Frequency-selective Rayleigh Fading Channels Research Articles

A space wavelet block codes MIMO SC-WDMA systems

In this paper, a novel space-wavelet block codes single-carrier wavelet-division multiple access (SWBC SC-WDMA) multiple-input multiple-output (MIMO) transceiver is proposed. The proposed MIMO transceiver system improves both of the bit error rate (BER) performance and the peak-to-average power ratio (PAPR) performance. Bit error rate (BER) analysis of the proposed SWBC SC-WDMA system over a frequency selective Rayleigh fading channel is presented for the case of zero-forcing (ZF) equalization and QPSK modulation. Comparisons of the BER and PAPR performances between the proposed SWBC SC-WDMA system and the conventional space-frequency block codes single-carrier frequency-division multiple access (SFBC SC-FDMA) system are illustrated. The simulation results show that the proposed SWBC SC-WDMA system has superior improvements in both PAPR and the BER performances.

Radio over Fibre Transport of Alamouti-coded MIMO Signals with Self-Recovery Capability

Abstract Radio over Fibre (RoF) transport of high-speed wireless data provides a comprehensive solution for the forthcoming highly-reliable and spectral-efficient wireless systems. MIMO is one of the most widely used wireless technologies to increase the system reliability and capacity without any increased demand of power/bandwidth. However, the inherent non-linearities of RoF link and the multipath fading of the wireless channel can degrade the overall performance of the wireless system. In this work, authors demonstrate RoF transport of adaptively modulated MIMO signals and report the improvement in spectral efficiency under the impact of RoF link non-linearity. The transmitter of the proposed RoF based wireless system selects the appropriate modulation scheme with the assumption of perfect channel state information to achieve the acceptable BER at the subscriber end. The spectral efficiency improvement by this self-recovering MIMO-RoF system is evaluated by incorporating orthogonal Space-Time Block Code with 2 × 2 antenna configuration over the frequency-selective Rayleigh fading channel.

BER Evaluation of OFDM Systems With Joint Effect of TI-ADC Circuit’s Gain Mismatch and Channel Estimation Error

The identification of maximum tolerable levels for potential mismatches is critical when designing communication systems. In this paper, we derive maximum tolerable levels for time-interleaved analog-to-digital-converter (TI-ADC) gain mismatch in orthogonal frequency-division multiplexing (OFDM) systems. To this end, we first analytically evaluate the bit error rate (BER) for square quadrature amplitude modulated-OFDM systems that are impaired by: 1) the gain mismatch of a TI-ADC and 2) the channel estimation errors (CEEs) of a zero-forcing equalizer. Our analysis includes the cases of a frequency-selective Rayleigh fading channel and a wired channel. Next, built on the obtained BER expressions, a threshold is established on the gain mismatch level, at which an error floor caused by the gain mismatch is below a given BER value at high signal-to-noise ratios in the absence of CEEs. Finally, numerical results further show that if and only if we set the gain mismatch level below 0.25 of this threshold, there is essentially no BER performance degradation compared with the mismatch-free case.

Symbol Error Probability Analysis of DFrFT-Based OFDM Systems With CFO and STO in Frequency Selective Rayleigh Fading Channels

In this paper, we derive exact symbol error probability (SEP) expressions for orthogonal frequency-division multiplexing (OFDM) based on discrete fractional Fourier transform (DFrFT) when symbol timing offset (STO) and carrier frequency offset (CFO) are present together. Closed form expressions are derived for binary phase shift keying, quadrature phase shift keying, and 16-ary quadrature amplitude modulation in the case of transmission over a frequency selective Rayleigh fading channel. As it is well known, in OFDM the presence of CFO destroys the orthogonality between the sub-carriers, generating inter-carrier interference (ICI), while the presence of STO introduces intersymbol interference, between successive symbols, and phase rotations in frequency domain, within the same symbol. It is well recognized that an OFDM system based on DFrFT is more robust to ICI introduced by CFO than that based on discrete Fourier transform (DFT). Motivated by this, the combined effect of CFO and STO on the SEP of a DFrFT-based OFDM system is analyzed. Our results show that the DFrFT-based OFDM system outperforms that based on the DFT for different values of the DFrFT “angle parameter.” Monte Carlo simulations are used to demonstrate the correctness of the derived analytical expressions.

