Field of the invention

The present invention relates to self-optimization in case of beam-forming.

Abbreviations

3GPP 3 ^rd Generation Partnership Project

4G / 5G 4 ^th / 5 ^th Generation

ACK Acknowledge

BCI Beam Change Indicator

BF Beamforming

BS Base Station

C-RNTI Cell RNTI

CSI Channel State Information

CSI-RS CSI Reference Signal

DL Downlink

eNB evolved NodeB (base Station in 4G)

gNB Base Station in 5G/NR

IE Information Element

L2 / L3 Layer 2 / Layer 3 (of OSI layer model)

LTE Long Term Evolution

MAC Medium Access Control

NR New Radio (air interface standard of 5G systems)

NUL Normal UL

NW Network

PRACH Physical Random Access Channel

RA Random Access

RACH Random Access Channel

RA-RNTI Random Access RNTI

RNTI Radio Network Temporary Identifier

RRC Radio Resource Control

RS Reference Signal

RSRP Reference Signal Received Power

RSRQ Reference Signal Received Quality SON Self Optimisation Networks

SpCell Special Secondary Cell

SS Synchronization Signals

SSB Synchronization Signal Block

SUL Supplementary UL

T C-RNTI Temporary C-RNTI

TS Technical Specification

UE User Equipment

UL Uplink

Background of the invention

5G NR, especially the mmWave communication, may rely on highly-directional transmissions (beams) to overcome the large pathloss, and the use of directional transmissions significantly complicates initial access. In addition to detecting the presence of the base station and access request from the UE, the mmWave initial access procedure may provide a mechanism by which both the UE and the base station (BS) can determine suitable beamforming (BF) directions on which subsequent directional communication can be carried out.

Random Access

In wireless technologies like LTE or 5G, devices use random access procedures when they are not uplink synchronized with the network or when they do not have UL resources random access procedures may be used during a number of scenarios like initial access to the network, UL data arrival, handover etc. Random access can be contention free or contention based. Except when the network explicitly signals the random-access resources, contention-based RACH is used.

Typical steps for a contention-based RACH in wireless systems are below: i) UE --> NW: RACH Preamble (RA-RNTI, indication for L2/L3 message size)

ii) UE <-- NW: Random Access Response (Timing Advance, T_C-RNTI, UL grant for L2/L3 message)

iii) UE --> NW: L2/L3 message

iv) Message for early contention resolution

Typical steps for contention free RACH in wireless systems are below: i) UE <~NW: RACH Preamble (PRACH) Assignment

ii) UE --> NW: RACH Preamble (RA-RNTI, indication for L2/L3 message size)

iii) UE <--NW: Random Access Response (Timing Advance, C-RNTI, UL grant for L2/L3 message)

Additional steps in 5G NR during RACH

For NR is operating in beamforming mode, UE detects and selects a best beam for RACH process. This beam selection process is a fundamental difference between LTE RACH and NR RACH process.

Beam Selection and RACH

Since beamforming is frequently used in 5G, especially in the mmWave band, it is important that the devices select the best beam from minimizing the access delay and improving the system performance. It is possible to switch beams by using physical layer signaling using Beam Change Indicator (BCI) message. Beam switch will take place when (typically filtered, i.e. averaged in time domain) RSRP of a new beam is larger than RSRP of the source beam by a certain threshold. However, the threshold means that for certain time, the UE may not be with the best beam and there could be even a chance for beam failure. In the event of beam failure, 5G-UE starts Beam Recovery by sending Random Access Preamble on a best target beam.

Beam selection during RACH, for initial access or even for beam failure recovery by the UE is governed by the parameters set by the gNB and broadcasted in system information. The detailed description of the actions and parameters is present in the NR MAC specifications (3GPP TS 38.321 ).

NR RRC configures various parameters like the below mentioned ones with regards to the initial beam selection during the RACH process. rsrp-ThresholdSSB: an RSRP threshold for the selection of the SSB and corresponding random Access Preamble and/or PRACH occasion. If the random access procedure is initiated for beam failure recovery, rsrp-ThresholdSSB refers to rsrp-ThresholdSSB in BeamFailureRecoveryConfig IE; rsrp-ThresholdCSI-RS: an RSRP threshold for the selection of CSI-RS and corresponding random Access Preamble and/or PRACH occasion. If the random access procedure is initiated for beam failure recovery, rsrp-ThresholdCSI-RS shall be set to a value calculated by multiplying rsrp-ThresholdSSB in BeamFailureRecoveryConfig IE by powerControlOffset as specified in 3GPP TS 38.214.

rsrp-ThresholdSSB-SUL: an RSRP threshold for the selection between the NUL carrier and the SUL carrier;

powerControlOffset: a power offset between rsrp-ThresholdSSB and rsrp- ThresholdCSI-RS to be used when the random access procedure is initiated for beam failure recovery.

