Patent Description:
NR-Unlicensed (NR-U) is a technology being discussed in 3GPP, which is designed to provide NR cellular communications to users the unlicensed frequency. This implies that NR-U has to co-exist with other communication technologies such as IEEE <NUM> (WiFi), etc..

In order to fulfil the fair use requirements, the unlicensed band can be accessed through Listen-Before-Talk (LBT) procedures, in order to utilize the shared channel for cellular communications.

A key challenge in the unlicensed spectrum when compared to the licensed spectrum is the limited number of transmission opportunities, which require adaptation of certain specified NR operations.

More in general, procedures based on competition to the access to the communication may have inconvenients, as no time slot is granted to a user equipment (UE). For example, when a UE intends to send a transmission to a base station (BS), a delay may be caused, e.g., because of simultaneous transmissions of the BS with other UEs. Therefore, techniques for increasing the reliability are in general pursued, e.g., to speed up the communications. Some key issues to be addressed include:.

<CIT> discloses a method for communicating a time point for transmitting a TRS from another cell.

<CIT> discloses a method for choosing one base station among a plurality of base stations.

<CIT> discloses a method for requesting channel load information.

Reference can now be made to <FIG> in combination with <FIG> or <FIG>, which show two different possible operations for the system of <FIG>.

<FIG> shows a system including a first base station <NUM> (which may be a licensed or unlicensed base station, e.g., for NR-U), a second base station <NUM> (which may be an unlicensed base station, e.g., for NR-U), and a base station <NUM> (which may be a base station, e.g. operating on licensed spectrum, e.g., for LTE, <NUM>, <NUM>, <NUM>, etc.). Hereinafter, reference is made to "cells" instead of "base stations". Each cell may be operated by a base station. One base station may operate two different cells. Two different cells may be distinguished, for example, by the base station in case different cells are based on different base stations. Different cells may be based on different frequencies, different spaces, different directions, different codes, and/or different power.

A UE <NUM> may be connected, through a data link <NUM>, with a first cell <NUM> (here associated to the first base station). The first cell <NUM> may be a licensed or unlicensed cell. The UE <NUM> may exchange, in an uplink or downlink, control signals (generally indicated with <NUM>) with the first cell <NUM>. As can be seen from <FIG>, the UE <NUM> may potentially be connected to a second, unlicensed cell <NUM> (here associated to the second base station). In general terms, the UE <NUM> may potentially also communicate uplink or downlink data signals with the second cell <NUM>, even though the UE <NUM> is currently operating by exchanging data signals <NUM> with the first cell <NUM>. This situation generally occurs while the UE <NUM> is within a coverage area within which the UE <NUM> can receive/transmit signals from/to the cell <NUM>.

In the present example, the UE <NUM> happens to currently be in both the coverage area of the first cell <NUM> and in the coverage area of the second cell <NUM>. The UE <NUM> may also happen to be within or without a coverage area associated to the licensed cell <NUM> (which may be, for example, a gNB/eNB). Therefore, in some examples the UE <NUM> may communicate with the licensed cell <NUM>, which takes the role of the first cell. Therefore, the examples discussed below generally refer to the scenario of <FIG>, even though the first cell may be undifferentiated embodied by the cell <NUM> and the cell <NUM> (as, in this scenario, it is indifferent whether the first cell is a licensed cell or unlicensed cell). In general terms, the UE <NUM> may send and/or receive data communications through signals <NUM> (e.g., signals regarding voice traffic and signals regarding data traffic, such as web-based signals transmitting web-based content).

The UE <NUM> may be configured to exchange control signals <NUM> with the first cell <NUM>. As explained above, the UE <NUM> is currently exchanging data signals <NUM> and/or control signals <NUM> with the first cell <NUM>, as a consequence of the fact that the conditions associated to the first cell <NUM> are held as being a better quality than the conditions associated to the communication with the second cell <NUM>. Notwithstanding, the conditions may change, e.g., by virtue of one of several possible causes, such as traffic conditions, the UE <NUM> being moved towards a position more favorable for communicating the second cell <NUM>, conditions associated to the capacities of the cell(s) <NUM> and/or <NUM> to satisfy the traffic request of the UE <NUM> and of possible other UEs, etc..

