Research On Anti-interference Technology Of Power Line Carrier Communication Over Time-varying Load

In this paper, the key research is anti-interference technology of power line carrier communication based on adaptive OFDM system, aiming to solve the problem of harsh and complex noise environments over time-varying load power line channel, which is failed to give full consideration to the bad influence on the PLC communication in practical application.Firstly, the test of power line channel characteristics of time-varying load in north China oilfield power grid was carried out by using the channel tester, including the time domain and frequency domain characteristics. It can clearly see that the motor will produce a mass of pulse interference in addition to the background noise by noise measurement. Noise amplitude over a period of time is relatively small, while the amplitude relatively increased in another period of time.but the time-frequency noise characteristic can not be detennined by the test.According to this,the wigner time-frequency analysis which combined the time domain and frequency domain analysis is used to cognize the status of power line channel, which can accurately know the noise time-varying condition under different frequencies, providing the basis for OFDM subcarrier dynamic optimization and combination.Next, a subcarrier selection algorithm based on the feedback in the receiving end and bayes’ theorem and combined with spectrum sensing technology is put forward in the adaptive OFDM system. Available subcarriers are selected by the method of probability prediction, which can dynamically select a subcarrier with better quality according to the real-time change of communication channel characteristics. The simulation results show that the algorithm effectively reduces the system bit error rate, thus effectively overcoming the powerline channel noise problem and improving the communication reliability in OFDM system.Finally, noise suppression algorithm of power line for OFDM system is studied. Based on the theory that the lower peak to average power ratio in the sender of the OFDM system can effectively reduce the impulse noise detection error probability in the receiving end, a combination of the technology to reduce the peak to average power ratio and blanking/clipping denoising algorithm is proposed. The simulation results show that the algorithm can effectively restrain the powerline impulse noise and improve the system reliability of OFDM systems.