A Novel Time-Delay Estimation Methodology Based on Spread Spectrum Communications

The research on the balance of chaotic sequence has important significance to spread-spectrum communication. The relationship between the balance and the parameter of four typical chaotic maps (Chebyshev, improved Logistic, Logistic and Tent) was discussed. The new numeric ranges of initial value and fractal parameter were decided, which provided reference for the generation of chaotic spread-spectrum sequence. Through the graphs of the four chaotic sequences' balance and the error-bit rate performance of these systems with the four chaotic sequences' map parameters, the new numeric ranges were validated. Both simulation results and the analysis show that the balance of Chebyshev is the best.

Chaotic spread spectrum sequence is an important element in spread spectrum communication. To m sequences and Gold sequences with finite length and number, a new method for improved Chebyshev chaotic sequence is generated by the mixed iteration of the Tent map and Chebyshev map. It has a great significance to quantitative analysis of the new sequence generated by the improved Chebyshev mapping, and it can adapt the spread spectrum communication well in MC-CDMA system. Select m sequence, Gold sequence and improved Chebyshev chaotic sequence as the spread spectrum sequence through the BPSK modulation mode in the MC-CDMA downlink to simulation experiment. It can be proved that the error performance of the improved Chebyshev sequence is better than the other two sequences, and reveal the variation of the system error rate of the signal to noise ratio based on performed and analysis.

Low-density parity-check (LDPC) codes are commonly used in communication systems to improve the system performance, but LDPC codes takes too long for decoding, making communication inefficient and unsuitable for short-frame data transmission methods. In underwater acoustic channels, spread-spectrum communication becomes an effective way to realize long-distance communication. This paper combines short-block LDPC codes with a direct sequence spread spectrum and soft spread spectrum in underwater acoustic communication, addressing the problem of the inapplicability of conventional LDPC codes. The applicability of the proposed method in this paper is verified through simulation tests and pool experiments. The results indicate that the proposed communication system achieves lower bit error rates compared to the classical coding methods used in underwater acoustic spread-spectrum communication systems under the same channel conditions.

Spread spectrum communication is a typical scheme for covert communication because of its low detectability and antijam characteristic. However, the associated design concerns multiple factors, such as cochannel multiple access interference (MAI) and spread spectrum gain. In this paper, the lattice reduction theory is applied to MAI cancellation of spread spectrum communication and a novel lattice reduction aided multiple user detection method is proposed. The near maximum likelihood (ML) performance of MAI resistance is verified by simulation and theoretical analysis. The superiority of detection performance in strong MAI scenarios is especially addressed. Based on the algorithm, a collaborative covert communication system design is proposed. Low-power covert signals can be transmitted at a higher bit rate with the same coverage as more high-power cochannel signals. The covert transmission performance can be improved significantly compared to traditional designs.

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

Communication using power line as a medium of signal transmission offers a convenient and inexpensive solution for multimedia signal transmission and control applications. This paper aims to present a de-noising scheme which is a combination between chaotic spread spectrum sequence system and the wavelet transform in power line communications (PLC). The proposed communication scheme is based on two key ideas. The first concept consists of the use of the spread-spectrum based on chaotic sequence in order to minimize interference caused by the power line and to secure the transmission information. The second idea consists of the use of discrete wavelet transform to reduce the noise from a chaotic sequence. Signal-to-noise (SNR) and root mean squared error (RMSE) are made. Analyses of bit error rate (BER) illustrate the superior communication performance of the proposed PLC de-noising scheme based on chaotic spread spectrum and wavelet.

In-Band Full-Duplex (IBFD) Underwater Acoustic (UWA) communication technology can transmit and receive communication signals in the same frequency band at the same time. Theoretically, its frequency utilization efficiency can reach twice of the traditional half-duplex (HD) UWA communication systems. Therefore, it holds great research significance and application value for UWA communication where available spectrum resources are seriously limited. The main challenge in the implementation of IBFD-UWA communication system is to counteract the local self- interference (SI) signal. Generally, SI cancellation (SIC) can be divided into three main aspects, namely, SI suppression in space, SIC in analog domain and digital domain. Digitally Assisted Analog SIC (DAA-SIC) is concerned as it can deal with complexSI propagation channel. However, in the implementation process of the DAA-SIC scheme, its performance will be affected by hardware conditions, such as the effective number of bits of analog to digital converter (ADC) of auxiliary acquisition link, non-linear distortion of power amplifier (PA) and so on. To deal with the influence of hardware parameters on the performance of DAA-SIC scheme, this paper proposes a new analog SIC scheme. The core of this scheme is to reconstruct the output signal of PA and reduce the non-linear distortion of power amplifier and the influence of effective number of bits of auxiliary link through Memory Polynomial (MP) model and Digital Pre- Distortion (DPD) process. The performance of the existing scheme and the new DAA-SIC scheme is verified by numerical simulation. The simulation results show the effectiveness of the proposed scheme.

