Solution and signaling enabling cell-less MIMO transmission

Abstract

Systems, methods, apparatuses, and computer program products for enabling efficient cell-free MIMO transmissions. A method may include receiving a downlink reference signal; determining at least one cell-free multiple-input multiple-output transmission policy associated with at least one access point based at least on the downlink reference signal; and transmitting at least one of the at least one cell-free multiple-input multiple-output transmission policy and enabling information to a network entity.

Description

Technical Field

[0001] Some example embodiments may generally relate to mobile or wireless telecommunication systems, such as long term evolution (LTE), fifth generation (5G) radio access technology (RAT), new radio (NR) access technology, sixth generation (6G), and / or other communication systems. For example, certain example embodiments may relate to systems and / or methods for enabling efficient cell-free multiple-input multiple-output (MIMO) transmissions. Background Art

[0002] Examples of mobile or wireless telecommunication systems may include radio frequency (RF) 5G RAT, universal mobile telecommunication system (UMTS) terrestrial radio access network (UTRAN), LTE evolved UTRAN (E-UTRAN), advanced LTE (LTE-A), LTE-A Pro, NR access technology and / or MulteFire Alliance. 5G wireless system refers to the next generation (NG) of radio systems and network architectures. 5G systems are typically built on 5G NR, but 5G (or NG) networks can also be built on E-UTRA radios. It is expected that NR can support service categories such as enhanced mobile broadband (eMBB), ultra-reliable low latency communications (URLLC), and massive machine type communications (mMTC). NR is expected to deliver extremely broadband, ultra-robust, low-latency connectivity, and large-scale networking to support the Internet of Things (IoT). The next generation radio access network (NG-RAN) represents the RAN of 5G, which can provide wireless access for NR, LTE, and LTE-A. Note that a node in 5G that provides radio access functions to user equipment (e.g., similar to a Node B in UTRAN or an evolved Node B (eNB) in LTE) may be referred to as a next-generation Node B (gNB) when built on an NR radio, and may be referred to as a next-generation eNB (NG-e NB) when built on an E-UTRA radio. Summary of the invention

[0003] According to some example embodiments, a method may include: receiving, by a user equipment, a downlink reference signal. The method may also include: determining, by the user equipment, at least one cell-free multiple-input multiple-output transmission strategy associated with at least one access point based at least on the downlink reference signal. The method may also include: sending, by the user equipment, to a network entity at least one of: the at least one cell-free multiple-input multiple-output transmission strategy and enabling information.

[0004] According to certain example embodiments, an apparatus may include: means for receiving a downlink reference signal. The apparatus may also include: means for determining at least one no-cell multiple-input multiple-output transmission strategy associated with at least one access point based at least on the downlink reference signal. The apparatus may also include: means for sending at least one of the following to a network entity: the at least one no-cell multiple-input multiple-output transmission strategy and enabling information.

[0005] According to various example embodiments, a non-transitory computer readable medium may be encoded with instructions that, when executed in hardware, perform a method. The method may include receiving a downlink reference signal. The method may also include: determining at least one cell-free multiple-input multiple-output transmission strategy associated with at least one access point based at least on the downlink reference signal. The method may also include sending at least one of the following to a network entity: at least one cell-free multiple-input multiple-output transmission strategy and enabling information.

[0006] According to some example embodiments, a computer program product may perform a method. The method may include receiving a downlink reference signal. The method may also include: determining at least one no-cell multiple-input multiple-output transmission strategy associated with at least one access point based at least on the downlink reference signal. The method may also include sending at least one of the following to a network entity: at least one no-cell multiple-input multiple-output transmission strategy and enabling information.

[0007] According to certain example embodiments, an apparatus may include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus to at least: receive a downlink reference signal. The at least one memory and the computer program code may also be configured to, with the at least one processor, cause the apparatus to at least determine, based on at least the downlink reference signal, at least one cell-free multiple-input multiple-output transmission strategy associated with at least one access point. The at least one memory and the computer program code may also be configured to, with the at least one processor, cause the apparatus to at least send to a network entity at least one of the following: the at least one cell-free multiple-input multiple-output transmission strategy and enabling information.

[0008] According to various example embodiments, an apparatus may include circuitry configured to receive a downlink reference signal. The circuitry may also be configured to determine at least one no-cell multiple-input multiple-output transmission strategy associated with at least one access point based at least on the downlink reference signal. The circuitry may also be configured to send at least one of the following to a network entity: the at least one no-cell multiple-input multiple-output transmission strategy and enabling information.

[0009] According to some example embodiments, a method may include: sending, by a network entity, at least one downlink reference signal to a user equipment. The method may also include receiving, by the network entity, from the user equipment, at least one cell-free multiple-input multiple-output transmission strategy based on the at least one downlink reference signal. The method may also include: determining, by the network entity, a role for each of a plurality of access points based on at least one of the following from the user equipment: a policy and enabling information. The method may also include: sending, by the network entity, to the user equipment, an indication of an association between each of the plurality of access points and a policy.

[0010] According to certain example embodiments, an apparatus may include: means for sending at least one downlink reference signal to a user equipment. The apparatus may also include: means for receiving at least one cell-free multiple-input multiple-output transmission strategy based on the at least one downlink reference signal from the user equipment. The apparatus may also include means for determining a role of each of a plurality of access points based on at least one of the following from the user equipment: a policy and enabling information. The apparatus may also include means for sending to the user equipment an indication of an association between each of the plurality of access points and a policy.

[0011] According to various example embodiments, a non-transitory computer-readable medium may be encoded with instructions that, when executed in hardware, perform a method. The method may include: sending at least one downlink reference signal to a user equipment. The method may also include: receiving from the user equipment at least one cell-free multiple-input multiple-output transmission strategy based on the at least one downlink reference signal. The method may also include determining a role for each of a plurality of access points based on at least one of the following from the user equipment: a policy and enabling information. The method may also include: sending to the user equipment an indication of an association between each of the plurality of access points and the policy.

[0012] According to some example embodiments, a computer program product may perform a method. The method may include: sending at least one downlink reference signal to a user equipment. The method may also include receiving at least one cell-free multiple-input multiple-output transmission policy from the user equipment. The method may also include a component for determining a role of each of a plurality of access points based on at least one of the following from the user equipment: a policy and enabling information. The method may also include: sending an indication of an association between each of the plurality of access points and the policy to the user equipment.

[0013] According to certain example embodiments, an apparatus may include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code may be configured to, together with the at least one processor, cause the apparatus to at least send at least one downlink reference signal to a user equipment. The at least one memory and the computer program code may also be configured to, together with the at least one processor, cause the apparatus to at least receive at least one cell-free multiple-input multiple-output transmission strategy from the user equipment. The at least one memory and the computer program code may also be configured to, together with the at least one processor, cause the apparatus to at least determine the role of each of a plurality of access points based on at least one of the policy and enabling information from the user equipment. The at least one memory and the computer program code may also be configured to, together with the at least one processor, cause the apparatus to at least: send an indication of an association between each of the plurality of access points and the policy to the user equipment.

[0014] According to various example embodiments, an apparatus may include circuitry configured to send at least one downlink reference signal to a user equipment. The circuitry may also be configured to receive at least one cell-free multiple-input multiple-output transmission policy from the user equipment. The circuitry may also be configured to determine a role for each of a plurality of access points based on at least one of the policy and enabling information from the user equipment. The circuitry may also be configured to send an indication of an association between each of the plurality of access points and the policy to the user equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] For a proper understanding of the example embodiments, reference should be made to the accompanying drawings, in which:

[0016] Figure 1 An example of a general cell-free MIMO architecture is shown.

[0017] Figure 2 An explanation of the uplink signaling architecture is shown.

[0018] Figure 3 An example of a signaling diagram is shown in accordance with some example embodiments.

[0019] Figure 4 An illustrative example of uplink signaling for reporting the role of each access point is shown.

[0020] Figure 5 An example of coherent joint transmission is shown.

[0021] Figure 6 An example of non-coherent joint transmission is shown.

[0022] Figure 7Examples of coherent joint transmission and non-coherent joint transmission are shown.

[0023] Figure 8 An example of a flow chart of a method according to various example embodiments is shown.

[0024] Fig. 9 Another example of a flow chart of a method according to various example embodiments is shown.

[0025] Fig.10 Examples of various network devices are shown according to some example embodiments.

[0026] Fig.11 Examples of 5G network and system architectures are shown in accordance with certain example embodiments. DETAILED DESCRIPTION

[0027] It will be readily appreciated that the components of certain example embodiments as generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Therefore, the following detailed description of some example embodiments of systems, methods, apparatuses, and computer program products for implementing efficient cell-free MIMO transmission is not intended to limit the scope of certain example embodiments, but is representative of selected example embodiments.

[0028] Figure 1 Depicted is the general network architecture for cell-free MIMO transmission. Cell-free MIMO is one of many 6G features that can provide high system capacity at both sub-6G and millimeter wave (mmW) frequency bands. Figure 1 The network side shown may include at least two types of nodes: access points (APs) and central processing units (CPUs). The functionality of the AP and CPU nodes continues to be developed, especially on the layer 1 (L1) processes split between them.

[0029] An important feature of cell-free MIMO is that more than one AP can serve a user equipment (UE) for both UL and downlink (DL) communications, and the selection of APs to improve UE communications continues to be developed, especially for static clustering and / or UE-centric dynamic clustering schemes. With respect to static clustering schemes, predefined APs connected to the same CPU can be configured to serve some or all UEs within a predefined area regardless of the channel quality between the AP and the subject UE. For UE-centric dynamic clustering schemes, a corresponding AP can be selected based on the radio quality between the UE and the AP to facilitate data transmission, where the list of serving AP candidates can be updated when the UE moves and / or the radio channel quality changes.

[0030] The detailed transmission schemes may potentially involve coherent joint transmission (CJT) and / or non-coherent joint transmission (NCJT). Similarly, cell-free MIMO transmission may also include spatial multiplexing (SM), especially in cases of high radio channel quality, to improve system capacity. Each of these strategies may have different application scenarios and requirements; for example, in CJT, APs may be precisely synchronized with a small phase error between them, so that the received signal-to-noise ratio (SINR) may be increased on the UE side. In addition, NCJT may relax the requirements for phase error, but may require synchronization (similar to CJT) to ensure that the DL signals from the involved APs can be received by the UE within the cyclic prefix (CP) length.

[0031] As described above, different APs may support different transmission strategies for different situations, with the goal of providing optimal system performance. Thus, the network and UE may be aligned in terms of which AP follows which transmission strategy, thereby allowing the UE to optimally and correctly receive data. Therefore, certain embodiments may provide a means for providing such alignment.

[0032] Certain example embodiments described herein may have various benefits and / or advantages that overcome the above-mentioned shortcomings. For example, certain example embodiments may provide the UE with flexibility to accurately recommend an appropriate transmission strategy for each AP. If the phase error information is ignored, the UE may only need to report the role of each AP without reporting detailed information about the phase error and DL synchronization (SYN) status between all APs, thereby reducing UL signaling overhead. In addition, the availability of phase error information can provide important information to the network to make appropriate CJT decisions on the appropriate frequency band to obtain optimal system performance. This can also give the UE and the network sufficient flexibility to achieve a trade-off between performance and signaling overhead.

