Multicarrier Modulated Signals Research Articles

Dual-band hybrid fiber-wireless delivery system for high-speed data communications in CRAN based on polarization multiplexing with switching capabilities

This work presents a Radio-over-Fiber architecture for Cloud Radio Access Networks (CRAN) based on polarization division multiplexing for delivering up-converted high-speed data signals using a single laser-photodetector pair and free of polarization tracking devices. This system enables the allocation of data signals in two different bands defined as low-frequency (5–25 GHz) and high-frequency (55–65 GHz) millimeter waves (mmWave). Polarization multiplexing ensures minimal crosstalk when data signals are photonically up-converted while providing all-optical inter-band switching capabilities. Proof-of-concept experiments have been performed by simultaneously transmitting NRZ and multi-carrier modulated (Discrete Multitone - DMT) data signals over a radio-over-fiber link consisting of 1 km of standard optical fiber and radio transmission in the 7.5 GHz (wired) and 60 GHz (wireless) bands, respectively, with an estimated potential total throughput of at least 7.5 Gbps when considering the transmission of NRZ signals in these mmWave carriers. Results exhibit a BER below the FEC limit of 3.8 × 10−3 in all cases analyzed when the received optical power at the remote radio head (RRH) is above −4 dBm. The reduced number of components and versatility of this implementation provide a cost-effective solution for delivering and switching high-speed data signals in RF fronthaul for future 5G/6G communications.

Automatic classification of multi-carrier modulation signal using STFT spectrogram and deep CNN

In the realm of communication systems, categorizing Multi-Carrier Modulation (MCM) signals without cooperative communication poses a significant technical challenge. In this paper, we introduce a novel approach for accurately categorizing five distinct MCM signals, including Orthogonal Frequency Division Multiplexing (OFDM), Filter Bank Multicarrier (FBMC), Filtered Orthogonal Frequency Division Multiplexing (FOFDM), Windowed Orthogonal Frequency Division Multiplexing (WOLA), and Universal Filtered Multicarrier (UFMC). Each signal is considered with two types of subcarrier waveforms, Quadrature Amplitude Modulation 16 (QAM16) and Quadrature Amplitude Modulation 64 (QAM64), resulting in a total of 10 unique MCM signals for classification. Our proposed methodology leverages Short-Time Fourier Transform (STFT) spectrograms for feature extraction at the frontend, while at the backend, we employ three variants of Convolutional Neural Network (CNN) models; CNN, CNN with Dropout (CNN_d), CNN with both Dropout and L1 Regularization (CNN_dL1) and one deep CNN model; Xception, individually. We aim to provide an efficient and reliable means of categorizing MCM signals, with practical applications in signal processing and communication systems. Extensive simulations demonstrate the effectiveness of our approach, achieving remarkable accuracies. Notably, the Xception model exhibits the highest accuracy among the four models considered. Specifically, we attain an accuracy of 98% at 10 dB SNR using the Xception model. These results underscore the efficacy of our proposed methodology and highlight the potential for its deployment in real-world scenarios.

Reconfigurable Intelligent Surface-based Propagation Control in FBMC/OQAM Systems

In this paper, transmission of filter bank multi-carrier (FBMC) modulated signal through reconfigurable intelligent surfaces (RIS) is proposed as an assuring technique for future wireless communication. RIS deliberately alters phases of incident signals to enhance quality of the received signal. Simulation outcomes show that it is possible to establish RIS-based FBMC communications in which RIS functions as an intelligent reflector with information concerning channel phases. It is observed that RIS-based FBMC transmissions may be a prospective solution for beyond 5G communication.

FFSCN: Frame Fusion Spectrum Center Net for Carrier Signal Detection

Carrier signal detection is a complicated and essential task in many domains because it demands a quick response to the existence of several carriers in the wideband, while also precisely predicting each carrier signal’s frequency centers and bandwidths, including single-carrier and multi-carrier modulation signals. Multi-carrier modulation signals, such as FSK and OFDM, could be incorrectly recognized as several single-carrier signals by using the spectrum center net (SCN) or FCN-based method. This paper designed a deep convolutional neural network (CNN) framework for multi-carrier signal detection by fusing the features of multiple consecutive frames of the broadband power spectra and estimating the information of each single-carrier or multi-carrier modulation signal in the broadband, called frame fusion spectrum center net (FFSCN), including FFSCN-R, FFSCN-MN, and FFSCN-FMN. FFSCN includes three base parts, the deep CNN-based backbone, the feature pyramid network (FPN) neck, and the regression network (RegNet) head. FFSCN-R and FFSCN-MN fusing the FPN out features, which use the Residual and MobileNetV3 backbone, respectively, and FFSCN-MN cost less inference time. To further reduce the complexity of FFSCN-MN, the designed FFSCN-FMN modifies the MobileNet blocks and fuses the features at each block of the backbone. The multiple consecutive frames of broadband power spectra not only preserve the high-resolution ratio of the broadband frequency, but also add the features of the signal changes in the time dimension. Extensive experimental results demonstrate that the proposed FFSCN can effectively detect multi-carrier and single-carrier modulation signals in the broadband power spectrum and outperform SCN in accuracy and efficiency.

