Publications
Optical down-sampling of wide-band microwave signals
December 1, 2003
Journal Article
Published in:
J. Lightwave Technol., Vol. 21, No. 12, December 2003, pp. 3116-3124.
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Summary
Phase-encoded optical sampling allows radio-frequency and microwave signals to be directly down-converted and digitized with high linearity and greater than 60-dB (10-effective-bit) signal-to-noise ratio. Wide-band electrical signals can be processed using relatively low optical sampling rates provided that the instantaneous signal bandwidth is less than the Nyquist sampling bandwidth. We demonstrate the capabilities of this technique by using a 60-MS/s system to down-sample two different FM chirp signals: 1) a baseband (0-250 MHz) linear-chirp waveform and 2) a nonlinear-chirp waveform having a 10-GHz center frequency and a frequency excursion of 1 GHz. We characterize the frequency response of the technique and quantify the analog bandwidth limitation due to the optical pulse width. The 3-dB bandwidth imposed by a 30-ps sampling pulse is shown to be 10.4 GHz. We also investigate the impact of the pulse width on the linearity of the phase-encoded optical sampling technique when it is used to sample high-frequency signals.
Summary
Phase-encoded optical sampling allows radio-frequency and microwave signals to be directly down-converted and digitized with high linearity and greater than 60-dB (10-effective-bit) signal-to-noise ratio. Wide-band electrical signals can be processed using relatively low optical sampling rates provided that the instantaneous signal bandwidth is less than the Nyquist sampling bandwidth. We...
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Passive operating system identification from TCP/IP packet headers
November 19, 2003
Conference Paper
Published in:
ICDM Workshop on Data Mining for Computer Security, DMSEC, 19 November 2003.
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Accurate operating system (OS) identification by passive network traffic analysis can continuously update less-frequent active network scans and help interpret alerts from intrusion detection systems. The most recent open-source passive OS identification tool (ettercap) rejects 70% of all packets and has a high 75-class error rate of 30% for non-rejected packets on unseen test data. New classifiers were developed using machine-learning approaches including cross-validation testing, grouping OS names into fewer classes, and evaluating alternate classifier types. Nearest neighbor and binary tree classifiers provide a low 9-class OS identification error rate of roughly 10% on unseen data without rejecting packets. This error rate drops to nearly zero when 10% of the packets are rejected.
Summary
Accurate operating system (OS) identification by passive network traffic analysis can continuously update less-frequent active network scans and help interpret alerts from intrusion detection systems. The most recent open-source passive OS identification tool (ettercap) rejects 70% of all packets and has a high 75-class error rate of 30% for non-rejected...
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Biometrically enhanced software-defined radios
November 17, 2003
Conference Paper
Published in:
Software Defined Radio Tech. Conf., SDR, 17-19 November 2003.
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Software-defined radios and cognitive radios offer tremendous promise, while having great need for user authentication. Authenticating users is essential to ensuring authorized access and actions in private and secure communications networks. User authentication for software-defined radios and cognitive radios is our focus here. We present various means of authenticating users to their radios and networks, authentication architectures, and the complementary combination of authenticators and architectures. Although devices can be strongly authenticated (e.g., cryptographically), reliably authenticating users is a challenge. To meet this challenge, we capitalize on new forms of user authentication combined with new authentication architectures to support features such as continuous user authentication and varying levels of trust-based authentication. We generalize biometrics to include recognizing user behaviors and use them in concert with knowledge- and token-based authenticators. An integrated approach to user authentication and user authentication architectures is presented here to enhance trusted radio communications networks.
Summary
Software-defined radios and cognitive radios offer tremendous promise, while having great need for user authentication. Authenticating users is essential to ensuring authorized access and actions in private and secure communications networks. User authentication for software-defined radios and cognitive radios is our focus here. We present various means of authenticating users...
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Normalized analysis of interceptor missiles using the four-state optimal guidance system
November 1, 2003
Journal Article
Published in:
J. Guid. Control Dyn., Vol. 26, No. 6, November-December 2003, p. 838-845.
Summary
Performance prediction of miss distance due to sensor measurement errors and random target manuevers for missiles using proportional navigation guidance has been analyzed using the adjoint technique; a normalization technique has been usedto reduce the solution of the set of differential equations describing the proportional navigationguidance problemto a set of algebraic equations using normalized steady-state adjointmiss distance coefficients. The four-state optimalguidance system is generally accepted to yield superior miss distance performance to that of proportional navigation guidance. The previously mentioned normalization technique is described and extended to the four-state optimal guidance system to calculate a new set of values for the normalized steady-state adjointmiss distance coef. cients for this con. guration. Plots of these normalized coefficients as a function of a normalized tuning parameter provide designers with insight into system performance sensitivities to design parameter and intercept parameter variations. The advantage of this technique is that the results are closed-form equations, and the analyst neither needs to perform simulations nor even to solve the adjoint differential equations. In addition, optimalguidance system results formiss distance due to target spiral maneuver are presented asmiss distance normalized to the target maneuver spiral radius, thus providing valuable insights into interceptor performance.
