CATT's RAR window proposal and 2.9 ms timing concern

Both CATT contributions address satellite access in New Radio (NR) non-terrestrial networks (NTN) under Global Navigation Satellite System (GNSS) resilience. Here, resilience means handling a device position that is unavailable or inaccurate. RAN2 is the working group for radio layer 2 and radio resource control. At RAN2 #135, CATT proposed starting the random access response (RAR) window using device-to-base-station round-trip time (RTT). The calculation could use a cell or beam reference location, or an inaccurate or last known GNSS position. CATT wrote "The RAR monitoring time needs to be extended" to account for uncertainty in that round-trip time.

Source: R2-2604771, CATT, 3GPP TSG RAN WG2 #135. © CATT.

At RAN2 #135-bis, CATT described a mismatch between actual response arrival and a window start calculated from inaccurate location. It estimated an offset of up to about 2.9 milliseconds. CATT warned that the offset "potentially results in RAR falling outside the RAR window and leads to random access failure". The later observation does not state whether CATT retained, changed or withdrew its earlier monitoring proposal. The register records no decision for the RAN2 #135-bis contribution.

Source: R2-2606856, CATT, 3GPP TSG RAN WG2 #135-bis. © CATT.