Filter Bank Multicarrier With Offset Quadrature Amplitude Modulation Research Articles

Channel estimation techniques based on intrinsic interference mitigation for FBMC/OQAM systems

Filter bank multicarrier with offset quadrature amplitude modulation (FBMC/OQAM) emerges as a noteworthy alternative to orthogonal frequency division multiplexing (OFDM). FBMC/OQAM addresses the limitations of OFDM by utilizing real-valued, even-symmetrical prototype filters with smaller side lobes and faster spectrum decay. This results in lower out-of-band energy and higher spectral efficiency (SE). However, the orthogonality condition of FBMC/OQAM in the real domain introduces an intrinsic interference (II) component that poses challenges for channel estimation (CE). The conventional straightforward OFDM CE techniques cannot be applied directly. To obtain a precise CSI with the FBMC/OQAM system, Kalman filter (KF) is altered and incorporated into the use of AP and coding. The first proposed method, KalCod, employs a data spreading method to diminish the II effect. The simulation results indicate that KalCod has a superior capacity to the other CE methods, while still maintaining a reasonable level of complexity. In the second proposed method, modified Kalman-auxiliary pilot (KAP), an AP is used to eliminate the II at pilot symbols then updating the channel coefficients using modified KF. When used as a CE method for FBMC/OQAM systems, the modified KAP outperforms its competitors in terms of estimation accuracy, simpler implementation, as well as higher throughput and spectral efficiency.

A hybrid approach based on companding and PTS methods for PAPR reduction of 5G waveforms

ABSTRACT As a crucial enabler for the fifth-generation air interface, the filter bank multicarrier with offset quadrature amplitude modulation (FBMC/OQAM) is being investigated by several researchers. This article suggests using partial transmit sequence (PTS) and companding to create a hybrid peak-to-average power ratio (PAPR) reduction strategy for FBMC/OQAM signals. In the novel PTS Companding scheme, there are several segments to the data block signal, and the overlapping factor determines the number of data blocks in each segment. To obtain the lowest signal power in each segment, we choose the best data block to broadcast and examine the next overlapping data block concurrently. After that, the segment FBMC/OQAM signal peaks are compressed using companding. Based on simulation results and analysis, the proposed hybrid PTS Companding method in FBMC/OQAM systems may reduce PAPR more effectively than conventional PTS and Companding schemes. According to simulation results, the hybrid process can achieve around 5 dB greater PAPR performance than the conventional PTS and companding schemes.

PAPR and BER Analysis in FBMC/OQAM System with Pulse Shaping Filters and Various PAPR Minimization Methods

Filter Bank Multicarrier with Offset Quadrature Amplitude Modulation(FBMC/OQAM) system design based on frequency sampling prototype filter takes into account the low frequency utilization of Orthogonal Frequency Division Multiplexing(OFDM) caused by adding Cyclic Prefix(CP). The CP decreases spectral efficiency and increases Peak to Average Power Ratio(PAPR). FBMC is an OFDM enhancement. In this paper to reduce the PAPR, we explained companding methods. We have proposed an FBMC that makes use of prototype pulse shaping filters which can be adjusted to meet system requirements in order to defeat these limitations. Due to its significant effect on the performance of FBMC-OQAM, choosing the right filter is crucial. Different prototype filters are used to investigate the performance of the FBMC-OQAM in this paper. Using the validated system, it was found that frequency utilization is more and good out-band suppression as well as an excellent application value in 5G technology. By using ?-law companding method, FBMC/OQAM provides better performance. It produces low PAPR, low out of band(OoB), high BER performance, less computational complexity and high spectral efficiency as compared to other methods.

