The Internet Power Line Adapter - University of Queensland

Home Automation, Power Lines and the Internet Quenten Alick
The data rates achieved by the development boards were close to 9600 bits per
second. This figure matches fairly closely with the specifications for the CEBus
standard, which states that all command channel data should be transmitted at
10k bits per second regardless of medium.
The reliability and noise / load immunity all relate to each other. Generally, the
noise immunity was good. The testing was conducted in the Axon building,
which has many pieces of electrical equipment & computers in use at one time.
In tests it was found that the boards could communicate well across the entire
building provided that they were on the same power phase. Overall, while on the
same phase the boards achieved close to perfect data transmission.
However, when a computer was plugged into the power lines between the two
boards, the performance decreased. Computers are a special problem due to the
large capacitance in their power supply. This capacitance tends to filter out the
communications signal. When the boards used unacknowledged signals, the
reliability of transmission dropped to almost zero. However, when the boards
used the acknowledged modes, the reliability of transmission only dropped to
80-90%. This shows that using the more reliable modes, although slower, are
much more effective even when large loads are being used in the circuit.
The last sets of tests were conducted with the boards attempting to communicate
across the different power phases in the building. The results from these tests
indicated low reliability. However, it is impressive that there was any
communication at all since the phases in the building are not directly coupled.
Since some homes will use different phases for different parts of the house, it is
important that power line communications for home automation systems must
be able to communicate across phases. The normal solution for this is to directly
couple the phases. This can be done with some commercially available devices,
or more simply, a correctly rated capacitor can be connected across the two
phases. This is usually sufficient to allow communication to occur.
Unfortunately, we were unable to test this.
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