Mapping between PRACH preambles and PUSCH resource units for 2-step RACH
This disclosure describes improving a 4-step RACH procedure by using a 2-step RACH procedure. A UE transmits a PRACH preamble and associated MsgA physical uplink shared channel (PUSCH) on a configured time and frequency resource. After successful detection of the PRACH preamble, and decoding of the MsgA PUSCH, the gNB transmits MsgB in the second step. Generally, a mapping is used between the PRACH preamble and the PUSCH resource unit for 2-step RACH. This disclosure describes the mapping for 2-step RACH.
1. One or more processors configured to perform operations comprising:
configuring a first number of preambles per Physical Random Access Channel (PRACH) occasion;
configuring multiple disjoint sets of Physical Uplink Shared Channel (PUSCH) occasions, wherein the multiple disjoint sets of PUSCH occasions are multiplexed in a time division multiplexing manner, and wherein an ordering of time resource indexes for time multiplexed PUSCH occasions is based on the multiple disjoint sets of PUSCH occasions;
associating PRACH preambles in PRACH occasions with the time multiplexed PUSCH occasions associated with a Demodulation Reference Signal (DMRS);
receiving a PUSCH transmission from a remote device in accordance with the first number of preambles and the association; and
encoding a message to send to the remote device, the message including random access response (RAR) data in response to the received and PUSCH transmission.
2. The one or more processors of claim 1 , wherein the preambles are ordered based on:
first, an increasing order of preamble indexes within a single PRACH occasion;
second, an increasing order of frequency resource indexes wherein the PRACH occasion is a frequency multiplexed occasion;
third, an increasing order of time resource indexes wherein the PRACH occasion is a time multiplexed occasion;
fourth, an increasing order of indexes for PRACH slots; or
a combination thereof.
3. The one or more processors of claim 1 , wherein a PUSCH occasion includes a number of PUSCH resource units, and wherein the number of PUSCH resource units are ordered based on:
first, an increasing order of Demodulation Reference Signal (DMRS) ports or sequences within the PUSCH occasion;
second, an increasing order of frequency resource indexes, wherein the PUSCH occasion is frequency multiplexed;
third, an increasing order of time resource indexes, wherein the PUSCH occasion is for time multiplexed within a PUSCH slot;
fourth, an increasing order of indexes for MsgA PUSCH slots; or
a combination thereof.
4. The one or more processors of claim 1 , wherein the operations further comprise:
determining the multiple disjoint sets of the PUSCH occasions based on a starting and length indicator value (SLIV) of each of the PUSCH occasions, the SLIV including the index of a first slot.
5. The one or more processors of claim 1 , wherein a synchronization signal block (SSB) is associated at least two PRACH occasions, and wherein a preamble index associated with a PUSCH resource unit is mapped starting from a given preamble for a number of consecutive valid PRACH occasions associated with the SSB, wherein the number is inversely proportional to a number of the PRACH occasions.
6. The one or more processors of claim 1 , wherein a plurality of SSBs are associated with each of the PRACH occasions, wherein operations further comprise mapping a preamble index to a PUSCH resource unit of the PUSCH occasion based on, for an SSB of the plurality, a function the first number of preambles and a number of synchronization signal/physical broadcast channel (SS/PBCH) blocks associated with a PRACH occasion of the PRACH occasions.
7. The one or more processors of claim 1 , further comprising mapping in a consecutive order a DMRS port index associated with a PRACH occasion of the PRACH occasions.
8. The one or more processors of claim 1 , wherein a PRACH occasion of the PRACH occasions has a one-to-one association with the PUSCH occasion, the operations further comprising:
mapping a PUSCH resource unit or a DMRS antenna port associated with the PRACH occasion starting from 0 and increasing consecutively.
9. The one or more processors of claim 1 , wherein separate preamble indexes for the PRACH occasion indicate a corresponding modulation and coding scheme (MCS) or transport block size TBS for transmission of a MsgA PUSCH.
10. One or more processors configured to perform operations comprising:
determining a mapping of Physical Random Access Channel (PRACH) preambles in PRACH occasions with a plurality of Physical Uplink Shared Channel (PUSCH) occasions associated with a Demodulation Reference Signal (DMRS) resource, the determining including:
determining a first number of preambles per PRACH occasion; and
determining multiple disjoint sets of PUSCH occasions in a first slot, wherein an ordering of time resource indexes for time multiplexed PUSCH occasions of the plurality of PUSCH occasions is based on the multiple disjoint sets of PUSCH occasions in the first slot;
encoding for transmitting, to a remote device, a PUSCH transmission based on the first number of preambles and the determined mapping; and
decoding a message from the remote device, the message including random access response (RAR) data in response to the transmitted PUSCH transmission.