Single Carrier Frequency Division Multiple Access Systems Research Articles

Deep Learning-Based SC-FDMA Channel Equalization

It is very challenging to design an effective wireless communication system. That’s because of numerous factors affecting the performance of a typical wireless communication system, such as nonlinear channel distortions and impairments. single carrier frequency division multiple access (SC-FDMA) is a multiple access scheme that is an important part of the long-term evolution (LTE) standard for uplink transmission. An advanced mobile radio system’s multiple access schemes should indeed meet stringent requirements, such as a low bit error rate (BER). In this article, we investigate the equalization problem for nonlinear channel distortions and impairments using deep neural networks (NN). We introduce a novel combined deep neural network channel equalization and symbol detection scheme based on a deep learning (DL) recurrent feedback (RF) long short-term memory (LSTM) neural network to achieve blind equalization and decoding for SC-FDMA systems without knowing the channel state information (CSI). To train the model efficiently, the training data is gathered by simulation, with channel effects and noise treated as a complete black box. CSI and constellation demapping are learned by a deep neural network (DNN) model. Then, the frequency-domain sequences that have been corrupted are implicitly equalized to get the broadcasted signal back. Our specified SC-FDMA system, which uses a quadrature phase-shift keying (QPSK) modulation method and the suggested Deep Learning-based model channel equalizer, performs better than the existing equalizers by an average of 1 to 4 dB at moderate signal-to-noise (SNR) ratios, according to simulation data. A complexity comparison between the proposed and the conventional equalizers was conducted in terms of training time, execution time, and number of operations. On combined channel equalization and symbol detection, the suggested system delivers state-of-the-art performance.

On companding techniques for PAPR reduction in DCT SC-FDMA system in the presence of CFOs

In the single carrier frequency division multiple access (SC-FDMA) system, the use of discrete cosine transform (DCT) instead of discrete Fourier transform (DFT) has shown improved bit error rate (BER) performance. Nevertheless, peak-to-average power ratio (PAPR) in the DCT-based SC-FDMA system is higher than that in the DFT-based system. This paper investigates the performance of various companding schemes to reduce PAPR in DCT-based SC-FDMA systems by considering carrier frequency offsets (CFOs). Simulation results, considering parameters like BER, PAPR, and power spectral density (PSD), are provided to find the best companding technique. Furthermore, the results have been validated in a real-time indoor channel using a wireless open-access research platform (WARP) hardware.

Equalization Techniques for SC-FDMA Systems Under Radio Imbalances at Both Transmitter and Receiver

Orthogonal frequency division multiple access (OFDMA) is a multi-carrier, multiple access (MA) technique, which is widely adopted in contemporary wireless standards. Single carrier-frequency division multiple access (SC-FDMA) is a modified version of OFDMA which employs single carrier transmission by pre-coding the data symbols using discrete Fourier transform (DFT). However, these systems are highly vulnerable to the adverse effects arising in the channel, carrier frequency offset (CFO) and in-phase/quadrature phase (I/Q) imbalances. In the uplink communication scenario, the signal received at base station is the superposition of signals from all the active users. Even though the adverse effects caused by the communication channel and CFOs are addressed in the related literature extensively, the effect of I/Q-imbalances at the transmitter and the receiver is rarely considered. The effect of I/Q-imbalances will make the equalization process at the base station more complex. It is because the overall effective channel with radio impairments must be included in the system modelling. Hence the receiver processing should contain the equalization for effect of the channel, CFOs and I/Q imbalances. In this paper, we propose a novel technique based on the oblique projection (OP) technique for equalizing the channel, radio imbalances and synchronization errors caused by both transmitter (TX) and receiver (RX) for OFDMA/SC-FDMA uplink systems. We also propose an equalization technique with reduced computational complexity to overcome the adverse effects caused by I/Q imbalances and CFOs. The results of the simulation studies illustrate that the proposed techniques can compensate all the above-mentioned effects and they offer very good performance under both TX and RX I/Q imbalances.

