Apparatus, methods and computer programs relating to transmission configuration indicator states

Abstract

A UE receiving information indicating two or more target transmission configuration indicator (TCI) states, and for at least one of the multiple target TCI states, a mapping between the target TCI sta

Description

Field This disclosure generally relates to communication systems and in particular but not exclusively to apparatus, methods and computer programs relating to transmission configuration indicator states. Background A communication system can be seen as a facility that enables communications between two or more communication devices, or provides communication devices access to a data network. A mobile or wireless network is one example of a communication system. A communication device may be provided with a service by an application server. Such communication systems operate in according with standards such as those provided by 3GPP (Third Generation Partnership Project) or ETSI (European Telecommunications Standards Institute). Examples of standards are the so-called 5G (5th Generation) standards provided by 3GPP. Summary According to an aspect, there is provided a user equipment comprising: means for receiving: information, the information indicating two or more target transmission configuration indicator states, and for at least one of the two or more target transmission configuration indicator states, a mapping between the target transmission configuration indicator state and a respective aperiodic reference signal; and one or more respective aperiodic reference signals; and means for synchronising with the received one or more respective aperiodic reference signals. The information with the mapping between the target transmission configuration indicator state and a respective aperiodic reference signal may be received from a base station when one or more user equipment conditions are satisfied. The one or more respective aperiodic reference signals may be received from a base station when one or more user equipment conditions are satisfied. The synchronising with the received one or more respective aperiodic reference signals may be performed when one or more user equipment conditions are satisfied. The user equipment may comprise means for determining whether the one or more user equipment conditions are satisfied. The one or more user equipment conditions may comprise one or more of: a time for synchronising with a synchronisation signal of a target transmission configuration indicator state would be greater than a threshold time; the user equipment is not capable of synchronising with different synchronisation signals at the same time, where the different synchronisation signals would be associated with different ones of the two or more target transmission configuration indicator states; or there is no quasi co-location relationship between one or more of the target transmission configuration indicator states and one or more current transmission configuration indicator states of the user equipment. The synchronization signals may comprise synchronisation signal blocks. One of the two or more target transmission configuration indicator states may be associated with a first transmission reception point and another of the two or more target transmission configuration indicator states may be associated with a second transmission reception point. The information may be received in a medium access control control element. The user equipment may comprise means for decoding the information in the medium access control control element. The user equipment may comprise means for activating a respective one of the two or more target transmission configuration indicator states after synchronising with the received respective aperiodic reference signal. The one or more respective aperiodic reference signals may comprise one or more respective aperiodic temporary reference signals. According to another aspect, there is provided a user equipment comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the user equipment to perform at least: receiving information, the information indicating two or more target transmission configuration indicator states, and for at least one of the two or more target transmission configuration indicator states, a mapping between the target transmission configuration indicator state and a respective aperiodic reference signal; receiving one or more respective aperiodic reference signals; and synchronising with the received one or more respective aperiodic reference signals. According to another aspect, there is provided an apparatus comprising: means for causing information to be transmitted to a user equipment, the information indicating two or more target transmission configuration indicator states, and for at least one of the two or more target transmission configuration indicator states, a mapping between the target transmission configuration indicator state and a respective aperiodic reference signal; and means for causing one or more respective aperiodic reference signals to be transmitted to the user equipment. The information with the mapping between the target transmission configuration indicator state and a respective aperiodic reference signal may be transmitted to the user equipment when one or more user equipment conditions are satisfied. The one or more respective aperiodic reference signals may be transmitted to the user equipment when one or more user equipment conditions are satisfied. The apparatus may comprise means for determining whether the one or more user equipment conditions are satisfied. The one or more user equipment conditions may comprise one or more of: a time for synchronising with a synchronisation signal of a target transmission configuration indicator state would be greater than a threshold time; the user equipment is not capable of synchronising with different synchronisation signals at the same time, where the different synchronisation signals would be associated with different ones of the two or more target transmission configuration indicator states; or there is no quasi co-location relationship between one or more of the target transmission configuration indicator states and one or more current transmission configuration indicator states of the user equipment. The synchronization signals may comprise synchronisation signal blocks. One of the two or more target transmission configuration indicator states may be associated with a first transmission reception point and another of the two or more target transmission configuration indicator states may be associated with a second transmission reception point. The information may be provided in a medium access control control element. The one or more respective aperiodic reference signals comprise one or more respective aperiodic temporary reference signals. The apparatus may comprise a base station. According to another aspect, there is provided an apparatus comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to perform at least: causing information to be transmitted to a user equipment, the information indicating two or more target transmission configuration indicator states, and for at least one of the two or more target transmission configuration indicator states, a mapping between the target transmission configuration indicator state and a respective aperiodic reference signal; and causing one or more respective aperiodic reference signals to be transmitted to the user equipment. The apparatus may comprise a base station. According to another aspect, there is provided a method comprising: receiving information, the information indicating two or more target transmission configuration indicator states, and for at least one of the two or more target transmission configuration indicator states, a mapping between the target transmission configuration indicator state and a respective aperiodic reference signal; receiving one or more respective aperiodic reference signals; and synchronising with the received one or more respective aperiodic reference signals. The information with the mapping between the target transmission configuration indicator state and a respective aperiodic reference signal may be received from a base station when one or more user equipment conditions are satisfied. The one or more respective aperiodic reference signals may be received from a base station when one or more user equipment