SYNC and SFD are parts of the IEEE 802.15.4z ranging packet that are good indicators of the link margin performance of UWB ranging transceivers. To successfully receive and timestamp a ranging packet, an UWB receiver must be able to reliably detect at least these two parts of the packet.
Since the SYNC is typically used for clock offset extraction, synchronization, and channel impulse response estimation, it is difficult to use it for a performance comparison in terms of link margin. On the other hand, the SFD, although used for coarse ranging and RSSI, shall be detected. Therefore, the SFD determines link margin performance because its detection can be quantified by known communication mechanisms (pattern detection).