Digital Modulation Schemes Research Articles

Tighter Bounds on the Gaussian $Q$ Function and Its Application in Nakagami- ${m}$ Fading Channel

In this letter, using the Trapezoidal rule of numerical integration, we propose simpler and tighter approximations for the Gaussian ${Q}$ function. These can be efficiently applied to compute the integrals in symbol error probability (SEP) expressions of various digital modulation schemes over additive white Gaussian noise as well as fading channels. Using the proposed approximations, we present a closed-form solution to these integrals for Nakagami- ${m}$ fading channel, which are valid for the entire range of fading parameter ( ${m}$ ). To further validate the closed-form solution of these integrals, the SEP of 16-HQAM signal is also analyzed and compared with existing approximations.

Digital constant‐envelope modulation scheme for radar using multicarrier OFDM signals

Multicarrier signals using orthogonal frequency division multiplexing (OFDM) bring many advantages to radar such as low probability of intercept, improved target detection performance, optimisation of both radar transmitter and receiver etc. A major drawback of multicarrier OFDM signals is their high peak-to-mean envelope power ratio, which reduces the working efficiency of the used power amplifiers. To solve this problem, a digital constant-envelope modulation scheme is proposed for radar using multicarrier OFDM signals. The scheme can transmit multicarrier OFDM signals through power amplifiers being operated near saturation levels (and thus maximising power efficiency) with little spectral distortion, even in the presence of channel mismatch. Given the speed limitations of field programmable gate arrays (FPGAs), the proposed scheme is implemented in an FPGA at intermediate frequency level using a polyphase processing structure.

Simplified approximations to the average of some useful forms of Gaussian Q functions with MRC diversity reception over Nakagami-q and Rician fading channels and their applications

In this paper, using an accurate exponential based approximation on the Gaussian Q function, the simplified novel approximations to the average of some useful forms of Gaussian Q functions, with maximal-ratio combining (MRC) diversity reception, over independent but not necessarily identical Nakagami-q (Hoyt) and Rician fading channels are proposed. The results proved to be useful in accurate estimation of the symbol error probability (SEP) for various digital modulation schemes like cross-QAM, triangular-QAM (TQAM), rectangular-QAM and square-QAM (SQAM), over the same fading statistics. Asymptotic expressions of the proposed approximations are also derived in this paper. Various simulation results are provided to verify the accuracy and significance of the proposed work.

Blind signal modulation recognition through clustering analysis of constellation signature

Modulation classification using OPTICS clustering algorithm has been proposed.Algorithm is reliably classifying 4ASK, 8ASK, BPSK, QPSK and 8QAM above 9dB SNR.Classification is unsupervised and generalized for any orders ASK, PSK and QAM.Algorithm is implemented and tested on real time RF signal using labVIEW. Automatic recognition of digital modulation schemes is becoming an active research area in many covert operations. It has many military applications where surveillance and electronic warfare requires a type of modulation in intercepted signal to prepare jamming signals. Most of the approaches are based on modulated signal's component, but the modulation type can be best identified with the use of constellation diagram. The proposed technique is able to recognize M-QAM, M-ASK, and M-PSK modulation scheme in Additive White Gaussian Noise (AWGN) environment. As the constellation points form clusters in the I-Q plane, the order of the modulation can be obtained by estimating the correct number of clusters, which is calculated by OPTICS algorithm. The least square error has been calculated using linear regression from the obtained constellation points, to identify either ASK or PSK and QAM. The error is least for ASK which differentiates ASK from PSK and QAM. To identify between the PSK and QAM, k-means clustering is employed to find the number of centroids equal to order of modulation estimated by OPTICS. With the difference in maximum and minimum absolute value of the centroids, PSK or QAM is recognized. The proposed method shows an improvement in the classification accuracy which reaches 100% using 1024 symbols at 20dB compared to 98.89%, 98.05%, and 98% when using more complex classifiers like Support Vector Machine, Naive Bayes Classifier, KNN respectively. The method used is unsupervised whereas most of the methods in the literature require training phase to set the thresholds or weights for final model to detect modulation type. This algorithm is also implemented in LabVIEW, and tested on real-time signals. An intelligent system is made which does not require any knowledge of symbol rate, carrier frequency, and any training phase to set thresholds, and detects the type of modulation blindly in real time. Modulated RF signals are generated by NI PXIe-5673 (RF transmitter). NI PXI 5600 is used to downconvert RF signal and NI PXI-5142 (100 MS/s OSP digitizer) is used to sample the downverted signal.

