Controlling transmission of uplink reference signals

Abstract

It is provided a method for controlling transmission of uplink reference signals (20) by a plurality of user equipments, UEs (2, 2', 2"). The method being performed by a reference signal controller (1). The method comprises: determining (40) a UE group (5) comprising a plurality of UEs (2, 2', 2") that are in the same area; selecting (42) at least one UE in the UE group (5) to be a selected UE (2'), and wherein the remaining UEs are excluded UEs (2"); controlling (46) the excluded UEs (2") to decrease their frequency of signalling uplink reference signals (20); utilizing (48), for each excluded UE (2"), respective measurements of previously received reference signals (20); determining (50) that uplink signalling reference signals from the at least one selected UE (2') have changed more than a threshold amount; and triggering (52) the excluded UEs (2") to transmit a new uplink reference signal (20).

Description

CONTROLLING TRANSMISSION OF UPLINK REFERENCE SIGNALSTECHNICAL FIELD

[0001] The present disclosure relates to the field of controlling transmission of uplink reference signals by a plurality of user equipments.BACKGROUND

[0002] Beamforming is a key feature in 5G (fifth generation) communication networks and as well as for future networks, such as 6G (sixth generation) communication networks. Beamforming enhances network performance by focusing transmission and reception of signals in specific directions, thereby increasing the efficiency of data transmission and reducing interference. This directional focus is achieved by using uplink (UL) reference signals, such as the sounding reference signal (SRS), which can be used to gain information about the channel conditions between the user equipment (UE) and the radio network node.

[0003] The uplink SRS is thus utilised to calculate channel estimates and determine the beamforming weights, which are subsequently used to direct the power towards the UE in an efficient manner. Accurate channel estimation is vital for optimising the beamforming, as it allows the network to adapt to a dynamic radio environment.

[0004] UL SRS can be scheduled using both periodic and aperiodic transmission schemes. Periodic SRS is transmitted at regular intervals, providing consistent updates on the channel conditions, while aperiodic SRS is transmitted based on specific events or triggers, offering a more flexible approach to resource allocation. Nevertheless, both periodic and a-periodic SRS transmissions consume valuable SRS resources, which are inherently limited within the network. Furthermore, each transmission of an SRS signal uses power in the UE, which can be of concern over time, especially for battery-operated UEs.

[0005] Given the limited capacity for SRS resources and the power constraints of UEs, it is known to reduce the frequency of SRS transmissions by the UEs. While this method can effectively decrease the consumption of SRS resources and conserve UE power, reduced transmission frequency can lead to outdated channel information,which in turn can degrade the performance of beamforming and other network functions that rely on accurate channel state information.

[0006] Consequently, there is a need for a solution for reducing the number of reference signal transmissions without compromising the frequency of reference signal transmissions. Such a method would allow the network to maintain high-performance beamforming and other associated functions, while efficiently managing the limited SRS resources and conserving power consumption in the UEs.SUMMARY

[0007] One object is to reduce the number of reference signal transmissions without compromising the frequency of these transmissions.

[0008] According to a first aspect, it is provided a method for controlling transmission of uplink reference signals by a plurality of user equipments, UEs, the method being performed by a reference signal controller being connected to a radio network node. The method comprises: determining a UE group comprising a plurality of UEs that are in the same area; selecting at least one UE in the UE group to be a selected UE, wherein the one or more UEs in the UE group that are not selected are excluded UEs; controlling the excluded UEs to decrease their frequency of signalling uplink reference signals; utilizing, for each excluded UE, respective measurements of previously received reference signals; determining that uplink signalling reference signals from the at least one selected UE have changed more than a threshold amount; and triggering the excluded UEs to transmit a new uplink reference signal.

[0009] The controlling the excluded UEs may comprise controlling the excluded UEs to suspend transmitting uplink reference signals until activated again.

[0010] The same area may be defined, at least partly, that the UEs in the UE group belong to the same set of one or more contiguous beams from the radio network node, wherein the set of one or more contiguous beams is a strict subset of all available beams.[oon] The same area may be defined, at least partly, as an area of a predetermined size, and / or that a largest distance between UEs in the UE group is smaller than a threshold distance.

