Low-rank adaptation (LoRA) and its variants have recently gained much interest due to their ability to avoid excessive inference costs. However, LoRA still encounters the following challenges: (1) Limitation of low-rank assumption; and (2) Its initialization method may be suboptimal. To this end, we propose PMSS(Pre-trained Matrices Skeleton Selection), which enables high-rank updates with low costs while leveraging semantic and linguistic information inherent in pre-trained weight. It achieves this by selecting skeletons from the pre-trained weight matrix and only learning a small matrix instead. Experiments demonstrate that PMSS outperforms LoRA and other fine-tuning methods across tasks with much less trainable parameters. We demonstrate its effectiveness, especially in handling complex tasks such as DROP benchmark(+3.4%/+5.9% on LLaMA2-7B/13B) and math reasoning (+12.89%/+5.61%/+3.11% on LLaMA2-7B, Mistral-7B and Gemma-7B of GSM8K).The code and model will be released soon.

Transformer-based large language models (LLMs) have achieved impressive performance in various natural language processing (NLP) applications. However, the high memory and computation cost induced by the KV cache limits the inference efficiency, especially for long input sequences. Compute-in-memory (CIM)-based accelerators have been proposed for LLM acceleration with KV cache pruning. However, as existing accelerators only support static pruning with a fixed pattern or dynamic pruning with primitive implementations, they suffer from either high accuracy degradation or low efficiency. In this paper, we propose a ferroelectric FET (FeFET)-based unified content addressable memory (CAM) and CIM architecture, dubbed as UniCAIM. UniCAIM features simultaneous support for static and dynamic pruning with 3 computation modes: 1) in the CAM mode, UniCAIM enables approximate similarity measurement in $\mathcal{O}(1)$ time for dynamic KV cache pruning with high energy efficiency; 2) in the charge-domain CIM mode, static pruning can be supported based on accumulative similarity score, which is much more flexible compared to fixed patterns; 3) in the current-domain mode, exact attention computation can be conducted with a subset of selected KV cache. We further propose a novel CAM/CIM cell design that leverages the multi-level characteristics of FeFETs for signed multibit storage of the KV cache and in-place attention computation. With extensive experimental results, we demonstrate UniCAIM can reduce the area-energy-delay product (AEDP) by $8.2 \sim 831 \times$ over the state-of-the-art CIM-based LLM accelerators at the circuit level, along with high accuracy comparable with dense attention at the application level, showing its great potential for efficient long-context LLM inference.

Lookup tables (LUTs) are widely used for reconfigurable computing applications due to the capability of implementing arbitrary logic functions. Various emerging non-volatile memories (eNVMs) have been introduced for LUT designs with reduced hardware cost and power consumption compared with conventional SRAM-based LUT. However, the existing designs still follow the conventional LUT architecture, where the memory cells are only used for storage of configuration bits, requiring dedicated bulky multiplexer (MUX) for computation of each LUT, resulting in inevitable high area, latency, and energy cost. In this work, a compact and efficient non-volatile LUT architecture based on ferroelectric FET (FeFET) array is proposed, where the configuration bit storage and computation can be implemented within the FeFET array through in-situ combinatorial one-hot encoding, eliminating the need of costly MUX for each LUT. Moreover, multibit LUTs can be efficiently implemented in the FeFET array using only one shared decoder instead of multiple costly MUXs. Due to the eliminated MUX in the calculation path, the proposed LUT can also achieve enhanced computation speed compared with the conventional LUTs. Based on the proposed LUT architecture, the input expansion of LUT, full adder, and content addressable memory are further implemented and demonstrated with reduced hardware and energy cost. Evaluation results show that the proposed FeFET array-based LUT architecture achieves 51.7×/8.3× reduction in area-energy-delay product compared with conventional SRAM-based/FeFET-based LUT architecture, indicating its great potential for reconfigurable computing applications.

With the continued proliferation of Large Language Model (LLM) based chatbots, there is a growing demand for generating responses that are not only linguistically fluent but also consistently aligned with persona-specific traits in conversations.However, existing role-play and persona-based chat approaches rely heavily on static role descriptions, coarse-grained signal space, and low-quality synthetic data, which fail to capture dynamic fine-grained details in human-like chat.Human-like chat requires modeling subtle latent traits, such as emotional tone, situational awareness, and evolving personality, which are difficult to predefine and cannot be easily learned from synthetic or distillation-based data.To address these limitations, we propose a Verbal Variational Auto-Encoding (V-VAE) framework, containing a variational auto-encoding module and fine-grained control space which dynamically adapts dialogue behaviour based on fine-grained, interpretable latent variables across talking style, interaction patterns, and personal attributes.We also construct a highquality dataset, HumanChatData, and benchmark HumanChatBench to address the scarcity of high-quality data in the human-like domain.Experiments show that LLMs based on V-VAE consistently outperform standard baselines on HumanChatBench and DialogBench, which further demonstrates the effectiveness of V-VAE and HumanChatData.