[0033] In addition, the proposed architecture of certain embodiments can achieve flexible hybrid cell-free MIMO transmission, which can be applicable to UEs with multiple antenna ports and / or multiple sub-panel scenarios. If the UE has multiple antenna ports, the UE can recommend different transmission strategies for different antenna ports at the same time. For example, assuming that the 6G UE has 3 antenna ports, the UE can recommend CJT_AP for antenna port 1 and SM_AP for antenna ports 2 and 3. This hybrid transmission strategy enables the network to optimally schedule transmissions between APs in each service cluster. Another example embodiment may include a UE with only one antenna / RF chain configuration, where each transmission time interval (TTI) can send only one data stream on the air interface; in this case, the UE can recommend only one AP for each transmission, or propose multiple APs with CJT transmission. In this way, the UE behavior and UL signaling framework can support different UE-side configurations to improve system performance. Therefore, certain example embodiments discussed below relate to improvements in computer-related technologies.

[0034] Some example embodiments described herein relate to recommending and configuring APs to use appropriate transmission strategies in the time domain simultaneously or separately. In addition, certain example embodiments may define new UL / DL signaling solutions to use the network and UE on the adopted transmission strategy for appropriate UE behavior and implement hybrid transmission schemes between APs to achieve optimal system performance.

[0035] Various example embodiments may provide solutions and related UL / DL signals to schedule / determine appropriate transmission strategies for each AP and achieve corresponding alignment between UE and network. Some example embodiments may also provide hybrid cell-free MIMO transmission strategies, where the same or different types of cell-free MIMO transmission strategies between serving APs may be scheduled simultaneously.

[0036] The UE may initiate the process by requesting a DL cell-free MIMO information update from the CPU; the CPU may respond by simultaneously sending different reference signals to the UE through the corresponding APs within the CPU's current serving cluster, so that the UE may measure phase error information between these APs, DL SYN status information, and the radio channel quality of each AP.

[0037] The UE can then recommend certain roles for each AP, and the corresponding appropriate transmission strategy. Figure 2 ), the UE may report the determined proposal / recommendation to the CPU, specifically, which APs will apply which transmission strategy. In addition, the UE may report the phase error of each subband or broadband to the CPU across APs to support the final decision of the CPU on the role of each AP.

[0038] Based on the proposal / recommendation received from the UE and the actual situation, the CPU can make the final decision and inform the UE, for example via DL signaling, which APs should perform which type of DL transmission. This information can then allow the UE to take appropriate actions when DL data is received.

[0039] Figure 3 An example of a signaling diagram depicting a system for implementing efficient cell-free MIMO transmission is shown. According to certain example embodiments, UE 310, AP 320, and CPU 330 may be similar to NE 1010 and UE 1020, such as Fig.10 As described above, UE 310, AP 320, and CPU 330 may be configured to use multiple cell-free MIMO transmission strategies, such as CJT, NCJT, and SM. Although only one AP is shown, AP 320 may include any number of APs.

[0040] In various example embodiments, different types of AP subclusters may be dedicated to performing different types of cell-free MIMO transmission strategies. For example, an AP_CJT subcluster may indicate that the APs within the subcluster may perform CJT transmission, where all APs may send the same DL data stream to improve the DL receive SINR of the UE 310. In addition, the UE 310 may not need to distinguish each radio link between the UE 310 and each AP 320 within the subcluster.

[0041] In addition, the AP_NCJT subcluster can indicate that the APs 320 within the subcluster can perform NCTJ transmission, which can transmit the same DL data stream. Using the subcluster, the UE 310 can first distinguish each radio link between the UE 310 and the AP 320 of the subcluster; then the UE 310 can demodulate these radio links to the soft bit level and combine for combining gain.

[0042] In addition, the AP_SP subcluster can instruct the APs within the subcluster to perform SM to achieve multiple stream transmission for higher throughput. For this subcluster, the UE 310 can process each radio link independently without any combining action.

[0043] Similarly, the AP_NO subcluster may indicate that the APs within the subcluster may not be scheduled to serve the UE 310 during a predefined time period, even if the AP is within the current serving cluster. For example, the DL transmission arrival times of these APs may be outside the CP, which may otherwise cause significant interference. If all APs are DL SYN, then the subcluster may not exist, and all APs in the subcluster may belong to one of the first three subclusters.

[0044] UE 310 and CPU 330 may be aligned on a serving AP cluster determination. For example, APs 320 connected to the same CPU (CPU 330) with a received RSRP above a predefined threshold may be selected to create a serving cluster of UE 310. Within the serving cluster, the type of transmission strategy applicable to each AP may be determined based on optimal system performance.

[0045] At 301, UE 310 may send a request for DL ​​cell-free MIMO transmission update to CPU 330. The request may be triggered, for example, due to a serving cluster update, a radio channel quality change, and / or a degradation of decoding performance at the UE side.

[0046] At 302, CPU 330 may simultaneously configure and trigger different DL wideband reference signal transmissions on APs 320 within the current serving cluster of UE 310 (ie, AP1 of UE1 and AP 15 ; UE2's AP7 and AP 9至11 ; UE3 AP 13至17 UE4 AP 16 and AP 18至20 ). In some example embodiments, prior to cell-free MIMO transmission, UE 310 may select a serving cluster, for example, based on large-scale information.

[0047] At 303, the CPU 330 may notify the UE 310 of the configured DL reference signaling resources, including frequency domain, time domain, and code domain resources, via the AP 320, so that the UE 310 knows when to receive which reference signals from which APs 320. This action may be performed in advance. For example, the DL reference signal frequency resources and code domain information may be sent to the UE 310 in advance via RRC signaling. For the time domain information notification, the UE 310 and the CPU 330 may be synchronized on the reference signal transmission time slot based on the X+n information, where X is the time slot for the UE to request transmission / reception at the UE 310 and the AP 320, respectively, and n may be a previously configured parameter related to the link transmission delay of the CPU 330 and the AP 320.

[0048] In various example embodiments, the CPU 330 may inform the UE 310 which of the APs 320 is the master AP; therefore, non-master APs within the serving cluster may then be slave APs. This information may enable the UE 310 to measure and estimate the phase error between the master AP and all slave APs. The CPU 330 may configure each AP 320 with a different reference signal to distinguish each radio link between the UE 310 and the AP 320. In addition, the APs 320 may be triggered to transmit different reference signals simultaneously, enabling the UE 310 to measure the phase error between the APs 320 in the case of simultaneous transmissions, wherein the measured phase error may be accurate enough to support CJT at a subsequent stage.

[0049] At 304, UE 310 may estimate relevant information (e.g., enabling information, channel quality, network load, and / or resource utilization information) used in making a proposal, such as phase error and radio link quality of each AP 320. Specifically, after UE 310 receives a wideband reference signal from AP 320, UE 310 may estimate the phase error between the APs involved, for example, estimating the phase error between the master AP and all slave APs. For example, UE 310 may use a signal (such as the signal of the master AP) as a baseline. A phase rotation may be applied to the reference signal of each slave AP, with an offset value based on a predefined phase offset book. Phase rotation may be performed for each subband so that UE 310 may derive phase error information for each subband. Then, at 305, UE 310 may combine the signal of the baseline with the post-phase rotation process to determine their joint signal power. The process may be repeated until all offset values ​​of the predefined phase offset book are tested. In some example embodiments, the "offset value" may refer to the highest joint signal power that is considered as the phase error between the master AP and the corresponding slave AP on the passed subband. Alternatively, if and when the joint signal power is above a predefined threshold, the UE 310 may stop the test and the corresponding offset value may be considered as a phase error.

[0050] By performing phase error estimation, the UE 310 can accurately determine the phase error for each subband between the APs 320, which can improve CJT transmission. For example, if the maximum phase error between all subbands is below a predefined threshold, the UE 310 can propose CJT transmission for those APs. Alternatively, if the minimum phase error for all subbands is above a predefined threshold, the UE 310 may not propose a CJT strategy because the benefit provided by the CJT strategy may be minimal. CJT proposals for each subband are possible, where the UE 310 and / or the CPU 330 can specify CJT for a subband if the associated phase error is below a predefined threshold. In addition, a wideband phase error can be estimated based on all subband phase error information and used as a matrix for CJT decisions; if the calculated wideband phase error is below or above a predefined threshold, CJT and / or NCJT can be proposed.

[0051] At 306, UE 310 may send a proposal indicating the determined role for each AP 320. Specifically, after UE 310 measures and calculates phase error information, DL SYN status, and radio link quality information, UE 310 may propose a transmission strategy for AP 320 in order to optimize system performance.

[0052] For APs 320 with phase errors within a preconfigured threshold, UE 310 may also determine the corresponding radio link quality to see if a CJT or SM strategy should be proposed for these APs. For APs 320 with good radio link quality, UE 310 may roughly estimate the corresponding throughput (assuming that CJT or SM will be performed, respectively) and recommend these APs for a strategy with higher throughput. For example, if CJT will result in higher throughput than SM, UE 310 may recommend AP_CJT for these APs; otherwise, AP_SP may be recommended. For APs with suboptimal radio link quality, SM may not achieve sufficient performance gain because UE 310 may not be able to decode each radio link independently; therefore, UE 310 may recommend CJT transmission for these APs to improve SINR combining gain.

[0053] For APs with small phase errors with reference to the master AP, the proposal of UE 310 can cover three potential scenarios: AP_CJT, AP_SP, or both AP_CJT and AP_SP. For both AP_CJT and AP_SP, some APs 320 can perform CJT transmissions together, while other APs can perform SM independently. This hybrid cell-free MIMO transmission concept may be valid for multiple antenna ports and / or subarrays at UE 310. For example, one antenna port can be used to receive CJT transmissions from the relevant AP, while other ports and / or subarrays can be used to receive SM transmissions from other APs 320.

[0054] In various example embodiments, for APs 320 with a phase error above a preconfigured threshold, CJT may not provide the best performance gain, so the UE 310 may only consider these APs 320 for NCJT or SM, which may depend on the radio link quality. For example, for APs 320 in this category, the UE 310 may check the radio link quality; for APs 320 with sufficient radio link quality, the UE 310 may check whether SM can improve the performance gain of multiple data streams to be transmitted. If so, the UE 310 may propose AP_SP for these APs 320; otherwise, the UE 310 may propose AP_NCJT for these APs 320. Similarly, for APs 320 with insufficient radio link quality, the UE 310 may not be able to successfully decode each radio link independently, so the UE 310 may propose NCJT based solely on the combined gain in order to improve successful data reception. Therefore, for APs 320 with large phase errors, the proposal of UE 310 may include three potential scenarios: AP_NCJT, AP_SP, or both AP_NCJT and AP_SP. For APs 320 within this category, for both AP_NCJT and AP_SP, UE 310 may propose AP_NCJT for some of these APs 320 and AP_SP for other APs 320.

[0055] Various example embodiments may include APs 320 where the DL reception time difference of the UE 310 exceeds a pre-configured CP length. For these APs 320, the UE 310 may not propose those APs 320 to serve DL transmissions due to potential interference. Instead, the UE 310 may propose AP_NO for these APs 320; however, if all APs 320 in the serving cluster are well synchronized, AP_NO may not exist.

[0056] In some example embodiments, UE 310 may classify all APs 320 within the current serving cluster into four categories: AP_CJT, AP_NCJT, AP_SP, and AP_NO.1. However, there may be more transmission mechanisms and categories for AP classification. UE 310 may recommend only one of the above four sub-clusters for each AP 320 within the current serving cluster.

[0057] Additionally, at 306, UE 310 may perform a Figure 2 The UL signaling shown explicitly proposes the four categories to the CPU 330 for data transmission. If the UE 310 proposes AP_CJT, the UE 310 may also report the corresponding phase error information of the corresponding AP 320 to the CPU 330. Alternatively, the UE 310 may only report the phase error information from the AP to the CPU 330 so that the CPU 330 can design appropriate precoding and scheduling operations to mitigate the impact of the phase error. If the phase error is associated with a subband situation, the proposal from the UE 310 may also include such subband information. Therefore, the proposal may allow the CPU 330 to schedule CJT on the reported subband information, thereby optimizing the performance of the UE 310.

