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US-20260129671-A1 - Determination of PRACH Occasions and PUSCH Occasions for 2-Step Random Access

US20260129671A1US 20260129671 A1US20260129671 A1US 20260129671A1US-20260129671-A1

Abstract

Operation in unlicensed spectrum requires Clear Channel Assessment (CCA), where a transmitter must monitor the channel before transmitting, to ensure it is free. An exception is a brief gap that allows for Rx/Tx turn-around, so that an ACK can be transmitted following reception, without performing a new CCA. NR introduces a 2-step Random Access (RA) procedure, where MsgA includes both PRACH and PUSCH transmission. To minimize CCA delays in unlicensed spectrum, only those RACH opportunities (ROs) and PUSCH opportunities (POs) that result in a very small delay between the PRACH and PUSCH transmissions of MsgA should be employed. RO configurations are defined for LTE 4-step RA. Embodiments provide methods for selecting which of these be may be shared for 2-step RA, for selecting which should be used in case of collisions, for selecting ROs and POs when the configurations are not shared, and for communicating RO configurations to UEs.

Inventors

  • Jan Christoffersson
  • Min Wang
  • Stephen Grant
  • Robert Mark Harrison
  • Zhipeng Lin
  • Johan Rune
  • Johan Axnäs

Assignees

  • TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

Dates

Publication Date
20260507
Application Date
20260106

Claims (20)

