Determining random-access channel transmission occasions

1 . A Central Unit (CU) of a base station (gNB) comprising:

at least one processor; and

at least one memory including computer program code that, when executed by that at least one processor, cause the at least one processer to perform the following operations:

receive, from a control center (CC), a measurement configuration comprising instructions to provide at least one of interference measurement information and load measurement information to the CC;

transmit, to at least one Distributed Unit (DU), at least a subset of the measurement configuration;

transmit, to at least one User Equipment (UE), a request for a UE Random-Access Channel (RACH) report;

in response to the transmitted request, obtain RACH information associated with the at least one UE, wherein the RACH information comprises the UE RACH report defining one or more experienced contention events;

in response to the transmitted subset of the measurement configuration, receive, from the at least one DU, the load measurement information, and the interference measurement information, for a Physical RACH (PRACH) slot allocation procedure, wherein the load measurement information comprises a number of detected random-access preambles on a first set of candidate Random-Access Channel (RACH) transmission occasions, and wherein the interference measurement information comprises a measurement of received signal power over thermal noise;

receive, from one or more neighbor CUs, RACH slot allocation information;

transmit, to the CC, supportive data comprising the received load measurement information, the received interference measurement information, the obtained RACH information, and the received RACH slot allocation information;

in response to the transmitted supportive data, receive, from the CC, a second set of candidate RACH transmission occasions, wherein the second set of candidate RACH transmission occasions comprises a subset of the first set of candidate RACH transmission occasions and is determined by the CC based on the supportive data;

determine, from the second set of candidate RACH transmission occasions and based at least partly on the RACH information, the load measurements, the interference measurement information, and the RACH slot allocation information, a third set of candidate RACH transmission occasions for the at least one DU, wherein the third set of candidate RACH transmission occasions is within a physical RACH (PRACH) slot, and wherein determining the third set of candidate RACH transmission occasions further comprises selecting the third set of candidate RACH transmission occasions to be non-overlapping in time with RACH transmission occasions used by the one or more neighbor CUs;

transmit, to the at least one DU, the third set of candidate RACH transmission occasions;

in response to the transmitted third set of candidate RACH transmission occasions, receive, from the at least one DU, a message that defines a selected subset of RACH transmission occasions selected from the third set of candidate RACH transmission occasions;

release, based on the selected subset of RACH transmission occasions, one or more unused RACH transmission occasions from the third set of candidate RACH transmission occasions;

transmit, to the CC, the selected subset of RACH transmission occasions; and

transmit, to the at least one UE via a system information block-type-1 (SIB1) Radio Resource Control (RRC) message, a bit string indicating the selected subset of RACH transmission occasions, wherein the bit string comprises a plurality of bits, each bit of the plurality of bits corresponds to a unique preamble transmission start symbol within the PRACH slot, and wherein a value of each bit of the plurality of bits indicates an enabled state or a disabled state for the corresponding unique preamble transmission start symbol.

2 . The CU according to claim 1 , wherein the computer program code, when executed by the at least one processor, further cause the at least one processor to perform the following operations:

receive, from the at least one UE, a random-access preamble on at least one RACH transmission occasion indicated by the selected subset of RACH transmission occasions.

3 . The CU according to claim 2 , wherein the computer program code, when executed by the at least one processor, further cause the at least one processor to perform the following operations:

request, from the one or more neighbor CUs, the RACH slot allocation information.

4 . The CU according to claim 3 , wherein the computer program code, when executed by the at least one processor, further cause the at least one processor to perform the following operations:

indicate, to the one or more neighbor CUs, the selected subset of RACH transmission occasions.

5 . The CU according to claim 1 , wherein the load measurement information and the interference measurement information are received from the at least one DU via a message on an F1 application protocol (F1AP) interface, and wherein the message is one of a GNB-DU STATUS INDICATION message or a RESOURCE STATUS UPDATE message.