Summary
Performance prediction of miss distance due to sensor measurement errors and random target manuevers for missiles using proportional navigation guidance has been analyzed using the adjoint technique; a normalization technique has been usedto reduce the solution of the set of differential equations describing the proportional navigationguidance problemto a set of...
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Auditory signal processing as a basis for speaker recognition
October 19, 2003
Conference Paper
Published in:
IEEE Workshop on Applications of Signal Processing to Audio and Acoustics, 19-22 October, 2003, pp. 111-114.
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In this paper, we exploit models of auditory signal processing at different levels along the auditory pathway for use in speaker recognition. A low-level nonlinear model, at the cochlea, provides accentuated signal dynamics, while a a high-level model, at the inferior colliculus, provides frequency analysis of modulation components that reveals additional temporal structure. A variety of features are derived from the low-level dynamic and high-level modulation signals. Fusion of likelihood scores from feature sets at different auditory levels with scores from standard mel-cepstral features provides an encouraging speaker recognition performance gain over use of the mel-cepstrum alone with corpora from land-line and cellular telephone communications.
Summary
In this paper, we exploit models of auditory signal processing at different levels along the auditory pathway for use in speaker recognition. A low-level nonlinear model, at the cochlea, provides accentuated signal dynamics, while a a high-level model, at the inferior colliculus, provides frequency analysis of modulation components that reveals...
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System adaptation as a trust response in tactical ad hoc networks
October 13, 2003
Conference Paper
Published in:
IEEE MILCOM 2003, 13-16 October 2003, pp. 209-214.
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While mobile ad hoc networks offer significant improvements for tactical communications, these networks are vulnerable to node capture and other forms of cyberattack. In this paper we evaluated via simulation of the impact of a passive attacker, a denial of service (DoS) attack, and a data swallowing attack. We compared two different adaptive network responses to these attacks against a baseline of no response for 10 and 20 node networks. Each response reflects a level of trust assigned to the captured node. Our simulation used a responsive variant of the ad hoc on-demand distance vector (AODV) routing algorithm and focused on the response performance. We assumed that the attacks had been detected and reported. We compared performance tradeoffs of attack, response, and network size by focusing on metrics such as "goodput", i.e., percentage of messages that reach the intended destination untainted by the captured node. We showed, for example, that under general conditions a DoS attack response should minimize attacker impact while a response to a data swallowing attack should minimize risk to the system and trust of the compromised node with most of the response benefit. We show that the best network response depends on the mission goals, network configuration, density, network performance, attacker skill, and degree of compromise.
Summary
While mobile ad hoc networks offer significant improvements for tactical communications, these networks are vulnerable to node capture and other forms of cyberattack. In this paper we evaluated via simulation of the impact of a passive attacker, a denial of service (DoS) attack, and a data swallowing attack. We compared...
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Utilizing local terrain to determine targeted weather observation locations
September 9, 2003
Conference Paper
Published in:
Conf. on Battlespace Atmospheric and Cloud Impacts on Military Operations, BACIMO, 9-11 September 2003.
Summary
Many of the recent conflicts where the United States (US) military forces have been deployed are regions that contain complex terrain (i.e. Korea, Kosovo, Afghanistan, and northern Iraq). Accurate weather forecasts are critical to the success of operations in these regions and are typically supplied by numerical weather prediction (NWP) models like the US Navy NOGAPS, CAOMPS, and US Airforce MM5. Unfortunately the weather observations required to generate accurate initial conditions needed by these models are often not available. In these cases it is desirable to deploy additional weather sensors. The question then becomes: Where should the military planners deploy their sensor resources? This study demonstrates that knowledge of just the terrain within the model domain may be a useful factor for military planners to consider. For NWP, model forecast errors in mountainous areas are typically thought to be due to poorly resolved terrain, or model physics not suited for use in a complex terrain environment. Recent advances in computational technology are making it possible to run these models at resolutions where many of the significant terrain features are now being well resolved. While terrain can be accurately specified, often the gradients in wind, temperature, and moisture fields associated with the higher resolution terrain are not. As a result, initial conditions in complex terrain environments are not be adequately specified. Since not all initial condition errors contribute significantly to model forecast error, knowledge of terrain induced NWP model forecast sensitivity may be important when developing and deploying a weather sensor network to support a regional scale NWP model. The terrain induced model sensitivity can provide an indication of which variables in the initial conditions have a significant influence on the forecast and where initial conditions need to be most accurate to minimize model forecast error. A sensor network can then be designed to minimize these errors by deploying critical sensors in sensitive locations, thereby reducing relevant initial condition error without the costly deployment of a high-density sensor network. This is similar to the targeted observation technique first suggested by Emanuel et al. (1995), except that in this example the targeted observations would be designed to reduce initial condition error associated with poorly resolved atmospheric features created by the terrain. This paper is organized as follows. Section 2 contains a brief description of the data collection effort designed to support this study. The experimental design and the specifics of the case used in this study are described in section 3. The analysis and results from both the forward and adjoint simulations are presented in section 4. Section 5 contains a summary of the results, and a brief discussion of their implications.
