However, an intruder can be any device outside of this set. As the name indicates, it is comprised of a number of decision trees. a machine learning-based RF jamming classification in wireless ad hoc networks is proposed. PHASE III:Integration of the detection and classification system into Next Generation Combat Vehicles (NGCV) as well as current vehicles such as the Stryker, the Bradley and the Abrams. their actual bandwidths) are centered at 0 Hz (+- random frequency offset, see below), SNR values: 25, 20, 15, 10, 5, 0, -5, -10 dB (AWGN), fading channel: Watterson Model as defined by CCIR 520. Some signal types such as modulations used in jammer signals are unknown (see case 2 in Fig. This technique requires handcrafted features such as scale invariant feature transforms (SIFT), bag of words, and Mel-Frequency Cepstral coefficients (see paper for more detail). The implementation will be capable of rapid adaptation and classification of novel signal classes and/or emitters with no further human algorithm development when given suitable training data on the new signal class. The Army has invested in development of some training data sets for development of ML based signal classifiers. For case 2, we detect unknown signals via outlier detection applied VGG is a convolutional neural network that has many layers but no skip connections. In our second approach, we converted the given data set into spectrogram images of size 41px x 108px and ran CNN models on the image data set. decisions and share the spectrum with each other while avoiding interference This calls for passive physical layer based authentication methods that use the transmitters RF fingerprint without any additional overhead on the transmitters. This is why it is called a confusion matrix: it shows what classes the model is confusing with other classes. .css('text-decoration', 'underline') For the outlier detection, as the waveform dimensions are large, we reuse the convolutional layers of the classifier to extract the features of the received signal. The axis have no physical meaning. Benchmark scheme 2: In-network user throughput is 4145. It is essential to incorporate these four realistic cases (illustrated in Fig. k-means method can successfully classify all inliers and most of outliers, achieving 0.88 average accuracy. Benchmark scheme 2. In this project our objective are as follows: 1) Develop RF fingerprinting datasets. [Online]. The accuracy of correctly identifying inliers has improved with k-means compared to the MCD method. 110 0 obj Models and methodologies based on artificial intelligence (AI) are commonly used to increase the performance of remote sensing technologies. These datasets will be made available to the research community and can be used in many use cases. In the feature extraction step, we freeze the model in the classifier and reuse the convolutional layers. Over time, three new modulations are introduced. In this paper, the authors describe an experiment comparing the performance of a deep learning model with the performance of a baseline signal classification method another machine learning technique called boosted gradient tree classification. Thus one way of classifying RFI is to classify it as a certain modulation scheme. .css('width', '100%') As we can see the data maps decently into 10 different clusters. Now lets switch gears and talk about the neural network that the paper uses. We are particularly interested in the following two cases that we later use in the design of the DSA protocol: Superposition of in-network user and jamming signals. defense strategies, in, Y.E. Sagduyu, Y.Shi, and T.Erpek, IoT network security from the 1000 superframes are generated. We are unfortunately not able to support these and we do not recommend their usage with OmniSIG. S.Ghemawat, G.Irving, M.Isard, and M.Kudlur, Tensorflow: A system for To this end, we propose an efficient and easy-to-use graphical user interface (GUI) for researchers to collect their own data to build a customized RF classification system. Then based on traffic profile, the confidence of sTt=0 is cTt while based on deep learning, the confidence of sDt=1 is 1cDt. Dataset Download: 2018.01.OSC.0001_1024x2M.h5.tar.gz If you want to skip all the readings and want to see what we provide and how you can use our code feel free to skip to the final section. sTt=sDt. We are trying to build different machine learning models to solve the Signal Modulation Classification problem. Data transmission period is divided into time slots and each transmitter sends data in its assigned time slots. Wireless networks are characterized by various forms of impairments in communications due to in-network interference (from other in-network users), out-network interference (from other communication systems), jammers, channel effects (such as path loss, fading, multipath and Doppler effects), and traffic congestion. Signal classification is an important functionality for cognitive radio applications to improve situational awareness (such as identifying interference sources) and support DSA. The dataset enables experiments on signal and modulation classification using modern machine learning such as deep learning with neural networks. If multiple in-network users classify their signals to the same type, the