Methods and apparatus for mobility management between fixed transmission points and mobile transmission points
In a network comprising both fixed transmission points and mobile transmission points, the transmission points may transmit discovery reference signals that allow WTRUs to detect and/or synchronize to the transmission points. The fixed and mobile transmission points may transmit discovery reference signals with different characteristics that allow the WTRUs to distinguish between fixed and mobile transmission points. The mobile transmission points may also transmit a separate maintenance reference signal that allows WTRUs to maintain a connection with the mobile transmission point. For networks in which fixed a mobile transmission points operate in different frequency bands, the mobile transmission points may also periodically transmit discovery beacon signals in the frequency band of the fixed transmission points to allow discovery. Conditions may be imposed on WTRUs before the WTRU will transmit to the network a measurement report reporting on a potential transmission point to which it may be switched. Such conditions may include the speed of a WTRU relative to the transmission point with which it is currently associated, the speed of the WTRU relative to the newly discovered transmission point or both.
1. A method implemented in a wireless transmit receive unit (WTRU), the method comprising:
receiving a discovery reference signal (Disc-RS) from a mobile transmission point (Mbl-TRP);
responsive to the Disc-RS and determinations that:
a) a first estimated speed of the WTRU relative to a fixed transmission point (Fxd-TRP) with which the WTRU is associated is greater than a first threshold; and
b) a first signal measurement of a first signal received from the Fxd-TRP is less than a second threshold,
determining (i) a second estimated speed of the WTRU relative to the Mbl-TRP and (ii) a second signal measurement of the Disc-RS; and
transmitting a measurement report to a network responsive to determinations that:
c) the second estimated speed is less than a third threshold; and
d) the second signal measurement is greater than a fourth threshold.
2. The method of claim 1 , further comprising:
receiving a handover command from the Fxd-TRP; and
synchronizing to the Mbl-TRP.
3. The method of claim 2 , wherein synchronizing to the Mbl-TRP comprises: synchronizing to the Mbl-TRP using the Disc-RS or a maintenance reference signal (Maint-RS) received from the Mbl-TRP.
4. The method of claim 2 , further comprising:
receiving from the Mbl-TRP a maintenance reference signal (Maint-RS), wherein the Maint-RS has signal characteristics different from the signal characteristics of the Disc-RS; and
using the Maint-RS to maintain connection with the Mbl-TRP.
5. The method of claim 1 , further comprising:
determining that the Disc-RS is from the Mbl-TRP based on signal characteristics of the Disc-RS, wherein the signal characteristics comprise at least one of:
a timing offset between the Disc-RS and a frame timing at which Disc-RSs are received;
a periodicity of the Disc-RS;
a set of physical resource blocks (PRBs) over which the Disc-RS is received;
a frequency over which the Disc-RS is received;
a beam parameter of the Disc-RS;
a synchronization signal block (SS block) used to transmit the Disc-RS;
a signal sequence type of the Disc-RS; and
a sequence parameter of the Disc-RS.
6. The method of claim 1 , wherein the measurement report comprises information indicating the second signal measurement.
7. The method of claim 1 , wherein the second signal measurement comprises at least one of a signal strength of the Mbl-TRP and a signal quality of the Mbl-TRP, including any of:
a reference signal received power (RSRP) of the Mbl-TRP; and
a plurality of RSRP measurements of the Mbl-TRP.
8. The method of claim 1 , determining the second estimated speed comprises at least one of:
estimating a channel coherence time using signal characteristics of the Disc-RS;
determining a level of consistency between multiple RSRP measurements of the Mbl-TRP; and
using information obtained from a vehicle-to-vehicle message or a vehicle-to-infrastructure message received by the WTRU, wherein the information indicates at least one of an identification of a vehicle with which the Mbl-TRP is associated, a speed of the vehicle, a direction of the vehicle, and location of the vehicle.
9. The method of claim 1 , wherein receiving the Disc-RS comprises:
detecting a discovery beacon on a first carrier, wherein the first carrier is the same carrier on which the WTRU received the first signal;
transmitting, toward the Fxd-TRP, a request for a measurement gap;
receiving, from the Fxd-TRP, information indicating the measurement gap; and
monitoring for the Disc-RS on a second carrier during the measurement gap.
