摘要：How does signal acquisition with batch processing (i.e., FFTs) work? How is it different from traditional serial search techniques?
A: In order to answer these questions, let us briefly review the serial-search acquisition process.
Numerically controlled oscillators (NCOs) drive the so-called "local" code and carrier generators (recall that in order to track the signal, the receiver must generate local copies of the code and carrier and must synchronize them with the received signal). The locally generated code and carrier signals are multiplied with the received signal (which itself has been amplified, filtered, down-converted in frequency and digitized with an analog-to-digital or A/D converter), and the results are then accumulated (discrete-time equivalent of integration).
In order to account for the as yet unknown phase of the received signal, the locally generated carrier is broken into two components, which are phase-shifted by 90 degrees with respect to each other. These two orthogonal signals, after multiplication with the received signal and local code, and subsequent accumulation, are referred to as the in-phase (I) and quadrature or quadraphase (Q) components. The code-lock detector then is given simply by the sum of the squares of the I and Q components:
Code_Lock_Detector = 12 + Q2