conditions are satisfied. The synchronising with the received one or more respective aperiodic reference signals may be performed when one or more user equipment conditions are satisfied. The method may comprise determining whether the one or more user equipment conditions are satisfied. The one or more user equipment conditions may comprise one or more of: a time for synchronising with a synchronisation signal of a target transmission configuration indicator state would be greater than a threshold time; the user equipment is not capable of synchronising with different synchronisation signals at the same time, where the different synchronisation signals would be associated with different ones of the two or more target transmission configuration indicator states; or there is no quasi co-location relationship between one or more of the target transmission configuration indicator states and one or more current transmission configuration indicator states of the user equipment. The synchronization signals may comprise synchronisation signal blocks. One of the two or more target transmission configuration indicator states may be associated with a first transmission reception point and another of the two or more target transmission configuration indicator states may be associated with a second transmission reception point. The information may be received in a medium access control control element. The method may comprise decoding the information in the medium access control control element. The method may comprise activating a respective one of the two or more target transmission configuration indicator states after synchronising with the received respective aperiodic reference signal. The one or more respective aperiodic reference signals may comprise one or more respective aperiodic temporary reference signals. The method may be performed by a user equipment. According to another aspect, there is provided a method comprising: causing information to be transmitted to a user equipment, the information indicating two or more target transmission configuration indicator states, and for at least one of the two or more target transmission configuration indicator states, a mapping between the target transmission configuration indicator state and a respective aperiodic reference signal; and causing one or more respective aperiodic reference signals to be transmitted to the user equipment. The information with the mapping between the target transmission configuration indicator state and a respective aperiodic reference signal may be transmitted to the user equipment when one or more user equipment conditions are satisfied. The one or more respective aperiodic reference signals may be transmitted to the user equipment when one or more user equipment conditions are satisfied. The method may comprise determining whether the one or more user equipment conditions are satisfied. The one or more user equipment conditions may comprise one or more of: a time for synchronising with a synchronisation signal of a target transmission configuration indicator state would be greater than a threshold time; the user equipment is not capable of synchronising with different synchronisation signals at the same time, where the different synchronisation signals would be associated with different ones of the two or more target transmission configuration indicator states; or there is no quasi co-location relationship between one or more of the target transmission configuration indicator states and one or more current transmission configuration indicator states of the user equipment. The synchronization signals may comprise synchronisation signal blocks. One of the two or more target transmission configuration indicator states may be associated with a first transmission reception point and another of the two or more target transmission configuration indicator states may be associated with a second transmission reception point. The information may be provided in a medium access control control element. The one or more respective aperiodic reference signals comprise one or more respective aperiodic temporary reference signals. The method may performed by an apparatus. The apparatus may comprise a base According to a further aspect, there is provided a computer program comprising instructions, which when executed by an apparatus, cause the apparatus to perform any of the methods set out previously. According to a further aspect, there is provided a computer program comprising instructions, which when executed cause any of the methods set out previously to be performed. According to an aspect there is provided a computer program comprising computer executable code which when run cause any of the methods set out previously to be performed. According to an aspect, there is provided a computer readable medium comprising program instructions stored thereon for performing at least one of the above methods. According to an aspect, there is provided a non-transitory computer readable medium comprising program instructions which when executed by an apparatus, cause the apparatus to perform any of the methods set out previously. According to an aspect, there is provided a non-transitory computer readable medium comprising program instructions which when executed cause any of the methods set out previously to be performed. According to an aspect, there is provided a non-volatile tangible memory medium comprising program instructions stored thereon for performing at least one of the above methods. In the above, many different aspects have been described. It should be appreciated that further aspects may be provided by the combination of any two or more of the aspects described above. Various other aspects are also described in the following detailed description and in the attached claims. Description of Figures Embodiments will now be described, by way of example only, with reference to the accompanying Figures in which: Figure 1 shows an overview of some embodiments; Figure 2 shows a hierarchical beam-based approach; Figure 3 shows a timing scenario where two SSBs would be received generally at the same time; Figure 4 shows a timing scenario of some embodiments; Figure 5 shows an overview method of some embodiments; Figure 6a and 6b shows a first example procedure of some embodiments; Figure 7 shows a schematic representation of a 5G system: Figure 8 shows a schematic representation of an apparatus; Figures 9 shows a schematic representation of a user equipment (UE); Figure 10 shows a method of some embodiments; and Figure 11 shows another method of some embodiments. Detailed description Reference is made to Figure 1 which shows a simplified overview of some embodiments. A UE 300 (user equipment) is connected to a network via two or more transmission and reception points (TRP). The TRPs may be part of one or more radio access networks. In this example, a first TRP, TRP1, and a second TRP, TRP2, are shown. Some embodiments may be described in relation to a 5G system. However, this is by way of example only, and other embodiments may be used with any other system. In the example of Figure 1, the UE is connected to each TRP by a respective beam 102 and 104. Abeam represents the direction in which one of the UE and the TRP transmits to the other of the UE and the TRP. The uplink and downlink beam directions between a given TRP and the UE may be the same or different. In other embodiments, the UE may be connected to more than two TRPs. In some embodiments, for a given TRP, there may be two or more beams. The UE should be synchronized to each TRP. The UE may be synchronized in time and / or frequency to a given TRP. In some embodiments, each TRP will transmit to the UE information which is used by the UE to synchronize to that TRP. In 5G synchronization signal blocks (SSBs) are used for synchronizing the respective TRP and the UE. In the following example, SSBs will be described as example synchronization signals. However, is should be appreciated that in other embodiments, different synchronization signals may be used. An SSB is a signal transmitted by a respective TRP on a broadcast channel. The SSB may comprises a combination of a synchronization signal (SS) and physical broadcast channel (PBCH)). In one example a SSB may comprise four symbols (e.g., four orthogonal frequency division multiplex (OFDM) symbols): 1 symbol for a primary synchronization signal (PSS), 1 symbol for a secondary synchronization signal (SSS), and 2 symbols for PBCH. An SS burst comprises one or more SSBs. This is by way of example and SSBs, for example of different standards or versions of standards, may comprise different information and / or length. The SSB transmitted by a TRP may comprise system information, which is information usable by a receiving UE to access the radio access network associated with the TRP. The system information may be provided in the form of a master information block (MIB) and a plurality of different system information blocks (SIBs). Beam management is used in some embodiments. Beam management is a set of procedures to assist UE to set its spatial receive (Rx) and transmit (Tx) beam settings for downlink and uplink transmissions, respectively. 