Study Of OFDM Modulation Technology Based On Low-voltage Distribution Network And The Application

Low-voltage power line carrier communication (PLC) was a relatively new research direction of communication technology development, its technical research and applications became the hot topic at home and abroad, which had far-reaching theoretical significance and wide practical value. However, low-voltage power line network channel characteristics was time-varying and complexity, the transmission signals had a higher frequency-selective attenuation characteristics, so that low-voltage power line data transfer rate was limited, with the high bit error rate, In order to give full play to the potential of low-voltage power line communication, It needed to study a high spectrum efficiency, anti-noise and anti-signal attenuation capability of the transmission technology, In contrast to a variety of existing advantages and disadvantages of the transmission modulation techniques, it was an ideal solution to choose orthogonal frequency division multiplexing (OFDM) technology to achieve high-speed data transmission in low-voltage power networks, key technical issues of the noise model, transmission model, channel capacity in which was involved was researched in this paper, main works include:1,On the basis of the experimental measurement, impedance characteristics, noise characteristics and attenuation characteristics which must be faced in low-voltage power line communication were studied, calculating and analyzing the relations of channel impedance, signal attenuation to frequency, and all kinds of noise of time-domain characteristics and frequency-domain characteristics.2,According to characteristics of PLC transmission network to established the channel transmission model, experimental simulation results shown that the transmission model build was close with the actual channel characteristics; On the basis of the signal input power optimized, The impact of channel capacity was studied such factors as the branch number, the branch load as well as the branch length in the indoor and outdoor low-voltage power network.3,an adaptive estimation and Equalization Technique based on direct decision estimation method was proposed OFDM systeme of low-voltage power line channel. the sub-carrier symbol received presented a competitive neural networks in the method proposed. The method proposed self-adaptively estimates changes of weight value in the channel by the neurons of the neural networks, and then estimated the channel according to the channel of the weight values, finally achieved the channel equalization by the use of removing the nonlinearity effects to compensate the constellation symmetry.4,By optimizing the correlation coefficient to estimate the maximum likelihood, time-domain correlation and energy detection algorithm based on a data-aided loop sequence was proposed, simulation results shown that the algorithm implements the frequency offset estimation, time synchronization problems in OFDM modulation.5,A PAPR reduction algorithm was studied, it utlized pseudo-random sequence of very low non-periodic self-correlation characteristics to disturb the send sequence in the time domain, Then the sequences was splited by the adjacent in the frequency domain, the phase of the group signal was disturbed after the split, carrying the transform for the sequence disturbed through IDFT in frequency domain. It got a number of time-domain signal, finally chosen the minimum PAPR signal as the transmission signal. This algorithm simulation demonstrated its complementary cumulative distribution function(CCDF) curves drop faster, with significantly reduced OFDM signal PAPR.6,Designing a data frame format and relaying application layer protocol, and achieving a network 7 level relay function; routing algorithm marked the network communications nodes through the establishing the node of the transfer matrix, routing table algorithm was established by the concentrator collection ways which divided into single-point data collection and multi-point data collection. It realized the automatic route of the meter reading network.The paper studied systematicly a number of key issues which the OFDM modulation technology encountered, theoretical analysis and experimental results shown that the results have a certain amount of innovation.