6 . The CU according to claim 5 , wherein the load measurement information comprises a sequence of integer values, and wherein each integer value is an index that maps to a predefined load level in a load mapping table accessible by the CU.

7 . The CU according to claim 6 , wherein the RACH slot allocation information is received from the one or more neighbor CUs via a message on an Xn interface, and wherein the message is one of an XN SETUP message or an NG-RAN NODE CONFIGURATION UPDATE message.

8 . The CU according to claim 7 , wherein the computer program code, when executed by the at least one processor, further cause the at least one processor to perform the following operations:

after releasing the one or more unused RACH transmission occasions, perform an optimization of RACH slot allocations across one or more DUs controlled by the CU based on the selected subset of RACH transmission occasions.

9 . The CU of claim 8 , wherein the bit string is a bit string of size 14.

10 . The CU of claim 9 , wherein the computer program code, when executed by the at least one processor, further cause the at least one processor to perform the following operations: determine the third set of candidate RACH transmission occasions in response to a trigger event, the trigger event comprising at least one of a periodic timer expiring or a detection of an interference level exceeding a predefined threshold.

11 . A method performed by a Central Unit (CU) of a base station (gNB), the method comprising:

receiving, from a control center (CC), a measurement configuration comprising instructions to provide at least one of interference measurement information and load measurement information to the CC;

transmitting, to the at least one Distributed Unit (DU), at least a subset of the measurement configuration;

transmit, to at least one User Equipment (UE), a request for a UE Random-Access Channel (RACH) report;

in response to the transmitted request, obtaining RACH information associated with the at least one UE, wherein the RACH information comprises the UE RACH report defining one or more experienced contention events;

in response to the transmitted subset of the measurement configuration, receiving, from the at least one DU, the load measurement information, and the interference measurement information, for a Physical RACH (PRACH) slot allocation procedure, wherein the load measurement information comprises a number of detected random-access preambles on a first set of candidate Random-Access Channel (RACH) transmission occasions, and wherein the interference measurement information comprises a measurement of received signal power over thermal noise;

receiving, from one or more neighbor CUs, RACH slot allocation information;

transmitting, to the CC, supportive data comprising the received load measurement information, the received interference measurement information, the obtained RACH information, and the received RACH slot allocation information;

in response to the transmitted supportive data, receiving, from the CC, a second set of candidate RACH transmission occasions, wherein the second set of candidate RACH transmission occasions comprises a subset of the first set of candidate RACH transmission occasions and is determined by the CC based on the supportive data;

determining, from the second set of candidate RACH transmission occasions and based at least partly on the RACH information, the load measurements, the interference measurement information, and the RACH slot allocation information, a third set of candidate RACH transmission occasions for the at least one DU, wherein the third set of candidate RACH transmission occasions is within a physical RACH (PRACH) slot, and wherein determining the third set of candidate RACH transmission occasions further comprises selecting the third set of candidate RACH transmission occasions to be non-overlapping in time with RACH transmission occasions used by the one or more neighbor CUs;

transmitting, to the at least one DU, the third set of candidate RACH transmission occasions;

in response to the transmitted third set of candidate RACH transmission occasions, receiving, from the at least one DU, a message that defines a selected subset of RACH transmission occasions selected from the third set of candidate RACH transmission occasions;

releasing, based on the selected subset of RACH transmission occasions, one or more unused RACH transmission occasions from the third set of candidate RACH transmission occasions;

transmitting, to the CC, the selected subset of RACH transmission occasions; and

transmitting, to the at least one UE via a system information block-type-1 (SIB1) Radio Resource Control (RRC) message, a bit string indicating the selected subset of RACH transmission occasions, wherein the bit string comprises a plurality of bits, each bit of the plurality of bits corresponds to a unique preamble transmission start symbol within the PRACH slot, and wherein a value of each bit of the plurality of bits indicates an enabled state or a disabled state for the corresponding unique preamble transmission start symbol.

