Showing papers on "Direct-sequence spread spectrum published in 2022"

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.

Development of a Methodology for the Quality Management of Duplex Stainless Steels

Abstract: The use of traditional materials leads to failures and breakdowns of expensive equipment, so advanced materials are needed that can provide reliable and durable solutions. The ability to control the quality of duplex stainless steels (DSSs) can greatly help with the development of new compositions or choosing existing DSSs. In this case, it is necessary to consider the final consumer properties—corrosion resistance and mechanical properties, which depend on the phase composition, contamination with non-metallic inclusions (NMIs), and the presence of undesirable secondary phases. In this research, specimens of cast DSSs of different grades, produced at laboratory and industrial scales, were studied. A technique for quantifying the microstructure of DSSs was developed. A thermodynamic database was chosen that adequately describes the processes of phase formation in DSSs. The effects of heat treatment on the microstructure and corrosion properties of cast DSSs were studied. The effects of the structural state on the changes in consumer properties of the final product are shown. It is shown that using various deoxidation technologies, it is possible to obtain both NMIs that are dangerous in terms of corrosive activity and ones that are relatively safe.

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.

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.

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.

A Galvanic-Free Secondary-Side Control Flyback Converter with Digital Adaptive On-Time Control and Direct Sequence Spread Spectrum Technique for 15.5% Error Recovery Rate Improvement

Abstract: For today's convenient lightweight AC power adapters, the proposed galvanic-free secondary-side controlled flyback converter can reduce power modules, since the bulky pulse transformer and photo-coupler can be eliminated by using the main transformer to send the feedback control signal. The proposed direct sequence spread spectrum (DSSS) can have good encryption on the system side and improve the bit error recovery rate from 0% to 15.5%, which can tolerate large noise interference. In addition, digital adaptive on-time control is adopted to improve steady-state efficiency, with light-load and heavy-load efficiencies reaching 92% and 93.8%, respectively.

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

Implementation of an Underwater Acoustic Mobile Modem Based on the Direct Sequence Spread Spectrum Scheme

Abstract: 본 논문에서는 6.25kHz의 반송주파수에서 약 2.1kHz의 대역폭을 사용하고, 심볼당 16개의 칩심볼로 확산하여 약 97.6 심볼율을 갖는 직접수열확산 기반 수중 이동 통신 모뎀 구현에 대해 설명한다. 구현한 수중 이동 통신 모뎀은 수신기에서의 신호처리를 간단하게 하기 위해 DQPSK변조를 사용하였다. 또한, 한 패킷 길이 동안 통신 모뎀의 이동 속도가 변하는 것에 대응하기 위해 한 패킷을 20개의 부프레임으로 나누어 전송하고, 수신부에서는 부프레임별로 도플러 편이를 추정하여 부프레임별로 이를 보상하는 방법을 사용하였다. 구현한 모뎀의 실효 정보데이터 전송속도는 부호율 1/2인 Turbo 부호를 사용할 때 약 82.5bps이고, 부호율 2/3인 Turbo 부호를 사용할 때 약 109.8bps이다. 구현한 모뎀은 채널시뮬레이터를 이용하여 18m/s까지 이동속도에서 잘 동작함을 검증하였으며, 정상출력의 1/10 크기로 낮추고 5km 거리에서 성공적으로 데이터를 수신함을 실증하였다. 구현한 모뎀은 장거리 이동환경에서 단문 메시지 등을 전달하기 위한 용도로 사용될 수 있을 것이다.

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.

A Unified Waveform for Optical Wireless Integrated Sensing and Communication

Abstract: The integrated sensing and communication with optical wireless (ISAC-OW) can effectively reduce the demand of spectrum and hardware while improving the sensing resolution and data rate. However, the key challenge is to design a fully unified waveform that enables both light detection and ranging (LiDAR) and communication. To this issue, an ISAC-OW unified waveform is proposed based on quadrature phase shift keying (QPSK) and direct sequence spread spectrum (DSSS). The key idea of the proposal is to load the modulated user data on the pseudorandom noise (PN) sequence by direct spread spectrum (DSS). Subsequently, the proposed ISAC-OW system is simulated and analyzed under Gamma-Gamma atmospheric turbulence channels. The results show that our proposal can not only guarantee the excellent ranging performance of LiDAR, but also realize high-speed and reliable data transmission.

