Image Processing Reference
In-Depth Information
Medium access mechanism
Contention-based
Schedule-based
CSMA
TDMA
1998
PAMAS
2002
S-MAC
2003
T-MAC
TRAMA
2004
D-MAC
LMAC
WISEMAC
B-MAC
MS-MAC
2005
PMAC
MMAC
Z-MAC
FLAMA
2006
Sift
CC-MAC
MMSN
PEDAMAC
LMAC m.c.
MCMAC
2007
Crankshaft
2008
MHMAC
FIGURE .
Classification of MAC protocols for WSNs.
to deal with mobile nodes and network changes. On the other hand, schedule-based protocols
are energy-efficient, as they have a duty cycle built-in and are collision-free, but they are more com-
plex to implement. The need for broadcasting a schedule in advance requires some coordination
between the nodes, and also limits scalability and flexibility to handle mobile nodes and to deal with
varying topology and network size. Moreover, maintaining a list of neighbors' schedules requires a
significant amount of memory.
From what was said above, it is clear that schedule-based protocols offer some advantages which
contention-based ones do not have, and vice-versa. In the WSN literature therefore we hardly find
MAC protocols that strictly belong to one of these categories, e.g., a pure carrier-sense multiple access
(CSMA) or a pure time division multiple access (TDMA) protocol. For the sake of energy efficiency
and performance improvement, the majority of protocols try to combine the positive features of the
twoclasses,sointherangefrompurecontention-basedtopureschedule-basedprotocols,theycan
be placed in an intermediate region between two extremes, respectively CSMA and TDMA, as shown
in Figure ..
In the following, notable example of MAC protocols belonging to the different classes will be
addressed.
8.2.1 Power-Aware Multi-Access Protocol with Signaling
The Power-Aware Multi-Access Protocol with Signaling (PAMAS) [Sin] is based on the idea of
switching of the radio of nodes when they are likely to overhear transmissions, i.e.,
•
If a node has no packets to transmit and a neighbor begins transmitting or
•
If at least one neighbor of a node is transmitting and another one is receiving, as in this
case the node cannot transmit or receive a packet (even if it has a packet to transmit).
