Spectrum Communication System Research Articles

The Application of RAKE Receiving Technology in the Underwater SS Communication

In recent years, the strategic significance of the oceans is growing as well as its research and development needs. The underwater wireless communication is becoming more and more important. The underwater acoustic communication is one of the few mediums which can conduct the underwater transmission over a long distance, and the multipath effect is the major obstacle of affecting the systems high speed and high reliability. The characteristics of underwater acoustic fading and coherent multi-path channel are studied, and the model of underwater acoustic spreading spectrum (SS) communication system is established. The affect of coding technique on the systems performance are analyzed in detail. The improved RAKE receiving technical solution is put forward, whose simulation analysis and data in different combining ways are given. It is proved that the scheme can better solve the problem of multipath interference in underwater acoustic transmission.

Research on the Equivalence of Pulsed Interference Signal and CW Signal in DSSS Communication System

Pulsed interference signal and pure frequency continuous wave (CW) jamming signal have the same effect on performance of bit error rate (BER). Due to equivalence, we can effectively simplify the complex of the direct sequence spread spectrum (DSSS) communication system. The equivalence will be simulated by the software SystemView in systematic level.

ANALYSIS OF THE SEQUENCES WITH OPTIMAL CROSS-CORRELATION PROPERTY

The design of large family size with the optimal cross-correlation property is important in spread spectrum and code division multiple access communication systems. In this paper we present the sequences with the decimation $d

Self-encoded multi-carrier spread spectrum with iterative despreading for random residual frequency offset

In this study, we investigate the multi-carrier spread spectrum (MCSS) communication system which adopts the self-encoded spread spectrum in a downlink synchronous channel. It is very difficult to completely eliminate the frequency offset in practical channel scenarios. We demonstrate that the self-encoded MCSS (SE-MCSS) with iterative despreading manifests a remarkable immunity to residual frequency offset. The SE-MCSS can be an excellent candidate for the future generation of wireless services.

Multicomponent Chirp-like Jammer Excision in DSSS Communication Systems Using Hilbert-Huang Hough Transform

A novel and efficient approach for multicomponent chirp-like jammer excision in direct sequence spread spectrum (DSSS) communication systems using Hilbert-Huang Hough (HH-H) transform is proposed, which is the generalization of marginal Hilbert spectrum. The approach iteratively decomposes the received signal into intrinsic mode functions (IMFs) and applies Hilbert transform to each IMF to yield Hilbert spectrum (HS), by which the embedded jammers can be well concentrated in the time-frequency plane along their instantaneous frequency laws. By performing Hough transform over the HS and searching peaks in the parameter space, parameters estimation and components reconstruction of the multicomponent chirp-like jammer are implememted. Simulation results are presented showing performance comparison between the proposed method and the fractional Fourier transform (FrFT) based method in the case of two chirp-like jammer components. DOI: http://dx.doi.org/10.11591/telkomnika.v11i4.2372

Optical Wireless N-CSK with Modified Pseudo Orthogonal M-Sequence Sets

In this paper, N-CSK (N parallel Codes Shift Keying) using modified pseudo orthogonal M-sequence sets (MPOMSs) to realize the parallel combinatory spread spectrum (PC/SS) communication system for the optical communications is proposed. Moreover, the upper bound of data transmission rate and the bit error rate (BER) performance of this N-CSK system using the chip-level detection are evaluated through theoretical analysis by taking into account the scintillation, background-noise, avalanche photo-diode (APD) noise, thermal noise, and signal dependence noise. It is shown that the upper bound of data transmission rate of the proposed system is better than those of OOK/CDM and SIK/CDM. Moreover, the upper bound of data transmission rate of the proposed system can achieve about 1.5[bit/chip] when the code length of MPOMS is 64[chip].

Partial-code-aided scheme for narrowband interference suppression in direct-sequence spread spectrum systems

The non-linear filtering is a commonly used time-domain technique for narrowband interference (NBI) suppression in the direct-sequence spread spectrum (DSSS) communication systems. In this study, the authors analyse how the decision feedback error of the spread spectrum (SS) signal influences the performance of the NBI prediction. A partial-code-aided scheme is proposed, which despreads partial chips in a spreading sequence and reconstructs the rest part by spreading the bit decision. This method utilises partial spreading gain to improve the decision accuracy of the SS signals while keeping similar time consumption and implementation complexity with the traditional scheme. It has been verified by simulation that with different NBI models and under different channel conditions, the proposed non-linear filtering method always outperforms the traditional one with chip-wise decision feedback.

Symbol error rate of the dm-mpsk under the influence of jamming signals

Focusing on the performance of the chirp spread spectrum (CSS) communication system under the influence of jamming, we analytically derive the symbol error rate (SER) for the direct modulation CSS system with M-ary phase shift keying in the presence of broadband and tone jamming signals. From numerical results, it is confirmed that the analytic result agrees closely with the empirical SER.

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.

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.

Blind identification of autoregressive system using chaos

The problem of identifying an autoregressive (AR) model using chaos is investigated here. Based on the Cramer-Rao bound (CRB) analysis, it is proved here that when chaos is used to drive an AR system, identification using only the output signal can be as good as that based on using both input and output signals, that is, blind identification is equivalent to nonblind identification. A deterministic maximum likelihood (ML) is, therefore, developed to blindly identify an AR system driven by chaos. Combined with the global search technique genetic algorithm (GA), the proposed GA-ML method is found to achieve the optimal identification performance imposed by the CRB. The theoretical mean square error (MSE) performance of the proposed GA-ML method is derived, and the result is validated using computer simulations. Compared to conventional methods based on white Gaussian driving signal, the chaos approach is shown to have superior performance. The improvement is proved to be the result of the positive and finite Lyapunov exponent of the chaotic signal. The proposed chaos identification method is applied to blind equalization of a spread spectrum (SS) communication system where chaos is used to modulate the information signal. Computer simulations show that the proposed chaos approach has a satisfactory equalization performance even under strong channel effects.

