Methods and network nodes for controlling transmissions of aperiodic uplink reference signals

Abstract

A method performed by a network node (130) of a wireless communication network (100), for controlling transmission of aperiodic uplink reference signals from a User Equipment, UE (140) to the network node (130), the method comprising: based on a determination of a condition (202) of whether a downlink reference triggering signal being transmitted in a first slot (362) will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot (366); transmitting (210) a scheduled first downlink data as well as the downlink reference triggering signal in a second slot (364) later than the first slot (362), and the transmitted downlink reference triggering signal being used for triggering the transmission of the aperiodic uplink reference signal in the aperiodic uplink reference signal scheduled slot (366).

Description

METHODS AND NETWORK NODES FOR CONTROLLING TRANSMISSIONS OF APERIODIC UPLINK REFERENCE SIGNALSTECHNICAL FIELD

[0001] The present disclosure relates generally to methods and network nodes of wireless communication network for controlling transmissions of aperiodic uplink reference signals. The present disclosure further relates to computer programs and carriers corresponding to the methods and network nodes.BACKGROUND

[0002] To meet the huge demand for higher bandwidth, higher data rates and higher network capacity, due to e.g., data centric applications, existing 4thGeneration (4G) wireless communication network technology, aka Long Term Evolution (LTE) is being extended or enhanced into a 5thGeneration (5G) technology, also called New Radio (NR) access. The following are requirements for 5G wireless communication networks:- Data rates of several tens of megabits per second should be supported for tens of thousands of users;- 1 gigabit per second is to be offered simultaneously to tens of workers on the same office floor;- Several hundreds of thousands of simultaneous connections are to be supported for massive sensor deployments;- Spectral efficiency should be significantly enhanced compared to 4G;- Coverage should be improved;- Signaling efficiency should be enhanced; and- Latency should be reduced significantly compared to 4G.

[0003] Massive Multiple Input Multiple Output (MIMO) is one of the most important technologies used in both LTE and NR because of its remarkable spatial multiplexing gain and powerful interference cancelation ability.

[0004] For single user (SU) and multiple user (MU) downlink MIMO, channel reciprocity is utilized to calculate SU or MU downlink beamforming weight, which can suppress both the intra-cell and inter-cell interferences.

[0005] In terms of channel reciprocity utilization, a reference signal, e.g., sound reference signal (SRS), is a key uplink resource to be used for Sil and MU downlink beamforming. The SRS is a reference signal transmitted by the UE in the uplink direction, and used by a network node, e.g. eNB in LTE or gNB in NR, to estimate the uplink channel quality over a wide bandwidth. Due to channel reciprocity, the estimated channel quality can also be applied to the downlink channel.

[0006] There are three different types of SRS, i.e. , periodic SRS (P-SRS), semi- persistent SRS (SP-SRS) and aperiodic SRS (AP-SRS). The P-SRS is configured by Radio Resource Control (RRC) messaging, then UE periodically sends SRS without further triggering, which is the most static type. The SP-SRS is also configured by RRC messaging, then eNB or gNB activates or deactivates the SP-SRS by a Media Access Control (MAC) control element. The UE will send the SP-SRS periodically if it is activated and stop sending SP-SRS after deactivation command being received. SP-SRS is more flexible than P-SRS.

[0007] AP-SRS is even more flexible than SP-SRS and P-SRS because it is configured by an RRC message and then triggered by a Downlink Control Indicator (DCI) of Physical Downlink Control Channel (PDCCH) on demand. For example, the AP-SRS can be configured by a two-bit field “SRS request” in the DCI.

[0008] Fig. 1 shows a typical message sequence chart for AP-SRS configuration and triggering, i.e., from a network node, here exemplified with a gNB 10, to a wireless device, called UE 20, in 5G networks. The gNB 10 transmits 1.1 an AP-SRS configuration message as an RRC message to the UE 20. The configuration message comprises an offset for corresponding UE 20. The offset indicates a number of time slots, which means the UE 20 will transmit an AP-SRS to the gNB 10 after the number of time slots upon receiving a triggering signal from the gNB 10.When it is time for triggering the UE to transmit an AP-SRS, the gNB 10 transmits 1 .2 a triggering signal as a DCI to the UE 20 for triggering the AP-SRS procedure. Upon receiving the DCI, the UE 20 will 1 .3 wait for a time period corresponding to the offset, then the UE 20 sends 1.4 an AP-SRS to the gNB 10. The gNB 10 can thus utilize the AP-SRS to estimate the channel quality.

[0009] However, it has been observed in networks today that the triggering of AP- SRS often fails. That is, even if the gNb or eNb sends the AP-SRS triggering signal to a UE, the AP-SRS is not scheduled in a time slot which is adapted for AP-SRS transmission, i.e. , the AP-SRS actually cannot be sent from the UE to the network node. Therefore, the AP-SRS triggering is not successful.

[0010] Unexpected or sudden network traffic volume peaks and troughs are commonly referred to as bursty traffic. The term "burst" refers to data burst, which means a sudden behavior of data traffic. Data burst means data package or traffic data which happens in a sudden. The data burst is received by the network node from baseband, then being sent to the UE by the network node. Usually, the network node sends the data burst to the UE together with the AP-SRS, i.e., the data burst is sent to the UE in Physical Downlink Shared Channel (PDSCH) and the AP-SRS is sent to the UE in corresponding PDCCH. The AP-SRS triggering success rate is observed to be particularly low and depends on luck when there is busty traffic pattern for UE. This situation will be discussed in detail in Detailed Description.

