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In underwater acoustic communication (UWA), there is a significant presence of multipath and Doppler spread. The integration of orthogonal frequency division multiplexing (OFDM) with index modulation (IM), utilizing subcarrier index modulation to enhance system performance underwater, has garnered considerable interest from researchers. Multiple mode modulation can enhance utilization by transmitting symbols of different modes on different subcarriers. Inspired by the concepts of index modulation and multiple mode modulation, this paper proposes a method that combines multiple mode indexing with the filter bank multicarrier system (MM-FBMC-IM), enabling the transmission of different modulation orders on each subcarrier to increase system flexibility. Simulations demonstrate that under the same spectral efficiency, multiple mode indexing FBMC offers superior bit error rate (BER) performance compared to conventional FBMC and index modulation FBMC. [ABSTRACT FROM AUTHOR]

Summary Deep learning (DL)‐based channel estimation for orthogonal frequency division multiplexing with index modulation (OFDM‐IM) under Rayleigh fading channel conditions is presented in this paper. A deep neural network (DNN) is utilized to estimate the channel response in simulations. The proposed DNN is trained using the channel coefficient derived through the least squares (LS) method. Then channel estimation is conducted using the trained DNN. Within the DNN, the long short‐term memory (LSTM) layer is included as the hidden layer. Different scenarios are handled in simulations and the proposed DNN is compared with traditional channel estimation methods. The simulations demonstrate that the DL‐based channel estimation significantly surpasses the LS and minimum mean‐square error (MMSE) techniques. [ABSTRACT FROM AUTHOR]

Abstract In underwater acoustic communication (UWA), there is a significant presence of multipath and Doppler spread. The integration of orthogonal frequency division multiplexing (OFDM) with index modulation (IM), utilizing subcarrier index modulation to enhance system performance underwater, has garnered considerable interest from researchers. Multiple mode modulation can enhance utilization by transmitting symbols of different modes on different subcarriers. Inspired by the concepts of index modulation and multiple mode modulation, this paper proposes a method that combines multiple mode indexing with the filter bank multicarrier system (MM-FBMC-IM), enabling the transmission of different modulation orders on each subcarrier to increase system flexibility. Simulations demonstrate that under the same spectral efficiency, multiple mode indexing FBMC offers superior bit error rate (BER) performance compared to conventional FBMC and index modulation FBMC.

Given the issues of low transmission rate and poor bit error performance in traditional differential chaos shift keying systems, a dual-mode three-dimensional index modulation differential chaos shift keying (DMTD-IM-DCSK) system was proposed. This system simultaneously utilized time slots, orthogonal codes, and sort index to transmit information on both selected and unselected time slots. At the receiver, the variance of noise was reduced and the system’s error performance was improved by the use of denoising techniques. Formulas for bit error rate (BER) were derived for additive white Gaussian noise channels and multipath Rayleigh fading channels. Simulation results demonstrate that, compared to similar chaotic keying systems, the proposed system achieves higher data rates and superior error performance.

To meet the rigorous demands for reliability and spectral efficiency (SE) in the beyond-5th generation mobile network (5G) and the upcoming 6th generation mobile network (6G), a merging codebook based codeword position index modulation scheme for sparse code multiple access (SCMA) is proposed for the uplink SCMA. The scheme expands the codeword position in the time domain, allowing the codeword positions to be fully populated and carry additional information bits by their index, and provides flexibility in adjusting the system SE by changing the codeword position number and the index modulation order. Furthermore, a corresponding joint detection algorithm based on message passing algorithm (MPA) is designed and the design criteria of the merging codebook are given. System analysis and simulation results show that compared with other index modulation schemes, the proposed scheme better balances reliability and SE, and also has advantages in bit error rate (BER) performance and robustness. [ABSTRACT FROM AUTHOR]

Energy minimization is crucial in designing Wireless Sensor Networks (WSNs), especially for multi-hop transmission. To address this challenge, an Intra-Cluster and Inter-Cluster (ICIC) energy reduction mechanism was developed, which includes dynamic duty cycle allocation for intra-cluster transmission and selection of the lowest Energy Consumption (EC) path for inter-cluster transmission. Conversely, randomly selecting Cluster Heads (CHs) can lead to inefficient distribution of tasks among nodes, impacting network lifetime. Additionally, small errors in the data received can lead to the Sink Node (SN) making an unsuccessful global decision in different WSN applications. Therefore, this manuscript introduces a new Progressive Index-Modulation (PIM)-based CH selection algorithm in ICIC (PIM-ICIC) for multi-hop WSNs. In this algorithm, a novel broadcasting scheme called index-shift is adopted to distribute the CH role more evenly among sensor nodes. First, Cluster Member (CM) nodes are divided into sets where nodes within the same set collaborate in selecting CHs to balance the CH loads. The CH is chosen according to the local cluster data in each cycle. If a node reaches a threshold limit for being chosen as a CH, an alternative node from a similar set can assume the CH role to transmit data to the SN. Thus, the PIM-ICIC algorithm can prolong network lifetime and reduce packet loss effectively. Finally, extensive simulations demonstrate that the PIM-ICIC achieves a Packet Delivery Ratio (PDR) of 5.8×105 packets, EC of 14J, and 20 dead nodes over 1000 rounds. With 400 nodes in the network, it achieves a PDR of 6.9×105 packets, 78% EC, and 86 dead nodes. At a 40dB Signal-to-Noise Ratio (SNR), PIM-ICIC achieves a Data Error Rate (DER) of 0.0002, surpassing ICIC, Hybrid Particle Swarm Optimization with Improved Low Energy Adaptive Clustering Hierarchy (HPSO-ILEACH), and Sine Cosine Algorithm with Levy mutation (SCA-Levy) in multi-hop WSNs. [ABSTRACT FROM AUTHOR]