[0058] Some example embodiments may use appropriate UL signaling so that the UE 310 may explicitly indicate the four types of AP subclusters to the CPU 330. For example, the UL signaling may be sent to the CPU 330 by UL L1 or medium access control (MAC) layer signaling, depending on the feedback speed required by the CPU 330. For L1 UL signaling, the CPU 330 may receive proposals from the UE 310 as quickly as possible and take immediate action to optimize performance. For UL L2 signaling, the CPU 330 may receive feedback after a period of delay; however, since the phase error change may not be dynamic, layer 2 (L2) signaling may be used because the L1 signaling overhead may have a greater impact on UL system coverage.

[0059] In various example embodiments, UE 310 may use a method similar to Figure 2The phase error may be reported in the structure shown in , which may include two parts: the role of AP 320 and related enabling information. The first part may include a proposal from UE 310 about which AP should be used for data transmission on which policy. The second part may include phase error information, which may be used for APs proposed for CJT, or for all APs within the current serving cluster of UE 310. The phase error may be at the sub-band or wideband level. If the phase error is reported at the sub-band level, UE 310 may also include the corresponding sub-band information in the UL report, indicating to CPU 330 which frequency band to schedule CJT transmission.

[0060] Figure 4 An example of UL signaling for reporting the role of each AP is shown. Figure 4 As shown in the first part, the variable-size signaling may include X number of fields, where X is the identifier of the AP 320 within the current service cluster. The detailed value of each field may explicitly indicate the corresponding role of the AP 320 in the subsequent transmission. The bits of each field may be determined by the supported cell-free MIMO transmission strategy. For example, three strategies may be supported at the current stage, so 2 bits per field may be sufficient to identify each strategy. The detailed signal value of each field may correspond to a specific strategy, depending on the role of the corresponding AP recommended by the UE 310. For example, 00 may indicate that the corresponding AP may perform CJT with other APs 320 marked as "00"; 01 may indicate that the corresponding AP 320 may perform NCJT with other APs 320 with the same value marked as "01"; 10 may indicate that the corresponding AP 320 may send a dedicated data stream to the UE 310; and 11 may indicate that the corresponding AP 320 will not send a data stream to the UE 310 (even if it is within the current service cluster).

[0061] In various example embodiments, if more transmission strategies are added to Cell-free MIMO, the number of bits per field may also be changed without affecting Figure 2 The structure shown in .

[0062] Figure 2The second portion shown may include the phase error of the APs recommended for CJT transmission. Alternatively, phase error information may be reported for all slave APs, thereby increasing flexibility and providing an opportunity for CPU 330 to schedule CJT transmission. Specifically, the phase error may be at a subband level or a wideband level. If at a subband level, the UE 310 may include the corresponding subband information in the report. The CPU 330 may then perform CJT scheduling on the corresponding subband to improve system performance. After a decision is made on the subband or wideband phase error and the phase error granularity, the detailed design and the number of bits required may vary.

[0063] The UL signaling architecture can follow Figure 2 and Figure 4 The example depicted in Figure 4 As shown, AP1, AP3 and the last AP can be candidates to coherently send the same data stream to UE 310 to improve SINR, and UE 310 may not change the corresponding radio links between these APs, but can combine the signals for demodulation and decoding. In addition, AP4 may be recommended not to serve UE 310 due to large phase error and / or lack of DL SYN with other APs in the current service cluster.

[0064] At 307, after CPU 370 receives the proposal from UE 310, CPU 330 may determine the role of each of APs 320 within the recommended range of UE 310. For example, Figure 4 As shown, CPU 330 may consider the load and resource conditions of each AP and / or side antenna port configuration of UE 310 and determine which transmission strategies may be assigned to each AP. CPU 370 may then determine a corresponding demodulation reference signal (DMRS) for each selected AP.

[0065] At 308, after making the determination in 307, the CPU 330 may indicate its final decision to the UE 310 to improve the performance of the UE 310. For example, the CPU 330 may explicitly inform the UE 310 which AP will perform which transmission strategy. For each ultimately selected AP, the CPU 330 may explicitly or implicitly inform the UE 310 of the corresponding DMRS, which may assist the UE 310 with the best behavior. For example, for those APs 320 decided to be used for CJT, the same DMRS signal may be sent from these APs, and the UE 310 may not need to distinguish each radio link between the UE 310 and these APs. For APs that perform NCJT or SM transmission, different DMRS may be sent by these APs to enable the UE 310 to distinguish each radio link from these APs. The CPU 330 may not include APs that are not recommended for DL ​​transmission in DL signaling, thereby reducing DL signaling overhead.

[0066] In various example embodiments, the DMRS configuration for each AP may enable the UE 310 to correctly perform DL reception behavior. Each AP may be pre-configured with at least two types of DMRS, such as DMRS_CJT (one DMRS common to all APs in its service cluster) and / or DMRS_Other (a different DMRS for each AP to enable the UE to distinguish each radio link between the AP 320 and the UE 310).

[0067] Each DMRS configuration can be per UE level; therefore, for each UE in the case of no-cell MIMO transmission, the CPU can configure (or reconfigure) these two types of DMRS based on the serving AP list. In addition, the definition of DMRS_CJT and DMRS_Other may mean that before no-cell MIMO transmission, UE 310 should know which types of DMRS can be used for subsequent DL data reception.

[0068] The CPU 330 may need to inform the UE 310 via DL signaling which AP 320 may adopt which strategy, and may use two options (discussed in more detail below) to perform the corresponding DL signaling. Figure 2 DL signaling similar to the DL signaling shown in can be used to explicitly inform UE 310 which APs 320 may be involved in subsequent transmissions and with which transmission strategy. Alternatively, DL signaling can explicitly indicate that APs 320 will be involved in subsequent transmissions, but implicitly indicate which transmission strategy can be used for these APs by indicating DMRS information. Figure 5 depicts the first and last AP in a CJT subcluster scheduled for DL ​​CJT, while Figure 6Depicted are two APs scheduled for NCJT.

[0069] To explicitly inform each UE, DL signaling can use something like Figure 2 In this option, the CPU 330 can explicitly inform the UE 310 which APs 320 to select for which transmission strategy to optimize system performance. Figure 4 One difference is that the detailed signaling size may not exceed Figure 4 In the DL signaling, the selected AP may be indicated within the range of APs 320 recommended by the UE 310, but those APs 320 marked as no transmission recommendation may be excluded. Therefore, the DL signaling may include Y 2-bit fields, where Y is equal to the number of APs recommended by the UE 310, excluding those APs marked as "11." Each 2-bit field may indicate the transmission strategy of the corresponding AP. Since more than 3 cell-free MIMO transmission strategies are not supported, 2 bits per AP may be used. However, more transmission strategies may be added with more bits, which are designed to indicate each AP situation without affecting the DL signaling architecture.

[0070] When explicitly notifying UE 310, CPU 330 may mark AP 320 as "11", which is within the recommended range of UE 310 but is not selected for transmission. Therefore, some APs may be recommended by UE 310 for DL ​​transmission, but are ultimately not selected by CPU 330 for various reasons. CPU 330 may notify UE 310 of this information so that UE 310 knows which AP 320 to receive DL transmission from and with which mechanism.

[0071] In addition, explicitly notifying each UE can enable decoding of DL signaling because UE 310 knows the Y information based on its previous recommendation. Specifically, based on the previous UL signal of UE 310, UE 310 can know the value of Y in advance and then correctly decode the DL signaling to improve data demodulation and decoding. DL signaling architecture such as Figure 5 and Figure 6 shown.

[0072] exist Figure 5 In the DL signaling, the CPU can make a final decision that the first AP, the second AP, and the last AP can jointly send the same data stream to the UE. After the UE decodes the DL signaling, the UE can know that the same DMRS_CJT will be sent from the first AP, the second AP, and the last AP, and may not receive DMRS from other APs. The UE can combine the DL transmissions from these APs to perform a reception operation.

[0073] exist Figure 6In the example, the UE 310 can know that only two APs are jointly sending the same data stream to the UE incoherently, and different DMRS can be sent from these two APs. The UE may not attempt to decode information from other APs because they are marked as "11" and will not receive data transmissions from them. The UE 310 can distinguish the two radio links from the two APs by different DMRS. The UE 310 can then demodulate the two radio links independently of the soft bit level and combine to improve the combined gain and decoding performance. This can enable the UE 310 to clearly identify which AP 320 will use which transmission strategy and perform the best reception function.

[0074] Although the above two examples only indicate one transmission strategy per TTI, such a signaling structure can be very flexible to indicate a mixed transmission strategy in the time domain. For example, some APs can jointly coherently send the same data stream to UE 310. In addition, some APs can send the same data stream to UE 310 non-coherently and can even support SM. This can depend on the number of antenna ports configured at UE 310 that support reception of one or more data streams.

[0075] Another benefit of explicit DL signaling is that the CPU 330 may have sufficient flexibility to ultimately determine which AP 320 should use which transmission strategy. For example, based on the proposal of the UE 310, some APs 320 may be recommended for NCJT due to their large phase error. However, if the CPU 330 knows such phase error (e.g., based on phase error information reported by the UE 310), the CPU 330 may utilize precoding operations to help compensate for such phase error. Any such AP may be configured for CJT, which may be different from the recommendation of the UE 310. Instead, the CPU 330 may indicate any difference to the UE 310. Although the cost of DL signaling overhead is greater, each role of the AP 320 may be indicated. If such DL signaling is sent by L2 MAC signaling, such overhead may be minimal.

[0076] Explicit indication enables indicating one transmission strategy per TTI, but such a signaling structure may also be flexible to indicate a hybrid transmission strategy in the time domain. For example, some APs may jointly coherently send the same data stream to UE 310. In addition, some APs may non-coherently send the same data stream to UE 310 and support SM. This may depend on the number of antenna ports configured at UE 310 that support reception of one or more data streams.

[0077] In addition, explicit indication can provide flexibility to the CPU 320 to determine which AP 320 should use which transmission strategy. For example, based on the recommendation of the UE 310, some APs 320 may be recommended for NCJT due to the phase error between them. If the CPU 330 knows the phase error, for example, based on the phase error information reported by the UE 310, the CPU 330 can use precoding operations to help compensate for this phase error. Such APs 320 can be configured for CJT, which may be different from the recommendation of the UE 310. For this case, the CPU 330 can clearly indicate this difference to the UE 310. The cost of more DL signaling overhead can clearly indicate the role of each AP. If such DL signaling is sent via L2 MAC signaling, such overhead may not be significant.

[0078] With implicit DMRS signaling, the 2-bit signal content for each field can indicate the corresponding AP 320 to which transmission strategy is assigned; then the UE 310 can implicitly know which type of DMRS will be sent from these APs 320 for subsequent actions. The cost for such signaling can be 2*Y-bit signaling size to obtain sufficient flexibility for selecting APs for any type of transmission. When implicit DMRS signaling is used, the recommendation of the UE 310 can follow each AP 320 role, and the CPU 330 can only make the final decision about which APs 320 will be involved in subsequent transmissions; there may be no operation to change the role of the AP 320 here. This option can also be effective and feasible because the UE 310 understands the phase error information, DLSYN state, and DL channel state information of each AP 320. The UE 310 can recommend sufficiently reliable and accurate roles of APs 320 for CJT, NCJT, SM, or no transmission. Furthermore, the CPU 330 may not attempt to change the recommended role for each AP 320, but makes the final decision on whether each AP 320 will be scheduled for transmission. Figure 7 ) may only indicate whether each AP 320 will be scheduled.

