Method and apparatus for power control in random access procedure

1 . A method implemented at a terminal device for two-step contention free random access (CFRA), the method comprising:

obtaining a plurality of power control parameters to be used for a request message for the two-step CFRA; and

transmitting, to a network node, the request message for the two-step CFRA;

wherein a power of the request message for the two-step CFRA is controlled based on the plurality of power control parameters; and

wherein the request message comprises: a random access channel, RACH, preamble and a physical uplink shared channel, PUSCH, and

wherein the plurality of power control parameters comprise:

a dedicated alpha value for PUSCH configured in a dedicated signaling, wherein the dedicated alpha value is a scaling factor of a path loss;

a power offset of PUSCH relative to a preamble received target power in a broadcast signaling; and

a power ramping step for PUSCH in the two-step CFRA.

2 . The method according to claim 1 , wherein the plurality of power control parameters configured in the dedicated signalling further comprises at least one of:

an indication of whether to apply delta modulation and coding scheme, MCS;

an indication of whether transmit power control, TPC, with accumulation is enabled or not; and

a TPC command for PUSCH.

3 . The method according to claim 2 , wherein

when the power offset of PUSCH relative to a preamble received target power is configured in the dedicated signalling, the power offset of PUSCH relative to a preamble received target power configured in the dedicated signalling is used for calculating the power of the PUSCH of the request message; or

when the power offset of PUSCH relative to a preamble received target power is absent in the dedicated signalling and the power offset of PUSCH relative to a preamble received target power in the broadcast signaling is configured, the power offset of PUSCH relative to a preamble received target power in the broadcast signaling is used for calculating the power of the PUSCH of the request message; or

when the power offset of PUSCH relative to a preamble received target power is absent in the dedicated signalling and the power offset of PUSCH relative to a preamble received target power in the broadcast signaling is absent and the power offset of PUSCH relative to a preamble received target power in the four-step random access is configured, the power offset of PUSCH relative to a preamble received target power in the four-step random access is used for calculating the power of the PUSCH of the request message.

4 . The method according to claim 3 ,

wherein a range of the values of the power offset of PUSCH relative to a preamble received target power configured in the dedicated signalling comprises −1 dB, 0 dB, 1 dB, 2 dB, 3 dB, 4 dB, 5 dB, 6 dB.

5 . The method according to claim 3 ,

wherein the power offset of PUSCH relative to a preamble received target power in the broadcast signaling is used for calculating the power of the PUSCH of the request message.

6 . The method according to claim 3 ,

wherein the power offset of PUSCH relative to a preamble received target power in the four-step random access is used for calculating the power of the PUSCH of the request message.

7 . The method according to claim 3 , wherein

when the dedicated alpha value for PUSCH is configured in the dedicated signalling, the dedicated alpha value for PUSCH configured in the dedicated signalling is used for calculating the power of the PUSCH of the request message; or

when the dedicated alpha value for PUSCH is absent in the dedicated signalling and the alpha value in the broadcast signaling is configured, the alpha value in the broadcast signaling is used for calculating the power of the PUSCH of the request message; or

when the dedicated alpha value for PUSCH is absent in the dedicated signalling, the alpha value in the broadcast signaling is absent and the alpha value in the four-step random access is configured, the alpha value in the four-step random access is used for calculating the power of the PUSCH of the request message; or

when the dedicated alpha value for PUSCH is absent in the dedicated signalling, the alpha value in the broadcast signaling is absent and the alpha value in the four-step random access is absent, the dedicated alpha value for PUSCH is set to 1.

8 . The method according to claim 3 ,

wherein a range of the dedicated alpha value for PUSCH configured in the dedicated signalling is {alpha0, alpha04, alpha05, alpha06, alpha07, alpha08, alpha09, alpha1}, wherein alpha0 corresponds to 0, alpha04 corresponds to 0.4, alpha05 corresponds to 0.5, alpha06 corresponds to 0.6, alpha07 corresponds to 0.7, alpha08 corresponds to 0.8, alpha09 corresponds to 0.9 and alpha1 corresponds to 1.

9 . The method according to claim 3 ,

wherein the alpha value in the broadcast signaling is used for calculating the power of the PUSCH of the request message.

10 . The method according to claim 3 ,

wherein the alpha value in the four-step random access is used for calculating the power of the PUSCH of the request message.

11 . The method according to claim 3 ,

wherein a range of the power ramping step for PUSCH configured in the dedicated signalling is {dB0, dB2, dB4, dB6}, wherein dB0 corresponds 0 dB power ramping step size, dB2 corresponds 0 dB power ramping step size, dB4 corresponds 0 dB power ramping step size, dB6 corresponds 0 dB power ramping step size.

12 . The method according to claim 3 ,

wherein when the power ramping step for PUSCH in the broadcast signaling is configured, the power ramping step for PUSCH in the broadcast signaling is used for calculating the power of the PUSCH of the request message.

13 . The method according to claim 3 , wherein

delta MCS indication in the four-step random access is used for calculating the power of the PUSCH of the request message.

14 . The method according to claim 3 , wherein

TPC accumulation indication in the four-step random access is used for calculating the power of the PUSCH of the request message, and the TPC accumulation indication is an indication of whether a sum of TPC command values in a set of TPC command values should be used for PUSCH power control.

15 . The method according to claim 3 , wherein

at least one of the power ramping step for PUSCH and the TPC command for PUSCH is used for calculating the power of the PUSCH of the request message.

16 . The method according to claim 1 , wherein the dedicated signaling comprises at least one of:

a dedicated signalling for random access in one radio resource control, RRC, message;

a handover command message;

a beam failure recover message; and

a physical downlink control channel, PDCCH, ordering the random access with two-step CFRA.

17 . The method according to claim 1 , wherein the network node is a handover target network node, the method further comprises:

receiving the dedicated signalling from a handover source network node, wherein the plurality of power control parameters configured in the dedicated signalling are sent by the handover target network node to the handover source network node.

18 . The method according to claim 1 , further comprising:

receiving, from the network node, a response indicating whether the two-step CFRA is successful.

19 . A method implemented at a network node for two-step contention free random access (CFRA), the method comprising:

transmitting a plurality of power control parameters to a terminal device; and

receiving, from the terminal device, a request message for the two-step CFRA;

wherein a power of the request message for the two-step CFRA is controlled based on the plurality of power control parameters; and

wherein the request message comprises: a random access channel, RACH, preamble and a physical uplink shared channel, PUSCH, and

wherein the plurality of power control parameters comprise:

a dedicated alpha value for PUSCH configured in a dedicated signaling, wherein the dedicated alpha value is a scaling factor of a path loss;

a power offset of PUSCH relative to a preamble received target power in a broadcast signaling; and

a power ramping step for PUSCH in the two-step CFRA.

20 . A terminal device that is configured to perform two-step contention free random access (CFRA), comprising:

a processor; and

a memory, the memory containing instructions, which when executed by the processor, cause the terminal device to:

obtain a plurality of power control parameters to be used for a request message for the two-step CFRA; and

transmit, to a network node, the request message for the two-step CFRA;

wherein a power of the request message for the two-step CFRA is controlled based on the plurality of power control parameters; and

wherein the request message comprises: a random access channel, RACH, preamble and a physical uplink shared channel, PUSCH, and

wherein the plurality of power control parameters comprise:

a dedicated alpha value for PUSCH configured in a dedicated signaling, wherein the dedicated alpha value is a scaling factor of a path loss;

a power offset of PUSCH relative to a preamble received target power in a broadcast signaling; and

a power ramping step for PUSCH in the two-step CFRA.