5G supports a hierarchical beam-based approach as shown in Figure 2. As shown in Figure 2, the SSB beam is the root beam. Level 1 provides the SS / PBCH block beams on which the SSB is transmitted. Level 2-n provides CSI-RS (channel state information reference signal) beams. For example, CS-RS#0, CS-RS#1, CS-RS#2, CS-RS#3, and CS-RS#4 beams are associated with the SSB #n beam. A quasi co-location (QCL) framework may be used for beam indication. Two antenna ports are said to be quasi co-located if properties of the channel over which a symbol on one antenna port is conveyed can be inferred from the channel over which a symbol on the other antenna port is conveyed. A TRP may be provided by a base station. In 5G, a base station may be referred to a gNB. A gNB or TRP may provide beam indication information which is used to configure a UE with information about which gNB or TRP transmit (Tx) beam is to be used for downlink (DL) (this is so the UE can select the required spatial receive Rx settings) and which Tx beam is to be used for uplink (UL) (so that UE can direct its transmit beam towards the Rx beam used at the gNB or TRP). The UE may be configured with a list of up to M TCI (transmission configuration indicator)-state configurations. This may be within the higher layer parameter PDSCH (Physical Downlink Shared Channel) configuration to decode the PDSCH according to a detected PDCCH (physical downlink control channel) with a DCI (downlink control information) intended for the UE and the given serving cell. M may depend on the UE capability - for example maxNumberConfiguredTCIstatesPerCC. Each TCI-state may contain parameters for configuring a quasi-co-location relationship between one or two downlink reference signals (RS) and the DM-RS (demodulation reference signal) ports of the PDSCH, the DM-RS port of PDCCH, or the CSLRS port(s) of a CSI-RS resource. The quasi-co-location relationship may be configured by the higher layer parameter qcl-Typel for the first DL RS (downlink reference signal), and qcl-Type2 for the second DL RS (if configured). For the case of two DL RSs, the QCL types may not be the same, regardless of whether the references are to the same DL RS or different DL RSs. The quasi-co-location types corresponding to each DL RS may be given by the higher layer parameter qcl-Type in QCL-Info and may take one of the following values: o QCL types A: Doppler shift, Doppler spread, average delay, delay spread o QCL types B: Doppler shift, Doppler spread o QCL types C: average delay, Doppler shift o QCL types D: Spatial Rx A transmission configuration indication (TCI) framework is used for beam indication for downlink. A UE can be configured with up to 128 TCI states. A beam for a target channel or signal can be indicated by a TCI. The TCI provides a source reference signal and an intended QCL type to be applied. A base station may signal a DO scheduling of a channel to the UE. The DCI can select a TCI to be used for the reception of that channel. The UE can set its beamforming coefficients such that the scheduled channel can be received. The gNB or TRP configures the UE via RRC (radio resource control) signaling with TCI states where each TCI state may have one or two source RSs that provide QCL parameters for the target RS - only one RS providing QCL type D per TCI state. ADL TCI chain consists of an SSB, and one or more CSI-RS resources, and the TCI state of each reference signal includes another reference signal in the same TCI chain, where the SSB can be associated with serving cell PCID (physical cell identity) or associated with a PCID different from serving cell PCID. The UE can be configured to measure on a set of beams from different TRPs and report back the receive power levels of a reference signal. The UE may provide LI RSRP (layer 1 reference signal receive power) levels back to the network. This may be in the form of a CSI report. Based on the UE feedback, the network sends a TCI state for the associated channel. A MAC CE (medium access control control element) may indicate the TCI state, This may be for the PDCCH. In some embodiments, a UE may be unable to simultaneously receive and / or process two synchronization signals (one from each of the TRPs) at the same time. Some embodiments will make use of one or more aperiodic reference signals. In some embodiments, the aperiodic reference signals are A-TRS (aperiodic temporary reference signals). However, in other embodiments, any other suitable aperiodic reference signal. This signal may be used for activation of target TCI states. A-TRS is a temporary aperiodic reference signal. The A-TRS reference signal is temporary, and aperiodic. A UE in RRC connected mode may be expected to receive the higher layer UE specific configuration of anNZP-CSI-RS (non-zero power) CSI-RS resource set. The CSI-RS resource set may be configured with higher layer parameter trs-Info. The IE (information element) NZP-CSI-RS resource set may be a set of NZP-CSI-RS resources (e.g. their IDs) and set specific parameters. For a NZP-CSI-RS resource set configured with the higher layer parameter trs-Info, the UE may assume the antenna port with the same port index of the configured NZP CSI-RS resources in the NZP-CSI-RS resource set is the same. Where there are two or more TRPs with which a UE communicates, this is sometimes referred to as multiple transmit / receive point (M-TRP). A cell may comprise one or more TRPs. TRPs of the same cell may have a common SS / PBCH block which is cell specific. In M-TRP operation, a serving cell can schedule the UE from for example two TRPs such as shown in Figure 1. This may provide better coverage, reliability and / or data rates for channels. The channels may be one or more of PDSCH, PDCCH, PUSCH (physical uplink shared channel), and PUCCH (physical uplink control channel). There are two different operation modes to schedule multi-TRP PDSCH transmissions: single-DCI and multi-DCI. For both modes, control of uplink and downlink operation can be done by the physical layer and the MAC layer, within the configuration provided by the RRC layer. In single-DCI mode, only one TRP is responsible for the transmission of control data (PDCCH) to the UE. As a result, the UE is scheduled by the same PDCCH containing a DCI for both TRPs. On the other hand, in a multi-DCI mode both TRPs are responsible for the transmission of control data to the UE. As a result, the UE is scheduled by independent DCIs from each TRP. Some embodiments when used in a 5G network may relate to the multi-DCI mode or the single-DCI mode. Reference is made to Figure 3 which shows a scenario where two SSBs would be received generally at the same time. SSB#1 would be transmitted by the first TRP, TRP1, and SSB#2 would be transmitted by the second TRP, TRP2. The UE may not be able to receive the two SSBs at the same time or to process the two SSBs at the same time. The gNB sends the MAC CE command indicating activation of TCI states for the PDSCH. The UE cannot receive SSB#1 and SSB#2 simultaneously as these are colliding in time. In s-DCI, there is one command for activating two TCI states. In m-TCI, a command is provided for each TRP. That collision may happen in case of inter cell scenario, i.e. the target TCI states have a different physical cell ID, PCI. This may be a problem where the TRP1 and TRP2 are configuring the same SSB indexes. In some cases, a UE may not be able to detect two SSBs from different directions simultaneously. In the example shown in Figure 3, the UE has to first synchronize with SSB#1 and then with SSB#2 or vice versa. After the MAC CE command has been received, a UE may only be capable of being scheduled