[0011] Consequently, there is a need of a solution for improving the possibility of correctly sending the AP-SRS triggering signal, then AP-SRS can be successfully sent from a UE at an AP-SRS scheduled slot.SUMMARY

[0012] It is an object of the invention to address at least some of the problems and issues outlined above. It is an object of the invention to improve triggering possibility or triggering success rate of an aperiodic uplink reference signal. It is possible to achieve these objects and others by using the methods and network nodes as defined in the attached independent claims.

[0013] According to one aspect, a method performed by a network node of a wireless communication network is disclosed. The method is used for controlling transmission of aperiodic uplink reference signals from a User Equipment, UE to the network node, the method comprising: based on a determination of a condition of whether a downlink reference triggering signal being transmitted in a first slot will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplinkreference signal scheduled slot; transmitting a scheduled first downlink data as well as the downlink reference triggering signal in a second slot later than the first slot , and the transmitted downlink reference triggering signal being used for triggering the transmission of the aperiodic uplink reference signal in the aperiodic uplink reference signal scheduled slot .

[0014] According to another aspect, a network node operable in a wireless communication network is disclosed. The network node is configured for controlling transmission of aperiodic uplink reference signals from a User Equipment, UE to the network node, the network node comprising a communication unit, a processing circuitry and a memory , said memory containing instructions executable by said processing circuitry, whereby the network node is operative for: based on a determination of a condition of whether a downlink reference triggering signal being transmitted in a first slot will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot; transmitting a scheduled first downlink data as well as the downlink reference triggering signal in a second slot later than the first slot, and the transmitted downlink reference triggering signal being used for triggering the transmission of the aperiodic uplink reference signal in the aperiodic uplink reference signal scheduled slot.

[0015] According to other aspects, computer programs and carriers are also provided, the details of which will be described in the claims and the detailed description.

[0016] Further possible features and benefits of this solution will become apparent from the detailed description below.BRIEF DESCRIPTION OF DRAWINGS

[0017] The solution will now be described in more detail by means of exemplary embodiments and with reference to the accompanying drawings, in which:

[0018] Fig. 1 is a signaling diagram of an AP-SRS triggering procedure between a network node and a UE.

[0019] Fig. 2 is a schematic block diagram of a wireless communication network in which the present invention may be implemented.

[0020] Fig. 3 is a schematic block diagram of a frame structure of an example of AP-SRS triggering schedule.

[0021] Fig. 4 is a schematic block diagram of a frame structure of an example of AP-SRS triggering success and failure.

[0022] Fig. 5a-5c are schematic block diagrams of frame structures of examples of correct and incorrect triggering slot in bursting traffic scenario.

[0023] Fig. 6 is a schematic diagram showing bursting traffic pattern in relation to time.

[0024] Fig. 7 is a schematic diagram showing SRS utilization ratio.

[0025] Fig. 8 is a flow chart illustrating a method performed by a network node, according to exemplary embodiments.

[0026] Fig. 9 is a schematic block diagram showing a method performed by the network node, according to exemplary embodiments.

[0027] Fig. 10 is a schematic block diagram of reciprocity transmission ratios.

[0028] Fig. 11 is a block diagram illustrating a network node in more detail, according to possible embodiments.DETAILED DESCRIPTION

[0029] Fig. 2 shows a wireless communication network 100 comprising a network node 130 that is in, or is adapted for, wireless communication with a number of wireless devices 140, 142, ...148, i.e., UEs. The network node 130 provides radio coverage in a cell 150, which can be interpreted as a geographical area. The number of wireless devices 140, 142, ... 148 shown in fig. 2 reside in the cell 150.

[0030] The wireless communication network 100 may be any kind of wireless communication network that can provide radio access to wireless communicationdevices. Example of such wireless communication networks are Global System for Mobile communication (GSM), Enhanced Data Rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), Code Division Multiple Access 2000 (CDMA 2000), Long Term Evolution (LTE) Frequency Division Duplex (FDD) and Time Division Duplex (TDD), LTE Advanced, Wireless Local Area Networks (WLAN), Worldwide Interoperability for Microwave Access (WiMAX), WiMAX Advanced, as well as 5G wireless communication networks based on technology such as New Radio (NR). However, the embodiments of the following detailed description are described for NR.

[0031] The network node 130 may be any kind of network node that provides wireless access to the number of wireless devices 140, 145 alone or in combination with another network node. The network node may also be called radio network node. Examples of a network node 130 are a base station (BS), a radio BS, a base transceiver station, a BS controller, a network controller, a Node B (NB), an evolved Node B (eNB), a gNodeB (gNB), a Multi-cell / multicast Coordination Entity, a relay node, an access point (AP), a radio AP, a remote radio unit (RRU), a remote radio head (RRH), nodes in a distributed antenna system (DAS) and a multi-standard radio BS (MSR BS).

[0032] The wireless devices 140, 142, ... 148 may be any type of device capable of wirelessly communicating with a network node 130 using radio signals. The wireless devices may also be called wireless communication devices or simply devices in this disclosure. For example, the wireless devices 140, 142, ...148 may be a User Equipment (UE), a machine type UE or a UE capable of machine to machine (M2M) communication, a sensor, a tablet, a mobile terminal, a smart phone, a laptop embedded equipped (LEE), a laptop mounted equipment (LME), a USB dongle, a Customer Premises Equipment (CPE) etc.