[0012] The determining a UE group may comprise determining that the each one of the plurality of UEs is stationary.

[0013] The selecting at least one UE may be reperformed to deselect the previous at least one selected UE and instead select another one of the UEs in the UE group, after which the remainder of the method is repeated.

[0014] The selecting one UE may be repeated according to a round-robin scheme.

[0015] The selecting at least one UE may be based on at least one of rank for the UE, modulation and coding scheme for the UE, size of downlink data buffer for the UE, location of the UE in the UE group.

[0016] The uplink reference signal may be a sounding reference signal, SRS.

[0017] The method may further comprise: controlling the at least one selected UE to increase its frequency of signalling uplink reference signals.

[0018] According to a second aspect, it is provided a reference signal controller for controlling transmission of uplink reference signals by a plurality of user equipments, UEs, the reference signal controller being connectable to a radio network node. The reference signal controller comprises: processing circuitry; and memory circuitry storing instructions that, when executed by the processing circuitry, cause the reference signal controller to: determine a UE group comprising a plurality of UEs that are in the same area; select at least one UE in the UE group to be a selected UE, wherein the one or more UEs in the UE group that are not selected are excluded UEs; control the excluded UEs to decrease their frequency of signalling uplink reference signals; utilize, for each excluded UE, respective measurements of previously received reference signals; determine that uplink signalling reference signals from the at least one selected UE have changed more than a threshold amount; and trigger the excluded UEs to transmit a new uplink reference signal.

[0019] The instructions to control the excluded UEs may comprise instructions that, when executed by the processing circuitry, cause the reference signal controller to control the excluded UEs to suspend transmitting uplink reference signals until activated again.

[0020] The same area may be defined, at least partly, that the UEs in the UE group belong to the same set of one or more contiguous beams from the radio network node, wherein the set of one or more contiguous beams is a strict subset of all available beams.

[0021] The same area may be defined, at least partly, as an area of a predetermined size, and / or that a largest distance between UEs in the UE group is smaller than a threshold distance.

[0022] The instructions to determine a UE group may comprise instructions that, when executed by the processing circuitry, cause the reference signal controller to determine that the each one of the plurality of UEs is stationary.

[0023] The reference signal controller may further comprise instructions that, when executed by the processing circuitry, cause the reference signal controller to repeat the instructions to select one UE is to deselect the previous at least one selected UE and instead select another at least one of the UEs in the UE group, after which the remainder of the instructions are repeated.

[0024] The reference signal controller may further comprise instructions that, when executed by the processing circuitry, cause the reference signal controller to repeat the instructions to select one UE according to a round-robin scheme.

[0025] The instructions to select one UE may be based on at least one of rank for the UE, modulation and coding scheme for the UE, size of downlink data buffer for the UE, location of the UE in the UE group.

[0026] The uplink reference signal may be a sounding reference signal, SRS.

[0027] The reference signal controller may further comprise instructions that, when executed by the processing circuitry, cause the reference signal controller to: control the at least one selected UE to increase its frequency of signalling uplink reference signals.

[0028] According to a third aspect, it is provided a computer program for controlling transmission of uplink reference signals by a plurality of user equipments, UEs. The computer program comprises computer program code which, when executed on a reference signal controller being connectable to a radio network node causes the reference signal controller to: determine a UE group comprising a plurality of UEs that are in the same area; select at least one UE in the UE group to be a selected UE, wherein the one or more UEs in the UE group that are not selected are excluded UEs; control the excluded UEs to decrease their frequency of signalling uplink reference signals; and utilize, for each excluded UE, respective measurements of previously received reference signals; determine that uplink signalling reference signals from the at least one selected UE have changed more than a threshold amount; and trigger the excluded UEs to transmit a new uplink reference signal.

[0029] According to a fourth aspect, it is provided a computer program product comprising a computer program according to claim 21 and a computer readable means comprising non-transitory memory in which the computer program is stored.

