WO2020089779A1

WO2020089779A1 - Methods and nodes for performing random access in case of lbt failure

Info

Publication number: WO2020089779A1
Application number: PCT/IB2019/059239
Authority: WO
Inventors: Min Wang; Jan Christoffersson
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2018-11-01
Filing date: 2019-10-28
Publication date: 2020-05-07

Abstract

A method is provided for performing a random access in case of LTB failures. The method comprises: receiving a Physical Downlink Control Channel (PDCCH) signaling for Random Access (RA) from a network node, the PDCCH signaling comprising a fallback indicator; and 5 in response to determining that one or more Listen Before Talk (LBT) operations have failed for transmitting a preamble, performing a random access procedure based on the fallback indicator. A wireless device for carrying out this method is also provided.

Description

METHODS AND NODES FOR PERFORMING RANDOM ACCESS IN CASE OF LBT

FAILURE

RELATED APPLICATIONS

[0001] The present application claims the benefits of priority of U.S. Provisional Patent Application No. 62/753978, entitled“Methods for performing random access based on CBRA in case of LBT failure for NR-U“ and filed at the United States Patent and Trademark Office on November 1, 2018, the content of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] The present description generally relates to wireless communication systems and more specifically to random access procedures in these systems.

BACKGROUND

[0003] Next generation systems are expected to support a wide range of use cases with varying requirements ranging from fully mobile devices to stationary Internet of Things (IoT) or fixed wireless broadband devices. The traffic pattern associated with many use cases is expected to consist of short or long bursts of data traffic with varying length of waiting periods in between (herein called inactive state). In New Radio (NR), both License Assisted access (LAA) and standalone unlicensed operations are to be supported in Third Generation Partnership Project (3GPP). Hence the procedure of Physical Random Access Channel (PRACH) transmission and/or Scheduling Request (SR) transmission in unlicensed spectrum shall be investigated in 3GPP. In the following, channel sensing scheme based on Listen Before Talk (LBT), random access procedure and LBT scheme for PRACH and short Physical Uplink Control Channel (sPUCCH) are introduced as a basis to understand the embodiments described later on.

[0004] In legacy NR, the Random Access (RA) procedure may be initiated by a Physical Downlink Control Channel (PDCCH) order. This is done e.g. to obtain UpLink (UL) to synchronize to a Secondary Cell (Scell), when the gNB is about to commence DownLink (DL) transmissions to the UE on the SCell. In NR, it is only possible to do a Random Access to a SCell triggered by a PDCCH order. No possibility to do a Contention based Random Access (CBRA) on an SCell exists.

[0005] The PDCCH order for the Random Access is specified in TS 38.212, Section 7.3.1.2.1 according to the following: "If the CRC of the DCI format 1 0 is scrambled by C-RNTI and the "Frequency domain resource assignment" field are of all ones, the DCI format 1 0 is for random access procedure initiated by a PDCCH order, with all remaining fields set as follows:

- Random Access Preamble index - 6 bits according to ra-Preamblelndex in Subclause 5.1.2 of [8, TS38.321]

- UL/SUL indicator - 1 bit. If the value of the "Random Access Preamble index" is not all zeros and if the UE is configured with SUL in the cell, this field indicates which UL carrier in the cell to transmit the PRACH according to Table 7.3.1.1.1-1; otherwise, this field is reserved

- SS/PBCH index - 6 bits. If the value of the "Random Access Preamble index" is not all zeros, this field indicates the SS/PBCH that shall be used to determine the RACH occasion for the PRACH transmission; otherwise, this field is reserved

- PRACH Mask index - 4 bits. If the value of the "Random Access Preamble index" is not all zeros, this field indicates the RACH occasion associated with the SS/PBCH indicated by "SS/PBCH index" for the PRACH transmission, according to Subclause 5.1.1 of [8, TS38.321]; otherwise, this field is reserved

- Reserved bits - 10 bits"

[0006] As can be seen, the PDCCH order contains a preamble index, an index to determine if normal Uplink (NUL) or Supplementary uplink (SUL) is used, a Synchronization signal Block (SSB) index and a PRACH mask index to determine the RACH occasion where the preamble is to be transmitted.

[0007] Upon receiving the PDCCH order, the UE will transmit the preamble (according to TS 38.321, Section 5.1.2) in the next available PRACH occasion taking the SSB index, as follows: “determine the next available PRACH occasion from the PRACH occasions corresponding to the selected SSB permitted by the restrictions given by the ra-ssb-OccasionMasklndex if configured (the MAC entity shall select a PRACH occasion randomly with equal probability amongst the consecutive PRACH occasions according to subclause 8.1 of TS 38.213 [6], corresponding to the selected SSB; the MAC entity may take into account the possible occurrence of measurement gaps when determining the next available PRACH occasion corresponding to the selected SSB)".

[0008] In this way, the resource reservation for the contention free preamble index and PRACH resources is very limited since it is only booked (or used) for a single PRACH occasion and can be re-assigned to a different UE directly after the preamble transmission.

[0009] For NR unlicensed spectrum, the NR standalone scenario was the newly defined scenario. For this scenario, the existing RACH procedure and scheduling procedure must be enhanced to ensure differentiated latency requirements considering the LBT impact.

SUM MARY

[0010] Currently there exists some challenges. [0011] In Long Term Evolution (LTE) LAA/enhanced LAA (eLAA)/further enhanced LAA (feLAA), only PDCCH order triggered Contention Free Random Access (CFRA) is supported in an SCell where the RA in the SCell is intended for the establishment/obtainment/re-obtainment of the UL sync. For New Radio Unlicensed spectrum (NR-U) carrier aggregation scenarios, it is expected that similar rules for RA would be reused and supported for an NR-U SCell.