On the application of the sum of generalized Gaussian random variables: maximal ratio combining

In most wireless communication systems, the additive noise is assumed to be Gaussian. However, there are many practical applications where non-Gaussian noise impairs the received signal. Examples include co-channel and adjacent channel interference in mobile cellular systems, impulsive noise in wireless and power-line communications, ultra-wide-band interference and multi-user interference in wireless systems, and spectrum sensing. To cover this issue, we consider in this paper the application of the sum of generalized Gaussian (GG) random variables (RVs). To this end, we consider single-input multiple-output (SIMO) systems that operate over Nakagami-m fading channels in the presence of an additive white generalized Gaussian noise (AWGGN). Specifically, we derive a closed-form expression for the bit error rate (BER) of several coherent digital modulation schemes using maximal ratio combining diversity in the Nakagami-m fading channels subject to an AWGGN. The derived expression is obtained based on the fact that the sum of L GG RVs can be approximated by a single GG RV with a suitable shaping parameter. In addition, the obtained BER expression is valid for integer and non-integer value of the fading parameter m. Analytical results are supported by Monte-Carlo simulations to validate the analysis.

Realization of Simple Electronic Functions Using EXCCII

The paper presents a simple circuit for the realization of two digital modulation schemes: BPSK and ASK simultaneously, with the advantage of high input impedance at the signal input nodes and use of grounded resistors. The new circuits are based on the use of extra-[Formula: see text] current conveyor. Detailed analysis is given and circuit verification is carried out through simulations with a supply voltage of [Formula: see text][Formula: see text]V and [Formula: see text]m CMOS parameters to support the proposed circuit. Nonideal study is also given. An extended application of the circuit in realizing precision half-wave and full-wave rectifiers is further proposed by incorporating a simple modification to the proposed topology. The new proposed CMOS compatible electronic circuits enrich the utility of extra-[Formula: see text] current conveyor for realizing diverse electronic functions.

Realizing ReMoRa (Reflection of Modulated Radio) Ambient Scatter Communication Links With Perfect Pulses

This paper explains how to construct and apply perfect pulses —antipodal binary waveforms with extraordinary dc-nulling properties—to an ambient scatter communications link. Several methods for employing perfect pulses in digital modulation schemes, with particular emphasis on backscatter (and simply scatter) radio modulation, are demonstrated. These waveforms enable a completely new type of RF information exchange by piggy-backing useful information onto ambient wireless signals using low-powered electronics. A mathematical model of perfect pulses is shared as well as an overview of their spectral properties. A signal parameter calculation method is presented for desired backscatter message design and spectral characteristics, later implemented in an experimental set-up. Software simulations of perfect pulse enabled communications depict the creation of the channel waveforms, modulation onto a pseudo-random ambient carrier, and retrieval of the intended message data from the noisy and interference laden received signal. A robust receiver system is described which can be implemented via simple post-processing techniques in a software defined system or as a low-cost, low-power RF circuit using commercial-off-the-shelf components. Experimentally retrieved data is used to create a realistic estimate of bit rate errors compared to more traditional waveforms using an ambient FM radio station signal.

Symbol detection based on Voronoi surfaces with emphasis on superposition modulation

A challenging task when applying high-order digital modulation schemes is the complexity of the detector. Particularly, the complexity of the optimal a posteriori probability (APP) detector increases exponentially with respect to the number of bits per data symbol. This statement is also true for the Max-Log-APP detector, which is a common simplification of the APP detector. Thus it is important to design new detection algorithms which combine a sufficient performance with low complexity. In this contribution, a detection algorithm for two-dimensional digital modulation schemes which cannot be split-up into real and imaginary parts (like phase shift keying and phase-shifted superposition modulation (PSM)) is proposed with emphasis on PSM with equal power allocation. This algorithm exploits the relationship between Max-Log-APP detection and a Voronoi diagram to determine planar surfaces of the soft outputs over the entire range of detector input values. As opposed to state-of-the-art detectors based on Voronoi surfaces, a priori information is taken into account, enabling iterative processing. Since the algorithm achieves Max-Log-APP performance, even in the presence of a priori information, this implies a great potential for complexity reduction compared to the classical APP detection.

A cross layer protocol to mitigate effects of radio's linear impairments

The impact of signal-to-noise ratio (SNR) of an additive white Gaussian noise (AWGN) channel on bit error rate (BER) has been extensively studied in the literature through theoretical, simulation-based, and experimental results. However, it is too simplistic to assume that BER in a real-world communication system is influenced by AWGN alone. The system's radio, which contributes both linear and nonlinear impairments, also impacts BER. This paper studies the impact of linear impairments, namely quadrature skew and gain imbalance, on the BER of an angular digital modulation scheme, such as M-ary phase shift keying (M-PSK). It presents a mathematical derivation of a technique to measure these impairments. It implements this technique on an experimentation system and presents statistical properties of these measurements. A novel contribution of this paper is a cross layer protocol through which the receiver shares these measured values with the transmitter. The transmitter uses this information to combat the effects of radio's impairments on BER, thereby improving system performance. This paper also presents a cost benefit analysis which proves that the idea proposed in this paper is feasible and practical to implement on real-world systems.

