Initiation of channel information acquisition procedures in D-MIMO networks

Abstract

Techniques are provided for initiating a channel information acquisition procedure in a D-MIMO network. A method is performed by a centralized node in a D-MIMO network. The method includes calculating an AP-based utility score for the AP to initiate a channel information acquisition process. The method includes calculating a UE-based utility score for the UE to initiate a channel information acquisition procedure. The method includes selecting an AP or a UE for initiating a channel information acquisition process according to which of the utility scores is the highest.

Description

[0001] Under grant agreement No. 101013425, the project leading to this application has received funding from the European Union's Horizon 2020 research and innovation programme. Technical Field

[0002] The embodiments provided herein relate to methods, central nodes, user equipment, computer programs, and computer program products for initiating a channel information acquisition process in a distributed multiple-input multiple-output network. Background Art

[0003] Multiple-antenna techniques can significantly improve the data rate and reliability of wireless communication systems. Performance is particularly improved if both the transmitter and the receiver are equipped with multiple antennas, which results in a multiple-input multiple-output (MIMO) communication channel. Such systems and / or related technologies are generally referred to as MIMO systems, or simply MIMO for short.

[0004] Distributed MIMO (D-MIMO, also known as cell-free massive MIMO, RadioStripes, RadioWeaves, and ubiquitous MIMO) is a candidate technology component for the physical layer of sixth-generation (6G) telecommunications systems. D-MIMO is based on antennas that are geographically distributed across a network and configured to operate together in phase coherence. The deployment of a D-MIMO network can be used to provide good coverage and high capacity for areas with high traffic requirements, such as factory buildings, stadiums, office premises, and airports, to name just a few examples.

[0005] In a typical architecture, multiple access points (APs) are interconnected and configured such that two or more APs can cooperate when coherently decoding data for a given user equipment (UE) served by the network, and such that two or more APs can cooperate when coherently transmitting data to the UE. Thus, the APs can jointly define the access part of the D-MIMO network. Each AP has one or more antenna panels. Each antenna panel can include multiple antenna elements configured to operate together in phase coherence.

[0006] For robust, high-throughput communication, the preferred mode of D-MIMO operation is time-division duplexing (TDD), which relies on the reciprocity of the propagation channel between the serving AP and the served UE. Thus, pilot signals transmitted by the UE can be used by the AP to simultaneously obtain the uplink channel response (i.e., the channel response for the radio channel from the UE towards the AP) and the downlink channel response (i.e., the channel response for the radio channel from the AP towards the UE). This type of TDD operation particularly facilitates reciprocity-based beamforming in the downlink.

[0007] As will be explained next, there are several fundamental differences between traditional cellular MIMO networks and D-MIMO networks.

[0008] Figure 1 FIG. schematically shows a traditional cellular MIMO network 10 including two APs 110, each AP 110 serving its own cell 20. Each AP serves a plurality of UEs 300, and thus also in each cell. From Figure 1 As can be seen, the APs are surrounded by UEs; the number of UEs is several orders of magnitude higher than the number of APs. In addition, the number of antenna units per AP is typically higher than the number of antenna units per UE, for example up to 64 antenna units per AP, but only 1-4 antenna units per UE. Even without ongoing data transmission, all APs are involved in the transmission of system information, cell definition reference signals, paging signals, etc.

[0009] Figure 2 FIG. schematically shows a D-MIMO network 100 including APs 110, each AP 110 serving its own cell. The APs 110 are controlled by a centralized controller 200. Only the cells served by four APs are shown. In addition, at a given point in time, only a subset of the APs 110 may be active while the remaining APs are inactive. Each AP 110 serves one or more UEs 300, but given the same number of UEs 300 as Figure 1 in, compared with the traditional cellular MIMO network in Figure 1 FIG., fewer UEs 300 are served by each AP 110 in the D-MIMO network 100. From Figure 1As can be seen, the UEs are surrounded by APs; the number of UEs and APs can be of the same order of magnitude. In addition, the number of antenna elements per AP is typically the same as or at least very similar to the number of antenna elements per UE. For example, the number of antenna elements per AP and UE can be in the range between 1 and 8. The APs in the D-MIMO network should be small and low-cost, which generally means that the APs in the D-MIMO network cannot have as many antenna elements as in the traditional cellular MIMO network. The active APs continuously send idle mode broadcast signals (e.g., perform beam scanning, system information broadcast, etc.) in the idle mode, while the inactive APs are only active during user plane data transmission and / or reception. Since the deployment of APs in the D-MIMO network is denser than in the traditional cellular MIMO network, only a subset of the APs is needed for transmitting system information, cell definition reference signals, paging signals, etc. This means that the UE cannot always obtain the channel state information related to the actual one or more APs serving the UE in the active mode by listening to the broadcast signals related to the idle mode transmission. This also means that most APs are only active during data transmission (in order to ensure multi-user communication with high spectral efficiency).

[0010] Note here that there are solutions for supporting multi-transmission point (mTRP) systems. In an mTRP system, the UE can receive data transmissions from multiple beams simultaneously. These beams can belong to the same cell or different cells. System information, cell definition reference signals, paging signals, etc. are defined as always-on signals. Therefore, this setup is similar to Figure 1 the scenario in. Although there are multiple TRPs in the mTRP system, the acquisition of channel information still works in the same way as in the traditional cellular MIMO network. Based on the above differences between the traditional cellular MIMO network and the D-MIMO network, these types of solutions cannot scale well to Figure 2 the fundamentally different D-MIMO network in.

[0011] Therefore, effective channel information acquisition is needed in the D-MIMO network. SUMMARY OF THE INVENTION

[0012] The purpose of the embodiments herein is to provide a channel information acquisition process suitable for the D-MIMO network.

[0013] According to a first aspect, a method for initiating a channel information acquisition process in a D-MIMO network is provided. The channel information acquisition process is initiated by transmitting a pilot signal in the D-MIMO network. The D-MIMO network includes an AP serving a UE. The method is performed by a centralized node in the D-MIMO network. The method includes: calculating an AP-based utility score for the AP to initiate the channel information acquisition process. If the channel information acquisition process is initiated by the AP, the AP-based utility score is related to an estimated network improvement and an estimated network resource cost. The method includes: calculating a UE-based utility score for the UE to initiate the channel information acquisition process. If the channel information acquisition process is initiated by the UE, the UE-based utility score is related to an estimated network improvement and an estimated network resource cost. The method includes: selecting the AP to initiate the channel information acquisition process when the AP-based utility score is the highest, and selecting the UE to initiate the channel information acquisition process when the UE-based utility score is the highest. The method includes: notifying the AP and the UE which one of the AP and the UE initiates the channel information acquisition process.

[0014] According to a second aspect, a centralized node for initiating a channel information acquisition process in a D-MIMO network is provided. The channel information acquisition process is initiated by transmitting a pilot signal in the D-MIMO network. The D-MIMO network includes an AP serving a UE. The centralized node includes a processing circuit. The processing circuit is configured to cause the centralized node to: calculate an AP-based utility score for the AP to initiate the channel information acquisition process. If the channel information acquisition process is initiated by the AP, the AP-based utility score is related to an estimated network improvement and an estimated network resource cost. The processing circuit is configured to cause the centralized node to: calculate a UE-based utility score for the UE to initiate the channel information acquisition process. If the channel information acquisition process is initiated by the UE, the UE-based utility score is related to an estimated network improvement and an estimated network resource cost. The processing circuit is configured to cause the centralized node to: select the AP to initiate the channel information acquisition process when the AP-based utility score is the highest, and select the UE to initiate the channel information acquisition process when the UE-based utility score is the highest. The processing circuit is configured to cause the centralized node to: notify the AP and the UE which one of the AP and the UE initiates the channel information acquisition process.