The UE <NUM> exchanges control signals <NUM> with the first cell <NUM>. In particular, the UE <NUM> may receive, from the first cell <NUM>, assistance information <NUM> (as part of the control signal <NUM>) for assisting the UE <NUM> in receiving a discovery reference signal <NUM> (also indicated with <NUM>). The assistance information <NUM>, for example, may be a DMTC (discovery measurement time configuration). The discovery reference signal (<NUM>, <NUM>) may be in a time window, for example, within a DMTC period. The discovery reference signal (DRS) <NUM> may be used to discover, measure, and/or estimate the channel. The assistance information <NUM> can contain information about the time of the one or more DRS, such as periodicity, offset, time window, frequency information, periodicity, etc..

The discovery reference signal <NUM> is transmitted by a cell different from the first cell <NUM>, i.e., the second cell <NUM> (e.g. a different base station). The assistance information <NUM> may therefore instruct the UE <NUM> regarding timing information on the discovery reference signal <NUM>. The discovery reference signal <NUM> is periodically sent by the second cell <NUM>. It is here to be noted that, even though only one single discovery reference signal is here discussed, there is the possibility that a multiplicity of other, second cells send other discovery reference signals, each additional cell providing a particular discovery reference signal to the UE <NUM>.

An example of the discovery reference signal <NUM> is shown in <FIG> and may be configured as a discovery reference signal (DRS). The discovery references signal <NUM> may be, for example, based on a discovery measurement time configuration (DMTC). Examples of these operations are discussed below. Anyway, the first cell transmits, encoded within the assistance information <NUM>, information which permits the UE <NUM> to detect the discovery reference signal <NUM>.

The UE <NUM> may perform at least one measurement on the discovery reference signal <NUM> as acquired by the UE <NUM>. Accordingly, on the basis of the performed at least one measurement, the UE <NUM> obtains information associated to the (possible) communication with the first cell <NUM>. , on the basis of the discovery reference signal <NUM>, the UE <NUM> may understand whether it is preferable to handover to the second cell <NUM>, for example.

This is particularly appropriate when the UE <NUM> is moved from the coverage area of the first cell towards a coverage area of the second cell <NUM>, as the UE <NUM> may discover, for example, that the signal transmitted from the first cell <NUM> has an increased strength or an increase quality with respect to the signal from the first cell <NUM>.

Accordingly, the UE <NUM> may perform a handover, HO, procedure <NUM> so that, subsequently, the UE <NUM> will exchange data signals <NUM> (in uplink and/or in downlink) and/or control signals (in downlink and/or in uplink) with the second cell <NUM> instead of the first cell <NUM>.

The decision of triggering the handover procedure (which are herewith explained as HO decision and HO procedure <NUM>) may be triggered either by the UE <NUM> and/or by the cell (e.g., BS) <NUM> and/or <NUM>.

Examples are here provided. A first example is provided by <FIG>, associated to the UE <NUM> autonomously deciding of performing a HO procedure. <FIG> shows the UE <NUM>, a first cell <NUM> (which notwithstanding could also be the first cell <NUM>) and a second cell <NUM>. The communication is originally as in <FIG>. The UE <NUM> is originally communicating in uplink and/or downlink data signal (for data and/or voice traffic) <NUM> and/or control signals <NUM> with the first cell <NUM> (this is not shown in <FIG>). Among the control signals <NUM> received from the first cell <NUM>, the UE <NUM> receives assistance information <NUM> which assists the UE <NUM> to receive the discovery reference signal <NUM> from at least one second cell <NUM>. In particular, encoded in the assistance information <NUM>, there are provided timing information regarding the discovery reference signal <NUM>. Accordingly, the UE <NUM> obtains the knowledge of the discovery reference signal <NUM> to be received from the second cell <NUM> (e.g., timing of the discovery reference signal <NUM> and other information that permits the UE to receive the discovery reference signal <NUM>). It is to be understood that, in cases, a plurality of second cells may be implemented, each sending its own discovery reference signal. The assistance information <NUM> in general provides information on all the discovery reference signals <NUM> transmitted by second cells with which the UE <NUM> may communicate (in examples, discovery reference signals <NUM> is only transmitted by unlicensed cells, while licensed cells, such as NR/LTE, do not necessarily make use of discovery reference signals).

The different discovery reference signals sent by the different cells may be transmitted in non-simultaneous time slots, the different cells being synchronized with each other, e.g., through a non-shown backhaul network. An example is provided by <FIG>, where different cells send different discovery signals. The different base stations and/or different cells transmitting the different reference signals may, for example, be synchronized with each other, e.g., through a backhaul network (here not shown), for mobile communications. The timing information may relate, for example, to the periodicity of the reference signal (as indicated with <NUM> in <FIG>), the offset <NUM> and the length of a measurement window. Different cells may in general be awarded of different slots during time, so that the UE <NUM> may recognize the discovery reference signals <NUM> from different cells and to distinguish between them.

