Scheduling of sounding reference signals

Abstract

There is provided techniques for SRS transmissions. A method is performed by a network node. The method comprises detecting, an SRS transmission gap for a first UE, based on detection of unused SRS ports assigned to the first UE for periodic SRS transmission. The method comprises scheduling, in an upcoming SRS transmission gap for the first UE, aperiodic SRS transmissions for at least one second UE on the detected unused SRS ports.

Description

[0001] SCHEDULING OF SOUNDING 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 scheduling sounding reference signal transmissions.

[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 (DL) 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 0.5 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 some other type of signaling on 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 timedomain 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.

[0012] 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.

[0013] 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.

[0014] 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. 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 signals are preferred. However, not all UEs support transmission of aperiodic uplink reference signals; many UEs support only periodic transmission of uplink reference signals. Further, in some scenarios, such as ultra-reliable low latency communication (URLLC) scenarios, use of aperiodic SRS is less preferred. This is because aperiodic SRS is less reliable since it is dependent on SRS scheduling. Periodic SRS is more reliable for such scenarios since periodic SRS is scheduled on regular basis and is for this reason more suitable for URLLC scenarios.

[0015] In view of the above, there is still a need for improved allocation of SRS transmissions to UEs.

[0016] SUMMARY

[0017] An object of embodiments herein is to address the above issues in terms of inefficient use of SRS transmissions.

[0018] A particular object is to address issues arising from inefficient use of periodic SRS transmissions.

[0019] According to a first aspect there is presented a method for SRS transmissions. The method is performed by a network node. The method comprises detecting an SRS transmission gap for a first UE, based on detection of unused SRS ports assigned to the first UE for periodic SRS transmission. The method comprises scheduling, in an upcoming SRS transmission gap for the first UE, aperiodic SRS transmissions for at least one second UE on the detected unused SRS ports.

[0020] According to a second aspect there is presented a network node for scheduling SRS transmissions. The network node comprises processing circuitry. The processing circuitry is configured to cause the network node to detect an SRS transmission gap for a first UE, based on detection of unused SRS ports assigned to the first UE for periodic SRS transmission. The processing circuitry is configured to cause the network node to schedule, in an upcoming SRS transmission gap for the first UE, aperiodic SRS transmissions for at least one second UE on the detected unused SRS ports.

[0021] According to a third aspect there is presented a computer program for scheduling SRS transmissions. 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 detect an SRS transmission gap for a first UE, based on detection of unused SRS ports assigned to the first UE for periodic SRS transmission. One action comprises the network node to schedule, in an upcoming SRS transmission gap for the first UE, aperiodic SRS transmissions for at least one second UE on the detected unused SRS ports.

[0022] 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.

[0023] Advantageously, these aspects enable already scheduled UL SRS resources for the first UE to be reused by at least one second UE in SRS transmission gaps of the first UE, where this at least one second UE is scheduled with aperiodic SRS transmission.

[0024] Advantageously, these aspects will increase the number of UEs that can be scheduled with SRS transmissions, yielding a mix of UEs scheduled with periodic and aperiodic SRS transmissions.

[0025] Advantageously, these aspects can increase the overall spectral efficiency by reusing unused SRS resources to other UEs. This will make it possible to perform beamforming for a larger number of UEs.

[0026] Advantageously, these aspects will make more efficient use of periodic SRS transmissions in terms of SRS resource allocation. 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.

[0027] 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.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

[0030] Fig. 1 schematically illustrates different types of resource types according to an example;

[0031] Fig. 2 is a schematic diagram illustrating a communication network according to embodiments;

[0032] Fig. 3 schematically illustrates transmission of SRS according to embodiments;

[0033] Fig. 4 is a flowchart of methods for scheduling SRS transmissions according to embodiments;

[0034] Fig. 5 is a flowchart of a method for recording SRS transmission state data according to an embodiment;

[0035] Fig. 6 is a flowchart of a method for predicting availability of unused SRS ports according to an embodiment;

[0036] Fig. 7 is a signaling diagram for scheduling SRS transmissions according to an embodiment;

[0037] Fig. 8 is a schematic diagram showing structural units of a network node according to an embodiment; Fig. 9 is a schematic diagram showing functional modules of a network node according to an embodiment; and

[0038] Fig. 10 shows one example of a computer program product comprising computer readable storage medium according to an embodiment.

