Opportunistic Spatiotemporal Routing in Wireless Sensor Networks

Seungmin Oh, Yongbin Yim, Jeongcheol Lee, Hosung Park and Sang-Ha Kim

Department of Computer Engineering, Chungnam National University, Daejeon, Republic of Korea

Keywords: Opportunistic Routing, Real-time Routing, Wireless Sensor Networks.

Abstract: We propose an opportunistic spatiotemporal data dissemination protocol in order to solve the transmission

failure problem in error-prone WSNs. Retransmission is well-known for recovery of transmission failure;

however, this may cause the severe time delay possibly to violate the real-time requirement. To solve the

problem, our protocol exploits both broadcasting nature and temporal opportunity concept. In a radio-range

of a sensor node, there may be multiple neighbor nodes to satisfy the real-time requirement. By

broadcasting property, all neighbors can receive a data from a node, and only each satisfying neighbor

decides its relay toward the destination by using temporal selection function. The temporal function is

related to the tolerable time period to be able to satisfy the real-time requirement. By giving the priority to

the node with smaller tolerable time, we have more opportunities to forward toward the destination. That is,

even if a node with a long tolerable time waits for the longer period of time, it still has a chance to forward

with the real-time requirement. In summary, the proposed protocol attains the high reliability and real-time

requirement by removing data retransmission and multiple opportunities with temporal consideration.

1 INTRODUCTION

Wireless Sensor Networks (WSNs) gather their

objective information from a large number of sensor

nodes with limited communication and computing

power. The sensor nodes generate reporting data

about events and forward them to sinks via multi-

hop communication. Many applications in WSNs,

such as battlefield surveillance and earthquake

response systems, should be tailored to interact with

fast changing events and required to gather the event

data in an application desired time deadline. The

geographical real-time data dissemination protocols

typically try to maintain a desired delivery speed

across the sensor network. The protocols choose the

nodes which have the relay speed faster than the

desired delivery speed. However, the protocols focus

the data dissemination within the desired time

deadline and do not consider the reliable

communication.

Several routing protocols have been developed

for reliable communication due to the limitation of

sensor nodes in error-prone WSNs. Some reliable

data dissemination schemes (Akyildiz, 2002) in

WSNs are based on the retransmission in which

either the source node or the relay nodes are

responsible for detecting packet loss and

retransmitting the lost packet for recovering error.

The schemes choose only a sensor node as a next-

hop node and transmit data packets to the selected

node. But, in case of transmission failure to the

selected node, the schemes should require data

retransmission to the same neighbor or possibly

another neighbour in order to increase reliability.

Other reliable data dissemination protocols

(Felemban, 2006) exploit the multipath routing. The

protocols make the multiple copies of data packets

and forward them through multiple paths. The data

redundancy could provide the high reliable

communication.

However, the reliable data dissemination

protocols still have some problems. The

retransmission protocols are well-known for

recovering the transmission failure; however, they

may cause the severe time delay possibly to violate

the real-time requirement. And the multipath routing

protocols only increase data delivery ratio but could

not assure that all data packet arrive at the

destination node. It also wastes an amount of

network energy, shortens the network lifetime and

leads to traffic congestion.

In this paper, we propose an opportunistic

spatiotemporal data dissemination protocol in order

to increase the reliability by using broadcasting

233

Oh S., Yim Y., Lee J., Park H. and Kim S..

Opportunistic Spatiotemporal Routing in Wireless Sensor Networks.

DOI: 10.5220/0004315702330236

In Proceedings of the 3rd International Conference on Pervasive Embedded Computing and Communication Systems (PECCS-2013), pages 233-236

ISBN: 978-989-8565-43-3

 2013 SCITEPRESS (Science and Technology Publications, Lda.)

nature and temporal opportunity concept. By

broadcasting property, all the neighbors can receive

a data from a node. Among the neighbors, there may

be multiple sensor nodes which could fulfil the real-

time requirement, and each neighbour among the

nodes decides its relay toward the destination by

using temporal selection function. The temporal

function is related to the remaining time, which

stands for the tolerable time period to be able to

satisfy the real-time requirement. By giving the

priority to the node with smaller remaining time, we

have more opportunities to forward toward the

destination. That is, even if a node with a long

remaining time waits for the longer period of time, it

still has a chance to forward with the real-time

requirement. In summary, the proposed protocol

attains the high reliability and real-time requirement

by removing data retransmission and multiple

opportunities with temporal consideration.

Simulation results show that the proposed protocol is

superior to the existing protocols in terms of real-

time data dissemination.

Figure 1: Next-hop candidate decision.

2 NETWORK MODEL

Our proposed protocol relies on several assumptions

that are explicitly and implicitly exploited in other

studies about real-time routing (He, 2005)

(Felemban, 2006) and many geographic unicasting

routing protocols (Akyildiz, 2002) as follows.

 A large number of homogeneous sensor nodes

are deployed over a vast field, and then the nodes

self-organize an ad-hoc network. Long distance data

delivery is performed through multi-hop

communication manner.