The UE <NUM> may perform at least one measurement on the discovery reference signal <NUM> obtained from the second cell <NUM>. The at least one measurement may be obtained, for example, by applying a RSSI technique. The at least one measurement may regard the strength of the received signal. The measurement may relate to the noise of the signal. The at least one measurement may relate to SNR (signal to noise ratio) and/or SNIR (Signal to noise + interference ratio). The at least one measurement may relate to correlation properties of the signal. Reference numeral <NUM> in <FIG> shows the time lost by the UE <NUM> in performing the at least one measurement on the discovery reference signal <NUM>.

On the basis of the performed at least one measurement, the UE <NUM> may perform the HO decision <NUM> (i.e., whether to initiate a HO procedure). The HO decision <NUM> may take into account the at least one measurement performed at <NUM>. For example, if the strength or power of the discovery reference signal <NUM> is detected as being higher than the strength or power of the signals from the first cell <NUM>, the UE <NUM> may decide, e.g., autonomously, to handover to the second cell <NUM>, by virtue of the strength or power of the discovery reference signal <NUM> from the second cell <NUM> being greater than the strength or power of the signals from the first cell <NUM>. If the decision has a negative result, the HO procedure is not initiated (e.g., by virtue of the strength or power of the discovery reference signal <NUM> from the second cell <NUM> being lower than the strength or power of the signal from the first cell <NUM>). If the decision has positive result, the UE <NUM> may decide (e.g., autonomously) to initiate a handover procedure <NUM>, e.g., by virtue of the increased strength or power of the signal from the second cell <NUM>, as determined from the at least one measurement on the discovery reference signal <NUM> in respect to the signals from the first cell <NUM>.

At the positive HO decision <NUM>, the UE <NUM> may send a notification <NUM> to at least one of the first cell <NUM> and second cell <NUM> (while <FIG> shows that the communication is sent to the second cell <NUM>, the notification <NUM> may be in addition or an alternative sent to the first cell <NUM>). At the reception of the notification <NUM>, the first cell <NUM> and/or second cell <NUM> obtains the knowledge that the HO procedure <NUM> is to be initiated. As shown by <FIG>, the second cell <NUM> may notify, through a notification 914a, the HO decision <NUM> to the first cell <NUM>, e.g. through the non-shown backhaul network.

Accordingly, a handover procedure <NUM> is started which will imply the fact that the UE <NUM> will communicate in the future with the second cell <NUM> instead of the first cell <NUM>. Subsequently, normal UL or DL communications <NUM> (data or control) may be performed between the UE <NUM> and the second cell <NUM> (the control communication between the UE <NUM> and the second cell <NUM> for permitting the handover is here not shown, apart for the notifications <NUM> and 914a).

<FIG> shows an alternative example <NUM> in which it is the cell <NUM> (e.g. the BS) which decides to trigger the handover, HO, <NUM>.

Also in this case, the UE <NUM> is originally exchanging data with the first cell <NUM> as in <FIG>. As explained above, the first cell <NUM> transmits assistance information <NUM> including timing information (the assistance information and the time information may have the same features of those discussed above, and may be, for example, included in Radio Resource Control, RRC, Signalling). In the timing information encoded in the assistance information <NUM>, the timing for the discovery reference signal <NUM> from the second cell <NUM> (even though a plurality of second cells may be provided) is provided to the UE <NUM>. The UE <NUM> may perform at least one measurement on the discovery reference signal <NUM>. The discovery reference signal <NUM> may have the same features of the discovery reference signal <NUM> discussed above. The at least one measurement may have the same features of the at least one measurement discussed above.

As can be seen from <FIG>, the UE <NUM>, in this example, does not autonomously decide whether to initiate or not initiate a HO procedure <NUM>. As can be seen, the reference numeral <NUM> is missing in <FIG>. Notwithstanding, the UE <NUM> transmits measurement information <NUM> (e.g. in a measurement report) providing information regarding the at least one measurement performed at <NUM>. The measurement report <NUM> may be transmitted either periodically (e.g. whatever the value of the obtained at least one measurement) or at the reaching of a particular event. One event may be, for example, the performed at least one measurement being over a measurement threshold indicative of a comparatively higher quality. Therefore, if the quality of the signal is high in the second cell, the first or second cell <NUM> or <NUM> may decide (at <NUM>) to initiate the handover <NUM>. The threshold may be in some cases static (e.g. based on a particular value which does not vary) or dynamic (e.g. based on a comparison between the strength or power of the signal sent by the first cell <NUM> with the strength or power of the discovery reference signal <NUM> sent by the second cell <NUM>).