[0030] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Aspects and embodiments are now described, by way of example, with reference to the accompanying drawings, in which:

[0032] Figs 1A-C are schematic diagrams illustrating environments in which embodiment presented herein can be applied;

[0033] Fig 2 is a schematic diagram illustrating an embodiment where functionality of the radio network node is split between a digital unit and a radio unit;

[0034] Figs 3A-D are schematic diagrams illustrating embodiments of where the reference signal controller can be implemented based on the embodiment illustrated by Fig 2;

[0035] Figs 4A-C are flow charts illustrating embodiments of methods for controlling transmission of uplink reference signals by a plurality of UEs;

[0036] Fig 5 is a schematic diagram showing functional modules of the reference signal controller of Figs 1A-C according to one embodiment;

[0037] Fig 6 is a schematic diagram illustrating components of the reference signal controller of Figs 1A-C; and

[0038] Fig 7 shows one example of a computer program product comprising computer readable means.DETAILED DESCRIPTION

[0039] The aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. These aspects may, however, be embodied in many different forms and should not be construed as limiting; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and to fully convey the scope of all aspects of invention to those skilled in the art. Like numbers refer to like elements throughout the description.

[0040] According to embodiments presented herein, when UEs are in the same area, the UEs are grouped in a UE group. Reference signals (e.g. SRS) from one UE in UE group can then be monitored if any changes in the radio channel occurs. As long as no significant changes occur, the preceding measurements of the reference signals can be reused for the other UEs in the group (at least part of the time). In this way, the similarity in radio environments, and thus reference signals, for UEs in the UE group is exploited to significantly reduce the amount of SRS signals from the UEs. This not only saves power use in the UEs, but also reduces resource use in the radio network for reference signals.

[0041] Figs 1A-C are schematic diagrams illustrating environments in which embodiments presented herein can be applied. The radio network node 3 forms part of a cellular communication network where embodiments presented herein may be applied. The cellular communication network comprises a core network (not shown) and one or more radio network nodes 3, here in the form of radio base stations being gNode Bs, also known as gNBs. The radio network node 3 could also be in the form of eNode Bs, Node Bs, etc. The radio network node 3 provides radio connectivity over a wireless interface 4 to a plurality of UEs 2. The term UE 2 is also known as mobile communication terminal, wireless device, mobile terminal, user terminal, user agent, wireless terminal, machine-to-machine device, etc., and can be implemented, for example, in what today is commonly known as an loT device, a mobile phone, smart phone or a tablet / laptop with wireless connectivity.

[0042] The cellular communication network may e.g. comply with any one or a combination of 5G NR (New Radio), 6G, LTE (Long Term Evolution), LTE Advanced, W-CDMA (Wideband Code Division Multiplex), or any other current or future wireless network, as long as the principles described hereinafter are applicable.

[0043] Over the wireless interface, downlink (DL) communication occurs from the radio network node 3 to the UE 2 and uplink (UL) communication occurs from the UE 2 to the radio network node 3. The quality of the wireless interface can vary over time and depending on the position of the UE 2, due to effects such as fading, multipath propagation, interference, temporary (e.g. moving) or permanent obstructions, etc.

[0044] A reference signal controller 1 is provided in connection with, or as part of, the radio network node 3. As explained in more detail below, the reference signal controller 1 is used to group nearby UEs together and only update reference signal measurements for all UEs when changes in reference signal measurements are detected for a subset (e.g. one) of selected UEs in the group. As long as no significant change is detected, the preceding measurements of reference signals are used for the UEs that are not selected. The reference signals can be SRS signals or any other current or future uplink reference signal that would benefit from the grouping described herein.

[0045] Turning now specifically to Fig 1A, there are three UEs 2 shown. Each UE 2 will transmit reference signals 20 to the radio network node 3, as instructed by the radio network node 3. This is the conventional case, which will consume resources in the air and in each UE for three parallel reference signals 20.

[0046] In the scenario shown in Fig 1B, the reference signal controller 1 has formed a UE group 5 for the three UEs that have been determined by the reference signal controller 1 to be in the same area. One of the UEs in the UE group 5 is selected to be used as a source of any changes in the radio environment, and is herein denoted the selected UE 2’. The other UEs of the group are herein denoted excluded UEs 2”. It is to be noted, though, that the excluded UEs 2” are part of the UE group 5 (as shown).

