MFSK Signals Research Articles

A Novel Weighted LLR Algorithm for Non-Coherent OFDM-MFSK System in Ionospheric Scatter Channel

A novel weighted log likelihood ratio (LLR) algorithm is proposed for the non-coherent orthogonal frequency division multiplexing with <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> -ary frequency shift keying (OFDM-MFSK) system in an ionospheric scatter channel (ISC) with serious frequency-selective fading. In the algorithm, the bit LLR is derived according to the probability distribution of non-coherent received signals in the MFSK symbol and is approximately simplified to a concise expression, which reveals that LLRs cannot indicate the effect of the frequency-selective fading channel on different MFSK symbols. The proposed weighted LLR algorithm maximizes the signal-to-noise ratio (SNR) of the metric combined with LLRs in channel decoding. The weighted factors were estimated blindly from the received MFSK signals. Simulation results show that the bit error rate (BER) of OFDM-MFSK systems with the proposed LLR-weighted algorithm is superior than that of conventional LLR algorithms, and has approximately 1.6 dB SNR gain when BER is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${10^{-4}}$ </tex-math></inline-formula> .

주파수 도약 M-FSK 신호의 블라인드 복조정확도 개선 연구

제3자가 통신 채널 주파수를 예측할 수 없도록 송수신기의 채널 주파수가 의사잡음 코드발생기에 의해 불규칙하고 아주 빠른 속도로 변경되면서 송신기와 수신기가 서로 약속된 도약 주파수(Hopping Frequency)로 통신하는 주파수 도약방식의 통신장비가 통신용으로 널리 이용되고 있다. 이러한 시스템의 불법적 사용 및 주파수 도용 방지를 위해서는 지속적으로 스펙트럼을 모니터링하여야 할 필요가 있는데 스펙트럼 모니터링 장비에서는 수신된 도약 주파수만으로 제원을 확보할 수밖에 없다. 이러한 블라인드 환경에서 도약 주파수를 수신하여 그 제원을 추출하기 위해서는 변조방식 추정 과정을 거쳐야 하는데, 다양한 아날로그 및 디지털 변조방식 중에서 FSK라고 추정된 신호에 대하여 2/4/8FSK과 같은 를 각각 분리할 필요가 있다. 본 연구에서는 투영중첩법을 이용하여 미상의 M-FSK 신호에 대해 4/8FSK의 신호를 분리하는 기법을 제안하였고, 궁극적으로 복조정확도를 개선하였다.

MFSK Signal Individual Identification Algorithm Based on Bi-spectrum and Wavelet Analyses

MFSK Signal Individual Identification Algorithm Based on Bi-spectrum and Wavelet Analyses

The Control Packet Collision Avoidance Algorithm for the Underwater Multichannel MAC Protocols via Time-Frequency Masking

Establishing high-speed and reliable underwater acoustic networks among multiunmanned underwater vehicles (UUVs) is basic to realize cooperative and intelligent control among different UUVs. Nevertheless, different from terrestrial network, the propagation speed of the underwater acoustic network is 1500 m/s, which makes the design of the underwater acoustic network MAC protocols a big challenge. In accordance with multichannel MAC protocols, data packets and control packets are transferred through different channels, which lowers the adverse effect of acoustic network and gradually becomes the popular issues of underwater acoustic networks MAC protocol research. In this paper, we proposed a control packet collision avoidance algorithm utilizing time-frequency masking to deal with the control packets collision in the control channel. This algorithm is based on the scarcity of the noncoherent underwater acoustic communication signals, which regards collision avoiding as separation of the mixtures of communication signals from different nodes. We first measure the W-Disjoint Orthogonality of the MFSK signals and the simulation result demonstrates that there exists time-frequency mask which can separate the source signals from the mixture of the communication signals. Then we present a pairwise hydrophones separation system based on deep networks and the location information of the nodes. Consequently, the time-frequency mask can be estimated.

