Showing papers on "Spread spectrum published in 2019"

“Jam Me If You Can:” Defeating Jammer With Deep Dueling Neural Network Architecture and Ambient Backscattering Augmented Communications

Abstract: With conventional anti-jamming solutions like frequency hopping or spread spectrum, legitimate transceivers often tend to “escape” or “hide” themselves from jammers. These reactive anti-jamming approaches are constrained by the lack of timely knowledge of jamming attacks (especially from smart jammers). Bringing together the latest advances in neural network architectures and ambient backscattering communications, this work allows wireless nodes to effectively “face” the jammer (instead of escaping) by first learning its jamming strategy, then adapting the rate or transmitting information right on the jamming signals (i.e., backscattering modulated information on the jamming signals). Specifically, to deal with unknown jamming attacks (e.g., jamming strategies, jamming power levels, and jamming capability), existing work often relies on reinforcement learning algorithms, e.g., ${Q}$ -learning. However, the ${Q}$ -learning algorithm is notorious for its slow convergence to the optimal policy, especially when the system state and action spaces are large. This makes the ${Q}$ -learning algorithm pragmatically inapplicable. To overcome this problem, we design a novel deep reinforcement learning algorithm using the recent dueling neural network architecture. Our proposed algorithm allows the transmitter to effectively learn about the jammer and attain the optimal countermeasures (e.g., adapt the transmission rate or backscatter or harvest energy or stay idle) thousand times faster than that of the conventional ${Q}$ -learning algorithm. Through extensive simulation results, we show that our design (using ambient backscattering and the deep dueling neural network architecture) can improve the average throughput (under smart and reactive jamming attacks) by up to 426% and reduce the packet loss by 24%. By augmenting the ambient backscattering capability on devices and using our algorithm, it is interesting to observe that the (successful) transmission rate increases with the jamming power. Our proposed solution can find its applications in both civil (e.g., ultra-reliable and low-latency communications or URLLC) and military scenarios (to combat both inadvertent and deliberate jamming).

Synchronous Online Diagnosis of Multiple Cable Intermittent Faults Based on Chaotic Spread Spectrum Sequence

Abstract: This paper proposes a method based on chaotic spread spectrum sequence for synchronous online diagnosis of intermittent faults for complex and cable. networks, such as the aircraft power system. The novelties of the proposed method include: 1) since chaotic spread spectrum signals are sensitive to initial values, the number of chaotic sequences are not limited and the proposed method is not limited by the number of cables under monitoring; 2) with the self-correlation characteristic and cross-correlation characteristic of chaotic sequence, the proposed method can be extended to online diagnosis of multiple cable intermittent faults; and 3) the signal source impedance amplification method is proposed for intermittent arc faults of multiple cables, which improves the reflection coefficient and increases the accuracy of online detection and location of intermittent arc faults. A series of simulations and experiments on multiple cables with different intermittent fault modes are conducted to verify the effectiveness of the proposed approaches.

Sea Clutter Cancellation for Passive Radar Sensor Exploiting Multi-Channel Adaptive Filters

Abstract: Sea clutter suppression in passive radar sensor is a challenging problem because the Doppler frequencies of low-velocity sea-surface targets are typically close to the spectrum of the sea clutter. Conventional approaches based on single-channel high-pass filters are effective for clutter suppression only when the clutter is concentrated in low Doppler region. For sea clutter that has a spread spectrum, however, these approaches have to compromise target signal reception. That is, they either form a narrow notch which does not effectively suppress clutter, or generate a broadened null that simultaneously mitigates low-velocity target signals. Therefore, it is desirable to design a filter that forms a notch broad enough to cover the entire clutter spectrum, with the frequency response rising sharply to a high gain outside the clutter band. Toward this end, in this paper, we develop a generalized multi-channel adaptive filter which, by forming multiple sharp notches over a set of discrete frequencies within the clutter spectrum, achieves effective clutter suppression and target signal preservation. We focus on the fast frequency-domain implementation, and the performance analysis in terms of the frequency response, signal energy loss, and computational complexities is also presented. The effectiveness of the proposed approaches is verified using real-data results.

