Improving Low Voltage Distribution Line Carrier Communication Systems for Transferring Data by Applying Efficient Modulation Techniques
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Proceedings of the 7th WSEAS International Conference on CIRCUITS, SYSTEMS, ELECTRONICS, CONTROL and SIGNAL PROCESSING (CSECS'08) Improving Low Voltage Distribution Line Carrier Communication Systems for Transferring Data by Applying Efficient Modulation Techniques SHAHRAM JAVADI PARASTOO POURANG Islamic Azad University –Central Tehran Islamic Azad University –South Tehran Branch Branch Electrical Engineering Department Computer Engineering Department Moshanir Power Engineering Consultants IRAN IRAN Email: Email: [email protected] [email protected] [email protected] Abstract: Distribution Line Communications technology allows the usage of electrical power supply networks for communications purposes and, today, also broadband communication services. The main idea behind DLC is the reduction in operational costs and expenditure for realization of new telecommunications networks. Using electrical supply networks for telecommunications has also been known since the beginning of the twentieth century. Thus high-, medium- and low-voltage supply networks have been used for internal communications of electrical utilities and for the realization of remote measuring and control tasks. Generally, we can divide DLC systems into two groups: narrowband DLC allowing communications services with relatively low data rates (up to 100 kbps) and ensuring realization of various automation and control applications as well as a few voice channels, and broadband DLC systems allowing data rates beyond 2Mbps and, accordingly, realization of a number of typical telecommunications services in parallel, such as telephony and internet access. This paper discusses the various methods of modulation techniques for application of distribution line carrier (DLC) systems on medium voltage lines for the purpose of energy management and system control. Depending on the attenuation the range of the technology is up to several kilometers. Keywords: Power Distribution Networks, Power Line Carrier, Communication, Modulation Technique. I. Introduction The direct connection of the During the last decades, the usage of customers/subscribers is realized over the telecommunications systems has increased access networks, realizing access of a number rapidly. Because of a permanent necessity for of subscribers situated within a radius of several new telecommunications services and additional hundreds of meters. However, the costs for transmission capacities, there is also a need for realization, installation and maintenance of the the development of new telecommunications access networks are very high. It is usually networks and transmission technologies. From calculated that about 50% of all network the economic point of view, telecommunications investments belongs to the access area. On the promise big revenues, motivating large other hand, a longer time is needed for paying investments in this area. Therefore, there are a back the invested capital because of the large number of communications enterprises that relatively high costs of the access networks, are building up high-speed networks, ensuring calculated per connected subscriber. Therefore, the realization of various telecommunications the network providers try to realize the access services that can be used worldwide. network with possibly low costs. ISSN: 1790-5117 289 ISBN: 978-960-474-035-2 Proceedings of the 7th WSEAS International Conference on CIRCUITS, SYSTEMS, ELECTRONICS, CONTROL and SIGNAL PROCESSING (CSECS'08) After the deregulation of the telecommunications • Amplitude modulation (AM) market in a large number of countries, the access o Double-sideband modulation networks are still the property of incumbent (DSB) network providers (former monopolistic telephone companies). Because of this, the new o Single-sideband modulation network providers try to find a solution to offer (SSB, or SSB-AM), their own access network. An alternative solution o Vestigial sideband modulation for the realization of the access networks is (VSB, or VSB-AM) offered by the DLC technology using the power o Quadrature amplitude supply grids for communications. Thus, for the modulation (QAM) realization of the DLC networks, there is no need for the laying of new communications cables. • Angle modulation Therefore, application of DLC in low-voltage o Frequency modulation (FM) supply networks seems to be a cost-effective o Phase modulation (PM) solution for so-called “last mile” communications networks, belonging to the access area. 2) Digital modulation methods However, power supply networks are not designed for communications and they do not In digital modulation, an analog carrier signal is present a favorable