Method and system for random access in 5G

Abstract

Methods and apparatus for performing random access of a mobile user equipment (UE) to a wireless communication network, especially when operating in a frequency band above 24 GHz, especially according to the 5G standard; wherein the UE monitors the quality of synchronization signal blocks (SSB), in particular received power (RSRP), and selects an SSB having a quality above a threshold THc of a network configuration for transmitting a preamble in a corresponding nominal RACH occasion (RO) using a respective beam; and wherein in case the UE is unable to find an SSB having a quality above the threshold THc, the UE selects an SSB having a quality below THc for transmission of a preamble in a corresponding (nominal) RACH occasion (RO) using the respective beam and selects an additional SSB for transmission of the preamble in a "mirrored" RACH occasion located on a "mirrored" frequency of a different beam.

Description

Technical Field

[0001] The present application relates generally to wireless communications, and more particularly to random access procedures in 5G telecommunication systems operating in frequency range 2 (FR2), i.e., the millimeter wave region above 24 GHz. More specifically, the present application relates to random access (RA) of a mobile user equipment (UE) to a wireless communication network according to 5G or beyond 5G standards, especially when operating in a frequency band above 24 GHz. For random access, the UE monitors the quality of synchronization signal blocks (SSBs), in particular the received power (RSRP), and selects a random access procedure whose quality is above a threshold TH configured by the network. C The SSB is used to transmit a preamble in the corresponding nominal RACH opportunity (RO) using the corresponding beam. Background Art

[0002] When a user equipment (UE) intends to communicate with the network, it first performs some cell search and selection procedures to obtain initial cell synchronization and system information. During frame synchronization, the UE looks for the cell identity, decodes the MIB and SIB1, and reads the synchronization signal block (SSB). In case of a multi-antenna system transmitting multiple beams, the UE detects some of the beams / SSBs transmitted by the gNB. During this process, the UE measures the beam strength by measuring the received signal power, thereby searching for the best beam using a predefined threshold criteria defined by the network. The UE selects the best beam identified by the highest reference signal received power (RSRP).

[0003] After the UE has selected a beam, it uses the interval of the Random Access Channel (RACH) to transmit a RACH preamble on that physical RACH (PRACH) corresponding to the SSB for which the best beam has been identified. For transmitting the RACH preamble, a region called RACH Occasion (RO) specified in the time and frequency domain may be used. Thus, the system provides an association between the SSB transmitted by the gNB and the RO to be used to perform random access.

[0004] As mentioned, in 5G New Radio (NR), synchronization signals (SSBs) can be associated with different beams, and the UE selects a certain beam, thereby starting random access in the uplink direction using the corresponding beam. In order for the network to know which beam the UE has selected, 3GPP defines a specific mapping between SSBs and RACH opportunities. By detecting which RO is used, the network can know which SSB beam the UE has selected.

[0005] The mapping between SSBs and RACH occasions is defined by the following RRC parameters: “msg1-FDM”, which specifies how many ROs are allocated in the frequency domain (at the same position in the time domain); and “ssb-perRACH-OccasionAndCB-PreamblesPerSSB”, which specifies how many SSBs can be mapped to one RO and how many preamble indexes can be mapped to a single SSB.

[0006] The overall mapping logic is described in TS 38.213-8.1 and listed below:

[0007] - First, in increasing order of preamble index within a single PRACH opportunity,

[0008] - Second, in ascending order of frequency resource indexes of frequency reused PRACH opportunities,

[0009] - Third, in increasing order of time resource index of time multiplexing PRACH opportunities within a PRACH time slot. Fourth, in increasing order of index of PRACH time slots.

[0010] Thus, the following scenario may actually occur (especially in FR2): All SSBs are detected to be of poor quality, i.e., RSRP is below a certain threshold. The current 5G specification instructs the UE to perform random access in the best beam. The UE is not expected to perform random access in other RACH resources; it may be performed at a later point in time until the current attempt is resolved.

