Method for coordinating uplink communications of airborne and terrestrial users for coexistence

Abstract

A method of providing non-orthogonal multiplexing of aerial UEs with terrestrial UEs in a network with terrestrial gNBs is presented. Multiple gNBs from a set of interconnected gNBs are grouped into a coordinated set. Using aerial UE CSI information, one gNB from the coordinated set is selected for decoding private RSMA data streams for the aerial UE while all gNBs in the set decode common data streams. Likewise, all gNBs decode UL transmissions from the attached terrestrial UEs. Coordinated resource allocation for RSMA based optimized transmissions from aerial UEs mitigates interference at terrestrial gNBs transmitting in the same RBs as the aerial UEs.

Description

Technical Field

[0001] This invention relates to optimizing communication between urban air mobility (UAM) user equipment (UE) and ground UE with ground base stations, for example, according to any standard (such as 4G / LTE and 5G / NR) specified by the 3rd Generation Partnership Project (3GPP).

[0002] Symbols and Definitions

[0003] 3GPP, short for "Third Generation Partnership Project," is a collective term for multiple standards organizations that develop mobile telecommunications protocols. In the context of 3GPP, the term "random" emphasizes that a User Equipment (UE) can request access to network resources at any time, as the UE is not bound by a predetermined or fixed access scheme. The expression "terrestrial wireless communication network" refers to a wireless communication network whose base stations are located on a terrestrial structure, and whose UEs are typically located within or on a terrestrial structure. The abbreviation "gNB," specifically used for 5G NR base stations, is used interchangeably with the abbreviation BS for base stations in this document, regardless of the naming conventions in various standards, which may use "eNB" or other abbreviations for base stations. UAM UEs may also be referred to as airborne UEs in this document. Background Technology

[0004] When integrating airborne UEs into terrestrial cellular networks, interference with existing terrestrial UE signals needs to be addressed. Much of this interference is likely caused by signals from airborne UEs. Because UAM UEs fly at considerable altitudes above the ground, they enjoy line-of-sight (LOS) paths to multiple base stations. Therefore, when airborne users (such as aircraft used for UAM) communicate with terrestrial gNBs, their signals cause interference at many gNBs due to the typically favorable LOS propagation conditions, which may not be easily mitigated using conventional interference management schemes. Interference from UL transmissions from airborne UEs affects multiple terrestrial gNBs, necessitating effective methods for interference management.

[0005] The traditional approach to interference management is to have users transmit on orthogonal (i.e., non-overlapping) time-frequency resource blocks (RBs) (e.g., the set of subcarriers (SCs) in an Orthogonal Frequency Division Multiple Access (OFDMA) system). However, allocating different time-frequency RBs in an OFDMA system to different UEs is inefficient because it fails to utilize all available degrees of freedom (DoF) in the radio channel, i.e., it does not fully utilize all available time-frequency resources.

[0006] Higher DoF can be achieved if the receiver and / or transmitter has multiple antennas, allowing the use of receive and / or transmit beamforming techniques to separate signals from different users transmitting on the same time-frequency RB. In this technique, known as Space Division Multiple Access (SDMA), the UE uses different precoded vectors or matrices to spatially separate its signals arriving at the gNB. While interference from airborne UEs can be managed by scheduling airborne and ground UEs on orthogonal RBs, or by using multiple receive antennas at the gNB to separate their signals and orthogonally multiplexing them on the same RB, these methods have certain limitations. A sufficient number of antennas are required at the gNB to distinguish transmissions from different UEs, which translates to higher hardware costs.

[0007] Even with a single antenna, the achievable DoF can be further improved by using Non-Orthogonal Multiple Access (NOMA) technology, where signals from multiple users can be superimposed on the same time-frequency RB, and more sophisticated interference cancellation techniques can be used at the receiver to extract these signals. In NOMA, some UEs share the same RB, and some UE signals are fully decoded and canceled before being decoded by other UE signals. In the specific use case of shared time-frequency RBs for terrestrial and airborne UEs discussed in this paper, NOMA requires the gNB, which is interfered with by airborne UEs, to fully decode and cancel the signals of terrestrial UEs before decoding their signals, and vice versa.

[0008] L. Lei, D. Yuan, CK Ho, and S. Sun in “Power and Channel Allocation for Non-Orthogonal Multiple Access in 5G Systems: Tractability and Computation” (IEEE Transactions on Wireless Communications, Vol. 15, No. 12, pp. 8580-8594, December 2016); S. Sruthy and NB Mehta in “Power and Discrete Rate Adaptation in Wideband NOMA in Frequency-Selective Channels” (IEEE Transactions on Wireless Communications, doi: 10.1109 / TWC.2023.3315709); W. Mei and R. Zhang in “Uplink Cooperative NOMA for Cellular-Connected UAVs”. In "UAV Communications Based on Non-Orthogonal Multiple Access" (IEEE Signal Processing Journal, Vol. 13, No. 3, pp. 644-656, June 2019), Y. Liu, Z. Qin, Y. Cai, Y. Gao, GY Li, and A. Nallanathan; and in "UAV Communications Based on Non-Orthogonal Multiple Access" (IEEE Wireless Communications, Vol. 26, No. 1, pp. 52-57, February 2019), L. Liu, S. Zhang, and R.Zhang discusses various aspects of NOMA in his paper "Exploiting NOMA for Multi-Beam UAV Communication in Cellular Uplink" (ICC2019 - 2019 IEEE International Conference on Telecommunications (ICC), Shanghai, China, 2019, pp. 1-6), and Mustafa Eroz and Lin-Nan Lee discuss various aspects of NOMA in their paper "System and Method for Asynchronous Multi-stream Transmission For NOMA" (Hughes Network Systems LLC, 2018, US2019140770 A1).

