Multi-Carrier Initial-Condition-Index-Aided DCSK Scheme: An Efficient Solution for Multipath Fading Channel

In this paper, we propose an adaptive multistage parallel interference cancellation (PIC) structure for multipath fading channels. Similarly to the previous partial interference cancellation (IC) approach suggested in Divsalar et al. (1998), only part of the multiaccess interference (MAI) estimate is canceled at each stage. However, the weights employed in this proposed scheme are derived from an LMS algorithm which tries to minimize the mean-square error between the actual signal received and its replica. The complexity of the proposed adaptive multistage PIC scheme is much lower than that of linear multiuser detectors. Performance of the proposed structure in single-path Rician and multipath Rayleigh fading channels is evaluated by simulations. Our results show that the proposed technique outperforms the existing interference cancellation methods in multipath fading channels.

In this paper, a novel differential chaotic bit-interleaved coded modulation (DC-BICM) system is proposed for band-limited transmission. This system combines protograph-based low density parity check codes with constellation-based M-ary differential chaos shift keying (DCSK) modulation by one bitwise interleaving. Bit error rate simulation results show that the system has higher coding gain compared with the constellation-based M-ary DCSK modulation system with the same spectral efficiency over multipath Rayleigh fading channels. At the same time, several simulations and P-EXIT analysis are used to analyze the performance of the proposed system. It is found that there is a lot of room for optimization of the system by comparing decoding thresholds and simulation results. Moreover, the system with only partial channel state information has better performance and lower complexity compared with the traditional bit-interleaved coded modulation (BICM) directsequence-spread-spectrum system. As a result, the DC-BICM system is a good candidate for band-limited transmission.

This paper proposes a chaos-based direct-sequence spread-spectrum (CDSSS) communication system using M-ary PSK modulation in combination with MIMO-OFDM technique. This combination aims at improving the performance as well as capacity of the conventional CDSSS systems over multipath fading channels. In the transmitter, the data is modulated by an M-PSK modulator whose output is fed to a MIMO encoder. Two resulting signals are spread by directly multiplying with chaos-NRZ sequences and then put into the corresponding OFDM modulators. The output signals are transmitted through a multipath fading channel using multiple transmitting and receiving antennas. In the receiver, beside the use of OFDM demodulation, chaotic despread-spectrum, and M-PSK demodulation, a V-BLAST algorithm with Minimum mean squared error (MMSE) equalization is applied to decode and recover the data. Schemes for the transmitter and receiver are described in detail and their BER performance over the multipath Rayleigh fading channel is evaluated by means of numerical simulations. The obtained results prove that the performance and capacity of the proposed system are significantly enhanced and can be adjusted by changing the values of M-ary level, spreading factor or the number of used antennas.

In this paper, we analyze the performance of multicarrier spread spectrum systems in a multipath Rayleigh fading channel using frequency domain equalizer. Pilot-based channel estimation is done to compensate for the amplitude and phase distortions of the signal in the channel. BER performance is found for both AWGN and fading channels. It is found that the performance degrades as the number of active users increases due to increase in MAI.

We evaluate the performance of the internally coded partial-band DS-CDMA scheme first introduced in [1], in a multipath Rayleigh fading channel. The scheme of [1] is based on frequency-hopping (FH) and direct-sequence (DS) spread spectrum techniques. The total bandwidth is divided into N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> subbands. The output of a super-orthogonal encoder and a pseudorandom (PN) sequence selects one subband, in which the user’s data is sent in the form of DS-CDMA signal using the second PN sequence. We consider soft detection at the receiver front end. We obtain the upper and lower bounds on the bit error rate. For comparison, we also consider the conventional DS-CDMA system. It is shown that for the same spectral efficiency the proposed multiple access method outperforms significantly the conventional DS-CDMA system over the fading channel as well without requiring any extra bandwidth.

Modulation classification, an intermediate step between signal detection and demodulation, is commonly deployed in many modern wireless communication systems. Although many approaches have been introduced in the last decades for identifying the modulation format of the incoming signal, they have the obstacle of mining radio characteristics for most traditional machine learning algorithms. To effectively handle this limitation, we propose an accurate modulation classification method by exploiting deep learning for being compatible with constellation diagram. A convolutional neural network (CNN), namely CRNet, is developed to proficiently learn the most relevant radio characteristics from transformed gray-scale constellation image by cross-residual connection, a novel structure for associating the intrinsic information between two processing flows specified by regular and grouped convolutional layers. Based on the experimental evaluation, CRNet achieves the classification rate of approximately 90% at +10 dB signal-to-noise ratio (SNR) under a multipath Rayleigh fading channel and further performs more accurately than some existing deep models for constellation-based modulation classification.

This paper presents the performance analysis of compound chaotic sequence (CCS)-based noise reduction differential chaos shift keying (NR-DCSK) system under multipath Rayleigh fading channel conditions. The special characteristics of chaotic sequences are their deterministic randomness behaviour that adds security and multipath immunity to the data when used as a carrier in communication systems. In this paper, the chaotic sequences are generated by combining the outputs of chaotic maps, such as logistic map, Chebyshev map, Bernoulli shift map, tent map, etc., leading to new complex sequences known as CCSs. This sequence possesses more randomness, overcomes severe interference levels encountered during transmission and provides higher multipath immunity compared with those of pseudo-noise (PN) codes. Since NR-DCSK is a spread spectrum technique, its performance in wireless multipath fading channels has important considerations. The CCS is used as a carrier in NR-DCSK systems, which leads to improved bit error rate (BER) performance. Comparisons of simulation results to theoretical BER expressions of additive white Gaussian noise (AWGN) and Rayleigh fading channels have been carried out to test the efficiency of the proposed CCS-based NR-DCSK system.