in a target TCI state after TuARQ+3ms and after the UE has synchronized with the first SSB after processing the MAC CE command. The example shown in Figure 3 shows an example SSB processing time Tssb of 2ms. In the example of Figure 3, because the UE is unable to process the two SSBs at the same time, the UE needs to wait for the next occurrence of the second SSB. In this example, this is 160ms after the first SSB has been processed. After the Tssb associated with the second SSB, the UE is able to receive the PDCCH DCI with TCI indication. After the PDCCH DO with TCI indication has been received, the UE is able to receive the PDSCHs from each of the TRPs. There is a time duration for QCL between receiving the PDCCH with TCI indication and being able to receive the PDSCHs. This is where the UE sets its spatial filter in the direction of the indicated beam. As shown in Figure 3, where the UE is not able to process / receive the SSBs from the two TRPs at the same time, an additional 160 ms is required when there is a TCI state switch. In case of multi-TRP, when a single codepoint contains 2 TCI states, the UE needs to switch and potentially synchronize with both target TCI states SSBs. The UE may not be able to synchronize simultaneously using separate RF chains if those SSBs are transmitted from different TRPs using the same OFDM symbols. In such cases, the UE either needs to synchronize via alternate means or need to synchronize to each TRP in a serial manner, when it receives the MAC CE command for TCI state activation. Some embodiments, aim to reduce the time for a TCI state switch. In some embodiments, a method for a reduced TCI state activation delay is proposed. In some embodiments, the QCL relationship with previously activated and / or current activated TCI states is considered. One or more additional RSs may be configured for a faster TCI activation as compared, for example, to the timing illustrated in Figure 3. In one embodiment, when sending a MAC CE command for TCI state activation to the UE, the gNB will transmit one or more aperiodic reference signals, e.g. A-TRS, which are QCL with the indicated TCI state for the UE to synchronize with. In the regard, reference is made to Figure 4. Reference is made to Figure 4 which illustrates a target TCI state activation with A-TRS, in accordance with some embodiments. In the example of Figure 4, a MAC-CE activation TCI is provided. This may be as described in more detail below. This may be for the PDSCH. This may be s-DCI. The MAC CE may comprise one command for activating two TCI states, TCI#1 and TC1#2. TCI # 1 is associated with the first TRP and the TC#2 is associated with the second TRP. The MAC CE may be received in the PDSCH. After Tharq+Sitis from receiving the MAC CE, the UE will receive one or more aperiodic reference signals. Currently, when the UE receives the MAC CE command for activating the TCI states for PDSCH, if the target TCI state is not a part of the active TCI state list, the UE needs to synchronize with the first SSB after Tharq + 3ms. In the example of Figure 4, the gNB transmits one or more A-TRS which are received after the Tharq + 3ms period. The one or more A-TRS may be received in a time window of 0.250ms. This window size is by way of example only. The processing time for the one or more A-TRS may be TATRsProc=2 ms. This is by way of example only and in other embodiments, the time may be more or less than 2ms. The A-TRS provides a similar function to the SSB. After the UE has processed the information in the A-TRS, the UE is able to receive the PDCCH DCI with TCI indication for the PDSCHs. After the PDCCH DCI with TCI indication has been received, the UE is able to receive the PDSCHs from each of the TRPs. There is a time duration for QCL between receiving the PDCCH with TCI indication and being able to receive the PDSCHs. As compared to the arrangement of Figure 3, there may be a time saving of the order of 160ms for the time taken for the UE to be able to receive the PDSCH from the receipt of the MAC - CE. In one embodiment, the gNB will always transmit one or more reference signals, e.g. A-TRS when the gNB has knowledge that the UE cannot synchronize simultaneously with two SSBs. In another embodiment, the gNB will only transmit one or more reference signals, e.g. A-TRS if there is no QCL relation between at least one of the TCI states in the UE’s active TCI state list and the newly indicated / activated TCI state(s). In another embodiment, the gNB will transmit one or more reference signals, e.g. A-TRS only when the time Tfirstssn greater than a pre-configured threshold. TfirstssB is the time to the first SSB transmission associated with the corresponding TCI state of the two TCI states after MAC CE command is decoded by the UE. In order to enable the fast TCI state activation and / or indication with reference signals, e.g. A-TRS, the UE is configured with an associated reference signal configuration. This may be for each cell in the case of inter-cell TRP where the TRPs are associated with different cells. The associated reference signal configuration may be a TRS (temporary reference signal) configuration for each cell. This may be via one or more RRC messages. The associated reference signal configuration, e.g. TRS configuration may be layer 1 (LI) related configuration associated with each cell. This associated reference signal configuration, e.g. TRS configuration may comprise a list of reference signal configuration, for example a temporary RS configuration. Each RS configuration may comprise one or more of: a unique RS configuration index; a number of RS bursts and the gap length between the RS bursts; a triggering offset of the RS; and / or QCL information Where the RS configuration is a temporary RS configuration, the temporary RS configuration may comprise one or more of: a unique temporary RS configuration index; a number of RS bursts and the gap length between the RS bursts; a triggering offset of the temporary RS; and / or QCL information The UE can be configured with number of reference signal configurations, for example, temporary RS configurations. The MAC-CE selects one of the RRC configured values. In some embodiments, the CSI-RS for tracking for fast TCI activation may be configured as NZP-CSI-RS- resource set. Each resource set may contain a number of NZP CSI-RS resources configured as a NZP-CSI-RS-Resource. One resource set may have a total of four NZP-CSI resources across two consecutive slots (that is two resources per slot). In some embodiments, the base station may provide information about one or more target TCI states. The base station may provide a mapping between a target TCI state and one or more aperiodic reference signals, e.g. A-TRS. The information about the target states and the mapping may be provided by a MAC CE. A separate MAC CE may be defined to trigger TCI state activation and corresponding reference signal, e.g., A-TRS. Alternatively, the MAC-CE command for TCI states activation may be extended to provide information about the reference signal, e.g., A-TRS The MAC CE may include the target TCI states and the configuration index for each reference signal, e.g., the A-TRS configuration index for each TRS, when applicable. Based on the TRS triggering indication in MAC CE, UE will have knowledge as to if the UE should use the reference signal, e.g., A-TRS for a particular to-be-activated TCI state. A value zero indicated by the configuration index in the MAC CE may mean no RS resource is transmitted. The TRS configuration index is an index to an RRC configuration which has one or more applicable parameters of the reference signal, e.g., the A-TRS. To enable faster TCI activation, when the UE receives a MAC-CE command with TCI states, the UE checks which TCI states in the old active list have the QCL relation to the same RS in comparison to the new active TCI state list. In case the RS of one of the TCI states received in the MAC-CE command for TCI activation is QCL with the RS of one of the TCI states in the active TCI state list, then the UE will only synchronize with the first SSB transmission associated with the other TCI state after MAC CE command is decoded by the UE. Reference is made to Figure 5 which shows an overview of some embodiment. As referenced 500, it is determined if there is a QCL relation between TCI states. As referenced 502, if it is determined that there is no QCL relation between