[0011] Especially when operating at high frequencies (e.g. in the mmWave region above 24 GHz), the entire set of best beams, including the best N beams, may be of poor quality. In this case, there is a high probability that MSG1 will not be received correctly even after several attempts with a stepwise increase in Tx power. This increases (access) latency and delays access to the network.

[0012] It is possible to consider sending multiple random accesses to increase the possibility of successfully receiving MSG1, where there are at least two conceivable possibilities of sending multiple MSG1: the first is to send them sequentially by using different ROs. This may be feasible, but is not allowed in 5G. Another possibility is to send them in parallel. This is not possible even with digital beamforming because ROs are time-multiplexed.

[0013] The object of the present invention is to increase the probability of successful transmission of MSG1 and to improve random access (RA).

[0014] The invention is characterized by the features of the independent claims 1, 10, 13 and 16. Advantageous embodiments can be found in the respective dependent claims. Summary of the invention

[0015] As can be seen from the main claims, the concept of the present invention becomes valuable in case of poor channel quality. In normal cases, when a UE receives a SSB (e.g., SSB1) of good quality, it should send MSG1 using the nominal RO at the corresponding frequency (e.g., f1) in the corresponding time slot (e.g., t1) associated with the SSB (e.g., SSB1). However, if each SSB received by the UE is of poor quality, i.e., the quality is below a defined threshold, it is proposed that the UE sends parallel access attempts (in particular through MSG1) with the same preconfigured preamble on multiple beams. In order to allow such multiple (more than one) MSG1s, the concept of the present invention introduces the so-called "mirror RO", which can also be used with the following rule: the mirror RO is used for the following beam (SSB) - the beam is different from the beam associated with the nominal RO occurring at any given time. Therefore, in the first mirror RO occurring simultaneously with the nominal RO, the UE can only reply using a beam different from SSB1.

[0016] In this way, the invention introduces a physical channel structure and a random access procedure to provide higher reliability for MSG1 in a way compatible with or beyond 5G. The solution of the invention assumes the possibility of transmitting multiple beams simultaneously, in particular by using digital beamforming.

[0017] As described above and as outlined in the claims, the present invention is applicable to a UE which is unable to find a device with a quality above a defined threshold TH C In this case, the UE first selects the SSB with quality lower than TH C The UE selects an additional SSB and transmits the preamble in the corresponding (nominal) RACH opportunity (RO) using the corresponding beam. In addition, the UE selects an additional SSB and transmits the same preamble in a “mirror RACH opportunity” located on a “mirror” frequency in a different beam. Therefore, the “mirror RO” occurs in the same timeslot as the nominal RO, but on a different frequency resource (“mirror”).

[0018] In other words, the UE monitors the SSBs and if the quality of all SSBs is below the threshold TH configured by the network C , the UE selects the preconfigured preamble and CMSG1 is transmitted in more than one selected beam of the 5G. Since the current 5G specification indicates that the UE should perform random access in the best beam, the solution of the present invention allows the UE to perform random access in other RACHs. Therefore, the proposed solution introduces the concept of mirror RACH opportunities ("mirror RO"), thereby creating the possibility of exploiting spatial diversity for UEs with the ability to transmit simultaneously on multiple beams. The solution also exploits frequency diversity and is backward compatible, i.e., transparent to "legacy UEs".

[0019] In order to establish access of the UE to the wireless communication system, the gNB and / or the wireless communication system network may preconfigure random access opportunities (ROs). To this end, the gNB or the wireless communication network may indicate which ROs are used by default, which ROs are used for special events and when triggered by predicted events. In a preferred embodiment of the invention, the gNB / network explicitly indicates the location of the mirrored RO as system information and defines frequency resources within the initial bandwidth part (BWP) that match the nominal RACH opportunities for each SSB. Thus, the gNB (respectively, the network) explicitly indicates which resources are to be used for random access and sets the mirrored frequency f for the mirrored RO. Mirr In an advantageous embodiment, the gNB determines to use a portion of the radio spectrum originally allocated for wireless communication for radar purposes, in particular the 400 MHz radio frequency band.