[0009] Another known technique is Rate Division Multiple Access (RSMA). As previously mentioned, conventional NOMA requires the receiver to completely decode and cancel the signal from interfering users in order to achieve higher performance compared to orthogonal transmission schemes or multi-antenna schemes. This may not always be feasible, depending on the wireless channel conditions. Note that in this specification, the terms "signal cancellation" and "stream cancellation" are used interchangeably unless explicitly stated otherwise or readily apparent from the appropriate context by a person skilled in the art. In RSMA, the transmitting user splits its data stream into a common or public portion, which can be decoded and canceled by receivers other than the intended receiver; and a private portion, which is intended to be decoded only by its intended receiver. RSMA improves upon conventional NOMA by enabling receivers to cancel the optimal portion of the signal from interfering users and achieves a smooth trade-off between treating interference as noise (which is optimal when interference is weak) and conventional NOMA (which is optimal when interference is strong) by adjusting the signal power allocated to the public and private data streams. By allocating different power levels to the "public" and "private" messages, the level of interference to unintended receivers can be dynamically controlled.

[0010] B. Clerckx et al., in “A Primer on Rate-Splitting Multiple Access: Tutorial, Myths, and Frequently Asked Questions” (IEEE Communications Journal, Vol. 41, No. 5, pp. 1265-1308, May 2023), and Y. Mao, B. Clerckx, and VOK Li, in “For Coordinated Multi-Point Joint Transmission” (IEEE International Conference on Communications (ICC Workshop), Shanghai, China, 2019, pp. 1-6), MM... L. Yin and B. Clerckx in “Multicarrier Rate-Splitting Multiple Access: Superiority of OFDM-RSMA Over OFDMA and OFDM-NOMA” (IEEE Communications Letters, Vol. 27, No. 11, pp. 3088-3092, November 2023); L. Yin and B. Clerckx in “Rate-Splitting Multiple Access for Satellite-Terrestrial Integrated Networks: Benefits of Coordination and Cooperation” (IEEE Transactions on Wireless Communications, Vol. 22, No. 1, pp. 317-332, January 2023); W. Jaafar, S. Naser, S. Muhaidat, PC Sofotasios, and H. Yanikomeroglu, in "On the Downlink Performance of RSMA-Based UAV Communications" (IEEE Transactions on Vehicle Technology, Vol. 69, No. 12, pp. 16258-16263, December 2020); X. Liu, J. Feng, F. Li, and VCM Leung, in "Downlink Energy Efficiency Maximization for RSMA-UAV Assisted Communications" (IEEE Communications on Wireless, Vol. 13, No. 1, pp. 98-102, January 2024); and Mao Xiaomao and Qiu Peiliang, in "Rate splitting based method for allocating user rates in wireless multiple access channels" (Zhejiang University, 2010, CN 101827452 A),Aasheesh Shukla and Abhay Chaturvedi Nira in "Rate Splitting Multiple Access (RSMA) System" (GLA University, Matura, IN 202111053727 A); Chao Dong, Zhiqiang He, Xinrui Huang, Kai Niu, and Zhongwei Si in "Method and Device For Transmitting Data Based On Rate Division Non-orthogonal Multiple Access Technology" (Beijing University of Posts and Telecommunications, 2016, WO2018023732 A1); Jiang Hao, Li Hao, Wu Jing, Zhou Changjia, and Zhou Jianguo in "Rate optimization method for uplink rate division multiple access system" (Wuhan University, 2022, CN 115866638 A); Daesung Yu, JunbeomKim, and Seok Hwan Park in "Common Message Generation Method for Rate-Splitting Multiple Access Based on Hierarchical User Clustering" (Jeonbuk National University Industry Cooperation Foundation, 2020, KR 102270993B1), and Kwak Kyung Sup and Liu Hongwu in "An Adaptive Rate Splitting Method and System for Uplink Non-Orthogonal Multiple Access Systems" (KR 102074217 B1),Liu Hongwu also discussed various aspects of RSMA in his paper, "Rate splitting method suitable for non-orthogonal multiple access uplink" (Shandong Jiaotong University, 2019, CN 110366234 A).

[0011] Although there are numerous academic papers on the general aspects of NOMA and RSMA, none of them discuss integrating RSMA to coexist with OFDMA, which exists in traditional terrestrial communication systems.

[0012] Similarly, a few academic papers have discussed the application of RSMA to airborne base stations, but none have discussed the coexistence of airborne UEs in traditional terrestrial communication networks.

[0013] To date, interference management between airborne UEs and ground UEs in the same conventional communication network has taken NOMA into account, but RSMA has not.

[0014] As mentioned above, when serving both airborne and terrestrial UEs, cellular networks need to intelligently allocate resources to accommodate both types of UEs. Therefore, technologies are needed to address this unique challenge of integrating airborne UEs into terrestrial cellular networks. Summary of the Invention

[0015] This invention aims to meet this need through the method according to claim 1, the base station according to claim 7, the central unit according to claim 8, the communication system according to claim 9, and the computer program product according to claim 10. A corresponding computer-readable storage medium is provided in claim 11. Advantageous embodiments and developments are described in the corresponding dependent claims.