[0015] According to a third aspect, a centralized node for initiating a channel information acquisition process in a D-MIMO network is provided. The channel information acquisition process is initiated by transmitting a pilot signal in the D-MIMO network. The D-MIMO network includes an AP serving a UE. The centralized node includes a computing module configured to: compute an AP-based utility score for the AP to initiate the channel information acquisition process. If the channel information acquisition process is initiated by the AP, the AP-based utility score is related to an estimated network improvement and an estimated network resource cost. The centralized node includes a computing module configured to: compute a UE-based utility score for the UE to initiate the channel information acquisition process. If the channel information acquisition process is initiated by the UE, the UE-based utility score is related to an estimated network improvement and an estimated network resource cost. The centralized node includes a selection module configured to: select the AP to initiate the channel information acquisition process when the AP-based utility score is the highest, and select the UE to initiate the channel information acquisition process when the UE-based utility score is the highest. The centralized node includes a notification module configured to: notify the AP and the UE which one of the AP and the UE initiates the channel information acquisition process.

[0016] According to a fourth aspect, a computer program for initiating a channel information acquisition process in a D-MIMO network is provided, the computer program including computer program code which, when run on a processing circuit of a centralized node of the D-MIMO network, causes the centralized node to perform the method according to the first aspect.

[0017] According to a fifth aspect, a method for initiating a channel information acquisition process in a D-MIMO network is provided. The channel information acquisition process is initiated by transmitting a pilot signal in the D-MIMO network. The D-MIMO network includes an AP serving a UE. The method is performed by one of the UEs. The method includes: obtaining information from a centralized node in the D-MIMO network as to whether the channel information acquisition process is to be initiated in the downlink or the uplink. The method includes: transmitting the pilot signal when the channel information acquisition process is to be initiated on the uplink. The method includes: receiving the pilot signal from at least some of the APs when the channel information acquisition process is to be initiated on the downlink.

[0018] According to a sixth aspect, there is provided a UE for initiating a channel information acquisition process in a D-MIMO network. The channel information acquisition process is initiated by transmitting a pilot signal in the D-MIMO network. The D-MIMO network includes an AP serving the UE. The UE includes a processing circuit. The processing circuit is configured to cause the UE to: obtain information from a centralized node in the D-MIMO network as to whether the channel information acquisition process is to be initiated on the downlink or the uplink. The processing circuit is configured to cause the UE to: transmit the pilot signal when the channel information acquisition process is to be initiated on the uplink. The processing circuit is configured to cause the UE to: receive the pilot signal from at least some of the APs when the channel information acquisition process is to be initiated on the downlink.

[0019] According to a seventh aspect, there is provided a UE for initiating a channel information acquisition process in a D-MIMO network. The channel information acquisition process is initiated by transmitting a pilot signal in the D-MIMO network. The D-MIMO network includes an AP serving the UE. The UE includes an obtaining module configured to: obtain information from a centralized node in the D-MIMO network as to whether the channel information acquisition process is to be initiated on the downlink or the uplink. The UE includes a transmitting module configured to: transmit the pilot signal when the channel information acquisition process is to be initiated on the uplink. The UE includes a receiving module configured to: receive the pilot signal from at least some of the APs when the channel information acquisition process is to be initiated on the downlink.

[0020] According to an eighth aspect, there is provided a computer program for initiating a channel information acquisition process in a D-MIMO network, the computer program including computer program code which, when run on a processing circuit of a UE, causes the UE to perform the method according to the fifth aspect.

[0021] According to a ninth aspect, there is provided a computer program product including the computer program according to at least one of the fourth aspect and the eighth aspect and a computer-readable storage medium in which the computer program is stored. The computer-readable storage medium may be a non-transitory computer-readable storage medium.

[0022] Advantageously, these aspects provide for efficient channel information acquisition in a D-MIMO network.

[0023] Advantageously, these aspects are able to increase the system capacity in a D-MIMO network by avoiding resource-expensive uplink / downlink pilot transmissions when the uplink / downlink capacity becomes a bottleneck.

[0024] Advantageously, these aspects can improve the user experience by reducing the interference and overhead costs associated with pilot transmission.

[0025] Advantageously, these aspects can reduce the latency of prioritized and latency-sensitive services.

[0026] Advantageously, these aspects can reduce network energy consumption and operating costs.

[0027] Advantageously, these aspects enable the AP to remain in the idle mode for a longer time. This in turn enables smaller and / or less expensive thermal management solutions.

[0028] Other objects, features, and advantages of the appended embodiments will be apparent from the following detailed disclosure, the appended dependent claims, and the drawings.

[0029] In general, unless explicitly defined herein, all terms used in the claims shall be interpreted according to their ordinary meaning in the technical field. All references to "an / the element, apparatus, component, part, module, step, etc." shall be construed publicly as referring to at least one instance of the element, apparatus, component, part, module, step, etc., unless explicitly stated otherwise. Unless explicitly stated otherwise, the steps of any method disclosed herein need not be performed in the exact order disclosed. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The concepts of the present invention will now be described by way of example with reference to the drawings, in which:

[0031] Figure 1 is a schematic diagram showing a conventional cellular MIMO network according to one example;

[0032] Figure 2 is a schematic diagram showing a D-MIMO network in which the embodiments disclosed herein are applied;

[0033] Figure 3 is a flowchart of a method according to an embodiment;

[0034] Figure 4 is a schematic diagram of a UE-initiated channel information acquisition process according to an embodiment;

[0035] Figure 5 is a schematic diagram of an AP-initiated channel information acquisition process according to an embodiment;

[0036] Figure 6 is a schematic diagram of a UE-initiated and AP-initiated channel information acquisition process according to an embodiment;

[0037] Figure 7 is a flowchart of a method according to an embodiment;

[0038] Figure 8 It is a schematic diagram of a scenario according to an embodiment in which the channel information acquisition process is initiated by a UE;

[0039] Figure 9 It is a schematic diagram of a scenario according to an embodiment in which the channel information acquisition process is initiated by an AP;

[0040] Figure 10 and 11 It is a signaling diagram according to an embodiment;

[0041] Figure 12 It is a schematic diagram showing the functional units of a centralized node according to an embodiment;

[0042] Figure 13 It is a schematic diagram showing the functional modules of a centralized node according to an embodiment;

[0043] Figure 14 It is a schematic diagram showing the functional units of a UE according to an embodiment;

[0044] Figure 15 It is a schematic diagram showing the functional modules of a UE according to an embodiment; and

[0045] Figure 16 It shows an example of a computer program product including a computer-readable component according to an embodiment. Detailed Description of the Invention

[0046] The concepts of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which specific embodiments of the concepts of the present invention are shown. However, the concepts of the present invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete and will fully convey the scope of the concepts of the present invention to those skilled in the art. Throughout the specification, the same numbers refer to the same elements. Any steps or features shown by dashed lines should be considered optional.

[0047] As described above, effective channel information acquisition is required in a D-MIMO network.

[0048] In addition, in this regard, several transmission schemes for traditional cellular MIMO networks rely heavily on obtaining channel state information (CSI) at the transmission side. Due to the differences described above for Figure 1 and Figure 2 the CSI acquisition schemes designed for traditional cellular MIMO networks are not very suitable for D-MIMO networks.

[0049] For example, in a fifth generation (5G) new radio (NR) network, each AP may transmit a downlink reference signal in the form of a synchronization signal block (SSB) in multiple beams. This scheme has extremely poor scalability for a D-MIMO network where the number of APs may be very large and each AP may have multiple antenna units. In a D-MIMO network, if each AP is required to always perform a full beam scan, hundreds of SSB transmissions may be required. This will generate a large amount of interference in the network (resulting in poor performance), lead to high network energy usage (high operating costs), and consume most of the precious radio resources for simple tasks such as distributing system information within the served area (reducing capacity).