The Performance of Chirp Signal Used in LEO Satellite Internet of Things

Abstract: The technology of chirp spread spectrum (CSS) has been around for decades, widely used in the fields of radar and sonar. In recent years, CSS has been used in the IEEE 802.15.4a and Long Range (LoRa) Internet of Things (IoT), called LoRa modulation. On the other hand, CSS has never been used in low-Earth-orbit (LEO) satellite communication systems for low-data-rate transmission. CSS applied in LoRa as a kind of successful commercial IoT technology will promote research on its application in satellite communication for IoT. Recently, new types of chirp signals with the same chirp rate have become available to realize multiple accesses. This letter examines those types of chirp signal and the revised SCS called Asymmetry Chirp Signal (ACS) is proposed for better performance in LEO satellite IoT.

Fundamental Bounds on the Age of Information in General Multi-Hop Interference Networks

Abstract: This paper studies the “age of information” of status updates in a general multi-source multi-hop wireless network with time slotted transmissions and general interference constraints. Specifically, the scenario considered in this paper assumes that each node in the network is both a source and a monitor of information and that all nodes wish to receive fresh status updates from all other nodes in the network. Lower bounds for the instantaneous peak and average age of information are derived for three interference models using properties of each interference model's family of feasible activation sets. These bounds generalize prior results derived for the “global” interference model where only one node transmits in each time slot. Achievability results are presented through the development of explicit schedules for ring networks in three specific interference models: (i) global interference, (ii) interference free, i.e., all nodes can transmit simultaneously without interference, and (iii) topologically-dependent interference where multiple nodes transmit simultaneously if they share no one-hop neighbors. Numerical examples are presented to quantify the gap between the achieved age and the bounds.

Eavesdropping-Aware Routing and Spectrum/Code Allocation in OFDM-Based EONs Using Spread Spectrum Techniques

Abstract: In this work, eavesdropping-aware routing and spectrum/code allocation techniques are proposed for elastic optical networks (EONs) using orthogonal frequency division multiplexing (OFDM). To introduce physical (optical) layer security and protect these networks against eavesdropping attacks, spread spectrum (SS) with signal overlapping techniques are used to encode each requested confidential connection. In order to make sense of accessed information and compromise a confidential connection, an eavesdropper will now have to lock on the correct frequency, determine the correct code and symbol sequence among co-propagated overlapped signals, and decode the signal. Different novel policies are presented for the assignment of spectrum and the codes for each confidential demand along with different routing strategies, resulting in an extra layer of security for confidential demands. Depending on the spectrum/code allocation and routing policies utilized, different (extra) levels of security are added for confidential connections while also considering the spectrum utilization, the blocking rate, and the algorithmic time complexity required for connection provisioning.

Green RF/FSO Communications in Cognitive Relay-Based Space Information Networks for Maritime Surveillance

Abstract: In this paper, we provide an overview of a space-based network for the maritime surveillance information sharing and evaluate the coverage, the throughput and the real-time reception capacity of the presented systems. The focus is on the feeder link of a multi-hop geostationary satellite system. We propose a cognitive relay-based architecture for the inter-satellite and satellite-to-ground communication with a multi-band spectrum sensing operating on both free-space optical (FSO) and radio frequency (RF) bands. Furthermore, modeling the spectrum sensing energy as a Gamma distribution we derive the formula of the network energy consumption in presence of multipath fading and considering two different data relay schemes: amplify-and-forward (AF) and decode-and-forward (DF). We prove that the RF/FSO communication in the proposed relay-based architecture enhances the data transmission increasing the throughput and the real-time reception capacity and reducing the network energy consumption. The performance evaluation shows that the DF scheme overcomes the AF one in terms of energy consumption while the AF scheme overcomes the DF one in terms of probability detection, both experience the same throughput. Finally, the proposed novel architecture has been compared with existing ones showing that it enhances the current maritime surveillance systems by jointly optimizing communication functionalities.

