WO2024172734A1 - Obtaining synchronization with a cell - Google Patents

Abstract

A User Equipment, UE, (400), receives (406) a first message from a first network node (402) on a serving cell of the UE. The first message comprises configuration information for an aperiodic synchronization signal to be transmitted on a second cell. The UE receives (410) a second message from the first network node on the serving cell of the UE. The second message is a Physical Downlink Control Channel, PDCCH, order for triggering a random access on the second cell. Responsive to receiving (410) the second message, the UE receives (412) the aperiodic synchronization signal on the second cell, in accordance with the configuration information, and acquires (414) downlink synchronization with respect to the second cell using the aperiodic synchronization signal received on the second cell.

Description

OBTAINING SYNCHRONIZATION WITH A CELL TECHNICAL FIELD The present disclose generally relates to wireless communication, and more particularly to ways to of obtaining synchronization with a cell. BACKGROUND Timing Advance (TA) and Uplink (UL) Sync in New Radio (NR) Different User Equipments (UEs) in the same cell may typically be located at different positions within the cell and then with different distances to the base station (e.g., gNodeB(gNB) in the case of 3^rd Generation Partnership Project (3GPP) New Radio (NR)). The transmissions from different UEs thus suffer from different delays until they reach the base station. In order to make sure that the Uplink (UL) transmissions from a UE reaches the base station within the corresponding receive window for the base station, an uplink timing control procedure is used. This avoids intracell interference occurring, both between UEs assigned to transmit in consecutive subframes and between UEs transmitting on adjacent subcarriers. Time alignment of the uplink transmissions is achieved by applying a timing advance (TA) at the UE transmitter, relative to the received downlink timing. The main role of this is to counteract differing propagation delays between different UEs, as shown in the example of Figure 1 for a Long Term Evolution (LTE) eNodeB (eNB). Figure 1 illustrates time alignment of uplink transmissions for a case (a) without timing advance and for a case (b) with timing advance. In order to achieve the time alignment, to obtain UL synchronization, the base station (e.g. gNodeB, eNodeB) derives the Timing Advance (TA) value that the UE needs to use for the UL transmissions in order to reach the base station within the receive window and indicates this to the UE. When the UE first accesses a cell, it uses the random-access procedure where the received Msg1 (i.e., the Physical Random Access Channel (PRACH) preamble) is used by the base station to determine the UE’s initial TA to use for UL transmissions in the cell. During the connection, the base station then continuously monitors whether the UE needs to advance/delay the UL transmissions, in order to compensate for changes in propagation delay, and indicates to the UE if there is a need to change the TA value. TA in L3 Mobility In legacy layer 3 (L3) mobility, also called a reconfiguration with sync for the Master Cell Group (MCG), when the UE changes its Primary Cell (PCell), the UE always performs random access with the target PCell. As part of that, the UE transmits a PRACH preamble in the UL, which enables the target gNodeB to calculate the TA value for the UE. The calculated TA value is provided to the UE in the Random-Access Response (RAR) such that from msg3 onwards the UE is able to transmit UL messages on Physical Uplink Control Channel (PUCCH) and/or Physical Uplink Shared Channel (PUSCH). PRACH In this section, a description is provided about what is transmitted in the PRACH preamble and when the PRACH preamble is transmitted. What is transmitted in PRACH? In NR, diverse implementation of the cells is possible. For example, some cells (e.g., Frequency Range 1 (FR1) cells) may be implemented to provide large coverage, and some other cells (e.g., Frequency Range 2 (FR2) cells) may be implemented to provide more throughput over a short coverage area. The maximum distance between a base station and a UE in a cell depends on the cell coverage area. Due to diverse implementations, the same set of PRACH preambles may not work well in all the scenarios. To solve this, different preamble formats with different lengths of PRACH preamble are introduced in NR. This was supported in NR by introducing various types of Preamble Formats such as Preamble Formats 0, 1, 2, 3, and Preamble Formats A1, A2, A3, B1, B2, B3, B4, C0, and C2. As shown in Table 1 and Table 2 below, each preamble format has a different PRACH preamble sequence length and subcarrier spacing. Table 1: PRACH preamble formats for ^{LRA ^ 839} and ^^ ^^_RA ∈ { ^^. ^^ ^^, ^^} kHz. F^ormat L _RA ^^ ^^_RA N _{u NC} R PA ^{Support for} restricted sets 0 839 1.25 kHz 24576κ 3168κ Type A, Type B 1 839 1.25 kHz 2 ⋅ 24576κ 21024κ Type A, Type B 2 839 1.25 kHz 4 ⋅ 24576κ 4688κ Type A, Type B 3 839 5 kHz 4 ⋅ 6144κ 3168κ Type A, Type B Table 2: Preamble formats for ^^_RA ∈ { ^^ ^^ ^^, ^^ ^^ ^^, ^^ ^^ ^^ ^^} and ^^ ^^_RA = ^^ ^^ ⋅ ^^ ^{^^} kHz where ^^ ∈ { ^^, ^^, ^^, ^^, ^^, ^^}. Forma ^{L RA ^^ ^^} _RA ^N RA u ^NCP Support t for ^^ ^^ ^^ restricte ∈ { ^^, ^^, ^^, ^^, ^^, ^^} ∈ { ^^, ^^} ∈ { ^^, ^^, ^^} d sets A1 139 1151 571 15 ^ 2 ^{^} kHz 2 ^2048 ^ ^ 2 ^{^ ^} 288 ^ ^2 ^{^ ^ -} A2 139 1151 571 15 ^ 2 ^{^} kHz 4 ^2048 ^ ^ 2 ^{^ ^} 576 ^ ^ 2 ^{^ ^ -} A3 139 1151 571 15 ^ 2 ^{^} kHz 6 ^2048 ^ ^ 2 ^{^ ^} 864 ^ ^ 2 ^{^ ^ -} B1 139 1151 571 15 ^ 2 ^{^} kHz 2 ^2048 ^ ^ 2 ^{^ ^} 216 ^ ^2 ^{^ ^ -} B2 139 1151 571 15 ^ 2 ^{^} kHz 4 ^2048 ^ ^ 2 ^{^ ^} 360 ^ ^ 2 ^{^ ^ -} B3 139 1151 571 15 ^ 2 ^{^} kHz 6 ^2048 ^ ^ 2 ^{^ ^} 504 ^ ^ 2 ^{^ ^ -} B4 139 1151 571 15 ^ 2 ^{^} kHz 12 ^2048 ^ ^ 2 ^{^ ^} 936 ^ ^ 2 ^{^ ^ -} C0 139 1151 571 15 ^ 2 ^{^} kHz 2048 ^ ^ 2 ^{^ ^} 1240 ^ ^ 2 ^{^ ^ -} C_{2 139 1151 571} ^{15 ^ 2 ^ kHz 4 ^2048 ^ ^ 2 ^ ^ 2048 ^ ^ 2 ^ ^} The structure of a PRACH preamble contains a cyclic prefix (CP), preamble sequence, and Guard Period (GP). The length of preamble sequence and CP are derived from Table 6.3.3.1-1 or 6.3.3.1-2 of 3GPP Technical Specification (TS) 38.211 v17.2.0, which are reproduced herein as Table 1 and Table 2 above. In Table 1 and Table 2, N_u is the preamble length and^N RA C^P is the CP length. The guard period is computed as described in 3GPP TS 38.214 v17.2.0. The details of preamble sequence generation can be found in 3GPP TS 38.211 v17.2.0 and some of the details are copied in the extract below for reference. ***** START EXCERPT FROM TS 38.211 ***** The set of random-access preambles ^{xu, v( n )} shall be generated according to xu,v(n) ^xu((n ^C v)mod L RA ) ^_j ^^ui( ^{i ^}1 ) x u(i) ^e L ^RA ,i ^0,1,..., L RA ^ 1 from which the frequency-domain representation shall be generated according to L RA^ 1 ^_j 2 ^^mn y_u,_v(n) ^ ^x_u , _v(m) ^ e L ^RA _where ^{LRA ^ 839} _, ^{LRA ^ 139} _{, LRA}