[0050] A more efficient method in a D-MIMO network (resulting in reduced interference, lower energy consumption, and higher capacity) is to assign the transmission of SSBs only to a subset of APs. However, such a scheme may lead to other problems. In 5G NR, beam scanning from all APs is always on. However, in a well-designed D-MIMO network, this will no longer be the case. This means that an AP in a D-MIMO network that is not assigned to perform continuous beam scanning will be active only when there is ongoing data service involving these APs. Therefore, a UE cannot use SSBs to derive information about potentially active mode beams as in 5G NR. In the active mode, each UE may be served by a different set of APs than the APs that the UE could detect before entering the active mode.

[0051] Accordingly, embodiments disclosed herein relate to techniques for initiating a channel information acquisition process in a D-MIMO network 100. To obtain such techniques, a centralized node 200, a method performed by the centralized node 200, and a computer program product including code (e.g., in the form of a computer program) are provided, which when run on the processing circuitry of the centralized node 200 causes the centralized node 200 to perform the method. To obtain such techniques, a UE 300, a method performed by the UE 300, and a computer program product including code (e.g., in the form of a computer program) are also provided, which when run on the processing circuitry of the UE 300 causes the UE 300 to perform the method.

[0052] The UE 300 may be equipped with one or more multi-antenna array panels to operate in a higher frequency band. To simplify the exposition of the present disclosure, it is assumed that each AP 110 is fully digital because each of its transceivers is associated with one and only one antenna unit. However, the concepts, methods, and devices disclosed herein are also applicable to APs 110 having antenna panels capable of performing analog beamforming or hybrid beamforming.

[0053] As an introduction, in a D-MIMO network 100, it is not obvious whether CSI acquisition should utilize downlink transmissions from the network side (as in 5G NR) or uplink transmissions from the UE side. Depending on whether pilot signals are sent in the downlink or uplink, there can be a significant difference in the resource utilization of pilot signals. In a typical D-MIMO network 100, the total number of UE and AP antenna elements is of the same order of magnitude. Additionally, the signaling overhead of sending pilot signals is using resources that could otherwise be used for data transmission.

[0054] Embodiments disclosed herein relate to a dynamic technique for acquiring channel information that dynamically determines whether the channel information acquisition process should be initiated by pilot signal transmission in the uplink (performed by UE 300) or the downlink (performed by AP 110). As will be further disclosed below, the decision on what channel information acquisition process to use depends on obtaining a utility metric. The utility metric takes into account parameters that are particularly relevant to the operation of the D-MIMO network 100 (such as resource cost, latency, etc.), which will be further disclosed below.

[0055] Furthermore, although described with reference to the D-MIMO network 100, the embodiments disclosed herein are also applicable to traditional MIMO cellular networks, such as 5G NR networks.

[0056] Now refer to Figure 3 , which shows a method for initiating a channel information acquisition process performed by a centralized node 200 in a D-MIMO network 100 according to an embodiment. The channel information acquisition process is initiated by sending pilot signals in the D-MIMO network 100. The D-MIMO network 100 includes an AP 110 serving a UE 300.

[0057] S102: The centralized node 200 calculates an AP-based utility score for the AP 110 to initiate the channel information acquisition process. If the channel information acquisition process is initiated by the AP 110, the AP-based utility score is related to the estimated network improvement and the estimated network resource cost.

[0058] S104: The centralized node 200 calculates a UE-based utility score for the UE 300 to initiate the channel information acquisition process. If the channel information acquisition process is initiated by the UE 300, the UE-based utility score is related to the estimated network improvement and the estimated network resource cost.

[0059] S106: When the AP-based utility score is the highest, the centralized node 200 selects the AP 110 to initiate the channel information acquisition process, and when the UE-based utility score is the highest, selects the UE 300 to initiate the channel information acquisition process.

[0060] S108: The centralized node 200 notifies the AP 110 and the UE 300 as to which of the AP 110 and the UE 300 starts the channel information acquisition process.

[0061] Embodiments related to further details of starting a channel information acquisition process in the D-MIMO network 100 performed by the centralized node 200 will now be disclosed.

[0062] There may be different examples of pilot signals. In some examples, the pilot signal transmitted by the AP 110 is a downlink reference signal covering the serving area, such as an SSB. In some examples, the pilot signal transmitted by the UE 300 is an uplink reference signal, such as a sounding reference signal (SRS).

[0063] One aspect relates to how the channel information acquisition process affects the network resource overhead for transmitting pilot signals and the alternative use of these network resources.

[0064] At Figure 4 400 in, a UE-initiated channel information acquisition process is shown. The term "UE-initiated" refers to the case where the UE starts the channel information acquisition process by transmitting an uplink pilot signal. At Figure 4 the resource allocation when the UE transmits a pilot signal is also shown. It can be seen that more resources are available for downlink data transmission compared to uplink data transmission. At Figure 5 500 in, an AP-initiated channel information acquisition process is shown. The term "AP-initiated" refers to the case where the AP starts the channel information acquisition process by transmitting a downlink pilot signal. At Figure 5 the resource allocation when the AP transmits a pilot signal is also shown. It can be seen that more resources are available for uplink data transmission compared to downlink data transmission.

[0065] In a TDD system with static or semi-static allocation of UL resources and DL resources, the pilot signal transmitted from the UE will consume UL radio resources, while the pilot signal transmitted from the AP will consume DL radio resources. In this case, it is important whether there is an alternative concurrent use of these UL resources or DL resources.

[0066] Transmitting DL pilot signals (from the serving AP) may increase DL interference, while transmitting UL pilot signals (from the active UE) may increase UL interference. This increase in interference may respectively reduce the signal-to-interference-plus-noise ratio (SINR) of the ongoing data transmission in the UL or DL. The physical resources (such as time and frequency resource elements) used for pilot signal transmission will also respectively reduce the physical resources available for data transmission in the UL or DL. In particular, in some embodiments, the network resource cost for estimating the utility score based on the AP depends on the amount of radio resources required to transmit pilot signals from the AP 110. Similarly, in some embodiments, the network resource cost for estimating the utility score based on the UE depends on the amount of radio resources required to transmit pilot signals from the UE 300.

[0067] The decision to select a "UE-initiated" or "AP-initiated" channel information acquisition process may respectively depend on the currently ongoing UL and DL data traffic volumes. Thus, in some embodiments, the network improvement for the utility score based on the AP is proportional to the expected or ongoing uplink data traffic volume, while the network improvement for the utility score based on the UE is inversely proportional to the expected or ongoing uplink data traffic volume. The higher the uplink data traffic volume, the higher the utility score based on the AP. Similarly, in some embodiments, the network improvement for the utility score based on the UE is proportional to the expected or ongoing downlink data traffic volume, while the network improvement for the utility score based on the AP is inversely proportional to the expected or ongoing downlink data traffic volume. The higher the downlink data traffic volume, the higher the utility score based on the UE. The terms "proportional" and "inversely proportional" used throughout this disclosure do not impose any linearity.

[0068] The overhead of pilot signal transmission also depends on the number of antenna elements in the UE and the AP. The more antenna elements the antenna panel has, the more pilot signal resources may be required (e.g., one pilot signal sequence per antenna element).

[0069] Therefore, the decision to select a "UE-initiated" or "AP-initiated" channel information acquisition process may consider the cost of transmitting pilot signals from the UE or the AP (e.g., represented by the number of antenna elements or the number of beam candidates or the number of pilot signal repetitions, etc.).

[0070] In some scenarios, the transmission of pilot signals from the AP can be used by more than one UE. This reduces the overhead cost because the transmission of one pilot signal in the downlink can potentially be received and measured by many UEs.

[0071] Therefore, the decision to select a "UE-initiated" or "AP-initiated" channel information acquisition process can depend on the number of UEs served by the same AP. Thus, in some embodiments, network improvement based on the AP's utility score is proportional to the number of active UEs 300 served by each AP 110 averaged over multiple transmission time intervals (TTIs). The higher the number of UEs 300, the higher the AP-based utility score.

