M-ary Spread Spectrum Research Articles

Doppler Compensation Techniques for M-Ary Sequence Spread Spectrum Signals Based on Correlation Cost Factors in Mobile Underwater Acoustic Communication

Unlike terrestrial radio, the speed of sound in the ocean is relatively slow, which results in mobile underwater M-ary spread spectrum communication typically exhibiting significant and variable multipath effects along with strong Doppler effects, leading to rapid carrier phase shifts in the received signal that severely impact decoding accuracy. This study aims to address the issue of rapid carrier phase shifts caused by significant time-varying Doppler shifts during mobile underwater M-SS communication. This paper innovatively proposes a method for updating matched filters based on correlation cost factors. By calculating the correlation cost factors for each received symbol, the method guides the direction of Doppler estimation and updates the matched filters. After identifying the optimal match, the received symbols are shifted, correlated, and decoded. Simulation and sea trial results indicate that this method demonstrates higher computational efficiency and improved decoding accuracy compared to traditional Doppler estimation matched filters under low signal-to-noise ratio conditions, and exhibits greater robustness under complex motion conditions.

Design and simulation of soft decision decoding based on chaotic M-ary spread spectrum system

In this paper, chaos sequence is used to replace the traditional spread spectrum sequence. From the perspective of the communication partner, a new method of generating the initial value of chaotic sequence is proposed, which is more suitable for the multi-base spread spectrum system and easy to extract. In order to further improve the error performance of the system and ensure the integrity of the system, an improved suboptimal soft information extraction method based on log-likelihood ratio (LLR) is proposed in the channel coding module, which can further improve the error performance of the system. On this basis, we choose the synchronization mode of multiple transmission of one reference signal to solve the problem that chaotic sequence is difficult to obtain synchronization because of its aperiodic characteristics. Finally, the system is simulated in the channel with low SNR. The simulation results show that chaotic sequence as spread spectrum code can make the signal transmit accurately in the worse channel environment. The performance gain of applying soft information decoding decision in the multibase spread spectrum system with chaotic sequence as spread spectrum code can reach 5.2 dB compared with the traditional direct spread spectrum system.

Recursive Decoding Based Multi-channel M-ary Spread Spectrum Underwater Acoustic Communication

The spread spectrum communication method has strong anti-noise and anti-fading capability, but it also brings the problem of low information transmission efficiency. The paper proposes a multi-channel M-ary spread spectrum communication method, using a recursive decoding algorithm to reduce the communication bit error rate. In combination with the channel equalization technique based on the virtual time reversal mirror technique, the scheme improves the communication rate of spread spectrum communication. It is verified through computer simulation and sea trial data that the communication method can effectively reduce the mutual interference between different channel signals, which provides a new idea for the design of hydroacoustic spread spectrum communication scheme.

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

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.

Long-range underwater acoustic communication of M-eyry spread spectrum with cyclic prefix

The Spread Spectrum is an effective transmission method for complex channels in underwater acoustic (UWA) communication because of the high correlation of pseudo-random noise (PN) sequence. In particular, the spread spectrum method is effective in an environment with a low signal-to-noise ratio. The bandwidth of UWA communication channel is limited due to the fact that sound wave attenuation in water is positively associated with frequency. The limited bandwidth directly leads to the low data rate of conventional direct-sequence spread spectrum UWA communication. M-ary spread spectrum (MSS) schemes using multiple orthogonal PN sequences were proposed as a solution to this problem. However, even in the MSS method, the performance may be limited by the delay spread characteristics in the multipath propagation channels. We propose a more robust communication method in the UWA channel by including Cyclic Prefix (CP) to achieve a more robust performance in the multipath channel. In the proposed method, a CP is inserted for every symbol. In the 160 km long-range UWA communication experiment conducted in the East Sea, the proposed method showed more reliable results than the conventional MSS method. [Work supported by the Agency for Defense Development, South Korea, Grant No. UD200010DD.]

Deep learning-based M-ary spread spectrum communication system in shallow water acoustic channel

A deep learning-based M-ary spread spectrum (SS) underwater acoustic (UWA) communication system is proposed. The long short-term memory (LSTM) model is used as the receiver of the system, enabling the direct demodulation of received signals without de-carrier and de-spreading operations. LSTM architecture-based neural network models are fed with the time-domain waveform of each symbol during the training process to learn the source information carried by each symbol. Simulation results show that the deep learning-based M-ary SS UWA communication system outperforms the conventional system under the low signal-to-noise ratio and complex shallow water acoustic channel. For optimal performance, different LSTM models can be selected according to the simulation conditions. Furthermore, a water tank experiment simulating the complex shallow water channel was conducted and the results show that experimental equipment, different training sample acquisition methods, and LSTM models can affect the performance of the system.

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

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.