Papr reduction of FBMC-OQAM signals using Phase Search-PTS and modified discrete fourier transform spreading

In this research, a novel peak-to-average power ratio (PAPR) reduction technique for filter bank multicarrier (FBMC) modulation systems is presented. With multicarrier systems like FBMC, the strategy focuses on the survival of the fittest principle to suit the value of PAPR. The Filter Bank Multicarrier with Offset Quadrature Amplitude Modulation (FBMC-OQAM) has recently captured the attention of numerous academics due to its minimal adjacent channel leakage ratio (CLR). Unfortunately, the issue of increased PAPR measurement has a negative impact on the effectiveness of the FBMC system's energy measurement. In this study, the Phase search-based Partial Transmit Sequence (PS-PTS) approach and Modified Discrete Fourier Transform Spreading (MDFT) are developed for the PAPR reduction of the FBMC-OQAM signals. The increased PAPR measurement is reduced using the PTS and MDFT with osprey optimization method, which may result in a PAPR reduction of roughly 5.1 dB as comparable to the conventional approach.

Analysis of peak-to-average power ratio in filter bank multicarrier with offset quadrature amplitude modulation systems using partial transmit sequence with shuffled frog leap optimization technique

<p class="Abstract">Because of its low adjacent channel leakage ratio, the Filter Bank Multicarrier with Offset Quadrature Amplitude Modulation (FBMC-OQAM) has sparked the attention of many researchers in recent times. However, the problem of high Peak-to-Average Power Ratio (PAPR) measurement has a detrimental influence upon the FBMC system's energy measurement efficiency. We study PAPR reduction of FBMC-OQAM signals using the Partial Transmit Sequence (PTS) methods in this work. The PTS with shuffled frog leap phase optimization method is proposed in this paper to reduce the larger PAPR measurement, which is the major disadvantage of the filter bank multicarrier with offset quadrature amplitude modulation system. According to the simulation software findings, the suggested approach has a considerably superior PAPR, which may reduce the PAPR by about 2 dB at complementary cumulative distribution function 10<sup>-3</sup> when compared to the traditional PTS method, and it has a much lower computational complexity than the previous ways. The experimental parameters are measured, and results are evaluated using MATLAB tool.</p>

Channel Estimation Based on Complex-Valued Neural Networks in IM/DD FBMC/OQAM Transmission System

Filter bank multicarrier with offset quadrature amplitude modulation (FBMC/OQAM) is a promising candidate for 5G mobile fronthaul system. Due to the inherent imaginary interference of FBMC/OQAM signals, an accurate channel estimation is particularly indispensable. In this paper, an efficient method is proposed based on complex-valued neural networks (CVNN) for an accurate channel estimation of FBMC/OQAM signals with low computational complexity and pilot overhead. Here, the channel frequency response (CFR) is first calculated for training the CVNN. Next, the CFR estimated from the extracted pilots is exploited as the input of the trained CVNN to yield the CFR of data symbols. We experimentally demonstrate a 12.5-GBd intensity modulation direct detection (IM/DD) FBMC/OQAM transmission system over 30-km and 50-km standard single mode fibers (SSMF). The experimental results show that the proposed method achieves 3-dB and 1-dB receiver sensitivity improvement at the bit error ratio (BER) of 3.8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> with only 5% pilot overhead respectively, compared to the conventional least square (LS) and linear minimum mean error (LMMSE) methods. When the pilot overhead decreases from 10% to 1%, its BER performance is always better than LS and LMMSE. For the computational complexity, its complexity is the same order of magnitude as LS and lower than LMMSE. On the other hand, the CVNN requires less hidden neurons to keep the similar BER performance as real-valued neural networks (RVNN). Meanwhile, it has excellent resilience to fiber chromatic dispersion over 30-km and 50-km SSMF.

