Single-carrier Signals Research Articles

A new single modulating and single carrier signal based control technique for symmetrical and asymmetrical multilevel inverter topology

Abstract In literature, to generate gate pulses for any inverter topology, most of the authors are using a single modulating signal with (level-1) or (level-1)/2 carrier-based pulse width modulation (PWM) techniques and single carrier (SC) signal with (level-1)/2 modulating signal based PWM techniques. Then, while going to higher-level inverter topologies, the complexity of the PWM control approach in both cases can increase. To reduce the control complexity, few authors have reported a single modulating signal with single carrier-based PWM techniques. However, these techniques need more mathematical equations and if-else loops. This article proposes a new single-modulating and single-carrier signal-based generalized PWM control approach using floor function (FF). This technique has been verified by considering one of the single-phase conventional symmetrical and asymmetrical multilevel inverter (MLI) topologies. Generally, FF rounds the value to the nearest integer towards the negative infinity. The proposed PWM control implementation process is very simple and suitable for both high switching frequency (HSF) and low switching frequency (LSF) operations. The proposed control technique (PCT) has been experimentally verified with different steady-state and transient-state studies of results under standalone operation.

Dual high-order QAM-modulated mm-wave signal transmission in the Q-band enabled by simple IM/DD architecture and bandpass delta-sigma modulation.

The intensity-modulation (IM)/direct-detection (DD) systems have been proven effective and low-cost due to their simple system architecture. However, the Mach-Zehnder modulator (MZM) of the IM/DD systems only reserves its driving signal intensity. Therefore, the IM/DD systems are generally unable to transmit vector signals and have a restricted spectrum efficiency and channel capacity. Similarly, the radio-over-fiber (RoF) transmission systems based on IM/DD are limited by their simple architecture and generally cannot transmit high-order quadrature amplitude modulation (QAM) signals, which hinders the improvement of their spectrum efficiency. To address the challenges, we propose a novel, to the best of our knowledge, scheme to simultaneously transmit the dual independent high-order QAM-modulated millimeter-wave (mm-wave) signals in the RoF system with a simple IM/DD architecture, enabled by precoding-based optical carrier suppression (OCS) modulation and bandpass delta-sigma modulation (BP-DSM). The dual independent signals can carry different information, which increases channel capacity and improves spectrum efficiency and system flexibility. Based on our proposed scheme, we experimentally demonstrate the dual 512-QAM mm-wave signal transmission in the Q-band (33-50 GHz) under three different scenarios: 1) dual single-carrier (SC) signal transmission, 2) dual orthogonal-frequency-division-multiplexing (OFDM) signal transmission, and 3) hybrid SC and OFDM signal transmission. We achieve high-fidelity transmission of dual 512-QAM vector signals over a 5 km single-mode fiber (SMF) and a 1-m single-input single-output (SISO) wireless link operating in the Q-band, with the bit error rates (BERs) of all three scenarios below the hard decision forward error correction (HD-FEC) threshold of 3.8 × 10-3. To the best of our knowledge, this is the first time dual high-order QAM-modulated mm-wave signal transmission has been achieved in a RoF system with a simple IM/DD architecture.

Discrete Spectral Encryption of Single-Carrier Signals With Pseudo Random Dynamic Keys

Discrete Spectral Encryption of Single-Carrier Signals With Pseudo Random Dynamic Keys

Fabry-Pérot optical frequency comb based mm-wave RoF system using pilot-assisted equalizer.