As the widely investigation of chaotic sequence in the application of communication, binary and quaternary phaseshift keying modes have been extensively adopted in spread spectrum communication. Based on Chebyshev chaotic mapping, binary-phase and quadric-phase chaotic spreading sequences are generated, and the relationship among the performance of balance and fractal parameter, initial value and the period of sequence are analyzed. The non-balanced points which should be avoided in the chaotic sequence when applying in CDMA system are proposed. Aiming at the problem which the conventional degree of balance functions only investigates the balance of the 2- valued sequence, the maximum balanced difference method is proposed. The definition of maximum balanced difference is proposed. We analyze the balance performance of quadric-phase Chebyshev sequence. Experimental results show that the maximum balanced difference function can replace the traditional binary-phase degree of balance function to research the balance of digital 2-valued and multi-valued sequence, which has better universality.

In this letter, the weighted fractional Fourier transform (WFRFT) is performed on the chaotic sequence to enhance the security of the chaotic direct sequence spread spectrum (CD3S) communication, and a WFRFT-CD3S system that spreads the information bits through the WFRFT-chaotic sequence is proposed. In the proposed system, the transmitter scrambles the phase space trajectory of the chaotic sequence through WFRFT and make the distribution of the transmitted signal be Gaussian-like. The receiver synchronizes the WFRFT-chaotic sequence through bidirectional correlation search and demodulates the information through the synchronized local WFRFT-chaotic sequence. Simulations are implemented to evaluate the security performance, synchronization performance, and demodulation performance of the proposed system.

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.

Preface. 1 Spread spectrum signals and systems. 1.1 Basic definition. 1.2 Historical sketch. 2 Classical reception problems and signal design. 2.1 Gaussian channel, general reception problem and optimal decision rules. 2.2 Binary data transmission (deterministic signals). 2.3 M-ary data transmission: deterministic signals. 2.4 Complex envelope of a bandpass signal. 2.5 M-ary data transmission: noncoherent signals. 2.6 Trade-off between orthogonal-coding gain and bandwidth. 2.7 Examples of orthogonal signal sets. 2.8 Signal parameter estimation. 2.9 Amplitude estimation. 2.10 Phase estimation. 2.11 Autocorrelation function and matched filter response. 2.12 Estimation of the bandpass signal time delay. 2.13 Estimation of carrier frequency. 2.14 Simultaneous estimation of time delay and frequency. 2.15 Signal resolution. 2.16 Summary. Problems. 3 Merits of spread spectrum. 3.1 Jamming immunity. 3.2 Low probability of detection. 3.3 Signal structure secrecy. 3.4 Electromagnetic compatibility. 3.5 Propagation effects in wireless systems. 3.6 Diversity. 3.7 Multipath diversity and RAKE receiver. Problems. 4 Multiuser environment: code division multiple access. 4.1 Multiuser systems and the multiple access problem. 4.2 Frequency division multiple access. 4.3 Time division multiple access. 4.4 Synchronous code division multiple access. 4.5 Asynchronous CDMA. 4.6 Asynchronous CDMA in the cellular networks. Problems. 5 Discrete spread spectrum signals. 5.1 Spread spectrum modulation. 5.2 General model and categorization of discrete signals. 5.3 Correlation functions of APSK signals. 5.4 Calculating correlation functions of code sequences. 5.5 Correlation functions of FSK signals. 5.6 Processing gain of discrete signals. Problems. 6 Spread spectrum signals for time measurement, synchronization and time-resolution. 6.1 Demands on ACF: revisited. 6.2 Signals with continuous frequency modulation. 6.3 Criterion of good aperiodic ACF of APSK signals. 6.4 Optimization of aperiodic PSK signals. 6.5 Perfect periodic ACF: minimax binary sequences. 6.6 Initial knowledge on finite fields and linear sequences. 6.7 Periodic ACF of m-sequences. 6.8 More about finite fields. 6.9 Legendre sequences. 6.10 Binary codes with good aperiodic ACF: revisited. 6.11 Sequences with perfect periodic ACF. 6.12 Suppression of sidelobes along the delay axis. 6.13 FSK signals with optimal aperiodic ACF. Problems. 7 Spread spectrum signature ensembles for CDMA applications. 7.1 Data transmission via spread spectrum. 7.2 Designing signature ensembles for synchronous DS CDMA. 7.3 Approaches to designing signature ensembles for asynchronous DS CDMA. 7.4 Time-offset signatures for asynchronous CDMA. 7.5 Examples of minimax signature ensembles. Problems. 8 DS spread spectrum signal acquisition and tracking. 8.1 Acquisition and tracking procedures. 8.2 Serial search. 8.3 Acquisition acceleration techniques. 8.4 Code tracking. Problems. 9 Channel coding in spread spectrum systems. 9.1 Preliminary notes and terminology. 9.2 Error-detecting block codes. 9.3 Convolutional codes. 9.4 Turbo codes. 9.5 Channel interleaving. Problems. 10 Some advancements in spread spectrum systems development. 10.1 Multiuser reception and suppressing MAI. 10.2 Multicarrier modulation and OFDM. 10.3 Transmit diversity and space-time coding in CDMA systems. Problems. 11 Examples of operational wireless spread spectrum systems. 11.1 Preliminary remarks. 11.2 Global positioning system. 11.3 Air interfaces cdmaOne (IS-95) and cdma2000. 11.4 Air interface UMTS. References. Index.