Design and Validation of the Physical Layer Functions of FBMC/OQAM Transceiver With Improved Residual Phase Error Correction

In this paper, we report experimental results on the development and improvement of the physical layer functions of a filter bank multicarrier with off-set quadrature amplitude modulation (FBMC/OQAM) transceiver using a testbed implemented with programmable software-defined radio (SDR). The developed physical layer approach is similar to the IEEE 802.11a standard, and it has been tested for timing synchronization, carrier frequency offset (CFO) correction, channel estimation and equalization. An investigation into the inherent intrinsic imaginary interference in FBMC/OQAM has been carried out, with initial findings indicating the seriousness of the effect of phase noise (PN). The conventional pilot structure used in IEEE 802.11a cannot be directly applied to FBMC/OQAM, thus, a specially designed pilot scheme is proposed to deal with the residual phase error. Three phase noise estimation schemes have been evaluated, namely phase noise compensation (PNC), extended Kalman filter (EKF) and modified blind phase searching (MBPS) methods. To further suppress the residual interference and enhance the phase error correction, an iterative technique is used after the pilot equalization. The performance of the proposed methods has been evaluated experimentally and via simulation for an indoor environment. The results verify the capabilities of the proof-of-concept transceiver and the developed physical layer functions.

Minimizing the PAPR for FBMC/OQAM Signals Using Enhanced-PTS with Low Complexity Search

The filter bank multicarrier with offset quadrature amplitude modulation (FBMC/OQAM) scheme has recently become a focus of interest for many scholars and researchers. Despite its impressive advantages over Orthogonal Frequency Division Multiplexing (OFDM), the FBMC/OQAM system exhibits high Peak-to-Average Power Ratio (PAPR) which could plague its performance if it is not properly managed. In this paper, we proposed a PAPR reduction scheme that improves the Partial Transmit Sequence (PTS) to an enhanced PTS (EPTS), then employs a low complexity search to determine the optimal combination of phase factors. In the enhanced PTS, the FBMC/OQAM data blocks are partitioned into sub-blocks by taking into account their overlapping arrangement, then a segmentation operation is performed to the overall overlapping partitioned data blocks in order to form several segments of sub-blocks. After that, the segments are optimized consecutively by applying a phase factor search approach. Referred to as enhanced PTS with iterative flipping (EPTS-IF), the proposed scheme optimizes consecutively the segments of sub-blocks by employing Iterative Flipping approach. The PAPR reduction performance and the computational complexity of the proposed scheme have been evaluated through computer simulations and theoretical analysis which revealed a significant PAPR reduction gain of approximately 30.48%, and at a low computational cost.

Partial transmit sequence based on discrete particle swarm optimization with threshold about PAPR reduction in FBMC/OQAM system

Partial transmit sequence (PTS) is an effective method to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) system, but it is not suitable for the filter bank multi-carrier with offset quadrature amplitude modulation (FBMC/OQAM) system because of the overlapping structure of FBMC/OQAM signals. And PTS needs the traversal method to search for the optimal solution, which will increase the complexity of the system. To overcome this shortcoming, a PTS based on discrete particle swarm optimization with threshold (PTS-DPSO-TH) is proposed and applied to FBMC/OQAM system in this paper. PTS-DPSO-TH uses discrete particle swarm optimization (DPSO) to search for the optimal solution, effectively reducing the excessively high PAPR of the FBMC/OQAM system and avoiding the increase of system complexity. Secondly, the threshold is introduced to decrease the number of iterations and further reduce the system's complexity on the premise of guaranteeing the performance of PAPR reduction. Furthermore, through simulation, the effects of multiple parameters on PAPR reduction performance of PTS-DPSO-TH are compared and analysed.

Precoding-Enabled FBMC/OQAM for Short-Reach IMDD Transmission

Filter bank multicarrier with offset quadrature amplitude modulation (FBMC/OQAM) can provide higher spectral efficiency and lower out-of-band spectral/power leakages than conventional orthogonal frequency-division multiplexing with QAM (OFDM/QAM). Due to the imperfect frequency response of electrical/optical devices and various interferences, significant subcarrier SNR fluctuation may result in poor bit error rate (BER) performance. In this work, channel-independent precoding techniques are employed for the short-reach FBMC/OQAM-based intensity-modulated and direct-detection (IMDD) system. Four commonly used precoding techniques are experimentally investigated in a directly-modulated laser-based IMDD FBMC/OQAM and OFDM/QAM systems over a 20-km fiber link. The relevant results exhibit that the receiver sensitivity of these two systems can be improved by about 2 dB with precoding techniques at the BER of 3.8e-3. A slight BER enhancement can also be achieved by the precoded FBMC/OQAM compared to the precoded OFDM/QAM.