[0012] However, in a NR-U SCell, the Random Access procedure is subject to FBT and potentially FBT failure. This means that the Media Access Control (MAC) layer instructs the physical layer to transmit a random access preamble, at a specific physical resource but does not know if the physical layer will be able to carry out the request, since the result of the FBT is not known at the time the PDCCH order is received. Several issues exist.

[0013] For the first issue, in FTE FAA/eFAA/feFAA, there is only one PRACH configuration per MAC entity in the primary cell. In other words, there is no PRACH configuration/resource configured in an SCell. It is expected that an NR-U SCell would adopt the same concept as in FTE FAA. If a UE misses the RA occasion in an SCell, that is indicated by a PDCCH order, due to FBT failures, the UE would then just wait for the next RA occasion and retry FBT operations. If the FBT operations are failed again, the UE has to wait for yet another next available RA occasion. In this case, the UE does not increment the preamble transmission counter. The UE may have a long delay until the UE can manage to access the media to start a Random Access (RA) procedure.

[0014] In the second issue, the UE may eventually manage to transmit a RA in the SCell where the PDCCH order was intended to. However, the preamble transmission may not be acknowledged by the gNB. When the maximum preamble transmission counter is reached, according to the existing specification, the UE would declare the Random Access procedure unsuccessfully completed on that SCell. Furthermore, the UE would not be able to fallback to the CBRA based procedure.

[0015] In the third issue, in legacy NR, there is a possibility to do a fallback for failed CFRA preamble transmissions (when configured by Radio Resource Control (RRC)) in a primary cell, for example, if there is no Synchronization Signal Block (SSB)/Channel State Information- Reference Signal (CSI-RS) resource available to meet the Reference Signal Received Power (RSRP) threshold for CFRA. In this case, the UE does a new resource selection and may in this case select CBRA resources. This is however not possible on SCells as CBRA is not allowed on SCells.

[0016] Some embodiments allow to overcome or mitigate the challenges as described above. [0017] According to one aspect, some embodiments include a method performed by a wireless device. The method comprises: receiving a Physical Downlink Control Channel (PDCCH) signaling for Random Access (RA) from a network node, the PDCCH signaling comprising a fallback indicator; and in response to determining that one or more Listen Before Talk (LBT) operations have failed for transmitting a preamble, performing a random access procedure based on the fallback indicator.

[0018] According to another aspect, some embodiments include a wireless device configured, or operable, to perform one or more functionalities (e.g. actions, operations, steps, etc.) of the wireless device as described herein.

[0019] In some embodiments, the wireless device may comprise one or more communication interfaces configured to communicate with one or more other radio nodes and/or with one or more network nodes, and processing circuitry operatively connected to the communication interface, the processing circuitry being configured to perform one or more functionalities as described herein. In some embodiments, the processing circuitry may comprise at least one processor and at least one memory storing instructions which, upon being executed by the processor, configure the at least one processor to perform one or more functionalities as described herein.

[0020] In some embodiments, the wireless device may comprise one or more functional modules configured to perform one or more functionalities as described herein.

[0021] According to another aspect, some embodiments include a non-transitory computer- readable medium storing a computer program product comprising instructions which, upon being executed by processing circuitry (e.g., at least one processor) of the wireless device, configure the processing circuitry to perform one or more functionalities as described herein.

[0022] According to yet another aspect, there is provided a method performed by a network node. The method comprises: sending a Physical Downlink Control Channel (PDCCH) signaling for Random Access (RA) to a wireless device, the PDCCH signaling comprising a fallback indicator, for use in case the wireless device fails one or more Listen Before Talk (LBT) operations for transmitting a preamble; and receiving the preamble based on the fallback indicator from the wireless device.

[0023] According to another aspect, some embodiments include a network node configured, or operable, to perform one or more functionalities (e.g. actions, operations, steps, etc.) of the network node as described herein.

[0024] In some embodiments, the network node may comprise one or more communication interfaces configured to communicate with one or more other radio nodes and/or with one or more network nodes, and processing circuitry operatively connected to the communication interface, the processing circuitry being configured to perform one or more functionalities as described herein. In some embodiments, the processing circuitry may comprise at least one processor and at least one memory storing instructions which, upon being executed by the processor, configure the at least one processor to perform one or more functionalities as described herein.

[0025] In some embodiments, the network node may comprise one or more functional modules configured to perform one or more functionalities as described herein.

[0026] According to another aspect, some embodiments include a non-transitory computer- readable medium storing a computer program product comprising instructions which, upon being executed by processing circuitry (e.g., at least one processor) of the network node, configure the processing circuitry to perform one or more functionalities as described herein.

[0027] The advantages/technical benefits of the embodiments of the present disclosure are as follows:

[0028] - The embodiments allow the UE to continue the Random Access procedure even if it would fail a first LBT operation, in which case the normal behavior would be to cancel the Random Access procedure.

[0029] This summary is not an extensive overview of all contemplated embodiments, and is not intended to identify key or critical aspects or features of any or all embodiments or to delineate the scope of any or all embodiments. In that sense, other aspects and features will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Exemplary embodiments will be described in more detail with reference to the following figures, in which:

[0031] Figure 1 illustrates a signalling diagram of the random access (RA) procedure.

[0032] Figure 2A illustrates a signaling diagram of a contention based RA procedure.

[0033] Figure 2B illustrates a signaling diagram of a contention free RA procedure.

[0034] Figure 3 is a flow chart of a method in a wireless device, in accordance with some embodiments.

[0035] Figure 4 is a flow chart of a method in a network node, in accordance with some embodiments.

[0036] Figure 5 illustrates one example of a wireless communications system in which embodiments of the present disclosure may be implemented. [0037] Figures 6 and 7 are block diagrams that illustrate a wireless device according to some embodiments of the present disclosure.

[0038] Figures 8 and 9 are block diagrams that illustrate a network node according to some embodiments of the present disclosure.

[0039] Figure 10 illustrates a virtualized environment of a network node, according to some embodiments of the present disclosure.

