Configuration of user equipment with reference signals

Abstract

There is provided techniques for configuring UEs with uplink reference signal resources. A method is performed by a network node. The method comprises dividing a set of uplink reference signal resources among at least two disjoint subsets. The set of uplink reference signal resources is available for transmission of uplink reference signals in a time window. Each of the at least two subsets is associated with its own time-domain behaviour with respect to the transmission of the uplink reference signals within the time window. The method comprises configuring the UEs with the uplink reference signal resources of the associated time-domain behaviour from the subsets of uplink reference signal resources. With which subset of uplink reference signal resources each of the UEs is configured with depends on characteristics of the UEs.

Description

[0001] CONFIGURATION OF USER EQUIPMENT WITH REFERENCE SIGNALS

[0002] TECHNICAL FIELD

[0003] Embodiments presented herein relate to a method, a network node, a computer program, and a computer program product for configuring user equipment with uplink reference signal resources.

[0004] BACKGROUND

[0005] Uplink reference signals, such as sounding reference signals (SRSs) are examples of reference signals transmitted by user equipment (UE) in the uplink direction. Uplink reference signals can be used by the network, such as by one or more network nodes, to estimate the uplink channel quality over a wide bandwidth. Unlike demodulation reference signals (DM-RS), uplink reference signals are not associated with any physical uplink channels, and they support uplink channel-dependent scheduling and link adaptation.

[0006] It is understood that, in order to utilize the channel sounding function, the uplink reference signals are assumed to be known by both the transmitter (i.e., the UE) and the receiver (i.e., the network node). Uplink reference signals can be used to provide information about the combined effect of multipath fading, scattering, Doppler effects, and power loss of transmitted signals. Just to give some non-limiting examples, uplink reference signals can be used to assist in codebook-based closed- loop spatial multiplexing, control of uplink transmit timing, reciprocity-based downlink precoding in multi-user multiple-input multiple-output (MIMO) system setups, and quasi co-location of physical channels and reference signals.

[0007] As an example, for communication over the New Radio (NR) air interface, the SRS is an orthogonal frequency division multiplexing (OFDM) signal filled with a Zadoff- Chu sequence on different subcarriers. As a further example, with respect to the NR air interface, based on Numerology 1, a 5 ms long time division duplex (TDD) slot is subdivided into 14 OFDM symbols. SRS signals are transmitted during so-called special slots and can span 1, 2 or 4 OFDM symbols mapped to the last 6 OFDM symbols of each special slot. SRS is configured via Radio Resource Control (RRC) layer signaling for different resource types. As illustrated in Fig. 1, three different time-domain behaviors are supported for transmission of uplink reference signals; aperiodic transmission, semi-persistent transmission, and periodic transmission.

[0008] An aperiodic transmission of uplink reference signals can be dynamically triggered by the network, for example by means of a (SRS) request field in downlink control information (DCI) or a downlink control channel (such as a physical downlink control channel, PDCCH). That is, the network node can on fine time granularity control the transmission of uplink reference signals by UEs in its served cell by sending a DCI to request UE to send uplink reference signals. The aperiodic uplink reference signals is a one-shot transmission. The UEs can be configured using RRC signaling with aperiodic uplink reference signals resources (bundled together in resource sets) which defines the frequency, sequence, and time-domain position within a slot. However, the UEs are only transmitting aperiodic uplink reference signals in slots a certain slot offset later upon where it received the trigger.

[0009] A semi-persistent transmission of uplink reference signals can be activated and deactivated by the network node by sending medium access control (MAC) control elements (CEs) on a downlink data channel (such as a physical downlink shared channel, PDSCH). When a UE receives an activation command it starts to periodically transmit uplink reference signals according to a predefined periodicity and slot offset, and only stops transmitting in this manner when the UE receives a MAC CE deactivation command.

[0010] Periodic transmission of uplink reference signals represent always-on signals the UEs are transmitting upon receiving RRC configuration of periodic uplink reference signals resources with a certain periodicity and slot offset. Thus, no dynamic triggering is required after configuration and the UEs do not require an activation instruction after it receives uplink reference signal resource set configuration via RRC signaling. As an example, periodic uplink reference signals can be scheduled with a periodicity that ranges from 5 ms to 320 ms.