[0079] like Figure 7As shown, the DL signaling design may include multiple parts based on the recommendation from the UE 310, wherein each part refers to the AP recommended by the UE 310 for CJT, NCJT, and SM, respectively. Each part may include a certain number of fields, the number of which is equal to the number of APs of the corresponding transmission strategy previously recommended by the UE 310. The detailed value may be 1-bit per field to indicate that the corresponding AP 320 is scheduled for transmission. For example, if the bit is "1", it means that the corresponding AP is scheduled to adopt the transmission strategy recommended by the UE. On the other hand, the corresponding AP may not be incorporated into the following transmission. The total DL signal size may be Y bits, where Y is the number of APs recommended by the UE 310 for transmission.

[0080] Figure 6 The techniques described in the foregoing may improve the reception behavior of UE 310 and may support hybrid transmission strategy execution in the time domain, but are not consistent with Figure 5 One benefit of using implicit DMRS signaling is that the CPU may not need to change the role of AP 320 recommended by UE 310. This cost may be minimal since the recommendation of UE 310 can be based on its accurate DL information.

[0081] Figure 8 According to various example embodiments, a UE such as Fig.10 An example of a flowchart of a method performed by UE 1020) shown in FIG.

[0082] As described above, the UE and AP and the CPU (such as Fig.10 The NE 1010 shown in FIG. 10A can be configured to use multiple cell-free MIMO transmission strategies, such as CJT, NCJT, and SM. Although only one AP is shown, any number of APs can be included.

[0083] In various example embodiments, different types of AP subclusters may be dedicated to performing different types of cell-free MIMO transmission strategies. For example, an AP_CJT subcluster may indicate that the APs within the subcluster may perform CJT transmission, where all APs may send the same DL data stream to improve the UE's DL receive SINR. In addition, it may not be necessary for the UE to distinguish each radio link between the UE and each AP within the subcluster.

[0084] In addition, the AP_NCJT subcluster can indicate that the APs within the subcluster can perform NCTJ transmission, which can send the same DL data stream. With this subcluster, the UE can first distinguish each radio link between the UE and the APs of the subcluster; then the UE can demodulate these radio links to the soft bit level and combine them to combine the gain.

[0085] In addition, the AP_SP sub-cluster can instruct the APs within the sub-cluster to perform SM to enable multiple stream transmissions for higher throughput. For this sub-cluster, the UE can handle each radio link independently without any combining action.

[0086] Similarly, the AP_NO subcluster may indicate that the APs in this subcluster may not be scheduled to serve the UE within a predefined time period, even if the AP is in the current serving cluster. The DL transmission arrival times of these APs may be outside the CP, which may otherwise cause significant interference. If all APs are DL SYN, this subcluster may not exist, and all APs in this subcluster may belong to one of the first three subclusters.

[0087] UEs and CPUs may be aligned on a serving AP cluster determination. For example, APs connected to the same CPU with a received RSRP above a predefined threshold may be selected to create a serving cluster of UEs. Within the serving cluster, the type of transmission strategy applicable to each AP may be determined based on optimal system performance.

[0088] At 801, the method may include transmitting a request for DL ​​cell-free MIMO transmission update to the CPU. The request may be triggered, for example, due to a serving cluster update, a radio channel quality change, and / or a degradation of decoding performance at the UE side.

[0089] At 802, the method may include receiving the configured DL reference signaling resources from the CPU via the AP, including frequency domain, time domain and code domain resources, so that the UE knows when to receive which reference signals from which APs. This action may be performed in advance. For example, the DL reference signal frequency resources and code domain information may be sent to the UE in advance via RRC signaling. For time domain information notification, the UE and the CPU may be synchronized on the reference signal transmission time slot based on X+n information, where X is the time slot for the UE to request to send / receive at the UE and AP, respectively, and n may be a previously configured parameter related to the CPU and AP link transmission delay.

[0090] In various example embodiments, the CPU may inform the UE which of the APs 320 is the master AP; therefore, non-master APs within the serving cluster may then be slave APs. This information may support the UE in measuring and estimating the phase error between the master AP and all slave APs. The CPU may configure each AP with a different reference signal to distinguish each radio link between the UE and the AP. Additionally, the APs may be triggered to send different reference signals simultaneously, enabling the UE to measure the phase error between the APs in the case of simultaneous transmissions, wherein the measured phase error may be accurate enough to support CJT at a subsequent stage.

[0091] At 803, the method may include estimating relevant information (e.g., enabling information, channel quality, network load and / or resource utilization information) used in the process of making a proposal (at 804), such as phase error and radio link quality for each AP. Specifically, after the UE receives a broadband reference signal from the AP, the UE can estimate the phase error between the master AP and all slave APs. For example, the UE can use a signal (such as the signal of the master AP) as a baseline. A phase rotation can be applied to the reference signal of each slave AP, with an offset value based on a predefined phase offset thin. Phase rotation can be performed for each subband so that the UE can derive phase error information for each subband.

[0092] At 804, the method may include combining the signal of the baseline and the post phase rotation process to determine their joint signal power. The process may be repeated until all offset values ​​of the predefined phase offset book are tested.

[0093] In some example embodiments, the "offset value" may refer to the highest joint signal power considered as a phase error between the master AP and the corresponding slave AP on the passed subband. Alternatively, if and when the joint signal power is above a predefined threshold, the UE may stop testing and the corresponding offset value may be considered as a phase error.

[0094] By performing phase error estimation, the UE can accurately determine the phase error for each subband between APs, which can improve CJT transmission. For example, if the maximum phase error in all subbands is below a predefined threshold, the UE can propose CJT transmission for those APs. Alternatively, if the minimum phase error for all subbands is above a predefined threshold, the UE may not propose a CJT strategy because the benefit provided by the CJT strategy may be minimal. CJT proposals for each subband are possible, where the UE and / or CPU can specify CJT for a subband if the relevant phase error is below a predefined threshold. In addition, a wideband phase error can be estimated based on all subband phase error information and used as a matrix for CJT decisions; if the calculated wideband phase error is below or above a predefined threshold, CJT and / or NCJT can be proposed.

[0095] At 805, the UE may send a proposal indicating the determined role for each AP. Specifically, after the UE measures and calculates phase error information, DL SYN status, and radio link quality information, the UE may propose a transmission strategy for the AP in order to optimize system performance.

[0096] For APs with phase errors within a pre-configured threshold, the UE can also determine the corresponding radio link quality to see if a CJT or SM strategy should be proposed for these APs. For APs with good radio link quality, the UE can roughly estimate the corresponding throughput (assuming that CJT or SM will be performed, respectively) and recommend these APs for a strategy with higher throughput. For example, if CJT will result in higher throughput than SM, the UE can recommend AP_CJT for these APs; otherwise, AP_SP can be recommended. For APs with suboptimal radio link quality, SM may not achieve sufficient performance gain because the UE may not be able to decode each radio link independently; therefore, the UE can recommend CJT transmission for these APs to improve the SINR combining gain.

[0097] For APs with a small phase error with reference to the master AP, the UE's proposal may cover three potential scenarios: AP_CJT, AP_SP, or both AP_CJT and AP_SP. For both AP_CJT and AP_SP, some of the APs may perform CJT transmissions together, while other APs may perform SM independently. This hybrid cell-free MIMO transmission concept may be valid for multiple antenna ports and / or subarrays at the UE. For example, one antenna port may be used to receive CJT transmissions from the associated AP, while other ports and / or subarrays may be used to receive SM transmissions from other APs.

[0098] In various example embodiments, for APs with a phase error above a preconfigured threshold, CJT may not provide the best performance gain, so the UE may only consider these APs for NCJT or SM, which may depend on the radio link quality. For example, for APs in this category, the UE may check the radio link quality; for APs with sufficient radio link quality, the UE may check whether SM can improve the performance gain of multiple data streams to be transmitted. If so, the UE may propose AP_SP for these APs; otherwise, the UE may propose AP_NCJT for these APs. Similarly, for APs with insufficient radio link quality, the UE may not be able to successfully decode each wireless link independently, so the UE may propose NCJT based solely on the combined gain in order to improve successful data reception. Therefore, for APs with large phase errors, the UE's proposal may include three potential scenarios: AP_NCJT, AP_SP, or both AP_NCJT and AP_SP. For APs within this category, for both AP_NCJT and AP_SP, the UE may propose AP_NCJT for some of these APs and AP_SP for other APs.

[0099] Various example embodiments may include APs where the UE's DL reception time difference exceeds a pre-configured CP length. For these APs, the UE may not propose those APs to serve DL transmissions due to potential interference. Instead, the UE may propose AP_NO for these APs; however, if all APs in the serving cluster are well synchronized, AP_NO may not exist.

[0100] In some example embodiments, the UE may classify all APs within the current serving cluster into four categories: AP_CJT, AP_NCJT, AP_SP, and AP_NO.1. However, there may be more transmission mechanisms, and categories for AP classification. The UE may recommend only one of the above four sub-clusters for each AP within the current serving cluster.

[0101] In addition, at 805, the UE may Figure 2 The UL signaling shown explicitly proposes the four categories to the CPU for data transmission. If the UE proposes AP_CJT, the UE may also report the corresponding phase error information of the corresponding AP to the CPU. Alternatively, the UE may only report the phase error information from the AP to the CPU so that the CPU can design appropriate precoding and scheduling operations to mitigate the impact of the phase error. If the phase error is associated with a subband situation, the proposal from the UE may also include such subband information. Therefore, the proposal may allow the CPU to schedule CJT on the reported subband information, thereby optimizing the performance of the UE.

[0102] Some example embodiments may use appropriate UL signaling so that the UE can explicitly indicate the four types of AP subclusters to the CPU. For example, the UL signaling may be sent to the CPU by UL L1 or MAC layer signaling, depending on the feedback speed required by the CPU. For L1 UL signaling, the CPU may receive proposals from the UE as quickly as possible and take immediate action to optimize performance. For UL L2 signaling, the CPU may receive feedback after a period of delay; however, since the phase error change may not be dynamic, layer 2 (L2) signaling may be used because the L1 signaling overhead may have a greater impact on UL system coverage.

[0103] In various example embodiments, the UE may use a method similar to Figure 2The phase error may be reported in the structure shown in , which may include two parts: the role of the AP and the related enabling information. The first part may include a proposal from the UE about which AP should be used for data transmission on which policy. The second part may include phase error information, which may be used for the AP proposed for CJT, or for all APs within the UE's current serving cluster. The phase error may be at the subband or broadband level. If the phase error is reported at the subband level, the UE may also include the corresponding subband information in the UL report, indicating to the CPU which frequency band to schedule CJT transmission.

[0104] Figure 4 An example of UL signaling for reporting the role of each AP is shown. Figure 4 As shown in Figure 2 In the first part, the variable-sized signaling may include X number of fields, where X is the identifier of the AP within the current service cluster. The detailed value of each field may explicitly indicate the corresponding role of the AP in subsequent transmissions. The bits of each field may be determined by the supported cell-free MIMO transmission strategy. For example, three strategies may be supported, so 2 bits per field may be sufficient to identify each strategy. The detailed signal value of each field may correspond to a specific strategy, depending on the role of the corresponding AP recommended by the UE. For example, 00 may indicate that the corresponding AP may perform CJT with other APs marked as "00"; 01 may indicate that the corresponding AP may perform NCJT with other APs with the same value marked as "01"; 10 may indicate that the corresponding AP may send a dedicated data stream to the UE; and 11 may indicate that the corresponding AP will not send a data stream to the UE (even if it is within the current service cluster).

[0105] In various example embodiments, if more transmission strategies are added to Cell-free MIMO, the number of bits per field may also be changed without affecting Figure 2 The structure shown in .