A review of Peak to Average Power Ratio Reduction Schemes in OFDM Systems

This paper is concerned with the Orthogonal Frequency Division Multiplexing (OFDM) system that is adopted by a wireless communication system for transmitting multicarrier modulated signals simultaneously with robustness against interference and noise facing the system. It presents a significant issue related to the OFDM system known as the raise of Peak to Average Power Ratio (PAPR) that is the high peaks of OFDM signals compared to its average power. Increasing the PAPR yields in the component devices of the OFDM system does not cope with the high peaks resulting in distortion and signal losses. Therefore, the objective of this article is to review different approaches of PAPR reduction techniques and compare them to select the best technique for a particular system. The approaches are mainly of three classifications; distortion, probabilistic, and coding schemes with each including several techniques.

Genetic Algorithm Based Bilayer PTS Scheme for Peak-to-Average Power Ratio Reduction of FBMC/OQAM Signal

Partial transmit sequence (PTS) scheme has been well applied to reduce the high peak-to-average power ratio (PAPR) of the orthogonal frequency division multiplexing (OFDM) signal. However, due to the signal structure differences between the filter bank multicarrier and offset quadrature amplitude modulation (FBMC/OQAM) signal and the OFDM signal, the conventional PTS scheme is not applicable to the FBMC/OQAM signal. Considering the PAPR reduction issue for the FBMC/OQAM signal, this paper proposes a genetic algorithm (GA) based bilayer partial transmit sequence (GA-BPTS) scheme. In order to reduce the computational complexity, the proposed scheme continues to partition each subblock, transforming the single layer structure of the conventional PTS into a bilayer phase factor search structure, and introduces a penalty threshold. Then the suboptimal phase factor vector is obtained by using the GA. Meanwhile, before PAPR reduction processing, aided by the proposed prototype filter which has the better performance of out-of-band attenuation than the PHYDAYS filter, the GA-BPTS scheme can effectively reduce the PAPR of the FBMC/OQAM signal. The simulations have confirmed that the proposed scheme not only provides an excellent PAPR performance but also decreases the computational complexity compared with the conventional PTS scheme.

Analysis of Simplified Frame Synchronization Scheme for Burst-Mode Multi-Carrier System

Frame synchronization is one of the basic function units in a burst-mode digital communication receiver. In a lot of burst communication systems, a preamble is placed at the start of a signal burst for synchronization and channel estimation. Using a cross-correlation detector to calculate the correlation between the local preamble sequence and the received preamble sequence is a common synchronization method. Simplified cross-correlation-detector which quantizes each detected sample into 1 bit can dramatically reduce the consumption of the chip resource when implemented in hardware. In this letter, the performance analysis for a simplified cross-correlation-detector whose input is multi-carrier modulated signal is presented. The relationships between correlation length, decision threshold, and the probabilities of false alarm and missing detection are given. The correctness of the detector is validated through system simulations and numerical calculations.

Classification of multi-carrier digital modulation signals using NCM clustering based feature-weighting method

This work presents a novel digital modulation signal classification model by combining Neutrosophic c-means (NCM) based feature weighting (NCMBFW) and classifier algorithms. As the digital modulation signal, the multi-carrier amplitude shift keying (MC-ASK), frequency shift keying (MC-FSK), and phase shift keying (MC-PSK) modulation types are employed. In the first step, the feature extraction process has been conducted from the raw digital modulation signals and thereby extracted time, frequency, and time-frequency domain features from the multi-carrier ASK, FSK, and PSK signals. After that, these features have been weighted by using NCMBFW. Finally, classifier algorithms including Linear Discriminant Analysis (LDA), Support Vector Machine (SVM), k-nearest neighbor (k-NN), AdaBoostM1, and Random Forest, have been used to determine the types of digital modulation signals automatically. Many metrics are used to evaluate the performance in the experiments. The proposed method in the classification of MC digital modulation signals is the first work with respect to the classification of MC modulation signals in the literature. For worst case (in 5 dB), while the obtained f-measure values are 0.842, 0.848, 0.863, 0.842, and 0.894 using LDA, SVM, k-NN, AdaBoostM1, and Random Forest classifiers without NCMBFW, respectively, while the f-measure values by combining NCMBFW with classifier algorithms are 0.983, 0.976, 0.992, 0.988, and 0.991, respectively. The experimental results show that the proposed NCMBFW can be considered as a promising tool to improve the classification performance of digital multi-carrier modulation signals.