DETAILED DESCRIPTION

[0040] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments. Upon reading the following description in light of the accompanying figures, those skilled in the art will understand the concepts of the description and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the description.

[0041] In the following description, numerous specific details are set forth. However, it is understood that embodiments may be practiced without these specific details. In other instances, well-known circuits, structures, and techniques have not been shown in detail in order not to obscure the understanding of the description. Those of ordinary skill in the art, with the included description, will be able to implement appropriate functionality without undue experimentation.

[0042] References in the specification to“one embodiment,”“an embodiment,”“an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0043] As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms“comprises,”“comprising,”“includes,” and/or“including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0044] Embodiments of the present disclosure provide several methods in the User Equipment (UE) and the network node. Generally stated, in one example, it is proposed that the PDCCH signaling (or PDCCH order) contains a fallback indication. The fallback indication can indicate to the UE to perform the RA procedure from another cell, which may belong to the same Timing Advance Group (TAG), or a cell which has comparable UL timing advance with the cell that has triggered RA. This new cell should have CBRA resources. In this case, the fallback operation will be executed if the UE fails the LBT operation when trying to transmit the preamble according to the PDCCH order. The fallback indication can also allow the UE to autonomously choose a cell to do CBRA on, having the above conditions. It should be noted that by“LBT failure”, it is meant that the UE fails to grasp a channel (to transmit the preamble), the channel being busy, for example. In this example, the fallback operation is indicated explicitly by the fallback indicator.

[0045] In another example, the PDCCH order is enhanced to carry/indicate multiple RA occasions. The RA occasions may be provided in the time domain or frequency domain and may be from different cells which have comparable uplink timing advance values. The multiple resources may be sorted in a priority order. The UE in principle can initiate a LBT operation for each of them independently, and selects the one which succeeds the LBT operation to transmit the RA preamble. In this example, the fallback operation is indicated implicitly by the fallback indicator (given by the plurality of RA occasions).

[0046] It should be noted that the embodiments will be described in the context of NR unlicensed spectrum (NR-U). However, they are not limited to the NR-U scenarios. They are also applicable to other unlicensed operation scenarios such as LTE LAA/eLAA/FeLAA.

[0047] Before describing the embodiments in more detail, the random access procedure will be explained herein below.

[0048] Figure 1 illustrates a signaling diagram 100 for a UE or wireless device to access the network in order to transmit data. Before accessing the network, the UE needs to synchronize with the network node (e.g. gNB).

[0049] In step 110, the network node (or gNB) broadcasts some synchronization signals, such as Primary synchronization signals (PSS) or secondary synchronization signals (SSS). These signals allow the UE to be synchronized with the network node.

[0050] In step 120, the network node sends a PDCCH to the UE. The PDCCH may contains Downlink Control Information (DCI), system information block and other information such as indications of preambles.

[0051] In step 130, upon receipt of the PDCCH, the UE selects a preamble.

[0052] In step 140, the UE transmits the selected preamble to the network node.

[0053] In step 150, the network node, upon receiving the preamble, processes the preamble. [0054] In step 160, the network node sends a random access response to the UE.

[0055] Then, the UE can start sending data to the network node.

[0056] Now, turning to Figure 2A, a contention based RA (CBRA) procedure 200 will be described.

[0057] In step 210, the UE sends a RA preamble to the network node (this step corresponds to step 140 of Figure 1).

[0058] In step 220, the network node sends a RARto the UE (this step corresponds to step 160 of Figure 1).

[0059] In step 230, the UE sends a scheduled transmission to the network node.

[0060] In step 240, the network node sends a contention resolution to the UE. The Contention Resolution phase helps to uniquely identify the UE that has been selected. The contention resolution will resolve the random access procedure between different UEs that have selected the same preamble, for example.

[0061] In Figure 2B, a contention free random access (CFRA) procedure 250 is illustrated.

[0062] In step 260, the network node sends a message to the UE, the message comprising a preamble assignment (PA). This message could be the PDCCH order, for example.

[0063] In step 270, the UE transmits a random access preamble to the network node.

[0064] In step 280, the network node replies with a random access response to the UE.

[0065] Now, the embodiments will be described in more detail.

[0066] An example may comprise a fallback indicator indicating that the UE shall fallback to contention based RA (CBRA) procedure in another cell in order to continue the RA procedure that has been triggered by the PDCCH order, in case the UE has failed the LBT operations consecutively for a configured number of attempts in the cell that the PDCCH order is intended to. The cell in which the UE does the fallback may be a cell that has a comparable/similar uplink timing alignment for the UE as the cell the PDCCH order is intended to. It means that the UE has similar uplink alignment values in both cells. The timing alignment in one cell can be derived based on the timing alignment in another cell, since the uplink timing differences may be known by the UE, or the gNB. In some examples, one or multiple cell/carrier indices for the UE to do the fallback may be carried by the PDCCH order. The cell/carrier index may be a physical cell identifier (ID), or a global cell ID, or a local value indicating the cell/carrier in a cell group. Furthermore, those cells/carriers may be required to be configured at least with CBRA resources. The UE may reset the counters for the LBT failures, when the UE has managed to get at least one successful LBT operation. [0067] In some examples, a set of the reserved bits in the PDCCH order can be used to indicate the fallback. For example, if the Cyclic Redundancy Check (CRC) of the DCI format 1 0 is scrambled by C-RNTI and the“Frequency domain resource assignment” field are all ones, the DCI format 1 0 is for random access procedure initiated by a PDCCH order (See TS 38.212, section 7.3.1.2.1).

[0068] More specifically, the set of reserved bits in the PDCCH order can be used to indicate that the UE should use another cell, having CBRA resources configured and the same TAG than the current cell, for performing the RA procedure. The UE may autonomously select any cell among the possible cells satisfying the conditions to perform CBRA on. The fallback is done if the CFRA indicated by the PDCCH order fails the LBT operation. In case an indication of multiple cells/carriers is signaled to the UE for the fallback, the UE may select a cell/carrier randomly, or following a priority order, e.g. the cells/carriers may be signaled in a priority order.

