Improving Reliability

Start code

To increase the reliability, X10 chose a simple method using a tone to transmit a one or zero data bit, and uses repeatable signaling, and transmitting twice for improving reliability. To ensure that no error-message can be mistaken, then X10 protocol provides mechanisms for framing messages and rules for sending and receiving messages. To mark the start of each message, the start code will send to receiver for realization where is a bit stream starts. The start code transmitted in the sequence tone-tone-tone-no tone (1110). This code is a unique code which cannot occur within a message. From the figure below, the first waveform cycle which is consist of 2 tones is called an invalid sequence, and  the second full cycle is a valid sequence, representing only a one bit.

                                 

Detecting Error from Zero Crossing Point 

The second method of increasing reliability is detecting error from zero crossing point. Figure below shows bursts at the rising voltage zero crossing points. When the X10 signal sends the data bit, the bursts will follow along with the line phase. This is because the signal is provided error checking at the receiver on the received signal. For example, if a tone rise at zero crossing, there will not be any tone at the falling zero crossing, and vice versa. However this scheme may no error correction, it helps the receiver detect when a bit has been corrupted

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Checking Status

 X10 modules are not reliable, in the sense that they do not provide any mechanism to check if a particular command is successful. For example if an appliance is turned on using an appliance module, X10 provides no means to find out if the appliance is actually turned on. If an appliance is faulty and does not turn on in response to an “on” command, the X10 module attached to still respond to a “status” command, with status “on”. This aspect can be easily improved by adding a simple AC current sensor to the X10 module. The sensor detects the current through the device and accordingly checks the X10 to respond to the “status” command. This modification is shown in figure below.

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