In addition to this, below parameters are also affected based on the beam selected or if the action is a beam failure recovery:

ra-ResponseWindow: the time window to monitor RA response(s) (SpCell only); ra-ssb-OccasionMasklndex: defines PRACH occasion(s) associated with an SSB in which the MAC entity may transmit a random-access Preamble (see subclause 7.4);

ra-OccasionList: defines PRACH occasion(s) associated with a CSI-RS in which the MAC entity may transmit a random access Preamble;

powerControlOffset: a power offset between rsrp-ThresholdSSB and rsrp- ThresholdCSI-RS to be used when the random access procedure is initiated for beam failure recovery;

ssb-perRACH-OccasionAndCB-PreamblesPerSSB (SpCell only): defines the number of SSBs mapped to each PRACH occasion and the number of random access Preambles mapped to each SSB;

Self-Optimization Networks-SON

SON technology allows to collect and analyze various information elements, in particular information elements from the user devices, and to perform self-optimization, self-organization and self-healing in the telecommunication network. A major use case for SON in current wireless technologies like LTE is optimization of random access parameters.

SON for Random Access

SON techniques are particularly useful for contention based RACH optimization because UE selects the random-access resources autonomously and in the absence of SON information send from the UE, there is no way for the network to know if the UE has faced any contention, or if the random access resources or parameters need to be optimized.

SON RACH in LTE

According to LTE RRC specification 3GPP TS 36.331 , RACH report includes the below rach-Report-r9 SEQUENCE {

numberOfPreamblesSent-r9 NumberOfPreamblesSent-r1 1 ,

contention Detected-r9 BOOLEAN

}

A device sends RACH report to the eNodeB according to the below clause from the same specification 3GPP TS 36.331 , section 5.6.5.3:

1 > if rach-ReportReq is set to true, set the contents of the rach-Report in the UEInformationResponse message as follows:

2> set the numberOfPreamblesSent to indicate the number of preambles sent by MAC for the last successful completed random access procedure;

2> if contention resolution was not successful as specified in 3GPP TS 36.321 for at least one of the transmitted preambles for the last successfully completed random access procedure:

3> set the contentionDetected to true;

Further details are described in

1. 3GPP TS 38.321 - 3GPP 5G NR MAC specification

2. 3GPP TS 36.331 - 3GPP 4G LTE RRC specification

Summary of the invention

It is an object of the present invention to improve the prior art.

According to a first aspect of the invention, there is provided an apparatus, comprising means for monitoring configured to monitor if an access procedure to a beam of a cell fails, wherein a value of a beam related index is selected in the access procedure based on a measured quality of a beam parameter indexed by the beam related index; means for transmitting configured to transmit a failure indication comprising the selected value of the beam related index and an indication of the measured quality to the cell if the access procedure fails. According to a second aspect of the invention, there is provided an apparatus, comprising means for monitoring configured to monitor if a failure indication is received that an access procedure to a beam of a cell fails, wherein the failure indication comprises a beam related index and an indication of a measured quality of a beam parameter indexed by the beam related index; means for optimizing configured to optimize network parameters based on the received value of the beam related index and the quality indication if the failure indication is received.

According to a third aspect of the invention, there is provided a method, comprising monitoring if an access procedure to a beam of a cell fails, wherein a value of a beam related index is selected in the access procedure based on a measured quality of a beam parameter indexed by the beam related index; transmitting a failure indication comprising the selected value of the beam related index and an indication of the measured quality to the cell if the access procedure fails.

According to a fourth aspect of the invention, there is provided a method, comprising monitoring if a failure indication is received that an access procedure to a beam of a cell fails, wherein the failure indication comprises a beam related index and an indication of a measured quality of a beam parameter indexed by the beam related index; optimizing network parameters based on the received value of the beam related index and the quality indication if the failure indication is received.

Each of the methods of the third and fourth aspects may be a method of network optimization.

According to a fifth aspect of the invention, there is provided a computer program product comprising a set of instructions which, when executed on an apparatus, is configured to cause the apparatus to carry out the method according to any of the third and fourth aspects.

According to some example embodiments of the invention, at least one of the following advantages may be achieved:

• optimization of the network taking into account the beamforming;

• more reliable self-optimizing of the network;

• higher rate of successful (random) access procedures. It is to be understood that any of the above modifications can be applied singly or in combination to the respective aspects to which they refer, unless they are explicitly stated as excluding alternatives.

