| 摘要 |
An adaptive predistortion circuit with memory for a digital transmission system includes a set (10) of input registers storing various consecutive data symbols a predistortion circuit (11) for predistorting the data of the consecutive data symbols before they pass through a modulator (14) and then through an amplifier (15) and an adaptation circuit (19) which, in response to a demodulation (16, 171, 172, 181, 182) of the stream of transmitted data symbols continuously adapts the predistortion circuit (11) to the stream of input data symbols. The adaptation circuit (19) includes a set (21) of counters/accumulators which determine the center of gravity of the smeared spots (clouds) created by the distortion by calculating a set of errors that is used for adapting the predistortion circuit (11). Preferably, the predistortion circuit is a random access memory. In order to reduce the size of this random access memory the symmetry of the constellation is used and therefore at data input the constellation is reduced to a quarter of the constellation. Reverse operations are thus necessary at the output and in the adaptation loop.
|
