EP4652762A1

EP4652762A1 - Optimizing master unit performance in a distributed antenna system (das)

Info

Publication number: EP4652762A1
Application number: EP24745182.6A
Authority: EP
Inventors: Suresh N. SRIRAM; Sudarshana Varadappa
Original assignee: Outdoor Wireless Networks LLC
Current assignee: Outdoor Wireless Networks LLC
Priority date: 2023-01-20
Filing date: 2024-01-18
Publication date: 2025-11-26
Also published as: WO2024155772A1

Abstract

The present disclosure describes methods and apparatus implemented for optimizing master unit performance in a distributed antenna system (DAS). The MU receives, from a plurality of radio units (RUs), a plurality of uplink data associated with reception at the plurality of RUs of uplink reference transmissions from a plurality of UEs. The MU determines, for each UE, respective signal reception metrics for the plurality of RUs using the plurality of uplink data. The MU compares the respective signal reception metrics with a signal threshold value. The MU further determines, for each UE, a limited RU subset among the plurality of RUs for serving a corresponding UE based on the comparison such that the respective signal reception metrics is above the signal threshold value. Further, the MU serves at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for the corresponding UE.

Description

OPTIMIZING MASTER UNIT PERFORMANCE IN A DISTRIBUTED ANTENNA

SYSTEM (DAS)

TECHNICAL FIELD

[1] The present disclosure in general relates to wireless communication systems and methods. More particularly, but not exclusively, the present disclosure relates to techniques for optimizing master unit performance in a distributed antenna system (DAS).

BACKGROUND

[2] A distributed antenna system (DAS) typically includes one or more central units or nodes (also referred to here as “master units” or “MUs”) that are communicatively coupled to a plurality of remotely located radio units (RUs) (also referred to here as “remote units” or “access points”), where each RU can be coupled directly to one or more of the MUs directly or indirectly via one or more other RUs and/or via one or more intermediary or expansion units or nodes (also referred to here as “transport expansion nodes” (TENs)). A DAS is typically used to improve the coverage provided by one or more base stations that are coupled to the MUs. These base stations can be coupled to the one or more MUs via one or more cables or via a wireless connection, for example, using one or more donor antennas. The wireless service provided by the base stations can include commercial cellular service and/or private or public safety wireless communications.

[3] In general, each MU receives one or more downlink analog radio frequency (RF) signals from one or more base stations and generates one or more downlink transport signals derived from one or more of the received downlink base station signals. For each base station, the associated MU transmits one or more downlink transport signals to all of the RUs used to serve that base station. Each RU used to serve a base station receives the downlink transport signals transmitted to it from the associated MU and uses the received downlink transport signals to generate one or more downlink analog RF signals that are radiated from one or more coverage antennas associated with that RU. The downlink radio frequency signals are radiated for reception by user equipment (UEs) served by the base station. Typically, the downlink radio frequency signals associated with each base station are simulcasted from multiple RUs. In this way, the DAS increases the coverage area for the downlink capacity provided by the base station.

[4] Likewise, for each base station, each RU receives one or more uplink analog RF signals transmitted from the UEs being served by that base station. Each RU generates one or more uplink transport signals derived from the one or more uplink radio frequency signals and transmits them to the associated MU. The MU associated with the base station receives the respective uplink transport signals transmitted to it from the RUs and uses the received uplink transport signals to generate one or more uplink analog RF signals that are provided to the base station. Typically, this involves, among other things, summing uplink signals received from all of the multiple RUs used to serve the base station in order to produce the uplink analog RF signals provided to the base station. In this way, the DAS increases the coverage area for the uplink capacity provided by the base station.

[5] Traditionally, a DAS is operated in a “full simulcast” mode in which downlink signals for each base station are transmitted from all of the RUs used to serve a base station and in which uplink signals for the base station are generated by summing uplink data received from all of the RUs used to serve the base station. This full simulcast mode is traditionally used despite the fact that each UE is typically located near only a few of the RUs. Hence, it increases the burden on the MU which is typically required to sum all uplink data received from all the RUs during uplink (UL) operation. Since MU can support a limited number of RUs in a given deployment, it faces a bandwidth issue.

[6] The information disclosed in this background section is only for enhancement of understanding of the general background of the disclosure and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

SUMMARY [7] According to an aspect of the present disclosure, a method and apparatus are provided for optimizing master unit (MU) performance in a distributed antenna system (DAS).

[8] In one non-limiting embodiment of the present disclosure, a method includes receiving, by master unit (MU), from a plurality of radio units (RUs) used to serve a donor base station, a plurality of uplink data associated with reception at the plurality of RUs of uplink reference transmissions from a plurality of UEs. The uplink reference transmissions comprise sounding reference signals (SRS) transmitted by the plurality of UEs. The method further includes determining, by the MU, for each UE, respective signal reception metrics for the plurality of RUs using the plurality of uplink data. Further, the method includes comparing, by the MU, the respective signal reception metrics with signal threshold value. The method further includes determining, by the MU, for each UE, a limited RU subset among the plurality of RUs for serving a corresponding UE based on the comparison such that the respective signal reception metrics is above the signal threshold value. Further, the method includes serving at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for the corresponding UE.

[9] In another non-limiting embodiment of the present disclosure, the MU, the plurality of RUs, and the plurality of UEs are implemented in a distributed access system (DAS).

[10] In another non-limiting embodiment of the present disclosure, the method further comprises determining, by the MU, identification and scheduling information for each UE being served by the donor base station.

[HJ In another non-limiting embodiment of the present disclosure, wherein the identification and scheduling information for each UE is determined using downlink control-plane message and downlink user-plane message received from the donor base station. [12] In another non-limiting embodiment of the present disclosure, the signal reception metrics for the plurality of RUs is determined using SRS transmitted by the UE for the plurality of RUs, wherein the signal reception metric comprises at least one of a Signal -to- Noise-plus-Interference Ratio (SINR), a Received Signal Strength indicator (RSSI) or a combination thereof.