Supervised learning and frequency domain averaging‐based adaptive channel estimation scheme for filterbank multicarrier with offset quadrature amplitude modulation

Filterbank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) is an attractive alternative to the orthogonal frequency division multiplexing (OFDM) modulation technique. In comparison with OFDM, the FBMC-OQAM signal has better spectral confinement and higher spectral efficiency and tolerance to synchronization errors, primarily due to per-subcarrier filtering using a frequency-time localized prototype filter. However, the filtering process introduces intrinsic interference among the symbols and complicates channel estimation (CE). An efficient way to improve the CE in FBMC-OQAM is using a technique known as windowed frequency domain averaging (FDA); however, it requires a priori knowledge of the window length parameter which is set based on the channel's frequency selectivity (FS). As the channel's FS is not fixed and not a priori known, we propose a k-nearest neighbor-based machine learning algorithm to classify the FS and decide on the FDA's window length. A comparative theoretical analysis of the mean-squared error (MSE) is performed to prove the proposed CE scheme's effectiveness, validated through extensive simulations. The adaptive CE scheme is shown to yield a reduction in CE-MSE and improved bit error rates compared with the popular preamble-based CE schemes for FBMC-OQAM, without a priori knowledge of channel's frequency selectivity.

Cyclic Shift Based Tone Reservation PAPR Reduction Scheme with Embedding Side Information for FBMC-OQAM Systems

The tone reservation (TR) scheme is an attractive method to reduce peak-to-average power ratio (PAPR) in the filter bank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) systems. However, the high PAPR of FBMC signal will severely degrades system performance. To address this issue, a cyclic shift based TR (CS-TR) scheme with embedding side information (SI) is proposed to reduce the PAPR of FBMC signals. At the transmitter, four candidate signals are first generated based on cyclic shift of the output of inverse discrete Fourier transform (IDFT), and the SI of the selected signal with minimum peak power among the four candidate signals is embedded in sparse symbols with quadrature phase-shift keying constellation. Then, the TR weighted by optimal scaling factor is employed to further reduce PAPR of the selected signal. At the receiver, a reliable SI detector is presented by determining the phase rotation of SI embedding symbols, and the transmitted data blocks can be correctly demodulated according to the detected SI. Simulation results show that the proposed scheme significantly outperforms the existing TR schemes in both PAPR reduction and bit error rate (BER) performances. In addition, the proposed scheme with detected SI can achieve the same BER performance compared to the one with perfect SI.

Alamouti code based on block repetition in FBMC/OQAM systems

In this paper, we address the Alamouti code in Filter-Bank Multicarrier with Offset Quadrature Amplitude Modulation (FBMC/OQAM) and propose a novel block-wise Alamouti code, in which a repeated block is designed to eliminate the imaginary interference among FBMC/OQAM symbols. The proposed approach exhibits a higher spectral efficiency than the conventional block-wise Alamouti scheme, as only one column of zero symbols is used as a guard interval instead of two. Furthermore, compared to the conventional scheme, the bit error ratio is improved in the proposed block-wise Alamouti, as the assumption on channel invariance at two adjacent subcarriers is not required. Simulation results indicate that, with a significantly reduced overhead, the proposed Alamouti scheme achieves better performance over the conventional block-wise Alamouti scheme.

