Sequence Spread Spectrum Communication System Research Articles

Breaking a chaotic direct sequence spread spectrum communication system using interacting multiple model-unscented Kalman filter

In this paper, a new method to break chaotic direct sequence spread spectrum (CD3S) communication systems is proposed. Here, the CD3S communication system transmitting different information symbols is considered as a combination of two subsystems which are driven by two different chaotic dynamic models, respectively. At every single time moment, the CD3S signal can be regarded as generated by the subsystem corresponding to the information symbol transmitted. Then, based on the multiple model form of CD3S signals, an interacting multiple model unscented Kalman filter with model switching detection mechanism is exploited to track the CD3S signals. The l(2)-norm of tracking errors is used to choose the model which best matches the intercepted signals. Thus, the information symbols are recovered indirectly. Compared with the existing methods, the proposed algorithm can: (1) reduce the influence of a low spreading factor; (2) calculate the spreading factor using the length of time intervals between model switching; and (3) be more effective under scenarios of low signal-to-noise ratio or multipath fading. Simulation results verify the superiority of the proposed method.

Breaking chaotic direct sequence spreading spectrum communication systems using DM-UKF chaotic fitting method

In this paper, a dual model unscented Kalman filter chaotic fitting breaking method is proposed to break chaotic direct sequence spread spectrum communication systems in the cases of low spreading factor, low signal-to-noise ratio or severe multipath fading. Based on the characteristic that the range of information symbol is a finite set, the proposed algorithm fits the original chaotic signal through different filters which work in parallel. The fitting errors are used to choose the optimum matching filter, thus to estimate the information symbols. Furthermore, an error-controlling-factor is introduced to increase the distance of model based tracking errors, which can not only facilitate the information extracting process, but also reduce the influence of noise and multipath fading. Theoretical analysis and simulation results prove that the proposed algorithm is superior to the existing breaking method.

Research of Direct Sequence Spread Spectrum Communication System Based on MATLAB

This paper described the theory which based on the spread spectrum communication system, a simulation model was designed based on MATLAB, and each module of the model was briefly introduced. In a particular simulation condition, ran the simulation program, and an expected result was obtained. Meanwhile, by design a spread spectrum communication system of two users, detect the bit error rate corresponding with the two users in different bit error rate (SNR), directly verified the validity of the model system.

A Tracking System Using a Differential Detector for M-ary Bi-orthogonal Spread Spectrum Communication Systems

As an application of the direct sequence spread spectrum (SS) communication system, there is an M-ary bi-orthogonal SS communication system. In its system, several spreading sequences (bi-orthogonal sequences) are used in a code shift keying basis. Hence, design of the spreading code synchronization system has been an issue in the M-ary bi-orthogonal SS systems. In this paper, the authors focus on a code tracking system using a differential detector and a Delay Lock Loop (DLL). They investigate a tracking performance of their code tracking system by theoretical analysis. In addition, a multi-stage interference canceler is applied to the M-ary bi-orthogonal SS system. As the result, it is shown that the tracking performance of the theoretical analysis is almost the same as that of computer simulations in a multi-user environment. It is also shown that the multi-stage interference canceler is effective in improvement of the BER performance.

PARAFAC-based channel estimation and data recovery in nonlinear MIMO spread spectrum communication systems

In this paper, a new tensorial modeling is first proposed for nonlinear multiple-input multiple-output (MIMO) direct sequence spread spectrum communication systems. The channel is modeled as an instantaneous MIMO Volterra system. Then, a direct data approach for joint blind channel estimation and data recovery is developed using the parallel factor (PARAFAC) decomposition of a third-order tensor composed of received signals, exploiting space, time and code diversities. A blind channel estimation method based on the PARAFAC decomposition of a fifth-order tensor composed of covariances of the received signals is also proposed, considering phase shift keying (PSK) modulated transmitted signals. The proposed estimation algorithms are evaluated by simulating a nonlinear uplink MIMO radio over fiber (ROF) communication system.

A Minimum Value Based Threshold Setting Strategy for Frequency Domain Interference Excision

We present a robust threshold setting strategy with modest computational complexity for frequency domain interference excision in direct sequence spread-spectrum (DSSS) communication systems. The proposed strategy calculates the threshold by multiplying the minimum value of the averaged squared magnitude with a predefined scaling factor. An analytical framework for choosing the scaling factor is developed based on the principle of constant false-alarm rate (CFAR). Numerical results indicate that the new strategy outperforms existing ones in a wide range of partial-band jamming scenarios.

Code-aided interference suppression in direct sequence spread spectrum systems with eigenvector sign spreading code

For direct sequence spread spectrum (DSSS) communication systems suffering interference, it is known that code-aided interference suppression technique outperforms all of the previous linear or nonlinear methods. In this paper, we proposed an improved code-aided technique which can improve the system performance greatly by using the eigenvector sign (EVS) spreading sequence which depends on the statistical characteristics of the interference and the thermal noise.