[0011] Third generation partnership program (3GPP) specifications do neither restrict nor specify how these three resource types (i.e., aperiodic transmission, semi-persistent transmission, and periodic transmission of uplink reference signals) are supported in a cell. Also other parameters can be configured for uplink reference signals. The cyclic shift allows to send multiple orthogonal signals, e.g., a cyclic shift equal to 4 allows the network node to configure four UEs in the same OFDM symbol. The transmission comb parameter defines which subcarrier are being used for uplink reference signal transmission; it also provides the network node with the capability of multiplexing two UEs by assigning them the same cyclic shift, frequency, and time resources, but different transmission comb. An uplink reference signals transmission can occupy up to 272 physical resource blocks (PRBs) in the frequency domain, but an individual UE does not necessarily transmit uplink reference signals on every subcarrier, but rather selects a specific subcarrier set based on the transmission comb.

[0012] From a network node perspective, the uplink reference signal resource management logic is a challenge since many UEs capable of transmitting uplink reference signals may be served by the network node at the same time, taken also into account that the available amount of uplink reference signal resources (from the perspective of the network node) is limited by a number of factors. First and foremost, there are only so many possible places where uplink reference signal can be transmitted in the timedomain resource grid. Typically, it is desirable to transmit SRS only in the uplink part of the special slot (which typically ranges between 2-4 symbols). This immediately limits how many uplink reference signals that can be transmitted in a certain time window from the air interface perspective. Whereas uplink reference signals could also be transmitted in (ordinary) uplink slots, this is less desirable since the uplink reference signal then compete for resources with data symbols.

[0013] Typically, in order to improve the channel estimation accuracy in the presence of mobility it is desirable to have a frequent transmission of uplink reference signals for a certain UE. In this way, the potential to use time-division of uplink reference signal resources between two or more UEs is limited. The network node may also have a processing limitation bottleneck, memory limitation bottleneck or an interface transmission bottleneck limiting how many uplink reference signal channel estimations can be performed or stored per time unit. Such limitations may be more severe than the air interface limitations.

[0014] How to allocate the scarce uplink reference signal resources to UEs is thus a challenge, and it is beneficial to make sure that the right UEs have an uplink reference signal resource allocated at a certain time. Periodic uplink reference signal resources are slow to reallocate between UEs as it requires RRC reconfigurations, which could take in the order of hundreds of milliseconds, whereas aperiodic uplink reference signal resources can be dynamically reallocated between UEs. Thus, from such a re-use perspective, aperiodic uplink reference signal is preferred. However, not all UEs support transmission of aperiodic uplink reference signals; many UEs support only periodic transmission of uplink reference signals.

[0015] According to state-of-the-art, either only aperiodic uplink reference signals or only periodic uplink reference signals are used for all UEs in a cell, as this simplifies the uplink reference signal resource management. However, if only periodic uplink reference signals are used in a cell, this may limit the number of UEs to which uplink reference signals can be allocated. On the other hand, if only aperiodic uplink reference signals are used in a cell, UEs which do not have the capability to support aperiodic transmission of uplink reference signals do not have an opportunity to get any uplink reference signal allocation at all.

[0016] Hence, there is a need for improved resource management of uplink reference signals.

[0017] SUMMARY

[0018] An object of embodiments herein is to address the above issues and enable allocation of uplink reference signals that improve the uplink reference signal resource management.

[0019] A particular object is to provide improved distribution of uplink reference signals among UEs in a cell.

[0020] A particular object is to provide efficient use of periodic, aperiodic, and semi- persistent transmission of uplink reference signals.

[0021] According to a first aspect there is presented a method for configuring UEs with uplink reference signal resources. The method is performed by a network node. The method comprises dividing a set of uplink reference signal resources among at least two disjoint subsets. The set of uplink reference signal resources is available for transmission of uplink reference signals in a time window. Each of the at least two subsets is associated with its own time-domain behaviour with respect to the transmission of the uplink reference signals within the time window. The method comprises configuring the UEs with the uplink reference signal resources of the associated time-domain behaviour from the subsets of uplink reference signal resources. With which subset of uplink reference signal resources each of the UEs is configured with depends on characteristics of the UEs.

[0022] According to a second aspect there is presented a network node for configuring UEs with uplink reference signal resources. The network node comprises processing circuitry. The processing circuitry is configured to cause the network node to divide a set of uplink reference signal resources among at least two disjoint subsets. The set of uplink reference signal resources is available for transmission of uplink reference signals in a time window. Each of the at least two subsets is associated with its own time-domain behaviour with respect to the transmission of the uplink reference signals within the time window. The processing circuitry is configured to cause the network node to configure the UEs with the uplink reference signal resources of the associated time-domain behaviour from the subsets of uplink reference signal resources. With which subset of uplink reference signal resources each of the UEs is configured with depends on characteristics of the UEs.