[0047] In the scenario shown in Fig 1C, a temporary blocking object 7, such as a lorry, has appeared between the radio network node 3 and at least part of the UEs, which results in a significant change in measurements (at the radio network node 3) of the received reference signal. When the change in measurements of the received reference signal is detected, this indicates a change in the radio channel characteristics, whereby the reference signal transmission for all UEs should be triggered. According to one embodiment, the UE group 5 is then, at least temporarily, broken up and all the individual UEs 2 that formed part of the UE group 5 are now triggered to transmit their own reference signals. Since the blocking object can affect the radio interface differently, the individual reference signals are sent again, to characterise the (now likely changed) radio channel between each UE 2 and the radio network node 3.

[0048] Fig 2 is a schematic diagram illustrating an embodiment where functionality of the radio network node 3 is split between a digital unit (DU) 10 and a radio unit (RU) 11. The DU 10 and the RU 11 can be provided in different locations, connected via a front haul link 12. The front haul link 12 can e.g. be implemented based on common public radio interface (CPRI) or enhanced CPRI (eCPRI). The DU 10 handles baseband processing, resource management and higher layer protocols, such as media access control (MAC) and radio link control (RLC). The RU 11 handles radio frequency (RF) processing, antenna control and low-level protocols, such as the physical layer.

[0049] Figs 3A-D are schematic diagrams illustrating embodiments of where the reference signal controller 1 can be implemented based on the embodiment illustrated by Fig 2.

[0050] In Fig 3A, an embodiment is shown where the reference signal controller 1 is implemented in the DU 10. The DU 10 is thus the host device for the reference signal controller 1 in this implementation.

[0051] In Fig 3B, an embodiment is shown where the reference signal controller 1 is implemented in the RU 11. The RU 11 is thus the host device for the reference signal controller 1 in this implementation.

[0052] In Fig 3C, an embodiment is shown where the reference signal controller 1 is implemented partly in the DU 10 and partly in the RU 11. Both the DU 10 and the RU 11 are thus host devices for the reference signal controller 1 in this implementation.

[0053] In Fig 3D, an embodiment is shown where the reference signal controller 1 is implemented as a stand-alone device. The reference signal controller 1 thus does not have a host device in this implementation. The reference signal controller 1 can also be implemented in a radio network node 3 that is not split into a DU and a RU (not shown).

[0054] Figs 4A-C are flow charts illustrating embodiments of methods for controlling transmission of uplink reference signals 20 by a plurality of UEs 2, 2’, 2”. The method being performed by a reference signal controller 1 being connected to (or forming part of) a radio network node 3. The uplink reference signal can e.g. be a sounding reference signal (SRS) or other similar uplink reference signal.

[0055] In a determine group step 40, the reference signal controller 1 determines a UE group 5 comprising a plurality of UEs 2, 2’, 2” that are in the same area. The same area can also be considered to be in the same location. Optionally, it is determined that the each one of the plurality of UEs 2, 2’, 2” is stationary. In other words, in this case, it is a condition for any UE of the group to be determined to be stationary for it to be part of the group. By only including stationary UEs in the UE group 5, a more stable group is likely, where if the radio channel for one UE (or only a limited number of UEs) in theUE group 5 is stable, the radio channels for all UEs in the UE group 5 are likely to be stable. A stationary UE can be determined based on measurements, subscription type (e.g. fixed device subscription) and / or device type (e.g. loT device). For instance, a stationary UE can be determined based on the reference signal measurements being relatively static for a period of time.

[0056] The same area can be defined in various way. In one embodiment, the same area is defined, at least partly, in that the UEs in the UE group 5 belong to the same set of one or more (contiguous) beams from the radio network node 3. The set of one or more contiguous beams is a strict subset of all available beams When applied in line-of- sight situations, this implies that the UEs in the UE group 5 are in the same range of directions from the radio network node 3, corresponding to the beams as applied in clustering algorithms known per se.

