China_final-exam (1) (No Solutions)

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Final Take Home Exam for Wireless Sensor Networks

October 2007

Note: o! are re"!ire# to finis$ t$e exam in#e%en#entl&' (n& form of

collaboration wit$ ot$ers is strictl& forbi##en)

Name: ***************************

St!#ent +,: ***********************

-roblem . /!lti%le 1$oices 20 %oints 2 %oints eac$3: For each question, please select all

the correct choices out of the five choices. Note that the answer(s) to each question may not be

unique.

(1) Which of the following statement(s) are true for a wireless link over sensor net?Your choice !!!!!!!!!

(") #he percentage of as$mmetric links is ver$ small% (&) 'ink as$mmetries are mainl$cause $ harware caliration% (*) time variailit$ is not correlate with the istance from

the transmitter% (+) time variailit$ is correlate with the mean reception rate% () wireless

channel is isotropic.

(-) Which of the following is the most ominant factor in energ$ waste of a sensor "*?

Your choice !!!!!!!!(") long ile perio% (&) collisions% (*) retransmissions for corrupte packets% (+)

overhearing all transmitte traffic% () control packet overhea such as /#0 an *#0.

() 2ow oes irecte iffusion select a high3qualit$ path? Your choice !!!!!!!!!!!!!!(") 4t floos the interest to ever$ noe to learn the est3qualit$ path% (&) 4t can onl$ select

one graient at each noe to its ownstream noe% (*) 4t positivel$ reinforces the high3

qualit$ path% (+) #he high3qualit$ path self3recovers from noe failures% () 4t can nevereliminate route loops.

(5) Which statement is true? Your choice !!!!!!!!!!!!!!!!!!!!!!!!!(") *onnectivit$ oes not ensure coverage% (&) coverage ensures connectivit$ when /c 6

-/s% (*) **7 alwa$s ensures oth connectivit$ an coverage% (+) **7 has to e use with

07"N together when /c 8 -/s% () #he ounar$ oes not nee to e covere $ enough

sensors to ensure connectivit$ an coverage.

(9) Which statement on :igee stanar is N;# true? Your choice !!!!!!!!!!!!!!!

(") 4t can support multiple ata rates% (&) 4t can operate at ifferent frequenc$ ans% (*) 4tonl$ supports star topolog$% (+) 4n the contention perio, it uses a reservation3ase "*%

() 4t can onl$ support perioic traffic.

(


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(") 0/# oes not support application3specific reliailit$ notion% (&) 0/# is the same as

=+7 an oes not support reliailit$% (*) 0/# supports application3efine partial

reliailit$% (+) 0/# oes not support en3to3en reliailit$% () 0/# oes not measureevent reports at the sink.

(>) Wh$ is a simple "* not secure for wireless roacast? Your choice !!!!!!!!!!

(") "ttackers can generate false messages an roacast to others% (&) "ttackers can overhearthe message% (*) "ttackers can elete the roacast message% (+) "ttackers can ela$ the

eliver$ of the roacast message% () "ttackers can ecipher all the secret ke$s etween the

ase station an each sensor.

() 2ow oes 03"* enale in3network processing? Your choice !!!!!!!!!

(") through perioic sleeping% (&) through aaptive listening% (*) through coorinate

scheule% (+) through message passing% () through /#03*#0 control packets.

(@) Which of the following time components oes reference roacast s$nchroniAation (/&0)

remove from the critical path? Your choice !!!!!!!!!!!!!!!!

(") sen time% (&) access time% (*) propagation time% (+) receive time% () all of the aove.

(1B) Which of the following statement(s) are wrong on localiAation?Your choice !!!!!!!!!!!!!!!!

(") ifferent applications ma$ have ifferent requirements on localiAation in terms of

granularit$ an scale, accurac$ an precision, etc. (&) 4n active localiAation, s$stems erivelocation from oservation of signals that are alrea$ present% (*) 4n cooperative target active

localiAation, target sens a signal with unknown characteristics% (+) 4n passive self3localiAation,

a noe estimates istances to a set of eacons% () 4n lin localiAation, s$stem estimates

location of the target with some priori omain knowlege of the target.