[0039] DETAILED DESCRIPTION

[0040] 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.

[0041] 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. The uplink reference signal resources are identified by, for instance, their frequency-domain 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.

[0042] As noted above there is still a need for improved allocation of SRS transmissions to UEs 23oa:23oN.

[0043] The embodiments disclosed herein therefore relate to techniques for scheduling SRS transmissions. 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.

[0044] At least some of the herein disclosed embodiments are based on utilizing the fact that UEs assigned with periodic SRS measurements may not transmit SRS on all ports when these UEs have no ongoing data transmission. Here, the number of ports used may be specific for different types and versions of UEs. These unused SRS ports will be detected by the network node and can be scheduled to other UEs (that hence are scheduled using aperiodic SRS transmission).

[0045] To illustrate this, a comparison of different scenarios will be made next with reference to Fig. 3. It is assumed that a first UE, denoted UEi, is scheduled with periodic SRS transmission. It is further assumed that there are two SRS transmission gaps, denoted SRS transmission gap 1 and SRS transmission gap 2, for UEi. For example, UEi is scheduled for period SRS transmission with cyclic shift alpha and transmission comb beta in special slots of the SRS transmission gaps. The nature of the periodic SRS is that the UE is still scheduled with SRS transmissions even if there is a gap in DL traffic, or if there is any other reason for the UE to not send an SRS. This means, for example, that the UE is still requested by the network node to transmit SRS even with no data. This is illustrated in Fig. 3(a). In further detail, in Fig. 3(a) is illustrated a first scenario where the periodic SRS transmission from UEi is always on, also during the SRS transmission gaps. In Fig. 3(b) and in Fig. 3(b) is illustrated a second scenario. However, dependent on UE implementation, a given UE might, in connected DRX mode, transmit SRS only on specific ports also with gaps in between the occasions. An example of this is illustrated in Fig. 3(b). The pattern of what antenna ports UEi is not transmitting SRS on might be different from UE to UE. According to Fig. 3(b), the periodic SRS transmission from UE1 is off during the SRS transmission gap. For example, an SRS is not sent from UE1 with cyclic shift alpha and transmission comb beta in the SRS transmission gaps. Thus, SRS is not transmitted from UE1 even if it has been scheduled with periodic SRS transmission. Hence, there are unused SRS resources in the SRS transmission gap. At least some of the herein disclosed embodiments are based on finding the pattern used by UEi for (not) transmitting the SRSs. This pattern can, for example, be obtained by recording UL SRS state data (UL SRS or no UL SRS) in the SRS transmission gap and feeding the UL SRS state data as input to a prediction algorithm. The prediction algorithm can then predict the ports from which SRS is not transmitted in the SRS transmission gap for a given UE. For example, also other types of information, such as any, or any combination, of information of historical SRS transmissions, information of historical UE payload, and the UE chipset identifier (ID) can be used for predicting the ports from which SRS is not transmitted in the SRS transmission gap for the UE. As will be disclosed below, there are also other ways in which information about the pattern used by UEi for (not) transmitting the SRSs can be obtained. In any case, this information can then be used to schedule other UEs (such as UE2 and UE3 in the present example) with the thus already scheduled but unused SRS resources. According to Fig. 3(c), the unused SRS resources for UEi are reused by being scheduled for aperiodic SRS transmissions for UE2 and UE3. In this illustrative example, there is one aperiodic SRS transmission each for UE2 and UE3 in each of the two SRS transmission gaps for UEi.

[0046] Fig. 4 is a flowchart illustrating embodiments of methods for scheduling SRS transmissions. The methods are performed by the network node 210. The methods are advantageously provided as computer programs. With reference back to Fig. 3, the method is based on that information about detected unused SRS ports for UEi is used to schedule aperiodic SRS for UE2 and / or UE3.

[0047] S102: The network node 210 detects an SRS transmission gap for a first UE 230a, based on detection of unused SRS ports assigned to the first UE 230a for periodic SRS transmission. In Fig. 3, this first UE 230a is UEi.