Abstract Human beings capable of making and using tools can accomplish tasks far beyond their innate abilities, and this paradigm of integration with tools may not be limited to humans themselves. Recently, the large language model (LLM) has demonstrated immense potential across various fields with its unique planning and reasoning abilities. However, there are still many challenges beyond its capabilities due to deficiencies in its training data and inherent illusions. Thus, integrating LLMs and tools into tool learning agents has become a new emerging research direction. To this end, we present a systematic investigation and comprehensive review of tool-learning agents in this paper. We start by introducing the definition of the tool learning task for Agents and then illustrating the typical architecture of the tool-learning models. Since these tools are all defined by users, LLM does not know what tools there are and what their functions are. Thus, LLMs should first find appropriate tools and split the tool retrieval methods into two categories: training-based and non-training-based. To accurately complete the user task, it is important to decompose the task into several sub-tasks and execute them in the correct order. Following that, we introduce the tool planning methods and organize these works by whether they rely on the model’s inherent reasoning capabilities for planning or utilize external reasoning tools. Due to the rapid development of this field, we also introduce an emerging frontier direction: using multimodal tools for LLM. In addition, we compile current open-source benchmarks and evaluation metrics, focusing on their scale, composition, calculation methods, and assessment dimensions. Next, we introduce several application scenarios for the LLM-based tool learning methods. Finally, we discuss the safety and ethical issues involved in tool learning.

Abstract The detection of road potholes plays a crucial role in ensuring passenger comfort and the structural safety of vehicles. To address the challenges of pothole detection in complex road environments, this paper proposes a model focusing on shape features (pothole detection you only look once, PD‐YOLO). The model aims to overcome the limitations of multi‐scale feature learning caused by the use of fixed convolutional kernels in the baseline model, by constructing a feature extraction module that better adapts to variations in the shape of potholes. Subsequently, a cross‐stage partial network was designed using a one‐time aggregation method, simplifying the model while enabling the network to fuse information between feature maps at different stages. Additionally, a dynamic sparse attention mechanism is introduced to select relevant features, reducing redundancy and suppressing background noise. Experiments conducted on the VOC2007 and GRDDC2020_Pothole datasets reveal that compared to the baseline model YOLOv8, PD‐YOLO achieves improvements of 3.9% and 2.8% in mean average precision, with a frame rate of approximately 290 frames per second, effectively meeting the accuracy and real‐time requirements for pothole detection. The code and dataset for this paper are located at: https://github.com/woyijiankou/PD‐YOLO .

Shihan Deng, Weikai Xu, Hongda Sun, Wei Liu, Tao Tan, Jianfeng Liu, Ang Li, Jian Luan, Bin Wang, Rui Yan, Shuo Shang. Proceedings of the 62nd Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers). 2024.

Hongda Sun, Weikai Xu, Wei Liu, Jian Luan, Bin Wang, Shuo Shang, Ji-Rong Wen, Rui Yan. Proceedings of the 62nd Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers). 2024.

Content addressable memory (CAM) has triggered a lot of attention for data-intensive applications due to highly parallel pattern searching capability. Most state-of-the-art works focus on reducing hardware cost of CAM by exploiting various emerging non-volatile memory (NVM) technologies. However, the existing CAM designs still mainly follow the conventional encoding scheme which requires two complementary storage nodes and search signals for each bit of entry and query respectively, along with separate precharging and evaluation phases for bit-vector searching, limiting the further improvement of area- and energy-efficiency. In this work, a compact and efficient CAM architecture is proposed through two techniques: (1) a combinatorial encoding scheme for CAM by encoding entry/query states with permutations and combinations of multiple storage nodes as a group, which can significantly improve the encoding efficiency and thus greatly reduce the hardware implementation cost of CAM compared with conventional encoding scheme; (2) an one-step self-terminating searching scheme for CAM by detecting matching condition during precharging phase and terminating precharging once a match is detected, which can further reduce the search delay and energy. The experiments and evaluations of the proposed CAM architecture with co-optimization of combinatorial encoding and self-terminating searching are carried out based on ferroelectric FET (FeFET), which can reduce the area-energy-delay product (AEDP) by 1182X over the conventional CMOS-based CAM in data searching tasks, showing its great potential for area- and energy-efficient in-memory-searching accelerator.

Abstract To tackle challenges in road multi‐object detection, such as object occlusion, small object detection, and multi‐scale object detection difficulties, a new YOLOv8n‐RSFM structure is proposed. The key improvement of this structure lies in the introduction of the transformer decoder head, which optimizes the matching between the ground truth and predicted boxes, thereby effectively addressing issues of object overlap and multi‐scale detection. Additionally, a small object detection layer is incorporated to retain crucial information beneficial for detecting small objects, significantly improving the detection accuracy for small targets. To enhance learning capacity and reduce redundant computations, the FasterNet backbone is employed to replace CSPDarknet53, thus accelerating the training process. Finally, the INNER‐MPDIoU loss function is introduced to replace the original algorithm's complete IoU to accelerate the convergence and obtain more accurate regression results. A series of experiments were conducted on different datasets. The experimental results show that the proposed model YOLOv8N‐RSFM outperforms the original model YOLOv8n in small target detection. On the VisDrone, TinyPerson, and VSCrowd datasets, the mean accuracy percentage improved by 7.9%, 12.3%, and 4.5%, respectively.

