WO2021064439A1

WO2021064439A1 - A method of transmitting prach in nru system

Info

Publication number: WO2021064439A1
Application number: PCT/IB2019/001165
Authority: WO
Inventors: Hao Lin
Original assignee: Orope France Sarl
Priority date: 2019-10-04
Filing date: 2019-10-04
Publication date: 2021-04-08

Abstract

The disclosure is related to a physical random access channel (PRACH) transmission method, performed by a user equipment in unlicensed spectrum, wherein a PRACH frequency domain preamble for the transmission over multiple random access channel occasions (ROs) is configured, the method comprising: - obtaining the configuration about the number of ROs in frequency domain, each RO being assigned with an RO index; - obtaining the configuration about RO indexes among the number of ROs to be used for simultaneous PRACH preamble transmission; - obtaining the configuration about a range representing at least a part of cyclic shift candidates, each cyclic shift candidate being defined by a cycle shift value, a position associated with the cyclic shift value and a parameter T chosen among a plurality of possible parameter values, the configured range containing one reference cycle shift value; - selecting one position to associate with the reference cyclic shift value and/or one parameter value of T among the possible parameter values; - determining the cyclic shift values at other positions within the configured range; - determining the PRACH preamble for ROs to be used for simultaneous PRACH preamble transmission; - mapping the PRACH preamble to the configured RO indexes; transmitting simultaneously the PRACH preamble over the multiple ROs to be used.

Description

A method of transmitting PRACH in NRU system

Technical Field

[0001] The present disclosure relates to the field of communication technologies in unlicensed spectrum, and in particular, to a physical random access channel (PRACH) transmission method, performed by a user in a wireless communication system supporting an unlicensed band and apparatuses supporting the same.

[0002] The communication technology is for example a 5G (fifth generation) network using the 5G NR (New Radio) as radio access technology (RAT) defined by 3GPP. The present disclosure is applicable to 5G NR-U (NR in unlicensed spectrum).

Background

[0003] In NR Rel. 15, the PRACH is transmitted in the initial BWP which can be configured having 24, 48, 96 RB. In the initial BWP, the network can configure multiple RACH occasions (RO) with each RO containing 12 RBs. Figure 1 shows an example of 4 ROs, each containg 12 RBs. These multiple ROs can be configured in time domain and/or in frequency domain. In NR, once the UE obtains the RO configuration, it will select one RO to PRACH transmission. The PRACH is obtained by selecting one sequence out of a pre-defined sequence group, which contains max 64 sequences for UE selection.

[0004] PRACH in NR-U

[0005] In unlicensed band, there is a regulation imposing that for every transmission in a 20MHz band, the actual transmission has to ensure at least 80% of the bandwidth usage, aka., Occupancy channel bandwidth (OCB) requirement. As shown in the example of Figure 1 , for a NR-U system with 30Khz subcarrier space, if the network configures 48 RB initial BWP (i.e. 17.28Mhz bandwidth), and if the UE reuses Rel.15 PRACH over one selected RO (1 RO=360KHz bandwidth). Thus the OCB requirement is not satisfied. To solve this OCB issue, the UE has to transmit PRACH over multiple frequency domain ROs, e.g. transmit over RO#0,1 ,2,3 simultaneously or over RO#0,3, simultaneously. It is to note that the OCB regards the bandwidth between the lowest frequency up to the highest frequency of the transmission, which does not impose a transmission without gap in the transmission spectrum. Thus, transmission over RO#0~3 is equivalent to over RO#0,3. [0006] In NR Rel.15, PRACH only transmits over one RO, but in NR-U, UE needs to transmit over multiple ROs, which raise at least two issues. The first issue is that if the UE simply repeats the NR Rel.15 PRACH over multiple ROs in frequency domain, the Peak-to-Average Power Ratio (PAPR) will be significantly increased leading to reduced coverage. The second issue is that using more ROs will reduce the system multiplexing capacity resulting in a reduced number of UEs accessing the network simultaneously.

