Spread Spectrum Research Articles

LoRa and Rotating Polarization Wave: Physical Layer Principles and Performance Evaluation

Link reliability and enhanced coverage are the primitive concerns of Low-Power Wide-Area Networks (LPWANs) for suitability to critical Internet of Things (IoT) applications. Reliability is limited by the destructive multipath propagation, data rate and sensitivity, that ultimately limits the coverage range. LoRa by far is the predominant LPWAN operating on unlicensed spectrum. Despite its robust Chirp Spread Spectrum (CSS) modulation, there is a severe degradation in its error performance particularly in hostile propagation environments, and an excessive reduction in coverage. Rotating Polarization Wave (RPW) is a potential LPWAN recently emerged to achieve a highly reliable IoT and Machine-to-Machine (M2M) communication. This is the first paper to provide comprehensive error performance comparison between LoRa and RPW. Okumura-Hata model is used for median path loss calculation. Shadowing and fast fading margins of RPW and LoRa are estimated. Effective gain of RPW is computed from error performance. Results have shown that LoRa offers a sensitivity of 23 dB higher than RPW under AWGN conditions. However, under fading conditions, RPW exhibits a sensitivity of 15 dB higher than LoRa. At a reference distance of 100 m, the maximum received signal strength of RPW is -39 dBm, which is 29 dB above LoRa. The maximum coverage distance attained by RPW is 15 km, which is 1.5 times of LoRa.

Novel Algorithm for Blind Estimation of Scramblers in DSSS Systems

In this paper, we propose a novel algorithm for blind estimation of a linear scrambler, which is a synchronous scrambler or a self-synchronous scrambler, in direct sequence spread spectrum systems and analyze its estimation performance. We first examine the statistics considering the linearity of the scrambled data and the repetition property of the spreading code. Based on this, we then propose an improved estimation algorithm for the feedback polynomial of the linear scrambler constituting a search process and a verification process of feedback polynomial candidates to determine the correct feedback polynomial of the scrambler. To validate the proposed algorithm, we show through computer simulations that the proposed algorithm outperforms the conventional algorithm in terms of estimation performance.

Fast Beam Discovery and Adaptive Transmission Under Frequency Selective Attenuations in Sub-Terahertz Bands

Sub-THz-based communication needs ultra-large antenna arrays to generate pencil-like beams under the stringent requirements of line-of-sight (LoS) to overcome the effect of the rapid attenuation of signal strength, including atmospheric attenuation. In addition, the complexity of attaining narrower beamwidth, which also requires fast and perfect alignment between the TX-RX pair, makes the sector sweeping-based beam discovery approach no longer suitable. To solve these challenging problems, in this paper we propose a leaky waveguide (LWG)-assisted, high-resolution codebook-based beam discovery, precoding, and combining scheme together with an adaptive frequency hopping spread spectrum (FHSS) for a network with relays and small base stations (SBS). The proposed method can help the transmitter quickly determine a suitable beam pattern for an LoS path requiring only limited feedback information. In the beam discovery phase, we use LWG to attain valuable information about the angle of departure (AoD) and angle of arrival (AoA). LWG has also been used to identify frequency selective attenuated regions, which can change from time to time depending on the local atmospheric moisture conditions. To mitigate the impact of such attenuations, we opt for an adaptive Frequency Hopping Spread Spectrum (FHSS). The simulation results indicate that our beam discovery and FHSS based method can achieve a much higher performance than baseline methods.

Airborne Acoustic Chirp Spread Spectrum Communication System for User Identification in Indoor Localization

In this contribution, we propose a reliable, longrange, communication system based on chirp spread spectrum techniques for aerial ultrasonic channels, to be employed for user identification in ultrasonic indoor localization systems. We adopt binary orthogonal keying, where the binary information, modulates the shape of the chirp instantaneous frequency, mapping zeros onto down-chirps and ones onto up-chirps. In order to reduce the demodulation computational costs, we exploit the band-pass sampling theorem and develop an ad-hoc algorithm to under-sample the received signal. The incoming packet detection and frame synchronization are guaranteed by employing a characteristic chirp signal, typically utilized for localization purposes, as a pilot for the transmitted identification packet. A simple, yet efficient, pilot detection scheme enables live features by constantly listening to the channel, triggering the demodulator only when the pilot is detected. The performance of our system has been evaluated in low power and ultra-low power real-world experiments in a warehouse-like environment. It is demonstrated that our system is capable of error-free communication up to a range of 22 m in the low power setup, where the transmitter had a transmission power of 80 mW, corresponding to a sound pressure level of approximately 37 dBSPL at 1 m distance. In the ultra-low power mode, with a transmission power to 15 mW, corresponding to a sound pressure level of approximately 29 dBSPL at 1 m, the system achieved 99% success rate up to 16 m. Moreover, the capability of the system to be robust against the Doppler effect and in a multi-user environment has been tested via simulations.