[0023] According to a third aspect there is presented a computer program for configuring UEs with uplink reference signal resources. The computer program comprises computer code which, when run on processing circuitry of a network node, causes the network node to perform actions. One action comprises the network node to divide a set of uplink reference signal resources among at least two disjoint subsets. The set of uplink reference signal resources is available for transmission of uplink reference signals in a time window. Each of the at least two subsets is associated with its own time-domain behaviour with respect to the transmission of the uplink reference signals within the time window. One action comprises the network node to configure the UEs with the uplink reference signal resources of the associated time-domain behaviour from the subsets of uplink reference signal resources. With which subset of uplink reference signal resources each of the UEs is configured with depends on characteristics of the UEs. According to a fourth aspect there is presented a computer program product comprising a computer program according to the third aspect and a computer readable storage medium on which the computer program is stored. The computer readable storage medium could be a non-transitory computer readable storage medium.

[0024] Advantageously, these aspects provide efficient resource management of uplink reference signal.

[0025] Advantageously, these aspects allow periodic, aperiodic, as well as semi-persistent allocation of uplink reference signals to be used in parallel in a cell.

[0026] Advantageously, these aspects enable uplink reference signals to be dynamically allocated to the UEs as the characteristics of the UEs change over time.

[0027] Advantageously, these aspects enable the available uplink reference signal resources to be divided between uplink reference signals with different time-domain behaviour.

[0028] Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

[0029] 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, module, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, 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.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

[0032] Fig. 1 schematically illustrates different types of resource types according to an example; Fig. 2 is a schematic diagram illustrating a communication network according to embodiments;

[0033] Fig. 3 is a flowchart of methods according to embodiments;

[0034] Fig. 4 is a signalling diagram of a method according to an embodiments;

[0035] Fig. 5 is a schematic diagram showing structural units of a network node according to an embodiment;

[0036] Fig. 6 is a schematic diagram showing functional modules of a network node according to an embodiment; and

[0037] Fig. 7 shows one example of a computer program product comprising computer readable storage medium according to an embodiment.

[0038] DETAILED DESCRIPTION

[0039] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

[0040] Fig. 2 is a schematic diagram illustrating a communication network 200 where embodiments presented herein can be applied. The communication network 200 comprises a network node 210 and a transmission and reception point (TRP) 220. The network node 210 is configured to control the TRP 220. In this respect, although separated with respect to hardware, the network node 210 and the TRP 220 can be regarded as one logical unit and together form a (radio) access network node, (radio) base station, base transceiver station, node B (NB), evolved node (eNB), gNB, access node, access point, integrated access and backhaul (IAB) node, or the like. The network node 210 is, via the TRP 220, configured to serve UEs 230a, 230b, ..., 230N. Non-limiting examples of UEs are portable wireless devices, mobile stations, mobile phones, handsets, wireless local loop phones, smartphones, laptop computers, tablet computers, network equipped vehicles, network equipped sensors, and Internet of Things (loT) devices. The network node 210 is assumed to be capable of configuring the UEs 230a: 230N with uplink reference signal resources associated with different types of time-domain behaviour, such as periodic, aperiodic, or semi-persistent transmission of uplink reference signals.

[0041] The uplink reference signal resources are identified by, for instance, their frequencydomain position, comb offset, cyclic shift, and symbol position within a slot. Each uplink reference signal resource is uniquely identifiable and cannot be overlapped with any other uplink reference signal resources. Thus, the number of possible available uplink reference signal resources are at least limited from the air interface. The network node 210 may also have a processing limitation bottleneck, memory limitation bottleneck or an interface transmission bottleneck limiting how many uplink reference signal based channel estimations can be performed or stored per time unit. Thus, in general, based on aforementioned limitations, the network node 210 will know how many uplink reference signal resources are possible to use in the cell. As a non-limiting and illustrative example, 16 possible uplink reference signal resources can be available for use in the cell if one uplink reference signal symbol, 4 comb offsets and 4 cyclic shifts are used to define the set of uplink reference signal resources.

[0042] As noted above, there is a need for improved resource management of uplink reference signals.

[0043] The herein disclosed embodiments are therefore based on providing resource management of a set of available uplink reference signal resources.

[0044] The embodiments disclosed herein in particular relate to techniques for configuring UEs 230a: 230N with uplink reference signal resources such that the above issues are avoided, or at least mitigated or reduced. In order to obtain such techniques there is provided a network node 210, a method performed by the network node 210, a computer program product comprising code, for example in the form of a computer program, that when run on a network node 210, causes the network node 210 to perform the method. Fig. 3 is a flowchart illustrating embodiments of methods for configuring UEs 23oa:23oN with uplink reference signal resources. The methods are performed by the network node 210. The methods are advantageously provided as computer programs.