Summary [0007] A first object of the present disclosure is a physical random access channel (PRACH) transmission method, performed by a user equipment in unlicensed spectrum, wherein a PRACH frequency domain preamble for the transmission over multiple random access channel occasions (ROs) is configured, the method comprising: - obtaining the configuration about the number of ROs in frequency domain

(N_R0), each RO being assigned with an RO index l_R0 = 0, ... , N_RO - l);

- obtaining the configuration about RO indexes among the number of ROs to be used for simultaneous PRACH preamble transmission,

and its total number is

- obtaining the configuration about a range representing at least a part of cyclic shift candidates ( m_cs = 0, ...,L_RA - 1), each cyclic shift candidate being defined by a cycle shift value m_cs, a position (r) associated with the cyclic shift value and a parameter (T) chosen among a plurality of possible parameter values, the configured range containing one reference cycle shift value; - selecting one position (r) to associate with the reference cyclic shift value

(rn.cs) and/or one parameter value of T among the possible parameter values;

- determining the cyclic shift values at other positions (j) within the configured range;

- determining the PRACH preamble for ROs to be used for simultaneous PRACH preamble transmission

- mapping the PRACH preamble

to the configured RO indexes

- transmitting simultaneously the PRACH preamble over the multiple ROs to be used.

[0008] Such method allows to generate and transmit simultaneously the PRACH preamble over the multiple ROs to be used for transmission and securing that the PRACH preamble is not simply repeated in each RO.

[0009] Advantageously, the range of cyclic shift candidates is restricted to a part of cyclic shift candidates depending on services provided by the user equipment or on the type of user equipment.

[0010] Advantageously, the method comprises:

- obtaining the reference cyclic shift value either by a direct indication, an indirect indication or by a default value.

[0011] Advantageously, the method comprises :

- obtaining the configuration about a range representing at least a part of possible positions associated with the reference cyclic shift value.

[0012] Advantageously, the range of possible positions associated with the reference cyclic shift value is pre-defined.

[0013] Advantageously, the method comprises :

- obtaining the configuration about a range representing at least a part of possible parameter T values

[0014] Advantageously, the range representing possible parameter T values is pre-stored by the user equipment.

[0015] Advantageously, wherein the PRACH frequency domain preamble is defined with a PRACH sequence length and wherein the parameter T value is a co prime number of the PRACH sequence length and is smaller than the PRACH sequence length.

[0016] Advantageously, the cyclic shift values determination at other positions is derived in a way such that the following relation is satisfied:

[0017] Advantageously, the PRACH preamble determination for ROS is

determined by:

[0018] Advantageously, a Random Access - Radio Network Temporary Identifier (RA-RNTI) value is defined, the RA-RNTI value being depending either on the first RO index used for simultaneous PRACH preamble transmission or on an initial RO index used for simultaneous PRACH preamble transmission, the initial RO index being associated with an synchronization signal block (SSB) beam index and determined as the RO in which the UE uses the reference cyclic shift value to transmit the PRACH preamble.

[0019] Such RA-RNTI definition allows to increase UE multiplexing especially when using initial RO index used for simultaneous PRACH preamble transmission. [0020] A second object of the present disclosure is a user equipment transmitting a physical random access channel (PRACH) to a base station in a wireless communication system in unlicensed spectrum, wherein a PRACH frequency domain preamble for the transmission over multiple random access channel occasions (ROs) is configured, the user equipment comprising:

- a processor configured to o obtain the configuration about the number of ROs in frequency domain, each RO being assigned with an RO index; o obtain the configuration about RO indexes among the number of ROs to be used for simultaneous PRACH preamble transmission; o obtain the configuration about a range representing at least a part of cyclic shift candidates, each cyclic shift candidate being defined by a cycle shift value, a position associated with the cyclic shift value and a parameter T chosen among a plurality of possible parameter values, the configured range containing one reference cycle shift value; o select one position to associate with the reference cyclic shift value and/or one parameter value of T among the possible parameter values; o determine the cyclic shift values at other positions within the configured range; o determine the PRACH preamble for ROs to be used for simultaneous PRACH preamble transmission; o map the PRACH preamble to the configured RO indexes; and

- a transmitter to transmit simultaneously the PRACH preamble over the multiple ROs to be used.

[0021] Advantageously, the range of cyclic shift candidates is restricted to a part of cyclic shift candidates depending on services provided by the user equipment or on the type of user equipment.

[0022] Advantageously, the processor is confugred to obtain the reference cyclic shift value either by a direct indication, an indirect indication or by a default value.

[0023] Advantageously, the processor is confugred to obtain the configuration about a range representing at least a part of possible positions associated with the reference cyclic shift value.

[0024] Advantageously, the range of possible positions associated with the reference cyclic shift value is pre-defined.

[0025] Advantageously, the processor is confugred to obtain the configuration about a range representing at least a part of possible parameter T values.