Ultranarrowband Waveform for IoT Direct Random Multiple Access to GEO Satellites

Abstract: Direct access of small terminals in the Internet of Things (IoT) to geostationary satellites may provide wide coverage and almost 100% availability for remote locations without access to terrestrial networks. However, existing waveforms and IoT solutions do not close the link to the geostationary earth orbit (GEO) for massively deployed small devices. We present a novel modulation and signaling scheme based on chirp-spread spectrum (CSS) that enables reliable transmission at ultra low bit-rate. The proposed structure for the transmit signal applies unipolar codes in a novel manner, which allows random multiple access to a common channel for a large number of devices. Further, the transmit signal is designed to allow robust signal detection with low effort even at high carrier frequency offsets. We propose a system concept for the receiver including synchronization, and provide the results of extensive simulations carried out on system and link levels. As a result, we demonstrate that the proposed scheme, referred to as unipolar-coded CSS (UCSS), enables true random multiple access for a very large number of devices, closing the challenging link between IoT devices and satellites in the GEO even at high carrier frequencies from C-band to Ka-Band.

High-Performance Self-Synchronous Blind Audio Watermarking in a Unified FFT Framework

Abstract: This paper presents a blind audio watermarking method that uses two different schemes to hide binary bits and auxiliary information within separate ranges of a fast Fourier transform (FFT) sequence. An adaptive vector norm modulation (AVNM) scheme is introduced to achieve a satisfactory balance of imperceptibility, robustness, and payload capacity. An improved spread spectrum (ISS) scheme is developed to produce a striking correlation peak, which facilitates the detection of synchronization codes in the FFT domain. The combination of robust audio segment extraction and recursive FFT makes it possible to execute these two FFT-based schemes in tandem on a sample-by-sample basis. The experiment results confirm that watermark embedding causes merely a negligible degradation in perceptual quality. A detectability test proved the effectiveness of the ISS scheme in self-synchronization as well as hiding auxiliary data. Three versions of AVNM with capacities ranging from 344.53 to 1033.59 bits per second were demonstrated. Compared with six recently developed schemes, AVNM exhibited advantages in terms of negligible quality distortion, flexible payload capacity, and excellent robustness against a variety of common signal processing attacks.

"Jam Me If You Can'': Defeating Jammer with Deep Dueling Neural Network Architecture and Ambient Backscattering Augmented Communications

Abstract: With conventional anti-jamming solutions like frequency hopping or spread spectrum, legitimate transceivers often tend to "escape" or "hide" themselves from jammers. These reactive anti-jamming approaches are constrained by the lack of timely knowledge of jamming attacks. Bringing together the latest advances in neural network architectures and ambient backscattering communications, this work allows wireless nodes to effectively "face" the jammer by first learning its jamming strategy, then adapting the rate or transmitting information right on the jamming signal. Specifically, to deal with unknown jamming attacks, existing work often relies on reinforcement learning algorithms, e.g., Q-learning. However, the Q-learning algorithm is notorious for its slow convergence to the optimal policy, especially when the system state and action spaces are large. This makes the Q-learning algorithm pragmatically inapplicable. To overcome this problem, we design a novel deep reinforcement learning algorithm using the recent dueling neural network architecture. Our proposed algorithm allows the transmitter to effectively learn about the jammer and attain the optimal countermeasures thousand times faster than that of the conventional Q-learning algorithm. Through extensive simulation results, we show that our design (using ambient backscattering and the deep dueling neural network architecture) can improve the average throughput by up to 426% and reduce the packet loss by 24%. By augmenting the ambient backscattering capability on devices and using our algorithm, it is interesting to observe that the (successful) transmission rate increases with the jamming power. Our proposed solution can find its applications in both civil (e.g., ultra-reliable and low-latency communications or URLLC) and military scenarios (to combat both inadvertent and deliberate jamming).