Efficient Transmission of 2D Chaotic Maps Encrypted Images with DWT-Based SC-FDMA LTE System

The single-carrier frequency division multiple access (SC-FDMA) is a promising technique that has been adopted as an uplink transmission scheme in the long-term evolution (LTE) cellular system. This is attributed to its advantages such as the low peak-to-average power ratio (PAPR) and the utilization of frequency-domain equalizers to resolve the problem of inter-symbol interference (ISI). In this paper, a Discrete Wavelet Transform (DWT) based SC-FDMA system is proposed for the effective transmission of encrypted images. The 2D Chaotic baker map encryption algorithm has been used to encrypt images to enhance their security during transmission via SC-FDMA- based systems. The performance of the process of encrypted image transmission using the 2D Chaotic baker map algorithm with wavelet transform-based SC-FDMA (DWT SC-FDMA) system is evaluated in terms of different performance metrics, with comparison to Discrete Fourier Transform SC-FDMA (DFT SC-FDMA) and, Discrete Cosine Transform SC-FDMA (DCT SC-FDMA) systems. The viability of the proposed scheme was tested with different wireless channel models and different subcarriers mapping schemes. Experimental results show that the proposed method of the encrypted image transmission via the DWT SC-FDMA system provides a remarkable performance gain compared to the other versions of the SC-FDMA system in terms of the PSNR, and the BER metrics in the wireless channel models. It also demonstrates the effectiveness of the proposed scheme and adds a degree of encryption to the transmitted images through the wireless channels.

Design and Testbed Implementation of Multiuser CFOs Estimation for MIMO SC-FDMA System

In this paper, we propose and implement blind multiuser carrier frequency offsets (CFOs) estimation for multi-input multi-output (MIMO) single carrier frequency division multiple access (SC-FDMA) uplink system using orthogonal propagator method (OPM) over a noisy frequency-selective channel. The performance of typical OPM is limited at low signal-to-noise ratio (SNR) due to its noise-free signal model. The additive white Gaussian noise mainly impacts the diagonal elements of the data covariance matrix (DCM) of the received signal. First, the proposed fractional CFOs estimator minimizes the noise effect by reconstructing the denoised diagonal elements of the DCM for the received signal through cubic Hermite interpolation. Therefore, we use modified OPM to estimate multiple CFOs for MIMO SC-FDMA systems. Second, we have used an iterative method based on the first-order Taylor series approximation of the CFO vector to avoid peak ambiguity and reduce the number of iterations required in the grid search. The mean square error of the proposed CFO estimator considerably improves compared with the existing methods at a low SNR regime. The bit error rate performance of the proposed method for MIMO SC-FDMA is also compared with the existing methods. Finally, the proposed estimator is validated by implementing it on radio frequency hardware testbed over an indoor propagation environment.

Carrier frequency offset estimation for MIMO single-carrier FDMA system in wireless communication

Multiple-Input Multiple-Output (MIMO) Orthogonal Frequency-Division Multiplexing (OFDM) systems and Single-Carrier Frequency-Division Multiple Access (SC-FDMA) are so susceptible to carrier frequency offset (CFO) between transceivers. In this paper, a novel sequence called CAZBAR is proposed. The proposed CAZBAR sequence is based on constant amplitude zero autocorrelation (CAZAC) sequence and barker code. CAZBAR sequence shows better autocorrelation with higher peak at zero shift without ripples, which facilitates estimating carrier frequency offset in communication systems compared to other compensation methods in terms of mean square error (MSE). By applying CAZBAR sequence in MIMO SC-FDMA system 2 × 2 and 4×4, the bit error rate (BER) performance has improved significantly. At a BER=10-2, a SNR reduction of 11 dB is achieved for 2 × 2 system and 7 dB reduction for 4 × 4 system compared to other sequences. Which improves the performance of the whole system MIMO SC-FDMA. The CAZBAR sequence can be applied in 5G techniques, MIMO-OFDM, and MIMO SC-FDMA systems.

LDPC coded hybrid discrete cosine transform and Fejér–Korovkin wavelet transform-based SC-FDMA for image communication

A low-density parity-check (LDPC) coded single-carrier frequency-division multiple access (SC-FDMA) system is proposed for effective image transmission. The employment of the Fejér–Korovkin wavelet transform (FKWT) in combination with a discrete cosine transform (DCT) has been conceived in the proposed system. SC-FDMA is capable of mitigating the channel-induced dispersion at a low peak-to-average power ratio (PAPR). The performance of the proposed scheme is compared to that of the traditional wavelet transform-based SC-FDMA system in terms of different performance metrics. The scheme provides a remarkable performance gain compared to its LDPC coded wavelet transform-based SC-FDMA counterpart. Additionally, FKWT provides improved performance compared to the commonly used Haar wavelet transform-based system.

