Spread Spectrum Research Articles

A novel spread spectrum underwater acoustic communication system for the inter-symbol interference reduction

A novel spread spectrum underwater acoustic communication system for the inter-symbol interference reduction

Static and dynamic evaluations of acoustic positioning system using TDMA and FDMA for robots operating in a greenhouse

Acoustic positioning system has great potential to be applied in a greenhouse due to its centimeter-level accuracy, low cost, and ability of extensive greenhouse coverage. Spread Spectrum Sound-based local positioning system (SSSLPS) was proposed to be a navigation tool for multiple agricultural robots by the authors' research team. However, to increase the system capacity for positioning multiple robots in a greenhouse, the near-far problem caused by the interference between speakers needs to be overcome. The use of different access methods, Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA), is essential in the SSSLPS system for solving the near-far problem. The static positioning in a greenhouse was first evaluated by setting different parameters to determine the optimal signal setting for a dynamic experiment. From that, the moving robot tests were added with a motion capture system and tested the performance of TDMA and FDMA. The results demonstrated that TDMA can be used in a stationary sound-based positioning system with 12.2 mm accuracy, but it has a time delay problem in dynamic positioning. A simulation was designed to mimic the position error increases with different moving speeds. Although FDMA has the sound damping problem in high-frequency regions creating a peak detection issue, it achieved a higher accuracy with an average position error of 62.1 mm compared to 180.3 mm of TDMA. This study shows that the TDMA method is suitable for static measurements, while the FDMA method is suitable for measuring dynamic objects and controlling mobile robots. Keywords: greenhouse robots, positioning system, near-far problem, TDMA, FDMA DOI: 10.25165/j.ijabe.20221505.6796 Citation: Tsay L W J, Shiigi T, Zhao X Y, Huang Z C, Shiraga K, Suzuki T, et al. Static and dynamic evaluations of acoustic positioning system using TDMA & FDMA for robots operating in a greenhouse. Int J Agric & Biol Eng, 2022; 15(5): 28–33.

Quantifying the Environmental Sensitivity of SSTDR Signals for Monitoring PV Strings

Current spread spectrum time-domain reflectometry (SSTDR) fault detection methods in photovoltaics compare measurements with a fault-free baselin.Yet, environmental factors, such as illuminance, temperature, and humidity, affect these signals and can negatively affect our ability to detect and locate faults. This article explains and quantifies the effects of environmental factors on SSTDR measurements. We demonstrate that illuminance, temperature, and humidity each significantly affect reflections from photovoltaic panels, which require the use of up to 240 baselines to prevent environmental variation from obscuring faults. We present a method to determine the number of required baselines in any given climate and motivate future work in baseline prediction.

FFT Spectrum Spread With Machine Learning (ML) Analysis of Triaxial Acceleration From Shirt Pocket and Torso for Sensing Coughs While Walking

FFT Spectrum Spread With Machine Learning (ML) Analysis of Triaxial Acceleration From Shirt Pocket and Torso for Sensing Coughs While Walking

Analysis of interference-protected operating modes of modern military VHF radio stations of the tactical link of management and practical recommendations of recommendations.

At present, the Armed Forces of Ukraine have organized and operate VHF radio networks, built mainly using equipment “Motorola”, “Harris”, “Aselsan”. The main problem with the use of “Motorola” communications is the operation at fixed frequencies, in a fairly narrow frequency range (136 - 174 MHz), which leads to low noise immunity of radio lines. Unlike Motorola equipment, “Harris” and “Aselsan” radios implement modern noise-tolerant modes, including with frequency hopping spectrum spreading (FHSS).The experience of combat operations in the area of the Operation Joint Forces (OJF) indicates the need to increase the efficiency of the use of the existing VHF capabilities of tactical radio stations. In the conditions of active radio-electronic counteraction of the enemy, the increase of noise protection of radio communication lines becomes especially relevant and requires constant improvement of radio communication means on the basis of the achievements of modern science.The study, on the example of VHF radio tactical control unit “Harris” RF-7850M-HH, analyzed the current noise-protected modes of operation and developed practical recommendations for their use in the face of major types of intentional interference.The practical recommendations set out in the article can be used in the development of instructions for ensuring the operation of VHF radio stations of the tactical management in the conditions of radio interference.