[0048] In other words, that there is an SRS transmission gap for the first UE 230a is by the network node 210 detected by not receiving any SRS from one or more ports assigned to the first UE 230a for periodic SRS transmission. Expressed differently, the network node 210 realizes that, during some time period, the network node 210 does not receive any expected SRS from one or more ports of the first UE 230a, and therefore the network node 210 concludes that this time period represents (or defines) an SRS transmission gap.

[0049] S106: The network node 210 schedules, in an upcoming SRS transmission gap for the first UE 230a, aperiodic SRS transmissions for at least one second UE 23ob:23oN on the detected unused SRS ports. In Fig. 3, this at least one second UE 230b: 230N is UE2 and / or UE3.

[0050] Embodiments relating to further details of scheduling SRS transmissions as performed by the network node 210 will now be disclosed with continued reference to Fig. 4-

[0051] There may be different ways for the network node 210 to detect that there are unused SRS ports assigned to the first UE 230a in the SRS transmission gap for the first UE 230a. In some aspects, the detection is based on detecting an absence of transmission from the first UE 230a in the SRS transmission gap. In particular, in some embodiments, the detection of the unused SRS ports is based on detecting absence of SRS transmission from the first UE 230a during the SRS transmission gap. In some aspects, the absence of transmission from the first UE 230a is defined by the received power from the first UE 230a being below some threshold power value. That is, in some embodiments, the detection of the unused SRS ports is based on determining that received power associated with the first UE 230a during the SRS transmission gap is below a threshold power value. In some aspects, the detection is based on information about configured transmission gaps. That is, in some embodiments, the detection of the unused SRS ports is based on identification of transmission gaps as configured by the network node 210. Further, as disclosed above, the network node 210 might find the pattern for the UE by recording UL SRS state data (in terms of recording whether SRS is present or not present) in the SRS transmission gap and feed this information to a prediction algorithm. Hence, in some embodiments, the network node 210 is configured to perform (optional) step S104.

[0052] S104: The network node 210 predicts availability of unused SRS ports for the first UE 230a in the upcoming SRS transmission gap by recording SRS transmission state data for the first UE 230a during previous SRS transmission gaps and feeding the SRS transmission state data into a prediction algorithm executed in the network node 210.

[0053] An example of a method for recording SRS transmission state data for a UE will be disclosed below with reference to Fig. 5. An example of a method for predicting the availability of unused SRS ports for a UE will be disclosed below with reference to Fig. 6.

[0054] There could be different types of SRS transmission state data. In some aspects, the SRS transmission state data is provided per time and frequency resource (possibly also taking the cyclic shift into account) in the previous SRS transmission gaps. For example, The SRS transmission state data could specify whether an SRS transmission from the first UE 230a is present or not in the time and frequency resources in the previous SRS transmission gaps.

[0055] In some aspects, the prediction algorithm is used to predict from which ports, and when in the SRS transmission gap, SRS is not transmitted for a given UE. That is, in some embodiments, the prediction algorithm is configured to, based on the recorded SRS transmission state data, predict which SRS ports of the first UE 230a will be unused by the first UE 230a and when (in time) the unused SRS ports will be available in the upcoming SRS transmission gap.

[0056] There can be different types of prediction algorithms. For example, the prediction algorithm can be a machine learning algorithm that is trained using historical SRS transmission state data recorded in previous SRS transmission gaps. Further, as in the examples of Fig. 6, the SRS states in the SRS transmission gaps can be predicted based on a sliding window. Hence, in some embodiments, the prediction algorithm utilizes a sliding window approach to predict SRS transmission states for the first UE 230a in at least one upcoming SRS transmission gap.

[0057] As disclosed in step S106, the network node 210 schedules, in an upcoming SRS transmission gap for the first UE 230a, aperiodic SRS transmissions for at least one second UE 230b: 230N on the detected unused SRS ports. There could be different ways for the network node 210 to determine the scheduling in step S106, for example in terms of which unused SRS ports should be assigned to which other UE 230b: 230N, etc.

