wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

53-12 Industrial Communication Systems
S
Y
N
C
T 0
Scheduled activities
period
(constrained by a
hierarchical tree)
Deterministic MAC
period
T 1 T 2 T 3
Global cycle
Unscheduled activities
period
(slotted CSMA/CA)
Optimized network
lifetime
energy-aware OLSR
FIGURE 53.11
MaCARI concept.
is repeated in cascade through the tree and contains all synchronization information. Every node synchronizes
on T 1 and knows the next T 0 . Within the unscheduled activities period, MaCARI gives the
control to the network layer that takes care of routing packets using EOLSR, an Energy-aware OLSR
protocol (RFC 3626), which is described in [MM081]. MaCARI also deals with network initialization
such as address allocation and IEEE 802.15.4 PAN association control. The detailed description of
MaCARI is out of scope here.
53.4.3 Network Layer and Topologies
OCARI topologies are specified as follows (Figure 53.12):
OCARI End Device is a “radio fixed” network node (i.e., its position varies very little comparing to
its initial location, so that its radio link is always managed by the same cell coordinator). It is a reduce
function device (RFD) as defined in IEEE 802.15.4 specification.
OCARI cell and workshop coordinators are FFDs as specified in IEEE 802.15.4. They are fixed
devices in the infrastructure and are equivalent to ZigBee coordinator. The functions of cell coordinator
consist of coordinating the intra-cell network nodes using a star topology and routing data
packets from end device network nodes (e.g., sensors) to the workshop coordinator per workshop
domain.
Workshop domain is a permissive volume (delimited by a threshold of the RSSI) to electromagnetic
wave that is covered by a unique workshop coordinator network node.
Workshop coordinator is a gateway between the wireless sensors network resided in a workshop
domain and the industrial facility backbone.
OCARI network layer is based on a cross-layering approach. It manages packet routing for unscheduled
activities period according to EOLSR proactive protocol (refer to [MM081] for a detailed description).
It also offers a Scheduling RoutEr Node Activity (SERENA) strategy, which uses a three-hops
neighbors decentralized coloring algorithm to schedule the router activities, so that energy consumption
can be reduced, and the bandwidth efficiency is improved by avoiding the interferences between
routers (a timeslot is assigned to a node according to its color and there is a spatial reuse of color code).
The principle of SERENA is as follows [MM082].
A router node is woken up in the timeslots where
• It transmits
• One of its one-hop neighbors transmits
• It sleeps otherwise
© 2011 by Taylor and Francis Group, LLC