New scheme for PAPR reduction in FBMC-OQAM systems based on combining TR and deep clipping techniques

Filter bank multi-carrier with offset quadrature amplitude modulation (FBMC-OQAM) system is a very efficient multicarrier modulation technique for 5G, but it suffers as all multicarriers designs from large peak-to-average power ratio (PAPR). Tone reservation (TR) is a method designed to solve this problem by reserving several subcarriers called tones in the frequency domain to generate a cancellation signal in the time domain to eliminate high peaks. In this paper, we suggest a serial combination of tone reservation (TR) method with an enhanced version of clipping called deep clipping (DC) method (TR&amp;DC) to enhance the peaks (PAPR) mitigation in FBMC-OQAM signal model without significantly impacting the quality of transmission. Numerical results and analysis show that the new TR&amp;DC approach allows better overall performance and offers remarkable gain in term of PAPR mitigation than the TR method, with similar BER performance to TR over additive white gaussian noise channel and Rapp HPA model.

Sparse Bayesian learning based channel estimation in FBMC/OQAM industrial IoT networks

The next generation of communication technology is accelerating the transformation of industrial internet of things (IIoT). Filter bank multicarrier with offset quadrature amplitude modulation (FBMC/OQAM), as a candidate wireless transmission technology for beyond fifth generation (5G), has been widely concerned by researchers. However, effective channel estimation (CE) in IIoT communication should be solved. In practice, wireless channels have block–sparse structures. For the conventional sparse channel model, the general sparse channel estimation methods do not take the potential block–sparse structure information into account. In this paper, we have investigated the sparse Bayesian learning (SBL) framework for sparse multipath CE in FBMC/OQAM communications. Block SBL (BSBL) algorithm is proposed to estimate the channel performance by exploiting the block–sparse structure of sparse multipath channel model. The BSBL method can improve the estimation performance by using the block correlation of the training matrix. Computer simulation results demonstrate the robustness of the BSBL CE approach in FBMC/OQAM systems, which can achieve lower mean square error (MSE) and bit error rate (BER) than traditional least squares (LS) method and classical compressive sensing methods. The state of art compressive sampling matching pursuit (CoSaMP) greedy algorithm with a prior knowledge of sparse degree can provide slightly better CE performance than BSBL algorithm, but the proposed method maintains robustness in practical channel scenario without the prior knowledge of sparse degree.

Channel Estimation Approach with Low Pilot Overhead in FBMC/OQAM Systems

In filter bank multicarrier with offset quadrature amplitude modulation (FBMC/OQAM) systems, a large pilot overhead is required due to the existence of the imaginary interference. In this paper, we present an approach to reduce the pilot overhead of channel estimation. A part of pilot overhead is used for transmitting data, and compensating symbols are required and designed to remove the imaginary interference. It is worthwhile to point out that the power of compensating symbols can be helpful for data recovery; hence, the proposed approach decreases the overhead of pilots significantly without the cost of additional pilot energy. In addition, the proposed scheme is extended into multiple input multiple output systems without the performance loss. Compared with the conventional preamble consisting of 3 columns symbols, the pilot overhead is equivalent to 2 column symbols in the proposed preamble. To verify the proposed preamble, numerical simulations are carried out with respects to bit error ratio.

Peak-to-Average Power Ratio Reduction Method Based on Partial Transmit Sequence and Discrete Fourier Transform Spreading

Recently, filter bank multicarrier with offset quadrature amplitude modulation (FBMC/OQAM) has received increasing attention from researchers, owing to its merits and superior spectral efficiency. High peak-to-average power ratio (PAPR) occurs in approximately all multicarrier systems, including FBMC/OQAM, and may cause bit-error-rate (BER) degradation if not appropriately handled. Conventional PAPR reduction methods for orthogonal frequency division multiplexing (OFDM), such as partial transmit sequence (PTS), selective mapping (SLM), and discrete Fourier transform (DFT) spreading, are ineffective in FBMC/OQAM because of the different structure of the symbols. This study proposes a novel method combining DFT spreading and PTS methods to reduce the PAPR of FBMC/OQAM systems with reasonable computational complexity. Numerical results obtained from various computer simulations show that the proposed method achieves a noticeable enhancement in the PAPR performance of the FBMC/OQAM signal compared to other existing methods without affecting the BER performance. Further, the computational complexity analysis and BER performance of the proposed method are presented in comparison to typical existing methods. From our computer simulations, the proposed method reduces the PAPR by approximately 32.8% compared to that of the conventional methods, and the BER performance is improved by 25% with a high-power amplifier effect.

