Decentralized detection for censored binary observations with statistical dependence

This paper analyzes the problem of distributed detection in a sensor network of binary sensors. In particular, statistical dependence between local decisions (at binary sensors) is assumed, and two complementary methods to save energy have been considered: censoring, to avoid some transmissions from sensors to fusion center, and a sleep and wake up random schedule at local sensors. The effect of possible failures in transmission has been also included, considering the probability of having a successful transmission from a sensor to the fusion center. In this scenario, the necessary statistical information has been identified, the optimal decision rule at the fusion center has been obtained, and some examples have been used to analyze the effect of statistical dependence in a simple network with two sensors

Fusing Censored Dependent Data for Distributed Detection

In this paper, we consider a distributed detection problem for a censoring sensor network where each sensor's communication rate is significantly reduced by transmitting only "informative" observations to the Fusion Center (FC), and censoring those deemed "uninformative". While the independence of data from censoring sensors is often assumed in previous research, we explore spatial dependence among observations. Our focus is on designing the fusion rule under the Neyman-Pearson (NP) framework that takes into account the spatial dependence among observations. Two transmission scenarios are considered, one where uncensored observations are transmitted directly to the FC and second where they are first quantized and then transmitted to further improve transmission efficiency. Copula-based Generalized Likelihood Ratio Test (GLRT) for censored data is proposed with both continuous and discrete messages received at the FC corresponding to different transmission strategies. We address the computational issues of the copula-based GLRTs involving multidimensional integrals by presenting more efficient fusion rules, based on the key idea of injecting controlled noise at the FC before fusion. Although, the signal-to-noise ratio (SNR) is reduced by introducing controlled noise at the receiver, simulation results demonstrate that the resulting noise-aided fusion approach based on adding artificial noise performs very closely to the exact copula-based GLRTs. Copula-based GLRTs and their noise-aided counterparts by exploiting the spatial dependence greatly improve detection performance compared with the fusion rule under independence assumption

Heterogeneous Sensor Signal Processing for Inference with Nonlinear Dependence

Inferring events of interest by fusing data from multiple heterogeneous sources has been an interesting and important topic in recent years. Several issues related to inference using heterogeneous data with complex and nonlinear dependence are investigated in this dissertation. We apply copula theory to characterize the dependence among heterogeneous data. In centralized detection, where sensor observations are available at the fusion center (FC), we study copula-based fusion. We design detection algorithms based on sample-wise copula selection and mixture of copulas model in different scenarios of the true dependence. The proposed approaches are theoretically justified and perform well when applied to fuse acoustic and seismic sensor data for personnel detection. Besides traditional sensors, the access to the massive amount of social media data provides a unique opportunity for extracting information about unfolding events. We further study how sensor networks and social media complement each other in facilitating the data-to-decision making process. We propose a copula-based joint characterization of multiple dependent time series from sensors and social media. As a proof-of-concept, this model is applied to the fusion of Google Trends (GT) data and stock/flu data for prediction, where the stock/flu data serves as a surrogate for sensor data. In energy constrained networks, local observations are compressed before they are transmitted to the FC. In these cases, conditional dependence and heterogeneity complicate the system design particularly. We consider the classification of discrete random signals in Wireless Sensor Networks (WSNs), where, for communication efficiency, only local decisions are transmitted. We derive the necessary conditions for the optimal decision rules at the sensors and the FC by introducing a hidden random variable. An iterative algorithm is designed to search for the optimal decision rules. Its convergence and asymptotical optimality are also proved. The performance of the proposed scheme is illustrated for the distributed Automatic Modulation Classification (AMC) problem. Censoring is another communication efficient strategy, in which sensors transmit only informative observations to the FC, and censor those deemed uninformative . We design the detectors that take into account the spatial dependence among observations. Fusion rules for censored data are proposed with continuous and discrete local messages, respectively. Their computationally efficient counterparts based on the key idea of injecting controlled noise at the FC before fusion are also investigated. In this thesis, with heterogeneous and dependent sensor observations, we consider not only inference in parallel frameworks but also the problem of collaborative inference where collaboration exists among local sensors. Each sensor forms coalition with other sensors and shares information within the coalition, to maximize its inference performance. The collaboration strategy is investigated under a communication constraint. To characterize the influence of inter-sensor dependence on inference performance and thus collaboration strategy, we quantify the gain and loss in forming a coalition by introducing the copula-based definitions of diversity gain and redundancy loss for both estimation and detection problems. A coalition formation game is proposed for the distributed inference problem, through which the information contained in the inter-sensor dependence is fully explored and utilized for improved inference performance