[0072] In some D-MIMO scenarios, active UEs are served by a small number of APs (e.g., only by a single AP or by two or three APs). In other scenarios, active UEs are served by a large number of APs (e.g., all APs deployed within a given building when the UEs are located within the building).

[0073] Therefore, the decision to select a "UE-initiated" or "AP-initiated" channel information acquisition process can depend on the number of APs serving each active UE. Thus, in some embodiments, network improvement based on the UE's utility score is proportional to the number of APs 110 serving each active UE 300 averaged over multiple TTIs. The higher the number of APs 110, the higher the UE-based utility score.

[0074] In addition, by comparing the total number of current active UEs (denoted as N UE ) with the number of serving APs (denoted as N AP ), the relative cost of sending pilot signals from the AP versus from the UE can be estimated. If N AP << N UE , then the cost of initiating the channel information acquisition process by having the serving AP send pilot signals may be lower. Similarly, if N UE << N AP , then the cost of initiating the channel information acquisition process by having the active UE send pilot signals may be lower. If N AP ≈ N UE , then other considerations (such as latency, alternative use of radio resources, etc.) become more important.

[0075] Therefore, the decision to select a "UE-initiated" or "AP-initiated" channel information acquisition process can depend on the total number of current serving APs and the total number of current active UEs. Thus, in some embodiments, network improvement based on the AP's utility score is proportional to the total number of active UEs 300 served by any AP 110. Similarly, in some embodiments, the estimated network resource cost based on the UE's utility score is proportional to the total number of APs 110 serving any active UE 300. If there are more UEs 300 than APs 110, then for this parameter, the AP-based utility score is higher than the UE-based utility score.

[0076] By combining two or more of the above considerations for determining whether to select a "UE-initiated" or "AP-initiated" channel information acquisition process, the relative cost of transmitting pilot signals from the AP and from the UE can be estimated by comparing the total number (N AP-total ) of beam candidates from all serving APs with the total number (N UE-total ) of beam candidates from all currently active UEs.

[0077] Therefore, the decision to select a "UE-initiated" or "AP-initiated" channel information acquisition process can depend on the total number of beam candidates from all serving APs and the total number of beam candidates from all currently active UEs.

[0078] Another aspect is the bandwidth required for UL and DL data transmission. When transmitting a small amount of data, a small amount of bandwidth is required and the UEs can be frequency multiplexed. In this case, the pilot signal transmission in the reverse radio link only needs to cover the bandwidth of the data transmission for which the acquired channel information is to be used. For example, when a small amount of UL or DL data is to be scheduled, a pilot signal with a narrow bandwidth can be used to obtain the channel information. When the bandwidth of the pilot signal is narrow, it costs less to transmit the pilot signal, and vice versa.

[0079] One aspect relates to how the channel information acquisition process affects latency. The latency here refers to the delay of data transmission (in the uplink or downlink).

[0080] For latency-sensitive services, it is important whether the UE initiates the channel information acquisition process by transmitting a pilot signal or the AP initiates the channel information acquisition process. Consider the four different examples A, B, C, and D shown in Figure 6 . For efficient data transmission, the channel information should be available at the transmitter side. In a TDD system, this channel information is obtained by first having the receiver side transmit a pilot signal in the opposite direction. Thus, in some embodiments, the network improvement based on the AP's utility score is proportional to the latency requirement for uplink data traffic, while the network improvement based on the UE's utility score is inversely proportional to the latency requirement for uplink data traffic. The more stringent the latency requirement, the higher the AP-based utility score. Similarly, in some embodiments, the network improvement based on the UE's utility score is proportional to the latency requirement for downlink data traffic, while the network improvement based on the AP's utility score is inversely proportional to the latency requirement for downlink data traffic. The more stringent the latency requirement, the higher the UE-based utility score.

[0081] Consider the case where there is data in the uplink direction, as in Examples A and B. If the AP initiates the channel information acquisition process by sending a pilot signal (as in Example B), then the channel information required for UL transmission is first obtained at the UE side. Then, UL data may have been sent in step 2 of Example B. If instead the UE initiates the channel information acquisition process by sending a pilot signal, then the channel information is first obtained at the AP side, as in Example A. However, since UL data is to be sent, the AP first needs to send a second pilot signal to the UE. Only after receiving this second pilot transmission from the AP can the UE obtain the channel information for UL MIMO transmission. Data transmission occurs in step 3 of Example A, which results in a greater delay than in Example B.

[0082] Consider the case where there is data in the downlink direction, as in Examples C and D. If the UE initiates the channel information acquisition process by sending a pilot signal (as in Example C), then the channel information required for DL transmission is first obtained at the AP side. Then, DL data may have been sent in step 2 of Example C. If instead the AP initiates the channel information acquisition process by sending a pilot signal, then the channel information is first obtained at the UE side, as in Example D. However, since DL data is to be sent, the UE first needs to send a second pilot signal to the AP. Only after receiving this second pilot transmission from the UE can the AP obtain the channel information for DL MIMO transmission. Data transmission occurs in step 3 of Example D, which results in a greater delay than in Example C.

[0083] Therefore, the decision to select a "UE-initiated" or "AP-initiated" channel information acquisition process can depend on the alternative that results in the minimum data transmission delay for uplink and downlink data, respectively.

[0084] Therefore, in some embodiments, if the channel information acquisition process is initiated for AP 110, the network improvement based on the AP's utility score is inversely proportional to the expected data transmission delay of uplink and / or downlink data transmission, while if the channel information acquisition process is initiated for UE 300, the network improvement based on the UE's utility score is inversely proportional to the expected data transmission delay of uplink and / or downlink data transmission.

[0085] Another aspect to consider is the time taken for the pilot transmissions involved in a UE-initiated or AP-initiated CSI acquisition process in the network setup. Thus, in some embodiments, the network improvement based on the AP's utility score is inversely proportional to the duration for establishing the channel information acquisition process initiated for AP 110, while the network improvement based on the UE's utility score is inversely proportional to the duration for establishing the channel information acquisition process initiated for UE 300.

[0086] For example, consider the case where the UE 300 is configured by the network (represented by the centralized node 200) to transmit the SRS as an uplink pilot signal. If such SRS transmission is triggered by the network non-periodically, the network first needs to perform radio resource control (RRC) configuration of the UE in terms of configuring the SRS signaling (e.g., which time / frequency resources to use, which antenna ports to use, etc.). After the RRC configuration is performed, a one-time SRS trigger is sent in the downlink control information (DCI) of the physical downlink control channel (PDCCH). When deciding to initiate channel information acquisition with pilot signal transmission from the UE or from the AP, the latency associated with establishing such pilot signal transmission (i.e., both RRC configuration and DCI-based triggering) and subsequent pilot transmission should be considered. Similar considerations can be made when the DL pilot signal transmission is performed on the AP side instead.

[0087] Therefore, the decision to select a "UE-initiated" or "AP-initiated" channel information acquisition process can respectively depend on which alternative results in the shortest time taken to establish such a process.

[0088] There can be different ways to numerically calculate the AP-based utility score and the UE-based utility score respectively. The following is a non-limiting example of how these calculations can be performed.

[0089] Assume N UE and N AP are the total numbers of currently active UEs and serving APs respectively. The total cost of transmitting pilot signals from the UE and the AP can be expressed as:

[0090] Cost UE-initiated = αNN UE

[0091] Cost AP-initiated = βMN AP

[0092] where N and M are the numbers of UE and AP antenna elements respectively, and α and β are constants indicating the relative costs of the uplink pilot signal (from the UE) and the downlink pilot signal (from the AP). One reason for the possible difference in costs is that there may be differences in the output power between the AP and the UE and the receiver noise.

