Image Processing Reference
In-Depth Information
7.3.6 Two-Tier Data Dissemination Protocol
Ye et al. addresses in [Ye] the problem of data dissemination in the presence of mobile sink nodes.
This protocol is designed for large-scale reactive sensor networks, where stationary and location-
aware sensor nodes may detect target events, and multiple mobile sink nodes collect information
while moving across the network. he TTDD protocol achieves scalable and efficient dissemination
for query and data by proactively creating a grid structure when an event is detected. As sensor nodes
are location-aware, a node with coordinates (
x
,
y
) that has sensed an event can set itself as a crossing
point in the grid and send announcements to elect as dissemination nodes those closest to positions
(
x
α),whereαisthesideofeachcell.hiscanbeachievedbyusingagreedygeographic
forwarding scheme, i.e., a routing algorithm that chooses the neighbor closest to the destination.
These announcements are sent recursively until the grid has been fully created. Once the grid has been
set up, sinks can flood queries to their cell, i.e., the first tier. However, flooding is conined within the
cell. Once the query reaches the closest dissemination node, it will be propagated toward the source
node through the second tier, that is, the set of dissemination nodes. This mechanism significantly
reduces the number of messages and hence energy as compared to standard query flooding. During
this process, dissemination nodes store the location of nodes from which they receive queries. his
information is used for subsequent data forwarding from the source to the sink node. In fact, data
is forwarded through the reverse path until the cell of the sink is reached. Once it reaches that cell,
a trajectory forwarding scheme is used to find the moving sink. According to this scheme, the sink
includes in its queries the location of a designated sensor node, called a primary agent. This node
represents the mobile sink for the immediate dissemination nodes. As the sink moves within the cell,
the location of a close sensor node, the immediate agent, is updated. he immediate agent is initially
the primary agent. So data is forwarded from the immediate dissemination node to the primary agent.
If the sink has moved, this node will relay data to the new immediate agent. his node directly sends
data to the sink. When a sink moves out of the cell, it may pick a new primary agent and re-flood
the query.
The energy consumption problem is addressed here by dynamically creating a virtual grid in which
only elected nodes perform data forwarding. In addition, query flooding is performed only within the
grid, so both bandwidth and energy are saved. Compared with Data Difusion [Int], TTDD features
reduced energy consumption when the number of sinks is low. However, its power consumption
rapidly increases when the number of sinks increases, so when the number of sinks is large, Directed
Diffusion could perform better in terms of energy consumption. However, TTDD also features lower
delays when there are many sources and provides support for sink mobility.
±
α,
y
±
7.4 Optimization-Based Power-Aware Routing Protocols
7.4.1 Minimum-Cost Forwarding Protocol
In [Ye] Ye et al. propose an algorithm aiming to provide message delivery through the minimum-
costpathfromasensornodetothesinkinalarge-scaleWSN.hisworktriestoexploreanewscalable
solution to the minimum-cost forwarding problem, i.e., the cost field-based approach. he cost field
for packets is something similar to the gravity field for water: as water flows from high to low posts,
once the cost field is established, packets flow from source to sink nodes through the minimum-cost
path. In order to achieve this behavior, each message has to keep the minimum required cost from the
source to the sink node as well as the consumed cost from the source to the current node. he sender
always uses broadcast packets. Intermediate nodes that receive the packet forward the message only
iftheconsumedcostofthepacketplusitsownminimumcosttothesinkisequaltotheminimum
cost specified by the source node. Hence, only nodes belonging to the minimum-cost path from the
source to the sink perform data forwarding. Each node has to maintain only the minimum cost from
