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

Variable-dwell time code acquisition based on multiple-dwell or sequential linear test is investigated for direct-sequence spread spectrum systems on time-varying multipath Rayleigh fading channels. Not like the case of conventional additive white Gaussian noise channels, the channel memory incurred by multipath fading renders the exact analysis of the acquisition systems extremely difficult, if not impossible. A novel method is developed to evaluate the mean acquisition time of the acquisition systems to any desired accuracy. The effects of multipath fading are evaluated, and comparisons are made between the multiple-dwell and sequential linear tests. Numerical results show that multipath fading may result in 1-4 dB loss in performance, and the sequential linear test can outperform the multiple-dwell test by a margin of 1-2.5 dB. The analytical results are verified by computer simulations.

This paper investigates the use of convolutional coding in space-time minimum mean-square-error (MMSE) multiuser-based receivers over asynchronous multipath Rayleigh fading channels. We focus on the performance gain attained through error control coding when used with binary-phase-shift-keyed modulation (BPSK) and multiuser access based on direct sequence-code-division multiple access (DS-CDMA). In our analysis, we derive an approximation for the uncoded probability of bit-error in multipath fading channels. This bit-error rate (BER) approximation is shown to be very accurate when compared to the exact performance. For a convolutionally coded system, we obtain a closed form expression for the bit-error rate upper bound. This error bound is noted to be tight as the number of quantization levels increased beyond eight. Using our theoretical results, we obtain an estimate for the achieved user-capacity that accrues due to error control coding. It is found that using convolutional coding with 3-bit soft-decision decoding, a user-capacity gain as much as 300% can easily be achieved when complete fading state information plus ideal channel interleaving are assumed.

The paper analyzes time synchronization performance of non-coherent frequency hop spread spectrum (FH-SS) systems in multipath Rayleigh fading channels. The mean values and variances of the estimator are derived with the consideration of various multipath fading channel conditions. Results show that multipath fading has a greater effect on the mean values of the timing error estimation than on its standard deviations. The fact that the mean values of the estimated timing error may lose linear and zero-crossing properties due to the corruption of the multipath fading may mean that the usage of the spectral timing error estimation method for the time synchronization of an FH-SS system in multipath Rayleigh fading channels, currently a very common model for urban mobile radios, is inappropriate. >

The work is related to the use of Artificial Neural Network (ANN) assisted equalization as an aid to Maximal Ratio Combining (MRC) in order to improve bit error rate (BER) values of demodulated signals in wireless channels that have both Gaussian and multipath fading characteristics. Modulation technique used in this work is Bipolar Phase Shift Keying (BPSK) in Gaussian and multipath Rayleigh fading channels. The work considers the use of ANN block as part of a MRC set-up and is tested under SNR variation between -10 to 10 dB in Gaussian and multipath fading channels. The results generated justify the use of the ANN block as an aid to the MRC setup.

Spectrum sensing is one of the key challenges in the cognitive radio network. Primary user signal must be detected reliably in the low signal-to-noise ratio (SNR) regime and in multipath fading environments. This paper analyzes effects of time-variant multipath Rayleigh fading channel on cyclostationary characteristics and derives the relationship between cyclostationary statistics of transmitted and received signal. Depending on the distinct feature and the set of tested cyclic frequencies, the test statistics may have different performances. Cyclostationary features of small scale should be selected to be detected taking multipath effects into account. A novel solution to detect cyclostationary features combining time and frequency domain is proposed. Simulation results illustrating the reliability of solution as well as the effects of time-variant multipath fading channel on features are presented.

The performance of Reed-Solomon (RS) coded direct-sequence code division multiple-access (DS-CDMA) systems using noncoherent M-ary orthogonal modulation is investigated over multipath Rayleigh fading channels. Equal gain combining (EGC) diversity reception is invoked and the related performance is evaluated for both uncoded and RS-coded DS-CDMA systems. 'Errors-and-erasures' decoding is considered, where the erasures are based on Viterbi's (1982) so-called ratio threshold test (RTT). The performance of the 'errors-and-erasures' decoding technique employing the RTT is compared to that of 'error-correction-only' decoding over multipath Rayleigh fading channels. The numerical results show that when using RTT-based 'errors-and-erasures' decoding, RS codes of a given code rate can achieve a higher coding gain than without erasure information.