Spatial modulation (SM) has the potential to meet the requirements of 5G and beyond communication systems with features such as reduced hardware complexity and good trade-off between spectral efficiency and energy efficiency. In this study, an efficient non-square differential spatial modulation (DSM) scheme is presented in which the number of time slots is one more than the number of transmit antennas. The introduced scheme includes one empty time slot. At the other time slots, the time slots of the conventional DSM (CDSM) are used (the Gray code order (GCO) can also be used). There is one active antenna at each time slot of the proposed scheme. The index of empty time slot conveys information. Thus, in comparison with CDSM (or GCO), for the same number of transmit antennas, the introduced scheme has more energy-free bits (index bits). It is free of pilot overhead, channel estimation complexity, and potential channel state information (CSI) estimation errors. Further, a detector with no error propagation is presented. Analytical expressions for the bit error rate (BER) are derived at high signal-to-noise ratios (SNRs) and high SNRs per bit (SNRbs). Simulation results verify the theoretical evaluation and demonstrate the efficiency of the proposed scheme.

Spatial modulation (SM) has the potential to meet the requirements of 5G and beyond communication systems with features such as reduced hardware complexity and good trade-off between spectral efficiency and energy efficiency. In this study, an efficient non-square differential spatial modulation (DSM) scheme is presented in which the number of time slots is one more than the number of transmit antennas. The introduced scheme includes one empty time slot. At the other time slots, the time slots of the conventional DSM (CDSM) are used (the Gray code order (GCO) can also be used). There is one active antenna at each time slot of the proposed scheme. The index of empty time slot conveys information. Thus, in comparison with CDSM (or GCO), for the same number of transmit antennas, the introduced scheme has more energy-free bits (index bits). It is free of pilot overhead, channel estimation complexity, and potential channel state information (CSI) estimation errors. Further, a detector with no error propagation is presented. Analytical expressions for the bit error rate (BER) are derived at high signal-to-noise ratios (SNRs) and high SNRs per bit (SNRbs). Simulation results verify the theoretical evaluation and demonstrate the efficiency of the proposed scheme. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Chongqing University of Posts & Telecommunications (Natural Science Edition) is the property of Chongqing University of Posts & Telecommunications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a novel variant of filter bank multicarrier (FBMC) communication, which carries additional bits through mapping the real and imaginary parts of the symbol to the active time-frequency (TF) points, called FBMC with real part and imaginary part index modulation (FBMCRIIM). Spectral efficiency is improved by doubling the index bits and the inherent interference in each index group is significantly reduced. In this paper, an efficient combination set selection strategy, which synthetically considers the average Hamming distance, average poor index number and average interference coefficient, is also designed. The BER performance comparison between the proposed and reference schemes is obtained under different index modes, spectral efficiency, modulation order and prototype filters. The enhanced performance demonstrates that the proposed scheme is a promising alternative for multicarrier transmission by outperforming the existing FBMC-IM counterpart.

Intelligent Reconfigurable Surface has become a promising technique in recent years due to its inherent ability to overcome the severe wireless fading channel characteristics such as reflection, refraction, scattering, and diffraction, etc. On the other hand, spatial modulation (SM) is a special type of index modulation technique that is utilized to enhance the spectral efficiency of wireless communication systems. In this paper, we combine these two techniques and propose the two IRS-assisted bi-constellation index spatial modulation (BCI-SM) and multi-constellation index spatial modulation (MCI-SM) schemes operating under Nakagami-m fading channels. The main idea is to select the receive antenna and constellation set indices according to the incoming information bits, thus yielding enhanced spectral efficiency and bit error rate (BER) performance. We also propose the low complex log-likelihood ratio detector for both schemes. In addition, we derive the analytical results for the union bound on the average BER with the ML detector. These results can be generalized for both IRS-assisted BCI-SM and IRS-assisted MCI-SM schemes and are valid for any arbitrary value of m in Nakagami-m fading channels. Simulation results show the superiority of IRS-assisted BCI-SM and IRS-assisted MCI-SM schemes over the existing IRS-aided SM in terms of BER performance. In particular, BCI-SM shows an SNR gain of around 3-5 dB while MCI-SM exhibits an SNR gain of nearly 7-12 dB when compared with the existing IRS-aided SM scheme.