[0069] In some examples, the set of reserved bits in the PDCCH order can be used to indicate a specific cell that the UE should use as fallback for performing the CBRA on. The fallback is done only if the CFRA indicated by the PDCCH order fails the LBT operation. Upon reception of the PDCCH order, the UE selects the cell indicated by the fallback indicator in the PDCCH order for the RA fallback, in case the UE has failed the LBT operations consecutively for a configured number of attempts in the cell that the PDCCH order is intended to, for example. For the selected cell, the UE may determine similar uplink alignment in that cell compared to the cell to which the received PDCCH order was intended. The UE may reset the counters for the LBT failures, when the UE has managed to get at least one successful LBT operation.

[0070] In another example, the fallback indicator can indicate a plurality of RA occasions or RA attempts for the UE to perform the RA procedure. The RA occasions indicated by the fallback indicator in the PDCCH order may belong to different cells. For the multiple RA occasions assigned/indicated by the PDCCH order, the UE may perform the LBT operation for each RA occasion sequentially or simultaneously in time.

[0071] In some examples, a number of attempts is configured for the UE to transmit/retransmit the first message (which can be the preamble in the 4-step RA or the first message in the 2-step RA). Once the configured number of attempts is reached, the fallback is triggered and may be signaled via System Information Block (SIB) signaling, or dedicated signaling, or carried by the PDCCH order. In other words, when the UE has missed all the RA occasions, the UE performs the fallback operation to CBRA. [0072] In some examples, the PDCCH order may carry a maximum allowed time period for the UE to try different RA occasions upon occurrence of LBT failures. In this example, the fallback operating is indicated implicitly by the fallback indicator (given by a maximum allowed time period for CFRA). When the maximum allowed time period is elapsed, the UE may further be guided to switch to other cells for fallback (i.e. may continue with CBRA in other cells). In other words, upon expiration of the maximum time period, the UE performs the fallback operation to CBRA.

[0073] For instance, the fallback operation to the other cells is allowed when the UE transmits/retransmits the preamble indicated by the PDCCH order up to a configured number of attempts. In the existing specification, the UE would declare the Random Access procedure unsuccessfully completed on an SCell, after the configured number of attempts of transmitting the preamble is reached.

[0074] The examples can be also applicable if the UE does not receive a Random Access Response (RAR) or DCI signaling indicating reception of the first RA message in response to the CFRA preamble transmission.

[0075] Furthermore, all the examples are applicable to both 4-step RA and 2-step RA. Additionally, the PDCCH order may also carry an indicator indicating the chosen RA type, i.e., either 4-step A or 2-step RA. The UE may switch between 4-step RA and 2-step RA when the UE switches between different RA occasions (in the same cell or between different cells).

[0076] In some examples, the PDCCH order may also carry signaling on COT (channel occupancy time) sharing information. In this case, the UE may be guided to do RA without a LBT operation, or with a short LBT operation (i.e., LBT type 2). The information may include, for example, COT duration, location of DL-UL switch in a shared COT, etc.

[0077] In some examples, the PDCCH order may carry signaling of LBT options for the RA procedure, such as the priority class in case the LBT type 1 is signaled. In case multiple RA occasions are signaled in the PDCCH order, the LBT option for each of them may be different.

[0078] For example, the configurable LBT schemes/options comprise at least one of the LBT categories (for example, according to 3GPP specification, e.g., TS 37.213 Release 15): no LBT, LBT type 1 and LBT type 2.

[0079] According to 3GPP TR 38.889 V 16.0.0, No LBT may be also referred to as Category 1 LBT, LBT type 1 may be also referred to as Category 4 LBT, LBT type 2 may be also referred to as Category 2 LBT, which are shown as below:

[0080] Category 1 : No LBT; [0081] Category 2: LBT without random back-off;

[0082] Category 3 : LBT with random back-off with fixed size of contention window;

[0083] Category 4: LBT with random back-off with variable size of contention window.

[0084] Even though the term“PDCCH order” has been used in the description above, a person skilled in the art would understand that the term“PDCCH order” can be interchangeably used with the term“PDCCH signaling”.

[0085] Figure 3 illustrates a flow chart of a method 300 for performing a random access procedure in a communication network such as 500 of Figure 5. The method can be performed in a wireless device or UE, such as 510 of Figure 5, for example.

[0086] The method 300 comprises:

[0087] Step 310: Receiving a Physical Downlink Control Channel (PDCCH) signaling for Random Access (RA), from a network node, the PDCCH signaling comprising a fallback indicator.

[0088] Step 320: In response to determining that one or more Fisten Before Talk (FBT) operations have failed for transmitting a preamble, performing a random access procedure based on the fallback indicator.

[0089] It should be noted that the fallback operation given by the fallback indicator can be applied in the following cases:

[0090] 1) When the UE consecutively experiences FBT failures, the UE can perform the fallback option to other cells, based on the fallback indicator.

[0091] 2) The UE has transmitted/retransmitted the first message (e.g. the preamble in the 4-step RA, or the first message in 2-step RA) up to a configured number of attempts, in this case, the UE can do the fallback, either perform the CBRA in its own cell that triggered the RA (for example, this cell is an SCell, with CBRA resources configured) or to another cell which contains CBRA resources.

[0092] In some examples, performing the random access procedure can comprise transmitting the preamble based on the fallback indicator.

[0093] In some examples, the PDCCH signaling may be a PDCCH order.

[0094] In some examples, the fallback indicator can indicate that the wireless device can use a second cell to transmit the preamble, the second cell being different from the first cell to which the PDCCH order was intended. The wireless device may select a second cell that belongs to a same Timing Advancing Group (TAG) as the first cell, or that has similar uplink timing alignment as the first cell. The timing alignment in the first cell is derived based on the timing alignment of the second cell.

