Mobility Aspects in WSN - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 130

cost-efficient routing protocols, which can efficiently disseminate information in
the sensor network using resource- and mobility-adaptive algorithms. Therefore,
more appropriate and novel algorithms and protocols need to be defined [ 34 ].
One of the most prominent research aspects in mobile WSNs is the efficient data
propagation . Several data dissemination protocols have been proposed for WSNs
with static nodes, starting from the basic approaches of flooding and direct trans-
mission, to more efficient transmission protocols.
Flooding technics consume more resources than necessary and should be
avoided whenever possible. It is a simple scheme where each sensor aggressively
propagates its data messages to any neighboring nodes, resulting in the lowest
delivery delay, but causing high overhead and energy consumption. In the direct
transmission design, the messages from the sensors are directly transmitted to the
sink, and a sensor does not receive or transmit any data messages of other sensors.
This is inappropriate in large networks where the sensors can be far away from the
sinks. Direct transmission will be too energy consuming or can fail due to the lim-
ited communication range of the sensor nodes.
Directed Diffusion (DD) [ 35 ] and Low-Energy Adaptive Clustering Hierarchy
(LEACH) [ 36 ] are widely used data propagation and routing methods. The DD
approach assumes that each sink periodically must flood its location information
through the sensor field. This procedure sets up a gradient from the sensor nodes to
the sink so that each sensor is aware of the sink location for sending future events
and measurements. However, such a strategy does not scale with the network size
and increases the network congestion, while in a mobile scenario it is an inappropri-
ate solution because of the numerous topology changes. LEACH is a hierarchy-
based protocol, where elected CHs transmit aggregated data directly to the sink. It
is appropriate only for small networks, and it does not really support movement of
nodes. M-LEACH is a proposed protocol which adds a feature to LEACH to sup-
port mobile nodes and also reduces the consumption of the network resources [ 37 ].
The nodes with less mobility are preferred to be CHs, and the basic idea of the
proposed approach is to divide the sensing area into sub-areas and try to optimize
the location of CH in these sub-areas.
Overlaying a virtual infrastructure over the physical network has often been
investigated as an efficient strategy for effective data dissemination in the presence
of mobile sinks. This strategy is implemented in protocols like two-tier data dissemi-
nation (TTDD) [ 38 ], geographic hash table (GHT) [ 39 ], line-based data dissemina-
tion (LBDD) [ 40 ], and dynamic directed backbone (DDB) [ 41 ]. They all use the
concept of virtual infrastructure, which acts as a rendezvous area for storing and
retrieving the collected measurements. The sensor nodes belonging to the rendez-
vous area are designated to store the generated measurements during the absence of
the sink. After the mobile sink crosses the network, the designated nodes are que-
ried to report the sensory input. A survey of the existing data dissemination proto-
cols for network containing mobile sinks can be found in [ 42 ].
A research trend on data dissemination in WSNs where the mobility of some of
the sensor nodes is exploited for facilitating the delivery of the sensed data to the
sinks, thus enhancing the system's performances, is gaining more attention recently.
Data propagation in a scenario with mobile sensor nodes is a completely different