[0093] The availability of any particular pilot signal transmission can depend on the number of APs or UEs that can use it. Assume that NUE,l is the number of active UEs served by each AP l (l = 1, …, L), and assume that NAP,k is the number of APs serving each current active UE k (k = 1, …, K). The availability Usability of the "UE-initiated" channel information acquisition process UE-initiated and the availability Usability of the "AP-initiated" channel information acquisition process AP-initiated can then be calculated as:

[0094]

[0095] The delay benefit Delay of the "UE-initiated" channel information acquisition process UE-initiated and the delay benefit Delay of the "AP-initiated" channel information acquisition process AP-initiated can then be calculated as:

[0096] Delay UE-initiated = f1(DL latency reduction ) - f2(UL latency increase )

[0097] Delay AP-initiated = f2(UL latency reduction ) - f1(DL latency increase )

[0098] where f1(·) and f2(·) are some possible non-linear functions that describe the quality-of-service impact of DL delay and UL delay, respectively. An example of a function that can be used here is the mean normalization and scaling function:

[0099]

[0100] where is the average value of the variable x, and α is a scaling factor (e.g., α = 1). Other functions are also possible.

[0101] The alternative cost of the resources for the pilot signal transmission for the "UE-initiated" channel information acquisition process and for the "AP-initiated" channel information acquisition process UE-initiated and Alternative cost AP-initiated depends on the current UL and DL data traffic. For example, this can be expressed as:

[0102] Alternative cost UE-initiated = g1(N UE , UL data volume )

[0103] Alternative cost AP-initiated =g2(N AP ,DL data volume )

[0104] where g1(·) and g2(·) are functions of the number of active UEs and APs that need to perform pilot signal transmission and the amount of data currently required in UL and DL, respectively.

[0105] Utility score based on UE UE-initiated ) and AP-based utility scores AP-initiated ) can then be obtained as:

[0106] Utility UE-initiated =h1(Cost UE-initiated ,Usability UE-initiated ,Delay UE-initiated ,Alternative cost UE-initiated )

[0107] Utility AP-initiated =h2(Cost AP-initiated ,Usability AP-initiated ,Delay AP-initiated ,Alternative cost AP-initiated )

[0108] where h1(·) and h2(·) are functions used to combine resource cost, availability benefit, latency benefit, and substitution cost into a single metric (preferably a linear combination of these terms).

[0109] Reference now Figure 7 , which shows a method for starting a channel information acquisition process in a D-MIMO network 100 performed by a UE 300 according to an embodiment. The channel information acquisition process is started by sending a pilot signal in the D-MIMO network 100. The D-MIMO network 100 includes an AP 110 serving the UE 300.

[0110] S202: The UE 300 obtains information from the centralized node 200 in the D-MIMO network 100 whether the channel information acquisition process is to be started in the downlink or uplink.

[0111] S204: When the channel information acquisition process is to be initiated on the uplink, the UE 300 sends a pilot signal.

[0112] S206: When the channel information acquisition process is about to be initiated on the downlink, the UE 300 receives pilot signals from at least some of the APs 110 in the AP 110.

[0113] Embodiments related to further details of initiating the channel information acquisition process in the D-MIMO network 100 by the UE 300 will now be disclosed.

[0114] Figure 8 Denote a scenario 800 in which the channel information acquisition process is initiated by the UE 300 (as denoted by the UE Figure 9 in k ). In Figure 8 , the following notations are used. The channel between the UE k and the AP l is denoted as G k,l . The beamformer for the AP l is denoted as w l = [w l,1 ... w l,M T . The downlink pilot signal transmitted by the AP l is denoted as θ l . The downlink data signal transmitted by the AP l is denoted as y l . The uplink pilot signal transmitted by the UE k is denoted as The beamformer for the AP k used by the UE l is denoted as The signal received by the UE k from the AP l is denoted as u k,l = y l w l G k,l v k,l + n k , where n k is the channel noise. The actions represented by the circled numbers 1, 2, and 3 in Figure 8 will now be disclosed.

[0115] 1: The UE k first transmits the pilot signal denoted by . The AP 110 (represented by AP1 and AP2 in Figure 8 ) receives the uplink pilot signal and uses it to obtain the channel information. With this channel information, AP1 and AP2 can determine the vectors of the transmit beamforming weights (denoted as w1 and w2 respectively).

[0116] ​2: Using the transmit beamforming weight w1, AP1 can transmit a downlink data signal (represented as w1y1 by the scalar y1 in Figure 8 ). In addition, AP1 can transmit a downlink pilot signal (represented as w1θ1 by the scalar θ1 in Figure 8 ). Similarly, AP2 can transmit the beamformed data signal w2y2 and the beamformed downlink pilot signal w2θ2.

[0117] 3: UE k can use the received beamformed downlink pilot signals w1θ1 and w2θ2 to obtain receiver-side CSI for determining a set of receive antennas that combines the weight vectors v1 and v2.

[0118] Here, it is assumed that the UE (and AP) has beam correspondence capabilities because it 1) can obtain a suitable direction to direct the transmit beam based on the DL reference signal, or 2) can obtain complete UL channel information (e.g., the amplitude and phase of all subcarriers, or the physical resource blocks (PRBs) of all beams and / or antennas), and thus direct the transmit beam accordingly based on the DL reference signal.

[0119] Figure 9 represents a scenario 900 in which the channel information acquisition process is initiated by AP 110 (represented by AP1 and AP2 in Figure 9 ). In Figure 9 , the following notations are used. The channel between UE k and AP l is denoted as G k,l . The beamformer for AP l is denoted as w l = [w l,1 … w l,M T . The downlink pilot signal transmitted by AP l is denoted as θ l . The downlink data signal transmitted by AP l is denoted as y l . The uplink pilot signal transmitted by UE k is denoted as The beamformer for AP k used by UE l is denoted as The signal received by UE k from AP l is denoted as u k,l = y l w l G k,l v k,l + nk , where n k is the channel noise. Next, the actions represented by circled numbers 1, 2, and 3 in Figure 9 will be disclosed.

[0120] 1: AP1 and AP2 respectively send pilot signals represented as and .

[0121] 2: UE k receives these downlink pilot signals and uses them to obtain channel information. With this channel information, UE k can determine the beamforming weights (represented as v k,1 and v k,2 ) for AP1 and AP2. Using the weights v k,1 and v k,2 , UE k can send the uplink pilot signal as and send as .

[0122] 3: AP1 and AP2 can then obtain channel information based on the received and . This channel information can be used by the AP to determine the beamforming vectors w1 and w2, and then w1 and w2 are used to send the downlink data signals y1 and y2 (possibly sent together with the downlink pilots θ1 and θ2) within the narrow beams defined by w1 and w2.

[0123] Figure 8 and Figure 9 both represent examples of data that need to be sent in the downlink. It is straightforward to construct a similar example for the case where uplink data needs to be sent.

[0124] Next, the channel information acquisition process initiated by one of the UEs in the UE will be disclosed with reference to the signaling diagram of Figure 10 .

[0125] S301: The centralized node (Cent.) executes the steps S102 - S106 of Figure 3 .

[0126] S302: Here, it is assumed that the utility score based on the UE is the highest. Therefore, the centralized node decides that the channel information acquisition process should be initiated from the UE side.

[0127] S303a: The controller entity notifies the UE to initiate the channel information acquisition process (as in step S108), and provides pilot signal configuration to the serving AP.

[0128] S303b: The AP forwards the pilot signal configuration to the UE.

[0129] Note here that in some examples, the UE is not explicitly notified of the pilot signal configuration, and thus step S305b is optional. In an alternative, the absence of expected downlink pilot signal transmission is used to implicitly indicate to the UE to initiate the channel information acquisition process. In an alternative, a default time window is assigned for uplink pilot signal transmission. In an alternative, the pilot signal configuration is preconfigured in the UE (e.g., during a previous active mode transmission).

[0130] S304: The UE obtains the downlink control information (either explicitly or implicitly).

[0131] S305: The UE initiates the channel information acquisition process by transmitting a pilot signal.

