Spread Spectrum Research Articles

The Effect of Spread Spectrum Modulation on Power Line Communications

Interference in Power Line Communication (PLC) is examined in this paper. PLC is a wired communication technology that provides communication and data transmission over the existing electrical network. It uses the electrical wiring in buildings or the electrical grid to transmit data signals between devices, rather than using dedicated communication cables or wireless signals. Many applications employ PLC technologies, which have the benefit of leveraging existing power connections for both power and data transfer, reducing cost and complexity. These interactions may be observed in contemporary smart grids and automobile power networks, where lengthy cables, switching power supplies and communication links all work together but exacerbate Electromagnetic Interference (EMI) problems. This research examines the effects of spread spectrum methods used to reduce EMI from power converters on PLC systems. Spread Spectrum Modulation (SSM) and its three variants, Sine, Random and Sawtooth, are frequently employed to meet the requirements of electromagnetic compatibility, however, there are some repercussions that may be detrimental to the converter or the rest of the electrical network. These outcomes occur for various modulation algorithm settings and at various frequencies. Measurements are made utilising the Frame Error Rate (FER) value provided by the PLC link system to ascertain the interference produced by a Silicon Carbide (SiC)-based DC-DC converter in order to investigate these concerns and standardise an assessment approach. To examine the effect of SSM on reducing EMI in the frequency domain, the peak index of a CISPR-16 EMI receiver is used.

Spread spectrum modulation recognition based on phase diagram entropy

Wireless communication technologies are undergoing intensive study and are experiencing accelerated progress which leads to a large increase in the number of end-users. Because of this, the radio spectrum has become more crowded than ever. These previously mentioned aspects lead to the urgent need for more reliable and intelligent communication systems that can improve the spectrum efficiency. Specifically, modulation scheme recognition occupies a crucial position in the civil and military application, especially with the emergence of Software Defined Radio (SDR). The modulation recognition is an indispensable task while performing spectrum sensing in Cognitive Radio (CR). Spread spectrum (SS) techniques represent the foundation for the design of Cognitive Radio systems. In this work, we propose a new method of characterization of Spread spectrum modulations capable of providing relevant information for the process of recognition of this type of modulations. Using the proposed approach, results higher than 90% are obtained in the modulation classification process, thus bringing an advantage over the classical methods, whose performance is below 75%.

Synchronization techniques for underwater acoustic communications

SummaryUnderwater acoustic channel is a challenging medium for communication due to the presence of significant multipath, high noise, frequency‐dependent propagation loss, and high and non‐uniform Doppler spread. Doppler shift is non‐negligible in underwater communication due to the low velocity of underwater signals. Synchronization and Doppler estimation are important requirements for achieving good performance in this channel. Synchronization algorithms that give good performance in radio communication do not work well in underwater communication. Hence, this area has received a lot of attention from researchers. This paper surveys important works in the area. The techniques proposed in the literature for frame synchronization, frequency and phase synchronization, and timing synchronization in single carrier communications are reviewed here. The synchronization techniques proposed for OFDM, MIMO OFDM, and spread spectrum communication are also surveyed. Doppler estimation methods proposed in the literature are also reviewed. It is found that most of the recent works in underwater acoustic communication focus on OFDM synchronization. Deep learning‐based methods proposed in the literature are also reviewed. Key open problems and areas that require future research attention in the field of synchronization and Doppler estimation in underwater communications are highlighted in this paper. The area needing most attention of underwater communication researchers was found to be MIMO OFDM due to the difficulty in synchronization in such systems while used in underwater communication. Reducing the computational complexity of the algorithms used is also important for future work. Schemes that work with Doppler due to relative velocity over 10 m/s also need to be developed.

A Novel Electromagnetic Noise and Image Stripe Noise Suppression Method Between SMA-OIS Actuator and CMOS Image Sensor

In order to solve the electromagnetic compatibility (EMC) problem between shape memory alloy (SMA) optical image stabilization (OIS) actuator and CMOS image sensor (CIS), a novel electromagnetic noise and image stripe noise (ISN) suppression method is proposed in this paper. The electromagnetic interference mechanism of SMA-OIS actuator is analyzed by electromagnetic field simulation and magnetic dipole mathematical model. The CIS noise mechanism based on the readout circuit model and image signal processing (ISP) pipeline is analyzed and the ISN evaluation method of CIS is proposed. The drive frequency and ISN model is established by frequency sweep experiment through the joint experimental platform of SMA-OIS actuator and CIS. Furthermore, the random frequency modulation PWM method based on the spread spectrum principle is proposed to suppress the electromagnetic noise and ISN. The experimental results show that the state-of-the-art noise suppression method proposed in this paper can not only eliminate ISN, but also have good technical adaptability in practical applications.

