Orthogonal Modulation Research Articles

Mimicking Multiple Whale Whistles-Based Underwater Covert Communication

In underwater biomimetic covert communications, multiple whale whistles are mimicked for improving covertness. The conventional mimicking methods suffered from the trade-off between the mimicking performance and the bit error rate (BER). In this paper, we propose a continuous phase-multiple chirp modulation (CP-MCM) and a hybrid orthogonal whistle modulation (HOWM) to improve the BER and the mimicking performance of the biomimetic covert communication with the multiple whistles. The proposed CP-MCM utilizes chirp signals as the carriers of transmission symbols to mimic the frequency contour of the whistles accurately. The proposed HOWM utilizes the conventional OFDM in the overlapping whistle regions to avoid the interferences and the CP-MCM in the nonoverlapping regions to attain the large mimicking performance. Computer simulations and practical ocean experiments demonstrated that the proposed HOWM mimicked the multiple whistles with better BER performance than conventional methods.

A Novel Multisensor Orthogonal Attention Fusion Network for Multibolt Looseness State Recognition Under Small Sample

Bolts are common and effective fasteners for connecting steel structures, and bolt looseness detection is essential to ensure structural reliability and equipment safety. However, due to the complex spatial structure and multi-bolt of pipeline flange bolt connections, it is difficult for existing methods to implement fast and precise detection with single-sensor information and scarce data. To overcome these challenges, a novel multi-sensor orthogonal attention fusion network (MsOAFN) is proposed for multi-bolt looseness state recognition under a small sample in this paper. MsOAFN consists of feature extraction, feature fusion and state classification. A sensor-to-channel (STC) multi-scale convolution is used to extract features of different sensors to avoid data conflicts among sensors. In addition, a feature self-calibration attention module is built to expand the receptive field, alleviate information loss and enrich depth features during the down-sampling process. Then, a lightweight orthogonal attention fusion module is constructed, which fuses the shallow and depth features to further supplement and enhance feature information. Finally, the fusion features are input into the classification module to finish bolt loosening state recognition. Two case studies were conducted on a pair of typical flanged multi-bolt connection to verify the effectiveness of the proposed method, with an average accuracy of 99.77% and 98.84%, respectively. The superiority of this method in loosening detection of flanged bolt connection structure is compared with other algorithms.

High-security OCDM-PON system of 7-core fiber based on CFCM encryption

In this paper, we propose a high-security orthogonal chirped division multiplexing passive optical network (OCDM-PON) based on three-dimensional (3D) encryption, including the encryption of bitstream, constellation, and subcarriers. Cascaded fractional-order chaotic mapping (CFCM) is used to generate three masking factors to achieve ultra-high-security encryption in three different dimensions. Logistic mapping is used to control the order of the scheme, which effectively increases the key space to 10152 and improves the security performance of the system. The experiment proves the feasibility of the encryption scheme on OCDM after 16 orthogonal amplitude modulation (16QAM). The encrypted 16QAM-OCDM signal transmits data at a rate of 56 Gb/s on a 2-km 7-core optical fiber, and simultaneously transmits the 16QAM orthogonal frequency division multiplexing (OFDM) signal under the same conditions. It is shown that OCDM-PON is 1.3 dB higher than OFDM-PON in terms of receiver sensitivity when the bit error rate (BER) is 10-3.

Orthogonal Time Sequency Multiplexing Modulation: Analysis and Low-Complexity Receiver Design

This paper proposes orthogonal time sequency multiplexing (OTSM), a novel single carrier modulation scheme that places information symbols in the delay-sequency domain followed by a cascade of time-division multiplexing (TDM) and Walsh-Hadamard sequence multiplexing. Thanks to the Walsh Hadamard transform (WHT), the modulation and demodulation do not require complex domain multiplications. For the proposed OTSM, we first derive the input-output relation in the delay-sequency domain and present a low complexity detection method taking advantage of zero-padding. We demonstrate via simulations that OTSM offers high performance gains over orthogonal frequency division multiplexing (OFDM) and similar performance to orthogonal time frequency space (OTFS), but at lower complexity owing to WHT. Then we propose a low complexity time-domain channel estimation method. Finally, we show how to include an outer error control code and a turbo decoder to improve error performance of the coded system.