  1. 1 . A method, performed by a wireless device operative in a wireless communication network, of performing a Random Access (RA) procedure, the method comprising: receiving signaling indicating a plurality of pre-configured Random Access Channel (RACH) occasions (RO) which are candidates for specific Physical Random Access Channel (PRACH) transmissions of a 2-step or prioritized RA procedure; and transmitting, to the network, an RA preamble in one of the plurality of pre-configured ROs.
  2. 2 . The method of claim 1 , wherein the signaling indicates which ROs are shared between the 2-step RA procedure and a 4-step RA procedure.
  3. 3 . The method of claim 1 , wherein the signaling comprises a PRACH mask indicating which ROs are shared between the 2-step RA procedure and a 4-step RA procedure.
  4. 4 . The method of claim 1 , wherein the method comprises: receiving signaling indicating a plurality of Physical Uplink Shared Channel (PUSCH) occasions (PO), each comprising a plurality of periodically recurring symbols in which a PUSCH transmission may occur; receiving signaling indicating a subset of RA resources, each comprising one of the pre-configured RO immediately followed by a first symbol of one of the PO; and transmitting to the network a PUSCH transmission in a PO associated with the transmitted RA preamble.
  5. 5 . The method of claim 1 , wherein the received indication of a plurality of pre-configured ROs comprises: a flag indicating whether the plurality of candidate ROs includes only the last RO in a RACH slot or all ROs of the plurality of candidate Ros; an integer N≥1 indicating that the plurality of candidate ROs consists of the last N ROs in a RACH slot; or an indication of a bitmask indicating which pre-configured ROs are candidates for specific PRACH transmissions.
  6. 6 . The method of claim 1 , wherein the signaling indicating a plurality of pre-configured ROs includes or references a new or modified PRACH configuration table that includes short PRACH formats spanning only one PRACH occasion at the end of or within a PRACH slot.
  7. 7 . The method of claim 6 , wherein the PRACH configuration or RO is allocated for a 2-step RA, and the associated msgA PUSCH resources can be configured to follow the PRACH occasion within the PRACH slot within a predetermined duration.
  8. 8 . The method of claim 1 , wherein the plurality of pre-configured ROs comprises separately configured 2-step ROs for use in 2-step RA and 4-step ROs for use in 4-step RA.
  9. 9 . The method of claim 8 , further comprising, for each collision between 2-step ROs and 4-step ROs: if the colliding 2-step RO is the last 2-step RO in a PRACH slot, invalidating colliding 4-step ROs and using the 2-step RO for 2-step RA; and if the colliding 2-step RO is other than the last 2-step RO in a PRACH slot, invalidating the 2-step ROs and using the 4-step RO for 4-step RA.
  10. 10 . The method of claim 9 , further comprising, for each collision between 2-step ROs and 4-step ROs: if the colliding 2-step RO is configured with a gap until the first symbol of an associated PUSCH transmission of less than a predetermined duration, invalidating colliding 4-step ROs and using the 2-step RO for 2-step RA; and otherwise, invalidating the 2-step ROs and using the 4-step RO for 4-step RA.
  11. 11 . The method of claim 9 , further comprising: if a 4-step RO collides with a 2-step msgA PUSCH resource allocation that is allocated with a gap from its associated preceding 2-step RO of less than a predetermined duration, invalidating colliding 4-step ROs and using the 2-step RO for 2-step RA; and otherwise, invalidating the colliding msgA PUSCH resource allocation and using the 4-step RO for 4-step RA.
  12. 12 . The method of claim 1 : wherein the plurality of pre-configured ROs comprises shared or separately configured 2-step ROs for use in 2-step RA and 4-step ROs for use in 4-step RA; and wherein the signaling indicates only the last 2-step RO in a PRACH slot for 2-step RA.
  13. 13 . The method of claim 12 , wherein selecting only the last 2-step RO in a PRACH slot for 2-step RA comprises selecting only the last 2-step RO in a PRACH slot only if the wireless device is operating in unlicensed spectrum.
  14. 14 . The method of claim 1 : wherein the signaling indicating a plurality of pre-configured ROs comprises a PRACH mask indicating which RO of a PRACH configuration can be used; wherein the PRACH mask index indicates: that only the last RO in a PRACH slot can be used; that only the last k ROs in a PRACH slot can be used, where K is an integer ≥1; that all ROs other than the RO in a PRACH slot can be used; that only the ROs having an associated PUSCH resource allocation that immediately follows the RO can be used for 2-step RA; or that only the ROs having an associated PUSCH resource allocation that immediately follows the RO with a gap of 25 usec or less can be used for 2-step RA.
  15. 15 . The method of claim 4 : wherein the plurality of pre-configured ROs comprises separately configured 2-step ROs for use in 2-step RA and 4-step ROs for use in 4-step RA; wherein one or more 4-step ROs are invalidated by one or more 2-step ROs; wherein the plurality of pre-configured ROs is identified by a first configuration signaled to the wireless device; and wherein the subset of RA resources comprises one or more ROs wherein the wireless device may only transmit a RA preamble associated with the PUSCH.
  16. 16 . 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: receive signaling indicating a plurality of pre-configured Random Access (RA) Channel (RACH) occasions (RO) which are candidates for specific Physical Random Access Channel (PRACH) transmissions of a 2-step or prioritized RA procedure; and transmit to the network an RA preamble in one of the plurality of pre-configured ROs.
  17. 17 . The wireless device of claim 16 , wherein the signaling comprises a PRACH mask indicating which ROs are shared between the 2-step RA procedure and a 4-step RA procedure.
  18. 18 . A method, performed by a base station operative in a wireless communication network, of participating in a Random Access (RA) procedure, the method comprising: sending, to one or more wireless devices, signaling indicating a plurality of pre-configured Random Access Channel (RACH) occasions (RO) which are candidates for specific Physical Random Access Channel (PRACH) transmissions of a 2-step or prioritized RA procedure of a 2-step or prioritized RA procedure; and receiving, from a wireless device, an RA preamble in one of the plurality of pre-configured ROs.
  19. 19 . The method of claim 18 , wherein the signaling indicates which ROs are shared between the 2-step RA procedure and a 4-step RA procedure.
  20. 20 . The method of claim 18 , wherein the signaling comprises a PRACH mask indicating which ROs are shared between the 2-step RA procedure and a 4-step RA procedure.

