Method of adapting wireless random access channel configuration based on air traffic information

Abstract

A method of adapting wireless random access channel configuration of a first base station (gNB) comprises obtaining, at the first gNB, information about active air corridors and / or specific UAM UEs association, receiving, at the first gNB, a connection request from a UAM UE, requesting, from the UAM UE, information on the air corridor the UAM UE is associated with, and receiving a response to the request from the UAM UE, determining a distance range between the UAM UE and the first gNB based on the received information and the known location of the first gNB and / or determining a mapping between the received information and a radio coverage range above the gNB, and adjusting the PRACH preamble cyclic shift gap configuration, the PRACH to SSB resource mapping and / or the PRACH resource allocation in accordance with the determined distance range or mapping.

Description

[0001] METHOD OF ADAPTING WIRELESS RANDOM ACCESS CHANNEL CONFIGURATION BASED ON AIR TRAFFIC INFORMATION

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to random access (RA) procedures in 3GPP-based terrestrial wireless communication networks, in particular to procedures for use by mobile nodes, e.g., urban air mobility (UAM) nodes.

[0004] NOTATIONS AND DEFINITIONS

[0005] 3GPP, the abbreviation of ‘3rdGeneration Partnership Project’, is an umbrella term for a number of standards organizations which develop protocols for mobile telecommunications. In the context of 3GPP the term ‘random’ emphasizes that user equipment (UE) may request access to a network resource at any time, as the UE is not bound by a predetermined or fixed access scheme. The expression ‘terrestrial wireless communication networks’ is meant to refer to wireless communication networks whose base stations are located on ground-based structures, and whose UEs are typically likewise located in or on ground-based structures. The abbreviation ‘gNB’ is used herein for base stations irrespective of the naming conventions in various standards, which may use ‘eNB’ or other abbreviations for base stations.

[0006] BACKGROUND

[0007] Access of UE to 3GPP-based terrestrial wireless communication networks is controlled through corresponding RA procedures. At the beginning of existing RA procedures, once a UE detects a synchronization signal block (SSB) transmission from the network, i.e. , through a nearby gNB, the UE decodes the system information broadcast (SIB) transmitted from the network. Based on the configuration information carried in the SIB, the UE transmits a preamble on the physical RA channel (PRACH) resource indicated via the SIB. Each SSB transmission is associated with its own PRACH occasion, which refers to a time-frequency resource that is received by any UE which is able to detect the SSB transmissions and decode the SIB message, i.e., achieve downlink synchronization, and in which the UE may transmit the PRACH preamble to further achieve uplink synchronization. The PRACH preamble is a Zadoff-Chu sequence of a certain indicated length that is determined by two parameters: a root sequence index and a cyclic shift value denoted by and parameterized by an index While the root sequence index is provided by the network, the cyclic shift value is determined with the aid of additional information provided by the network, including the ‘restricted set’ to which the cyclic shift value belongs, and further parameters that the UE can determine based on the indications from the network and tables provided in the specification. Specifically, a cyclic shift gap parameter denoted as effectively determines, in combination with certain other parameters, the number of unit cyclic shifts between consecutive v parameter values.

[0008] Existing 3GPP RA procedures are designed for terrestrial users, i.e., users located on solid ground, and are not optimized for UAM nodes' access, while UAM nodes will typically be airborne while communicating. This added dimension within a coverage area or, more precisely, within a coverage space, poses several problems for the existing RA procedures:

[0009] 1 . For terrestrial networks, the set of values of Ncs configured by the cell may be determined based on the maximum coverage range of the cell, i.e., of the gNB serving that cell. However, UAM UEs, i.e., UEs associated with aerial nodes that may carry passengers or cargo, or UEs associated with passengers transported by such aerial nodes, may fly at considerable heights from the ground-based, low-height gNBs, even above currently commercially available traditional low flying drones that are smaller than UAM aircraft. Moreover, UAM UEs would fly in active air corridors, which are regions in the air that are designated for traffic use by the Uncrewed Aircraft System (UAS) Service Supplier (USS) or the UAS Traffic Manager (UTM).

[0010] The UTM is a system for safely and efficiently integrating flying Uncrewed Aerial Vehicles (UAV) along with other airspace users. It provides a set of functions and services for managing a range of autonomous vehicle operations, e.g., authenticating a UAV, authorizing UAS services, managing UAS policies, and controlling UAV traffic in the airspace. The USS is an entity that provides services to support the safe and efficient use of airspace by providing services to the UAS operator or pilot. The term USS may refer to both the USS and the USS / UTM.

[0011] While the aviation domain is generally outside of the scope of 3GPP, 3GPP networks may implement the communication with UAVs and UAM UEs through a UAS Network Function (UAS NF). UAS NF is a network function implemented via the 3GPP Network Exposure Function (NEF) for support of aerial functionality related to UAV identification, authentication / authorization and tracking, and to support Remote Identification. NEF is a 3GPP standard node that exposes network services to apps. Access to those services enables apps to interact with smart loT devices such as sensors, meters, smart vehicles, or television sets, and the like. NEF provides a large flexibility and can, inter alia, be used for retrieving a location of a UE, set service parameters and / or broadcast emergency notifications for smart vehicles, and the like.

[0012] Figure 1 shows a high-level conceptual block diagram showing the decoupling of 3GPP specifications from aviation-related aspects. The relevant information between the 3GPP system components and the aviation related components is exchanged through corresponding APIs.

[0013] Figure 2 shows a high-level example of the integration of UAV entities in 3GPP Release 17. In the example, it is readily apparent that the UAS NF 3GPP system component serves for connecting the UAV and the UAV controller, using information from a USS and / or UTM connected thereto.

