A New Threshold Calculation Approach in the Performance Enhancement of Spread Spectrum System Using Double Density Discrete Wavelet Filter

The spread spectrum technology has been widely used in ground communication systems. With the development of global satellite communication, spread spectrum communication has also been widely used in satellite communication system. However, spread spectrum communication has many challenges to address, such as multi-user interference, near-far effect, random phase, delay and so on. Multi-user detection technology makes use of spreading sequence, delay, amplitude and phase information of each user for joint detection, which can effectively suppress multiple access interference, make full use of the frequency spectrum resources at the uplink and improve system capacity. Thus, the multiple user detection is one of the key technologies in CDMA communication systems. This paper adopts the multiple user detection scheme that is based on convolution coding block parallel iteration interference cancellation and conducts MATLAB simulation on multiple user detection algorithms. Though the study of three different data rate scenarios, this paper verifies that the multiple user detection algorithm can reduce the bit error rate of the reference user and improve system capacity.

Spread spectrum communication is to use spread spectrum code to modulate the information data to be transmitted in order to realize the frequency spectrum extension, then transmission. The receiver uses the same spread spectrum yards to conduct solution and the related signal processing and restore the original information data. Then CDMA communication system is using the approximate orthogonal characteristics of address codes to distinguish users on the basis of the spread spectrum communication.

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.

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.

Spread spectrum communications rely on the selection of suitable sets of so-called spreading codes, also known as signatures, to ensure satisfactory system performance. Comparing different sets of spreading codes may be not a straightforward process, due to the amount of different code-related parameters that should be taken into account, and to the inherent differences in the codes generation algorithms. This paper presents a practical software tool to facilitate the evaluation and comparison of different families of spreading codes, under different parameters and constraints. Simulations to evaluate the selected signatures in a CDMA system, under AWGN or multipath channel, are also supported by the tool. The tool may be usefully applied in the design of communication systems and networks relying upon spread spectrum techniques.

Spread spectrum communication technology is one of the most critical core technologies in anti‐jamming satellite communication systems. However, it has certain technical limitations in anti‐jamming applications. For instance, frequency‐hopping spread spectrum technology exhibits weak resistance against spot jamming, while direct‐sequence spread spectrum technology is less effective in mitigating wideband interference. With the continuous development of satellite countermeasure technologies, these technical limitations will significantly constrain the performance of satellite communication systems and compromise the reliable transmission of space‐based information. Aiming at the technical limitations of spread spectrum anti‐jamming satellite communication, this paper proposes a solution based on blind source separation technology to enhance the anti‐jamming capability of spread spectrum communication. This paper establishes a blind source separation‐based anti‐jamming communication prototype system, verifying the feasibility of applying blind source separation to communication anti‐jamming. It conducts an in‐depth analysis of the characteristics and existing issues in spread spectrum anti‐jamming satellite communication systems, identifies the problems and challenges of applying blind source separation to such systems, and proposes potential solutions.

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.

Compared with traditional Spread Spectrum (DS-SS) communication method, in terms of bandwidth efficiency and information transmission capacity, position Code Parallel Combinatory Spread Spectrum (PC/PC/SS) communication system has better performance. At the same time, total maximum PN sequences should be chosen accurately by PC/PC/SS system fromPN sequences which are correlated, or it will lead to masses of error. The current method is not capable of distinguishing and rectifying one random false sequence. In order to deal with this issue, this paper put forward a PC/PC/SS communication system which is on the basis of the iterative method and analyzed system performances. The PC/PC/SS system with iterative method can distinguish and rectify a sequence error. Under the identical circumstance, the PC/PC/SS system has less BER than traditional PC/SS system, which is proved by computer simulation.