 Once a phenomenon appears, the sensor nodes

surrounding the phenomenon collectively gather

information and one of them becomes the source to

generate data of the phenomenon.

 The source nodes that generate event data could

be provided the location of sink by one of the sink

location services.

 For the geographic unicasting routing, which is

one of the stateless routing method, each sensor

node is aware of its own location after deployment

by receiving Global Positioning System (GPS)

signals or using some localization techniques.

 Every sensor node has its own neighbor node

table including the coordinates and the estimated

delay of its neighbors by periodic beacon signaling.

The existing protocols (He, 2005); (Felemban, 2006)

for real-time data dissemination mainly exploit the

spatiotemporal approach in order to deliver data

from a source to a static sink within a desired time

deadline T

setdeadline

. While in multi-hop wireless

sensor network, since communication is physically

bounded, the end-to-end delay depends not only on

single hop delay (temporal), but also on the distance

a packet travels (spatial). For this, source nodes

initially calculate a desired delivery speed S

setspeed

with the time deadline and the end-to-end distance

d(source, sink) from the source to the sink as follows:



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

, 





In the protocols, each node on the dissemination

route selects a node as its next-hop node which is

nearer to the sink and provides a better relay speed

than the desired delivery speed S

setspeed

. The relay

speed means the advance in distance to each next

node dividing by the delay to forward a packet to the

each next node. The end-to-end real-time data

dissemination is achieved by maintaining the desired

delivery speed from sources to the sink. However, if

the sink moves around, the distance between them

changes dynamically, so that the end-to-end distance

and the data delivery speed S

setspeed

should be also

altered. But the re-calculation of the distance and the

delivery speed per every hops let the sensor nodes

have an amount of computing overhead.

3 OPPORTUNISTIC REAL-TIME

ROUTING PROTOCOL (ORRP)

For routing, sender nodes have the two following

tasks: next-hop selection and data forwarding. The

sender nodes select one node as the next-hop node

among its 1-hop neighbor nodes. Then, the nodes

include the address or geographical coordinates of

the next-hop node into data packets for the next-hop

node to receive the packets. In the proposed

Broadcasting Range

Greedy Area

N1 – 3m/s

N2 – 6m/s

N3 – 7m/s

N4 – 4m/s

N5 – 8m/s

N7 – 3m/s

N8 – 5m/s

N9 – 6m/s

N10 – 4m/s

N6 – 5m/s

setspeed

= 5m/s

N16

N15

N14

N13

N12

N11

N1, N2, N3, N4, N5,

N6, N7, N8, N9, N10

Greedy Nodes

N2, N3, N5, N6, N8, N9

Forwarding Candidates

N5, N8, N9, N3, N2, N6

(if, T

< T

)

Ordered Forwarding Candidates

Node_Number – Delivery Speed

Toward Si nk

PECCS2013-InternationalConferenceonPervasiveandEmbeddedComputingandCommunicationSystems

234

protocol, the selection of the next-hop node is

determined by the next-hop candidates. The next-

hop candidates could receive the data packets from

its previous sender. The proposed protocol gives the

opportunity for data packet forwarding to receiver

nodes that receive the data packets successfully.

Before the data forwarding, each nodes obtain the

information of its own neighbor nodes by beacon

signaling. The information includes the location of

neighbor nodes and the processing time for a data

packet, namely, hop delay. Similar to other real-time

data dissemination protocols, each node keeps a

neighbor table to store the information. By the

information, the each forwarding nodes select the

candidate node as its next-hop node which are closer

to the destination (sink) and which delay speed is

faster than desired speed Ssetspeed. In the proposed

protocol, sender nodes include the list of candidates

into the packet header. The data packets are

broadcasted by the sender node. The neighbor nodes

which receive the data packets determine whether

itself will forward the data packets or not, with the

information of the packets.

Figure 2: Temporal opportunity.

Before forwarding data packets, sender nodes

(including source nodes) select the candidates that

will receive the data packets. Neighbor node set NS

includes the multiple neighbor nodes within the

radio range of the node i. As described above, the

node i stores the coordinates and single hop delay of

the members in NS

i. The node divides NSi with the

forwarding candidate set and the non-forwarding

candidate set. For the forwarding candidate set, the

proposed protocol chooses some nodes which are

closer than the sender node toward the destination.