[0026] Advantageously, the range representing possible parameter T values is pre-stored by the user equipment.

[0027] Advantageously, the PRACH frequency domain preamble is defined with a PRACH sequence length and wherein the parameter T value is a co-prime number of the PRACH sequence length and is smaller than the PRACH sequence length.

[0028] Advantageously, the cyclic shift values determination at other positions is derived in a way such that the following relation is satisfied:

[0029] Advantageously, the PRACH preamble determination for ROS is

determined by:

[0030] Advantageously, a Random Access - Radio Network Temporary Identifier (RA-RNTI) value is defined, the RA-RNTI value being depending either on the first RO index used for simultaneous PRACH preamble transmission or on an initial RO index used for simultaneous PRACH preamble transmission, the initial RO index being associated with an synchronization signal block (SSB) beam index and determined as the RO in which the UE uses the reference cyclic shift value to transmit the PRACH preamble.

[0031] A third object of the present disclosure is a computer readable medium comprising program instructions for causing a user equipment to perform the steps of the PRACH transmitting method according to the first aspect.

Brief description of the drawings

[0032] The appended drawings required in description of embodiments or the prior art will be briefly described below.

- Fig. 1 shows an example of 4 ROs;

- Fig. 2A-2B show examples of possible choices for position selection;

- Fig. 3A-3G show several examples choices for NR-U PRACH preamble selection; - Fig. 4A-4B shows two additional example choices;

- Fig. 5 shows the PRACH preamble transmitted over 4 ROs for 2 user equipments.

Description of embodiments

[0033] In the following disclosure and examples to illustrate this disclosure, if the PRACH is transmitted over multiple ROs in frequency domain at the same time, we propose that the PRACH sequence in frequency domain at /- th RO has the following expression :

where is /-th cyclic shift value for /-th RO, S^R15(n) is the NR Rel.15 PRACH preamble in frequency domain, n is element index of the NR Rel.15 PRACH preamble in frequency domain, L_RA is the sequence length within one RO (e.g. in NR Rel.15, L_RA = 139 for subcarrier space 30kHz), is the number of simultaneously

transmitted RO in frequency domain.

[0034] For multiple RO index in frequency domain, the cyclic shift values of different RO index should verify the following relation :

where T is a co-prime integer of L_RA and smaller than L_RA.

[0035] UE selects NRU PRACH mechanism

[0036] There are 64 pre-defined NR Rel.15 PRACH sequences, noted hereafter S^R15.

[0037] For NR-U, assuming that the network configures N_R0 in the frequency domain and among them can be used to transmit PRACH simultaneously (note

that can be set equal to N_R0). Then we will define a reference cyclic shift value equal to 0, and its corresponding RO index,

For example, the network configured 4 ROs in frequency domain ( N_R0 = 4) and two ROs are selected to be transmitted simultaneously

. Thus the possible choices for r are r =0,1.

[0038] As shown in Figure 2A, if UE selects r = 0, that is meaning

that the reference cyclic shift value is used at the first Tx RO in frequency domain. As shown in Figure 2B, if the UE selects r - 1, that is meaning that the

reference cyclic shift value is used at the second Tx RO in frequency domain.

[0039] Then the rest of cyclic shift values for

ROs will be derived by

[0040] Therefore, besides S^R15 , the network can have reference cyclic

shift position r. Moreover, since T is a co-prime integer of L_RA and smaller than L_RA, and if L_RA = 139, the number of candidate values of T is T_tot = 138, i.e. T = 1, ... ,138. In total, UE can have max choices for NR-U PRACH preamble

selection. Some examples are given in relation with Figures 3A-3G.

[0041] The network can of course disable parts of the choices in order to reduce the blind detection on the base-station side. One option to do so, is to fix T and only let UE to select r and S^R15. Or it can also be fixing r and let UE to select T and S^R15.

[0042] RA-RNTI determination based on initial RO

[0043] In NR Rel.15 only one RO is used to transmit PRACFI preamble, then the RA-RNTI depends on the transmitted RO index. In NR-U, multiple ROs are used to transmit NRU PRACFI preamble. Here we present how the UE and base-station (BS) determine the RA-RNTI for the PRACH transmission.