STATISTIC CHARACTERISTICS OF M-ARY FSK SIGNAL IN THE PRESENCE OF GAUSSIAN NOISE, IMPULSE NOISE AND VARIABLE SIGNAL AMPLITUDE

In this paper the receiver for the demodulation of M-FSK signals in the presence of Gaussian noise, impulse noise and variable signal amplitude is considered. The communication systems are subject to Gaussian noise, impulse noise and Rayleigh signal amplitude that can seriously degrade their performance.

Correlation-Index Blind Classification for MFSK with Unreconstructed Compressive Samplings

—To improve the speed of traditional signal sampling and processing, which is based on the Nyqusit-sampling theorem, a new theorem called Compressive Sensing (CS) is presented. Most work in CS has focused on reconstructing the high-bandwidth signals from nonuniform low-rate samples. However, the signal reconstruction process of CS needs large amount of computation. In this paper, under the frame of CS, a method called Correlation-Index Blind Classification (CIBC) using the Correlation-Index to realize MFSK signal classification is presented, which exploits the compressive measurements without reconstructing the original signal or knowing any parameter. CIBC processes the compressive measurements directly, avoiding the high computation of reconstruction. What’s more, compared with the traditional Peak-Index, the promotion of computing speed is significant, and the performance decreases very little. The simulation results show that CIBC has good performance and low computation complexity. It’s an effective method to improve the real-time performance of communication system.

An Improved Algorithm Based on First-order Cyclostationarity for Recognition of M-FSK Signals

This paper proposes an improved algorithm based on Piecewise Auto Correlation Accumulation (PACA) and first-order cyclostationarity for recognition of M-ary frequency shift keying (M-FSK, M = 2/4/8) signals in communication systems. Theoretical analysis indicates that the number of first-order Cycle Frequencies (CFs) is equal to the modulation order of M-FSK signals. Therefore, by estimating the first-order cyclic moment of the autocorrelation of M-FSK signals and detecting the number of CFs, the modulation order of M-FSK signals can be identified. Based on its multicarrier characteristics, the proposed algorithm does not require a priori information and is not significantly influenced by factors such as timing delay and frequency offset. Further, PACA suppresses noise, and thereby helps to improve the antinoise performance of the algorithm’s modulation recognition. The results of simulations conducted confirm the efficacy of the proposed algorithm.

A Novel Algorithm for MFSK Signal Classification

A new classification algorithm of M-ary FSK signals based on the extraction of signals features is presented in this paper. The implementation of the methodology does not require any apriori information. By extracting some basic features of intermediate frequency signals both in time domain and frequency domain, the classification of M-ary FSK signals is achieved. Simulation result shows that the proposed algorithm can classify 2FSK, 4FSK and 8FSK signals effectively under AWGN and and still keeps a good performance even at low input SNR.

Modulation Recognition of MFSK Signals Based on Multifractal Spectrum

In order to solve the problem that modulation recognition of MFSK signals in alpha-stable distribution noise, a novel algorithm using multifractal spectrum is proposed. Multifractal spectrum characteristics of signals and noise are discussed firstly. Then algorithm extracts the difference between maximum and minimum values of spectrum as classification feature. Finally, algorithm employs threshold decision method to achieve modulation recognition of 2FSK, 4FSK and 8FSK signals. Numerical results show that algorithm has good performance in both alpha-stable distribution noise and Gaussian noise, and it is less affected by characteristic exponent of noise and data points.

Time Delay Estimation Using Windowed Differential agnitude of Cross Correlation and Its Hilbert Transform

A method is proposed for estimating time delay between MFSK signals received at two spatially separated sensors. onsidering the periodical characteristic of the peaks of cross correlation, the proposed method combines window echnology and differential magnitude between cross correlation and its Hilbert transform. The time argument at hich the differential magnitude achieves the peak in the range of window is the delay estimate. The method is ompared with several other methods. Simulation results show that the proposed method can get better performance. nder certain conditions the performance of proposed method can be better than CRLB by using priori information bout the transmitter and receivers.

