Image Processing Reference
In-Depth Information
The NP and SEP allow nodes to exchange two-hop neighbor information and their schedules. The
AEA uses this information to select the transmitters and receivers for the current time-slot, thus
enabling noninvolved nodes to switch to a low-power mode.
NP propagates one-hop neighbor information among neighboring nodes during the random-
access period using the signaling slots. SEP is used to exchange schedules with neighbors, where
a schedule contains information on traffic coming from a node, i.e., the set of receivers for the traffic
originating at the node. Before transmitting, a node has to announce its schedule using SEP. This
mechanism provides a consistent view of schedules across neighbors and periodic schedule updates.
AEA selects transmitters and receivers to achieve collision-free transmission using the information
obtained from NP and SEP. AEA uses traffic information (i.e., which sender has traffic for which
receivers) to improve channel exploitation.
TRAMA provides support for unicast, broadcast, and multicast traffic and differs from S-MAC for
two main aspects:
•
TRAMAisinherentlycollision-free,asitsMACmechanismisschedule-based,while
S-MAC is contention-based.
•
TRAMA uses an adaptive approach based on current traffic to switch nodes to low-power
mode, while S-MAC is based on a predefined static duty cycle.
In [Raj] simulation results showed that TRAMA achieves higher end-to-end throughput and
energy saving than S-MAC and other contention-based MAC protocols, but also higher delays than
random-selection protocols due to the scheduling overhead.
8.2.9 Flow-Aware Medium Access
he Flow-Aware Medium Access (FLAMA) protocol [Raj] uses a simple traffic adaptive, distributed
election scheme for energy-efficient channel access. Similarly to TRAMA, it requires two-hop neigh-
borhood information. In addition, FLAMA uses flow information in the neighborhood to perform
the election. FLAMA adapts medium access schedules to the application traffic flows. As the adaptive
scheme is simple, it can be executed even by nodes with limited resources and processing capabilities.
Similarly to TRAMA, FLAMA assumes a single channel for data and signaling and divides time into
contention-based channel access periods, called random-access intervals, and collision-free chan-
nel access periods, called scheduled-access intervals. Random-access intervals are used for neighbor
discovery, time synchronization, and implicit traffic information exchange, while scheduled-access
intervals are used for data transmission. Periodic random-access periods allow FLAMA to adapt to
topology and traffic changes in the WSN. Unlike TRAMA, FLAMA does not require explicit schedule
announcements during scheduled access periods. Instead, nodes exchange application-specific traffic
information during random-access interval to acquire the application-specific traffic flows. FLAMA
then exploits the information to calculate transmission schedules for each node. FLAMA achieves
adaptivity to the varying traffic conditions by assigning slots to a node depending on the amount of
traffic generated by that node, using weights that depend on the amount of the node's incoming and
outgoing traffic flows. As nodes with more outgoing flows receive higher weights, they are assigned
more slots.
8.2.10 Sift
The Sift protocol proposed in [Jam] is a MAC protocol for event-driven WSNs that is based on the
observation that in many WSN scenarios spatially correlated contention causes latency and through-
put degradation. Such a contention occurs when multiple nodes located in the same neighborhood
sense the same event and transmit to report it to the sink. In many WSN applications, however, not all
the nodes that sense an event need to report it. he first
R
of
N
potential reports are the most crucial