A low-power high-performance digital predistorter for wideband power amplifiers

In this paper, we present a low-power high-performance digital predistorter (DPD) for the linearization of wideband RF power amplifiers (PAs). It is based on the novel FIR memory polynomial (FIR-MP) predistorter model, which significantly augments the performance of the conventional memory polynomial predistorter with the use of complex baseband digital FIR filter prior to the memory polynomial. The adjacent channel leakage ratio (ACLR) performance comparison between the conventional MP and the proposed FIR-MP is done based on simulations with multi-carrier modulated signals of 20 and 80 MHz bandwidths. The PA models used for the simulations are extracted from the measurements of a commercial $$1\,\hbox {W}$$ GaAs HBT PA. At the ideal system-level simulations, the improvements in ACLR over the conventional MP are 7.2 and 15.6 dB, respectively, for 20 and 80 MHz signals. The choice of selection of various parameters of the predistorter along with the subsequent digital-to-analog converter (DAC) is presented. The impact of fixed-point representation is assessed using ACLR metrics, which shows that a wordlength of 14 bits is sufficient to obtain ACLR beyond $$45\,\hbox {dBc}$$ with a margin of $$10\,\hbox {dB}$$ . The proposed predistorter is synthesized in $$28\,\hbox {nm}$$ fully-depleted silicon-on-insulator (FDSOI) CMOS process. It is shown that with a fraction of the power and die area of that of the MP a huge improvement in ACLR is attained. With an overall power consumption of 8.2 and 88.8 mW, respectively, for 20 and 80 MHz signals, the FIR-MP DPD proves to be a suitable candidate for small-cell base station PA linearization.

PAPR reduction scheme: wavelet packet‐based PTS with embedded side information data scheme

Partial transmit sequence (PTS) is an effective scheme to reduce high peak-to-average power ratio (PAPR) for multicarrier modulation (MCM) signal transmission systems. This approach produces side information (SI) data as a result of the MCM signal optimisation process. The generated SI data are required to be transmitted with the original data over the channel for successful data recovery at the receiver. An effective method for SI data transmission has not yet been identified and research is still ongoing. Hence, the authors introduce a technique that embeds SI data into the original data frame. In this study, a wavelet packet (WP)-based PTS (WP-PTS) scheme is selected as the MCM transmission method. The proposed scheme is called WP-PTS with embedded SI data. In addition, a suitable scheme for reconstructing the original data is developed. Simulation result shows that the PAPR performance of the proposed scheme improves by up to 2.5 dB at a complementary cumulative distribution function level of 10−4 compared with the original WP-orthogonal frequency-division multiplexing system without the PAPR reduction scheme when the number of selected disjoint subblocks is 16.

Flexible and scalable wavelength multicast of coherent optical OFDM with tolerance against pump phase-noise using reconfigurable coherent multi-carrier pumping.

Recently the ever-growing demand for dynamic and high-capacity services in optical networks has resulted in new challenges that require improved network agility and flexibility in order for network resources to become more "consumable" and dynamic, or elastic, in response to requests from higher network layers. Flexible and scalable wavelength conversion or multicast is one of the most important technologies needed for developing agility in the physical layer. This paper will investigate how, using a reconfigurable coherent multi-carrier as a pump, the multicast scalability and the flexibility in wavelength allocation of the converted signals can be effectively improved. Moreover, the coherence in the multiple carriers prevents the phase noise transformation from the local pump to the converted signals, which is imperative for the phase-noise-sensitive multi-level single- or multi-carrier modulated signal. To verify the feasibility of the proposed scheme, we experimentally demonstrate the wavelength multicast of coherent optical orthogonal frequency division multiplexing (CO-OFDM) signals using a reconfigurable coherent multi-carrier pump, showing flexibility in wavelength allocation, scalability in multicast, and tolerance against pump phase noise. Less than 0.5 dB and 1.8 dB power penalties at a bit-error rate (BER) of 10-3 are obtained for the converted CO-OFDM-quadrature phase-shift keying (QPSK) and CO-OFDM-16-ary quadrature amplitude modulation (16QAM) signals, respectively, even when using a distributed feedback laser (DFB) as a pump source. In contrast, with a free-running pumping scheme, the phase noise from DFB pumps severely deteriorates the CO-OFDM signals, resulting in a visible error-floor at a BER of 10-2 in the converted CO-OFDM-16QAM signals.