Robust Technique To Overcome Thwarting Communication Under Narrowband Jamming In Extremely Low Frequency Of Cdma-Dsss System On Coding-Based Matlab Platform

Abstract: This chapter illustrates an approach for smooth communication to mitigate the jamming under narrow band in code division multiple access (CDMA) system in case of direct sequence spread spectrum (DSSS) single user system. In security sector improvement based communication under narrowband frequency is highly demandable. An analytical as well as experimental comparison of power spectral density (PSD) of CDMA under narrowband frequency with and without jamming condition is illustrated in 334the chapter. By variation of signal power and Barker code, an optimized system is illustrated supported by bit error rate (BER) and signal to noise ratio (Eb/N) curve. Experimental fluctuation of signal power provides us low narrowband jamming as well as jamming free PSD. Variations of Spreading factor supported by Barker Code illustrate the results in favor of optimized model of the system under narrow band jamming condition. The abovementioned unique proposal of CDMA-DSSS system designing, modeling, and performance analysis are implemented using coding based MATLAB® platform.

An Interference-Tolerant Synchronization Scheme for Wireless Communication Systems Based on Direct Sequence Spread Spectrum

Abstract: In this paper, an interference-tolerant three-level synchronization scheme for wireless communication systems based on Direct Sequence Spread Spectrum (DSSS) is presented. Although the proposed synchronization scheme is demonstrated in a mixed signal IC solution, it is exportable to fully digital realizations. The proposed technique synchronizes the received pseudo-random sequence (PRS) modulated signal with the receiver (RX) reference PRS by making use of its autocorrelation properties. The proposed scheme employs 3 levels that make the proposed scheme tolerant to strong in-band interferences. Experimental results for the prototype demonstrate the capabilities of the proposed approach to achieve over 50% of clock cycle tracking even in the presence of interferences with a power of 5dB higher than the desired signal power. Fabricated in a mainstream 40nm CMOS technology, the synchronization scheme employs 100MHz PRS at TX and RX; the proposed solution consumes 18.7mW power and around 0.087mm ² silicon area.

A Narrowband Interference Reduction Technique: Embedding Modulation and Spread Spectrum in FPGA

Abstract: With the update of existing technology, technology growth has become extremely significant in all industries. Wireless communication is a popular and exciting topic in the world of communication. The demand for wireless devices are growing every day, putting a strain on bandwidth and power resources. The bandwidth is well limited to support a large number of users, but it comes at the expense of other characteristics such as interference between signals of the same bandwidth, coverage area, and so on. A single band-limited channel is used to transmit the narrowband signal. Narrowband interference is reduced using spread spectrum techniques. The narrowband signal is mixed with pseudo random noise, and the intended users can remove the noise using the same pseudo code. In order to transmit the signal to long distance with the reduced distortion, the modulation in performed on the message and spreaded. This Narrow-band suppression techniques is designed in FPGA and Performance of the system is analyzed. The combination of modulation and Spreading technique improve the system performance, power consumption. The system is analyzed with the existing technologies and it is found that estimated power for FH/BPSK is 113.45 mW in FPGA.

Implementation of FGPA based Channel Sounder for Large scale antenna systems using RFNoC on USRP Platform

Abstract: This paper concentrates on building a multi-antenna FPGA based Channel Sounder with single transmitter and multiple receivers to realize wireless propagation characteristics of an indoor environment. A DSSS signal (spread with a real maximum length PN sequence) is transmitted, which is correlated with the same PN sequence at each receiver to obtain the power delay profile . Multiple power delay profiles are averaged and the result is then sent to host. To utilize high bandwidth, the computationally expensive tasks related to generation and parallel correlation of PN sequences are moved to the FPGA present in each USRP (Universal Software Radio Peripheral). Channel sounder blocks were built using Vivado HLS and integrated with RFNoC (RF Network on Chip) framework, which were then used on USRP X310 devices.

Double-gain backscatter modulation based on chirp spread spectrum signals

Abstract: This work presents an improved active backscatter tag based on a double processing gain modulation. All wireless communications remain subject to trade-offs between range, power consumption, and data rate. This research aims to increase the backscatter range without compromising power consumption. To do this, a chirp spread spectrum (CSS) modulation is used to illuminate the tag. The idea behind this work is to bounce incoming CSS signals by modulating the switching frequency of the tag with a down-chirp of identical bandwidth and duration as the incoming signal, resulting in the reflection of a constant frequency signal with significant processing gain. To encode the tag information an On-Off Keying (OOK) modulation is used. In addition, a Barker sequence is used to further improve the detectability of the tag, providing an additional processing gain on the receiver side.