[0057] Alternatively or additionally, the same area is defined, at least partly, as an area of a predetermined size, and / or that a largest distance between UEs in the UE group 5 is smaller than a threshold distance. This implies that the UEs in the UE group 5 are near each other physically (i.e. not further away from each other than the threshold distance).

[0058] In a select UE step 42, the reference signal controller 1 selects at least one UE in the UE group 5 to be a selected UE 2’. The selected UE(s) 2’ will later be the one or those that transmit reference signals that are used to detect when the radio environment changes, which is used to trigger reference signal updates for the other UEs in the UE group 5. The one or more UEs in the UE group 5 that are not selected are here denoted excluded UEs 2”. The excluded UE(s) 2” are still part of the UE group 5. The first time a UE is selected in a UE group 5, the selected UE 2’ can be chosen at random, or it can be the UE that is the UE that is most centrally located (that, of distances to other UEs, has the smallest maximum distance to another UE in the UE group 5) or the UE that is likely to suffer more due to any radio environment changes (see more on this below).

[0059] In a decrease excluded UE r.s. step 46, the reference signal controller 1 controlling the excluded UEs 2” to decrease their frequency of signalling uplink reference signals 20. For instance, the reference signal controller 1 can control theexcluded UEs 2” to suspend transmitting uplink reference signals 20 until activated again.

[0060] In a utilize previous r.s.for excluded UEs step 48, the reference signal controller 1 utilizes respective measurements of previously received reference signals 20. This is performed for each one of the excluded UEs. In other words, for at least some of the time, instead of receiving a new measurement of a reference signal for the excluded UEs 2”, the previous measurement of the reference signal from the respective excluded UE 2” is used. All processing of the reference signal for the excluded UEs 2” is performed as normal; the use of the previous reference signal reception for the excluded UEs 2” is transparent for any processing of the reference signals for the excluded UEs 2”.

[0061] In a conditional r.s change step 50, the reference signal controller 1 determines whether uplink signalling reference signals from the selected UE 2’ have changed more than a threshold amount, (see the scenario illustrated in Fig 1C, explained above). If there is a significant change in the measurement of the reference signal of the selected UE(s)’, this indicates that something has occurred that is likely to affect the radio channel characteristics of the excluded UEs 2”. Hence, if the uplink signalling reference signals from the selected UE 2’ have changed more than a threshold amount, the method proceeds to a trigger excluded UEs r.s. step 52. Otherwise, the method returns to the utilize previous r.s.for excluded UEs step 48.

[0062] In the trigger excluded UEs r.s. step 52, the reference signal controller 1 triggers the excluded UEs 2” to transmit a new uplink reference signal 20, based on the determining that the uplink signalling reference signals have changed. Optionally, this can be implemented by breaking up the UE group 5 so that each UE transmits its own reference signal. Alternatively, this can be implemented by signalling to the excluded UEs 2” to perform an aperiodic reference signal transmission.

[0063] Optionally (not shown in Fig 4A), the method is periodically repeated to redetermine the UE group 5 to capture the occurrence of any devices that may have appeared or disappeared.

[0064] Turning now to Fig 4B, only new or modified steps compared to Fig 4A will be described. Here, after a negative result of the conditional r.s. change step 50, the method proceeds to an optional conditional select new UE step 49. Also, the trigger excluded UEs r.s. step 52 is a step that is only performed when the reference signal has changed, whereby it is beneficial to determine a new group to adapt to the changed radio environment. Hence, after the trigger excluded UEs r.s. step 52, the method returns to the determine group step 40.

[0065] if no significant reference signal change is detected in the conditional r.s. change step 50, the method proceeds to the optional conditional new UE step 49.

[0066] In the optional conditional select new UE step 49, the reference signal controller 1 determines whether to select another at least one UE or whether the current selected UE 2’ should continue to be the selected UE 2’.

[0067] The reason for selecting a new UE can be to share the burden between the UEs in the UE group 5 to transmit reference signals. A new UE can e.g. be selected according to a round-robin scheme.

