Image Processing Reference
In-Depth Information
Energy efficient
Mobility support
SMAC
MS-MAC
IEEE 802.11
Sensor network
MSN
MANETs
FIGURE .
MS-MAC and mobility in WSNs. (Redrawn from Pham, H. and Jha, S., An adaptive mobility-aware
MAC protocol for sensor networks (MS-MAC), in
Proceedings of the st IEEE International Conference on Mobile Ad-
Hoc and Sensor Systems (MASS-)
,FortLauderdale,FL,Oct.)
However, when multiple mobile nodes are detected, only information on the node with the highest
estimated speed is included. he mobility information is used to create a so-called active zone around
the moving node that is a region in which the synchronization period is smaller. This means that
nodes within the active zone have a higher energy consumption, but also that the time needed to
setup a new connection is shorter. This mechanism highly improves the performance of the WSN
under mobility. In fact, using the standard synchronization periods, a mobile node might lose the
connection with the old neighbors before it has setup a new schedule. he node might stay therefore
disconnected for a long time, until a new synchronization phase starts (the default period is min).
On the other hand, decreasing the synchronization periods, a node can speed up connection setup,
so that a new schedule can be created before the old connections are lost. Under stationary condi-
tions no active regions are created, so the node features low energy consumption, whereas when the
mobility of a node is detected, only the surrounding nodes increase their synchronization rates. he
nodes in the active zone adjust their duty cycles depending on the estimated speed of the moving
nodes and will also stay awake all the time if a threshold speed is exceeded. This way, a trade-off
between performance and energy consumption is obtained in both stationary and mobile scenarios.
8.3.2 Mobility-Adaptive Collision-Free MAC
AdiferentapproachtohandlemobilityisusedbytheMobility-AdaptiveCollision-FreeMAC
(MMAC) protocol proposed in [Mun]. This protocol uses a dynamic frame containing both
scheduled-access and random-access time-slots. The division between scheduled-access and
random-access slots is adaptively changed according to the expected mobility changes, e.g., node
joins or node failures. he MMAC protocol assumes that WSN nodes are location-aware. he location
information is used to predict the mobility patterns of nodes, through a real-time mobility estimation
scheme(AR-)basedonairst-orderautoregressivemodel[Zai].hekeyideaistousetheinforma-
tion obtained from the mobility estimation model to reduce the frame time when a large number of
nodes is expected to enter or leave the two-hop neighborhood, and vice-versa to increase the frame
time when less node mobility is expected. The main issues of such an approach are how to obtain
