Ashok Kumar Agrawala

7224984, May 29, 2007

Aug 15, 2001

10/344857

Ashok Kumar Agrawala - Ashton MD, US
Ronald L Larsen - Pittsburgh PA, US
A. Udaya Shankar - Silver Spring MD, US
Douglas C Szajda - Richmond VA, US

University of Maryland, College Park - College Park MD

H04Q 7/20
H04M 11/04

4554561, 4554562, 4554563, 455466, 4554042

An asset positioning method and system () rapidly and accurately determine the special location of wireless nodes distributed in three-dimensional space. Furthermore, as a by-product, every node also determines the relative offset and drift of every other node's clock, so that it is possible for all nodes to carry out a precise synchronized action (). The positioning and synchronization protocol has significant implications for a broad range of wireless networking infrastructure and applications. For instance, the rapid availability of accurate location information greatly simplifies and optimises the implementation of ad-hoc networks and sensor-based applications (). Additionally, the synchronized node operations facilitate the development of new applications, such as phase-locked arrays, in which several low power transmitters coordinate to form a powerful group transmitter. Since the positioning protocol yields rapid responses and positional accuracy in the range of a few centimeters, the positioning protocol permits mobile nodes to be tracked while they are moving.

7406116, Jul 29, 2008

Mar 26, 2004

10/529372

Ashok K Agrawala - Ashton MD, US
Moustafa Youssef - Hyattsville MD, US

University of Maryland - College Park MD

H04B 17/02
H04B 7/185

375213, 34235701

In a wireless communication network, the location of an addressable receiver relative to the locations of a plurality of addressable sources of electromagnetic radiation is found using probabilistic models of the signal strength measured at the addressable receiver. The inventive method provides location determination on a finer spatial scale than was heretofore available. A region of interest is calibrated via a discrete-space radio map storing probability distributions of received signal strength at the measurement locations. The stored probability distributions are compensated for temporal variability and biases, such as through temporal correlations of the sampled received signal strength. A measurement of the signal strength at the addressable receiver from each of the plurality of addressable sources is used in conjunction with the discrete-space radio map to identify one of the coordinates thereof that maximizes the conditional probability P(xls), where x is the radio map location and s is a vector of measured signal strengths.

8219670, Jul 10, 2012

Nov 10, 2008

12/267921

Ashok K. Agrawala - Ashton MD, US
Amitabh Varshney - Ellicott City MD, US
Christian B. Almazan - Greenbelt MD, US

University of Maryland - College Park MD

G06F 15/173
G06F 15/16

709224, 709219

A multifunctional interaction system which is capable of spatio-temporal context localization of users and of communication of audio/video streams to an entity of interest defined by the user, includes a communication domain supporting a predefined localization service, a server associated with the communication domain, client devices, and a dynamically changing context database which is customized in accord with the dynamics of interaction sessions of client devices with the server. The client communicates with the system to either request services therefrom or to send a message to the entity of interest. The system is provided with a panic alert mechanism which, upon actuation, transmits an audio/video data stream along with the client location tag, time stamp, and client ID, to a police precinct for prompt action.

20050055568, Mar 10, 2005

Aug 12, 2004

10/916545

Ashok Agrawala - Ashton MD, US
Moustafa Amin Youssef - Hyattsville MD, US
Layla Shahamat - Rockville MD, US

G06F011/30

713200000

A system for detecting the presence of an intruder in a protected area utilizes a received signal strength indicator (RSSI) value of signals broadcast from transmitting stations deployed in the protected area. The system includes monitoring points for receiving broadcast signals, measuring the RSSI values of the received signals, and transmitting the measured RSSI values to a security system server. The security system server analyzes the RSSI values, and initiates security measures when the physical security of the protected area is violated which is detected when the measured RSSI values deviate from a predetermined strength of the broadcast signals. The security system also has the ability to track objects in the protected area and keep track of their movement in real time and report such movement. The system may be based on a Wi-Fi infrastructure in the protected area.

20070058564, Mar 15, 2007

Jul 21, 2006

11/491420

Ashok Agrawala - Ashton MD, US
Michael Trinh - Rockville MD, US

University of Maryland - College Park MD

H04L 12/26
H04J 1/16

370252000

A Cyclone Network Synchronization algorithm is presented that does not depend on highly stable and expensive clocks or hardware, yet it can synchronize nodes in a network with a very high degree of accuracy. It is very light-weight since no clock synchronization is performed, and subsequently does not incur any overhead in message passing. Instead, synchronization is done solely by listening to the regular network traffic. Finally, the amount of padding or time overhead incurred by the CNS algorithm is extremely small, even when used with system clocks that have high drift rates (e.g. 1000 PPM or more).

20070201412, Aug 30, 2007

Feb 28, 2006

11/363208

Lusheng Ji - Randolph NJ, US
Jonathan Russell Agre - Brinklow MD, US
Tamer Nadeem - Plainsboro NJ, US
Ashok Agrawala - Ashton MD, US

H04Q 7/24

370338

Disclosed is a protocol used by wireless stations sharing a single wireless channel. When a local station senses a communication between remote stations using the channel, the local station estimates whether its local transmissions would disrupt this on-going remote communication. To estimate, the local station forms capture models of the remote stations. From the capture models, the local station determines if its local transmission would prevent each remote station from capturing the signal from the other remote station. If the local transmission would not disrupt the remote communications, the local station transmits its message over the channel at the same time the remote stations use the channel. The local station performs the estimation using parameters of the remote stations. The stations could share their parameters by including them in headers of frames. The protocol can be implemented as an enhancement to the IEEE 802.11 standard.

20110268097, Nov 3, 2011

Mar 14, 2011

13/047790

ASHOK K. AGRAWALA - ASHTON MD, US
MATTHEW MAH - GREENBELT MD, US

UNIVERSITY OF MARYLAND - COLLEGE PARK MD

H04W 56/00
H04W 84/02

370338, 370350

A system and method are provided for adaptive synchronization of timing information provided in communications messages transmitted between independently clocked communication nodes of a wireless communications network. The system and method include measures for collecting timestamps of messages generated by a plurality of the nodes, each timestamp being generated by one of the nodes relative to a local time reference thereof. A pairwise clock error is computed for at least one pair of nodes based upon a plurality of network messages passed therebetween. A global time reference is adaptively established for the timestamps responsive to the pairwise clock error. A plurality of mapping factors are defined each for translating from one local time reference to the global time reference. The mapping factors are selectively applied to corresponding ones of the timestamps.

63208652, Nov 20, 2001

Jun 9, 1997

8/871533

Ashok K. Agrawala - Ashton MD
Christopher A. Landauer - Falls Church VA
Sung Lee - Silver Spring MD

University of Maryland at College Park - College Park MD

H04L 1256

370413

Nodes in a network transmit information among one another without the need for identifying headers. A calendar is maintained, indicating the times at which various data chunks are to be sent. When a request is made, the calendar is checked to see whether resources are free to accommodate the request. If so, the calendar is revised to reserve resources for the request.