Configuration of Listen-before-talk Procedure During Random Access
A base station transmits, to a wireless device, at least one radio resource control (RRC) message comprising configuration parameters of an unlicensed cell. The base station transmits a first physical downlink control channel (PDCCH) to initiate a random access procedure on the unlicensed cell. In response to a listen-before-talk (LBT) procedure indicating a clear channel for uplink transmission of a first preamble of the random access procedure, the base station receives the first preamble via a random access channel (RACH) of the unlicensed cell and transmits a second PDCCH for a random access response (RAR). In response to the LBT procedure indicating an LBT failure, the base station receives a second preamble based on a random access resource selection procedure and does not transmit the second PDCCH for the RAR.
1 . A method comprising:
transmitting, by a base station to a wireless device, at least one radio resource control (RRC) message comprising configuration parameters of an unlicensed cell;
transmitting a first physical downlink control channel (PDCCH) to initiate a random access procedure on the unlicensed cell;
in response to a listen-before-talk (LBT) procedure indicating a clear channel for uplink transmission of a first preamble of the random access procedure:
receiving, by the base station, the first preamble via a random access channel (RACH) of the unlicensed cell; and
transmitting, by the base station, a second PDCCH for a random access response (RAR); and
in response to the LBT procedure indicating an LBT failure:
receiving, by the base station, a second preamble based on a random access resource selection procedure; and
not transmitting, by the base station, the second PDCCH for the RAR.
2 . The method of claim 1 , wherein the at least one RRC message further comprises:
a first maximum counter value of a preamble transmission counter; and
a second maximum counter value of a second counter.
3 . The method of claim 2 , further comprising, in response to the LBT procedure indicating the clear channel, incrementing the preamble transmission counter.
4 . The method of claim 3 , further comprising setting a preamble power parameter using a value of the preamble transmission counter.
5 . The method of claim 2 , further comprising, in response to the LBT procedure indicating the LBT failure, maintaining a same value of the preamble transmission counter.
6 . The method of claim 1 , further comprising, in response to the receiving the first preamble via the RACH, transmitting the second PDCCH for the RAR.
7 . The method of claim 1 , further comprising, in response to the LBT procedure indicating the LBT failure, not receiving the first preamble.
8 . A base station comprising:
one or more processors; and
memory storing instructions that, when executed by the one or more processors, cause the base station to:
transmit, to a wireless device, at least one radio resource control (RRC) message comprising configuration parameters of an unlicensed cell;
transmit a first physical downlink control channel (PDCCH) to initiate a random access procedure on the unlicensed cell;
in response to a listen-before-talk (LBT) procedure indicating a clear channel for uplink transmission of a first preamble of the random access procedure:
receive the first preamble via a random access channel (RACH) of the unlicensed cell; and
transmit a second PDCCH for a random access response (RAR); and
in response to the LBT procedure indicating an LBT failure:
receive a second preamble based on a random access resource selection procedure; and
not transmit the second PDCCH for the RAR.
9 . The base station of claim 8 , wherein the at least one RRC message further comprises:
a first maximum counter value of a preamble transmission counter; and
a second maximum counter value of a second counter.
10 . The base station of claim 9 , wherein the instructions further cause the base station to, in response to the LBT procedure indicating the clear channel, increment the preamble transmission counter.
11 . The base station of claim 10 , wherein the instructions further cause the base station to set a preamble power parameter using a value of the preamble transmission counter.
12 . The base station of claim 9 , wherein the instructions further cause the base station to, in response to the LBT procedure indicating the LBT failure, maintain a same value of the preamble transmission counter.
13 . The base station of claim 8 , wherein the instructions further cause the base station to, in response to receiving the first preamble via the RACH, transmit the second PDCCH for the RAR.
14 . The base station of claim 8 , wherein the instructions further cause the base station to, in response to the LBT procedure indicating the LBT failure, not receive the first preamble.
15 . A non-transitory computer-readable medium comprising instructions that, when executed by one or more processors of a base station, cause the base station to:
transmit, to a wireless device, at least one radio resource control (RRC) message comprising configuration parameters of an unlicensed cell;
transmit a first physical downlink control channel (PDCCH) to initiate a random access procedure on the unlicensed cell;
in response to a listen-before-talk (LBT) procedure indicating a clear channel for uplink transmission of a first preamble of the random access procedure:
receive the first preamble via a random access channel (RACH) of the unlicensed cell; and
transmit a second PDCCH for a random access response (RAR); and
in response to the LBT procedure indicating an LBT failure:
receive a second preamble based on a random access resource selection procedure; and
not transmit the second PDCCH for the RAR.
16 . The non-transitory computer-readable medium of claim 15 , wherein the at least one RRC message further comprises:
a first maximum counter value of a preamble transmission counter; and
a second maximum counter value of a second counter.
17 . The non-transitory computer-readable medium of claim 16 , wherein the instructions further cause the base station to, in response to the LBT procedure indicating the clear channel, increment the preamble transmission counter.
18 . The non-transitory computer-readable medium of claim 17 , wherein the instructions further cause the base station to set a preamble power parameter using a value of the preamble transmission counter.
19 . The non-transitory computer-readable medium of claim 16 , wherein the instructions further cause the base station to, in response to the LBT procedure indicating the LBT failure, maintain a same value of the preamble transmission counter.
20 . The non-transitory computer-readable medium of claim 15 , wherein the instructions further cause the base station to. in response to receiving the first preamble via the RACH. transmitting the second PDCCH for the RAR.