For many years, we  have sought to exploit the ubiquitous electrical power Line network as a means for high speed data communications. As we turn to increasingly hostile media to meet mankind's veracious technological appetite for communication, we must continue to develop ever more ingenious technological tools. The existing power line infrastructure is growing in importance as a commercially viable, low cost option and communication researchers are well motivated in this field.

Throughout the world, close collaboration with industry is helping to deepen our understanding of the digital power line environment. We began this work in 1995 at Lancaster University  in parallel with Essen University in Germany, by modelling channel characteristics, exploring different modulation schemes and novel modem technology.

Our common  project goals  with Essen were:

• The development of power line communications and power line control as a cost effective and rapid mechanism for delivering communication and control services

• To determine the best  mix of hard and software to support infrastructure development for particular applications using power line communication            

•  Building a demonstrator for an audio application on the basis of programmable hardware.

At what rates can we use the 220 V power lines for communications?

We estimated the capacity to be about 1 Mbit/sec for the CENELEC band 9-94 kHz. The power-line communication channel is one of the practical channels where Shannon theory partly gives an answer to the question about channel capacity. From measurements it followed that the logarithm of the noise power spectral density is a linear decreasing function of the frequency. We could apply the "water-filling" arguments to show that the channel can be used at a data rate of about 1 Mbit/sec. on a bandwidth of 100 kHz. In practice it means that most of the power should go to the higher frequency region. We presented these results on the "2nd International Symposium on Power-Line Communications and its Applications" in Japan.

What kind of modulation and coding is suitable for the 220V channel?

Modulation schemes with a constant envelope signal modulation such as binary-FSK and M-ary FSK are in agreement with the CENELEC norms, EN 50065.1, part 6.3.2. In our research at that moment we focused on the low frequency range below 150 kHz.  In this region, there are several channel characteristics like attenuation, permanent frequency disturbances and impulsive noise that need special attention.
The main goal was to show that a combination of M-ary FSK modulation and coding can provide for a constant envelope modulation signal, frequency spreading to avoid bad parts of the frequency spectrum, and time spreading to facilitate correction of frequency disturbances and impulse noise simultaneously. A transmission scheme combining 4-FSK modulation with diversity and coding can make the transmission over power lines robust against permanent frequency disturbances and impulse noise.

We suggest simple non-coherent detection and derive the corresponding error correcting capabilities of the scheme. Since we use 4-FSK, the scheme is in agreement with the existing CENELEC norms. The scheme can be considered as a form of coded Frequency Hopping