[13] In another non-limiting embodiment of the present disclosure, wherein serving at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for the corresponding UE further comprising: when serving in the downlink transmission, processing the downlink control-plane message and downlink userplane message received from the donor base station to identify downlink message intended for the corresponding UE, forwarding the downlink message to only the limited RU subset for the corresponding UE so that only the limited RU subset generates downlink RF signals received by the MU, and when serving in the uplink transmission, processing uplink controlplane messages received from the donor base station to identify uplink message intended for the corresponding UE, and forwarding the uplink message to only the limited RU subset for the corresponding UE so that only the limited RU subset receives associated uplink transmission from the corresponding UE.

[14] In another non-limiting embodiment of the present disclosure, an apparatus may comprise a memory and a circuitry in communication with the memory and configured to cause a master unit (MU) to receive, from a plurality of radio units (RUs) used to serve a donor base station, a plurality of uplink data associated with reception at the plurality of RUs of uplink reference transmissions from a plurality of UEs, wherein the uplink reference transmissions comprise sounding reference signals (SRS) transmitted by the plurality of UEs. The circuitry further causes the MU to determine, for each UE, respective signal reception metrics for the plurality of RUs using the plurality of uplink data. The circuitry further causes the MU to compare the respective signal reception metrics with signal threshold value. Further, the circuitry causes the MU to determine, for each UE, a limited RU subset among the plurality of RUs for serving a corresponding UE based on the comparison such that the respective signal reception metrics are above the signal threshold value. Further, the circuitry causes the MU to serve at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for the corresponding UE.

[15] In another non-limiting embodiment of the present disclosure, a non-transitory computer readable media stores one or more instructions which, when executed by at least one processor, cause a master unit (MU) to receive, from a plurality of radio units (RUs) used to serve a donor base station, a plurality of uplink data associated with reception at the plurality of RUs of uplink reference transmissions from a plurality of UEs, wherein the uplink reference transmissions comprise sounding reference signals (SRS) transmitted by the plurality of UEs. The one or more instructions further causes the MU to determine, for each UE, respective signal reception metrics for the plurality of RUs using the plurality of uplink data. The one or more instructions further causes the MU to compare the respective signal reception metrics with signal threshold value. Further, the one or more instructions causes the MU to determine, for each UE, a limited RU subset among the plurality of RUs for serving a corresponding UE based on the comparison such that the respective signal reception metrics is above the signal threshold value. Further, the one or more instructions causes the MU to serve at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for the corresponding UE.

[16] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF DRAWINGS

[17] Further aspects and advantages of the present disclosure will be readily understood from the following detailed description with reference to the accompanying drawings. Reference numerals have been used to refer to identical or functionally similar elements. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present disclosure wherein:

[18] Figure 1 shows an environment 100 in which the techniques of the present disclosure may be implemented, in accordance with some embodiments of the present disclosure.

[19] Figure 2 shows one example of the operation of method 200 in the environment 100 of Figure 1, in accordance with some embodiments of the present disclosure.

[20] Figure 3 shows an example 300 of SINR thresholding, in accordance with some embodiments of the present disclosure.

[21] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of the illustrative systems embodying the principles of the present disclosure. Similarly, it will be appreciated that any flowcharts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.

DETAILED DESCRIPTION

[22] In the present document, the word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or implementation of the present disclosure described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[23] While the disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will be described in detail below. It should be understood, however, that it is not intended to limit the disclosure to the particular form disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and the scope of the disclosure.

[24] The terms “comprise(s)”, “comprising”, “include(s)”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device, apparatus, system, or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or apparatus or system or method. In other words, one or more elements in a device or system or apparatus preceded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the system.

[25] The terms like “at least one” and “one or more” may be used interchangeably throughout the description. The terms like “a plurality of’ and “multiple” may be used interchangeably throughout the description. The terms like “master unit”, “master unit entity” and “MU” may be used interchangeably throughout the description. The terms like “radio unit”, “radio unit entity” and “RU” may be used interchangeably throughout the description. The terms like “network operator”, “operator”, and “service provider” may be used interchangeably throughout the description.

[26] In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration of specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense. In the following description, well known functions or constructions are not described in detail since they would obscure the description with unnecessary detail. [27] Referring now to Figure 1 which shows a block diagram illustrating an exemplary distributed antenna system (DAS) 100. In the exemplary embodiment shown in Figure 1, the DAS 100 includes one or more master units (MUs) 102 that are used to couple the DAS 100 to one or more donor base stations 104. The DAS 100 also includes a plurality of remotely located radio units (RUs) 108 (also referred to as “antenna units,” “access points,” “remote units,” or “remote antenna units”). The RUs 108 are communicatively coupled to the MUs 102.

[28] Each RU 108 includes, or is otherwise associated with, a respective set of coverage antennas 112 via which downlink analog RF signals can be radiated to user equipment (UEs) 110 and via which uplink analog RF signals transmitted by UEs 110 can be received. The DAS 100 is configured to serve each base station 104 using a respective set of RUs 108. Also, the set of RUs 108 used to serve a given base station 104 may differ from the set of RUs 108 used to serve another base station 104. The set of RUs points 108 used to serve a given base station 104 is also referred to here as the “simulcast zone” for that base station 104. In general, the wireless coverage of a base station 104 served by the DAS 100 is improved by radiating a set of downlink RF signals for that base station 104 from the coverage antennas 112 associated with one or more RUs 108 in that base station’s simulcast zone and by producing a single “combined” set of uplink base station data that is provided to that base station 104. The single combined set of uplink base station data is produced by a combining or summing process that uses inputs derived from the uplink RF signals received via the coverage antennas 112 associated with one or more of the RUs 108 in that base station’s simulcast zone.