An Orthogonal Polynomial-Based Analytical Expression of Nonlinear Power Amplifier for FBMC Systems

A filter bank multicarrier modulation (FBMC) is a strong promising solution for the fifth generation (5G) and beyond in broadband wireless communications. Nonetheless, one of the main disadvantages of the multicarrier techniques-based communication systems is the high peak-to-average power ratio (PAPR) of transmitting signals resulting in a nonlinear distortion of the signals, which is caused by a high power amplifier (HPA). Many kinds of research related to the nonlinear distortions induced by HPA have been proposed. However, there are solely limited studies on the analytical derivation of the nonlinear HPA characteristic. In this paper, an orthogonal polynomial based-analytical expression of a nonlinear power amplifier for baseband uniform, exponential, and Rayleigh input distribution of FBMC systems is proposed. The probability of error performances (BER) comparison between the proposed orthogonal polynomial method and the conventional polynomial method is determined. In addition, a theoretical performance analysis of the proposed method is derived to evaluate the BER performances in the frequency-selective Rayleigh fading channel. In the simulation, the BER performance of a nonlinearly amplified FBMC systems is investigated at a different IBO. The simulation results indicate that the proposed orthogonal polynomial method significantly outperforms the conventional polynomial method in terms of a normalized mean squared error (NMSE) and BER performance. Moreover, the theoretical error probability is compared with the simulation results and it could be found that the theoretical BER performance is relatively close to the simulated result.

Improved distance metric technique for deriving soft reliability information over Rayleigh Fading Channel

This paper presents an improved Distance Metric (DM) technique for deriving soft reliability information over Rayleigh fading channel. We compared this proposed DM technique with the conventionally used DM technique in the literature. The conventional DM method derives the soft reliability information from the output received symbols while the proposed DM method derives the soft reliability information from the Channel State Information (CSI) which result due to variations in the channel gain. Performance analysis of these DM methods are verified over flat Rayleigh fading channels, and on time-varying frequency-selective Rayleigh fading channels using rectangular M-QAM and OFDM systems respectively. Also, two channel estimation techniques are used to derived the CSI assuming different normalized Doppler frequency and frame length size. The performance of the conventional and proposed soft reliability derivation methods are documented through computer simulations assuming Koetter and Vardy, Reed-Solomon (KV-RS) soft decision decoding algorithm as the Forward Error Correction (FEC) scheme. From the computer simulation results, the proposed DM method offers significant improvement in Codeword Error Rate (CER) performance in comparison with the conventional DM method with no significant increase in computational delay and time complexity. Keywords: CSI, cubic estimators, DM, fading channels, KV-RS decoder, LMMSE, OFDM, R-matrix, 16QAM

Distributed Polar Code Based on Plotkins Construction with MIMO Antennas in Frequency Selective Rayleigh Fading Channels

A Plotkin based polar coded orthogonal frequency division multiplexing (OFDM) with multiple input and multiple output (MIMO) antennas scheme is proposed and its performance over frequency selective Rayleigh fading channel has been evaluated. In the considered Plotkins construction, the longer length code word is formed on the basis of two shorter length code words. Due to the presence of a parallel split in the design of the considered Plotkins construction, the proposed scheme is efficiently extended to coded cooperative scenarios. As the relay always plays crucial role in the design of cooperative communication system, therefore an intelligent criteria for the selection of information bits is employed at the relay node. To check the efficacy and to maintain the complete fairness in the performance of the proposed coded cooperative scheme, the authors have also developed the traditional nested polar coded cooperative scheme in the context of OFDM with MIMO antennas. The Monte Carlo simulated bit error rate (BER) performance revealed that the proposed coded cooperative scheme outperforms the traditional nested polar coded cooperative OFDM with MIMO antennas scheme by gain of $$0.5 \;{\sim}\; 0.6$$ dBs. This significant gain in BER performance of the proposed coded cooperative scheme is made possible due to the efficient selection criteria and the joint successive cancellation (SC) decoding tecnique employed at relay node and at the destination node, respectively. Moreover, the proposed coded cooperative scheme outperforms its corresponding coded non-cooperative counterpart scheme by roughly a gain of 1 dB under identical conditions.

Estimation non-paramétrique par méthode à noyau de la probabilité d'erreur binaire dans les systèmes de communication numériques : un estimateur pour le calcul du taux d'erreur binaire des systèmes MAQ codés