[0095] In some examples, the fallback indicator can comprise one or more cell/carrier indices. The one or more cell/carrier indices may be a physical cell identifier, a global cell identifier or a local value indicating a cell in a cell group.

[0096] In this case, the wireless device selects a second cell corresponding to one of the cell indices given by the fallback indicator.

[0097] The second cell selected by the UE or indicated by the cell/carrier index may have Contention Based Random Access (CBRA) resources.

[0098] In some examples, the fallback indicator can be given by a set of reserved bits in the PDCCH order.

[0099] In some examples, the fallback indicator may indicate a plurality of cells from which a random access procedure can be performed.

[0100] In this case, the wireless device may select a cell randomly for performing the random access procedure or select a cell based on a priority order.

[0101] In some examples, the fallback indicator may comprise a plurality of RA occasions or RA attempts.

[0102] The RA occasions may be allocated in the frequency domain or time domain and may belong to different serving cells.

[0103] In this case, the wireless device may perform independent LBT operations for each RA occasion and select one RA occasion that is successful with a LBT operation.

[0104] In some examples, the fallback indicator may further comprise (or may be given by) a time indicator, the time indicator indicating a maximum time period for the wireless device to perform the plurality RA occasions with the LBT operations.

[0105] In some examples, the random access procedure may comprise a 4-step RA or 2-step RA.

[0106] In some examples, the PDCCH order may comprise signaling of Channel Occupancy time (COT) sharing information. The information can comprise COT duration and/or location of Downlink-Uplink (DL-UL) switch in a shared COT.

[0107] Lurthermore, the PDCCH order may comprise information on LBT options for RA. Lor example, the information can comprise no LBT, short LBT (such as type 2) or LBT of type 1.

[0108] Ligure 4 illustrates a flow chart of a method 400 for a random access procedure in a communication network, such as 500 of Ligure 5. The method can be implemented in a network node, such as a gNB, such as 520 of Ligure 5, for example. [0109] Method 400 comprises:

[0110] Step 410: Sending a PDCCH signaling for Random Access (RA) to a wireless device, the PDCCH signaling r comprising a fallback indicator, for use in case the wireless device fails one or more Listen Before Talk (LBT) operations for transmitting a preamble.

[0111] Step 420: Receiving the preamble based on the fallback indicator from the wireless device.

[0112] In some examples, the fallback indicator can indicate that the wireless device can use a second cell from which the wireless device can transmit the preamble, the second cell being different from the first cell to which the PDCCH signaling was intended.

[0113] In some embodiments, the fallback indicator can comprise a plurality of cells from which a random access procedure can be performed.

[0114] In some examples, the fallback indicator can comprise one or more cell indices.

[0115] In some examples, the fallback indicator can comprise one or more carrier indices.

[0116] In some examples, the fallback indicator can comprise a plurality of RA occasions.

[0117] Figure 5 illustrates an example of a wireless network 500 that may be used for wireless communications. Wireless network 500 includes UEs 510 and a plurality of radio network nodes 520 (e.g., Node Bs (NBs) Radio Network Controllers (RNCs), evolved NBs (eNBs), next generation NB (gNBs), etc.) directly or indirectly connected to a core network 530 which may comprise various core network nodes. The network 500 may use any suitable radio access network (RAN) deployment scenarios, including Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access Network (UTRAN), and Evolved UMTS Terrestrial Radio Access Network (EUTRAN). UEs 510 may be capable of communicating directly with radio network nodes 520 over a wireless interface. In certain embodiments, UEs may also be capable of communicating with each other via device-to-device (D2D) communication. In certain embodiments, network nodes 520 may also be capable of communicating with each other, e.g. via an interface (e.g. X2 in LTE or other suitable interface).

[0118] As an example, UE 510 may communicate with radio network node 520 over a wireless interface. That is, UE 510 may transmit wireless signals to and/or receive wireless signals from radio network node 520. The wireless signals may contain voice traffic, data traffic, control signals, and/or any other suitable information. In some embodiments, an area of wireless signal coverage associated with a radio network node 520 may be referred to as a cell.

[0119] It should be noted that a UE may be a wireless device, a radio communication device, target device, device to device (D2D) UE, machine type UE or UE capable of machine to machine communication (M2M), a sensor equipped with UE, iPAD, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), Universal Serial Bus (USB) dongles, Customer Premises Equipment (CPE) etc. Examples of a wireless device 510 are described in more detail below with respect to Figures 6 and 7.

[0120] In some examples, the“network node” can be any kind of network node which may comprise of a radio network node such as a radio access node (which can include a base station, radio base station, base transceiver station, base station controller, network controller, gNB, NR BS, evolved Node B (eNB), Node B, Multi-cell/multicast Coordination Entity (MCE), relay node, access point, radio access point, Remote Radio Unit (RRU), Remote Radio Head (RRH), a multi standard BS (also known as MSR BS), etc.), a core network node (e.g., MME, SON node, a coordinating node, positioning node, MDT node, etc.), or even an external node (e.g., 3rd party node, a node external to the current network), etc. The network node may also comprise a test equipment.

[0121] In certain examples, network nodes 520 may interface with a radio network controller (not shown). The radio network controller may control network nodes 520 and may provide certain radio resource management functions, mobility management functions, and/or other suitable functions. In certain embodiments, the functions of the radio network controller may be included in the network node 520. The radio network controller may interface with the core network node 540. In certain embodiments, the radio network controller may interface with the core network node 540 via the interconnecting network 530.

[0122] The interconnecting network 530 may refer to any interconnecting system capable of transmitting audio, video, signals, data, messages, or any combination of the preceding. The interconnecting network 530 may include all or a portion of a public switched telephone network (PSTN), a public or private data network, a local area network (LAN), a metropolitan area network (MAN), a wide area network (WAN), a local, regional, or global communication or computer network such as the Internet, a wireline or wireless network, an enterprise intranet, or any other suitable communication link, including combinations thereof.

