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*sing in military +attleeld surveillance and monitoring, guidance systems
of intelligent missiles, detection of attack by weapons ofmass destruction such as chemical, biological, or nuclear
*sing in nature $orest re, -ood detection, habitat exploration of animals
*sing in health onitor the patient/s heart rate or blood pressure, and sent
regularly to alert the concerned doctor, provide patients agreater freedom of movement
*sing in home 0smart home1 Sensor node can built into appliances at home, such as
ovens, refrigerators, and vacuum cleaners, which enable
them to interact with each other and be remote%controlled
*sing in o2ce building #ir-ow and temperature of di)erent parts of the building
can be automatically controlled
*sing in warehouse 3mprove their inventory control system by installing
sensors on the products to track their movement
12.1.2 Comparison with Ad Hoc Wireless Networks
&i)erent from #d 4oc wireless networks
he number of nodes in sensor network can be severalorders of magnitude large than the number of nodes in anad hoc network.
Sensor nodes are more easy to failure and energy drain,and their battery sources are usually not replaceable orrechargeable.
Sensor nodes may not have uni(ue global identiers 03&1,so uni(ue addressing is not always feasible in sensor
networks. Sensor networks are data%centric, the (ueries in sensor
networks are addressed to nodes which have datasatisfying some conditions. #d 4oc networks are address%centric, with (ueries addressed to particular nodesspecied by their uni(ue address.
&ata fusion'aggregation: the sensor nodes aggregate thelocal information before relaying. he goals are reduce
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bandwidth consumption, media access delay, and powerconsumption for communication.
12.1.3 Issues and Challenges in esigning a Sensor Network
3ssues and Challenges Sensor nodes are randomly deployed and hence do not t
into any regular topology. 5nce deployed, they usually donot re(uire any human intervention. 4ence, the setup andmaintenance of the network should be entirelyautonomous.
Sensor networks are infrastructure%less. herefore, allrouting and maintenance algorithms need to bedistributed.
Energy problem
4ardware and software should be designed to conservepower
Sensor nodes should be able to synchroni6e with eachother in a completely distributed manner, so that schedules can be imposed.
# sensor network should also be capable of adapting tochanging connectivity due to the failure of nodes, or newnodes powering up. he routing protocols should be able todynamically include or avoid sensor nodes in their paths.
"eal%time communication over sensor networks must besupported through provision of guarantees on maximumdelay, minimum bandwidth, or other 7oS parameters.
Provision must be made for secure communication oversensor networks, especially for military applications whichcarry sensitive data.
Classification of sensor network protocol
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12.2 Sensor Network Architecture
he two basic kinds of sensor network architecture
!ayered #rchitecture
Clustered #rchitecture
12.2.1 Layered Architecture
# layered architecture has a single powerful base station, andthe layers of sensor nodes around it correspond to the nodes thathave the same hop%count to the +S.
3n the in%building scenario, the +S acts an access point to a wirednetwork, and small nodes form a wireless backbone to provide
wireless connectivity.
he advantage of a layered architecture is that each node isinvolved only in short%distance, low%power transmissions tonodes of the
neighboringlayers.
Unified Network Protocol Framework (UNPF)
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*8P$ is a set of protocols for complete implementation of alayered architecture for sensor networks
*8P$ integrates three operations in its protocol structure:
8etwork initiali6ation and maintenance #C protocol "outing protocol
Network initialization and maintenance
he +S broadcasts its 3& using a known C code on thecommon control channel.
#ll nodes which hear this broadcast then record the +S 3&. heysend a beacon signal with their own 3&s at their low defaultpower levels.
hose nodes which the +S can hear form layer one +S broadcasts a control packet with all layer one node 3&s. #ll
nodes send a beacon signal again. he layer one nodes record the 3&s which they hear 0form layer
two1 and inform the +S of the layer two nodes 3&s. Periodic beaconing updates neighbor information and change the
layer structure if nodes die out or move out of range.
MA !rotocol
&uring the data transmission phase, the distributed
receiver oriented channel 0&"5C1 assignment #C protocol isused.
wo steps of &"5C :
Channel allocation :Each node is assigned a receptionchannel by the +S, and channel reuse is such that collisionsare avoided.
