Efficient buffer status reporting over 2-step RA
Buffer Status Reports (BSR), by which the network is made aware of uplink transmission needs of wirless devices, are specifically enabled to be transmitted using 2-step Random Access (RA), to reduce latency and network resource use. In one embodiment, 2-step RA configurations tailored to BSR-transmissions are introduced. These may, for example, use a subset of the configured resources in the configured 2-step RA resources for BSR. In another embodiment, conditions for triggering BSR over 2-step RA, depending on the traffic, are introduced. For example, the priority or the the delay budget of the traffic may be used to determine whether a BSR over 2-step RA should be triggered. In another embodiment, simplified procedures when receiving the response to MsgA are introduced. These may include, for example, not transmitting a full MsgB, but rather having the UE receive an UL grant.
1. A method of buffer status reporting performed by a wireless device operative in a wireless communication network, the method comprising:
obtaining, from the wireless communication network, one or more configurations specifically for sending a Buffer Status Report (BSR) using a 2-step Random Access (RA) procedure by the one or more configurations defining at least one RACH opportunity as exclusive to the BSR reporting; and
transmitting, to the wireless communication network the BSR, in the MsgA of the 2-step RA;
wherein the one or more configurations is different to a configuration for a MsgA transmission which does not comprise a BSR.
2. The method of claim 1 , wherein the method comprises, prior to the transmitting, determining, from a MsgA configuration index, time and frequency domain resources available for the BSR reporting.
3. The method of claim 1 , wherein the method comprises, after the transmitting the BSR, monitoring a Physical Downlink Control Channel (PDCCH) to obtain an uplink grant.
4. The method of claim 1 , wherein the obtaining comprises obtaining:
a configuration for sending the BSR using the 2-step RA procedure that is specific to a logical channel or a logical channel group;
a configuration specifying which logical channel or logical channel group is used for the BSR;
a configuration that is configured specifically for triggering a transmission of the BSR using the 2-step RA procedure;
a configuration wherein only a subset of Physical Uplink Shared Channel (PUSCH) resources allocated to the 2-step RA MsgA are allocated for the BSR;
a configuration specifying a power ramping step and/or a specific power ramping counter for retransmissions of MsgA PUSCH containing the BSR;
a configuration specifying a maximum number of attempts to transmit the MsgA in the 2-step RA before failure or fallback initiation; or
a configuration specifying one or both of a MsgB window duration and a maximum count of the MsgA retransmissions when no associated MsgB is received within the MsgB window.
5. The method of claim 1 , wherein the obtaining comprises obtaining:
a configuration specifying a zero Back-Off indicating immediate retransmission of the MsgA when no associated MsgB is received within a specified MsgB window;
a configuration specifying a prioritized Back-Off indicating a smaller delay for retransmission of the MsgA, when no associated MsgB is received within the specified MsgB window, than for 2-step RA procedures not transmitting BSR;
a configuration specifying a prioritized Back-Off indicating a delay for retransmission of the MsgA, when no associated MsgB is received within the specified MsgB window, wherein the delay is scaled by priority;
a configuration specifying that one or more thresholds related to Physical Uplink Shared Channel (PUSCH) resource selection or the 2-step RA are specifically configured or may be omitted for the 2-step RA reporting the BSR; or
a configuration wherein the preamble is associated with PUSCH Resource Units (RU) with sizes suitable for the BSR transmission but too small to contain an RRC signaling message.
6. The method of claim 1 , wherein the obtaining comprises obtaining a configuration wherein only a subset of Physical Uplink Shared Channel (PUSCH) occasion (PO) sets in the time domain are specified to be used for the BSR reporting.
7. The method of claim 6 , wherein the PO sets allocated for the BSR reporting, out of all PO sets, are indicated by a bit map signaled by the wireless communication network.
8. The method of claim 1 , wherein the obtaining comprises obtaining a configuration specifying that the configuration is valid only when the wireless device does not have any Physical Uplink Control Channel (PUCCH) resources for Scheduling Request (SR) transmission.
9. The method of claim 1 , wherein the transmitting comprises:
transmitting only the BSR, using a configuration with Physical Uplink Shared Channel (PUSCH) Resource Units (RUs) only suitable for BSR transmission; or
transmitting the BSR together with non-BSR data using a configuration with PUSCH RUs large enough for more than BSR transmission.
10. The method of claim 1 , wherein the method comprises, when the transmitted MsgA of the 2-step RA containing the BSR is not received by the wireless communication network, or the wireless device cannot decode a responsive MsgB, performing a Scheduling Request (SR) procedure.
11. The method of claim 1 , wherein the method comprises:
prior to transmitting the BSR in a MsgA, determining that conditions allow a BSR using the 2-step RA procedure; and
wherein transmitting the BSR in a MsgA comprises transmitting the BSR in a MsgA of a 2-step RA according to the determined conditions.