[0106] Figure 2 The second part shown may include the phase error of the APs recommended for CJT transmission. Alternatively, the phase error information may be reported for all slave APs, thereby increasing flexibility and providing the CPU with an opportunity to schedule CJT transmission. Specifically, the phase error may be at the subband level or the broadband level. If at the subband level, the UE may include the corresponding subband information in the report. The CPU may then perform CJT scheduling on the corresponding subband to improve system performance. After a decision is made on the subband or broadband phase error and the phase error granularity, the detailed design and the number of bits required may vary.

[0107] The UL signaling architecture can follow Figure 2 and Figure 4 The example depicted in Figure 4 As shown, AP1, AP3 and the last AP can be candidates to coherently send the same data stream to the UE to improve SINR, and the UE may not change the corresponding radio links between these APs, but can combine the signals for demodulation and decoding. In addition, AP4 may be recommended not to serve the UE due to large phase error and / or lack of DL SYN with other APs in the current service cluster.

[0108] At 806, the method may include: receiving an indication from the CPU regarding a final decision to improve the performance of the UE. For example, the UE may receive an explicit indication of which AP will perform which transmission strategy. For each ultimately selected AP, the UE may be explicitly or implicitly notified of the corresponding DMRS, which may assist the UE with optimal behavior. For example, for those APs decided to be used for CJT, the same DMRS signal may be sent from these APs, and the UE may not need to distinguish each radio link between the UE and these APs. For APs performing NCJT or SM transmission, different DMRS may be sent by these APs to enable the UE to distinguish each radio link from these APs. The UE may not include APs that are not recommended for DL ​​transmission in DL signaling, thereby reducing DL signaling overhead.

[0109] In various example embodiments, the DMRS configuration for each AP may enable the UE to correctly perform DL reception behavior. Each AP may be pre-configured with at least two types of DMRS, such as DMRS_CJT (one DMRS common to all APs in its service cluster) and / or DMRS_Other (a different DMRS for each AP to enable the UE to distinguish each radio link between the AP and the UE).

[0110] Each DMRS configuration can be per UE level; therefore, for each UE in the case of cell-free MIMO transmission, the CPU can configure (or reconfigure) these two types of DMRS based on the serving AP list. In addition, the definition of DMRS_CJT and DMRS_Other may mean that before cell-free MIMO transmission, the UE should know which types of DMRS can be used for subsequent DL data reception.

[0111] The CPU may need to inform the UE via DL signaling which APs can adopt which strategy, and can use two options (discussed in more detail below) to perform the corresponding DL signaling. Figure 2DL signaling similar to the DL signaling shown in can be used to explicitly inform UE 310 which APs may be involved in subsequent transmissions and with which transmission strategy. Alternatively, DL signaling can explicitly indicate that APs 320 will be involved in subsequent transmissions, but implicitly indicate which transmission strategy can be used for these APs by indicating DMRS information. Figure 5 depicts the first and last AP in a CJT subcluster scheduled for DL ​​CJT, while Figure 6 Depicted are two APs scheduled for NCJT.

[0112] To explicitly inform each UE, DL signaling can use something like Figure 2 In this option, the CPU can explicitly inform the UE which APs to select for which transmission strategy to optimize system performance. Figure 4 One difference is that the detailed signaling size may not exceed Figure 4 signaling size. In the DL signaling, the selected AP can be indicated within the range of APs recommended by the UE, but those APs marked as no transmission recommendation can be excluded. Therefore, the DL signaling may include Y 2-bit fields, where Y is equal to the number of APs with UE recommendation number, excluding those APs marked as "11.". Each 2-bit field can indicate the transmission strategy of the corresponding AP. Since more than 3 cell-free MIMO transmission strategies are not supported, 2 bits per AP can be used. However, more transmission strategies can be added with more bits, which are designed to indicate each AP situation without affecting the DL signaling architecture.

[0113] When explicitly notifying the UE, the CPU may mark the AP as "11", which is within the UE's recommended range but is not selected for transmission. Therefore, some APs may be recommended by the UE for DL ​​transmission, but are ultimately not selected by the CPU for various reasons. The CPU may notify the UE of this information so that the UE knows which AP to receive DL transmission from and with which mechanism.

[0114] In addition, explicitly notifying each UE can enable decoding of DL signaling because the UE knows the Y information based on its previous recommendation. Specifically, based on the UE's previous UL signal, the UE can know the value of Y in advance and then correctly decode the DL signaling to improve data demodulation and decoding. DL signaling architecture such as Figure 5 and Figure 6 shown.

[0115] exist Figure 5In the DL signaling, the CPU can make a final decision that the first AP, the second AP, and the last AP can jointly send the same data stream to the UE. After the UE decodes the DL signaling, the UE can know that the same DMRS_CJT will be sent from the first AP, the second AP, and the last AP, and may not receive DMRS from other APs. The UE can combine the DL transmissions from these APs to perform a reception operation.

[0116] exist Figure 6 In the example, the UE can know that only two APs are sending the same data stream to the UE in an incoherent manner, and different DMRS can be sent from these two APs. The UE may not attempt to decode information from other APs because they are marked as "11" and will not receive data transmissions from them. The UE can distinguish the two radio links between the two APs by different DMRS. The UE can then demodulate the two radio links independently of the soft bit level and combine to improve the combined gain and decoding performance. This can enable the UE to clearly identify which AP will use which transmission strategy and perform the best reception function.

[0117] Although the above two examples only indicate one transmission strategy per TTI, such a signaling structure can be very flexible to indicate a mixed transmission strategy in the time domain. For example, some APs can jointly coherently send the same data stream to the UE. In addition, some APs can send the same data stream to the UE incoherently and can even support SM. This may depend on the number of antenna ports configured at the UE that support reception of one or more data streams.

[0118] Another benefit of explicit DL signaling is that the CPU can have enough flexibility to ultimately determine which AP should use which transmission strategy. For example, based on the UE's proposal, some APs may be recommended for NCJT due to their larger phase error. However, if the CPU knows this phase error (e.g., based on phase error information reported by the UE), the CPU can use precoding operations to help compensate for this phase error. Any such AP can be configured for CJT, which may be different from the UE's recommendation. Instead, the CPU can indicate any differences to the UE. Although the cost of DL signaling overhead is greater, each role of the AP can be indicated. If such DL signaling is sent by L2 MAC signaling, such overhead may be minimal.

[0119] Explicit indication enables indicating one transmission strategy per TTI, but such signaling structure can also be flexible to indicate a hybrid transmission strategy in the time domain. For example, some APs may jointly coherently send the same data stream to the UE. In addition, some APs may non-coherently send the same data stream to the UE and support SM. This may depend on the number of antenna ports configured at the UE that support reception of one or more data streams.

[0120] In addition, explicit indication can provide flexibility to the CPU to determine which AP should use which transmission strategy. For example, based on the UE's recommendation, some APs may be recommended for NCJT due to the phase error between them. If the CPU knows the phase error, for example, based on the phase error information reported by the UE, the CPU can use precoding operations to help compensate for this phase error. Such APs can be configured for CJT, which may be different from the UE's recommendation. For this case, the CPU can clearly indicate this difference to the UE. The cost of more DL signaling overhead can clearly indicate the role of each AP. If such DL signaling is sent via L2MAC signaling, such overhead may not be significant.

[0121] For implicit DMRS signaling, the 2-bit signal content for each field can indicate which transmission strategy the corresponding AP is assigned with; then the UE can implicitly know which types of DMRS will be sent from these APs for subsequent actions. The cost for such signaling can be 2*Y-bit signaling size to obtain sufficient flexibility for selecting APs for any type of transmission. When using implicit DMRS signaling, the UE's recommendation can follow each AP role, and the CPU can only make the final decision about which APs will be involved in subsequent transmissions; there may not be any operation to change the role of the AP here. Since the UE 310 understands the phase error information, DL SYN state, and DL channel state information of each AP 320, this option can also be effective and feasible. The UE 310 can recommend a role of an AP that is sufficiently reliable and accurate for CJT, NCJT, SM, or no transmission. In addition, the CPU may not attempt to change the recommended role for each AP, but makes the final decision whether each AP will be scheduled for transmission. For this option, the DL signaling design (in Figure 7 ) may only indicate whether each AP will be scheduled.

[0122] like Figure 7As shown, the DL signaling design may include multiple parts based on recommendations from the UE, wherein each part refers to the AP recommended by the UE for CJT, NCJT, and SM, respectively. Each part may include a certain number of fields, and the number of fields is equal to the number of APs of the corresponding transmission strategy previously recommended by the UE. The detailed value may be 1-bit per field to indicate that the corresponding AP is scheduled for transmission. For example, if the bit is "1", it means that the corresponding AP is scheduled to adopt the transmission strategy recommended by the UE. On the other hand, the corresponding AP may not be incorporated into the following transmission. The total DL signal size may be Y bits, where Y is the number of APs recommended by the UE for transmission.

[0123] Figure 6 The techniques described in can improve the reception behavior of UEs and can support hybrid transmission strategy execution in the time domain, but are not compatible with Figure 5 Compared to the technique depicted in , the signaling size is half. One benefit of using implicit DMRS signaling is that the CPU may not need to change the role of the AP recommended by the UE. This cost may be minimal since the UE's recommendation can be based on its accurate DL information.

[0124] Fig. 9 According to various example embodiments, a NE such as Fig.10 An example of a flowchart of a method performed by NE 1010) shown in FIG.

[0125] As described above, NEs and APs as well as UEs (such as Fig.10 The NE 1010 and UE 1020 shown in FIG. 1 may be configured to use multiple cell-free MIMO transmission strategies, such as CJT, NCJT, and SM. Although only one AP is shown, any number of APs may be included.

[0126] In various example embodiments, different types of AP subclusters may be dedicated to performing different types of cell-free MIMO transmission strategies. For example, an AP_CJT subcluster may indicate that the APs within the subcluster may perform CJT transmission, where all APs may send the same DL data stream to improve the UE's DL receive SINR. In addition, it may not be necessary for the UE to distinguish each radio link between the UE and each AP within the subcluster.

[0127] In addition, the AP_NCJT subcluster can indicate that the APs within the subcluster can perform NCTJ transmission, which can send the same DL data stream. With this subcluster, the UE can first distinguish each radio link between the UE and the APs of the subcluster; then the UE can demodulate these radio links to the soft bit level and combine them to combine the gain.

[0128] In addition, the AP_SP sub-cluster can instruct the APs within the sub-cluster to perform SM to enable multiple stream transmissions for higher throughput. For this sub-cluster, the UE can handle each radio link independently without any combining action.

[0129] Similarly, the AP_NO subcluster may indicate that the APs in this subcluster may not be scheduled to serve the UE within a predefined time period, even if the AP is in the current serving cluster. The DL transmission arrival times of these APs may be outside the CP, which may otherwise cause significant interference. If all APs are DL SYN, this subcluster may not exist, and all APs in this subcluster may belong to one of the first three subclusters.

[0130] UEs and CPUs may be aligned on a serving AP cluster determination. For example, APs connected to the same CPU with a received RSRP above a predefined threshold may be selected to create a serving cluster of UEs. Within the serving cluster, the type of transmission strategy applicable to each AP may be determined based on optimal system performance.

[0131] At 901, the method may include receiving a request for a DL cell-free MIMO transmission update from a UE. The request may be triggered, for example, due to a serving cluster update, a radio channel quality change, and / or a degradation of decoding performance at the UE side.