Brief description of the drawings

Further details, features, objects, and advantages are apparent from the following detailed description of the preferred example embodiments of the present invention which is to be taken in conjunction with the appended drawings, wherein:

Fig. 1 shows a method according to an example embodiment of the invention;

Fig. 2 shows a method performed by a terminal according to an example embodiment of the invention;

Fig. 3 shows a method performed by a base station according to an example embodiment of the invention;

Fig. 4 shows an apparatus according to an example embodiment of the invention;

Fig. 5 shows a method according to an example embodiment of the invention;

Fig. 6 shows an apparatus according to an example embodiment of the invention;

Fig. 7 shows a method according to an example embodiment of the invention;

Fig. 8 shows an apparatus according to an example embodiment of the invention; and

Fig. 9 shows an example scenario on which example embodiments of the invention may be applied.

Detailed description of certain example embodiments

Herein below, certain example embodiments of the present invention are described in detail with reference to the accompanying drawings, wherein the features of the example embodiments can be freely combined with each other unless otherwise described. However, it is to be expressly understood that the description of certain example embodiments is given by way of example only, and that it is by no way intended to be understood as limiting the invention to the disclosed details.

Moreover, it is to be understood that the apparatus is configured to perform the corresponding method, although in some cases only the apparatus or only the method are described.

Fig. 9 shows an example scenario on which example embodiments of the invention may be applied. A gNB supports beamforming B1 and B2 represent two beams transmitted from the gNB. gNB transmits different SS blocks in different predefined directions (beams) in regular time intervals. SSBIocks corresponding to the B1 are indicated as bars of the arrow from gNB to UE. SSBIocks corresponding to B2 are not shown.

UE measures the RSRP corresponding to the SS blocks of the different beams and selects a suitable beam. Let us assume the UE has selected B1.

For Random Access, UE transmits the random access preambles allocated to B1 in the random access occasions provided for B1 . During the initial deployment, operator may have allocated a same number of preambles for B1 and B2.

There may be different reasons for random access failure. Hereinafter, two cases are considered as examples:

Case 1 : If there are issues in the radio environment for B1 (e.g. due to non-optimal antenna tilting), there may be more random access failures in B1 , and UE may need to transmit with higher power for successful random access. According to some embodiments of the invention, UE reports the beam which was selected when the random access failed as well as the power of the SS block due to which B1 was selected for the failed random access attempt. Based on the inputs from the UE (and maybe further UEs which may face the same issue), gNB identifies that there is an issue with the radio environment for B1 and would adapt the antenna tilting.

Case 2: The number of UEs that select B1 for Random Access is much higher than the one's selecting B2 at a particular time period. Thus, there are more random access failures in B1 due to a lack of preambles. In the conventional system, UE will report that there was a collision, but gNB wouldn’t be able to identify on which beam it has occurred. But according to some embodiments of the invention, UE reports that the random access was failed in B1. Thus, gNB can allocate more preambles for B1 .

According to some example embodiments of the invention, the information on failed SSB and/or CSI-RS is included in the RACH report sent from the UE to gNB.

I.e., the NR RACH report to be specified in NR RRC specification 3GPP TS 38.331 is modified as below:

(Proposed changes in bold italics, along with LTE baseline from 3GPP TS 36.331 ) rach-Report-r9 SEQUENCE {

numberOfPreamblesSent-r9 NumberOfPreamblesSent-r1 1 ,

contention Detected-r9 BOOLEAN

FailedSSB-lnfo SEQUENCE { OPTIONAL

ssb-lndex SSB-lndex,

rsrp RSRP-Range

}

FailedCSI-RS-lnfo SEQUENCE { OPTIONAL

csi-RS-lndex CSI-RS-SSB-lndex,

rsrp RSRP-Range

}

}

A device (terminal, UE) sends RACH report to the gNodeB according to the below clause from the same specification 3GPP TS 36.331 (amendments in bold italics):

1 > if rach-ReportReq is set to true, set the contents of the rach-Report in the UEInformationResponse message as follows:

2> set the numberOfPreamblesSent to indicate the number of preambles sent by MAC for the last successfully completed random access procedure;

2> if contention resolution was not successful as specified in TS 36.321 for at least one of the transmitted preambles for the last successfully completed random access procedure:

3> set the contentionDetected to true;

2>lf a RACH attempt is not successful for at least one SSB selected

3> For each of the SSBs where the RACH attempt is failed

4> Include the ssb-index in FailedSSB-lnfo

4> Include the RSRP measured during the latest attempt for this SSB in in FailedCSI-RS-lnfo

2>lf a RACH attempt is not successful for at least one CSI-RS selected 3> For each of the CSI-RSs where the RACH attempt is failed

4> Include the csi-rs-index in FailedCSI-RS-lnfo

4> Include the RSRP measured during the latest attempt for this CSI-RS in FailedCSI-RS-lnfo According to some example embodiments of the invention, gNB uses the received information on SSB index and/or CSI-RS index for optimising RACH parameters for beam related operations.