[0123] In some examples, the core network node 540 may manage the establishment of communication sessions and various other functionalities for wireless devices 510. Examples of core network node 540 may include MSC, MME, SGW, PGW, O&M, OSS, SON, positioning node (e.g. E-SMLC), MDT node, etc. Wireless devices 110 may exchange certain signals with the core network node 540 using the non-access stratum layer. In non-access stratum signaling, signals between wireless devices 510 and the core network node 540 may be transparently passed through the radio access network. In certain examples, network nodes 520 may interface with one or more other network nodes over an intemode interface. For example, network nodes 520 may interface each other over an X2 interface.

[0124] Although Figure 5 illustrates a particular arrangement of network 500, the present disclosure contemplates that the various embodiments described herein may be applied to a variety of networks having any suitable configuration. For example, network 500 may include any suitable number of wireless devices 510 and network nodes 520, as well as any additional elements suitable to support communication between wireless devices or between a wireless device and another communication device (such as a landline telephone). The embodiments may be implemented in any appropriate type of telecommunication system supporting any suitable communication standards and using any suitable components and are applicable to any radio access technology (RAT) or multi-RAT systems in which the wireless device receives and/or transmits signals (e.g., data). While certain embodiments are described for NR and/or LTE, the embodiments may be applicable to any RAT, such as UTRA, E-UTRA, narrow band internet of things (NB-IoT), WiFi, Bluetooth, next generation RAT (NR, NX), 4G, 5G, LTE FDD/TDD, etc.

[0125] Figure 6 is a schematic block diagram of the wireless device 510 according to some embodiments of the present disclosure. As illustrated, the wireless device 510 includes circuitry 600 comprising one or more processors 610, e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and/or the like) and memory 620. The wireless device 510 also includes one or more transceivers 630 that each include one or more transmitters 640 and one or more receivers 650 coupled to one or more antennas 660. The wireless device 510 may also comprise a network interface and more specifically an input interface 670 and an output interface 680 for communicating with other nodes. The wireless device may also comprise a power source 690.

[0126] In some examples, the functionality of the wireless device 510 described above may be fully or partially implemented in software that is, e.g., stored in the memory 620 and executed by the processor(s) 610. For example, the processor 610 is configured to perform method 300 of Figure 3.

[0127] In some examples, a computer program including instructions which, when executed by the at least one processor 610, causes the at least one processor 610 to carry out the functionality of the wireless device 510 according to any of the embodiments described herein is provided (e.g. method 300 of Figure 3). In some examples, a carrier containing the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory).

[0128] Figure 7 is a schematic block diagram of the wireless device 510 according to some other embodiments of the present disclosure. The wireless device 510 includes one or more modules 700, each of which is implemented in software. The module(s) 700 provide the functionality of the wireless device 510 described herein. The module(s) 700 may comprise, for example, a receiving module operable to perform step 310 of Figure 3. The module(s) 700 may further comprise a performing module operable to perform step 320 of Figure 3.

[0129] Figure 8 is a schematic block diagram of a network node 520 according to some embodiments of the present disclosure. As illustrated, the network node 520 includes a processing circuitry 800 comprising one or more processors 810 (e.g., CPUs, ASICs, FPGAs, and/or the like) and memory 820. The network node also comprises a network interface 830. The network node 520 also includes one or more transceivers 840 that each include one or more transmitters 850 and one or more receivers 860 coupled to one or more antennas 870. In some examples, the functionality of the network node 510 described above may be fully or partially implemented in software that is, e.g., stored in the memory 820 and executed by the processor(s) 810. For example, the processor 810 can be configured to perform the method 400 of Figure 4.

[0130] Figure 9 is a schematic block diagram of the network node 520 according to some other embodiments of the present disclosure. The network node 520 includes one or more modules 900, each of which is implemented in software. The module(s) 900 provide the functionality of the network node 520 described herein. The module(s) 900 may comprise, for example, a sending module operable to perform step 410 of Figure 4, and a receiving module operable to perform step 420 of Figure 4.

[0131] Figure 10 is a schematic block diagram that illustrates a virtualized embodiment of the wireless device 510 or network node 520, according to some embodiments of the present disclosure. As used herein, a“virtualized” node 1100 is a network node 520 or wireless device 510 in which at least a portion of the functionality of the network node 520 or wireless device 510 is implemented as a virtual component (e.g., via a virtual machine(s) executing on a physical processing node(s) in a network(s)). For example, in Figure 10, there is provided an instance or a virtual appliance 1120 implementing the methods or parts of the methods of some embodiments. The one or more instance(s) runs in a cloud computing environment 1100. The cloud computing environment provides processing circuits 1130 and memory 1190-1 for the one or more instance(s) or virtual applications 1120. The memory 1190-1 contains instructions 1195 executable by the processing circuit 1160 whereby the instance 1120 is operative to execute the methods or part of the methods described herein in relation to some embodiments.

[0132] The cloud computing environment 1100 comprises one or more general-purpose network devices including hardware 1130 comprising a set of one or more processor(s) or processing circuits 1160, which may be commercial off-the-shelf (COTS) processors, dedicated Application Specific Integrated Circuits (ASICs), or any other type of processing circuit including digital or analog hardware components or special purpose processors, and network interface controller(s) (NICs) 1170, also known as network interface cards, which include physical Network Interface 1180. The general-purpose network device also includes non-transitory machine readable storage media 1190-2 having stored therein software and/or instructions 1195 executable by the processor 1160. During operation, the processor(s)/processing circuits 1160 execute the software/instructions 1195 to instantiate a hypervisor 1150, sometimes referred to as a virtual machine monitor (VMM), and one or more virtual machines 1140 that are run by the hypervisor 1150.