[0068] The round-robin scheme can be applied such that each UE in the UE group 5 transmits a certain number of reference signals before another at least one UE in the group is made the selected UE’. The certain number of reference signal can be any suitable number, even one, such that each UE in the group is only the selected UE for a single transmission of a reference signal. The time between reference signals can be selected so that the time between successive signals from the group is the same, and the time between reference signals from a UE is reduced compared to the signalling interval used for a non-grouped UE (typically reduced by a factor 1 / N where N is the number of UEs in the group. Thus effectively sharing the reference signal sending equally over the group and keeping the group signal load equal to the load of a single non-grouped UE).

[0069] The proportion of time that each UE is the selected UE 2’ can vary between UEs. For instance the proportion of time that each UE is selected can depend on at least one of rank for the UE, modulation and coding scheme (MCS) for the UE 2, size of downlink data buffer for the UE 2, and location of the UE 2 in the UE group 5. In thisway, UEs with higher throughput, e.g. indicated by MCS and / or downlink data buffer size, could be awarded a greater proportion of time being the selected UE, since such a UE could suffer more if the radio channel is poorly characterised. Alternatively or additionally, a UE that is centrally located in the UE group 5 can be awarded a greater proportion of time being the selected UE, since such a UE could be considered to be more representative of the group than UEs on the edge, geometrically, of the UE group 5. It is to be noted that, as mentioned above, multiple UEs can concurrently be selected UEs, if their characteristics justify the increased resource use for multiple reference signal transmissions.

[0070] When a new UE is to be the selected UE, the method returns to reperform the select UE step 42, to deselect the previous selected UE and instead select another at least one of the UEs in the UE group 5, after which the remainder of the method is repeated.

[0071] Whenever it is determined not to select a new UE, the UE 2’ that is currently selected is still the selected UE 2’, and the method returns to the utilize previous r.s. s. for excluded UEs step 48.

[0072] Turning now to Fig 4C, only new or modified steps compared to Figs 4A-B will be described.

[0073] In an optional increase selected UE r.s. step 44, the reference signal controller 1 controls the selected UE 2’ to increase its frequency of signalling uplink reference signals. In this way, the reference signals can be more frequent, and any changes in radio channel characteristics can be quickly detected. If the burden of transmitting reference signals is handed between the different UEs of the UE group 5, the energy spent for transmitting reference signals is still less than in the prior art, while the increased frequency of transmitting reference signals allows faster adaptation to a changing radio environment.

[0074] In an optional conditional determine new group step 53, the reference signal controller 1 determines whether a new or updated group is to be selected. For instance, an updated group can be determined based on one or more new UEs being detected inthe same area. Alternatively, a new group is determined after a certain time period to conclusively catch any appearing or disappearing UEs. If a new group is to be determined, the method returns to the determine group step 40. Otherwise, the method proceeds to the optional conditional r.s. change step 50.

[0075] Fig 5 is a schematic diagram showing functional modules of the reference signal controller 1 of Figs 1A-C according to one embodiment. The modules are implemented using software instructions such as a computer program executing in the reference signal controller 1. Alternatively or additionally, the modules are implemented using hardware, such as any one or more of an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or discrete logical circuits. The modules correspond to the steps in the methods illustrated in Figs 4A-C.

[0076] A group determiner 70, corresponds to step 40. A UE selector 72 corresponds to step 42. A selected UE r.s. increaser 74 corresponds to step 44. An excluded UE r.s. decreaser 76 corresponds to step 46. An r.s. utilizer 78 corresponds to step 48. A new UE selection determiner 79 corresponds to step 49. An r.s. change detector 80 corresponds to step 50. An excluded UE r.s. increaser 82 corresponds to step 52. A new group determiner 83 corresponds to step 53.

[0077] Fig 6 is a schematic diagram illustrating components of the reference signal controller 1 of Figs 1A-C. It is to be noted that when the reference signal controller 1 is implemented in a host device, one or more of the mentioned components can be shared with the host device. Processing circuitry 60 is provided using any combination of one or more of a suitable central processing unit (CPU), graphics processing unit (GPU), multiprocessor, neural processing unit (NPU), microcontroller, digital signal processor (DSP), etc., capable of executing software instructions 67 stored in memory circuitry 64, which can thus be a computer program product. The processing circuitry 60 could alternatively be implemented using an application specific integrated circuit (ASIC), field programmable gate array (FPGA), etc. The processing circuitry 60 can be configured to execute the method described with reference to Figs 4A-C above.