Based on the set, the sender node calculates the relay

speed RS

of each node n

with the following

equation:

where dist(n, dest) is the distance between the node

n and the destination and hopdelay

is the single

hop delay from the node i to the node Cn. In the

forwarding candidate set, only the neighbor nodes,

which have the larger relay speed than the desired

delivery speed, are included. The forwarding

candidate set list and the single hop delay of the

forwarding candidates are sent with the data packets

to the candidates. The forwarding candidate set in

the data packet is sorted with the single hop delay in

order to preferentially select the node which has the

shortest hop delay. As shown in Fig. 1, the sorted list

could provide the opportunity to forward data

packets to maximum candidates. The candidates

could relay the data packets after the sum of

transmission delay T

data

and their own single hop

delay T

due to the queueing delay of the sensor

nodes. And the data packets could not be forwarded

after the per-hop desired time deadline since the data

packet is out-dated after that time. The per-hop

desired time T

hop-deadline

between node i and node Cn is:

(dist(n

,dest)-dist(n

,dest))/ S

setspeed

. As a result, the

data packets should be forwarded in the time from

to T

hop-deadline

. The nodes have the data forwarding

opportunity in order of the single hop delay. By the

temporal opportunity, the i

node could forward data

packets in T

~ T

i+1

Figure 3: Time diagram for next-hop decision.

The sensor nodes, which receive data packets

and forwarding candidate list from their upstream

node, decide whether they will relay the data packets

or not. First, nodes check that the node is included in

the forwarding candidate list. If the node is one of

the candidates, the node sets its timer with its single

hop delay. As shown in Fig. 2 and 3, all candidates

start their timers. The node C1 needs not to start the

timer since C1 does not receive the data packets

successfully. The candidates overhear the same

packet transmission of the other candidates because

the multiple candidates could concurrently send the

packet. It might cause the transmission failure due to

the collision. The overheard node cancels its own

timer and discards the data packet. If the timer of a

candidate is released with no overheard transmission,

the node starts the next-hop forwarding for the data

DATA

Sender

Temporal Opportunity

data

((, ) (, ))/

iCn i

dist n dest dist n dest hopdelay





Sender Candidate1 Candidate2 Candidate3

Next-hop

Candidates

Broadcasting the packet #n from the sender

Transmission

Failure

Timer set

Broadcasting the packet #n from the candidate2

Overheard &

Timer canceled

Timer set

Overheard Overheard

OpportunisticSpatiotemporalRoutinginWirelessSensorNetworks

235

packet. The opportunistic routing has a constraint

that the nodes in forwarding candidate set should be

able to hear from each other. Otherwise, the packet

duplication would occur. For prohibiting from the

packet duplication, the previous node sends a control

message for timer cancel. Because only the previous

sender node could send the message to all candidates

including not-overheard candidates.

4 PERFORMANCE

EVALUATION

We have implemented the proposed protocol in the

Qualnet network simulator. We compare the

proposed protocol with SPEED (He, 2005) and

MMSPEED (Felemban, 2006), the most popular

real-time protocols. The simulation network space

consists of 500 sensor nodes uniformly deployed in

a 500m X 500m square area. The radio range of each

sensor nodes is about 50m. The source node

generates 30 byte-data packets with interval 0.05s.

The simulation time is 50s and the required

reliability is 85%. The results are the average value

of 100 times of simulation.

Figure 4: Time diagram for next-hop decision.

Figure 4 and 5 show the TDSR impacted by the

end-to-end distance and the number of sensor nodes.

In SPEED, the longer the end-to-end distance, the

lower the time deadline success ratio. It is because

that SPEED does not consider the packet reliability

and a number of data packets are lost in SPEED. The

TDSR of MMSPEED is similar to the desired

reliability since MMSPEED branches the multiple

paths when the calculated reliability is under the

desired reliability. The multiple path increases the

time deadline success ratio. The proposed protocol

results in the high TDSR since the per-hop reliability

is proportional to the opportunity to forward data.

The number of sensor nodes means the node density

in the sensor field. The larger the node density is, the

larger the number of 1-hop neighbor nodes is. As the

number of sensor nodes increases, the TDSR is

converged to almost 95%.

Figure 5: Time diagram for next-hop decision.

5 CONCLUSIONS

In this paper, we propose an opportunistic routing

protocol for real-time data in order to increase the

reliability of transmission. Since our protocol gives

the opportunities to forward data to multiple

neighbor nodes, using the nature of broadcasting and

the temporal opportunity distribution, the protocol

could increase the reliability of real-time data.

REFERENCES

Akyildiz, I. F. et al., 2002. A survey on sensor networks,

IEEE Communications, Vol. 40, No. 8, pp.102-114.

He, T. et al., 2005. A Spatiotemporal communication

protocol for wireless sensor networks, IEEE

Transactions on Parallel and Distributed Systems, Vol.

16, No. 10, pp.995-1006.

Felemban, E., Lee, C., and Ekici, E., 2006. MMSPEED:

Multipath Multi-SPEED Protocol for QoS Guarantee

of Reliability and Timeliness in Wireless Sensor

Networks, IEEE Transactions on Mobile Computing,

Vol. 5, No. 6, pp. 738-754.

100 150 200 250 300 350 400 450 500

100

TDSR (Time Deadline Success Ratio, %)

End-to-end Distance (m)

ORRP

MMSPEED

SPEED

100 150 200 250 300 350 400 450 500

100

TDSR (Time Deadline Success Ratio, %)

End-to-end Distance (m)

ORRP

MMSPEED

SPEED

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