[0044] In the 3GPP specification RA-RNTI is defined as follows:

where sjd is the index of the first OFDM symbol of the PRACH occasion (0 < sjd < 14), tjd is the index of the first slot of the PRACH occasion in a system frame (0 < tjd < 80), fjd is the index of the PRACH occasion in the frequency domain (0 < fjd < 8), and ul_carrier_id is the UL carrier used for Random Access Preamble transmission (0 for NUL carrier, and 1 for SUL carrier).

[0045] There are two options to determine the RA-RNTI. In the first option, the RA-RNTI only depends on the first RO index of the overall transmitted PRACH ROs. In the second option, the RA-RNTI depends on the initial RO index.

[0046] If one UE1 selects

and UE2 selects

then for UE1, the cyclic shift values for RO index {0,1 , 2, 3} are

determined as shown in Figure 4A and for UE2, the cyclic shift values for RO index {0,1 , 2, 3} are determined as shown in Figure 4B.

[0047] In the example as represented in Figure 5, we show the PRACH preamble transmitted over 4 ROs for UE1 and UE2. Note that S1 is the PRACH preamble obtained based on the cyclic shift value 0, S2 is based on the cyclic shift value 2, and S3 is based on the cyclic shift value 4. S4 is based on the cyclic shift value 6.

[0048] Example of option 1

[0049] With option 1 , the RA-RNTI is only depending on the first RO index of the overall transmitted bandwidth, then for UE1 and UE2 share the same PRACH transmission bandwidth, leading thus to the same RA-RNTI value. In this example, the first RO index is RO#0.

[0050] Example of option 2

[0051] For option 2, the RA-RNTI depends on the initial RO index. Here we determine the initial RO as the RO in which the UE uses the reference cyclic shift value to generate the PRACH preamble. Thus, in the example of Figure 5, the initial RO for UE1 is RO#0, but for UE2 the initial RO becomes RO#2. Thus, the RA-RNTI of UE1 depends on the RO#0, but the RA-RNTI of UE2 depends on RO#2. In this case, they have different RA-RNTI value.

[0052] The initial RO index can be used to associate with SSB beam index. Assuming the association is konwn by the UE, then the UE will select the initial RO index according to its detected SSB beam index. Thus, UEs will have different RA- RNTI. Then the BS will know which UE receives which SSB beam.

[0053] List of abbreviations in the description and drawings:

[0054] In the above description, the mobile telecommunication system is a 5G mobile network comprising a 5G NR access network. The present example embodiment is applicable to NR in unlicensed spectrum (NR-U). The present disclosure can be applied to other mobile networks, in particular to mobile network of any further generation cellular network technology (6G, etc.).

[0055] The above is only a specific implementation manner of the present disclosure, the protection scope of the present disclosure is not limited thereto, and changes or substitutions that can easily be thought of by those skilled in the art within the technical scope disclosed in the present disclosure should be covered by the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be subject to the protection scope of the claims.

[0056] The various embodiments / examples, aspects and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the disclosure.

Claims

1. A physical random access channel (PRACH) transmission method, performed by a user equipment in unlicensed spectrum, wherein a PRACH frequency domain preamble for the transmission over multiple random access channel occasions (ROs) is configured, the method comprising:

- obtaining the configuration about the number of ROs ( N_R0 ) in frequency domain, each RO being assigned with an RO index ( l_R0);

- obtaining the configuration about RO indexes among the number of ROs to be used for simultaneous PRACH preamble transmission

- obtaining the configuration about a range representing at least a part of cyclic shift candidates ( m_cs = 0, ...,L_RA - 1), each cyclic shift candidate being defined by a cycle shift value m_cs, a position (r) associated with the cyclic shift value and a parameter ( T) chosen among a plurality of possible parameter values, the configured range containing one reference cycle shift value;

- selecting one position (r) to associate with the reference cyclic shift value and/or one parameter value of T among the possible parameter values;

- mapping the PRACH preamble to the configured RO indexes

2. The physical random access channel (PRACH) transmission method according to claim 1 , wherein the range of cyclic shift candidates is restricted to a part of cyclic shift candidates depending on services provided by the user equipment or on the type of user equipment.

3. The physical random access channel (PRACH) transmission method according to claim 1 or 2, the method comprising :

4. The physical random access channel (PRACH) transmission method according to any of claims 1 to 3, the method comprising : - obtaining the configuration about a range representing at least a part of possible positions associated with the reference cyclic shift value.

5. The physical random access channel (PRACH) transmission method according to claim 4, wherein the range of possible positions associated with the reference cyclic shift value is pre-defined.