Efficacious Zero Sequence Voltage Elimination in Space Vector Modulation by Sigma Delta Modulation

The growing popularity of electric motor driven systems emphasize the need for proper motor maintenance and necessitates zero sequence voltage (ZSV) elimination in electrical machines and drives. A spread spectrum modulation scheme for eliminating zero sequence voltage, utilizing space vector pulse density modulation (SVPDM) approach is proposed in this article. In the presented five-level inverter scheme, when vectors that do not contribute zero sequence voltage are considered, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$30^{0}$</tex-math></inline-formula> tilted three-level space vector diagram with inner and outer layer is formed. Reference vector residing in outer layer is mapped to inner layer and is vector quantized in a space vector quantizer to generate inner layer switching vectors. Outer layer switching vectors are then realized by the process of reverse mapping. The article investigates two-level SVPDM scheme and ZSV eliminated two-level SVPDM scheme, to prove that effectiveness of ZSV elimination can be determined from the shape of demodulated waveform. Better the ZSV elimination, better will be the resemblance of demodulated waveform to sinusoidal signal. The scheme is experimentally validated with 2.2 kW five-level dual inverter fed induction motor drive and is compared with space vector pulse width modulation (SVPWM) scheme. Results of comparison confirms the effectiveness of proposed scheme.

False data injection attack detection for nuclear reactor based on chaotic time/frequency-hopping spread spectrum

False data injection (FDI) attacks represent a serious threat to securing nuclear reactor operation. Efficient FDI attack detection is essential to prevent related unforeseen nuclear accidents. However, owing to their design principles, the existing detection methods are limited in their ability to detect multiple types of FDI attacks. To address this issue, we propose a detection scheme for FDI attacks on a nuclear reactor based on the chaotic time/frequency-hopping (TH/FH) spread spectrum. The proposed scheme uses frequency hopping modulation, demodulation, and filtering of the signal based on hyper-chaotic sequences to limit the attacker's access to the system's real data and eliminate the adverse effects of attacks on the system. Furthermore, theoretical analysis derives the stability constraint of the frequency hopping frequency and demonstrates the detectability and defendability of the proposed scheme. Experimental simulations demonstrated that our proposed scheme can detect two typical FDI attacks, replay attacks and covert attacks, without compromising system operation, and defend against and reproduce covert attack signals.

TCN-based M-ary mobile spread spectrum underwater acoustic communication

A deep learning-based direct sequence spread spectrum (DSSS) underwater acoustic (UWA) communication system was proposed in this study to improve the performance of the conventional system under Doppler effects and low signal-to-noise ratio (SNR). The Temporal Convolutional Network (TCN) model was used as the receiver of the system. Simulation results showed that the TCN-based M-ary DSSS UWA communication system outperformed the conventional system under Doppler effects and complex shallow water acoustic channel. A transfertraining algorithm was used for fine-tuning of the model based on sea real-time data to achieve optimal performance. Sea experimental results showed that the fine-tuned TCN model improved the communication effect under Doppler background in the complex dynamic environment of shallow water.

Low Noise Ultra-Flexible SiP Switching Platform for mmWave OCDM &amp; Multi-Band OFDM ARoF Fronthaul

A highly flexible wavelength and space switched analog radio-over-fiber (ARoF) fronthaul transmission of a millimeter-wave (mmWave) emerging 6G waveform over a centralized/ cloud radio access network (C-RAN) is experimentally demonstrated in this work. A spread spectrum multiplexing technique — orthogonal chirp division multiplexing (OCDM) — which is highly resilient to inter-channel interference and enables enhanced channel estimation is utilized in the fronthaul transmission demonstration. The flexible properties of a low noise silicon photonic (SiP) microring resonator (MRR) based tunable laser and a low cross-talk 4×4 SiP optical wavelength/space switch are combined to form a reconfigurable 10 km fronthaul system enabling 64-QAM OCDM transmission at 24 GHz with consistent performances ~5% EVM across all test wavelengths/ports. A signal constituting Wi-Fi and 5G NR standard compatible 64-QAM orthogonal frequency division multiplexing (OFDM) bands, at 10 GHz and 24 GHz respectively, are also transmitted and evaluated in the proposed system with EVM performances below 64-QAM EVM limit (8%) achieved, thus demonstrating the system’s potential in a future converged multi-service environment.