12 . The method according to claim 11 , wherein the method further comprises:

receiving, from the at least one UE, a random-access preamble on at least one RACH transmission occasion indicated by the selected subset of RACH transmission occasions.

13 . The method according to claim 12 , wherein the method further comprises:

requesting, from the one or more neighbor CUs, the RACH slot allocation information.

14 . The method according to claim 13 , wherein the method further comprises:

indicate, to the one or more neighbor CUs, the selected subset of RACH transmission occasions.

15 . A non-transitory computer readable medium comprising program instructions for causing an apparatus, the apparatus being a Central Unit (CU) of a base station (gNB), to perform at least the following:

receiving, from a control center (CC), a measurement configuration comprising instructions to provide at least one of interference measurement information and load measurement information to the CC;

transmitting, to at least one Distributed Unit (DU), at least a subset of the measurement configuration;

transmitting, to at least one User Equipment (UE), a request for a UE Random-Access Channel (RACH) report;

in response to the transmitted request, obtaining RACH information associated with at least one UE, wherein the RACH information comprises the UE RACH report defining one or more experienced contention events;

in response to the transmitted subset of the measurement configuration, receiving, from the at least one DU, the load measurement information, and the interference measurement information, for a Physical RACH (PRACH) slot allocation procedure, wherein the load measurement information comprises a number of detected random-access preambles on a first set of candidate Random-Access Channel (RACH) transmission occasions, and wherein the interference measurement information comprises a measurement of received signal power over thermal noise;

receiving, from one or more neighbor CUs, RACH slot allocation information;

transmitting, to the CC, supportive data comprising the received load measurement information, the received interference measurement information, the obtained RACH information, and the received RACH slot allocation information;

in response to the transmitted supportive data, receiving, from the CC, a second set of candidate RACH transmission occasions, wherein the second set of candidate RACH transmission occasions comprises a subset of the first set of candidate RACH transmission occasions and is determined by the CC based on the supportive data;

determining, from the second set of candidate RACH transmission occasions and based at least partly on the RACH information, the load measurements, the interference measurement information, and the RACH slot allocation information, a third set of candidate RACH transmission occasions for the at least one DU, wherein the third set of candidate RACH transmission occasions is within a physical RACH (PRACH) slot, and wherein determining the third set of candidate RACH transmission occasions further comprises selecting the third set of candidate RACH transmission occasions to be non-overlapping in time with RACH transmission occasions used by the one or more neighbor CUs;

transmitting, to the at least one DU, the third set of candidate RACH transmission occasions;

in response to the transmitted third set of candidate RACH transmission occasions, receiving, from the at least one DU, a message that defines a selected subset of RACH transmission occasions;

releasing, based on the selected subset of RACH transmission occasions, one or more unused RACH transmission occasions from the third set of candidate RACH transmission occasions;

transmitting, to the CC, the selected subset of RACH transmission occasions; and

transmitting, to the at least one UE via a system information block-type-1 (SIB1) Radio Resource Control (RRC) message, a bit string indicating the selected subset of RACH transmission occasions, wherein the bit string comprises a plurality of bits, each bit of the plurality of bits corresponds to a unique preamble transmission start symbol within the PRACH slot, and wherein a value of each bit of the plurality of bits indicates an enabled state or a disabled state for the corresponding unique preamble transmission start symbol.

16 . The non-transitory computer readable medium according to claim 15 , comprising instructions for causing the apparatus to perform:

receiving, from the at least one UE, a random-access preamble on at least one RACH transmission occasion indicated by the selected subset of RACH transmission occasions.

17 . The non-transitory computer readable medium according to claim 16 , comprising instructions for causing the apparatus to perform:

requesting, from the one or more neighbor CUs, the RACH slot allocation information.

18 . The non-transitory computer readable medium according to claim 17 , comprising instructions for causing the apparatus to perform:

indicate, to the one or more neighbor CUs, the selected subset of RACH transmission occasions.