[0132] At 902, the method may include sending the configured DL reference signaling resources to the UE via the AP, including frequency domain, time domain and code domain resources, so that the UE knows when to receive which reference signals from which APs. This action may be performed in advance. For example, the DL reference signal frequency resources and code domain information may be sent to the UE in advance via RRC signaling. For time domain information notification, the UE and the CPU may be synchronized on the reference signal transmission time slot based on X+n information, where X is the time slot for the UE to request to send / receive at the UE and AP, respectively, and n may be a previously configured parameter related to the CPU and AP link transmission delay.

[0133] In various example embodiments, the CPU may inform the UE which of the APs is the master AP; therefore, non-master APs within the serving cluster may then be slave APs. This information may support the UE in measuring and estimating the phase error between the master AP and all slave APs. The CPU may be configured with a different reference signal for each AP to distinguish each radio link between the UE and the AP. Additionally, the APs may be triggered to send different reference signals simultaneously, enabling the UE to measure the phase error between the APs in the case of simultaneous transmissions, wherein the measured phase error may be accurate enough to support CJT at a subsequent stage.

[0134] At 903, the NE may receive a proposal indicating the determined role of each AP. Specifically, after the UE measures and calculates phase error information, DL SYN status, and radio link quality information, the UE may propose a transmission strategy for the AP in order to optimize system performance.

[0135] For APs with phase errors within a pre-configured threshold, the UE can also determine the corresponding radio link quality to see if a CJT or SM strategy should be proposed for these APs. For APs with good radio link quality, the UE can roughly estimate the corresponding throughput (assuming that CJT or SM will be performed, respectively) and recommend these APs for a strategy with higher throughput. For example, if CJT will result in higher throughput than SM, the UE can recommend AP_CJT for these APs; otherwise, AP_SP can be recommended. For APs with suboptimal radio link quality, SM may not achieve sufficient performance gain because the UE may not be able to decode each radio link independently; therefore, the UE can recommend CJT transmission for these APs to improve the SINR combining gain.

[0136] For APs with a small phase error with reference to the master AP, the UE's proposal may cover three potential scenarios: AP_CJT, AP_SP, or both AP_CJT and AP_SP. For both AP_CJT and AP_SP, some of the APs may perform CJT transmissions together, while other APs may perform SM independently. This hybrid cell-free MIMO transmission concept may be valid for multiple antenna ports and / or subarrays at the UE. For example, one antenna port may be used to receive CJT transmissions from the associated AP, while other ports and / or subarrays may be used to receive SM transmissions from other APs.

[0137] In various example embodiments, for APs with a phase error above a preconfigured threshold, CJT may not provide the best performance gain, so the UE may only consider these APs for NCJT or SM, which may depend on the radio link quality. For example, for APs in this category, the UE may check the radio link quality; for APs with sufficient radio link quality, the UE may check whether SM can improve the performance gain of multiple data streams to be transmitted. If so, the UE may propose AP_SP for these APs; otherwise, the UE may propose AP_NCJT for these APs. Similarly, for APs with insufficient radio link quality, the UE may not be able to successfully decode each wireless link independently, so the UE may propose NCJT based solely on the combined gain in order to improve successful data reception. Therefore, for APs with large phase errors, the UE's proposal may include three potential scenarios: AP_NCJT, AP_SP, or both AP_NCJT and AP_SP. For APs within this category, for both AP_NCJT and AP_SP, the UE may propose AP_NCJT for some of these APs and AP_SP for other APs.

[0138] Various example embodiments may include APs where the UE's DL reception time difference exceeds a pre-configured CP length. For these APs, the UE may not propose those APs to serve DL transmissions due to potential interference. Instead, the UE may propose AP_NO for these APs; however, if all APs in the serving cluster are well synchronized, AP_NO may not exist.

[0139] In some example embodiments, the UE may classify all APs within the current serving cluster into four categories: AP_CJT, AP_NCJT, AP_SP, and AP_NO.1. However, there may be more transmission mechanisms, and categories for AP classification. The UE may recommend only one of the above four sub-clusters for each AP within the current serving cluster.

[0140] In addition, at 903, the NE may be based on Figure 2 The UL signaling shown explicitly receives four categories proposed to the CPU for data transmission. If the UE proposes AP_CJT, the UE may also report the corresponding phase error information of the corresponding AP to the CPU. Alternatively, the UE may only report the phase error information from the AP to the CPU so that the CPU can design appropriate precoding and scheduling operations to mitigate the impact of the phase error. If the phase error is associated with a subband situation, the proposal from the UE may also include such subband information. Therefore, the proposal may allow the CPU to schedule CJT on the reported subband information, thereby optimizing the performance of the UE.

[0141] Some example embodiments may use appropriate UL signaling so that the UE can explicitly indicate the four types of AP subclusters to the CPU. For example, the UL signaling may be sent to the CPU by UL L1 or MAC layer signaling, depending on the feedback speed required by the CPU. For L1 UL signaling, the CPU may receive proposals from the UE as quickly as possible and take immediate action to optimize performance. For UL L2 signaling, the CPU may receive feedback after a period of delay; however, since the phase error change may not be dynamic, layer 2 (L2) signaling may be used because the L1 signaling overhead may have a greater impact on UL system coverage.

[0142] In various example embodiments, the UE may use a method similar to Figure 2 The phase error may be reported in the structure shown in , which may include two parts: the role of the AP and the related enabling information. The first part may include a proposal from the UE about which AP should be used for data transmission on which policy. The second part may include phase error information, which may be used for the AP proposed for CJT, or for all APs within the UE's current serving cluster. The phase error may be at the subband or broadband level. If the phase error is reported at the subband level, the UE may also include the corresponding subband information in the UL report, indicating to the CPU which frequency band to schedule CJT transmission.

[0143] Figure 4 An example of UL signaling for reporting the role of each AP is shown. Figure 4 As shown in the first part, the variable-size signaling may include X number of fields, where X is the identifier of the AP within the current service cluster. The detailed value of each field may explicitly indicate the corresponding role of the AP in subsequent transmissions. The bits of each field may be determined by the supported cell-free MIMO transmission strategy. For example, three strategies may be supported, so 2 bits per field may be sufficient to identify each strategy. The detailed signal value of each field may correspond to a specific strategy, depending on the role of the corresponding AP recommended by the UE. For example, 00 may indicate that the corresponding AP may perform CJT with other APs marked as "00"; 01 may indicate that the corresponding AP may perform NCJT with other APs with the same value marked as "01"; 10 may indicate that the corresponding AP may send a dedicated data stream to the UE; and 11 may indicate that the corresponding AP will not send a data stream to the UE (even if it is within the current service cluster).

[0144] In various example embodiments, if more transmission strategies are added to Cell-free MIMO, the number of bits per field may also be changed without affecting Figure 2 The structure shown in .

[0145] Figure 2 The second part shown may include the phase error of the APs recommended for CJT transmission. Alternatively, the phase error information may be reported for all slave APs, thereby increasing flexibility and providing the CPU with an opportunity to schedule CJT transmission. Specifically, the phase error may be at the subband level or the broadband level. If at the subband level, the UE may include the corresponding subband information in the report. The CPU may then perform CJT scheduling on the corresponding subband to improve system performance. After a decision is made on the subband or broadband phase error and the phase error granularity, the detailed design and the number of bits required may vary.

[0146] The UL signaling architecture can follow Figure 2 and Figure 4 The example depicted in Figure 4 As shown, AP1, AP3 and the last AP can be candidates to coherently send the same data stream to the UE to improve SINR, and the UE may not change the corresponding radio links between these APs, but can combine the signals for demodulation and decoding. In addition, AP4 may be recommended not to serve the UE due to large phase error and / or lack of DL SYN with other APs in the current service cluster.

[0147] At 904, after the CPU receives the proposal from the UE, the method may also include determining a role for each AP within the recommended range of the UE. The role of each AP may be determined based on at least one of the policy and activation information received from the user equipment at 805. In addition, when determining the role of each AP, channel quality information for each UE that is already available at the CPU may be considered, either alone or in combination with other information. For example, Figure 4 As shown, the CPU may consider the load and resource conditions of each AP and / or side antenna port configuration of the UE and determine which transmission strategies may be assigned to each AP. The CPU may then determine a corresponding demodulation reference signal (DMRS) for each selected AP.

[0148] At 905, the method may include sending an indication of the CPU regarding the final decision to improve performance to the UE. For example, the NE may send an explicit indication of which AP will perform which transmission strategy. For each ultimately selected AP, the UE may be explicitly or implicitly notified of the corresponding DMRS, which may assist the UE with having the best behavior. For example, for those APs decided to be used for CJT, the same DMRS signal may be sent from these APs, and the UE may not need to distinguish each radio link between the UE and these APs. For APs performing NCJT or SM transmission, different DMRS may be sent by these APs to enable the UE to distinguish each radio link from these APs. The UE may not include APs that are not recommended for DL ​​transmission in DL signaling, thereby reducing DL signaling overhead.

[0149] In various example embodiments, the DMRS configuration for each AP may enable the UE to correctly perform DL reception behavior. Each AP may be pre-configured with at least two types of DMRS, such as DMRS_CJT (one DMRS common to all APs in its service cluster) and / or DMRS_Other (a different DMRS for each AP to enable the UE to distinguish each radio link between the AP and the UE).

[0150] Each DMRS configuration can be per UE level; therefore, for each UE in the case of cell-free MIMO transmission, the CPU can configure (or reconfigure) these two types of DMRS based on the serving AP list. In addition, the definition of DMRS_CJT and DMRS_Others can mean that before cell-free MIMO transmission, the UE should know which types of DMRS can be used for subsequent DL data reception.

[0151] The CPU may need to inform the UE via DL signaling which APs can adopt which strategy, and can use two options (discussed in more detail below) to perform the corresponding DL signaling. Figure 2 DL signaling similar to the DL signaling shown in can be used to explicitly inform UE 310 which APs may be involved in subsequent transmissions and with which transmission strategy. Alternatively, DL signaling can explicitly indicate that APs 320 will be involved in subsequent transmissions, but implicitly indicate which transmission strategy can be used for these APs by indicating DMRS information. Figure 5 depicts the first and last AP in a CJT subcluster scheduled for DL ​​CJT, while Figure 6 Depicted are two APs scheduled for NCJT.

[0152] To explicitly inform each UE, DL signaling can use something like Figure 2In this option, the CPU can explicitly inform the UE which APs to select for which transmission strategy to optimize system performance. Figure 4 One difference is that the detailed signaling size may not exceed Figure 4 signaling size. In the DL signaling, the selected AP can be indicated within the range of APs recommended by the UE, but those APs marked as no transmission recommendation can be excluded. Therefore, the DL signaling may include Y 2-bit fields, where Y is equal to the number of APs recommended by the UE, excluding those APs marked as "11.". Each 2-bit field may indicate the transmission strategy of the corresponding AP. Since more than 3 cell-free MIMO transmission strategies are not supported, 2 bits per AP may be used. However, more transmission strategies may be added with more bits, which are designed to indicate each AP situation without affecting the DL signaling architecture.

[0153] When explicitly notifying the UE, the CPU may mark the AP as "11", which is within the UE's recommended range but is not selected for transmission. Therefore, some APs may be recommended by the UE for DL ​​transmission, but are ultimately not selected by the CPU for various reasons. The CPU may notify the UE of this information so that the UE knows which AP to receive DL transmission from and with which mechanism.

[0154] In addition, explicitly notifying each UE can enable decoding of DL signaling because the UE knows the Y information based on its previous recommendation. Specifically, based on the UE's previous UL signal, the UE can know the value of Y in advance and then correctly decode the DL signaling to improve data demodulation and decoding. DL signaling architecture such as Figure 5 and Figure 6 shown.