TCI states,, the gNB activates the use of aperiodic reference signals, e.g., A-TRS. This may be if one or more conditions are satisfied. As referenced 504, if it is determined that there is a QCL relation between TCI states, the UE takes the decision for TCI activation and no signalling is required. Thus, in the case the RS of both of the TCI states received in the MAC-CE command for TCI activation is QCL with RS of the TCI states in the active TCI state list, then the UE will not need any further synchronization. This may reduce the entire measurement time and does not involve any additional signaling between the gNB and the UE. Reference is made to Figure 6a and 6b which show methods of some embodiments. As referenced SI, the gNB receives a CSI report with the best beam pair from the UE. As referenced S2, a determination is made by the gNB as to whether the SSBs for the beam pair for the UE collide in time. If not, then this is followed by the part of the procedure referenced SI6. This will be discussed later. If so, then this is followed by the part of the procedure referenced S3. As referenced S3, the gNB determines if the UE is capable of monitoring the two SSBs for the target TCI states simultaneously. If so, then this is followed by the part of the procedure referenced S9. This will be discussed later. If not, then this is followed by the part of the procedure referenced S4. As referenced S4, the gNB determines if a QCL relation exists. If so, then this is followed by the part of the procedure referenced SI 6. This will be discussed later. If not, then this is followed by the part of the procedure referenced S5. As referenced S5, the gNB transmits a MAC-CE for PDSCH target state activation with aperiodic reference signal, e.g. A-TRS, mapping. This MAC-CE may be as previously discussed. As referenced S6, the UE receives the MAC-CE and decodes that MAC-CE. As referenced S7, the UE synchronizes with the aperiodic reference signal, e.g. A-TRS. As referenced S8, the UE activates the target TCI states. Reference is now made to the part of the procedure referenced S9. As referenced S9, the gNB determines if Tfirstssn is greater than a threshold. If not, then this is followed by the part of the procedure referenced S12. This will be discussed later. If so, then this is followed by the part of the procedure referenced S10. As referenced S10, the UE synchronizes with the Tumssb of each of the target TCI states. As referenced SI 1, the UE activates the target TCI states. Reference is now made to the part of the procedure referenced SI 2. As referenced SI 2, the gNB transmits a MAC-CE for PDSCH target state activation with aperiodic reference signal, e.g. A-TRS, mapping. This MAC-CE may be as previously discussed. As referenced SI3, the UE receives the MAC-CE and decodes that MAC-CE As referenced S14, the UE synchronizes with the aperiodic reference signal, e.g. A-TRS. As referenced SI5, the UE activates the target TCI states. Reference is now made to the part of the procedure referenced S16. As referenced S16, the gNB determines that the RS of both of the active TCI is QCL A or QCL C with the RS of the target TCI states. If not, then this is followed by the part of the procedure referenced S19. This will be discussed later. If so, then this is followed by the part of the procedure referenced S17. As referenced SI7, it is determined by the gNB that no further synchronization with the SSBs is required. As referenced SI8, the UE activates the target TCI states. Reference is now made to the part of the procedure referenced SI 9. As referenced SI 9, the gNB determines if Th^ssb is greater than a threshold. If not, then this is followed by the part of the procedure referenced S22. This will be discussed later. If so, then this is followed by the part of the procedure referenced S20. As referenced S20, the UE synchronizes with only one TfkstssB. As referenced S21, the UE activates the target TCI states. Reference is now made to the part of the procedure referenced S22. As referenced S22, the gNB transmits a MAC-CE for PDSCH target TCI state activation with aperiodic reference signal, e.g. A-TRS, mapping. This MAC-CE may be as previously discussed. As referenced S23, the UE receives the MAC-CE and decodes that MAC-CE As referenced S24, the UE synchronizes with the aperiodic reference signal, e.g. A-TRS. As referenced S25, the UE activates the target TCI states. One or more of the steps of Figures 6a and 6b may be omitted. One or more parts of the method of Figures 6a and 6b may be omitted. In the example shown in Figures 6a and 6b, the use of the aperiodic reference signal, e.g. A-TRS is based on one or more conditions: the UEs ability to simultaneously monitor two SSBs; the QCL relation between at least one of the TCI states in the UE’s active TCI state list and the newly indicated / activated TCI state(s); and / or the time TfiretssB with respect to a threshold. The method of Figure 6a and 6b may be modified to take into account only one of the conditions, or any two of the conditions. Some embodiments may provide a faster target TCI state activation. This may be in the case when two TCI states are activated simultaneously. This may be in cases where the UE cannot synchronize with SSBs having QCL relations with the target TCI states at the same time. Some embodiments may make use of the activation of an aperiodic RS. This may be based on the CSI-RS for tracking. This may result in shorter measurement delays. In some embodiments, the measurement delay resulting from the activation of the aperiodic reference signal, e.g. A-TRS, may be reduced as compared to the case where synchronization is done with consecutively received SSBs. In some embodiments, the gNB may send the aperiodic reference signal, e.g. A-TRS, only under certain conditions. This may reduce the impact signalling burden associated with the use of the aperiodic reference signal, e.g. A-TRS on the gNB. In some embodiments, when two TCI states are activated to the same codepoint of the active TCI state list simultaneously, upon receiving a PDSCH carrying MAC-CE active TCI state list update at slot n, when both TCI states are known, UE is able to receive the PDCCH or PDSCH with the new target TCI states at the first slot that is after n + Tharq + (max(Tfirst.Rsi , Tfirst-RS2)+ Trs-ptoc) / NR slot length Where: - For each of Tfirst-Rsi and Tfirst-RS2, if an aperiodic TRS associated to the corresponding TCI state is configured after the MAC-CE active TCI state list update, Tfirst-RSx = Ta-trsx. Otherwise Tfirst-Rsx = Tfirst-ssBx. reference signal associated with one TRP. Tfirst-Rsi is the first reference signal associated with one TRP and TseCondRS2 is the second reference signal associated with the other TRP. Trs-ptoc is the processing time of the reference signal. NR slot length is the new radio or 5G slot length. Where, Ta-trsx is the time to the A-TRS associated with the corresponding TCI state of the two TCI states to be activated. Tfirst-ssBx is the time to the first SSB transmission associated with the corresponding TCI state of the two TCI states after MAC CE command is decoded by the UE. Tfirst-SSBx = 0, if: - The TCI state with a QCL-relation to the first SSB is already in the active TCI state list, or A RS of the TCI state in the previously activated TCI state list has QCL A / C relation with a RS of the activated TCI state. - If Tfirst-Rsi = 0 and Tfirst-RS2 = 0 thenTRs-proc = 0. Otherwise Trs-ptoc = 2 ms. In some embodiments an explicit indication may be used in some embodiments. An IE is provided in RRC signalling, and a MAC-CE is defined to trigger TCI state activation and corresponding A-TRS mapping. A TCIActivationRS-Config may be provided. This may be provided in the RRC specification TS38.331 1.1.1. TCIActivationRS-Config The IE TCIActivationRS-Config is used to configure a Reference Signal for fast activation of the TCI state where the IE is included (see TS 38.214). Usage of TCXActivationRS-Config is indicated by including its TCIlActivationRS-Id'm the Enhanced TCI activation MAC CE (see TS 38.321 ) TCIActivationRS-Config information element - ASN1 START - TAG-TCIACTIVATIONRS-CONFIG-START TCIActivationRS-Config ::= SEQUENCE { tciActivationRS-Id TCIActivationRS-Configld, re source S et-r 18 NZP -C S I-RS-Resource Setld, qcl-Info-r!8 TCI-Stateld, } - TAG-TCIACTIVATIONRS-CONFIG-STOP - ASN1STOP The explicit indication may be a UE specific PDSCH MAC CE indicating mapping