2 Smart home control system architecture
2.3 Communication network

Communications network provides connectivity between devices under control, sensors and actuators on the one side and controllers, including remote control on the other side. Currently, the networks can be divided into three main categories, according to the transmission medium in the process:

  • communication through the supply network
  • communication via wired network
  • communication via wireless network

Communication through the supply network

It is based on the principle of using electrical installation of a flat. The signal transmission is at the level of 20 kHz to 100 MHz. Standard, which until recently dominated in this area was X.10, later replaced by HomePlug. HomePlug entered into force in 2010 (IEEE 1901). His recent version - AV2 - help to achieve data transfer rates up to 500MB/s.

The great advantage of this type of communication is the possibility of using the existing electricity grid in the apartment.

The disadvantage can be the actual phase separation and the presence of the electrometer in the electrical system, which prevents transmission of data signals.

Communication via wired network

In this area two open standards are known - KNX and LON. KNX is a European (EN50090, 2003) and international (ISO / IEC 14543-3, 2006) standard for home automation and building automation. This is an abbreviation from the name Konnex. This standard replaces the older European standards EIB (European Installation Bus), Batibus (used primarily in France) and EHS (European Home Systems).

LON stands for Local Operating Network, originally introduced in 1990 and later in 2008 as ISO/IEC 14908 as a solution for automation in industrial buildings, airports, stadiums and street lighting.

Compared KNX and LON, Local Operating Network architecture uses decentralized management. For large installations, the management and can avoid a central control point, which is important particularly for public installations with high demands on availability.

Communication via wireless network

Today there are more technologies that allow wireless transmission for both the home automation and building automation.

Transmission speeds, frequency and modulations used for each technology are different. An important distinguishing criterion can be the way how to power sensors, or battery life supplying independent sensor. The table below summarizes the wireless technology used in home automation [2].

Wireless technologies used in home automation

EnOcean

Z-Wave or KNX-RF

ZigBee (802.15.4)

ZigBee (802.15.4)

Bluetooth (802.15.1)

WLAN (802.11)

Frequency

868

868

868

2400

2400

2400

Data rate (kbit/s)

125

30

20

250

720

11000-54000-100000

Range (indoor/outdoor in meters)

30/300

9.6/20

30/500

30/500

10/100

20/50

Energy needed

extremely low

low

low

low

medium

high

Risk of data colison

very low

medium

medium

low

very low

high

In the building management was the use of wireless sensors always the second option, particularly in existing buildings. But the existence of new standards using very low power consumption of power supply gradually changes this situation.

Wireless interfaces such as Z-Wave, ZigBee, BLE (Bluetooth Low Energy) and RFID (Radio-frequency identification) is now being progressively integrated into power outlets, lighting controls, and household appliances. The same goes for audio and video electronics, where the WLAN (WiFi) module is part of the device, ready to stream multimedia content directly from the Internet, with possibility to be fully controlled via smartphones. A new generation of wireless technology is the standard EnOcean, able to communicate on a wireless line through energy from light or temperature changes in the environment or through energy recovery from mechanical switching lighting controls.

The control system (controller)

Under the controller is meant a control device that acts as a "brain" in the whole home automation system. Into this unit are directed information collected by sensors and vice versa sensor receives control commands. Under orders for sensors is meant for example setting the level at which the sensor send messages, etc. Mostly, the sensor is unit that unidirectional sends collected information to the control unit where are evaluated. Based on predefined rules, control unit sends a command to the appropriate actuator that performs the desired action. The role of this component in the whole architecture is also texting, e-mailing or sending notification directly to the control unit (via the application in the smartphone/tablet).

These units already have the standard Operating System (OS) such as Linux/Windows/OS-X, which are specially adapted for these units.

If necessary, the control units supplied Uninterruptable Power Supplies (UPS - Uninterruptable Power Supplies) or contain a battery that some time can provide independence from the main power source during a power failure.