According to some embodiments of the invention, a method comprising the following steps is performed (see also the ladder diagram of Fig. 1 , which shows both the UE side and the gNB side according to some example embodiments of the invention):

When a RACH attempt is failed, a 5G UE which is capable of sending RACH reports to the network will:

1 .a) If a SSB was selected during the random-access resource selection, store the ssb-index and the SS-RSRP used for selection in FailedSSB-lnfo. In some example embodiments, if ssb-index is already stored, it will not be stored again, but the SS-RSRP will be updated with the latest value.

1 .b) If a CSI-RS was selected during the random-access resource selection, store the CSI-RS index and the CSI-RSRP used for selection in FailedCSI-RS-lnfo. In some example embodiments, if csi-rs-index is already stored, it will not be stored again, but the CSI-RSRP will be updated with the latest value.

In some example embodiments, only one of 1.a) and 1 .b) is executed.

2.Gnb sends UE information request to the 5G device as in LTE with rach-ReportReq. 5G UE sends the rach report including FailedSSB-lnfo and/or FailedCSI-RS-lnfo (if they are available) in UE information response.

3. gNB receives the FailedSSB-lnfo and/or FailedCSI-RS-lnfo in UE information response and utilises this information for RACH parameter optimisation.

I.e., as shown in Fig. 1 , UE stores the SSB index and/or SS-RSRP index for the last failed attempt and SS-RSRP/CSI-RSRP for the last failed attempt on a RACH failure. It includes this information (i.e., FailedSSB-lnfo and FailedCSI-RS-lnfo) in the RACH-report during UE information response and sends it to gNB. gNB uses this information for SON. Fig. 2 shows the method according to some example embodiments of the invention performed at the UE side. In detail, Fig. 2 illustrates how the failedcsi-rs-info and failedssb-info are stored in NR UE during RACH failure. This information is reported back to the gNB in UE information response when a UE information request is received by the UE.

Fig. 3 shows the method according to some example embodiments of the invention performed at the gNB side. Compared to the SON-RACH LTE baseline, it involves receiving the new RACH optimisation parameters and perform self-optimisation using the same.

Fig. 4 shows an apparatus according to an example embodiment of the invention. The apparatus may be a control unit which may be implemented in base station (e.g. gNB) or an element thereof. Fig. 5 shows a method according to an example embodiment of the invention. The apparatus according to Fig. 4 may perform the method of Fig. 5 but is not limited to this method. The method of Fig. 5 may be performed by the apparatus of Fig. 4 but is not limited to being performed by this apparatus.

The apparatus comprises means for monitoring 10 and means for transmitting 20. The means for monitoring 10 and means for transmitting 20 may be a monitoring means and transmitting means, respectively. The means for monitoring 10 and means for transmitting 20 may be a monitor and a transmitter, respectively. The means for monitoring 10 and means for transmitting 20 may be a monitoring processor and transmitting processor, respectively.

The means for monitoring 10 monitors if an access procedure to a beam of a cell fails (S10). In the access procedure, a value of a beam related index is selected based on a measured quality of a beam parameter. The beam parameter is indexed by the beam related index. The access procedure may be a random access procedure.

If the access procedure fails (S10 = yes”), the means for transmitting 20 transmits a failure indication to the cell (S20). The failure indication comprises the selected value of the beam related index and an indication of the measured quality.

Fig. 6 shows an apparatus according to an example embodiment of the invention. The apparatus may be a control unit which may be implemented in a base station (e.g. gNB) or an element thereof. Fig. 7 shows a method according to an example embodiment of the invention. The apparatus according to Fig. 6 may perform the method of Fig. 7 but is not limited to this method. The method of Fig. 7 may be performed by the apparatus of Fig. 6 but is not limited to being performed by this apparatus.

The apparatus comprises means for monitoring 1 10 and means for optimizing 120. The means for monitoring 1 10 and means for optimizing 120 may be a monitoring means and optimizing means, respectively. The means for monitoring 1 10 and means for optimizing 120 may be a monitor and a optimizer, respectively. The means for monitoring 1 10 and means for optimizing 120 may be a monitoring processor and optimizing processor, respectively.

