Image Processing Reference
In-Depth Information
from other nodes, which is not the case for a single-hop system. In addition, intermediate
nodes do not know when they may be called upon to route packets for others. This is
what motivates the Hybrid Mesh Topology with mains-powered router nodes shown in
Figure ..
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Data package size: The size of the payload, header, CRC, etc., all have a direct impact
on how long the radio needs to be turned on to send its data. his is regardless of what
media access scheme is employed. When designing the protocol, a trade-off has to be
made between throughput, latency, and power consumption; and at least one of them has
to suffer.
•
Security: It is important that the data are secured from intentional corruption (i.e.,
integrity), and that it is sent from a valid device (i.e., authentication). Security adds over-
headtothepacketsandtothecomputationperformedatthedevices(i.e.,tocheckthe
integrity and authenticity). This, in turn, possibly leads to the need of specific hard-
ware (i.e., encryption support) in order to achieve the required communication timing
requirements.
Details in the communication protocol thus dictate the lower bounds of the consumption. Some
communication protocols are notoriously inefficient and no smart embedded programming in the
world will help get the consumption down to an acceptable level. Others are designed to give low
consumption without unduly compromising communication performance. he WISA [] platform
is one such low-power protocol. he high performance can be attributed to two reasons: it is single
hop and it uses time division multiplexing. he former avoids delays in intermediate nodes. he latter
guarantees that a node will be alone on the channel, i.e., there will be no collisions. WISA is designed
for manufacturing control applications, which require high node density and deterministic response
times, but have rather relaxed requirements on throughput and range.
The recently developed WirelessHART specification with the underlying .. protocol is more
general, but will have lower communication performance. It specifies multi-hop, where a message
can use several radio hops to get to its destination. This introduces uncertainty in the delivery
time of a message, but extends the range while keeping power consumption acceptable.
In short, the WISA protocol is well adapted to the requirements of discrete manufacturing, while
WirelessHART is ideally suited for asset monitoring applications.
Wireless Vibration Monitoring Case Example
In the WSN of the reference case, all nodes have the capability of routing traffic. The Network
manager continuously changes communication links in the mesh network, in order to cope with
fading and interference, as well as trying to evenly spread traffic over all nodes (thus evenly spread-
ing the power consumption between the nodes).
Furthermore, the TSMP solution provided by DUST Networks allows the designation of leaf
nodes, i.e., nodes that will never route any traffic. This provides the possibility to form a mesh
backbone network consisting of pure routing nodes (i.e., without vibration measurement capa-
bility) and to have all sensor nodes configured as leaf nodes, which will further decrease their
energy consumption.
27.7 Packaging
27.7.1 IP Rating
The international standard IEC [] classifies the degrees of protection of an electric system
against solid and/or liquid. The rating consists of the letters IP (International Protection rating)
