Digital Modulation Schemes Research Articles

Automatic Modulation Recognition Based on the Optimized Linear Combination of Higher-Order Cumulants.

Automatic modulation recognition (AMR) is used in various domains—from general-purpose communication to many military applications—thanks to the growing popularity of the Internet of Things (IoT) and related communication technologies. In this research article, we propose an innovative idea of combining the classical mathematical technique of computing linear combinations (LCs) of cumulants with a genetic algorithm (GA) to create super-cumulants. These super-cumulants are further used to classify five digital modulation schemes on fading channels using the K-nearest neighbor (KNN). Our proposed classifier significantly improves the percentage recognition accuracy at lower SNRs when using smaller sample sizes. A comparison with existing techniques manifests the supremacy of our proposed classifier.

A Direct Antenna Modulator With Beam Steering Capability Based on Space-Time-Coding Arrays

We propose an RF front-end architecture with simultaneous direct antenna modulation and beam steering capability based on space-time-coding (STC) arrays. In an STC array, digital codes control the state of each array element. The element state determines the amplitude and phase of the radiated wave, and in a time scale over which the state of the elements is changed by a few successive codes, the frequency harmonics are generated. We first introduce a vector representation of bits in a code and their effects on the resultant harmonic wavefront. We show that by choosing proper codes with a minimum of two repetitions, one can modulate data on the phase and amplitude of a desired far-field harmonic where proof-of-concept simulations are given for a 16-APSK digital modulation scheme. We investigate the data rate, spectral efficiency, and the limitation of switching speed in our proposed scheme. Moreover, it is shown that the harmonic beam patterns of an STC array can be easily steered by a consecutive shifting of bits in the code without affecting the transmitted data symbols. Through cosimulation of digital design and coded antenna array, we calculate the constellation of the QPSK digital modulation scheme for a steered beam and study its angular dependency. Finally, we provide an upper bound for the efficiency of STC arrays.

FPGA Implementation of Digital Modulation Schemes Using Verilog HDL

Abstract: This paper describes the design and development of an FPGA-based digital Modulation Scheme for high-resolution Communication Application. We are focusing on implementation of Verilog based code simulation for fundamental and widely used digital modulation techniques such as Binary Amplitude-shift keying (BASK), Binary Frequency-shift keying (BFSK), Binary Phase-shift keying (BPSK) and Quadrature Phase Shift Keying(QPSK). In this work the idea of sinusoidal signals that have been generated is plain sailing in nature and based on fundamentals of signal sampling and quantization. Such concept of sinusoidal signals generation is not unfamiliar but somehow simplified using sampling and quantization in time and amplitude domain, respectively. The whole simulation is done on Modelsim and Xilinx-ISE using VERILOG Hardware descriptive language. The work has been accomplished on Thirty two bit serial data transmission with self-adjustable carrier frequency and bit duration length.

A Mixed-Integer Solution for TDOA Based Direct Positioning of Digital Modulation Signal

This paper proposes a direct position determination (DPD) method for a digital modulation signal based on time difference of arrival (TDOA) measurements. Unlike the two-step positioning process, the measurements are used to directly estimate the source position. Fully utilizing information in a transmitted waveform can improve the accuracy of source localization in a single-step method. Based on maximum likelihood (ML) estimates, when the digital modulation scheme is known to the location system, an alternating iterative DPD method is developed to locate the emitter. The objective function of the proposed algorithm takes into account the source position and transmitted symbol sequence, which makes it a mixed-integer optimization problem. In particular, ML sequence estimation is adopted and the complex envelope is restored using a genetic algorithm. Then, based on Newton’s method, an alternating iterative algorithm is proposed to update the position and symbol sequence results. Compared with the existing DPD method, the proposed algorithm gives more accurate location results for unknown waveforms. In addition, the proposed algorithm can reach the Cramér-Rao bound (CRB) for known signal waveforms, as verified using comprehensive simulations.

