M-ary Quadrature Amplitude Modulation Research Articles

Optimized pilot structure for PS-PDM ultrahigh-order QAM coherent optical transmission

We proposed and experimentally demonstrated a general pilot structure for probabilistic shaped (PS)-polarization division multiplexing (PDM) M-ary quadrature amplitude modulation (MQAM) coherent optical transmission, where a portion of PS-MQAM symbols is exploited as the pilot symbols with the same information entropy as the transmitted signal. The pilot symbols are simultaneously used in the entire digital signal processing (DSP) modules for polarization de-multiplexing, frequency offset estimation, carrier phase recovery, nonlinear equalization, and linear equalization. Compared to the conventional quadrature phase shift keying (QPSK) pilot structure, the proposed MQAM pilot structure can yield the nonlinear properties of the overall signal so that nonlinear equalization can effectively improve the performance of the normalized generalized mutual information. The remarkable performance has been achieved at the shaping parameters of 3.25 and 4.35 for 1024QAM and 4096QAM signals based on the proposed pilot scheme, which corresponds to the raw spectral efficiency of 16.190 and 20.381 bit/s/Hz, respectively. The pilot ratio is optimized to 5% for higher achievable information rates (AIRs).

Concurrent M-QAM transmission performance assessment in a combined four SOA-MZIs arrangement

In this paper, the utilization of four semiconductor optical amplifier Mach-Zehnder interferometers (SOA-MZIs) is explored to achieve concurrent M-QAM (M-ary Quadrature Amplitude Modulation) transmission. Utilizing an actively mode-locked laser, we generate pulses with a duration of 0.5 ps at a repetition rate of 20 GHz, serving as our sampling source. The incoming M-QAM signals, spanning various frequencies, undergo down-mixing at the SOA-MZIs combined exit, resulting in diverse output frequencies by respecting the bandpass sampling procedures. The unparalleled simultaneous M-QAM transmission is assessed through critical metrics such as error vector magnitude (EVM) and bit error rate (BER). The SOA-MZI conversion efficiency (CE) exhibits a notable transition, ranging from 90 % at 76 GHz to 68 % at 84 GHz based on 1024-QAM data. The concurrent down-mixed signals showcase EVM values of 3, 2, 1, and 0.25 % for 16-, 64-, 256-, and 1024-QAM, respectively, at the first range of output frequencies. Besides, an exceptional BER value of 93×10−6 is attained at a symbol rate of 0.25 GSymb/s at 84 GHz for the 1024-QAM replica. A comparative analysis reveals that under identical parameter settings, the proposed Gaussian filter expounds lower EVM values compared to the root raised cosine (RRC) filter. These results highlight the success of the novel experimental approach employing SOA-MZIs for simultaneous down-mixing of four M-QAM carriers with varying levels, showcasing outstanding performance outcomes.

Error analysis for face coded modulation system

AbstractThis paper discusses a new mapping scheme known as face coded modulation (FCM) system. In FCM, peak energy symbols are mapped onto an innermost ring according to the eight sockets in the human face, that is, brain, mouth, nostrils, eyes and ears. For example, FCM is formed when the constellation diagram from M‐ary quadrature amplitude modulation (MQAM) system is modified to reduce peak‐to‐average power ratio (PAPR) by relocating the four corner symbols of the MQAM, with peak energy, to the innermost ring in a way that forms the figure of a cross. Unlike APSK, FCM mapping introduces non‐uniform sequence of symbols on the ring, face width factor and multiple modulator circuits that can be used to lower power requirements for high power amplifiers (HPA) as used in MQAM transmission systems. Symbol error rate (SER) for FCM is calculated and the results compared with MQAM and MPSK. It is shown that at equal energy efficiency, FCM scheme has a better response to errors than both MPSK and MQAM and a better energy efficiency due to lowered PAPR than MQAM. Moreover, the simulation results exhibit a tight match for the proposed analytical framework when assessed under Additive White Gaussian Noise (AWGN) channel.