[0033] The embodiments described herein may be applicable to single carrier as well as to multicarrier (MC) or carrier aggregation (CA) operation of the wireless devices. The term carrier aggregation (CA) may also be called multi-carrier system, multi-cell operation, multi-carrier operation, and multi-carrier transmission and / orreception. The embodiments may equally apply for Multi radio bearers (RAB) on some carriers, which means that data and speech are simultaneously scheduled.

[0034] The network node 130 and each one of the UEs 140, 142, ... 148 within one cell 150 will perform the AP-SRS triggering procedure described in fig. 1 . Fig. 3 shows a frame structure which illustrates the triggering schedule. For example, if a triggering signal i.e. , DCI in fig.1 , is transmitted to a UE in a downlink slot 160 which is illustrated by “D” in fig. 3, and the UE is configured with an offset 3, then the UE will send its AP-SRS in slot 166, which is 3 time slots after the transmission of the trigging signal in the downlink slot 160. Please note that the reference numbers in fig. 3 160, 162...176 do not represent the order of the slots but are only used to distinguish different slots, whereas the offset relates to order of the illustrated slots. Since the slot 166 is an SRS slot which is illustrated as “S” in fig. 3, i.e., a slot scheduled for transmitting SRS from the UE, the SRS transmission is successfully triggered. In the example shown in fig. 3, only slots 166 and 176 are used as SRS slots. Similarly, if a triggering signal is transmitted to a UE in a downlink slot 162, and the UE is configured with an offset 2, the UE will send its SRS in the SRS slot 166, the SRS transmission is also successfully triggered. The SRS slot can also be utilized to transmit a triggering signal. For example, if the triggering signal is transmitted to a UE in the SRS slot 166, and the UE is configured with an offset 5, the UE will send its SRS in SRS slot 176. Since the slot 176 is also an SRS slot, the SRS transmission is also successfully triggered. The slot 168 which is illustrated by “U” is an uplink slot and scheduled to receive uplink data from the UE.

[0035] However, if the AP-SRS is not scheduled to be sent in an SRS slot, the triggering becomes a failure. In other words, the AP-SRS can only be transmitted in an SRS slot, which is adapted for transmitting uplink AP-SRS from UE to the network node. Fig. 4 shows a frame structure which illustrates examples of triggering success and failure. UE0 is triggered in downlink slot 160. Since the configured offset of the UE0 is 1 , the AP-SRS is scheduled to be sent in a downlink slot 162, which is one time slot later than the triggering slot 160. However, since the downlink slot 162 is not an SRS slot adapted for transmitting uplink AP-SRS, i.e., an AP-SRS cannot be sent from the UE0 to the network node in the downlink slot 162, the triggering of the AP-SRS of the UEO in the slot 160 is not successful. Thus the slot 160 is not a valid AP- SRS triggering slot for the UEO. Similarly, if UE2 is triggered in the downlink slot 162, considering the offset 3 of the UE2, the AP-SRS is scheduled to be sent in slot 168, which is not an SRS slot either, but an uplink slot. Thus the triggering of the AP-SRS of UE2 is also a failure and the slot 162 is not a valid AP-SRS triggering slot for the UE2. UE3 is triggered in slot 166, and its AP-SRS is scheduled to be sent in an SRS slot 176 according to its offset 5. Since the SRS slot 176 is a valid slot for transmitting AP-SRS, the AP-SRS transmission of UE3 is successfully triggered in the slot 166, and the slot 166 is a valid AP-SRS triggering slot for UE3. Among the four UEs, only the UE3 is successfully triggered, and the triggering possibility is quite low, thereby the SRS processing capability cannot be fully utilized, and the reciprocity gain also becomes low.

[0036] As mentioned in Background, the AP-SRS triggering success rate is particularly low when UE has burst traffic pattern. Referring to figs. 5a-5c, the AP- SRS offset of UE 140 is 1. Since the slot 166 is scheduled for AP-SRS transmission, i.e. , an AP-SRS slot, the correct AP-SRS triggering slot should be the slot 164, which is one slot before the AP-SRS slot 166. Only the downlink data burst for the UE 140 being sent in the slot 164 will result in a successful triggering of the AP-SRS transmission in the slot 166, since the AP-SRS triggering signal is sent together with the downlink data burst in the slot 164. That is, among all the slots shown in the fig. 5a, only the slot 164 is a correct slot to trigger the AP-SRS being sent in the slot 166. Similarly, the slot 174 and the slot 184 are the respective correct AP-SRS trigger slot for the AP-SRS slots 176 and 186. As shown in the figures, downlink data burst sent in the slot 162, the slot 176 and the slot 180 are all failures in triggering AP-SRS. In other words, the slots 162, 176 and 180 are incorrect triggering slots for the AP-SRS.

[0037] From filed testing, the bursting traffic pattern is very often and dominant, referring to fig. 6. In fig .6, each dot indicates a buffer size which is needed to be drained for a specific UE at that moment. The buffer size indicates the amount of data burst for the UE. Therefore, it is clearly shown in fig. 6 that the data bursts for the UE come quite often to the network node at different time points. Due to the bursty traffic pattern, as shown in Fig. 7, when AP-SRS is used, the SRS utilizationratio significantly drops compared to periodic SRS. The SRS can be utilized only when the SRS transmission is successfully triggered, therefore, the SRS utilization ratio indicates the SRS triggering success rate.