In general terms, when, from the measurement information <NUM>, the cell <NUM> or <NUM> understands that the communication with the second cell <NUM> is preferable, the cell may trigger the HO <NUM>. It is to be noted that the measurement information <NUM> may be sent, in an additional alternative, to the second cell <NUM>. The HO decision <NUM> may therefore be performed by the second cell <NUM>. The first and second cells <NUM> and <NUM> may communicate with each other, for example, through a backhaul network not shown. The handover procedure <NUM> may be initiated though a notification <NUM> sent by the first cell <NUM> to the UE <NUM>, while a notification 917a from the first cell <NUM> to the second cell <NUM> may permit to notify the HO decision of starting the HO procedure <NUM>. The notification 917a may be transmitted, for example, through the backhaul network. After that, additional control communication (which is here not shown) may be exchanged between the UE <NUM> and the second cell <NUM>, within the HO procedure <NUM>.

In examples like the above and/or below, after the handover procedure <NUM> is performed, the communication may continue, even though between the UE <NUM> and the second cell <NUM>. At this point, the roles of the first and second cells are inverted with each other. For example, while communicating in UL and/or DL with the UE <NUM>, the second cell <NUM> may send the assistance information <NUM> including time information relating to the discovery reference signal <NUM> transmitted by the first cell <NUM>.

In the examples above and/or below, therefore, the HO decision may be performed either by the UE <NUM> (HO decision <NUM>) and/or by the first cell <NUM> (and/or by the second cell <NUM>) (in this case, it is referred to HO decision <NUM>). Notwithstanding, the HO decision is based on the at least one measurement performed by the UE <NUM> of the discovery reference signal <NUM> sent by the second cell <NUM> (and/or by other second cells here not shown). The HO decision <NUM> or <NUM> is based on measurement value(s) being over a measurement threshold indicative of an increased quality. The HO decision <NUM>, <NUM> mis based at least on the status of the communication between the UE <NUM> and the first cell <NUM> and/or the occupancy of the first cell <NUM> and at least one second cell <NUM>, so that the HO decision <NUM> or <NUM> may be based on the status associated to a better quality offered by at least one second cell <NUM>.

In examples, the HO decision <NUM> or <NUM> may involve a choice between a plurality of second cells, wherein the choice is based at least on the performed at least one measurement (at <NUM>) on the multiple discovery reference signals <NUM> (as acquired by the UE <NUM>) from the plurality of second cells, and/or on the status of the second cell <NUM>, so as to choose a second cell associated to an increased quality (e.g., the best quality). Therefore, in case of a plurality of second cells, the HO decision <NUM> or <NUM> will choose that cell that permits to maximize the quality of the communication and/or minimize and/or balance the network occupancy.

In examples above, the decision <NUM> or <NUM> is performed after the at least one measurement. However, in some alternative examples, the at least one measurement may be performed after the HO decision. The HO decision may be based, for example, on a selection (e.g., user selection). The HO decision may be, for example, based on information regarding the status of the network (e.g. the occupancy of the network). For example, the first cell or second cell may decide the HO to the second cell <NUM> when the conditions of the network do not permit a satisfactory data or voice transmission between the UE <NUM> and the first cell <NUM>. For example, if the second cell <NUM> is not occupied while the first cell <NUM> is occupied, the cell <NUM> and/or <NUM> may decide the HO autonomously, without taking into account measurement information. However, after having notified the decision (at <NUM>) to the UE <NUM>, the UE <NUM> will have to perform a at least one measurement on the discovery reference signal <NUM> from the second cell <NUM> on the basis of the timing information encoded in the assistance information <NUM>.

Alternatively, the UE <NUM> may decide the handover autonomously, even without having performed the at least one measurement. For example, the UE <NUM> may autonomously decide to the handover after having experienced bad conditions of the channel for the communication <NUM> with the first cell <NUM>. For example, the UE <NUM> may have experienced a high latency times for the communication <NUM> or <NUM> with a first cell <NUM>. Accordingly, the UE <NUM> may autonomously decide to initiate the HO procedure <NUM> even without having measured the discovery reference signal <NUM>. Notwithstanding, after the HO decision <NUM> (e.g., after and/or before the notification <NUM>) the UE <NUM> may perform the at least one measurement on the discovery reference signal <NUM> on the basis of the timing information encoded in the assistance information <NUM>.