Rolling Shutter OFDM Scheme for Optical Camera Communication Considering Mobility Environment Based on Deep Learning

This paper presents a rolling shutter orthogonal frequency-division multiplexing (RS-OFDM) optical camera communication higher rate longer range proposed in IEEE 802.15.7a Task Group (TG7a) using an image sensor as a receiver. OFDM is a digital multi-carrier modulation scheme deployed for broadband wireless communication to resolve the inter-symbol interference (ISI) effect caused by the multipath channel. In optical wireless communication systems, OFDM was applied widely for indoor applications: internet of things, e-health, vehicular, and localization systems. The mobility scenario is a big problem for OWC systems, which reduces the system performance due to the optical channel variation in the processing time. In addition to that, signal detection should be considered in the mobility environment to improve the signal-to-noise ratio of OWC systems. In this paper, we proposed the convolution neural network (CNN) for LED detection in the RS-OFDM system, considering the mobility effect. In addition to that, the deep neural network was applied to detect the start of OFDM frame instead of conventional technology (Van De Beek algorithm). By applying our approach, the RS-OFDM system can achieve long communication (18 m distance) with a low error rate in the 2 m/s velocity environment.

A Study of BER and EVM Degradation in Digital Modulation Schemes Due to PLL Jitter and Communication-Link Noise

A phase-locked-based frequency synthesizer – ubiquitously used to generate local oscillation in a communication transceiver – exhibits phase noise and jitter which considerably degrades bit-error rate (BER) and error vector magnitude (EVM) of a digital communication link. This paper presents an analytical study of EVM and BER degradation for a variety of widely used digital modulation schemes. Phase noise and jitter of a generic integer-N phase-locked loop (PLL) as a local oscillator feeding an RF mixer are derived, while accounting for the reference spurs and cyclo-stationarity of the mixer operation as well as the additive noise of the communication link. This jitter model is then utilized to directly study its impact on digital modulation constellations. Specifically, the EVM and BER degradation due to the PLL jitter in communication systems incorporating M-ary phase-shift keying (M-PSK) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${4^{M}}$ </tex-math></inline-formula> quadrature amplitude modulation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${4^{M}}$ </tex-math></inline-formula> QAM) are analyzed. Comparison between analytical models and system-level simulations verifies an excellent accuracy of these models.

Design and Analysis of a Short Reference Orthogonal Double Bit Rate Differential Chaotic Shift Keying Communication Scheme

With the broadband, noise-like, and non-periodic characteristics of chaotic signals, chaotic digital modulation schemes have received extensive attention. A new short reference orthogonal double bit rate differential chaotic shift keying (SR-ODBR-DCSK) communication scheme is proposed in the paper. The modulation technology generates two orthogonal chaotic signals by using the orthogonality of the chaotic signals acting on the Walsh function and modulates the continuous two-bit data information respectively to achieve the simultaneous transmission of two signals at the same time slot. Odd information bits and even information bits are modulated to two orthogonal signals so as to reach a double transmission rate on the basis of the original channel. In this paper, the performance of SR-ODBR-DCSK in the additive white Gaussian noise (AWGN) channel is analyzed, and a Monte Carlo simulation test is carried out. The bit error rate of this modulation method is compared with that of SR-DCSK. The results show that the SR-ODBR-DCSK system is excellent and promising.

Implementing Enhanced MIMO with F-OFDM to Increase System Efficiency for Future 5G Cellular Networks

The upcoming fifth generation of cellular communication system is most likely to be deployed by the year 2020. The new generation of mobile network is expected to have high data rates, low latency and support a huge number of devices. Aside from this, machine type communication (MTC) and internet of things (IoT) are expected to be handled by 5G system in a better and efficient way. For this reason, a number of waveform candidates have been proposed. Filtered orthogonal frequency division multiplexing (F-OFDM) is one of the proposed candidates for 5G systems, which highly resembles to its predecessor that is orthogonal frequency division multiplexing (OFDM). The crucial difference between the two multicarrier waveforms is the use of a well-designed filter. F-OFDM in comparison with OFDM thus provides reduced out of band emission, which enables it to utilize the allocated spectrum efficiently. This research paper provides a brief review of F-OFDM performance with multiple input multiple output (MIMO) implementation. Using MATLAB, the MIMO system with F-OFDM has been tested for different configurations such as SIMO (receive diversity) and MISO (transmit diversity) with different digital modulation schemes including QPSK, 16-QAM, 64-QAM and 256-QAM. The bit error rate (BER) vs the signal to noise ratio (SNR) plots judge the performance of the system.