Secure Communication for Cognitive Networks Based on MIMO and Spreading LDPC Codes

The existing cognitive radio (CR) systems lack the ability to deal with the attack of a pretended primary user (PPU), which can palsy cognitive network. To solve the problem, in this paper, a secure cognitive radio (CR) system is proposed. The proposed systems combines MIMO and spread spectrum techniques as well as low density parity check (LDPC) codes to cancel the electronic interference of PPU. The simulation results in Rayleigh flat-fading channel show that, comparing with MIMO cognitive system without the proposed method, the proposed approach can effectively cancel electronic interference from enemy and channel noises interference, and obtain about 9dB gain.

Performance Evaluation of MC-CDMA Systems with Single User Detection Technique using Kernel and Linear Adaptive Method

Among all the techniques combining multi-carrier modulation and spread spectrum, the multi-carrier code division multiple access (MC-CDMA) system is by far the most widely studied. In this paper, we present the performance of the MC-CDMA system associated with key single-user detection techniques. We are interested in problems related to identification and equalization of mobile radio channels, using the kernel method in Hilbert space with a reproducing kernel, and a linear adaptive algorithm, for MC-CDMA systems. In this context, we tested the efficiency of these algorithms, considering practical frequency selective fading channels, called broadband radio access network (BRAN), standardized for MC-CDMA systems. As far as the equalization problem encountered after channel identification is concerned, we use the orthogonality restoration combination (ORC) and the minimum mean square error (MMSE) equalizer techniques to correct the distortion of the channel. Simulation results demonstrate that the kernel algorithm is efficient for practical channels.

Spread Spectrum Sound with TDMA and INS Hybrid Navigation System for Indoor Environment

Indoor navigation plays an essential role in agricultural robots that operate in greenhouses. One of the most effective methods for indoor navigation is the spread spectrum sound (SS-sound) system. In this system, the time of arrival (ToA) of the spread spectrum modulated sound is used for localization. However, there is a near-far problem. Transmitting the SS-sound from multiple anchors using time division multiple access (TDMA) is adequate to solve the near-far problem. However, localization is impossible because the ToA from multiple anchors cannot be simultaneously acquired. To solve this problem, a method for combining the SS-sound system with TDMA and an inertial navigation system is proposed in this study. The effectiveness of the proposed method was demonstrated through numerical simulations of a ground robot and experimentally using a crawler robot.

Multi-Valued Automatic Cab Signalling System Based on the CDMA Technology

Purpose. The work is aimed at the development of principles for the construction of multi-valued automatic cab signalling system (ACS) using the wide-band pseudorandom signals. Methodology. An analysis of existing ACS systems and modern telecommunication technologies has been performed to achieve the stated purpose. The multi-valued automatic cab signalling system CDMA-ACS has been proposed. The mentioned system utilizes wide-band pseudo-noise signals to transmit commands. System parameters: frequency band – 155...395 Hz, pseudorandom codes – 16-bit Walsh codes, spectrum spreading factor – 16, source signal bandwidth – 15 Hz, carrier modulation – DBPSK (differential binary phase-shift keying), information rate – 15 bit/sec, code combination length – 4 bits, maximum amount of commands – 256, the duration of single command transmission – 0.27 sec. Functional diagrams of generator and receiver of the multi-valued automatic cab signalling system have been designed. It has been suggested to apply the correlation method to receive the ACS signals. Findings. To investigate the proposed CDMA-ACS system the simulation modelling has been accomplished in MATLAB in two stages: at the first stage, the CDMA-ACS system was investigated as disturbance-free; at the second stage – under the influence of powerful narrow-band disturbances (traction current harmonics). It has been found that the system shows high immunity to narrow-band harmonic disturbances. The most significant harmonics of the traction current related to the system are 250 Hz and 300 Hz, since they are the closest to the carrier frequency of 275 Hz. It has been determined that errors in decoding the ACS commands occur if the signal-to-noise ratio becomes lower than -8 dB. To reduce the influence of 250 Hz and 300 Hz, harmonics the application of additional band-reject filters was proposed. Originality. For the first time, the authors of this work carried out research on the multi-valued automatic cab signalling system with the use of wide-band pseudo-random Walsh codes. Practical value. Implementation of solutions being proposed allows improving the informativeness and interference immunity for the automatic cab signalling system, reducing the duration of command transmission from the railway track to the cab.