[0016] This method proposes using OFDMA for ground-based UEs and OFDMA-based RSMA for airborne UEs to achieve coordinated reception. Since the initially mentioned problems primarily occur in uplink (UL) transmissions (i.e., transmissions from the UE to the gNB), this method only considers UL transmissions.

[0017] The proposed method enables gNBs to operate within a coordination set to efficiently implement RSMA-based UL communication for air UEs coexisting with ground UEs, thereby allowing these air UEs to transmit on the same RBs as the ground UEs. This is achieved by gNBs in the coordination set cooperating with each other to share the channel state information (CSI) of the air UEs, which enables all gNBs in the coordination set to decode and eliminate the “common” data streams of air UEs scheduled on the same RBs as other ground UEs.

[0018] The method of this invention assumes the following conditions: 1) A set of gNBs is configured to communicate with each other to obtain UL CSI information of air UEs on the same RB within their coverage area. This can be achieved using the concept of a gNB coordination set, as available in current 3GPP specifications. gNBs can be organized as multiple DUs connected to the same Central Unit (CU) or a set of multiple CUs and Distributed Units (DUs).

[0019] In the first case, the CU calculates and coordinates resource allocations for all DUs, while in the second case, a CU can calculate and coordinate resource allocations for other CUs belonging to the coordination set.

[0020] 2) An OFDMA-based communication system with multiple subcarriers (SCs) is used, where time and frequency blocks (RBs) are allocated to users in accordance with current 3GPP standards. Signal transmission and reception of airborne UEs are synchronized at all gNBs in the coordination set via joint resource allocation.

[0021] 3) For ground UEs, gNBs may or may not form a coordination set.

[0022] 4) Both the UE and gNB can have one or more antenna elements and can transmit more than one data stream on their assigned RB. The network determines the number of data streams to be transmitted based on CSI feedback as specified in the current 3GPP standard.

[0023] According to a first aspect of the invention, a method 100 is provided for coordinating uplink UL communication between coexisting airborne and ground user equipment (UEs) that are at least temporarily communicatively attached to a terrestrial communication network. Reference will be made below. Figure 1The method is described below. In step 110, Channel State Information (CSI) measurements related to one or more ground UEs and one or more air UEs are performed in a set of interconnected base station gNBs of a terrestrial communication network. In step 120, resource allocation for the ground and air UEs is performed in the set of interconnected gNBs of the terrestrial communication network. Resource allocation may include, for example, sending information about resource allocation to the air and ground UEs in corresponding broadcasts. Resource allocation may be based on information about the effective distance between the gNB and the UE. In step 130, one or more gNB coordination sets are formed or composed from the gNBs of the interconnected gNB set. A single gNB may be part of multiple coordination sets. Each gNB from the corresponding gNB coordination set processes signals from one or more air UEs and signals from one or more ground UEs, and is specifically configured to decode a common or public RSMA data stream of at least one air UE that may be at least temporarily communicatively attached to the coordination set. Using RSMA, signals from the air UEs are multiplexed on the same RB as signals from the ground UEs. Although coordination sets are typically formed for each air UE, two or more air UEs may have associated coordination sets sharing the same gNB. In step 140, a selected gNB is determined from the gNBs in the coordination set. The selected gNB is configured to decode, in addition to decoding general or common data streams, the private RSMA data streams of at least one of one or more air UEs temporarily attached to the corresponding gNB coordination set. Selection may include sharing CSI information associated with the associated air UE among the gNBs in the corresponding coordination set to determine the selected gNB. Resource allocation among the gNBs included in the corresponding gNB coordination set is performed in a joint manner. Resource allocation includes UE-RB or UE-subcarrier (SC) allocation, transmission precoding and / or power allocation for the UE on each RB or SC, determining membership of the gNB coordination set for each air UE, and determining the data stream decoding order for UEs allocated on a particular RB or SC. The gNB coordination set may vary for each air UE and may be optimally selected from a larger set of interconnected gNBs based on measured CSI and other UE parameters such as location, signal-to-noise ratio, signal level, etc. Combinations of parameters may be used to compose the coordination set. Typically, the gNBs selected for forming the coordination set for air UEs do not include all gNBs capable of receiving transmissions from the respective air UEs (i.e., within radio range).

[0024] Airborne UEs transmit their messages by segmenting them into one or more “general” or “public” data streams and one or more “private” data streams, as in RSMA. The segmented data streams are transmitted simultaneously according to RSMA technology, while ground UEs can retain the same transmission format as in current standards and do not need to use RSMA. Therefore, method 100 further includes, in step 150, receiving data at all gNBs in the gNB coordination set from one or more airborne UEs associated with the gNB coordination set, and at each corresponding gNB receiving data from a ground UE attached to or associated with that corresponding gNB.