[29] The 0-RAN Alliance promulgates a group of specifications for implementing radio access networks in an open manner. (“O-RAN” is an acronym for “Open Radio Access Network”). One set of 0-RAN specifications relates to implementing a fronthaul interface for control-plane, user-plane, synchronization-plane, and management-plane communications between a distributed unit (DU) and a radio unit (RU) used to implement a base station entity. In the example shown in Figure 1, each MU 102 is configured to communicatively couple the DAS 100 to a base station 104 using an 0-RAN fronthaul interface. This type of base station 104 is typically an 0-RAN distributed unit (DU) and is also referred to here as an 0-RAN DU 104. For each 0-RAN DU 104 served by a MU 102, the MU 102 is coupled to the 0-DU 104 using the 0-RAN digital baseband fronthaul interface that would otherwise be used to couple the 0-RAN DU 104 to an 0-RAN RU (if the DAS 100 were not being used). An 0-RAN DU 104 can be coupled to a corresponding MU 102 via a switched Ethernet network. Alternatively, an 0-RAN DU 104 can be coupled to a corresponding MU 102 via a direct Ethernet or eCPRl connection.

[30] Each MU 102 serves as an interface between each served 0-RAN DU 104 and the rest of the DAS 100 and receives downlink base station signals from, and outputs uplink base station signals to, each 0-RAN DU 104. Each MU 102 performs at least some of any conversion processing necessary to convert the base station data received from the DU 104 to and from the digital fronthaul interface format natively used in the DAS 100. The downlink and uplink base station data communicated between each O-RAN DU 104 and the MU 102 comprise downlink and uplink fronthaul data generated and formatted in accordance with the 0-RAN baseband fronthaul interface, where the user-plane data comprises frequency-domain baseband IQ data. Also, in this example, the digital fronthaul interface format natively used in the DAS 100 for communicating 0-RAN fronthaul data is the same O-RAN fronthaul interface used for communicating base station signals between each O-RAN DU 104 and the MU 102, and the “conversion” performed by each MU 102 (and/or one or more other entities of the DAS 100) includes performing any needed “multicasting” of the downlink data received from each O-RAN DU 104 to one or more of the RUs 108 in a simulcast zone for that O-RAN DU 104 (for example, by communicating the downlink fronthaul data to an appropriate multicast address and/or by copying the downlink fronthaul data for communication over different fronthaul links) and performing any need combining or summing of the uplink data received from the RUs 108 to produce combined uplink data provided to the O-RAN DU 104. It is to be understood that other digital fronthaul interface formats can also be used.

[31] In general, each base station 104 is configured to communicate with a core network (not shown) of the associated wireless operator using an appropriate backhaul network (typically, a public wide area network such as the Internet). Also, base stations 102 from multiple, different wireless operators may be used with the DAS 100 and/or base stations 102 supporting multiple, different wireless protocols and/or RF bands may be used with the DAS 100.

[32] In one implementation, one of the units of the DAS 100 is also used to implement a “master” timing entity for the DAS 100 (for example, such a master timing entity can be implemented as a part of a MU 102). In another example, a separate, dedicated timing master entity (not shown) is provided within the DAS 100. In either case, the master timing entity synchronizes itself to an external timing master entity (for example, a timing master associated with one or more of the O-RAN-DUs 104) and, in turn, that entity serves as a timing master entity for the other units of the DAS 100. A time synchronization protocol (for example, the Institute of Electrical and Electronics Engineers (IEEE) 1588 Precision Time Protocol (PTP), the Network Time Protocol (NTP), or the Synchronous Ethernet (SyncE) protocol) can be used to implement such time synchronization. A management system (not shown) can be used to manage the various nodes of the DAS 100.

[33] Each base station 104 (including each 0-RAN DU 104), master unit 102, RU 108, and any of the specific features described here as being implemented thereby, can be implemented in hardware, software, or combinations of hardware and software, and the various implementations (whether hardware, software, or combinations of hardware and software) can also be referred to generally as “circuitry,” a “circuit,” or “circuits” that are configured to implement at least some of the associated functionality. When implemented in software, such software can be implemented in software or firmware executing on one or more suitable programmable processors (or other programmable device) or configuring a programmable device (for example, processors or devices included in or used to implement special-purpose hardware, general-purpose hardware, and/or a virtual platform). In such a software example, the software can comprise program instructions that are stored (or otherwise embodied) on or in an appropriate non-transitory storage medium or media (such as flash or other non-volatile memory, magnetic disc drives, and/or optical disc drives) from which at least a portion of the program instructions are read by the programmable processor or device for execution thereby (and/or for otherwise configuring such processor or device) in order for the processor or device to perform one or more functions described here as being implemented the software. Such hardware or software (or portions thereof) can be implemented in other ways (for example, in an application specific integrated circuit (ASIC), etc.). Such entities can be implemented in other ways.

[34J The DAS 100 can be implemented in a virtualized manner or a non-virtualized manner. When implemented in a virtualized manner, one or more nodes, units, or functions of the DAS 100 are implemented using one or more virtual network functions (VNFs) executing on one or more physical server computers (also referred to here as “physical servers” or just “servers”) (for example, one or more commercial-off-the-shelf (COTS) servers of the type that are deployed in data centers or “clouds” maintained by enterprises, communication service providers, or cloud services providers). More specifically, in the exemplary embodiment shown in Figure 1, each master unit 102 is implemented as a VNF running on a server. The server can execute other VNFs that implement other functions for the DAS 100 (for example, other fronthaul, management plane, and synchronization plane functions).