[0038] Therefore, it is needed to improve the possibility of successfully triggering the AP-SRS even if the downlink data burst comes in an incorrect AP-SRS triggering slot.

[0039] The basic idea of the present invention is that to store a subset of the downlink data burst in a buffer, no matter when the downlink data burst comes from the baseband to the network node. The subset of the downlink data burst as well as the AP-SRS triggering signal are kept in the buffer until being sent in a correct AP- SRS triggering slot. Therefore, no matter when the downlink data burst comes, at least one part of the downlink data burst and the AP-SRS triggering signal are always transmitted in the correct AP-SRS triggering slot, so that the AP-SRS transmission is successfully triggered accordingly.

[0040] Fig. 8 disclose a method performed by a network node 130 of a wireless communication network 100, for controlling transmission of uplink aperiodic uplink reference signals from a UE 140 to the network node 130. The method comprises based on a determination of a condition 202 of whether a downlink reference triggering signal being transmitted in a first slot 362 will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot 366; transmitting 210 a scheduled first downlink data as well as the downlink reference triggering signal in a second slot 364 later than the first slot 362, and the transmitted downlink reference triggering signal being used for triggering the transmission of the aperiodic uplink reference signal in the aperiodic uplink reference signal scheduled slot 366.

[0041] In this method, the aperiodic uplink reference signal typically can be the AP- SRS signal. It can also be other kind of aperiodic uplink reference signal transmitted from the UE 130 to the network node 140, for example, aperiodic Channel State Information (CSI) report signal. The types of the network node and the wireless communication network are defined in the detailed description related to fig. 2.

[0042] In the step 202, it is determined if a downlink reference triggering signal being transmitted in a first slot 362 will result in the aperiodic uplink reference signal successfully transmitted in an aperiodic uplink reference signal scheduled slot 366. In other words, it is determined if the first slot 362 is a correct trigging slot for the aperiodic uplink reference signal scheduled slot 366. The downlink reference triggering signal can be DC I, or other downlink signal which can trigger the transmission of the aperiodic uplink reference signal.

[0043] Based on the determination in the step 202, in the step 210, a scheduled first downlink data as well as the downlink reference triggering signal are transmitted in a second slot 364 which is later than the first slot 362. In other words, the transmission of the scheduled first downlink data as well as the downlink reference triggering signal is delayed according to the condition determined in the step 202, so that the first downlink data as well as the downlink reference trigging signal are transmitted in a later slot 364.

[0044] By such an embodiment, the first downlink data and the downlink reference triggering signal are transmitted in a later triggering slot, based on whether the aperiodic uplink reference signal can be successfully triggered in the first slot. Therefore, the network node proactively controls that the first downlink data and the downlink reference triggering signal are not transmitted in an incorrect triggering slot, so that a triggering failure of the aperiodic uplink reference signal is avoided, and the aperiodic uplink reference signal triggering possibility is increased.

[0045] According to another embodiment, referring to fig. 8 and fig. 9, the network node 130 has instructed the UE 140 to transmit the aperiodic uplink reference signal with an offset of one or more time slots from receiving the downlink reference triggering signal from the network node 130, the method comprising, when the network node 130 has received a downlink data burst to be transmitted to the UE 140 in a first slot 362: the determination of the condition 202 comprises determining 202 whether the downlink reference triggering signal being transmitted in the first slot 362 will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot 366; scheduling 204, at least a firstsubset of the downlink data burst to be transmitted to the UE 140, when it is determined 202 that the downlink reference triggering signal being transmitted in the first slot 362 will not result in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot 366; the transmitting 210 of a scheduled first downlink data comprises transmitting 210 the scheduled at least first subset of the downlink data burst as well as the downlink reference triggering signal in the second slot 364 later than the first slot 362, wherein the second slot 364 will result in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot 366.

[0046] In this embodiment, the network node 130 has already instructed the UE 140 about the offset, so that the UE 140 is aware of the transmission of the aperiodic uplink reference signal after the offset upon receiving the downlink reference triggering signal. A downlink data burst for the UE 140 is received by the network node 130 in the first slot 362, so that the network node 130 should schedule a transmission of the downlink data burst to the UE 140.

[0047] In the step 202, it is determined whether the aperiodic uplink reference signal can be transmitted successfully in an aperiodic uplink reference signal scheduled slot 366, considering the first slot 362 and the offset. In the example shown by fig. 9, since the offset of the UE 140 is 1 and the downlink data burst as well as the downlink reference triggering signal comes to the network node 130 in the first slot 362, it is determined that the aperiodic uplink reference signal cannot be transmitted in the slot 366. This step 202 is corresponding to the step 202 in the previous embodiment.

[0048] In the step 204, upon the determination in the step 202, i.e. , the downlink reference triggering signal being transmitted in the first slot 362 will not result in the downlink reference triggering signal being transmitted in the downlink reference triggering signal scheduled slot 366, at least a first subset of the downlink data burst is scheduled. Being scheduled means that the at least a first subset of the downlink data burst is stored or reserved for later scheduling, for example in a buffer or in a storage / memory of the network node 130. The scheduled first subsetof the downlink data burst in this step is corresponding to the scheduled first downlink data in the previous embodiment. By being scheduled, the first subset of the downlink data burst is not transmitted to the UE 140 in the first slot 362.