[0025] In step 160, at least all gNBs in the coordination set associated with one or more airborne UEs first decode the received common data stream of one or more airborne UEs, and then in step 170, remove the received common data stream from the signal received on a specific RB. Ideally, the common data stream is removed by all interconnected gNBs. Because the common data stream can be decoded and removed at gNBs in the gNB coordination set, airborne UEs can be multiplexed on the same RB as ground UEs, and interference with the signals of ground UEs is reduced. Furthermore, after removing the common data stream of airborne UEs in step 170, in step 180, each gNB in ​​the gNB coordination set continues to decode the data stream of its own ground UE (i.e., the ground UE attached to or associated with the corresponding gNB). Finally, in step 190, in addition to the common data stream, selected gNBs in the coordination set also specifically decode the private data stream of airborne UEs. The selected gNBs have been previously determined jointly, for example, based on parameters such as the measured CSI, the location of the UE, and have been associated with the airborne UE. The selection of a gNB configured to decode the private data streams of an over-the-air UE can be dynamically chosen within the gNB coordination set to compensate for the movement of the over-the-air UE over time. Other gNBs in the corresponding coordination set only decode the public data streams of the over-the-air UE. The public data streams may include data about the altitude of the over-the-air UE, or, if the over-the-air node is an IAB node, the number of other UEs attached to it, etc.

[0026] In one or more embodiments, the method further includes: in step 125, receiving information about a corresponding spatial location from one or more airborne UEs, and providing that information to component step 130 and / or selection step 140. The spatial location-related information may be absolutely indicated, for example, indicated as a geographic location including latitude and longitude, or indicated relative to one or more gNBs.

[0027] In an embodiment of the method, step 130 includes: for each air UE, selecting those gNBs closest to the air UE, those gNBs with the highest signal-to-noise ratio and / or signal level, or combinations thereof, instead of selecting all gNBs capable of receiving transmissions from the corresponding air UE.

[0028] In one or more embodiments of the method, assembling one or more gNB coordination sets from the interconnected gNB set includes: for each air UE, selecting those gNBs closest to that air UE, those gNBs with the highest signal-to-noise ratio and / or signal level, or combinations thereof, instead of selecting all gNBs capable of receiving transmissions from the corresponding air UE.

[0029] In one or more embodiments, the method further includes: repeating the CSI measurement and selection steps for dynamic adaptation selection when a gNB has already been selected in the gNB coordination set. The selection can be performed within the gNB coordination set or within a group of interconnected gNBs. The latter may result in a reorganization of the coordination set associated with the airborne UE, for example, if the UAM has moved out of the radio range of some gNBs in a previous gNB coordination set and is now within the radio range of a gNB that is not part of the previous gNB coordination set.

[0030] In one or more embodiments, the method further includes: adjusting the power allocation for public and private data streams and / or the modulation and coding schemes for public data streams, private data streams and / or data streams that do not use rate-segmented multiple access, with the aim of maximizing the weighted total rate on all data streams while keeping the block error rate and / or total transmit power of each transmitter transmitting data streams within the same subchannel and / or resource block below a corresponding predetermined maximum value.

[0031] Figure 2 A schematic representation of an exemplary scenario for implementing the method according to the first aspect of the invention is shown. The outermost circle represents the overall set of interconnected gNBs. gNBs are represented by radio tower icons. The smaller circle numbered "1" represents the gNB coordination set for airborne UE1, represented by a helicopter icon, and the smaller circle numbered "2" represents the gNB coordination set for airborne UE2, also represented by a helicopter icon. Within each gNB coordination set, a gNB is selected for decoding all data streams of airborne UEs associated with the corresponding gNB coordination set, indicated by a dashed circle surrounding the gNB.

[0032] Figure 3A further schematic representation of an exemplary scenario for implementing the method according to the invention is shown. Multiple airborne UEs, represented by helicopter icons, exist in the airspace above various gNBs, represented by radio tower icons; these gNBs form a gNB coordination set. Each gNB serves multiple ground UEs, indicated by smartphone symbols, as shown by dashed circles. Airborne UE1 sends public and private data stream portions to all gNBs in the coordination set, indicated by dotted-line arrows, but only the gNB selected for that airborne UE will decode the public and private data stream portions from airborne UE1.

[0033] Figure 4 A more descriptive schematic flowchart of an embodiment of the method according to a first aspect of the invention is shown. First, the interconnecting gNB performs CSI measurements for all air UEs and its own ground UE. Next, the interconnecting gNB performs RB allocation for the ground and air UEs, and then selects a subset of gNBs to form a corresponding gNB coordination set for common data stream decoding for each air UE. Then, if necessary, gNBs in the gNB coordination set can perform additional CSI measurements for the air UEs. In the next step, gNBs in each gNB coordination set decide which gNB should decode the private data stream of the air UE. Air UEs and ground UEs scheduled on the same RB transmit their UL data. Air UEs use RS, while ground UEs do not. All gNBs in the gNB coordination set decode and eliminate the common data stream from the air UEs, and each gNB further decodes the data stream of its associated or attached ground UEs scheduled in the RB. Finally, only the selected gNBs in the gNB coordination set decode the private data stream of the associated air UE.

[0034] In a first alternative embodiment of the method, the ground UE may use the RS to segment its UL data, while the airborne UE may not use the RS to segment its UL data. In this case, the coordination set is only used to select the best gNB to decode each data stream of the airborne UE. Each gNB first decodes and eliminates the common data streams of the ground UEs it schedules on the RB or sub-channel (SC), and then continues to decode the data streams of the airborne UEs, followed by the private data streams of the ground UEs.

[0035] In a second alternative embodiment of the method, both the airborne UE and the ground UE use RS for their UL data transmission. In this case, each gNB can select the decoding and cancellation order between the airborne UE data stream and its own ground UE data stream.