[0045] In general terms, the method is based on the network node 210 configuring the UEs 230a: 230N with uplink reference signal resources that have been divided into at least two subsets, as in steps S102 and S104.

[0046] S102: The network node 210 divides a set of uplink reference signal resources among at least two disjoint subsets. The set of uplink reference signal resources is available for transmission of uplink reference signals in a time window. Each of the at least two subsets is associated with its own time-domain behaviour with respect to the transmission of the uplink reference signals within the time window. As disclosed above, and as will be disclosed below in further detail, the time-domain behaviour generally pertains to periodic, aperiodic, or semi-persistent transmission of the uplink reference signals.

[0047] S104: The network node 210 configures the UEs 23oa:23oN with the uplink reference signal resources of the associated time-domain behaviour from the subsets of uplink reference signal resources. Which subset of uplink reference signal resources each of the UEs 230a: 230N is configured with depends on characteristics of the UEs 230a: 230N. Examples of such characteristics will be provided below.

[0048] Embodiments relating to further details of configuring UEs 230a: 230N with uplink reference signal resources as performed by the network node 210 will now be disclosed with continued reference to Fig. 3.

[0049] There may be different types of characteristics of the UEs 230a: 230N. In some nonlimiting examples, the characteristics of the UEs 230a: 230N pertain to at least one of: capabilities of the UEs 230a: 230N, the speed of the UEs 230a: 230N, the number of transmissions from the UEs 230a: 230N, data rates of the UEs 230a: 230N, traffic patterns of the UEs 23oa:23oN, network load caused by the UEs 23oa:23oN. Here, the characteristics of the UEs 230a: 230N could be provided individually per each UE 230a: 230N, as an average of all UEs 230a: 230N, as distribution across the UEs 230a: 230N etc. The capabilities of the UEs 230a: 230N may pertain at least to their capabilities to transmit uplink reference signals. To determine user speed, Doppler estimation can be used on analysis of uplink signals according to conventional methods. The traffic patterns may characterize the traffic to / from the UEs

[0050] 230a: 230N as representing any of web browsing traffic, video streaming traffic, voice traffic, video call traffic, file download traffic, file upload traffic, online gaming traffic, extended reality application traffic, social media interaction traffic, instant messaging traffic, Internet-of-things traffic, cloud computing traffic, Enhanced Mobile Broadband (eMBB), Ultra Reliable Low Latency Communications (URLLC), Massive Machine Type Communications (mMTC).

[0051] As disclosed above, the set of uplink reference signal resources are split up among two or more subsets, each associated with their own time-domain behavior with respect to the transmission of the uplink reference signals. Aspects of different ways in which the set of uplink reference signal resources can be divided among the at least two disjoint subsets will be disclosed next.

[0052] In some aspects the number of time-domain behaviors is two; representing periodic transmission and aperiodic transmission. Hence, in some embodiments, the timedomain behaviour of a first subset of the at least two subsets corresponds to periodic transmission of the uplink reference signal resources, and the time-domain behaviour of a second subset of the at least two subsets corresponds to aperiodic transmission of the uplink reference signal resources. However, there could also be a third timedomain behavior, namely semi-persistent transmission. Thus, in some embodiments, the time-domain behaviour of a third subset of the at least two subsets corresponds to semi-persistent transmission of the uplink reference signal resources.

[0053] In some aspects, there is a fixed and equal division between uplink reference signal resources for periodic transmission and uplink reference signal resources for aperiodic transmission. Hence, in some embodiments, the set of available uplink reference signal resources is equally divided among the at least two subsets. For example, 16 SRS resource can be divided into 8 periodic SRS resources and 8 aperiodic SRS resources.

[0054] In other aspects, the ratio between uplink reference signal resources for periodic transmission and uplink reference signal resources for aperiodic transmission, and hence, dividing the set of uplink reference signal into at least two subsets is dynamically updated over time. For example, different splits between uplink reference signal resources for periodic transmission and uplink reference signal resources for aperiodic transmission can be defined as follows with respect to percentage: Aperiodic-Periodic-SRS-Split = {0-100, 25-75, 40-60, 50-50, 60-40, 75- 25, 100-0}. Here, among 16 total SRS resources, the split “25-75” would imply that 4 SRS resources are allocated for aperiodic transmission and the remaining 12 SRS resources are allocated for periodic transmission. Reference is here made to Table 1 in which two examples of splits, namely “25-75” and “60-40”, are shown for 16 available uplink resources split over two symbols (denoted “Symboli” and “Symbol 2”), with four combs (denoted “Combo”, “Combi”, “Comb2”, “Combs”) and four cyclic shifts (denoted “CSo”, “CS”, “CS2”, “CS3”). In the table, “A” denotes uplink reference signal resources for aperiodic transmission and “P” denotes uplink reference signal resources for periodic transmission resources for aperiodic and periodic transmission.

