Showing papers on "Spread spectrum published in 2022"

Analysis and Simulation of LoRaWAN LR-FHSS for Direct-to-Satellite Scenario

Abstract: Long Range-Frequency Hopping Spread Spectrum (LR-FHSS) has been recently introduced into the LoRaWAN protocol specification to increase network capacity and collision robustness, and enable direct connectivity between machine devices and the Low Earth Orbit (LEO) satellites. In this letter, we first construct the analytical and simulation models for packet delivery over LR-FHSS from ground nodes to a LEO satellite, and then use the developed analytic and simulation models to generate the numerical results. Our results reveal the potential feasibility of large-scale networks, demonstrate some trade-offs between the two new LR-FHSS-based data rates for the EU region, and reveal the key reasons for packet losses.

Constructions of Optimal Uniform Wide-Gap Frequency-Hopping Sequences

Abstract: In frequency hopping (FH) communication systems, frequency hopping sequences (FHSs) are crucial in determining the system’s anti-jamming performance. If FHSs can ensure a wide-gap between two adjacent frequency points to avoid the frequency points with high interference probability, it will significantly improve the FH communication system’s anti-interference ability. Moreover, if each frequency point appears at the same number of times in a sequence period, the system’s anti-electromagnetic interference will be enhanced. Therefore, it is desirable to employ FHSs with low Hamming autocorrelation, wide frequency-hopping gap, and good uniformity in practical applications. However, to the best of our knowledge, no such infinite classes of FHSs have been reported in the literature to date. This paper aims to present two constructions of uniform wide-gap frequency-hopping sequences (WGFHSs) by concatenating two or three adequately designed sequences. For the first time, we obtain two infinite classes of WGFHSs, which are optimal with respect to the well-known Lempel-Greenberger bound.

Enhanced Index Modulation-Based Frequency Hopping: Resist Power-Correlated Reactive Jammer

Abstract: Reactive jammer has emerged as a relatively intelligent jamming with low energy cost and high jamming efficiency. Moreover, the jammer can obtain the power-correlated reactive jamming via the cooperation with a malicious user, which imposes a severe threat on the reliability of legitimate users. To solve this issue, this letter proposes an enhanced index modulation based frequency hopping spread spectrum (EIM-FHSS) scheme. Specifically, the strategy of power control in EIM-FHSS is provided where the main step of the strategy is formulated as a general optimization problem. Then we calculate a closed form solution for high signal to noise ratio (SNR), and propose a fast search algorithm for general case to obtain the approximate optimal power with low complexity. Simulation results show that EIM-FHSS can obtain enhanced anti-jamming performance as well as low-complexity compared with the benchmarks.

Photonics based frequency hopping spread spectrum system for secure terahertz communications.

Abstract: Terahertz (THz) spectrum (100 GHz-10 THz) is considered the next frontier in the design of high-speed wireless communication systems. While the high-power THz sources have commercially become available, it increases the possibility of developing THz jammers to disrupt the THz communication link. Therefore, the development of novel anti-jamming solutions is the need of the hour. In this work, we present the photonics-based THz communication system and demonstrate the frequency hopping spread spectrum (FHSS) technique which acts against the single/multi-tone jamming attack in the frequency window of 110 GHz-170 GHz. By tuning the output wavelength of the distributed feedback lasers, the THz carrier frequencies are swept back and forth within the scanning window. The frequency tuning range was measured for different scanning rates of the laser which decreases rapidly with the increase in the scanning rate. Next, we demonstrate the THz FHSS technique in a real-time communication system by transmitting a 6 Gbps NRZ signal in both wireless and THz-fiber-based links within the link distance of 1.75 m. We experimentally found that the measured bit error rate in the THz FHSS system is the time average of the measured BER for individual carrier frequencies within the hopping frequency window. By combining with the forward error correction codes and by using the tunable filter in the receiver, we believe that the proposed technique will offer a novel and compact solution against the single/multi-tone jammer for high-bit rate THz communications.