[0036] The basic mathematical concepts of coordinated reception for ground UEs using OFDMA transmission and air UEs using RSMA transmission will now be explained in more detail.

[0037] A.1 Resource allocation for OFDMA-based single-input single-output transmission

[0038] This section provides a detailed system model and problem statement for OFDMA-based systems with single-input single-output (SISO) architecture, and for potentially non-orthogonal transmission over any SC by airborne UEs and ground UEs, where airborne UEs employ rate segmentation (RS). Consider a system where the set of airborne UEs... and UL to ground BS collection Transmit data. Each ground UE is associated with only one BS, while for each SC... Every airborne UE , will exist by The coordination set represents the set of services (BSs) that work together for the UE. Perform channel estimation, and by A BS will represent a UE Decode the private data stream.

[0039] Assuming a set of ground-based UEs With BS Related, among which, , and Assume all users and the BS have a single antenna. We will then consider extending this to multiple antennas. We assume the BS has its own CSI for ground-based UEs and airborne UEs, and the BS forms a coordinated set for these UEs. Therefore, if This indicates that it is targeting its BS If the set of airborne UEs is a part of the coordinated set on all SCs, then BS Having on the corresponding SC The CSI of all UEs. In practice, this can be obtained by the BS coordinating CSI-RS allocation and transmission to the airborne UEs on the same RB.

[0040] Assuming the UE performs OFDMA-based transmission, where the system bandwidth... exist Bandwidth is allocated among OFDM SCs, with each SC occupying a certain amount of bandwidth. However, unlike traditional OFDMA systems where only one user transmits on each SC, consider a network scheduler that can multiplex one ground UE and one air UE on each SC using RSMA, where RS is performed by the corresponding air UE. Let

[0041] Similarly, let

[0042] but

[0043] and

[0044] Airborne UE In SC The signal sent above is given by the following formula:

[0045] in, It is an aerial UE Use transmission power The sent complex-valued common data stream, and It is an aerial UE Use transmission power Send a private stream of complex values.

[0046] Ground users exist The signal sent above is given by the following formula:

[0047] in, Power used by the user A single data stream is sent.

[0048] Now, suppose that at each BS, one ground UE and one airborne UE are scheduled on all SCs, that is, Assume that since two different ground users are transmitting to two different cells from the same SC, inter-cell interference can be ignored. Then, at BS... In The received signal is given by the following formula:

[0049] in, and It is additive white Gaussian noise (AWGN) at the BS receiver, with an assumed variance. In all SC The same applies above. On each SC, it is assumed that each BS first decodes and removes the common data stream of the airborne UE, and then decodes the signal of the ground UE, treating the private data stream of the airborne UE as noise. On the other hand, a BS decodes the signal of the airborne UE on each SC (i.e., on different SCs, possibly different BSs can decode the data stream of the airborne UE). Furthermore, in the BS... In SC Up to air UE The signal-to-interference-plus-noise ratio (SINR) for decoding the public data stream is given as a function of the transmit power of both the ground UE and the air UE by the following formula:

[0050] Then, in BS In SC UAM UE on The rate of the public data stream is given by the following formula:

[0051] In SC After decoding and canceling the common data stream of the airborne UE, the BS then processes the data stream from the ground UE. The transmitted data stream is decoded, treating the private data stream of the airborne UE as noise. Therefore, the SINR of the decoded ground UE signal is given as a function of the transmit power of both the ground UE and the airborne UE by the following formula:

[0052] Therefore, in SC For use with ground UE The achievable speed is:

[0053] make

[0054] because Only one BS needs to be in SC Up to air UE We decode the signal, therefore we have

[0055] If BS exist Up to the air Decoding the private data stream, that is, Then BS SNR at the location as airborne UE The transmit power of the private data stream is given by the following formula:

[0056] When by BS During decoding, in SC UE in the air The rate of the private data stream is given by the following formula:

[0057] Order in SC UE in the air The rate of the public data stream is determined by This indicates that... Furthermore, it must be made to... All BS are in SC All of the above are decodeable, that is,

[0058] Furthermore, in Used in the air The achievable speed is given by the following formula:

[0059] A.1.1 Problem Statement

[0060] The goal now is to maximize the weighted total rate of ground and air UEs, which are constrained by transmit power at the UE and by RSMA common data stream decoding at the BS. Let Indicates that it is assigned to ground users The weights, and Indicates that it is assigned to an airborne UE The weights. Let Indicates UE in the air above all SCs A vector of common data flow rates. Similarly, let and Indicates that it is used for airborne UE on all SCs. The vector of public and private data stream power allocation, and Indicates that it is used for ground UE on all SCs. The vector of power allocation for the data stream. Furthermore, let... Indicates the air UE Is it in SC? The vector of indicator variables sent on top, and Indicates in SC For use with ground UE The corresponding vector. Similarly, let Indicates instructions Is it in SC? Up to UE The vector of indicator variables used to decode the private data stream. Then, the overall problem A.19 can be formulated as follows:

[0061] Subject to the following constraints

[0062] Problem A.19 is nonconvex because of the variables , and The binary constraints on, and due to the use of ground users The function of the realizable rate The non-concaveness of .

[0063] A.2 Modulation and coding schemes and power allocation for a single physical resource block or PRB set

[0064] In NR, The 12 SCs form a Physical RB (PRB). In the current system, the same power allocation is used for the entire set of PRBs allocated to users. We focus on a single PRB comprising 12 SCs and assume that air UEs and ground UEs multiplex it, with air UEs using RSMA for transmission.

