Method and apparatus for uplink timing determination in a wireless communication system
A method and apparatus are disclosed from the perspective of a User Equipment (UE). In one embodiment, the UE performs an Uplink (UL) transmission of an UL signal to a base station in an UL subframe wherein the UL subframe begins at a timing derived based on an absolute time.
1 . A method for a User Equipment (UE), comprising:
performing, by the UE, an Uplink (UL) transmission of an UL signal to a base station in an UL subframe, wherein the UL subframe begins at a timing derived based on an absolute time, wherein the absolute time is based on a clock of the UE, with the clock of the UE based on Global Positioning System (GPS) time from at least four satellites, wherein at least three satellites of the at least four satellites are used to obtain location of the UE and a fourth satellite of the at least four satellites is used to derive a timing error, and wherein the timing error is derived from propagation delays based on time stamps and timings the UE receives from the time stamps.
2 . The method of claim 1 , wherein the UE receives an indication from the base station indicating the absolute time.
3 . The method of claim 2 , wherein the absolute time is an absolute time when a DL subframe transmission begins at a base station.
4 . The method of claim 1 , wherein the UE derives the timing based on a second absolute time which is based on a clock of the UE.
5 . The method of claim 1 , wherein the UE derives a propagation delay between the base station and the UE using the absolute time.
6 . The method of claim 5 , wherein the UE derives the propagation delay based on an UL reception time.
7 . The method of claim 6 , wherein the UL reception time is based on a GPS time.
8 . The method of claim 1 , wherein the UE derives the timing based on a propagation delay.
9 . The method of claim 1 , wherein the UE derives the timing based on a difference between UL transmission timing and DL transmission timing at the base station.
10 . The method of claim 1 , wherein the UE derives the timing without a timing advance command from the base station.
11 . The method of claim 1 , wherein the clock of the UE is precise.
12 . The method of claim 1 , wherein the clock of the UE is not precise.
13 . A method for a base station, comprising:
transmitting, by the base station, a timing information to a User Equipment (UE), wherein the timing information comprises an absolute time for the UE to determine the Uplink (UL) transmission timing, and wherein the absolute time is based on a clock of the UE, with the clock of the UE based on Global Positioning System (GPS) time from at least four satellites, wherein at least three satellites of the at least four satellites are used to obtain location of the UE and a fourth satellite of the at least four satellites is used to derive a timing error, and wherein the timing error is derived from propagation delays based on time stamps and timings the UE receives from the time stamps.
14 . The method of claim 13 , wherein the absolute time is an absolute time when a DL subframe transmission begins at a base station.
15 . The method of claim 13 , wherein the absolute time is used for deriving a propagation delay between the base station and the UE.
16 . The method of claim 13 , wherein the base station indicates a difference between UL transmission timing and DL transmission timing at the base station to the UE.
17 . The method of claim 13 , wherein the base station does not send a timing advance command to the UE for determining the UE's UL transmission timing.