Part Of The Key Technologies Of Ofdm-based Powerline Communications In The Study

PLC (Power line communication) uses the existed power line network as an information transmission media. For the wide spreading of power line network, we need not to rebuild a new communication infrastructure. For its low costing and easy connecting, it is attracting more and more attention.The communication channel is the basis for communication. As it is with the wireless communication, the performance of power line communication is also constrained by the power line channel. We have to use some complicated signal processing methods to combat with it, such as channel coding,adaptive modulation and demodulation and coherent detection and so on. All of these techniques require that the transmitter have to know the channel state information.The orthogonal frequency division multiplexing (OFDM) technique can combat with the frequency selective fading,multi-path delay and with higher frequency efficiency. This technique can also combat with the horrible noise in power line channel; we can use this technique to realize the high speed and reliable data transmission. This article gives a basic idea about adaptive OFDM modulation and demodulation.First we introduce the general idea of power line communication and the present researching situation of the power line communication, and then give a general idea of this thesis.In the second part, we introduce the character of the power line channel including the noise in the power line channel and the fading property of the channel. Then give a simulation channel model based on the basic parameter of the power line. In this thesis we model the power channel as a multi-path fading channel using a from top-to-bottom method.At the receiver, in order to realize the coherent demodulation, we should know the channel state information firstly. In this thesis, we use the pilot symbol assisted modulation mothed with different algorithms to estimate the channel state information.For the power line channel is a slow fading channel, in the topic of SNR estimation, we treat some coherent channels as a sub-band. The frequency width of a sub-band should be smaller than the coherent bandwith in order to overcome frequency selective fading. Based on the minmum mean square error algorithm, we take advantage of the received pilot signal to estimate each sub-band's SNR.Then give the idea of the adaptive modulation and demodulation in power line communication. The AMC should base on the feed-back of the channel state information and then at the transmitter we can adaptively adjust the modulation modes and transmission power of each sub-band. We can also obtain the channel state information by applying TDD where assuming channel reciprocity. By adopting this technique, we can improve the system's performance and spectrum efficience.The research results about the power line channel modeling,channel estimation, SNR estimation and adaptive modulation-demodulation can be applied to a wireless access system based on lamp. The signal processing method can be used in power line communication system. Then we can construct a low radiation wireless-wire acess system. We can also apply the researching results on the broadband internet access to realize high speed data transmission.