[0133] A virtual machine 1140 is a software implementation of a physical machine that runs programs as if they were executing on a physical, non- virtualized machine; and applications generally do not know they are running on a virtual machine as opposed to running on a“bare metal” host electronic device, though some systems provide para-virtualization which allows an operating system or application to be aware of the presence of virtualization for optimization purposes. Each of the virtual machines 1140, and that part of the hardware 1130 that executes that virtual machine 1140, be it hardware 1130 dedicated to that virtual machine 1140 and/or time slices of hardware 1130 temporally shared by that virtual machine 1140 with others of the virtual machine(s) 1140, forms a separate virtual network element(s) (VNE).

[0134] The hypervisor 1150 may present a virtual operating platform that appears like networking hardware to virtual machine 1140, and the virtual machine 1140 may be used to implement functionality such as control communication and configuration module(s) and forwarding table(s), this virtualization of the hardware is sometimes referred to as network function virtualization (NFV). Thus, NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in Data centers, and customer premise equipment (CPE). Different embodiments of the instance or virtual application 1120 may be implemented on one or more of the virtual machine(s) 1140, and the implementations may be made differently. [0135] In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory).

[0136] Some embodiments may be represented as a non-transitory software product stored in a machine -readable medium (also referred to as a computer-readable medium, a processor-readable medium, or a computer usable medium having a computer readable program code embodied therein). The machine-readable medium may be any suitable tangible medium including a magnetic, optical, or electrical storage medium including a diskette, compact disk read only memory (CD-ROM), digital versatile disc read only memory (DVD-ROM) memory device (volatile or non-volatile), or similar storage mechanism. The machine-readable medium may contain various sets of instructions, code sequences, configuration information, or other data, which, when executed, cause a processor to perform steps in a method according to one or more of the described embodiments. Those of ordinary skill in the art will appreciate that other instructions and operations necessary to implement the described embodiments may also be stored on the machine-readable medium. Software running from the machine -readable medium may interface with circuitry to perform the described tasks.

[0137] The above-described embodiments are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the description, which is defined solely by the appended claims.

Claims

CLAIMS: What is claimed is:

1. A method in a wireless device, comprising:

receiving a Physical Downlink Control Channel (PDCCH) signaling for Random Access (RA) from a network node, the PDCCH signaling comprising a fallback indicator; and in response to determining that one or more Listen Before Talk (LBT) operations have failed for transmitting a preamble, performing a random access procedure based on the fallback indicator.

2. The method of claim 1, wherein performing the random access procedure comprises

transmitting the preamble based on the fallback indicator.

3. The method of claim 1 or 2, wherein the PDCCH signaling is a PDCCH order.

4. The method of claim 2 or 3, wherein the fallback indicator indicates that the wireless device can use a second cell to transmit the preamble, the second cell being different from the first cell to which the PDCCH order was intended.

5. The method of claim 4, wherein the wireless device selects the second cell, the second cell belonging to a same Timing Advancing Group (TAG) as the first cell.

6. The method of claim 4, wherein the wireless device selects the second cell, the second cell having similar uplink timing alignment as the first cell.

7. The method of claim 6, wherein the timing alignment in the first cell is derived based on the timing alignment of the second cell.

8. The method of any one of claims 1 to 3, wherein the fallback indicator comprises one or more cell indices.

9. The method of claim 8, wherein the one or more cell indices comprise one of a physical cell identifier, a global cell identifier and a local value indicating a cell in a cell group.

10. The method of claim 8 or 9, wherein the wireless device selects a second cell corresponding to one of the cell indices given by the fallback indicator.

11. The method of any one of claims 1 to 3, wherein the fallback indicator comprises one or more carrier indices.

12. The method of claim 11, wherein the one or more carrier indices comprise one of a physical cell identifier, a global cell identifier and a local value indicating a cell in a cell group.

13. The method of any one of claims 4 to 11, wherein the second cell has Contention Based Random Access (CBRA) resources.

14. The method of any one of claims 1 to 13, wherein the fallback indicator is given by a set of reserved bits in the PDCCH signaling.

15. The method of any one of claims 1 to 3, wherein the fallback indicator indicates a plurality of cells from which a random access procedure can be performed.

16. The method of claim 15, further comprising selecting a cell randomly for performing the random access procedure.

17. The method of claim 15, further comprising selecting a cell based on a priority order.

18. The method of any one of claims 1 to 3, wherein the fallback indicator is given by a plurality of RA occasions or RA attempts.

19. The method of claim 18, wherein the plurality of RA occasions or RA attempts is allocated in one of frequency domain and time domain.

20. The method of claim 18 or 19, wherein the plurality of RA occasions or RA attempts

belongs to different serving cells.

21. The method of any one of claims 18 to 20, wherein the wireless device performs

independent LBT operations for each RA occasion and selects one RA occasion that is successful with a LBT operation.

22. The method of any one of claims 18 to 21, wherein the fallback indicator further comprises a maximum time period for the wireless device to perform the plurality of RA occasions with the LBT operations.

23. The method of any one of claims 1 to 22, wherein the random access procedure comprises one of a 4-step RA and 2-step RA.

24. The method of any one of claims 1 to 23, wherein the PDCCH signaling comprises signaling of Channel Occupancy time (COT) sharing information.

25. The method of claim 24, wherein the information of COT sharing comprises one or more of COT duration, location of Downlink-Uplink (DL-UL) switch in a shared COT.

26. The method of any one of claims 1 to 23, wherein the PDCCH signaling comprises

information on LBT options for RA.

27. The method of claim 26, wherein the information comprises one of no LBT, short LBT of type 2 and LBT of type 1.

28. A computer program product comprising a non-transitory computer readable storage medium having computer readable program code embodied in the medium, the computer readable program code comprising computer readable program code to operate according to any of the methods 1 to 27.