_{on the PRACH preamble}

by Tables 6.3.3.1-1 and 6.3.3.1-2. ***** END EXCERPT FROM TS 38.211 ***** When is PRACH transmitted? A Random Access Channel (RACH) transmission occasion, or RACH occasion, depends on the type of RACH. A RACH occasion is an area specified in the time and frequency domains that is available or reserved for the transmission of a RACH preamble by a UE. In NR, two types of RACH are supported, namely contention-based RACH and contention free RACH. For contention-based RACH, the RACH occasion is computed at the UE based on configuration from the network and certain conditions observed at the UE. In NR, each beam is associated with different synchronization signal (e.g., Synchronization Signal Block (SSB) which is also referred to as a Synchronization Signal (SS)/Physical Broadcast Channel (PBCH) block). Each SSB is configured with certain preamble indexes and certain RACH transmission occasions. Based on the strongest SSB seen by the UE, the UE determines the preamble index to be transmitted and the RACH occasion where the preamble is to be transmitted. The network can determine which beam the UE has selected, as the network configured the mapping between SSBs and RACH Occasions (ROs). By detecting the RO in which the UE transmitted the PRACH, the network can determine which SSB Beam was selected by the UE. The mapping between SSBs and RACH Occasions is defined by the following two Radio Resource Control (RRC) parameters. ^ msg1-FDM (it is configured in RACH-ConfigGeneric and can be found in 3GPP TS 38.331 v17.1.0) ^ ssb-perRACH-OccasionAndCB-PreamblesPerSSB (it is configured in RACH- ConfigCommon and can be found in 3GPP TS 38.331 v17.1.0) Contention free RACH is scheduled by the network, and the scheduling information includes information about what to transmit and where to transmit. This information is conveyed to the UE by a combination of RRC message and Physical Downlink Control Channel (PDCCH) (e.g., through Downlink Control Information (DCI) message) order. The RRC message that carries the Contention Free Random Access (CFRA) related information is RACH-ConfigDedicated and can be found in 3GPP TS 38.331-v17.1.0. L1/L2 Inter-Cell Mobility or L1/L2 Triggered Inter-Cell Mobility (LTM) in Rel-18 In Rel-18, 3GPP has agreed on a Work Item (WI) on Further New Radio (NR) mobility enhancements, in particular, in a technical area entitled L1/L2 based inter-cell mobility. See the WI description (WID) in RP-213565 for further details. According to the WID, when the UE moves from the coverage area of one cell to that of another cell, at some point, a serving cell change needs to be performed. Currently serving cell change is triggered by L3 measurements and is done by RRC signaling triggered Reconfiguration with Synchronization for change of PCell and Primary Secondary Cell (PSCell), as well as release add for Secondary Cells (SCells) when applicable. All cases involve complete L2 (and L1) resets, leading to longer latency, larger overhead, and longer interruption time than beam switch mobility. The goal of L1/L2 mobility enhancements is to enable a serving cell change via L1/L2 signaling in order to reduce the latency, signaling overhead, and interruption time. As part of L1-L2 inter-cell mobility measurement framework, it was agreed to support at least Layer 1 (L1) Reference Signal Received Power (RSRP) (i.e., L1-RSRP) as the reporting quantity. That means the UE is required to report L1-RSRP of the candidate cells to the network so that the network can use them for LTM HO decisions. In Rel-17, as part of inter-cell beam management, a solution has been standardized where L1-RSRP is measured and reported on a Channel State Information (CSI) resource that are not associated to a Physical Cell Identity (PCI) of the serving cells. L3 HO Procedure vs LTM HO Procedure from Total Delay Perspective L3 Handover (HO) delay requirements from 3GPP TS 38.133 are copied below. ***** START EXCERPT FROM TS 38.133 ***** 6.1.1.2.1 Handover delay When the UE receives a RRC message implying handover the UE shall be ready to start the transmission of the new uplink PRACH channel within D_handover msec from the end of the last TTI containing the RRC command. Where: D_handover equals the applicable RRC procedure delay defined in clause 12 in TS 38.331 [2] plus the interruption time stated in clause 6.1.1.2.2. 6.1.1.2.2 Interruption time The interruption time is the time between end of the last TTI containing the RRC command on the old PDSCH and the time the UE starts transmission of the new PRACH, excluding the RRC procedure delay. When intra-frequency or inter-frequency handover is commanded, the interruption time shall be less than Tinterrupt Tinterrupt = Tsearch + TIU + Tprocessing + T∆ + Tmargin ms Where: Tsearch is the time required to search the target cell when the target cell is not already known when the handover command is received by the UE. If the target cell is known, then Tsearch = 0 ms. If the target cell is an unknown intra-frequency cell and the target cell Es/Iot≥-2 dB, then Tsearch = Trs ms. If the target cell is an unknown inter-frequency cell and the target cell Es/Iot≥-2 dB, then T_search = 3* T_rs ms. Regardless of whether DRX is in use by the UE, Tsearch shall still be based on non-DRX target cell search times. T∆ is time for fine time tracking and acquiring full timing information of the target cell. T∆ = Trs for both known and unknown target cell. Tprocessing is time for UE processing. Tprocessing can be up to 20ms. Tmargin is time for SSB post-processing. Tmargin can be up to 2ms. TIU is the interruption uncertainty in acquiring the first available PRACH occasion in the new cell. T_IU can be up to the summation of SSB to PRACH occasion association period and 10 ms. SSB to PRACH occasion associated period is defined in the table 8.1-1 of TS 38.213 [3]. T_rs is the SMTC periodicity of the target NR cell if the UE has been provided with an SMTC configuration for the target cellin the handover command, otherwise Trs is the SMTC configured in the measObjectNR having the same SSB frequency and subcarrier spacing. If the measObjectNRs having the same SSB frequency and subcarrier spacing configured by MN and SN have different SMTC, Trs is the periodicity of one of the SMTC which is up to UE implementation. If the UE is not provided SMTC configuration or measurement object on this frequency, the requirement in this clause is applied with T_rs=5ms assuming the SSB transmission periodicity is 5ms. There is no requirement if the SSB transmission periodicity is not 5ms. If the UE has been provided with higher layer in TS 38.331 [2] signaling of smtc2 prior to the handover command, Trs follows smtc1 or smtc2 according to the physical cell ID of the target cell. In the interruption requirement a cell is known if it has been meeting the relevant cell identification requirement during the last 5 seconds otherwise it is unknown. Relevant cell identification requirements are described in Clause 9.2.5 for intra-frequency handover and Clause 9.3.4 for inter-frequency handover. ***** END EXCERPT FROM TS 38.133 ***** As per the above requirements shown, L3 HO delay (D_handover) equals the RRC processing delay of the HO command and the interruption time. The interruption delay comprises the following components: ^ Software (SW) and Hardware (HW) processing, ^ Cell search, ^ Acquisition of fine timing, and ^ Delay uncertainty of obtaining PRACH preamble. As per the initial discussions of Rel-18 LTM, two potential approaches and two potential timelines are discussed. These are shown in Figure 2 and Figure 3. Figure 2 illustrates the RAN2 agreed baseline timeline for L1/L2 inter-cell mobility. Figure 3 illustrates a timeline for L1/L2 inter-cell mobility with TA acquisition before cell switch command. As per the approach shown in Figure 2, the UE starts acquiring DL synchronization and UL synchronization after receiving the cell switch command. As per the approach shown in Figure 3, the UE may acquire DL synchronization and starts acquiring UL synchronization with some of the candidate cells. As part of the UL synchronization acquisition procedure, the UE first needs to acquire DL synchronization with the cell first and then start performing the RACH procedure to acquire the UL synchronization. SUMMARY There currently exist certain challenge(s). In LTM HO, the UE may be configured with multiple candidate cells as the potential target cells. Based on the measurement reports from the UE, the network (e.g., a network node such as, e.g., a base station (e.g., gNB in the case of NR)) may configure the UE to be handed over to one of the candidate cells. Though the UE could measure multiple cells, the UE may not be able to maintain the DL synchronization with all the candidate cells as it may result in higher UE complexity and cost. In LTM, the option of pre-acquiring DL synchronization (also referred to as pre-sync) is being discussed, and the details of how the pre-sync is acquired are not yet specified in 3GPP. Relying on periodic reference signals for DL synchronization may lead to a longer delay, since the interval between the transmission occasions of periodic synchronization signals is long. Certain aspects of the disclosure and their embodiments may provide solutions to these or other challenges. Apparatus and methods are disclosed herein that enable the possibility to send an aperiodic synchronization signal from one cell and a triggering message for the aperiodic synchronization signal from another cell. A first aspect provides embodiments of a method performed by a User Equipment (UE). The method comprises receiving a first message from a first network node on a serving cell of the UE. The first message comprises configuration information for an aperiodic synchronization signal to be transmitted on a second cell. The method comprises receiving a second message from the first network node on the serving cell of the UE. The second message is a Physical Downlink Control Channel (PDCCH) order for triggering a random access on the second cell. The method comprises, responsive to receiving the second message, receiving the aperiodic synchronization signal on the second cell, in accordance with the configuration information, and acquiring downlink synchronization with respect to the second cell using the aperiodic synchronization signal received on the second cell. Embodiments of a corresponding UE are also provided. A second aspect provides embodiment of a method performed by a first network node that operates a serving cell of a user equipment (UE). The method comprises transmitting a first message to the UE on the serving cell of the UE. The first message comprises configuration information for an aperiodic synchronization signal to be transmitted on a second cell. The method comprises transmitting a second message to the UE on the serving cell of the UE for triggering the UE to acquire downlink synchronization with respect to the second cell using the aperiodic synchronization signal on the second cell. The second message is a Physical Downlink Control Channel (PDCCH) order for triggering a random access on the second cell. Embodiments of a corresponding first network node are also provided. A third aspect provides embodiments of a method performed by a second network node. The method comprises cooperating with a first network node that operates a serving cell of a User Equipment (UE) about transmission of an aperiodic synchronization signal on a second cell operated by the second network node. The method comprises transmitting the aperiodic synchronization signal on the second cell, in accordance with a result of the cooperating. Embodiments of a corresponding second network node are also provided. Certain embodiments may provide one or more of the following technical advantage(s). At least some embodiments of the present disclosure facilitate fast downlink (DL) synchronization to a LTM candidate cell, avoiding the need to wait for the occurrence of a periodic synchronization signal. BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the disclosed embodiments and their features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: Figure 1 illustrates time alignment of uplink transmissions for a case (a) without timing advance and for a case (b) with timing advance; Figure 2 illustrates the RAN2 agreed baseline timeline for L1/L2 inter-cell mobility; Figure 3 illustrates a timeline for L1/L2 inter-cell mobility with TA acquisition before cell switch command; Figure 4 illustrates the operation of a UE, a first network node that operates a serving cell of the UE, and a second network node that operates a candidate LTM cell of the UE, in accordance with at least some of the embodiments described herein; Figure 5 shows an example of a communication system in accordance with some embodiments; Figure 6 shows a UE in accordance with some embodiments; Figure 7 shows a network node in accordance with some embodiments; Figure 8 is a block diagram of a host in accordance with various aspects described herein; Figure 9 is a block diagram illustrating a virtualization environment 900 in which functions implemented by some embodiments may be virtualized; and Figure 10 shows a communication diagram of a host communicating via a network node with a UE over a partially wireless connection in accordance with some embodiments. DETAILED DESCRIPTION Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art. The description herein refers to the term “L1/L2 based inter-cell mobility” as used in the Work Item Description in 3GPP, though it interchangeably also uses the terms L1/L2 mobility, L1-mobility, L1 based mobility, L1/L2-centric inter-cell mobility, L1/L2 triggered mobility (LTM) or L1/L2 inter-cell mobility. In one embodiment, a UE receives a lower layer signaling from the network (e.g., from a network node such as, e.g., a base station (e.g., a gNB in the case of NR)) indicating to the UE a change of its serving cell (e.g., change of the Primary Cell (PCell) of the UE from a source PCell to a target PCell), wherein the lower layer signaling is a message/signaling of a lower layer protocol. A lower layer protocol refers to a lower layer protocol in the air interface protocol stack compared to the Radio Resource Control (RRC) protocol, e.g., Medium Access Control (MAC) is considered a lower layer protocol as it is “below” RRC in the air interface protocol stack, and in this case a lower layer signaling/message may correspond to a MAC Control Element (MAC CE). Another example of lower layer protocol is the Layer 1 (or Physical Layer, L1), and in this case a lower layer signaling/ message may correspond to a Downlink Control Information (DCI). Signaling information in a protocol