Anti-interference of Direct Sequence Spread Spectrum System Based on Wavelet and Eigenvalue Decomposition

Abstract: Limited by the processing gain of the spread spectrum system, the high power interference in the satellite space-to-earth communication cannot be suppressed effectively. It will bring high Bit Error Rate(BER) to the telemetry、track and command(TT&C) link. Based on the analysis of the Direct Sequence Spread Spectrum (DSSS) system in anti-interference, a method of anti-interference in DSSS is proposed in this paper. Combining the advantages of Wavelet Transform(WT) in singularity detection and Eigenvalue Decomposition(ED) in blind source separation, the method based on WD and ED is proposed. The simulation results indicate that the method can suppress the interference effectively and will improve the anti-interference ability of DSSS.

Combating Stealthy Thermal Covert Channel Attack With Its Thermal Signal Transmitted in Direct Sequence Spread Spectrum

Abstract: Many-core systems are susceptible to attacks launched by thermal covert channel (TCC) attacks. Detection of TCC attacks often relies on the use of threshold-based approaches or variants, and a countermeasure to thwart the channel can be applied only after an attack is deemed to be present. In this article, we describe a direct sequence spread spectrum (DSSS)-based TCC, where its thermal data are modulated by a pseudo-random bit sequence. Unfortunately, such DSSS-based TCC has an extremely low signal strength that the signal is nearly indistinguishable from the noise and thus cannot be detected by any existing threshold-based detection methods. To combat this stealthy TCC, we propose a novel detection scheme that lets the received signal pass through a differential filter where irrelevant frequency components occupied mainly by the noise gets eliminated and the filtered signal is next compared against a threshold for successful detection. Experimental results show that the DSSS-based TCC can effectively survive detection by the existing detection methods with its BER as low as 4%. In contrast, with the proposed detection and countermeasure applied, the detection accuracy jumps to 89%, and the BER of the DSSS-based TCC soars to 50%, which indicates that the TCC is practically shut down.

Expansion the signal spectrum by increasing the bandwidth through the channel

Abstract: Preventing interference is the main advantage of Spread Spectrum communication technique, this is crucial in different intelligent applications such as Narrowband Internet of Things (NB-IoT). The concept behind spread spectrum is using more bandwidth than the original data message without changing the signal power, this generates a signal that does not have a clearly distinguishable peak, which makes the signal hard to jam or intercept. Through the use of the spectrum spread process, exercises of interference and interruption are intended. The jamming process is a congestion process for the transmitted signal. However, with increasing bandwidth, several challenges occur. This paper presents the challenges of Spread Spectrum in regards to increasing bandwidth and proposes a modulation technique that uses frequency-hopping spread spectrum (FHSS) and direct sequencing. So bandwidth increasing has used both above techniques which resulted in low band of spectrum is modulated, while the high band is parameterised.

High-Reliability Underwater Acoustic Communication Using an M-ary Cyclic Spread Spectrum

Abstract: Multipath propagation, frequency selective fading, low-propagation velocity, and narrow bandwidth are all characteristics of underwater acoustic channels. Doppler shifts and diffusions can occur as a result of the low transmission speed of an acoustic signal, which can be caused by the movement of ocean currents or the transceiver. Furthermore, frequency selective fading and excessive noise interference can disrupt underwater acoustic communication on a continual basis. Because of its high anti-interference ability and high confidentiality, spread spectrum technology is commonly adopted in underwater acoustic communications. Although the direct sequence spread spectrum method has a low data rate, it is advantageous in a multipath propagation channel environment or an environment with a low signal-to-noise ratio (SNR). This advantage is suitable for long-distance transmission or LPD (Low Probability of Detection) communication, and the direct sequence spread spectrum method is applied. In this paper, we propose a highly reliable M-ary cyclic spread spectrum technique by superimposing the M-ary spread spectrum, an extension of the direct sequence spread spectrum technique, and cyclic shift keying. Furthermore, by estimating the Doppler frequency using M-ary spread spectrum codes and performing synchronization correction of the ensuing symbol based on the estimation results, higher performance can be attained. Simulations and experiments showed that the M-ary cyclic spread spectrum method can reduce Doppler estimation and synchronization error accumulation while maintaining a high data rate. Furthermore, the MCSS method had a lower bit error rate than the standard spread spectrum method.

