7. Signal Acquisition and Synchronization#
After we capture the TX signal at the RX, the next step is to determine whether the captured signal is of interest and if so synchronize to the symbol timing of the captured signal for demodulation later.
These two functions are often achieved in two steps:
Acquisition: This is the step to determine of the captured signal is of interest and establish a coarse synchronization to the start of a packet.
Symbol synchronization: This is a fine synchronization step that aligns the RX clock to the symbol boundary of the RX signal. The ideal performance is to archive a zero timing error modulo the symbol period.
Acquisition is important since the packet may contain different types of symbols organized in larger units, such as a packet header and data payload, for different purposes. The acquisition step allows us to synchronize to the boundaries between different units so that we may process the relevant information. In addition, because of how acquisition is commonly implemented, it also serves to identify whether the captured signal is one of our interest.
In a typical digital communication system, acquisition is only performed once after the packet’s signal is captured. If the packet is long, symbol synchronization is achieved and maintained by closed-loop circuitry during the whole duration of the packet to account for the possibility of hardware clock frequency offset and drift. On the other hand, if the packet is short, one-shot symbol synchronization may be performed at the beginning together with acquisition.