Database-Assisted Spectrum Prediction in 5G Networks and Beyond: A Review and Future Challenges

Abstract: This article surveys the state of the art in spectrum prediction and learning, summarizes applications, techniques, main metrics, computational complexity, and provides practical examples. We focus on a cellular case study and define required improvements to database-assisted spectrum sharing. The use of history information and predictive spectrum modeling at different time scales provides valuable information to regulators, operators, and users of dynamic spectrum access networks. Prediction enables dynamic spectrum sharing systems to operate proactively, and consequently improves the performance in terms of reducing delays and interference among coexisting systems. Current database-assisted spectrum sharing concepts are in fact too static for many applications. Our numerical results on local-aware predictive spectrum allocation show the advantage of predictive operation in a vehicle-to-everything (V2X) scenario.

Tutorial: GPS receiver architectures, front-end and baseband signal processing

Abstract: This tutorial provides an overview of the hardware architectures and signal processing that form the core of satellite-based navigation receivers such as GPS. The concepts of spread spectrum and code division multiple access are introduced along with their roles in signal acquisition and tracking. The super-heterodyne front-end architecture will be described as well as the baseband architecture that utilizes in-phase and quadrature processing. Tracking loops are discussed along with measurement generation. The tutorial concludes with a brief look at so-called "modernized" satellite-based navigation signals.

A DDS-Based Wait-Free Phase-Continuous Carrier Frequency Modulation Strategy for EMI Reduction in FPGA-Based Motor Drive

Abstract: In ac motor drives, the fixed-frequency harmonic components of output voltage and current from the inverter with fixed-frequency pulsewidth modulation usually lead to electromagnetic interference (EMI). The spread spectrum clock generation (SSCG) is a widely used solution for this problem. Adjusting the switching frequency to reduce EMI is one kind of practicable scheme among SSCG methods. How to design an optimal or suitable modulation profile is a research emphasis of scholars and has been discussed in depth in many literatures. However, apart from the modulation profile, the mode and quality of carrier are also important and can be improved. In most frequency modulation methods, due to the limitation of the conventional carrier generation mode, the implementation of the new frequency instruction has to wait for the termination of the last switching period. In order to eliminate the waiting state and design a simpler algorithm, this paper has proposed a wait-free phase-continuous carrier frequency modulation (WPCFM) strategy by combining the direct digital frequency synthesizer theory and proper temporal planning of control interruptions. Besides, a theoretical analysis of WPCFM, including quantization error, frequency jitter, phase delay, and voltage distortion, has been finished. Moreover, compared with conventional methods, a more convenient, feasible, and simpler field-programmable gate array based algorithm implementation method and the control structure of WPCFM are also introduced. The analysis shows that, although WPCFM causes a slight increase of the current ripple, it can solve the partial frequency nonuniform distribution problem of the conventional method, and it has a potential value of applications in the wide band gap motor drive systems. The effectiveness of the WPCFM is verified by several sets of EMI reduction experiments where classical periodic carrier frequency modulations are applied.

Sparse Signal Recovery in MIMO Specular Meteor Radars With Waveform Diversity

Abstract: Since the 1950s, specular meteor radars (SMRs) have been used to study the mesosphere and lower thermosphere (MLT) dynamics. Atmospheric parameters derived from SMRs are highly dependent on the number of detected meteors and the accuracy of the meteors’ locations. Recently, incoherent and coherent multiple-input-multiple-output (MIMO) radar approaches combined with waveform diversity have been proposed to increase the number of detected meteors and to improve time, altitude, and horizontal resolution of the estimated wind fields. The incoherent MIMO approach refers to the addition of new transmit sites (widely separated), whereas the coherent MIMO refers to the addition of new transmit antennas in the same site (closely separated). In both the cases, a different pseudorandom sequence is transmitted from each antenna element. Unfortunately, the addition of new transmit antennas with different code sequences degrades the performance of conventional signal recovery algorithms. This is a consequence of the cross-interference between the transmitted waveforms, making it worse as the number of transmitters increases. In this article, we propose a signal recovery approach based on compressed sensing, taking advantage of the sparse nature of specular meteor echoes. The approach allows the exact recovery of weak echoes even in interference environments. Besides the advantage of the proposed approach to recover the meteor signal, we discuss the optimal selection of the transmitted waveforms and the minimum code length required for exact recovery. Additionally, we propose a modification of the orthogonal matching pursuit algorithm used in sparse problems to make it applicable in real-time analysis of large data. The success of the proposed approach is corroborated using Monte Carlo simulations and real data from a multi-static spread spectrum meteor radar network installed in northern Germany.