[0132] S306: The AP receives the pilot signal from the UE, obtains the channel information, and determines the antenna weights for performing other narrow beam transmissions and receptions (data channels, reference signals, control channels, etc.) related to the UE.

[0133] S307: The AP performs precoded downlink transmission according to the determined antenna weights, which may include both pilot signals and data.

[0134] S308: The UE obtains the required channel information from the precoded downlink transmission, and determines the transmit and receive antenna weights for transmitting and receiving data related to the serving AP, and may also determine the data itself.

[0135] S309: The UE performs precoded uplink transmission according to the determined antenna weights.

[0136] Next, the channel information acquisition process initiated by the AP will be disclosed with reference to Figure 11 the signaling diagram.

[0137] S401: The Centralized Node (Cent.) performs Figure 3 steps S102 - S106 of

[0138] S402: Here it is assumed that the AP has the highest utility score. Therefore, the centralized node decides that the channel information acquisition process is to be initiated from the AP side.

[0139] S403a: The controller entity notifies the AP to initiate the channel information acquisition process (as in step S108), and provides the pilot signal configuration to the serving AP.

[0140] S403b: The AP sends control information (such as UL grant, pilot signal reception information, etc.) to the UE.

[0141] S404: The UE receives the control information.

[0142] Note here that in some examples, the UE is not explicitly notified of the pilot signal reception information, and thus this information in step S403b is optional. In an alternative, a default time window is assigned for downlink pilot signal transmission. In an alternative, the control information is preconfigured in the UE (e.g., during a previous active mode transmission).

[0143] S405: The AP starts the channel information acquisition process by sending a pilot signal.

[0144] S406: The UE receives the pilot signal from the AP, obtains the channel information, and determines the antenna weights for performing other narrow beam transmissions and receptions (data channels, reference signals, control channels, etc.) related to the AP.

[0145] S407: The UE performs precoded uplink transmission according to the determined antenna weights, which may include both pilot signals and data.

[0146] S408: The AP obtains the required channel information from the precoded uplink transmission, determines the transmit and receive antenna weights for sending and receiving data related to the UE, and may also determine the data itself.

[0147] S409: The AP performs precoded downlink transmission according to the determined antenna weights.

[0148] To quantify some of the advantages of the embodiments disclosed herein, the total overhead cost of reference signal transmission required for channel information acquisition in a downlink data transmission scenario will be considered. Assume the scenario has 10 APs (each AP has 8 antenna units) and 20 active UEs (each active UE has 4 antenna units). The total number of antenna ports on the AP side is then 10 × 8 = 80, while the total number of antenna ports on the UE side is 20 × 4 = 80.

[0149] The pilot signal transmission overhead cost can be measured according to the total number of antenna ports that need to be observed. For example, if there are 8 antenna points at a given AP, the given AP can create 8 orthogonal narrow beams, which will together form a wide beam. In this example, the cost of sending a pilot signal from the AP and the cost of sending a pilot signal from the UE are the same; each requires 80 pilot signals.

[0150] Since this example considers the downlink transmission of data, if the UE initiates the channel information acquisition process, no additional pilot signal transmission is required (as in Figure 6 Example C). The channel information from the UE-initiated channel information acquisition process eventually reaches the transmitter side, which in this case is in the AP. Therefore, the total number of pilot signals for the UE-initiated channel information acquisition process is 80.

[0151] For the AP-initiated channel information acquisition process, the channel information from the channel information acquisition process is first obtained at the UE side. Another set of 20 pilot signal transmissions (one per UE) is required to enable the transmitter side to obtain the required channel information (as in Figure 6 Example D). In this case, the total number of pilot signal transmissions is 80 (in DL) + 20 (in UL) = 100 (in total).

[0152] Therefore, in this example, using the UE-initiated channel information acquisition process has a small overhead advantage.

[0153] However, the number of active UEs changes dynamically on the TTI time scale, and in a real system, there will not always be a constant number (20) of active UEs. In Table 1 below, the total overhead costs in terms of pilot signal transmission are summarized for the case of 20 active UEs (denoted as the baseline) as described above, the case where 2 UEs are active in the same TTI (denoted as Case 1), and the case where 40 UEs are active in the same TTI (denoted as Case 2).

[0154] It can be observed that in some cases, the difference between the alternatives (UE-initiated channel information acquisition process versus AP-initiated channel information acquisition process) can be very large (for Case 1, the difference is more than 10 times).

[0155]

[0156] Table 1: Total number of pilot signals required for channel information acquisition for downlink data transmission.

[0157] For the case with UL data transmission, a similar comparison can be made. The data transmission delay may also affect the preferred selection of the channel information acquisition process. In addition, in a real system, not all UEs will have 4 antenna elements. Some UEs may have, for example, 8 antenna elements, while other UEs may have only a single antenna element, for example. In a realistic scenario, there will be a mixture of UEs with different numbers of antenna elements. However, it is clear from the examples shown in Table 1 that neither the fixed AP-initiated channel information acquisition process nor the fixed UE-initiated channel information acquisition process is the best choice in all the different scenarios considered.

[0158] Figure 12 The components of the centralized node 200 according to one embodiment are schematically shown in the form of a plurality of functional units. The processing circuit 210 is provided by any combination of one or more of a suitable central processing unit (CPU), a multi-processor, a microcontroller, a digital signal processor (DSP), etc., which are capable of executing software instructions stored in a computer program product 1610a in the form of, for example, a storage medium 230 (as in Figure 16 ). The processing circuit 210 can also be provided as at least one application specific integrated circuit (ASIC) or a field programmable gate array (FPGA).

[0159] In particular, the processing circuit 210 is configured such that the centralized node 200 performs a set of operations or steps as disclosed above. For example, the storage medium 230 can store the set of operations, and the processing circuit 210 can be configured to obtain the set of operations from the storage medium 230 to cause the centralized node 200 to perform the set of operations. The set of operations can be provided as a set of executable instructions. Thus, the processing circuit 210 is thereby arranged to execute the methods disclosed herein.

[0160] The storage medium 230 may also include a permanent storage device, which can be any one or combination of, for example, a magnetic memory, an optical memory, a solid-state memory, or even a remotely mounted memory.

[0161] The centralized node 200 may also include a communication interface 220 for communicating with the AP 110 as in Figure 2 . Thus, the communication interface 220 can include one or more transmitters and receivers, which include analog and digital components.

[0162] The processing circuit 210 controls the overall operation of the centralized node 200, for example, by sending data and control signals to the communication interface 220 and the storage medium 230, by receiving data and reports from the communication interface 220, and by retrieving data and instructions from the storage medium 230. Other components of the centralized node 200 and related functions are omitted so as not to obscure the concepts provided herein.

[0163] Figure 13 The components of the centralized node 200 according to one embodiment are schematically shown in the form of a plurality of functional modules. Figure 13 The centralized node 200 includes a plurality of functional modules: a computing module 210a configured to execute step S102, a computing module 210b configured to execute step S104, a selection module 210c configured to execute step S106, and a notification module 210d configured to execute step S108. Figure 13 The centralized node 200 may further include a plurality of optional functional modules, as represented by the functional module 210e. Generally, each of the functional modules 210a - 210e may be implemented in hardware or software. Preferably, one or more or all of the functional modules 210a - 210e may be implemented by the processing circuit 210 (possibly in cooperation with the communication interface 220 and / or the storage medium 230). Thus, the processing circuit 210 may be arranged to retrieve instructions provided by the functional modules 210a - 210e from the storage medium 230 and execute these instructions, thereby performing any step of the centralized node 200 disclosed herein.