Channel scheduling :he node schedules transmissionslots for all its neighbors and broadcasts the schedule. his
enables collision%free transmission and saves energy, asnodes can turn o) when they are not involved on asend'receive operation.
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"outin# !rotocol
&ownlink from the +S is by direct broadcast on the controlchannel. *plink from the sensor nodes to +S is by multi%hop data
forwarding.
he node to which a packet is to be forwarded is selectedconsidering the remaining energy of the nodes. his achieves ahigher network lifetime.
UNPF$"
5ptimi6e the network performance by make the sensor nodesadaptively vary their transmission range.
+ecause while a very small transmission range cause network
partitioning, a very large transmission range reduce the spatialreuse of fre(uencies.
he optimal range 0"1 is determined by simulated annealing
5b9ective function :Nn
dRf
!" =
8 : the total number of sensors n : the number of nodes in layer one : the energy consumption per packet d : the average packet delay
3f no packet is received by the +S from any sensor node for
some interval of time, the transmission range increase by. 5therwise, the transmission range is either decrease bywith probability .; x 0 n ' 8 1, or increase by withprobability < = > .; x 0 n ' 8 1 ?.
3f , then the transmission range "/ is adopt.5therwise, " is modied to "/ with probability
: the temperature parameter
he advantage of the *8P$%" : inimi6e the energy x delay aximi6e the number of nodes which can connect to
the +S
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12.2.2 Clustered Architecture
# clustered architecture organi6es the sensor nodes into clusters,each governed by a cluster%head. he nodes in each cluster are
involved in message exchanges with their cluster%heads, andthese heads send message to a +S.
Clustered architecture is useful for sensor networks because ofits inherent suitability for data fusion. he data gathered by allmember of the cluster can be fused at the cluster%head, and onlythe resulting information needs to be communicated to the +S.
he cluster formation and election of cluster%heads must be anautonomous, distributed process.
Low$%ner#y Ada!ti&e lu'terin# ierarchy (L%A)
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!E#C4 is a clustering%based protocol that minimi6es energydissipation in sensor networks. he operation of !E#C4 is spiltinto two phases : setup and steady.
Setup phase : each sensor node chooses a randomnumber between and =. 3f this is lower than the threshold
for node n, 0n1, the sensor node becomes a cluster%head.he threshold 0n1 is calculated as
P : the percentage of nodes which are cluster%heads r : the current round @ : the set of nodes that has not been cluster%heads
in the past ='P rounds
#fter selection, the cluster%heads advertise their selection to allnodes. #ll nodes choose their nearest cluster%head by signal strength0"SS31. he cluster%heads then assign a schedule for their clustermembers.
Steady phase :data transmission takes place based onthe schedule, and the cluster%heads perform dataaggregation'fusion.
#fter a certain period of time in the steady phase, cluster%heads areselected again through the setup phase.
12.3 ata issemination
&ata dissemination is the process by which (ueries or data arerouted in the sensor network. he data collected by sensor nodeshas to be communicated to the node which interested in thedata.
he node that generates data is call source and the informationto be reported is called an event. # node which interested in an
event is called sink. Data dissemination consist of a two-step process :interest
propagation and data propagation. Interest propagation : for every event that a sink is
interested in, it broadcasts its interest to is neighbor, andacross the network.
Data dissemination : Ahen an event is detected, itreported to the interested nodes 0sink1.
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12..1 Floodin#
Each node which receives a packet 0(ueries'data1 broadcasts it ifthe maximum hop%count of the packet is not reached and thenode itself is not the destination of the packet.
&isadvantages :
Implosion:this is the situation when duplicate messagesare send to the same node. his occurs when a nodereceives copies of the same messages from many of itsneighbors.
Overlap: the same event may be sensed by more thanone node due to overlapping regions of coverage. hisresults in their neighbors receiving duplicate reports of thesame event.
Resource blindness: the -ooding protocol does notconsider the available energy at the nodes and results inmany redundant transmissions. 4ence, it reduces thenetwork lifetime.
12..2 *o''i!in#
odied version of -ooding
he nodes do not broadcast a packet, but send it to a randomlyselected neighbor.
#void the problem of implosion
3t takes a long time for message to propagate throughout thenetwork.
