Alternatives to ZigBee - Part 1

Project May 19th, 2008

Current alternatives to ZigBee in the home automation market are divided into two broad groups – those that are wired, which includes powerline and other cables, and those that are wireless. The main wired technologies include X10, CEBus and LonWorks. Wireless technologies that compete directly with ZigBee are Z-Wave and Insteon. All of these are explained below.

X10

The story of X10 is that its developers tried 9 experiments that failed. They made a breakthrough on the tenth and so experiment 10, or X10, was born. X10 is a protocol that allows devices to communicate with each other over existing 110V wiring in a house.

There are 3 device groups: Transmitters, receivers and transmitter/receivers (2 Way X10 devices). Each device has an address. The transmitter devices send a coded low voltage signal that is superimposed over the 110VAC current. Any receiver device plugged into the household 110V power supply will see this signal but will only respond if the signal has its address.

Benefits

A major benefit of X10 is that it uses existing wiring in the home - no new wiring is necessary. This saves on cost and allows for both new and existing homes to be automated.

Up to 256 different addresses are available. This means that you can have 256 devices in the home. This can also be a limitation.

Limitations

X10 is restricted to countries using 110V. A user can attempt to modify X10 products but this can be costly and time consuming.

A disadvantage of using powerlines is that electrical noise or simultaneous sending of codes means that some codes may not be received. Also, there is a slight delay from the time a code is sent and when the code is received and acted upon. This is due to its unidirectional broadcast mode When speed and reliability are necessary X10 may not be the best solution.

CEBus

CEBus stands for Consumer Electronic Bus. The standard was released in 1992 by engineers representing international companies that were members of the Electronics Industry Alliance (EIA). It defines protocols for how to make products communicate through powerlines wires, low voltage twisted pairs, coax, infrared, RF, and fiber optics.

The CEBus powerlines standard works in bursts to represent a digit 1 or a digit 0.

A burst is called a ‘superior’ state and the absence of a burst is called an ‘inferior’ state. Each burst starts at 100 kHz and increases, linearly, to 400 kHz during a 100 microsecond duration. A digit 1 is created by an inferior or superior state that lasts 100 microseconds, and a digit 0 is created by an inferior or superior state that lasts 200 microseconds. This means that the transmission rate is variable, depending upon how many of the characters are 1’s and how many are 0’s. The average data rate is 7.5kbps.

The CEBus transmissions are based on strings, or packets, of data that vary in length. The minimum packet size is 64 bits and, at the average rate of 7.5kbps, will take about 8.5ms to be transmitted and received.

Benefits

A major benefit of CEBus is that it uses existing wiring in the home - no new wiring is necessary. This saves on cost and allows for both new and existing homes to be automated.

Device addresses are set in hardware and include 4 billion possibilities, so there are almost a limitless number of devices on the network.

The standard is an open standard, allowing for vendors to easily manufacture products and therefore there is greater choice for the consumer.

Limitations

A disadvantage of using powerlines is that electrical noise means that some codes are not received.

It has a very low data rate – 60bps.

LonWorks

Echelon was founded in 1988 and they supply the LonWorks technology which is for building, industrial, and home automation networking. The LonWorks technology became a standard known as EIA - 709 for integrated home systems.

LonWork nodes on the network communicate with each other via a LonTalk protocol, which is implemented in the firmware of a Neuron chip. The Neuron chip is actually three 8-bit inline processors in one. Two are optimized for executing the protocol, leaving the third for the node’s application. The Neuron chip is a trademark of Echelon Corporation.

The LonTalk Protocol is designed to follow the International Organization for Standardization (ISO) standard Open Systems Interconnection (OSI) Reference Model, which includes a full set of protocol features, and classifies them according to seven functional categories known as layers, thus the seven layer OSI model.

Benefits

Both powerlines transmission and other physical media transmission (twisted pair) are available with LonWorks. Different transceivers are required for each.

In May 1994, the LonMark Interoperability Association was formed by 36 companies and currently has over 300 members. The LonMark logo is an indicator that a product has completed the conformance tests and has been designed to interoperate across a LonWorks network. This interoperability allows for greater flexibility for both users and manufacturers.