The emergence of the millimeter wave (mm-Wave; 30 GHz to 300 GHz) frequency band holds a lot of promise for addressing the congestion at low frequency in future mobile networks. Among many mm-Wave generation schemes, optical heterodyning is considered one of the most promising approaches due to its scalability and potential for integration on chip. Employing optical frequency combs (OFC) for optical heterodyning alleviates the significant phase distortions/noise introduced by the optical sources. However, any residual phase noise in these systems can deteriorate the transmission performance. Here we demonstrate a high-capacity mm-Wave radio-over-fiber (RoF) system using Fabry-Pérot (FP) laser comb overcoming the typical limitations of this source. The temporal phase perturbation induced by the frequency fluctuation of the FP laser is theoretically analyzed, and then estimated and compensated by a pilot-based phase equalizer. Performance evaluation of the proposed phase equalizer is conducted through experiment and simulation. Enabled by the proposed compensation scheme, ten 200 MHz filtered orthogonal frequency division multiplexing (f-OFDM) signal bands modulated by 16-quadrature amplitude modulation (QAM) are transmitted over 10 km fiber, with the ability to serve multiple users. The transmission of 16-QAM modulated single carrier signals with 2 GBd and 8 Gbps data rate is also performed for comparison, which offers better resilience to phase noise, demonstrating the first commercial Quantum Well FP laser-based optical heterodyning mm-Wave RoF system for both multi-carrier and single carrier signals.

Detection of OFDM modulations based on the characterization in the phase diagram domain

Signal modulation identification is of high interest for applications in military communications, but is not limited only to this specific field. Some possible applications are related to spectrum surveillance, electronic warfare, quality services, and cognitive radio. Distinguishing between multi-carrier signals, such as orthogonal frequency division multiplexing (OFDM) signals, and single-carrier signals is very important in several applications. Conventional methods face a stalemate in which the classification accuracy process is limited, and, therefore, new descriptors are needed to complement the existing methods. Another drawback is that some features cannot be extracted using conventional feature extraction techniques in practical OFDM systems. This paper introduces a new signal detection algorithm based on the phase diagram characterization. First, the proposed algorithm is described and implemented for simulated signals in MATLAB. Second, the algorithm performance is verified in an experimental scenario by using long-term evolution OFDM signals over a software-defined radio (SDR) frequency testbed. Our findings suggest that the algorithm provides good detection performance in realistic noisy environments.

On the Mitigation of WSS Filtering Penalties: Single- vs Multi-Carrier Modulation

The tight channel filtering imposed by long cascades of reconfigurable optical add-drop multiplexers (ROADMs) represents, nowadays, one of the major performance-limiting aspects for optically-routed coherent optical fiber systems. This makes it vital to perform a ROADM-aware optimization of the network performance at the physical layer. In particular, the use of different modulation options is known to have a strong impact on the extent of the filtering-induced penalties. In that regard, a long debate between single- and multi-carrier modulation has been taking place during the last few years, sometimes leading to apparently contradictory results. Following the open scientific discussion on this topic, in this work, we investigate by simulation and experimentally the wavelength selective switch (WSS) filtering tolerance of single-carrier (SC) and digital subcarrier multiplexing (DSCM) signals. In order to promote a fair comparison, both modulation options are carefully designed to minimize the ROADM-filtering penalties, namely resorting to the use of entropy loading together with baud rate optimization. After some preliminary numerical assessment, a comprehensive set of experiments are carried out for the transmission of 21-WDM 95–105 Gbaud SC and DSCM signals over a 2040 km straight line of fiber with regularly spaced WSSs. In general, our results allow to conclude that the two modulation options yield similar performance if the overall baud rate is optimized for each filtering scenario, keeping the baud rate at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 5% of the optimized value.