Joint Channel Estimation and Equalization Using New AFB Output Signal Models for FBMC/OQAM Systems

Filter bank multicarrier with offset quadrature amplitude modulation (FBMC/OQAM) has been studied as an alternative waveform for post-orthogonal frequency division multiplexing (OFDM) wireless communications. However, due to the intrinsic imaginary inter-carrier/inter-symbol interference of FBMC/OQAM signals, accurate channel estimation and equalization remain open issues for FBMC/OQAM systems in dispersive channels. In this article, two new signal models of the analysis filter bank (AFB) output are first derived in the absence of any channel assumption and in the presence of a relaxed channel assumption, respectively. Based on the new-built models, initial channel estimation with least squares (LS) (IniCE-LS) is presented and its output is used as the initial condition of recursive weighted LS (RWLS) estimation; moreover, non-iterative and iterative channel equalization combined with RWLS channel estimation (i.e., N-ICE-RWLS and ICE-RWLS) are proposed by using the real-time reconstructed FBMC/OQAM data symbols as pilots. The proposed N-ICE-RWLS and ICE-RWLS schemes not only allow to improve channel estimation and equalization performance, but also achieve high transmission efficiency. Considering the requirements of practical application, we further develop the low-complexity implementation methods of N-ICE-RWLS and ICE-RWLS. All these schemes are validated by analyzing the channel estimation accuracy and bit error rate (BER) over various frequency selective channels.

Reduced PAPR Model Predictive Control based FBMC/OQAM signal for NB-IoT paradigm

The competent class of fifth-generation mobile network used in NB-IoT demands for an extended and efficient massive device to a device communication system that exhibits narrow band with a focus on maximum spectrum resource usage, time and frequency synchronization and minimum out of band leakage. Filter bank multi-carrier with offset quadrature amplitude modulation (FBMC/OQAM) based systems act as a remarkable candidate for the fulfilment of application requirements of NarrowBand Internet of Things (NB-IoT) but suffer high peak to average power ratio (PAPR). Due to the overlapping of signals in the FBMC/OQAM structure, the basic SLM and PTS techniques cannot be applied on FBMC/OQAM systems. Therefore, in this work, a novel, cost-effective and low computation complexity solution SLM-MPC scheme is proposed which utilizes Model Predictive Control (MPC) algorithm for the optimization of PAPR of FBMC/OQAM transmitted signal and a significant reduction in PAPR of the FBMC/OQAM signal has been observed with negligible change in the BER of the system. The mathematical analysis is provided which justifies the simulation results and addresses the effectiveness of the proposed technique achieving a PAPR reduction of 1.61 dB and 1.2 dB for the number of sub-carriers as 128 and 256, respectively in comparison of SLM based FBMC/OQAM system.

An Imaginary Interference-Free Method for MIMO Precoding in FBMC/OQAM Systems

Due to the imaginary interference, the filter bank multi-carrier with offset quadrature amplitude modulation (FBMC/OQAM) performs poor in context of multiple-input multiple-output (MIMO) communication scenarios. In this article, we propose an imaginary interference-free method for FBMC/OQAM, which is appropriate for both of the subcarrier-based singular valued decomposition (SVD) precoding as well as subband-based precoding with codebook schemes. Specifically, the critical design utilizes a repeated block with the reverse arrangement of symbols. Moreover, we investigate the leakage of imaginary interference of the precoding MIMO-FBMC/OQAM system under frequency selective channel. It is found that these developed precoding solutions may particularly inhibit the inter-carrier interference (ICI) via the meticulous designed symbols block. Theoretical analysis and simulation results over different frequency selective channels validate that the proposed precoding schemes are capable of providing considerable performance gains over the conventional schemes in terms of bit error rate (BER).