between A-TRS and TCI states to be activated. This may be provided in TS 38.214 and / or TS 38.321 R Serving Cell ID BWP ID Co TCI State IDo,i R TCI State IDo,2 ..... Cn TCI State IDn,i R TCI State IDn,2 TRSi ..... TRSn Oct 1 Oct n Here the Serving Cell ID, BWP ID, Ci, TCI State IDi,j and R are as specified in TS 38.214 Section 6.1.3.24. TCI state IDi,j denotes the jth TCI state indicated for the ith codepoint in the DO Transmission Configuration Indication field. A TRS IDk field is provided where TRS IDj corresponds to the jth TCI state indicated for the ith codepoint in the DCI Transmission Configuration Indication field. The signaling of the TRS field can be given such that the following options are enabled for each codepoint T: • No A-TRS is configured • A single A-TRS is configured for a codeword with 1 or 2 TCI states, where there is a clear relationship whether this A-TRS is configured for the first or second TCI state • Two A-TRS’s are configured for a codeword with 2 TCI states In some embodiments, there may be an implicit relationship between pre-configured A-TRS and the configured TCI states. The network configures the UE with a list of TCI states and a list of A-TRS, with a mapping between A-TRS and TCI state. This may be indicated by a field in the TCI state configuration for A-TRS. This may alternatively or additionally be indicated by configuring a list of A-TRS with a field of which TCI states this A-TRS is QCL’ed to. After the configuration, the UE can receive MAC CE command for TCI state indication or active list update. Once legacy MAC CE command is sent, the gNB and UE check the rules for A-TRS transmission, and no further explicit indication of TRS is included in the enhanced MAC CE command. The rules for A-TRS transmission are discussed later. Once there is a decision to send the ATRS, there will be a decision between TRP1 and TRP 2 on which will send the A-TRS or if both TRPs send the A-TRS. For example, in one scenario, the TCI with the smaller index could send the A-TRS. In another scenario, both TRPs may send the A-TRS. From UE perspective, if there is QCL relation for both target TCI states, then the UE will skip time / frequency synchronization. If UE is capable of synchronizing with both SSBs colliding in time simultaneously, then the UE will perform synchronization simultaneously. If the UE is not capable of synchronizing with both SSBs colliding in time simultaneously, then the UE may make use the A-TRS as set out previously. From gNB perspective, the gNB may define a threshold of time offset t. If there exists a QCL relation between the RS of at least one of the already active TCI states and RS of one of the TCI states TCI#A or TCI#B received in the MAC-CE command, the UE needs to synchronize with only one reference signal. If the TfirstssB >threshold, then the gNB will send the A-TRS. If there exists no QCL relation between the RS of at least one of the already active TCI states and RS for both of the TCI states TCI#A and TCI#B received in the MAC-CE command, then UE needs to synchronize with both reference signals. The gNB may send A-TRS only if the TfirstssB >threshold condition is satisfied. One or more rules for A-TRS transmission may be as follows: If there is a QCL relation for both target TCI states, then synchronization can be skipped. If there is a QCL relation for one target TCI state, and if TfirstssB >threshold, then a reference signal, e.g. A-TRS is sent. If there is a QCL relation for one target TCI state, and if Thmssb is not greater than the threshold, then the SSB is sent. The rules may be defined in pseudo code as follows: • If A - there is QCL relation for both target TCI states o Skip T / F sync • Else o If C - there is QCL relation for one target TCI state ■ If TfirstssB >threshold • SendATRS ■ Else • Legacy behaviour applies ■ End o else ■ If SSB#1 and SSB#2 will collide in time • If UE capable of dual sync o Do dual sync • Else o Send A-TRS • End ■ Else • If TfirstssB >threshold o Send ATRS • Else o Legacy behaviour applies • End ■ End o end • End For 1 Target TCI state • If A - there is QCL relation for the target TCI state o Skip T / F sync • Else o If TfustssB is too far away ■ Send ATRS o Else ■ Legacy behavior applies o End • End In some embodiments, where a UE is capable of monitoring two SSBs for the respective target states at the same time, the UE may indicate this to the network or base station. The UE may indicate this to the network by means of a UE capability indication. In this case, the network will not need to send the A-TRS. In some embodiments, where a UE is not capable of monitoring two SSBs for the respective target states at the same time, the UE may indicate this to the network or base station. The UE may indicate this to the network by means of a UE capability indication. It should be appreciated that embodiments may be used where two or more TCIs are required. This may be the case where there are two or more beams associated with one TRP or where there are multiple TRPs each associated with one or more beams. In the described embodiments, some example embodiments are provided at least in part by a 5G system. However, embodiments may be used in other systems as well as future systems. Figure 7 shows a schematic representation of a communication system operating based on a 5th generation radio access technology (generally referred to as a 5G system (5GS)) and with which some embodiments may be implemented. The 5GS may comprise a (radio) access network (RAN) or more generally a 5G access network that may e.g. correspond to a (radio) access network (RAN), to a wireline access gateway (W-AGF), to a N3IWF (non 3GPP interworking function), etc. The5GS may comprise a 5G core network (5GC), one or more application functions (AF) and one or more data networks (DN). The user equipment (UE) 300 may access or connect to the one or more DNs via the 5GS. The 5G (R)AN may comprise one or more base stations or radio access network (RAN) nodes, such as a gNodeB (gNB). A TRP is an example of an access node which may be provided by a gNB. A gNB may provide one or more TRPs. A base station or RAN node may comprise one or more distributed units connected to a central unit. The 5GC may comprise various network functions, such as an access and mobility management function (AMF), a session management function (SMF), an authentication server function (AUSF), a user data management (UDM), a user plane function (UPF), a network repository function (NRF), a network exposure function (NEF), a service communication proxy (SCP), edge application server discovery function (EASDF), policy control function (PCF), network slice access control function (NSACF), network slice specific authentication and authorization function (NSSAAF), and / or network slicing selection function (NSSF). Figure 8 illustrates an example of an apparatus 200. The apparatus 200 may comprise or implement one or more of the TRP or base station or access node functions shown, for example in Figures 1 or 7. The apparatus 200 may have at least one processor and at least one memory storing instructions of one or more the TRPs or base station or access nodes shown in Figures 1 or 7 that, when executed by at least one of the at least one processor cause operations or actions of the one or more TRPs or base station or access nodes to be performed. In this example, the apparatus 200 may comprise at least one random access memory (RAM) 211a, and / or at least one read only memory (ROM) 211b. The apparatus 200 may comprise at least one processor 212, 213 and / or a network interface 214. The at least one processor 212, 213 may be coupled to the at least one memory which in this example is the RAM 211a and the ROM 211b. The at least one processor 212, 213 may be configured to execute an appropriate software code 215.The software code 215 may, for example, include software code of one or more one or more the TRPs or base station or access nodes shown in Figures 1 or 7 including software, which allows the apparatus to perform one or more operations of one or more of the present aspects. Figure 9 illustrates an example of a communication device 300 or UE. The communication device 300 may be any device capable of or configured for sending and receiving wireless signals such as radio signals. The communication device 300 may comprise a mobile station (MS) or mobile device such as a mobile phone or what is known as a ’smart