[35] In the exemplary embodiment shown in Figure 1, the MUs 102 and RUs 108 are communicatively coupled to one another via a switched Ethernet network 106. Also, in the exemplary embodiment shown in Figure 1, an O-RAN DU 104 can be coupled to a corresponding MU 102 via the same switched Ethernet network 106 used for communication within the DAS 100 (though each O-RAN DU 104 can be coupled to a corresponding MU 102 in other ways). In the exemplary embodiment shown in Figure 1, the downlink and uplink transport data communicated between the units of the DAS 100 is formatted as O-RAN data that is communicated in Ethernet packets over the switched Ethernet network 106.

[36] According to an embodiment of Figure 1, a technique is disclosed to improve the efficiency of the MU 102 (and the DAS 100 more generally) so that it can serve more RUs 108 using a given hardware configuration. Figure 1 shows an uplink (UL) usage scenario for the DAS 100 in which the MU 102 handles UL signals transmitted from one of the UEs 110 for ultimate reception by donor BS 104. For simplicity and explanation, only one MU and eight RUs are shown in Fig. 1. However, it will be appreciated by a person skilled in the art that there can be a different number of MUs and RUs implemented in the DAS 100.

[37] In the example shown in Figure 1, the donor base station 104 (that is, the O-RAN DU 104) is served by eight RUs 108 (individually referenced in Figure 1 as RU1, RU2, . . . RU8). That is, in the example shown in Figure 1, the simulcast zone for the donor base station 104 includes the eight RUs RU1-RU8. However, although the donor base station 104 includes eight RUs 108 in its simulcast zone, only a few RUs 108 will have high signal strength with any given UE 110.

[38] As noted above, the O-RAN fronthaul interface is used for coupling the donor base station 104 to the MU 102 and for communications between the MU 102 and the RUs 108 over the DAS 100. In general, for each slot, the donor O-RAN DU 104 sends to the RUs 108 respective control-plane messages providing scheduling and configuration information. Among other things, the control-plane message identifies which resource blocks have been scheduled for use in wirelessly transmitting over the air interface. Also, for each slot, the donor O-RAN DU 104 sends to the RU 108 respective downlink user-plane messages providing baseband IQ data for the resource blocks scheduled on the downlink physical channels, and the RU 108 generates and sends uplink user-plane messages to the donor O- RAN DU 104 providing baseband IQ data for the resource blocks scheduled for use on the uplink physical channels and Sounding Reference Signals (SRSs) and providing baseband IQ data for the physical random access channel (PRACH). As explained in more detail below, the MU 102 uses the uplink control-plane and user-plane messages related to SRS signals for a given UE 110 in order to improve the operation of the DAS 100 in connection with serving that UE 110. [39] SRS signals have a defined periodicity. In each SRS opportunity, SRS signals for a maximum of 16 UEs can be multiplexed using distinguished cyclic shifts. In other words, 16 different UEs can transmit a respective SRS Signal in one SRS opportunity. In the following table, the SRS Periodicity/Window is “8” and the comb provided in each SRS periodicity is “2”, and the number of UEs multiplexed is “16”.

[40] From the above table it can be observed that a total of 16 UEs can transmit respective SRS signals when the donor base station 104 is configured as noted above. By analyzing how each SRS Opportunity is configured (for example, based on the associated uplink control -plane messages communicated from the donor base station 104), the MU 102 can derive the number of UEs 110 scheduled for transmitting SRS signals in each SRS opportunity (that is, the capacity of the donor BS 104 for supporting the UEs 110 or active UE 110 connections at a given point of time).

[41] Now in the first SRS opportunity, MU 102 will receive 8 UL signals from all the 8 RUs 108 (RU1-RU8) for a particular UE 110 during the UL operation. The MU 102 uses this opportunity to determine the signal strength of each of the 8 UL signals transmitted by all the 8 RUs 108 (RU1-RU8).

[42] Figure 2 is a flow diagram illustrating one embodiment of a method 200 of improving the performance of a DAS. The embodiment of method 200 is described here as being implemented in the DAS 100 of Figure 1, though it is to be understood that other embodiments can be implemented in other ways. Method 200 is performed, in this example, by the MU 102.

[43] The method 200 includes, at block 202, determining identification and scheduling information for each active UE 110 served by the donor base station 104. As a part of doing this, the MU 102 acts as a “pseudo” UE entity and performs at least some of the receiver processing that would be performed in a UE using the downlink control-plane and userplane messages received from the donor DU 104. As noted above, the downlink controlplane and user-plane messages are used by the RUs 108 in order to generate the downlink analog RF signals that are radiated from the coverage antennas 112 for reception by the UEs 110. The MU 102 can act as a “pseudo” or “virtual” UE entity and process the received control-plane and user-plane messages in order to decode information used to identify the active UEs 110 within the control-plane and user-plane messages communicated to and from the donor DU 104. This can include, for example, identifying UE identifiers used in the control-plane and user-plane messages communicated to and from the ORAN-DU 104. For example, the pseudo UE entity in the MU 102 can be configured to process the received control-plane and user-plane messages in order to decode information such as any Synchronization Signal Block (SSB), Master Information Block (MIB), System Information Block Type 1 (SIB1), System Information Block Type 2 (SIB2), and Radio Resource Control (RRC) messages that are being communicated to the UEs 110 via the air interface. Also, the pseudo UE entity in the MU 102 can be configured to determine when each active UE 110 is scheduled to receive and transmit downlink and uplink transmissions, respectively, (including the uplink reference transmissions that are used for the localization processing described below in connection with blocks 204-208).

