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As an attempt to tackle the low-data-rate issue of the conventional LoRa systems, we propose two novel frequency-bin-index (FBI) LoRa schemes. In scheme I, the indices of starting frequency bins (SFBs) are utilized to carry the information bits. To facilitate the actual implementation, the SFBs of each LoRa signal are divided into several groups prior to the modulation process in the proposed FBI-LoRa system. To further improve the system flexibility, we formulate a generalized modulation scheme and propose scheme II by treating the SFB groups as an additional type of transmission entity. In scheme II, the combination of SFB indices and that of SFB group indices are both exploited to carry the information bits. We derive the theoretical expressions for bit-error-rate (BER) and throughput of the proposed FBI-LoRa system with two modulation schemes over additive white Gaussian noise (AWGN) and Rayleigh fading channels. Theoretical and simulation results show that the proposed FBI-LoRa schemes can significantly increases the transmission throughput compared with the existing LoRa systems at the expense of a slight loss in BER performance. Thanks to the appealing superiorities, the proposed FBI-LoRa system is a promising alternative for high-data-rate Internet of Things (IoT) applications.

In recent years, flexible stress sensors capable of monitoring diverse body movements and physiological signals have been attracting great attention in the fields of healthcare systems, human–machine interfaces, and wearable electronics. Inspired by the structure of natural eggshell inner membrane (ESIM), we developed a pressure sensor based on MXene (Ti3C2Tx)/Ag NWs (silver nanowires) composite electrodes and the micro-structured dielectric layer to meet the application requirements of wide detection range and long-term stability for the sensors. In the light of the nanoscale-microarray of the dielectric layer and the rough surface of electrode materials, this pressure sensor is expected to allow great and persistent deformation during the loading process. As a result, the device is characterized by an improved sensitivity, fast response (in the millisecond range), wide detection range (0–600 kPa), and long-term stability. The outstanding performance of the proposed sensor makes it possible to detect various human activities, such as speaking, air blowing, clenching, walking, finger/knee/elbow bending, and striking, demonstrating its good application prospects in wearable and flexible electronic devices.

In this paper, a new non-coherent cross-quadrature amplitude modulation (XQAM)-based M-ary differential chaos shift keying (XQAM-MDCSK) system is proposed. In such a system, an autocorrelator is adopted at the receiver to obtain the channel compensation value. This framework can be extended to various amplitude phase shift keying-based MDCSK systems, such as star QAM-based MDCSK (star QAM-MDCSK) and square QAM-based MDCSK (SQAM-MDCSK) systems. Moreover, the bit error rate (BER) expression of the proposed XQAM-MDCSK system is derived over a multipath Rayleigh fading channel. Results show that the proposed XQAM-MDCSK system can achieve better BER performance and a lower peak-to-average power ratio (PAPR) compared to the star QAM-MDCSK system. Furthermore, we also show that the performance of the proposed system can be close to that of a system with perfect channel state information (CSI).

Code index modulated multi-carrier M -ary differential chaos shift keying (CIM-MC- M -DCSK) system not only inherits low-power and low-complexity advantages of the conventional DCSK system, but also significantly increases the transmission rate. This feature is of particular importance to Internet of Things (IoT) with trillions of low-cost devices. In particular, for e-health IoT applications, an efficient transmission scheme is designed to solve the challenge of the limited battery capacity for numerous user equipments served by one base station. In this paper, a new multiple-input-single-output simultaneous wireless information and power transfer (MISO-SWIPT) scheme for CIM-MC- M -DCSK system is proposed by utilizing orthogonal characteristic of chaotic signals with different initial values. The proposed system adopts power splitting mode, which is very promising for simultaneously providing energy and transmitting information of the user equipments without any external power supply. In particular, the new system can achieve desirable anti-multipath-fading capability without using channel estimator. Moreover, the analytical bit-error-rate expression of the proposed system is derived over multipath Rayleigh fading channels. Furthermore, the spectral efficiency and energy efficiency of the proposed system are analyzed. Simulation results not only validate the analytical expressions, but also demonstrate the superiority of the proposed system.