3t does not guarantee that all nodes of network will receive themessage.
12.. "umor "outin#
#gent%based path creation algorithm
#gent is a long%lived packet created at random by nodes, and itwill die after visit k hops.
3t circulated in the network to establish shortest paths to eventsthat they encounter.
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Ahen an agent nds a node whose path to an event is longerthan its own, it updates the node/s routing table.
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12..+ ,e-uential A''i#nment "outin# (,A")
he se(uential assignment routing 0S#"1 algorithm createsmultiple trees, where the root of each tree is a one%hop neighborof the sink.
o avoid nodes with low throughput or high delay.
Each sensor node records two parameters about each paththough it: available energy resources on the path and an additive7oS metric such as delay.
4igher priority packets take lower delay paths, and lowerpriority packets have to use the paths of greater delay, sothat the priority x delay 7oS metric is maintained.
S#" minimi6es the average weighted 7oS metric over thelifetime of the network.
12.. irected iffusion
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SP38 has three types of messages: #&J, "E7, and #.
SP38%H using an energy threshold to reduce participation. # nodemay 9oin in the #&J%"E7%# handshake only if it has su2cientresource above a threshold.
12.. Cost!"ieldApproach
he cost%eld approach considers the problem of setting uppaths to a sink. he rst phase being to set up the cost eld,based on metrics such as delay. he second phase being datadissemination using the costs.
# sink broadcasts an #&J packet with its own cost as .
Ahen a node 8 hears an #&J message from node , it sets itsown path cost to min 0!8,!KC81, where !8 is the total pathcost from node 8 to the sink, ! is the cost of node to the sink,C8 is the cost from 8 to .
3f !8 updated, the new cost is broadcast though another #&J.
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he back%o) time make a node defer its #&J instead ofimmediately broadcast it. he back%o) time is r x C8, where r isa parameter of algorithm.
12.. #eographic Hash $a%le H$'
@4 hashes keys into geographic coordinates and stores a 0key,value1 pair at the sensor node nearest to the hash value.
Stored data is replicated to ensure redundancy in case of nodefailures.
he data is distributed among nodes such that it is scalable andthe storage load is balanced.
he routing protocol used is greedy perimeter stateless routing0@PS"1, which again uses geographic information to route thedata and (ueries.
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12..3 Small (inimum )nerg* Communication Network
3f the entire sensor network is represented by @, the subgraph @/
is constructed such that the energy usage of the network isminimi6ed. he number of edges in @/ is less than @, and the connectivity
between any two nodes is not disrupted by @/. he power re(uired to transmit data between u and v is modeled
as
t : constant n : loss exponent indicating the loss of power with distance
from transmitter d0u,v1 : the distance between u and v
3t would be more economical to transmit data by smaller hops
Suppose the path between u 0i.e. u1 and v 0i.e. uk1 isrepresented by r D 0u, u=, L uk1, each 0ui, uiK=1 is edge in @/
he total power consumed for the transmission is
C
: the power needed to receive the data
he path r is the minimum energy path if C0r1 M C0r/1 for allpath/s r/ between u and v in @.
SEC8 uses only the E paths from @/ for data transmission, sothat the overall energy consumed is minimi6ed.
12.+ ata #athering
he ob9ective of the data gathering problem is to transmit thesensed data from each sensor node to a +S.
he goal of algorithm which implement data gathering is maximi6e the lifetime of network inimum energy should be consumed
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he transmission occur with minimum delay
he energy x delay metric is used to compare algorithm
12.+.1 4irect 5ran'mi''ion
#ll sensor nodes transmit their data directly to the +S.
3t cost expensive when the sensor nodes are very far from the+S.
8odes must take turns while transmitting to the +S to avoidcollision, so the media access delay is also large. 4ence, thisscheme performs poorly with respect to the energy x delaymetric.
12.+.2 Power$%fficient *atherin# for ,en'or 0nformation ,y'tem'
PE@#S3S based on the assumption that all sensor nodes know thelocation of every other node.
#ny node has the re(uired transmission range to reach the +S inone hop, when it is selected as a leader.
he goal of PE@#S3S are as following inimi6e the distance over which each node transmit inimi6e the broadcasting overhead inimi6e the number of messages that need to be sent to
the +S
&istribute the energy consumption e(ually across all nodes o construct a chain of sensor nodes, starting from the node
farthest from the +S. #t each step, the nearest neighbor whichhas not been visited is added to the chain.