Sedimentary provenance in continental rifts: U–Pb detrital zircon, Nd and Sr isotopes and lithogeochemistry of the Eocene alluvial sandstones of the Resende Basin, SE–Brazil

Multiproxy analysis of detrital minerals is a powerful tool for unravelling the source-to-sink evolution of syn-rift sedimentary basins that represent important depositional settings during major rift events. The Cenozoic Resende half-graben in SE Brazil is a classic example of a syn-rift basin developed under oblique extension, which preserves evidence of tectonic episodes and palaeoclimatic conditions during the opening of the Atlantic. Sediment in the basin was sourced from the surrounding basement rocks, which to the faulted margin consists of older Proterozoic orthogranulites and orthogneisses, whilst to the flexural margin is characterised by Neoproterozoic passive margin paragneisses. Cretaceous intra-plate alkaline stocks crop out at the western edge and in the central-south basement of the basin and represent a distinct provenance fingerprint. This study uses new detrital zircons U–Pb ages combined with previously published elemental and Nd and Sr isotopic data to characterise the sedimentary provenance of Eocene alluvial deposits and to understand how sediment sourcing has changed throughout the evolution of the basin. U–Pb detrital zircon analyses from samples collected across the Resende Basin are presented herein. Samples yield a spread of detrital age spectra from the Archaean to the Cretaceous. Precambrian zircons range from ca. 3228 Ma to ca. 542 Ma. Cretaceous zircons yield ages between ca. 138 Ma and ca. 67 Ma. The sediment source location is interpreted by comparing the yielded detrital zircon spectra with the age spectra of zircons from the basement rocks. The dominance of detrital zircons yielding ages of ca. 1500 Ma and ca. 1000 Ma is interpreted to be sourced from the Neoproterozoic basement rocks to the flexural border of the half-graben. Cretaceous zircons from samples with whole rock εNd40Ma > −10 are found in both the western and eastern portions of the half-graben but not in the central portions. It is interpreted that an along-axis fluvial system was responsible for a small increase in the compositional maturity of the Resende sandstones from west to east, resulting in the progressive dilution of Cretaceous alkaline igneous detritus along the basin axis. Preserved metamorphic rims in zircon grains indicate low transport abrasion, suggesting that Cretaceous zircons in the eastern depocentre could be associated with other small proximal sources. U–Pb zircon analyses and Nd and Sr isotopes provide reliable insights regarding sediment provenance and transport processes, whilst element geochemistry supplies evidence for hydraulic sorting effects. Consequently, the data represents a more robust estimation of the provenance patterns of the Resende Basin, showing chemical and geochronological differences that support the division of the basin into three depocentres (western, central, and eastern) connected by a longitudinal fluvial system sourced mostly by sediments coming from the south-western flexural border. This study highlights the usefulness of using multiple provenance proxies to unravel the complex development of rift basins, assessing multiple source terrains and the variable degrees of mixing in sedimentary basins.

M-Ary Direct Modulation Chirp Spread Spectrum for Spectrally Efficient Communications

Spread spectrum techniques, such as the Chirp Spread Spectrum (CSS) used by LoRa technology, are important for machine-to-machine communication in the context of the Internet of Things. They offer high processing gain, reliable communication over long ranges, robustness to interference and noise in harsh environments, etc. However, these features are compromised by their poor spectral efficiency, resulting in a very low data transmission rate. This paper deals with a spectrally efficient variant of CSS. The system uses M-ary phase keying to modulate the data and exploits CSS’s properties to transmit the modulated symbols as overlapping chirps. The overlapping of chirp signals may affect the system performance due to inter-symbol interference. Therefore, we analyse the relationship between the number of overlaps and the effect of inter-symbol interference (ISI), and we also determine the BER expression as a function of the number of overlaps. Finally, we derive the optimal number of overlapping symbols that corresponds to the minimum error probability.

Collaborative LEO Satellites for Secure and Green Internet of Remote Things

The Internet of Remote Things (IoRT) supported by Low Earth Orbit (LEO) satellites is becoming indispensable for remote sensing, and it will play an important role in the forthcoming sixth generation (6G) communication network. In exploring its applications in remote mining and smart grid, etc., it is found that the implementation of IoRT faces challenges, including limited energy supplies, high mobility, and security vulnerabilities. To address these challenges, we propose employing collaborative LEO satellites to enable the implementation of secure and green IoRT. By combining the uplink signals received at collaborative LEO satellites, the Signal-to-Noise Ratio (SNR) can be significantly improved, so that relieving the transmit power requirement of the energy-limited terminal. Aiming at constructing a collaborative LEO satellite-based IoRT network, this paper introduces the system design principles regarding to frequency planning, waveform selection, collaboration strategies, and terminal design. In order to obtain optimal collaboration performance, we propose a signal coherent combining scheme to compensate Doppler shift, propagation delay, and phase differences. Furthermore, we propose a modified SUMPLE algorithm to estimate and compensate phase differences among satellites, which is applicable to Direct Sequence Spread Spectrum (DSSS) signal scheme. Simulation results demonstrate that our proposed algorithm outperforms the traditional SUMPLE algorithm in combining gain.