Ultrawideband RF-IQ Modulator Using Segmented Nonlinearly Scaled RF-DACs and Nonoverlapping LO Signals

A wideband Cartesian in-phase and quadrature (I/Q) modulator based on dual 10 b RF-digital-to-analog converters (DACs) is presented. Nonoverlapping local oscillator (LO) signals and a segmented nonlinear scaling with scaled unit cells contribute to a high linearity and allow for a low-complexity digital predistortion (DPD). Unit-cell flip-flops (FFs) and a balanced clock distribution enable a high sample rate with little skew. Out-of-band emissions are reduced through drive-slope control of the data-switch inputs. The modulator, implemented in the 22-nm fully-depleted silicon-on-insulator (FDSOI) CMOS, operates between 20 and 26 GHz with a peak sample rate of 11 GS/s. It has been used to demonstrate the transmission of a 64-quadrature amplitude modulation (QAM) single-carrier (SC) signal at 13.2 Gb/s, a 256-QAM SC signal at 7.33 Gb/s, and an orthogonal frequency division multiplexing (OFDM) signal comprising four aggregated 400-MHz 64-QAM channels with an error vector magnitude (EVM) of 6.43%. These results demonstrate the potential of the proposed modulator for the realization of ultrawideband transmitters in high-performance millimeter-wave (mmW) systems.

Fiber-terahertz-fiber bridge system in the 355-GHz band using a simple optical frequency comb and a photonics-enabled receiver.

This Letter demonstrates a high-speed fiber-terahertz-fiber system in the 355-GHz band using stable optical frequency comb generation and a photonics-enabled receiver. At the transmitter, a single dual-drive Mach-Zehnder modulator is employed to generate a frequency comb by driving the modulator under an optimal condition. At the antenna site, a photonics-enabled receiver consisting of an optical local oscillator signal generator, a frequency doubler, and an electronic mixer is used to downconvert the terahertz-wave signal to the microwave band. Simple intensity modulation and a direct detection method are used for transmitting the downconverted signal to the receiver over the second fiber link. To demonstrate the proof of concept, we transmitted a 16-quadrature amplitude modulation (QAM) orthogonal frequency-division multiplexing signal over a system consisting of two radio-over-fiber links and a 4 m wireless link in the 355-GHz band and achieved a line rate of 60 Gb/s. We also successfully transmitted a 16-QAM subcarrier multiplexing single-carrier signal over the system and achieved a capacity of 50 Gb/s. The proposed system can facilitate the deployment of ultra-dense small cells in high-frequency bands in beyond-5G networks.

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.

Carrier Selection Strategy of Generalized Discontinuous PWM Method for Current Reduction in DC-Link Capacitors of VSI

This article proposes a new carrier selection strategy of generalized discontinuous pulsewidth modulation (GDPWM) method for the two-level three-phase voltage source inverter to reduce the dc-link capacitor current under all operating conditions while keeping the minimum switching losses. First, the root-mean-square value of dc-link capacitor current is effectively reduced by selectively using both single and double carrier signals and modifying the switching patterns of existing GDPWM method. Although the proposed carrier selection strategy depends on the power factor (PF), the PF calculation is avoided because the multicarrier signals are properly chosen based on the information of three-phase modulation signals and measured three-phase currents. Also, the switching losses can be kept to a minimum as the modulation signals of conventional GDPWM method, which are optimal in terms of the switching losses, remain the same and the proposed carrier selection strategy has little effect on the total number of switching events. The operating principle of proposed GDPWM method is theoretically analyzed. Then, its practical effectiveness is verified by experimental tests on a motor drive system.

Implementation of DOA Estimation System Based on HackRF One

In the practical direction of arrival (DOA) estimation applications, it is required that the multichannel signal acquisition equipment can synchronously collect the signals received by the array antenna. In addition, the signal phase relationships between channels are supposed to be stable. However, this kind of equipment is usually complex and expensive to manufacture. Since some SDR devices are reconfigurable and open source, this paper adopts HackRF Ones as the signal sampling devices to design the DOA estimation system. The clocks line is used to synchronize the clock frequencies between HackRF Ones. Besides, an external pulse is introduced to control the sampling devices to start sampling simultaneously. In this case, the stable phase difference between channels can be obtained. The experimental results show that the synchronization error between channels of the system is less than one sampling period. The system can be used to estimate the incident angles of single carrier signals or modulated signals. The RMS errors of the system when estimating one source and two sources are 1.94° and 2.85°, respectively.