[0049] As an example, referring to fig. 9, the downlink data burst for the UE 140 contains 10000 bits when it comes to the network node 130 in the first slot 362.Upon the determination that the first slot 362 is not the correct triggering slot for the UE 140, at least a subset of the downlink data burst is scheduled, e.g., 3000 bits are stored or reserved in a buffer of the network node 130.

[0050] The size of the first subset of the downlink data burst can be predefined. The size can either be denoted by bits or resource blocks (RB). The relationship between the number of bits and the number of RBs is:Number of bits = Number of RBs * noofRERB* noof Layer * ICCwidebandwherein the noof RERBis the number of resource elements for each RB depends on system configuration. In 5G New Radio (NR), a typical value is 144. noof Layer, can be 1 to 4, is the estimated transmission layer. ICCwidebandis the wideband information carrying capacity calculated by estimated wideband Signal to Interference & Noise Ratio (SINR). A typical size of the first subset denoted by bits can be 3000 bits; if denoted by RBs, a typical size is 4 RBs.

[0051] In the step 210, the scheduled at least first subset of the downlink data as well as the downlink reference triggering signal are transmitted to the UE 130 in the second slot 364 which is later than the first slot 362, the second slot 364 being the correct slot for triggering the aperiodic uplink reference signal, considering the offset 1 and the aperiodic uplink reference signal scheduled slot 366. As explained above, the transmitted first subset of the downlink data burst is corresponding to the transmitted first downlink data in the previous embodiment.

[0052] By this embodiment, the network node schedules that the downlink reference triggering signal is transmitted in the correct trigging slot, no matter when the downlink data burst comes. Even if the downlink data burst comes in an incorrect triggering slot, a subset of the downlink data burst and the downlinkreference triggering signal are always scheduled to be sent in a correct triggering slot. Therefore, the success rate for triggering the aperiodic uplink reference signal is increased significantly. As a result, the UE 140 can utilize the latest updated aperiodic uplink reference signal for obtaining channel quality, and the throughput of SU / MU-MIMO is increased, especially at the burst traffic case which is widely present in filed networks.

[0053] According to another embodiment, the method further comprises transmitting 216 a second subset of the downlink data burst to the UE 140 in the first slot 362, the second subset of the downlink data burst being the downlink data other other than the first subset of the downlink data burst.

[0054] In this embodiment, the second subset of the downlink data burst is the part of the downlink data burst which is not scheduled in the step 204. This second subset of the downlink data burst is transmitted directly to the UE 130 in the first slot 362, upon the network node 130 receiving it from baseband.

[0055] As an example, referring to fig. 9, the downlink data burst for the UE 140 contains 10000 bits when it comes from baseband to the network node 130 in the first slot 362. 3000 bits of the downlink data burst are scheduled for the second slot 364; the rest of them, i.e. , 7000 bits of the downlink data burst are transmitted to the UE 140 in the first slot 362 without delay.

[0056] By this embodiment, the second subset of the burst of downlink data, which is not used for triggering the aperiodic uplink reference signal, is transmitted to the UE in time without delay, so that the communication efficiency is increased.

[0057] According to another embodiment, the method further comprises determining 206 an aperiodic uplink reference signal transmission age, the aperiodic uplink reference signal transmission age being information on a time period between the first slot and a slot in which a latest aperiodic uplink reference signal transmission was received.

[0058] In this embodiment, an aperiodic uplink reference signal transmission age is determined. By such determination, the aperiodic uplink reference signaltransmission age can further be used for determining a necessity of the aperiodic uplink reference signal transmission.

[0059] According to another embodiment, the method further comprises determining 208 a downlink reference triggering signal age, the downlink reference triggering signal age being information on a time period between the first slot and a slot in which a latest downlink reference triggering signal was sent and resulted in an aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot.

[0060] In this embodiment, a downlink reference triggering signal age is determined. By such determination, the downlink reference triggering signal age can further be used for determining a necessity of the aperiodic uplink reference signal transmission.

[0061] According to another embodiment, the method further comprises: only when the aperiodic uplink reference signal transmission age is not shorter than an aperiodic uplink reference signal transmission age threshold and / or the downlink reference triggering signal age is not shorter than a downlink reference triggering signal age threshold plus the offset, the determining 202 of whether the downlink reference triggering signal being transmitted in the first slot 362 will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot 366 is performed.

[0062] In this embodiment, the aperiodic uplink reference signal transmission age and / or the downlink reference triggering signal age are compared with respective threshold. When the aperiodic uplink reference signal transmission age and / or the downlink reference triggering signal age are not shorter than respective thresholds, it indicates that the last transmitted / triggered aperiodic uplink reference signal is old enough and may not correctly represent current channel quality. Therefore, it is necessary to trigger / transmit a new aperiodic uplink reference signal to indicate an updated channel quality between the network node 130 and the UE 140. The determination step 202 is thus performed to determine if the first slot 362 is a correct slot to trigger a new aperiodic uplink reference signal. When the aperiodic uplinkreference signal transmission age and / or the downlink reference triggering signal age are shorter than respective thresholds, it indicates that the last transmitted / triggered aperiodic uplink reference signal is not old enough and can still correctly represent the current channel quality. Therefore it is unnecessary to trigger / transmit a new aperiodic uplink reference signal, so that the determination step 202 is not performed and no downlink reference triggering signal will be sent to the UE 140 to trigger a new aperiodic uplink reference signal. The aperiodic uplink reference signal transmission age and the downlink reference triggering signal age can be used separately as independent indication of whether to perform the determination 202, or can be used together as a combined indication of whether to perform the determination 202.