10. The method of claim 1 , wherein determining the first estimated speed comprises at least one of:
estimating a speed of the WTRU relative to a fixed reference point using a global positioning system; and
estimating channel correlation with respect to reference signals received from the Fxd-TRP at two time instances.
11. A wireless transmit receive unit (WTRU) comprising circuitry, including a transmitter, receiver and a processor, configured to:
receive a discovery reference signal (Disc-RS) from a mobile transmission point (Mbl-TRP);
responsive to the Disc-RS and determinations that:
a) a first estimated speed of the WTRU relative to a fixed transmission point (Fxd-TRP) with which the WTRU is associated is greater than a first threshold; and
b) a first signal measurement of a first signal received from the Fxd-TRP is less than a second threshold,
determine (i) a second estimated speed of the WTRU relative to the Mbl-TRP and (ii) a second signal measurement of the Disc-RS; and
transmit a measurement report responsive to determinations that:
c) the second estimated speed is less than a third threshold; and
d) the second signal measurement is above a fourth threshold.
12. The WTRU of claim 11 , wherein the circuitry is further configured to:
receive a handover command from the Fxd-TRP; and
synchronize to the Mbl-TRP.
13. The WTRU of claim 12 , wherein the circuitry is further configured to:
receive from the Mbl-TRP a maintenance reference signal (Maint-RS), wherein the Maint-RS has signal characteristics different from the signal characteristics of the Disc-RS; and
use the Maint-RS to maintain connection with the Mbl-TRP.
14. The WTRU of claim 12 , wherein the circuitry being configured to synchronize to the Mbl-TRP comprises the circuitry being configured to synchronize to the Mbl-TRP using the Disc-RS or a maintenance reference signal (Maint-RS) received from the Mbl-TRP.
15. The WTRU of claim 11 , wherein the circuitry is further configured to:
determine that the Disc-RS is from the Mbl-TRP based on signal characteristics of the Disc-RS, wherein the signal characteristics comprise at least one of:
a timing offset between the Disc-RS and a frame timing at which Disc-RSs are received;
a periodicity of the Disc-RS;
a set of physical resource blocks (PRBs) over which the Disc-RS is received;
a frequency over which the Disc-RS is received;
a beam parameter of the Disc-RS;
a synchronization signal block (SS block) used to transmit the Disc-RS;
a signal sequence type of the Disc-RS; and
a sequence parameter of the Disc-RS.
16. The WTRU of claim 11 , wherein the measurement report comprises information indicating the second signal measurement.
17. The WTRU of claim 11 , wherein the second signal measurement comprises at least one of a signal strength of the Mbl-TRP and a signal quality of the Mbl-TRP, including any of:
a reference signal received power (RSRP) of the Mbl-TRP; and
a plurality of RSRP measurements of the Mbl-TRP.
18. The WTRU of claim 11 , wherein the circuitry is configured to determine the second estimated speed based on at least one of:
a channel coherence time estimated using signal characteristics of the Disc-RS;
a determined level of consistency between multiple RSRP measurements of the Mbl-TRP; and
information obtained from a vehicle-to-vehicle message or a vehicle-to-infrastructure message received by the WTRU, wherein the information indicates at least one of an identification of a vehicle with which the Mbl-TRP is associated, a speed of the vehicle, a direction of the vehicle, and location of the vehicle.
19. The WTRU of claim 11 , wherein the circuitry being configured to receive the Disc-RS comprises the circuitry being configured to:
detect a discovery beacon on a first carrier, wherein the first carrier is the same carrier on which the WTRU received the first signal;
transmit, toward the Fxd-TRP, a request for a measurement gap;
receive, from the Fxd-TRP, information indicating the measurement gap; and
monitor for the Disc-RS on a second carrier during the measurement gap.
20. The WTRU of claim 11 , wherein the circuitry is configured to determine the first estimated speed based on at least one of:
an estimated speed of the WTRU relative to a fixed reference point using a global positioning system; and
a channel correlation estimated with respect to reference signals received from the Fxd-TRP at two time instances.