Broadband over Powerlines
There are those who see PLT as a major new development that will be able to provide broadband connectivity to the masses, and those who believe that because of its potential to interfere with radio communications, PLT is a non-starter.
The fact that it seems impossible to get agreement on an international standard is perhaps not strange as the various players cannot even agree on a name for the system. It is referred to as PLC, PLT and BPL. In South Africa the official designation is PLT – power line telecommunication. There are some subtle differences that are often overlooked. BPL is broadband over power lines while PLC and PLT have a broader scope and include BPL and narrowband over power lines.
Prof. Hendrik Ferreira from the University of Johannesburg (UJ) has a pragmatic view of PLT. He heads up the Telecommunications Research Group at UJ. He says that the infrastructure for PLT, namely electrical cables and wiring has been in place for a very long time. “The medium for communications is there, we just have to exploit it in an efficient manner, minimising interference to other RF users, and emphasising the most appropriate applications – perhaps ones which can function with some latency, necessary to overcome severe channel conditions.
PLT can complement wireless communications – RF bandwidth is ultimately a limited resource – just like real estate, there is no more available. Thus far our work has mostly been focussed on narrowband power line communication working at frequencies below 150 kHz within the long standing European CENELEC standard.
Independent Communications Autority of South Africa (ICASA’s) board has been sitting on the interim regulations for the past five months after the authority held a public hearing to hear objections to the first draft of the interim regulations. CISPR had two meeting to discuss PLT standards in the past few months, one in Osaka in November and the most recent one in Cape Town a few weeks ago. The body seems far from a final standard on broadband powerline telecommunication.
There is also a common belief that too little research has gone into the technology and particularly its potential interference aspects. The South African Radio League has on several occasions criticised manufactures of broadband PLT equipment for doing too little research into the radio interference potential and for lack of transparency when carrying out trials and pilot studies.
Prof. Ferreira said that PLT is an interesting research area as there are still many unresolved issues even although integrated cirucuits and systems have been available for several years. His group is focussing on a number PLT areas using a multidisciplinary vehicle which brings together researchers from several different areas in electrical engineering. Some of the research areas include: digital communications, information theory and coding, telecommunication networks, EMC and interference, power electronics and multimedia communications.
PLT offers many interesting applications such as telemetry applications, smart grid, and demand side management, remote metering, and prepaid power and slow scan video surveillance. Other applications are emergency telemetry during load shedding or power disaster recovery scenarios which may inhibit cellular communications.
The UJ telecommunications research group works in four main areas:
Focus on making narrowband PLC very robust by combining OFDM or MFSK with error control coding. “Our past extensive research record on information theoretic coding techniques, are put to good use here. The PLT channel is a really bad channel, with the most unusual types and combinations of noise from a telecommunications point of view.”
Coupling circuits are an essential part of all PLT modems. Up to now an empirical design has mostly been employed.
Noise phenomena is an important focus area. Study through measurements, e.g. whether the widely used theoretical model for impulsive noise really applies to PLT; how noise is affected by the coupling circuit, and learning about compensating for unusual PLT noise, may also be applied to other channels.
An exciting research result in the area of telecommunications networks is the development of network coding to enhance the network throughput. How can this research be adapted to networks residing on PLT?
The National Research Foundation has sponsored a joint project between UJ and
Prof. J Vinck of the University of Duisberg – Essen in Germany. Prof. Vinck founded the annual IEEE International Symposium on Powerline Communication in 1997.
The team’s recent proposal to the German BMBF (Federal Ministry of Education and Research) proposes investigating the combination of coding and modulation for channels with non-additive white Gaussian noise. “As a practical working example, we concentrate on the power line communication channel. This study will include characterisation of the noise and the reduction of its effects by using the proper combination of coding and modulation.
The project also makes provision for the practical implementation and application of the developed coding and modulation methods in a narrowband power line communication system. Consequently, a test bench and experimental set-up will be available for future emulations. An important part of our investigations will be the investigation of the effect of coupling circuits.
Fundamental research results will be published on noise modelling, combined coding/modulation, spectral shaping coding, decoding algorithms and coupling circuit design. This project can make a contribution to providing telecommunications facilities in developing and rural communities in South Africa and elsewhere in Africa,” said Prof. Ferreira
It is encouraging that serious research in PLT is being done. In the interim the debate will continue.
Broadband over Power Lines discussion
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