Optimized Doppler Estimation and Symbol Synchronization for Mobile M-ary Spread Spectrum Underwater Acoustic Communication

In mobile underwater acoustic (UWA) communications, the Doppler effect causes severe signal distortion, which leads to carrier frequency shift and compresses/broadens the signal length. This situation has a more severe impact on communication performance in the case of low signal-to-noise ratio and variable-speed movement. This paper proposes a non-data-aided Doppler estimation method for M-ary spread spectrum UWA communication systems in mobile scenarios. The receiver uses the spread spectrum codes dedicated to transmitting signals with different frequency offsets as local reference signals. Correlation operations are performed symbol by symbol with the received signal. The decoding and Doppler estimation of the present symbol are achieved by searching the correlation maximum in the code domain and frequency domain. The length of the current symbol is corrected for the next symbol synchronization using the estimated Doppler coefficient. To optimize the process of Doppler estimation and symbol synchronization, a heuristic search method is used. By adjusting the Doppler factor search step size, setting the threshold value, and using the Doppler factor estimation of the previous symbol, the search range can be significantly reduced and the computational complexity decreased. The Fisher-Yates shuffle algorithm is used to traverse the search range to ensure reliability of the results. Simulation results show that enlarging the frequency-domain search step size in some degree does not affect the decoding accuracy. On 15 May 2021, a shallow-water mobile UWA spread spectrum communication experiment was conducted in Weihai, China. The horizontal distance between the transmitter and the receiver is 3.7–4.0 km, and the communication rate is 41.96 bits per second. The transmitting ship moves at a speed of 0–3 m/s, and the bit error rate (BER) is lower than 1e−3, which is better than that of the sliding correlation despreading method with average Doppler compensation.

Mapping Algorithm of Multi - code combination spread spectrum technology for Short Packet Transmission

Multi-code combined spread spectrum (MCSS) is based on M-ary spread spectrum to improve information payload by combining multiple spread spectrum sequences, which solved the contradictions between spread spectrum gain and transmission efficiency under limited channel bandwidth conditions. This paper focuses on two mapping algorithms of multi-code combination spread spectrum and their decoding algorithms for MCSS, which transmits the information by combining multiple spreading sequences. The R-combined mapping algorithm is provided to keep the sequence orthogonal and the design complexity increases with the increase of the number of correlators at the receiver while the SVC algorithm is adopted and MMP algorithm is used to realize multi-code combination spread spectrum with increasing sequences. The BER performance of the two algorithms is compared through simulation analysis

Performance of orthogonal stochastic code signals in the presence of delayed interference

This article provides analytical expressions for performance evaluation of hybrid FH-DSSS system in delayed interference and fluctuation noise presence. Delayed interference is quite common in environment with multiple obstacles, occurring as consequence of signal reflection and multipath propagation (fig. 1). Introduction describes known methods of mitigating this interference many of whom include either use of direct sequence spreading or some variation on hybrid sequence spreading including pseudo random frequency hopping and periodical signal ensemble change. To improve on those methods considered dynamic program method for orthogonal stochastic spread spectrum code generation based on Viterby algorithm [6]. Section 1 of the paper describes FH-DSSS signal, it’s delayed interference, equation corresponding to their sum on the receiver input and noncoherent correlator response to it. By using Gaussian approximation, expressions derived for equivalent signal/noise level estimation and corresponding average probability of error at the output of the correlation receiver. By including actual signal statistic, like code length and cross-correlation value, final expressions (8)–(15) allow for accurate estimation of correlation receiver response to signal sequences with specific spread spectrum codes, as well as calculation for probability of error for M-ary spread spectrum communication system in delayed interference presence. Accuracy of the Gaussian approximation is examined in section 2 of the paper based on comparisons between analytical results and simulation modeling. Numerical results obtained, which showcase dependence of system performance on various signal characteristics, such as correlation properties, spreading code length, signal ensemble size and frequency hop delay time. Plotted graph on fig. 2 shows advantage from using M-ary orthogonal signals over binary in delayed interference presence for code sequences with length N = 32, 64, 128. Graph on fig. 3 shows gains from frequency hopping when interference delay equals to approximately half of signal information symbol. In the end performance gains from using hybrid FH-DSSS system under electronic suppression by delayed interference is also evaluated. As shown on fig. 4,a system performance significaly depend on value of delay between received signal and it’s delayed copy.

Generation of Orthogonal Sequence Sets for M-ary Spread Spectrum Communications with OFDM Modulation

The number of orthogonal sequences is a key point of M-ary spread spectrum (MSS) communication system since more sequences mean higher data rate. When orthogonal frequency division multiplexing (OFDM) modulation is used into MSS system, the additional low peak-to-average power ratio (PAPR) property is required due to high power efficiency. Based on the segmentation-shift operation, multiple orthogonal sequence sets with the same size and sequence length are generated in this paper. By combining these orthogonal sequence sets, the number of the generated orthogonal sequences is very large. For any two orthogonal sequence sets, there exists good cross-correlation performance between them at zero shift. In addition to large set size and good correlation property, the generated multiple orthogonal sequence sets possess low PAPR, which is very suitable for OFDM modulation. The generation algorithm of multiple orthogonal sequence sets is provided in this paper, and the corresponding simulation results show the effectiveness of the provide method.