[0164] The centralized node 200 may be provided as an independent device or as part of at least one other device. For example, the centralized node 200 may be provided in a node of a (radio) access network or a node of a core network. Alternatively, the functions of the centralized node 200 may be distributed between at least two devices or nodes. These at least two nodes or devices may be part of the same network portion (e.g., a (radio) access network or a core network), or may be distributed between at least two such network portions. Generally, instructions that need to be executed in real time may be executed operationally closer to the device or node of the cell compared to instructions that do not need to be executed in real time. Thus, a first portion of the instructions executed by the centralized node 200 may be executed in a first device, while a second portion of the instructions executed by the centralized node 200 may be executed in a second device; the embodiments disclosed herein are not limited to any particular number of devices on which the instructions executed by the centralized node 200 may be executed. Thus, the method according to the embodiments disclosed herein is suitable for execution by the centralized node 200 located in a cloud computing environment. Thus, although in Figure 12A single processing circuit 210 is shown, but the processing circuit 210 can be distributed among multiple devices or nodes. This also applies to Figure 13 the functional modules 210a - 210e of Figure 16 and the computer program 1620a of

[0165] Figure 14 The components of the UE 300 according to one embodiment are schematically shown in the form of multiple functional units. The processing circuit 310 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., which are capable of executing software instructions stored in a computer program product 1610b in the form of, for example, a storage medium 330 (as in Figure 16 ). The processing circuit 310 can also be provided as at least one application - specific integrated circuit (ASIC) or field - programmable gate array (FPGA).

[0166] In particular, the processing circuit 310 is configured such that the UE 300 performs a set of operations or steps as disclosed above. For example, the storage medium 330 can store the set of operations, and the processing circuit 310 can be configured to obtain the set of operations from the storage medium 330 to cause the UE 300 to perform the set of operations. The set of operations can be provided as a set of executable instructions. Thus, the processing circuit 310 is arranged to perform the methods disclosed herein.

[0167] The storage medium 330 can also include a permanent storage device, which can be any one or combination of, for example, a magnetic memory, an optical memory, a solid - state memory, or even a remotely - mounted memory.

[0168] The UE 300 can also include a communication interface 320 for communicating with the AP 110 as in Figure 2 . Thus, the communication interface 320 can include one or more transmitters and receivers, which include analog and digital components.

[0169] The processing circuit 310 controls the overall operation of the UE 300, for example, by sending data and control signals to the communication interface 320 and the storage medium 330, by receiving data and reports from the communication interface 320, and by obtaining data and instructions from the storage medium 330. Other components of the UE 300 and related functions are omitted so as not to obscure the concepts provided herein.

[0170] Figure 15 The components of the UE 300 according to one embodiment are schematically shown in the form of multiple functional modules. Figure 15The UE 300 includes a plurality of functional modules; an obtaining module 310a configured to execute step S202, a sending module 310b configured to execute step S204, and a receiving module 310c configured to execute step S206. Figure 15 The UE 300 may further include a plurality of optional functional modules, as represented by functional module 310d. Generally speaking, each of the functional modules 310a - 310d may be implemented in hardware or software. Preferably, one or more or all of the functional modules 310a - 310d may be implemented by a processing circuit 310 (possibly in cooperation with a communication interface 320 and / or a storage medium 330). Thus, the processing circuit 310 may be arranged to retrieve instructions provided by the functional modules 310a - 310d from the storage medium 330 and execute these instructions, so as to execute any of the steps of the UE 300 disclosed herein.

[0171] Figure 16 An example of computer program products 1610a, 1610b including a computer-readable component 1630 is shown. On this computer-readable component 1630, a computer program 1620a may be stored, and this computer program 1620a may cause the processing circuit 210 and entities and devices operatively coupled thereto (such as a communication interface 220 and a storage medium 230) to execute the methods according to the embodiments described herein. Thus, the computer program 1620a and / or the computer program product 1610a may provide components for executing any of the steps of the centralized node 200 disclosed herein. On this computer-readable component 1630, a computer program 1620b may be stored, and this computer program 1620b may cause the processing circuit 310 and entities and devices operatively coupled thereto (such as a communication interface 320 and a storage medium 330) to execute the methods according to the embodiments described herein. Thus, the computer program 1620b and / or the computer program product 1610b may provide components for executing any of the steps of the UE 300 disclosed herein.

[0172] In Figure 16In the example, computer program products 1610a, 1610b are shown as optical discs, such as CD (compact disc) or DVD (digital versatile disc) or Blu-ray Disc. Computer program products 1610a, 1610b can also be embodied as memories (such as random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM) or electrically erasable programmable read-only memory (EEPROM)), and more specifically, as non-volatile storage media of devices in external memories (such as USB (universal serial bus) memory or flash memory (such as compact flash)). Thus, although computer programs 1620a, 1620b are schematically shown herein as tracks on the illustrated optical discs, computer programs 1620a, 1620b can be stored in any manner suitable for computer program products 1610a, 1610b.

[0173] The concepts of the present invention have been described above mainly with reference to several embodiments. However, as will be readily understood by those skilled in the art, other embodiments beyond the embodiments disclosed above are equally within the scope of the concepts of the present invention defined by the appended patent claims.

Claims

1. A method for initiating a channel information acquisition process in a distributed multiple-input multiple-output D-MIMO network (100), the channel information acquisition process being initiated by transmitting a pilot signal in the D-MIMO network (100), the D-MIMO network (100) including an access point AP (110) serving a user equipment UE (300), the method being performed by a centralized node (200) in the D-MIMO network (100), the method comprising: Calculating (S102) an AP-based utility score for the AP (110) to initiate the channel information acquisition process, wherein if the channel information acquisition process is initiated by the AP (110), the AP-based utility score is related to an estimated network improvement and an estimated network resource cost; Calculating (S104) a UE-based utility score for the UE (300) to initiate the channel information acquisition process, wherein if the channel information acquisition process is initiated by the UE (300), the UE-based utility score is related to an estimated network improvement and an estimated network resource cost; Selecting (S106) the AP (110) to initiate the channel information acquisition process when the AP-based utility score is the highest, and selecting (S106) the UE (300) to initiate the channel information acquisition process when the UE-based utility score is the highest; and Notifying (S108) the AP (110) and the UE (300) which one of the AP (110) and the UE (300) initiates the channel information acquisition process.

2. The method according to claim 1, wherein, The estimated network resource cost for the AP-based utility score depends on the amount of radio resources required to transmit the pilot signal from the AP (110).

3. The method according to claim 1 or 2, wherein The estimated network resource cost for the UE-based utility score depends on the amount of radio resources required to transmit the pilot signal from the UE (300).

4. The method according to any one of the preceding claims, wherein, The network improvement for the AP-based utility score is proportional to the number of active UEs (300) served by each AP (110) averaged over a plurality of transmission time intervals TTI.

5. The method according to any one of the preceding claims, wherein, The network improvement for the UE-based utility score is proportional to the number of APs (110) serving each active UE (300) averaged over a plurality of transmission time intervals TTI.

6. The method according to any one of the preceding claims, wherein, The network improvement for the AP-based utility score is proportional to the total number of active UEs (300) served by any one of the APs (110).

7. The method according to any one of the preceding claims, wherein, The estimated network resource cost for the UE-based utility score is proportional to the total number of APs (110) serving any active UE (300).

8. The method according to any one of the preceding claims, wherein, The network improvement for the AP-based utility score is proportional to the expected or ongoing uplink data traffic volume, while the network improvement for the UE-based utility score is inversely proportional to the expected or ongoing uplink data traffic volume.

9. The method according to any one of the preceding claims, wherein, The network improvement for the UE-based utility score is proportional to the expected or ongoing downlink data traffic, while the network improvement for the AP-based utility score is inversely proportional to the expected or ongoing downlink data traffic.

10. The method according to any one of the preceding claims, wherein, The network improvement for the AP-based utility score is proportional to the latency requirement for uplink data traffic, while the network improvement for the UE-based utility score is inversely proportional to the latency requirement for uplink data traffic.

11. The method according to any one of the preceding claims, wherein, The network improvement for the UE-based utility score is proportional to the latency requirement for downlink data traffic, while the network improvement for the AP-based utility score is inversely proportional to the latency requirement for downlink data traffic.