On the performance of digital systems in α-[formula omitted] fading and non-Gaussian noise channels

In this paper, a closed-form expression is derived for the bit error probability (BEP) under several digital modulation schemes, considering the channel subject to α-F fading and non-Gaussian noise, characterized by the additive generalized Gaussian noise (AWGGN) distribution. An asymptotic BEP analysis is carried out in this work. A closed-form and unified BEP expression is derived for a wide range of modulation schemes, under α-F fading and AWGGN for the maximal-ratio combining (MRC), equal gain combining (EGC), and selection combining (SC) based receivers. Comments are provided on the special cases encompassed by the α-F fading and AWGGN noise, as well as on the convergence and complexity analysis of the BEP expressions derived. BEP curves are shown for different parameters that characterize the channel and are corroborated by simulations performed with the Monte-Carlo method.

Performance enhancement of hybrid fiber wavelength division multiplexing passive optical network FSO systems using M-ary DPPM techniques under interchannel crosstalk and atmospheric turbulence

The performance of moment generating function approaches, specifically Chernoff bound (CB) and modified Chernoff bound (MCB), is examined and improved in this study. We evaluates and enhances the performance of a wavelength division multiplexing (WDM) technique for free-space optical (FSO) fibre communications based on passive optical network (PON) using the M-ary digital pulse-position modulation (M-ary DPPM) schemes under amplified spontaneous emission (ASE) noise effects, interchannel crosstalk (ICC), and atmospheric turbulence (AT). We use a data rate of 2.5 Gbps for eight channels over a PON/DWDM-FSO optical fibre system in the C-band with 100 GHz channel spacing start from 1550 nm. The results achieve 20 Gbit/s transmissions (2.5 Gbps $$\times $$ 8 channels). This is a technology that can have extended leverage, higher data rates, power-efficient, and is considered an ideal option for the provision of bandwidth for potential access networks. When compared to the CB at a low gain (G = 8), the MCB outperforms the Gaussian approximation at high gain (G = 30). Because of its superior performance at a high gain (G = 30), the MCB offers the tightest limit on the bit error rate (BER). In comparison to an equivalent on–off keying (OOK) non-return-to-zero (NRZ), the M-ary DPPM scheme with a coding level (M) of 2 improves average power about by 2.9 dB at a data rate of 2.5 Gbps on the 1550 nm wavelength and BER of $${10}^{-{9}}$$ . The sensitivity of the M-ary DPPM modulation scheme remains improved over OOK in the presence of ICC. The lower power penalty is predicted to be approximately 0.2–3.0 dB in the DWDM-FSO systems for low coding level M $$=$$ 2. We achieve a lower power penalty at 0.2–3.0 dB for the hybrid fiber DWDM/PON-FSO optical communication system at a BER of $${10}^{-{9}}$$ . At a target BER of $${10}^{-{12}}$$ , the hybrid OOK-NRZ/M-ary DPPM offers about 4–8 dB of optical signal-to-noise-ratio improvements over the M-DPPM of the WDM-PON/FSO link for strong turbulence. The results demonstrated that the M-ary DPPM and the optical relaying amplification technique are powerful treatments for mitigating the impacts of ASE noise, AT, and ICC.

Asymptotic characteristics of multichannel access systems with orthogonal filteration

The proposed article deals with digital modulation schemes that use a certain number of equidistant orthogonal subcarriers (the socalled OFDM technology). The theory of radio engineering chains and signals is used as the scientific and technical basis of the problem. The spectra of discrete signals were analysed, the influence of violations of the conditions of Kotelnikov's theorem and the asymptotics of the recovery errors of the original continuous signals were investigated. Methods of forming composite signals with arbitrary frequency difference of subcarriers have been developed. It is shown that when the amount of frequency shift of the basic series decomposition functions and the width of the spectrum of the main and side lobes in the spectrum of the output signal are matched, it is possible to count on the minimal influence of mutual interference and intersymbol interference of the composite signal. It was established that the method of orthogonal frequency multiplexing of channels (OFDM) allows to significantly increasing the bandwidth of the wireless communication system. In addition, with dynamic load changes in wireless networks, the impact of frequency collisions and an increase in the level of intra-system interference is minimized. Graphical analysis of the results of the series expansion on the quasiorthogonal system of basis functions shows that the errors of restoration of the original signals can reach unacceptable values. It was also established that when expanding into a non-orthogonal series with a larger number of members, the situation with the restoration of the original signals becomes a little more suitable, but no guarantees of monotonous improvement of the situation with restoration errors can be given in principle. This problem requires additional analytical research.