[0063] The aperiodic uplink reference signal transmission age threshold can be predefined, a typical value is 40 slots. The downlink reference triggering signal age threshold can also be predefined and preferably less than the aperiodic uplink reference signal transmission age threshold, a typical value is 10 slots.

[0064] By this embodiment, the triggering / transmission of aperiodic uplink reference signal is only performed when necessary. Thus the amount of signal interactions is reduced significantly and the network resource is saved, without affecting the communication quality.

[0065] According to another embodiment, the method further comprises: when it is determined 202 that the downlink reference triggering signal being transmitted in the first slot will result in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot 366, transmitting 212 the downlink data and / or the scheduled 204 at least first subset of the downlink data burst to the UE 140 as well as the downlink reference triggering signal in the first slot.

[0066] In this embodiment, it defines another possibility of the determination step 202: the first slot can correctly trigger the transmission of the aperiodic uplink reference signal in the aperiodic uplink reference signal scheduled slot 366, e.g., the first slot is the slot 364 in fig. 9. In this situation, a downlink data burst which comes in the slot 364, and if any, the scheduled first subset of downlink data burst, e.g.,scheduled in the slot 362, should be transmitted in the slot 364 together with the downlink reference triggering signal, so that the aperiodic uplink reference signal is triggered correctly and will be transmitted in the slot 366.

[0067] By this embodiment, it is guaranteed that downlink data burst and / or scheduled first subset of downlink data burst will be transmitted in a slot which correctly triggers the aperiodic uplink reference signal. The downlink reference triggering signal is also transmitted in this slot.

[0068] According to another embodiment, the method further comprises updating 214 the slot in which a latest downlink reference triggering signal was sent and resulted in an aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot to be the first slot which result in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot 366.

[0069] As defined in previous embodiment, the slot in which a latest downlink reference triggering signal was sent and resulted in an aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot is used for determining the downlink reference triggering signal age. When the slot in which a latest downlink reference triggering signal was sent and resulted in an aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot is updated to be the first slot which results in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot 366, i.e. , 364 in the example shown in fig. 9, the downlink reference triggering signal age will be determined correctly for future use.

[0070] According to another embodiment, when it is determined that the first slot is the correct triggering slot for the aperiodic uplink reference signal, a scheduling priority of the UE 140 is configured to be higher than a regular data radio bearer (DRB) priority weight. The burst of downlink data for the UE 140 is scheduled according to the priority weight, e.g., all the downlink data burst for the UE 140 will be transmitted to the UE 140 in the first slot.

[0071] Fig. 10 shows reciprocity transmission ratios of prior art and present invention. By using the present invention, the aperiodic uplink reference signal triggering opportunity is increased, resulting in a higher reciprocity ratio and a higher downlink throughput gain. As shown in fig. 10, by using the present invention, the reciprocity transmission ratio increases significantly, from 35.35% to 89.36%.

[0072] Fig. 11 discloses a block diagram of a network node 130. The network node 130 is operable in a wireless communication network 100, and configured for controlling transmission of aperiodic uplink reference signals from a User Equipment, UE 140 to the network node 130, the network node 130 comprising a communication unit 602, a processing circuitry 603 and a memory 604, said memory 604 containing instructions executable by said processing circuitry 603, whereby the network node 130 is operative for: based on a determination of a condition 202 of whether a downlink reference triggering signal being transmitted in a first slot 362 will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot 366; transmitting a scheduled first downlink data as well as the downlink reference triggering signal in a second slot 364 later than the first slot 362, and the transmitted downlink reference triggering signal being used for triggering the transmission of the aperiodic uplink reference signal in the aperiodic uplink reference signal scheduled slot 366.

[0073] According to another embodiment, the network node 130 has instructed the UE 140 to transmit the aperiodic uplink reference signal with an offset of one or more time slots from receiving the downlink reference triggering signal from the network node 130, the network node 130 is further operative for, when the network node 130 has received a downlink data burst to be transmitted to the UE 140 in a first slot 362: the determination of the condition 202 comprises determining whether the downlink reference triggering signal being transmitted in the first slot 362 will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot 366; scheduling, at least a first subset of the downlink data burst to be transmitted to the UE 140, when it is determined 202 that the downlink reference triggering signal being transmitted in the first slot 362 will not result in the aperiodic uplink reference signal being transmitted in the aperiodic uplink referencesignal scheduled slot 366, the transmitting of a scheduled first downlink data comprises transmitting 210 the scheduled at least first subset of the downlink data burst as well as the downlink reference triggering signal in the second slot 364, wherein the second slot 364 will result in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot 366.

[0074] According to another embodiment, the network node 130 is further operative for: transmitting a second subset of the downlink data burst to the UE 140 in the first slot 362, the second subset of the downlink data burst being the downlink data burst other than the first subset of the downlink data burst.

