  Uplink sensing in integrated sensing and communications (ISAC) systems, such
as Perceptive Mobile Networks, is challenging due to the clock asynchronism
between transmitter and receiver. Existing solutions typically require the
presence of a dominating line-of-sight path and the knowledge of transmitter
location at the receiver. In this paper, relaxing these requirements, we
propose a novel and effective uplink sensing scheme with the assistance of
static anchor points. Two major algorithms are proposed in the scheme. The
first algorithm estimates the relative timing and carrier frequency offsets due
to clock asynchronism, with respect to those at a randomly selected reference
snapshot. Theoretical performance analysis is provided for the algorithm. The
estimates from the first algorithm are then used to compensate for the offsets
and generate the angle-Doppler maps. Using the maps, the second algorithm
identifies the anchor points, and then locates the UE and dynamic targets.
Feasibility of UE localization is also analyzed. Simulation results are
provided and demonstrate the effectiveness of the proposed algorithms.
