Research On Synchronization Technology In Low Voltage Power Line OFDM Communication System

The rapid development of smart grid requires the low-voltage power line system hashigher communication capabilities. However, as a non-dedicated communication medium, thecommunication through the low voltage power line networks presents great challenges forcommunications engineer such as strong noise, transmission attenuation and variableimpedance. OFDM is robust to multipath fading, high spectrum efficiency and simpleimplementation. So PRIME、G3-PLC and other power line communication system are usingOFDM as the specification of the physical layer. However the OFDM technology is verysensitive to the symbol timing error and carrier frequency offset. So symbol timing andcarriers frequency offset estimation for an OFDM system is significantly important.For the timing metric plateau inherent of Schmidl&Cox algorithm, the multi-peak in thePark method and Hamed algorithm is susceptible to impulse noise interference, theinterleaving and judgment timing synchronization algorithm is proposed. Using theinterleaving properties, the proposed method can obtain only one sharp pulse peak, avoid theplatform and multi-peak problems. Using the judgment cure and the standard curve, we caneffective to distinguish impulse noise interference peak and timing sync pulse peak. Theproposed synchronization algorithm ensures the synchronization timing accuracy in the lowpower line communication system.The estimated range of the phase difference frequency offset algorithm is small. But thealgorithm has a high estimation accuracy and is easy to implement. The frequency offsetestimation error of the frequency difference frequency offset algorithm and the cycle diagramfrequency offset algorithm is bigger. These algorithms have a large frequency offset estimatedrange, and the performance of the cycle diagram frequency offset algorithm does not dependon the structure of the synchronization training sequence. Take into account the frequency offset estimation accuracy and the estimated range, combined the phase difference frequencyoffset and the cycle diagram frequency offset algorithm is discussed.Analysis of the impulse noise interference peak in low voltage power line channel, usingthe weighted judgment idea, we can effectively avoiding the vague symbol timingsynchronization and pulse interference. Using the weighted training sequence structure toovercome the platform effect, with the combination of judgment idea makes more efficientand accurate in symbols capture. The combination of the phase difference frequency offsetalgorithm and the cycle diagram frequency offset algorithm achieve the performance of lowcomplexity, large-scale and high-precision frequency offset estimation. For the multipathtransmission in low voltage power line channel, windowed average method is proposed, toensure that the timing time for the first path rather than the strongest. Matlab simulationcompare the performance of proposed symbol timing synchronization algorithm,Schmidl&Cox algorithm and Hamed algorithm, then verify the accuracy of the proposedsymbol timing synchronization algorithm, frequency offset estimation algorithm performanceclose to the Cramer-Rao frequency offset estimation lower bound.