Walsh‐Hadamard‐transform‐based SC‐FDMA system using WARP hardware

Single-carrier frequency division multiple access (SC-FDMA) is currently being used in long-term evolution uplink communications owing to its low peak-to-average power ratio (PAPR). This study proposes a new transceiver design for an SC-FDMA system based on Walsh-Hadamard transform (WHT). The proposed WHT-based SC-FDMA system has low-PAPR and better bit-error rate (BER) performance compared with the conventional SC-FDMA system. The WHT-based SC-FDMA transmitter has the same complexity as that of discrete Fourier transform (DFT)-based transmitter, while the receiver's complexity is higher than that of the DFT-based receiver. The exponential companding technique is used to reduce its PAPR without degrading its BER. Moreover, the performances of different ordered WHT systems have been studied in additive white Gaussian noise and multipath fading environments. The proposed system has been verified experimentally by considering a real-time channel with the help of wireless open-access research platform hardware. The supremacy of the proposed transceiver is demonstrated based on simulated and experimental results.

WITHDRAWN: Iterative SIC algorithm based detection for multiuser MIMO SC-FDMA uplink system

Abstract In this article, an iterative successive interference cancellation (SIC) method is investigated for uplink multiple input multiple output (MIMO) single carrier frequency division multiple access (SC-FDMA). The real challenge of wireless communication is reliable symbol detection in MIMO SC-FDMA system. An iterative SIC detection method is a prominent technique which acquires low complexity and near -optimal performance for MIMO systems. MIMO SC-FDMA system with renowned multiuser linear data estimation methods are minimum mean square error (MMSE) and zero forcing (ZF) which are frequently employed in single-input single- output detector scheme owing to its affordable estimation and noteworthy performance improvement. Nevertheless, this technique performs matrix inverse calculation whose matrix size related to set of subcarriers utilized in the scheme, generally, it has around thousands. In realistic scenario, matrix inversion operations turn to very high the computational complexity. Therefore, in this contribution proposes an iterative SIC algorithm which achieves near optimal performance with lower complexity. The performance of linear receiver scheme and iterative SIC algorithm is simulated for diverse antennas configuration in MIMO SC-FDMA systems. As a results illustrate that iterative SIC algorithm outperforms conventional linear detection techniques. The analysis of the new detection approach observes good performance and the reduced complexity detection in MIMO SC-FDMA systems.

A low complexity iterative equalization technique for OFDMA and SC-FDMA uplink systems with Tx-Rx IQ imbalance and CFO under doubly selective channels

The next-generation wireless communication systems must address the compensation of in-phase and quadrature phase imbalance (IQI), carrier frequency offset (CFO), and doubly selective channel (DSC) to provide a high quality of service for high mobility users with low-cost radio . None of the existing works consider all these RF impairments under DSC for multi-user scenario. To address this gap, in this paper, we propose an iterative equalization technique to compensate the multi-user interference (MUI) and self inter-carrier interference (S-ICI) induced by the joint effect of transmitter IQI, receiver IQI, CFO and DSC for single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA) uplink systems. In each iteration of the proposed equalization technique, the extrinsic information from the decoder is used to cancel the MUI and S-ICI from the received signal. After interference cancellation, each mirror subcarriers pairs are equalized simultaneously. Additionally, unlike existing works, our proposed technique does not put any restriction on the carrier assignment scheme (CAS) used with OFDMA/SC-FDMA systems. Further, to validate the performance of the proposed compensation scheme analytically, we derive an upper bound on the bit error rate (BER) of coded OFDMA and SC-FDMA system without MUI and S-ICI. It is established that the system BER with the proposed technique satisfies the derived upper bound as the iteration converges, demonstrating the effective cancellation of MUI and S-ICI due to all the impairments.

Multiple transmit antennas for low PAPR spatial modulation in SC-FDMA: single vs. multiple streams

The main reason for the selection of single-carrier frequency division multiple access (SC-FDMA) modulation technique in mobile high data rate communications lays in its low value of peak-to-average power ratio (PAPR). If spatial modulation, a multiple-input multiple-output technique that achieves bitrate increase, is applied to the SC-FDMA system in its conventional form, the PAPR level is increased. Hence, based on previously mentioned, in this paper, we provide the general design criteria for low PAPR spatial modulation (LPSM) implemented in SC-FDMA systems with multiple transmit antennas. The straightforward generalization of LPSM is derived and it is shown that it requires the number of transmit antennas to be doubled in order to add another bit in the spatial component. Based on that, the alternative generalized technique with higher number of spatial bits is proposed. As these techniques present single-stream generalizations, the approach with multiple-streams is proposed as well. After PAPR and performance comparisons, it is concluded that single-stream techniques outperform multiple-stream techniques in the cases of low overall data rate, whereas multiple-stream approach is better in high overall data rate scenarios. All proposed techniques maintain low PAPR level on all transmit antennas.