[0075] According to another embodiment, the network node 130 is further operative for: determining an aperiodic uplink reference signal transmission age, the aperiodic uplink reference signal transmission age being information on a time period between the first slot and a slot in which a latest aperiodic uplink reference signal transmission was received.

[0076] According another embodiment, the network node 130 is further operative for: determining a downlink reference triggering signal age, the downlink reference triggering signal age being information on a time period between the first slot and a slot in which a latest downlink reference triggering signal was sent and resulted in an aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot.

[0077] According to another embodiment, the network node 130 is further operative for: only when the aperiodic uplink reference signal transmission age is not shorter than an aperiodic uplink reference signal transmission age threshold and / or the downlink reference triggering signal age is not shorter than a downlink reference triggering signal age threshold plus the offset, the determining of whether the downlink reference triggering signal being transmitted in the first slot 362 will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot 366 is performed.

[0078] According to another embodiment, the network node 130 is further operative for: when it is determined 202 that the downlink reference triggering signal being transmitted in the first slot will result in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot 366, transmitting the downlink data and / or the scheduled 204 at least first subset of the downlink data burst to the UE 140 as well as the downlink reference triggering signal in the first slot.

[0079] According to another embodiment in fig. 11 , the network node 130 may further comprise a communication unit 602, which may be considered to comprise conventional means for wireless communication with the UEs 140, 142, 148, such as a transceiver for wireless transmission and reception of signals. The instructions executable by said processing circuitry 603 may be arranged as a computer program 605 stored e.g., in said memory 604. The processing circuitry 603 and the memory 604 may be arranged in a sub-arrangement 601 . The sub-arrangement 601 may be a micro-processor and adequate software and storage therefore, a Programmable Logic Device, PLD, or other electronic component(s) / processing circuit(s) configured to perform the method mentioned above. The processing circuitry 603 may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these adapted to execute instructions.

[0080] The computer program 605 may be arranged such that when its instructions are run in the processing circuitry, they cause the network node 130 to perform the steps described in any of the described exemplary embodiments of the network node 130 and its method. The computer program 605 may be carried by a computer program product connectable to the processing circuitry 603. The computer program product may be the memory 604, or at least arranged in the memory. The memory 604 may be realized as for example a RAM (Random-access memory), ROM (Read- Only Memory) or an EEPROM (Electrical Erasable Programmable ROM). In some embodiments, a carrier may contain the computer program 605. The carrier may be one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or computer readable storage medium. The computer-readable storage medium may be e.g., a CD, DVD orflash memory, from which the program could be downloaded into the memory 604. Alternatively, the computer program may be stored on a server or any other entity to which the network node 130 has access via the communication unit 602. The computer program 605 may then be downloaded from the server into the memory 604.

[0081] Although the description above contains a plurality of specificities, these should not be construed as limiting the scope of the concept described herein but as merely providing illustrations of some exemplifying embodiments of the described concept. It will be appreciated that the scope of the presently described concept fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the presently described concept is accordingly not to be limited. Reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more." Further, the term “a number of”, such as in “a number of wireless devices” signifies one or more devices. All structural and functional equivalents to the elements of the above-described embodiments that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed hereby. Moreover, it is not necessary for an apparatus or method to address each and every problem sought to be solved by the presently described concept, for it to be encompassed hereby. In the exemplary figures, a broken line generally signifies that the feature within the broken line is optional.

Claims

CLAIMS1. A method performed by a network node (130) of a wireless communication network (100), for controlling transmission of aperiodic uplink reference signals from a User Equipment, UE (140) to the network node (130), the method comprising: based on a determination of a condition (202) of whether a downlink reference triggering signal being transmitted in a first slot (362) will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot (366); transmitting (210) a scheduled first downlink data as well as the downlink reference triggering signal in a second slot (364) later than the first slot (362), and the transmitted downlink reference triggering signal being used for triggering the transmission of the aperiodic uplink reference signal in the aperiodic uplink reference signal scheduled slot (366).

2. A method as claimed in claim 1 , wherein the network node (130) has instructed the UE (140) to transmit the aperiodic uplink reference signal with an offset of one or more time slots from receiving the downlink reference triggering signal from the network node (130), the method comprising, when the network node (130) has received a downlink data burst to be transmitted to the UE (140) in a first slot (362): the determination of the condition (202) comprises determining (202) whether the downlink reference triggering signal being transmitted in the first slot (362) will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot (366); scheduling (204), at least a first subset of the downlink data burst to be transmitted to the UE (140), when it is determined (202) that the downlink reference triggering signal being transmitted in the first slot (362) will not result in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot (366), the transmitting (210) of a scheduled first downlink data comprises transmitting (210) the scheduled at least first subset of the downlink data burst as well as the downlink reference triggering signal in the second slot (364), wherein thesecond slot (364) will result in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot (366).

3. A method as claimed in claims 1 or 2, wherein the method further comprises: transmitting (216) a second subset of the downlink data burst to the UE (140) in the first slot (362), the second subset of the downlink data burst being the downlink data burst other than the first subset of the downlink data burst.

4. A method as claimed in claims 1- 3, wherein the method further comprises: determining (206) an aperiodic uplink reference signal transmission age, the aperiodic uplink reference signal transmission age being information on a time period between the first slot and a slot in which a latest aperiodic uplink reference signal transmission was received.

5. A method as claimed in any one of the preceding claims, wherein the method further comprises: determining (208) a downlink reference triggering signal age, the downlink reference triggering signal age being information on a time period between the first slot and a slot in which a latest downlink reference triggering signal was sent and resulted in an aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot.