In this article, we propose three index modulation (IM) aided unsourced random access schemes in the block-fading multiple-antenna channel. In all the proposed schemes, the signal frame is partitioned into multiple time slots, and only part of time slots are activated to transmit signal. The active time slots are determined by the active time slot pattern (ATP) information through utilizing the principle of IM. In the first two schemes, each time slot includes pilot sub-slot and data sub-slot. The multiple-stage orthogonal pilots (MSOPs) are employed for both channel estimation and user identification, and the pilot-hopping pattern (PHP) of MSOPs determines the pilots transmitted over the active pilot sub-slots. Moreover, in the first scheme, the polar-coded signal is transmitted repeatedly in the data sub-slots of active time slots. In the second scheme, the ATP and PHP information is first transmitted through the sparse-regression-code (SPARC) in the first time slot, and the polar-coded signal is divided into multiple parts which are transmitted in those active data sub-slots, respectively. At the receiver, the iterative orthogonal pilot-aided channel estimation and decoding with successive interference cancellation is presented. In the third scheme, the signal frame is also partitioned into multiple time slots where only two time slots are activated by each user. The first time slot is always activated to transmit the ATP and active channel-use pattern (ACP) information by the SPARC. The other ATP-guided active time slot transmits the remaining message by IM over the ACP-guided active channel uses. Different from the first two schemes, the third scheme has no pilot signal and thus the blind detection based on the bilinear generalized approximate message passing algorithm is employed to decode the message. Finally, computer simulations show that, compared with the state-of-the-art scheme, the first scheme has better performance for all the numbers of active users from 50 to 500, while the last two schemes much better only when less than about 200 active users exist.

Index Modulated Orthogonal Frequency-Division Multiplexing (IM-OFDM) based Integrated Sensing and Communication (ISAC) is potentially capable of outperforming Orthogonal Frequency-Division Multiplexing (OFDM) ISAC, since Index Modulation (IM) concentrates increased power on the activated subcarriers. This has been confirmed by authoritative publications for the IM-OFDM communication component. However, no evidence is found in the open literature that IM-OFDM sensing is capable of outperforming OFDM sensing, because the blank subcarriers impair the system's sensing functionality. The existing solutions either insert a radar signal into the deactivated subcarriers, thereby using a radar signal for sensing, or employ compressed sensing, which leads to a lower sensing performance than OFDM ISAC. Hence, a novel low complexity algorithm is proposed for ensuring that an IM-OFDM ISAC system outperforms its OFDM ISAC counterpart for both communication and sensing. The algorithm collects observations of the received signal to “fill in” the blank subcarriers in the sensing data created by IM-OFDM, whilst taking advantage of the increased subcarrier power attained by activating fewer subcarriers. This occurs over multiple transmit frames, which inevitably delays the target estimation. As OFDM sensing assumes low target velocities, this delay is shown to have a negligible impact on the sensing performance of IM-OFDM. The simulation results show that IM-OFDM ISAC is indeed capable of outperforming its OFDM ISAC counterpart for both sensing and communication. The impact of block interleaving and of the modulation type on the sensing performance is also discussed.

Index Modulation (IM) is a flexible transmission scheme capable of striking a flexible performance, throughput, diversity and complexity trade-off. The concept of Multi-dimensional IM (MIM) has been developed to combine the benefits of IM in multiple dimensions, such as space and frequency. Furthermore, Compressed Sensing (CS) can be beneficially combined with IM in order to increase its throughput. However, having accurate Channel State Information (CSI) is essential for reliable MIM, which requires high pilot overhead. Hence, Joint Channel Estimation and Detection (JCED) is harnessed to reduce the pilot overhead and improve the detection performance at a modestly increased estimation complexity. We then circumvent this by proposing Deep Learning (DL) based JCED for CS aided MIM (CS-MIM) of significantly reducing the complexity, despite reducing the pilot overhead needed for Channel Estimation (CE). Furthermore, we conceive training-aided Soft-Decision (SD) detection. We first analyze the complexity of the conventional joint CE and SD detection followed by proposing our reduced-complexity learning-aided joint CE and SD detection. Our simulation results confirm a Deep Neural Network (DNN) is capable of near-capacity JCED of CS-MIM at a reduced pilot overhead and reduced complexity both for Hard-Decision (HD) and SD detection.

In this paper, a novel index modulation-based non-orthogonal multiple access (IM-NOMA) system is proposed and investigated for both perfect and imperfect channel state information (CSI) uncertainty over Nakagami-m fading channel. The proposed system has added advantages of NOMA and IM systems. NOMA supports more users by allowing all users to utilize the same resources simultaneously whereas IM boosts spectral efficiency by conveying information to the users through both constellation domain and index domain symbols. Maximum likelihood (ML) and successive interference cancellation (SIC) detectors are used at the receiver side to detect index and data symbols. The proposed system is analyzed for different values of Nakagami-m channel parameters as well as for three different CSI conditions - perfect, fixed, and MMSE-based variable CSI uncertainty. The simulation results for the bit error rate and spectral efficiency parameters show that the proposed system outperforms the existing NOMA and OMA schemes.