Reference can now be made to <FIG>, which refer to a different scenario useful to understand the invention. <FIG> shows a scenario of a UE <NUM> (which may be the UE above and/or below) which is within a coverage area of a first cell <NUM> (e.g. BS) which is an unlicensed cell, while the UE <NUM> is currently also within the coverage area of a second cell <NUM> (which in this case is a licensed cell, but in other examples could be an unlicensed cell). An unlicensed cell <NUM> is also shown which could have the same role of the licensed cell <NUM>. That would have in case the UE <NUM> were moved in an area which is both covered by the first cell <NUM> and by the second cell <NUM>. The examples herewith below are notwithstanding disclosed without taking into account the cell <NUM>, even though it is to be understood that the second cell <NUM> may substitute the cell <NUM> in a variance.

While <FIG> shows a backhaul channel <NUM> (e.g. backhaul network) and <FIG> does not, it shall be understood that the example of <FIG> also has the backhaul channel <NUM>. In other examples, are different systems without the backhaul channel <NUM> that may be used. In general terms, some examples below are discussed by starting with a scenario of <FIG> and moved towards the scenario of <FIG>.

As can be seen, in the configuration of <FIG>, the UE <NUM> is exchanging data through the communication data channel <NUM> in uplink and/or downlink (e.g. voice traffic and/or data traffic), e.g., in single connectivity (no dual connectivity). Also control signals <NUM> are exchanged by the UE <NUM> with the first cell <NUM>. It will be shown that a dual connectivity (or more in general multiple connectivity or multi-connectivity) may be initiated so that the UE <NUM> simultaneously communicates with both the first cell <NUM> (through the communication control signals <NUM>) and the second cell <NUM> (control signals <NUM>). The UE <NUM> may be configured to exchange control signals <NUM>, in uplink and/or downlink, with the first cell <NUM> and at least one second cell <NUM> and <NUM>. The UE <NUM> may be configured to exchange data transmissions, e.g. for voice and/or data traffic, in uplink and/or downlink, with the first cell <NUM> and at least one second cell <NUM> and <NUM>. The first cell <NUM> is an unlicensed cell and the at least one second cell <NUM> and <NUM> is a licensed or an unlicensed cell.

The UE <NUM> may be configured to perform, with the first cell <NUM>, an uplink and/or downlink communication to a listen before talk, LBT medium access strategy. The UE <NUM> may receive configuration data from the first cell <NUM> in case of fulfilment of a predetermined pre-condition for initiating the connectivity procedure (the pre-condition may be for example associated to the detection of high occupancy of the communication link between the UE <NUM> and the first cell <NUM>). The configuration data may include access information of the dual connectivity procedure to be established. The configuration data may indicate the selected second cell (e.g. whether the cell <NUM> or the cell <NUM> is chosen). After the reception of the configuration data, the UE <NUM> may evaluate a condition (e.g., a link deterioration condition) associated to the access of the communication with the first cell <NUM>. In case of fulfilment of the condition (e.g., indicating a comparatively high link deterioration), the UE <NUM> may start the dual connectivity procedure with the selected second cell.

Therefore, a double condition may be checked:.

Only after the fulfilment of the second of the two conditions, the UE <NUM> will start the multi connectivity with the first and the second cells <NUM> and <NUM>.

An example of the two-condition criteria is provided by <FIG>. At step <NUM>, the first cell may detect the pre-condition (e.g. high occupancy of the communication). At step <NUM>, the first cell <NUM> may check (e.g. through the backhaul channel <NUM>) whether a neighboring cell (e.g. a licensed cell) is present. At step 720a, the first cell <NUM> may request, to the second cell <NUM>, whether the second cell <NUM> may accept the dual connectivity (this communication may be performed through the backhaul channel <NUM>, for example). At step 720b, the second cell <NUM> may notify (e.g., through the backhaul channel <NUM>) to the first cell <NUM> an acknowledgement or non-acknowledgement to operate multi connectivity (e.g. to become a secondary cell for the multi connectivity). In case of positive acknowledgement, the first cell <NUM> may transmit (at <NUM>) configuration data including access of information for the dual connectivity procedure. The configuration data may indicate which is the selected second cell (which is in this case the cell <NUM>, but it would be possible that the second cell is chosen between a multiplicity of cells).