[0014] Hence, if the existing way of configuring the cyclic shift gap Ncs between two consecutive preamble sequences is used directly for UAM UEs, there are two options:

[0015] 1 . The network sets the minimum value of Ncs for UAM UEs based on the terrestrial coverage. It is reminded that airborne UAM UEs can potentially access the network from distances much beyond the range available to ground-based UEs, owing to more favourable line-of-sight propagation conditions. Even if two UAM UEs at different distances from the gNB transmit preambles with respective different cyclic shifts, the transmissions may arrive at the gNB more or less simultaneously, if the gap between the cyclic shifts to be chosen in accordance with the network-set value is not large enough to cover the transmission delay difference between the UAM UEs. In this scenario, the transmissions would collide at the gNB, which may force a retransmission of the PRACH preamble by one of the UAM UEs.

[0016] 2. The network sets the minimum value of Ncs based on the maximum coverage distance it can achieve for airborne UAM UEs. In this case, a large value needs to be set as the minimum value of Ncs, since the propagation delay for airborne UAM UEs can be much larger than that for ground-based UEs, for which a smaller range may be available. A large value of Ncs means that the number of orthogonal preambles available for RA is reduced, which affects the number of UEs that can perform RA in the same occasion.

[0017] One large problem in integrating terrestrial UEs and aerial UEs communication is that in terrestrial networks, PRACH preamble cyclic shift gaps to be applied by every UE within a cell are determined based on the round-trip delay corresponding to the maximum coverage of the cell. However, if the same principle is followed for UAM UEs, this can increase the chance of preamble collisions due to the nonorthogonality at the gNB by virtue of the large distances between UAM UEs flying in different air corridors and between UAM UEs and gNBs.

[0018] Additionally, in terrestrial networks the SSBs associated with PRACH resources are typically transmitted in all azimuth beams, i.e., horizontal directions, around the gNB. However, since there is a limited number of SSBs in a burst, it may not be possible to also scan all elevation directions for aiding RA by airborne UAM UEs, since this would create a trade-off with ground-based UEs' RA performance. Thus, it is important to carefully associate the SSBs with the appropriate PRACH occasions for RA by UAM UEs. Further, when performing contention-free RA it is necessary to optimize the PRACH resource allocation to the UAM UEs.

[0019] Finally, PRACH resource allocation for contention-free RA by terrestrial and UAM UEs need to be optimized to avoid sacrificing performance of either. While adjusting PRACH preamble configuration, including the cyclic shift, SSB to PRACH resource assignment and PRACH resource allocation are generally known, none of the known methods addresses the specific requirements of airborne UAM UEs at all.

[0020] It is, therefore, an object of the present invention to propose improved RA procedures and / or protocols and / or parameter sets that overcome or at least alleviate the shortcomings of known terrestrial RA procedures.

[0021] SUMMARY OF THE INVENTION

[0022] The aforementioned object is achieved by the methods of claims 1 and 8, the gNB of claim 7, the wireless UE of claim 9, and the computer program product of claim 8. A corresponding computer-readable storage medium is presented in claim 10.

[0023] Advantageous developments and embodiments are provided in the respective dependent claims.

[0024] The method in accordance with the invention improves the RA procedures for including UAM UEs into terrestrial communication networks by also taking the properties of active air corridors and range information into consideration when determining the PRACH configuration, performing the PRACH resource allocation and / or performing SSB to PRACH resource assignment. To do so, the present invention addresses the above-mentioned problems by:

[0025] 1 . Introducing a mapping between the cyclic shift gap parameters and the geographical regions above the gNB based on the distance of each region from the gNB. Such a mapping may be provided for each gNB, e.g., through corresponding simulations or measurements. The geographical regions may, for example, be represented as quantisations of the volumes around a gNB up to a maximum distance. Each volume quantisation may be associated with one or multiple cyclic shift gap parameters..

[0026] 2. Allowing the gNB in the 3GPP system to request for information about all active air corridors in its coverage area from the Uncrewed Aircraft System (UAS) Service Supplier (USS) or UAS Traffic Management (UTM) (outside the 3GPP system). This may be achieved by introducing a new message / protocol in the interface between the 3GPP system and USS / UTM system. This request may be periodic, aperiodic or event-triggered.

[0027] 3. Allowing the gNB to request for information on the air corridor the UAM UE is associated with, either from the USS / UTM or from the UAM UE itself. This may be achieved by introducing a new message / protocol in the interface between the 3GPP system and USS / UTM system or by a new information element in the medium access control (MAC) control element (CE) or the Radio Resource Control (RRC). This request may be periodic, aperiodic or event-triggered.

[0028] 4. Allowing the gNB to transfer the information obtained using the procedure in 2 or 3 to one or more target gNB(s) to aid the PRACH resource allocation for RA during handover by the target gNB(s).

[0029] 5. A gNB may use the active air corridor information combined with the mapping in 1 , to change the configuration of the cyclic shift gap parameter in the system information broadcast (SIB) or in a UE-specific manner.

[0030] 6. A gNB may use the active air corridor information to adapt the association between the SSB beams and the PRACH occasions in the SIB or in a UE-specific manner.

[0031] 7. A gNB may use the UAM UE-air corridor association information to allocate PRACH occasions / resources.

[0032] Prior to discussing the details of the invention, the common RA procedure, also referred to herein as Random Access Channel (RACH) procedure, will be discussed in greater detail, using the 5G New Radio (NR) standard as example. The RACH plays a significant role in establishing an initial connection (Initial Access) between a UE and a network. When a device wants to connect to a network for the first time or after a period of inactivity, it uses the RACH to request access to the network. In NR Rel-15, the RACH procedure is triggered when uplink data becomes available at the UE buffer and the UE is in one of the following states:

[0033] • the RRCJDLE / INACTIVE state (RACH procedure triggered for state transition)

[0034] • the RRC_CONNECTED state and the uplink is not synchronized (RACH procedure is used to re-establish uplink synchronization)

[0035] • the RRC_CONNECTED state, and the UE has no Physical Uplink Control Channel (PUCCH) resources available for a scheduling request (SR) or the SR procedure fails (where the RACH procedure serves as an SR)

[0036] In addition, the RACH procedure is used for beam failure and recovery, on-demand System Information (SI) request, or it can be explicitly triggered by the network with Radio Resource Control (RRC) for handover.