[44] The method 200 includes, at block 204, receiving, from all of the RUs 108 used to serve the donor base station 104, respective uplink data associated with the reception at all of the RUs 108 of uplink reference transmissions from the UEs 110. In the exemplary embodiment described here in connection with Figure 2, the uplink reference transmissions comprise SRS signals wirelessly transmitted by the UEs 110. In this exemplary embodiment, the MU 102 is configured to determine when each active UE 110 is scheduled to transmit uplink reference transmissions and which uplink user-plane messages communicated from the RUs 108 contain baseband IQ data for the scheduled uplink reference transmissions. In this exemplary embodiment, the DAS 100 is configured so that all of the RUs 108 in the simulcast zone for the donor base station 104 receive these uplink reference transmissions (that is, the SRS signals) via the coverage antennas 112 associated with the RUs 108 and generate, for each of the coverage antennas 112 associated with each RU 108, baseband IQ data for any resource blocks that are scheduled for transmitting the uplink reference transmissions. This baseband IQ data is communicated to the MU 102 from all of the RUs 108 over the switched Ethernet network 106 in uplink user-plane messages. In addition to any “normal” uplink processing of the baseband IQ data for uplink reference transmissions (that is, combining the baseband IQ data received from one or more of the RUs 108 for each antenna port to produce combined baseband IQ data and communicating the combined baseband IQ data to the donor base station 104 in respective uplink user-plane messages), the MU 102 also uses the baseband IQ data for the uplink reference transmission for the localization processing described below in connection with blocks 206-208.

[45] At block 206, the method 200 includes determining, for each active UE 110, respective signal reception metrics for all of the RUs 108 in the simulcast zone of the donor base station 104 using the uplink data associated with the reception at all of the RUs 108 of the uplink transmissions from that UE 110. In the embodiment described here in connection with Figure 2, for each RU 108 in the simulcast zone of the donor base station 104, the MU 102 uses the baseband IQ data for one or more of the UE’s SRS transmissions received from that RU 108 in order to determine a signal reception metric for that RU 108. For example, the signal reception metric may comprise, be determined using, or otherwise be based on, a Signal-to-Noise-plus-Interference Ratio (SINR) or Received Signal Strength indicator (RSSI) or combination thereof. The signal reception metric may comprise, be determined using, or otherwise be based on, other data related to the uplink reference transmission (for example, the transmit power of the SRS transmission and/or stored “ideal” or “reference” data for the SRS transmission). Other signal reception metrics can be determined.

[46] At block 208, the method 200 includes determining, for each active UE 110, a respective limited subset of the RUs 108 in the simulcast zone of the donor base station 104 for serving that UE 100, where this determination is performed as a function of the respective signal reception metrics determined for that UE 10 for all of the RUs 108 in the simulcast zone of the donor base station 104. The respective “limited” subset of the RUs 108 for each active UE 110 includes less than all of the RUs 108 included in the simulcast zone of the donor base station 104 and is also referred to here as the respective “limited RU subset” for each active UE 100. Because each UE 110 will experience different RF conditions relative to the various RUs 108 in the simulcast zone of the donor base station 104 (for example, due to the UE 110 likely being physically closer to some RUs 108 and farther away from other RUs 108 and/or experiencing different types or degrees of channel impairment in connection with the various RUs 108), the signal reception metrics determined for the uplink reference transmissions from the UE 110 (that is, SRS signals transmitted from the UE 110 in this example) will vary from RU 108 to RU 108.

[47] The respective limited subset of the RUs 108 for a given UE 110 includes only those RUs 108 that have relatively “good” or “strong” signal reception metrics associated therewith and does not include those RUs 108 that have relatively “bad” or “weak” signal reception metrics associated therewith. This determination can be made, for given UE 110, by comparing the signal reception metrics determined for the RUs 108 to a signal threshold value and including in the UE’ s respective limited RU subset only those RUs 108 having an associated signal reception metric that exceeds the signal threshold value.

[48] For example, in the example illustrated in Figure 1, one UE 110 is shown as transmitting an uplink reference transmission (that is, an SRS signal). Due the location of that UE 110, the signal reception metric (illustrated using dotted lines) determined for RU1, RU2, RU3, RU4, RU7, and RU8 based on the uplink reference transmission from that UE 110 will be below the signal threshold value whereas the signal reception metric (illustrated using solid lines) determined for RU5 and RU6 will be above the signal threshold value. As a result, the limited RU subset determined for that UE 110 based on those signal reception metrics will include only RU5 and RU6 and will not include RU1, RU2, RU3, RU4, RU7, or RU8.

[49] Also, because the RF conditions experienced by each UE 110 relative to the RUs 108 in the simulcast zone will tend to vary over time (for example, due to movement of the UE 110 or changes in the RF environment), the processing associated with method 200 can be repeated for each UE 110 over time in order to update the respective limited subset of RUs 108 used for the UE 110. Figure 3 illustrates one example of how the limited RU subset of a given UE can change over time. In the example shown in Figure 3, a UE is generally in the vicinity of four of the RUs 108 shown in Figure 1 - RU1, RU2, RU3, and RU4. In this example, the uplink reference transmissions comprise SRS signals, and the signal reception metric that is determined for the uplink reference transmissions comprises a SINR value. In the example illustrated in Figure 3, initially (at time = 0), the UE is located closest to RU1 and the determined signal reception metrics for the uplink reference transmissions from that UE for the RUs are ranked in the following order (from highest signal reception metric to the lowest signal strength): RU1, RU2, RU3, and then RU4. At this point in time, only the determined signal reception metrics for RUl, RU2, and RU3 are above the signal threshold value (1 dBm in this example) and, therefore, only RU1, RU2, and RU3 are included in the limited RU subset for that UE at that time. Then, the UE begins to move towards RU4.