Index modulation (IM) and intelligent reflecting surface (IRS) are emerging mobile communication technologies.In order to improve the reliability of traditional orthogonal frequency division multiplexing (OFDM) system, an orthogonal frequency division multiplexing with index modulation (OFDM-IM) system based on IRS-assisted was designed.Firstly, the OFDM-IM system was designed by using spatial modulation and frequency domain modulation to increase the Euclidean distance between subcarriers.Then, by establishing an equivalent circuit model, a practical IRS model was obtained.Finally, an alternating optimization algorithm was used to optimize the active transmission power of the access point (AP) and passive beamforming of the IRS jointly.The simulation results show that compared to the benchmark scheme, the symbol error rate (SER) or bit error rate (BER) of the OFDM-IM system based on IRS-assisted can be reduced by 60%～90%.Especially in the case of high signal-to-noise ratio, the SER or BER of the system can reach 1.0×10-6, which indicates that the introduction of IM and IRS technologies has optimized the link transmission quality of end-to-end communication system.In addition, based on the IRS-assisted OFDM-IM system as the standard, simulations are conducted to demonstrate the impact of various parameters from the IRS model and IM.It concludes that the parameters in the system should be selected reasonably according to channel state information (CSI).

In this paper, a novel index modulation-based non-orthogonal multiple access (IM-NOMA) system is proposed and investigated for both perfect and imperfect channel state information (CSI) uncertainty over Nakagami-m fading channel. The proposed system has added advantages of NOMA and IM systems. NOMA supports more users by allowing all users to utilize the same resources simultaneously whereas IM boosts spectral efficiency by conveying information to the users through both constellation domain and index domain symbols. Maximum likelihood (ML) and successive interference cancellation (SIC) detectors are used at the receiver side to detect index and data symbols. The proposed system is analyzed for different values of Nakagami-m channel parameters as well as for three different CSI conditions - perfect, fixed, and MMSE-based variable CSI uncertainty. The simulation results for the bit error rate and spectral efficiency parameters show that the proposed system outperforms the existing NOMA and OMA schemes. [ABSTRACT FROM AUTHOR]

To address the drawback that subcarrier activation pattern (SAP) of the orthogonal frequency division multiplexing with index modulation (OFDM-IM) cannot match the binary numbers which affects the system performance, the orthogonal frequency division multiplexing with subcarrier supply index modulation (OFDM-SSIM) transmission scheme was proposed.The index utilization of the system was improved and the spectral efficiency (SE) of the system was enhanced by adding the supply index.Also, as the subcarrier activation pattern of the proposed scheme match the binary numbers, low complexity log-likelihood ratio (LLR) detection was made easy to adopt and bit error rate (BER) performance was maintained good.Theoretical analysis and simulation results show that the proposed scheme effectively improves the SE and BER performance over classical OFDM-IM scheme in additive white Gaussian noise (AWGN) channels and Rayleigh fading channels.

The orthogonal time frequency space (OTFS) modulation technique can provide reliable communication in time-varying channels. Due to the dispersive characteristics of underwater acoustic channels, this paper proposes an OTFS-IM underwater acoustic communication system based on Hamming distance optimization to reduce the impact of dispersion in underwater acoustic communication. Firstly, the OTFS-IM underwater acoustic communication system is introduced, which introduces index modulation into the Delay–Doppler (DD) domain to make the OTFS system have stronger anti-Delay–Doppler capability. In contrast, since there is index sequence redundancy in a specific index combination, a Hamming distance optimization model is used to eliminate the redundant combination in the specific index combination sequence and further improve the bit error rate performance of the system. In addition, the Hamming distance optimized OTFS-IM underwater acoustic communication system is verified by simulation analysis. The results show that the proposed Hamming distance optimized OTFS-IM can achieve more reliable bit error rate performance. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunications Science is the property of Beijing Xintong Media Co., Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In a multiple-sequences-spread-spectrum (MSSS) communication system, the transmitted signal is made up of superimposed cyclic shift sequences, each sequence carrying a symbol, so the data rate is inceased. In this context, we propose an in-phase/quadrature index modulation-aided MSSS system (MSSS-I/Q-IM), which achieves higher data rate and better bit-error-rate (BER) performance. The new system maps the additional bits to the cyclic shift length of the superimposed sequences of I/Q branches. The sequences in two branches carry the real and imaginary parts of the M-ary phase-shift-keying (MPSK) symbols, respectively. We derive the theoretical BER of the MSSS-I/Q-IM system over an additive white Gaussian noise (AWGN) channel. Then, the simulation experiments of the proposed system and MSSS system over an underwater acoustic channel are analyzed and compared. Finally, field experiments are carried out in the pool environment. The experiment results show that the proposed scheme can achieve higher data rate or better BER performance via adjusting the IM parameter. This is important for the time-variant underwater acoustic transmission environments. [ABSTRACT FROM AUTHOR]

