A Research on Modulation and Detection in OFDM-IM System

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.

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.

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.

Recently, orthogonal frequency division multiplexing (OFDM) with index modulation (OFDM-IM) as well as frequency and quadrature amplitude modulation (FQAM) have been proven to be promising techniques for the multicarrier transmission over frequency selective fading channels by successfully mitigating the induced interference due to multipath, while at the same time boosting the overall spectral efficiency. In this paper, we present a thorough study of OFDM-IM and FQAM schemes and conduct a comparison between them and the classic OFDM system. Different configurations are considered and evaluated in terms of their spectral efficiency and error performance, capitalizing on recent results from the literature.

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.

One of the critical missions for next-generation wireless communication systems is to fulfill the high demand for massive Machine-Type Communications (mMTC). In mMTC systems, a sporadic transmission is performed between machine users and base station (BS). Lack of coordination between the users and BS in time destroys orthogonality between the subcarriers, and causes inter-carrier interference (ICI). Therefore, providing services to asynchronous massive machine users is a major challenge for Orthogonal Frequency Division Multiplexing (OFDM). In this study, OFDM with index modulation (OFDM-IM) is proposed as an eligible solution to alleviate ICI caused by asynchronous transmission in uncoordinated mMTC networks. In OFDM-IM, data transmission is performed not only by modulated subcarriers but also by the indices of active subcarriers. Unlike classical OFDM, fractional subcarrier activation leads to less ICI in OFDM-IM technology. A novel subcarrier mapping scheme (SMS) named as Inner Subcarrier Activation is proposed to further alleviate adjacent user interference in asynchronous OFDM-IM-based systems. ISA reduces inter-user interference since it gives more activation priority to inner subcarriers compared with the existing SMS-s. The superiority of the proposed SMS is shown through both theoretical analysis and computer-based simulations in comparison to existing mapping schemes for asynchronous systems.

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 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.

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.

The increasing demand for higher data rates, better quality of service, fully mobile and connected wireless networks lead the researchers to seek new solutions beyond 4G wireless systems. It is anticipated that 5G wireless networks, which are expected to be introduced around 2020, will achieve ten times higher spectral and energy efficiency than current 4G wireless networks and will support data rates up to 10 Gbps for low mobility users. The ambitious goals set for 5G wireless networks require dramatic changes in the design of different layers for next generation communications systems. Massive multiple-input multiple-output (MIMO) systems, filter bank multi-carrier (FBMC) modulation, relaying technologies, and millimeter-wave communications have been considered as some of the strong candidates for the physical layer design of 5G networks. In this article, we shed light on the potential and implementation of index modulation (IM) techniques for MIMO and multi-carrier communications systems which are expected to be two of the key technologies for 5G systems. Specifically, we focus on two promising applications of IM: spatial modulation (SM) and orthogonal frequency division multiplexing with IM (OFDM-IM), and we discuss the recent advances and future research directions in IM technologies towards spectral and energy-efficient 5G wireless networks.

In this paper, we propose a secure index and data symbol modulation scheme for orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems. By exploiting the notion of the channel reciprocity in time division duplexing mode over wireless channels for shared channel state information as a secret key, we investigate randomized mapping rules for index modulation as well as data symbol modulation. Due to the randomized mapping rules for index and data symbol modulation in OFDM-IM, an eavesdropper is not able to correctly decide message bits even though active subcarriers and their symbols are correctly estimated. In particular, we exploit a characteristic of OFDM-IM which uses a fraction of subcarriers for transmissions to enhance security of data symbol modulation. In addition, to design a set of mapping rules for data symbol modulation, we investigate both a random-selection-based set and a bit-mismatch-based set. Through the analysis and simulation results, we demonstrate that the proposed scheme based on the randomized mapping rules for index modulation and data symbol modulation has a better performance than an existing scheme (modified for OFDM-IM) in terms of bit error rate (BER) and successful attack probability. In particular, we can show that the BER at an eavesdropper is much higher if the bit-mismatch-based set of mapping rules is used.

In the past decades, researchers/scientists have paid attention to the physical layer of underwater communications (UWCs) due to a variety of scientific, military, and civil tasks completed beneath water. This includes numerous activities critical for communication, such as survey and monitoring of oceans, rescue, and response to disasters under the sea. Till the end of the last decade, many review articles addressing the history and survey of UWC have been published which were mostly focused on underwater sensor networks (UWSN), routing protocols, and underwater optical communication (UWOC). This paper provides an overview of underwater acoustic (UWA) physical layer techniques including cyclic prefix orthogonal frequency division multiplexing (CP-OFDM), zero padding orthogonal frequency division multiplexing (ZP-OFDM), time-domain synchronization orthogonal frequency division multiplexing (TDS-OFDM), multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM), generalized frequency division multiplexing (GFDM), unfiltered orthogonal frequency division multiplexing (UF-OFDM), continuous phase modulation orthogonal frequency division multiplexing (CPM-OFDM), filter bank multicarrier (FBMC) modulation, MIMO, spatial modulation technologies (SMTs), and orthogonal frequency division multiplexing index modulation (OFDM-IM). Additionally, this paper provides a comprehensive review of UWA channel modeling problems and challenges, such as transmission loss, propagation delay, signal-to-noise ratio (SNR) and distance, multipath effect, ambient noise effect, delay spread, Doppler effect modeling, Doppler shift estimation. Further, modern technologies of the physical layer of UWC have been discussed. This study also discusses the different modulation technology in terms of spectral efficiency, computational complexity, date rate, bit error rate (BER), and energy efficiency along with their merits and demerits.

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.

Recently, the generalisation of orthogonal frequency division multiplexing with index modulation (OFDM-IM) was proposed in the authors’ previous works. Two generalisation schemes of OFDM-IM, named as OFDM with type-1 generalised index modulation (OFDM-GIM1) and OFDM-GIM2, have been proposed and investigated. In OFDM-GIM1, the number of active subcarriers in an OFDM subblock is no longer fixed. In OFDM-GIM2, independent index modulation is performed on the in-phase and quadrature component of quadrature phase shift keying symbol of each subcarrier. Through such ways, a higher spectral efficiency than that of OFDM-IM may be achieved. In this study, the authors focus on further improving OFDM-GIM2's spectral efficiency by introducing joint I/Q index modulation where the two index modulations on the in-phase and quadrature components are no longer entirely independent. In other words, in the proposed scheme, the input bit string jointly decides the indices of active subcarriers for in-phase and quadrature components. As a result, more bits can be transmitted per OFDM frame. Computer simulation results clearly show the proposed scheme's superiority in both spectral efficiency and bit error rate performance compared with the existing OFDM-GIM2.