Abstract This paper proposes a multilevel cyclic shift index modulation aided differential chaotic shift keying (MCSI‐DCSK) system to improve data rate and energy efficiency. In the MCSI‐DCSK system, the bit stream is divided into blocks with bits which are further divided into N groups equally. In each group, the first M bits are mapped into an index of cyclic shift in the chaotic reference sequence, while the last bit is used to modulate the shifted chaotic reference sequence. Finally, the all modulated shifted chaotic reference sequences are superimposed to form the information‐bearing signal. So the proposed system improves the data rate. The analytical bit‐error‐rate (BER) expressions of the MCSI‐DCSK system are derived over additive white Gaussian noise and multipath Rayleigh fading channels and validated via simulations. In addition, the BER performance of the proposed system is compared with other non‐coherent, chaotic communication systems. Simulation results indicate that the MCSI‐DCSK system has better performance in data rate and BER.

A lightweight secure communication scheme, i.e., orthogonal frequency division multiplexing with index modulation using artificial noise (OFDM-IM AN), is proposed in this letter, which integrates the artificial noise into OFDM-IM to interfere the eavesdropper (Eve) from physical layer. In the proposed scheme, ANs are generated using channel state information (CSI) of legitimate link through a differential way, so the ANs will be eliminated at the legal receiver by the differential demodulation. Since the wiretap channel is independent of the legitimate channel, Eve will be confused by AN and make wrong detection. We derive both the tight upper bound on the bit error rate (BER) and the security rate of the proposed scheme. Simulation results show that though the BER performance of OFDM-IM AN is worse than that of OFDM-IM with the same configuration, the proposed scheme can enhance the security of OFDM-IM with a low complexity.

Device-to-device (D2D) communications can allow different devices to communicate in short range, which greatly meets the demand of effective transmissions. In this paper, a spectral and energy-efficient carrier index keying-aided$M$-ary differential chaos cyclic shift keying (CIK-MDCCSK) system is proposed for D2D communications, where multiple cyclic-shifted$M$-ary information-bearing signals are superimposed and transmitted by a subcarrier, and extra keying bits are transmitted by indices of the selected subcarriers. Furthermore, a carrier keying detection and$M$-ary de-mapping algorithm is proposed to retrieve the information bits transmitted by$M$-ary symbols and indices of carrier keying. The bit error rate (BER) expressions of the proposed CIK-MDCCSK system are derived over the additive white Gaussian noise (AWGN) and D2D channels, and the optimal power coefficient is deduced for performance enhancement. Then, the spectral efficiency, energy efficiency, and complexity of CIK-MDCCSK are analyzed and compared to benchmark systems to show its superiority. Next, the proposed CIK-MDCCSK system is expanded into its enhanced version for more effective transmission without degrading the BER performance. It is demonstrated by performance comparisons that the proposed CIK-MDCCSK system can achieve more than twice energy efficiency and up to 3 dB gain in BER performance compared to state-of-the-art benchmarks.

Chaotic secure communication systems using chaotic waveforms as their spreading carriers can hide the transmitted information bits over a wide frequency range of chaotic waveform, which disguises the transmitted information waveform as noise. In this paper, a reconfigurable intelligent surface (RIS) enabled$M$-ary differential chaos shift keying with block interleaving (RIS-MDCSK-BI) system is proposed for chaotic secure communications, where an RIS is deployed at the transmitter to assist communications and a pair of block interleaving patterns are used to interleave$M$-ary information-bearing signals to enhance security performance. Moreover, we propose a chaotic merging sort algorithm to generate different block interleaving patterns, where these interleaving patterns are encrypted by using the non-periodic and noise-like properties of chaotic signals. To estimate information bits at the legitimate receiver, we propose a sequential detection algorithm and a joint detection algorithm. Then, theoretical bit error rate (BER) performances of the proposed RIS-MDCSK-BI system with the legitimate receiver and the eavesdropping receiver are derived. The security performance metrics, including information leakage and secrecy outage probability, are also analyzed. Monte Carlo simulations are performed to verify the superior BER performance and security performance of the proposed RIS-MDCSK-BI system compared to benchmark systems.

In reconfigurable intelligent surface (RIS)-aided coherent communications, channel state information (CSI) is often assumed to be perfectly estimated at the receiver. However, perfect CSI cannot be available in practice. Furthermore, the complex and ever-changing channel makes the acquisition of accurate CSI often unaffordable because of the large overhead in transmitting pilot signals. Motivated by these considerations, a novel non-coherent RIS-aided joint index keying$M$-ary differential chaos shift keying (RIS-JIK-MDCSK) system is proposed in this paper, where the receiver can retrieve information bits by performing non-coherent correlation demodulation without requiring CSI, thereby reducing the system complexity. In RIS-JIK-MDCSK, the states of the reference signal, RIS elements, and information-bearing subcarriers are jointly optimized to devise a joint index keying mechanism, where additional information bits are implicitly transmitted by these state indices, thus increasing the throughput and spectral efficiency. Furthermore, an effective joint index keying detection algorithm is proposed to recover the information bits. The analytical bit error rate (BER) of RIS-JIK-MDCSK is derived over a Rayleigh fading channel. Other evaluation metrics, including the throughput, spectral efficiency, and system complexity are also analyzed and compared against benchmark systems. Numerical simulations are performed to evaluate the superiority of RIS-JIK-MDCSK compared to existing systems.