Overview of commonly used spread spectrum techniques

Overview of commonly used spread spectrum techniques

A Survey on Scalable LoRaWAN for Massive IoT: Recent Advances, Potentials, and Challenges

Long-range (LoRa) technology is most widely used for enabling low-power wide area networks (WANs) on unlicensed frequency bands. Despite its modest data rates, it provides extensive coverage for low-power devices, making it an ideal communication system for many internet of things (IoT) applications. In general, LoRa is considered as the physical layer, whereas LoRaWAN is the medium access control (MAC) layer of the LoRa stack that adopts a star topology to enable communication between multiple end devices (EDs) and the network gateway. The chirp spread spectrum modulation deals with LoRa signal interference and ensures long-range communication. At the same time, the adaptive data rate mechanism allows EDs to dynamically alter some LoRa features, such as the spreading factor (SF), code rate, and carrier frequency to address the time variance of communication conditions in dense networks. Despite the high LoRa connectivity demand, LoRa signals interference and concurrent transmission collisions are major limitations. Therefore, to enhance LoRaWAN capacity, the LoRa Alliance released many LoRaWAN versions, and the research community has provided numerous solutions to develop scalable LoRaWAN technology. Hence, we thoroughly examine LoRaWAN scalability challenges and state-of-the-art solutions in both the physical and MAC layers. These solutions primarily rely on SF, logical, and frequency channel assignment, whereas others propose new network topologies or implement signal processing schemes to cancel the interference and allow LoRaWAN to connect more EDs efficiently. A summary of the existing solutions in the literature is provided at the end of the paper, describing the advantages and disadvantages of each solution and suggesting possible enhancements as future research directions.

New Random PWM Method at Constant Switching Frequency and Maximum Harmonic Reduction Created With a Flexible FPGA-Based Test Bench

It has been shown that the converters that integrate random PWM produce a spread spectrum in their harmonic emission, shortening the emission peaks. On the converter’s input side, the reduction minimizes electromagnetic interference EMI. On the output side of the converter, the reduction manages to smooth the voltage and current ripple in the load. We have built a flexible test bench (FTB) developed with FPGA to generate most of the proposed random PWM modes for converters. The conducted harmonic voltage emission of these modes, both on the input side of the converter and on the load side, has been measured and compared in a DC-DC Buck converter. FTB also has the ability to create new random PWM modes. Of the random modes, the ones that produce the greatest peak reductions are those with variable switching frequency. However, variable frequency modes lead to load feedback problems. A new random PWM method has been developed that significantly reduces the amplitude of the emission peaks but keeps the switching frequency constant.

A Novel Recognition Method for Direct Sequence Spread Spectrum (DSSS) Signals Based on Secondary Power Spectrum

A Novel Recognition Method for Direct Sequence Spread Spectrum (DSSS) Signals Based on Secondary Power Spectrum

Comparative Analysis of Execution of CNN-Based Sanguine Data Transmission with LSB-SS and PVD-SS

The intact data transmission to the authentic user is becoming crucial at every moment in the current era. Steganography; is a technique for concealing the hidden message in any cover media such as image, video; and audio to increase the protection of data. The resilience and imperceptibility are improved by choosing an appropriate embedding position. This paper gives a novel system to immerse the secret information in different videos with different methods. An audio and video steganography with novel amalgamations are implemented to immerse the confidential auditory information and the authentic user’s face image. A hidden message is first included in the audio from the multimedia file; using LSB Technique. The Stego-video is created in the second stage by merging the authorized user’s face into the frame of the video; by using PVD technology. Stego-audio is linked again with the stego-video in the third stage. The incorporated perspective techniques (LSB-SS and PVD-SS algorithms) with more significant data immersing capacity, good robustness and imperceptibility are proposed in this research work. The spread spectrum approach is used to increase the complexity of secret data recognition. Two different video files are tested with different voice files with the results such as PSNR, SSIM, RMSE and MSE as 52.3, 0.9963, 0.0024 and 0.0000059, respectively.