The standard Monte Carlo estimations of rare events probabilities suffer from too much computational time. To make estimations faster, kernel-based estimators proved to be more efficient for binary systems whilst appearing to be more suitable in situations where the probability density function of the samples is unknown. We propose a kernel-based Bit Error Probability (BEP) estimator for coded M-ary Quadrature Amplitude Modulation (QAM) systems. We defined soft real bits upon which an Epanechnikov kernel-based estimator is designed. Simulation results showed, compared to the standard Monte Carlo simulation technique, accurate, reliable and efficient BEP estimates for 4-QAM and 16-QAM symbols transmissions over the additive white Gaussian noise channel and over a frequency-selective Rayleigh fading channel. Les estimations de probabilités d'événements rares par la méthode de Monte Carlo classique souffrent de trop de temps de calculs. Des estimateurs à noyau se sont montrés plus efficaces sur des systèmes binaires en même temps qu'ils paraissent mieux adaptés aux situations où la fonction de densité de probabilité est inconnue. Nous proposons un estimateur de Probabilité d'Erreur Bit (PEB) à noyau pour les systèmes M-aires codés de Modulations d'Amplitude en Quadrature (MAQ). Nous avons défini des bits souples à valeurs réelles à partir desquels un estimateur à noyau d'Epanechnikov est conçu. Les simulations ont montré, par rapport à la méthode Monte Carlo, des estimées de PEB précises, fiables et efficaces pour des transmissions MAQ-4 et MAQ-16 sur canaux à bruit additif blanc Gaussien et à évanouïssements de Rayleigh sélectif en fréquence.

End-to-End Performance Evaluation for MIMO-OSTBC Adaptive Modulation Over Rayleigh Fading Channel

This paper presents end-to-end performance evaluation for adaptive Orthogonal Space-Time Block Codes (OSTBC) Multiple Input Multiple Output (MIMO) communication system over frequency selective Rayleigh fading channel. The system operates with one, two, three or four transmit or receive antennas to transmit and receive any frame. The system uses an adaptation algorithm that dynamically adjusts the used number of transmit and receive antennas based on the difference between the target and actual frame-error rates (FER) of the overall system. In this way, the performance of the system can be controlled adaptively. Alamouti and other adaptation algorithms are implemented in this system. The results show that FER improve significantly as the SNR increases and when the SNR is small, the adaptive algorithms successfully adjust the use of MIMO antenna to compensate the impairment caused by the faded and noisy channel.

Fast Convolution Filter-Bank Based Non-Orthogonal Multiplexed Cognitive Radio (NOMCR) Receiver Design Using Cyclostationarity Based FRESH Filtering

Non-orthogonal multiple access (NOMA) systems are being considered as candidates for 5G wireless systems due to their promise of improved spectral efficiency. NOMA schemes are being combined with popular multicarrier schemes such as orthogonal frequency division multiplexing (OFDM) to take advantage of the benefits of multicarrier signals. A variant of the power domain NOMA is Layer Division Multiplexing (LDM). The most commonly deployed power domain LDM scheme involves successive interference cancellation (SIC) based decoding at the receiver. Fast convolution based filtered-OFDM (FC-F-OFDM) systems are becoming popular among 5G wireless access technologies due to their ability to process 5G physical layer signals efficiently. In this work, firstly, a cognitive multicarrier non-orthogonal multiplexed system based on the concept of LDM is discussed, which uses FC-F-OFDM and conventional OFDM as its component layers. Secondly, cyclostationary FREquency SHift (FRESH) filter based SIC decoding is used at the receiver side, which also utilizes artificial neural network (ANN) processing. Computer simulations indicate that the system provides good bit error rate (BER) performance under frequency selective Rayleigh fading channels.

Multi‐level construction of polar‐coded single carrier‐FDMA based on MIMO antennas for coded cooperative wireless communication

A multi-level construction of polar-coded single carrier frequency division multiple access (SC-FDMA) with multiple input multiple output (MIMO) antennas scheme is proposed and its bit error rate performance over frequency selective Rayleigh fading channels has been evaluated. The existence of a parallel split in the design of multi-level construction of polar code has enabled the authors to effectively extend the proposed scheme in coded cooperative scenarios. As in coded cooperation communication, the relay plays a crucial role in the design of communication system; therefore, an efficient selection criterion for reinforcing the bad channels has been adopted at the relay node. Moreover, the joint successive cancellation decoding is employed at the destination node. To check the efficacy in the performance of the proposed coded cooperative scheme, the authors have also upgraded the traditional nested polar-coded cooperative scheme in the context of SC-FDMA with MIMO antennas as a useful benchmark. Monte Carlo simulated results revealed that the proposed coded cooperative scheme have triumphed the conventional nested polar coded cooperative scheme based on SC-FDMA system by gain of 0.5 dB under identical conditions. Moreover, the proposed cooperative schemes outperform their corresponding non-cooperative counterpart schemes by the gain of 1 dB under identical conditions.