The spread spectrum GFDM schemes for integrated satellite-terrestrial communication system

Abstract: Recently, integrated Satellite-Terrestrial (S-T) communication system, especially the integration of satellite communication with 5G/6G, is regarded as a research hotpot. Future integrated S-T communication systems are demanding a more compatible and robust physical layer waveform. Considering physical layer access waveform design, this paper proposed a novel Spread Spectrum Generalized Frequency Division Multiplexing (SS-GFDM) scheme for integrated S-T communication system. Traditional GFDM has many advantages such as excellent adaptability and low out-of-band (OOB) radiation. However, because of intrinsic inter carrier interference (ICI) and low signal-to-noise ratio (SNR), the multiple access performance is degraded. In this paper, we introduced CDMA technology into GFDM. Two different spread spectrum modes, Cyclic Code Shift Keying (CCSK) soft spread spectrum and Direct Sequence Spread Spectrum (DSSS), are considered and compared in this paper to illustrate the benefits of GFDM-CDMA in low SNR scenario. Moreover, this scheme integrates the slot-ALOHA protocol with GFDM-CDMA, which extends access freedom in frequency, time and code domain. The simulation and analysis results show that the proposed GFDM-CDMA scheme reduces the performance degradation caused by interference. It is effective in typical satellite channel with low complexity. Meanwhile, the peak-average-power-ratio (PAPR) and access performance has been enhanced significantly.

Spread-Spectrum Technique Employing Phase-Shift Modulation to Reduce EM Noise for Parallel–Series LLC Resonant Converter

Abstract: A spread-spectrum technique (SST) has been developed to mitigate an electromagnetic interference in power converters. However, for resonant converters using a pulse-frequency modulation, it is difficult to regulate its output voltage with the SST, because the switching-frequency variation according to the spread spectrum induces large output-voltage fluctuation. In this letter, an enhanced phase-shift algorithm of the frequency modulation of the SST and a parallel–series structure for an LLC resonant converter are proposed to obtain a tight output-voltage regulation under the spread-spectrum operation. The performance of the proposed methods is experimentally verified using a 600-W prototype parallel–series LLC resonant converter.

Postprocessing for Improved Accuracy and Resolution of Spread Spectrum Time-Domain Reflectometry

Abstract: Reflectometry, which is commonly used for locating faults on electrical wires, produces sampled time domain signatures with peaks that are often missed due to this sampling. Resultant errors in these sampled peaks translate to errors in calculating the impedance and location of the fault. Typical signal processing methods to improve the accuracy of these sampled peaks have complexity on the order of O(N2). For embedded fault location applications, algorithms with lower complexity are desired. In this article, we introduce three algorithms for improving the accuracy of the peak with a complexity of O(N). We evaluate these algorithms on the practical case of calculating the velocity of propagation and the characteristic impedance of a photovoltaic (PV) cable using spread spectrum time-domain reflectometry.

Interference of Spread-Spectrum Modulated Disturbances on Digital Communication Channels

Abstract: In this paper, the effects of random spread spectrum (SS) electromagnetic interference (EMI) on digital communications are addressed. For this purpose, the influence of EMI on a communication channel is described in the framework of information theory in terms of an equivalent channel capacity loss, which is analytically predicted and validated by experimental results. The EMI-induced channel capacity loss for non-modulated and SS-modulated interference generated by a switching-mode DC-DC power converter are then evaluated for different EMI and channel characteristics so that to compare different scenarios of practical interest.