Advanced wireless communication with high spectrum efficiency and energy efficiency has always fascinated humanity, especially with the explosive increase of global mobile data services. Index modulation (IM) has recently been found to be a promising technique due to the transmission of additional data bits via the indices of the available transmit entities. However, the practical implementation of IM remains a great challenge associated with complicated radio components. Herein, IM with intelligent spatiotemporal metasurfaces is experimentally demonstrated. The spatiotemporal metasurfaces provide a natural and versatile platform to achieve IM in a green and lightweight manner. The whole system is driven by a built‐in inverse‐design agent that automates spatiotemporal metasurfaces to cater to diverse application demands. In doing so, how to mitigate the inherent nonuniqueness issue and how to setup the input target from practical scenes are concretely discussed. In the microwave experiment, the spatiotemporal metasurfaces are fabricated and demonstrate the feasibility by harvesting two harmonic waves as communication channels. An intelligent electromagnetic platform that can manipulate electromagnetic waves in multidimensions is provided, meriting other numerous intelligent meta‐devices that avoid overburdening data analysis networks in smart cities of the future. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Chongqing University of Posts & Telecommunications (Natural Science Edition) is the property of Chongqing University of Posts & Telecommunications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, a physical layer security scheme is proposed for index modulation aided orthogonal time frequency space (IM-OTFS) modulation systems working in Frequency Division Duplex (FDD) mode. In FDD systems, the channel reciprocity, which is the basic assumption for most physical layer security (PLS) techniques, is not applicable. To deal with the security challenge in FDD IM-OTFS systems, Chaos sequence is generated by exploiting the angular reciprocity of the legitimate link to construct the secure mapping rule between the information bits and the modulation symbols as well as the symbol indices. A PLS scheme based on the proposed secure mapping is introduced. The secrecy performance of the proposed PLS scheme is analyzed in terms of Bit Error Rate (BER) and the ergodic secrecy rate. Furthermore, a close-form approximated ergodic secrecy rate is derived to reduce the computational complexity. A truncation method is proposed to obtain robust secure transmissions when the angles of the uplink and downlink legitimate channels are estimated with errors. Simulation results show that the theoretical BER curve approaches the simulated BER curve closely for medium and high signal to noise ratio (SNR) regions, and the eavesdropper’s BER is always around 0.5 for all SNRs. The closed-form approximated ergodic secrecy rate fits the ergodic secrecy rate exactly in low and high SNR regions, and can work as a lower bound of the ergodic secrecy rate in medium SNR region. The secure mapping at the legitimate users is not affected by the angle estimation errors by using the truncation method, while the eavesdropper’s BER is influenced and the influence is analyzed.

The index modulation based on multiple-antenna architecture is a prospective information embedding approach for the joint radar-communication system (JRCS). Current investigations mainly focus on the spatial and frequency index modulation applied in phased array (PA) radar and multiple-input multiple-output (MIMO) radar. In this article, we design an information embedding strategy by combining phase modulation and frequency index modulation for random frequency diverse array (RFDA) based on MIMO radar. The devised system can perform joint range and angle estimation in radar operation, which is currently not achievable in dual-function systems based on PA and MIMO radar. Considering the time-variance of the transmit waveform, we propose a multichannel receiver for the joint system. For radar, the impact of the random frequency assignment on the transmit-receive virtual beampattern and Cramér-Rao bounds (CRBs) of range and angle are analyzed. For communication, a maximum ratio combining (MRC) assisted ML detector is introduced to improve the accuracy of the information decoding. Extensive numerical results are presented to verify the feasibility and effectiveness of the proposed system scheme.

This study proposes a novel secure uplink index modulation-based orthogonal frequency division multiple access (IM-OFDMA) systems using artificial in-phase and quadrature imbalance (A-IQI). The fact of the distinct A-IQI induced at the users’ end and the unpredictable allocation of users based on confidential data brings a different perspective on physical layer security. Accordingly, in this study, the non-identical effect of A-IQI is exploited to provide a physical-layer security scheme for the IM-OFDMA systems. Specifically, the estimation method is created with preamble data in order to achieve each user’s unique A-IQI information from a legitimate receiver. The A-IQI will help to secure the transmitted data against a potential eavesdropper, and hence, improving data confidentiality. The proposed scheme’s performance is analytically evaluated by deriving closed-form expressions of the average bit error rate (BER) at both the base station and the eavesdropper. The image rejection ratios of A-IQI and practical IQI are provided for IM-OFDMA to indicate the region of intentionally generated A-IQI. Under the different system model specifications of IM-OFDMA, the analytical results are provided with simulation results obtained using the Monte Carlo simulation method. Further, the proposed secure scheme is compared with the state-of-the-art artificial noise method. Results reveal a significant improvement in the BER at the base station, accompanied by severe degradation in the BER at the eavesdropper.

Index-Modulation (IM) has been recently emerged as a promising direction towards improving error performance and spectral efficiency in wireless networks. To this end, IM-based Wireless Sensor Networks (IM-WSN) has been recently applied as a decision gathering scheme in clustered Wireless Sensor Networks, by which a significant improvement in the decision error rate (DER) is achieved. Later, following the same IM principle, efficient IM-WSN scheme (EIM-WSN) has been introduced, but with the emphasis on reducing the computational complexity of IM-WSN while improving the error performance. Although in these schemes cluster heads (CHs) vary dynamically, still they suffer from the unfair distribution of the CH role among nodes. As a result, nodes energy will be unequally dissipated, and hence the network lifetime will be deteriorated. In this study, aiming at balancing the CH role among cluster nodes, a new decision reporting scheme, namely index-shift, is proposed. The performance of proposed scheme is analysed in terms of DER and network lifetime and compared with the previous IM reporting schemes, IM-WSN and EIM-WSN. Analytical and simulation results show that the proposed scheme demonstrates fair distribution of CH role among all cluster nodes. This, in turn, led to extend the network lifetime up to 50% compared to other schemes, in addition to acheive DER that is better than IM-WSN and almost identical to EIM-WSN.

