György Balogh

Sensor network-based countersniper system

An ad-hoc wireless sensor network-based system is presented that detects and accurately locates shooters even in urban environments. The system consists of a large number of cheap sensors communicating through an ad-hoc wireless network, thus it is capable of tolerating multiple sensor failures, provides good coverage and high accuracy, and is capable of overcoming multipath effects. The performance of the proposed system is superior to that of centralized countersniper systems in such challenging environment as dense urban terrain. In this paper, in addition to the overall system architecture, the acoustic signal detection, the most important middleware services and the unique sensor fusion algorithm are also presented. The system performance is analyzed using real measurement data obtained at a US Army MOUT (Military Operations in Urban Terrain) facility.

Radio interferometric geolocation

We present a novel radio interference based sensor localization method for wireless sensor networks. The technique relies on a pair of nodes emitting radio waves simultaneously at slightly different frequencies. The carrier frequency of the composite signal is between the two frequencies, but has a very low frequency envelope. Neighboring nodes can measure the energy of the envelope signal as the signal strength. The relative phase offset of this signal measured at two receivers is a function of the distances between the four nodes involved and the carrier frequency. By making multiple measurements in an at least 8-node network, it is possible to reconstruct the relative location of the nodes in 3D. Our prototype implementation on the MICA2 platform yields an average localization error as small as 3 cm and a range of up to 160 meters. In addition to this high precision and long range, the other main advantage of the Radio Interferometric Positioning System (RIPS) is the fact that it does not require any sensors other than the radio used for wireless communication.

Countersniper system for urban warfare

An ad-hoc wireless sensor network-based system is presented that detects and accurately locates shooters even in urban environments. The localization accuracy of the system in open terrain is competitive with that of existing centralized countersniper systems. However, the presented sensor network-based solution surpasses the traditional approach because it can mitigate acoustic multipath effects prevalent in urban areas and it can also resolve multiple simultaneous shots. These unique characteristics of the system are made possible by employing novel sensor fusion techniques that utilize the spatial and temporal diversity of multiple detections. In this article, in addition to the overall system architecture, the middleware services and the unique sensor fusion algorithms are described. An analysis of the experimental data gathered during field trials at US military facilities is also presented.

Shooter localization and weapon classification with soldier-wearable networked sensors

The paper presents a wireless sensor network-based mobilecountersniper system. A sensor node consists of a helmetmountedmicrophone array, a COTS MICAz mote for internodecommunication and a custom sensorboard that implementsthe acoustic detection and Time of Arrival (ToA) estimationalgorithms on an FPGA. A 3-axis compass providesself orientation and Bluetooth is used for communicationwith the soldiers PDA running the data fusion and the userinterface. The heterogeneous sensor fusion algorithm canwork with data from a single sensor or it can fuse ToA orAngle of Arrival (AoA) observations of muzzle blasts andballistic shockwaves from multiple sensors. The system estimatesthe trajectory, the range, the caliber and the weapontype. The paper presents the system design and the resultsfrom an independent evaluation at the US Army AberdeenTest Center. The system performance is characterized by 1-degree trajectory precision and over 95% caliber estimationaccuracy for all shots, and close to 100% weapon estimationaccuracy for 4 out of 6 guns tested.

Radio interferometric tracking of mobile wireless nodes

Location-awareness is an important requirement for many mobile wireless applications today. When GPS is not applicable because of the required precision and/or the resource constraints on the hardware platform, radio interferometric ranging may offer an alternative. In this paper, we present a technique that enables the precise tracking of multiple wireless nodes simultaneously. It relies on multiple infrastructure nodes deployed at known locations measuring the position of tracked mobile nodes using radio interferometry. In addition to location information, the approach also provides node velocity estimates by measuring the Doppler shift of the interference signal. The performance of the technique is evaluated using a prototype implementation on mote-class wireless sensor nodes. Finally, a possible application scenario of dirty bomb detection in a football stadium is briefly described.

Multiple simultaneous acoustic source localization in urban terrain

Experiences developing a sensor network-based acoustic shooter localization system are presented. The system is able to localize the position of a shooter and the trajectory of the projectile using observed acoustic events, such as the muzzle blast and the ballistic shockwave. The network consists of a large number of cheap sensors communicating through an ad-hoc wireless network, which enables the system to resolve multiple simultaneous acoustic sources, eliminate multipath effects, tolerate multiple sensor failures while providing good coverage and high accuracy, even in such challenging environment as urban terrain. The paper describes the hardware and software platform developed for this application and summarizes the lessons learned during the development of the system.

InTrack: high precision tracking of mobile sensor nodes

Radio-interferometric ranging is a novel technique that allows for fine-grained node localization in networks of inexpensive COTS nodes. In this paper, we show that the approach can also be applied to precision tracking of mobile sensor nodes. We introduce in Track, a cooperative tracking system based on radio-interferometry that features high accuracy, long range and low-power operation. The system utilizes a set of nodes placed at known locations to track a mobile sensor. We analyze how target speed and measurement errors affect the accuracy of the computed locations. To demonstrate the feasibility of our approach, we describe our prototype implementation using Berkeley motes. We evaluate the system using data from both simulations and field tests.

Weapon classification and shooter localization using distributed multichannel acoustic sensors

A wireless sensor network-based wearable countersniper system prototype is presented. The sensor board is connected to a small helmet-mounted microphone array that uses time of arrival (ToA) estimates of the ballistic shockwave and the muzzle blast to compute the angle of arrival (AoA) of both acoustic events. A low-power radio is used to form an ad-hoc multihop network that shares the detections among the nodes. Utilizing all available ToA and AoA data, a novel sensor fusion algorithm then estimates the shooter position, bullet trajectory, miss distance, caliber, and weapon type. A single sensor relying only on its own detections is able determine the shooter position when both the shockwave and the muzzle blast are detected by at least three microphones each. Even with just one shockwave and one muzzle blast detection, the miss distance and range can be accurately estimated by a single sensor. The system has been tested multiple times at the US Army Aberdeen Test Center and the Nashville Police Academy. The demonstrated performance is 1-degree trajectory precision, over 95% caliber estimation accuracy, and close to 100% weapon estimation accuracy for 4 out of the 6 guns tested.

Acoustic Source Localization Fusing Sparse Direction of Arrival Estimates

This paper proposes a wireless sensor network based acoustics source localization and tracking system. Each individual node has a special purpose sensor board with four acoustic channels and a digital compass enabling direction of arrival (DOA) estimation of acoustic sources. Upon detecting a source of interest, the sparsely deployed sensor nodes report their DOA estimates to the base station that fuses the data for accurate localization. Due to the widely distributed sensing and the novel sensor fusion technique, the method can handle multiple measurement errors prevalent in reverberant environments. The paper presents the overall architecture of the system, as well as that of the advanced sensor board. Furthermore, it describes the DOA estimation algorithm and the applied middleware services for coordinated sensing and communication, introduces the sensor fusion algorithm and presents a detailed error analysis