M-ary Cyclic Shift Keying Spread Spectrum Underwater Acoustic Communications Based on Virtual Time-Reversal Mirror

Abstract: Underwater acoustic communications are challenging because channels are complex, and acoustic waves when propagating in the ocean are subjected to a variety of interferences, such as noise, reflections, scattering and so on. Spread spectrum technique thus has been widely used in underwater acoustic communications for its strong anti-interference ability and good confidentiality. Underwater acoustic channels are typical coherent multipath channels, in which the inter-symbol interference seriously affects the performance of underwater acoustic communications. Time-reversal mirror technique utilizes this physical characteristic of underwater acoustic channels to restrain the inter-symbol interference by reconstructing multipath signals and reduce the influence of channel fading by spatial focusing. This paper presents an M-ary cyclic shift keying spread spectrum underwater acoustic communication scheme based on the virtual time-reversal mirror. Compared to the traditional spread spectrum techniques, this method is more robust, for it uses the M-ary cyclic shift keying spread spectrum to improve the communication rate and uses the virtual time-reversal mirror to ensure a low bit error rate. The performance of this method is verified by simulations and pool experiments.

Multi-carrier chaotic communication scheme for underwater acoustic communications

Abstract: 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.

Detection of Fast Frequency-Hopping Signals Using Dirty Template in the Frequency Domain

Abstract: The frequency-hopping technique is widely used in commercial and military communications for its superiority in anti-jamming and low probability of interception and detection capabilities. To further lower its detection probability, a frequency-hopping signal randomly changes its carrier frequency within a transmission symbol. Conventional detection methods have poor performance in the presence of fast frequency-hopping signals. To solve this problem, we propose a dirty-template-based detection scheme. Dirty Template was originally proposed to blindly estimate the time delay in an ultra-wide-band system. We propose that it can be employed in the frequency domain to detect fast frequency-hopping signal. The decision statistic derived from the cross-correlation between the template and received signals in the frequency domain is analyzed. Using this cross-correlation, a detection scheme, based on the Neyman–Pearson test is proposed. The simulation results show that the dirty-template-based scheme outperforms the autocorrelation-based scheme when the hopping period is short.

Direction-of-Arrival (DOA) Estimation based on Spacetime-Modulated Metasurface

Abstract: We introduce the concept of DOA estimation based on spacetime-modulated 2D-patch-array metasurface. Such a system, compared to conventional DOA estimators, offers the key advantage of requiring only one receiving antenna, with the metasurface placed in front of it. The patch rows of the metasurfaces are time-modulated by different orthogonal codes, so that the metasurface is de facto spacetime-modulated. The DOA is found by measuring the delay between the different waveforms obtained by multiplication of the received mixed-signal with the different codes.

Experimental Interference Robustness Evaluation of IEEE 802.15.4-2015 OQPSK-DSSS and SUN-OFDM Physical Layers for Industrial Communications

Abstract: In this paper, we experimentally evaluate and compare the robustness against interference of the OQPSK-DSSS (Offset Quadrature Phase Shift Keying-Direct Sequence Spread Spectrum) and the SUN-OFDM (Smart Utility Network-Orthogonal Frequency Division Multiplexing) physical layers, as defined in the IEEE 802.15.4-2015 standard. The objective of this study is to provide a comprehensive analysis of the impact that different levels of interference produce on these modulations, in terms of the resulting PDR (Packet Delivery Ratio) and depending on the length of the packet being transmitted. The results show that the SUN-OFDM physical layer provides significant benefits compared to the ubiquitous OQPSK-DSSS in terms of interference robustness, regardless of the interference type and the packet length. Overall, this demonstrates the suitability of choosing the SUN-OFDM physical layer when deploying low-power wireless networks in industrial scenarios, especially taking into consideration the possibility of trading-off robustness and spectrum efficiency depending on the application requirements.