layer lower than RRC reduces the processing time and, consequently, reduces the interruption time during mobility. In addition, it may also increase the mobility robustness as the network may respond to faster changes in the channel conditions. The description herein uses the term “LTM candidate cell” to refer to a cell the UE is configured with when configured with L1/L2 inter-cell mobility. That is a cell the UE can move to in a L1/L2 inter-cell mobility procedure, upon reception of a lower layer signaling. These cells may also be called candidate cells, candidates, mobility candidates, non-serving cells, additional cells, etc. This is a cell the UE performs measurements on (e.g., L1-RSRP measurements or CSI measurements) as disclosed herein, so that the UE reports these measurements and the network may make an educated decision on which beam (e.g., Transmission Configuration Indication (TCI) state) and/or cell the UE is to be switched to. A L1/L2 inter-cell mobility candidate cell may be a candidate to be a target PCell or PSCell, or an SCell of a cell group (e.g., Master Cell Group (MCG) SCell). In that sense, when the description herein refers to a resource configuration to indicate Synchronization Signals (SSs) (e.g., PSS or SSS) and/or Reference Signals (RSs) for the UE to measure for Channel State Information (CSI) for reporting, it may be referring to SSs and/or RSs of a candidate SCell of the MCG, a candidate SCell of the Secondary Cell Group (SCG), a candidate PSCell, and/or a candidate PCell. Another aspect in L1/L2 inter-cell mobility is that UE may be capable of acquiring downlink (DL) and uplink (UL) synchronization before receiving the cell switch command. For a UE which can acquire DL synchronization before receiving the cell switch command, there may be limitation on the number of cells for which the UE can acquire such a synchronization before receiving the cell switch command. Also, for acquiring the UL synchronization, the UE needs to transmit UL signals such as PRACH preamble or Sounding Reference Signal (SRS) to the target base station (e.g., gNB in the case of NR). Unless the UE has acquired DL synchronization, UE shall not transmit PRACH or SRS to acquire the UL synchronization. As discussed above, each PRACH preamble may be associated with an SSB and a RACH occasion (RO) where the preamble can be transmitted. The RO can be a periodically repeating occasion. For example, a first RO associated with a PRACH preamble is at 10ms, then the 2^nd RO associated with the same preamble may be at 10ms + (160ms), and 3^rd RO associated with the same preamble may be at 10ms +( 2*160ms), and the 4^th RO is 10ms + (3*160ms), etc. In general, when the UE is configured to measure on neighboring cells (e.g., L3-RSRP or L1-RSRP) for LTM, the UE is not required to meet any synchronization requirements for measuring the neighbor cells. As part of the measurement requirements the UE needs to meet, the UE is needed to meet only the accuracy requirement of the measurement and measurement delay of the measurement and the number of cells or beams that the UE is required to measure. In existing 3GPP specifications, the synchronization requirements are not specified for neighbor cell measurements, and the synchronization requirements are specified only for the transmission and reception to serving cells in the current 3GPP specification TS 38.133 v17.7.0. To achieve the better and standardized performance, synchronization behavior of the UE needs to be standardized so that the network and UE are on the same page regarding the pre-sync. In a preferred embodiment, the UE performs DL synchronization for an LTM candidate cell using an aperiodic synchronization signal (sig1) transmitted from the LTM candidate cell, where the aperiodic synchronization signal measurement is triggered from the serving cell. In other words, the UE is signaled from the serving cell that the aperiodic synchronization signal is transmitted from the LTM candidate cell. The UE receives the synchronization signal from the LTM candidate cell and performs the DL synchronization. In some embodiments, the UE receives the full configuration of the synchronization signal in a first message which may be, for example, and RRC message, and the UE subsequently receives the synchronization signal trigger transmitted in a second message which (e.g., only) informs the UE that the aperiodic synchronization signal can be received. In other embodiments, the UE receives part of the configuration of the synchronization signal in a first message which may be an RRC message, and the UE subsequently receives the remaining configuration in the signal trigger in a second message. The subsequent triggering may be transmitted for example using DCI in a PDCCH order that triggers a random access procedure. In some embodiments, the part of the configuration included in the second message includes a start offset of the aperiodic sync signal (sig1) transmission with respect to a reference time such as, e.g., a time of reception of the second message (e.g., the start of the second message or the end of the second message). In one example embodiment, the start offset of the sig1 is explicitly indicated in a PDCCH order (e.g., a PDCCH order that triggers a random access procedure). In some embodiments, the start offset of the sig1 is a fixed value with respect to the second message reception. In this case, the start offset is not explicitly indicated to UE, but it is a constant offset with respect to reception of the second message. In some examples, if the PDCCH order is received at time unit n, sig1 is always transmitted at n+N1 time units, where time unit may be, e.g., millisecond, slots, or subframes. In some embodiments, the synchronization signal trigger is included in a PDCCH order that triggers a random access procedure. In this case, the UE synchronizes using the aperiodic synchronization signal, and the UE uses the acquired DL timing reference to transmit an UL signal, e.g., a PRACH or an SRS to the LTM candidate cell. By using the aperiodic sync signal, the UE gets quick DL sync. Then, the UE can do random access to get UL sync. Then handover can be performed. Hence, embodiments of the present disclosure can be used to make handover faster. Note that in some embodiments, the UE transmits a RACH preamble to the candidate cell using the DL synchronization it has obtained via the aperiodic synchronization signal, but the network does not respond with a random access response (RAR). Instead, the network determines a timing advance (TA) based on the RACH preamble and saves this TA. Later, when the network sends the UE a cell switch command to switch to the candidate cell, the cell switch command may include the TA so that the UE can use this TA for UL synchronization with the candidate cell. So, the UE does not need to maintain TAs for multiple candidate cells just in case there will be a cell switch to one of these cells. Instead, the network can maintain TAs for multiple candidate cells, and can provide the appropriate TA to the UE with the cell switch command. In some embodiments, the synchronization signal is a synchronization signal block (SSB). In other embodiments, the synchronization signal is a tracking reference signal (TRS) or a channel state information reference signal (CSI-RS). In some embodiments, a method in a UE comprises receiving a message triggering reception of a synchronization signal (e.g., an aperiodic synchronization signal), where receive timing of the synchronization signal is different from receive timing of the triggering message. Figure 4 illustrates the operation of a UE 400, a first network node 402 that operates a serving cell of the UE 400, and a second network node 404 that operates a candidate LTM cell of the UE 400, in accordance with at least some of the embodiments described herein. Optional steps are represented by dashed lines/boxes. Note that the first network node 402 and the second network node 404 may be different network nodes (e.g., a first base station or gNB and a second base station or gNB) or the first network node 402 and the second network node 404 may be a single network node (e.g., a single base station or gNB) that operates both the serving cell and the candidate LTM cell. As illustrated, the first network node 402 sends a first message to the UE 400 on the serving cell, where the first message includes configuration information for an aperiodic synchronization signal (sig1) to be received by the UE 400 from the candidate LTM cell (step 406). As discussed above, in one example embodiment, the first message is an RRC message. As also discussed above, in one embodiment, the first message includes the full configuration of the aperiodic sync signal (sig1). However, in another embodiment, the first message includes a subset of the configuration of the aperiodic sync signal (sig1) where the remaining part of the configuration of the aperiodic sync signal (sig1) is sent to the UE 400 in a separate message (e.g., a second message such as, e.g., a PDCCH order) on the serving cell. Further details regarding the first message are described above and are equally applicable here to step 406. The first network node 402 and the second network node 404 cooperate to initiate transmission of the aperiodic sync signal (sig1) on the candidate LTM at a certain time (step 408). For example, in one embodiment, the first network node 402 and the second network node 404 communicate to agree upon the time at which the aperiodic sync signal (sig1) is to be transmitted on the candidate LTM cell (step 408A). In another embodiment, the first network node 402 sends a request to the second network node 404 to transmit the aperiodic sync signal (sig1) on the candidate LTM cell (step 408B). In one example embodiment, the request of step 408B includes an indication of a certain time at which the aperiodic sync signal (sig1) is to be transmitted (e.g., an indication of one of a set of predefined, configured, or agreed (candidate) transmission occasions for aperiodic sync signal (sig1)). In another example embodiment, the request of step 408 is an implicit request to transmit the aperiodic sync signal (sig1) in a next (in time) one of a set of predefined, configured, or agree candidate transmission opportunities for the aperiodic sync signal (sig1) (the next one that is greater than a minimum threshold amount of time after the request). In another embodiment, the second network node 404 notifies the first network node 402 of when the second network node 404 is going to transmit the aperiodic sync signal (sig1) on the candidate LTM cell (step 408C). This notification may then trigger the first network node 402 to transit the second message to the UE 400 in step 410 described below. The first network node 402 transmits, to the UE 400 on the serving cell, the second message that triggers the UE 400 to receive the aperiodic synchronization signal (sig1) on the candidate LTM cell (step 410). As discussed above, in one example embodiment, the second message (msg2) is a PDCCH order. Note that further details regarding the second message are descried above and equally applicable here. The second network node 404 transmits the aperiodic sync signal (sig1) on the candidate LTM cell (step 412). Responsive to receiving the second message, the UE 400 receives the aperiodic sync signal (sig1) on the candidate LTM cell (in accordance with the configuration received in the first message and optionally the second message) and acquires DL synchronization with respect to the candidate LTM cell using the aperiodic sync signal (sig 1) (step 414). As illustrated, in this example embodiment, the aperiodic sync signal (sig1) is offset with respect to the second message by a certain time offset. As discussed above, this time offset may be a fixed offset (e.g., predefined or configured offset that is fixed) or may be a dynamic offset (e.g., indicated in the second message). Once the UE 400 has acquired DL synchronization with respect to the candidate LTM cell, the UE 400 may utilize this acquired DL synchronization to perform one or more operations (step 416). For example, by using the aperiodic sync signal in step 414, the UE 400 gets quick DL sync to the candidate LTM cell. Then, in step 416, the UE 400 can perform random access on the candidate LTM cell (e.g., a random access triggered by a PDCCH order used as the second message in step 410) to get UL sync with respect to the candidate LTM cell. Then, handover of the UE 400 to the candidate LTM cell can be performed if desired. Figure 5 shows an example of a communication system 500 in accordance with some embodiments. In the example, the communication system 500 includes a telecommunication network 502 that includes an access network 504, such as a Radio Access Network (RAN), and a core network 506, which includes one or more core network nodes 508. The access network 504 includes one or more access network nodes, such as network nodes 510A and 510B (one or more of which may be generally referred to as network nodes 510), or any other similar Third Generation Partnership Project (3GPP) access node or non-3GPP Access Point (AP). The network nodes 510 facilitate direct or indirect connection of User Equipment (UE), such as by connecting UEs 512A, 512B, 512C, and 512D (one or more of which may be generally referred to as UEs 512) to the core network 506 over one or more wireless connections. Note that, in one embodiment, the UE 400 corresponds to one of the UEs 512 in Figure 5, and the first and second network nodes 402 and 404 correspond to two of the network nodes 510 or alternatively the same network node 510 (where the same network node operates both the serving cell of the UE 400 and the candidate LTM cell). Example wireless communications over a wireless connection include transmitting and/or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and/or other types of signals suitable for conveying information without the use of wires, cables, or other material conductors. Moreover, in different embodiments, the communication system 500 may include any number of wired or wireless networks, network nodes, UEs, and/or any other components or systems that may facilitate or participate in the communication of data and/or signals whether via wired or wireless connections. The communication system 500 may include and/or interface with any type of communication, telecommunication, data, cellular, radio network, and/or other similar type of system. The UEs 512 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and/or operable to communicate wirelessly with the network nodes 510 and other communication devices. Similarly, the network nodes 510 are arranged, capable, configured, and/or