In the multiple sequences spread spectrum (MSSS) system, multiple cyclic shifted spreading sequences are superimposed to increase the data rate. This paper proposes a dual-mode MSSS system with index modulation aided by a secondary pilot symbol (DM-MSSS-IM) for underwater acoustic communication. The proposed system divides the bit stream into index bits and modulated bits. The modulated bits are mapped to dual-mode constellations. The index bits are used to select a place for the first modulation mode symbol. The unselected place is used to carry the second mode symbols, which is regarded as the secondary pilot symbol (SPS) to enhance channel estimation. The simulation results show that the proposed system achieves a higher data rate than the existing MSSS system over time-frequency doubly selective fading channels and underwater acoustic channels as the cost of a slight BER performance loss. Additionally, the field experiment verifies the superiority of the proposed scheme.

Knowledge graph is ubiquitous and plays an important role in many real-world applications, including recommender systems, question answering, fact-checking, and so on. However, most of the knowledge graphs are incomplete which can hamper their practical usage. Fortunately, knowledge graph completion (KGC) can mitigate this problem by inferring missing edges in the knowledge graph according to the existing information. In this paper, we propose a novel KGC method named ABM (Attention-Based Message passing) which focuses on predicting the relation between any two entities in a knowledge graph. The proposed ABM consists of three integral parts, including (1) context embedding, (2) structure embedding, and (3) path embedding. In the context embedding, the proposed ABM generalizes the existing message passing neural network to update the node embedding and the edge embedding to assimilate the knowledge of nodes' neighbors, which captures the relative role information of the edge that we want to predict. In the structure embedding, the proposed method overcomes the shortcomings of the existing GNN method (i.e., most methods ignore the structural similarity between nodes.) by assigning different attention weights to different nodes while doing the aggregation. Path embedding generates paths between any two entities and treats these paths as sequences. Then, the sequence can be used as the input of the Transformer to update the embedding of the knowledge graph to gather the global role of the missing edges. By utilizing these three mutually complementary strategies, the proposed ABM is able to capture both the local and global information which in turn leads to a superb performance. Experiment results show that ABM outperforms baseline methods on a wide range of datasets.

A Noise Suppression aided Multi-Carrier$M$-ary Differential Chaos Shift Keying (NS-MC-MDCSK) system is proposed here where each information subcarrier transmits an$M$-ary information-bearing signal and the$M$-ary constellation symbols are constructed by orthogonal Walsh codes to improve the energy efficiency. Exploiting the redundant information available in the received signal, we propose a noise suppression algorithm to suppress channel noise in the reference and$M$-ary information-bearing signals. In the proposed algorithm, correlation coefficients detected between the received reference and information-bearing signals are fed back to suppress the noise corrupting the signal received. This method reduces the channel noise significantly and provides an outstanding Bit Error Rate (BER) performance. A performance analysis is performed for the NS-MC-MDCSK system over Additive White Gaussian Noise (AWGN) and multipath fading channels. Finally, the BER performance of the NS-MC-MDCSK system is compared to that of other chaotic communications systems. It is shown that the NS-MC-MDCSK system offers better BER performance than its competitors.

A joint energy and correlation detection aided orthogonal frequency division multiplexing differential chaos shift keying (JECD-OFDM-DCSK) system is presented in this paper, where the reference and information-bearing signals of JECD-OFDM-DCSK are superimposed in the same time slot so that the phase offset between the reference and information-bearing signals is addressed. In JECD-OFDM-DCSK, only some subcarriers are activated and additional information bits are transmitted by the indices of these activated subcarriers, thereby improving the data rate while reducing the energy consumption. The energy efficiency, peak to average power ratio (PAPR) performance and system complexity of JECD-OFDM-DCSK are analyzed and then compared to other systems. The comparison results show JECD-OFDM-DCSK can obtain higher energy efficiency and better PAPR performance compared to its competitors at the cost of higher system complexity. Furthermore, the bit error rate (BER) expressions of JECD-OFDM-DCSK are derived in additive white Gaussian noise (AWGN) and multipath fading channels. Simulation results show that the BER performance of JECD-OFDM-DCSK outperforms that of other OFDM-based DCSK systems. Finally, JECD-OFDM-DCSK performs much better than other systems over the underwater acoustic (UWA) channel, which validates the robustness of JECD-OFDM-DCSK.