The means for monitoring 1 10 monitors if a failure indication is received (S1 10). The failure indication indicates that an access procedure to a beam of a cell fails. The failure indication comprises a beam related index and an indication of a measured quality of a beam parameter indexed by the beam related index. The access procedure may be a random access procedure.

If the failure indication is received (S1 10 =“yes”), the means for optimizing 120 optimizes network parameters based on the received value of the beam related index and the quality indication (S120).

Fig. 8 shows an apparatus according to an example embodiment of the invention. The apparatus comprises at least one processor 810, at least one memory 820 including computer program code, and the at least one processor 810, with the at least one memory 820 and the computer program code, being arranged to cause the apparatus to at least perform at least one of the methods according to Figs. 5 and 7.

According to the above description, the UE stores the SSB index and/or CSI-RS index (beam related index) before it transmits the same to the gNB on request. However, in some embodiments, the UE does not store the beam related index but transmits it immediately when the random access fails. For example, a frequency resource may be reserved for a contention- based transmission of the beam related index. Furthermore, UE may transmit the beam related index without being requested by the gNB.

SSB index and CSI-RS index are examples of beam related indices and CSI and CSI-RS are examples of beam parameters (beam related signals). CSI-RS is typically used for identifying the beam in RRC-Connected mode. SSB-index is typically used for beam identification in RRC idle mode (and can be used for connected mode, too). In some example embodiments, the term“beam related indices” may include other indices and the term“beam parameters” may include other parameters which are related to the beam.

RSRP is an example measurement value to determine the quality of the respective parameter. In some example embodiments, other parameters such as RSRQ may be used instead of RSRP or in addition to RSRQ in order to determine the quality of the received beam parameter (beam related signal e.g. SSB, CSI-RS).

The term“storing along” means that one piece of information is stored such that its relation to the other piece of information may be obtained. E.g., these pieces of information may be stored in a same row of a table, or one after the other in a sequence of pairs of pieces of information.

Some example embodiments of the invention are described which are based on a 3GPP network (e.g. NR). However, the invention is not limited to NR. It may be applied to any generation (3G, 4G, 5G, etc.) of 3GPP networks. However, the invention is not limited to 3GPP networks. It may be applied to other radio networks and wired networks with a random access procedure. Further, some example embodiments of the invention may be applied to any access procedure (such as an autonomous beam selection), wherein the access procedure may be or may not be different from a random access procedure.

A UE is an example of a terminal. However, the terminal (UE) may be any device capable to connect to the radio network such as a MTC device, a D2X device etc.

A cell may be represented by the base station (e.g. gNB, eNB, etc.) serving the cell. The base station (cell) may be connected to an antenna (array) serving the cell by a Remote Radio Head. A base station may be realized as a combination of a central unit (one for plural base stations) and a distributed unit (one per base station). The central unit may be employed in the cloud.

One piece of information may be transmitted in one or plural messages from one entity to another entity. Each of these messages may comprise further (different) pieces of information.

Names of network elements, protocols, and methods are based on current standards. In other versions or other technologies, the names of these network elements and/or protocols and/or methods may be different, as long as they provide a corresponding functionality. If not otherwise stated or otherwise made clear from the context, the statement that two entities are different means that they perform different functions. It does not necessarily mean that they are based on different hardware. That is, each of the entities described in the present description may be based on a different hardware, or some or all of the entities may be based on the same hardware. It does not necessarily mean that they are based on different software. That is, each of the entities described in the present description may be based on different software, or some or all of the entities may be based on the same software. Each of the entities described in the present description may be embodied in the cloud.

According to the above description, it should thus be apparent that example embodiments of the present invention provide, for example, a terminal (e.g. a UE or a MTC device), or a component thereof, an apparatus embodying the same, a method for controlling and/or operating the same, and computer program(s) controlling and/or operating the same as well as mediums carrying such computer program(s) and forming computer program product(s). According to the above description, it should thus be apparent that example embodiments of the present invention provide, for example, a base station (e.g. a gNB or eNB,) or a cell thereof, or a component thereof, an apparatus embodying the same, a method for controlling and/or operating the same, and computer program(s) controlling and/or operating the same as well as mediums carrying such computer program(s) and forming computer program product(s).

Implementations of any of the above described blocks, apparatuses, systems, techniques or methods include, as non-limiting examples, implementations as hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

It is to be understood that what is described above is what is presently considered the preferred example embodiments of the present invention. However, it should be noted that the description of the preferred example embodiments is given by way of example only and that various modifications may be made without departing from the scope of the invention as defined by the appended claims.