6. The physical random access channel (PRACH) transmission method according to any of claims 1 to 5, the method comprising :

- obtaining the configuration about a range representing at least a part of possible parameter T values.

7. The physical random access channel (PRACH) transmission method according to claim 6, wherein the range representing possible parameter T values is pre-stored by the user equipment.

8. The physical random access channel (PRACH) transmission method according to claim 6 or 7, wherein the PRACH frequency domain preamble is defined with a PRACH sequence length and wherein the parameter T value is a co-prime number of the PRACH sequence length and is smaller than the PRACH sequence length.

9. The physical random access channel (PRACH) transmission method according to any of claims 1 to 8, wherein the cyclic shift values determination at other positions is derived in a way such that the following relation is satisfied:

10. The physical random access channel (PRACH) transmission method according to claim 9, wherein the PRACH preamble determination for

ROs is determined by:

11. The physical random access channel (PRACH) transmission method according to any of claims 1 to 10, wherein a Random Access - Radio Network Temporary Identifier (RA-RNTI) value is defined, the RA-RNTI value being depending either on the first RO index used for simultaneous PRACH preamble transmission or on an initial RO index used for simultaneous PRACH preamble transmission, the initial RO index being associated with an synchronization signal block (SSB) beam index and determined as the RO in which the UE uses the reference cyclic shift value to transmit the PRACH preamble.

12. A user equipment transmitting a physical random access channel (PRACH) to a base station in a wireless communication system in unlicensed spectrum, wherein a PRACH frequency domain preamble for the transmission over multiple random access channel occasions (ROs) is configured, the user equipment comprising:

- a processor configured to o obtain the configuration about the number of ROs in frequency domain, each RO being assigned with an RO index; o obtain the configuration about RO indexes among the number of ROs to be used for simultaneous PRACH preamble transmission; o obtain the configuration about a range representing at least a part of cyclic shift candidates, each cyclic shift candidate being defined by a cycle shift value, a position associated with the cyclic shift value and a parameter T chosen among a plurality of possible parameter values, the configured range containing one reference cycle shift value; o select one position to associate with the reference cyclic shift value and/or one parameter value of T among the possible parameter values; o determine the cyclic shift values at other positions within the configured range; o determine the PRACH preamble for ROs to be used for simultaneous PRACH preamble transmission; o map the PRACH preamble to the configured RO indexes; and - a transmitter to transmit simultaneously the PRACH preamble over the multiple ROs to be used.

13. The user equipment according to claim 12, wherein the range of cyclic shift candidates is restricted to a part of cyclic shift candidates depending on services provided by the user equipment or on the type of user equipment.

14. The user equipment according to claim 12 or 13, wherein the processor is confugred to

- obtain the reference cyclic shift value either by a direct indication, an indirect indication or by a default value.

15. The user equipment according to any of claims 12 to 14, wherein the processor is confugred to :

- obtain the configuration about a range representing at least a part of possible positions associated with the reference cyclic shift value.

16. The user equipment according to claim 15, wherein the range of possible positions associated with the reference cyclic shift value is pre-defined.

17. The user equipment according to any of claims 12 to 16, wherein the processor is confugred to :

- obtain the configuration about a range representing at least a part of possible parameter T values.

18. The user equipment according to claim 17, wherein the range representing possible parameter T values is pre-stored by the user equipment.

19. The user equipment according to claim 17 or 18, wherein the PRACH frequency domain preamble is defined with a PRACH sequence length and wherein the parameter T value is a co-prime number of the PRACH sequence length and is smaller than the PRACH sequence length.

20. The user equipment according to claim 12 or 19, wherein the cyclic shift values determination at other positions is derived in a way such that the following relation is satisfied:

21.The user equipment according to claim 20, wherein the PRACH preamble determination for

ROs is determined by:

22. The user equipment according to claim 12 or 21 , wherein a Random Access - Radio Network Temporary Identifier (RA-RNTI) value is defined, the RA-RNTI value being depending either on the first RO index used for simultaneous PRACH preamble transmission or on an initial RO index used for simultaneous PRACH preamble transmission, the initial RO index being associated with an synchronization signal block (SSB) beam index and determined as the RO in which the UE uses the reference cyclic shift value to transmit the PRACH preamble.

23. A computer readable medium comprising program instructions for causing a user equipment to perform the steps of the PRACH transmission method according to any of claim 1 to 11.