In the literature, the performance of maximum-likelihood sequence estimation (MLSE) equalization on multipath fading channels is analysed under the assumption of perfect channel estimates. In reality, this condition is difficult to attain, especially for fast fading channels. It is therefore of great significance to study the performance degradation due to imperfect channel estimates. In this paper, we consider a practical MLSE equalizer in conjunction with a least mean square (LMS) channel estimator and a simple channel predictor. A new upper-bound on block error rate is derived for multipath Rayleigh fading channels. >

The finite field wavelet spread signature CDMA (FFWSS-CDMA) system, with temporal and spectral diversities, is proposed data transmission in multipath slow fading channels. A scheme with hybrid successive and intracode interference cancellation (HSIIC) is developed for data detection. It is well known that the BER, performance of parallel interference cancellation (PIC) is superior to that of successive interference cancellation (SIC) in the situation of approximately equal received powers among different users. On the contrary, the SIC scheme outperforms PIC when the received powers are dissimilar in a fading channel. Due to the parallel transmitting structure of every user in FFWSS-CDMA, we employ the merit of PIC in the situation of equal received powers and that of SIC in a fading channel to design the HSIIC scheme. The interference cancellation has efficiently suppressed both intracode and multiple access interference of FFWSS-CDMA. Simulation results show that the proposed FFWSS-CDMA system with the HSIIC yields lower bit error rate (BER) than conventional DS-CDMA with SIC system in a multipath fading channel.

The problem of estimating code timings in DS-CDMA systems with multiple antennas is considered in the presence of multipath time-varying fading channels and near-far environments. We present an efficient algorithm for an approximate maximum likelihood approach of jointly estimating the multipath timings of a desired user for DS-CDMA systems that consist of multiple antennas either uncorrelated or fully correlated in space. The procedures of the algorithm to estimate code-timings are developed in order to better exploit the time-varying characteristics of the fading process. In the multipath fading channels, the solution of the proposed algorithms is based on successively optimizing the criterion for increasing numbers of multipath delays. It is shown via simulation results that the modified approaches of the approximate maximum likelihood algorithm much more improve its acquisition performance in the time-varying fading channels. It is seen that the acquisition performance of multiple antennas based acquisition scheme is much better than that of a single antenna based timing estimator in the presence of multipath fading channels and the near-far problem. Furthermore, it is observed that the proposed algorithms outperform the correlator and MUSIC estimator in the multiuser environments with near-far situation on time-varying Rayleigh fading channels.

The throughput enhancement of Space-Time Spreading (STS)-based Code Division Multiple Access (CDMA) system is investigated in this paper. Adaptive Modulation is utilized to improve the data throughput of the system in multipath Rayleigh fading channel. In this contribution, an analytical approach is proposed to compute a new expression for the Bit Error Rate (BER) performance and the output Signal-to-Interference-and-Noise Ratio (SINR) of the RAKE receiver-assisted STS-based CDMA system for QAM data, considering multipath and multiuser interferences. The other contribution of the paper is deriving a new closed form expression for computing the throughput enhancement and the BER performance of the adaptive modulated STS-based CDMA system over multipath fading channel. Simulation and analytical results demonstrate that using adaptive modulation method in this system improves the average throughput by keeping the BER performance at a target level. The novel expressions presented in this paper bring out the facility of evaluation of the proposed system with no need to more calculations and simulations.

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 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.

A combined precoding and turbo decoding strategy for multi-path frequency-selective fading channels is presented. The precoder and multi-path fading channel are jointly modeled as a finite-state probabilistic channel to provide the multistage turbo decoder with its statistics information. Both a priori and a posteriori probabilities are used in the metric computation to improve the system performance. Structures of the combined turbo-encoder, interleaver, and precoder in the transmitter and two-stage turbo decoder in the receiver are described. Performance of the proposed scheme in fixed, Rician and Rayleigh multi-path fading channels are evaluated by simulation. The results indicate that the combined precoding and two-stage turbo decoding strategy provides a considerable performance improvement while maintaining the same inner structure of a conventional turbo decoder.

Vehicle to everything (V2X) communication supports vehicle to anything communication for vehicle safety and cooperative Intelligent Transport System in vehicular environments. IEEE 802.11p modem has been developed and applied for V2X communication system. V2X radio channel has multipath fast fading due to moving vehicles and surrounded road structure. We proposed a new DFCE-AD which combines DFCE and antenna diversity for OFDM reception and analyzed the performance improvement in multipath fading channel. Through computer simulation, SNR gain of DFCE-AD over DFCE for QPSK modulation is approximately 6 dB at PER = 10%. In other word, PER of DFCE-AD is improved over that of DFCE by about 20% at SNR = 10 dB. This result will be applied for the short sized packet and low order OFDM modulation in vehicular multipath fading channel.

This study attempts to develop a time-scale deconvolution filter for optimal signal reconstruction of nonstationary processes with a stationary increment transmitted through a multipath fading and colored noisy channel with stochastic tap coefficients. A deconvolution filter based on wavelet analysis/synthesis filter bank is proposed to solve this problem via a three-stage filter bank. A fractal signal transmitted through a multipath fading and noisy channel is provided to demonstrate the design procedure's effectiveness and to exhibit the signal reconstruction performance of the proposed optimal time-scale deconvolution filter.