SNR-Optimal Spreading Sequences for Chip-Wise Faster-Than-Nyquist Signaling

This letter proposes signal-to-noise ratio (SNR)-optimal spreading sequences for faster-than-Nyquist (FTN) transmission. The peculiar association of direct sequence spread spectrum with FTN proves relevant to mitigate noticeable cyclostationary features, leading up to covert communications schemes. Considering a matched-filter-based receiver, the proposed SNR-optimal spreading sequences and their closed-form approximations outperform traditional pseudo-random noise sequences by achieving near-interference-free bit-error-probability. Our results pave the way for the design of FTN-specific multiple access techniques while ensuring a low probability of detection/intercept.

Stepped-Frequency Binary Offset Carrier Modulation for Global Navigation Satellite Systems

In this paper, we propose Stepped-Frequency Binary Offset Carrier (SFBOC) modulation for Global Navigation Satellite Systems (GNSS) that use spread spectrum signals. SFBOC modulation generates a Binary Offset Carrier (BOC) signal of which the subcarrier frequency varies stepwise within each period of the pseudorandom-noise (PRN) code. The generated SFBOC signal can have a sharp autocorrelation function (ACF) output and an almost flat spectrum over a wide frequency band. These characteristics result in correlation properties, multipath mitigation, and anti-interference that are superior to those of conventional GNSS modulations. To testify, we compare the performance of SFBOC in various aspects to conventional GNSS modulations and other time-varying subcarrier frequency (TVSF) modulations. From numerical simulations, we show that the proposed SFBOC has higher ranging accuracy, lower tracking ambiguity, and more robustness to noise, interference, and multipath than the conventional GNSS modulations. In addition, we demonstrate that the proposed SFBOC moulation has two advantages while other modulations with TVSF cannot have both; that SFBOC is robust to code-Doppler and that, when filterbank is employed, SFBOC improves the signal-to-noise ratio (SNR) significantly without any loss of weak early arrival path in the Non-line of sight (NLOS) multipath environments.

CSMA Protocol performance with dynamic spreading factor in LPWAN networks with LoRa RF transceivers

Long Range (LoRa) is a spread spectrum modulation technology designed for Low-Power Wide-Area Networking (LPWAN) with a growing application in Internet of Things (IoT), which plays an important role in the global digitalization process. The expansion of LORAWAN networks demands careful circuit, system and network design to improve energy efficiency and quality of service. To support this task, advanced CAD tools can offer reliable network simulations results, where the effects of building blocks can be found. LoRaSim, one of the most popular simulators available for LoRa and LoraWan, had solely implemented an ALOHA access model protocol, which is not the most common protocol in real life scenarios. To mitigate this limitation and taking advantage of the open-source nature of both LoRaWAN and LoRaSim, it is proposed a Carrier Sense Multiple Access/ Collision Avoidance (CSMA/CA) protocol extension, as well as active adaptive parameters selection to cope with collisions. To demonstrate the effectiveness of these additions to the base solution, a comparison between both on different scenarios and their simulated performance key indicators will be presented.

Confidentiality Enhancement Using Spread Spectrum Modulation Technique for Aggregated Data in Wireless Sensor Networks

Wireless Sensor Networks (WSN) play a crucial role in transmitting bulk data remotely on Internet of Things (IoT). The data transmitted by the tiny sensor nodes of the network are basically the physical parameters of the environment like temperature, vibration, pressure etc. There exists a huge co-relation in the data sent by the nodes. This bulk data needs to be aggregated in order to conserve the energy of the network and thereby enhance the network lifetime. Although the aggregation might lead to loss of actual data, aggregating helps in reducing energy requirement during transmission which is of primary importance and hence is considered as a suitable method in WSN. Adding confidentiality to aggregated data helps in sending the data more securely. Spread spectrum modulation is a widely used technique to provide confidentiality in communication systems. In this research work, we implement a data aggregation technique and apply the spread spectrum modulation technique to provide confidentiality to the aggregated data that needs to be transmitted from the cluster head node to the gateway. Here, data aggregation process consists of averaging the number of data that are sensed by a sensor node and transmitting only its average value to the gateway. This reduces the amount of data transmission and helps in conserving energy. Further, the spread spectrum technique implements Binary Phase Shift Keying (BPSK) method with Frequency Hopping Spread Spectrum (FHSS) carried out using six different frequencies on MATLAB 2020a. The simulation results evaluate the performance of the system. The graphs are plotted for modulated and demodulated signals, spread and de-spread sequences, Bit Error Rate (BER) of BPSK/ FHSS over Rayleigh flat fading channel, Power Spectral Density (PSD) and Fast Fourier Transform (FFT) of frequency hopped signal. The results show that BER value decreases with increase in Signal to Noise Ratio (SNR). The maximum power consumption in the network is 7.518 mW at 5MHz frequency, for adding confidentiality to the aggregated data to be transmitted. Thus, the proposed work promises efficient energy consumption, longer network lifetimes with added confidentiality.