[0055] Further aspects of dividing the set of uplink reference signals into at least two subsets is dynamically updated over time will be disclosed next.

[0056] In general terms, the division of uplink reference signal resources can be dynamically adapted depending on a number of criteria in order to optimize network performance. Dynamically allocating uplink reference signal resources between different time-domain behaviors requires an advanced algorithm that can manage the scheduling and resource allocation for these different resource types of uplink reference signals.

[0057] In some aspects, how many of the available uplink reference signal resources to have in each subset depends on the characteristics of the UEs 230a: 230N and how many UEs 230a: 230N that are served. That is, in some embodiments, the set of available uplink reference signal resources is divided among the at least two subsets dependent on any of the above defined characteristics of the UEs 230a: 230N as well as the number of UEs 230a: 230N served by the network node 210, 500, 600.

[0058] Here, the ratio between aperiodic, periodic, and semi-persistent transmission of the uplink reference signal resources could be adapted as the characteristics of the UEs 23oa:23oN and / or the number of served UEs 23oa:23oN change over time. Hence, in some embodiments, the dividing the set of uplink reference signal into at least two subsets is dynamically updated over time as the characteristics and / or the number of served UEs 230a: 230N change.

[0059] As an example, for a comparatively low number of served UEs 230a: 230N, it is probable that all UEs 230a: 230N capable of transmitting uplink reference signals can be allocated a periodic uplink reference signal resource without the network node 210, 500, 600 running out of uplink reference signal resources. On the other hand, for a comparatively higher number of served UEs 230a: 230N, it is probable that such a configuration would severely limit the number of UEs 230a: 230N which can get allocated uplink reference signal resources.

[0060] Therefore, in some aspects the network node 210 switches its configuration between having uplink reference signal resources for only periodic transmission or only aperiodic transmission based on whether the number of served UEs 230a: 230N is above or below some pre-configured threshold. That is, in some embodiments, the uplink reference signal resources are divided to all be either in the first subset or in the second subset, and wherein whether to put all the uplink reference signal resources in the first subset or in the second subset depends on speed of the UEs 23oa:23oN. For instance, the network node 210 may allocate all its available uplink reference signal resources to only periodic transmission if the number of served UEs 230a: 230N is below some threshold (say, 50 UEs 230a: 230N) and allocate all its available uplink reference signal resources to only aperiodic transmission if the number of served UEs 230a: 230N is equal to, or above, this threshold.

[0061] In other aspects, instead of having fixed sizes of the different subsets, the pool of resources is gradually switched so that more uplink reference signal resources for aperiodic transmission are allocated as the number of served UEs 230a: 230N increases. Hence, in some embodiments, the at least two subsets are dynamically updated such that the first subset grows as the number of served UEs 230a: 230N decreases, and such that the second subset grows as the number of served UEs 230a: 230N increases.

[0062] For slow-moving UEs 230a: 230N, it may be preferred to allocate uplink reference signal resources for periodic transmission whilst for fast-moving UEs 230a: 230N it may be preferred to allocate uplink reference signal resources for aperiodic transmission. Therefore, in some embodiments, the UEs 230a: 230N for which speed is lower than a speed threshold are configured with uplink reference signal resources from the first subset, and the UEs 230a: 230N for which the speed is higher than the speed threshold are configured with uplink reference signal resources from the second subset.

[0063] Further, the periodicity of the transmission of uplink reference signals from a given UE 230a: 230N may be adapted based on the speed of that given UE 230a: 230N. Hence, in some embodiments, the periodic transmission of the uplink reference signal resources has a periodicity that is adaptively set according to at least the speed of the UEs 230a: 230N. One reason to adapt the periodicity according to the speed of the UEs 230a: 230N is to get more frequent channel estimates of fast-moving UEs 230a: 230N compared to the channel estimates of slow-moving UEs 230a: 230N, where older channel estimates can be relied on.