Summary
Many of the recent conflicts where the United States (US) military forces have been deployed are regions that contain complex terrain (i.e. Korea, Kosovo, Afghanistan, and northern Iraq). Accurate weather forecasts are critical to the success of operations in these regions and are typically supplied by numerical weather prediction (NWP)...
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Fusing high- and low-level features for speaker recognition
September 1, 2003
Conference Paper
Published in:
EUROSPEECH 2003, 1-4 September 2003.
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Summary
The area of automatic speaker recognition has been dominated by systems using only short-term, low-level acoustic information, such as cepstral features. While these systems have produced low error rates, they ignore higher levels of information beyond low-level acoustics that convey speaker information. Recently published works have demonstrated that such high-level information can be used successfully in automatic speaker recognition systems by improving accuracy and potentially increasing robustness. Wide ranging high-level-feature-based approaches using pronunciation models, prosodic dynamics, pitch gestures, phone streams, and conversational interactions were explored and developed under the SuperSID project at the 2002 JHU CLSP Summer Workshop (WS2002): http://www.clsp.jhu.edu/ws2002/groups/supersid/. In this paper, we show how these novel features and classifiers provide complementary information and can be fused together to drive down the equal error rate on the 2001 NIST Extended Data Task to 0.2%-a 71% relative reduction in error over the previous state of the art.
Summary
The area of automatic speaker recognition has been dominated by systems using only short-term, low-level acoustic information, such as cepstral features. While these systems have produced low error rates, they ignore higher levels of information beyond low-level acoustics that convey speaker information. Recently published works have demonstrated that such high-level...
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Person authentication by voice: a need for caution
September 1, 2003
Conference Paper
Published in:
8th European Conf. on Speech Communication and Technology, EUROSPEECH, 1-4 September 2003.
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Summary
Because of recent events and as members of the scientific community working in the field of speech processing, we feel compelled to publicize our views concerning the possibility of identifying or authenticating a person from his or her voice. The need for a clear and common message was indeed shown by the diversity of information that has been circulating on this matter in the media and general public over the past year. In a press release initiated by the AFCP and further elaborated in collaboration with the SpLC ISCA-SIG, the two groups herein discuss and present a summary of the current state of scientific knowledge and technological development in the field of speaker recognition, in accessible wording for nonspecialists. Our main conclusion is that, despite the existence of technological solutions to some constrained applications, at the present time, there is no scientific process that enables one to uniquely characterize a person's voice or to identify with absolute certainty an individual from his or her voice.
Summary
Because of recent events and as members of the scientific community working in the field of speech processing, we feel compelled to publicize our views concerning the possibility of identifying or authenticating a person from his or her voice. The need for a clear and common message was indeed shown...
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Integration of speaker recognition into conversational spoken dialogue systems
September 1, 2003
Conference Paper
Published in:
EUROSPEECH 2003, 1-4 September 2003.
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In this paper we examine the integration of speaker identification/verification technology into two dialogue systems developed at MIT: the Mercury air travel reservation system and the Orion task delegation system. These systems both utilize information collected from registered users that is useful in personalizing the system to specific users and that must be securely protected from imposters. Two speaker recognition systems, the MIT Lincoln Laboratory text independent GMM based system and the MIT Laboratory for Computer Science text-constrained speaker-adaptive ASR-based system, are evaluated and compared within the context of these conversational systems.
Summary
In this paper we examine the integration of speaker identification/verification technology into two dialogue systems developed at MIT: the Mercury air travel reservation system and the Orion task delegation system. These systems both utilize information collected from registered users that is useful in personalizing the system to specific users and...
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