Mapping Obfuscation-Based PHY Security Scheme for Resource-Constrained Wireless Sensor Network

ABSTRACT Wireless sensor network (WSN) physical layer (PHY) uses M-ary spread spectrum (MaSS). This paper explores MaSS and emphasizes that based on the implementation approach; the technology has the potential to provide security at the PHY of wireless devices. The MaSS parameters, namely, spreading sequences and symbol to sequence mapping logic, can be obfuscated for security implementation. In this paper, we have focused our analysis on obfuscating mapping logic, i.e. Mapping Obfuscation (MO). Mathematical analysis reveals that an eavesdropper with processing speed in the order of 1018 operations/sec can intercept and decode short length (maximum 8–10 bytes) packets in <100 s. Simulation exposes that the eavesdropper can achieve a success rate of 50% for short-length packets if its signal-to-noise ratio exceeds −1 dB. An attacker has only one check metric for mapping sequence detection that is correct frame check sequence (FCS) detection. However, FCS detection may be misleading; if packet-embedded FCS and eavesdropper-generated FCS are the same for the wrong mapping sequence. For MO-based MaSS, false FCS detection probability is 30 times more than valid FCS detection probability. To reduce false FCS probability attacker need to analyse multiple radio frequency (RF) packets for detecting a valid mapping key; this increases the computation time. For MO-based PHY security, correct mapping sequence identification by exhaustive search demands cluster-based parallel processing.

An image-in-image communication scheme using secret sharing and M-ary spread spectrum watermarking

Secret image sharing is a means of secure transmission of images on an open network through meaningful share generation that reduces suspiciousness of conventional image encryption. This paper proposes, an image-in-image communication scheme as SIS for progressive quality access control coupled with data hiding. The secret image is partitioned into few noise-like shadows of reduced size. These are then embedded into a group of host images to generate stego images. Since spread spectrum watermarking meets data imperceptibility and retain hidden data even after different deliberate attacks and unintentional operations, an M-ary SS modulation based watermarking scheme is performed to embed the shadows into the respective set of cover images. Progressive quality access for the secret image depends on the number of the authenticated users participated in the decoding process. Extensive simulation results are reported to highlight the performance of the proposed scheme.

An Effective Scheme of M-Ary Spread Spectrum System Based on Orthogonal Spread Spectrum and CPSK

A hybrid M-ary spread spectrum (SS) communication scheme which combined with orthogonal SS and CPSK technique is proposed. Based on dual orthogonal SS, every SS code is treated as original code to adopt CPSK modulation, the unattached synchronous code is chosen to achieve system synchronization. At the receiver, A circular correlator based on transform domain processing is employed to de-spread the received signals. Compared with M-ary SS and CPSK, the proposed scheme is able to obtain higher bandwidth efficiency, stronger anti-intercept capability, and better synchronous performance. The Monte-Carlo simulation results demonstrate that the proposed scheme can achieve better synchronous and bit error rate (BER) performance under additional white gauss noise channel models.

Orthogonal multicarrier M-ary cycle shift keying spread spectrum underwater acoustic communication

To solve the problem of low bandwidth efficiency of underwater acoustic spread spectrum communication, a multicarrier modulation scheme combined with M-ary spread spectrum and cycle shift keying (CSK) is proposed in this paper. The code sequences chosen by M-ary modulation are then modulated by CSK, simultaneously, they are modulated by the orthogonal multicarrier. The approach enhances the bandwidth efficiency greatly. The performances of the system with m-sequence, Kasami-sequence, and Gold sequence as the code sequence are compared over the underwater acoustic multipath channel with the same data rate and the same bandwidth. The simulations and the results of pool experiment show that m-sequence as the code sequence performs best and Gold sequence performs worst. The number of the m-sequence is limited. In order to increase the data rate further and make the performances of other sequences close to the m-sequence, a new approach to suppressing the inter-carrier interference (ICI), named multiple sequences, is proposed. The approach can greatly suppress the ICI caused by multipath and make the performance close to the performance of the m-sequence.