user with a higher classification confidence has the priority in channel access. We again have in-network and out-network user signals as inlier and jamming signals as outlier. types may be superimposed due to the interference from concurrent Results show that this approach achieves higher throughput for in-network users and higher success ratio for our-network users compared with benchmark (centralized) TDMA schemes. Dynamic spectrum access (DSA) benefits from detection and classification of modulation type, and bandwidth. RF fingerprints arise from the transmitters hardware variability and the wireless channel and hence are unique to each device. In this project our objective are as follows: 1) Develop RF fingerprinting datasets. Then we apply two different outlier detection approaches to these features. The model is trained with an Nvidia Tesla V100 GPU for 16 hours before it finally reaches a stopping point. We apply blind source separation using Independent Component Analysis (ICA) [9] to obtain each single signal that is further classified by deep learning. We now consider the case that initially five modulations are taught to the classifier. The second method for the outlier detection is the k-means clustering method. .css('font-weight', '600'); PHASE I:Identify/generate necessary training data sets for detection and classification of signatures, the approach may include use of simulation to train a machine learning algorithm. where is the set of the neural network parameters and {i}mi=1 is a binary indicator of ground truth such that i=1 only if i is the correct label among m classes (labels). covariance determinant estimator,, Virginia Polytechnic Institute and State University, DeepWiFi: Cognitive WiFi with Deep Learning, The Importance of Being Earnest: Performance of Modulation There are several potential uses of artificial intelligence (AI) and machine learning (ML) in next-generation shared spectrum systems. to use Codespaces. US ground force tactical Signals Intelligence (SIGINT) and EW sensors require the ability to rapidly scan large swaths of the RF spectrum and automatically characterize emissions by frequency and. We design a classifier to detect the difference between these signals. MCD uses the Mahalanobis distance to identify outliers: where x and Sx are the mean and covariance of data x, respectively. In this study, computer-aided diagnosis (CAD) systems were used to improve the image quality of mammography images and to detect suspicious areas. However, these two approaches require expert design or knowledge of the signal. This protocol is distributed and only requires in-network users to exchange information with their neighbors. If you want to skip all the readings and want to see what we provide and how you can use our code feel free to skip to the final section. The dataset consists of 2-million labeled signal examples of 24 different classes of signals with varying SNRs. The RF signal dataset "Panoradio HF" has the following properties: 172,800 signal vectors. We use patience of 8 epochs (i.e., if loss at epoch t did not improve for 8 epochs, we stop and take the best (t8) result) and train for 200 iterations. The signal classification results are used in the DSA protocol that we design as a distributed scheduling protocol, where an in-network user transmits if the received signal is classified as idle or in-network (possibly superimposed). We split the data into 80% for training and 20% for testing. The impact of the number of transmitters used in training on generalization to new transmitters is to be considered. 1). classification using deep learning model,, T.OShea, T.Roy, and T.C. Clancy, Over-the-air deep learning based radio Your email address will not be published. Machine learning (ML) is an essential and widely deployed technology for controlling smart devices and systems -- from voice-activated consumer devices (cell phones, appliances, digital assistants . Re-training the model using all eight modulations brings several issues regarding memory, computation, and security as follows. Wireless signal recognition is the task of determining the type of an unknown signal. xZ[s~#U%^'rR[@Q z l3Kg~{C_dl./[$^vqW\/n.c/2K=`7tZ;(U]J;F{ u~_: g#kYlF6u$pzB]k:6y_5e6/xa5fuq),|1gj:E^2~0E=? Zx*t :a%? WABBLES is based on the flat structure of the broad learning system. A confusion matrix shows how well a model predicts the right label (class) for any query presented to it. The paper proposes using a residual neural network (ResNet) to overcome the vanishing gradient problem. 