decoding_steg_add_tab.zip_Tabú_loadupo_matlab_speak recognition

In the past several years, the demand for broadband multimedia applications has significantly increased and continues to grow at a rapid pace. Power-line Communication (PLC) is a type of communication using power-line in which modulated radio-frequency signals are transmitted. Thanks to recent advances in digital communications technology, it is becoming possible to achieve communications speeds in excess of 100Mbps. The potential implementation of PLC, with the main focus on Internet access, is being studied in various European and Asian countries as well as in the United States, and huge markets have begun forming. Power lines were originally devised to transmit electric power from a small number of sources (the generators) to a large number of sinks (the consumers) in the frequency range of 50-60 Hz. It is a fact that power transmission towers and lines are some of the most robust structures ever built. Historically, the PLC technology has very limited applications but now we are witnessing the possibility of it being acclaimed universally as a prime mode of long-haul data communication.[1] With the inevitable arrival of broadband access, the demand for sending digital voice, video and Internet data within the home increases continuously. While retrofitting the houses and neighborhoods with special wires is one option, it is expensive and time consuming. PLC Technology allows the use of the existing and widespread power distribution infrastructure to provide high speed networking capabilities along with many other benefits. The basic principle of power-line communications (PLC) is to use the existing electrical power-line networks for telecommunication purposes. Over the years, power-line networks have served as a medium of transmission and distribution of electricity signals. Until recently, communication over power lines was restricted to low-speed functions such as remote metering and operations management that serve the needs of power supply utilities. This limited scope of power-line functions changed recently, on account of the tremendous demand for high-speed broadband multimedia communications. PLC exploits already-existing electrical networks to deliver high-speed broadband communications. In addition to solving the last-mile connectivity issue, PLC uses the in-building electrical wiring as a local area network providing high-speed networking that includes broadband Internet access, voice over IP and home entertainment services to virtually every power socket in residential or business premises. The driving advantage of PLC is that it uses an infrastructure that is much more ubiquitous than any other wired infrastructure, hence does not require new wiring.[2] 2. History of Power-Line Communications The early history of power-line communications is introduced in (Brown, 1999). According to (Brown, 1999), the idea of using power lines for signalling is old. In 1838, Edward Davy proposed remote electricity supply metering for the purpose of checking the voltage levels of batteries at unmanned sites in the London–Liverpool telegraph system (Fahie, 1883). In 1897, Joseph Routin and C. E. L. Brown patented their power-line signalling electricity meter in Great Britain (Routin, 1897). Chester Thoradson from Chicago patented his system for remote reading of electricity meters in 1905 (Thoradson, 1905). Thoradson’s system used an additional wire for signalling, which, however, was not taken into use because the commercial benefits of the system were insufficient. The carrier frequency transmission (CTS) of voice over high voltage transmission networks began in the 1920’s. The extensive network offered a bi-directional communications channel e.g.[3] between transformer stations and power plants. It was important for management and monitoring purposes, because there was no full-coverage of telephone network at the beginning of electrification. Due to the favorable transmission characteristics, low noise levels and relatively high carrier frequencies (15 kHz – 500 kHz), the maximum distance between transmitter and receiver could be even 900 kilo-metres with a transmit power of 10 W (Dostert, 2001). First, only voice was transmitted and amplitude modulation (AM) was used in transmission, as carrier frequency transmission was brought into use. Later, telemetering and telecontrolling functions were implemented. Simultaneously with the carrier frequency transmission over high voltage networks, the ripple carrier signalling (RCS) was implemented for medium and low voltage distribution networks. According to (Dostert, 2001), the first practical applications of RCS systems constructed in Germany were the Telenerg project by Siemens in Potsdam in 1930 and Transkommando constructed by AEG in Magdeburg and Stuttgart in 1935. RCS systems were primarily meant for load management functions e.g. switching heating on/off. Contrary to CTS, the data transfer of RCS was unidirectional. The RCS operated at low carrier frequencies about 125-3000 Hz. Due to the low frequency, the injected carrier signal propagated with minor losses in the medium and the low voltage distribution networks and passed through the distribution transformers. 14 However, at low carrier frequency, the input impedance of the distribution network was also low. Thus, the RCS transmitter required enormous transmit power. Transmit powers between 10 and 100 kW were commonly used. From the very beginning, RCS was used to transmit digital information. The modulation methods amplitude shift keying (ASK) and frequency shift keying (FSK) were mainly used in modulation because of their simplicity of implementation. Due to the low carrier frequency and simple narrowband modulation methods, the data rates of RCS systems were also low.[4] The next generation devices meant for load management in medium and low voltage distribution networks were based on more effective modulation methods providing higher data transfer rates. The transmit power decreased and some of the systems supported bi-directional data transfer. The decrease in transmit power was reached by increasing the frequency of the carrier signal and using more sophisticated communication electronics. An example of this kind of system is Enermet MELKO, which was published in 1984 (Figure 1). It provided a data transfer rate of 50 bits/s and was capable of transferring bi-directional data in medium and low voltage distribution networks between substation and measurement and control units. The frequency band 3025-4825 Hz and PSK (phase shift keying) modulation was used in data transmission (Pitk?nen, 1991). The main functions supported by the MELKO system are remote meter reading and load management. Due to the low frequency, the carrier signal passes through the low voltage distribution transformers. The MELKO systems are still used in Finnish distribution companies. Corresponding systems for distribution network companies are: ABB DLC-M and RMS Power-Net. They use carrier frequencies ranging from 10 kHz to100 kHz. Thus, the required transmit power is lower than with MELKO and distribution transformers have to be bypassed. The Melko systems are commonly used in Finnish distribution companies. The invention of integrated circuits in 1958-59 by Jack Kilby from Texas Instruments and Robert Noyce from Fairchild Semiconductor and the invention of microprocessor in 1971 by Ted Hoff at Intel launched the development of low-cost integrated circuits for power-line communications. In consequence of the advancements in modulation techniques, in processing capacity and in error control in 1980’s, the data transfer capacity of the integrated circuits for power-line communications improved significantly. The first low-cost power-line data transfer module for domestic use was published by Pico Electronics. The developed product was named “Experiment #10” or abbreviated X-10. The sale of these X-10 modules started in 1979. The