[0065] A.2.1 Single BS

[0066] First, consider the case with only a single BS. Then, for both airborne and ground-based UEs, each in the PRB... The channel gain on is respectively from and This indicates that power allocation is restricted to be the same for all SCs within that RB; that is, power allocation is performed on a per-RB basis, rather than per RB. Based on this. Note that this assumes the same decoding order as used in part A discussed further above. Let and This indicates the power allocation on the RB for public and private data streams used by the over-the-air UE, and This indicates the power allocation used for ground UEs on the RB. Furthermore, the SC in the PRB... The SINR for decoding the common data stream of the over-the-air UE is given by the following formula:

[0067] Similarly, the SINR for a ground-based UE is:

[0068] Furthermore, the SINR for the private data stream of the over-the-air UE is:

[0069] make This represents the vector of SINR for the common data stream of an airborne UE on the PRB, and similarly, for a ground UE, it is... And for the private data stream of the airborne UE, .make This represents the set of discrete modulation and coding schemes (MCS) that can be used by any UE on each SC. We then aim to select the MCS tuple for the three data streams corresponding to the public and private data streams of airborne UEs and the data stream of ground UEs. Note that the same MCS is used for each type of data stream across all SCs belonging to the same PRB. For example, It is used in PRB The MCS for all common data streams of airborne UEs on 12 SCs, and also applicable to and For MCS tuples For each selection, there exists a corresponding rate tuple implemented on the PRB. Our goal is to select the MCS tuple and power allocation to maximize the weighted total rate of the two users scheduled on this PRB. The Block Error Rate (BLER) for each data stream transmission is a function of both the received SINR at the BS for each data stream and the MCS used for each data stream. Let... , and This represents the BLER of the corresponding data stream. Then, we want the BLER of each data stream to be below a certain threshold. Therefore, the problem can be formulated as:

[0070] Subject to the following constraints

[0071] A.2.2 Multiple base stations

[0072] Now, consider the following scenario: multiple BSs coordinate to estimate the channel of the airborne UE, and thus are able to decode and cancel the common data stream of the airborne UE. In this case, different ground UEs share the same RB at different BSs. Let... BS The ground-based UE at that location. Furthermore, and Representing airborne UE and ground UE respectively In SC Channel gain on BS. Then, in BS The SINR for decoding the common stream of an over-the-air UE is given by the following formula:

[0073] Similarly, in BS UE at ground The SINR of the decoded signal is given by the following formula:

[0074] Finally, let Instructions BS Should the over-the-air UE private data stream also be decoded? In BS The SINR for decoding the private data stream of the over-the-air UE is given by the following formula:

[0075] Similar to the case of a single BS, let Indicates in BS The vector of SINR of the common data stream of the UE over the PRB. Similarly, let Indicates in BS The vector of SINR of the ground UE at that location, and Indicates in BS The vector of SINR of the private data stream of the airborne UE.

[0076] Similar to the single BS scenario, we want to select for the two data streams corresponding to the public and private data streams of the airborne UE, as well as the data stream of each ground UE. tuple Note that for each type of data stream on all SCs belonging to the same PRB, the same MCS is used, for example, It is used in PRB The MCS for all common data streams of airborne UEs on 12 SCs, and also applicable to and UE of For MCS tuples For each selection, there exists a corresponding rate tuple implemented on the PRB. Therefore, the problem is to select discrete MCS and power allocation for public and private data streams of airborne UEs, select decoding BS for private data streams of airborne UEs, and select discrete MCS and power allocation for each ground UE. Let , and This indicates the corresponding data stream (if they are in the BS). The BLER (decoded at the point). Then, the problem can be formulated as:

[0077] According to a second aspect of the invention, a gNB in ​​a group of interconnected gNBs of a terrestrial communication network includes one or more antennas coupled to a first wireless communication interface and a second communication interface, the first and second wireless communication interfaces being adapted to communicate with the gNB in ​​the group of interconnected gNBs of the terrestrial communication network and / or communicatively connected to a central unit (CU) of the group. The gNB further includes one or more microprocessors and associated volatile and non-volatile memory. The non-volatile memory stores computer program instructions that, when executed by the one or more microprocessors, configure the gNB to perform an embodiment of the method according to the first aspect of the invention as described above.

[0078] According to a third aspect of the invention, a central unit for a terrestrial communication network is provided. The central unit includes one or more second communication interfaces configured to communicate with one or more base stations according to a second aspect of the invention. The central unit further includes one or more microprocessors and associated volatile and non-volatile memories. The aforementioned components are communicatively coupled via one or more signal and / or data lines or buses. The non-volatile memory stores computer program instructions that, when executed by the one or more microprocessors, configure the central unit to perform an embodiment of the method according to the first aspect of the invention as described above.

[0079] According to a fourth aspect of the invention, a communication system includes a plurality of gNBs as described above according to a second aspect of the invention, the plurality of gNBs being communicatively connected to each other. Each gNB has one or more antennas and is configured to communicate with one or more ground UEs within its coverage area via OFDMA. The communicatively connected gNBs or a central unit (CU) connected thereto are configured to form one or more gNB coordination sets. Each of the one or more gNB coordination sets is associated with one or more ground UEs and one or more airborne UEs. Furthermore, each of the one or more gNB coordination sets is configured to communicate with one or more ground UEs and one or more associated airborne UEs when using a corresponding step of the method according to a first aspect of the invention.