[0078] The memory circuitry 64 can be any combination of random-access memory (RAM) and / or read-only memory (ROM). The memory circuitry 64 also comprises non-transitory persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid-state memory or even remotely mounted memory.

[0079] A data memory 66 is also provided for reading and / or storing data during execution of software instructions in the processing circuitry 60. The data memory 66 can be any combination of RAM and / or ROM.

[0080] The reference signal controller 1 further comprises an I / O interface 62 for communicating with external and / or internal entities, such as the radio network node 3.

[0081] Other components of the reference signal controller 1 are omitted in order not to obscure the concepts presented herein.

[0082] Fig 7 shows one example of a computer program product 90 comprising computer readable means. On this computer readable means, a computer program 91 can be stored in a non-transitory memory. The computer program can cause processing circuitry to execute a method according to embodiments described herein. In this example, the computer program product 90 is in the form of a removable solid-state memory, e.g. a Universal Serial Bus (USB) drive. As explained above, the computer program product could also be embodied in a memory of a device, such as the computer program product 64 of Fig 6. While the computer program 91 is here schematically shown as a section of the removable solid-state memory, the computer program can be stored in any way which is suitable for the computer program product, such as another type of removable solid-state memory, or an optical disc, such as a CD (compact disc), a DVD (digital versatile disc) or a Blu-Ray disc.

[0083] The aspects of the present disclosure have mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims. Thus, while various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects andembodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims.

Claims

CLAIMS1. A method for controlling transmission of uplink reference signals (20) by a plurality of user equipments, UEs (2, 2’, 2”), the method being performed by a reference signal controller (1) being connected to a radio network node (3), the method comprising: determining (40) a UE group (5) comprising a plurality of UEs (2, 2’, 2”) that are in the same area; selecting (42) at least one UE in the UE group (5) to be a selected UE (2’), wherein the one or more UEs in the UE group (5) that are not selected are excluded UEs (2”); controlling (46) the excluded UEs (2”) to decrease their frequency of signalling uplink reference signals (20); utilizing (48), for each excluded UE (2”), respective measurements of previously received reference signals (20); determining (50) that uplink signalling reference signals from the at least one selected UE (2’) have changed more than a threshold amount; and triggering (52) the excluded UEs (2”) to transmit a new uplink reference signal (20).

2. The method according to claim 1, wherein the controlling (46) the excluded UEs (2”) comprises controlling the excluded UEs (2”) to suspend transmitting uplink reference signals (20) until activated again.

3. The method according to claim 1 or 2, wherein the same area is defined, at least partly, that the UEs in the UE group (5) belong to the same set of one or more contiguous beams from the radio network node (3), wherein the set of one or more contiguous beams is a strict subset of all available beams.

4. The method according to any one of the preceding claims, wherein the same area is defined, at least partly, as an area of a predetermined size, and / or that a largest distance between UEs in the UE group (5) is smaller than a threshold distance.

5. The method according to claim 3 or 4, wherein the determining (40) a UE group (5) comprises determining that the each one of the plurality of UEs (2, 2’, 2”) is stationary.

6. The method according to any one of the preceding claims, wherein the selecting (42) at least one UE is reperformed to deselect the previous at least one selected UE (2’) and instead select another one of the UEs in the UE group (5), after which the remainder of the method is repeated.

7. The method according to claim 6, wherein the selecting (42) one UE is repeated according to a round-robin scheme.

8. The method according to claim 6 or 7, wherein the selecting (42) at least one UE is based on at least one of rank for the UE, modulation and coding scheme for the UE, size of downlink data buffer for the UE, location of the UE in the UE group (5).

9. The method according to any one of the preceding claims, wherein the uplink reference signal is a sounding reference signal, SRS.

10. The method according to any one of the preceding claims, further comprising: controlling (44) the at least one selected UE (2’) to increase its frequency of signalling uplink reference signals (20).