Simulation-Enhanced MQAM Modulation Identification in Communication Systems: A Subtractive Clustering-Based PSO-FCM Algorithm Study

Signal modulation recognition is often reliant on clustering algorithms. The fuzzy c-means (FCM) algorithm, which is commonly used for such tasks, often converges to local optima. This presents a challenge, particularly in low-signal-to-noise-ratio (SNR) environments. We propose an enhanced FCM algorithm that incorporates particle swarm optimization (PSO) to improve the accuracy of recognizing M-ary quadrature amplitude modulation (MQAM) signal orders. The process is a two-step clustering process. First, the constellation diagram of the received signal is used by a subtractive clustering algorithm based on SNR to figure out the initial number of clustering centers. The PSO-FCM algorithm then refines these centers to improve precision. Accurate signal classification and identification are achieved by evaluating the relative sizes of the radii around the cluster centers within the MQAM constellation diagram and determining the modulation order. The results indicate that the SC-based PSO-FCM algorithm outperforms the conventional FCM in clustering effectiveness, notably enhancing modulation recognition rates in low-SNR conditions, when evaluated against a variety of QAM signals ranging from 4QAM to 64QAM.

Space–time labeling diversity for distributed Goppa-coded cooperative networks over Nakagami-[formula omitted] channels

This paper proposes the novel space–time labeling diversity for the distributed Goppa-coded cooperation (STLD-DGCC) scheme over the Nakagami-q fading channel to improve the performance of the short-to-medium information block transmission. Two different Goppa codes with the same information length are deployed in the source and the relay, respectively, with the Goppa code at the relay providing additional redundancy. Meanwhile, two distinct labeling mappers of M-ary quadrature amplitude modulation (M-QAM) are used in the novel space–time labeling diversity (STLD) to achieve the extra diversity gain and decrease the error floor (EF) region in the Goppa coding scheme. To lower the computational complexity of the maximum likelihood (ML) detection, a near-ML reduced-complexity (RC) detection approach that compromises the system performance and the computation complexity is proposed. In addition, two novel joint decoding algorithms based on the critical signal-to-noise ratio (SNR) threshold are presented at the destination, namely the parallel algorithm and serial algorithm, to enhance the overall performance of the proposed STLD-DGCC scheme. In the case of the Nakagami-q fading model, the analytical union bound of the average bit error probability is provided, which tightly matches the Monte Carlo simulated results at high SNR. The simulation results further indicate that the proposed STLD-DGCC scheme significantly outperforms both the corresponding non-cooperative Goppa coding scheme and the DGCC scheme without the STLD technique under identical conditions. Furthermore, the performance of the STLD-DGCC scheme surpasses that of the existing transmission scheme, offering a promising candidate for further small information block communications.

Coded Orthogonal Frequency Division Multiplexing System : An Overview

This article compares the performance of two modulation techniques—quadrature phase shift keying (QPSK) and M-ary quadrature amplitude modulation (M-QAM) with M=8, 16, 32, and 64—in a coded orthogonal frequency division multiplexing system. As an error-correcting code, convolutional technology is employed. A vehicular channel with additive white gaussian noise (AWGN) is utilized for communication. According to simulation data, for QPSK and M-QAM, a coded orthogonal frequency division multiplexing system performs better than an uncoded one. Additionally, the system performs better with QPSK than it does with M-QAM. Additionally, when M rises, the performance declines.

Gain of Spatial Diversity with Conjoint Signals in Arbitrarily Correlated Rayleigh Fading Channels

Coding gains for arbitrarily correlated signals in a spatial diversity system with conjoint signals are presented in this study. The basic form of the proposed signal synthesizer evenly produces phase changes in the output signals. The mixer is an orthogonal transformation matrix, which is energy preserving and blind to the channel correlation matrix. The idea is to synthesize additional conjoint signal copies from the received signals that would be received if there were more antennas. However, these conjoint signals contain a level of correlation with the received signals. With the assumption of flat Rayleigh fading channels, simulation results for symbol error probability (SEP) are presented for different numbers of receive branches and varying correlation conditions. It is shown that under binary phase shift keying (BPSK), the synthesizer achieves decorrelation coding gains of about 1 dB when selection combining (SC) or equal gain combining (EGC) is used. The synthesizer’s performance across M-ary quadrature amplitude modulation (MQAM) signals is also tested. In addition, analytical frameworks are derived for BPSK and MQAM, which are tightly bound by the Monte Carlo simulation results obtained using Matlab. The correlation analysis is performed for different numbers of antennas and varied antenna spacings.