Application of kernel methods in signals modulation classification

A new approach to common signals classification of relevance vector machine (RVM) was presented and two signal classifiers based on kernel methods of support vector machine (SVM) and RVM were compared and analyzed. First several robust features of signals were extracted as the input of classifiers, then the kernel thought was used to map feature vectors impliedly to the high dimensional feature space, and multi-class RVM and SVM classifiers were designed to complete AM, CW, SSB, MFSK and MPSK signals recognition. Simulation result showed that when chose proper parameter, RVM and SVM had comparable accuracy but RVM had less learning time and basis functions. The classification speed of RVM is much faster than SVM.

A Novel Algorithm for MFSK Signal Classification

A Novel Algorithm for MFSK Signal Classification

A blind SNR estimator for digital bandpass signals

A subspace-based blind Signal-to-Noise Ratio (SNR) estimation algorithm for digital bandpass signals in Additive White Gaussian Noise (AWGN) channel is discussed. The lower bounds of the mean and variance of the estimation are derived, and simulations are performed for the commonly used digital bandpass signals, such as MPSK (M=2, 4, 8), MFSK (M=2, 4) and MQAM (M=16, 64, 128, 256) signals. Theoretical analyses and simulation results indicate that the proposed algorithm is effective even when the SNR is below 0dB. Furthermore, the algorithm can provide a blind estimator in that it needs neither the parameters of the received signals, such as the carrier frequency, symbol rate and modulation scheme, nor the synchronization of the system.

Synthesis of a Quasioptimal Receiver of MFSK Signal against a Background of FM Interference and Gaussian Noise for a Double-Channel Observation. The General Case and Case of a Perfect Reference Channel

Synthesis of a Quasioptimal Receiver of MFSK Signal against a Background of FM Interference and Gaussian Noise for a Double-Channel Observation. The General Case and Case of a Perfect Reference Channel

Classification of MFSK signals over time-varying flat correlated fading channels under class-A impulsive noise environment

A classifier for MFSK signals contaminated with Middleton's class-A impulsive noise and transmitted over a time-varying flat correlated fading channel is developed. The correlated fading process of the channel is expanded using the Karhunen-Loeve expansion. The classifier is derived for both synchronous and asynchronous waveforms. Asymptotic theoretical performance evaluation of the classifier is derived. Computer simulations are illustrated to validate the theoretical developments. The performance of the developed classifier is compared with the performance of the conventional classifier (designed for AWGN). It is shown that the conventional classifier has severe performance degradation if it is subject to impulsive noise. A greater performance improvement is obtained when using the developed classifier, especially for smaller impulsive indexes of the noise. It is also shown that the performance of the developed classifier is sensitive to the impulsive index (A) of the noise. Increasing A enhances the performance of the classifier.

Channel characterization using FSK wave forms

Automatic characterization of underwater acoustic communication channels can support connectivity over a wide range of operational ocean environments. With quantitative measures of the prevailing channel, adaptive modems may optimize the modulation and initialize the demodulation equalizer. A novel channel-estimation technique involving noncoherent processing of received FSK wave forms has been described recently by Green and Rice (Proc. IEEE Oceans’98) and Rice and Green (Proc. MTS Ocean Community Conference, 1998). This technique uses received handshake signals to measure temporal and spectral spreading and signal excess directly, and to estimate coherence parameters. This effort will focus on applying this channel-estimation technique to received and autonomously recorded 8–13 kHz MFSK signals using shallow horizontal channels. [Work supported by ONR 32 and SPAWARSYSCEN.]