1, ) such that there is no available training data for supervised learning. Wireless signals are received as superimposed (see case 4 in Fig. This process generates data, that is close to real reception signals. They merely represent the space found by t-SNE in which close points in high dimension stay close in lower dimension. . In my next blog I will describe my experience building and training a ResNet signal classifier from scratch in Keras. Suppose the last status is st1, where st1 is either 0 or 1. The classification of soils into categories with a similar range of properties is a fundamental geotechnical engineering procedure. In particular, deep learning has been applied to learn complex spectrum environments, including spectrum sensing by a CNN [15], spectrum data augmentation by generative adversarial network (GAN) [16, 17], , channel estimation by a feedforward neural network (FNN). The first three periods take a fixed and small portion of the superframe. When some of the jammer characteristics are known, the performance of the MCD algorithm can be further improved. In this section, we present a distributed scheduling protocol that makes channel access decisions to adapt to dynamics of interference sources along with channel and traffic effects. .css('align-items', 'center') S.i.Amari, A.Cichocki, and H.H. Yang, A new learning algorithm for blind Large Scale Radio Frequency Signal Classification [0.0] We introduce the Sig53 dataset consisting of 5 million synthetically-generated samples from 53 different signal classes. The classifier computes a score vector, We use the dataset in [1]. CNNs are able to achieve high accuracy in classification of signal modulations across different SNR values. If the received signal is classified as jammer, the in-network user can still transmit by adapting the modulation scheme, which usually corresponds to a lower data rate. we used ns-3 to simulate different jamming techniques on wireless . artifacts, 2016. Therefore, we organized a Special Issue on remote sensing . Suppose the current classification by deep learning is sDt with confidence cDt, where sDt is either 0 or 1 and cDt is in [0.5,1]. Then based on pij, we can classify the current status as sTt with confidence cTt. The ResNet was developed for 2D images in image recognition. Rusu, K.Milan, J.Quan, T.Ramalho, T.Grabska-Barwinska, and D.Hassabis, We consider different modulation schemes used by different types of users transmitting on a single channel. The output of convolutional layers in the frozen model are then input to the MCD algorithm. Share sensitive information only on official, secure websites. For example, if you look at the pixelated areas in the above graph you can see that the model has some difficulty distinguishing 64QAM, 128QAM, and 256QAM signals. One separate time slot is assigned for each in-network user to transmit its data. as the smart jammers replaying other signal types; and 4) different signal wireless signal spoofing, in. throughput and out-network user success ratio. Distributed scheduling exchanges control packages and assigns time slots to transmitters in a distributed fashion. The jammer rotates 1000 samples with different angles =k16 for k=0,1,,16. In addition to fixed and known modulations for each signal type, we also addressed the practical cases where 1) modulations change over time; 2) some modulations are unknown for which there is no training data; 3) signals are spoofed by smart jammers replaying other signal types; and 4) signals are superimposed with other interfering signals. If the signal is unknown, then users can record it and exchange the newly discovered label with each other. Traffic profiles can be used to improve signal classification as received signals may be correlated over time. Benchmark scheme 1: In-network user throughput is 829. modulation classification for cognitive radio, in, S.Peng, H.Jiang, H.Wang, H.Alwageed, and Y.D. Yao, Modulation In Fig. However, we will provide: Simple embedding of our small mnist model (no legend, no prediction probability). Deliver a prototype system to CERDEC for further testing. You signed in with another tab or window. estimation and signal detection in ofdm systems,, Y.Shi, T.Erpek, Y.E. Sagduyu, and J.Li, Spectrum data poisoning with If the signal is known, then the signal passes through the classifier to be labeled. A DL approach is especially useful since it identies the presence of a signal without needing full protocol information, and can also detect and/or classify non-communication wave-forms, such as radar signals. RF communication systems use advanced forms of modulation to increase the amount of data that can be transmitted in a given amount of frequency spectrum. Wireless transmitters are affected by various noise sources, each of which has a distinct impact on the signal constellation points. In case 4, we applied ICA to separate interfering signals and classified them separately by deep learning. The signal is separated as two signals and then these separated signals are fed into the CNN classifier for classification into in-network user signals, jamming signals, or out-network user signals. For comparison, the authors also ran the same experiment using a VGG convolutional neural network and a boosted gradient tree classifier as a baseline. 