Anti-Jamming Wireless Communication Using Chaos-Based Code Selection Spread Spectrum Technique

Abstract: Physical layer performance of wireless communication, which is subjected to reactive jamming attack, is analyzed in this paper. The main problem in conventional direct sequence spread spectrum (DSSS) is the requirement of pre-shared key between sender and receiver. Many researchers focused to remove pre-shared keys for anti-jamming communication, but in those techniques, it requires enough time to de-spread the data. So to overcome the problem of pre-shared key and to enhance the security of wireless communication with minimum de-spreading time, chaos-based code selection (CCS) DSSS has been proposed in this paper. Matlab simulation results show that our proposed technique CCS DSSS indicates much better performance when compared with other unshared secret spreading keys in terms of security and de-spreading time. The de-spreading time required to extract the original message of size 512 bits is almost 0.05888 ms, which is minimum compared with other unshared secret spreading key spread spectra.

Direct sequence spread spectrum for QAM-16 with Rayleigh and AWGN channels for rake receiver

Abstract: In communication, wireless communication is most popular, but there are number of challenges to implement these systems. In digital communication, to decrease the complete interference in signal, Spread Spectrum is a special system designed. A DS-SS(Direct Sequence Spread Spectrum) is described here in the paper with both Rayleigh and AWGN channels using Quadrature Amplitude Modulation (QAM). It has been observed that results obtained are better AWGN channel as compared to Rayleigh channel.

Research on Spread Spectrum Signal Acquisition

Abstract: Compared with conventional communication systems, spread spectrum communication system has the advantages of anti-interference, multiple access multiplexing, strong confidentiality and so on. Therefore, spread spectrum communication has been widely used in civil and military fields. Acquisition is one of the core technologies of spread spectrum communication system. How to capture spread spectrum signal in the case of low signal-to-noise ratio and large Doppler frequency offset becomes the most critical link for the establishment of spread spectrum system. This scheme adopts a two-dimensional acquisition method based on FFT, which can combine time-domain search and frequency-domain search, and provide a two-dimensional spread spectrum signal acquisition method with high-precision through matched filter.

Frequency hopping spread spectrum: History, principles and applications

Abstract: Introduction/purpose: The frequency hopping spread spectrum (FH-SS) technique assumes the carrier generated by the syntesizer to hop from frequency to frequency over a wide bandwidth, according to a pseudonoise code sequence defined by the code sequence generator. The article presents the history, principles and applications of the FH-SS technique. Both military and commercial applications are discussed. Methods: This article presents an overview of data from the technical literature, with appropriate comments. Results: After presenting the history and principles of the FH-SS technique, the article summarizes its use with examples of military and commercial applications. The importance of using FH-SS in the described applications is highlighted. Conclusion: The FH-SS technique has been successfully implemented in many military and commercial technologies due to its high protection against interference, making communication difficult for reconnaissance and eavesdropping, and its ability to provide code division multiple access.

Research and Implementation of a Tamed Spread Spectrum System Based on Walsh Coding

Abstract: Spread spectrum communication is well-known by its excellent ability of anti-interference, anti-fading and good performance in confidentiality. The tamed spread spectrum communication system is developed on the basis of it. Most of the literature does not distinguish this spread spectrum technique from direct spread spectrum. In this paper, the performance of tamed spread spectrum with single -frequency interference is analyzed and simulated compared with direct spread spectrum. The conclusion is drawn that the tamed spread spectrum technology has a strong ability to resist random noise interference, but for human interference, its performance is seriously declined. The FPGA implementation method of tamed spread spectrum communication system is mainly studied as well.

Code Index Modulation CSK Spread Spectrum Underwater Acoustic Communications

Abstract: Limited bandwidth restricts the data rate of spread spectrum underwater acoustic communication systems. In this paper, we propose a novel high-rate spread spectrum underwater acoustic communication approach, which utilizes spread spectrum code index modulation (CIM-SS), cyclic shift keying (CSK) and maximum ratio combined frequency domain equalization (MRC-FDE). In this approach, information bits are jointly conveyed by CIM, CSK and the M-ary PSK modulated symbols. PeCAN polyphase sequences with excellent correlation characteristics are used as spreading codes, and spreading code index modulation is to select spreading code from predefined spreading code set. CSK uses the cyclic shifted version of the selected spreading codes to obtain higher transmission efficiency than direct sequence spread spectrum (DSSS) system. A low complexity detector is designed at the receiver to detect the code index and cyclic shift value of the selected spreading code, so as to despread and demodulate the symbols. Simulation and lake experiment show that the proposed method can improve the data rate and spectrum utilization, and resist the underwater acoustic multipath effect.