Generation of Single Sideband-Suppressed carrier (SSB-SC) Signal Based on Stimulated Brillouin Scattering

A novel cost-effective wavelength shifter is suggested in this paper. This paper shows how to shift signals in the mm-wave area using a frequency shifter. Due to stimulated Brillouin scattering in optical fibre, the proposed approach produces a single sideband signal without the carrier signal. When compared to SSB-SC transmissions, the bandwidth efficiency of double sideband signals is lower. Because it employs an optical fibre with a performance degrading condition such as SBS as an application, the frequency shifter is entirely optical. The theory of Gain and Loss Spectrum of SBS within optical fibre is utilised to minimise the upshifted frequency component and boost the low shifter frequency component in order to generate improved carrier power and single sideband. The SBS phenomenon produces a single sideband, which is advantageous in advanced modulation systems and consumes less bandwidth. It’s worth noting that the SSB-SC signal may be generated using any optical approach, and the proposed work eliminates the need for non-optical components like 90-degree hybrid couplers. SSB-SC signals are capable of combating pulse broadening difficulties and have the ability to operate at terahertz frequencies. Transmission of an SSB-SC signal is also shown to validate the performance of the produced signal. Furthermore, the Q factor of SSB-SC, SSB with carrier, DSB-SC, and DSB with carrier signals is studied at various connection lengths.

Comparison of DC-Value Method and Kramers–Kronig Receiver in Optical OFDM SSB-DD Transmission

Short reach optical communications are desperate for cost-effective solutions to improve capacity and compatibility in dealing with massive access and applications. Single sideband-direct detection (SSB-DD) is highly recognized for improving capacity with single PD, but it is confronted with signal-signal beating interference (SSBI). Recently, a DC-Value method has been proposed for optical signal phase retrieval for single carrier signal transmission. To further explore the effectiveness and compatibility of DC-Value method, in this letter for the first time, the orthogonal frequency division multiplexing (OFDM)-based multi-carrier modulation formats are processed by the DC-Value method in the receiver. Simulation results demonstrate that, for both OFDM and Nyquist-shaped single carrier (SC), the DC-Value method is beneficial in applying lower sampling rate to achieve comparable transmission performance than that of Kramers-Kronig receiver. In addition, althrough OFDM holds 2 dB increment of the optimum carrier-signal power ratio (CSPR) than Nyquist-SC, it offers more robustness to fibre transmission.

Performance Improvement of the Free-Space Optical Communication Link Using Spatial Diversity Reception-Assisted OFDM Signals

Orthogonal frequency division multiplexing (OFDM) technology is presented for use in free-space optical (FSO) communications accompanied by the spatial diversity reception. Using quadrature phase shift keying (QPSK) modulation formats, the OFDM signals show robustness to support high spectral efficiency and compatibility with the spatial diversity reception to improve receiver sensitivity. Compared with the single-carrier QPSK signal, the OFDM-QPSK signal with 64 sub-carriers can reduce the BER from 2.87 × 10−3 to 2.98 × 10−4 at the SNR of 6 dB. Using a two-aperture spatial diversity reception with OFDM, the BER can be reduced from 2.45 × 10−3 of a single receiver to 6.10 × 10−4 under moderate turbulence conditions. Under strong turbulence, the BER of the single receiver is 2.14 × 10−2. It can be improved to 1.16 × 10−3 by using four-aperture receivers, and even 6.87 × 10−4 by using six-aperture receivers. The optimized aperture number should be selected according to channel conditions.