Multiple tone interference of frequency-hopped noncoherent MFSK signals transmitted over Ricean fading channels

This paper investigates the performance degradation resulting from multitone interference of orthogonal, frequency-hopped, noncoherent M-ary frequency-shift keyed receivers (FH/MFSK) where the effect of thermal and other wideband noise is not neglected. The multiple, equal power jamming tones are assumed to correspond to some or all of the possible FH M-ary orthogonal signaling tones. Furthermore, the channel is modeled as a Ricean fading channel; and both the signaling tones and the multiple interference tones are assumed to be affected by channel fading. It is also assumed that channel fading need not necessarily affect the signaling tones and the interference tones in the same-way. When the information signal power exceeds the power of the individual interference tones, poorer overall system performance is obtained when the multiple interfering tones experience fading. This trend is accentuated as M increases. When the information signal experiences fading, the effect of fading multiple interference tones on overall system performance lessens, and for a Rayleigh-faded information signal, fading of the multiple interference tones has no effect on overall system performance regardless of M.

A hyperstable adaptive line enhancer for fast tracking of sinusoidal inputs

An IIR adaptive filter is presented for the application of tracking sinusoidal inputs. The filter uses a hyperstable update to provide very fast convergence, and is capable of tracking multiple sinusoids, with the order of the filter being twice the number of sinusoids. The convergence of the filter depends on a certain transfer function being strictly positive real (SPR), and necessary conditions are derived, for this transfer function to be SPR. These conditions hold for the completely general case, and can be very simply expressed in terms of the input sinusoidal frequencies, because of the specific application that is addressed, and because of the filter topology (a resonator-based filter structure) that is used. Further, these conditions are derived under the assumption that no post-error filter is used (unlike most hyperstable schemes). Further, these conditions are also shown to be sufficient for convergence, for the case of up to two input sinusoids (4th order filter). For a larger number of input sinusoids, though it has not been possible to prove the sufficiency of these conditions, we have conducted several experiments and obtained convergence in all cases, leading to the conjecture that the conditions are sufficient for convergence, for the general case as well. Simulations of the performance of the filter structure are also provided to support the theory and the conjectured condition for convergence. The capability of the adaptive filter to track fast changes in frequency make it a candidate for applications like demodulating MFSK signals. Alternatively, the speed can be traded for complexity because for slow adaptation (low /spl mu/), the algorithm reduces to a pseudo-gradient-based update that can be implemented very simply.

Optimization of a hybrid SFH/DS MFSK link in the presence of worst case multitone jamming

The performance of a hybrid slow frequency hopped direct sequence multiple frequency shift keyed (SFH/DS MFSK) communication link in the presence of partial band multitone jamming is considered. The communication signal is characterized by a DS-spread MFSK signal bandwidth that may exceed the FH slot spacing, and the signal consists of multiple M-ary symbols per DS code period. An equation for the bit error rate (BER) is developed for the signal in the presence of multitone jamming. The equation is flexible enough to allow examination of optimization of jamming strategy. It is shown that the jamming strategy may be optimized by varying the number of tones, their placement, or both. It is shown that in the presence of optimized jamming, overlapping systems are more resistant to jamming than nonoverlapping systems with equal parameters (except for the number of FH slots). It is also demonstrated that, in some cases, the addition of DS spreading to an FH system, without increasing the total system bandwidth, can significantly improve the system's resistance to partial band multitone jamming. >

Cutoff rates of multichannel MFSK and DPSK signals in mobile satellite communications

This paper studies the coded performance of multichannel MFSK and DPSK signalings in mobile satellite environments characterized by various kinds of multipath fading. Rician, Rician/lognormal, and a convex combination of Rician and Rician/lognormal or Rayleigh/lognormal distributions are used to model these communication channels. We investigate the minimum average signal-energy-to-noise ratio required to yield a cutoff rate that is greater than or equal to a given code rate. Also examined are system design issues such as the effect of quantization and metric conversion, the choice between binary codes and M-ary symbol codes, the optimization of the diversity order and the signal size, and the order of deinterleaving and diversity combining. Numerical examples are given to answer concerns raised by these issues.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>