The remote control

One of the main reasons for the growing popularity of home automation systems in the residential segment is the ability to control the entire system via smartphone or tablet, more precisely said through the applications installed on the endpoint device. Over the past few years and also nowadays the great development of new applications for households is taking place.

The terminal equipment is via WLAN (WiFi), 3G/4G (via the Internet) connected to the home system. The control setting is possible not only of the areas of the house, but also at a distance. In the past, such a remote control was realized as the connection of control unit to the telephone line.

Comparison of wireless technologies

ZigBee

ZigBee is a networking standard operating in the so called routed mode, developed by members of the ZigBee Alliance [3]. His current name was established in the 90s, the original was called "HomeRF" protocol. Ratified standard was publicly released in June 2005, as "ZigBee radio standard". This standard also defines the network security as an additional layer to the existing IEEE 802.15.4 standard [4].

ZigBee has been proposed for use in a wide range of different types of applications, starting with home automation which uses mainly battery-powered sources and ending with industrial use in the management of large objects.

IEEE 802.15.4 standard was finalized in 2003 as a Low-Rate Wireless Personal Area Network (WPAN), which includes several layers. In particular it is the so-called Direct Sequence Spread Spectrum (DSSS - Direct Sequence Spread Spectrum), Physical Radio layer (PHY) and software layer Media Access Control (MAC).

Several manufacturers of chips offer 802.15.4 as part of one integrated board with a microprocessor and 128 kilobytes of memory for ZigBee applications.

The main objectives of the ZigBee standard are:

  • wireless networking for industry management, connecting medical equipment and home automation
  • Mesh network with its own organization, without the need for a control unit, for example in the case of a failure of communication on the road. The role so called “data forwarder” from remote sensor takes over the closest sensor nearby
  • low data demands
  • low energy consumption, at least one year without battery requires recharging or replacement

ZigBee defines several types of entities or devices:

Only the FFD devices can control the routing in the mesh network. ZigBee for this purpose defines the star-structure containing RFD at the edges of the network but also the hybrid network, called cluster tree.

ZigBee 802.15.4 radio uses the 2.4 GHz frequency, in the USA it is 915 MHz and in Europe 868 MHz. The last two lower frequencies did not receive support from manufacturers operating on the market for end consumers.

Manufacturers of end devices must be members of the ZigBee Alliance.

Z-Wave

Z-Wave is just as ZigBee networking standard operating in the routed mode. The owner of the patent for this protocol is the company Sigma Design [4], which bought the patent from its creator, company ZenSys of Denmark, in 2008 [4].

This wireless communication protocol is focused primarily on applications for home automation where the main objectives are:

  • low cost solutions for standard households
  • very long battery life of powering sensors
  • easy installation which can be handled also by regular user
  • possibility to easy connect sensor to the network
  • interoperability between network devices from different manufacturers

The communication protocol of the Z-Wave technology routes messages using Source Routing Algorithm (SRA). Source routing algorithm requires from the initiator of the report (under initiator is meant device/sensor) knowledge about the layout of other sensors/devices in the network. Based on this knowledge the messages are routed always via the shortest route. Maintaining the current database and forwarding the network topology of active devices in the network is a task of complicated software device, which is also responsible for other devices that may be mobile in the area, i.e. they may change their position.

Z-Wave (Fig. 2.1) defines a different categorization of equipment because the mentioned logic can cause the price of device/sensor will be too high. Thus Z-Wave defines so called slaves (subordinate devices). Slave device cannot monitor conditions mentioned above like moving, and is therefore statically programmed to communicate with a specific device in the network. Described logic is the most important functionality of this protocol.

image
Fig. 2.1 – Z-Wave technology

Z-Wave radio networking is designed for limited quantities so called nodes, which may be up to the 232 in the network. However, producers recommend a maximum number of nodes 30 to 50, where each one communicates in an interval of 5-15 minutes.

Z-Wave reports are of variable length. Just for information, message body may have an average of 4 to 6 bytes; the latency must not exceed 200 milliseconds.

Also in case of Z-Wave the manufacturers of equipment supporting this communication protocol have to be members of the Z-Wave Alliance.