FHSS Signals Classification by Linear Discriminant in a Multi-signal Environment

Abstract: Frequency-hopping spread spectrum (FHSS) spreads the signal over a large bandwidth where the carrier frequencies change quickly according to a pseudorandom number making signal classification difficult. Furthermore, classification becomes more complex with the presence of additive white Gaussian noise (AWGN) and interference due to background signals. In this paper, a linear discriminant (LD) method based on the Euclidean distance is proposed for the classification of FHSS signals in the presence of AWGN and background signal. Probability of correct classification (PCC) of the FHSS signals is performed by the LD method for the signal-to-noise ratio (SNR) range of −6 to 15 dB. Results show that the proposed method has achieved 90% detection rate at the SNR range of −1.6 to 3.5 dB in the presence of AWGN only, while its performance is degraded to 0.9 to 12 dB when the background signal is present.

Blind Estimation of Self-Synchronous Scrambler Using Orthogonal Complement Space in DSSS Systems

Abstract: In a non-cooperative context, a receiver has to estimate the communication parameters without any prior knowledge of the transmitter, which is highly demanding. Estimating a self-synchronous scrambler is even more challenging because the scrambling sequence of the self-synchronous scrambler is affected by the input sequence. This paper proposes an improved algorithm for blind estimation of a self-synchronous scrambler using the orthogonal property without any bias condition of the received signals in direct sequence spread spectrum (DSSS) systems. We first examine the linear relation of a scrambling sequence using the repetitive property of the spreading code used in a DSSS system. Using the obtained linear relation and the basis of the orthogonal complement space, we then acquire the feedback polynomial candidates of the scrambler. Finally, by calculating the greatest common divisor polynomial of the feedback polynomial candidates, we estimate the correct feedback polynomial. Through computer simulations, we verify that the proposed method achieves superior estimation performance compared to the existing method. Furthermore, we show that the proposed method has practically acceptable computational complexity. For these reasons, it is expected that the proposed method can be applied to blind estimation of a self-synchronous scrambler in a practical non-cooperative system.

Adaptive M-ary spread spectrum based dual-function detection and communication system

Abstract: In this paper, we propose a joint detection-communication technique for continuous active sonar (CAS) systems. Particularly, we embed information in the waveforms used for sonar detection via the adaptive M-ary Spread Spectrum modulation, enabling simultaneous communication-detection. To improve the overall performance of the integrated system, we apply the Generalized Sinusoidal Frequency Modulated waveforms and optimize it through the Genetic Algorithm. The numerical simulation and field experimental results show that the proposed technique can perform the CAS detection and communication simultaneously with remarkable reliability.

Examining the Performance of MIL-STD-188-110D Waveform 0 Against FBMC-SS Over Skywave HF Channels

Abstract: This paper provides a comprehensive performance comparison between a current robust military waveform; namely, MIL-STD-188-110D, Waveform 0, and a filter bank multicarrier spread-spectrum (FBMC-SS) waveform proposed for communications through ionospheric/skywave HF channels. Waveform 0 is effectively a direct sequence spread spectrum waveform that uses Walsh multi-codes to enhance the information transmission rate. It may thus be referred to as Walsh-DSSS. FBMC-SS, on the other hand, makes use of filter banks to provide excellent performance when the received signal is subject to partial band interference. Successful application of FBMC-SS for communications across skywave HF channels has been previously demonstrated, both theoretically and through experimental work. However, very little has been done to contrast FBMC-SS against Walsh-DSSS. The goal of this paper is to first add new features to FBMC-SS to bring it on par with Walsh-DSSS. These features include: (i), introduction of multi-codes that achieve a comparable (or better) data rate to Walsh-DSSS; and (ii), addition of a scrambling step applied to the multi-codes to make the receiver detection robust against widely spread multipaths. With this established, in the second part of the paper, we examine the performance of the developed FBMC-SS against Walsh-DSSS when both are applied for communications across skywave HF channels. The two waveforms are compared both through a theoretical study and through experimental works across several skywave channels ranging from hundreds to thousands of kilometers.

Millimeter-Precision Ultrasonic DSSS Positioning Technique With Geometric Triangle Constraint

Abstract: In this paper, we present a 3-D ultrasonic measurement technique that uses direct sequence spread spectrum (DSSS) with simultaneous multiple code-division multiple access (CDMA) signals. This technique can be applied in precise indoor locating systems. By placing three microphones close to one another separated by distances on the order of the ultrasound wavelength and imposing the constraint that one transducer and two from the three microphones form three triangles in the space (i.e., the triangle constraint) for 3-D ultrasonic DSSS trilateration measurement, millimeter 3-D positioning precision is achieved. The experimental results for a positioning system comprising a set of three microphones and four ultrasound transducers, each of them transmitting its respective 256-bit DSSS code, demonstrate that the proposed system can measure the spatial 3-D location of the receiver with a standard deviation of less than 1.21 mm. The proposed technique is suitable for potential future indoor positioning system (IPS) applications that require sub-centimeter 3-D positioning.