[0037] RACH resources can be configured for Contention-based RA (CBRA), i.e., for initial access, and Contention-free RA (CFRA), i.e., when triggered by the Physical Downlink Control Channel (PDCCH), mobility, beam failure recovery.

[0038] The RACH procedure comprises the following steps:

[0039] Msg1 (RACH Preamble, UE to gNB):

[0040] - UE selects a RA preamble from set of predefined preambles and a random sequence number for the preamble

[0041] - UE transmits the preamble on the PRACH

[0042] Msg2 (Random Access Response on PDCCH / PDSCH, gNB to UE):

[0043] - Upon receiving Msg1 , gNB sends response (Msg2) consisting Time Advance (TA) command, the Random Access Preamble ID (RAPID) matching the preamble sent by the UE, and an initial uplink grant for the UE

[0044] - gNB also assigns a temporary identifier called Random Access Radio Network Temporary Identifier (RA-RNTI) to the UE Msg3:

[0045] - Using the initial uplink grant provided in Msg2, the UE transmits Msg3 on the PUSCH (Physical Uplink Shared Channel).

[0046] Msg4 (Contention Resolution):

[0047] - After processing Msg3, gNB sends Msg4 to the UE

[0048] - Msg4 is MAC data for Contention Resolution

[0049] - Contention Resolution message contains the UE's identity, confirming that the gNB has correctly identified the UE, and contention has been resolved.

[0050] - At this step, the network provides the UE with C-RNTI (Cell Radio Network Temporary Identifier)

[0051] The message flow discussed above is shown in the swim-lane diagram of figure 3.

[0052] Further prior to discussing the details of the invention, aspects of the PRACH will be discussed. In 5G NR beamforming and beam tracking features have been introduced in the NR RA procedure, making the overall process different from the 4G LTE process in frequencies above 6 GHz. In NR RA, UEs need to detect and select the best beam for the RACH process (beam selection process) prior to the actual PRACH sequence selection and transmission. The SI informs the UE of the association between the SSBs and the RACH resources.

[0053] The SSB / PBCH block indices are mapped to PRACH occasions:

[0054] - first, in increasing order of preamble indices within a single PRACH occasion,

[0055] - followed by, in increasing order of frequency resource indices of frequency- multiplexed PRACH occasions,

[0056] - then, in increasing order of time resource indices of the time-multiplexed PRACH occasions within a PRACH slot and,

[0057] - finally, in increasing order of indices of PRACH slots.

[0058] Figure 4 shows a schematic representation of the PRACH time slots and the PRACH structure in the time and frequency domain, as presented in Chapter 4 - New Radio Access Physical Layer Aspects (Part 2) of “5G NR - Architecture, Technology, Implementation, and Operation of 3GPP New Radio Standards”, Editor(s): Sassan Ahmadi, Academic Press, 2019, Pages 411-654. Next, the PRACH sequence generation will be briefly discussed. The set of randomaccess preambles shall be generated according to from which the frequency-domain representation shall be generated according to where LRA=839, LRA=139, LRA=1151, or LRA=571 depending on the PRACH preamble format as given by tables in the specifications, e.g., 3GPP TS 38.211 V17.5.0 (2023- 06); 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; Physical channels and modulation (Release 17).

[0059] There are 64 preambles defined in each time-frequency PRACH occasion, enumerated in increasing order of first increasing cyclic shift Cv of a logical root sequence, and then in increasing order of the logical root sequence index, starting with the index obtained from the higher-layer parameter prach-RootSequencelndex or rootSequencelndex-BFR or by msgA-PRACH-RootSequencelndex if configured and a type-2 random access procedure is initiated as described in clause 8.1 of TS 38.213. Additional preamble sequences, in case 64 preambles cannot be generated from a single root Zadoff-Chu sequence, are obtained from the root sequences with the consecutive logical indices until all the 64 sequences are found. The logical root sequence order is cyclic; the logical index 0 is consecutive to LRA-2. The sequence number u is obtained from the logical root sequence index according to Tables 6.3.3.1 -3 to 6.3.3.1 -4B in TS 38.211 . The basic structure for the generation of the NR random-access preamble and the placement thereof in the time-frequency domain signals is shown in figure 5.

[0060] Next, the PRACH cyclic shift will be briefly discussed. The cyclic shift Cv is given by where Ncs is given by Tables 6.3.3.1-5 to 6.3.3.1-7 tables in the specifications, e.g., 3GPP TS 38.211 V17.5.0 (2023-06); 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; Physical channels and modulation (Release 17). The higher-layer parameter msgARestrictedSetConfig, if provided, determines the type of restricted sets (unrestricted, restricted type A, restricted type B). Otherwise, the higher-layer parameter restrictedSetConfig determines the type of restricted sets (unrestricted, restricted type A, restricted type B), and Tables 6.3.3.1-1 and 6.3.3.1-2 indicate the type of restricted sets supported for the different preamble formats.

[0061] Examples for the Ncs value are shown in the table below:

[0062] Note that the Zadoff-Chu (ZC) sequences generated from a cyclic shift of a single root sequence are orthogonal. Sequences obtained from cyclic shifts of different root sequences are not strictly orthogonal but have low cross-correlation.

[0063] The cyclic shift is indirectly provided to the UE via the parameter zeroCorrelationZoneConfig. The parameter Ncs, set according to zeroCorrelationZoneConfig or msgAZeroCorrelationZoneConfig parameters provided by the gNB, specifies the number of cyclic shifts between preamble sequences.