Rectangular differential spatial modulation (RDSM) is a multi-antenna incoherent modulation technology with high spectral efficiency, low power consumption, and zero-overhead for channel estimation.RDSM is especially suitable for 6G communication systems, such as fast-moving Internet of vehicles, Internet of things, cellular networks, etc.However, the construction of the sparse rectangular unitary space-time dispersion matrix (DM) at transmitter is a problem.The proposed Genetic algorithm (GA) will result in less computational complexity than the currently used random research.The fitness of GA was calculated by the rank and determinant criterion (RDC) method to avoid discussions in differential system.Due to characteristics of constellation symbols of RDSM, the proposed method reduced the computational complexity during each single iteration in GA.The simulation results show that the optimized DMS can significantly improve the bit error rate (BER) performance of the RDSM system.Compared with random search, the low-complexity GA effectively improves the DMS optimization efficiency of RDSM.The computational complexity required for optimizing DMS is about 0.1% of random search optimization method.

Abstract With the continuous improvement of the application requirements of Direct Sequence Spread Spectrum (DSSS), especially the high requirements of data transmission rate, the advantages of traditional DSSS system are limited, so the index modulation DSSS technology appears. However, at present, there are still some key problems such as high‐order data rate, high bit error rate and high synchronisation complexity. Therefore, in view of the above bottleneck problems, the code index modulation method with multidimensional invisible data (MID‐CIM) is proposed. On the basis of deeply mining the hidden features of DSSS communication mechanism, the index order and shift order are established, and the two‐dimensional invisible data index transmission rules are established using a bit reversed and pseudo code (PN) set mapping mechanism, and then the three‐dimensional invisible data index transmission rules are established by using the cyclic displacement and pseudo code offset mechanism. The MID‐CIM method not only ensures the effective transmission of one‐dimensional data, but also uses the transmission of low‐speed one‐dimensional data to index transmit high‐speed two‐dimensional and three‐dimensional invisible data. This research can provide the technical basis for the efficient application of DSSS system, and also provide theoretical support and technical support for the new development and application of a communication system based on the spread spectrum system.

Multicarrier backscattering has been proposed to improve the communication rate, but the complex circuit structure of multicarrier backscattering devices requires more power consumption, resulting in devices far away from the radio frequency (RF) source without enough power to maintain communication, which greatly reduces the limited communication range in backscattering. To solve this problem, this paper introduces carrier index modulation (IM) into orthogonal frequency division multiplexing (OFDM) backscattering and proposes a dynamic subcarrier activated OFDM-IM uplink communication scheme suitable for passive backscattering devices. When the existing power collection level of the backscatter device is detected, only a subset of carrier modulation is activated using part of the circuit modules to reduce the power threshold required for device activation. The activated subcarriers are mapped by a block-wise combined index using the look-up table method, which can not only transmit information using traditional constellation modulation but also carry additional information through the frequency domain carrier index. Monte Carlo experiments show that this scheme can effectively increase the communication distance and improve the spectral efficiency of low-order modulation backscattering when the power of the transmitting source is limited. [ABSTRACT FROM AUTHOR]

To address the drawback that subcarrier activation pattern (SAP) of the orthogonal frequency division multiplexing with index modulation (OFDM-IM) cannot match the binary numbers which affects the system performance, the orthogonal frequency division multiplexing with subcarrier supply index modulation (OFDM-SSIM) transmission scheme was proposed. The index utilization of the system was improved and the spectral efficiency (SE) of the system was enhanced by adding the supply index. Also, as the subcarrier activation pattern of the proposed scheme match the binary numbers, low complexity log-likelihood ratio (LLR) detection was made easy to adopt and bit error rate (BER) performance was maintained good. Theoretical analysis and simulation results show that the proposed scheme effectively improves the SE and BER performance over classical OFDM-IM scheme in additive white Gaussian noise (AWGN) channels and Rayleigh fading channels. [ABSTRACT FROM AUTHOR]

Advanced wireless communication with high spectrum efficiency and energy efficiency has always fascinated humanity, especially with the explosive increase of global mobile data services. Index modulation (IM) has recently been found to be a promising technique due to the transmission of additional data bits via the indices of the available transmit entities. However, the practical implementation of IM remains a great challenge associated with complicated radio components. Herein, IM with intelligent spatiotemporal metasurfaces is experimentally demonstrated. The spatiotemporal metasurfaces provide a natural and versatile platform to achieve IM in a green and lightweight manner. The whole system is driven by a built‐in inverse‐design agent that automates spatiotemporal metasurfaces to cater to diverse application demands. In doing so, how to mitigate the inherent nonuniqueness issue and how to setup the input target from practical scenes are concretely discussed. In the microwave experiment, the spatiotemporal metasurfaces are fabricated and demonstrate the feasibility by harvesting two harmonic waves as communication channels. An intelligent electromagnetic platform that can manipulate electromagnetic waves in multidimensions is provided, meriting other numerous intelligent meta‐devices that avoid overburdening data analysis networks in smart cities of the future.