[0058] In this respect, the network node 210 can use a scheduling criterion when determining which unused SRS ports should be assigned to which other UE or UEs. In particular, in some embodiments, the scheduling comprises dynamically assigning the unused SRS ports to the at least one second UE 230b: 230N based on at least one scheduling criterion. There could be different types of scheduling criteria. For example, the scheduling criteria could pertain to the availability of SRS ports and / or communication requirements of other UEs 23ob:23oN served by the network node 210, speed of the UE 230a, payload volume of the UE 230a, as well as channel quality and network load. Hence, in some non-limiting examples, the scheduling criterion pertains to at least one of: availability of the unused SRS ports in the at least one second UE 23ob:23oN, communication requirements of the at least one second UE 230b: 230N. The communication requirements may at least pertain to prioritized transmission of the at least one second UE 230b: 230N.

[0059] An example of a method for recording SRS transmission state data for a first UE 230a will be disclosed next with reference to the flowchart in Fig. 5.

[0060] S201: The network node 210 identifies the start of the SRS transmission gap for the first UE 230a. The start can be identified based on the SRS signal to interference plus noise ratio or the SRS signal power and thresholding to detect the SRS transmission gap. In other words, the SRS transmission gap starts where there is no SRS transmission from the first UE 230a.

[0061] S202: The network node 210 starts measuring in the SRS transmission gap on resources on which a periodic SRS transmission has been scheduled for the first UE 230a.

[0062] S203: The network node 210 checks whether any SRS transmissions were received or not from the first UE 230a in the SRS transmission gap. If yes, step S204 is entered. If no, step S205 is entered.

[0063] S204: The network node 210 checks whether the SRS transmission gap has ended or not. If no, step S206 is entered. If yes, the procedure is ended. S205: The network node 210 stores the transmission occasion where no SRS transmission was received from the first UE 230a.

[0064] S206: The network node 210 stores the transmission occasion where SRS transmission was received from the first UE 230a.

[0065] Step S201 can then be entered again for identifying the next SRS transmission gap for the same first UE 230a or for identifying an SRS transmission gap for another UE.

[0066] This method describes how UL SRS states are recorded in the SRS transmission gap. The result is thus a sequence of UL SRS states, where the UL SRS state for a given resource on which a periodic SRS transmission has been scheduled for a given UE indicates whether SRS is present or not. This sequence of UL SRS states can then be provided as input to a predicting algorithm.

[0067] An example of a method for predicting the availability of unused SRS ports for a first UE 230a will be disclosed below with reference to the flowchart in Fig. 6.

[0068] S301: The network node 210 identifies the start of the SRS transmission gap for the first UE 230a. The start can be identified based on the SRS signal to interference plus noise ratio or the SRS signal power and thresholding to detect the SRS transmission gap. In other words, the SRS transmission gap starts where there is no SRS transmission from the first UE 230a.

[0069] S302: The network node 210 starts measuring in the SRS transmission gap on resources on which a periodic SRS transmission has been scheduled for the first UE 230a.

[0070] S303: The network node 210 adds SRS transmission occasions with UL SRS states (e.g., as recorded in accordance with the method in Fig. 5) to a sliding window of size x.

[0071] S304: The network node 210 checks whether the SRS transmission gap has ended or not. If no, step S305 is entered. If yes, the procedure is ended.

[0072] S305: The network node 210 checks whether the sliding window has been filled or not. If no, step S303 is entered again. If yes, step S306 is entered. S306: The network node 210 provides the UL SRS states in the sliding window as input to a prediction algorithm. The prediction algorithm outputs a prediction of the next y UL SRS states for the first UE 230a.

[0073] S307: The network node 210 identifies at least one second UE 23ob:23oN not scheduled with period SRS transmission but with matching port configuration with respect to the first UE 230a.

[0074] S308: The network node 210 schedules at least one second UE 230b: 230N with one or more aperiodic SRS transmissions on the predicted time and frequency occasions with no SRS transmissions from the first UE 230a.

[0075] This method describes how a prediction algorithm can be used to predict UL SRS states in the SRS transmission gaps based on a sliding window. Information of the predicted UL SRS states is used for scheduling aperiodic SRS transmissions from other UEs 23ob:23oN when no SRS is predicted to be transmitted from a UE already scheduled with period SRS transmission.