Given the high transmission loss, severe Doppler spread and large multipath delay in the underwater acoustic (UWA) channel, the channel estimation and tracking in the conventional orthogonal frequency division multiplexing (OFDM) based UWA systems are severely unaffordable. In this paper, we propose a low-complexity and cost-friendly OFDM-based differential cyclic-shifted differential chaos shift keying (OFDM-DCS-DCSK) system which offers a high data rate, superior robustness and enhanced system security for UWA communications without the need for channel state information (CSI). In the system, the information bits are carried by different step lengths of the cyclic shifts. At the receiver, a low-complexity detection method is used to search the position of maximum from the cyclic correlation values and therefore estimate the information bits. Finally, simulation results demonstrate the proposed OFDM-DCS-DCSK system outperforms its competitors both in bit error rate (BER) performance and in system security.

The rise of social media has changed the nature of the fashion industry. Influence is no longer concentrated in the hands of an elite few: social networks have distributed power across a broader set of tastemakers. To understand this new landscape of influence, we created FITNet --- a network of the top 10k influencers of the larger Twitter fashion graph. To construct FITNet, we trained a content-based classifier to identify fashion-relevant Twitter accounts. Leveraging this classifier, we estimated the size of Twitter's fashion subgraph, snowball sampled more than 300k fashion-related accounts based on following relationships, and identified the top 10k influencers in the resulting subgraph. We use FITNet to perform a large-scale analysis of fashion influencers, and demonstrate how the network facilitates discovery, surfacing influencers relevant to specific fashion topics that may be of interest to brands, retailers, and media companies.

In this paper, we propose a Sparse Code Spreading-aided Multi-Carrier Differential Chaos Shift Keying (SCS-MC-DCSK) transceiver to improve the efficiency and reliability performances for multiuser transmissions. With the aim to improve the spectrum efficiency and enhance the reliability, we construct a multi-dimension codebook based on a factor graph matrix to spread information bits in a non orthogonal way, thus the signals could overlap and multiple users are allowed to share all sub-carrier resources via the non orthogonal spreading. The information bits using the same codebook are regarded as a layer, while each user could choose to use one or multiple layers. Then the resultant symbols are spread by the reference chaotic sequence and its quadrature version generated by Hilbert transform in the time domain. At the receiver, reverse operations are conducted, and we propose the Minimum Distance (MD) detection method to retrieve the estimates. Furthermore, theoretical performances, including the Symbol Error Rate (SER), capacity, energy efficiency, spectrum efficiency and computational complexity, are analyzed and compared among the proposed design and benchmarks. Simulation results are then provided to validate the theoretical analysis. Moreover, the Bit Error Rate (BER) performances under different channel conditions demonstrate the superior reliability and efficiency to benchmarks.

In this paper, we focus on designing a high-data-rate noncoherent chaotic communication scheme to satisfy the demand of the explosive growth in data traffic. To achieve this goal, a joint time-frequency index modulation assisted multiple-mode DCSK (JTFIM-MM-DCSK) system is proposed, where a pair of distinguished signal modes are modulated into the selected subcarriers and another signal mode is transmitted by the unselected subcarriers. In this configuration, besides the modulated bits used for physical transmission, the carrier index bits and time slot index bits, conveyed by the state of whether subcarriers and time slots are selected or not, are also transmitted implicitly to achieve higher data rate. Moreover, the design of multiple-mode signals ensures that it is taking full advantage of all subcarriers and time slots to transmit the information bits, thereby improving the data rate significantly. The bit error rate (BER) expressions of the JTFIM-MM-DCSK system are derived over additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels, which are checked by computer simulations. Finally, the advantage of the JTFIM-MM-DCSK system over other up-to-date noncoherent chaotic communication systems is demonstrated in terms of BER performance through extensive computer simulations.

A new multicarrier M-ary orthogonal chaotic vector shift keying with index modulation (MC-MOCVSK-IM) is presented in this paper. In this design, information bits are conveyed not only by the multiple groups of M-ary information bearing signals, but also by the specific indices of the selected reference signals which depend on the incoming mapped bits. Benefiting from the favorable features of multicarrier modulation, M-ary modulation and index modulation, MC-MOCVSK-IM system is capable to offer higher energy efficiency and spectral efficiency at some expense of hardware complexity. In addition, the analytical bit error rate (BER) expressions of MC-MOCVSK-IM system are derived over additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels. The BER performance comparison between MC-MOCVSK-IM system and other non-coherent chaotic communication systems is carried out to highlight the superiority of MC-MOCVSK-IM system in terms of BER performance. Considering the dramatically increased demand for high-data-rate transmission and the harsh environment of future wireless communication, MC-MOCVSK-IM system shows strong robustness and offers competitive solutions for high-data-rate non-coherent chaotic communication systems.

