| 摘要 |
Digital data (particularly encoded television program signals) are communicated from a transmitter to a terrestrial receiver by convolutional encoding the data into a first and a second signal during different periods representing a rate 1/2 signal. During the different periods, the two signals are combined and punctured into one serial punctured bit stream for producing a forward error correction convolutional encoded signal having a manually or automatically selected rate e.g. rate 2/3 or 6/7. Signals being encoded into different variable rates are transmitted at mutually exclusive times at first and second power levels to the receiver via a satellite. At the variable rates, parallel punctured bit streams are simultaneously derived and modulate simultaneously the pair of orthogonal carriers (QPSK). The improved puncturing method is capable of handling all of the optimum punctured codes and uses a punctured clock, multiplexer, FIFO, RAM, ROM, rate control source. The punctured clock is used to derive a pair of wavetrains comprising the I and Q channels sequential bits and dummy bits inserted into the serial signal. The receiver responds to the QPSK carrier and derives first a serial signal having one sequential bit stream of alternating both I and Q sequential bits. Further they are sequentially re-arranged as signals I and Q at the same time slots.
|