[0020] Additionally, it is advantageous to define a set of preconfigured preambles for use with the proposed parallel RACH. C If the preamble is a preconfigured (marked) preamble signaled or indicated by the base station (gNB) in the mirrored RO, the UE shall use the same preamble for RA in the mirrored RO, whereby the UE may use the mirrored RO to send the preamble using any beam other than the nominal beam defined in that timeslot. When the gNB receives such a marked preamble in the nominal RO, it recognizes that one or more (number M) other preambles should be present in the corresponding mirrored RO.

[0021] The number M of multiple beams transmitted simultaneously in parallel (especially by using digital beamforming) may be defined by a rule implemented in the UE. In this case, the UE has a certain rule (e.g., table, formula) that states how many parallel beams (M) to use for transmitting MSG1 based on the received beam quality. In an advantageous embodiment, the rule defines M=f(N,TH0), i.e., depending on the threshold TH0 and a variable N, the variable N corresponds to the power at the defined TH0. S The number of SSBs between TH0 and TH1. Sis the minimum power that can be detected, and TH0 is defined by the system, where TH S ≤TH0 <TH C In a preferred embodiment, the values ​​of TH0 and / or N are given by system information or hard-coded in the specification so that they are known to all participants in the communication system.

[0022] The various steps of the claimed method may be performed by instructions of a computer program. Therefore, the present invention further relates to corresponding computer programs on an information medium. These programs are suitable for implementation in a user equipment device and a base station, or more generally in a computer, respectively. These programs respectively include instructions suitable for implementing the steps of the method of the present invention, which are supported by the user equipment disclosed herein and executed by the base station disclosed herein, respectively. These programs may use any programming language and may be in the form of source code, object code, or an intermediate code between source code and object code, such as a partially compiled form or any other desired form.

[0023] On the other hand, it is related to a computer-readable information medium, which includes instructions such as the computer program mentioned above. The information medium can be any entity or device capable of storing a program. For example, the medium can include a storage device, such as a ROM (read-only memory) (for example, a CD ROM or a microelectronic circuit ROM), an EEPROM (electrically erasable programmable read-only memory), a FLASH memory, or any magnetic recording device (for example, a hard disk drive). In addition, the information medium can be a transmissible medium, such as an electrical signal or an optical signal, which can be transmitted via a cable or an optical cable by radio or by other means. A program according to an embodiment of the present invention can be downloaded from a network. Alternatively, the information medium can be an integrated circuit containing the program, which is arranged to execute or be used to execute the method discussed. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Other advantages and characteristics of the invention will become more apparent on reading the following description, given by way of simple illustrative and non-limiting examples, and the accompanying drawings, in which:

[0025] Figure 1 shows that a mirrored RO can be used to send (tag) a preamble using any beam other than the nominal beam defined in that time slot,

[0026] Figure 2 shows how the gNB indicates the location of the mirrored RO defined as a frequency resource matching the nominal RACH occasion for each SSB,

[0027] Figure 3A flowchart showing the main steps of a state machine suitable for performing parallel MSG-1 on multiple beams at the UE side, and

[0028] Figure 4 is a flow chart showing the main steps of a state machine suitable for performing parallel MSG-1 on multiple beams on the gNB side. DETAILED DESCRIPTION

[0029] The specific embodiments described below with reference to the accompanying drawings are intended as descriptions of various configurations and are not intended to represent the only configurations in which the concepts described herein may be practiced. The specific embodiments include specific details to provide a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In particular, although terminology from 3GPP 5G NR may be used in this disclosure to illustrate the embodiments herein, this should not be viewed as limiting the scope of the invention.

[0030] Figure 1 The concept of a mirrored RO that can be used to transmit (signal) a preamble using any beam other than the nominal beam defined in that time slot is shown. In the example shown, a UE implemented in a vehicle 4 monitors the quality of several SSBs 5 submitted by a gNB 6 according to standardized specifications and functions. In the example, the power (reference signal received power, RSRP) of none of the SSBs is above a network configured threshold (TH C ). This is possible and likely in FR2 scenarios. Among these several SSBs, the UE can detect three SSBs 1, 2 and 3 with quality below the threshold but with sufficient quality. The remaining beams are completely undetectable to UE 1.