Adaptive link selection for buffer-aided relaying can achieve significant performance gain compared with the conventional relaying with fixed transmission criterion. However, most of the existing link-selection strategies are designed based on perfect channel state information (CSI), which are very complex by requiring channel estimator. To solve this issue, in this paper, we investigate a buffer-aided differential chaos-shift-keying based simultaneous wireless information and power transfer (DCSK-SWIPT) relay system, where a decode-and-forward protocol is considered and the relay is equipped with a data buffer and an energy buffer. In particular, we propose two link-selection protocols for the proposed system based on harvested energy, data-buffer status and energy-shortage status, where the CSI is replaced by the harvested energy to avoid the channel estimation and the practical problem of the decoding cost at the relay is considered. Furthermore, the bit-error-rate (BER) and average-delay closed-form expressions of the proposed protocols are derived over multipath Rayleigh fading channels, which are validated via simulations. Finally, results demonstrate that both the proposed protocols not only provide better BER performance than the conventional DCSK system and DCSK-SWIPT relay system but also achieve better BER performance and lower average delay in comparison to the conventional signal-to-noise-ratio-based buffer-aided DCSK-SWIPT relay systems.

In this letter, we derive a closed-form bit error rate (BER) of M-ary differential chaos shift keying (M-DCSK) systems over multipath Rayleigh fading channels via approximating Gaussian Q-function by polynomials. The approximation is made piecewisely using polynomials of different degrees and Remez algorithm is applied to achieve the minimax approximation. Our method can be extended into the existing non-coherent transmit-reference chaos-based modulation systems, e.g., short-reference DCSK and multi-carrier DCSK systems. The derived closed-form BERs are compared with the simulated ones in order to verify the efficiency of proposed approximation scheme. This work was supported in part by the NSF of China (Nos. 61701121, 61801128), the Research Project of the Education Department of Guangdong Province (No. 2018KTSCX057), the Project of Department of Education of Guangdong Province (No. 2018SFJD-01).

The rational design and scalable assembly of nanoarchitectures are important to deliver highly uniform, functional films with high performance. However, fabrication of large-area and high-performance films is quite difficult because of the challenges in controlling homogeneous microstructures, interface properties, and the high cost of the conventional vacuum deposition technique. Here, we report a solution-processed molecular level assembly approach to fabricate self-supported (without any binders or conductive additives) large-area (up to 810 cm ) functional films with controllable thickness and high homogeneity. We show that the assembled prototypical Fe(II)-based metallo-supramolecular polymer (polyFe) film exhibits unprecedented electrochromic performance such as ultrahigh coloration efficiency (750.3 cm C ), fast switching speed (

The conventional orthogonal multiple-access-based downlink transmission for the differential chaos shift keying system with pulse-position modulation (PPM-DCSK) suffers from lower energy efficiency and data rate. To tackle this problem, a low-complexity superposition coding PPM-DCSK (SC-PPM-DCSK) system for downlink multi-user chaotic communication is proposed in this paper. The proposed system exploits the superposition coding principle on the reference signal and the information-bearing signal to achieve multi-user simultaneous information transmission for the downlink scenario, thus significantly improving the energy efficiency and transmission rate. Furthermore, the analytical expression for the error performance and the throughput of the proposed system are precisely derived over additive white Gaussian noise and multipath Rayleigh fading channels. Simulation results not only verify the accuracy of the analytical method but also illustrate the proposed transmission scheme in achieving significant performance gain compared with the time-sharing-based PPM-DCSK and multiresolution DCSK systems. Due to such superiority, the proposed SC-PPM-DCSK system can be deemed to be an outstanding scheme for downlink multi-user short-range wireless communications.