Reverse-link Power Allocation with Distributed Dynamic Channel Assignment in Mobile Cellular Systems

In this paper, assuming Direct Stage Code Division Multiple Access (DS-CDMA) [1], the author evaluate the throughput performance of turbo coded ARQ schemes over frequency-selective Rayleigh fading channel with antenna diversity reception and Rake combining. The theoretical expression for the turbo code in the presence of multiple channels was derived and the throughput performance evaluated by computer simulations firstly for ideal channel estimation and later compared with a practical channel estimation scheme called weighted multi-slot averaging (WMSA) channel estimation [2]. Studying the effect of various system parameters like the frame length, the fading rate, the spreading factor, the number of diversity antennas, the number of transmissions, number of users and propagation parameters like the fading rate and the power delay profile of the multipath channel (number of paths and profile shape) is the major contribution of this work.

Distributed polar-coded OFDM based on Plotkin’s construction for half duplex wireless communication

ABSTRACTA Plotkin-based polar-coded orthogonal frequency division multiplexing (P-PC-OFDM) scheme is proposed and its bit error rate (BER) performance over additive white gaussian noise (AWGN), frequency selective Rayleigh, Rician and Nakagami-m fading channels has been evaluated. The considered Plotkin’s construction possesses a parallel split in its structure, which motivated us to extend the proposed P-PC-OFDM scheme in a coded cooperative scenario. As the relay’s effective collaboration has always been pivotal in the design of cooperative communication therefore, an efficient selection criterion for choosing the information bits has been inculcated at the relay node. To assess the BER performance of the proposed cooperative scheme, we have also upgraded conventional polar-coded cooperative scheme in the context of OFDM as an appropriate bench marker. The Monte Carlo simulated results revealed that the proposed Plotkin-based polar-coded cooperative OFDM scheme convincingly outperforms the conventional polar-coded cooperative OFDM scheme by 0.5 ~ 0.6 dBs over AWGN channel. This prominent gain in BER performance is made possible due to the bit-selection criteria and the joint successive cancellation decoding adopted at the relay and the destination nodes, respectively. Furthermore, the proposed coded cooperative schemes outperform their corresponding non-cooperative schemes by a gain of 1 dB under an identical condition.

A Low Complexity Linear Moving Average Filtering Technique for PAR Reduction in OFDM Systems

In this paper, a linear moving average recursive filtering technique is proposed to reduce the peak-to-average power ratio (PAR) of orthogonal frequency division multiplexing (OFDM) signals. The proposed low complexity technique is analyzed in an oversampled OFDM system and a simple distribution approximation of the oversampled and linearly filtered OFDM signals is also proposed. Corresponding time domain linear equalizers are developed to recover originally transmitted data symbols. Through extensive computer simulations, effects of the new filtering technique on the oversampled OFDM peak-to-average power ratio (PAR), power spectral density (PSD) and corresponding linear equalizers on the frequency selective Rayleigh fading channel transmission symbol-error-rate (SER) performance are investigated. The newly proposed recursive filtering scheme results in attractive PAR reduction, requires no extra fast Fourier transform/inverse fast Fourier transform (FFT/IFFT) operations, refrains from transmitting any side information, and reduces out-of-band radiation. Also, corresponding linear receivers are shown to perform very close to their frequency domain counterparts.

Performance Analysis for the ${N}$ -Continuous Precoded SM-OFDM System

Combined with N -continuous (NC) precoding, the spatial modulation (SM) orthogonal frequency division multiplexing (OFDM) system offers considerable sidelobe suppression for the downlink transmission, at the cost of additional interference to the transmit signal. Therefore, this paper focuses on investigating the impact of the NC precoder on the bit error rate (BER) performance of the SM-OFDM system. The BER performance is analyzed over the frequency-selective Rayleigh fading channel under two distinct scenarios, i.e., perfect channel estimation and interference suppression based minimum mean square error (MMSE) channel estimation. First, we propose an approximate system model for the NC precoded SM-OFDM system along with an analysis on the introduced interference, and then derive the average BER performance of the system with perfect channel estimation. Based on the above proposed approximate system model, we further analyze the interference based upon MMSE channel estimation, and investigate the characteristics of channel estimation errors. Furthermore, we derive the average BER performance of the NC precoded SM-OFDM system with imperfect channel estimation. The numerical results show that the analytical BER closely matches its simulated counterpart under different system configurations, and demonstrate that the proposed approximate system model is in good agreement with the precise one.