12. The method of claim 11 , wherein the determining that conditions allow the BSR transmission by the 2-step RA comprises:
determining that no uplink shared channel resource is available for the BSR transmission and a Scheduling Request (SR) is triggered;
determining that the data received in a buffer exceeds a threshold;
determining that a logical channel triggering the BSR has no SR configuration;
determining that a valid Physical Uplink Control Channel (PUCCH) resource is not available before a configured time after SR has been triggered;
determining that a logical channel or a logical channel group for which the BSR is triggered uses, or is configured to use, the 2-step RA to report the BSR;
determining that a logical channel or a logical channel group for which the BSR is triggered has a delay metric less than a threshold; or
determining that a logical channel or a logical channel group for which the BSR is triggered has a priority higher than a configured value.
13. A wireless device operative in a wireless communication network, comprising:
communication circuitry configured to wirelessly communicate with one or more nodes of the wireless communication network; and
processing circuitry operatively connected to the communication circuitry, the processing circuitry configured to cause the wireless device to:
obtain, from the wireless communication network, one or more configurations specifically for sending a Buffer Status Report (BSR) using a 2-step Random Access (RA) procedure by the one or more configurations defining at least one RACH opportunity as exclusive to the BSR reporting, wherein the one or more configurations is different to a configuration for a MsgA transmission which does not comprise the BSR;
receive data in a buffer; and
transmit, to the wireless communication network, the BSR in the MsgA of the 2-step RA.
14. A method, performed by a base station operative in a wireless communication network, of receiving a Buffer Status Report (BSR) from a wireless device with low latency, the method comprising:
configuring one or more wireless devices with one or more configurations in a cell with 2-step Random Access (RA) resources specifically for use in BSR, wherein the one or more configurations is different to a configuration for a MsgA transmission which does not comprise the BSR; and
receiving, from a wireless device of the one or more wireless devices, the BSR in a MsgA of the 2-step RA.
15. The method of claim 14 , wherein the configuring comprises:
providing a configuration that is specific to a logical channel or a logical channel group;
providing a configuration that is configured specifically for triggering a transmission of the BSR using the 2-step RA procedure;
providing a configuration wherein only a subset of Physical Uplink Shared Channel (PUSCH) resources allocated to the 2-step RA MsgA are allocated for BSR;
providing a configuration specifying one or both of a power ramping step and a specific power ramping counter for retransmissions of MsgA PUSCH containing the BSR;
providing a configuration specifying a maximum number of attempts to transmit MsgA in the 2-step RA before failure or fallback initiation; or
providing a configuration specifying one or both of a MsgB window duration and a maximum count of the MsgA retransmissions when no associated MsgB is received within the MsgB window.
16. The method of claim 14 , wherein the configuring comprises:
providing a configuration specifying a zero Back-Off indicating immediate retransmission of the MsgA when no associated MsgB is received within a specified MsgB window;
providing a configuration specifying a prioritized Back-Off indicating a smaller delay for retransmission of the MsgA, when no associated MsgB is received within a specified MsgB window, than for the 2-step RA procedures not transmitting the BSR;
providing a configuration specifying a prioritized Back-Off indicating a delay for retransmission of the MsgA, when no associated MsgB is received within a specified MsgB window, wherein the delay is scaled by priority;
providing a configuration specifying that one or more thresholds related to Physical Uplink Shared Channel (PUSCH) resource selection or 2-step RA are specifically configured or may be omitted for the 2-step RA reporting the BSR; or
providing a configuration specifying that the configuration is valid only when the wireless device does not have any Physical Uplink Control Channel (PUCCH) resources for Scheduling Request (SR) transmission.
17. The method of claim 14 , wherein the configuring comprises providing a configuration wherein only a subset of Physical Uplink Shared Channel (PUSCH) occasion (PO) sets in the time domain are specified to be used for BSR transmission.
18. The method of claim 14 , wherein the configuring comprises providing a configuration wherein a preamble is associated with Physical Uplink Shared Channel (PUSCH) Resource Units (RUs) with sizes suitable for the BSR transmission but too small to contain an RRC signaling message.
19. The method of claim 14 :
wherein the base station is able to determine, from a preamble and Physical Uplink Shared Channel (PUSCH) Resource Unit associated with the received MsgA, that the MsgA transmission contains the BSR, but the base station is unable to decode a full MsgA;
wherein the method comprises:
selecting a size for an uplink data transmission from the wireless device based on one of expected characteristics of data traffic, an average of prior data traffic, and a preconfigured size; and
transmitting to the wireless device an uplink grant of the selected size.
20. A base station operative in a wireless communication network, comprising:
communication circuitry configured to wirelessly communicate with one or more wireless devices; and
processing circuitry operatively connected to the communication circuitry, the processing circuitry configured to cause the base station to:
configure one or more wireless devices with one or more configurations in a cell with 2-step Random Access (RA) resources specifically for use in a Buffer Status Report (BSR), wherein the one or more configurations is different to a configuration for a MsgA transmission which does not comprise the BSR; and
receive, from a wireless device of the one or more wireless devices, the BSR in the MsgA of the 2-step RA.