposed OFDM-IM system with the maximum likelihood (ML) detection. The simulation results show that the bit error rate (BER) and SER of our proposed scheme is better than that of the traditional OFDMIM system. We also investigate the effect of channel estimation error on our proposed scheme.

Orthogonal frequency-division multiplexing with index modulation (OFDM-IM) has recently attracted many researchers' attention due to its superior spectrum efficiency and reliability compared to the traditional OFDM. Cooperative decode-and-forward relaying has been incorporated with OFDM-IM, which provides a higher energy efficiency and better network coverage. However, it might not be feasible in realistic applications, owing to the high system complexity and transmission delay rendered by complex decoding and channel estimation procedures. Therefore, in this paper, we propose a fixed-gain (FG) amplify-and-forward (AF) relay-assisted OFDM-IM system, which does not need to perform complex decoding and channel estimation at the relay, but only requires a pre-processing capability at the relay, e.g., cyclic prefix removal and re-insertion. Therefore, the system complexity can be reduced and the forwarding delay as well as power consumption caused by processing at the relay also decline. We analyze the average outage probability, block error rate, and achievable rate of the proposed system and verify all analysis by numerical results. The proposed FG AF relay-assisted OFDM-IM provides a simple solution to the implementation of OFDM-IM in new network paradigms, where nodes are simple, power limited, and/or complexity limited.

In this paper, orthogonal frequency division multiplexing with differential index modulation (OFDM-DIM) is proposed for visible light communication. Compared with traditional OFDM with index modulation (OFDM-IM), the proposed scheme decreases the average number of used subcarriers when transmits the same amount of information bits, therefore higher spectral efficiency can be achieved. The simulation results present that OFDM-DIM can provide higher data transmission rate and lower bit error rate (BER) over additive white gaussian noise (AWGN) optical channel. Meanwhile, simulations over reference channels of short range optical wireless communication are implemented, where OFDM-DIM performances better than OFDM-IM when line-of-sight (LOS) components are dominant.

With the rapid development of the information industry, the amount of data for communications is growing, and people are demanding communication of higher performance and faster speed. The index modulation (M) technique attracts great attention from scholars due to its high spectral and energy efficiency. Recently, a new technique for implementing index modulation using orthogonal frequency division multiplexing (OFDM) subcarriers has been proposed. This technique is called OFDM with index modulation (OFDM-IM). Instead of activating all subcarriers, OFDM-IM technology selectively activates a portion of subcarriers to transmit modulation symbols. This paper first briefly introduces the OFDM - IM system. Then, the BER and BER performance of OFDM-IM under different 5G mainstream modulation modes and different detection, such as ML and LLR, are studied. Finally, the OFDM-IM system performance with (7, 4) hamming code is studied. Compared to the classical OFDM system, the OFDM-IM system can improve performance.

Today, Orthogonal Frequency Division Multiplexing (OFDM) is the most preferred and commonly used scheme for all communication systems. A new multicarrier technique called OFDM with Index Modulation (OFDM-IM) has been developed recently where the indices of the active subcarriers are used to transmit information in addition to the constellation symbols. In this article, system models of OFDM-IM and the two generalized schemes of OFDM-IM called OFDM with Generalized Index Modulation 1 (OFDM-GIM1) and OFDM with Generalized Index Modulation 2 (OFDM-GIM2) are studied. Here, noncoherent detection has been introduced for the two generalized schemes—OFDM-GIM1 and OFDM-GIM2 with the need for increasing the spectral efficiency. The probability of index error (Pie) is derived for OFDM-IM, OFDM-GIM1 and OFDM-GIM2. The developed noncoherent generalized schemes have reduced Pie and better performance with minimum Signal-to-Noise Ratio (SNR). This is clear from the simulation results that OFDM-GIM1 has less Pie than the other OFDM-IM schemes and it is around 10−1 when the required SNR is low about 8 dB.

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.

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) has been recently proposed to increase the spectral efficiency and improve the error performance of multicarrier communication systems. However, all the OFDM-IM systems assume that the perfect channel state information is available at the receiver. Nevertheless, channel estimation is a challenging problem in practical wireless communication systems for coherent detection at the receiver. In this paper, a novel method based on the pilot symbol-aided channel estimation technique is proposed and evaluated for OFDM-IM systems. Pilot symbols, which are placed equidistantly, allow the regeneration of the response of the channel so that pilot symbol spacing can fulfill the sampling theorem criterion. Our results shows that the low-pass interpolation and SPLINE techniques perform the best among all the channel estimation algorithms in terms of bit error rate and mean square error performance.

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is shown to be an efficient modulation scheme for underwater optical wireless communication (UOWC) systems due to its high power efficiency and excellent flexibility. Differing from conventional OFDM, the modulation parameters of OFDM-IM consist of not only M-ary constellations but also subcarrier indices. In this Letter, we propose and demonstrate an intelligent automatic modulation recognition (AMR) scheme for OFDM-IM in UOWC systems by using Swin Transformer (Swin-T). Moreover, transfer learning with a hybrid training approach is further proposed to substantially enhance the AMR performance. Experimental results successfully demonstrate the feasibility and superiority of the proposed intelligent AMR scheme based on Swin-T with transfer learning and hybrid training in UOWC systems. More specifically, a recognition accuracy of 96% can be obtained by using Swin-T with transfer learning and hybrid training for a relatively small received signal-to-noise ratio (SNR) of 3.6 dB.