A Hybrid Modulation Scheme for Dual-Output Five-Leg Indirect Matrix Converter

This paper proposes a hybrid modulation method for a dual-output five-leg indirect matrix converter topology. The proposed control technique combines a space vector modulation scheme (SVPWM) applied to the rectifier stage so as to control the input currents and a new digital scalar modulation scheme (DSPWM) designed to control the two loads output voltages. A generalized expression of the output voltage references is also developed showing the capability of the proposed method to control more than two independent loads without requiring additional mathematical development. Furthermore, a new modified expression of the output voltages references is proposed to enable the correct operation of the converter under unbalanced grid voltages. Also, this paper proposes a detailed mathematical analysis that allows evaluating the effect of output loads unbalances on the input current harmonic content. Simulation and experimental results are provided to show the effectiveness of the proposed theoretical investigations and confirm the capability of the proposed method to control multiple drive systems as well as ac input currents.

Piecewise linear detection for direct superposition modulation

Considering high-order digital modulation schemes, the bottleneck in consumer products is the detector rather than the modulator. The complexity of the optimal a posteriori probability (APP) detector increases exponentially with respect to the number of modulated bits per data symbol. Thus, it is necessary to develop low-complexity detection algorithms with an APP-like performance, especially when performing iterative detection, for example in conjunction with bit interleaved coded modulation. We show that a special case of superposition modulation, dubbed Direct Superposition Modulation (DSM), is particularly suitable for complexity reduction at the receiver side. As opposed to square QAM, DSM achieves capacity without active signal shaping. The main contribution is a low-cost detection algorithm for DSM, which enables iterative detection by taking a priori information into account. This algorithm exploits the approximate piecewise linear behavior of the soft outputs of an APP detector over the entire range of detector input values. A theoretical analysis and simulation results demonstrate that at least max-log APP performance can be reached, while the complexity is significantly reduced compared to classical APP detection.

On Distortion in Digital Microwave Power Amplifiers

Abstract In this paper, a first study of distortion in digital power amplifiers (PA) is presented. The work is based on a voltage mode class-S PA with a GaN MMIC for the 900 MHz frequency band. The investigation focuses on the quasi-static amplitude-to-amplitude (AM-AM) and amplitude-to-phase (AM-PM) distortions. Different digital modulation schemes are applied and studied versus output power back-off. This includes two pulse-width modulation (PWM) versions as well as band-pass delta-sigma (BPDS) modulation. The results are verified by measurement data.

Simulation of BASK,BPSK,BFSKmodulators using verilog

This project presents the simulation results of digital modulation schemes BASK,BPSK and BFSK. In long distance transmission digital communication is more efficient and secure. In digital communication part noise detection and correction is very simple than analog communication. Digital modulation represents the transfer of digital bit stream from the transmitter to the receiver via the analog channels in an easy way. During the modulation the information signal modifies one or more carrier signal parameters leading to shift keying techniques. So it has more importance in modern communication systems. These three digital modulation schemes can be implemented using FPGA (Field Programmable Gate Array). This project employs the advantages of reliability, concurrent operation and minimum cost .It uses minimum number of blocks necessary for achieving BASK,BPSK and BFSK modulation techniques. In this project BASK,BPSK and BFSK modulation techniques have been implemented on FPGA using Verilog Hardware Description Language on Xilinx ISE 10.1 and simulated with Modelsim SE 6.5.

CLASSIFICATION OF MODULATION SCHEMES FOR ANALOG & DIGITAL SIGNALS USING FUZZY LOGIC

Modulation classifier detects the modulation type of received communication signals. AMR is a new technology implemented into communication receivers to automatically recognize the modulation type of a received signal. It has important applications in military for jamming signal, intelligence, and surveillance monitoring and threat analysis. It is also used in spectrum management. In this paper both analog and digital modulation scheme detection is explained. This paper work is done using the latest mathematical software including MATLAB. The program considers the classification of various modulation types using fuzzy logic classifier. This method successfully identifies modulation types without any priori information. After determining the type of modulation, the received signal is given to the demodulator respectively to get the original message signal back.