[0031] Perception of the car's surroundings is key to advanced driver assistance systems (ADAS) and autonomous driving. These systems use sensing systems including radar, lidar, cameras, and ultrasonic sensors. Unfortunately, automotive radar systems can interfere with each other, which can affect the detection quality of SSB.

[0032] Figure 2 The RO of the above SSBs 1, 2, and 3 in their corresponding time and frequency domains (f1 / t1 and f2 / t2) are shown. As can be seen from the figure, each SSB has its own RO in the characteristic time domain (t) and frequency domain (f). In addition, in the special image frequency domain (f Mirr ) is present in the gNB 3, which is indicated as system information. Thus, the mirror RO is defined as a frequency resource that matches the nominal RACH occasion of each SSB. From the UE's perspective, the mirror RO can be used to send (signal) the preamble using any beam other than the nominal beam defined in that timeslot.

[0033] In the current example, the SSBs that can be used by the UE for random access have indices 1, 2, and 3. The corresponding index determines the RO. As of Release 17, each SSB has a fixed (nominal) RACH occasion. Knowing the SSB index, the UE knows what RO to use. In the current example, in the case where SSB 1 is selected for random access, the UE can submit a predetermined preamble using the nominal RO8. The UE submits the preconfigured preamble in parallel in a mirrored RO 9, which is different from the nominal RO 8 but defined in the same time slot and has a different frequency f Mirr . Thus, the gNB indicates as system information the presence and / or location of a mirror RO that is defined within the initial bandwidth part (BWP) but is itself a frequency resource that matches the nominal RO of the corresponding SSB. From the UE's perspective, the mirror RO is used to send (signal) the preamble using any beam other than the nominal beam defined in that timeslot. Thus, the UE can send parallel MSG-1s on multiple beams of number M.

[0034] In this example, the UE monitors the entire period (all beams) and finds no SSB above TH C , then the UE uses beam SSB=1 at t1 with f1, and uses beam SSB=2 at t2 with f Mirr The preamble is transmitted in the mirror image RO of t2; or beam SSB = 2 is used at t2, with f2, and beam SSB = 1 is used at t2 with f Mirr The preamble code is transmitted in the mirrored RO.

[0035] The preambles used for this operation are preconfigured so the gNB knows that when such a preamble is detected in any nominal RO, it is also transmitted in the mirror RO. The benefit of this is better detection of such preambles, which by definition are transmitted in weak beams. This is because of diversity and the knowledge that a preamble is present in the mirror RO (if detected in the nominal RO) enables the cancellation of interference from other concurrent preambles.

[0036] Although outside the scope of the present concept, the transmission of MSG2 may be enhanced if the gNB knows that one of such preconfigured preambles has been used.

[0037] According to 3GPP TS 38.331 (Version 17.1.0, Section 5.2.1), as specified in TS 38.213

[13] clause 13, SIB1 is transmitted on DL-SCH with a periodicity of 160 ms and a variable transmission repetition periodicity within 160 ms. The default transmission repetition periodicity of SIB1 is 20 ms, but the actual transmission repetition periodicity depends on the network implementation. For SSB and CORESET (COntrol REsourceSET) multiplexing mode 1, the repetition transmission period of SIB1 is 20 ms. For SSB and CORESET multiplexing modes 2 / 3, the transmission repetition period of SIB1 is the same as the SSB period (TS 38.213

[13] clause 13). SIB1 includes information about the availability and scheduling of other SIBs (e.g., SIB to SI message mapping, periodicity, SI window size), indicating whether one or more SIBs are provided only on demand, and in the case where one or more SIBs are provided only on demand, including the configuration required for the UE to perform the SI request. SIB1 is a cell-specific SIB.

