Which RTLS technique uses the nearest position of a client to an AP to track the location of the client?

Lateration (trilateration or multilateration) estimates location by calculating distances from at least three APs using RSSI values, not by using a single nearest AP.

Location pattern matching (RF fingerprinting) compares real-time signal signatures against a pre-collected database of known RF patterns to estimate position, not just nearest-AP association.

Cell of Origin derives client location from the known physical position of the AP the client is currently associated with, effectively placing the client within the coverage cell of that AP. It is the simplest and least accurate RTLS method because it does not use RSSI from multiple APs or angle-of-arrival measurements - the client is simply assumed to be co-located with its serving AP.

Angulation uses the angle of arrival of a client's signal measured across multiple antennas or APs to calculate position, which is a fundamentally different geometric technique than cell of origin.