Although LoRa modulation can achieve low-power and long-range transmission, its performance is significantly affected by fading channels. On the other hand, its low data rate limits the capacity. To mitigate these disadvantages, a new reconfigurable intelligent surface (RIS) assisted LoRa uplink system is proposed in this paper, where the reflection coefficients of the RIS are generated by utilizing an M-ary differential phase shift keying modulator. Moreover, a low-complexity non-coherent receiver is designed for the proposed system. The new system is able to inherit the non-coherent detection of the conventional LoRa system and also transmit additional information of log2M bits while reducing the impact of the fading channels. Furthermore, the bit-error-rate, symbol-error-rate and throughput expressions of the system are derived in closed form. Theoretical and simulated results show that the system has better performance than the conventional LoRa system and single-relay LoRa system. This work was supported in part by NSF of China under Grants 62071129 and 61801128, in part by the Hong Kong Research Grants Council under the GRF Grant CityU 11206320, and in part by the Project of Department of Education of Guangdong Province under Grant 2021XSLT020.

The conventional LoRa system is not able to sustain long-range communication over fading channels. To resolve the challenging issue, this paper investigates a two-hop opportunistic amplify-and-forward relaying LoRa system. Based on the best relay-selection protocol, the analytical and asymptotic bit error rate (BER), achievable diversity order, coverage probability, and throughput of the proposed system are derived over the Nakagamim fading channel. Simulative and numerical results show that although the proposed system reduces the throughput compared to the conventional LoRa system, it can significantly improve BER and coverage probability. Hence, the proposed system can be considered as a promising platform for low-power, long-range and highly reliable wireless-communication applications., 7 pages, 6 figures, conference

With the continual increase of storage density, NAND flash memory cells are particularly vulnerable to channel noise, which significantly degrades the storage reliability. To overcome this issue, low-density parity check (LDPC) codes have been considered as a preferable choice for flash memory systems. To further improve the efficiency of the decoder, the convergence speed and the error-rate performance are the key performance indicators for LDPC-coded NAND flash memory. In this study, a threshold-voltage-drift-aware scheduling for belief propagation (BP) decoding of LDPC-coded NAND flash memory is introduced to improve the convergence speed and the error-rate performance. The basic idea of the proposed scheduling is to find an appropriate updated order of variable nodes according to their corresponding locations of threshold voltages. Since the proposed scheduling updates less reliable variable nodes with higher priority, it can improve the efficiency of BP decoding. Simulation results show that the proposed scheduling not only significantly improves the convergence speed, but also obtains better error-rate performance than the conventional serial scheduling.

As a bandwidth-efficient technique, bit-interleaved coded modulation with iterative demapping and decoding (BICM-ID) has attracted much research attention in the field of wireless communication. In this paper, we put forth a joint design of root-protograph (RP) low-density parity-check (LDPC) codes and BICM-ID, referred to as RP-based BICM-ID (RP-BICM-ID), over block-fading (BF) channels so as to boost the throughput under limited bandwidth. To preserve the full-diversity property of RP codes, we propose an efficient modulation strategy for the RP-BICM-ID system by taking the fading-block length into consideration. We also analyze the outage-probability limit of the RP-BICM-ID systems to establish the fundamental lower-limit on their word-error-rate (WER) performance. Moreover, we conceive a multi-level protograph extrinsic information transfer (ML-PEXIT) algorithm to derive the asymptotic WER and bit error rate (BER) of the RP-BICM-ID systems over BF channels. As a further insight, we develop a novel unequal-error-protection (UEP) bit-to-symbol (B2S) mapping scheme for the RP-BICM-ID systems, which gives rise to an additional performance improvement. Analyses and simulations show that the proposed RP-BICM-ID systems can not only realize desirable spectral efficiency, but also obtain near-outage-limit performance over BF channels. Therefore, the proposed RP-BICM-ID systems are very promising in achieving high-reliability and high-rate transmissions under slow-fading wireless-communication environments.