[0076] The algorithm can be a machine learning algorithm that is trained based on the UL SRS states in the SRS transmission gap. However, also other algorithms, such as different types of time series analysis algorithms, can be used to predict patterns based on historical data.

[0077] Reference is next made to the signaling diagram in Fig. 7. This signaling diagram illustrates a procedure where one UE, denoted UEi, that is scheduled with periodic SRS transmission skips SRS transmissions and where the thus unused SRS resources are allocated to another UE, denoted UE2, for aperiodic SRS transmission.

[0078] S401: The network node 210 configures UEi with periodic SRS transmission by transmitting an RRC message indicating periodic SRS to UEi.

[0079] S402: UEi acknowledges receipt of the RRC message sent to UEi in step S401 by responding with an RRC message complete.

[0080] S403: The network node 210 configures UE2 with aperiodic SRS transmission by transmitting an RRC message indicating aperiodic SRS to UE2. S4O4:UE2 acknowledges receipt of the RRC message sent to UE2 in step S403 by responding with an RRC message complete.

[0081] S405: The network node 210 transmits downlink information (e.g., on a control channel, such as a new radio (NR) physical downlink control channel (PDCCH), or on a data channel, such as an NR physical downlink shared channel (PDSCH) to UE1.

[0082] S406: UEl transmits SRS in accordance with the configured periodic SRS transmission. The SRS is received by the network node 210.

[0083] S407: UEl transmits SRS in accordance with the configured periodic SRS transmission.

[0084] S408: UEl notices an SRS transmission gap and therefore stops its transmission of the configured periodic SRS transmission.

[0085] S409: UEl refrains from transmitting its configured periodic SRS transmission. The network node 210 detects absence of the SRS transmission.

[0086] S410: UEl refrains from transmitting its configured periodic SRS transmission. The network node 210 detects absence of the SRS transmission.

[0087] S411: The network node 210, based on the detected absence of the SRS transmissions in steps S409 and S410, predicts availability of unused SRS ports for UEl in at least one upcoming SRS transmission gap.

[0088] S412: The network node 210 sends a message instructing UE2 to make an aperiodic SRS transmission in the predicted unused SRS ports for UEl in the at least one upcoming SRS transmission gap.

[0089] An illustrative scenario where the herein disclosed embodiments can be applied will be disclosed next. In this scenario, a first UE 230a is provided in vehicle configured for vehicle-to-eveiything (V2X) communication. Assume that the vehicle is driving on a street in an urban environment. Assume that the first UE 230a is used for a traffic safety application run in the vehicle and that the traffic safety application has URLLC requirements. Assume that the first UE 230a is used for uploading sensor data collected by the traffic safety application from sensors in the vehicle to a computational cloud service. Assume that the computational cloud service is configured to process the sensor data and to provide control signals to the vehicle. Assume further that the first UE 230a is configured with periodic SRS transmission (e.g., because of the URLLC requirements).

[0090] Assume now that the vehicle is facing a red light and needs to stop. This reduce the amount of sensor data that is sent from the vehicle to the computational cloud service because of the vehicle is not moving. Also, because the vehicle is not moving, less control signals need to be sent in the downlink to the vehicle. Hence, as the vehicle moves from one traffic light to the next, the vehicle in this case receives bursty data in the downlink. During the SRS transmission gap, the first UE 230a will still be requested to transmit SRS, since the first UE 230a was configured with periodic SRS transmission.

[0091] However, due to the SRS transmission gap, the first UE 230a decides to not transmit any SRS on some of its antenna ports in the SRS transmission gap. The network node 210 being in communication with the first UE 230a detects the pattern of how the first UE 230a does not transmit SRS. Based on this pattern, the network node 210 schedules, in an upcoming SRS transmission gap for the first UE 230a, aperiodic SRS transmissions for at least one second UE 230b: 230N on the detected unused SRS ports.