[0064] In some aspects the network node 210 switches its configuration between having uplink reference signal resources for only periodic transmission or only aperiodic transmission based on the distribution of speed estimates of the UEs 230a: 230N. For example, the network node 210 may estimate an average speed of the UEs 230a: 230N it serves (i.e., averaging across all served UEs 230a: 230N for which it has speed estimates of), and use that estimate to switch to uplink reference signal resources for only aperiodic transmission when the average speed is above some thresholds (say, 10 km / h) and switch to uplink reference signal resources for only periodic transmission when the average user speed is equal to, or below, this threshold.

[0065] Further, in some embodiments, the at least two subsets are dynamically updated such that the first subset grows as speed of the UEs 230a: 230N decreases, and such that the second subset grows as the speed of the UEs 230a: 230N increases.

[0066] In relation to the number of served UEs 230a: 230N, and / or the speed of the UEs 230a: 230N, uplink reference signal resources for semi-persistent transmission may be allocated if there is moderate number of served UEs 230a: 230N and / or moderate user speed. Hence, in some embodiments, the third subset is dynamically updated such that the third subset is largest when either the number of served UEs 230a: 230N is above a first threshold but below a second threshold or when speed of the UEs 230a: 230N is above a third threshold but below a fourth threshold.

[0067] In some aspects, the network node 210 jointly determines the different subsets and the periodicity of the periodic transmission of the uplink reference signals. In particular, in some embodiments, the periodicity is jointly set with determining how many of the available uplink reference signal resources to put in each subset when dividing the set of available uplink reference signal resources among at least two disjoint subsets. One example of such joint determination is provided in Table 2. For different combinations of number of served UEs and average speed of the UEs.

[0068] Table 2: Criteria for determination of uplink reference signal resource pool split based on number of served UEs and UE mobility.

[0069] It is assumed that the UEs 230a: 230N transmit the uplink reference signals on the configured uplink reference signal resources and hence that the network node 210 receives the uplink reference signals accordingly. Thus, in some embodiments, the network node 210 is configured to perform (optional) step S106.

[0070] S106: The network node 210 receives uplink reference signals from the UEs 230a: 230N on the configured uplink reference signal resources.

[0071] One particular embodiment for configuring UEs 230a: 230N with uplink reference signal resources as performed by the network node 210 in accordance with any of the above embodiments, aspects, and examples, will be disclosed next with reference to the signalling diagram of Fig. 4. In this embodiment, the allocation of resources is dynamically changed between uplink reference signal resources for either only periodic transmission or only aperiodic transmission based on network load and traffic conditions. In this embodiment, the uplink reference signals are SRSs.

[0072] S20ia, S20ib: The network node (denoted NN) provides two served UEs (denoted UEl and UE2) with a cell-specific periodic SRS configuration, including a common periodicity (denoted ti) for periodic transmission of the SRS. S202a, S202b: UE1 and UE2 perform a respective first transmission of the SRS in accordance with the cell-specific periodic SRS configuration.

[0073] 8203a, 8203b: After the periodicity ti has passed, UE1 and UE2 perform a respective second transmission of the SRS in accordance with the cell-specific periodic SRS configuration.

[0074] S204: The network node detects a change in network load and traffic conditions, causing the network node to trigger a switch to aperiodic transmission of SRSs from the UEs

[0075] 8205a, 8205b: The network node reconfigures UE1 and UE2 with a cell-specific aperiodic SRS configuration. Accordingly, UE1 and UE2 are configured with a slot offset (denoted t2).

[0076] 8206a, 8206b: The network node transmits a request for an aperiodic SRS transmission from UE1 and UE2.

[0077] 8207a, 8207b: UEl and UE2 perform a respective aperiodic transmission of the SRS in accordance with the cell-specific aperiodic SRS configuration and the received request.

[0078] Fig. 5 schematically illustrates, in terms of a number of structural units, the components of a network node 500 according to an embodiment. Processing circuitry 510 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 710 (as in Fig. 7), e.g. in the form of a storage medium 530. The processing circuitry 510 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0079] Particularly, the processing circuitry 510 is configured to cause the network node 500 to perform a set of operations, or steps, as disclosed above. For example, the storage medium 530 may store the set of operations, and the processing circuitry 510 may be configured to retrieve the set of operations from the storage medium 530 to cause the network node 500 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry 510 is thereby arranged to execute methods as herein disclosed. The storage medium 530 may also comprise 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. The network node 500 may further comprise a communications (comm.) interface 520 at least configured for communications with other entities, functions nodes, devices, etc. such as the UEs 230a: 230N, as well as other network entities. As such the communications interface 520 may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry 510 controls the general operation of the network node 500 e.g. by sending data and control signals to the communications interface 520 and the storage medium 530, by receiving data and reports from the communications interface 520, and by retrieving data and instructions from the storage medium 530. Other components, as well as the related functionality, of the network node 500 are omitted in order not to obscure the concepts presented herein.