An Acoustic Based Local Positioning System for Dynamic UAV in GPS-Denied Environments

Highlights A positioning system for mobile UAVs is needed in a GPS-denied environment. A Doppler shift compensation algorithm was proposed. The successful detection rate and positioning errors were 90.2% and 75.9 ± 39.1 mm, respectively. The system performance meets the requirements for mobile UAVs in an indoor environment. Abstract. An alternative positioning system, the Spread Spectrum Sound-based Local Positioning System (SSSLPS), was developed to extend the usage of UAVs in GPS-denied environments, such as greenhouses. To date, it has been proven that the SSSLPS could provide a centimeter-level locational accuracy of static objects and dynamic ground robots. In this research, the ranging and positioning performance of SSSLPS were evaluated with the system mounted on a UAV. Meanwhile, to minimize the Time of Arrival (ToA) estimation error and improve positioning accuracy, a novel Doppler shift compensation algorithm was proposed. Experiments were conducted, and the measurement accuracy was evaluated by comparing the measurement of the motion capture system. The results show a successful detection rate of 90.2% using the proposed algorithm and a position error of 75.9 mm. These results demonstrate that the SSSLPS with spectrum peak algorithm can improve positioning accuracy and enable the SSSLPS to be an accurate positioning system for UAVs in a greenhouse. Keywords: Dopper shift, Greenhouse robots, Positioning system, ToA estimation, UAV.

Drivers’ Warning Application Through Personalized DSSS-CDMA Data Transmission by Using the FM Radio Broadcasting Infrastructure

In this paper, a new drivers’ warning application through personalized Direct-Sequence Spread Spectrum Code-Division Multiple Access (DSSS-CDMA) transmissions, performed using the FM radio broadcasting infrastructure is presented. The proposed application is designed to simultaneously transmit a maximum of 15 low-resolution image notifications together with standard FM radio broadcasting in different geographical areas. The application is intended to warn drivers of significant driving events in major traffic areas of a country. The proposed solution is low-cost and rapid to put into practice because the modifications, both on the transmission infrastructure and on the receiver’s side, are relatively easy to implement. The transmission of image notifications is performed in subsidiary bands of commercial FM radio systems. The receiver is implemented using the Software-Defined Radio (SDR) paradigm and is able to extract the audio signal (corresponding to the usual FM transmission) and the data component, depending on the geographical area in which the vehicle is located. The receiver is based on a novel implementation of a modified Costas loop using two new nonlinear limiters. Appropriate image notification is selected using a specific decoding key, generated according to the geographical position of the vehicle. The performance of the data transmission system is analyzed by plotting the Bit Error Rate (BER) versus the signal-to-noise ratio of the data signal for different numbers of image notifications simultaneously transmitted. The proposed radio communication system was validated through an experimental setup based on Universal Software Radio Peripheral (USRP) devices driven by MATLAB/Simulink software.

GENERALIZED MODEL OF THE ADS-B UNMANNED AERIAL VEHICLE DATA TRANSMISSION PROCESS IN A STEGANOGRAPHIC SYSTEM

The subject of the article is a model of the ADS-B data transmission process of an unmanned aerial vehicle in a steganographic system using direct spectrum expansion technology. The aim of the publication is to improve the security of unmanned aerial vehicles with an integrated ADS-B system. Particular scientific tasks: analysis of basic methods of ADS-B format data protection; development of the scheme of ADS-B drone data transfer in steganographic system with the use of direct spectrum expansion technology; improvement of the model of ADS-B drone data transfer in steganographic system with the use of direct spectrum expansion technology; determination of qualitative and quantitative characteristics as well as security properties of ADS-B format data. The following research results were obtained: as the result of the scientific works analysis the hypothesis about the perspectives of the ADS-B format steganographic data protection usage was put forward; the scheme of an unmanned aerial vehicle ADS-B data transmission in the steganographic system with the usage of the direct spectrum spreading technology was developed; the main safety properties as well as the safety parameters and characteristics of the ADS-B format information signal were formulated; the generalized model of an unmanned aerial vehicle ADS-B data transmission was further developed. This will improve the safety of UAVs. The advantages and disadvantages of the model were revealed, which allowed to determine the priority of further research and possible promising ways of solving the assigned tasks.