DCO-OTFS-based full-duplex relay-assisted visible light communications

In this paper, a direct current biased optical orthogonal time frequency space (DCO-OTFS) based full-duplex relay-assisted visible light communication system is proposed to enhance the spectral efficiency of visible light communications (VLC). The DCO-OTFS modulation method is described and the spectral efficiency of the system is analyzed. Simulation results indicate that the proposed method can achieve higher spectrum efficiency and robustness than the traditional direct current biased optical orthogonal frequency division modulation (DCO-OFDM).

Future OFDM-based Communication Systems Towards 6G and Beyond: Machine Learning Approaches

The vision towards 6G and beyond communication systems demands higher rate transmission, massive amount of data processing, and low latency communication. Orthogonal Frequency Division Modulation (OFDM) has been adopted in the current 5G networks and has become one of the potential candidates for the future communication systems. Although OFDM offers many benefits including high spectrum efficiency and high robustness against the multipath fading channels, it has major challenges such as frequency offset and high Peak to Power Ratio (PAPR). In 5G communication network, there is a significant increase in the number of sensors and other low-power devices where users or devices may create large amount of connection and dynamic data processing. In order to deal with the increasingly complex communication network, Machine Learning (ML) has been increasingly utilised to create intelligent and more efficient communication network. This paper discusses challenges and the impacts of embedding ML in OFDM-based communication systems.

Multi-octave linearized RF/photonic link based on orthogonal modulation and optimized demodulation.

In this Letter, we propose and demonstrate a multi-octave linearized analog radio-frequency (RF)/photonic link with orthogonal modulation and optimized demodulation. In our proposed link, the DC-reserved (DCR) digital method is utilized in a parallel Mach-Zehnder-modulator scheme to greatly improve the tolerance to the in-phase/quadrature amplitude imbalance and Q-path DC error, which inevitably exist during digital processing. The fault tolerance and transmission performance of the link are theoretically analyzed and experimentally verified. Compared with the traditional digital-signal-processing method, higher signal-to-distortion ratios can be achieved by the DCR method when the amplitude imbalance and DC errors are considered. As a result, the SFDR2 and SFDR3 (spurious-free dynamic ranges) of our system are measured to be 103.74dB⋅Hz1/2 and 116.31dB⋅Hz2/3, respectively. Furthermore, the linearization of the link is demonstrated by testing the RF signals with various frequencies, which proves the potential in broadband applications.

First Responders Got Wings: UAVs to the Rescue of Localization Operations in Beyond 5G Systems

Natural and human-made disasters have dramatically increased in recent decades. Given the strong relationship between first responders' localization time and the final number of deaths, the modernization of search and rescue operations has become imperative. In this context, unmanned-aerial-vehicle-based solutions are the most promising candidates to take on the localization challenge by leveraging emerging technologies such as artificial Intelligence, reconfigurable intelligent surfaces, and orthogonal time-frequency space modulations. In this article, we capitalize on such recently available techniques by shedding light on the main challenges and future opportunities to boost the localization performance of state-of-the-art techniques to give birth to unprecedentedly effective missing victims localization solutions.

Hybrid Beam-Steering OFDM-MIMO Radar: High 3-D Resolution With Reduced Channel Count

We report on the realization of a multichannel imaging radar that achieves uniform 2-D cross-range resolution by means of a linear array of a special form of leaky-wave antennas. The presented aperture concept enables a tradeoff between the available range resolution and a reduction in the number of channels required for a given angular resolution. The antenna front end is integrated within a multichannel radar based on stepped-carrier orthogonal frequency-division modulation, and the advantages and challenges specific to this combination are analyzed with respect to signal processing and a newly developed calibration routine. The system concept is fully implemented and verified in the form of a mobile demonstrator capable of soft real-time 3-D processing. By combining radio frequency (RF) components operating in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> -band (85–105 GHz) with the presented aperture, a 3-D resolution of less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1.5}^\circ \times {1.5}^\circ \times $ </tex-math></inline-formula> 15 cm is demonstrated using only eight transmitters and eight receivers.