[0038] As mentioned, the UE has certain rules (e.g., table, formula) that explain how many parallel beams (M) to use to transmit MSG1 based on the received beam quality. Therefore, a mapping of the form M=f(N,TH0) is implemented on the UE side, which depends on the threshold TH0 and a variable N corresponding to the power at TH0. S The number of SSBs between TH0 and TH1, where TH S is the minimum power that can be detected and TH0 is defined by the system, where TH S ≤TH0 <TH C .

[0039] In the current example, assume that the UE observes the following:

[0040]

[0041] This means that SSB=1 and SSB=2 are above TH0, and SSB=3 is detected but below TH0, so N=2. N corresponds to below TH C But it is higher than the number of beams in TH0. Therefore, in this example, N is not a given parameter, but a variable to be checked. M, on the other hand, is the number of parallel beams to be used. In the current case, M turns out to be 2, because among the 3 detected beams (in TH C With TH S Among them, only 2 are higher than TH0. Therefore, in this case, M is equal to N.

[0042] But if N is defined asC For the “N best beams” between them and TH0, the situation may be different. In this alternative definition, N does not depend on TH0, but is a fixed input parameter on the UE side. For example, if N = 4 and the UE only observes 2 beams between TH C but higher than TH0, then M will be 2 (M ≠ N), but if the UE observes, for example, 5 beams between TH C but higher than TH0, then M will be 4 (M = N).

[0043] The parameters TH0 and / or N can be given by system information or precoded in the specification. In addition, there can be a library or catalog of formulas or rules, and the network indicates which one to use.

[0044] A natural example is: M = f(N, TH C,dB – K dB ) = N – A, where 0 ≤ A < N, where A is an integer and K dB ∈ (TH S,dB , TH C,dB ). It can be assumed that M = f(N, TH0 = TH C,dB – 2) = N. Therefore, the UE will transmit MSG1 in the beams higher than TH C,dB – 2, that is, M = N. The gain is 2 dB.

[0045] Figure 3 is a flowchart showing the main steps of a state machine suitable for parallel MSG-1 on multiple beams on the UE side. At the start 10, the UE monitors all reachable SSBs 11. In step 12, it is checked whether all SSBs are below the threshold TH configured by the network. If “no”, the random access behavior known in the art continues. If “yes”, then in step 14, M is determined according to the implementation rules, a preconfigured preamble is selected, and MSG1 with this preamble is transmitted in the selected beam. After that, the method on the UE side terminates 15.

[0046] Figure 4 is a flowchart showing the main steps of a state machine suitable for parallel MSG-1 on multiple beams on the gNB side 16. In the first step 17, the gNB 16 indicates that the mirror frequency f of the mirror RO resource is included in the system information Mirr and a set of pre-preambles to be used for the proposed parallel RACH. In step 18, the gNB monitors the nominal RO and the mirror RO. If in step 19, the gNB detects an RO, it checks whether the preamble is a preconfigured preamble. In the case of “no”, the gNB continues in the manner of the prior art at 20. In the case of “yes”, the gNB detects the mirror RO at 21, then ends the process at 22 and authorizes the UE to access.

[0047] In the above examples, the user equipment may be referred to as a mobile station, a wireless terminal, etc. In some examples, the user equipment may be a cellular phone, a wireless modem, a wireless communication device, a handheld device, a laptop computer, etc. The user equipment may also be an IoT (Internet of Things) device, such as a wireless camera, a smart sensor or smart meter, a vehicle, a global positioning system device, or any other device configured to communicate over a wireless network.

[0048] A base station, in particular a gNB, may include a channel quality sensor. The channel quality sensor may be configured by computer program instructions to measure the signal strength on one or more available SSBs (synchronization signal blocks), and to compare the measured value with a preconfigured threshold to determine whether the RSRP of all SSBs is below the threshold.

