RFXCOM RFXtrx433 Especificações descarregar pdf (Página 15)

Chapter 2. Related Work/Fundamentals 8

Security: Wireless systems are generally more insecure than comparable wired solutions. The

wireless media can be easily accessed by unwanted listeners or other interfering systems.

Most systems encrypt their data, but low-cost hardware often does not have this feature.

Hence, this oﬀers the possibility for attacks and vandalism.

Reliability: Radio-based systems can malfunction, if the distance between two nodes is too high,

or if disturbances such as metal objects impair reception.

Directionality: Low-cost systems are usually unidirectional which means that devices can either

send or receive. Transmitted messages cannot be acknowledged and the state of receivers

cannot be read out. Therefore, errors can lead to an undetermined state of the system.

Bidirectional systems can register package losses and failures, but they are higher priced.

Tethered systems:

Cables are the classic transmission medium and have been since 1980, when the ﬁrst wired au-

tomation systems came on the market. However, line transmission is gradually shifting towards

wireless solutions, as evidenced by the increasing number of wireless systems on the market. The

advantages of tethered systems can be summarised as:

Noise immunity: Screened cables are robust against electromagnetic interference, which enables

fast and reliable data transmission.

Power feeding: Devices can be supplied with power via cable, involving beneﬁts in cost and size.

The main drawbacks of wired systems are the inﬂexibility and the resulting burdensome retroﬁtting

of new devices. Consequently, new customers often choose wireless-based solutions for equipping

already existing buildings. However, tethered system can be integrated into new constructions with

little eﬀort, which can lead to a more reliable and secure solution than comparable wireless systems.

Examples of wired bus systems are: LAN, CAN, KNX, USB and power-line-communication (PLC).

2.2.4. Example Systems

In this section, some selected systems for home and building automation are introduced in order

to give a brief overview of current technologies.

X10

X10 is an open communication standard for power line based home automation systems. It was

developed in 1975 by the Scottish company Pico Electronics [8], with the aim of enabling the

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