Dynamic Small-Cell Clustering Using Affinity Propagation Algorithm in Asynchronous 5G NR OFDM Systems

In a joint transmission (JT) system using orthogonal frequency-division modulation (OFDM), performance degradation due to asynchronous interference resulting from the time difference of arrival is unavoidable. We propose an affinity propagation clustering (APC) algorithm for radio remote heads clustering for downlink JT in an asynchronous OFDM system. In particular, by closely connecting the principles of APC and JT with synchronization mismatch, we newly design pairwise similarities and preferences of the APC algorithm. The proposed algorithm provides 1.5 times higher 5-percentile user spectral efficiency than the APC algorithm with a conventional similarity matrix, and it has the same time complexity in term of big O notation.

A low-complexity orthogonal time frequency space modulation method for underwater acoustic communication

Compared with the orthogonal frequency division multiplexing (OFDM) modulation, the orthogonal time frequency space(OTFS) modulation has a lower peak-to-average power ratio. It can effectively resist the time selective fading caused by the Doppler effect and has significant performance advantages over doubly dispersive channels. However, the conventional OTFS linear minimum mean square error (LMMSE) method has a high complexity and is not easy to process in real time. In order to solve this problem, we propose a low-complexity equalization algorithm with infinite norm constraints based on the optimal coordinate reduction. The equalization algorithm not only obtains the optimal solution through a certain number of iterations and avoids direct matrix inversion but also equalizes infinite norm constraints to improve the symbol detection performance gains. At the same time, the OTFS delay-Doppler channel matrix we utilize is sparse and the two-norm squares of each column vector equally reduces the complexity of optimal coordinate descent. Finally, the simulation in the underwater acoustic communication scenario we designed verify the effectiveness of the proposed equalization algorithm. The simulation results show that the performance of the proposed equalization algorithm is close to that of the LMMSE method, while its low complexity is ensured.

Non-Uniform Non-Orthogonal Multicarrier Underwater Communication for Compressed Sonar Image Data Transmission

Efficient and reliable underwater sonar image transmission is increasingly desired for underwater investigation by autonomous underwater vehicles (AUV). However, it is extremely challenging due to the severe interference nature of underwater acoustic channels and the large data size of sonar images. In this paper, we first combine multicarrier modulation techniques with characteristics of compressed sonar image data to improve the transmission performance, where in previous research, image compression and multicarrier modulation were investigated separately. The compressed bitstream of sonar images is regarded as a new type of image with unique frequency characteristic. A non-uniform non-orthogonal multicarrier modulation scheme based on frequency characteristics of compressed sonar image data (F-NNMC) is proposed to meet the requirements of efficient and reliable sonar image transmission. The non-orthogonality between subcarriers improves the spectrum efficiency, and the non-uniform subcarrier structure can carry more effective information of the transmitted compressed data to improve the reliability. The simulation and experiment show that the proposed F-NNMC needs less frequency resource and has better peak signal-to-noise ratio (PSNR), structural similarity (SSIM), as well as lower bit error rate (BER) compared to orthogonal and non-orthogonal modulations.

Residual Doppler Effect Analysis of the FBMC/OQAM Communication System in Underwater Acoustic Channel

The filterbank multicarrier (FBMC) waveform has better properties in spectral as compared to the Orthogonal Frequency Division Multiplexing (OFDM) and it exhibits good anti-interference performance. We mainly consider an important variety of the FBMC systems, namely FBMC based on offset orthogonal amplitude modulation (FBMC/OQAM). This letter presents an analysis of the residual Doppler effect in the multipath underwater acoustic (UWA) channel for the FBMC/OQAM system. Assuming the received signal has gone through coarse non-uniform Doppler compensation by resampling, we model the compensated signal with residual Doppler effect and multipath effect. Especially, we derive a simplified closed-form expression for the received FBMC signal after non-uniform Doppler compensation under the signal-to-interference ratio. The theoretical results and the simulations show better compliance in the UWA multipath channel. Furthermore, the results obtained demonstrate that FBMC has better BER performance than the cyclic prefix (CP) based OFDM in the case of residual Doppler effect under the UWA channel.

