1.

1 Introduction
The low ‘media cost’ for power line communication (PLC) technology renders it suitable for
home and industry automation purposes. PLC uses an infrastructure already existing in every
home and industrial facility, which eliminates the unnecessary expense and the difficulties of
installing new wires for achieving high signal penetration. This enables a plug and play type
use of PLC-enabled systems. In this chapter, an overview of PLC-based home and industry
automation systems with interesting application examples is presented.

1.2 Home and Industry Automation Using PLC

Home and industry automation is a main part of modern life that helps to control and monitor
the large variety of home and industry devices such as air-condition, refrigeration or lighting
systems. In addition to the functionality and comfort these systems provide, they also help to
improve energy efficiency of appliances and other electrical devices. The fast development of
communication technologies has spurred the integration of automation systems into cyber-
physical networks which enables managing these systems remotely, but on the other hand
calls for improved measures to ensure security and also privacy.

PLC provides a large range of communication frequencies and systems are broadly classified
into two categories. Narrowband PLC is used mainly for automation in a general sense, and
broadband PLC enables home networking (multimedia) applications. A large number of
home and industry automation solutions based on PLC are now available [1]. Figure 1.1
illustrates the connection of appliances, sensors and controllers via power lines in a home
automation setting.

Figure 1.1 Illustration of home automation based on PLC.

Sensors like light, temperature and smoke sensors are deployed in every room of a modern
home and their signals are sent through a communication interface such as Ethernet, RS232,
etc. to the control unit, which is a central unit in a home automation system that records
data and determines the required commands and sends them to actuator and regulators to
switch appliances on and off. Appliances like air-condition units with thermostat and washing
machines are also directly connected to actuators and switched off according to demand
response notifications from the communication interface during peak times and cut off from
the power board when unused. Central control units usually provide a friendly graphical user
interface (GUI) for end users with a screen and keyboard to manage the system. The sensors,
control unit(s), appliances and actuators are connected to each other via a communication
channel, which in the case of PLC are the existing power lines.
Before the recent narrowband PLC standardizations such as IEEE 1901.2 and ITU-T G.990x,
only relatively few companies developed and provided power line modem chip-sets and a
limited number of applications reached quantities that allowed the development of individual
chip-sets. The X10, KNX PL 110 and LONWorks systems are fairly representative of the used
physical (PHY) layer technologies. In addition, three other systems, which are little known
in the scientific community, will be discussed in this chapter. The first is an ISO standard
for PLC on refrigeration container ships, which implements two PHY layers with frequency
separation to simultaneously use the power lines. The second system is based on a published
specification of a proprietary smart metering system, which is already in use by utilities. The
selected approach for the same application is completely different from IEEE 1901.2 or ITU-T
G.990x (see Chapter 9). The third system uses a PHY layer that enables very small form-factor
modems without a coupling capacitor or transformer. A brief overview of these PLC systems
for home and industry automation is presented in Table 1.1.

1.3 Popular Home Automation Protocols

Many popular home and building automation system protocols have been developed some
time ago. In the following, we present a brief overview of important such protocols.

7.3.1 X10 Protocol

X10 is a narrowband PLC protocol for communication between electronic equipment for home
automation. The X10 protocol delivers signals among transmitters and receivers over the house
electrical wiring.

Table 1.1 Overview of PLC home and industrial automation standards.

These signals are short radio frequency (RF) bursts that repre- sent the transmitted
information and control the electrical devices, such as lighting systems and audio/video
equipment. X10 was developed in 1975 by Pico Electronics of Glenrothes, Scotland, and is
also known as domotics network technology. It remains the most popular technology
available for home automation systems because of the millions of installed units worldwide,
and the low price of new units.

1.3.11 X10 Physical Layer Specification and Transmission

X10 transmissions are synchronized to the zero crossing point of the AC power line. The
transmission bursts should be done as close to the zero crossing point as possible from
negative to positive of the power signal, within 200 microseconds of the zero crossing point.
Bursts are 120 kHz signals of 1 ms duration. The presence of a burst represents a ‘1’, while
the absence of a burst means ‘0’. Except for the Start Code (see below) binary information is
encoded into burst pairs. That means, a binary ‘1’ is transmitted as the presence of a pulse in
one half cycle followed by no pulse in the next half cycle. A binary ‘0’ is transmitted as the
absence of a pulse, immediately followed by the presence of a pulse. In three-phase systems,
the burst is sent three times, to reach the zero crossing point of each phase. Figure 1.2 shows
the timing of the X10 signals in a 60 Hz system. Timing the signal at the zero crossings
simplifies the receivers, by reading only from the power line for a short time after it detected a
zero crossing point. Since the system only transmits one bit per cycle of the carrier, the raw
signaling bit rate of the X10 system is 60 bps [2].
A complete code transmission includes eleven cycles of the power line. The first two cycles
represent a Start Code. The next four cycles represent the House Code and the last five cycles
represent either the Number Code (1 through 16) or a Function Code (On, Off, etc.). This
complete block, (Start Code, House Code, Key Code) should always be transmitted in groups
of 2 with 3 power line cycles between each group of 2 codes, as shown in Figure 1.3.

Figure 1.2 X10 transmission timing.

 Figure 1.3 X10 coding and transmission. Numbers are mains cycles.

1.3.1.2 X10 Limitations

The most common problem of X10 is the large attenuation of signals between the two live
conductors in the 3-wire 120/240 volt system that is used in North America because of the
high impedance of the distribution transformer winding between the live conductors. This
problem could be overcome by installing a capacitor between the leg wires as a path for the
X10 signals. Furthermore, a bare uninsulated wire is used for the ground connection. If the
sender is connected to phase 1 and the receiver is connected to phase 2, the signal would
sometimes be so poor that the X10 units would react intermittently. The X10 protocol is also
slow and takes three quarters of a second to transmit an electronic device address and a
command.

1.3.2 KNX/EIB PL 110 Standard

KNX/EIB is an open standard used in home and building automation bus systems. The
standard is based on the OSI network communication protocol of EIB but amended with the
physical layers, configuration modes and application experience of BatiBUS and European
Home Systems (EHS). It is optimized for low-speed control applications like lighting
systems. KNX/EIB is specified over various physical media, including power line (KNX PL
110), twisted pair, radio, infrared and Ethernet, and designed to be independent of any
particular hardware platform [3].

1.3.2.1 KNX PL 110 Physical and Data Link Layer Specification

The KNX standard provides the possibility for developers to select between several physical
layers, or to combine them. The KNX PL 110 enables communication over the power lines.
The main communication characteristics are spread frequency-shift keying (FSK) signaling,
asynchronous transmission of data packets and half duplex bi-directional communication. It
uses a center frequency of 110 kHz and the rate is 1200 bit/s, which corresponds to a bit
duration of 833 μs. The frequency for transmission a logical ‘0’ is 105.2 kHz ± 100 ppm and
the frequency for transmission a logical ‘1’ is 115.2 kHz ± 100 ppm. The transmission starts
at the mains zero crossing with a maximum level of 122 dBμV according to EN 50065-1 [3].
Each telegram starts with a 4-bit training sequence and a 16-bit preamble. The training
sequence enables the receivers to adjust their reception to the network conditions. The
preamble field has two purposes. First, it marks the start of the transmission and second, it
controls the bus access. All frame information, except training sequence and preamble, is
coded into 12-bit characters which allows correcting any two bits in the transmitted character
as shown in Figure 1.4.