[0080] Fig. 6 schematically illustrates, in terms of a number of functional modules, the components of a network node 600 according to an embodiment. The network node 600 of Fig. 6 comprises a number of functional modules; a divide module 610 configured to perform step S102, and a configure module 620 configured to perform step S104. The network node 600 of Fig. 6 may further comprise a number of optional functional modules, such as a receive module 630 configured to perform step S106. In general terms, each functional module 610:630 may in one embodiment be implemented only in hardware and in another embodiment with the help of software, i.e., the latter embodiment having computer program instructions stored on the storage medium 530 which when run on the processing circuitry makes the network node 210 perform the corresponding steps mentioned above in conjunction with Fig 7. It should also be mentioned that even though the modules correspond to parts of a computer program, they do not need to be separate modules therein, but the way in which they are implemented in software is dependent on the programming language used. Preferably, one or more or all functional modules 610:630 maybe implemented by the processing circuitry 510, possibly in cooperation with the communications interface 520 and / or the storage medium 530. The processing circuitry 510 may thus be configured to from the storage medium 530 fetch instructions as provided by a functional module 610:630 and to execute these instructions, thereby performing any steps as disclosed herein.

[0081] The network node 210, 500, 600 may be provided as a standalone device or as a part of at least one further device. For example, the network node 210, 500, 600 maybe provided in a node of the radio access network or in a node of the core network. Alternatively, functionality of the network node 210, 500, 600 may be distributed between at least two devices, or nodes. These at least two nodes, or devices, may either be part of the same network part (such as the radio access network or the core network) or may be spread between at least two such network parts. In general terms, instructions that are required to be performed in real time may be performed in a device, or node, operatively closer to the cell than instructions that are not required to be performed in real time. Thus, a first portion of the instructions performed by the network node 210, 500, 600 may be executed in a first device, and a second portion of the of the instructions performed by the network node 210, 500, 600 may be executed in a second device; the herein disclosed embodiments are not limited to any particular number of devices on which the instructions performed by the network node 210, 500, 600 may be executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a network node 210, 500, 600 residing in a cloud computational environment. Therefore, although a single processing circuitry 510 is illustrated in Fig. 5 the processing circuitry 510 may be distributed among a plurality of devices, or nodes. The same applies to the functional modules 610:630 of Fig. 6 and the computer program 720 of Fig. 7.

[0082] Fig. 7 shows one example of a computer program product 710 comprising computer readable storage medium 730. On this computer readable storage medium 730, a computer program 720 can be stored, which computer program 720 can cause the processing circuitry 510 and thereto operatively coupled entities and devices, such as the communications interface 520 and the storage medium 530, to execute methods according to embodiments described herein. The computer program 720 and / or computer program product 710 may thus provide means for performing any steps as herein disclosed.

[0083] In the example of Fig. 7, the computer program product 710 is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 710 could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial

[0084] Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 720 is here schematically shown as a track on the depicted optical disk, the computer program 720 can be stored in any way which is suitable for the computer program product 710. The inventive concept has 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 inventive concept, as defined by the appended patent claims.

[0085] CLAIMS

[0086] 1. A method for configuring UEs (230a: 230N) with uplink reference signal resources, wherein the method is performed by a network node (210, 500, 600), and wherein the method comprises: dividing (S102) a set of uplink reference signal resources among at least two disjoint subsets, wherein the set of uplink reference signal resources is available for transmission of uplink reference signals in a time window, and wherein each of the at least two subsets is associated with its own time-domain behaviour with respect to the transmission of the uplink reference signals within the time window; and configuring (S104) the UEs (230a: 230N) with the uplink reference signal resources of the associated time-domain behaviour from the subsets of uplink reference signal resources, wherein with which subset of uplink reference signal resources each of the UEs (230a: 230N) is configured with depends on characteristics of the UEs (23oa:23oN).

[0087] 2. The method according to claim 1, wherein the characteristics of the UEs (230a: 230N) pertain to at least one of: capabilities of the UEs (230a: 230N), speed of the UEs (230a: 230N), number of transmissions from the UEs (230a: 230N), data rates of the UEs (230a: 230N), traffic patterns of the UEs (230a: 230N), network load caused by the UEs (230a: 230N).