Chaotic sequences have good correlation properties and they can be used as address sequences in Spread Spectrum Communication. Chaotic functions are highly sensitive to initial condition and exhibit non-linear behavior. In Chaotic spread spectrum communication systems, different user may be assigned different sequences generated with different initial conditions. Set of binary sequences with good pair wise cross- correlation property finds applications in Direct Sequence- Code Division Multiple Access (DS-CDMA) systems. Security in Direct Sequence-Code Division Multiple Access systems is relatively limited. To enhance security in Direct Sequence- Code Division Multiple Access systems, chaotic sequences are generated. In this paper we analyze the generation of chaotic binary sequences and study of auto correlation and cross correlation properties.

The bandwidth ratio increasing of spread spectrum (SS) communication limits the performance of wideband adaptive interference cancellation (WAIC) for strong wideband interference signal. To improve the interference cancellation radio (ICR), wideband interference signal is divided into subbands to reduce the computational bandwidth of the WAIC algorithm. In this paper, a method that fits the wideband interference signal by multi-tone signals is proposed to explicitly analyze the effect of the signal bandwidth on the cancellation system and quantitatively calculate the analytical solution of the ICR. Basing on the method proposed, the performance can be evaluated by the amplitude and phase difference between the received signals from the main antenna and the auxiliary antenna. Simulations and experiments are conducted to verify the theoretical analysis, and the results are consistent. Therefore, the analytical method proposed in this paper provides the design guidelines between the ICR requirement and subband bandwidth, which can reduce the complexity in the implementation of the WAIC system.

Wavelets are considered as powerful signal processing tools that provide an effective alternative to conventional signal transforms. Spread spectrum plays an important role in CDMA communication system. Because of its unique characteristics, it has been first used for military applications. So spread spectrum communication via, discrete wavelet transform and thresholding becomes effective now a days. This paper describes a near optimal threshold estimation technique for signal denoising in spread spectrum communication using Double Density Discrete Wavelet filter. A new threshold calculating formula is utilized. Performance of the proposed system is found to be better than the conventional spread spectrum receiver.

Spread spectrum communication has good performances such as anti-noise, anti-interference and fast transmission rate, so it has been widely used in military communication and civil communication fields and others. The M-ary spread spectrum system has its unique advantages and strong practical application background with respect to direct sequence spread spectrum, and effectively solves the problem of limited bandwidth of direct spread spectrum. This paper firstly expounds the principle of traditional direct sequence spread spectrum system and then focuses on the research of the principle and system model of M-ary spread spectrum system. The error performance of M-ary spread spectrum system is also simulated and analyzed. The simulation results show that M-ary spread spectrum has a greater advantage in the bandwidth-constrained field, where high-speed data transmission is required and certain anti-noise capability is required.