AU-KBC RESEARCH CENTRE
Measurements, Modeling and Characterization
The Objective of the measurements
and characterization of the power line channels is to have a thorough understanding
of the complex channel characteristics, and to develop a statistical channel
model. In this work wideband characterization of channel transfer characteristics
up to 20 MHz over out door channel (230 V), up to 50 MHz over indoor channel
( 230 V), and broadband noise characteristics up to 30 MHz had been carried
out. Two types of measurements are performed to obtain the channel characteristics
they are 1) Transmission measurements 2) Noise measurements.
Transmission measurements are performed using a) Swept frequency method (frequency domain), b) Impulse channel sounding method (time domain). Swept frequency measurements indicates that, powerline channel is a frequency selective medium, having high attenuation levels approximately 60 dB over a distance of 200m. Impulse channel sounding measurements indicates that, powerline channel is a multipath environment having a rms delay spread of 200ns, resulting in a data rates of 2.5 Mbps over a outdoor campus network. It also indicates that multipath structure is time and location dependent. Statistical characterization of short-term fluctuations (amplitude) indicates that, the powerline channel is a lognormal fading channel. Unlike in wireless environment, the channel characteristics vary very slowly compared to typical symbol duration, representing a slow fading channel.
Generally powerline noise can be categorized into four types a) Background noise b) Impulsive noise c) Narrow band noise d) Harmonic noise. In the present work noise measurements had been carried out both in frequency and time domains. The main purpose of these measurements is to develop simple analytical models, and to generate the correspondig time domain equivalents for the above-mentioned noise.
Background noise present over the powerline channel all the time and mainly occurs due to the distribution transformer, public lighting system, and distant loads. Conducted measurements indicates that, background noise decreases with increasing frequency and is observed that at many locations this noise level is more below 5MHz compared to the rest of the spectrum.
Impulse noise occurs mainly due to switching on/off of loads and lightening. Impulse noise measurements indicates that, impulses generated due to switching transients on the network have duration of some microseconds to few msec, and amplitudes of the order of few volts (1V-10V) are quite common. Narrow band noise mainly occurs due to MW (300KHz-3MHz) and SW (3MHz-30MHz) radio broadcasting signals that are radiated on to the power line, and also due to switched power supply that produces periodic line spectrum. Normally narrow band noise amplitudes are 10-30 dB above the background noise level in their respective bands.
In the present work narrow band noise measurements over a frequency range of 500 KHz-30 MHz were carried out. It is observed from conducted measurements that the narrow bands of noise are spread all over the frequency range. Harmonic noise normally occurs due to power supplies operating in synchronous with mains supply, and also due to SMPS that normally have repetition rate in between 15KHz to 200 kHz. Powerline noise shows time and location dependency, a variation of 15 - 25 dB is quite common from peak load to normal load conditions.