Superposition Modulation-Based Cooperation for Oversampled OFDM Signals

This paper proposes an iterative detector for uncoded OFDM signals in cooperative networks, where the information symbols are simply partitioned through a time-domain matrix at the OFDM transmitter. We analytically show that our proposed iterative detector at the partner node converges and can completely recover the user’s data from its partitioned version, if sufficient redundancy is inserted in the user’s data. For efficient use of the redundancy in the user’s data, a coded cooperative transmission based on superposition modulation is proposed. Additionally, a closed-form input–output relationship for the partitioning and reconstruction algorithm in the proposed cooperative scenario is derived. We also obtain closed-form expressions for symbol error rate performance of the proposed coded cooperative scenario over Rayleigh frequency-selective fading channels. Numerical comparisons shed light on the relative merits of the proposed coded cooperation under various inter-user and uplink channel conditions.

Adaptive Double-Dwell Code Acquisition Scheme of PN Sequences Using Smart-Antenna and Automatic Censoring Techniques

An adaptive non-coherent smart-antennas double-dwell code acquisition scheme for code division multiple access (CDMA) communication systems is studied and analyzed in this work. A combination of adaptive thresholding based on constant false alarm rate algorithms and smart-antennas technique is considered. One of the most important problems of PN code acquisition for DS/SS-CDMA communication systems is the presence of multipath signals, which have a random structure. Accordingly, an adaptively varying threshold scheme using automatic censoring algorithm based on ordered data variability, namely the automatic censoring adaptive processor (ACAP) is considered to improve the system performance. The drawback of this algorithm is that a large processing time is required if the serial search code acquisition scheme is used. Hence, the double-dwell search-scheme is proposed to solve this problem. The performance of the proposed system is analyzed in frequency-selective Rayleigh fading channels. It is shown through simulation results that, the smart-antennas double-dwell acquisition scheme with the ACAP algorithm significantly outperforms the existing adaptive smart-antenna serial search single-dwell systems.

On the SINR statistics of a VFDM cognitive spectrum sharing system

An analytical precise approximation of the SINR statistics of the two-tier Vandermonde-subspace frequency division multiplexing (VFDM) cognitive spectrum sharing systems over frequency-selective Rayleigh fading channels is presented. It is shown that the gamma distribution provides the best fitting accuracy and that its use leads to simple, yet accurate, closed-form expressions for evaluating the ergodic capacity (EC) and average bit error probability (ABEP) performance of such systems. In deriving these expressions, the parameters of the gamma distribution have been obtained for various operating conditions of the considered VFDM system using distribution fitting. Furthermore, regression analysis has been used to obtain approximate analytical expressions for these parameters in relation to the system operating parameters. Performance evaluation results, obtained for various system implementations, including the standardized IEEE 802.11 and 3GPP LTE, are presented to demonstrate the validity of the proposed methodology. Its accuracy has been verified by means of computer simulations.

Channel estimation with ISFLA based pilot pattern optimization for MIMO OFDM system

In multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) systems, the channel state information should be known by the receiver for obtaining transmitted data. Channel estimation algorithms are used to examine the multipath effects of frequency selective Rayleigh fading channels. In this paper, Compressed Sensing (CS) based channel estimation technique is considered for reconstructing the signal with improved spectral efficiency. It requires transmitting the known pilot data to the receiver for estimating channel information. The optimum pilot patterns are selected through reducing the mutual coherence of measurement matrix. In order to maximize the accuracy of sparse channel estimation and to reduce the computational complexity, an optimization algorithm Improved Shuffled Frog Leaping (ISFL) is proposed. When compared with the traditional estimation methods like least squares (LS), and minimal mean square error (MMSE), 4.7% of spectral efficiency is increased with ISFLA based channel estimation. Implementation results show that, by using the proposed algorithm, the bit error rate (BER) and Mean Square Error (MER) performance of the system is increased with 1.5dB and 2dB respectively.

Mean Spectral Efficiency Evaluation of the Uplink of MC-CDMA Cellular Systems

The mean spectral efficiency of the uplink of MC-CDMA cellular systems is evaluated. The complete system employs the multicarrier-code division multiple access (MC-CDMA) technique, a linear antenna array at the base stations, frequency interleaving, maximal ratio combining, adaptive modulation, perfect power control and a cyclic prefix large enough to eliminate the intersymbol and intercarrier interferences effects. This scenario assumes the presence of multiple access interference, co-channel interference, additive white Gaussian noise, exponential path-loss and slow and frequency selective Rayleigh fading channel. In this context, a procedure to calculate the mean spectral efficiency of the cellular network is proposed, which depends of the mean bit error rate, the channel reuse factor, the increase of bandwidth due to the cyclic prefix, the system load, the spreading factor, the cell radius and the modulation schemes. Results show that an unitary channel reuse factor is the most efficient way to use the spectrum, but it is critical in relation to the transmission rates. Also, as orthogonal frequency division multiple access technique is a particular case of MC-CDMA, the spectral efficiency of both techniques is compared.