QPSK, or Quadrature Phase Shift Keying, is a digital modulation scheme that encodes two bits of data onto a single carrier wave by shifting the carrier wave's phase by one of four possible values (0, 90, 180, or 270 degrees).

Here is an example of VHDL code that implements a QPSK modulator:

Turbo codes are a type of error-correcting code that are designed to provide very high levels of error correction while still maintaining a reasonable data rate. They were developed in the 1990s and have since become widely used in a variety of applications, including satellite communication, wireless communication, and data storage.