Abstract-We consider the prohlem of a user querying for information over a sensor network, where the user does not have prior knowledge of the location of the information. We consider three information query strategies: (i) B Source-only search, where tlie snurce (user) tries to Icrcate tlie destination hy initiating query which propagates as a rnntinuons time random walk (Brnwnian motion); (ii) a Source and Receiver Driven "Sticky" Search, where hnth the .source and the destination send U qnery nr an advertisement (hoth propagating as random wnlks), and these leave a "sticky" trail to aid in locating the destination; and (iii) where the destination information is spatially cached (i.e., repented over space), and the snurce tries to locate any one of the caches. After a random interval of time with average t . if the infomiation is not located, the query times-out, and the search is unsuccessful. We consider a problem where a querying node ithe sourceluser) transmits a query for some information (the destination). which is located at a (normalized) distance of ' 1' from the source. However. we assume that the source has no knowledge of the location of the information (the destination). nor that they are separated hy a distance of ' 1' (i.e.. no drstinarion location infonriation is available). Further. we assume that the nodes (lo not have any "direction" iifoi-ination. In other words. nodes only know who thcir local neighbors are. but do not have their geographical position or direction information. We consider three search/query strategies: (i) A Source-only search. where the source (i.e.. the user) tries to locate the destination by initiating a query which propagates as a "continuous time" random walk (Brownian motion); (ii) a Source and Receiver Driven "Stickv" Search. where both the source and the tially periodic &lie is employed. we show that ihe probahiiity destination send a a&v or a advertisement (both nmnacatinr L~r c that a query is unsuccessful decays no faster than f r ' . Thus, we Driate numher of queries. as to aid in locat. with that spatial stratea using Hn approin: the destination: and (iii) where the destination inlormation is spatially cached (i.e.. repeated periodically over space), and walks), and these leave can niatch the decay rates ofthe source and the destination driven O n the other hand. we n e n e that the niemory requirement for spatial caching is larger (in an order sense) than that for "sticky" searches. This indicates tliat the appropriate strategy for querying over large sensor networks would he to use multiple queries and advertisements using the "Sticky" search strategy. the Source tries to locate any one ofthe caches. an aside. we note that if partial destination location infor. mation was available, one could design strategies which itly use this knowledge. For instance. if it was known a-priori that the destination was at a distance ' I ' from the source. constrained flooding would he a candidate strategy for locating the position ofthe destination. Further. the availability of direction information (for instance. with GPS equipptd nodes) would enkeywords: Stochastic prcresseeslQueueing theory
In REF , asymptotics of three query strategies over a sensor network are discussed.
Asymptotics of query strategies over a sensor network
IEEE INFOCOM 2004
IEEE INFOCOM 2004
Computer Science