Orthogonal code shift keying spread spectrum underwater acoustic communication

Code shift keying (CSK) is generally used to overcome the spreading gain versus data rate limitation in underwater acoustic (UWA) communication as generalized M-ary spread spectrum technology. In addition, the concept of orthogonal CSK is introduced into the UWA communication to achieve higher rate, mitigate crosstalk from the other thoroughfare and utilize the redundant information of CSK adequately. In this paper, we propose a new scheme employing orthogonal double thoroughfare CSK spread spectrum UWA communication with utilizing code phase information combined. First, each symbol integration output form of the proposed method is deduced. Furthermore, the property of orthogonal CSK is analyzed and its bit error rate is investigated as compared with conventional CSK and double thoroughfare CSK via simulation. Finally, the validity of simulation comparison is verified in experiment. 580.6 bps data rate of the proposed communication scheme is realized in 104 bit volume and 4 kHz bandwidth efficiently. It is shown that the proposed method provides significantly improved communication performance through formula, simulation and test.

M-ary code shift keying spread spectrum underwater acoustic communication

Aiming at the low data rate of traditional direct sequence spread spectrum, M-ary spread spectrum and code shift keying underwater acoustic spread spectrum communication, a new combine method of M-ary code shift keying underwater acoustic spread spectrum communication is proposed based on the small Kasami sequence with good self and mutual correlation. Different sequence information and the same sequence code phase information are used in this method. The influences of self and mutual correlation function on M-ary code shift keying underwater acoustic spread spectrum communication over gaussian and fading channel are analyzed. The performances under the two kinds of channels are simulated. The simulation shows that the ability for M-ary code shift spread spectrum to overcome the noise is better than for the direct sequence spread spectrum, M-ary spread spectrum and code shift keying spread spectrum. The comparative experiment is conducted to compare the M-ary spread spectrum, code shift keying spread spectrum and M-ary code shift keying spread spectrum in the pool. The M-ary code shift keying communication rate of 256.3 bps with no transmitting error in 104 bit data volume is realized.

Sparse acoustic response function estimation with a mixture Gaussian model

Underwater acoustic response functions at high frequencies and large bandwidths exhibit significant spatio-temporal variability that depends greatly on volume, boundaries, and the source–receiver motion. Considered here is a mixture Gaussian assignment over Doppler, beam-angle, and channel bandwidth employed to describe the behavior of the sparse acoustic response function over received signal duration, aperture, and bandwidth. Accurate modeling of the dependence between the mixture components can be handled by considering dependence among neighboring indicator variables of the mixture assignment. This allows for a more accurate and adaptable description of the natural persistence that acoustic paths exhibit and improve channel estimation quality. This adaptive structure is applied to underwater M-ary spread spectrum acoustic communication transmissions during the MACE10 experiment of the coast of Martha's Vineyard at near 10 kHz of bandwidth and at ranges of 1 and 2 km. Posterior conditional expectations of the acoustic response are compared with least squares type estimates and performance is quantified in terms of the observed bit error rate (BER) as a function of received SNR. A BER = E-6 at rSNR = −16 dB for 12 element combining is demonstrated. [This work is supported by the Office of Naval Research and by NISE BAR.]

Cyclic shift keying spread spectrum underwater acoustic communication

Aimed at solving the problem of low data rate of direct sequence spread spectrum underwater acoustic communication and that of complexity of the receivers of M-ary spread spectrum underwater acoustic communication, cyclic shift keying spread spectrum underwater acoustic communication is proposed based on the good characteristic of spread sequences. At the transmitter, base waveform is cyclically shifted according to the input information. At the receiver, only one correlator is used to estimate the time delay and decode. Multi-code spread spectrum based on cyclic shift is presented. Lake experiments at both middle and long range were conducted for the proposed methods. Single and two code cyclic shift keying underwater acoustic communication were realized in the range of 15 km and the bandwidth of 2 kHz. The data rate was 438 bit/s with bit error ratio around 10-2—10-5. The result demonstrated the bandwidth efficiency and low complexity of the proposed methods and the applicability for long range underwater acoustic communication and multi-user underwater acoustic communication network.

Studies on Novel Anti-jamming Technique of Unmanned Aerial Vehicle Data Link

Based on the M-ary spread spectrum (M-ary-SS), direct sequence spread spectrum (DS-SS), and orthogonal frequency division multiplex (OFDM), a novel anti-jamming scheme, named orthogonal code time division multi-subchannels spread spectrum modulation (OC-TDMSCSSM), is proposed to enhance the anti-jamming ability of the unmanned aerial vehicle (UAV) data link. The anti-jamming system with its mathematical model is presented first, and then the signal formats of transmitter and receiver are derived. The receiver's bit error rate (BER) is demonstrated and anti-jamming performance analysis is carried out in an additive white Gaussian noise (AWGN) channel. Theoretical research and simulation results show the anti-jamming performance of the proposed scheme better than that of the hybrid direct sequence frequency hopping spread spectrum (DS/FH SS) system. The jamming margin of the OC-TDMSCSSM system is 5 dB higher than that of DS/FH SS system under the condition of Rician channel and full-band jamming, and 6 dB higher under the condition of Rician channel environment and partial-band jamming.