Transceiver Impairment Mitigation by 8×2 Widely Linear MIMO Equalizer With Independent Complex Filtering on IQ Signals

High-order modulation formats with high symbol rates are promising candidates for meeting the growing traffic requirements of digital coherent transmission. In using these modulation formats, the impact of transceiver impairment on the signal quality becomes significant. In this paper, we propose an 8×2 widely linear (WL) multiple-input multiple-output (MIMO) equalizer with independent complex filtering on IQ signals to mitigate linear transceiver impairments. Furthermore, we extend the equalizer for digital subcarrier (SC) multiplexing. Accordingly, a 16×4 WL MIMO equalizer is also proposed to mitigate linear transceiver impairments, through application to a pair of SC inputs. Experimental results show that, for transmission of a 58-GBaud polarization-multiplexing 64 quadrature amplitude modulation (PM-64QAM) single-carrier signal, the proposed method effectively compensates for various receiver impairments and also mitigates transmitter (Tx) impairments. Q-penalties of 0.1 dB up to a 10-ps skew, 2.5-dB gain imbalance, 7.2-degree phase error, and –15-dB crosstalk in Tx were achieved for 100-km standard single-mode fiber transmission. Moreover, for a 29-GBaud PM-64QAM dual-SC signal, the proposed 16 × 4 WL MIMO equalizer shows transceiver impairment mitigation performance similar to that in the single-carrier case, even though dual-SC transmission is less tolerant of laser phase noise.

Design and Analysis of a 140-GHz T/R Front-End Module in 22-nm FD-SOI CMOS

This article presents novel methodologies and practical design considerations for a <inline-formula> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula>-band transmit/receive (T/R) front-end module (FEM) in 22-nm fully depleted silicon-on-insulator (FD-SOI/FDX) CMOS technology for beyond-5G wireless communication. An ABCD-matrix-based synthesis methodology is proposed to co-design the T/R switch (SW) topology, including the power amplifier (PA) output and the low noise amplifier (LNA) input matching networks, to minimize the losses in both Tx and Rx modes. Based on this synthesis, an asymmetric T/R SW topology is realized with intrinsic electrostatic discharge (ESD) protection. Both the stacked-field-effect transistor (FET) PA and LNA adopt differential topologies with transformer-based matching networks to eliminate unwanted effects from common-mode parasitics. Passive gain-boosting techniques are used for both PA and LNA to enhance different TRx specifications. A reusable unit-cell layout strategy is applied for transistor arrays to accelerate the multiple-stage PA implementation and maintain uniform performance and minimal parasitics. At 140 GHz, the Tx achieves a power gain <inline-formula> <tex-math notation="LaTeX">$G_{p}$ </tex-math></inline-formula> of 33.6/35.7 dB, a saturated output power <inline-formula> <tex-math notation="LaTeX">$P_{\mathrm{ sat}}$ </tex-math></inline-formula> of 12.5/14.7 dBm, a peak power-added efficiency (PAE) of 10.8/11.3&#x0025;, and an output 1-dB compression point (OP1dB) of 9.4/11.2 dBm with nominal/boosted supplies. An average output power (<inline-formula> <tex-math notation="LaTeX">${P_{out}}_{avg}$ </tex-math></inline-formula>)/PAE of 4.9 dBm/2&#x0025; is obtained for a 4-GHz bandwidth 64-QAM single-carrier signal at an error-vector magnitude (EVM) of &#x2212;24.8 dB. Moreover, its Tx-mode reliability has been assessed. At 140 GHz, the Rx achieves a 20-dB <inline-formula> <tex-math notation="LaTeX">$G_{p}$ </tex-math></inline-formula>, a &#x2212;24-dBm input 1-dB compression point (IP1dB), and a 9.2-dB noise figure (NF) with only 20-mW power consumption from a 0.8-V supply. This compact FEM has a PA/LNA core area of 0.024/0.032 mm², respectively.

