Important Technical Parameters in PLC Communication
Noise on Residential Power Circuit (RPC):
A variety of noises may occur during the communication caused by the home appliances. Following are some of the types:
1. Noise synchronous to the power system frequency (50Hz or 60 Hz) – This type of noise is generated because of different kind of switching devices.
2. Noise with a smooth spectrum – The sources of such type of noise are the appliances that are not operating synchronously with the power line frequency. For example the small motors with several windings can generate such type of noise.
3. Single Event Impulse Noise – Switching of devices, that contain a capacitor, generates such type of noise. The reason is sudden discharge of the capacitor in the RPC.
4. Periodic Noise – The type of noise is generated by fluorescent lights, television receivers etc.
These are some ways to reduce the noise in between the communication over power lines:
a. Implementation of Forward Error Correction (FEC) codes with interleaving can reduce the noise in category 1, 2 and 3.
b. Frequency Hopping with the FEC coding can be implemented to deal with the unknown frequencies.
c. While modulating the signal on to the power lines, television line frequencies should be avoided.
Signal to Noise Ratio:
Signal to Noise Ratio (SNR) is a measurement of quality of the signal. It indicates the amount of the noise in a signal. SNR can be formulated in the following way:
SNR = Received Power / Noise Power
Increasing SNR means increasing the performance of the communication system. By applying noise filters on household appliances, the noise entering into the power system can be reduced. However it will increase the cost of the appliances but is a better solution to improve overall performance.
Signal attenuation is basically the reduction in strength of the signal. A signal attenuation of about 100dB/Km occurs for low voltage power lines and 10dB/km for high voltage lines. It creates a need of continuous repeaters over a fixed distance. A number of factors that are responsible for signal attenuation include distance, time, frequency of the signal, etc.