Secure Spread Spectrum Communication Using Super-Orthogonal Optical Chaos Signals

Abstract: This paper proposes an analog spread spectrum secure communication system by designing a super-orthogonal two-dimensional electro-optic time delayed chaotic system. Two negatively correlated (called “super-orthogonal”) broadband optical chaotic signals can be generated. According to the binary symbol to be transmitted, the two signals are coupled into channel in turn. Benefiting from the wide spectrum and super-orthogonal characteristics of the two optical chaotic signals, the scheme shows excellent anti-noise performance which is verified by numerical simulations. Moreover, by introducing the modulation signal time delay feedback, the security of the system can be improved. The system is capable of resisting time delay signature extraction and return map attack, which are inherent vulnerabilities of time-delayed chaotic system and chaotic shift keying mechanism.

Direct Spread Spectrum Technology for Data Hiding in Audio

Abstract: Direct spread spectrum technology is traditionally used in radio communication systems with multiple access, for example, in CDMA standards, in global satellite navigation systems, in Wi-Fi network wireless protocols, etc. It ensures high security and reliability of information transfer. In addition, spread spectrum technology provides the transmitted signals with a noise-like appearance, thus hiding the semantic content of the messages. We researched this technology for other implementations. The purpose of our study was to investigate new technologies for hiding data in multimedia files. In particular, we investigated the direct spread spectrum in the context of the development of methods for hiding data in audio containers. We considered various spreading sequences (chip codes) and also explored their use for hiding information in audio files. We conducted experimental studies and estimated the bit error rate (BER) in the recovered data. The article also evaluates the distortion of an audio container by the peak signal-to-noise ratio (PSNR). The results of our research enable us to find out which method of forming chip codes gives a lower BER with equal PSNR. We provide recommendations on the formation of spreading sequences to reliably and safely hide informational messages in audio files.

A Chirp Spread Spectrum Modulation Scheme for Robust Power Line Communication

Abstract: This paper proposes the use of a LoRa like chirp spread spectrum physical layer as the basis for a new Power Line Communication modulation scheme suited for low-bandwidth communication. It is shown that robust communication can be established even in channels exhibiting extreme multipath interference, impulsive noise and low SNR (−40 dB), with synchronisation requirements relaxed compared to conventional LoRa. ATP-EMTP simulations using frequency dependent line and transformer models, and simulations using artificial Rayleigh channels demonstrate the effectiveness of the new scheme in providing load data from LV feeders back to the MV primary substation. Our results demonstrate error-free communication at SNRs of −40 dB, and can be further improved by trading-off data rate. We further present experimental results based on a Field Programmable Gate Array hardware implementation which match the simulated performance.

Performance Analysis of DSSS-PDMA with SIC in GEO Satellite-Terrestrial Uplink Networks

Abstract: There is a growing trend to utilize satellite networks for the construction of 5G and Beyond 5G high-capacity systems. The power division scheme used in non-orthogonal multiple access (NOMA), which is a key technology for terrestrial networks, can contribute to improving the system capacity of satellite networks. In this paper, we propose a direct sequence spread spectrum-power level division multiple access (DSSS-PDMA) scheme that combines non-orthogonal PDMA with DSSS technology to mitigate the depletion of communication resources and interference to terrestrial terminals. Finally, simulation results with ETS-9 as the high throughput satellite (HTS) and active electronically scanned array (AESA) antenna as the earth station validate the effectiveness and superiority of the proposed schemes as compared with several existing schemes.

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

Abstract: 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.