Reduction of Peak-to-Average Power Ratio of Multicarrier Modulation Signals with Adaptive Companding Scheme

High peak-to-average power ratio (PAPR) of transmitted signals is a major drawback in Multicarrier modulation (MCM) systems. Companding transform is a well-known method to reduce the PAPR without restrictions on system parameters such as the number of subcarriers, frame format and constellation type. In this paper, a novel adaptive companding scheme, mainly focuses on compressing the large signals into the desirable distribution, is proposed to reduce the PAPR with low implementation complexity. In addition, formulas to calculate its PAPR and bit error rate (BER) performance are also derived. Simulation results confirm that the proposed scheme can achieve an effective tradeoff between PAPR reduction and BER performance by carefully choosing the companding parameter.

Performance Improvement Techniques for OFDM system using Software Defined Radio

Improved spectral and energy efficiency are two key requirements for the next generation (5G) wireless communication systems. The inefficiency and non-linearity of traditional power amplifiers (PA) pose significant challenges to meet these requirements, especially for multicarrier modulation signals with high peak to average power ratio (PAPR). Orthogonal frequency division multiplexing (OFDM) is currently the most widely used multi carrier modulation technique; it has been adopted in many wireless communication standards including IEEE 802.11, 802.16, 3GPP Long Term Evolution and WiMAX. When a high PAPR signal process through a nonlinear power amplifier (PA), intermodulation distortion is generated, creating out-of-band emission that can interfere with other transmission in adjacent bands. In addition, in-band distortion, which degrades the bit error rate performance, occurs. Hence, I have addressed these problems by employing four different PAPR reduction techniques such as Phase modulation, Rail clipping, Sample and Hold approach and Threshold methods based on amplitude clipping. For practical proof of the proposed concepts, I have chosen software defined radio as an experimental setup that employs USRP N210 as hardware and GNU Radio as software.

Feasibility of multi‐carrier modulation signals as new illuminators of opportunity for passive radar: orthogonal frequency division multiplexing versus filter‐bank multi‐carrier

In this study, the feasibility of multi-carrier modulation signals for passive radar is investigated. The illuminators of opportunity involve orthogonal frequency division multiplexing (OFDM) and filter-bank multi-carrier (FBMC). Average ambiguity functions (AAFs) of OFDM and FBMC are derived in the similar expressions, while the discrepancies differ at the prototype filters and symbol periods. Simulation results validate the derivation of AAF and demonstrate that (i) both OFDM and FBMC are nearly perfect illuminators of opportunity in passive coherent location systems owing to their thumbtack-shaped ambiguity function; (ii) the time delay resolutions of OFDM, CP–OFDM (cyclic prefix-OFDM) and FBMC are all extraordinary because of the broadband property, despite the existence of two sidelobes as a consequence of CP insertion for CP–OFDM; (iii) the Doppler shift resolution is affected by the CP length and prototype filter designs, thus FBMC's Doppler bandwidth is larger than OFDM and CP–OFDM's Doppler bandwidth, but FBMC guarantees no existence of sidelobes due to the use of specially designed prototype filter. Therefore, multi-carrier modulation signals are attractive new candidates for passive radar surveillance.

Parallelized Structures for MIMO FBMC Under Strong Channel Frequency Selectivity

A novel architecture for MIMO transmission and reception of filterbank multicarrier (FBMC) modulated signals under strong frequency selectivity is presented. The proposed system seeks to approximate an ideal frequency-selective precoder and linear receiver by Taylor expansion, exploiting the structure of the analysis and synthesis filterbanks. The resulting architecture is implemented by linearly combining conventional MIMO linear transceivers, which are applied to sequential derivatives of the original filterbank. The classical per-subcarrier precoding/linear receiver configuration is obtained as a special case of this architecture, when only one stage is fixed at both transmitter and receiver. An asymptotic expression for the resulting intersymbol/intercarrier (ISI/ICI) distortion is derived assuming that the number of subcarriers grows large. This expression can in practice be used in order to determine the number of parallel stages that need to be implemented in the proposed architecture. Performance evaluation studies confirm the substantial advantage of the proposed scheme in practical frequency-selective MIMO scenarios.

