| 摘要 |
<p>There is described a method for recovering symbol synchronism useable in the demodulators MPSK or QAM. In accordance with the method in question there is used a VCO inserted in a PLL for sampling the symbols at the double-frequency of the symbol frequency and for generating the symbol reading clock. The algebraic sum with alternating sign of the absolute value of four consecutive samples constitutes a generic term of an error sequence which, appropriately filtered, controls the VCO. The central values of the symbols at the reading instants are obtained by interpolating the respective samples. A hangup of the PLL is revealed by the sign discordance between samples taken in pairs. In case of detection, the sequential order of the interpolated samples is changed and the symbol reading clock phase inverted. The sign of the error sequence controlling the VCO is also inverted in order to stabilise the equilibrium point of the PLL. <IMAGE></p> |