Waveform Reconstruction of DSSS Signal Based on VAE-GAN

Abstract: The complex electromagnetic environment will limit the efficacy of communication equipment. It is critical to construct a complex electromagnetic environment to test communication equipment in order to maximize its capability. One of the most important methods for constructing a complex electromagnetic environment is signal reconstruction. This paper proposes a VAE-GAN-based method for reconstructing direct sequence spread spectrum (DSSS) signals. In this method, the deep residual shrinkage network (DRSN) and self-attention mechanism are added to the encoder and discriminator of VAE-GAN. In feature learning, the DRSNs can reduce the redundant information caused by noise in the collected signal. The self-attention mechanism can establish the long-distance dependence between the input sequences, making it easier for the network to learn the samples’ pseudonoise (PN) sequence features. In addition, feature loss is applied to the encoder and generator to improve network stability during training. The results of the experiments indicate that this method can reconstruct DSSS signals with the characteristics of the target signal.

Performance study of chaos-based DSSS and FHSS multi-user communication systems

Abstract: Deployment of wireless sensor networks (WSNs) with a large number of nodes have reinstated interest in spread spectrum (SS) technologies as they allow to establish multiple access for nodes with simple hardware and limited power budget. Chaotic spreading is one of the still insufficiently explored areas which can lead to higher security and lower multiple access interference (MAI). This research is intended to bring new information about the performance of binary direct sequence spread spectrum (DSSS) and frequency hopping spread spectrum (FHSS) communication systems which employ chaos-based spreading codes and compare them against classical systems employing m-sequences. Unlike existing research, this investigation is based on the simulation of passband communication systems with up/down-conversion and respective filtering. Performance comparison in terms of bit error ratio (BER) versus signal-to-noise ratio (SNR) at the different number of users and MAI dependence on carrier frequency offset among users in case of additive white Gaussian noise (AWGN) channel are presented. Obtained results highlight several scenarios where chaotic-sequences-based binary DSSS and FHSS systems have advantages over classical solutions.

A Study on One Fast Acquisition Method for DS/FH Hybrid Spread Spectrum Signal in Physical Layer of Aircraft Communication Network

Abstract: In order to meet the requirements of large dynamic and short acquisition time of DS/FH hybrid spread spectrum signal in the physical layer of aircraft communication network, this article proposes a fast acquisition method based on digital wideband sampling and pseudo noise code phase search via Fast Fourier Transform (FFT) in frequency domain. This method highlights parallel reception on synchronous hopping frequencies, all-phase search on pseudo noise code phases, and sequential scanning on Doppler frequency of pseudo noise code. This method turns the 3D search process consisting of hopping frequency, pseudo noise code Doppler frequency, pseudo noise code phase into 1D search while performing DS/FH signal acquisition, as the theoretical analysis and calculated results indicated, the acquisition time performance by such method is improved in a large scale.

Adaptive Measurement and Decoding of Frequency-Hopping Spread Spectrum Signals Based on Knowledge Enhanced Compressed Sensing

Abstract: The frequency-hopping spread spectrum (FHSS) signals can be sparsely represented in frequency domain at any given time. In this letter, we render a dictionary and propose non-cooperative adaptive compressed measurement and decoding methods of FHSS signals, where the measurement kernels (i.e. non-zeros coefficients in the sensing matrix) are adaptively designed based on the gradually obtained measurement results and the decoding can be done without the signal reconstruction step. Besides the ideal adaptive compressed method that achieves the best decoding accuracy with short measurement kernel design time periods, two alternative strategies enabling longer periods in the adaptive measurement design stages are also proposed for economic computational cost consideration. Simulations show the proposed methods to get improved decoding accuracy than the compared non-adaptive and state-of-art compressed methods.

Design and implementation of Polyphase based FHSS modulator using GNU Radio and SDR

Abstract: Wireless communication is the fastest-growing sector in the communication industry. The nature of wirelessly transmitted signals makes them prone to eavesdropping and jamming. The intercepting of these signals leads to the leaking of sensitive data and poses a threat. As a result, the security and dependability of wireless systems are jeopardized. Spread Spectrum enables the signal to be spread out over a larger bandwidth before transmission. Frequency Hopping Spread Spectrum (FHSS) prevents the transmitted signal from eavesdropping by hopping onto different carrier frequencies. FHSS has been prominently used in military applications and wireless standards such as Bluetooth. The higher the hopping bandwidth, the more immune is the system to interferences. A digital FHSS system based on Polyphase channelizers is designed using Software Defined Radios (SDR). Polyphase channelizers utilize N-point Inverse Fast Fourier Transform (IFFT) for inverse Fourier transformation, the computational efficiency of using IFFT is discussed. The SDR approach is used to implement Frequency Hopping Spread Spectrum as they offer faster prototyping and reliability. Using GNU Radio and Universal Software Radio Peripheral, a digital-based Frequency Hopping Spread Spectrum modulator using Polyphase channelizers is designed and implemented in real time.

