Modems of DPLC Equipment
This chapter considers the DPLC equipment as the digital transmission system with characteristics adapted to work along high-voltage power lines. It observes what technologies and methods of digital modulation, encoding, channel equalization and echo canc
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Modems of DPLC Equipment
2.1 D PLC Equipment as a Digital Transmission System: Shannon’s Limit Theoretical foundations of digital communication were laid in the 20–30s of the twentieth century by R. Hartley [10], G. Nyquist [22], K. Shannon [27], and V. A. Kotel’nikov [15] who proved the basic theorems of information theory. Modern digital transmission systems are well-described in the books by B. Sklyar, D. Prokis, and L. Hanzo [9, 26, 28]. Figure 2.1 shows structure of DPLC equipment as a classic digital transmission system. Detailed information about the principles of DTS design and technologies is presented in [9]. Such digital transmission system includes information sources, source encoders, multiplexer, channel encoder, modulator, communication line, channel decoder, demultiplexer, source decoders, and information receivers. Various devices for collecting and transmitting information which output and input signal has a digital form (Fig. 2.2) and use two-level or three-level encoding at the physical level can also be sources and receivers of the signal. Examples are RS-232, E1, and Ethernet digital interfaces. The following codes are applied: NRZ (No Return to Zero), RZ (Return to Zero), Manchester encoding, HDB3 (high- density bipolar code), etc. Multiplexer combines several incoming information signals into one aggregated signal intended for channel encoding in the encoder. Demultiplexer performs the reverse conversion, accordingly. Channel encoder and decoder are used to increase noise immunity of the DPLC. When decoding information, error correcting encoding allows detecting and correction of a certain number of errors by adding redundancy to the source code combination.
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 A. G. Merkulov et al., High Voltage Digital Power Line Carrier Channels, https://doi.org/10.1007/978-3-030-58365-1_2
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2 Modems of DPLC Equipment
Fig. 2.1 DPLC equipment as a digital transmission system
Fig. 2.2 Sampling and quantization of analog signal
Adding redundancy to the original message inevitably increases requirements to DPLC bit rate. For example, when using code with an encoding rate of 1/2, each bit of the original data code sequence is encoded with two bits, and, accordingly, amount of data transmitted to the line is doubled, and bit rate required is doubled. Error correcting codes are divided into two main classes: continuous and block codes. Continuous convolutional codes perform sequential processing of small fragments of input information. Block cyclic codes do not operate with individual bits, but with blocks, i.e., groups of bits, some codes operate with bytes (octets) of information. Convolutional codes are good at correcting single errors caused by noise, but they are not good at dealing with error packets which occur, for example, due to pulse interference. Cyclic codes, on the other hand, can correct packets of errors
2.1 DPLC Equipment as a Digital Transmission System: Shan
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