[50] As noted above, the processing associated with method 200 is repeated periodically in order to update the determined signal reception metrics for the UE and the respective limited RU subset used for the UE. As the UE moves towards RU4 and away from RU1, at time at some point between time = 100 and time = 120, the UE will have moved sufficiently far away from RU1 so that the determined signal reception metric for RU1 will decrease sufficiently to be below the signal threshold value and, as a result, the RU1 will be removed from the limited RU subset for the UE (that is, the limited RU subset for the UE includes only RU2, RU3, and RU4).

[51] In the exemplary embodiment described here in connection with Figures 1 and 2, the MU 102 makes the determination of the limited subset of RUs 108 for each active UE 110. The manner and frequency of the determination of the limited subset of RUs 108 for each active UE 110 can be configurable, for example, to accommodate different types of DAS deployments and/or UE mobility profiles. For example, in indoor or campus deployments (such as buildings, stadiums, and arenas), the mobility of the UEs 110 is typically relatively minimal, whereas in outdoor deployments near train tracks or highways the mobility of the UEs 110 is typically relatively high. The DAS 100 can be configured to repeat the processing associated with method 200 (to determine a new, updated limited subset of RUs 108 for each UE 110) more frequently in deployments where UE 110 mobility is relatively high and less frequently in deployments where UE mobility is relatively low.

[52] The DAS 100 can be configured to determine the size and content of the respective limited subset of RUs 108 as a function of the degree and nature of UE 110 mobility in the DAS deployment. For example, in deployments where UE mobility is relatively low, the DAS 100 can be configured to include no more than two or three RUs 108 in the limited subset and/or use a relatively high threshold value, whereas in deployments where UE 110 mobility is relatively high, the DAS 100 can be configured to include a relatively higher number of RUs 108 in the limited subset and, also, can be configured to determine the primary direction of travel of the UE 110 and include more RUs 108 associated with the direction of travel (for example, by determining for which RUs 108 the associated signal reception metrics have recently increased and for which RUs 108 the associated signal reception metrics have recently decreased (and the rate at which such changes are occurring) and including more of the former RUs 108 and less of the latter RUs 108 in the limited subset of RUs 108 for the associated UE 110).

[53] The processing associated with blocks 206 and 208 can be performed using machine learning (ML) or artificial intelligence (Al). For example, the DAS 100 (and/or an entity external to the DAS 110 such a Service Management and Orchestration (SMO) or RAN Intelligent Controller (RIC)) can track performance parameters related to serving the UEs 110 using each limited RU subset and the ML/AR algorithms can use such information in refining the subset-determination process.

[54] At block 210, the method 200 includes serving at least some downlink and/or uplink transmissions for each active UE 110 using the respective limited RU subset determined for that UE 110. In the exemplary embodiment described here in connection with Figure 2, the respective limited RU subset is used by the DAS 100 to serve each active UE 110 downlink and uplink transmissions that are specific to that UE 110 other than the uplink reference and PRACH transmissions. For example, in this exemplary embodiment, the respective limited RU subset for a given UE 100 is used by the DAS 100 to serve user-specific Physical Uplink Shared Channel (PUSCH), Physical Uplink Control Channel (PUCCH), Physical Downlink Shared Channel (PDSCH), and Physical Downlink Control Channel (PDCCH) transmissions to the UE 110. Other downlink and uplink transmissions can be served by the DAS 100 using all of the RUs 108 in the simulcast zone of the donor base station 104. In this exemplary embodiment, all of the RUs 108 are used to serve the other downlink and uplink transmissions — for example, common downlink transmissions (such as SSB, cell specific reference signal (CSRS), tracking reference signal (TRS) transmissions) and uplink PRACH and reference transmissions (such as PRACH, SRS, and TRS transmissions).

[55] For example, in the example illustrated in Figure 1, where the respective limited RU subset determined for the one UE 110 shown as transmitting an uplink reference transmission includes only RU5 and RU6, only RU5 and RU6 are used by the DAS 100 serve the UE 100 such user-specific downlink and uplink transmissions and RU1, RU2, RU3, RU4, RU7, and RU8 are not used to do so and are “muted” for such transmissions.

[56] When a limited RU subset is used by the DAS 100 to serve a UE 110 a downlink transmission, the downlink control-plane messages and downlink user-plane messages associated with that transmission are received from the donor base station 104, processed by the MU 102 (for example, to identify that those messages are intended for the UE 110 and are of a type for which the limited RU subset is to be used), and forwarded on to only those RUs 108 in the limited RU subset for that UE 110. As a result, only the RUs 108 in the limited RU subset for that UE 110 will generate downlink RF signals for wireless transmission from the coverage antennas 112 associated with those RUs 108 and the other RUs 108 not included in the limited RU subset for that UE 110 will not do this and, instead, are “muted” for those downlink transmissions.

[57] When a limited RU subset is used by the DAS 100 to serve a UE 110 an uplink transmission, the uplink control-plane messages associated with that transmission are received from the donor base station 104, processed by the MU 102 (for example, to identify that those messages are intended for the UE 110 and are of a type for which the limited RU subset is to be used), and forwarded on to only those RUs 108 in the limited RU subset for that UE 110. Only the RUs 108 in the limited RU subset for that UE 110 will receive the uplink control-plane messages. As a result, only the RUs 108 in the limited RU subset for that UE 110 will receive the associated uplink transmission via the coverage antennas 112 associated with the RUs 108, generate, for each of the coverage antennas 112 associated with each RU 108, baseband IQ data for any resource blocks that are scheduled for transmitting that uplink transmission, and communicate the baseband IQ data to the MU 102 over the switched Ethernet network 106 in uplink user-plane messages. The other RUs 108 not included in the limited RU subset for the UE 110 will not do this and, instead, are “muted” for those uplink transmissions. The MU 102 will perform the “normal” uplink processing of the uplink user-plane messages received from only the RUs 108 in the limited RU subset for that UE 110 for that uplink transmission (that is, the MU 102 will combine the baseband IQ data for each antenna port communicated in the uplink user-plane messages in order to produce combined baseband IQ data for the uplink transmission and communicate the combined baseband IQ data to the donor base station 104 in respective uplink user-plane messages).