Summary: In the fourth‐generation communication system (4G), orthogonal frequency division multiplexing (OFDM) is widely used. However, due to the cyclic prefix (CP) being added, the low spectrum efficiency and high out‐of‐band radiation (OOB) cause OFDM not to be suitable for the beyond fifth‐generation (B5G) communication system. Therefore, to meet the rigorous demands in B5G for the Internet of Things (IoT) and massive machine‐type communications (MMTC), generalized frequency division multiplexing (GFDM) technology has received significant attention. On the other hand, index modulation (IM) can provide flexible settings of different parameters to achieve the ideal system goals. Therefore, this paper considers the combination of spread spectrum (SS) and IM under the framework of GFDM, called SS‐IM‐GFDM. In this scheme, the information bits are jointly conveyed by the indices of spreading codes and the conventional M‐ary modulated symbols, which increase the spectrum efficiency and improve the bit error rate performance. Furthermore, a low‐complexity maximum likelihood (ML) detector is proposed to recover the transmitted signal effectively at the receiver. Finally, the space‐time block code (STBC) is employed to construct the multi‐input multi‐output SS‐GFDM‐IM (MIMO SS‐GFDM‐IM) system to improve the system's reliability. The simulation results show that the proposed scheme is superior to the existing systems. [ABSTRACT FROM AUTHOR]

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With the continuous improvement of the application requirements of Direct Sequence Spread Spectrum (DSSS), especially the high requirements of data transmission rate, the advantages of traditional DSSS system are limited, so the index modulation DSSS technology appears. However, at present, there are still some key problems such as high‐order data rate, high bit error rate and high synchronisation complexity. Therefore, in view of the above bottleneck problems, the code index modulation method with multidimensional invisible data (MID‐CIM) is proposed. On the basis of deeply mining the hidden features of DSSS communication mechanism, the index order and shift order are established, and the two‐dimensional invisible data index transmission rules are established using a bit reversed and pseudo code (PN) set mapping mechanism, and then the three‐dimensional invisible data index transmission rules are established by using the cyclic displacement and pseudo code offset mechanism. The MID‐CIM method not only ensures the effective transmission of one‐dimensional data, but also uses the transmission of low‐speed one‐dimensional data to index transmit high‐speed two‐dimensional and three‐dimensional invisible data. This research can provide the technical basis for the efficient application of DSSS system, and also provide theoretical support and technical support for the new development and application of a communication system based on the spread spectrum system. [ABSTRACT FROM AUTHOR]

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This paper proposes a novel spread spectrum and sub-carrier index modulation (SS-SIM) scheme, which is integrated to orthogonal frequency division multiplexing (OFDM) framework to enhance the diversity over the conventional IM schemes. Particularly, the resulting scheme, called SS-SIM-OFDM, jointly employs both spread spectrum and sub-carrier index modulations to form a precoding vector which is then used to spread an M-ary complex symbol across all active sub-carriers. As a result, the proposed scheme enables a novel transmission of three signal domains: SS and sub-carrier indices, and a single M-ary symbol. For practical implementations, two reduced-complexity near-optimal detectors are proposed, which have complexities less depending on the M-ary modulation size. Then, the bit error probability and its upper bound are analyzed to gain an insight into the diversity gain, which is shown to be strongly affected by the order of sub-carrier indices. Based on this observation, we propose two novel sub-carrier index mapping methods, which significantly increase the diversity gain of SS-SIM-OFDM. Finally, simulation results show that our scheme achieves better error performance than the benchmarks at the cost of lower spectral efficiency compared to classical OFDM and OFDM-IM, which can carry multiple M-ary symbols. [ABSTRACT FROM AUTHOR]

Index modulation represents the transmitted information in two parts: by selecting a subset of available transmission dimensions (antennas, sub-carriers, or time-slots) whose selection index carries information, and by modulation symbols transmitted in the selected dimensions. Index modulation is motivated by reducing the transmitter hardware complexity and has attracted significant research attention in the past decade. In practice, knowing the spectral efficiency or capacity is essential for setting the parameters of modulation and coding for index modulation, but approximations and bounds thus far have not been accurate enough for that purpose. We calculate close lower and upper bounds for the spectral efficiency of index modulation. Our lower and upper bounds meet at high-SNR when the number of receive antennas is greater than or equal to the number of transmit antennas, thus the high-SNR capacity of index modulation in these cases has been fully characterized. A catalog of results is provided for spatial modulation, generalized spatial modulation, time and frequency index modulation. Extensive simulations illustrate the usefulness and accuracy of our results. For example, for spatial modulation with $4\times 2$ antennas at 8 bits/s/Hz, our results are 2dB tighter than the best available bounds in the literature. [ABSTRACT FROM AUTHOR]