Co-design of Joint Radar and Communications Systems utilizing Frequency Hopping Code Diversity

Abstract: Most of the dual-function radar communications (DFRC) systems in the literature require a multi-sensor transmit array and assume a prior knowledge of several parameters, such as channel state information and accurate transmit array geometry. In this paper, we propose a new co-design strategy for joint systems between radar and communications with a single transmit antenna and no assumptions of any prior knowledge. The communication information embedding is achieved using the diversity of frequency hopping waveforms. The communication receiver detects the embedded symbols by estimating frequency components of the sub-pulses contained in one pulse, where Fast Fourier Transform (FFT) can be utilized. Assume that the discrete frequency coding deploys $Q$ distinct, equally spaced frequencies and only one frequency is transmitted during one sub-pulse. There are $Q!$ different frequency hopping orders, thus a data rate of megabits per second can be achieved for a moderate number $Q$ of sub-pulses and a single transmit antenna. The possible data rate is analyzed and bit error rate using simulated and experimental data are provided for performance evaluations.

Spread Spectrum Technique for Decreasing EM Noise in High-Frequency APWM HB Resonant Converter With Reduced EMI Filter Size

Abstract: A spread spectrum technique (SST) has been proposed as a solution to mitigate electromagnetic (EM) interference in power converters. In the previous research, the SST has been widely applied to the power converters that have insensitive voltage gain according to switching frequency variation, such as buck, boost and flyback topologies. However, resonant converters have sensitive voltage gain according to the switching frequency variation, which cannot regulate the output voltage with the SST. In this paper, a high-frequency (HF) half-bridge (HB) resonant converter employing the SST is developed for power supply applications with 100-W power capability. The design methodology of its resonant tank and the SST is proposed to obtain the tight output voltage regulation performance and the EM noise reduction. In addition, the size reduction of EM noise filters is analyzed by employing the SST. The output voltage regulation performance and the filter size reduction will be experimentally verified using a 100-W prototype HF HB resonant converter.

Cognitive Multi-Hop Multi-Branch Relaying: Spectrum Leasing and Optimal Power Allocation

Abstract: In this paper, for an overlay cognitive radio network in which the primary user’s transmission is assisted by a cognitive multi-hop multi-branch network, we propose and analyze a spectrum leasing scheme that achieves full diversity in both the primary and secondary networks. Among the available branches, the best one is selected to establish a multi-hop relay link between the primary users. In return, the secondary users of the selected branch are rewarded with a fraction of spectrum to transmit their own signals over a nonorthogonal multiple-access channel. We jointly optimize the branch selection and the spectrum allocation such that the sum-rate of the secondary users is maximized under the constraint that a minimum quality-of-service (QoS) requirement in terms of the achievable rate is satisfied in the primary network. We also optimize the power allocation to the secondary users such that the asymptotic outage probability of the primary network is minimized. The analytical results show that this spectrum leasing scheme guarantees the full diversity of order $M$ in both the primary and secondary networks, where $M$ is the number of cognitive branches. The simulation results also show that optimizing the allocation of power significantly decreases the risk of spectrum leasing failure.

A Novel VLSI Architecture for Multi-Constellation and Multi-Frequency GNSS Acquisition Engine

Abstract: This paper proposes a novel VLSI architecture of GNSS acquisition engine based on short-time correlation combined with an FFT scheme. The architecture supports multi-constellation systems and multi-frequency satellite signals flexibly by the manner of time-division multiplexing. The supported signals include GPS, BDS, GLONASS, GALILEO, QZSS, IRNSS, and SBAS. Compared with other direct acquisition structures, the search efficiency of the acquisition engine is improved by using the IF playback structure. Based on the characteristics of L1C and B1C signal spread spectrum codes, an efficient generation method and the circuit structure of Legendre sequence which is compatible with L1C and B1C spread spectrum codes are proposed. It can effectively reduce the die area of the spread spectrum code generator and the generation time of the L1C/B1C spread spectrum code. Combining with the acquisition scheme adopted in this paper, the structure of the short-time correlators’ array is optimized, and the maximum clock frequency of the acquisition engine is significantly improved. The acquisition engine proposed in this paper is implemented in a 55-nm CMOS technology. The system occupied a silicon area of 2.1 mm2 and consumes only 72.02-mW power while realizing the maximum clock frequency at about 333.33 MHz.