[0092] Fig. 8 schematically illustrates, in terms of a number of structural units, the components of a network node 800 according to an embodiment. Processing circuitry 810 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 1010 (as in Fig. 10), e.g. in the form of a storage medium 830. The processing circuitry 810 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0093] Particularly, the processing circuitry 810 is configured to cause the network node 800 to perform a set of operations, or steps, as disclosed above. For example, the storage medium 830 may store the set of operations, and the processing circuitry 810 may be configured to retrieve the set of operations from the storage medium 830 to cause the network node 800 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry 810 is thereby arranged to execute methods as herein disclosed. The storage medium 830 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 800 may further comprise a communications (comm.) interface 820 at least configured for communications with other entities, functions, nodes and device, such as the UEs 230a: 230N and the TRP 220 in Fig. 2. As such the communications interface 820 may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry 810 controls the general operation of the network node 800 e.g. by sending data and control signals to the communications interface 820 and the storage medium 830, by receiving data and reports from the communications interface 820, and by retrieving data and instructions from the storage medium 830. Other components, as well as the related functionality, of the network node 800 are omitted in order not to obscure the concepts presented herein.

[0094] Fig. 9 schematically illustrates, in terms of a number of functional modules, the components of a network node 900 according to an embodiment. The network node 900 of Fig. 9 comprises a number of functional modules; a detect module 910 configured to perform step S102, and a schedule module 930 configured to perform step S106. The network node 900 of Fig. 9 may further comprise a number of optional functional modules, such as a predict module 920 configured to perform step S104. In general terms, each functional module 9io:93omay 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 820 which when run on the processing circuitry 810 makes the network node 800 perform the corresponding steps mentioned above in conjunction with Fig 9. 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 9io:93omay be implemented by the processing circuitry 210, possibly in cooperation with the communications interface 220 and / or the storage medium 830. The processing circuitry 810 may thus be configured to from the storage medium 830 fetch instructions as provided by a functional module 9io:93oand to execute these instructions, thereby performing any steps as disclosed herein.

[0095] The network node 210, 800, 900 may be provided as a standalone device or as a part of at least one further device. For example, the network node 210, 800, 900 maybe provided in a node of a radio access network or in a node of a core network. Alternatively, functionality of the network node 210, 800, 900 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, 800, 900 may be executed in a first device, and a second portion of the of the instructions performed by the network node 210, 800, 900 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, 800, 900 maybe executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a network node 210, 800, 900 residing in a cloud computational environment. Therefore, although a single processing circuitry 810 is illustrated in Fig. 8 the processing circuitry 810 may be distributed among a plurality of devices, or nodes. The same applies to the functional modules 910:930 of Fig. 9 and the computer program 1020 of Fig. 10.

[0096] Some (radio) access network architectures define network nodes (or gNBs) comprising multiple component parts or nodes: a central unit (CU), one or more distributed units (DUs), and one or more radio units (RUs). The protocol layer stack of the network node is divided between the CU, the DUs and the RUs, with one or more lower layers of the stack implemented in the RUs, and one or more higher layers of the stack implemented in the CU and / or DUs. The CU is coupled to the DUs via a fronthaul higher layer split (HLS) network; the CU / DUs are connected to the RUs via a fronthaul lower-layer split (LLS) network. The DU may be combined with the CU in some embodiments, where a combined DU / CU may be referred to as a CU or simply a baseband unit. A communication link for communication of user data messages or packets between the RU and the baseband unit, CU, or DU is referred to as a fronthaul network or interface. Messages or packets may be transmitted from the network node 210, 800, 900 in the downlink (i.e., from the CU to the RU) or received by the network node 210, 800, 900 in the uplink (i.e., from the RU to the CU).

[0097] Fig. 10 shows one example of a computer program product 1010 comprising computer readable storage medium 1030. On this computer readable storage medium 1030, a computer program 1020 can be stored, which computer program 1020 can cause the processing circuitry 810 and thereto operatively coupled entities and devices, such as the communications interface 820 and the storage medium 830, to execute methods according to embodiments described herein. The computer program 1020 and / or computer program product 1010 may thus provide means for performing any steps as herein disclosed.

[0098] In the example of Fig. 10, the computer program product 1010 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 1010 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 Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 1020 is here schematically shown as a track on the depicted optical disk, the computer program 1020 can be stored in any way which is suitable for the computer program product 1010.

