![](bg2.png)
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:
,
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
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
N5
< T
N8
< T
N9
< T
N3
< T
N2
< T
N6
)
Ordered Forwarding Candidates
Node_Number – Delivery Speed
Toward Si nk
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