Real-Valued Spreading Sequences for PSSS Based High-Speed Wireless Systems

In past years, Parallel Sequence Spread Spectrum (PSSS) has attracted significant attention as a modulation technique for wireless communication systems targeting data rates of 100 Gb/s and beyond. PSSS allows designing high-speed baseband processors, which can be partially implemented in the analog domain. It uses multiple analog-to-digital converters (ADCs) to sample the received baseband signal in parallel, significantly relaxing the sampling rate and ADC complexity. However, due to the sidelobe effects of bipolar <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$m$ </tex-math></inline-formula> -sequences, PSSS shows lower performance than standard digital modulation schemes. This paper proposes real-valued PSSS spreading sequences with attenuated autocorrelation sidelobes. Such sequences show excellent bit error rate (BER) performance. Moreover, our sequences do not have length restrictions of 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sup> – 1, like in the case of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$m$ </tex-math></inline-formula> -sequences, and reduce the chip area required to implement PSSS transceiver. The proposed sequences also reduce the peak-to-average power ratio (PAPR) of PSSS.

Over-the-Air Modulation Classification using Deep Learning in Fading Channels for Cognitive Radio

Background/Objectives: The ability to recognize the type of modulation is a critical function of Cognitive Radio. The objective of this study is to increase the modulation classification efficiency in Over-The-Air (OTA) signals by utilizing channel characteristics that are strong. Methods: In this work, we demonstrate how to classify Over-The-Air modulation using a deep learning technique under various fading channels simulating real-time data. The network recognizes eight different digital modulation schemes and three different analogue modulation methods. Each modulation scheme will consist of 10,000 frames with 1024 samples per frame and a sampling rate of 200 kHz. Each sample will pass through fading channels prior to training, with 80% of samples are for training, 10% for validation, and 10% for testing. Six convolutional layers and one fully linked layer comprise our network. The final convolution layer is followed by a batch normalization layer, an activation layer utilizing rectified linear units (ReLUs), and a maximum pooling layer. As a result, the final convolution layer contains soft-max activation instead of the maximum pooling layer. Findings: Modulation categorization OTA is done with two separate ADALM-PLUTO SDRs working in various channel configurations. Network-I has a forecast accuracy of 91.4 percent using 12 Mini-Batch Size and 256 Epochs, whereas Network-II has a prediction accuracy of 95.3 percent using 24 Mini-Batch Size and 128 Epochs. There are a number of ways in which SDR technology can aid to make computer-generated data more realistic, such as adopting alternative channel models. Novelty: Using Software Defined Radio hardware; the same network was used to analyze various fading situations, such as Rayleigh, Rician or Lognormal distributions, and to optimize the network topology by adjusting hyper-parameters to increase accuracy. Keywords: Cognitive Radios (CR), Fading Channel, OTA, SDR, and Modulation

Modulation Recognition of Communication Signal Based on Convolutional Neural Network

In the noncooperation communication scenario, digital signal modulation recognition will help people to identify the communication targets and have better management over them. To solve problems such as high complexity, low accuracy and cumbersome manual extraction of features by traditional machine learning algorithms, a kind of communication signal modulation recognition model based on convolution neural network (CNN) is proposed. In this paper, a convolution neural network combines bidirectional long short-term memory (BiLSTM) with a symmetrical structure to successively extract the frequency domain features and timing features of signals and then assigns importance weights based on the attention mechanism to complete the recognition task. Seven typical digital modulation schemes including 2ASK, 4ASK, 4FSK, BPSK, QPSK, 8PSK and 64QAM are used in the simulation test, and the results show that, compared with the classical machine learning algorithm, the proposed algorithm has higher recognition accuracy at low SNR, which confirmed that the proposed modulation recognition method is effective in noncooperation communication systems.

Study of Modulation Schemes over a Multipath Fading Channels

Communications systems concerted over wireless channels depend on the environment. Communications system can be more reliable and efficient by properly analyzing wireless channels. Today's most important features are a high data rate and reliable performance to exploiting viable networks during this new information age. The channel is not time-invariant in wireless communication, so the received signal exhibits amplitude, phase, and angle variations due to multipath fading. Increasing data rates and reducing bandwidth make Orthogonal Frequency Division Multiplexing (OFDM) an important component of wireless communication systems. The OFDM technique uses many carriers very efficiently. With this scheme, interference is robustly reduced, and fading scenarios are easily accommodated. Analyzing digital modulation schemes requires evaluating link performance with fading channels. The paper compares channel performance over varying fading environments using a variety of modulation schemes. We study the BER and SNR properties of the AWGN, Rician fading and Rayleigh fading channels modulated with BPSK, QPSK, and M-ary QAM.

