12.) Receiving Data.

Working with Complex Data
In order to make full use of the efficiency of Digital Signal Processing, the
conversion of the Information data into complex symbols occurs before the modulation.
The system generates complex PN codes made up of 2 independent components, PNi
+jPNq. To spread the Information data the system performs complex multiplication
between the complex PN codes and the complex data.
Summing Many Channels Together
Many channels are added together and transmitted simultaneously. This addition
happens digitally at the chip rate.
Receiving Data
The receiver performs the following steps to extract the Information:
Demodulation
The receiver generates two reference waves, a Cosine wave and a Sine wave.
Separately mixing each with the received carrier, the receiver extracts I(t) and Q(t).
Analog to Digital converters restore the 8-bit words representing the I and Q chips.
Code Acquisition and Lock
The receiver, as described earlier, generates its own complex PN code that matches
the code generated by the transmitter. However, the local code must be phase-locked to
the encoded data. The RCS and FSU each have different ways of acquiring and locking
onto the other’s transmitted code. Each method will be covered in more detail in later
sections.
Correlation and Data Dispreading
Once the PN code is phase-locked to the pilot, the received signal is sent to a
correlator that multiplies it with the complex PN code, extracting the I and Q data meant
for that receiver. The receiver reconstructs the Information data from the I and Q data.