Frequency-modulated differential chaos shift keying ultrawideband (FM-DCSK UWB) system has attracted more and more attention in recent years because of its low-complexity and low-power advantages. Nevertheless, its system performance is severely degraded in the presence of narrowband interference (NBI), which further limits its practical applications. In this paper, an enhanced energy-based detector (EED) is proposed for the FM-DCSK UWB system to tackle this problem. Compared with the conventional energy detector (ED), the proposed EED significantly enhances the anti-NBI capability while maintaining the low-power and low-complexity feature. As a further insight, the analytical bit-error-rate (BER) expression of the proposed EED-based FM-DCSK UWB system is derived over additive white Gaussian noise as well as IEEE 802.15.4a multipath fading channels. Moreover, simulation results are carried out to demonstrate the accuracy of the theoretical analysis and the merit of the proposed EED. It is illustrated that the proposed EED achieves better performance than the conventional ED in various transmission scenarios. Thanks to the above-mentioned advantages, the proposed EED-based FM-DCSK UWB system appears to be an excellent candidate for low-power and low-complexity tactile Internet-of-Things applications, e.g., wireless sensor networks and wireless body area networks.

Graphene nanosheet films (GNSF) show great potential as solid lubricants. They, however, usually suffer from short lifetime and low load capability, limiting their further engineering application. In this work, we try to address these crucial challenges, for the first time, by inducing a unique three-dimensional microstructure into the GNSF. The as-prepared three-dimensional graphene nanosheet films (3D-GNSF) are composed of many crumpled and partially standing graphene nanosheets (GNS) that overlap with each other and form a three-dimensional interconnected network. The morphology, composition and structure of the 3D-GNSF are investigated in detail using scanning electron microscope, X-ray diffractometer, transmission electron microscope and X-ray photoelectron spectroscopy to deduce their possible formation mechanism. Tribological tests are conducted in air as a function of contact pressure that is up to about 1GPa. The results suggest it is the unique architecture of the 3D-GNSF that quickly produces a compact and stable sliding interface consisting of GNS against GNS, enabling 3D-GNSF as promising solid lubricants with low friction, excellent anti-wear ability, good durability and high load capability. The authors are grateful to the National Natural Science Foundation of China (51605097) and Training Programs of Innovation and Entrepreneurship for Undergraduates (201811845148) for financial support.

Present challenges in electrochromic devices include the limited transmissive and reflective inter‐switchability, while achieving high optical contrast, fast switching speed, and cycling stability, simultaneously. In article number 1903198, Pooi See Lee and co‐workers develop a quasi‐solid‐state tristate reversible electrochemical mirror device, which offers highly reversible switching between transparent, greyish‐blue, and mirror (reflective) optical states. The alloying approach facilitates the electrodeposition and dissolution of Cu mirror film, allowing enhanced device stability. [Image: see text]

LoRa is a modulation technology for low power wide area networks (LPWAN) with enormous potential in 5G era. However, the performance of LoRa system deteriorates seriously in fading-channel environments. To tackle this problem, in this paper we introduce multiple-input-multiple-output (MIMO) configuration employing space-time block coding (STBC) schemes into the LoRa system to formulate an STBC-MIMO LoRa system. Then, we investigate the theoretical performance of the proposed system over Rayleigh fading channels. To this end, we derive the distribution of the decision metric for the demodulator in the proposed system. Based on the above distribution, we propose a closed-form approximate BER expression of the proposed system when perfect and imperfect channel state information (CSI) are considered. Furthermore, we analyze the diversity order and the throughput of the proposed system. The results of the diversity analysis demonstrate that the diversity order of the system in the imperfect CSI scenario with fixed channel estimate error variance is zero. However, in the imperfect CSI scenario with a decreasing channel estimate error variance and the perfect CSI scenario, the system can achieve full diversity. In addition, the results of the throughput analysis show that the throughput of the proposed system is little affected by CSI conditions. Simulation results verify the accuracy of the theoretical analysis and the excellent performance of the proposed system. Due to such superiority, the proposed STBC-MIMO LoRa system can be considered as a good scheme for LPWAN.