Comparative Study of Bit Error Rate of Different M-ary Modulation Techniques in AWGN Channel

This paper focuses on various digital modulation schemes and their effect on bit error rate (BER); and to ascertain which has the lowest bit error rate. Further analysis includes: to compare bit error rates of various digital modulation schemes using the M-ary modulation technique, analyse the effect of varying signal energy per bit to Noise ratio (E_b/N_o) on the error rate of various digital modulation schemes, analyse graphically the relationship between E_b/N_o and BER, analyse graphically the relationship between BER and M-ary number. A model-based design methodology was employed in the research using MATLAB/SIMULINK. The comparison between different M-ary (M-PAM, M-PSK, and M-QAM) (M = 2, 4, 8, 16, 32, and 64) modulation schemes in normal AWGN channel was done. By analysing the graphical illustration of E_b/N_o vs BER of these M-PSK schemes it was strongly observed that increase in the value of M causes a correspondent increase in the error rate. Therefore, as the error rate increases with increasing M; lower level should be used for long distance communication and vice versa. High level modulation techniques are always preferred for high data rate.

Recovery of Image through Alamouti Channel with Incorporation of RSA Algorithm

In many applications, it is necessary to transmit images at a remote station, where wired Internet service is not available. In this case, wireless local loop (WLL) can help in making wireless link between one end node of the internet and remote service center. In such link, the communication is heavily affected by large and small scale fading; hence the received signal experiences huge distortion in case of forward error correction. Otherwise, huge service delay arises due to frequent negative acknowledgements. To combat the situation, we can choose Alamouti channel of full rate and fully orthogonal space-time block code (OSTBC). Our aim is to transmit images through Alamouti channel and to observe the quality of the recovered image, in context of bit error rate (BER). We have also observed the impact of fading and additive white Gaussian noise (AWGN) on the image without application of error correction or detection technique of channel coding. To ensure security, we apply the RSA algorithm on each pixel prior transmitting and decrypt them at the receiving end, where we found no impairment from the algorithm. Finally, we observe that the relative performance of the system changes digital modulation schemes.

Performance Evaluation of Hybrid Precoded Millimeter Wave Wireless Communication System on Color Image Transmission

In this paper, a comprehensive study has been on the suitability of implementation of hybrid precoding scheme in performance analysis of the future generation wireless communication system. The 256-by-32 multi antenna supported simulated system incorporates various types of modern and classical channel coding schemes such as Low density parity check (LDPC), Repeat and Accumulate (RA), ½-rated convolutional and non-binary Bose-Chadhuri-Hocquenghem (BCH) and Zero-Forcing (ZF) signal detection technique. With consideration of ray path geometry based mmWave MIMO fading channel and properly designed precoders and combiners and their applicability in simulation works, it is seen from computer simulation results that the presently considered simulated system outperforms in retrieving color image in LDPC channel coding and 16QAM digital modulation and Zero-Forcing (ZF) signal detection schemes.

BER Performance Analysis of FEC Incorporated OFDM-MPSK over Rician Channel

OFDM comes out as a key technology in contemporary wireless communication systems. OFDM offers a diverse kind of advantages like fading immunity, eminent data rate transmission, and efficient bandwidth capabilities. In order to have a reliable error-free communication, various channel coding schemes viz. Convolution Codes (CC), BCH and Reed-Solomon (RS) encoding and decoding schemes are being used at the transmitter and receiver side. These channel encoding schemes makes possible the error detection and correction possible at the receiver end. In present work, an OFDM system based on the diverse level of M-PSK digital modulation scheme is demonstrated integrating dissimilar channel encoding techniques over the Rician fading channel. BER assessment as a function of SNR is being presented for the simulated test-bed. The simulation results present a substantial enhancement in BER performance of the simulated system using BCH over CC and RS.

BER Performance of Digital Modulation Schemes With and Without OFDM Model for AWGN, Rayleigh and Rician Channels

BER Performance of Digital Modulation Schemes With and Without OFDM Model for AWGN, Rayleigh and Rician Channels

Wind farms' interference effects on the error performance of wireless line-of-sight communications using binary digital modulations

The main objective of this paper is to examine the deterioration on the average error performance of military and civilian wireless communications systems (WCSs) that are in the vicinity of wind farms. By treating the total interference signal caused by any wind turbine (WT) as the ensemble of scattering signal replicas over the uniformly segmented parts of the WT that face different Doppler frequency shifts, path loss factors, etc., the time-varying characteristics of the total signal have been investigated by means of the varying configuration parameters. To expose the degrading effects of the wind farms on the received signal and the overall error performance of the WCSs, the scattering signal contribution of the segments of the mast and blades have been evaluated analytically by also taking physical optics-based radar cross-section (RCS) estimation method into account. Average bit error rate performances of digital modulation schemes have been examined theoretically and numerically via Monte Carlo simulations through the entire rotation period of the blades. With the aim of providing useful insights on the assessment of the performance degradation caused by the WT interference, this paper exposes miscellaneous numerical results related to different configurations and settlings.