[0064] While each UE will utilize a different cyclic shift of a root ZC sequence in a cell, the delay, and delay spread, of the channel will make the ZC sequence of a UE farther away from a gNB look just the same as the ZC sequence of a UE closer to the gNB that has been cyclically shifted. In order to prevent this, the cyclic shift of the UEs must be kept further apart than the sum of the round-trip delay time (RTD) and the delay spread (τdelay spread). i.e., the following relation must hold:

[0065] Figure 6 shows an illustration of the cyclic shift separation Ncs between preamble sequences.

[0066] Next, the airspace as used in this specification will be defined. As presented by

[0067] S. I. Muna, S. Mukherjee, K. Namuduri, M. Compere, M. I. Akbas, P. Molnar and R. Subramanian in Air Corridors: Concept, Design, Simulation, and Rules of Engagement, Sensors 2021 , 21(22), 7536; https: / / doi.org / 10.3390 / s21227536, the airspace comprises several building blocks having respective properties.

[0068] A geofence defines a specific volume in space whose borders may not be crossed. The geofence volume g = {n, v[ ], Zƒ , zc, m, h[ ]} is defined by a list of n vertices on the horizontal plane v[ ] = [(x1, y1), (x2, y2), ... , (xn, yn)], where n ≥ 3, and zƒdenotes the altitude floor and zcdenotes the altitude ceiling, g is defined relative to a set of home locations h[ ] = [h1, , hm], where hi= (Φi, λi, zi, t ) and m ≥ 2. Lateral home positions are represented as latitude, longitude pairs (Φi, λi). ziis the altitude of the home location i from mean sea level (MSL). tiis the activation time for the home location i, 1 < i < m. tmis the deactivation time for the geofence g. The geofence boundaries are defined relative to a home location hi= (Φi, λi, zi, ti) (geofence centroid). The vertical floor zf and ceiling zcare defined in terms of meters relative to zi. The horizontal boundary is defined by a list of vertices v = [v1, ... , vn]. Each Vi= (xi, yi), i ∈ [1 , n], is defined w.r.t. to a local Cartesian frame with its origin at the home location given by latitude and longitude. Horizontal vertices and vertical limits are constant relative to a sequence of two or more home locations defined in h[ ].

[0069] An air cube is a building block for a skylane in 3D airspace and can be considered a geofence in its most simplified form. All aircubes are assumed similar in size, and an aircube is exclusively reserved for a UAV in transit at any given time. Each aircube has a unique identifier cid which helps UAVs to understand the cube occupancy information while moving, centre = (Φ, λ, zc), indicates the centre point of the air cube, while Φ, λ, zcrepresent latitude, longitude, and ceiling altitude, respectively. From the side length s and the centre, the overall air cube volume can be determined, direction indicates the traffic flow direction inside the cube. c[cid] = {cid, centre, s, direction}

[0070] A skylane or track is a designated region of airspace for UAV in transit. An aircraft must fly within the skylane during its transit. A skylane or track be defined as a volume consisting of several cubes with the same direction. An entrance gate is used to enter the skylane and one exit gate is used to exit the skylane.

[0071] S[sid] = {sid, direction, nc, c[cid], gates} sid represents the unique identifier of the skylane, direction represents one of the four directions of travel (East-to-West), (West-to-East), (South-to-North), or (North-to- South). The length L of the skylane is equal to nc-s, where s is the side length of an air cube defined in meters and ncis the number of air cubes. Figure 7 depicts the general structure of a skylane. The boxes with a solid outline represent variables that define the data elements of skylane. Boxes with a dashed outline represent variables that define movement directions of vehicles inside the skylane.

[0072] An intersection is the junction where one skylane crosses another in the horizontal plane, i.e., a projection of the skylanes onto the Earth’s surface. In the skylane, this is the place where vehicles may turn or change their direction. In order to avoid collisions, an intersection is designed to include three layers. The middle layer is used for a temporary hovering before a UAV makes the intended turn. A vertical airport or vertiport (V) is a place for take-off and landing for UAVs.

[0073] V[vpid] = [vpid, v[ ], zc, ids[ ]}

[0074] Each vertiport has a unique identifier vpid. The volume of a vertiport is defined by its horizontal vertices v[(x1, y1), (x2, y2), (x3, y3), (x4, y4)] and its maximum ceiling altitude zc. The array ids[ ] is the sequence of identification numbers of the UAVs that are permitted to land or take off from the vertiport.

[0075] A gate is a connection between a skylane and a vertiport. It regulates the take-off and landing operations of the UAVs. Vehicles need to go through the gates to enter or exit the skylanes.

[0076] An air corridor is a 3D volume of airspace reserved for UASs. It is a complete airspace structure that includes all skylanes, intersections, and gates.

[0077] Figure 8 a) shows a schematic representation of air corridors in the 3D space, and figure 8 b) shows a projected view thereof. The skylanes in level 1 carry traffic in the East-to-West and the West-to-East directions, the skylanes in level 3 carry traffic in the North-to-South and South-to-North directions. Level 2 is the temporary hover space for UAV making turns. Figure 8 b) shows the projection of the skylanes of figure 8 a). The dark boxes represent vertiports, i.e. , a vertical take-off and landing (VTOL) starting and landing infrastructure, and the dashed box indicates the intersection that extends over three levels.

[0078] The invention will now be presented with reference to a 3GPP wireless communication system. It is noted that the procedures may also be used in wireless communication systems operating in accordance with other, similar standards.

[0079] In a first step, if a gNB is configured to support UAM UEs, the gNB in the 3GPP system requests for information about all active air corridors in its coverage area from the USS / UTM, which USS / UTM is not part of the 3GPP communication system. The request may include an indication of geographical and / or territorial boundaries within which the air corridor information is required by the gNB. The information about the boundaries may denote a hemisphere of coverage around the gNB represented by a centre coordinate and a radius. Figure 13 shows an example of a coverage hemisphere around a gNB. The request may be transmitted periodically, e.g., every 30 minutes, or on an event-triggered basis, e.g., when a UAM UE connects to the gNB or when the gNB detects that the available information is outdated.