DETECTION OF THE DSSS SIGNAL WITH VARIABLE PN CODES USING THE ANN

- Direct sequence spread spectrum systems appeared and are used to protect the transmitted data DSSS Systems might be one of the solutions for reliable and secured communications. Also, it is one of the approaches used by signals for transmitting bandwidth larger compared to the satisfied frequency related to the original information. The communication systems of SS were vital to suppress interference, complicating the detection and processing of secure communications, the technology of spread spectrum (DSSS) has been initially created for military applications. In a traditional DSSS system, the PN code is the primary key to make the receiver recover the transmitted data. In this paper, by using the MATLAB R2020a is used to simulate the proposed system, it is considered that the transmitter sends data bits and wants to protect the sent data by making each bit send with a PN code consisting of 127 bits randomly without informing the receiver of that. here the artificial neural network (ANN) was used as a tool to find the PN code for each initial value of 7 flip-flops. so, the receiver could detect the transmitted data with BER =0.

РЕАЛІЗАЦІЯ ПІДХОДІВ ДО ІМІТУВАННЯ ДИНАМІЧНОЇ РАДІОЕЛЕКТРОННОЇ ОБСТАНОВКИ В ШИРОКІЙ СМУЗІ ЧАСТОТ

One of the main principles of the armed conflict in the east of Ukraine remains warfare in a dynamic change of complex electronic environment. The constant increase frequency bands occupancy, the use of various types of data transmission protocols necessitates an increase in the level of training of military specialists in the field of technical analysis of signals and radio emissions recognition. This, in turn, necessitates the development of approaches to simulating wideband scenarios for use in training process. The formation of the electronic environment using the technology of software-defined radio allows us to create a scenario of almost any complexity. Wideband scenarios can be generated in real time or be pre-generated and recorded in desired format. It is advisable to use the GNU Radio digital signal processing platform to develop software modules for generating real-time radio signals. Using this software it is possible to generate signals with analog and digital types of modulation, including frequency hopping and spread spectrum signals. The maximum bandwidth of the scenario corresponds to the maximum sampling frequency of the transceiver used. With this approach, you can change the power and carrier frequency of all components online. The limitations of real-time signal generation using GNU Radio are due to the fact that the bandwidth and complexity of the signal environment that can be generated depends on the performance of the computer's processor. Wideband scenario can be generated in any format using the high-level Python programming language. Further such files can be used for their analysis offline using appropriate software or as a signal source for radiation by software-defined radio systems.

Uplink grant‐free pattern division multiple access transmission scheme by exploiting poly complementary sequence

AbstractNon‐orthogonal multiple access (NOMA) technology is a key technology of the future cellular mobile communication system. It provides services for users under different channel conditions through signal superposition transmission and spectrum multiplexing. Pattern division multiple access (PDMA) is a new NOMA technology based on the overall optimization of multi‐user communication system. Since the performance of PDMA mainly depends on the gain of the pattern matrix, we propose a design scheme of uplink PDMA pattern matrix for ultra‐reliable low latency communication (uRLLC). For the interference between users is a common problem in NOMA system, first, we use poly complementary sequence (PCS) as the spread codebook to spread the PDMA transmission signal and reduce interference. Meanwhile, an uplink power control scheme is proposed. It allocates wireless resources reasonably by jointly considering the interference between users and resource blocks within users (JUR), the corresponding outage probability formula is also derived. Simulation results show that compared with the previous researches, the pattern matrix design scheme and JUR power control scheme proposed in this article have greatly improved the transmission performance. The addition of PCS spread spectrum technology can significantly reduce the block error rate and outage probability.