-roblem 2 /S$ort answer: 40 %oints 4 %oints eac$3:7lease brieflyanswer each question.

(1) Wh$ is the en3to3en transport consiere harmful for sensor networks? What is thepossile solution?

(-) +escrie three spatial characteristics of a wireless link in a sensor network.

() 2ow to avoi overhearing unnecessar$ traffic in 03"*?


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(5) +escrie what is the asic iea to hanle sink moilit$.

(9) +escrie how ata is manage in a sensor network through naming.

() You are require to use :igee harware noes to construct a static wireless sensor network.2ow o $ou esign the network topolog$ to achieve highest level of energ$ savings among

all noes in the sensor network?

() When /c 8 -/s (/c is the communication range of a sensor noe, an /s is the sensing

range), how can $ou ensure oth k3coverage an k3connectivit$ (i.e., each area is covere $

k sensing noes an each noe has k neighor noes for communications)?


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(@) +escrie the main steps in efening against faricate event attacks. "ssume that there are

at most compromise noes that are working together in the network.

(1B) +escrie two methos on uiling graient3ase routes for wireless sensor networks.

-roblem 4 /.0 %oints3: ,irecte# ,iff!sion an# to%olo5& control' 4n the following Figure,

is the source sensor that generates sensing reports, an 0 is the sink noe that nees the sensing

reports from .0ensor noes "1, "-, ", G, "-B can communicate with each other% 0ensor noes &1, &-, &,

G, &-B can also communicate with each other. "n noe "i can N;# communicate with &i (iH1,

-, G, -B). " G "@ "1B G "1@ "-B

"1 "-

&1B 0

&1

&- & G &@ &11 G &1@ &-B

*

(1) 4nitiall$, "ll noes "1, G "-B an &1, G, &-B are all active, ut other noes are

sleeping. +escrie how irecte iffusion uils up the graient an sets up the path.


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(-) 0uppose the path from "1"- G"-B0 is worse than the path &1&-G

&-B0, how oes irecte iffusion select the etter path?

() Now &1B fails ue to lack of energ$, another noe * starts to work after the topolog$control algorithm works. "ssume that the path "1"- G "-B0 is not use.

+escrie how irecte iffusion inclues * in the path (that is, the current path ecomes

&1G&@*&11&1- G&-B0) without using IinterestJ flooing.

(5) Now oth * an &1B are waking up (&1B is repaire now). #here is a route loop&@*&1B&@. 2ow oes irecte iffusion eliminate the route loop?

-roblem 6 /.0 %oints3: Trans%ort' "ssume that the esire event reliailit$ / is -BKsecon.

"ppl$ 0/# in the following cases.(1) "ssume that there is no congestion in the sensor network at #1. 4f the oserve event

reliailit$ is 1BKs at #1. 2ow oes 0/# upate the reporting rate at the source sensor?

(-) "ssume that there is no congestion in the sensor network at #-. Now the oserve event

reliailit$ is BKs at #-. 2ow oes 0/# upate the reporting rate at the source sensor?

() "ssume that there is congestion etecte in the sensor network at #. Now the oserve

event reliailit$ is -9Ks at #. 2ow oes 0/# upate the reporting rate at the source

sensor?


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-roblem /.0 %oints3: 1onnecti8it& an# 1o8era5e' 4n the connectivit$ an coverage

protocols we talke aout in class, the authors assume that wireless communication has isotropicconnectivit$ (that is, the communication is possile in all


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-roblem 7 /.0 %oints3: Time S&nc$roniation #he reference roacast s$stem (/&0)

s$nchroniAation assumes that all noes are static. 2ow well oes the /&0 solution works for a

moile receiver? "ssume that onl$ one receiver is moile, while the sener an other receivers areall static.

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China_final-exam (1) (No Solutions)