Ashok K. Agrawala

Challenges: device-free passive localization for wireless environments

The proliferation of RF networks coupled with the diverse and growing set of mobile devices, opened the doors for a new class of context awareness through contact-free ambient sensing. Since our initial challenges paper in 2007, the field of device-free passive sensing has witnessed an exponential growth; covering areas such as intrusion detection, mobile healthcare, whole-home gesture recognition, traffic estimation, border protection, among others. In this talk, we give a holistic overview of the area of contact-free ambient sensing based on RF technology, highlighting how it evolved over a decade from binary-detection in controlled environments to commercial systems for border protection and smart homes. We also give insights about the current trends and possible future research challenges.

A framework for wireless LAN monitoring and its applications

Many studies on measurement and characterization of wireless LANs (WLANs) have been performed recently. Most of these measurements have been conducted from the wired portion of the network based on wired monitoring (e.g. sniffer at some wired point) or SNMP statistics. More recently, wireless monitoring, the traffic measurement from a wireless vantage point, is also widely adopted in both wireless research and commercial WLAN management product development. Wireless monitoring technique can provide detailed PHY/MAC information on wireless medium. For the network diagnosis purpose (e.g. anomaly detection and security monitoring) such detailed wireless information is more useful than the information provided by SNMP or wired monitoring. In this paper we have explored various issues in implementing the wireless monitoring system for an IEEE 802.11 based wireless network. We identify the pitfalls that such system needs to be aware of, and then provide feasible solutions to avoid those pitfalls. We implement an actual wireless monitoring system and demonstrate its effectiveness by characterizing a typical computer science department WLAN traffic. Our characterization reveals rich information about the PHY/MAC layers of the IEEE 802.11 protocol such as the typical traffic mix of different frame types, their temporal characteristics and correlation with the user activities. Moreover, we identify various anomalies in protocol and security of the IEEE 802.11 MAC. Regarding the security, we identify malicious usages of WLAN, such as email worm and network scanning. Our results also show excessive retransmissions of some management frame types reducing the useful throughput of the wireless network.

Experimental assessment of end-to-end behavior on Internet

A simple experiment designed to capture the end-to-end behavior of the Internet is described. The measurements indicate that the IP level service provided in the network yields high losses, duplicates, and reorderings of packets. In addition, the round-trip transit delay varies significantly. These measurements indicate that the network may have several problems which still need to be analyzed in order to improve the efficiency of protocols and control mechanisms that it uses.<<ETX>>

CARS: a new code generation framework for clustered ILP processors

Clustered ILP processors are characterized by a large number of non-centralized on-chip resources grouped into clusters. Traditional code generation schemes for these processors consist of multiple phases for cluster assignment, register allocation and instruction scheduling. Most of these approaches need additional re-scheduling phases because they often do not impose finite resource constraints in all phases of code generation. These phase-ordered solutions have several drawbacks, resulting in the generation of poor performance code. Moreover the iterative/back-tracking algorithms used in some of these schemes have large turning times. In this paper we present CARS, a code generation framework for Clustered ILP processors, which combines the cluster assignment, register allocation, and instruction scheduling phases into a single code generation phase, thereby eliminating the problems associated with phase-ordered solutions. The CARS algorithm explicitly takes into account all the resource constraints at each cluster scheduling step to reduce spilling and to avoid iterative re-scheduling steps. We also present a new on-the-fly register allocation scheme developed for CARS. We describe an implementation of the proposed code generation framework and the results of a performance evaluation study using the SPEC95/2000 and MediaBench benchmarks.

WSN16-5: Distributed Formation of Overlapping Multi-hop Clusters in Wireless Sensor Networks

Clustering is a standard approach for achieving efficient and scalable performance in wireless sensor networks. Most of the published clustering algorithms strive to generate the minimum number of disjoint clusters. However, we argue that guaranteeing some degree of overlap among clusters can facilitate many applications, like inter-cluster routing, topology discovery and node localization, recovery from cluster head failure, etc. We formulate the overlapping multi-hop clustering problem as an extension to the k-dominating set problem. Then we propose MOCA; a randomized distributed multi-hop clustering algorithm for organizing the sensors into overlapping clusters. We validate MOCA in a simulated environment and analyze the effect of different parameters, e.g. node density and network connectivity, on its performance. The simulation results demonstrate that MOCA is scalable, introduces low overhead and produces approximately equal-sized clusters.

Equivalence of Hough curve detection to template matching

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An Approach to the Workload Characterization Problem

A major problem in the evaluation of the performance of a multiprogrammed computer system is the development of an accurate description of its normal workload. This paper formulates the workload characterization problem for a computing environment and presents three types of simplified models for the system workload. The probabilistic models of the workload presented here can be validated with respect to the real workload and are easy to use in a performance evaluation study. The results of a study of the workloads on the Univac 1108 computer at the Computer Science Center of the University of Maryland are also presented.

Analysis of the fork-join queue

A fork-join queue is considered as a typical model of parallel processing systems with arrival and departure synchronizations. An approach for obtaining the transient and the steady-state solutions of the fork-join queue in terms of the virtual waiting times, which can be used to obtain the response time and the delay between the fork and the join instants, is presented. With the restriction of the service time being the Erlangian distribution, the formulations result in a form of a series, the worth of which is in actually computing numerical results. The joint-state-occupancy probabilities can be easily deduced from the results. The approximate solutions in the steady state are presented for the cases where the interarrival time distributions are exponential and hyperexponential, and the service-time distributions are exponential and two-state Erlangian. The parallelism achievable with synchronization constraints is examined from the approximations. >

Efficient decentralized consensus protocols

Decentralized consensus protocols are characterized by successive rounds of message interchanges. Protocols which achieve a consensus in one round of message interchange require O(N2) messages, where N is the number of participants. A communication scheme based on finite projective planes is presented which requires only O(N√N) messages for each round. Using this communication scheme, decentralized consensus protocols which achieve a consensus within two rounds of message interchange are developed. The protocols are symmetric, and the communication scheme does not impose any hierarchical structure. The scheme is illustrated using blocking and nonblocking commit protocols, decentralized extrema finding, and computation of the sum function.

The MARUTI hard real-time operating system

The MARUTI operating system is designed to support real-time applications on a variety of hardware systems. The kernel supports objects as primitive entities, and provides a communication mechanism that allows transparent distribution in networked systems. Fault tolerance is provided through replication and consistency-control mechanisms. Most importantly, MARUTI supports guaranteed-service scheduling, in which jobs that are accepted by the system are verified to satisfy general time constraints.Guaranteed-service scheduling means that, given a job with a set of service requirements and time constraints, the system automatically verifies the schedulability of each component of the job with respect to the jobs constraints and those of other jobs in the system. These time constraints include those that govern interrupt processing, which allows the MARUTI approach to succeed where tess rigorous approaches do not. The result is that MARUTI applications can be executed in a predictable, deterministic fashion.