[0080] The request may be transmitted by a suitable modification of existing network protocols between the gNB and the core network, and by introducing an additional message in the interface between the UAS-NF in the core network and the USS / UTM. Following the request from the gNB, the USS / UTM provides information about all the active air corridors within the region indicated by the gNB. Active air corridor information may include parameters of the skylanes in the air corridor, which in turn are constituted by the air cubes and their directions. Similarly, for a request on the UAM-UE-air corridor association, the USS / UTM - using a mechanism similar to the above - or the UAM UE itself directly provides the information to the gNB. This information comprises an appropriate index of the air corridor the UAM UE is associated with.

[0081] Based on the information about the air corridors within its region of interest, the gNB adapts its PRACH configuration in three ways: 1 . The gNB configures the cyclic shift gap parameter Ncs to accommodate the different round-trip delays that would be caused by the UAM UEs sending PRACH preambles from different air corridors. The potential cyclic shifts possible may be associated with different aerial geographical volumes within the coverage of the gNB and may be hard-coded in the specifications. For example, a hemispherical coverage region maybe quantised into concentric shells that may be associated with different cyclic shift gap parameter values. An exemplary configuration following this idea is shown in figure 14, where the different shells are referred to as regions numbered from 1 to 4.

[0082] The association between the geographical area and the active air corridors is made by the gNB and the corresponding cyclic shift indication is provided in the PRACH configuration in the system information block (SIB). If the active air corridor configuration changes, then the gNB adapts the PRACH configuration in the SIB accordingly. The gNB may use multiple PRACH configurations in case active air corridors extend across multiple regions. An example for multiple active air corridors extending across multiple regions is shown in figure 15. The active air corridor 1 , shown as running at an oblique angle to the ground, exclusively extends across region 4, while the active air corridor 2, running parallel to the ground extends across regions 3 and 4. Note that active air corridor 2 running parallel to the ground is running perpendicular to the plane of the figure.

[0083] 2. The gNB also adapts the SSB beams associated with the PRACH resources, based on the air corridor information. Specifically, the gNB associates the SSB beams pointing in the direction of the air corridor with the PRACH resources with the appropriate Ncs configuration. An example for the SSB beams pointing at different sectors of the coverage hemisphere and being associated with respective different PRACH resources is shown in figure 16. In the figure, it is assumed that the gNB gets information from the USS / UTM that there are two active air corridors, 1 and 2. Based on its own classification of coverage regions and the required cyclic shift separation, the gNB transmits PRACH configurations with the appropriate cyclic shift gap parameters Further, it associates the SSB beams pointing in those directions with the corresponding PRACH resources, e.g., beams 1 and 2 are associated with the PRACH resources configured with beam 3 is associated with both PRACH resources configured with

[0084] 3. The gNB uses the air-corridor to UAM UE association information to measure the congestion in an air corridor and accordingly assign PRACH resources during handover and other contention-free RACH processes for the UAM UEs. To this end the source gNB may, e.g., exchange the air-corridor to UAM UE association information to the target gNB in a handover request, which is then used by the target gNB to configure a contention-free RACH resource and appropriate PRACH resources. An exemplary swim-lane diagram of the message flow between the source gNB, the target gNB and the UAM UE for contention-free RA using UAM UE- air corridor information is shown in figure 17.

[0085] Next, after a UAM UE, e.g., an air taxi, connects to a gNB, the gNB requests information on the air corridor the UAM UE is associated with, from the USS / UTM or from the UAM UE itself. It is noted that both the above requests can be periodic or event triggered. In response to the request, the USS / UTM and / or the UAM UE itself provides the requested information to the gNB.

[0086] Figure 9 shows a swim-lane diagram of the message flow between the gNB, the UAS NF and the USS or UTM for active air corridor and / or specific UAM UE association information retrieval from the USS / UTM, in accordance with the present method.

[0087] The gNB uses the air corridor information and air corridor-UAM UE association together with the above mapping in the specification to adjust the PRACH preamble cyclic shift gap configuration, the PRACH to SSB resource mapping and the PRACH resource allocation.

[0088] The above information is used to adapt the PRACH preamble cyclic shift gap configuration and PRACH to SSB resource mapping in both contention-based RA and contention-free RA mechanisms. While the PRACH resource allocation may be performed for contention-free RA. The optimizations are applicable for both 4-step RA and 2-step RA. The RA configuration may be modified by changing the parameters that are broadcasted in the system information for contention-based RA or changing the parameters via UE specific messages for the case of contention-free RA.

[0089] Figure 10 shows a swim-lane diagram of the message flow between the gNB and the UAM UE for UAM UE-air corridor association information retrieval from the UAM UE.

[0090] Figure 11 shows a flow diagram of an exemplary basic method for active air corridor information retrieval and use by the gNB.

[0091] Figure 12 shows a flow diagram of an exemplary basic method for UAM UE-active air corridor association and use by the gNB.

[0092] In accordance with a first aspect of the invention a method of adapting wireless random access channel configuration is presented. The method 100, an exemplarily flow diagram of which is represented in figure 21 comprises, in step 110, obtaining, at the first gNB, first information about active air corridors and / or specific UAM UEs association therewith. The first information may be limited to air corridors within a radio coverage range above the gNB. Optionally, corresponding information pertaining to neighbouring gNBs having radio coverage ranges adjacent to or overlapping with the first gNBs radio coverage range may also be obtained. The method further comprises receiving, in step 120, at the first gNB, a connection request from a UAM UE. In response to the connection request the first gNB requests, in step 130, from the UAM UE, second information on the air corridor the UAM UE is associated with, and receives, in step 140, a response to the request from the UAM UE. The received first and / or second information is then used in the first gNB for determining, in step 150a, a distance range between the UAM UE and the first gNB based on the received first and / or second information and the known location of the first gNB and / or for determining, in step 150b, a mapping between the received information and a radio coverage range above the gNB. The mapping may comprise an association of a respective gNB with a volume in the space around each respective gNB. The volume in space may be represented by a plurality of quantised sub-volumes. To this end, the locations of a plurality of quantised sub-volumes in space around each gNB may be determined, through measurements or simulations, up to a maximum distance. The respective mapping for each gNB may be stored in the gNB. Finally, the PRACH preamble cyclic shift gap configuration, the PRACH to SSB resource mapping and / or the PRACH resource allocation in accordance with the determined distance range are adjusted in accordance with the determined distance range or mapping, step 160.