operable to communicate directly or indirectly with the UEs 512 and/or with other network nodes or equipment in the telecommunication network 502 to enable and/or provide network access, such as wireless network access, and/or to perform other functions, such as administration in the telecommunication network 502. In the depicted example, the core network 506 connects the network nodes 510 to one or more hosts, such as host 516. These connections may be direct or indirect via one or more intermediary networks or devices. In other examples, network nodes may be directly coupled to hosts. The core network 506 includes one more core network nodes (e.g., core network node 508) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the UEs, network nodes, and/or hosts, such that the descriptions thereof are generally applicable to the corresponding components of the core network node 508. Example core network nodes include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-Concealing Function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and/or a User Plane Function (UPF). The host 516 may be under the ownership or control of a service provider other than an operator or provider of the access network 504 and/or the telecommunication network 502, and may be operated by the service provider or on behalf of the service provider. The host 516 may host a variety of applications to provide one or more service. Examples of such applications include live and pre-recorded audio/video content, data collection services such as retrieving and compiling data on various ambient conditions detected by a plurality of UEs, analytics functionality, social media, functions for controlling or otherwise interacting with remote devices, functions for an alarm and surveillance center, or any other such function performed by a server. As a whole, the communication system 500 of Figure 5 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system 500 may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and/or other suitable Second, Third, Fourth, or Fifth Generation (2G, 3G, 4G, or 5G) standards, or any applicable future generation standard (e.g., Sixth Generation (6G)); Wireless Local Area Network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and/or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and/or any Low Power Wide Area Network (LPWAN) standards such as LoRa and Sigfox. In some examples, the telecommunication network 502 is a cellular network that implements 3GPP standardized features. Accordingly, the telecommunication network 502 may support network slicing to provide different logical networks to different devices that are connected to the telecommunication network 502. For example, the telecommunication network 502 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing enhanced Mobile Broadband (eMBB) services to other UEs, and/or massive Machine Type Communication (mMTC)/massive Internet of Things (IoT) services to yet further UEs. In some examples, the UEs 512 are configured to transmit and/or receive information without direct human interaction. For instance, a UE may be designed to transmit information to the access network 504 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the access network 504. Additionally, a UE may be configured for operating in single- or multi-Radio Access Technology (RAT) or multi-standard mode. For example, a UE may operate with any one or combination of WiFi, New Radio (NR), and LTE, i.e. be configured for Multi-Radio Dual Connectivity (MR-DC), such as Evolved UMTS Terrestrial RAN (E-UTRAN) NR - Dual Connectivity (EN-DC). In the example, a hub 514 communicates with the access network 504 to facilitate indirect communication between one or more UEs (e.g., UE 512C and/or 512D) and network nodes (e.g., network node 510B). In some examples, the hub 514 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, the hub 514 may be a broadband router enabling access to the core network 506 for the UEs. As another example, the hub 514 may be a controller that sends commands or instructions to one or more actuators in the UEs. Commands or instructions may be received from the UEs, network nodes 510, or by executable code, script, process, or other instructions in the hub 514. As another example, the hub 514 may be a data collector that acts as temporary storage for UE data and, in some embodiments, may perform analysis or other processing of the data. As another example, the hub 514 may be a content source. For example, for a UE that is a Virtual Reality (VR) headset, display, loudspeaker or other media delivery device, the hub 514 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which the hub 514 then provides to the UE either directly, after performing local processing, and/or after adding additional local content. In still another example, the hub 514 acts as a proxy server or orchestrator for the UEs, in particular in if one or more of the UEs are low energy IoT devices. The hub 514 may have a constant/persistent or intermittent connection to the network node 510B. The hub 514 may also allow for a different communication scheme and/or schedule between the hub 514 and UEs (e.g., UE 512C and/or 512D), and between the hub 514 and the core network 506. In other examples, the hub 514 is connected to the core network 506 and/or one or more UEs via a wired connection. Moreover, the hub 514 may be configured to connect to a Machine-to-Machine (M2M) service provider over the access network 504 and/or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with the network nodes 510 while still connected via the hub 514 via a wired or wireless connection. In some embodiments, the hub 514 may be a dedicated hub – that is, a hub whose primary function is to route communications to/from the UEs from/to the network node 510B. In other embodiments, the hub 514 may be a non-dedicated hub – that is, a device which is capable of operating to route communications between the UEs and the network node 510B, but which is additionally capable of operating as a communication start and/or end point for certain data channels. Figure 6 shows a UE 600 in accordance with some embodiments. As used herein, a UE refers to a device capable, configured, arranged, and/or operable to communicate wirelessly with network nodes and/or other UEs. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, Voice over Internet Protocol (VoIP) phone, wireless local loop phone, desktop computer, Personal Digital Assistant (PDA), wireless camera, gaming console or device, music storage device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, Laptop Embedded Equipment (LEE), Laptop Mounted Equipment (LME), smart device, wireless Customer Premise Equipment (CPE), vehicle-mounted or vehicle embedded/integrated wireless device, etc. Other examples include any UE identified by the 3GPP, including a Narrowband Internet of Things (NB-IoT) UE, a Machine Type Communication (MTC) UE, and/or an enhanced MTC (eMTC) UE. A UE may support Device-to-Device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), Vehicle-to-Vehicle (V2V), Vehicle-to-Infrastructure (V2I), or Vehicle-to-Everything (V2X). In other examples, a UE may not necessarily have a user in the sense of a human user who owns and/or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter). The UE 600 includes processing circuitry 602 that is operatively coupled via a bus 604 to an input/output interface 606, a power source 608, memory 610, a communication interface 612, and/or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 6. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc. The processing circuitry 602 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine-readable computer programs in the memory 610. The processing circuitry 602 may be implemented as one or more hardware-implemented state machines (e.g., in discrete logic, Field Programmable Gate Arrays (FPGAs), Application Specific Integrated Circuits (ASICs), etc.); programmable logic together with appropriate firmware; one or more stored computer programs, general purpose processors, such as a microprocessor or Digital Signal Processor (DSP), together with appropriate software; or any combination of the above. For example, the processing circuitry 602 may include multiple Central Processing Units (CPUs). In the example, the input/output interface 606 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and/or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into the UE 600. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an input device. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device. In some embodiments, the power source 608 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic device, or power cell, may be used. The power source 608 may further include power circuitry for delivering power from the power source 608 itself, and/or an external power source, to the various parts of the UE 600 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging the power source 608. Power circuitry may perform any formatting, converting, or other modification to the power from the power source 608 to make the power suitable for the respective components of the UE 600 to which power is supplied. The memory 610 may be or be configured to include memory such as Random Access Memory (RAM), Read Only Memory (ROM), Programmable ROM (PROM), Erasable PROM (EPROM), Electrically EPROM (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, the memory 610 includes one or more application programs 614, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 616. The memory 610 may store, for use by the UE 600, any of a variety of various operating systems or combinations of operating systems. The memory 610 may be configured to include a number of physical drive units, such as Redundant Array of Independent Disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, High Density Digital Versatile Disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, Holographic Digital Data Storage (HDDS) optical disc drive, external mini Dual In-line Memory Module (DIMM), Synchronous Dynamic RAM (SDRAM), external micro-DIMM SDRAM, smartcard memory such as a tamper resistant module in the form of a Universal Integrated Circuit Card (UICC) including one or more Subscriber Identity Modules (SIMs), such as a Universal SIM (USIM) and/or Internet Protocol Multimedia Services Identity Module (ISIM), other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable UICC commonly known as a ‘SIM card.’ The memory 610 may allow the UE 600 to access instructions, application programs, and the like stored on transitory or non-transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system, may be tangibly embodied as or in the memory 610, which may be or comprise a device-readable storage medium. The processing circuitry 602 may be configured to communicate with an access network or other network using the communication interface 612. The communication interface 612 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 622. The communication interface 612 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 618 and/or a receiver 620 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 618 and receiver 620 may be coupled to one or more antennas (e.g., the antenna 622) and may share circuit components, software, or firmware, or alternatively be implemented separately. In the illustrated embodiment, communication functions of the communication interface 612 may include cellular communication, WiFi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, NFC, location-based communication such as the use of the Global Positioning System (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented according to one or more communication protocols and/or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband CDMA (WCDMA), GSM, LTE, NR, UMTS, WiMax, Ethernet, Transmission Control Protocol/Internet Protocol (TCP/IP), Synchronous Optical Networking (SONET), Asynchronous Transfer Mode (ATM), Quick User Datagram Protocol Internet Connection (QUIC), Hypertext Transfer Protocol (HTTP), and so forth. Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 612, or via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., when moisture is detected an alert is sent), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient). As another example, a UE comprises an actuator, a motor, or a switch related to a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input the states of the actuator, the motor, or the switch may change. For example, the UE may comprise a motor that adjusts the control surfaces or rotors of a drone in flight according to the received input or to a robotic arm performing a medical procedure according to the received input. A UE, when in the form of an IoT device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application, and healthcare. Non-limiting examples of such an IoT device are a device which is or which is embedded in: a connected refrigerator or freezer, a television, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door/window sensor, a flood/moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a head-mounted display for Augmented Reality (AR) or VR, a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an IoT device comprises circuitry and/or software in dependence of the intended application of the IoT device in addition to other components as described in relation to the UE 600 shown in Figure 6. As yet another specific example, in an IoT scenario, a UE may represent a machine or other device that performs monitoring and/or measurements and transmits the results of such monitoring and/or measurements to another UE and/or a network node. The UE may in this case be an M2M device, which may in a 3GPP context be referred to as an MTC device. As one particular example, the UE may implement the 3GPP NB-IoT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship, an airplane, or other equipment that is capable of monitoring and/or reporting on its operational status or other functions associated with its operation. In practice, any number of UEs may be used together with respect to a single use case. For example, a first UE might be or be integrated in a drone and provide the drone’s speed information (obtained through a speed sensor) to a second UE that is a remote controller operating the drone. When the user makes changes from the remote controller, the first UE may adjust the throttle on the drone (e.g., by controlling an actuator) to increase or decrease the drone’s speed. The first and/or the second UE can also include more than one of the functionalities described above. For example, a UE might comprise the sensor and the actuator and handle communication of