[58] As used herein, a phrase referring to “at least one” or “one or more” of a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c. The terms “a”, “an” and “the” mean “one or more”, unless expressly specified otherwise.

[59] The terms “an embodiment”, “embodiment”, “embodiments”, “the embodiment”, “the embodiments”, “one or more embodiments”, “some embodiments”, and “one embodiment”, “other embodiment”, “yet another embodiment”, “non-limiting embodiment” mean “one or more (but not all) embodiments of the disclosure(s)” unless expressly specified otherwise.

[60] The terms “including”, “comprising”, “having” and variations thereof mean “including but not limited to”, unless expressly specified otherwise. [61] The enumerated listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise.

[62] A description of an embodiment with several components in communication with each other does not imply that all such components are required. On the contrary, a variety of optional components are described to illustrate the wide variety of possible embodiments of the disclosed methods and systems.

[63] Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the disclosure be limited not by this detailed description, but rather by any claims that issue on an application based here on. Accordingly, the embodiments of the present disclosure are intended to be illustrative, but not limiting, of the scope of the disclosure, which is set forth in the appended claims.

EXEMPLARY EMBODIMENTS

[64] Example 1 includes a method comprising: receiving, by the MU, from a plurality of radio units (RUs) used to serve a donor base station, a plurality of uplink data associated with reception at the plurality of RUs of uplink reference transmissions from a plurality of UEs, wherein the uplink reference transmissions comprise sounding reference signals (SRS) transmitted by the plurality of UEs; determining, by the MU, for each UE, respective signal reception metrics for the plurality of RUs using the plurality of uplink data; comparing, by the MU, the respective signal reception metrics with a signal threshold value; determining, by the MU, for each UE, a limited RU subset among the plurality of RUs for serving a corresponding UE based on the comparison such that the respective signal reception metrics is above the signal threshold value; and serving at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for the corresponding UE. [65] Example 2 includes the method of Example 1, wherein the MU, the plurality of RUs, and the plurality of UEs are implemented in a distributed access system (DAS).

[66] Example 3 includes the method of any of Examples 1-2, comprising determining, by the MU, identification and scheduling information for each UE being served by the donor base station.

[67] Example 4 includes the method of Example 3, wherein the identification and scheduling information for each UE is determined using downlink control-plane message and downlink user-plane message received from the donor base station.

[68] Example 5 includes the method of any of Examples 1-4, wherein the signal reception metrics for the plurality of RUs is determined using SRS transmitted by the UE for the plurality of RUs, wherein the signal reception metric comprises at least one of a Signal -to- Noise-plus-Interference Ratio (SINR), a Received Signal Strength indicator (RSSI) or a combination thereof.

[69] Example 6 includes the method of any of Examples 1 -5, wherein serving at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for the corresponding UE further comprising: when serving in the downlink transmission, processing the downlink control-plane message and downlink user-plane message received from the donor base station to identify downlink message intended for the corresponding UE; and forwarding the downlink message to only the limited RU subset for the corresponding UE so that only the limited RU subset generates downlink RF signals received by the MU; and when serving in the uplink transmission, processing uplink controlplane messages received from the donor base station to identify uplink message intended for the corresponding UE; and forwarding the uplink message to only the limited RU subset for the corresponding UE so that only the limited RU subset receives associated uplink transmission from the corresponding UE. [70] Example 7 includes an apparatus comprising: a memory; and circuitry in communication with the memory and configured to cause a master unit (MU) to: receive, from a plurality of radio units (RUs) used to serve a donor base station, a plurality of uplink data associated with reception at the plurality of RUs of uplink reference transmissions from a plurality of UEs, wherein the uplink reference transmissions comprise sounding reference signals (SRS) transmitted by the plurality of UEs; determine, for each UE, respective signal reception metrics for the plurality of RUs using the plurality of uplink data; compare the respective signal reception metrics with signal threshold value; determine, for each UE, a limited RU subset among the plurality of RUs for serving a corresponding UE based on the comparison such that the respective signal reception metrics is above the signal threshold value; and serve at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for the corresponding UE.

[71] Example 8 includes the apparatus of Example 7, wherein the MU, the plurality of RUs, and the plurality of UEs are implemented in a distributed access system (DAS).

[72] Example 9 includes the apparatus of any of Examples 7-8, wherein the circuitry further causes the MU to determine identification and scheduling information for each UE being served by the donor base station.

[73] Example 10 includes the apparatus of Example 9, wherein the circuitry further causes the MU to determine the identification and the scheduling information for each UE using downlink control-plane message and downlink user-plane message received from the donor base station.

[74] Example 11 includes the apparatus of any of Examples 7-10, wherein the circuitry causes the MU to determine the signal reception metrics for the plurality of RUs is using SRS transmitted by the UE for the plurality of RUs, wherein the signal reception metric comprises at least one of a Signal-to-Noise-plus-Interference Ratio (SINR), a Received Signal Strength indicator (RSSI) or a combination thereof. [75] Example 12 includes the apparatus of any of Examples 7-11, wherein for serving at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for the corresponding UE, the circuitry further causes the MU to: when serving in the downlink transmission, process the downlink control-plane message and downlink user-plane message received from the donor base station to identify downlink message intended for the corresponding UE; and forward the downlink message to only the limited RU subset for the corresponding UE so that only the limited RU subset generates downlink RF signals received by the MU; and when serving in the uplink transmission, process uplink control-plane messages received from the donor base station to identify uplink message intended for the corresponding UE; and forward the uplink message to only the limited RU subset for the corresponding UE so that only the limited RU subset receives associated uplink transmission from the corresponding UE.