[0093] In one or more embodiments of the method obtaining comprises transmitting a request for such information to a UAS NF implemented in the core network, represented by step 110-1 of figure 21 , which UAS NF receives the information from a USS or UTM in response to a corresponding request, and receiving the response to the request from the UAS NF, represented by step 110-2 of figure 21.

[0094] In one or more embodiments the method further comprises broadcasting, step 170 in figure 21 , the adjusted parameters in the system information broadcast (SIB), or transmitting, step 172 in figure 21 , the adjusted parameters in messages directed to a specific UAM UE.

[0095] In one or more embodiments the method further comprises, at the occurrence of a handover of the UAM UE’s network connection from the first gNB to a second gNB, transmitting, from the first gNB, a handover request to the second gNB, step 174 in figure 21 , and receiving, from the second gNB, a handover acknowledgement and an optimised PRACH resource configuration for remote access (RA) through the UAM UE, step 176 in figure 21. The first gNB then transmits a radio resource configuration (RRC) including the previously received optimised PRACH resource configuration to the UAM UE, step 178 in figure 21.

[0096] In one or more embodiments the method further comprises adapting the SSB beams associated with the PRACH resources based on the obtained first and / or second information and / or information determined therefrom, step 180 in figure 21.

[0097] In one or more embodiments the method further comprises measuring or determining a congestion in the air corridor using the obtained first and / or second information and / or information determined therefrom for measuring a congestion, step 182 in figure 21 , and accordingly assigning PRACH resources during handover and other contention-free RACH processes for the UAM UEs, step 184 in figure 21 .

[0098] In accordance with a second aspect of the invention a gNB of a wireless communication network is presented. The gNB 500, an exemplary block diagram of which is shown in figure 18, comprises one or more wireless first interfaces 501 configured for wireless communication with terrestrial UEs and / or aerial UEs in accordance with a predetermined communication standard. The one or more first wireless interfaces 501 may comprise one or more antennas and associated RF circuitry for transmitting and / or receiving processing radio frequency signals (not shown in the figure). The gNB 500 further comprises a second communication interface 502 configured for communicating with a network backbone and / or a network management unit, and further configured to communicate with a UAM NF implemented with the network backbone or the network management unit (network components not shown in the figure). The gNB 500 further comprises one or more microprocessors 503 and associated volatile and non-volatile memory 504, 505. The aforementioned elements of the gNB 500 are communicatively connected via one or more data and / or signal lines and / or buses 506. The non-volatile memory 505 stores computer program instructions which, when executed by the one or more microprocessors 503, configure the gNB 500 to execute, implement or carry out embodiments of the method in accordance with the first aspect of the invention, and to accordingly control hardware and / or software elements and / or components of the gNB 500.

[0099] In accordance with a third aspect of the invention a method of operating a wireless urban air mobility user equipment, UAM UE, is presented. The method 200, an exemplarily flow diagram of which is represented in figure 19, comprises, in step 210, transmitting a connection request to a base station, gNB, 500 of a wireless communication network, receiving, in step 220, a request from the gNB 500 for providing second information on an air corridor the UAS UE is currently associated with, providing, in step 230, a response to the request, receiving in step 240, an SSB / PRACH resource allocation from the gNB 500, and subsequently operating radio communication in accordance with the received SSB / PRACH resource allocation, represented by step 250. In accordance with a fourth aspect of the invention a wireless UE 600 of a UAS is presented. The wireless UE 600, an exemplary block diagram of which is shown in figure 20, comprises one or more wireless first interfaces 601 configured for wireless communication with a gNB 500, one or more microprocessors 603 and associated volatile and non-volatile memory 604, 605. The one or more first wireless interfaces 601 may comprise one or more antennas and associated RF circuitry for transmitting and / or receiving processing radio frequency signals (not shown in the figure). The aforementioned elements of the wireless UE 600 are communicatively connected via one or more data and / or signal lines and / or buses 606. The non-volatile memory 605 stores computer program instructions which, when executed by the one or more microprocessors 603, configure the wireless UE 600 to execute, implement or carry out embodiments of the method in accordance with the third aspect of the invention, and to accordingly control hardware and / or software elements and / or components of the wireless UE 600.

[0100] The method described hereinbefore may be represented by computer program instructions. Thus, in accordance with a fifth aspect of the present invention a computer program product comprises computer program instructions which, when executed by a microprocessor of or functionally coupled with a gNB in accordance with the second aspect of the invention, cause the processor to carry out a method in accordance with the first aspect of the invention, and / or to accordingly control hardware and / or software blocks or modules of the gNB or, when executed by a microprocessor of or functionally coupled with a wireless UE of a UAS in accordance with the fourth aspect of the invention, cause the processor to carry out a method in accordance with the third aspect of the invention, and / or to accordingly control hardware and / or software blocks or modules of the wireless UE.

[0101] Computer program instructions, or code, for carrying out operations for embodiments may be any number of lines and may be written in any combination of one or more programming languages including an object- oriented programming language such as Python, Ruby, Java, Smalltalk, C++, or the like, and conventional procedural programming languages, such as the “C” programming language, or the like, and / or machine languages such as assembly languages. The code may execute entirely on the user’s computer, partly on the user’s computer, as a stand-alone software package, partly on the user’s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user’s computer through any type of network, including a local area network (LAN), wireless LAN (WLAN), or a wide area network (WAN), or the connection may be made to an external computer, for example, through the Internet using an Internet Service Provider (ISP).

