A New Iterative Method for Position Code Parallel Combinatory Spread Spectrum Communication Based on Underwater Communication

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.

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.

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.

This study introduces the group delay and its characteristics in satellite channel, meanwhile, the model of the impact of group delay ripple on performance of direct sequence spread spectrum communication system is established and simulated for analysis. The simulation results indicate the specific impact of group delay ripple on system, as well as the impact of group delay ripple on the transmission and reception signals in the spread spectrum communication system. For transmission signals in the spread spectrum system, the group delay ripple can worsen the EVM and Eye-diagram of spread spectrum signal, cause signal distortion and the deterioration of noise tolerance. For the reception performance of the spread spectrum system, the group delay ripple has little effect on the spread spectrum acquisition using incoherent accumulation and energy judgment, but it can cause a deterioration in the error performance of the reception signal. For example, when relative group delay increases from 0.011 to 0.9, the error performance decreases by about 2 dB. When designing satellite spread spectrum communication systems, power resources are extremely precious, it is necessary to consider the impact of group delay on the communication system, and take certain measures to reduce the impact of group delay ripple to the 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.

Jammer suppression in spread spectrum communication using novel independent component analysis approach

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.

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 has been widely used in many communication system because of its anti-interfere and anti-interception properties. The existing multi access interference (MAI) restraint technology which could be classified as associated determination and interfere cancellation cannot achieve the unification of low arithmetic complexity and high determination performance. For instance, the usual linear associated determination method has low arithmetic complexity but poor performance, while the maximum likelihood (ML) method has the best performance but no feasibility. In this article, the causation and the influence to the system performance of MAI are analyzed systematically based on the theory of spectrum communication, and the representative methods are described and summarized. Based on normal interfere cancellation algorithm, a new dimensional reduced associated determination algorithm with near ML performance is presented and proved to be with low complexity and near the highest theoretical performance by theoretical calculation, complexity analysis and simulation validation. This algorithm significantly improves the application value and feasibility of associated determination technology and has significant importance in solving the possible MAI problem in the spread spectrum communication systems in the future.

Clock and carrier recovery are very critical in high speed digital wireless communication for achieving high data rate with low packet error rate. In this paper, we propose a linear estimator for both clock and carrier recovery in a direct sequence spread spectrum (DSSS) communication system and show that this is also the maximum likelihood (ML) estimator. We present simulation results to illustrate the convergence of the estimator under different multipath channel conditions.

To address the inability to quantitatively analyze the performance of the direct sequence spread spectrum (DSSS) communication system in the presence of short-period pseudo-noise (PN) sequences, this study derives the interference components resulting from correlation processing of single-frequency interference. Given the short period of the spread spectrum sequence used in underwater acoustic systems, a theoretical expression is proposed for analyzing the anti-single-frequency interference performance of DSSS communication systems in underwater acoustics. This expression combines the interference power output by the system to enable quantitative analysis. Simulations are conducted to validate the accuracy of the theoretical expression. The results reveal that the interference sequence generated by correlation processing assumes either a direct current (DC) or sinusoidal distribution. The bit error rate (BER) of the system is influenced by signal-to-interference ratio (SIR), interference frequency offset, phase deviation, and the structure of the spreading code itself. The BER exhibits regular variation with changes in the interference phase. In all working conditions where the interference frequency offset is an integer multiple of the bit bandwidth, single-frequency interference with a frequency offset equivalent to the bit bandwidth has the greatest impact on the system. The concise theoretical expression presented in this study has significant practical value as it allows for quick prediction of variation in the anti-single-frequency interference performance of underwater acoustic DSSS communication systems using short-period PN sequences.

The performance of a direct sequence spread spectrum (DS/SS) communication system in land mobile satellite channels is evaluated with experiments. Field test results in the L-band with the ETS-V satellite are presented, in which the use of a multibit-quantized coherent matched filter receiver improves the initial acquisition and the bit error rate performances. The bit error rate characteristics in urban and suburban environments are found to agree with those of non-SS BPSK (binary phase-shift keyed) on a nonselective Rician fading channel.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A fast acquisition method is proposed to improve the detection speed of direct sequence/frequency hopping spread spectrum (DS/FHSS) communication system. A novel digital wideband receiver by using folded sampling is presented to reduce the searched hopping frequencies in coarse acquisition. There are two selective filters connected with the RF downconverter in the new scheme, one of which is wideband and the other is narrow and similar as the traditional one. The acquisition is achieved on two stages: firstly, the folded sampling is used when the wideband filter is selected and the hopping frequencies on multiple Nyquist zones are folded together on the first one, then fine acquisition is performed while the narrow band filter is selected. The detection performance of the propose method is deduced through state flow graph and verified by simulation. The results show the new method performs better when compared with the traditional one. It can effectively promote the detection speed with few detection performance loss.

The performance of anti narrowband noise of direct sequence spread spectrum (DSSS) communication system is investigated in this paper. The new result given in the paper shows that performance of anti noise in DSSS system is different from classic result. The attenuation of narrowband noise in DSSS system is the function of the relative distance between the narrowband noise and carrier frequency of DSSS system, and it is discontinuous. The attenuation of broadband noise is little, and the process gain is about 0.46dB. The results can be utilized in design and application of spread spectrum system.

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.