[0080] The methods described above can be represented by computer program instructions. Therefore, according to a third aspect of the invention, a computer program product includes computer program instructions that, when executed by a microprocessor of a communication system according to a second aspect of the invention, or a microprocessor functionally coupled to the gNB and / or CU, cause the processor and / or gNB and / or CU to perform the methods according to the first aspect of the invention.

[0081] Computer program instructions can be retrievably stored or transmitted on a computer-readable medium or data carrier. This medium or data carrier can be physically embodied, for example, in the form of a hard disk, solid-state drive, or flash memory device. However, the medium or data carrier may also include modulated electromagnetic, electrical, or optical signals that are received by the computer using a corresponding receiver and transmitted to and stored in the computer's memory.

[0082] This invention provides a method for non-orthogonal multiplexing of airborne UEs and ground UEs in a network with terrestrial gNBs, requiring minimal cooperation in sharing CSI and resource allocation among gNBs in a coordination set, which can differ for each airborne UE. To this end, a method is provided for coordinated reception of UL transmissions from airborne and ground UEs scheduled in the same RB. One embodiment of this method employs rate segmentation for airborne UEs to achieve non-orthogonal multiplexing with ground UEs using the same RB. Here, coordinated reception refers to forming a "coordination set" in the interconnecting gNBs from the perspective of the airborne UE, then continuing to jointly obtain the airborne UE's CSI, and continuing to perform resource allocation for both airborne and ground UEs. Coordinated resource allocation for RSMA-based optimized transmissions from airborne UEs mitigates interference at the terrestrial gNB.

[0083] The interference level when decoding terrestrial UE signals on each RB can be adjusted by modifying the precoding and / or power allocation of the public and private data streams used by the air UE. Since the public data streams of the air UE reach multiple gNBs in the coordination set, they can be eliminated at all gNBs. From the perspective of the terrestrial UE, gNBs do not need to form a coordination set.

[0084] This invention offers several advantages over conventional multiplexing using SDMA, while treating interfering signals as noise, and particularly enables the multiplexing of a larger number of UEs for the same number of antennas and data streams at both the gNB and UE. Furthermore, even if only one gNB needs to decode the signals from airborne UEs, when using conventional SDMA to decode signals from ground UEs and treat the signals from airborne UEs as noise, multiple ground gNBs need to optimize their reception processing to align the signals from airborne UEs and reduce their interference impact. In the proposed method using RSMA, since the common data stream is decoded and eliminated, only the private data stream will cause residual interference to the ground UEs.

[0085] This invention further provides advantages over conventional NOMA by completely decoding and eliminating interference signals from airborne UEs. When using conventional NOMA, due to favorable channel conditions from the airborne UE to multiple ground gNBs, all gNBs need to be able to completely decode and eliminate the airborne UE's signal, even if essentially only one gNB needs the airborne UE's signal. This reduces the achievable rate for the airborne UE because the transmission rate cannot exceed the achievable rate on the worst-case airborne UE-gNB link. In the proposed RSMA method, only the public data stream rate is limited by this predicament, while the private data stream rate can typically be higher.

[0086] This invention can be used in current 4G and 5G networks as well as future 6G and higher versions of networks. Attached Figure Description

[0087] The invention will now be described with reference to the accompanying drawings, in which: Figure 1 A schematic flowchart illustrating an exemplary method according to the present invention is shown; Figure 2 A schematic representation of an exemplary scenario for implementing the method according to the invention is shown; Figure 3 Further illustrative representations of exemplary scenarios for implementing the method according to the invention are shown; Figure 4 A more descriptive schematic flowchart illustrating an embodiment of the method according to a first aspect of the invention; and Figure 5A schematic block diagram of a gNB according to a second aspect of the present invention is shown. Detailed Implementation

[0088] Figures 1 to 4 As described above, this will not be discussed further.

[0089] Figure 5 A schematic block diagram of a gNB according to a second aspect of the invention is shown. The gNB includes one or more antennas coupled to a first wireless communication interface 501 and a second communication interface 502, the first wireless communication interface 501 and the second communication interface 502 being adapted to communicate with a gNB in ​​a group of gNBs communicatively interconnected to a terrestrial communication network (not shown) and / or with a central unit (not shown) communicatively connected to said group. The gNB further includes one or more microprocessors 503 and associated volatile memory 504 and non-volatile memory 505. The above components are communicatively coupled via one or more signal and / or data lines or buses 506. The non-volatile memory 505 stores computer program instructions that, when executed by the one or more microprocessors 503, configure the gNB to perform embodiments of the method according to the first aspect of the invention.