[0102] The computer program instructions may be retrievably stored or transmitted on a computer-readable medium or data carrier. The medium or the data carrier may by physically embodied, e.g., in the form of a hard disk, solid state disk, flash memory device or the like. However, the medium or the data carrier may also comprise a modulated electro-magnetic, electrical, or optical signal that is received by the computer by means of a corresponding receiver, and that is transferred to and stored in a memory of the computer.

[0103] The described features, structures, or characteristics of the embodiments may be combined in any suitable manner. In this description, numerous specific details are provided, such as examples of programming, software modules, user selections, network transactions, database queries, database structures, hardware modules, hardware circuits, hardware chips, etc., to provide a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that embodiments may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of an embodiment. Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment, but mean “one or more but not all embodiments” unless expressly specified otherwise. The terms “including,” “comprising,” “having,” and variations thereof mean “including but not limited to,” unless expressly specified otherwise. An enumerated listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise. The terms “a,” “an,” and “the” also refer to “one or more” unless expressly specified otherwise.

[0104] Where aspects of the embodiments are described in this specification with reference to schematic flowchart diagrams and / or schematic block diagrams of methods, apparatuses, systems, and program products according to embodiments it will be understood that each block of the schematic flowchart diagrams and / or schematic block diagrams, and combinations of blocks in the schematic flowchart diagrams and / or schematic block diagrams, can be implemented by code. This code may be provided to a processor of a general-purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions / acts specified in the flowchart diagrams and / or block diagrams.

[0105] It should be noted that, in some implementations or embodiments, the functions noted in the exemplary embodiments shown in the figures may occur out of the order shown in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more blocks, or portions thereof, shown in the figures.

[0106] The proposed mapping between the cyclic shift gap parameter and the coverage region above the gNB helps to achieve a better trade-off between the number of orthogonal preambles available for RA and the possibility of collision between two orthogonal preambles arriving at the same time.

[0107] Air corridor information obtained from the USS / UTM is helpful for the gNB to identify if there are any active air corridors with the possibility of UAM UEs flying through them, and configure PRACH resources accordingly as it is necessary to adapt the PRACH configuration for better performance of RA by UAM UEs. Air corridor association information obtained from the UAM UEs or USS / UTM is helpful for the gNB to determine the level of congestion in each air corridor and the direction of movement of the UAM UEs and adapt the PRACH resource configuration accordingly.

[0108] The present invention can be used with great advantage in cellular networks, particularly wireless communication systems, e.g., 5G+ and 6G, where artificial intelligence and machine learning concepts are envisioned to be used to optimize the performance of the radio access network.

[0109] BRIEF DESCRIPTION OF THE DRAWING

[0110] In the foregoing the invention was described with reference to the attached drawing, in which

[0111] Fig. 1 shows a high-level conceptual block diagram showing the decoupling of 3GPP specifications from aviation-related aspects,

[0112] Fig. 2 shows a high-level example of the integration of UAV entities in 3GPP Release 17,

[0113] Fig. 3 shows a schematic swim-lane diagram of the RACH procedure message flow,

[0114] Fig. 4 shows a schematic representation of the PRACH time slots and the PRACH structure in the time and frequency domain,

[0115] Fig. 5 shows the basic structure for the generation of the NR random-access preamble,

[0116] Fig. 6 shows an illustration of the cyclic shift separation Ncs between preamble sequences,

[0117] Fig. 7 depicts the general structure of a skylane,

[0118] Fig. 8 shows a schematic representation of air corridors and a projected view thereof,

[0119] Fig. 9 shows a swim-lane diagram of the message flow between the gNB, the UAS NF and the USS or UTM for active air corridor and / or specific UAM UE association information retrieval from the USS / UTM, Fig. 10 shows a swim-lane diagram of the message flow between the gNB and the UAM UE for UAM UE-air corridor association information retrieval from the UAM UE,

[0120] Fig. 11 shows a flow diagram of an exemplary basic method for active air corridor information retrieval and use by the gNB,

[0121] Fig. 12 shows a flow diagram of an exemplary basic method for UAM UE-active air corridor association and use by the gNB,

[0122] Fig. 13 shows an example of a hemispherical coverage area around a gNB,

[0123] Fig. 14 shows an exemplary configuration of a hemispherical coverage region quantised into concentric shells,

[0124] Fig. 15 shows an example for multiple active air corridors extending across multiple regions,

[0125] Fig. 16 shows an example for the SSB beams pointing at different sectors of the coverage hemisphere and being associated with respective different PRACH resources,

[0126] Fig. 17 shows an exemplary swim-lane diagram of the message flow between the source gNB, the target gNB and the UAM UE for contention-free RA using UAM UE-air corridor information,

[0127] Fig. 18 shows an exemplary block diagram of a gNB of a wireless communication network configured to execute a method in accordance with aspects of the present invention,

[0128] Fig. 19 shows an exemplary flow diagram of a method of operating a wireless UE of a UAS in accordance with aspects of the present invention,

[0129] Fig. 20 shows an exemplary block diagram of a wireless UE of a UAS configured to execute a method in accordance with aspects of the present invention, and

[0130] Fig. 21 shows an exemplary flow diagram of a method of operating a gNB of a wireless communication network in accordance with the first aspect of the invention.