Cognitive Radio Spectrum Sensing-Based QAM Technique Using Blockchain

Cognitive radio (CR) is a novel concept developed to solve concerns such as spectrum underutilization and scarcity. Spectrum detection methods are employed in the blockchain-based CR to make optimum use of the spectrum reserves. In this paper, an attempt is made to evaluate the effectiveness of an energy sensor using collaborative spectrum detection. Wideband is defined as the frequency range between 470 MHz and 790 MHz, and additive white Gaussian noise (AWGN) is employed. The probability of detection ( P d ) under different situations is examined using detection in the receiver operational curve (ROC). According to the findings, the P d increases with the number of samples. This form of sensing, which is thought to be the easiest and best, uses energy-detecting spectrum sensing. To address ambiguity, the M-ary QAM technique is provided, which increases aggregate effectiveness in terms of the percentage of false alarm ( P f ) and probability of missed detection ( P m ) by 5% at a comparable delay period. When CR encounters shadowing and impacts situations, the client cannot tell the difference between an underutilized zone and fading. In comparison to the existing model, this study increases the likelihood of detecting a 3 dBm SNR for a 64-QAM modulated signal by at least 15%.

Frequency-Shift Monitoring of Optical Filter Based on Optical Labels over FTN-WDM Transmission Systems

Optical network monitoring and soft failure identification such as optical filter shifting and filter tightening are increasingly significant for the complex and dynamic optical networks of the future. Center frequency shift of optical filtering devices in optical networks has a serious impact on the performance of multi-span transmission, especially in high spectrum efficiency faster-than-Nyquist (FTN) transmission systems with various optical switching and add/drop nodes. Existing monitoring schemes generally have the problems of high cost, high complexity, and inability to realize multi-channel online monitoring, which makes it difficult for them to be applied in a wavelength division multiplexing (WDM) system with numerous nodes. In this paper, a monitoring scheme of frequency shift of optical filtering devices based on optical label (OL) is proposed and demonstrated. The signal spectrum of each channel is intentionally divided into many sub-bands with corresponding optical labels loading. The characteristics of spectrum power changing caused by frequency shift can be reflected on labels power changing of each sub-band, which are used to monitor and estimate the value of frequency shift via DSP algorithm. Simulation results show that the monitoring errors of frequency shift can be kept reasonably below 0.5 GHz after 10-span WDM transmission in FTN polarization multiplexing m-ary quadrature amplitude modulation (PM-mQAM) systems. In addition, 250 km fiber transmission experiments are also carried out, and similar results are obtained, which further verify the feasibility of our proposed scheme. The characteristics of low cost, high reliability, and efficiency make it a better candidate for practical application in future FTN-WDM networks.

SIMULASI SKEMA MODULASI 1024-QAM DAN 4096-QAM PADA SISTEM KOMUNIKASI DIGITAL

Quadrature amplitude modulation (QAM) is a modulation scheme used by digital communication systems to obtain high data rates in bandwidth-limited channels. M-ary QAM schemes with M values greater than 256 are currently used by wireless network standards, such as WiFi 6 and WiFi 7 (final standard will be released in 2024), which use the 1024-QAM and 4096-QAM modulation schemes, respectively. With the continuous development of technology for digital communication systems, both wireline and wireless, it is essential to research regarding advanced modulation schemes. This study discusses the simulation of the 1024-QAM and 4096-QAM modulation schemes using MATLAB software to compare the performance of the two modulation schemes in data transmission through the AWGN channel without using an error control code. The simulation results show that 4096-QAM is superior to 1024-QAM but requires higher Eb/N0 and SNR values. The Eb/N0 value required by the 4096-QAM to achieve a bit error ratio (BER) of 10-4 is 31 dB, while the 1024-QAM requires an Eb/N0 value of 26 dB.

Performance analysis of a RIS-assisted RoFSO communication system over Malaga distribution for smart city applications.

Radio over free space optics (RoFSO) is one of the potential technologies that can satisfy the requirements of 5G services in a smart city. However, as RoFSO is line-of-sight (LOS) communication, one of its limitations is the occurrence of a skip zone in the targeted areas. In this work, a reconfigurable intelligent surface (RIS) is proposed as the solution to overcome this connection difficulty, which prevents signal blocking by generating LOS connections. These RIS modules extend the communication channel coverage, making it more intelligent and controllable. The performance analysis based on outage probability, ergodic channel capacity, and bit error rate has been performed using heterodyne detection. Malaga distribution has been used to model atmospheric turbulence. The exact closed-form expressions of the probability density function and cumulative distribution function of the end-to-end signal-to-noise ratio are derived. Exploiting these derived statistics, system performance is investigated through the ergodic channel capacity, outage probability, and average bit error rate for M-ary quadrature amplitude modulation and two binary modulation schemes: non-coherent binary frequency-shift keying and coherent binary phase-shift keying. Numerical results are compared among different turbulence conditions, link lengths, and scattering errors. The results show that the proposed RIS-assisted RoFSO technology has the potential to be effective for 5G smart city applications.