12. The method according to any one of the preceding claims, wherein, If the channel information acquisition process is initiated for the AP (110), the network improvement for the AP-based utility score is inversely proportional to the expected data transmission latency of uplink and / or downlink data transmission, while if the channel information acquisition process is initiated for the UE (300), the network improvement for the UE-based utility score is inversely proportional to the expected data transmission latency of uplink and / or downlink data transmission.

13. The method according to any one of the preceding claims, wherein, The network improvement for the AP-based utility score is inversely proportional to the duration for establishing the channel information acquisition process initiated for the AP (110), while the network improvement for the UE-based utility score is inversely proportional to the duration for establishing the channel information acquisition process initiated for the UE (300).

14. A method for initiating a channel information acquisition process in a distributed multiple-input multiple-output D-MIMO network (100), the channel information acquisition process being initiated by transmitting a pilot signal in the D-MIMO network (100), the D-MIMO network (100) including an access point AP (110) serving a user equipment UE (300), the method being executed by one of the UEs (300) in the UE (300), the method comprising: Obtaining (S202) from a centralized node (200) in the D-MIMO network (100) information on whether the channel information acquisition process is to be initiated in the downlink or the uplink; Transmitting (S204) the pilot signal when the channel information acquisition process is to be initiated on the uplink; And Receiving (S206) the pilot signal from at least some of the APs (110) in the AP (110) when the channel information acquisition process is to be initiated on the downlink.

15. The method according to any one of the preceding claims, wherein, The pilot signal transmitted by the AP (110) is a downlink reference signal covering the service area.

16. The method according to any one of the preceding claims, wherein, The pilot signal transmitted by the UE (300) is an uplink reference signal.

17. A centralized node (200) for initiating a channel information acquisition process in a distributed multiple-input multiple-output D-MIMO network (100), the channel information acquisition process being initiated by transmitting a pilot signal in the D-MIMO network (100), the D-MIMO network (100) including access points AP (110) serving user equipment UE (300), the centralized node (200) including processing circuitry (210), the processing circuitry being configured to cause the centralized node (200) to: Calculate an AP-based utility score for the AP (110) to initiate the channel information acquisition process, where, If the channel information acquisition process is initiated by the AP (110), the AP-based utility score is related to the estimated network improvement and the estimated network resource cost; Calculate a UE-based utility score for the UE (300) to initiate the channel information acquisition process, wherein if the channel information acquisition process is initiated by the UE (300), the UE-based utility score is related to the estimated network improvement and the estimated network resource cost; When the AP-based utility score is the highest, select the AP (110) to initiate the channel information acquisition process, and when the UE-based utility score is the highest, select the UE (300) to initiate the channel information acquisition process; and Notify the AP (110) and the UE (300) which one of the AP (110) and the UE (300) initiates the channel information acquisition process.

18. A centralized node (200) for initiating a channel information acquisition process in a distributed multiple-input multiple-output D-MIMO network (100), the channel information acquisition process being initiated by transmitting a pilot signal in the D-MIMO network (100), the D-MIMO network (100) including access points AP (110) serving user equipment UE (300), the centralized node (200) including: A calculation module (210a) configured to: calculate an AP-based utility score for the AP (110) to initiate the channel information acquisition process, wherein if the channel information acquisition process is initiated by the AP (110), the AP-based utility score is related to the estimated network improvement and the estimated network resource cost; A calculation module (210b) configured to: calculate a UE-based utility score for the UE (300) to initiate the channel information acquisition process, wherein if the channel information acquisition process is initiated by the UE (300), the UE-based utility score is related to the estimated network improvement and the estimated network resource cost; A selection module (210c) configured to: when the AP-based utility score is the highest, select the AP (110) to initiate the channel information acquisition process, and when the UE-based utility score is the highest, select the UE (300) to initiate the channel information acquisition process; and A notification module (210d) configured to notify the AP (110) and the UE (300) as to which one of the AP (110) and the UE (300) initiates the channel information acquisition process.

19. The centralized node (200) according to claim 17 or 18, further configured to perform the method according to any one of claims 2 to 13.

20. A user equipment UE (300) for initiating a channel information acquisition process in a distributed multiple-input multiple-output D-MIMO network (100), the channel information acquisition process being initiated by transmitting a pilot signal in the D-MIMO network (100), the D-MIMO network (100) including an access point AP (110) serving the UE (300), the UE (300) including a processing circuit (310) configured to cause the UE (300) to: Obtain information from a centralized node (200) in the D-MIMO network (100) as to whether the channel information acquisition process is to be initiated on the downlink or the uplink; Transmit the pilot signal when the channel information acquisition process is to be initiated on the uplink; And Receive the pilot signal from at least some of the APs (110) in the AP (110) when the channel information acquisition process is to be initiated on the downlink.

21. A user equipment UE (300) for initiating a channel information acquisition process in a distributed multiple-input multiple-output D-MIMO network (100), the channel information acquisition process being initiated by transmitting a pilot signal in the D-MIMO network (100), the D-MIMO network (100) including an access point AP (110) serving the user equipment UE (300), the UE (300) including: An obtaining module (310a) configured to obtain information from a centralized node (200) in the D-MIMO network (100) as to whether the channel information acquisition process is to be initiated on the downlink or the uplink; A transmitting module (310b) configured to transmit the pilot signal when the channel information acquisition process is to be initiated on the uplink; And A receiving module (310c) configured to receive the pilot signal from at least some of the APs (110) in the AP (110) when the channel information acquisition process is to be initiated on the downlink.

22. The UE (300) according to claim 20 or 21, further configured to perform the method according to any one of claims 15 or 16.

23. A computer program (1620a) for initiating a channel information acquisition process in a distributed multiple-input multiple-output D-MIMO network (100), the channel information acquisition process being initiated by transmitting a pilot signal in the D-MIMO network (100), the D-MIMO network (100) including an access point AP (110) serving a user equipment UE (300), the computer program including computer code which, when run on a processing circuit (210) of a centralized node (200) in the D-MIMO network (100), causes the centralized node (200): Calculate (S102) an AP-based utility score for the AP (110) to initiate the channel information acquisition process, where, If the channel information acquisition process is initiated by the AP (110), the AP-based utility score is related to the estimated network improvement and the estimated network resource cost; Calculate (S104) a UE-based utility score for the UE (300) to initiate the channel information acquisition process, wherein, if the channel information acquisition process is initiated by the UE (300), the UE-based utility score is related to the estimated network improvement and the estimated network resource cost; When the AP-based utility score is the highest, select (S106) the AP (110) to initiate the channel information acquisition process, and when the UE-based utility score is the highest, select (S106) the UE (300) to initiate the channel information acquisition process; and Notify (S108) the AP (110) and the UE (300) which one of the AP (110) and the UE (300) initiates the channel information acquisition process.

24. A computer program (1620b) for initiating a channel information acquisition process in a distributed multiple-input multiple-output D-MIMO network (100), the channel information acquisition process being initiated by transmitting a pilot signal in the D-MIMO network (100), the D-MIMO network (100) including an access point AP (110) serving a user equipment UE (300), the computer program including computer code which, when run on a processing circuit (310) of one of the UEs (300) in the UE (300), causes the one UE (300) in the UE (300): Obtain (S202) from a centralized node (200) in the D-MIMO network (100) information on whether the channel information acquisition process is to be initiated on the downlink or the uplink; When the channel information acquisition process is to be initiated on the uplink, transmit (S204) the pilot signal; And When the channel information acquisition process is to be initiated on the downlink, receive (S206) the pilot signal from at least some of the APs (110) in the AP (110).

25. A computer program product (1610a, 1610b) comprising a computer program (1620a, 1620b) according to at least one of claims 23 and 24 and a computer-readable storage medium (1630) storing the computer program therein.

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