Design of double ring lock ring in extensible frequency clock generator chip

With the continuous development of computer technology and the continuous improvement of interface data rate, the clock frequency has reached the demand of several gigahertz, which makes the electromagnetic interference problem very serious. Spread spectrum clock is an effective method to reduce electromagnetic interference of digital chips. Therefore, this paper designs a double-loop phase-locked loop that can spread spectrum and has strong anti-electromagnetic noise interference ability. The designed dual-loop phase-locked loop can be used in the clock generator chip. The overall structure of the circuit consists of a main loop and a secondary loop. The main loop is an adjustable phase-locked loop circuit that can provide an output with a center frequency of 500MHz. The secondary loop can realize the spread spectrum function by charging and discharging the filter capacitor of the main loop loop, and at the same time, the spreading depth can be set by the feedback based on the frequency division. The dual-loop phase-locked loop designed in this paper has a good effect in spread spectrum and anti-electromagnetic interference noise.

Turbo Iterative DSSS Acquisition in Satellite High-Mobility Communications

Satellite high-mobility communications can provide global communication services for mobile terminals, which plays a vital role in today's world of wireless communications. Different from traditional terrestrial-satellite communications, high-mobility terminals impose more challenges on the direct sequence spread spectrum (DSSS) signal acquisition in satellite communications. On the one hand, the spread spectrum sequence used in satellite communication systems is relatively long, which inevitably increases the computational complexity. On the other hand, high Doppler frequency offsets and time-varying Doppler rates caused by high-mobility terminals make satellite DSSS signal acquisition become the bottleneck. To solve such a problem in high-mobility satellite communications, we propose a new acquisition algorithm based on the new factor graph where time-varying Doppler rate is modeled by the random walk model, named the turbo iterative acquisition algorithm. It consists of the constraint-detection loop and the Doppler-estimation loop. By means of soft messages passed between these loops, the negative influence of time-varying Doppler frequency offsets can be eliminated effectively. Simulation results show that, compared with traditional algorithms, the proposed algorithm improves acquisition performance more than 1.3 dB with low computational complexity, which demonstrates the superiority of the proposed algorithm in terms of acquisition performance and complexity.

FPGA implementation of LDPC soft-decision decoders based DCSK for spread spectrum applications

<span lang="EN-US">Spread spectrum (SS) communications have attracted interest because of their channel attenuation immunity and low intercept potential. Apart from some extra features such as basic transceiver structures, chaotic communication would be the analog alternative to digital SS systems. Differential chaos shift keying (DCSK) systems, non-periodic and random characteristics among chaos carriers as well as their interaction with soft data are designed based on low-density parity-check (LDPC) codes in this brief. Because of simple structure, and glorious ability to <span>correct errors. Using the Xilinx kintex7 FPGA development kit, we investigate the hardware performance and resource requirement tendencies of the DCSK</span> communication system based on LDPC decoding algorithms (Prob. Domain, Log Domain and Min-Sum) over AWGN channel. The results indicate that the proposed system model has substantial improvements in the performance of the bit error rate (BER) and the real-time process. The Min-Sum decoder has relatively fewer FPGA resources than the other decoders. The implemented system will achieve 10-4 BER efficiency with 5 dB associate E<sub>b</sub>/N<sub>o</sub> as a coding gain.</span>

Electromagnetic Interference of Spread-Spectrum Modulated Power Converters in G3-PLC Power Line Communication Systems

The impact of spread-spectrum techniques used to mitigate EMI from power converters on Power Line Communication (PLC) systems is studied in this paper. A buck converter, utilizing a Random Carrier Frequency Modulation with Fixed Duty cycle (RCFMFD) based control is considered as a source of conducted EMI and a narrowband G3-PLC as the victim. It is shown that, although considered to be an EMI mitigating technique, the spread spectrum technique has a detrimental effect on the communication channel, which can be explained in the framework of Shannon’s information theory. Conventional emission evaluation methods are therefore incompatible with modern day’s technology.