11. A reference signal controller (1) for controlling transmission of uplink reference signals (20) by a plurality of user equipments, UEs (2, 2’, 2”), the reference signal controller (1) being connectable to a radio network node (3), the reference signal controller (1) comprising: processing circuitry (60); and memory circuitry (64) storing instructions (67) that, when executed by the processing circuitry, cause the reference signal controller (1) to: determine a UE group (5) comprising a plurality of UEs (2, 2’, 2”) that are in the same area; select at least one UE in the UE group (5) to be a selected UE (2’), wherein the one or more UEs in the UE group (5) that are not selected are excluded UEs (2”); control the excluded UEs (2”) to decrease their frequency of signalling uplinkreference signals (20); utilize, for each excluded UE (2”), respective measurements of previously received reference signals (20); determine that uplink signalling reference signals from the at least one selected UE (2’) have changed more than a threshold amount; and trigger the excluded UEs (2”) to transmit a new uplink reference signal (20).

12. The reference signal controller (1) according to claim 11, wherein the instructions to control the excluded UEs (2”) comprise instructions (67) that, when executed by the processing circuitry, cause the reference signal controller (1) to control the excluded UEs (2”) to suspend transmitting uplink reference signals (20) until activated again.

13. The reference signal controller (1) according to claim 11 or 12, wherein the same area is defined, at least partly, that the UEs in the UE group (5) belong to the same set of one or more contiguous beams from the radio network node (3), wherein the set of one or more contiguous beams is a strict subset of all available beams.

14. The reference signal controller (1) according to any one of claims 11 to 13, wherein the same area is defined, at least partly, as an area of a predetermined size, and / or that a largest distance between UEs in the UE group (5) is smaller than a threshold distance.

15. The reference signal controller (1) according to claim 13 or 14, wherein the instructions to determine a UE group (5) comprise instructions (67) that, when executed by the processing circuitry, cause the reference signal controller (1) to determine that the each one of the plurality of UEs (2, 2’, 2”) is stationary.

16. The reference signal controller (1) according to any one of claims 11 to 15, further comprising instructions (67) that, when executed by the processing circuitry, cause the reference signal controller (1) to repeat the instructions to select one UE is to deselect the previous at least one selected UE (2’) and instead select another at least one of the UEs in the UE group (5), after which the remainder of the instructions are repeated.

17. The reference signal controller (1) according to claim 16, further comprising instructions (67) that, when executed by the processing circuitry, cause the referencesignal controller (1) to repeat the instructions to select one UE according to a roundrobin scheme.

18. The reference signal controller (1) according to claim 16 or 17, wherein the instructions to select one UE is based on at least one of rank for the UE, modulation and coding scheme for the UE, size of downlink data buffer for the UE, location of the UE in the UE group (5)).

19. The reference signal controller (1) according to any one of claims 11 to 18, wherein the uplink reference signal is a sounding reference signal, SRS.

20. The reference signal controller (1) according to any one of claims 11 to 19, further comprising instructions (67) that, when executed by the processing circuitry, cause the reference signal controller (1) to: control the at least one selected UE (2’) to increase its frequency of signalling uplink reference signals (20).

21. A computer program (67, 91) for controlling transmission of uplink reference signals (20) by a plurality of user equipments, UEs (2, 2’, 2”), the computer program comprising computer program code which, when executed on a reference signal controller (1) being connectable to a radio network node (3) causes the reference signal controller (1) to: determine a UE group (5) comprising a plurality of UEs (2, 2’, 2”) that are in the same area; select at least one UE in the UE group (5) to be a selected UE (2’), wherein the one or more UEs in the UE group (5) that are not selected are excluded UEs (2”); control the excluded UEs (2”) to decrease their frequency of signalling uplink reference signals (20); and utilize, for each excluded UE (2”), respective measurements of previously received reference signals (20); determine that uplink signalling reference signals from the at least one selected UE (2’) have changed more than a threshold amount; and trigger the excluded UEs (2”) to transmit a new uplink reference signal (20).

22. A computer program product (64, 90) comprising a computer program according to claim 21 and a computer readable means comprising non-transitory memory in which the computer program is stored.

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