A Novel Scheme for Discrete and Secure LoRa Communications

Abstract: In this paper, we present a new LoRa transceiver scheme to ensure discrete communications secure from potential eavesdroppers by leveraging a simple and elegant spread spectrum philosophy. The scheme modifies both preamble and payload waveforms by adapting a current state-of-the-art LoRa synchronization front-end. This scheme can also be seen as a self-jamming approach. Furthermore, we introduce a new payload demodulation method that avoids the adverse effects of the traditional cross-correlation solution that would otherwise be used. Our simulation results show that the self-jamming scheme exhibits very good symbol error rate (SER) performance with a loss of just 0.5 dB for a frequency spread factor of up to 10.

A New Tracking Measurement Method Based on QPSK Spread Spectrum Communication Signal

Abstract: AbstractHongyan satellite adopts QPSK spread spectrum communication signal, which can carry out signal enhancement ability verification. The key is to realize accurate tracking and measurement based on communication signal, and then realize the positioning function. However, the I and Q branches of the Hongyan QPSK signal use the same code sequence, which is different from traditional satellite navigation signals and cannot directly use the current satellite navigation signal tracking measurement scheme. Therefore, this paper proposes a tracking measurement scheme based on QPSK spread spectrum communication signals. This method does not strictly require that the carrier reproduced by the receiver is cos and sin. The data symbol estimation method is given based on FFT and m sequence. The periodic I, Q data symbol product is estimated, which prolongs the coherent integration time, realizes signal tracking and measurement, and improves the measurement accuracy.KeywordsQPSKSpread spectrumTracking measurement

Comparison of Bit Error Rate And Performance Analysis For Multicode CDMA Techniques in Fading and AWGN Channels

Abstract: In recent years, wireless communication technology has made great progress. With the rapid growth of video, voice, and data communications, mobile phones have become ubiquitous and so need mobile multimedia communications. To meet the increasing demands of mobile communication services, many solutions have been proposed to reduce the impact of channel effects and increase the speed of data transmission. One of those methods is the use of Multicode Code Division Multiple Access (MTC -CDMA). Two techniques of the MTC-CDMA system have been used, which are multicode system and orthogonal code system. The MTC-CDMA system can support different data rates as needed by next-generation standards. The bit error rate (BER) of the two systems is analyzed in AWGN and Rayleigh fading channels. The multicode system has been simulated with different codes for both code sequence sets and user-specific sequences. These codes are Walsh-Hadamard, orthogonal variable spreading factor (OVSF), Gold, Kasami, and Maximum length sequence (M-sequences) codes. The orthogonal code system is simulated with Walsh-Hadamard spreading code. The results show that the use of Walsh-Hadamard code as user specific sequence and the Gold code as a code sequence gives better BER performance compared with other types of codes for the multicode system. Also, the using of Walsh-Hadamard for sequence sets and PN codes for user specific sequences gives good performance. For the same M-ary, the number of users, and spreading code length, the orthogonal code system can achieve better BER performance than the multicode system, but the maximum number of users that can be accessed is less.

A proposal of FH-SS synchronization with FPGA multichannel correlator implementation

Abstract: This paper presents a proposal for code synchronization for frequency agile systems based on the use of a real-time clock and a multi-channel digital correlator. The proposed synchronization scheme ensures reliability, short synchronization times and resistance to electronic interference and interception. In addition, a proposal for a multi-channel digital correlator has been developed and implemented for use in the synchronization scheme. This type of correlator is suitable for code synchronization in spread spectrum communication systems (DS-SS and FH-SS). The implemented correlator was later used to measure the false alarm probability and the detection probability of the code sequence. Finally, simulation and measurement results are summarized and presented graphically.

Research on EMI and ripple suppression of LLC Resonant Converter based on symmetric chaotic spread spectrum

Abstract: Spread spectrum technology can effectively reduce the peak value of electromagnetic interference(EMI), but it will bring more serious ripple problem to class E resonant converter. Based on spread spectrum modulation technology, this paper proposes a symmetrical chaotic spread spectrum method, which takes the traditional chaotic number as a symmetrical arrangement, so that the working frequency of the circuit changes with the symmetrical chaotic number, so as to achieve the effect of spread spectrum modulation, In this way, without changing the EMI suppression effect of the circuit, the voltage change of the circuit shows a central symmetrical trend, which reduces the ripple of the circuit to a certain extent, and the EMI of the circuit is also reduced due to the addition of spread spectrum signal.