[76] Example 13 includes a non-transitory computer readable media storing one or more instructions which, when executed by at least one processor, cause a master unit (MU) to: receive, from a plurality of radio units (RUs) used to serve a donor base station, a plurality of uplink data associated with reception at the plurality of RUs of uplink reference transmissions from a plurality of UEs, wherein the uplink reference transmissions comprise sounding reference signals (SRS) transmitted by the plurality of UEs; determine, for each UE, respective signal reception metrics for the plurality of RUs using the plurality of uplink data; compare the respective signal reception metrics with signal threshold value; determine, for each UE, a limited RU subset among the plurality of RUs for serving a corresponding UE based on the comparison such that the respective signal reception metrics is above the signal threshold value; and serve at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for that UE.

Claims

1. A method comprising: receiving, by the MU, from a plurality of radio units (RUs) used to serve a donor base station, a plurality of uplink data associated with reception at the plurality of RUs of uplink reference transmissions from a plurality of UEs, wherein the uplink reference transmissions comprise sounding reference signals (SRS) transmitted by the plurality of UEs; determining, by the MU, for each UE, respective signal reception metrics for the plurality of RUs using the plurality of uplink data; comparing, by the MU, the respective signal reception metrics with a signal threshold value; determining, by the MU, for each UE, a limited RU subset among the plurality of RUs for serving a corresponding UE based on the comparison such that the respective signal reception metrics is above the signal threshold value; and serving at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for the corresponding UE.

2. The method of claim 1, wherein the MU, the plurality of RUs, and the plurality of UEs are implemented in a distributed access system (DAS).

3. The method of claim 1, comprising determining, by the MU, identification and scheduling information for each UE being served by the donor base station.

4. The method of claim 3, wherein the identification and scheduling information for each UE is determined using downlink control-plane message and downlink user-plane message received from the donor base station.

5. The method of claim 1, wherein the signal reception metrics for the plurality of RUs is determined using SRS transmitted by the UE for the plurality of RUs, wherein the signal reception metric comprises at least one of a Signal-to-Noise-plus-Interference Ratio (SINR), a Received Signal Strength indicator (RSSI) or a combination thereof.

6. The method of claim 1, wherein serving at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for the corresponding UE further comprising: when serving in the downlink transmission, processing the downlink control-plane message and downlink user-plane message received from the donor base station to identify downlink message intended for the corresponding UE; and forwarding the downlink message to only the limited RU subset for the corresponding UE so that only the limited RU subset generates downlink RF signals received by the MU; and when serving in the uplink transmission, processing uplink control-plane messages received from the donor base station to identify uplink message intended for the corresponding UE; and forwarding the uplink message to only the limited RU subset for the corresponding UE so that only the limited RU subset receives associated uplink transmission from the corresponding UE.

7. An apparatus comprising: a memory; and circuitry in communication with the memory and configured to cause a master unit (MU) to: receive, from a plurality of radio units (RUs) used to serve a donor base station, a plurality of uplink data associated with reception at the plurality of RUs of uplink reference transmissions from a plurality of UEs, wherein the uplink reference transmissions comprise sounding reference signals (SRS) transmitted by the plurality of UEs; determine, for each UE, respective signal reception metrics for the plurality of RUs using the plurality of uplink data; compare the respective signal reception metrics with signal threshold value; determine, for each UE, a limited RU subset among the plurality of RUs for serving a corresponding UE based on the comparison such that the respective signal reception metrics is above the signal threshold value; and serve at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for the corresponding UE.

8. The apparatus of claim 7, wherein the MU, the plurality of RUs, and the plurality of UEs are implemented in a distributed access system (DAS).

9. The apparatus of claim 7, wherein the circuitry further causes the MU to determine identification and scheduling information for each UE being served by the donor base station.

10. The apparatus of claim 9, wherein the circuitry further causes the MU to determine the identification and the scheduling information for each UE using downlink control-plane message and downlink user-plane message received from the donor base station.

11. The apparatus of claim 7, wherein the circuitry causes the MU to determine the signal reception metrics for the plurality of RUs is using SRS transmitted by the UE for the plurality of RUs, wherein the signal reception metric comprises at least one of a Signal -to- Noise-plus-Interference Ratio (SINR), a Received Signal Strength indicator (RSSI) or a combination thereof.

12. The apparatus of claim 7, wherein for serving at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for the corresponding UE, the circuitry further causes the MU to: when serving in the downlink transmission, process the downlink control-plane message and downlink user-plane message received from the donor base station to identify downlink message intended for the corresponding UE; and forward the downlink message to only the limited RU subset for the corresponding UE so that only the limited RU subset generates downlink RF signals received by the MU; and when serving in the uplink transmission, process uplink control-plane messages received from the donor base station to identify uplink message intended for the corresponding UE; and forward the uplink message to only the limited RU subset for the corresponding UE so that only the limited RU subset receives associated uplink transmission from the corresponding UE.

13. A non-transitory computer readable media storing one or more instructions which, when executed by at least one processor, cause a master unit (MU) to: receive, from a plurality of radio units (RUs) used to serve a donor base station, a plurality of uplink data associated with reception at the plurality of RUs of uplink reference transmissions from a plurality of UEs, wherein the uplink reference transmissions comprise sounding reference signals (SRS) transmitted by the plurality of UEs; determine, for each UE, respective signal reception metrics for the plurality of RUs using the plurality of uplink data; compare the respective signal reception metrics with signal threshold value; determine, for each UE, a limited RU subset among the plurality of RUs for serving a corresponding UE based on the comparison such that the respective signal reception metrics is above the signal threshold value; and serve at least one of downlink transmission and uplink transmissions for each UE using the limited RU subset determined for that UE.