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How are carrier tracking loops different from code tracking loops?


Asked by Jordyn Brewer on Dec 07, 2021 FAQ



While code tracking loops follow the code delay of the incoming signal using Delay Lock Loops (DLL), carrier tracking loops can be designed to follow either the phase of the incoming signal – using Phase Lock Loops (PLL), or the Doppler frequency of the incoming signal using Frequency Lock Loops (FLL).
In fact,
There are code tracking loops, the delay lock loops (DLL) and carrier tracking loops, and the phase locking loops (PLL) in the receiver. Typically, both the code and the carrier are being tracked in phase lock. The tracking loops connected to each of the receiver’s channels also work cooperatively with each other.
Besides, For that purpose, tracking loops are used in a closed loop to follow continuously the code and carrier parameters of the incoming signal. These loops are often designated as code and carrier tracking loops.
In respect to this,
Noting that the carrier loop jitter is much less noisy than the code loop jitter, it is possible to use the measurements from the carrier loop to remove the LOS (Line-Of-Sight) dynamics of the code loop, with the advantage of being able to lower the order of the code loop filter, as well as its bandwidth.
Additionally,
Then, this signal is sent on to the carrier tracking loop also known as the phase locking loop, PLL, where the voltage-controlled oscillator is continuously adjusted to follow the beat frequency exactly. This is basically how a GPS receiver locks on to that carrier and stays locked unless there is a loss of signal or a cycle slip.