data for both the speed sensor and the actuators. Figure 7 shows a network node 700 in accordance with some embodiments. As used herein, network node refers to equipment capable, configured, arranged, and/or operable to communicate directly or indirectly with a UE and/or with other network nodes or equipment in a telecommunication network. Examples of network nodes include, but are not limited to, APs (e.g., radio APs), Base Stations (BSs) (e.g., radio BSs, Node Bs, evolved Node Bs (eNBs), and NR Node Bs (gNBs)). BSs may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto BSs, pico BSs, micro BSs, or macro BSs. A BS may be a relay node or a relay donor node controlling a relay. A network node may also include one or more (or all) parts of a distributed radio BS such as centralized digital units and/or Remote Radio Units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such RRUs may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio BS may also be referred to as nodes in a Distributed Antenna System (DAS). Other examples of network nodes include multiple Transmission Point (multi-TRP) 5G access nodes, Multi-Standard Radio (MSR) equipment such as MSR BSs, network controllers such as Radio Network Controllers (RNCs) or BS Controllers (BSCs), Base Transceiver Stations (BTSs), transmission points, transmission nodes, Multi-Cell/Multicast Coordination Entities (MCEs), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g., Evolved Serving Mobile Location Centers (E-SMLCs)), and/or Minimization of Drive Tests (MDTs). The network node 700 includes processing circuitry 702, memory 704, a communication interface 706, and a power source 708. The network node 700 may be composed of multiple physically separate components (e.g., a Node B component and an RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which the network node 700 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple Node Bs. In such a scenario, each unique Node B and RNC pair may in some instances be considered a single separate network node. In some embodiments, the network node 700 may be configured to support multiple RATs. In such embodiments, some components may be duplicated (e.g., separate memory 704 for different RATs) and some components may be reused (e.g., an antenna 710 may be shared by different RATs). The network node 700 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 700, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, Long Range Wide Area Network (LoRaWAN), Radio Frequency Identification (RFID), or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within the network node 700. The processing circuitry 702 may comprise a combination of one or more of a microprocessor, controller, microcontroller, CPU, DSP, ASIC, FPGA, or any other suitable computing device, resource, or combination of hardware, software, and/or encoded logic operable to provide, either alone or in conjunction with other network node 700 components, such as the memory 704, to provide network node 700 functionality. In some embodiments, the processing circuitry 702 includes a System on a Chip (SOC). In some embodiments, the processing circuitry 702 includes one or more of Radio Frequency (RF) transceiver circuitry 712 and baseband processing circuitry 714. In some embodiments, the RF transceiver circuitry 712 and the baseband processing circuitry 714 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of the RF transceiver circuitry 712 and the baseband processing circuitry 714 may be on the same chip or set of chips, boards, or units. The memory 704 may comprise any form of volatile or non-volatile computer-readable memory including, without limitation, persistent storage, solid state memory, remotely mounted memory, magnetic media, optical media, RAM, ROM, mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD), or a Digital Video Disk (DVD)), and/or any other volatile or non-volatile, non-transitory device-readable, and/or computer-executable memory devices that store information, data, and/or instructions that may be used by the processing circuitry 702. The memory 704 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and/or other instructions capable of being executed by the processing circuitry 702 and utilized by the network node 700. The memory 704 may be used to store any calculations made by the processing circuitry 702 and/or any data received via the communication interface 706. In some embodiments, the processing circuitry 702 and the memory 704 are integrated. The communication interface 706 is used in wired or wireless communication of signaling and/or data between a network node, access network, and/or UE. As illustrated, the communication interface 706 comprises port(s)/terminal(s) 716 to send and receive data, for example to and from a network over a wired connection. The communication interface 706 also includes radio front-end circuitry 718 that may be coupled to, or in certain embodiments a part of, the antenna 710. The radio front-end circuitry 718 comprises filters 720 and amplifiers 722. The radio front-end circuitry 718 may be connected to the antenna 710 and the processing circuitry 702. The radio front-end circuitry 718 may be configured to condition signals communicated between the antenna 710 and the processing circuitry 702. The radio front-end circuitry 718 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. The radio front-end circuitry 718 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of the filters 720 and/or the amplifiers 722. The radio signal may then be transmitted via the antenna 710. Similarly, when receiving data, the antenna 710 may collect radio signals which are then converted into digital data by the radio front-end circuitry 718. The digital data may be passed to the processing circuitry 702. In other embodiments, the communication interface 706 may comprise different components and/or different combinations of components. In certain alternative embodiments, the network node 700 does not include separate radio front-end circuitry 718; instead, the processing circuitry 702 includes radio front-end circuitry and is connected to the antenna 710. Similarly, in some embodiments, all or some of the RF transceiver circuitry 712 is part of the communication interface 706. In still other embodiments, the communication interface 706 includes the one or more ports or terminals 716, the radio front- end circuitry 718, and the RF transceiver circuitry 712 as part of a radio unit (not shown), and the communication interface 706 communicates with the baseband processing circuitry 714, which is part of a digital unit (not shown). The antenna 710 may include one or more antennas, or antenna arrays, configured to send and/or receive wireless signals. The antenna 710 may be coupled to the radio front-end circuitry 718 and may be any type of antenna capable of transmitting and receiving data and/or signals wirelessly. In certain embodiments, the antenna 710 is separate from the network node 700 and connectable to the network node 700 through an interface or port. The antenna 710, the communication interface 706, and/or the processing circuitry 702 may be configured to perform any receiving operations and/or certain obtaining operations described herein as being performed by the network node 700. Any information, data, and/or signals may be received from a UE, another network node, and/or any other network equipment. Similarly, the antenna 710, the communication interface 706, and/or the processing circuitry 702 may be configured to perform any transmitting operations described herein as being performed by the network node 700. Any information, data, and/or signals may be transmitted to a UE, another network node, and/or any other network equipment. The power source 708 provides power to the various components of the network node 700 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source 708 may further comprise, or be coupled to, power management circuitry to supply the components of the network node 700 with power for performing the functionality described herein. For example, the network node 700 may be connectable to an external power source (e.g., the power grid or an electricity outlet) via input circuitry or an interface such as an electrical cable, whereby the external power source supplies power to power circuitry of the power source 708. As a further example, the power source 708 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail. Embodiments of the network node 700 may include additional components beyond those shown in Figure 7 for providing certain aspects of the network node’s functionality, including any of the functionality described herein and/or any functionality necessary to support the subject matter described herein. For example, the network node 700 may include user interface equipment to allow input of information into the network node 700 and to allow output of information from the network node 700. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for the network node 700. Figure 8 is a block diagram of a host 800, which may be an embodiment of the host 516 of Figure 5, in accordance with various aspects described herein. As used herein, the host 800 may be or comprise various combinations of hardware and/or software including a standalone server, a blade server, a cloud-implemented server, a distributed server, a virtual machine, container, or processing resources in a server farm. The host 800 may provide one or more services to one or more UEs. The host 800 includes processing circuitry 802 that is operatively coupled via a bus 804 to an input/output interface 806, a network interface 808, a power source 810, and memory 812. Other components may be included in other embodiments. Features of these components may be substantially similar to those described with respect to the devices of previous figures, such as Figures 6 and 7, such that the descriptions thereof are generally applicable to the corresponding components of the host 800. The memory 812 may include one or more computer programs including one or more host application programs 814 and data 816, which may include user data, e.g. data generated by a UE for the host 800 or data generated by the host 800 for a UE. Embodiments of the host 800 may utilize only a subset or all of the components shown. The host application programs 814 may be implemented in a container-based architecture and may provide support for video codecs (e.g., Versatile Video Coding (VVC), High Efficiency Video Coding (HEVC), Advanced Video Coding (AVC), Moving Picture Experts Group (MPEG), VP9) and audio codecs (e.g., Free Lossless Audio Codec (FLAC), Advanced Audio Coding (AAC), MPEG, G.711), including transcoding for multiple different classes, types, or implementations of UEs (e.g., handsets, desktop computers, wearable display systems, and heads-up display systems). The host application programs 814 may also provide for user authentication and licensing checks and may periodically report health, routes, and content availability to a central node, such as a device in or on the edge of a core network. Accordingly, the host 800 may select and/or indicate a different host for Over-The-Top (OTT) services for a UE. The host application programs 814 may support various protocols, such as the HTTP Live Streaming (HLS) protocol, Real-Time Messaging Protocol (RTMP), Real-Time Streaming Protocol (RTSP), Dynamic Adaptive Streaming over HTTP (DASH or MPEG-DASH), etc. Figure 9 is a block diagram illustrating a virtualization environment 900 in which functions implemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices, and networking resources. As used herein, virtualization can be applied to any device described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more Virtual Machines (VMs) implemented in one or more virtual environments 900 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, UE, core network node, or host. Further, in embodiments in which the virtual node does not require radio connectivity (e.g., a core network node or host), then the node may be entirely virtualized. Applications 902 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 900 to implement some of the features, functions, and/or benefits of some of the embodiments disclosed herein. Hardware 904 includes processing circuitry, memory that stores software and/or instructions executable by hardware processing circuitry, and/or other hardware devices as described herein, such as a network interface, input/output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 906 (also referred to as hypervisors or VM Monitors (VMMs)), provide VMs 908A and 908B (one or more of which may be generally referred to as VMs 908), and/or perform any of the functions, features, and/or benefits described in relation with some embodiments described herein. The virtualization layer 906 may present a virtual operating platform that appears like networking hardware to the VMs 908. The VMs 908 comprise virtual processing, virtual memory, virtual networking, or interface and virtual storage, and may be run by a corresponding virtualization layer 906. Different embodiments of the instance of a virtual appliance 902 may be implemented on one or more of the VMs 908, and the implementations may be made in different ways. Virtualization of the hardware is in some contexts referred to as Network Function Virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers and customer premise equipment. In the context of NFV, a VM 908 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each of the VMs 908, and that part of the hardware 904 that executes that VM, be it hardware dedicated to that VM and/or hardware shared by that VM with others of the VMs 908, forms separate virtual network elements. Still in the context of NFV, a virtual network function is responsible for handling specific network functions that run in one or more VMs 908 on top of the hardware 904 and corresponds to the application 902. The hardware 904 may be implemented in a standalone network node with generic or specific components. The hardware 904 may implement some functions via virtualization. Alternatively, the hardware 904 may be part of a larger cluster of hardware (e.g., such as in a data center or CPE) where many hardware nodes work together and are managed via management and orchestration 910, which, among others, oversees lifecycle management of the applications 902. In some embodiments, the hardware 904 is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a RAN or a BS. In some embodiments, some signaling can be provided with the use of a control system 912 which may alternatively be used for communication between hardware nodes and radio units. Figure 10 shows a