Reversible electrochemical mirror (REM) electrochromic devices with electrochemical tunability in multiple optical states are exciting alternatives to conventional electrochromic smart windows. Electrochromic devices are studied extensively, yet widespread adoptions have not been achieved due to problems associated with durability, switching speed, limited options on optical states, and cost. In this study, a REM electrochromic device based on CuSn alloy is developed, which offers highly reversible switching between transparent, greyish‐blue, and mirror states via reversible electrodeposition and dissolution. The alloying element, Sn acts as an electrochemical mediator, which facilitates the electrodeposition and dissolution of Cu. The CuSn‐based REM device shows superior cycling stability for 2400 cycles (transmittance mode) and 1000 cycles (reflectance mode). The electrodeposited CuSn alloy film is resistant to surface oxidation in ambient air, with a 2.9% difference in reflectance at 2000 nm after 3 days. In addition, the alloy film exhibits excellent NIR reflectance property with thermal modulation of 18.5 °C at a high temperature of 180 °C. The REM device with zero power consumption maintains its mirror state for at least 100 min, making it a promising candidate for energy‐efficient applications., The quasi‐solid‐state tristate reversible electrochemical mirror (REM) device offers highly reversible switching between transparent, greyish‐blue, and mirror states via reversible electrodeposition and dissolution. The REM shows superior thermal barrier property compared to the bare substrate. The extended memory effect of the REM device is achieved in the presence of quasi‐solid‐state polymer electrolyte.

The emergence of soft energy devices provides new possibilities for various applications, it also creates significant challenges in the selection of structural design and material compatibility. Herein, we demonstrate a stretchable transmissive electrochromic energy storage device by inkjet-printing single layer of WO3 nanoparticles on an elastomeric transparent conductor. Such hybrid electrode is highly conductive and deformable, making it an excellent candidate for the application: large optical modulation of 40%, fast switching speed (

Coded modulation (CM) is a bandwidth efficient framework to approach the capacity limit of the differential chaos shift keying (DCSK) systems. In this paper, we propose an ${M}$ -ary DCSK system operated with CM based on nonbinary protograph low-density parity-check (LDPC) codes over Rayleigh fading channels. First, we investigate the performance of the proposed nonbinary channel coded DCSK (CM-DCSK) and bit-interleaved coded DCSK (BICM-DCSK). In particular, we show that CM-DCSK outperforms BICM-DCSK over Rayleigh fading channels in terms of capacity limit. Compared with BICM-DCSK, CM-DCSK can simplify the receiver structure, since it does not require turbo iteration between the noncoherent detector and channel decoder. Second, guided by the modified extrinsic information transfer (EXIT) analysis, we put forth two new types of nonbinary protograph LDPC codes to approach the capacity limit of CM-DCSK. Both EXIT analysis and simulation results demonstrate that the proposed protograph-coded CM-DCSK achieves a better error performance than BICM-DCSK even with iterative decoding. Furthermore, we show the performance superiority of nonbinary protograph-coded CM-DCSK over a practical ultra-wideband channel. Hence, we conclude that this proposed scheme offers a good alternative for wireless local area network applications.

High-quality patterns were successfully prepared by inkjet-printing WO3-PEDOT:PSS composites on different substrates including the rigid FTO glass and most importantly, on flexible PEDOT:PSS/Ag grid/PET. Excellent electrochromic performances can be achieved, including large optical modulation (85.7% optical contrast at the wavelength of 633 nm on FTO glass substrate), fast switching speed (coloration/bleaching time of 2.4/0.8 s on the PEDOT:PSS/Ag grid/PET substrate), instantaneous coloration efficiency (68.8 cm2 C−1) and good cycling stability (up to 10,000 cycles). The effects of the applied potential window during electrochemical evaluation on the electrochromic performances were analyzed in detail. The printed electrochromics films on PEDOT:PSS/Ag grid/PET showed the best electrochemical stability, in agreement with its superior conductivity and transmittance at 633 nm of 0.6 Ω/sq and 66%, respectively. It sustained transmittance modulation of about 75.5% and 53.1% of its first cycle recorded contrast at 633 nm, after being subjected to 1000 and 5000 cycles, respectively, and maintained good electrochemical stability up to 10,000 cycles. Moreover, a robust mechanical stability was also achieved by the printed films on flexible PEDOT:PSS/Ag grid/PET substrate. The film maintained a transmittance modulation of 85.8% of its original contrast after 5000 bending cycles at a curvature radius of 1 cm. The inkjet-printed WO3 nanocomposite based flexible electrochromic displays exhibited excellent electrochromic performance, making it a promising candidate for energy efficient displays, e-books, e-cards and multifunctional electronic devices. NRF (Natl Research Foundation, S’pore)