An analog multi-user spread spectrum technique for wireless home automation

The emerging research interests in home network and other wireless consumer electronic products have led to an increased demand for an effective and low cost approach for multi-user communications. We propose a novel multi-user spread spectrum (SS) communication system based on chaos theory for multimedia transmission in a wireless home network environment. Using the ergodic property of chaos, the proposed chaotic SS system is shown to be able to modulate and transmit the multimedia signal effectively for point-to-point communication. In order to cater for home network service and other applications, our method is further extended for multi-user communication based on time division multiple access, while all users can share the whole frequency spectrum, different time slots are allocated to different users for transmission. Monte Carlo simulations are carried out to evaluate the effectiveness of the multi-user analog chaotic SS system. Compared with the conventional CDMA system, it is shown that the proposed system has improved and satisfactory performance in transmitting analog multimedia signals even when the channel measurement noise is strong. In addition, since the proposed system is with very low cost hardware implementation, it is quite suitable for home network and other consumer electronic products.

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.

A two-sensor array blind beamformer for direct sequence spread spectrum communications

We present an efficient blind beamformer dedicated to the problem of interference mitigation in direct sequence spread spectrum (DSSS) communication systems using a two-sensor array. A closed-form solution for the blind identification of the communication channel is derived by exploiting the temporal properties of the desired signal and the interference. The optimal beamformer is derived from the maximization of the signal-to-interference and noise ratio (SINR) at the output of the receiver in terms of the blindly estimated channel coefficients. Three structures of the DSSS receiver are presented. One structure consists of the blind beamformer followed by the spread spectrum demodulator. The other two structures consist of the spread spectrum demodulator followed by the blind beamformer. The performance of these structures is discussed in terms of the achieved SINR and the computational cost. Simulation results are provided to illustrate the effectiveness of the proposed blind beamformers in interference excision.

Performance of M-ary/spread spectrum communication system in the presence of continuous wave interference

This paper describes an evaluation method and performance improvement for an M-ary/spread spectrum (SS) communication system in the presence of continuous wave interference. First, we introduce a theoretical equation for the average bit error rate of M-ary/SS receiver in a transmission line with AWGN and single CW interference. Second, we define the required jamming margin for M-ary/SS receiver to satisfy a certain level of average bit error rate. Then we analyze the theoretical value of the required jamming margin and evaluate the performance of receiver by a simulation. From this study, we found that the jamming margin relates to the spectrum spreading factor of the total system and does not relate to code length of pseudo-random noise sequence. To improve performance against CW interference, we first examine the effect of improvement when we use error correcting code as a spreading code. However, we cannot find any effect of the improvement, even if the jamming margin relates to spectrum spreading factor and even if there is a coding gain by the error correcting code. Second, we studied the performance improvement when whitening filter based on LMS algorithm is added to the receiver to reduce CW jamming. For a spreading factor between 7 and 25 dB, the jamming margin can be improved by 15 dB to 25 dB. © 1998 Scripta Technica. Electron Comm Jpn Pt 3, 81(5): 32–40, 1998

Theoretical analysis of M-ary/SS communication systems using racing counters and a Hadamard matrix

The performance of M-ary spread spectrum (M-ary/SS) communication systems is discussed. Firstly, the initial acquisition time is evaluated. Secondly, the retention time, which is the average number of frames holding correct frame timing, and the recovery time, which is the average number of frames required to establish synchronization, are derived. Lastly, the bit-error rate (BER) performance is evaluated. M-ary/SS communication systems, which have more than one spreading code, can improve the BER performance under conditions in which there is additive white Gaussian noise (AWGN). However, the synchronization of M-ary/SS communication systems is difficult because they have several spreading codes. The frame synchronization method uses a Hadamard matrix and "racing counters." As a result, the retention time becomes longer than the recovery time when the size of the lower counter differs greatly from that of the upper counter in the racing counters. Then the BER gets close to the performance which is achieved under complete synchronization.

A spread spectrum communication system without a reference signal for a frequency‐selective fading channel

AbstractIn a spread spectrum communication system (SS), RAKE reception is effective as a measure against frequency‐selective fading. Channel impulse response should be known for RAKE reception. In a conventional system where a reference signal is added to a transmission signal to obtain an impulse response, a decrease in transmission efficiency occurs under fast fading.This paper proposes a scheme that does not use the reference signal by allocating different codes to information signals. In addition, a channel‐estimation scheme that alleviates effects of undesired autocorrelation values or cross‐correlation values of spreading codes is proposed. This scheme subtracts cross‐correlation values or excess autocorrelation values from a matched filter (MF) in measuring a channel impulse response and eliminates responses lower than a given threshold. Computer simulations under two‐path fading were performed. the error characteristics were improved with the proposed channel‐estimation scheme. It is shown that the proposed scheme is better than the scheme using a reference signal.

Direct sequence/spread spectrum communication systems using chip interleaving and its applications for high-speed data transmissions on power lines

This paper presents direct sequence/spread spectrum (DS/SS) systems using chip interleaving and its burst noise suppression effect for data transmissions on power lines. First, to protect from the impulsive or periodic burst noise, a convolutional chip interleaving method for randomizing the time intervals of interleaved chips and synchronizing with PN sequence is applied. Second, to obtain the randomness of chip intervals, multielement M-sequences and Tausworthe-Lewis-Payne (TLP) sequences are adopted, and several properties (generation frequency of each element, autocorrelation function, etc.) are shown. Finally, as an application, experimental results for high-speed (8.2 kbit/s) data transmissions on power lines are shown.