Mitigating EMI of Powerline Communications Using Carrier-less UWB Pulses
Powerline communications (PLC) is the technology that utilizes the electric network for broad band data communications on a frequency band up to 30 MHz. It is becoming a competing technology to other technologies for Home-networking and for “last-mile” access networking. It is also a basis for tomorrow’s ICT based E-energy. Electric socket outlets inside buildings, for example, can be used not only as outlets for the 50 Hz electric energy, but also as communication nodes for a LAN that can be realized over the electric network of the building. This saves both cost and inconveniences related to new cabling inside existing buildings. The PLC, however, is not without a challenge. The standard telecommunication cables, such as UTP, are for point-to-point links and have twisted pairs of wires which provide the minimum possible emission from the cables and the maximum possible immunity to the cables from external disturbance sources. In contrary, the PLC cables have many branches and the slight twisting is only for mechanical reasons. PLC cables are generally branched parallel-wire cables which, unfortunately, create a condition for both conducted and radiated interferences. Additionally, as a “new comer” to the competition of broadband technology, PLC is faced with different national and international emission and immunity limit lines that had been already established taking in to account the condition of standard telecommunication cables. As any other OFDM-realizations, the current PLC technology takes care of the issue of EMI by notching out sub-carriers to avoid interferences to other systems or when interferences from other systems are detected. For current (and future) PLC modems with PHY data rate of 200 Mbps (and beyond) notching out sub-carriers does adversely affect the data rate and hence may not always be a preference. FCC defines UWB as a signal with either a 500 MHz signal bandwidth or a 20% Fractional BW. These signals are characterized by high data rates, low interference levels and improved immunity. Since the introduction of the UWB technology, however, it has been widely implemented for wireless applications with the 500 MHz requirement due to the assignment of the 3.1 GHz to 10.6 GHz band without requiring any license. The basics behind the UWB technology which is thought to have evolved from classical high-power pulse transmissions for radar applications is based on exploiting the advantage of a wider BW that comes from transmission of a narrow pulse. An increased BW proportionally decreases signal Power Spectral Density (PSD) without compromising the total signal power. Viewed from EMI perspective, it is the signal PSD, and not the total power that is proportionally related to the interference levels (both conducted and radiated). Therefore, in this Dissertation (1) The possibility of transmitting and receiving carrier-less UWB signals has been investigated. The widths of the second derivative Gaussian pulses transmitted are adjusted to occupy the 1-30 MHz band of operation of the PLC channel with the Fractional BW requirement. (2) Both conducted and radiated Interferences from the carrier-less pulses have been theoretically analyzed and experimentally verified. The levels of interferences are then compared to interferences from carrier-based transmissions of same data rate. Results discussed in the Dissertation show a decrease in interferences by at least 15 dB by using carrier-less UWB pulses instead of carrier-based transmissions over the PLC band of frequency.