In situations where power lines exist between two devices which wish to communicate to each other, it has been recognised that the existing power lines may be used both for power transmission and communications, thereby avoiding the need to install separate communication cabling. In the past, this has been achieved by way of high speed power line modems, which are capable of connecting to the power line and inserting a carrier signal onto the power lines and additional to the power signal, and modulating the carrier signal with information to be transmitted. However, the circuitry of such modems must be able to withstand the large power levels present on the power lines, and the cost of such modems is usually significantly higher than standard modems which can be used where dedicated communications cabling is available, thereby offsetting some of the cost savings in using only a single line for both power and communications. Furthermore, devices connected to the power line are often quite simple in nature and consequently the required rate of communications will be extremely low, as only relatively small amounts of information need to be transmitted. In such situations, the high speed and high cost of a power line modem will go substantially unutilised.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.