Claims

1. A method for performing random access of a mobile user equipment (UE) to a wireless communication network, in particular according to the 5G standard, in particular when operating in a frequency band above 24 GHz, in, The UE monitors the quality of the synchronization signal block (SSB), especially the received power (RSRP), and selects the one with quality higher than the threshold TH configured by the network. C SSB for transmitting the preamble in the corresponding nominal RACH opportunity (RO) using the corresponding beam, It is characterized in that When UE cannot find a quality higher than the threshold TH C In the case of SSB, the UE selects a quality lower than TH C The present invention selects an SSB for transmitting a preamble in a corresponding (nominal) RACH opportunity (RO) using the corresponding beam, and selects an additional SSB for transmitting the preamble in a "mirror" RACH opportunity located on a "mirror" frequency of a different beam.

2. The method according to claim 1, It is characterized in that The location of the mirror RO is indicated by the gNB as system information and is defined as a frequency resource within the initial bandwidth part (BWP) that matches the nominal RACH opportunity of each SSB.

3. The method according to claim 1 or 2, in, No power higher than TH was found in UE C The preamble used in the case of SSB is a preconfigured (marked) preamble signaled / indicated by the base station (gNB), so this preamble is also transmitted in the mirrored RO.

4. The method according to claim 1, It is characterized in that The UE uses mirrored RO to send the preamble using any beam except the nominal beam defined in that time slot.

5. The method according to claim 1, It is characterized in that A plurality of beams, M in number, are transmitted simultaneously by using beamforming.

6. The method according to claim 5, It is characterized in that M is defined by rules implemented in the UE.

7. The method according to claim 6, It is characterized in that Rule definition: M = f(N, TH0), that is, it depends on the threshold TH0 and the variable N, which corresponds to the power at TH0. S The number of SSBs between TH0 and TH1, where TH S is the minimum power that can be detected and TH0 is defined by the system, where TH S ≤TH0 <TH C .

8. The method according to claim 7, It is characterized in that The values ​​of TH0 and / or N are given by the system information or are hard-coded in the specification.

9. The method according to any one of the preceding claims, It is characterized in that The gNB is determined to use a portion of the radio spectrum originally allocated for wireless communications for radar purposes, specifically the 400MHz radio frequency band.

10. A user equipment (UE) adapted to perform random access to a communication network, in particular according to the 5G standard, in particular when operating in a frequency band above 24 GHz, It is characterized in that A wireless transceiver, a processor coupled to a memory, wherein the memory stores computer program instructions, the instructions being configured to: select a wireless device with a quality lower than a threshold value TH C SSBs of the same beam, and transmitting the preamble in the corresponding (nominal) RACH opportunity (RO) using the corresponding beam, and selecting an additional SSB for transmitting the preamble in a "mirror" RACH opportunity located on a "mirror" frequency of a different beam.

11. The user equipment according to claim 10, It is characterized in that The implemented rules define the number of beams M that are transmitted simultaneously by using beamforming.

12. The user equipment according to claim 11, It is characterized in that The rule defines: M = f(N, TH0), that is, it depends on the threshold TH0 and the variable N, which corresponds to the power at TH0. S The number of SSBs between TH0 and TH1, where TH S is the minimum power that can be detected and TH0 is defined by the system, where TH S ≤TH0 <TH C .

13. A method performed by a base station, in particular a gNB, for providing a mobile user equipment (UE) with the possibility of random access to a wireless communication network, in particular according to the 5G standard, in particular when operating in a frequency band above 24 GHz, wherein: The base station transmits a synchronization signal block (SSB) with a corresponding RACH opportunity (RO), It is characterized in that The base station indicates the location of the “mirror” RACH opportunity located on the “mirror” frequency for receiving the preamble as system information.

14. The method according to claim 13, It is characterized in that The base station indicates that a preconfigured preamble code to be transmitted using a mirrored RACH opportunity is to be used in case of random access.

15. The method according to claim 13 or 14, It is characterized in that The base station indicates the location of the mirror RO as a frequency resource within the initial bandwidth part (BWP) that matches the nominal RACH opportunity for each SSB.

16. A base station, which is suitable for authorizing user equipment to perform random access, especially when operating in a frequency band above 24 GHz, especially according to the 5G standard, the base station comprising a wireless transceiver, a processor coupled to a memory, the memory storing computer program instructions, and the instructions are configured to implement the steps as described in claims 13, 14 or 15.

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