M-FSK Carrier Gain Adjustment for Improved Power-Line Communications

This paper describes carrier gain adjustment (CGA) in the CENELEC A-band, a counter-measure against the negative impact of a transmitter coupling circuit´s filter characteristic in this band. As the CENELEC A-band lies very close to the power waveform frequency, a steep -40 dB/decade coupler filtering slope is present in the lower parts of this band. Therefore, different symbol carriers (of different frequencies) are exposed to different attenuation factors. With linear amplification, only the least attenuated carrier can be amplified to the maximum level allowed by regulations, whilst the other carriers will be transmitted below the maximum level. Conversely, all carriers are exposed to similar noise levels, present on the power-line. CGA however, counters the unequal attenuation effect of the transmitter coupling circuit, by amplifying all carriers to an equal, maximum amplitude. As carrier gain adjustment is directly linked to the frequency response of the transmitter coupling circuit, this coupler needs to be characterized before implementing CGA. As measuring rod for this study, the performance of orthogonal M-ary frequency shift keying without coding, in the presence of white noise, is used. Results show that under the above conditions, carrier gain adjustment proves successful in equalizing the attenuating effect of the transmitter coupling circuit, thereby improving overall performance.