A contribution to fast telecommunication system conception: Application to a DS-SS tracking stage improvement

This paper presents an improvement of the synchronization and tracking stages of a direct sequence spread spectrum (DS-SS) communication system to reduce the acquisition time. We propose a multi-branches solution, implanted in a virtual prototype for a home automation application. The virtual prototype is based on the VHDL-AMS high-level language and the most significant physical parameters will be transferred at a high level. Finally, acquisition time simulations are compared to other classic methods and synthesis results dedicated to a real FPGA prototype are also presented.

Rapid Estimation for Spreading Functions of Multipath CDMA Wireless Communication Channels

In this paper, we present a robust and fast computational algorithm for estimating the spreading function of multipath CDMA wireless communication channels in multi-user Direct Sequence Spread Spectrum (DSSS) communication systems. Transmission channels spread the message signals in time and frequency and are typically modeled as random, time-varying systems. The proposed algorithm is to provide a time-frequency dependent windows that can be computed priori to estimate the spreading function of multipath wireless communications channels. Computing such windows priori at the receiver will reduce a significant amount of computational load and to improve the previous proposed channel estimation work. It is shown that the estimation of the parameters of such models is possible by means of the spreading function which is obtained from the discrete time-frequency evolutionary kernel of the received signal using the discrete evolutionary transformation DET.

Local Polynomial Fourier Transform Receiver for Nonstationary Interference Excision in DSSS Communications

The problem treated in this paper is monocomponent nonstationary interference excision in direct sequence spread spectrum (DSSS) communication systems by means of the local polynomial Fourier transform (LPFT). First, the interference is optimally concentrated in the time-frequency (t-f) plane and then its t-f signature is removed via a binary mask. The LPFT receiver is derived in matrix form and its optimization is performed, having in mind an influence of the binary mask on the received signal. The conventional (suboptimal) and the optimal LPFT receiver performances are compared by means of simulations carried out on the received signal corrupted by different FM types of interferences. The short-time Fourier transform (STFT) receiver is considered as a special case of the LPFT receiver and its performance is assessed simultaneously with the LPFT receiver, both in conventional and optimal case.

Joint scale-lag diversity in wideband mobile direct sequence spread spectrum systems

We consider the effect of mobility on a wideband direct sequence spread spectrum (DSSS) communication system, and study a scale-lag Rake receiver capable of leveraging the diversity that results from mobility. A wideband signal has a large bandwidth-to-center frequency ratio, such that the typical narrowband Doppler spread assumptions do not apply to mobile channels. Instead, we assume a more general temporal scaling phenomenon, i.e., a dilation of the transmitted signal's time support. Based on a uniform ring of scatterers model, we determine that the wideband scattering function, which quantifies the average scale spreading, has a "bathtub-shaped" scale profile. We compare the performances of a scale-lag Rake and a frequency-lag Rake, each capable of leveraging the diversity that results from mobility. Such analysis applies, for example, to ultra-wideband (UWB) radio frequency channels and underwater wideband acoustic channels.

IMPROVING PERFORMANCE OF SPACE-TIME TURBO CODES WITH SHORT FRAMES IN NARROWBAND JAMMING

This paper considers the performance enhancement of a space-time turbo codes processing system employing a combined turbo code and antenna transmission diversity scheme for direct sequence spread spectrum communication system. Turbo codes have been shown to approach the Shannon limit for error correcting capability at low signal-to-noise ratios given large sized frames. Extensive research efforts have been examining ways to enhance the performance of turbo codes forshort frames (e.g., voice transmission). The proposed system is investigated over Rayleigh fading channels only and also in case of narrowband jamming environment in addition to Rayleigh fading channels. This paper focuses on the implementation and performance of a modified turbo decoder for this model. Furthermore, the description of the concatenation of turbo code and direct sequence/spread spectrum with a space-time block codes are presented. Simulation results show that substantial benefits can be obtained by direct sequence spreading with space time coding the coded bits over Rayleigh fading and narrowband jamming environment.

Iterative low-complexity multi-user detection for asynchronous multi-sequence signalling based bit-interleaved coded modulation code division multiple access systems

An uplink direct sequence spread spectrum communications systems employing a multi-sequence model over a quasi-static frequency-selective fading channel is considered. In analogy with bit-interleaved coded modulation (BICM) technique, a group of bits at the output of a bit-wise interleaver is mapped uniquely to a complex signalling vector belonging to an orthogonal plane sequence modulation signal space, which is constructed over a set of expanded signature sequences. This transmission system provides not only bandwidth efficiency offered by additional signal planes but also time diversity resulting from the BICM technique. It is observed that at high system traffic load error performance could degrade substantially due to user cross-correlations, multi-access asynchronism as well as channel frequency selectivity. The authors employ a 'turbo principle' receiver, consisting of a soft interference cancellation scheme, soft demappers and maximum a posteriori decoders, to avert this capacity loss by exploiting the serially concatenating structure at the transmitter. After simple mathematical manipulation, a soft space-time linear minimum mean-square error multi-user detector could even be explored on the basis of per signal plane per user. Both analytical performance-bound and computer simulation of the proposed framework in terms of bit-error rate (BER) are revealed. Further, performance comparisons with convolutionally coded and conventional bandwidth-efficient coded direct sequence code division multiple access systems under the same system conditions are illustrated. The authors have also investigated the impact of labelling maps on the BER performance.