Alternative Chirp Spread Spectrum Techniques for LPWANs

Chirp spread spectrum (CSS) is the modulation technique currently employed by Long-Range (LoRa), which is one of the most prominent Internet of Things wireless communications standards. The LoRa physical layer (PHY) employs CSS on top of a variant of frequency shift keying, and non-coherent detection is employed at the receiver. While it offers a good trade-off among coverage, data rate and device simplicity, its maximum achievable data rate is still a limiting factor for some applications. Moreover, the current LoRa standard does not fully exploit the CSS generic case, i.e., when data to be transmitted is encoded in different waveform parameters. Therefore, the goal of this paper is to investigate the performance of CSS while exploring different parameter settings aiming to increase the maximum achievable throughput, and hence increase spectral efficiency. Moreover, coherent and non-coherent reception algorithm design is presented under the framework of maximum likelihood estimation. For the practical receiver design, the formulation of a channel estimation technique is also presented. The performance evaluation of the different variants of CSS is carried out by inspection of the symbol error ratio as a function of the signal-to-noise ratio together with the maximum achievable throughput each scheme can achieve.

Cancellation Techniques for Co-channel Interference in MIMO-OFDM Systems and Evaluating Their Performance

In a wireless communication system, the transmitted signal is exposed to various surfaces where it bounces and results in several delayed versions of the same signal at the receiver end. The delayed signals are in the form of electromagnetic waves that are diffracted and reflected from the various object surfaces. These result in co-channel interferences for wireless systems. MIMO has proven to be a striking solution for the new generation of wireless systems. MIMO-OFDM system with QPSK modulation is considered as the wireless system for studying the performance of interference cancellation techniques. The BER performance is studied in channels such as Rayleigh and Rician Fading Channels. The effects of interference are reduced to a certain extent by the inclusion of CDMA (spread spectrum technique) as Technique 1. The effects of interference on this system have been further reduced using the LMS filter as Technique 2. Hence, to show better performance in MIMO-OFDM systems, it is recommended to employ both CDMA and LMS filters to decrease the effects of co-channel interference. It is observed that the parameter BER reduces as the SNR increases for both these channels. Doi: 10.28991/esj-2021-01313 Full Text: PDF

Generalized Complementary Coded Scrambling Multiple Access for MIMO Communications

Spectrum efficiency is a critical performance metric in wireless communications due to an increasing demand for radio spectrum to support high data rate applications. Direct sequence spread spectrum technology enables a code division multiple access (CDMA) system a strong anti-interference capability but with a relatively low spectrum efficiency. To address this issue, complementary coded scrambling multiple access (CCSMA) (X. Liu <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al</i> ., in 2018) was proposed to use three-dimensional (space-time-frequency) resources for performance enhancement. However, in a CCSMA system, if the number of multipath returns is larger than the number of transmit (Tx) antennas, a code reuse problem occurs to degrade bit error rate performance significantly. This work designs a new scrambling code, namely generalized complementary coded scrambling multiple access (GCCSMA) codes, to overcome the code reuse problem in CCSMA. GCCSMA uses complementary codes, scrambling modulation, and multiple-input-multiple-output (MIMO) techniques jointly, which works well even in multipath channels with more paths than the number of Tx antennas. The analysis and simulations are conducted to validate the effectiveness of the proposed GCCSMA system.

A Cepstrum-Based Spectrum Sensing Approach for Detecting Spread Spectrum Signals

In this manuscript, we introduce a semi-blind spectrum sensing technique based on cepstral analysis for interweave cognitive systems. The misdetection problem of spread spectrum signals leads to erroneous sensing results, which affect the quality-of-service of a legitimate user. The simplicity and accuracy of cepstral analysis approaches make them reliable for signals detection. Therefore, we formulate the averaged autocepstrum detection technique that utilizes the strength of the autocepstral features of spread spectrum signals. The proposed technique is compared with the energy detection and eigenvalue-based detection techniques and shows reliability and efficacy in terms of detection accuracy.