Non Linear Companding Transform to Mitigate PAPR in DCT Based SC-FDMA System

Discrete cosine transform (DCT) based single carrier frequency division multiple access (SC-FDMA) system outperforms discrete Fourier transform based SC-FDMA (DFT SC-FDMA) system in terms of bit error rate (BER) performance. However, the peak-to-average power ratio (PAPR) of the DCT SC-FDMA system is slightly higher than that of the DFT SC-FDMA system. In this paper, a companding transform is proposed by approximating the distribution of magnitudes of DCT SC-FDMA signal and thereby transforming it into a triangular distribution. Proposed companding transform effectively reduces PAPR by maintaining the average power of companded signal. By clipping the companded signal to a specific threshold, PAPR can be reduced further. Moreover, the proposed technique causes fewer spectrum side-lobes than µ law and absolute exponential companding techniques. Simulated results ensure that proposed companding followed by clipping offers better PAPR and BER performances than the absolute exponential companding technique.

Low Complexity Linear Detection for Uplink Multiuser MIMO SC-FDMA Systems

In this article, the computational complexity reduction of zero forcing (ZF) and minimum mean square error (MMSE) detection is presented for the uplink multiple input multiple output (MIMO) single carrier frequency division multiple access (SC-FDMA) systems. MIMO SC-FDMA structure with detection of user’s data by the well-known multiuser linear detection approaches such as MMSE and ZF often use single input single output detection systems due to its simple detection and significant performance. Although, these approaches involve inversion of a matrix computation whose matrix dimension depend on number of subcarriers used in the system, mainly, it can be few thousands. In practical detection, the computational complexity of matrix inversion becomes very high. Also, the complexity of the receiver is raised because of the superposition of all the transmitted signals at each antenna received in the systems. The proposed conjugate gradient approach reduces the higher computational overhead of linear detectors, which updates iteratively the ZF and MMSE solution and avoids the direct computation of matrix inverse operation. The analysis of the proposed algorithm reveals the superior performance and the low complexity detection in spatial multiplexing SC-FDMA system. Simulations have investigated that the computational complexity of the proposed method has been greatly reduced and bit-error-rate performance is closer to matched filter bound.

On companding techniques to mitigate PAPR in SC-FDMA systems

Single Carrier Frequency Division Multiple Access (SC-FDMA) is being used successfully in the uplink communications of Long Term Evolution (LTE) standard. Owing to smaller envelope changes in SC-FDMA signal, it has a lower Peak to Average Power Ratio (PAPR) than Orthogonal Frequency Division Multiple Access (OFDMA) signal. But for higher order modulations, PAPR is still high and there is a requirement to mitigate PAPR in localised SC-FDMA systems. This paper discusses error function, exponential, rooting and logarithmic companding techniques that can be utilised to mitigate PAPR in SC-FDMA systems. Simulation results show that exponential companding technique provides better PAPR and Bit Error Rate (BER) performances at the cost of higher side lobes, and error function companding transform provides good PAPR and Power Spectral Density (PSD) performances at the cost of higher BER without increasing average signal power.

On companding techniques to mitigate PAPR in SC-FDMA systems

Single Carrier Frequency Division Multiple Access (SC-FDMA) is being used successfully in the uplink communications of Long Term Evolution (LTE) standard. Owing to smaller envelope changes in SC-FDMA signal, it has a lower Peak to Average Power Ratio (PAPR) than Orthogonal Frequency Division Multiple Access (OFDMA) signal. But for higher order modulations, PAPR is still high and there is a requirement to mitigate PAPR in localised SC-FDMA systems. This paper discusses error function, exponential, rooting and logarithmic companding techniques that can be utilised to mitigate PAPR in SC-FDMA systems. Simulation results show that exponential companding technique provides better PAPR and Bit Error Rate (BER) performances at the cost of higher side lobes, and error function companding transform provides good PAPR and Power Spectral Density (PSD) performances at the cost of higher BER without increasing average signal power.

Experimental Validation of Improved Exponential Companding Technique for SC-FDMA Systems Using WARP Hardware

As single-carrier frequency division multiple access (SC-FDMA) is used in long-term evolution (LTE) uplink communications, high peak-to-average power ratio (PAPR) increases power consumption in mobile devices. It is severe when localized subcarrier mapping is used with higher-order modulations. Companding is an attractive technique that offers a tradeoff between PAPR and bit error rate (BER) performances. This paper proposes an exponential companding technique that uses two companding levels based on a threshold, to reduce PAPR in SC-FDMA systems. It does not increase the average power level of transmitted signal and maintains the BER level without significant degradation from the original system. The proposed scheme has three parameters that can be adjusted for a tradeoff between PAPR, BER, and power spectral density (PSD) performances. Hence it offers more flexibility than the conventional exponential companding scheme. We also present scatter plots to find the optimum threshold value and companding levels. Finally, we verify the proposed technique considering a real-time indoor channel by using a wireless open-access research platform (WARP).