Targeted regulation of transcription in primary cells using CRISPRa and CRISPRi.

Targeted transcriptional activation or interference can be induced with the CRISPR-Cas9 system (CRISPRa/CRISPRi) using nuclease-deactivated Cas9 fused to transcriptional effector molecules. These technologies have been used in cancer cell lines, particularly for genome-wide functional genetic screens using lentiviral vectors. However, CRISPRa and CRISPRi have not yet been widely applied to ex vivo cultured primary cells with therapeutic relevance owing to a lack of effective and nontoxic delivery modalities. Here we develop CRISPRa and CRISPRi platforms based on RNA or ribonucleoprotein (RNP) delivery by electroporation and show transient, programmable gene regulation in primary cells, including human CD34+ hematopoietic stem and progenitor cells (HSPCs) and human CD3+ T cells. We show multiplex and orthogonal gene modulation using multiple sgRNAs and CRISPR systems from different bacterial species, and we show that CRISPRa can be applied to manipulate differentiation trajectories of HSPCs. These platforms constitute simple and effective means to transiently control transcription and are easily adopted and reprogrammed to new target genes by synthetic sgRNAs. We believe these technologies will find wide use in engineering the transcriptome for studies of stem cell biology and gene function, and we foresee that they will be implemented to develop and enhance cellular therapeutics.

A CMOS RF Receiver with Improved Resilience to OFDM-Induced Second-Order Intermodulation Distortion for MedRadio Biomedical Devices and Sensors

A MedRadio RF receiver integrated circuit for implanted and wearable biomedical devices must be resilient to the out-of-band (OOB) orthogonal frequency division modulation (OFDM) blocker. As the OFDM is widely adopted for various broadcasting and communication systems in the ultra-high frequency (UHF) band, the selectivity performance of the MedRadio RF receiver can severely deteriorate by the second-order intermodulation (IM2) distortion induced by the OOB OFDM blocker. An analytical investigation shows how the OFDM-induced IM2 distortion power can be translated to an equivalent two-tone-induced IM2 distortion power. It makes the OFDM-induced IM2 analysis and characterization process for a MedRadio RF receiver much simpler and more straightforward. A MedRadio RF receiver integrated circuit with a significantly improved resilience to the OOB IM2 distortion is designed in 65 nm complementary metal-oxide-semiconductor (CMOS). The designed RF receiver is based on low-IF architecture, comprising a low-noise amplifier, single-to-differential transconductance stage, quadrature passive mixer, trans-impedance amplifier (TIA), image-rejecting complex bandpass filter, and fractional phase-locked loop synthesizer. We describe design techniques for the IM2 calibration through the gate bias tuning at the mixer, and the dc offset calibration that overcomes the conflict with the preceding IM2 calibration through the body bias tuning at the TIA. Measured results show that the OOB carrier-to-interference ratio (CIR) performance is significantly improved by 4–11 dB through the proposed IM2 calibration. The measured maximum tolerable CIR is found to be between −40.2 and −71.2 dBc for the two-tone blocker condition and between −70 and −77 dBc for the single-tone blocker condition. The analytical and experimental results of this work will be essential to improve the selectivity performance of a MedRadio RF receiver against the OOB OFDM-blocker-induced IM2 distortion and, thus, improve the robustness of the biomedical devices in harsh wireless environments in the MedRadio and UHF bands.