29. A wireless device comprising a communication interface and processing circuitry connected thereto, the processing circuitry comprising a processor and a memory, the memory containing instructions that, when executed, cause the processor to:

receive a Physical Downlink Control Channel (PDCCH) signal for Random Access (RA) from a network node, the PDCCH signaling comprising a fallback indicator; and

in response to determining that one or more Listen Before Talk (LBT) operations have failed for transmitting a preamble, perform a random access procedure based on the fallback indicator.

30. The wireless device of claim 29, wherein the processor is configured to perform the random access procedure by transmitting the preamble based on the fallback indicator.

31. The wireless device of claim 30, wherein the fallback indicator indicates that the wireless device can use a second cell to transmit the preamble, the second cell being different from the first cell to which the PDCCH order was intended.

32. The wireless device of claim 31, wherein the processor is configured to select the second cell, the second cell belonging to a same Timing Advancing Group (TAG) as the first cell.

33. The wireless device of claim 31, wherein the processor is configured to select the second cell, the second cell having similar uplink timing alignment as the first cell.

34. The wireless device of claim 33, wherein the timing alignment in the first cell is derived based on the timing alignment of the second cell.

35. The wireless device of claim 29 or 30, wherein the fallback indicator comprises one or more cell indices.

36. The wireless device of claim 35, wherein the one or more cell indices comprise one of a physical cell identifier, a global cell identifier and a local value indicating a cell in a cell group.

37. The wireless device of claim 35 or 36, wherein the processor is configured to select a second cell corresponding to one of the cell indices given by the fallback indicator.

38. The wireless device of claim 29 or 30, wherein the fallback indicator comprises one or more carrier indices.

39. The wireless device of claim 38, wherein the one or more carrier indices comprise one of a physical cell identifier, a global cell identifier and a local value indicating a cell in a cell group.

40. The wireless device of any one of claims 29 to 39, wherein the second cell has Contention Based Random Access (CBRA) resources.

41. The wireless device of any one of claims 29 to 40, wherein the fallback indicator is given by a set of reserved bits in the PDCCH order.

42. The wireless device of claim 29 or 30, wherein the fallback indicator indicates a plurality of cells from which a random access procedure can be performed.

43. The wireless device of claim 42, wherein the processor is configured to select a cell

randomly for performing the random access procedure.

44. The wireless device of claim 42, wherein the processor is configured to select a cell based on a priority order.

45. The wireless device of claim 29 or 30, wherein the fallback indicator is given by a plurality of RA occasions or RA attempts.

46. The wireless device of claim 45, wherein the plurality of RA occasions or RA attempts is allocated in one of frequency domain and time domain.

47. The wireless device of claim 45 or 46, wherein the plurality of RA occasions or RA attempts belongs to different serving cells.

48. The wireless device of any one of claims 45 to 47, wherein the wireless device performs independent LBT operations for each RA occasion and selects one RA occasion that is successful with a LBT operation.

49. The wireless device of any one of claims 45 to 48, wherein the fallback indicator further comprises a maximum time period for the wireless device to perform the plurality of RA occasions with the LBT operations.

50. The wireless device of any one of claims 29 to 49, wherein the random access procedure comprises one of a 4-step RA and 2-step RA.

51. The wireless device of any one of claims 29 to 50, wherein the PDCCH signaling comprises signaling of Channel Occupancy time (COT) sharing information.

52. The wireless device of claim 51, wherein the information of COT sharing comprises one or more of COT duration, location of Downlink-Uplink (DL-UL) switch in a shared COT.

53. The wireless device of any one of claims 29 to 50, wherein the PDCCH signaling comprises information on LBT options for RA.

54. The wireless device of claim 53, wherein the information comprises one of no LBT, short LBT of type 2 and LBT of type 1.

55. A method in a network node, comprising:

sending a Physical Downlink Control Channel (PDCCH) signaling for Random Access (RA) to a wireless device, the PDCCH signaling comprising a fallback indicator, for use in case the wireless device fails one or more Listen Before Talk (LBT) operations for transmitting a preamble;

receiving the preamble based on the fallback indicator from the wireless device.

56. The method of claim 55, wherein the fallback indicator indicates that the wireless device can use a second cell from which the wireless can transmit the preamble, the second cell being different from the first cell to which the PDCCH signaling was intended.

57. The method of claim 55, wherein the fallback indicator comprises a plurality of cells from which a random access procedure can be performed.

58. The method of claim 55, wherein the fallback indicator comprises one or more cell indices.

59. The method of claim 55, wherein the fallback indicator comprises one or more carrier indices.

60. The method of claim 55, wherein the fallback indicator is given by a plurality of RA

occasions or RA attempts.

61. A network node comprising a communication interface and processing circuitry connected thereto, the processing circuitry comprising a processor and a memory, the memory containing instructions that, when executed, cause the processor to:

send a Physical Downlink Control Channel (PDCCH) signaling for Random Access (RA) to a wireless device, the PDCCH signaling comprising a fallback indicator, for use in case the wireless device fails one or more Listen Before Talk (LBT) operations for transmitting a preamble;

receive the preamble based on the fallback indicator from the wireless device.

62. The network node of claim 61, wherein the fallback indicator indicates that the wireless device can use a second cell from which the wireless can transmit the preamble, the second cell being different from the first cell to which the PDCCH signaling was intended.

63. The network node of claim 61, wherein the fallback indicator comprises a plurality of cells from which a random access procedure can be performed.

64. The network node of claim 61, wherein the fallback indicator comprises one or more cell indices.

65. The network node of claim 61, wherein the fallback indicator comprises one or more carrier indices.

66. The network node of claim 61, wherein the fallback indicator is given by a plurality of RA occasions or RA attempts.

67. A computer program product comprising a non-transitory computer readable storage

medium having computer readable program code embodied in the medium, the computer readable program code comprising computer readable program code to operate according to any of the methods 55 to 60.