Wireless location by spread spectrum communication can be severely corrupted by noise. Narrowband noise is the most effective interference that can make measurement signal undetected. In this paper, an adaptive wavelet filter is presented to suppress single and multiple narrowband interferences with additive white Gaussian noise that interferes with spread spectrum signals. The filter uses combinations of Gaussian wavelets with optimal time-frequency localization and computational efficiency for real-time denoising. The performance of the wavelet filter has been evaluated by experiments with spread spectrum communication system. Experimental results demonstrate that the proposed wavelet filter mitigates the narrowband noise in accordance with the corrupted frequency contents, and improves signal to noise ratio (SNR) for peak detection leading to higher accuracy of timing measurement for real-time wireless location.

At present, the spread spectrum (SS) sequences used in watermark include i.i.d. random sequences and the sequences used in SS communications. They appear earlier than digital watermark. Almost no researchers pay attention to whether they are really fit for watermark. In this paper, we compare the SS watermark channel and the traditional SS communication channel. We find out that their correlation property is different. Considering cropping and translation attacks, we define watermark auto- and cross-correlation and propose Loose Autocorrelation and Tight Cross-Correlation (LAC&TCC) properties for SS watermark. The LAC&TCC properties are that, whether or not synchronized, the autocorrelation is equal or close to 1 and the cross-correlation is equal or close to 0. Accordingly, the peak correlation is divided into the peak autocorrelation Ra(l) and the peak cross-correlation Rc(l). We establish the lower bound of Rc(l) and the higher bound of Ra(l), respectively. The two bounds indicate that, no matter how small the cover is reserved, the extractor can always find a threshold to distinguish auto- and cross-correlation in theory.

In this paper, we conduct research on effective and robust time-delay estimation methodology for spread spectrum communications. The development of underwater acoustic spread spectrum communication technology derived from the demand for underwater remote, reliable communication. Due to the underwater acoustic channel belt width, background noise and high rate of Doppler frequency shift, severe multipath effect, absorption problems such as uneven, makes the communication quality serious decline. We firstly analyze the fast time-delay estimators to serve as the prior knowledge, and later, we analyze the channel estimation techniques. Finally, we test the error and efficiency. Results show that the system has better ability to resist noise and multiple access interference, and improve the chaotic spread spectrum sequence to better the performance of the system of traditional chaotic spread spectrum sequence. The experimental result proves the effectiveness of proposed methodology. In the future, we plan to conduct more literature reviews to modify the current technique.

A novel spread spectrum (SS) system based on the unconventional self encoding principle has been proposed for highly secured data transmissions. This system inherits the antijamming (AJ) and low probability of interception (LPI) characteristics like any other SS system with the aid of truly random spreading codes, which are generated from the source stream itself. Therefore, the proposed system is unique in that the traditional transmit and receive PN code generators are not needed. In fact, the enhanced transmission security arises not only due to the SS nature of the signal, but also from the true randomness of the unique spreading processes. This paper describes the proposed system and presents the simulation results of the system performance under various kinds of jamming conditions, which is not been so far dealt. The obtained performance curves are compared with existing SS systems like direct sequence and frequency hopped SS.

Proposes a method for designing spread sequences for a spread spectrum (SS) communication and ranging system. The proposed sequence is composed by concatenated equivalently odd and even (EOE) inner-sequences and an M outer sequence. We have previously proposed EOE sequences that have equivalently good properties of both even and odd correlation, what are important features for acquisition and demodulation in SS communications. Usually, simple concatenation of pseudonoise-sequences results in sequences with bad autocorrelation properties. Unlike the latter, concatenation of EOE inner sequences result in sequences with good correlation properties, exhibiting low sidelobe peaks, what is useful for achieving stable acquisition. The proposed sequences have long period. Therefore, the single concatenated EOE sequence is suitable for a spread spectrum system with both communication and ranging functions.

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.

We discuss the application of trellis coding in a (direct sequence spread spectrum) CDMA system where orthogonal signaling is used. Our approach is to construct the trellis codes over the set of biorthogonal sequences. A general analysis is presented. We compared the analysis with computer simulation. The results show that the trellis coded CDMA system outperforms the corresponding uncoded DS/SSMA system.