[0088] 3. The method according to claim 1 or 2, wherein the set of available uplink reference signal resources is equally divided among the at least two subsets.

[0089] 4. The method according to claim 1 or 2, wherein the set of available uplink reference signal resources is divided among the at least two subsets dependent on the characteristics of the UEs (230a: 230N) as well as number of UEs (230a: 230N) served by the network node (210, 500, 600).

[0090] 5. The method according to claim 4, wherein the dividing the set of uplink reference signal into at least two subsets is dynamically updated over time as the characteristics and / or the number of served UEs (230a: 230N) change.

Claims

6. The method according to any preceding claim, wherein the time-domain behaviour of a first subset of the at least two subsets corresponds to periodic transmission of the uplink reference signal resources, and wherein the time-domain behaviour of a second subset of the at least two subsets corresponds to aperiodic transmission of the uplink reference signal resources7. The method according to claim 6, wherein the time-domain behaviour of a third subset of the at least two subsets corresponds to semi-persistent transmission of the uplink reference signal resources.

8. The method according to claim 6 or 7, wherein the at least two subsets are dynamically updated such that the first subset grows as the number of served UEs (230a: 230N) decreases, and such that the second subset grows as the number of served UEs (23oa:23oN) increases.

9. The method according to claim 6 or 7, wherein the at least two subsets are dynamically updated such that the first subset grows as speed of the UEs (230a: 230N) decreases, and such that the second subset grows as the speed of the UEs (230a: 230N) increases.

10. The method according to claim 7, wherein the third subset is dynamically updated such that the third subset is largest when either number of served UEs (230a: 230N) is above a first threshold but below a second threshold or when speed of the UEs (230a: 230N) is above a third threshold but below a fourth threshold.

11. The method according to claim 6 or 7, wherein the UEs (230a: 230N) for which speed is lower than a speed threshold are configured with uplink reference signal resources from the first subset, and wherein the UEs (230a: 230N) for which the speed is higher than the speed threshold are configured with uplink reference signal resources from the second subset.

12. The method according to claim 6 or 7, wherein the uplink reference signal resources are divided to all be either in the first subset or in the second subset, and wherein whether to put all the uplink reference signal resources in the first subset or in the second subset depends on speed of the UEs (230a: 230N).13- The method according to claim 11 or 12, wherein the periodic transmission of the uplink reference signal resources has a periodicity that is adaptively set according to at least the speed of the UEs (230a: 230N).

14. The method according to claim 13, wherein the periodicity is jointly set with determining how many of the available uplink reference signal resources to put in each subset when dividing the set of available uplink reference signal resources among at least two disjoint subsets.

15. The method according to any preceding, wherein the method further comprises: receiving (S106) uplink reference signals from the UEs (230a: 230N) on the configured uplink reference signal resources.

16. A network node (210, 500) for configuring UEs (230a: 230N) with uplink reference signal resources, the network node (210, 500) comprising processing circuitry (510), the processing circuitry being configured to cause the network node (210, 500) to: divide a set of uplink reference signal resources among at least two disjoint subsets, wherein the set of uplink reference signal resources is available for transmission of uplink reference signals in a time window, and wherein each of the at least two subsets is associated with its own time-domain behaviour with respect to the transmission of the uplink reference signals within the time window; and configure the UEs (230a: 230N) with the uplink reference signal resources of the associated time-domain behaviour from the subsets of uplink reference signal resources, wherein with which subset of uplink reference signal resources each of the UEs (230a: 230N) is configured with depends on characteristics of the UEs(230a: 230N).

17. The network node (210, 500) according to claim 16, further being configured to perform the method according to any of claims 2 to 15.

18. A computer program (720) for configuring UEs (230a: 230N) with uplink reference signal resources, the computer program comprising computer code which,when run on processing circuitry (510) of a network node (210, 500), causes the network node (210, 500) to: divide (S102) a set of uplink reference signal resources among at least two disjoint subsets, wherein the set of uplink reference signal resources is available for transmission of uplink reference signals in a time window, and wherein each of the at least two subsets is associated with its own time-domain behaviour with respect to the transmission of the uplink reference signals within the time window; and configure (S104) the UEs (230a: 230N) with the uplink reference signal resources of the associated time-domain behaviour from the subsets of uplink reference signal resources, wherein with which subset of uplink reference signal resources each of the UEs (230a: 230N) is configured with depends on characteristics of the UEs (23oa:23oN).

19. A computer program product (710) comprising a computer program (720) according to claim 18, and a computer readable storage medium (730) on which the computer program is stored.

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