BER Evaluation in LTE SC-FDMA under Multipath Channels

Channel equalization is very essential step in Single Carrier Frequency Division Multiple Access (SC-FDMA) transmission for overcoming the inter-symbol interference (ISI). Also, to evaluate the data-link and network scheduling of LTE technique, a particular channel modelling is crucial. Due to the techniques’ complexity and requirement of high bandwidth for data transmission in literature, we motivated to perform a comparative analysis for BER reduction in SCFDMA scheme with and without equalizer. Therefor, in order to enhance efficiency of performance and functionality of network application, due to huge demand for lower delay, latency and higher speed by the modern users, BER reduction is a significant factor for enhancing signal quality. The substantial focus of this research is to improve the uplink signal of LTE technology by using two type of linear equalization methods such as zero forcing (ZF) and minimum mean square error (MMSE) at receiver part. Moreover, analysis of BER and SNR for SC-FDMA systems are obtained under several channel models and two different sub-mapping. This evaluation is performed for SC-FDMA in uplink by aid of adaptive modulation techniques like QPSK. Finally, for evaluating the channel equalization efficiency with SC-FDMA and for investigating the response of an uplink transmitter, MATLAB framework, is applied in this study. The results reveal that PAPR reduction does not have significant impact on BER performance.

A New Method to Enhance SC-FDMA Communication with Channel Estimation Errors

The single-carrier frequency division multiple access (SC-FDMA) system is a popular system in mobile communication because of its advantage of low peak-to-average-power-ratio (PAPR), and the use of frequency-domain equalizers to reduce inter-symbol interference (ISI) and inter-carrier interference (ICI). This paper presents a comprehensive study of the SC-FDMA system with PAPR reduction using clipping and filtering in the presence of channel estimation errors for two different versions of SC-FDMA adopting the FFT and the DCT. The effect of peak power reduction and the channel estimation error on the system bit error rate (BER) is investigated. Simulation results prove that the BER performance is not much affected by the PAPR reduction.

Simplified approach for symbol error rate analysis of SC-FDMA scheme over Rayleigh fading channel

In this paper, we present a comprehensive analytical study of the symbol error rate (SER) of single-carrier frequency-division multiple access (SC-FDMA) with zero-forcing frequency domain equalization (ZF-FDE) over a Rayleigh fading channel. SC-FDMA is considered as a potential waveform candidate for fifth-generation (5G) radio access networks (RANs). First, the NC fold convolution of the noise distribution of an orthogonal frequency-division multiplexing (OFDM) system is computed for each value of the signal-to-noise ratio (SNR) in order to determine the noise distribution of the SC-FDMA system. NC is the number of subcarriers assigned to a user or the size of the discrete Fourier transform (DFT) precoding. Here, we present a simple alternative method of calculating the SER by simplifying the NC fold convolution using time and amplitude scaling properties. The effects of the NC fold convolution and SNR over the computation of the SER of the SC-FDMA system has been separated out. As a result, the proposed approach only requires the computation of the NC fold convolution once, and it is used for different values of SNR to calculate the SER of SC-FDMA systems.

Image Transmission in 4G LTE using DWT based SC-FDMA System

In recent trends, the image transmission over wireless communication system in 4G LTE (Long Term Evolution) grow into a challenging task. OFDMA (Orthogonal Frequency Division Multiple Access) plays a key role in data transmission (text, image and video) over wireless systems. In OFDMA several transformation techniques have been used for the transmission of images. But they have some drawbacks such as increased number of carriers, increased delay estimation, high ISI and ICI. Hence, to overcome these drawbacks, an image transmission over wireless communication is proposed using DWT technique. OFDMA has several benefits like less complexity, high flexibility and high spectral efficiency. However, still, it lacks in noise reduction and increased error rates. To avoid these issues, SC-FDMA (Single Carrier Frequency Division Multiple Access) techniques is introduced in this work for the image transmission over wireless communication systems. In this proposed work, a DWT based SC-FDMA system is implemented to reduce the noise and interference using wavelet transform analysis. The performance measure of SNR, PSNR, BER and MSE for the proposed DWT based SC-FDMA system is evaluated using MATLAB. The results indicate that the proposed technique affords superior performance with a reduced BER.