[0099] 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.

Claims

CLAIMS1. A method for scheduling sounding reference signal, SRS, transmissions, wherein the method is performed by a network node (210, 700, 800), and wherein the method comprises: detecting (S102), an SRS transmission gap for a first user equipment, UE (230a), based on detection of unused SRS ports assigned to the first UE (230a) for periodic SRS transmission; and scheduling (S106), in an upcoming SRS transmission gap for the first UE (230a), aperiodic SRS transmissions for at least one second UE (230b: 230N) on the detected unused SRS ports.

2. The method according to claim 1, wherein the detection of the unused SRS ports is based on detecting absence of SRS transmission from the first UE (230a) during the SRS transmission gap.

3. The method according to claim 1 or 2, wherein the detection of the unused SRS ports is based on determining that received power associated with the first UE (230a) during the SRS transmission gap is below a threshold power value.

4. The method according to any preceding claim, wherein the detection of the unused SRS ports is based on identification of transmission gaps as configured by the network node (210, 700, 800).

5. The method according to any preceding claim, wherein the method further comprises: predicting (S104) availability of unused SRS ports for the first UE (230a) in the upcoming SRS transmission gap by recording SRS transmission state data for the first UE (230a) during previous SRS transmission gaps and feeding the SRS transmission state data into a prediction algorithm executed in the network node (210, 700, 800).

6. The method according to claim 5, wherein the SRS transmission state data is provided per time and frequency resource in the previous SRS transmission gaps, and wherein the SRS transmission state data specifies whether an SRS transmission fromthe first UE (230a) is present or not in the time and frequency resources in the previous SRS transmission gaps.

7. The method according to claim 5 or 6, wherein the prediction algorithm is configured to, based on the recorded SRS transmission state data, predict which SRS ports of the first UE (230a) will be unused by the first UE (230a) and when the unused SRS ports will be available in the upcoming SRS transmission gap.

8. The method according to claim 5, 6, or 7, wherein the prediction algorithm is a machine learning algorithm trained using historical SRS transmission state data recorded in previous SRS transmission gaps.

9. The method according to claim 5, 6, 7, or 8, wherein the prediction algorithm utilizes a sliding window approach to predict SRS transmission states for the first UE (230a) in at least one upcoming SRS transmission gap.

10. The method according to any preceding claim, wherein the scheduling comprises dynamically assigning the unused SRS ports to the at least one second UE (230b: 230N) based on at least one scheduling criterion.

11. The method according to claim 10, wherein the scheduling criterion pertains to at least one of: availability of the unused SRS ports in the at least one second UE (230b: 230N), communication requirements of the at least one second UE(230b: 230N).

12. The method according to claim 11, wherein the communication requirements at least pertain to prioritized transmission of the at least one second UE (230b: 230N).

13. A network node (210, 700, 800) for scheduling sounding reference signal, SRS, transmissions, the network node (210, 700, 800) comprising processing circuitry (810), the processing circuitry being configured to cause the network node (210, 700, 800) to: detect, an SRS transmission gap for a first user equipment, UE (230a), based on detection of unused SRS ports assigned to the first UE (230a) for periodic SRS transmission; andschedule, in an upcoming SRS transmission gap for the first UE (230a), aperiodic SRS transmissions for at least one second UE (230b: 230N) on the detected unused SRS ports.

14. The network node (210, 700, 800) according to claim 13, further being configured to perform the method according to any of claims 2 to 12.

15. A computer program (1020) for scheduling sounding reference signal, SRS, transmissions, the computer program comprising computer code which, when run on processing circuitry (810) of a network node (210, 700, 800), causes the network node (210, 700, 800) to: detect (S102), an SRS transmission gap for a first user equipment, UE (230a), based on detection of unused SRS ports assigned to the first UE (230a) for periodic SRS transmission; and schedule (S106), in an upcoming SRS transmission gap for the first UE (230a), aperiodic SRS transmissions for at least one second UE (230b: 230N) on the detected unused SRS ports.

16. A computer program product (1010) comprising a computer program (1020) according to claim 15, and a computer readable storage medium (1030) on which the computer program is stored.

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