[0155] exist Figure 5 In the DL signaling, the CPU can make a final decision that the first AP, the second AP, and the last AP can jointly send the same data stream to the UE. After the UE decodes the DL signaling, the UE can know that the same DMRS_CJT will be sent from the first AP, the second AP, and the last AP, and may not receive DMRS from other APs. The UE can combine the DL transmissions from these APs to perform a reception operation.

[0156] exist Figure 6In the example, the UE can know that only two APs are sending the same data stream to the UE in an incoherent manner, and different DMRS can be sent from these two APs. The UE may not attempt to decode information from other APs because they are marked as "11" and will not receive data transmissions from them. The UE can distinguish the two radio links between the two APs by different DMRS. The UE can then demodulate the two radio links independently of the soft bit level and combine to improve the combined gain and decoding performance. This can enable the UE to clearly identify which AP will use which transmission strategy and perform the best reception function.

[0157] Although the above two examples only indicate one transmission strategy per TTI, such a signaling structure can be very flexible to indicate a mixed transmission strategy in the time domain. For example, some APs can jointly coherently send the same data stream to the UE. In addition, some APs can send the same data stream to the UE incoherently and can even support SM. This may depend on the number of antenna ports configured at the UE that support reception of one or more data streams.

[0158] Another benefit of explicit DL signaling is that the CPU can have enough flexibility to ultimately determine which AP should use which transmission strategy. For example, based on the UE's proposal, some APs may be recommended for NCJT due to their larger phase error. However, if the CPU knows this phase error (for example, based on phase error information reported by the UE), the CPU can use precoding operations to help compensate for this phase error. Any such AP can be configured for CJT, which may be different from the UE's recommendation. Instead, the CPU can indicate any differences to the UE. Although the cost of DL signaling overhead is greater, each role of the AP can be indicated. If such DL signaling is sent by L2MAC signaling, such overhead may be minimal.

[0159] Explicit indication enables indicating one transmission strategy per TTI, but such a signaling structure can also be flexible to indicate a mixed transmission strategy in the time domain. For example, some APs may jointly coherently send the same data stream to the UE. In addition, some APs may non-coherently send the same data stream to the UE and support SM. This may depend on the number of antenna ports configured at the UE that support reception of one or more data streams.

[0160] In addition, explicit indication can provide flexibility to the CPU to determine which AP should use which transmission strategy. For example, based on the UE's recommendation, some APs may be recommended for NCJT due to the phase error between them. If the CPU knows the phase error, for example, based on the phase error information reported by the UE, the CPU can use precoding operations to help compensate for this phase error. Such APs can be configured for CJT, which may be different from the UE's recommendation. For this case, the CPU can clearly indicate this difference to the UE. The cost of more DL signaling overhead can clearly indicate the role of each AP. If such DL signaling is sent via L2MAC signaling, such overhead may not be significant.

[0161] For implicit DMRS signaling, the 2-bit signal content for each field can indicate which transmission strategy the corresponding AP is assigned with; then the UE can implicitly know which types of DMRS will be sent from these APs for subsequent actions. The cost for such signaling can be 2*Y-bit signaling size to obtain sufficient flexibility for selecting APs for any type of transmission. When using implicit DMRS signaling, the UE's recommendation can follow each AP role, and the CPU can only make the final decision about which APs will be involved in subsequent transmissions; there may not be any operation to change the role of the AP here. Since the UE 310 understands the phase error information, DL SYN state, and DL channel state information of each AP 320, this option can also be effective and feasible. The UE 310 can recommend a sufficiently real and accurate role for the AP for CJT, NCJT, SM, or no transmission. In addition, the CPU may not attempt to change the recommended role for each AP, but makes the final decision whether each AP will be scheduled for transmission. For this option, the DL signaling design (in Figure 7 ) may only indicate whether each AP will be scheduled.

[0162] like Figure 7 As shown, the DL signaling design may include multiple parts based on recommendations from the UE, wherein each part refers to the AP recommended by the UE for CJT, NCJT, and SM, respectively. Each part may include a certain number of fields, and the number of fields is equal to the number of APs of the corresponding transmission strategy previously recommended by the UE. The detailed value may be 1-bit per field to indicate that the corresponding AP is scheduled for transmission. For example, if the bit is "1", it means that the corresponding AP is scheduled to adopt the transmission strategy recommended by the UE. On the other hand, the corresponding AP may not be incorporated into the following transmission. The total DL signal size may be Y bits, where Y is the number of APs recommended by the UE for transmission.

[0163] Figure 6The techniques described in can improve the reception behavior of UEs and can support hybrid transmission strategy execution in the time domain, but are not compatible with Figure 5 Compared to the technique depicted in , the signaling size is half. One benefit of using implicit DMRS signaling is that the CPU may not need to change the role of the AP recommended by the UE. This cost may be minimal since the UE's recommendation can be based on its accurate DL information.

[0164] Fig.10 An example of a system according to some example embodiments is shown. In an example embodiment, the system may include a plurality of devices, such as NE 1010 and / or UE 1020.

[0165] NE 1010 may be one or more of base stations, such as an eNB or gNB, a serving gateway, a server and / or any other access node or a combination thereof.

[0166] The NE 1010 may also include at least one gNB-CU, which may be associated with at least one gNB-DU. The at least one gNB-CU and the at least one gNB-DU may communicate with each other via at least one F1 interface, at least one X n -C interface and / or at least one NG interface communicates via 5GC.

[0167] UE 1020 may include one or more of mobile devices, such as a mobile phone, a smart phone, a personal digital assistant (PDA), a tablet computer or portable media player, a digital camera, a pocket camera, a video game console, a navigation unit (such as a global positioning system (GPS) device), a desktop or laptop computer, a single positioning device (such as a sensor or smart meter), or any combination thereof. In addition, NE 1010 and / or UE 1020 may be one or more of citizen broadband radio service devices (CBSDs).

[0168] NE 1010 and / or UE 1020 may include at least one processor, indicated as 1011 and 1021, respectively. Processors 1011 and 1021 may be embodied by any computing or data processing device, such as a central processing unit (CPU), an application specific integrated circuit (ASIC), or the like. The processor may be implemented as a single controller or multiple controllers or processors.

[0169] At least one memory may be provided in one or more devices, as shown in 1012 and 1022. The memory may be fixed or removable. The memory may include computer program instructions or computer codes contained therein. The memories 1012 and 1022 may independently be any suitable storage device, such as a non-transient computer readable medium. A hard disk drive (HDD), random access memory (RAM), flash memory or other suitable memory may be used. The memory may be combined on a single integrated circuit as a processor, or may be separated from one or more processors. In addition, the computer program instructions stored in the memory and that may be processed by the processor may be computer program codes in any suitable form, such as a compiled or interpreted computer program written in any suitable programming language.

[0170] Processors 1011 and 1021, memories 1012 and 1022, and any subset thereof may be configured to provide Figures 3 to 9 The devices corresponding to the respective boxes of the device. Although not shown, the device may also include positioning hardware, such as GPS or micro-electromechanical system (MEMS) hardware, which can be used to determine the location of the device. Other sensors are also allowed and can be configured to determine the location, altitude, speed, orientation, etc., such as a barometer, compass, etc.

[0171] like Fig.10 As shown, transceivers 1013 and 1023 may be provided, and one or more devices may also include at least one antenna, respectively shown as 1014 and 1024. The device may have many antennas, such as an antenna array configured for multiple-input multiple-output (MIMO) communication, or multiple antennas for multiple RATs. For example, other configurations of these devices may be provided. Transceivers 1013 and 1023 may be transmitters, receivers, both transmitters and receivers, or units or devices that may be configured for sending and receiving.

[0172] The memory and the computer program instructions may be configured together with a processor for a specific device to cause a hardware device such as a UE to perform any of the above processes (ie, Figures 3 to 9 ). Thus, in certain example embodiments, a non-transitory computer-readable medium may be encoded with computer instructions that, when executed in hardware, perform a process such as one of the processes described herein. Alternatively, certain example embodiments may be performed entirely in hardware.

[0173] In certain example embodiments, the apparatus may include a Figures 3 to 9. For example, the circuit may be a hardware circuit implementation only, such as an analog and / or digital circuit. In another example, the circuit may be a combination of hardware circuits and software, such as a combination of analog and / or digital hardware circuits with software or firmware, and / or any portion of a hardware processor with software (including a digital signal processor), software, and at least one memory that work together to enable the device to perform various processes or functions. In yet another example, the circuit may be a hardware circuit and / or a processor, such as a microprocessor or a portion of a microprocessor, that includes software for operation, such as firmware. When operation of the hardware is not required, the software in the circuit may not be present.

[0174] Fig.11 An example of a 5G network and system architecture according to certain example embodiments is shown. Multiple network functions are shown that can be implemented as software operating as part of a network device or dedicated hardware, as a network device itself or dedicated hardware, or as virtual functions operating as a network device or dedicated hardware. Fig.11 The NE and UE shown in the figure may be similar to NE 1010 and UE 1020, respectively. The user plane function (UPF) may provide services such as intra-RAT and inter-RAT mobility, routing and forwarding of data packets, inspection of packets, user plane quality of service (QoS) processing, buffering of downlink packets and / or triggering of downlink data notifications. The application function (AF) may primarily interface with the core network to facilitate application use of service routing and interact with the policy framework.

[0175] According to some example embodiments, the processors 1011 and 1021 and the memories 1012 and 1022 may be included in a processing circuit or a control circuit or may form a part of a processing circuit or a control circuit. In addition, in some example embodiments, the transceivers 1013 and 1023 may be included in a transceiver circuit or may form a part of a transceiver circuit.

[0176] In some example embodiments, an apparatus (e.g., NE 1010 and / or UE 1020) may include means for performing the methods, processes, or any variants discussed herein. Examples of apparatus may include one or more processors, memories, controllers, transmitters, receivers, and / or computer program codes for causing the execution of operations.

[0177] In various example embodiments, apparatus 1020 may be controlled by memory 1022 and processor 1021 to receive a downlink reference signal, determine at least one cell-free multiple-input multiple-output transmission strategy associated with at least one access point based at least on the downlink reference signal, and send at least one of the following to a network entity: the at least one cell-free multiple-input multiple-output transmission strategy and enabling information.

[0178] Certain example embodiments may be directed to an apparatus comprising means for performing any of the methods described herein, including, for example, means for receiving a downlink reference signal. The apparatus may also include means for determining, based at least on the downlink reference signal, at least one no-cell multiple-input multiple-output transmission strategy associated with at least one access point. The apparatus may also include means for sending, to a network entity, at least one of the at least one no-cell multiple-input multiple-output transmission strategy and enabling information.

[0179] In various example embodiments, apparatus 1010 may be controlled by memory 1012 and processor 1011 to: send at least one downlink reference signal to a user equipment; receive at least one cell-free multiple-input multiple-output transmission strategy from the user equipment; determine a role of each of a plurality of access points based on at least one of the following from the user equipment: a policy and enabling information; and send an indication of an association between each of a plurality of access points and a strategy to the user equipment.

[0180] Certain example embodiments may be directed to an apparatus comprising means for performing any of the methods described herein, including, for example, means for sending at least one downlink reference signal to a user equipment. The apparatus may also include means for receiving at least one cell-free multiple-input multiple-output transmission policy from the user equipment. The apparatus may also include means for determining a role of each of a plurality of access points based on at least one of a policy and enabling information from the user equipment. The apparatus may also include means for sending to the user equipment an indication of an association between each of the plurality of access points and a policy.

[0181] The features, structures, or characteristics of the example embodiments described throughout this specification may be combined in any suitable manner in one or more example embodiments. For example, the use of the phrases "various embodiments," "certain embodiments," "some embodiments," or other similar language throughout this specification refers to the fact that a particular feature, structure, or characteristic described in conjunction with the example embodiments may be included in at least one example embodiment. Thus, the phrases "in various embodiments," "certain embodiments," "in some embodiments," or other similar language throughout this specification do not necessarily all refer to the same group of example embodiments, and the described features, structures, or characteristics may be combined in any suitable manner in one or more example embodiments.