Reconfigurable Intelligent Surfaces (RISs) have garnered significant attention in the development of Internet of Things (IoT) networks and vehicular communication systems, offering improved spectral efficiency with reduced power consumption and complexity overhead. However, employing a single RIS (S-RIS) may limit certain application scenarios and prove insufficient for ensuring reliable communication between transmitters and receivers. Consequently, the use of multiple RISs is recommended to further enhance coverage, capacity, and spectral efficiency. In this paper, we introduce the concept of Index Modulation (IM) into the double RIS (D-RIS) uplink Multiple-Input Multiple-Output (MIMO) communications, utilizing the antenna indices at the base station (BS). IM is realized through a combination of Space-Shift Keying (SSK) and Spatial Modulation (SM) techniques. We present an analytical model for the Double RIS based on SSK/SM methods and obtain a closed-form expression for the theoretical bit error probability (BEP), employing a greedy detector. To validate our theoretical BEP derivations for d -RIS-SSK/SM, we compare them with simulated BEP results. Our simulation data reveals an excellent match between the derived BEP and the simulated BEP, especially at lower Signal-to-Noise Ratios (SNRs), specifically -34 dB for SSK and -24 dB for SM. Furthermore, we evaluate the performance of the proposed d -RIS-aided IM methods by contrasting them with conventional d -RIS and single RIS-aided IM systems. Our simulation results demonstrate that the d -RIS-assisted IM outperforms the conventional d -RIS and single RIS-aided IM, achieving lower BEP at lower SNRs. d -RIS aided IM saves 15 dB in SNR compared to d -RIS without IM. Moreover, it saves 9 dB and 7 dB in SNR compared to single RIS-SSK and single RIS-SM, respectively when N = 64 and saves 3.5 dB and 1 dB in SNR with N = 128. [ABSTRACT FROM AUTHOR]

This work introduces a non-orthogonal multiple access (NOMA) scheme suitable for low-rate ultra-reliable low-latency communication (URLLC) and enhanced mobile broadband (eMBB) services multiplexing in downlink communication. Tailored to minimize mutual interference, URLLC information is conveyed via a modified index modulation (IM) scheme on top of quadrature amplitude modulation (QAM) transferring eMBB traffic. Aiming at providing a proof of concept of the proposed scheme, we calculate the bit error rate of both services over Rayleigh fading with diversity, as well as the eMBB service achievable rate with typical multi-input multi-output (MIMO) configuration when the URLLC service utilizes space–time coding or diversity. The proposed scheme achieves a low bit error rate for the URLLC IM signal, at the cost of a lower information rate, while affecting the performance of the eMBB user mainly due to power sharing among the IM and QAM signals. To further investigate the feasibility of the proposed scheme, we calculate the transmission energy required by the base station to support both services over a typical cellular channel model, for various service requirements and user distances, in comparison to an orthogonal multiple access (OMA) puncturing scheme utilizing time-multiplexing of QAM for the eMBB traffic and BPSK for the URLLC traffic. Overall, our results show that the proposed scheme attains better performance compared to the puncturing scheme and offers a robust solution with easy user pairing for low-rate URLLC and typical eMBB downlink service multiplexing for 5G communications and beyond. [ABSTRACT FROM AUTHOR]

Unmanned aerial vehicles (UAVs) have been widely utilized for their various advantages. However, UAVs exhibit high mobility and energy storage restrictions in some applications, which can compromise the quality and reliability of communication links. This is a challenge that future aircraft and low-orbit aircraft will inevitably encounter. To effectively address the issue of dynamic Doppler spread in air-to-ground communication, this paper creatively introduces four-dimensional spherical code modulation into the orthogonal time–frequency space with an index modulation (OTFS-IM) system. The fundamental concept of the four-dimensional spherical code is elaborated in detail. Multiple resource symbols can be jointly used to increase the modulation dimension, thereby achieving a larger minimum Euclidean distance between constellation points. Furthermore, detailed analysis is conducted on the bit error rate (BER) and the peak-to-average-power ratio (PAPR) expressions of the proposed system to evaluate its performance and provide theoretical guidance. The proposed scheme not only adapts well to high-speed scenarios but also achieves better power consumption efficiency. The simulation results demonstrate that our proposed scheme outperforms conventional methods. Its robustness and generalization ability are also validated.

Among various index modulation technology, adaptive orthogonal frequency division multiplexing with index modulation (A-OFDM-IM) improves reliability by solving the problem of deep fading. However, the maximal likelihood (ML) detector of A-OFDM-IM has high complexity by simultaneously performing active subcarrier detection and quadrature amplitude modulation (QAM) symbol demodulation. A simpler type of ML detector can be applied since the A-OFDM-IM has independent active states of each subcarrier and uses a single QAM constellation. In this paper, we propose two low-complexity detectors for the A-OFDM-IM. The proposed detectors have a two-stage receiving process, active subcarrier detection, and QAM demodulation. In active subcarrier detection, the presence or absence of the QAM symbol is more important than its information. Therefore we derive the thresholds using the absolute value of the in-phase and quadrature components of the received signal in the frequency domain. Using the absolute value, the distribution of noise added to inactive subcarrier is half normal. This is different from noise distribution of the ML detector, and the proposed detectors select the threshold considering the corresponding noise distribution. The first proposed detector uses a threshold derived by the ML estimation method. The second detector estimates the active subcarriers via a support vector machine. The proposed detectors have lower complexity than the ML detector because of the divided receiving process. Moreover, the theoretical analysis and simulation results show that the proposed detectors have better reliability than the ML detector due to different noise distribution and thresholds.