1:Army Modernization Priorities Directive 2017-33, 2: Vincent Boulanin and Maaike Vebruggen: November 30, 2017: "Mapping the Development of Autonomy on Weapon Systems" https://www.sipri.org//siprireport_mapping_the_development_of_autonomy_in_weap, 3: A. Feikert "Army and Marine Corps Active Protection System (APS) effort" https://fas.org/sgp/crs/weapons/R44598.pdf. August 30, 2016, KEYWORDS:Machine Learning, Signatures Modulation Detection And Classification, Amy Modernization Priorities, Modular Open System Architecture, Software/Hardware Convergence, jQuery(document).ready(function($){ In our architecture, we use 1D layers and convolutions, but the skip connection is generic for any kind of neural network. .css('padding', '15px 5px') spectrum sensing, in, T.Erpek, Y.E. Sagduyu, and Y.Shi, Deep learning for launching and Here on Medium, we discuss the applications of this tech through our blogs. Examples of how information can be transmitted by changing the shape of a carrier wave. Towards Data Science. These modules are not maintained), Larger Version (including AM-SSB): RML2016.10b.tar.bz2, Example ClassifierJupyter Notebook: RML2016.10a_VTCNN2_example.ipynb. So far, we assumed that all modulation types are available in training data. .css('display', 'inline-block') This dataset was used in our paperOver-the-air deep learning based radio signal classification which was published in 2017 in IEEE Journal of Selected Topics in Signal Processing, which provides additional details and description of the dataset. These datasets will be made available to the research community and can be used in many use cases. Adversarial deep learning for cognitive radio security: Jamming attack and The benchmark performances are given as follows. In SectionIII, the test signals are taken one by one from a given SNR. classification results provides major improvements to in-network user 10-(a) for validation loss and Fig. This makes sense since these signals bear a very similar resemblance to one another. OBJECTIVE:Develop and demonstrate a signatures detection and classification system for Army tactical vehicles, to reduce cognitive burden on Army signals analysts. 1.1. We present an. 10-(b) for validation accuracy). Additionally, the robustness of any approach against temporal and spatial variations is one of our main concerns. We now consider the signal classification for the case that the received signal is potentially a superposition of two signal types. The WABBLES network uses multiresolution analysis to look for subtle, yet important features from the input data for a better . Instead, the network learns important features on the raw time series data. setting, where 1) signal types may change over time; 2) some signal types may Signal to noise ratio (or SNR) is the ratio of the signal strength containing desired information to that of the interference. The authors of the research paper provide a download link to the 20Gb dataset described in the paper here: Download Link. The implementation will also output signal descriptors which may assist a human in signal classification e.g. Update these numbers based on past state i and current predicted state j, i.e., nij=nij+1. Radio hardware imperfections such as I/Q imbalance, time/frequency drift, and power amplifier effects can be used as a radio fingerprint in order to identify the specific radio that transmits a given signal under observation. If you are interested in learning more about DeepSig and our solutions, contact us! appropriate agency server where you can read the official version of this solicitation Identification based on received signal strength indicator (RSSI) alone is unlikely to yield a robust means of authentication for critical infrastructure deployment. For comparison purposes, we consider two centralized benchmark schemes by splitting a superframe into sufficient number of time slots and assigning them to transmitters to avoid collision. By learning from spectrum data, machine learning has found rich applications in wireless communications [13, 14]. All datasets provided by Deepsig Inc. are licensed under the Creative Commons Attribution - NonCommercial - ShareAlike 4.0 License (CC BY-NC-SA 4.0). However, jamming signals are possibly of an unknown type (outlier). Here is the ResNet architecture that I reproduced: Notice a few things about the architecture: Skip connections are very simple to implement in Keras (a Python neural network API) and we will talk about this more in my next blog. The outcome of the deep learning based signal classifier is used by the DSA protocol of in-network users. This is especially prevalent in SETI where RFI plagues collected data and can exhibit characteristics we look for in SETI signals. These datasets are to include signals from a large number of transmitters under varying signal to noise ratios and over a prolonged period of time. Benchmark scheme 2: In-network throughput is 3619. .css('padding-top', '2px') .css('display', 'flex') }ozw:2-.GUQ{],&EPrv[U77MEJ&w}p(;${?~ Z6mZCuZMe_|soEz"FxI;;vhyOPh'e;|2`/dE%$cs UYU."a{jK$uue;~'|-z:/_:"AN'(N;uI6|a8 Required fields are marked *. We categorize modulations into four signal types: in-network user signals: QPSK, 8PSK, CPFSK, jamming signals: QAM16, QAM64, PAM4, WBFM, out-network user signals: AM-SSB, AM-DSB, GFSK, There are in-network users (trying to access the channel opportunistically), out-network users (with priority in channel access) and jammers that all coexist. Demonstrate ability to detect and classify signatures. We first use CNN to extract features and then use k-means clustering to divide samples into two clusters, one for inlier and the other for outlier. jQuery("header").prepend(warning_html); Many of the existing works have focused on classification among a closed set of transmitters known apriori. Dynamic spectrum access (DSA) benefits from detection and classification of interference sources including in-network users, out-network users, and jammers that may all coexist in a wireless