Learning in an Uncertain World: MIMO Covariance Matrix Optimization With Imperfect Feedback

A novel architecture for MIMO transmission and reception of filterbank multicarrier (FBMC) modulated signals under strong frequency selectivity is presented. The proposed system seeks to approximate an ideal frequency-selective precoder and linear receiver by Taylor expansion, exploiting the structure of the analysis and synthesis filterbanks. The resulting architecture is implemented by linearly combining conventional MIMO linear transceivers, which are applied to sequential derivatives of the original filterbank. The classical per-subcarrier precoding/linear receiver configuration is obtained as a special case of this architecture, when only one stage is fixed at both transmitter and receiver. An asymptotic expression for the resulting intersymbol/intercarrier (ISI/ICI) distortion is derived assuming that the number of subcarriers grows large. This expression can in practice be used in order to determine the number of parallel stages that need to be implemented in the proposed architecture. Performance evaluation studies confirm the substantial advantage of the proposed scheme in practical frequency-selective MIMO scenarios.

On-chip all-optical wavelength conversion of multicarrier, multilevel modulation (OFDM m-QAM) signals using a silicon waveguide

We report on-chip all-optical wavelength conversion of multicarrier multilevel modulation signals in a silicon waveguide. Using orthogonal frequency-division multiplexing (OFDM) combined with advanced multilevel quadrature amplitude modulation (QAM) signals (i.e., OFDM m-QAM), we experimentally demonstrate all-optical wavelength conversions of 3.2 Gbaud/s OFDM 16/32/64/128-QAM signals based on the degenerate four-wave mixing (FWM) nonlinear effect in a silicon waveguide. The measured optical signal-to-noise ratio (OSNR) penalties of wavelength conversion are ∼3 dB for OFDM 16-QAM and ∼4 dB for OFDM 32-QAM at 7% forward error correction (FEC) threshold and ∼3.5 dB for OFDM 64-QAM and ∼4.5 dB for OFDM 128-QAM at 20% FEC threshold. The observed clear constellations of converted idlers imply favorable performance obtained for silicon-waveguide-based OFDM 16/32/64/128-QAM wavelength conversions.

Blind channel‐shortening for multipath channels using a recursive prediction‐error filter with additional prediction delay

The prediction-error filter is a well-known tool for blind communication channel equalisation. For multipath channels, it has two disadvantages considered here. First, in transversal form, it must be substantially longer than the impulse response of the channel, with a consequent high computation cost; second, it cannot fully equalise mixed-phase channels. Here, the authors examine a recursive version of the linear predictor, used with additional prediction delay for blind channel-shortening of multipath channels with multi-carrier modulation signals using a cyclic prefix. The recursive mode of operation allows the filter length to be significantly shorter than in the transversal, non-recursive form. In tests using modelled channels, they observe two significant results. First, for channels that include maximum-phase terms, the additional prediction delay ameliorates the filter response to maximum-phase terms. Thus, channel-shortening may be achieved, at least partially, unless the maximum-phase terms are severe. Second, the recursive prediction-error filter impulse response adapts to a stable minimum-phase form. This low-cost technique, then, may be used to augment the use of a cyclic prefix in reducing inter-symbol interference in multipath channels.

Two-stage decoding algorithm for unmodulated parallel combinatory high-compaction multicarrier modulation signals

Abstract A new decoding algorithm that consists of two decoding stages to reduce the computational complexity of maximum likelihood decoding for parallel combinatory high-compaction multicarrier modulation is proposed. The first decoding stage is responsible for a preliminary decision that serves to roughly find candidate messages using the QRD-M algorithm, and the second decoding stage is responsible for the final decision that reduces the error contained in the candidate and determines the message using the minimum value of the Hamming distances between the candidate and the replicas of the message. The complexity is considerably reduced by the proposed two-stage decoding algorithm at a cost of approximately 1.5 dB or less in E b /N 0 with respect to the bit-error rate of 10-3 under the given parameter settings.

Nonlinear analysis of microwave amplifiers excited by multicarrier modulated signals using envelop transient technique

In this paper, an envelope transient-multi-tone harmonic balance (ET-MHB) technique is introduced. It is shown that this technique is an efficient method to obtain the response of a nonlinear microwave amplifier when it is excited by multi-carrier modulated signals. This method indeed extended ET-HB method to characterize the multi-carrier modulated signals by using multi-tone HB simulation. To accelerate the simulation speed two formulation of ET-MHB are presented. They called ET-MDHB and ET-FMHB. These formulas provide a compact form which simplify and accelerate the computer simulations. Then, the proposed methods are applied to analyze a nonlinear microwave amplifier. The circuit is investigated under excitation of single-tone modulated, 4-tone un-modulated, and 4-tone digitally modulated signals. The results show the accuracy, time efficiency, and simplicity of the new formulations.