phone’, a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), a personal data assistant (PDA) or a tablet, a machine-type communications (MTC) device, a Cellular Internet of things (CIoT) device or any combinations of these or the like. The communication device may be an XR (extended reality) device such as a headset or may be capable of supporting an XR application (e.g., capable of executing or running an XR application). The headset may be a VR headset. The communication device may be or part of a vehicle, a UAV, or an AVV. The communication device 300 may be a user equipment, such as the user equipment shown in Figure 1 or 7. The communication device 300 may be configured to send or receive wireless signals, for example, radio signals carrying communications. The communications may be one or more of voice, electronic mail (email), text message, multimedia, data, machine data and so on. The communication device may be configured to send and / or receive wireless signals, for example, radio signals, over an air or radio interface 307 via a transceiver apparatus 306. The transceiver apparatus 306 may comprise, for example, a radio part and associated antenna arrangement. The radio part may convert the base band signal to the radio frequency and / or vice versa. The antenna arrangement may be arranged internally or externally to the mobile device and may include a single antenna or multiple antennas. The antenna arrangement may be an antenna array comprising a plurality of antenna elements. The communication device 300 may comprise at least one processor 301, and / or at least one memory. The at least one memory may be at least one ROM 302a, and / or at least one RAM 302b. Other possible components 303 may be provided for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access networks, such as the 5G RAN and other communication devices. The at least one processor 301 is coupled to the RAM 302b and the ROM 302a. The at least one processor 301 may be configured to execute instructions of software code 308. Execution of the instructions of the software code 308 may for example allow the communication device 300 to perform one or more operations. The software code 308 may be stored in the ROM 302a. It should be appreciated that in other embodiments, any other suitable memory may be alternatively or additionally used. The at least one processor 301, the at least one ROM 302a, and / or the at least one RAM 302b can be provided on an appropriate circuit board, in an integrated circuit, and / or in chipsets. This feature is denoted by reference 304. The communication device 300 may optionally have a user interface such as keypad 305, touch sensitive screen or pad, combinations thereof or the like. Optionally, the communication device may have one or more of a display, a speaker and a microphone. In this document, the term UE or user equipment is used. This term encompasses any of the example of communication device 300 previously discussed and / or any other communication device. Reference is made to Figure 10 which shows a method of some embodiments. This method may be performed by an apparatus. The apparatus may a user equipment. The apparatus may comprise suitable means, such as circuitry for providing the method. Alternatively or additionally, the apparatus may comprise at least one processor and at least one memory storing instructions that, when executed by the at least one processor cause the apparatus at least to provide the method below. Alternatively or additionally, the apparatus may be such as discussed in relation to Figure 9. The method may be provided by computer program code or computer executable instructions. The method may comprise as referenced Al, receiving information, the information indicating two or more target transmission configuration indicator states, and for at least one of the two or more target transmission configuration indicator states, a mapping between the target transmission configuration indicator state and a respective aperiodic reference signal. The method may comprise as referenced A2, receiving one or more respective aperiodic reference signals. The method may comprise as referenced A3, synchronising with the received one or more respective aperiodic reference signals. It should be appreciated that the method outlined in Figure 10 may be modified to include any of the previously described features. Reference is made to Figure 11 which shows a method of some embodiments. This method may be performed by an access node or a base station or a TRP. The apparatus may comprise suitable means, such as circuitry for providing the method. Alternatively or additionally, the apparatus may comprise at least one processor and at least one memory storing instructions that, when executed by the at least one processor cause the apparatus at least to provide the method below. Alternatively or additionally, the apparatus may be such as discussed in relation to Figure 8. The method may be provided by computer program code or computer executable instructions. The method may comprise as referenced Bl, causing information to be transmitted to a user equipment, the information indicating two or more target transmission configuration indicator states, and for at least one of the two or more target transmission configuration indicator states, a mapping between the target transmission configuration indicator state and a respective aperiodic reference signal. The method may comprise as referenced B2, causing one or more respective aperiodic reference signals to be transmitted to the user equipment. It should be appreciated that the method outlined in Figure 11 may be modified to include any of the previously described features. Computer program code may be downloaded and stored in one or more memories of the apparatus described herein. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for communication systems operated by mobile network operators, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein. In this example, some embodiments have been described in relation to a 5G system (5GS). As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements. In general, the various embodiments may be implemented in hardware or special purpose circuitry, software, logic or any combination thereof. Some aspects of the disclosure may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the disclosure is not limited thereto. While various aspects of the disclosure may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof. As used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit(s) (such as only analog and / or digital circuit(s)) and (b) combinations of hardware circuits and software, such as (as applicable): (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.” This definition of circuitry applies to all uses of the term “means” in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, an integrated circuit such as a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device. The embodiments of this disclosure may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and / or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computerexecutable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it. Further in this regard it should be noted that any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disks or floppy disks, and optical media such as for example, DVD and the data variants thereof, CD. The physical media is a non-transitory media. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM). The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting examples. Embodiments of the disclosure may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate. The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiments of this disclosure. However, various 5 modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. Indeed, there are further embodiments comprising a combination of one or more embodiments with any of the other embodiments previously discussed. The scope of protection sought for some embodiments of the disclosure is set out by the claims. The 10 embodiments and features, if any, described in this specification that do not fall under the scope of the claims are to be interpreted as examples, useful for understanding various embodiments of the disclosure. It should be noted that different claims with differing claim scope may be pursued in related applications such as divisional or continuation applications.