Designing materials with appropriate crystal and electronic structures to enhance ionic and electronic transport simultaneously are highly desirable for both electrochromic and electrochemical energy storage devices. It remains a great challenge to simultaneously meet these requirements. Here, a Nb18W16O93 nanomaterial is successfully synthesized with superstructure motifs and uniform self-supported electrochromic films are prepared on a transparent conductive substrate. The results show that the films can effectively accommodate lithium ions and facilitate intercalation–deintercalation on transparent fluorine-doped tin oxide (FTO) substrates at high current density. Mechanistic insights into the excellent electrochromic and rechargeable energy storage properties are provided by density functional theory (DFT) calculations. Specifically, the Nb18W16O93 film displays a large optical modulation (up to 93% at 633 nm and 89% at 1200 nm), high coloration efficiency (105.6 cm2 C−1), high energy storage capacity (151.4 mAh g−1 at 2 A g−1), excellent rate capability, and long-term electrochemical stability (6000 cycles). As a demonstration of its application, an energy storage indicator is illustrated and a complementary electrochromic energy storage smart window is fabricated based on the Nb18W16O93 film. The results demonstrate that the Nb18W16O93 nanomaterial has a promising application in the field of high-performance electrochromic and energy storage devices. National Research Foundation (NRF) Published version This work is financially supported by the National Natural Science Foundation of China (U2004175, 51902086). The project is funded by the Campus for Research Excellence and Technological Enterprise (CREATE) programme under the National Research Foundation, Prime Minister’s Office, Singapore.

An unprecedented MXene-based actuator was developed, which mimicked the sophisticated leaf structure and its functionality., Natural leaves, with elaborate architectures and functional components, harvest and convert solar energy into chemical fuels that can be converted into energy based on photosynthesis. The energy produced leads to work done that inspired many autonomous systems such as light-triggered motion. On the basis of this nature-inspired phenomenon, we report an unprecedented bilayer-structured actuator based on MXene (Ti3C2Tx)–cellulose composites (MXCC) and polycarbonate membrane, which mimic not only the sophisticated leaf structure but also the energy-harvesting and conversion capabilities. The bilayer actuator features multiresponsiveness, low-power actuation, fast actuation speed, large-shape deformation, programmable adaptability, robust stability, and low-cost facile fabrication, which are highly desirable for modern soft actuator systems. We believe that these adaptive soft systems are attractive in a wide range of revolutionary technologies such as soft robots, smart switch, information encryption, infrared dynamic display, camouflage, and temperature regulation, as well as human-machine interface such as haptics.

Capacity bounds are calculated for the differential chaos shift keying (DCSK) system with non-coherent detectors, including differentially coherent detector and energy detector, over additive white Gaussian noise (AWGN) and Rayleigh fading channels. Through theoretical analysis and numerical simulations, it is found that the capacity characteristics of the non-coherent DCSK system are significantly different from those of the coherent case. It is shown that there are different capacity bounds corresponding to different spreading factor values. Optimal code rates are found, which minimise the required bit signal-to-noise ratio for a reliable communication system, and they are increasing with the increase of the spreading factor value over an AWGN channel while decreasing over a Rayleigh fading channel. As compared with the AWGN channel, the performance over a Rayleigh fading channel is much more sensitive to the code rate. The new results are useful as benchmark for designing capacity-approaching codes for the non-coherent DCSK system.