Wireless-optical-communication-based cooperative IoT and IoUT system for ocean monitoring applications.

This paper proposes the idea of a new cooperative communication between the Internet of Things (IoT) and the Internet of Underwater Things (IoUT) using wireless optical connectivity for ocean monitoring applications. We considered IoT communication using a hybrid radio frequency (RF)/free space optical (FSO) link and IoUT using a underwater wireless optical communication (UWOC) link. Channel models for RF, FSO, and UWOC links are considered to be Rayleigh, Malaga with pointing errors, and hyperbolic tangent log-normal distributions, respectively. The outage probability and the bit error rate (BER) expressions for the proposed system are derived over the combined channel model, which includes the effects of attenuation, turbulence, and pointing errors. The BER results are plotted for various binary digital modulation schemes such as on-off keying, binary phase-shift keying, binary frequency-shift keying, and differential phase-shift keying over UWOC, hybrid RF/FSO and RF-UWOC, FSO-UWOC with end-to-end systems. BER results are extended for various turbulence regions and pointing errors of the FSO link. Monte Carlo simulation results authenticate the correctness of the results.

Performance analysis of efficient digital modulation schemes over various fading channels

Using a simple yet accurate two-term exponential based approximation of the Gaussian Q function, in this paper, we simplify the intractable yet significant integrals which are used in the symbol error probability (SEP) expressions of various efficient digital modulation schemes over various well known fading statistics like Rayleigh, Nakagami-m, Nakagami-q and Nakagami-n. Precisely, we express these integrals in terms of simple moment generating function (MGF) whose solution for the aforementioned fading channels can be easily obtained from the literature. This MGF based approach simplifies the cumbersome integrals and eventually makes the SEP expressions tractable. The analytical work is further validated with the help of Monte-Carlo simulations.

Average of product of two Gaussian [formula omitted] functions as summation series and its significance in evaluating SEP integrals over fading channels

The product of two Gaussian Q-functions is actively used in computing the error probabilities of various digital modulation schemes. Evaluating symbol error probability (SEP) integral involving the product of Gaussian Q-functions over fading distributions is complicated. The closed-form solutions are not available always, therefore to derive these solutions approximations are used. In this paper, an approximation to the product of two Gaussian-Q functions as a sum of exponentials is presented. Further it is used to evaluate the error probabilities of modulation techniques over fading distributions in wide range of scenarios. The knowledge of moment generating function (MGF) of a fading model is sufficient enough to derive the closed-form solution to SEP integrals. Numerical results demonstrate superior accuracy of proposed approximation over other existing competing approximations. Furthermore the proposed solutions are fairly simple as the MGF of fading channels involve fundamental mathematical functions.

Novel MGF expressions of [formula omitted] composite fading channels with applications

In this paper, we provide novel expressions of moment generating function (MGF) for Fisher–Snedocor F composite fading channels. Precisely, we derive the exact MGF and its approximated expression to incorporate the heavy as well as the light shadowed conditions. With the help of these expressions, it is shown that the MGF of the F distribution turn to be valid for the entire range of the composite fading parameters yielding finite results for each value of the average signal to noise ratio. The significance of these expressions is further explained by simplifying the key integrals which are used in the error computation of widely used efficient digital modulation schemes. The analytical framework is also validated with the help of Monte-Carlo simulations.

Comparison of Bit Error Rate Performance of Various Digital Modulation Schemes over AWGN and Rayleigh Fading Channels using Simulink

Digital modulation increases information capacity, data security, and system availability while maintaining high communication quality. As a result, digital modulation techniques are in higher demand than analog modulation techniques due to their ability to transmit larger amounts of data. Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), Phase Shift Keying (PSK), Differential Phase Shift Keying (DPSK), and Quadrature Amplitude Modulation (QAM) are critical components of current communications systems development, particularly for broadband wireless communications. In this paper, the comparison of bit error rate performance of different modulation schemes (BPSK, QPSK, and16-QAM) and various equalization techniques such as constant modulus algorithm (CMA) and maximum likelihood sequence estimate (MLSE) for the AWGN and Rayleigh fading channels is analyzed using Simulink. BPSK outperforms QPSK and 16-QAM when compared to the other two digital modulation schemes. Among the three digital modulation schemes, BPSK is showing better performance as compared to QPSK and 16-QAM.