3t is reconstructed when nodes die out. #t every node, data fusion or aggregation is carried out.
# node which is designated as the leader nally transmits onemessage to the +S.
!eadership is transferred in se(uential order.
he delay involved in messages reaching the +S is 5081
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Figure12.8 Datagathering with PEGASIS
12.+. 6inary ,cheme
his is a chain%based scheme like PE@#S3S, which classiesnodes into di)erent levels.
his scheme is possible when nodes communicate using C,so that transmissions of each level can take placesimultaneously.
he delay is 50log81
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12.+.+ hain$6a'ed 5hree$Le&el ,cheme
$or non%C sensor nodes he chain is divided into a number of groups to space out
simultaneous transmissions in order to minimi6e interference.
Aithin a group, nodes transmit data to the group leader, and theleader fusion the data, and become the member to the nextlevel.
3n the second level, all nodes are divided into two groups. 3n the third level, consists of a message exchange between one
node from each group of the second level. $inally, the leader transmit a single message to the +S.
12., (AC -rotocols for Sensor Networks
he challenges posed by sensor network #C protocol 8o single controlling authority, so global synchroni6ation is
di2cult
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Power e2ciency issue $re(uent topology changes due to mobility and failure
here are three kinds of #C protocols used in sensor network: $ixed%allocation
&emand%based Contention%based
$ixed%allocation #C protocol Share the common medium through a predetermined
assignment. 3t is suitable for sensor network that continuously monitor
and generate deterministic data tra2c Provide a bounded delay for each node
4owever, in the case of bursty tra2c, where the channel
re(uirements of each node may vary over time, it may leadto ine2cient usage of the channel.
&emand%based #C protocol *sed in such cases, where the channel is allocated
according to the demand of the node Jariable rate tra2c can be e2ciently transmitted
"e(uire the additional overhead of a reservation process
Contention%based #C protocol
"andom%access%based contention for the channel whenpackets need to be transmitted
Suitable for bursty tra2c
Collisions and no delay guarantees, are not suitable fordelay%sensitive or real%time tra2c
12..1 ,elf$7r#anizin# MA for ,en'or Network' and %a&e'dro! and"e#i'ter
Self%5rgani6ing #C for sensor 0S#CS1 networks and eavesdropand register 0E#"1 are two protocols which handle networkinitiali6ation and mobility support, respectively.
3n S#CS
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neighbor discovery and channel assignment take placesimultaneously in a completely distributed manner.
# communication link between two nodes consists of a pairof time slots, at xed fre(uency.
his scheme re(uires synchroni6ation only between
communicating neighbors, in order to dene the slots to beused for their communication. Power is conserved by turning o) the transceiver during
idle slots.
3n E#" protocol Enable seamless connection of nodes under mobile and
stationary conditions. his protocol make use of certain mobile nodes, besides
the existing stationary sensor nodes, to o)er service tomaintain connections.
obile nodes eavesdrop on the control signals andmaintain neighbor information.
12..2 y8rid 54MA9F4MA
# pure scheme minimi6e the time for which a node has tobe kept on, but the associated time synchroni6ation cost are veryhigh.
# pure $ scheme allots the minimum re(uired bandwidth foreach connection
3f the transmitter consumes more power, a scheme is
favored, since it can be switch o) in idle slots to save power. 3f the receiver consumes greater power, a $ scheme is
favored, because the receiver need not expend power for timesynchroni6ation.
12.. ,MA$6a'e MA Protocol'
CS#%based schemes are suitable for point%to%point randomlydistributed tra2c -ows.
he sensing periods of CS# are constant for energy e2ciency,while the back%o) is random to avoid repeated collisions.
+inary exponential back%o) is used to maintain fairness in thenetwork.
*se an adaptive transmission rate control 0#"C1 to balanceoriginating tra2c and route%through tra2c in nodes. his ensuresthat nodes closer to the +S are not favored over farther nodes.
CS#%based #C protocol are contention%based and aredesigned mainly to increase energy e2ciency and maintainfairness.
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