transmission medium. Thus, modulated by a digital bit stream. Digital the DLC transmission channel is characterized by modulation methods can be considered as a large and frequency-dependent attenuation, digital-to-analog conversion, and the changing impedance and fading as well as corresponding demodulation or detection as unfavorable noise conditions. Various noise analog-to-digital conversion. The changes in the sources, acting from the supply network, due to carrier signal are chosen from a finite number different electric devices connected to the of M alternative symbols. network, and from the network environment, can negatively influence a DLC system, causing The most common digital modulation disturbances in an error-free data transmission. techniques are: On the other hand, to provide higher data rates, • Phase-shift keying (PSK): DLC networks have to operate in a frequency • Frequency-shift keying (FSK): spectrum of up to 30 MHz, which is also used by various radio services. Unfortunately, a DLC • Amplitude-shift keying (ASK) network acts as an antenna producing • on-off keying (OOK), the most common electromagnetic radiation in its environment and ASK form disturbs other services operating in the same • Quadrature amplitude modulation frequency range. (QAM) - a combination of PSK and ASK: II. Modulation Techniques Modulation is the process of varying a periodic • Continuous phase modulation (CPM) waveform, i.e. a tone, in order to use that signal methods: to convey a message. • Orthogonal frequency division multiplexing (OFDM) modulation: 1) Analog modulation methods • Wavelet modulation In analog modulation, the modulation is applied • Trellis coded modulation (TCM), also continuously in response to the analog known as trellis modulation information signal. A low-frequency message signal may be carried by an AM or FM radio 3) Spread-spectrum modulation: wave. Common analog modulation techniques are: These techniques are methods by which energy generated in a particular bandwidth is ISSN: 1790-5117 290 ISBN: 978-960-474-035-2 Proceedings of the 7th WSEAS International Conference on CIRCUITS, SYSTEMS, ELECTRONICS, CONTROL and SIGNAL PROCESSING (CSECS'08) deliberately spread in the frequency domain, Therefore, the DLC modulation must overcome resulting in a signal with a wider bandwidth. this problem without the need for a highly These techniques are used for a variety of complicated equalization. Impedance mismatch reasons, including the establishment of secure on power lines results in echo signal causing communications, increasing resistance to natural delay spread, consisting in another challenge for interference and jamming, and to prevent the modulation technique, which must detection. overcome this multi-path. The chosen Frequency-hopping spread spectrum (FHSS), modulation must offer a high flexibility in using direct-sequence spread spectrum (DSSS), time- and/or avoiding some given frequencies if these hopping spread spectrum (THSS), chirp spread are strongly disturbed or are allocated to spectrum (CSS), and combinations of these another service and therefore forbidden to be techniques are forms of spread spectrum. Each of used for DLC signals. these techniques employs pseudorandom number In this paper we have focused on two sequences, created using pseudorandom number modulation techniques that have shown good generators to determine and control the spreading performances in other difficult environment and pattern of the signal across the allotted were therefore adopted for different systems bandwidth. Ultra-wideband (UWB) is another with wide deployment. First, the Orthogonal modulation technique that accomplishes the same Frequency Division Multiplexing (OFDM), purpose, based on transmitting short duration which has been adopted for the European pulses. Wireless Ethernet standard IEEE 802.11 Digital Audio Broadcasting (DAB), the Digital uses either FHSS or DSSS in its radio interface. Subscriber Line (DSL) technology, and so on. To reduce the negative impact of distribution line Second, the spread-spectrum modulation, which transmission medium, DLC systems have to is widely used in wireless applications, offering apply efficient modulation, such as spread an adequate modulation to be applied with a spectrum and Orthogonal Frequency Division wide range of the multiple access schemes. Multiplexing (OFDM). Two important topics have been studied to III. Orthogonal Frequency Division improve the DLC performance: The first is Multiplexing related to the line couplers for low and high Orthogonal Frequency Division Multiplexing is voltage level lines [1], [2]. The second is related a special form of Multi-Carrier Modulation to the modulation techniques used for data (MCM) with densely spaced sub carriers and transmission. overlapping spectra, as shown by the OFDM The choice of the modulation