Claims

1. A user equipment comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the user equipment to perform at least:receiving information, the information indicating two or more target transmission configuration indicator states, and for at least one of the two or more target transmission configuration indicator states, a mapping between the target transmission configuration indicator state and a respective aperiodic reference signal;receiving one or more respective aperiodic reference signals; andsynchronising with the received one or more respective aperiodic reference signals.

2. The user equipment as claimed in claim 1, wherein the information with the mapping between the target transmission configuration indicator state and a respective aperiodic reference signal is received from a base station when one or more user equipment conditions are satisfied.

3. The user equipment as claimed in claim 1 or 2, wherein the one or more respective aperiodic reference signals are received from a base station when one or more user equipment conditions are satisfied.

4. The user equipment as claimed in any preceding claim , wherein synchronising with the received one or more respective aperiodic reference signals is performed when one or more user equipment conditions are satisfied.

5. The user equipment as claimed in claim 4, wherein the user equipment is caused to determine whether the one or more user equipment conditions are satisfied.

6. The user equipment as claimed in any of claims 2 to 5, wherein the one or more user equipment conditions comprise one or more ofa time for synchronising with a synchronisation signal of a target transmission configuration indicator state would be greater than a threshold time;the user equipment is not capable of synchronising with different synchronisation signals at the same time, where the different synchronisation signals would be associated with different ones of the two or more target transmission configuration indicator states; orthere is no quasi co-location relationship between one or more of the target transmission configuration indicator states and one or more current transmission configuration indicator states of the user equipment.

7. The user equipment as claimed in any preceding claim, wherein one of the two or more target transmission configuration indicator states is associated with a first transmission reception point and another of the two or more target transmission configuration indicator states is associated with a second transmission reception point.

8. The user equipment as claimed in any preceding claim, wherein the information is received in a medium access control control element.

9. The user equipment as claimed in any preceding claim, wherein the user equipment is caused to activate a respective one of the two or more target transmission configuration indicator states after synchronising with the received respective aperiodic reference signal.

10. The user equipment as claimed in any preceding claim, wherein the one or more respective aperiodic reference signals comprise one or more respective aperiodic temporary reference signals.

11. An apparatus comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to perform at least:causing information to be transmitted to a user equipment, the information indicating two or more target transmission configuration indicator states, and for at least one of the two or more target transmission configuration indicator states, a mapping between the target transmission configuration indicator state and a respective aperiodic reference signal; andcausing one or more respective aperiodic reference signals to be transmitted to the user equipment.

12. The apparatus as claimed in claim 11, wherein the information with the mapping between the target transmission configuration indicator state and a respective aperiodic reference signal is transmitted to the user equipment when one or more user equipment conditions are satisfied.

13. The apparatus as claimed in claim 11 or 12, wherein the one or more respective aperiodic reference signals are transmitted to the user equipment when one or more user equipment conditions are satisfied.

14. The apparatus as claimed in claim 12 or 13, wherein the apparatus is caused to determine whether the one or more user equipment conditions are satisfied.

15. The apparatus as claimed in any of claims 12 to 14, wherein the one or more user equipment conditions comprise one or more of:a time for synchronising with a synchronisation signal of a target transmission configuration indicator state would be greater than a threshold time;the user equipment is not capable of synchronising with different synchronisation signals at the same time, where the different synchronisation signals would be associated with different ones of the two or more target transmission configuration indicator states; orthere is no quasi co-location relationship between one or more of the target transmission configuration indicator states and one or more current transmission configuration indicator states of the user equipment.

16. The apparatus as claimed in any of claims 11 to 15, wherein one of the two or more target transmission configuration indicator states is associated with a first transmission reception point and another of the two or more target transmission configuration indicator states is associated with a second transmission reception point.

17. The apparatus as claimed in any of claims 11 to 16, wherein the one or more respective aperiodic reference signals comprise one or more respective aperiodic temporary reference signals.

18. A method comprising:receiving information, the information indicating two or more target transmission configuration indicator states, and for at least one of the two or more target transmission configuration indicator states, a mapping between the target transmission configuration indicator state and a respective aperiodic reference signal;5 receiving one or more respective aperiodic reference signals; andsynchronising with the received one or more respective aperiodic reference signals.

19. A method comprising:causing information to be transmitted to a user equipment, the information indicating10 two or more target transmission configuration indicator states, and for at least one of the two or more target transmission configuration indicator states, a mapping between the target transmission configuration indicator state and a respective aperiodic reference signal; andcausing one or more respective aperiodic reference signals to be transmitted to the user equipment.1520. A computer program comprising computer executable code, which when run, cause the method of claim 18 or claim 19 to be performed.

Images