In this paper, we analyze the performance of orthogonal frequency division multiplexing (OFDM) and carrier interferometry OFDM (CI/OFDM) for high-speed data rate wireless communication systems. For CI/OFDM realization, digital implementation of CI/OFDM structure is used in which CI code spreading and carrier allocation are separately processed by simple inverse fast Fourier transform. Based on previous work, a novel design of these systems is studied for multipath Rayleigh fading channel by using minimum mean square error equalization. The performance of OFDM and CI/OFDM wireless communication systems is compared based on peak to average power ratio, operating distance and bit error rate characteristics over independently additive white Gaussian noise and multipath Rayleigh fading channels. Simulation results show that CI/OFDM system is very useful for high-speed data rate wireless communication system and also provides wider operating range even in the presence of nonlinearity of the high power amplifier.

In multi-user wireless communication system, there is huge demand for higher data rates. One promising solution to achieve it is through the amalgamation of Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) technologies which results in Multi Carrier-CDMA (MC-CDMA) system. In CDMA system, the multiple access interference (MAI) can be reduced through proper selection of spreading codes. Bit error rate (BER) is an effective measure to evaluate the interference performance of a multi-user communication system. In this paper the BER and Peak to Average Power Ratio (PAPR) of MC-CDMA system is analyzed for different orthogonal spreading codes such as Walsh codes, complementary Golay codes and Orthogonal Gold codes in Rayleigh multipath fading channel employing Low Density Parity Check (LDPC) channel coding technique.

An approximate maximum likelihood (ML) method for joint estimation of time delays and directions-of-arrivals (DOAs) for the direct-sequence code-division multiple-access (DS-CDMA) systems over the multipath Rayleigh fading channels is developed. The proposed estimation scheme is developed by modeling the known training sequence of the desired user as the desired signal and the multiple access interference (MAI)-plus-AWGN as unknown colored Gaussian noise uncorrelated with the desired signal. An efficient iterative algorithm for estimating channel parameters (the time delays and DOAs of multipath signals) is proposed to reduce the computational complexity. The algorithm transforms the multi-dimensional maximization problem into two simple one-dimensional (1-D) maximization problems based on an iterative scheme. Analytical and simulation results are presented to illustrate the performance in comparison with the Cramer-Rao bounds (CRBs). It is shown that the proposed algorithm is near-far resistant for both time delay and DOA estimation and little performance loss is observed in comparison with the CRBs at reasonable SNRs.

This study assesses the performance of the decorrelating detector for DS-CDMA systems over multipath Rayleigh fading channels with AWGN. The decorrelating detector applies the inverse of the correlation matrix to decorrelate the matched filter outputs. The drawback of the decorrelating detector is that it enhances noise and that the inverse of the correlation matrix not always exists. The theoretical performance of the decorrelating detector is presented and the problem of inversion of the correlation matrix is discussed. This article also considers the case when the inverse of a smaller correlation matrix can be used for decorrelating the received data. The performance of the decorrelating detector is compared with other multi-user detectors proposed for DS-CDMA.

This letter investigates the issues on joint application of STBC systems and RAKE receivers in a CDMA system. We show the advantages of using STBC-RAKE receivers in multipath Rayleigh fading channels via error probability analysis and extensive computer simulations. Specifically, this study leads to a better understanding of the interplay between spatial diversity by STBC and multipath diversity via RAKE receivers.

Closed-form solutions for the average bit error rate (BER) performance of a direct-sequence code division multiple-access system with imperfect power control are derived for both coherent and noncoherent reception operating over a multipath Rayleigh fading channel. The RAKE structure receivers under consideration employ despreading sequences weighted by adjustable exponential chip waveforms optimized for multiple-access interference rejection. The chip-weighting waveforms employed are determined only by one parameter /spl gamma/ which leads to easy tuning of the waveforms in practice to achieve the best performance. The results indicate that the number of active users supported at a given BER for the case of /spl gamma/ tuned to maximize the average signal to interference plus noise ratio H/spl circ/ is much larger than the case of /spl gamma/=0 (fixed or rectangular despreading sequence). It is shown that imperfect power control affects the irreducible BER for the case of /spl gamma/=0. On the other hand, the effect of imperfect power control on the BER performance for the case of /spl gamma/ tuned to maximize H/spl circ/ is equivalent to a reduction in the average signal-to-noise ratio, and, hence, system performance can be compensated by increasing the transmitter power. It is further shown that the effect due to imperfect power control on BER performance is significant while that on the maximum value of H/spl circ/ obtained by tuning /spl gamma/ is rather insignificant.

This paper deals with performance evaluation of CDMA based on DS/SS/GMSK signaling with the differential detection over multipath Rayleigh fading channels. To demodulate DS/SS/GMSK signals, we consider differential detection, which does not need a carrier recovery. The bit-error-rate performance is evaluated in the presence of thermal noise and multiple-access interferences under the multipath Rayleigh fading environment.

Under the software environment of MATLAB/Simulink, the communication system of direct sequence spread spectrum (DSSS) is dynamically modeled and simulated over a new practical Rayleigh channel, and the relationship curves of the bit error rate (BER) with the signal-to-noise ratio (SNR) of DSSS communication systems are presented. It is analyzed that DSSS system can effectively overcome multipath fading in multipath Rayleigh Fading Channel (RFC). In addition, the anti-multipath fading performance improved by the way of increasing pseudo noise (PN) code length is better than that by the way of increasing the spread spectrum gain in the condition of strong multipath fading.