A new M-ary differential chaos shift keying with index modulation (IM-MDCSK), which has the advantages of high data rate and low energy consumption, is proposed in this paper. In the proposed scheme, each data frame is divided into several time slots where the reference signal is placed in the first time slot and the rest time slots with specific indices are provided for information bearing signals. More exactly, the information bearing signals with active indices are modulated by M-ary DCSK symbols, and the active indices are determined by mapped bits via the combination number mapping method. At the receiver, the absolute values of decision variables in all branches are used to find the indices of active time slots, while M-ary DCSK demodulation is applied to recover the modulated bits. Moreover, we derive the analytical bit-error-rate (BER) expressions for the proposed scheme over additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels, and then simulation results verify our theoretical derivations. Finally, the performance of IM-MDCSK scheme is compared with M-ary DCSK and other up-to-date chaotic modulation schemes based on index modulation (IM). IM-MDCSK scheme is proved to be competitive and preeminent.

In this study, an M ‐ary code‐shifted differential chaos shift keying system with in‐phase and quadrature code index modulation (I/Q‐CIM‐CS‐MDCSK) is presented. In the proposed system, the information bits are conveyed not only by the M ‐ary constellation symbols, but also by the specific Walsh codes indices corresponding to the in‐phase and quadrature branches of M ‐ary information bearing signals. Since the reference signal and the multiple M ‐ary information bearing signals are overlapped and transmitted within the identical time slot in a parallel manner, the spectral efficiency of the I/Q‐CIM‐CS‐MDCSK system is enhanced significantly. In addition, the analytical bit error rate (BER) expressions for the presented system are derived under the additive white Gaussian noise and multipath Rayleigh fading channels. Finally, the BER performance of the proposed system is compared to other chaotic communication systems. The results manifest that the I/Q‐CIM‐CS‐MDCSK system is a promising and competitive chaotic communication scheme.

Multi‐carrier (MC) and spread‐spectrum (SS) are two good technologies for underwater acoustic (UWA) communications. In this study, the authors propose a novel MC chaos modulation scheme, which combines code‐shifted differential chaos shift keying (CS‐DCSK) with orthogonal frequency division multiplexing (OFDM), namely MC‐CS‐DCSK. The proposed scheme exploits the orthogonal characteristic of the Walsh code to superimpose the chaotic reference chips and the information bearing chips in the same time/frequency unit. Besides, a cyclic‐shift interleaver is used on chips to harvest frequency diversity. To the in‐depth understanding of the proposed system, the bit error rate (BER) of the proposed system under Gaussian channels and multipath Rayleigh fading channels are derived and verified by simulation. Furthermore, the spectral efficiency of the proposed system is analysed and compared with some existing chaos‐based communication systems. Finally, they study BER performance of the system under UWA channels and compare it with traditional MC direct sequence SS and OFDM‐based MC‐DCSK systems. Simulation results show that the system has good robustness under time‐varying UWA channels.

In this study, a new chaos modulation scheme which combines M ‐ary differential chaos shift keying (DCSK) with code‐index modulation (CIM‐MDCSK) is proposed. In the CIM‐MDCSK scheme, the two Walsh codes that are used to generate two orthogonal chaos components are selected from the candidate codes, whose code indices are determined by information symbols. Thus, the information bits are conveyed not only by M ‐ary DCSK signal but also by the indices of the Walsh codes. Theoretical symbol error rate (SER) and bit error rate (BER) of the proposed scheme are derived and confirmed by simulations. Furthermore, by applying the noise‐reduction to reference signals of CIM‐MDCSK, the SER/BER expressions are also derived. Simulation results show that the proposed CIM‐MDCSK outperforms DCSK and M ‐ary DCSK based on Hilbert transform. Especially, the CIM‐MDCSK with noise‐reduction shows significant advantages. Moreover, the performance of CIM‐MDCSK scheme is compared with direct sequences spread‐spectrum system with code‐index modulation over flat and frequency selective fading channel. The proposed CIM‐MDCSK can offer good performance over frequency selective fading channel with a low complexity non‐coherent receiver which does not require any channel state information and channel equalisation.

In this paper, a dual-mode differential chaos shift keying with index modulation (DM-DCSK-IM) is proposed. In the proposed system, the bit stream is partitioned into two subblocks, where the first subblock is the mapped bits used to select the active time slot, which presents the time slot's constellation mode, and the second subblock is the modulated bits, which are further divided into two groups and modulated by a pair of distinguishable modem-mode constellations, respectively. Unlike the recently proposed pulse-position-modulation differential chaos shift keying (PPM-DCSK), since both the active and inactive time slots are applied to convey the information bits, the data rate of the proposed system can be promoted significantly. In order to detect the active time slots and recover the mapped bits as well as modulated bits correctly, we propose an effective detection algorithm for the proposed system. Furthermore, the theoretical bit error rate (BER) expressions are derived over additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels, and the simulation results validate the accuracy of our derivations. Finally, the BER performance of the proposed system is compared with the other non-coherent chaotic communication systems, and the results indicate that the proposed system can offer competitive and satisfactory BER performance.