Wifi

In recent years, WiFi (IEEE 802.11) has become the standard for broadband wireless networking at homes or corporate LANs. Increasing popularity therefore addressed the home automation especially in the field of streaming media content between devices at home.

IEEE 802.11 is a standard that currently comes with several versions a, b, g and n. 802.11a is licensed for 5GHz band and is unused in facilities for ordinary households. In the sector of ordinary users are used 802.11b, g and n. Version b has communication speed 11Mb/s (megabits per second), used since 1999. The next version is g with speed 54 Mb/s, launched in 2002. Version n with speed of 100Mb/s and higher began to use in 2006. WiFi network is typically implemented in a star network topology. This is not a mesh that means, it is always a point-to-point communications.

Wifi with its transmission speeds is on the top of all wireless technologies used at home.

The big disadvantage is the high energy consumption and a complex process configuration.

In case of star topology it is important to think about the reach limits what is usually 50 to 100 m in free area. Central access point is usually controller or router to which the controller is generally connected through an Ethernet connection.

The big advantage of WiFi is that the network connections and data transport use TCP/IP protocol, which is used on the internet.

Wifi is also used to connect the IP camera in home automation. IP cameras are connected to the supply network and are independent of the battery. Transmitted data stream is stored in the home data storage at specified intervals and quality. That can be controlled by designated recording equipment, which is increasingly common in the home but now being replaced by a universal solution in the form of a WiFi access point with household data storage.

In addition to transmission the video from IP cameras, WiFi is also used to connect any media device in the home, including mobile devices and computers, among which it is possible to share multimedia content.

Bluetooth

Bluetooth is defined by The Bluetooth SIG [5] and is standardized in IEEE 802.15.1 as wireless ad-hoc point-to-point technology for Personal Area Networking PAN (Personal Area Networking).

This technology has been proposed also to achieve low demand for power, but is limited on the roughly 10-meter radius (unobstructed). Bluetooth is used mainly in mobile phones and wireless headsets, tablets and PCs, especially as a replacement for wired peripherals.

The new version of the communication technology called Bluetooth Low Energy or Bluetooth Smart brings in PAN new opportunities. The development of this technology in home automation focuses on the field closely related to eHealth, which includes the so-called Assisted Living. It can be device or equipment placed on the body or as part of subject used daily, sensing biometric characteristics of the user.

This technology is very interesting also for the manufactures of mobile devices and tablets. The newest devices and the equipment containing Bluetooth interface referred it in specifications as Bluetooth 4.0. The latest version has become part of the Bluetooth standard in 2010, officially unveiled by Nokia under the name Wibree.

Bluetooth operates in the 2.4 GHz band using frequency hopping spread spectrum FHSS (Frequency Hopping Spread Spectrum), achieves data transfer rates do 3Mb/s and PAN supports the adding of additional seven nodes.

EnOcean

EnOcean is a wireless technology, which uses the energy from the surroundings to supply sensors, i.e. converts thermal, electromagnetic or solar energy into electricity. The principle of obtaining energy allows ultra low energy to power the sensor module.

EnOcean has become a standard in 2012 (ISO / IEC 14543-3-10). This standard covers three layers of the OSI model, namely physical, link and network. The patent owner is the company EnOcean, founded as a spin-off of Siemens AG. The aim of EnOcean was to develop wireless modules that can power themselves, without the need to add battery pack.

The transmitted packets are relatively small, only 14 bytes long with a transmission rate of 125kbit/s (kilobits per second). EnOcean is in specific implementation mainly used for not data-demanding applications, or sensors which do not transmit many data. This can be specifically the light switches, movement sensors, humidity and temperature sensors etc.

EnOcean uses multiple transport frequency: 902 MHz, 928.35 MHz and 315 MHz.

This standard is mainly used in building automation, logistics and goods transport in industry. Nowadays it becomes quite popular also in the area of home automation. Again, the module manufacturer must be a member of the EnOcean Alliance.