Reducing Detection Complexity of Direct Sequence Spread Spectrum Signal by Estimating Cyclic Frequencies

Abstract: 직접 시퀀스 대역 확산(DSSS, Direct sequence spread spectrum) 신호는 저피탐 특성으로 인하여 확산에 사용된 확산 부호를 알지 못하는 비협력 상황의 수신기 측에서의 신호 탐지가 매우 어렵다. 이러한 DSSS 신호를 탐지하기 위해 DSSS 신호의 순환 정상성을 이용한 신호 탐지 기법이 제안되었다. 순환 정상성을 이용한 신호탐지 기법은 낮은 신호 대 잡음비의 환경에서도 성능이 우수하다는 장점이 있으나 계산 복잡도가 높아 신호탐지에 있어 많은 시간이 소요된다. 본 논문에서는 수신 신호의 순환 주파수를 먼저 추정하여 알고리즘의 계산 복잡도를 개선한 새로운 알고리즘을 제안한다. 또한 컴퓨터 모의 실험을 통해 제안하는 알고리즘이 기존의 알고리즘보다 더 낮은 복잡도에서도 동일한 성능으로 신호 탐지가 가능함을 보인다.

Unjuk kerja kode orthogonal m-sequence dalam sistem direct sequence spread spectrum melalui kanal multipath fa

Abstract: 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.

Burst Frame Synchronization for MC-DS-CDMA System in Multipath Channels

Abstract: Multi-Carrier Direct-Sequence Code Division Multiple Access (MC-DS-CDMA) has gradually been widely used due to its advantages of high transmission rate and multi-user access. The burst frame synchronization detection indicates the start position of the information, which is an important step in the synchronization of the MC-DS-CDMA receiver. In this paper, we propose a time-frequency two-dimensional frame synchronization model, with coherent accumulation in the time dimension and non-coherent accumulation in the frequency dimension for enhancing its performance in multipath channels. Specifically, we derive the closed-form expressions of false alarm probability and detection probability, and verify the expressions through the simulation results. Finally, we conduct the comparative simulation between the MC-DS-CDMA system with the traditional Single-Carrier Direct-Sequence Code Division Multiple Access (SC-DS-CDMA) system. The result shows that the MC-DS-CDMA system has better performance.

Application of chaotic sequences to expand the spectrum

Abstract: The modern development of mobile communications applied in remote sensing techniques requires continuous improvement of methods for transmitting information and developing new types of signals in order to achieve better resistance to interference, energy and structural secrecy of radiation, increase the efficiency of radio systems. These features have broad spectrum signals, the main advantages of which are: ensuring confidential transmission of information, extracting the signal from below the noise level, ensuring the reliability of the received information, even with a relatively small signal-to-noise ratio (SNR). Traditionally, the expansion of the spectrum of signals is done by multiplying the information signal by a code sequence, which is a random sequence, most often of binary symbols, formed by a determined law, but having the properties of a random sequence. Different classes of code sequences are known and used, which meet a number of mandatory requirements. However, they all have one or another drawback. An important reason for this is the lack of a universal mathematical apparatus through which to form a random sequence with the necessary structural complexity and correlation properties to ensure confidentiality in the transmission of information. With the emergence of a new direction in the development of communication technologies, based on the theory of dynamic chaos, there are alternative opportunities to expand the spectrum of signals. These are discrete chaotic signals, which, like pseudo-random sequences, are characterized by a quasi-continuous spectrum with uniform spectral density, with a steeply decreasing autocorrelation function and orthogonality. In the present work a structural scheme of a communication system between sensors is proposed, in which the spectrum of the information signal is expanded by a chaotic sequence. The noise immunity of the system is assessed by determining the probability of bit error rate (BER). The dependence of BER on SNR is studied. The connection with remote sensing could be review in the field wireless network using nodes. The methodology is tested in a simulation and in in-situ experiments. Some of the nodes are coated by new material and put into extreme conditions. The obtained results are analyzed and discussed.