Jammer suppression in DS-CDMA arrays using independent component analysis

We propose using Independent Component Analysis (ICA) as an advanced pre-processing tool for blind suppression of interfering jammer signals in direct sequence spread spectrum communication systems utilizing antenna arrays. The role of ICA is to provide a jammer-mitigated signal to the conventional detection. If the jammer signal is weak or absent, preprocessing by ICA is not advisable. Therefore we also consider two possible switching schemes, called pre-switching and post-switching, which activate the ICA-based jammer canceller only when it is expected to improve conventional detection. ICA-RAKE pre-switching is less complex, while post-switching performs better, especially when the jammer is pulsed in nature. Simulations are given to illustrate the achieved performance gains for single- and multi-path channels.

Wideband time-varying interference suppression using matched signal transforms

We develop an interference suppression scheme for wideband jamming interference in direct sequence spread spectrum communication systems. We consider interference with time-varying spectral components that can be spread both in time and frequency. Our methodology uses the matched signal transform that is highly localized for signals with nonlinear phase along their frequency-modulation (FM) rate. We compare this method with the use of the more computationally intensive quadratic time-frequency representations whose performance is reduced when the interference is multicomponent.

Adaptive rate coding using convolutional codes for asynchronous code division multiple access communications over slowly fading channels

This paper presents a method of code rate adaptation using punctured convolutional codes for direct sequence spread spectrum communication systems over slowly fading channels. A blind channel estimation technique is used to estimate the nature of the multi-user channel at the detector (before the decoder). The path gains obtained from the channel estimation technique are used to adapt the code rates. Punctured codes derived from a specific rate 1/2 ( M = 4) mother code are used to provide error protection corresponding to the actual channel state. The upper and lower bounds on the bit error probability and the upper bound on the error event probability are derived for hard-decision and soft-decision decoding over Rayleigh and Rician fading channels. The throughput gains obtained using the adaptive scheme and the performances of the punctured codes are studied.

Broadband interference suppression in DS-SS system with modified discrete chirp Fourier transform

This paper presents a method of broadband interference excision by using a modified discrete chirp Fourier transform to improve bit error rate (BER) performance of direct sequence spread spectrum communication systems. With a computational complexity in the order of O(Nlog2N), the proposed method is shown to be effective for both mono- and multi-component interferences within a large range of interference to signal ratios. Theoretical analysis and simulation results show that the proposed method can achieve a better BER performance in the presence of white noise and linear chirp-like interference.

Performance evaluation of serial‐search strategies for the acquisition of DS/CDMA signals

AbstractSearch strategies for initial synchronization of direct sequence (DS) spread spectrum communication systems are compared, modelled and implemented using MATLAB then tested in the presence of additive white Gaussian noise (AWGN) and narrowband interference. The performance of these search strategies, namely, offset‐z‐search strategies and expanding alternate search strategies, in terms of the mean value of the search length is evaluated for different probabilities of detection. A truncated Gaussian probability phase distribution is assumed (as a priori information about the correct phase) and the performance of these search strategies is tested for different standard deviations (σ) of the phase.A novel search strategy, namely the offset‐z3, based on the offset z‐search strategy is introduced. Among all search strategies investigated the non‐uniform expanding alternate (NUEA) search strategy is found to perform best at high probability of detection. However, for a more peaked phase distribution, the offset‐z3‐search strategy is shown to offer better performance at low probability of detection. Outcomes of the simulated system support trends predicted by theory for the performance of different search strategies. Copyright © 2003 John Wiley & Sons, Ltd.

HOS and GA based interference rejection in direct sequence spread spectrum communication systems

A new Higher Order Statistics (HOS) and Genetic Algorithm (GA)-based interference rejection filter is introduced. Compared with the adaptive filters based on second-order statistics and gradient algorithm, the HOS and GA-based filter can reject the interference more efficiently, is independent of uncorrelated Gaussian noise, tends to converge to the optimum solution and is much less sensitive to the choice of the step size parameter. Computer simulations show that the method can reject narrowband interference efficiently.

Cyclostationary model based multiple-tone interference rejection in DSSS communication systems

Multiple-tone interference is a kind of narrow band interference appears in Direct Sequence (DS) Spread Spectrum (SS) communication system frequently that degrades the system performance. Most open literature studies on narrowband interference rejection assumed stationary SS signal and interference. SS signal and interference are modeled as cyclostationary and based on cyclostationary model, an interference rejection algorithm is proposed. Through computer simulation, it is shown that the performance of the SS system can be improved considerably after adopting this algorithm.