Comparative Examination of CO-OFDM Formats for Varied Fiber-Length and Bit Rate

The use of multiple carriers in Orthogonal Frequency Division Modulation (OFDM) makes it bandwidth-efficient and suitable for modern communication such as Long-Term Evolution (LTE), Digital Subscriber Line (DSL) internet access, optical fiber communication, digital television, audio broadcasting, etc. In this paper, four modulation formats by using Coherent Optical Orthogonal Frequency Division Modulations (CO-OFDM) have been analyzed. These are Single Port Dual Polarization (SP DP) 16 QAM, Single-Port Single Polarization (SP SP) 16 QAM, Dual Port Single Polarization (DP SP) QPSK 16-QAM, and Single Port Dual Polarization (SP DP) QPSK. Operation characteristics such as Bit Error Rate (BER) versus fiber-length and BER versus bit-rate have been examined. The range of fiber length used for this investigation is from 0 Km to 1000 Km with loop count equal to 2 and the range of bit rate of operation is from 20 Gbps to 200 Gbps. The present investigation helps in determining the relative suitability of CO-OFDM formats at various bit-rates of operation for different fiber lengths.

Ka-Band Stacked Power Amplifier Supporting 3GPP New Radio FR2 Band n258 Implemented Using 45 nm CMOS SOI

This paper presents a fully integrated, four-stack, single-ended, single stage power amplifier (PA) for millimeter-wave (mmWave) wireless applications that was fabricated and designed using 45 nm complementary metal oxide semiconductor silicon on insulator (CMOS SOI) technology. The frequency of operation is from 20 GHz to 30 GHz, with 13.7 dB of maximum gain. The maximum RF (radio frequency) output power (Pout), power-added efficiency (PAE) and output 1 dB compression point are 20.5 dBm, 29% and 18.8 dBm, respectively, achieved at 24 GHz. The error vector magnitude (EVM) of 12.5% was measured at an average channel power of 14.5 dBm at the center of the the 3GPP/NR (third generation partnership project/new radio) FR2 band n258—i.e., 26 GHz—using a 100 MHz 16-quadrature amplitude modulation (QAM) 3GPP/NR orthogonal frequency division modulation (OFDM) signal.

Variational autoencoder based receiver for orthogonal time frequency space modulation

The emerging orthogonal time frequency space (OTFS) modulation is demonstrated to offer reliable communication performance advantages over orthogonal frequency division multiplexing (OFDM) in doubly-dispersive fading channel. However, the existing embedded pilot-aided method to estimate channel impulse response (CIR) requires enormous spectral overhead to avoid the contamination of pilot symbols. In this paper, we present a variational autoencoder (VAE) based receiver for OTFS modulation that achieve a joint estimation and detection without pilot in delay-Doppler (DD) domain. The variational approach is considered to simplify the problem, and evidence lower bound (ELBO) is derived as loss function. In encoder step, an approximate posterior probability is introduced and utilized to minimize the Kullback-Leibler (KL) distance. Then we estimate CIR in decoder step and maximize the ELBO at last. From our simulation results, the proposed VAE based receiver for OTFS modulation enjoys a promising performance with other methods.

Clipping Noise Recovery of OTFS Signals Using Reliability-Based Compressed Sensing

In this correspondence, an efficient clipping noise recovery method using reliability-based compressed sensing (CS) is proposed for orthogonal time frequency space modulation with iterative clipping and filtering. Concretely, the message passing algorithm is first used to acquire the hard decision of transmit signal, along with the corresponding reliability. Then, an efficient method to determine the reliable observations of clipping noise is presented by utilizing the reliable hard decision signals and the sparsity of the equivalent delay-Doppler channel. Finally, from these reliable observations, the clipping noise can be recovered by CS techniques through utilizing its sparsity in the time-domain. Simulation results show that the proposed method can recover the clipping noise efficiently and thus improve the bit-error-rate performance significantly.

Single-beam three-axis optically pumped magnetometers with sub-100 femtotesla sensitivity

We demonstrate a single-beam three-axis parametric-resonance magnetometer operated in near-zero fields. By reflecting the incident laser beam at 90° in the vapor cell and applying three orthogonal parametric modulation fields, the three components of the magnetic field can be extracted from the transmitted light signal. Our vector magnetometer experimentally demonstrates magnetic-field sensitivities of 30 fT Hz−1/2 along x- and y-axes and 70 fT Hz−1/2 along the z-axis, and features a compact single-beam architecture, which is particularly attractive for applications requiring highly sensitive measurements of the vector components of magnetic fields with low power consumption and miniaturized magnetometers, such as magnetoencephalography and magnetocardiography.