Recursive Decoding Based Multi-channel M-ary Spread Spectrum Underwater Acoustic Communication

The spread spectrum communication method has strong anti-noise and anti-fading capability, but it also brings the problem of low information transmission efficiency. The paper proposes a multi-channel M-ary spread spectrum communication method, using a recursive decoding algorithm to reduce the communication bit error rate. In combination with the channel equalization technique based on the virtual time reversal mirror technique, the scheme improves the communication rate of spread spectrum communication. It is verified through computer simulation and sea trial data that the communication method can effectively reduce the mutual interference between different channel signals, which provides a new idea for the design of hydroacoustic spread spectrum communication scheme.

Subterranean mMTC in Remote Areas: Underground-to-Satellite Connectivity Approach

Wireless underground sensor networks (WUSNs) promise to deliver substantial social and economic benefits across different verticals. However, many of the relevant application scenarios are located in remote areas with no supporting infrastructure available. To address this challenge, we conceptualize in this study the underground direct-to-satellite (U-DtS) connectivity approach, implying the reception of the signals sent by the underground massive machine-type communication (mMTC) sensors by the gateways operating on the low Earth orbit satellites. We start by discussing the two alternative architectures for enabling such networks and underline their features and limitations. Then, we employ simulations to model a smart-farming application scenario for studying the feasibility and performance of UDtS mMTC based on LoRaWAN technology, with the focus on the effect of the parameters including the burial depths, soils characteristics, and communication settings. Our results reveal that the LoRa modulation fails to compete with the underground propagation losses and the high packets collision rate. However, the long range-frequency hopping spread spectrum (LR-FHSS) modulation is perspective for U-DtS networks and may enable connectivity for the subsurface nodes located at a depth of several dozens centimeters. Finally, we pinpoint the potential challenges and the research directions for future U-DtS studies.

Blind despreading and deconvolution of asynchronous multiuser direct sequence spread spectrum signals under multipath channels

AbstractIn non‐cooperative scenarios, the spreading sequences or waveforms of the direct sequence spread spectrum (DSSS) signals is unknown to the receiver. This paper focuses on addressing the problem of blind estimation of the spreading waveform under multipath channels. In the scenario of direct signal path transmission, the spreading sequences can be directly obtained based on the estimated spreading waveforms. However, in the presence of multipath channels, the spreading waveform becomes the convolution of the spreading sequence and channel response, thus deconvolution should also be performed after estimating the spreading waveforms. In order to perform blind despreading and deconvolution of asynchronous multiuser DSSS signals under multipath channels, the authors propose to exploit the finite symbol characteristics of information and spreading sequences and then the iterative least square with projection method is adopted. Besides, the Cramer‐Rao bound of spreading waveforms is derived in such a circumstance as a performance benchmark. The effectiveness of the proposed method is verified via simulation experiments.

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An improved synthetic signal injection routine for the Haloscope At Yale Sensitive To Axion Cold dark matter (HAYSTAC).

Microwave cavity haloscopes are among the most sensitive direct detection experiments searching for dark matter axions via their coupling to photons. When the power of the expected microwave signal due to axion-photon conversion is on the order of 10-24 W, having the ability to validate the detector response and analysis procedure by injecting realistic synthetic axion signals becomes helpful. Here, we present a method based on frequency hopping spread spectrum for synthesizing axion signals in a microwave cavity haloscope experiment. It allows us to generate a narrow and asymmetric shape in frequency space that mimics an axion's spectral distribution, which is derived from a Maxwell-Boltzmann distribution. In addition, we show that the synthetic axion's power can be calibrated with reference to the system noise. Compared to the synthetic axion injection in the Haloscope At Yale Sensitive to Axion Cold dark matter (HAYSTAC) Phase I, we demonstrated synthetic signal injection with a more realistic line shape and calibrated power.