[0131] In the figures identical or similar elements may be referenced using the same reference designators. LIST OF REFERENCE NUMERALS (PART OF THE DESCRIPTION)

[0132] 100 method 220 receive request for second

[0133] 110 obtain first information information

[0134] 110-1 transmit request for first 230 provide response to request for information second information

[0135] 110-2 receive first information 30 240 receive SSB / PRACH resource

[0136] 120 receive connection request allocation

[0137] 130 request second information 250 operate radio communication in

[0138] 140 receive response accordance with the received

[0139] 150a determine distance range SSB / PRACH resource allocation

[0140] 150b determine mapping 35

[0141] 160 adjust PRAC H 500 base station / gNB resources / parameters 501 first wireless interface

[0142] 170 broadcast adjusted parameters 502 second communication interface

[0143] 172 transmit adjusted parameters 503 microprocessor(s)

[0144] 174 transmit handover request 40 504 volatile memory

[0145] 176 receive handover 505 non-volatile memory acknowledgement 506 data / signal line(s) / bus(es)

[0146] 178 transmit RRC

[0147] 180 adapt SSB beams 600 UE

[0148] 182 measure air corridor congestion 45 601 wireless third interface

[0149] 184 assign PRACH resources 603 microprocessor(s)

[0150] 604 volatile memory

[0151] 200 method 605 non-volatile memory

[0152] 210 transmit connection request 606 data / signal line(s) / bus(es)

Claims

CLAIMS1 . A method (100) of adapting wireless random access channel configuration of a first base station, first gNB, comprising:- obtaining (110), at the first gNB, first information about active air corridors and / or about specific urban air mobility user equipment’s, UAM UE, association,- receiving (120), at the first gNB, a connection request from a UAM UE,- requesting (130), from the UAM UE, second information on the air corridor the UAM UE is associated with, and receiving (140) a response to the request from the UAM UE,- determining (150a) a distance range between the UAM UE and the first gNB based on the received first and / or second information and the known location of the first gNB and / or determining (150b) a mapping between the received information and a radio coverage range above the gNB, and- adjusting (160) the physical random access channel, PRACH, preamble cyclic shift gap configuration, the PRACH to synchronisation signal block, SSB, resource mapping and / or the PRACH resource allocation in accordance with the determined distance range and / or mapping.

2. The method (100) of claim 1 , wherein obtaining (110) comprises transmitting (110-1 ) a request for such information to an uncrewed aerial system network function, UAS NF, implemented in the core network, which UAS NF receives the information from an uncrewed aerial system service supplier, USS, or uncrewed aerial system traffic manager, UTM, in response to a corresponding request, and receiving (110-2) the response to the request from the UAS NF.

3. The method (100) of claim 1 or 2, further comprising broadcasting (170) the adjusted parameters in the system information broadcast, SIB, or transmitting (172) the adjusted parameters in messages directed to a specific UAM UE.

4. The method (100) of one of claims 1 to 3, further comprising, at the occurrence of a handover of the UAM UE’s network connection from the first gNB to a second gNB:- the first gNB transmitting (174) a handover request to the second gNB,- the first gNB receiving (176), from the second gNB, a handover acknowledgement and an optimised PRACH resource configuration for remote access, RA, by the UAM UE, and- the first gNB transmitting (178) a radio resource configuration, RRC, including the previously received optimised PRACH resource configuration to the UAM UE.

5. The method (100) of one of claims 1 to 4, further comprising the gNB adapting (180) the SSB beams associated with the PRACH resources based on the obtained first and / or second information and / information determined therefrom.

6. The method (100) of one of claims 1 to 5, further comprising the gNB using the obtained first and / or second information and / or information determined therefrom for measuring (182) a congestion in the air corridor and accordingly assigning (184) PRACH resources during handover and other contention-free RACH processes for the UAM UEs.

7. A base station, gNB, (500) of a wireless communication network comprising one or more wireless first interfaces (510) configured for wireless communication with terrestrial UEs and / or aerial UEs (600) in accordance with a predetermined communication standard, a second communication interface (502) configured for communicating with a network backbone and / or a network management unit, and further configured to communicate with a UAM NF implemented with the network backbone or the network management unit, further comprising one or more microprocessors (503) and associated volatile(504) and non-volatile memory (505), the aforementioned components or elements of the gNB (500) being communicatively connected via one or more signal and / or data lines and / or buses (506), wherein the non-volatile memory(505) stores computer program instructions which, when executed by the one or more microprocessors (503), configure the gNB (500) to execute the method of one or more of claims 1 to 6 and to accordingly control hardware and / or software elements and / or components of the gNB 500.

8. A method (200) of operating an urban air mobility system wireless user equipment, UAM UE, (600) comprising:- transmitting (210) a connection request to a base station, gNB, (500) of a wireless communication network,- receiving (220) a request from the gNB (500) for providing second information on an air corridor the UAM UE (600) is associated with,- transmitting (230) the second information to the gNB (500),- receiving (240) a synchronization signal block, SSB, I physical random access channel, PRACH, resource allocation from the gNB (500), and- operating (250) operating radio communication in accordance with the received SSB I PRACH resource allocation.

9. A wireless user equipment, UE, (600) comprising a wireless third interface (601 ) configured for wireless communication with a base station, gNB, (500) of a wireless communication network in accordance with a predetermined communication standard, further comprising one or more microprocessors (603) and associated volatile (604) and non-volatile (605) memory, the aforementioned components or elements of the wireless UE (600) being communicatively connected via one or more signal and / or data lines and / or buses (606), wherein the non-volatile memory (605) stores computer program instructions which, when executed by the one or more microprocessors (603, configure the wireless UE (600) to execute the method of claim 8 and to accordingly control hardware and / or software elements and / or components of the wireless UE (600).

10. A computer program product comprising computer program instructions, which, when executed by a microprocessor (503) of or functionally coupled with a base station, gNB, (500) in accordance with claim 7, cause the processor (503) and / or the gNB (500) to carry out the method of one or more of claims 1 to 6, or which, when executed by a microprocessor (603) of or functionally coupled with a wireless user equipment, UE, (600) in accordance with claim 9, cause the processor (603) and / or the UE (600) to carry out the method of claim 8.

11. Computer readable medium or data carrier retrievably transmitting or storing the computer program product of claim 10.

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