[0182] In addition, if necessary, the above-mentioned different functions or processes can be performed in different orders and / or simultaneously with each other. In addition, if necessary, one or more of the described functions or processes can be optional or can be combined. Therefore, the above description should be considered as an explanation of the principles and teachings of some example embodiments, rather than limitation.

[0183] Those of ordinary skill in the art will readily appreciate that the example embodiments discussed above may be practiced in different orders and / or with hardware elements in configurations different from those disclosed. Therefore, although some embodiments have been described based on these example embodiments, it will be apparent to those skilled in the art that certain modifications, variations, and alternative constructions will be apparent while remaining within the spirit and scope of the example embodiments.

[0184] Partial Glossary

[0185] 3GPP Third Generation Partnership Project

[0186] 5G fifth generation

[0187] 5GC fifth generation core

[0188] 5GS fifth generation system

[0189] 6G Sixth Generation

[0190] AMF access and mobility management function

[0191] AP Access Point

[0192] ASIC

[0193] BS Base Station

[0194] CBSD Citizens Broadband Wireless Service Device

[0195] CE control components

[0196] CG configuration authorization

[0197] CJT Coherent Joint Transmission

[0198] CN Core Network

[0199] CP cyclic prefix

[0200] CPU Central Processing Unit

[0201] DCI downlink control information

[0202] DL Downlink

[0203] DMRS demodulation reference signal

[0204] DRB Data Radio Bearer

[0205] DU Distributed Unit

[0206] eMBB Enhanced Mobile Broadband

[0207] eMTC Enhanced Machine Type Communication

[0208] eNB Evolved Node B

[0209] EPS Evolved Packet System

[0210] FDD Frequency Division Duplex

[0211] FR frequency range

[0212] gNBNext Generation Node B

[0213] GPS Global Positioning System

[0214] HDD Hard Drive

[0215] IoT

[0216] L1 Layer 1

[0217] L2 Layer 2

[0218] LTE Long Term Evolution

[0219] LTE-A Long Term Evolution Improvements

[0220] MAC Media Access Control

[0221] MBS Multicast and Broadcast System

[0222] MC Multicast

[0223] MCS modulation and coding scheme

[0224] MEMS micro-electromechanical systems

[0225] MIMO Multiple Input Multiple Output

[0226] MME mobility management entity

[0227] mMTC massive machine type communications

[0228] mmW millimeter wave

[0229] NAS non-access layer

[0230] NB-IoT Narrowband Internet of Things

[0231] NCJT Non-coherent Joint Transmission

[0232] NE network entity

[0233] NG Next Generation

[0234] NG-eNB Next Generation Evolved Node B

[0235] NG-RAN Next Generation Radio Access Network

[0236] NR New Radio

[0237] NR-U New Radio Unlicensed

[0238] PBR Prioritized Bitrate

[0239] PDA Personal Digital Assistant

[0240] PHY

[0241] QoS Quality of Service

[0242] RAM Random Access Memory

[0243] RAN Radio Access Network

[0244] RAT Radio Access Technology

[0245] RE resource element

[0246] RF

[0247] RRC Radio Resource Control

[0248] RS reference signal

[0249] RSRP reference signal received power

[0250] SINR Signal to Interference plus Noise Ratio

[0251] SM spatial multiplexing

[0252] SR Dispatch Report

[0253] SYN Synchronization

[0254] TDD Time Division Duplex

[0255] TTI transmission time interval

[0256] Tx transmission

[0257] UE User Equipment

[0258] UL Uplink

[0259] UMTS Universal Mobile Telecommunications System

[0260] UPF user plane function

[0261] URLLC ultra-reliable and low-latency communications

[0262] UTRAN Universal Mobile Telecommunications System Terrestrial Radio Access Network

[0263] WLAN Wireless Local Area Network

Claims

1. A method comprising: Receiving, by a user equipment, a downlink reference signal; determining, by the user equipment, at least one cell-free multiple-input multiple-output transmission strategy associated with at least one access point based at least on the downlink reference signal; At least one of the following is sent by the user equipment to a network entity: the at least one non-cell MIMO transmission strategy and activation information.

2. The method of claim 1, wherein the enabling information comprises phase error information, the phase error information being configured for at least one of: a coherent joint transmission proposed for an access point or all access points within a current serving cluster of the user equipment.

3. The method according to any one of claims 1 or 2, wherein the at least one cell-free multiple-input multiple-output transmission strategy is associated with at least one of the following: coherent joint transmission, non-coherent joint transmission, spatial multiplexing, or undefined transmission strategy.

4. The method according to any one of claims 1 to 3, further comprising: The user equipment sends a request for a downlink non-cell multiple-input multiple-output transmission update.

5. The method according to any one of claims 1 to 4, further comprising: Different downlink wideband reference signal transmissions are received simultaneously by the user equipment.

6. The method according to any one of claims 1 to 5, further comprising: Phase error, radio link quality, or other relevant information is estimated by the user equipment for each access point of the plurality of access points.

7. The method according to any one of claims 1 to 6, further comprising: An indication of an association between each access point of the plurality of access points and a transmission policy is received by the user equipment.

8. A method comprising: Sending, by a network entity, at least one downlink reference signal to a user equipment; receiving, by the network entity from the user equipment, at least one cell-free multiple-input multiple-output transmission strategy based on the at least one downlink reference signal; determining, by the network entity, a role for each of the plurality of access points based on at least one of: the policy and enabling information from the user equipment; as well as An indication of an association between each of the plurality of access points and the policy is sent, by the network entity, to the user equipment.

9. The method of claim 8, wherein the at least one cell-free MIMO transmission strategy is associated with coherent joint transmission, non-coherent joint transmission, spatial multiplexing, or an undefined transmission strategy.

10. The method according to claim 8 or 9, further comprising: A request for a downlink cell-free multiple-input multiple-output transmission update is received by the network entity from the user equipment.

11. The method according to any one of claims 8 to 10, further comprising: The network entity simultaneously configures and triggers transmission of multiple downlink broadband reference signals on the multiple access points in the current serving cluster.

12. The method according to any one of claims 8 to 11, further comprising: The role of each access point in the plurality of access points is determined by the network entity based at least on channel quality information.

13. An apparatus comprising: at least one processor; as well as at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, together with the at least one processor, cause the apparatus to at least: receiving a downlink reference signal; determining at least one cell-free multiple-input multiple-output transmission strategy associated with at least one access point based at least on the downlink reference signal; as well as At least one of the following is sent to a network entity: the at least one cell-free MIMO transmission strategy and activation information.

14. The apparatus of claim 13, wherein the enabling information comprises phase error information configured for at least one of: a coherent joint transmission proposed for an access point or all access points within a current serving cluster of the user equipment.

15. The apparatus of claim 13 or 14, wherein the at least one cell-free MIMO transmission strategy is associated with at least one of: coherent joint transmission, non-coherent joint transmission, spatial multiplexing, or an undefined transmission strategy.

16. The apparatus according to any one of claims 13 to 15, wherein the at least one memory and the computer program code are further configured to, together with the at least one processor, cause the apparatus to at least: Send a request for a downlink cell-free MIMO transmission update.

17. The apparatus according to any one of claims 13 to 16, wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to at least: Different downlink wideband reference signal transmissions are received simultaneously.

18. The apparatus according to any one of claims 13 to 17, wherein the at least one memory and the computer program code are further configured to, together with the at least one processor, cause the apparatus to at least: Phase error, radio link quality, or other relevant information is estimated for each access point of the plurality of access points.

19. The apparatus according to any one of claims 13 to 18, wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to at least: An indication of an association between each access point of the plurality of access points and a transmission policy is received.

20. An apparatus comprising: at least one processor; as well as at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, together with the at least one processor, cause the apparatus to at least: sending at least one downlink reference signal to a user equipment; receiving from the user equipment at least one cell-free multiple-input multiple-output transmission strategy based on the at least one downlink reference signal; determining a role for each of a plurality of access points based on at least one of the policy and the enabling information from the user equipment; as well as An indication of an association between each of the plurality of access points and the policy is sent to the user equipment.

21. The apparatus of claim 20, wherein the at least one cell-free MIMO transmission strategy is associated with coherent joint transmission, non-coherent joint transmission, spatial multiplexing, or an undefined transmission strategy.

22. The apparatus according to any one of claims 20 or 21, wherein the at least one memory and the computer program code are further configured to, together with the at least one processor, cause the apparatus to at least: A request for a downlink cell-free multiple-input multiple-output transmission update is received from the user equipment.

23. The apparatus according to any one of claims 20 to 22, wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to at least: Multiple downlink broadband reference signal transmissions are simultaneously configured and triggered on the multiple access points in the current serving cluster.

24. The apparatus according to any one of claims 20 to 23, wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to at least: The role of each access point in the plurality of access points is determined based at least on channel quality information.

25. An apparatus comprising: means for receiving a downlink reference signal; means for determining at least one cell-free multiple-input multiple-output transmission strategy associated with at least one access point based at least on the downlink reference signal; as well as Means for sending at least one of the following to a network entity: the at least one cell-free MIMO transmission strategy and enabling information.

26. The apparatus of claim 25, wherein the enabling information comprises phase error information configured for at least one of: a coherent joint transmission proposed for an access point or all access points within a current serving cluster of the user equipment.

27. The apparatus of any one of claims 25 or 26, wherein the at least one cell-free MIMO transmission strategy is associated with at least one of: coherent joint transmission, non-coherent joint transmission, spatial multiplexing, or an undefined transmission strategy.

28. The apparatus according to any one of claims 25 to 27, further comprising: Means for sending a request for a downlink cell-free multiple-input multiple-output transmission update.

29. The apparatus according to any one of claims 25 to 28, further comprising: Components for simultaneously receiving different downlink wideband reference signal transmissions.

30. The apparatus according to any one of claims 25 to 29, further comprising: Means for estimating phase error, radio link quality, or other relevant information for each access point of the plurality of access points.

31. The apparatus according to any one of claims 25 to 30, further comprising: Means for receiving an indication of an association between each access point of the plurality of access points and a transmission policy.

32. An apparatus comprising: means for sending at least one downlink reference signal to a user equipment; means for receiving from the user equipment at least one cell-free multiple-input multiple-output transmission strategy based on the at least one downlink reference signal; means for determining a role for each of a plurality of access points based on at least one of: the policy and enabling information from the user equipment; as well as Means for sending an indication of an association between each of the plurality of access points and the policy to the user equipment.

33. The apparatus of claim 32, wherein the at least one cell-free MIMO transmission strategy is associated with coherent joint transmission, non-coherent joint transmission, spatial multiplexing, or an undefined transmission strategy.

34. The apparatus according to any one of claims 32 or 33, further comprising: Means for receiving a request for a downlink cell-free multiple-input multiple-output transmission update from the user equipment.

35. The apparatus according to any one of claims 32 to 34, further comprising: A component for simultaneously configuring and triggering transmission of multiple downlink broadband reference signals on the multiple access points in the current serving cluster.

36. The apparatus according to any one of claims 32 to 35, further comprising: Means for determining the role of each access point of the plurality of access points based at least on channel quality information.

37. A non-transitory computer readable medium comprising program instructions stored thereon, the program instructions being used to execute the method according to any one of claims 1 to 12.

38. An apparatus comprising circuitry configured to perform the method of any one of claims 1 to 12.

39. A computer program product encoded with instructions for performing the method according to any one of claims 1 to 12.

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