Efficient Massive MIMO Detection for M-QAM Symbols

Massive multiple-input multiple-output (MIMO) systems significantly outperform small-scale MIMO systems in terms of data rate, making them an enabling technology for next-generation wireless systems. However, the increased number of antennas increases the computational difficulty of data detection, necessitating more efficient detection techniques. This paper presents a detector based on joint deregularized and box-constrained dichotomous coordinate descent (BOXDCD) with iterations for rectangular m-ary quadrature amplitude modulation (M-QAM) symbols. Deregularization maximized the energy of the solution. With the box-constraint, the deregularization forces the solution to be close to the rectangular boundary set. The numerical results demonstrate that the proposed detector achieves a considerable performance gain compared to existing detection algorithms. The performance advantage increases with the system size and signal-to-noise ratio.

Novel Real-Time Decision-Based Carrier Tracking for Software-Defined Radios Using M-ARY QAM Modulation

In this paper, a scalable and real-time decision-based carrier tracking for software defined radio (SDR) for M-ary QAM modulation has been proposed and tested in real-time using the universal software radio peripheral (USRP)-2922. The proposed system provides real-time decision-based carrier tracking for improved efficiency and performance. The real-time transfer of data has been done using the USRP-2922 hardware using the M-ary QAM modulation scheme for data transmission. The novelty of the proposed system is that one can transfer random data (binary bits), text or an image which can be encoded using the desired forward error correction codes (FEC) namely the convolution coding/Viterbi soft decision decoding and the turbo coding/decoding. The proposed novel SDR transceiver system with real-time decision-based carrier tracking shows an improved performance for different parameters such as the bit error rate (BER) and signal to noise ratio (Eb/No).

SYMBOL ERROR PROBABILITY PERFORMANCE FOR GENERALIZED SELECTION COMBINING DIVERSITY RECEPTION OF M-QAM OVER RAYLEIGH FADING CHANNEL

The performance of generalized selection combining (GSC) diversity reception symbol error probability (SEP) of square M-ary quadrature amplitude modulation (M-QAM) signals over frequency-flat Rayleigh fading channels is investigated in this work. The combining techniques considered in this paper are maximum ratio combining and selection combining (SC). We present closed-form approximate expressions for the average combined signal-to-noise ratio (SNR) and SEP in the fading channel for M-QAM signal reception in the GSC using diversity pathways that are independently, identically distributed. The simulation results validate the SEP expressions and demonstrate that, for a given number of accessible diversity paths, combining the strongest paths results in the majority of the diversity gain, and that the SNR declines as the number of combined paths increases. On the other hand, the numerical results demonstrate that, for a certain number of combined paths, increasing the number of available diversity paths can lead to a significant performance improvement.

Improved Subcarrier Selection Technique for Power Line Communications

This paper proposes Power Line Communication (PLC) schemes that improve the data rate of PLC systems while combating impairments resulting from frequency disturbances like impulse noise. Firstly, a modified subcarrier selection technique that can be employed to transmit one or more M-ary Phase-Shift Keying (MPSK) or M-ary Quadrature Amplitude Modulated (MQAM) symbols within a subset of the subcarriers of an orthogonal frequency division multiplexing symbol. The proposed subcarrier selection technique employs the cyclic rotation of a set of subcarriers, chosen from a group of subcarriers to transmit the selected MPSK or MQAM symbols. A second scheme that employs the rotation of MPSK or MQAM symbols among a group of subcarriers, to increase the data rate of the PLC system is proposed. The proposed schemes show improvement in error performance when tested over Additive White Gaussian Noise (AWGN) and impulse noise of a PLC system despite the increase in the data rate.

Performance of optimization methods for energy efficiency in cooperative communication

In cooperative communication the effect of channel fading can be improved by cooperation between the user terminals and the relay nodes in wireless networks. In a Wireless Sensor Network (WSN), cooperative relaying improves the link quality with a relatively high Energy Efficiency Gain (EEG). In this paper, optimized parameters are used in WSN to enhance the EEG using particle swarm optimization (PSO) and Real-Coded Genetic Algorithm (RGA). Maximum enhancements of EEG obtained using RGA for M-ary Quadrature Amplitude Modulation (M-QAM) is 64% for M=16, 87% for M=32, and 97% for M=64 compared to EEG obtained without optimization. The superiority proposed optimization methods are verified by comparing with results without optimization and by comparing with the published results for Energy Efficiency (EE).