communication diagram of a host 1002 communicating via a network node 1004 with a UE 1006 over a partially wireless connection in accordance with some embodiments. Example implementations, in accordance with various embodiments, of the UE (such as the UE 512A of Figure 5 and/or the UE 600 of Figure 6), the network node (such as the network node 510A of Figure 5 and/or the network node 700 of Figure 7), and the host (such as the host 516 of Figure 5 and/or the host 800 of Figure 8) discussed in the preceding paragraphs will now be described with reference to Figure 10. Like the host 800, embodiments of the host 1002 include hardware, such as a communication interface, processing circuitry, and memory. The host 1002 also includes software, which is stored in or is accessible by the host 1002 and executable by the processing circuitry. The software includes a host application that may be operable to provide a service to a remote user, such as the UE 1006 connecting via an OTT connection 1050 extending between the UE 1006 and the host 1002. In providing the service to the remote user, a host application may provide user data which is transmitted using the OTT connection 1050. The network node 1004 includes hardware enabling it to communicate with the host 1002 and the UE 1006 via a connection 1060. The connection 1060 may be direct or pass through a core network (like the core network 506 of Figure 5) and/or one or more other intermediate networks, such as one or more public, private, or hosted networks. For example, an intermediate network may be a backbone network or the Internet. The UE 1006 includes hardware and software, which is stored in or accessible by the UE 1006 and executable by the UE’s processing circuitry. The software includes a client application, such as a web browser or operator-specific “app” that may be operable to provide a service to a human or non-human user via the UE 1006 with the support of the host 1002. In the host 1002, an executing host application may communicate with the executing client application via the OTT connection 1050 terminating at the UE 1006 and the host 1002. In providing the service to the user, the UE's client application may receive request data from the host's host application and provide user data in response to the request data. The OTT connection 1050 may transfer both the request data and the user data. The UE's client application may interact with the user to generate the user data that it provides to the host application through the OTT connection 1050. The OTT connection 1050 may extend via the connection 1060 between the host 1002 and the network node 1004 and via a wireless connection 1070 between the network node 1004 and the UE 1006 to provide the connection between the host 1002 and the UE 1006. The connection 1060 and the wireless connection 1070, over which the OTT connection 1050 may be provided, have been drawn abstractly to illustrate the communication between the host 1002 and the UE 1006 via the network node 1004, without explicit reference to any intermediary devices and the precise routing of messages via these devices. As an example of transmitting data via the OTT connection 1050, in step 1008, the host 1002 provides user data, which may be performed by executing a host application. In some embodiments, the user data is associated with a particular human user interacting with the UE 1006. In other embodiments, the user data is associated with a UE 1006 that shares data with the host 1002 without explicit human interaction. In step 1010, the host 1002 initiates a transmission carrying the user data towards the UE 1006. The host 1002 may initiate the transmission responsive to a request transmitted by the UE 1006. The request may be caused by human interaction with the UE 1006 or by operation of the client application executing on the UE 1006. The transmission may pass via the network node 1004 in accordance with the teachings of the embodiments described throughout this disclosure. Accordingly, in step 1012, the network node 1004 transmits to the UE 1006 the user data that was carried in the transmission that the host 1002 initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In step 1014, the UE 1006 receives the user data carried in the transmission, which may be performed by a client application executed on the UE 1006 associated with the host application executed by the host 1002. In some examples, the UE 1006 executes a client application which provides user data to the host 1002. The user data may be provided in reaction or response to the data received from the host 1002. Accordingly, in step 1016, the UE 1006 may provide user data, which may be performed by executing the client application. In providing the user data, the client application may further consider user input received from the user via an input/output interface of the UE 1006. Regardless of the specific manner in which the user data was provided, the UE 1006 initiates, in step 1018, transmission of the user data towards the host 1002 via the network node 1004. In step 1020, in accordance with the teachings of the embodiments described throughout this disclosure, the network node 1004 receives user data from the UE 1006 and initiates transmission of the received user data towards the host 1002. In step 1022, the host 1002 receives the user data carried in the transmission initiated by the UE 1006. One or more of the various embodiments improve the performance of OTT services provided to the UE 1006 using the OTT connection 1050, in which the wireless connection 1070 forms the last segment. More precisely, the teachings of these embodiments may improve, e.g., latency particularly during a mobility event such as, e.g., a LTM event, and thereby provide benefits such as, e.g., better responsiveness. In an example scenario, factory status information may be collected and analyzed by the host 1002. As another example, the host 1002 may process audio and video data which may have been retrieved from a UE for use in creating maps. As another example, the host 1002 may collect and analyze real-time data to assist in controlling vehicle congestion (e.g., controlling traffic lights). As another example, the host 1002 may store surveillance video uploaded by a UE. As another example, the host 1002 may store or control access to media content such as video, audio, VR, or AR which it can broadcast, multicast, or unicast to UEs. As other examples, the host 1002 may be used for energy pricing, remote control of non-time critical electrical load to balance power generation needs, location services, presentation services (such as compiling diagrams etc. from data collected from remote devices), or any other function of collecting, retrieving, storing, analyzing, and/or transmitting data. In some examples, a measurement procedure may be provided for the purpose of monitoring data rate, latency, and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection 1050 between the host 1002 and the UE 1006 in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection 1050 may be implemented in software and hardware of the host 1002 and/or the UE 1006. In some embodiments, sensors (not shown) may be deployed in or in association with other devices through which the OTT connection 1050 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or by supplying values of other physical quantities from which software may compute or estimate the monitored quantities. The reconfiguring of the OTT connection 1050 may include message format, retransmission settings, preferred routing, etc.; the reconfiguring need not directly alter the operation of the network node 1004. Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling that facilitates measurements of throughput, propagation times, latency, and the like by the host 1002. The measurements may be implemented in that software causes messages to be transmitted, in particular empty or ‘dummy’ messages, using the OTT connection 1050 while monitoring propagation times, errors, etc. Although the computing devices described herein (e.g., UEs, network nodes, hosts) may include the illustrated combination of hardware components, other embodiments may comprise computing devices with different combinations of components. It is to be understood that these computing devices may comprise any suitable combination of hardware and/or software needed to perform the tasks, features, functions, and methods disclosed herein. Determining, calculating, obtaining, or similar operations described herein may be performed by processing circuitry, which may process information by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored in the network node, and/or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination. Moreover, while components are depicted as single boxes located within a larger box or nested within multiple boxes, in practice computing devices may comprise multiple different physical components that make up a single illustrated component, and functionality may be partitioned between separate components. For example, a communication interface may be configured to include any of the components described herein, and/or the functionality of the components may be partitioned between the processing circuitry and the communication interface. In another example, non-computationally intensive functions of any of such components may be implemented in software or firmware and computationally intensive functions may be implemented in hardware. In certain embodiments, some or all of the functionality described herein may be provided by processing circuitry executing instructions stored in memory, which in certain embodiments may be a computer program product in the form of a non-transitory computer-readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry without executing instructions stored on a separate or discrete device- readable storage medium, such as in a hardwired manner. In any of those particular embodiments, whether executing instructions stored on a non-transitory computer-readable storage medium or not, the processing circuitry can be configured to perform the described functionality. The benefits provided by such functionality are not limited to the processing circuitry alone or to other components of the computing device, but are enjoyed by the computing device as a whole and/or by end users and a wireless network generally. EMBODIMENTS Group A Embodiments 1. A method performed by a User Equipment, UE, (400), the method comprising: receiving (406) a first message from a first network node (402) on a serving cell of the UE (400), the first message comprising configuration information for an aperiodic synchronization signal to be transmitted on a second cell; and receiving (410) a second message from the first network node (402) on the serving cell of the UE (400); and responsive to receiving (410) the second message: receiving (410) the aperiodic synchronization signal on the second cell, in accordance with the configuration information; and acquiring (414) downlink synchronization with respect to the second cell using the aperiodic synchronization signal received on the second cell. 2. The method of embodiment 1 wherein the second message comprising or being a trigger for the UE (400) to perform measurement on the aperiodic synchronization signal on the second cell. 3. The method of embodiment 1 or 2 wherein the second cell is a candidate Layer 1/Layer 2 triggered inter-cell mobility, LTM, cell. 4. The method of any of embodiments 1 to 3 wherein the configuration information comprised in the first message provides a full configuration of the aperiodic synchronization signal on the second cell. 5. The method of any of embodiments 1 to 3 wherein the configuration information comprised in the first message provides a partial configuration of the aperiodic synchronization signal on the second cell. 6. The method of embodiment 5 wherein a remaining part of the configuration of the aperiodic synchronization signal is comprised in the second message. 7. The method of any of embodiments 1 to 6 wherein the first message is a Radio Resource Control, RRC, message. 8. The method of any of embodiments 1 to 7 wherein the second message is a Physical Downlink Control Channel, PDCCH, order for triggering a random access on the second cell. 9. The method of any of embodiments 1 to 8 wherein the aperiodic synchronization signal is offset in time with respect to a reference time. 10. The method of embodiment 9 wherein the reference time is a time of reception of the second message. 11. The method of embodiment 9 or 10 wherein an offset between the reference time and reception of the aperiodic synchronization signal is fixed. 12. The method of embodiment 9 or 10 wherein an offset between the reference time and reception of the aperiodic synchronization signal is dynamic or configurable. 13. The method of embodiment 9 or 10 wherein an offset between the reference time and reception of the aperiodic synchronization signal is indicated in the second message. 14. The method of any of embodiments 1 to 13 wherein the aperiodic synchronization signal is a primary synchronization signal, a secondary synchronization signal, a synchronization signal block, a tracking reference signal, or a channel state information reference signal. 15. The method of any of embodiments 1 to 14 further comprising performing (416) one or more operations using the acquired downlink synchronization with respect to the second cell. 16. The method of embodiment 15 wherein the one or more operations comprise a random access on the second cell. 17. The method of any of the previous embodiments, further comprising: providing user data; and forwarding the user data to a host via the transmission to the network node. Group B Embodiments 18. A method performed by a first network node (402) that operates a serving cell of a User Equipment, UE, (400), the method comprising: transmitting (406) a first message to the UE (400) on the serving cell of the UE (400), the first message comprising configuration information for an aperiodic synchronization signal to be transmitted on a second cell; and transmitting (410) a second message to the UE (400) on the serving cell of the UE (400). 19. The method of embodiment 18 wherein the second message for triggering the UE (400) to acquire downlink synchronization with respect to the second cell using the aperiodic synchronization signal on the second cell. 20. The method of embodiment 18 or 19 wherein the second cell is a candidate Layer 1/Layer 2 triggered inter-cell mobility, LTM, cell. 21. The method of any of embodiments 18 to 20 wherein the configuration information comprised in the first message provides a full configuration of the aperiodic synchronization signal on the second cell. 22. The method of any of embodiments 18 to 20 wherein the configuration information comprised in the first message provides a partial configuration of the aperiodic synchronization signal on the second cell. 23. The method of embodiment 22 wherein a remaining part of the configuration of the aperiodic synchronization signal is comprised in the second message. 