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This strategy is very simple and may be effective
in uniformly and densely deployed WSNs, but
forwarding opportunities can be loss in the practical
WSNs. In most of applications of WSNs, very small
and cheap sensor nodes are deployed to an interest
field by a plane in the air. Therefore, the network
commonly becomes an irregular shape that has lots
of partial network holes due to obstacles such as
buildings, lakes, or etc. If such holes are in the
restricted small forwarding area, it would be failed
to find a forwarding node even if there are
appropriate candidates in the rest area. In this case,
the sender has to send the data packet again or
change its routing mode from the greedy mode to the
recovery mode. Unfortunately, the neighbors cannot
be guaranteed to successfully receive data packet
again at the next time due to the error-prone nature
of wireless links. Also, if the routing mode is
changed, the protocol requires a number of control
messages and wastes lots of node energy because it
has to get the positions of all neighbors to detour the
holes.
Therefore, in order to both increase forwarding
opportunities and also prevent packet duplication
due to the hidden problem, we propose a novel
region-based beaconless routing protocol, which
gives different contention priorities into each region
in the sub-areas of the greedy forwarding area. In the
proposed protocol, nodes in high prioritized region
immediately find a next-hop forwarder in a fully
distributed manner after receiving a sender’s
broadcast data. On the other hand, nodes in low
prioritized region have to wait until contention of
high prioritized region is done. Namely, our protocol
has the two phase of contention process.
2 NETWORK MODEL
In the proposed protocol, the greedy forwarding area
is divided into two sub-areas: Hidden-less area and
the rest area, hidden area. The hidden-less area is
similar to the restricted forwarding area of the
previous protocols in the way that includes only
mutually communicable nodes. However, instead of
the previous protocols, the position of the hidden-
less area can be moved within the greedy forwarding
area by a learning mechanism. In order to switch the
hidden-less area with simple calculation, we choose
a 60’ radian area for the hidden-less area which is a
radial region that includes a 30’ radian area around
the line connecting the sender and the destination on
both sides. Except the hidden-less area, we call the
rest area as a hidden area. Note that all nodes in the
greedy forwarding area have been given data packet
from its previous sender at the same time, but their
relaying or answering times have to be different
from each other in order to prevent collisions. So,
we exploit the modified waiting function which is
based on both the distance from the destination
(closer node from the destination has lower timer)
and the priority value related to its geographic
position in the greedy forwarding area (higher
prioritized node has lower timer).
3 PROPOSED PROTOCOL
As shown in Fig. 1, a sender broadcasts its data to its
neighbors, so all nodes in the greedy forwarding area
can receive the sender’s data. The data packet
contains the original message, the position of the
sender and the destination, the maximum waiting
time, and the region information for the hidden-less
area. So, each neighbor in the greedy forwarding
area could realize whether it is in the hidden-less
area, or not. In this case, only the nodes A, B, C, D,
E, and F have been received the data successfully
among neighbors in the greedy forwarding area.
These nodes start to keep the received data into their
memories. Among these nodes, only both A and C
are in a high prioritized hidden-less area (fan-shaped
dashed region). After receiving the data, nodes in the
hidden-less area get higher priority than the hidden
area, and it immediately begins to find a next-hop
forwarder. These nodes have their own timer only
related to the distance from the destination by using
a predefined maximum time of T_max seconds. So,
in the hidden-less area, the closest node A from the
destination wake up first, becomes a next-hop
forwarder by itself, and broadcasts the received data
to its neighbors. Among all neighbors in the greedy
forwarding area, nodes that overhear this broadcast
data release its timer and received data. However, if
the node density is extremely high, this forwarding
message might be generated simultaneously among
neighbors because timers expire almost concurrently.
It might lead to lots of collisions, so the proposed
protocol exploits Distance and Angle based
Collision Avoiding Scheme, called DACAS.
On the other hand, nodes in the hidden area set
their own timer as a sum of distance-based value and
the T_max. Namely, every nodes in the hidden area
has to wait during T_max seconds first, it then
begins to start its distance-based timer. If the timer is
expired, the node in the hidden area sends a
FORWARDING_QUERY message to the sender. If
only there are no node that successfully rebroadcast
PECCS2013-InternationalConferenceonPervasiveandEmbeddedComputingandCommunicationSystems
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