Transparent Fiber–Millimeter-Wave–Fiber System in 100-GHz Band Using Optical Modulator and Photonic Down-Conversion

We demonstrate the first fiber–millimeter-wave–fiber system in the 100-GHz band using a low-loss optical modulator and direct photonic down-conversion technology. The utilization of a low-loss optical modulator for the direct conversion of a millimeter-wave signal to an optical signal significantly simplifies the millimeter-wave radio receiver because it includes only a radio front-end and an optical modulator. In addition, by adopting direct photonic down-conversion technology for simultaneous detection and down-conversion of the millimeter-wave signal to the microwave band, the fiber–radio receiver and subsequent digital signal processing can be considerably simplified. Using the proposed technologies, we successfully transmitted 32-/64-quadrature amplitude modulation orthogonal frequency division multiplexing and single-carrier signal with a line rate of 71.4 Gb/s and a net data rate of 53.7 Gb/s over a wired and wireless converged system consisting of two optical fiber links and a 20 m radio link at 101 GHz. The proposed system is promising for high-capacity, low-latency, and low-power consumption fiber-wireless transmission in beyond 5G networks.

Pulse-Width Modulation Template for Five-Level Switch-Clamped H-Bridge-Based Cascaded Multilevel Inverter

This article presents a carrier-based pulse-width modulation (PWM) template for a 5-level, H bridge-based cascaded multilevel inverter (MLI). The developed control concept generates adequate modulation template for this inverter topology wherein a sinusoidal modulating waveform is modified to fit in a single triangular carrier signal range. With this modulation approach, classical multiplicity and synchronization of the triangular carrier signals criterion for the extension of sinusoidal pulse-width modulation, SPWM, to several cascaded 5-level, H-bridge-based MLI topology are removed. The proposed template can be used on the inverter configuration of any level with no further control modification. Nearly even distribution of switching pulses and equalized individual cascaded cell output power were achieved with the proposed modulation scheme. Three 5-level, H-bridge-based MLI units were cascaded for 1-phase, 13-level inverter operation; simulation and experimental results are adequately presented.

Carrier Assisted Differential Detection With Generalized and Simplified Receiver Structure

Coherent detection has the primary advantage of optical field recovery, which enables channel impairment compensation and advanced modulation formats for high-capacity transmission. On the other hand, direct detection (DD) is more cost-effective due to its local oscillator (LO)-free detection. To gain the field recovery advantage while preserving the LO-free detection for DD-based receivers, carrier assisted differential detection (CADD) has been proposed to retrieve the complex-valued double-sideband (DSB) signal. In this paper, to extend the concept of CADD, we propose a simplified CADD scheme with reduced hardware complexity and present signal-to-signal beating interference (SSBI) iterative mitigation algorithms with and without symbol decision. The required number of photodetectors and analog-digital converters (ADCs) for the simplified CADD receiver becomes the same as the coherent homodyne counterpart but without needing the expensive narrow-linewidth LOs. The performance of the proposed simplified CADD receiver is evaluated by 60-Gbaud 16-QAM DSB signals. Extensive performance comparisons are made between (i) the generalized CADD receivers with and without the simplified receiver structure, (ii) SSBI iterative mitigation algorithm with and without the symbol decision, and (iii) single carrier (SC) and OFDM-modulated DSB signals for the simplified CADD receiver.

A Real-time Implementation for the Speech Steganography using Short-Time Fourier Transformior Secured Mobile Communication

Steganography can be described as approach of masking an undisclosed message with a normal message which is known as the Carrier message signal. DSP techniques, such as LSB encoding, have historically been implemented for secret information hiding. Utilization ofsteganography functions of deep neural networks for voice data is something this paper will present. This paper also demonstrate that the steganography techniques suggested for vision are less suitable for speech signals this paper present a implementation technique that involves the use of ISTFT and STFT as differentiablelayers in the network. Empirically, the efficacy of the proposed methods based on multiple datasets of speech should be demonstrated and the outcome are examined quantitatively and qualitatively. Using of multiple decoders or a single conditional decoder helps to hide multiple signals in a single carrier signal. Finally, under various channel distortion situations, this model Qualitative studies indicate that human listeners cannot detect changes made to the carrier and hence the decoded messages are highly intelligible.