Decentralized Detection in Realistic Sensor Networks

Tämä työ käsittelee kohteen ilmaisua sensoriverkolla, joka koostuu äänisensoreista. Työn pääpaino on epäideaalisen tilanteen käsittelyllä, jossa monet hajautettua ilmaisua käsittelevät oletukset, joita alan kirjallisuudessa tehdään, eivät enää päde. Sensoriverkko koostuu mielivaltaiseen verkkotopologiaan asetetuista sensoreista ja fuusiokeskuksesta, ja tavoite on ilmaista verkkoa lähestyvä kohde, joka tuottaa äänisignaalia. Tiedon käsittelyyn sensoreilla ja fuusiokeskuksella esitetään kaksi erilaista algoritmia. Toinen algoritmeista perustuu suurimman uskottavuuden menetelmään ja toinen on heuristinen, klassiseen ilmaisuteoriaan perustuva, lähestymistapa ongelmaan. Algoritmien suorituskykyä tutkitaan simulaatioiden avulla. Heuristisen algoritmin suorituskyky on huomattavasti parempi kaikissa simuloiduissa tilanteissa. Algoritmien johdossa taustakohina oletettiin normaalijakautuneeksi, mutta simulaatioiden perusteella algoritmit toimivat kohtuullisen hyvin myös pidempihäntäisen taustakohinajakauman tapauksessa. Heuristinen algoritmi tarjoaa paremman suorituskyvyn lisäksi myös helpomman tavan asettaa kynnysarvoparametrit niin, että sensoreilla ja fuusiokeskuksella on haluttu väärän hälytyksen todennäköisyys.This thesis discusses the detection of a target using a network of acoustic sensors. The focus of the work is on considering what to do in a non-ideal situation, where many of the assumptions often made in decentralized detection literature are no longer valid. The sensors and a fusion center are grouped in an arbitrary formation, and the object is to detect an approaching target which emits a sound signal. Two different schemes are considered for processing the data at sensors and the fusion center. One of the schemes is based on maximum likelihood estimation and the other one is a heuristic approach based on classical detection theory. The performances of the two schemes are studied in simulations. The heuristic scheme has a better detection performance for a given false alarm rate with all different sets of settings for the simulation. In derivation of the schemes, the background acoustic noise is assumed to be normal distributed, but, according to the simulations, the schemes still work relatively well under a long tailed noise distribution. In addition to better performance, the heuristic scheme offers easier setup of threshold values and approximation of false alarm rates for given thresholds using simple equations

Optimum energy allocation for detection in wireless sensor networks

The problem of binary hypothesis testing in a wireless sensor network is studied in the presence of noisy channels and for non-identical sensors. We have designed a mathematically tractable fusion rule for which optimal energy allocation for individual sensors can be achieved. In this thesis we considered two methods for transmitting the sensor observations; binary modulation and M-ary modulation. In binary modulation we are able to allocate the energy among the sensors and protect the individual quantized bits where as the M-ary modulation provides optimum energy allocation only among the sensors. The goal is to design a fusion rule and an energy allocation for the nodes subject to a limit on the total energy of all the nodes so as to optimize a cost function. Two cost functions were considered; the probability of error and the J-divergence distance measure. Probability of error is the most natural criteria used for binary hypothesis testing problem. Distance measure is applied when it is difficult to obtain a closed form for the error probability. Results of optimal energy allocation and the resulting probability of error are presented for the two cost functions. Comparisons are drawn between the two cost functions regarding the fusion rule, energy allocations and the error probability

Optimal quantization and power allocation for energy-based distributed sensor detection

We consider the decentralized detection of an unknown deterministic signal in a spatially uncorrelated distributed wireless sensor network. N samples from the signal of interest are gathered by each of the M spatially distributed sensors, and the energy is estimated by each sensor. The sensors send their quantized information over orthogonal channels to the fusion center (FC) which linearly combines them and makes a final decision. We show how by maximizing the modified deflection coefficient we can calculate the optimal transmit power allocation for each sensor and the optimal number of quantization bits to match the channel capacity