Data Generation

The QPSK system has the ability to transmit two bits of information for every symbol. The “Data Generation” block in the block diagram handles the process of converting two-bit ROM data to allocate bit streams for the I and Q channels. This data is then read, differential encoding applied, and each encoded symbol is grouped into a pair of one bits. These bits are then translated into corresponding amplitudes and polarities, as shown in Fig 1.

Fig. 1.  QPSK constellation grid.

    Converting real data from an image or a sound file requires special data conditioning prior to encoding or splicing of symbols. In our project, an 8 bit/pixel image is used. Each pixel is split into four consecutive two-bit symbols. This is completed using time division multiplexers to stream the symbols sequentially, and time division de-multiplexers to extract the corresponding symbols.