Knowledge-Enhanced Compressed Measurements for Detection of Frequency-Hopping Spread Spectrum Signals Based on Task-Specific Information and Deep Neural Networks

The frequency-hopping spread spectrum (FHSS) technique is widely used in secure communications. In this technique, the signal carrier frequency hops over a large band. The conventional non-compressed receiver must sample the signal at high rates to catch the entire frequency-hopping range, which is unfeasible for wide frequency-hopping ranges. In this paper, we propose an efficient adaptive compressed method to measure and detect the FHSS signals non-cooperatively. In contrast to the literature, the FHSS signal-detection method proposed in this paper is achieved directly with compressed sampling rates. The measurement kernels (the non-zero coefficients in the measurement matrix) are designed adaptively, using continuously updated knowledge from the compressed measurement. More importantly, in contrast to the iterative optimizations of the measurement matrices in the literature, the deep neural networks are trained once using task-specific information optimization and repeatedly implemented for measurement kernel design, enabling efficient adaptive detection of the FHSS signals. Simulations show that the proposed method provides stably low missing detection rates, compared to the compressed detection with random measurement kernels and the recently proposed method. Meanwhile, the measurement design in the proposed method is shown to provide improved efficiency, compared to the commonly used recursive method.

UNJUK KERJA KODE ORTHOGONAL M-SEQUENCE DALAM SISTEM DIRECT SEQUENCE SPREAD SPECTRUM MELALUI KANAL MULTIPATH FA

Multipath and multi-user interference are the main challenges in wireless communication systems. This has become a driving force for the development of data transmission technology that is focused to overcome these problems, one of which is spread spectrum. Spread spectrum is applied to CDMA technology which has the limitations of MAI, so a spreading code is required with specifications that have a very low cross-correlation value as in the orthogonal m-sequence code. In this study, simulate the orthogonal m-sequence code with a length of 8 chips on a multipath fading channel using the Direct Sequence Spread Spectrum system with aims of assessing the performance of the orthogonal m-sequence code on a multipath fading channel, based on the effect of changes in the number of multipath components. The research method used is a Monte Carlo simulation on simulink with the output data in the form of a graph of the comparison value of BER with Eb/No. The results show that on the flat fading channel with the number of components multipath 1, the BER value of the simulation results is in accordance with the BER theory so that the simulation is valid and can be applied to frequency selective fading channels. In the frequency selective fading channel with the number of multipath components 4,6, and 8, the best performance was shown in the multipath 4 component with the smallest BER value, this was influenced by the ACF and CCF values so that the multipath 4 component had the lowest ISI and interference between users.

NEW BARKER’s COMPOSITE CODES AS MODULATION SIGNALS IN BROADBAND COMMUNICATION SYSTEMS

Background. Currently noise-like signals (NLS) are widely used and provide high level of jamming immunity and security in broadband communication systems (BСS) when transmitting confidential information in an open radio channel, especially in emergencies. Increasing the efficiency of the NLS is possible when using more advanced code structures.
 Objective. The purpose of this research is to study new Barker’s composite codes as modulation signals in broadband communication systems.
 Method. Simulation modeling based on MatLab software package and analytical calculation methods are used.
 Results. Modeling in the MatLab software package showed the possibility for using new Barker’s composite codes as modulation signals in direct spread spectrum systems but efficiency depends on code words length as well as type synchronization signal.
 Conclusions. Analysis of research results shows that the new Barker composite codes 21a, 33a, 49, 77a, 121 can be effectively used as modulation code words in broadband systems with direct spectrum expansion.

Physical layer security using boundary technique for emerging wireless communication systems

AbstractThe broadcast nature of radio propagation in wireless communication has been suspected as the loopholes of passive or active attacks by unauthorized users (eavesdroppers). The physical layer security techniques operate at the lowest stack of OSI layer against conventional cryptographic approaches, operating at the upper layer. However, techniques such as channel coding, power (directional antenna and artificial noise), and spread spectrum have been (and continuously) deployed to safeguard against sophisticated attacks. Most of these deployments are theoretical, and a few are enhanced for efficient security against an intruder. In this article, a boundary technique approach is proposed and applied to the physical layer to improve its secrecy‐capacity and subdue adversary effects at the legitimate receiver. Hybrid performance metrics were adopted, and a Monte Carlo simulation was performed. The result obtained using secrecy outage probability, secrecy‐capacity, and intercept‐probability show that our proposed techniques enhance the secret transmission between the main transmitter and legitimate receiver. The simulation results were compared with the analytical methods. It was found that the channel between the transmitter and the main receiver has a better signal‐to‐noise ratio than the corresponding eavesdropper's channel. Conclusively, performance of the proposed technique is validated for applications in emerging wireless communication systems.