Novel Deep-Learning Modulation Recognition Algorithm Using 2D Histograms over Wireless Communications Channels.

Modulation recognition (MR) has become an essential topic in today’s wireless communications systems. Recently, convolutional neural networks (CNNs) have been employed as a potent tool for MR because of their ability to minimize the feature’s susceptibility to its surroundings and reduce the need for human feature extraction and evaluation. In particular, these investigations rely on the unrealistic assumption that the channel coefficient is typically one. This motivates us to overcome the previous constraint by providing a novel MR suited to fading wireless channels. This paper proposes a novel MR algorithm that is capable of recognizing a broad variety of modulation types, including M-ary QAM and M-ary PSK, without enforcing any restrictions on the modulation size, M. The analysis has shown that each modulation choice has a distinct two-dimensional in-phase quadrature histogram. This property is beneficially utilized to design a convolutional neural-network-based MR algorithm. When compared to the existing techniques, Monte Carlo simulations demonstrated the success of the proposed design.

5G NOMA Defense Application Environment and Stacked LSTM Network Architectures

In 5G and beyond 5G wireless communication networks, the NOMA scheme is widely considered a major non-orthogonal access technique for improving system capacity and data rates. The main challenges in current NOMA systems are limited channel feedback and the difficulty of integrating it with advanced adaptive coding and modulation algorithms. This study analyses S-LSTM-based DL NOMA receivers in i.i.d. Nakagami-m fading channel circumstances as opposed to previously presented solutions. The LSTM has the advantage of responding dynamically to changing channel conditions. When compared to a typical NOMA system, a typical NOMA system has a 12% lower outage probability, a 39% increase in net throughput, and a maximum SER reduction of 48%. Complex modulated M-ary PSK and M-ary QAM data symbols are employed in D/L NOMA transmission. Classic receivers such as LS and MMSE are outperformed by the S-LSTM-based DL-NOMA receiver. The CP and non-linear clipping noise simulation curves compare the performance of the MMSE and LS receivers with that of the DL NOMA receiver in real-time propagation circumstances. The DL-based detector outperforms the MMSE for SNRs greater than 15 dB because the S-LSTM method is more robust than the clipping noise.

Linear Regression vs. Deep Learning for Signal Quality Monitoring in Coherent Optical Systems

Error vector magnitude (EVM) is a metric for assessing the quality of m-ary quadrature amplitude modulation (mQAM) signals. Recently proposed deep learning techniques, e.g., feedforward neural networks (FFNNs) -based EVM estimation scheme leverage fast signal quality monitoring in coherent optical communication systems. Such a scheme estimates EVM from amplitude histograms (AHs) of short signal sequences captured before carrier phase recovery (CPR). In this work, we explore further complexity reduction by proposing a simple linear regression (LR) -based EVM monitoring method. We systematically compare the performance of the proposed method with the FFNN-based scheme and demonstrate its capability to infer EVM from an AH when the modulation format information is known in advance. We perform both simulation and experiment to show that the LR-based EVM estimation method achieves a comparable accuracy as the FFNN-based scheme. The technique can be embedded with modulation format identification modules to provide comprehensive signal information. Therefore, this work paves the way to design a fast-learning scheme with parsimony as a future intelligent OPM enabler.

Low-complexity and blind receiver in-phase/quadrature imbalances compensation and estimation in the frequency domain for high-order modulation formats.

A frequency domain (FD) 4×2 multi-input and multi-output (MIMO) equalizer based on radially directed equalizer is proposed to compensate receiver in-phase/quadrature (IQ) imbalances of M-ary quadrature amplitude modulation signals. This algorithm has a significantly lower complexity compared with a conventional time-domain 4×2 MIMO equalizer. Furthermore, each of imperfection estimations is derived from the converged discrete frequency response of the FD 4×2 MIMO equalizer. The simulation and experimental results indicated that the receiver (Rx) IQ imbalances were fully compensated by the proposed equalizer and precisely estimated by estimators, even for long-haul transmission with Rx IQ imbalances varying over a wide range.