24. The method of any of embodiments 18 to 23 wherein the first message is a Radio Resource Control, RRC, message. 25. The method of any of embodiments 18 to 24 wherein the second message is a Physical Downlink Control Channel, PDCCH, order for triggering a random access on the second cell. 26. The method of any of embodiments 18 to 25 wherein the aperiodic synchronization signal is offset in time with respect to a reference time. 27. The method of embodiment 26 wherein the reference time is a time of reception of the second message at the UE (400). 28. The method of embodiment 26 or 27 wherein an offset between the reference time and reception of the aperiodic synchronization signal is fixed. 29. The method of embodiment 26 or 27 wherein an offset between the reference time and reception of the aperiodic synchronization signal is dynamic or configurable. 30. The method of embodiment 26 or 27 wherein an offset between the reference time and reception of the aperiodic synchronization signal at the UE (400) is indicated in the second message. 31. The method of any of embodiments 18 to 30 wherein the aperiodic synchronization signal is a primary synchronization signal, a secondary synchronization signal, a synchronization signal block, a tracking reference signal, or a channel state information reference signal. 32. The method of any of embodiments 18 to 31 further comprising, prior to transmitting (410) the second message to the UE (400) on the serving cell, cooperating (408) with a second network node (404) that operates the second cell to initiate transmission of the aperiodic synchronization signal on the second cell. 33. The method of any of embodiments 18 to 31 further comprising, prior to transmitting (410) the second message to the UE (400) on the serving cell, communicating (408A) with a second network node (404) that operates the second cell to agree upon when the aperiodic synchronization signal is to be transmitted on the second cell. 34. The method of any of embodiments 18 to 31 further comprising, prior to transmitting (410) the second message to the UE (400) on the serving cell, sending (408B), to a second network node (404) that operates the second cell, a request for the second network node (404) to transmit the aperiodic synchronization signal on the second cell. 35. The method of any of embodiments 18 to 31 further comprising, prior to transmitting (410) the second message to the UE (400) on the serving cell, receiving (408C), from a second network node (404) that operates the second cell, a notification that the aperiodic synchronization signal will be transmitted on the second cell. 36. A method performed by a second network node (404), the method comprising: cooperating (408) with a first network node (402) that operates a serving cell of a User Equipment, UE, (400) about transmission of an aperiodic synchronization signal on a second cell operated by the second network node (404); transmitting (412) the aperiodic synchronization signal on the second cell, in accordance with a result of the cooperating (408). 37. The method of embodiment 36 wherein the second cell is a candidate Layer 1/Layer 2 triggered inter-cell mobility, LTM, cell. 38. The method of embodiment 36 or 37 wherein the aperiodic synchronization signal is offset in time with respect to a reference time. 39. The method of embodiment 38 wherein the reference time is a time of reception of a message on the serving cell at the UE (400) that triggers the UE (400) to perform measurement on the aperiodic synchronization signal. 40. The method of embodiment 38 or 39 wherein an offset between the reference time and reception of the aperiodic synchronization signal is fixed. 41. The method of embodiment 38 or 39 wherein an offset between the reference time and reception of the aperiodic synchronization signal is dynamic or configurable. 42. The method of any of embodiments 36 to 41 wherein the aperiodic synchronization signal is a primary synchronization signal, a secondary synchronization signal, a synchronization signal block, a tracking reference signal, or a channel state information reference signal. 43. The method of any of embodiments 36 to 42 wherein cooperating (408) with the first network node (402) comprises communicating (408A) with the first network node (402) to agree upon when the aperiodic synchronization signal is to be transmitted on the second cell. 44. The method of any of embodiments 36 to 42 wherein cooperating (408) with the first network node (402) comprises receiving (408B), from the first network node, a request for the second network node (404) to transmit the aperiodic synchronization signal on the second cell. 45. The method of any of embodiments 36 to 42 wherein cooperating (408) with the first network node (402) comprises sending (408C), to the first network node, a notification that the aperiodic synchronization signal will be transmitted on the second cell. 46. The method of any of embodiments 18 to 45 wherein the first network node (402) and the second network node (404) are separate network nodes. 47. The method of any of embodiments 18 to 45 wherein the first network node (402) and the second network node (404) are the same network node. 48. The method of any of the previous embodiments, further comprising: obtaining user data; and forwarding the user data to a host or a user equipment. Group C Embodiments 49. A user equipment comprising: processing circuitry configured to perform any of the steps of any of the Group A embodiments; and power supply circuitry configured to supply power to the processing circuitry. 50. A network node comprising: processing circuitry configured to perform any of the steps of any of the Group B embodiments; and power supply circuitry configured to supply power to the processing circuitry. 51. A user equipment (UE) comprising: an antenna configured to send and receive wireless signals; radio front-end circuitry connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry; the processing circuitry being configured to perform any of the steps of any of the Group A embodiments; an input interface connected to the processing circuitry and configured to allow input of information into the UE to be processed by the processing circuitry; an output interface connected to the processing circuitry and configured to output information from the UE that has been processed by the processing circuitry; and a battery connected to the processing circuitry and configured to supply power to the UE. 52. A host configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising: processing circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a cellular network for transmission to a user equipment (UE), wherein the UE comprises a communication interface and processing circuitry, the communication interface and processing circuitry of the UE being configured to perform any of the steps of any of the Group A embodiments to receive the user data from the host. 53. The host of the previous embodiment, wherein the cellular network further includes a network node configured to communicate with the UE to transmit the user data to the UE from the host. 54. The host of the previous 2 embodiments, wherein: the processing circuitry of the host is configured to execute a host application, thereby providing the user data; and the host application is configured to interact with a client application executing on the UE, the client application being associated with the host application. 55. A method implemented by a host operating in a communication system that further includes a network node and a user equipment (UE), the method comprising: providing user data for the UE; and initiating a transmission carrying the user data to the UE via a cellular network comprising the network node, wherein the UE performs any of the operations of any of the Group A embodiments to receive the user data from the host. 56. The method of the previous embodiment, further comprising: at the host, executing a host application associated with a client application executing on the UE to receive the user data from the UE. 57. The method of the previous embodiment, further comprising: at the host, transmitting input data to the client application executing on the UE, the input data being provided by executing the host application, wherein the user data is provided by the client application in response to the input data from the host application. 58. A host configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising: processing circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a cellular network for transmission to a user equipment (UE), wherein the UE comprises a communication interface and processing circuitry, the communication interface and processing circuitry of the UE being configured to perform any of the steps of any of the Group A embodiments to transmit the user data to the host. 59. The host of the previous embodiment, wherein the cellular network further includes a network node configured to communicate with the UE to transmit the user data from the UE to the host. 60. The host of the previous 2 embodiments, wherein: the processing circuitry of the host is configured to execute a host application, thereby providing the user data; and the host application is configured to interact with a client application executing on the UE, the client application being associated with the host application. 61. A method implemented by a host configured to operate in a communication system that further includes a network node and a user equipment (UE), the method comprising: at the host, receiving user data transmitted to the host via the network node by the UE, wherein the UE performs any of the steps of any of the Group A embodiments to transmit the user data to the host. 62. The method of the previous embodiment, further comprising: at the host, executing a host application associated with a client application executing on the UE to receive the user data from the UE. 63. The method of the previous embodiment, further comprising: at the host, transmitting input data to the client application executing on the UE, the input data being provided by executing the host application, wherein the user data is provided by the client application in response to the input data from the host application. 64. A host configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising: processing circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a network node in a cellular network for transmission to a user equipment (UE), the network node having a communication interface and processing circuitry, the processing circuitry of the network node configured to perform any of the operations of any of the Group B embodiments to transmit the user data from the host to the UE. 65. The host of the previous embodiment, wherein: the processing circuitry of the host is configured to execute a host application that provides the user data; and the UE comprises processing circuitry configured to execute a client application associated with the host application to receive the transmission of user data from the host. 66. A method implemented in a host configured to operate in a communication system that further includes a network node and a user equipment (UE), the method comprising: providing user data for the UE; and initiating a transmission carrying the user data to the UE via a cellular network comprising the network node, wherein the network node performs any of the operations of any of the Group B embodiments to transmit the user data from the host to the UE. 67. The method of the previous embodiment, further comprising, at the network node, transmitting the user data provided by the host for the UE. 68. The method of any of the previous 2 embodiments, wherein the user data is provided at the host by executing a host application that interacts with a client application executing on the UE, the client application being associated with the host application. 69. A communication system configured to provide an over-the-top service, the communication system comprising: a host comprising: processing circuitry configured to provide user data for a user equipment (UE), the user data being associated with the over-the-top service; and a network interface configured to initiate transmission of the user data toward a cellular network node for transmission to the UE, the network node having a communication interface and processing circuitry, the processing circuitry of the network node configured to perform any of the operations of any of the Group B embodiments to transmit the user data from the host to the UE. 70. The communication system of the previous embodiment, further comprising: the network node; and/or the user equipment. 71. A host configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising: processing circuitry configured to initiate receipt of user data; and a network interface configured to receive the user data from a network node in a cellular network, the network node having a communication interface and processing circuitry, the processing circuitry of the network node configured to perform any of the operations of any of the Group B embodiments to receive the user data from a user equipment (UE) for the host. 72. The host of the previous 2 embodiments, wherein: the processing circuitry of the host is configured to execute a host application, thereby 5 providing the user data; and the host application is configured to interact with a client application executing on the UE, the client application being associated with the host application. 73. The host of the any of the previous 2 embodiments, wherein the initiating receipt of the user data comprises requesting the user data. ¹⁰ 74. A method implemented by a host configured to operate in a communication system that further includes a network node and a user equipment (UE), the method comprising: at the host, initiating receipt of user data from the UE, the user data originating from a transmission which the network node has received from the UE, wherein the network node performs any of the steps of any of the Group B embodiments to receive the user data from the 15 UE for the host. 75. The method of the previous embodiment, further comprising at the network node, transmitting the received user data to the host.