FlyingLoRa: Towards energy efficient data collection in UAV-assisted LoRa networks

Energy efficiency is an increasingly crucial consideration due to the battery-powered end devices in LoRa networks. With the adoption of chirp spread spectrum modulation, end devices far apart from the gateway have to use a high spreading factor and transmit power to send uplink packets, which causes longer transmission time and higher energy consumption compared to the end devices near the gateway, and further causes unfairness issues on energy efficiency. To tackle this problem, we investigate a novel energy-efficient data collection scheme named FlyingLoRa, where an unmanned aerial vehicle carrying one gateway is dispatched to harvest packets from end devices. The goal of FlyingLoRa is to minimize the energy consumption of end devices for packet transmission by jointly optimizing the 3D UAV trajectory, scheduling strategies, and transmission parameters of end devices. We formulate our design as a mixed-integer non-convex optimization problem and propose an efficient iterative algorithm to find a sub-optimal solution. The proposed approach is numerically simulated and the results show that FlyingLoRa improves energy efficiency by 16.13× on average compared with the existing fixed gateway schemes. In addition, we realize FlyingLoRa in real scenarios and evaluate its performance by presenting the actual packet reception rate (PRR) and transmission energy consumption, which shows its effectiveness.

Parallel Combined Spread Spectrum Error Analysis And Succesive Error Correction Method

Traditional spread spectrum techniques provide a strong anti-interference capability but a relatively low transmission rate. This is addressed by the parallel combination spread spectrum technique which provides higher transmission efficiency, security, and spread gain. Nevertheless, the receiver of a parallel combined spread spectrum system requires to distinguish multiple spread spectrum sequences. Therefore, any reception errors are propagated in the receiver hence leading to a larger number of errors. Moreover, spread spectrum sequences with different mode values experience different probability of errors at the receiver. The existing analysis of the error location in the parallel combined spread spectrum is only an estimate after countless experiments. In this paper, we theoretically analyze the probability of correct discrimination of parallel combination spread spectrum with different modulus values. Furthermore, according to the probability analysis of correct discrimination therefore the parallel combination spread spectrum is improved. This significantly reduces the bit error rate of the system and improves the reliability only with a slight degradation of transmission efficiency.

‘Emancipatory nationalisms’? The nationalisms of nations without states

AbstractIn today’s seemingly ever‐globalizing societies, nationalism remains a potent force, most recently illustrated by national governments’ responses to the COVID‐19 crisis. Even though nationalism and its manifestations are deeply entrenched within societies, the term ‘nationalism’ itself continues to carry negative connotations, and the dichotomy between ‘good patriots’ vs ‘bad nationalists’ appears to be widely accepted in everyday life and the scholarly literature. Likewise, the association of ‘good’ (meaning ‘civic’ nationalism) with Western and ‘bad’ (for which read ‘ethnic’) nationalism with Eastern forms of nationalism remains prevalent. In this special issue, we critique these Eurocentric approaches to nationalism, highlighting two aspects of nationalism that are often overlooked: 1) nationalism takes many forms, and rather than viewing it as ‘good’ or ‘bad, it should be understood as a spectrum spreading across the Global North and South; 2) there is an emancipatory and creative potential within nationalism for marginalized and colonized peoples that has been illustrated through cases from the Global South. This potential – represented by the ‘nationalisms of nations without states’ – forms the central concern of this special issue. Our selection of cases from both the Global North and South reflects our own approach to nationalism.

A high dynamic weak spread spectrum signal acquisition strategy based on the transfer model

To solve the problem of low Earth orbit (Leo) satellite constellation link spread spectrum signal acquisition in the high dynamic weak environment, this paper proposes a acquisition strategy based on transfer model. In this paper, we analyze the dynamic characteristics of link signal. An improved method of parallel code phase search acquisition based on transfer model acquisition strategy is introduced, the improvement of the proposed acquisition strategy to the traditional acquisition algorithm is illustrated through theoretical analysis. Simulation results verify the superiority of the acquisition strategy based on the transfer model for high dynamic weak signal acquisition.