Differential Coding
Differential coding
is necessary to compensate for the errors induced from phase
ambiguity, an inherent problem of QPSK systems. As stated
previously, differential coding is a part of the data conditioning
where complex data is converted to a sequence of two-bit symbols.
Differential encoding is then applied to the stream of two-bit
symbols and later the decoding process is applied after the I and Q
channels have been re-combined at the receiver end. The result is a
data sequence corrected of phase ambiguity.
The encoding process calculates the difference between consecutive
symbols and that value is transmitted. This is achieved by putting
the symbol sequence through a discrete time integrator. Once the
data is transmitted and received, the decoding process begins by
feeding the encoded symbols through a discrete time differentiator.
Differential coding consists of a total of four Xilinx blocks for
implementation and provides a reliable method for correcting phase
ambiguity.