6. A method as claimed in claim 4 or 5, the method further comprises: only when the aperiodic uplink reference signal transmission age is not shorter than an aperiodic uplink reference signal transmission age threshold and / or the downlink reference triggering signal age is not shorter than a downlink reference triggering signal age threshold plus the offset, the determining (202) of whether the downlink reference triggering signal being transmitted in the first slot (362) will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot (366) is performed.

7. A method as claimed in any one of the preceding claims, the method further comprises: when it is determined (202) that the downlink reference triggeringsignal being transmitted in the first slot will result in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot (366), transmitting (212) the downlink data and / or the scheduled (204) at least first subset of the downlink data burst to the UE (140) as well as the downlink reference triggering signal in the first slot.

8. A method as claimed in any one of the claims 5-7, the method further comprises: updating (214) the slot in which a latest downlink reference triggering signal was sent and resulted in an aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot to be the first slot which results in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot (366).

9. A network node (130) operable in a wireless communication network (100), and configured for controlling transmission of aperiodic uplink reference signals from a User Equipment, UE (140) to the network node (130), the network node (130) comprising a communication unit (602), a processing circuitry (603) and a memory (604), said memory (604) containing instructions executable by said processing circuitry (603), whereby the network node (130) is operative for: based on a determination of a condition (202) of whether a downlink reference triggering signal being transmitted in a first slot (362) will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot (366); transmitting a scheduled first downlink data as well as the downlink reference triggering signal in a second slot (364) later than the first slot (362), and the transmitted downlink reference triggering signal being used for triggering the transmission of the aperiodic uplink reference signal in the aperiodic uplink reference signal scheduled slot (366).

10. The network node (130) as claimed in claim 9, wherein the network node (130) has instructed the UE (140) to transmit the aperiodic uplink reference signal with an offset of one or more time slots from receiving the downlink reference triggering signal from the network node (130), the network node (130) is furtheroperative for, when the network node (130) has received a downlink data burst to be transmitted to the UE (140) in a first slot (362): the determination of the condition (202) comprises determining whether the downlink reference triggering signal being transmitted in the first slot (362) will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot (366); scheduling, at least a first subset of the downlink data burst to be transmitted to the UE (140), when it is determined (202) that the downlink reference triggering signal being transmitted in the first slot (362) will not result in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot (366), the transmitting of a scheduled first downlink data comprises transmitting (210) the scheduled at least first subset of the downlink data burst as well as the downlink reference triggering signal in the second slot (364), wherein the second slot (364) will result in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot (366).11 . The network node (130) as claimed in claims 9 or 10, the network node (130) is further operative for: transmitting a second subset of the downlink data burst to the UE (140) in the first slot (362), the second subset of the downlink data burst being the downlink data burst other than the first subset of the downlink data burst.

12. The network node (130) as claimed in any one of the claims 9-11 , the network node (130) is further operative for: determining an aperiodic uplink reference signal transmission age, the aperiodic uplink reference signal transmission age being information on a time period between the first slot and a slot in which a latest aperiodic uplink reference signal transmission was received.

13. The network node (130) as claimed in any one of the claims 9-12, the network node (130) is further operative for: determining a downlink reference triggering signal age, the downlink reference triggering signal age being information on a time period between the firstslot and a slot in which a latest downlink reference triggering signal was sent and resulted in an aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot.

14. The network node (130) as claimed in claim 12 or 13, the network node (130) is further operative for: only when the aperiodic uplink reference signal transmission age is not shorter than an aperiodic uplink reference signal transmission age threshold and / or the downlink reference triggering signal age is not shorter than a downlink reference triggering signal age threshold plus the offset, the determining of whether the downlink reference triggering signal being transmitted in the first slot (362) will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot (366) is performed.

15. The network node (130) as claimed in any one of the claims 9-14, the network node (130) is further operative for: when it is determined 202 that the downlink reference triggering signal being transmitted in the first slot will result in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot (366), transmitting the downlink data and / or the scheduled 204 at least first subset of the downlink data burst to the UE (140) as well as the downlink reference triggering signal in the first slot.

16. The network node (130) as claimed in any one of the claims 13-15, the network node (130) is further operative for: updating the slot in which a latest downlink reference triggering signal was sent and resulted in an aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot to be the first slot which results in the aperiodic uplink reference signal being transmitted in the aperiodic uplink reference signal scheduled slot (366).

17. A computer program (605) comprising instructions, which, when executed by at least one processing circuitry (603) of a network node (130), configured for controlling transmission of aperiodic uplink reference signals from a User Equipment,UE (140) to the network node (130), causes the network node (130) to perform the following steps: based on a determination of a condition (202) of whether a downlink reference triggering signal being transmitted in a first slot (362) will result in the aperiodic uplink reference signal being transmitted in an aperiodic uplink reference signal scheduled slot (366); transmitting (210) a scheduled first downlink data as well as the downlink reference triggering signal in a second slot (364) later than the first slot (362), and the transmitted downlink reference triggering signal being used for triggering the transmission of the aperiodic uplink reference signal in the aperiodic uplink reference signal scheduled slot (366).

18. A carrier containing the computer program (605) according to claim 17, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, an electric signal, or a computer readable storage medium.

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