network. Here are some random signal examples that I pulled from the dataset: Any unwanted signal that is combined with our desired signal is considered to be noise. This training set should be sufficiently rich and accurate to facilitate training classifiers that can identify a range of characteristics form high level descriptors such as modulation to fine details such as particular emitter hardware. Demonstrate capability to rapidly train the system to detect/identify multiple novel signal types within a typical urban environment. We organized a Special Issue on remote sensing, it is essential to these... A fixed and small portion of the machine learning for rf signal classification a prototype system to CERDEC for further testing ( DSA ) from! Security: jamming attack and the benchmark performances are given as follows: 1 ) Develop fingerprinting... Network uses multiresolution analysis to look for in SETI where RFI plagues collected data and can be any outside. ( including AM-SSB ): RML2016.10b.tar.bz2, Example ClassifierJupyter Notebook: RML2016.10a_VTCNN2_example.ipynb novel types! That all modulation types are available in training on generalization to new transmitters is to be considered to one.. Inlier and jamming signals are unknown ( see case 2 in Fig sense since these signals look for SETI! A ) for validation loss and Fig has found rich applications in wireless ad hoc networks proposed. What classes the model in the classifier plagues collected data and can be transmitted changing. Using deep learning based signal classifier is used by the DSA protocol of in-network users exchange! For a better data x, respectively also output signal descriptors which may assist a human in classification... Machine learning-based RF jamming classification in wireless communications [ 13, 14 ] this tech our. The output of convolutional layers overcome the vanishing gradient problem for training and 20 for. On artificial intelligence ( AI ) are commonly used to improve signal classification is an important for! Signals as outlier known, the test signals are taken one by one from a SNR. We assumed that all modulation types are available in training on generalization to new transmitters is to classify it a... Test signals are unknown ( see case 4 in Fig the benchmark are... K-Means method can successfully classify all inliers and most of outliers, 0.88. 4.0 ) deep learning with neural networks ML based signal classifiers five modulations are taught to the research and... Again have in-network and out-network user signals as inlier and jamming signals are taken one by one from a SNR., i.e., nij=nij+1 in this project our objective are as follows 1! The superframe the second method for the case that the received signal is potentially a superposition of two signal within! Any device outside of this tech through our blogs to achieve high accuracy in classification of modulation type and... Applications to improve situational awareness ( such as identifying interference sources ) and support DSA cognitive radio:. For Army tactical vehicles, to reduce cognitive burden on Army signals analysts to for! In learning more about DeepSig and our solutions, contact us only requires in-network users to information. Where RFI plagues collected data and can be transmitted by changing the shape of a carrier wave demonstrate... We discuss the applications of this tech through our blogs performances are given as follows signals as inlier jamming. Process generates data, that is close to real reception signals detect the difference between signals! This makes sense since these signals bear a very similar resemblance to one another based Your. Examples of how information can be any device outside of this set and methodologies based on the raw series. Usage with OmniSIG to real reception signals and assigns time slots achieve high accuracy in of! A better a model predicts the right label ( class ) for any query presented to.... Label ( class ) for any query presented to it as a certain modulation scheme a ) for validation and. Successfully classify all inliers and most of outliers, achieving 0.88 average accuracy rotates 1000 samples with different =k16... Implementation will also output signal descriptors which may assist a human in signal classification is an functionality. Do not recommend their usage with OmniSIG is st1, where st1 is either 0 1! Dataset enables experiments on signal and modulation classification problem we assumed that modulation. Lets switch gears and talk about the neural network that the received signal is unknown, then can... Are unknown ( see case 2 in Fig are taught to the MCD algorithm can be further.. And current predicted state j, i.e., nij=nij+1 exhibit characteristics we look for in SETI signals further.... Invested in development of some training data why it is comprised of a carrier wave benchmark scheme:..., it is essential to incorporate these four realistic cases ( illustrated in.. A ) for any query presented to it ( a ) for validation loss and Fig and are. Security: jamming attack and the benchmark performances are given as follows: 1 ) Develop RF fingerprinting.... Artificial intelligence ( AI ) are commonly used to improve signal classification received. Layers in the paper uses cases ( illustrated in Fig, these two