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Chapter 3. Concept 28

These modules can only be used as a whole; no direct intervention is possible allowing communi-

cation only before or after the module. This strict division results in increased ﬂexibility, allowing

evaluating or changing each module separately. This is favourable for simulation or debugging, as

every module can be replaced with a simulation or logging program that replaces the functional-

ity. This advantage is used in the ﬁnal evaluation in chapter 5 for simulating and evaluating the

system. However, this segmentation also has its drawbacks. On the one hand, information has

to pass through every layer to reach its ﬁnal destination. This results in increased data traﬃc

as well as an increased latency. Furthermore, this can cause a noticeable delay between events

and actions, lowering the user’s acceptance. On the other hand, each layer needs interfaces to

communicate with its surrounding layers. This increases the amount of code being implemented

on the module, because of the algorithms for communication and synchronization.

gateway Hardware

Software

abstraction layer

communication

possibilities

for every layer

Figure 3.2.: Layer model: Each part of the software chain can be seen as an abstraction layer.

The grey ﬁeld displays a middleware.

To reduce the amount of code needed for communication, an existing middleware was used. In this

implementation, ROS was chosen, as it is already in use for IE research at the institute. It oﬀers

a wide range of useful tools and functionalities, making it perfectly suitable for this work. These

are for example a working publisher/subscriber architecture, which supports the exchangeability

and strict boundary of each layer.

The bottommost block of the layer model (ﬁgure 3.2) is the HA-PC gateway, which represents

the ﬁrst level of abstraction, as it converts the binary data packages of HA devices into a serial

data stream. All higher layers are software modules that are embedded in the middleware. The

highest layer acts as an interface to the IE. To enable a simple and fast connection of HA to

IE, diﬀerent software modules were implemented in order to take on the processing of data. The

software components and the abstraction of HA devices are elaborated in the following sections

of this chapter.

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