Description

RELATED APPLICATIONS This application is a continuation of prior U.S. application Ser. No. 17/765,497 filed 31 Mar. 2022, which was the National Stage of International Application PCT/EP2020/077747 filed 2 Oct. 2020, which claims priority to U.S. Application No. 62/910,294 filed 3 Oct. 2019, disclosure of each being hereby incorporated by reference herein. TECHNICAL FIELD The present invention relates generally to wireless communication, and in particular to systems and methods for determining PRACH and PUSCH occasions for a 2-step Random Access procedure. BACKGROUND Wireless communication networks, including network nodes and radio network devices such as cellphones and smartphones, are ubiquitous in many parts of the world. These networks continue to grow in capacity and sophistication. To accommodate both more users and a wider range of types of devices that may benefit from wireless communications, the technical standards governing the operation of wireless communication networks continue to evolve. The fourth generation (4G) of network standards has been deployed, and the fifth generation (5G, also known as New Radio, or NR) is in development. 5G is not yet fully defined, but in an advanced draft stage within the Third Generation Partnership Project (3GPP). 5G wireless access will be realized by the evolution of Long Term Evolution (LTE) for existing spectrum, in combination with new radio access technologies that primarily target new spectrum. Thus, it includes work on a 5G New Radio (NR) Access Technology, also known as next generation (NX). The NR air interface targets spectrum in the range from below 1 GHz up to 100 GHz, with initial deployments expected in frequency bands not utilized by LTE. Some LTE terminology may be used in this disclosure in a forward looking sense, to include equivalent 5G entities or functionalities, although a different term is or may eventually be specified in 5G. In addition to expanded bandwidth and higher bitrates to enrich User Equipment (UE) experience, the 5G NR technology will include expanded support for machine-to-machine (M2M) or machine type communications (MTC), variously known as the Networked Society or Internet of Things (IoT). Accordingly, use of the term “UE” herein is synonymous with “wireless device,” and specifically includes wireless devices that have no “user.” Although some M2M communications are anticipated to be intermittent, delay-tolerant, and low bandwidth, such as utility meter reading and similar status-reporting type applications, other anticipated applications will require very low latency—indeed, near-real-time—such as autonomous vehicle control. Reduced latency is also a requirement for many modes of service to conventional UE such as smartphones, such as high resolution video conferencing, interactive gaming, and the like. Accordingly, reducing latency in all aspects of wireless communication network operation stands as one major challenge in 5G systems and beyond. Additionally, in NR, both license assisted access (LAA) and standalone operation in unlicensed spectrum (NR-U) are to be supported in 3GPP. Hence the procedure of PRACH transmission and/or scheduling request (SR) transmission in unlicensed spectrum shall be investigated in 3GPP. With network operation in unlicensed spectrum follows a number of restrictions. One of them is that a device (e.g. a radio network node or a mobile terminal) must monitor the shared medium, i.e. the channel, and determine that it is free (not being used by any other device) before starting to transmit on the channel. This procedure is referred to as Listen-Before-Talk (LBT) or Clear Channel Assessment (CCA). In this mechanism, a radio device performs energy detection (ED) on the channel over a time period. The channel is determined to be idle—meaning transmission can proceed—if the detected energy is less than an energy detection threshold (ED threshold). In this case, the device may only transmit on the channel up to a predetermined time duration, referred to as the maximum channel occupancy time (MCOT). If the channel is determined to be occupied (detected energy >ED threshold), the transmitter performs a random back-off within a contention window before again attempting to access the channel. One exception to the need to perform LBT/CCA prior to accessing the network is that a device may transmit an ACK/NACK if it is within a predetermined “gap” timing following a received transmission. When first accessing the network, a UE performs a Random Access (RA) procedure. In LTE, this is a 4-step procedure, as indicated by FIG. 1. Briefly, the UE receives synchronization signals and system information periodically broadcast by the network. The UE then transmits a Random Access preamble on the Physical Random Access Channel (PRACH), referred to as message 1 (msg1). The network transmits a Random Access Response (RAR) message, or msg2, which includes timing and uplink resource information (as indicated, this