In this paper, an M -ary orthogonal multilevel differential chaos shift keying system with code index modulation (CIM-OM-MDCSK) is proposed. In the proposed system, the multiple information bearing signals are modulated by the selected Walsh codes with specific indices and the M -ary information signals which are composed of modulated bits, chaotic signals, and their Hilbert transform. Since the reference signal along with the information bearing signals are overlapping in time domain and orthogonal in code domain by using Walsh code sequences, the spectral efficiency of the CIM-OM-MDCSK system is improved largely. By combining the M -ary modulation, orthogonal multilevel modulation, and code index modulation, the proposed CIM-OM-MDCSK system can achieve high data rate and superior bit error rate (BER) performance compared to its rivals. Moreover, we derive the BER expressions of the proposed system over additive white Gaussian noise and multipath Rayleigh fading channels. Finally, we make a performance comparison between the proposed system and other state-of-the-art non-coherent chaotic communication systems. The results confirm the competitive benefits of the proposed system.

In this paper, we propose a constellation-based differential chaotic bit-interleaved coded modulation system with iterative receiver (DC-BICM-IR) over power line channels (PLCs) and then design a new protograph-based low density parity check (P-LDPC) code for the system.

In this paper, we develop a novel serial concatenated trellis-coded differential chaotic modulation (SCTC-DCM) system, which combines serial concatenated trellis-coded modulation (SCTCM) with M-ary differential chaotic shift keying (M-ary DCSK). The proposed system has lower error floor than turbo trellis-coded differential chaotic modulation (TTC-DCM). At the same time, when the signal to noise ratio (SNR) is relatively high, SCTC-DCM scheme achieves better bit error rate (BER) performance. Moreover, simulation results show that the proposed scheme can obtain considerable coding gain compared with uncoded M-ary differential chaotic shift keying over AWGN channel. Furthermore, SCTC-DCM system inherits the advantages of chaos-based modulation system and does not require channel state information (CSI) at the receiver. Therefore, the proposed system can be applied to band-limited communication scenes with poor channel condition.

Energy usage and data rate of differential chaos shift keying (DCSK) are both inefficient since half of the symbol duration is used to transmit reference. To improve the energy efficiency and data rate, we propose a new chaos modulation scheme which combines DCSK with code index modulation (CIM) referred to as CIM-DCSK. In the proposed scheme, a short reference signal is transmitted first. Then P repeated reference signals, which serve as information-bearing signals, are simultaneously modulated by an information bit and a Walsh code with a specific index which is determined by an extra information symbol. The analytical bit error rate (BER) performance of the proposed scheme is derived and verified by simulations. Further, we improve the performance of the proposed system by applying noise-reduction and optimizing power coefficients on the reference and the information-bearing signals of CIM-DCSK. Simulation and analytical results show that these optimization methods significantly boost the BER performances of the proposed schemes. Finally, the BER performances of the proposed systems are compared with that of the conventional DCSK system and the short reference DCSK (SR-DCSK) system. Numerical results show that the proposed schemes outperform both DCSK and SR-DCSK.

In this paper, a novel chaos modulation scheme, which combines code-shifted differential chaos shift keying (CS-DCSK) with orthogonal frequency division multiplexing (OFDM) is presented, namely OFDM-CS-DCSK. In the proposed scheme, the reference signal and the information bearing signal of CS-DCSK are firstly formed by Walsh code sequences, then different chips of the CS-DCSK signal are mapped onto different subcarriers of OFDM. Utilizing the characteristics of OFDM and CS-DCSK, the proposed scheme has robust performance over time-frequency doubly selective fading channel. In addition, the proposed system has low complexity because channel estimation, channel equalizer and the radio frequency (RF) delay circuits are not required at its receiver. By the computer simulations, bit error rate (BER) performances of the proposed scheme are compared with OFDM-DCSK and CS-DCSK under various channel parameters. Simulation results indicate that the proposed scheme has significant performance advantages over OFDM-DCSK and CS-DCSK in time-frequency doubly selective fading channel.

In this paper, by applying M-ary constellation modulation to code shifted differential chaos shift keying (CS-DCSK), a new M-ary DCSK which is called CS-MDCSK, is proposed. In the proposed scheme, the reference chaos signal is the same with the CS-DCSK, and the two orthogonal components of information bearing signal are obtained by two Walsh codes. Furthermore, the proposed CS-MDCSK is extended to general scheme (GCS-MDCSK), which transmits more than one M-ary constellation information bearing signals with one reference. Since high order constellations are used, the proposed scheme enhances the spectrum efficiency compared to CS-DCSK and GCS-DCSK. By computer simulations, the bit error rate (BER) performance of two proposed systems are compared to that of CS-DCSK and GCS-DCSK, respectively. Simulation results show that the proposed systems outperform the CS-DCSK and GCS-DCSK when 4-ary constellation is applied.

The turbo trellis-coded differential chaotic modulation (TTC-DCM) is a newly proposed scheme, which is very suitable for bandlimited communication applications with poor channel conditions due to the merits of high bandwidth efficiency, robustness to multipath fading and easy-to-implement property. In this paper, in-phase and quadrature-phase (IQ) interleaved turbo trellis-coded differential chaotic modulation (IQ-TTC-DCM) scheme is proposed, which is capable of increasing the diversity order of conventional TTC-DCM. The IQ-TTC-DCM can obtain significant gains while communicating over fading environment, compared with TTC-DCM scheme. Besides, a code search algorithm utilizing the Extrinsic Information Transfer (EXIT) charts is proposed, aiming to find the component code with the best convergence behavior. The searched codes for different channels are presented for 8-state 8-DCSK TTC-DCM scheme and simulations are carried out to testify their superiorities.