Claims

CLAIMS 1. A method performed by a User Equipment, UE, (400), the method comprising: receiving (406) a first message from a first network node (402) on a serving cell of the UE (400), the first message comprising configuration information for an aperiodic synchronization signal to be transmitted on a second cell; and receiving (410) a second message from the first network node on the serving cell of the UE, wherein the second message is a Physical Downlink Control Channel, PDCCH, order for triggering a random access on the second cell; and responsive to receiving the second message: receiving (412) the aperiodic synchronization signal on the second cell, in accordance with the configuration information; and acquiring (414) downlink synchronization with respect to the second cell using the aperiodic synchronization signal received on the second cell.

2. The method of claim 1, further comprising performing (416) one or more operations using the acquired downlink synchronization with respect to the second cell, wherein the one or more operations comprise transmitting a physical random access channel, PRACH, preamble on the second cell.

3. The method of any of claims 1-2, wherein the second cell is a candidate Layer 1/Layer 2 triggered inter-cell mobility, LTM, cell.

4. The method of any of claims 1-3, wherein the configuration information comprised in the first message provides a full configuration of the aperiodic synchronization signal on the second cell.

5. The method of any of claims 1-3, wherein the configuration information comprised in the first message provides a partial configuration of the aperiodic synchronization signal on the second cell, wherein a remaining part of the configuration of the aperiodic synchronization signal is comprised in the second message.

6. The method of any of claims 1-5, wherein the first message is a Radio Resource Control, RRC, message.

7. The method of any of claims 1-6, wherein the aperiodic synchronization signal is offset in time with respect to a reference time, wherein the reference time is a time of reception of the second message, wherein an offset between the reference time and reception of the aperiodic synchronization signal is fixed or is indicated in the second message.

8. A method performed by a first network node (402) that operates a serving cell of a User Equipment, UE, (400), the method comprising: transmitting (406) a first message to the UE on the serving cell of the UE, the first message comprising configuration information for an aperiodic synchronization signal to be transmitted on a second cell; and transmitting (410) a second message to the UE on the serving cell of the UE for triggering the UE to acquire downlink synchronization with respect to the second cell using the aperiodic synchronization signal on the second cell, wherein the second message is a Physical Downlink Control Channel, PDCCH, order for triggering a random access on the second cell.

9. The method of claim 8, wherein the second cell is a candidate Layer 1/Layer 2 triggered inter-cell mobility, LTM, cell.

10. The method of any of claims 8-9, wherein the configuration information comprised in the first message provides a full configuration of the aperiodic synchronization signal on the second cell.

11. The method of any claims 8-9, wherein the configuration information comprised in the first message provides a partial configuration of the aperiodic synchronization signal on the second cell, wherein a remaining part of the configuration of the aperiodic synchronization signal is comprised in the second message.

12. The method of any of claims 8-11, wherein the first message is a Radio Resource Control, RRC, message.

13. The method of any of claims 8-12, wherein the aperiodic synchronization signal is offset in time with respect to a reference time, wherein the reference time is a time of reception of the second message at the UE, wherein an offset between the reference time and reception of the aperiodic synchronization signal is fixed or is indicated in the second message.

14. The method of any of claims 8-13, further comprising, prior to transmitting the second message to the UE on the serving cell, cooperating (408) with a second network node (404) that operates the second cell to initiate transmission of the aperiodic synchronization signal on the second cell.

15. The method of any of claims 8-13, further comprising, prior to transmitting the second message to the UE on the serving cell, communicating (408A) with a second network node (404) that operates the second cell to agree upon when the aperiodic synchronization signal is to be transmitted on the second cell.

16. The method of any of claims 8-13, further comprising, prior to transmitting the second message to the UE on the serving cell, sending (408B), to a second network node (404) that operates the second cell, a request for the second network node to transmit the aperiodic synchronization signal on the second cell.

17. The method of any of claims 8-13, further comprising, prior to transmitting the second message to the UE on the serving cell, receiving (408C), from a second network node (404) that operates the second cell, a notification that the aperiodic synchronization signal will be transmitted on the second cell.

18. A method performed by a second network node (404), the method comprising: cooperating (408) with a first network node (402) that operates a serving cell of a User Equipment, UE, (400) about transmission of an aperiodic synchronization signal on a second cell operated by the second network node; and transmitting (412) the aperiodic synchronization signal on the second cell, in accordance with a result of the cooperating.

19. The method of claim 18, wherein the second cell is a candidate Layer 1/Layer 2 triggered inter-cell mobility, LTM, cell.

20. The method of any of claims 18-19, wherein cooperating with the first network node comprises communicating (408A) with the first network node to agree upon when the aperiodic synchronization signal is to be transmitted on the second cell.

21. The method of any of claims 18-19, wherein cooperating with the first network node comprises receiving (408B), from the first network node, a request for the second network node to transmit the aperiodic synchronization signal on the second cell.

22. The method of any of claims 18-19, wherein cooperating with the first network node comprises sending (408C), to the first network node, a notification that the aperiodic synchronization signal will be transmitted on the second cell.

23. The method of any of claims 15-22, wherein the first network node (402) and the second network node (404) are separate network nodes.

24. The method of any of claims 15-22, wherein the first network node (402) and the second network node (404) are the same network node.

25. A user equipment, UE, (400, 600) comprising: processing circuitry (602) configured to: receive a first message from a first network node (402) on a serving cell of the UE, the first message comprising configuration information for an aperiodic synchronization signal to be transmitted on a second cell; and receive a second message from the first network node on the serving cell of the UE, wherein the second message is a Physical Downlink Control Channel, PDCCH, order for triggering a random access on the second cell; and responsive to receiving the second message: receive the aperiodic synchronization signal on the second cell, in accordance with the configuration information; and acquire downlink synchronization with respect to the second cell using the aperiodic synchronization signal received on the second cell; and power supply circuitry configured to supply power to the processing circuitry.

26. The UE of claim 25, wherein the processing circuitry is configured to perform the method of any of claims 2-7.

27. A first network node (402, 700) comprising: processing circuitry (702) configured to: transmit a first message to the UE on the serving cell of the UE, the first message comprising configuration information for an aperiodic synchronization signal to be transmitted on a second cell; and transmit a second message to the UE on the serving cell of the UE for triggering the UE to acquire downlink synchronization with respect to the second cell using the aperiodic synchronization signal on the second cell, wherein the second message is a Physical Downlink Control Channel, PDCCH, order for triggering a random access on the second cell; and power supply circuitry configured to supply power to the processing circuitry.

28. The first network node of claim 27, wherein the processing circuitry is configured to perform the method of any of claims 8-17.

29. A second network node (404, 700) comprising: processing circuitry (702) configured to: cooperate with a first network node (402) that operates a serving cell of a User Equipment, UE, (400) about transmission of an aperiodic synchronization signal on a second cell operated by the second network node; and transmit the aperiodic synchronization signal on the second cell, in accordance with a result of the cooperating; and power supply circuitry configured to supply power to the processing circuitry.

30. The second network node of claim 29, wherein the processing circuitry is configured to perform the method of any of claims 19-24.