A New Multiple-Symbol Differential Detection Strategy for Error-Floor Elimination of IEEE 802.15.4 BPSK Receivers Impaired by Carrier Frequency Offset

Abstract: In this paper, we pay our attention towards the noncoherent demodulation aspect of binary phase shift keying (BPSK) receivers for IEEE 802.15.4 wireless sensor networks (WSNs), and a carrier frequency offset invariant as well as error-floor free multiple-symbol differential detection (MSDD) strategy is proposed over the flat fading channel. This detector is an alternative to the multiple-symbol detector that has been considered almost exclusively in the past. In this new configuration, the receivers do not perform chip-level precompensation as in conventional scheme but bit-level postcompensation. That is, the bit-level autocorrelation operation is first implemented with the “raw” chip sample, and then the carrier frequency offset effect (CFOE) embedded in the achieved statistic is compensated. Correspondingly, the cumulative error in the detection metric is decreased so much that the pervasive error floor for the conventional MSDD scheme is suppressed. Also, complexity efficient estimators for the MSDD scheme are reinvestigated, analyzed, and summarized. Simulation results demonstrate that this new detection strategy may achieve rather more encouraging gain from differential and spread spectrum coding than the conventional single differential coherent detection (SDCD) scheme. The pervasive error floor is also eliminated as compared with conventional MSDD scheme even if the most simple estimator is configured under large bit observation length. Then, much transmitting energy may be saved for each chip symbol, which is practically desired for transmit-only nodes in WSNs.

An Anti-Interference Scheme for UAV Data Links in Air-Ground Integrated Vehicular Networks.

Abstract: As one of the main applications of the Internet of things (IoT), the vehicular ad-hoc network (VANET) is the core of the intelligent transportation system (ITS). Air-ground integrated vehicular networks (AGIVNs) assisted by unmanned aerial vehicles (UAVs) have the advantages of wide coverage and flexible configuration, which outperform the ground-based VANET in terms of communication quality. However, the complex electromagnetic interference (EMI) severely degrades the communication performance of UAV sensors. Therefore, it is meaningful and challenging to design an efficient anti-interference scheme for UAV data links in AGIVNs. In this paper, we propose an anti-interference scheme, named as Mary-MCM, for UAV data links in AGIVNs based on multi-ary (M-ary) spread spectrum and multi-carrier modulation (MCM). Specifically, the Mary-MCM disperses the interference power by expanding the signal spectrum, such that the anti-interference ability of AGIVNs is enhanced. Besides, by using MCM and multiple-input multiple-output (MIMO) technologies, the Mary-MCM improves the spectrum utilization effectively while ensuring system performance. The simulation results verify that the Mary-MCM achieves excellent anti-interference performance under different EMI combinations.

Study of the GNSS Jamming in Real Environment

Abstract: GNSS systems are susceptible to radio interference despite then operating in a spread spectrum. The commerce jammers power up to 2 watts that can block the receiver function at a distance of up to 15 kilometers in free space. Two original methods for GNSS receiver testing were developed. The first method is based on the usage of a GNSS simulator for generation of the satellite signals and a vector signal RF generator for generating different types of interference signals. The second software radio method is based on a software GNSS simulator and a signal processing in Matlab. The receivers were tested for narrowband CW interference, FM modulated signal and chirp jamming signals, and scenarios. The signal to noise ratio usually drops down to 27 dBc-Hz while the jamming to signal ratio is different for different types of interference. The chirp signal is very effective. The jammer signal is well propagated in free space while in the real mobile urban and suburban environment it is usually strongly attenuated.