In the general code-shifted differential chaos shift keying (GCS-DCSK) system, multiple bit-streams are simultaneously carried by CS-DCSK signal using Walsh codes. However, its data rate is limited by the available Walsh codes in the Walsh code matrix due to orthogonality constraint of GCS-DCSK signal. In this paper, we propose a new GCS-DCSK scheme with code index modulation (CIM-CS-DCSK), which can achieve higher spectrum efficiency using code index modulation to carry additional bits. In the proposed scheme, the reference chaotic signal is the same as that of GCS-DCSK, and the multiple information bearing signals are simultaneously modulated by the information symbols and the selected Walsh codes with specific indices, which are determined by an integer sequence mapped from information symbols via the natural numbers to k-combinations mapping method. We derive bit error rate of the proposed scheme over the additive white Gaussian noise channel. The numerical results not only verify our analysis but also show the advantage of the proposed scheme over GCS-DCSK. Through analyzing and comparing the numbers of carried bits per transmitted symbol of CIM-CS-DCSK and GCS-DCSK, it is shown that the proposed scheme can obtain higher data rate than GCS-DCSK with the same resource constraints.

The M ‐ary differential‐chaos‐shift‐keying ( M ‐ary DCSK) system offers a good noise performance over an additive white Gaussian noise (AWGN) channel in the category of non‐coherent detection chaotic systems. However, the way that the M ‐ary DCSK system utilises the available Walsh codes results in a relatively low bandwidth efficiency (BE). Moreover, the number of delay elements required at the transmitter and receiver increases exponentially with the number of bits per symbol. To overcome the aforementioned problems, the authors propose a multilevel code‐shifted DCSK (MCS‐DCSK) system in this study. In the proposed MCS‐DCSK system, the reference chaotic signal and the information‐bearing chaotic signals are orthogonal and are transmitted in the same time slot. They show that the MCS‐DCSK system significantly outperforms the M ‐ary DCSK system in terms of BE and complexity. They also derive analytical bit‐error‐rate expressions for the MCS‐DCSK system over additive white Gaussian noise and multipath fading channels, and verify them with simulation results.

This paper evaluates the bit error rate (BER) performance of a code-shifted differential chaos shift keying (CS-DCSK) ultra-wide bandwidth (UWB) system over indoor communication channels under the impact of both single and multiple narrow band interference (NBI) signals. We analyze the BERs both in single NB interferer and multiple NB interferes. The analytic results and simulation results show that NBI signal has a noticeable impact on the performance of UWB systems which are independent of the carrier frequency.

In this paper, a differential chaos shift keying (DCSK) opportunistic relaying scheme is proposed and the system performance is analyzed over multipath Rayleigh fading channel, where all the relays adopt decode-and-forward (DF) strategy. Considering the effect of the path loss, the best relay is chosen by max-min selection criterion. We derive the probability density function (PDF) of the signal noise ratio (SNR) in each hop, and give the expression of the end-to-end bit error rate (BER). The effects of the number of relays, the propagation distance and the spread-spectrum factor on the system performance are investigated. It is shown that the BER performances are proportional to the number of relays and the propagation distance, while they are inverse ratio to the spread-spectrum factor. Numerical results prove an excellent match between simulations and our analysis expressions.

Frequency modulated differential chaos shift keying (DCSK/FM-DCSK), a joint modulation and spread spectrum technique, is a promising modulation technique for low-cost and low-complexity wireless transmission applications. The noise performance of DCSK/FM-DCSK is superior to most conventional modulation schemes in multipath-channel environment. Cooperative communication, on the other hand, is receiving increasing attention due to its efficiency in sharing single-antenna mobiles or network nodes with other antennas to achieve combating fading via transmitting diversity. By combining these two aspects of advantages, a novel chaotic communication system is proposed in this paper, aiming to achieve combating multipath and fading effects. Simulation results show that significant performance improvement can be achieved by the proposed system in comparison with non-cooperative systems. It is found that the choice of some key parameters, such as the spread spectrum factor and the relay selective strategy, affect the system performance prominently. It reveals that the combination of the DCSK/FM-DCSK framework with a cooperative strategy is of great practical value for certain wireless communication networks.

In this study, the performance of the frequency-modulated differential chaos shift keying (FM-DCSK) ultra-wideband (UWB) system is evaluated through two important system parameters, the guard interval and the integration interval of the integrator, over indoor communication channels. It is found that the existing FM-DCSK UWB system suffers severe performance degradation in the IEEE 802.15.4a low-rate application. To resolve this problem, a new optimising scheme for the integration interval is presented. Simulation results show that the performance of the proposed scheme is significantly improved and becomes insensitive to the data rate. In addition, some notable advantages are evident in the proposed system, such as moderate multiple-access capability and feasible cross-layer optimisation.