Claims

1. A method (100) for coordinating uplink UL communication between a coexisting air user equipment (UE) and a ground UE that are at least temporarily communicatively attached to a terrestrial communication network, comprising: - Perform (110) Channel State Information (CSI) measurements associated with one or more ground UEs and one or more airborne UEs in a set of interconnected base station gNBs of the terrestrial communication network. - Perform (120) resource allocation for the one or more ground UEs and the one or more air UEs in the set of interconnected gNBs of the terrestrial communication network. - From the set of interconnected gNBs, one or more gNB coordination sets are formed (130), and all gNBs from the respective gNB coordination sets are configured to decode common RSMA data streams received from one or more ground UEs, and to encode data streams from at least one air UE. - Select (140) a gNB from each gNB coordination set, the task of which is to decode the data stream from at least one of the one or more air UEs associated with the corresponding gNB coordination set. - At all gNBs in the gNB coordination set, data is received (150) from one or more airborne UEs associated with the gNB coordination set, and at each corresponding gNB, data is received from a ground UE attached to or associated with the corresponding gNB. The method (100) further includes: if the ground UE uses rate segmentation to send data to the gNB, while the air UE does not use rate segmentation to send data to the gNB, then: - In the selected gNB, the public data stream of the ground UE received at the selected gNB is decoded (160a) and eliminated (170a), then the data stream of the one or more air UEs assigned to the selected gNB is decoded (165a), and then the private data stream of the ground UE is decoded (180a). or The method (100) further includes: if the airborne UE uses rate segmentation to send data to the gNB, while the ground UE does not use rate segmentation to send data to the gNB, then: - At all gNBs in the gNB coordination set, the RSMA common data stream received from the one or more air gNBs is decoded (160), and the decoded RSMA common data stream is eliminated (170). - At each gNB in ​​the gNB coordination set, the data received from the corresponding attached or associated ground UE is decoded (180). - At the selected gNB in ​​each gNB coordination set, the RSMA private data stream received from the one or more air UEs is decoded (190). or The method (100) further includes: if both the ground UE and the airborne UE use rate segmentation to send data to the gNB, then: - Each gNB individually selects the order of the decoding (160) and the cancellation (170) for the public data stream and private data stream received from the air UE and the ground UE, respectively.

2. The method (100) according to claim 1, wherein, Selecting (140) a gNB whose task is to decode a data stream from at least one of the one or more air UEs associated with the corresponding gNB coordination set is based on the CSI measurement performed in step (110), and / or another additional CSI measurement performed by the gNBs in the gNB coordination set with respect to the one or more air UEs.

3. The method (100) according to claim 1 or 2, further comprising: Receive (125) information about their respective spatial locations (absolute or relative to the one or more gNBs) from the one or more air UEs, and provide such information to the constituent step (130) and / or the selection step (140).

4. The method (100) according to any one of claims 1 to 3, wherein, The set of interconnected gNBs (130) comprises one or more gNB coordination sets including, for each air UE, selecting those gNBs closest to that air UE, those gNBs with the highest signal-to-noise ratio and / or signal level, or combinations thereof, instead of selecting all gNBs capable of receiving transmissions from the corresponding air UE.

5. The method (100) according to any one of claims 1 to 4, further comprising: When a gNB has been selected in the gNB coordination set, the CSI measurement (110) and the selection step (140) are repeated to dynamically adapt the selection.

6. The method (100) according to one or more of claims 1 to 5, further comprising: Adjusting the power allocation for the public data stream and the private data stream, and / or the modulation and coding schemes for the public data stream, the private data stream, and / or data streams that do not use rate segmentation multiple access, with the goal of maximizing the weighted total rate on all data streams, while keeping the block error rate and / or total transmit power of each transmitter transmitting data streams within the same subchannel and / or resource block below the corresponding predetermined maximum value.

7. A gNB in ​​a group of interconnected base stations gNBs of a terrestrial communication network, the gNB comprising one or more antennas coupled to a first wireless communication interface (501) and a second communication interface (502), the first wireless communication interface (501) and the second communication interface (502) being adapted to communicate with the gNB in ​​the group of interconnected gNBs of the terrestrial communication network and / or with a central unit communicatively connected to the group, the gNB further comprising one or more microprocessors (503) and associated volatile memory (504) and non-volatile memory (505), the above components being communicatively coupled via one or more signal and / or data lines or buses (506), wherein, The non-volatile memory (505) stores computer program instructions that, when executed by the one or more microprocessors (503), configure the gNB to perform the method according to one or more of claims 1 to 6.

8. A central unit of a terrestrial communication network, the central unit comprising one or more second communication interfaces (502) configured to communicate with one or more base stations according to claim 7, the central unit further comprising one or more microprocessors (503) and associated volatile memory (504) and non-volatile memory (505), the aforementioned components being communicatively coupled via one or more signal and / or data lines or buses (506), wherein, The non-volatile memory (505) stores computer program instructions that, when executed by the one or more microprocessors (503), configure the gNB to perform the method according to one or more of claims 1 to 6.

9. A communication system comprising a plurality of base stations (gNBs) communicatively connected to each other, each gNB having one or more antennas, each gNB being configured to communicate with one or more terrestrial user equipments (UEs) within a coverage area, wherein, The communication-connected gNB or the central unit connected thereto is configured to form one or more gNB coordination sets, each of the one or more gNB coordination sets being associated with one or more ground UEs and one or more air UEs, and each of the one or more gNB coordination sets being configured to communicate with the one or more ground UEs and the one or more associated air UEs using the method according to one or more of claims 1 to 6.

10. A computer program product comprising computer program instructions that, when executed by a microprocessor (503) of a gNB or central unit of the system according to claim 6 or by a microprocessor (503) functionally coupled to the gNB or the central unit, cause the processor (503), the gNB, and / or the central unit to perform the method according to one or more of claims 1 to 6.

11. A computer-readable medium or data carrier for retrievably transmitting or storing a computer program product according to claim 10.

Images