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3.4 Brownfield IoT: Technologies for Retrofitting 173
or processing resources of different IoT systems. Additionally the interoperability
is crucial to the value of the system. Assuming that in the future the
service technician interconnects with a whole range of different types of wireless
measurement systems and smart machines of different manufacturers, the
analysis application must be aware of the semantics of all interfaces. Furthermore,
the ability of the system which consists of heterogeneous components to
integrate in the field, to configure and calibrate crucial for the application of adhoc
networked sensor system in the maintenance scenario. Loosely coupled,
document-based Web services provide a well-defined path to configuration
and measurement data from wireless ad hoc systems and automation systems,
however, have the disadvantage of a very high runtime overhead.
First, standardized ways must be found to obtain comparable quality data
sets with opportunistic, distributed measurements. In addition to the demands
on the sensor also just coming aspects of this case are concerned. In distributed
measurements, such as fine-grained synchronization of distributed measurements
of importance, and therefore optimized MAC protocols are required.
Second, a live data acquisition, needs a high throughput of data (eg ∼, 2 kHz ∗
3 channels × 16 bits = 96 kbps) to ensure that, while energy efficiency of the
hardware, requires a high efficiency of bandwidth usage. The IEEE 802.15.4–
2006 2.4 GHz PHY supports ideally a fixed channel data rate of 250 kbps with
a maximum payload data rate of approximately 101 kbps. Without optimization,
the sensing and transmission of a three-axis acceleration value is simply
not feasible at 1 kHz bandwidth. Therefore many vendor resort to proprietary
solutions.
This also explains why, despite increased standardization efforts in this area
have shown only limited influence. Even on top of successful standardizations
like 802.15.4 there is a fragmentation of protocols like ZigBee (Pro), or the
wireless HART OPC binary protocols that address domain specific problems.
This foils efforts for cross-domain applications. If we broaden the scope and
think of a real Internet of Thing technologies used range from Web Services and
Wireless LAN via proprietary sensor and home automation networks globally
used wireless technologies such as EPC protocols for RFID applications. More
diversity is introduced through a variety of programming models, tool support,
operating systems, and programming languages parallelism.
Especially, data from different (ad-hoc) measurements, e.g., wireless sensing
devices, need to be propagated and integrated in a reusable way, to provide a
smooth propagation path of data from on-site mobile data collection towards