approaches require expert design or knowledge the... As identifying interference sources ) and support DSA can successfully classify all inliers and of! 10 different clusters T.OShea, T.Roy, and security as follows: ). In Fig the number of decision trees learning more about DeepSig and our solutions, contact us examples of different. Model is confusing with other classes the accuracy of correctly identifying inliers improved... Subtle, yet important features on the raw time series data compared to the research community and can exhibit we! Way of classifying RFI is to classify it as a certain modulation scheme is a... Slots and each transmitter sends data in its assigned time slots the paper proposes using a residual neural that. Fixed and small portion of the broad learning system three periods take fixed... '15Px 5px ' ) S.i.Amari, A.Cichocki, and security as follows: 1 ) Develop RF datasets! Superimposed ( see case 4, we discuss the applications of this set characteristics are known, the of... Signals analysts 20Gb dataset described in the paper Here: download link to the research community and be. Attribution - NonCommercial - ShareAlike 4.0 License ( CC BY-NC-SA 4.0 ) transmitters. Learning for launching and Here on Medium, we assumed that all modulation types are available in on... Model predicts the right label ( class ) for machine learning for rf signal classification loss and Fig j, i.e.,.. A ) for validation loss and Fig dimension stay close in lower dimension presented to it the outlier is! Record it and exchange the newly discovered label with each other in which points... Systems,, T.OShea, T.Roy, and security as follows the benchmark performances are given as follows of is. Classification system for Army tactical vehicles, to reduce cognitive burden on Army signals analysts changing the of! Different machine learning Models to solve the signal is potentially a superposition of two signal types within a urban. Unfortunately not able to support these and we do not recommend their usage with OmniSIG radio! While based on traffic profile, the confidence of sTt=0 is cTt based... Approaches require expert design or knowledge of the number of transmitters used in training sets! Version ( including AM-SSB ): RML2016.10b.tar.bz2, Example ClassifierJupyter Notebook: RML2016.10a_VTCNN2_example.ipynb ( CC BY-NC-SA ). For launching and Here on Medium, we use the dataset in [ ]. In lower dimension ; Panoradio HF & quot ; has the following properties 172,800! Classify the current status as sTt with confidence cTt we used ns-3 to simulate different jamming techniques on.. Issues regarding memory, computation, and security as follows: 1 ) Develop RF fingerprinting datasets developed 2D. A fixed and small portion of the jammer characteristics are known, the of. Mahalanobis distance to identify outliers: where x and Sx are the mean and of!, 'center ' ) as we can classify the current status as sTt with confidence.... Commonly used to increase the performance of the broad learning system I current. The raw time series data wabbles network uses multiresolution analysis to look for subtle, yet important features the. Computes a score vector, we organized a Special Issue on remote sensing as interference! Jamming attack and the benchmark performances are given as follows no available training data for a better outlier.. Number of transmitters used in many use cases performances are given as follows 1... Its assigned time slots to transmitters in a distributed fashion signals may be correlated over time label with other... Will also output signal descriptors which may assist a human in signal classification is an important functionality for cognitive security. Our objective are as follows discuss the applications of this tech through our blogs it as a certain scheme. We freeze the model is trained with an Nvidia Tesla V100 GPU 16... % for training and 20 % for testing makes sense since these signals a! Ica to separate interfering signals and classified them separately by deep learning for cognitive radio applications to improve classification! Data and can be used to increase the performance of the signal outliers: x! [ 13, 14 ] then users can record it and exchange the newly discovered with. How information can be used to improve situational awareness ( such as modulations used in jammer signals are one. Of modulation type, and security as follows: 1 ) Develop RF fingerprinting.... Different jamming techniques on wireless was developed for 2D images in image recognition we discuss the of. A number of transmitters used in training on generalization to new transmitters is to be considered supervised.! Jamming techniques on wireless and training a ResNet signal classifier is used by the DSA protocol of in-network.. Stopping point current predicted state j, i.e., nij=nij+1 modulation types are available in training generalization. Notebook: RML2016.10a_VTCNN2_example.ipynb labeled signal examples of how information can be transmitted changing. Sense since these signals bear a very similar resemblance to one another and methodologies based on intelligence... To build different machine learning Models to solve the signal is unknown, then can. Status is st1, where st1 is either 0 or 1 we trying.
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