At step <NUM>, the UE <NUM> may send configuration information. At 722a, the UE <NUM> may evaluate the condition (e.g., link deterioration condition). In case of high link deterioration, the UE <NUM> will actually start the dual connectivity procedure <NUM>' (which may include at least one of the steps <NUM>, <NUM> and <NUM>, for example). Therefore, by performing a procedure <NUM>', the UE <NUM> may start operating in dual connectivity with both the cells <NUM> and <NUM>, using a multi-connectivity channel divided between the channels <NUM> with the first cell <NUM> and the channel <NUM> with the second cell <NUM>.

In general terms, the initiation of the dual connectivity is evaluated on two conditions. The first (pre-)condition is evaluated by the first cell <NUM> (or by the second cell, or by the network, more in general), which may take into consideration the general status of the communication. The second, final, condition is evaluated by the UE <NUM>, which actually starts the dual connectivity procedure for example only at the determination of an effective, high deterioration of the network. In some cases, it may be understood that both the first cell <NUM> (for evaluating the pre-condition) and the UE <NUM> (for evaluating the final, link deterioration condition) evaluate the status, link deterioration conditions, and/or for at least one measurement on the signals and/or the latency of the transmissions. Notwithstanding, in examples, the determination of the pre-condition is based on a threshold which is associated to a less deteriorated communication channel than the condition evaluated by the UE <NUM>. Therefore, the pre-condition evaluated by the first cell <NUM> may be associated to a status from which a high link deterioration is foreseeable, even though not necessarily present yet. Hence, the pre-condition may be in general verified before the real necessity of the dual connectivity, but permits to alert and/or configure the UE <NUM>, so that the UE <NUM> prepares for the dual connectivity. The UE <NUM> will actually start the dual connectivity after determined the fulfilment of the condition, for example a threshold of the link deterioration is met, so as to initiate the dual connectivity procedure only when effectively necessary.

In examples, the pre-condition may be dependent on the services/QoS requested by the UE or a network entity.

In addition or alternative, different choices may be made. For example, the pre-condition is based on a selection. The selection could be, for example, a user selection. The selection can be based on at least one of the following aspects; a number of LBT failures, high cell utilization, channel quality or quality of service, QOS, requirements.

In addition or alternative, the pre-condition may be based on the status of the first cell. The pre-condition may be at least on: an occupancy status of the at least one of the plurality of cells different from the first cell, at least one measurement performed by the first cell, at least one measurement performed by the UE <NUM> and signaled to the first cell <NUM>, at least one measurement performed by the at least one second cell and signaled to the first cell <NUM> through a backhaul link <NUM>, at least one measurement on interference, or metrics associated to the failures in accessing the communication between the UE and the first cell.

Also the final condition (as evaluated by the UE <NUM>) may be based on several aspects. The condition may be at least based on a metrics associated to failed accesses, by the UE <NUM>, to the communication with the first cell, the configuration data provided by the first cell <NUM>, or a maximum number of failed accesses expiration of a maximum access timer.

In examples, the condition may be a link deterioration condition: it may be fulfilled when a comparatively high link deterioration is determined. The condition may be associated to the number of LBT failures: it may be fulfilled at the determination that a comparatively higher number of LBT failures has occurred. The condition may be associated to the number of packet losses: it may be fulfilled when the number of packet losses is over a threshold. The condition may be associated to the quality of service and/or service requirements: it may be fulfilled when the quality of service cannot be guaranteed anymore. The condition may be associated to the channel occupancy: it may be fulfilled when the channel occupancy is over a threshold.

In some cases, it is possible to arrive at preparing other configurations for the dual connectivity before the real necessity of starting the dual connectivity communication. This is extremely advantageous, as it permits to start the dual connectivity communication as soon as there is the real necessity, after that both the second cell and the UE <NUM> are configured for performing the dual connectivity. Accordingly, the procedure for starting a dual connectivity is sped up.

With LBT, a UE starts sending a transmission after having detected that a particular resource (e.g., channel) is not occupied by other transmissions in a current time slot.

There are two LBT mechanisms standardized by ETSI (European Telecommunications Standards Institute) to adaptively access a channel in order to avoid concurrent transmissions from other devices.

It can be noted that FBE has simpler channel access mechanisms, when compared to LBE.

3GPP has defined <NUM> categories of LBT for LAA and NR-based access for unlicensed spectrum [<NUM>, <NUM>]:.

One of these instruments may be used for the techniques above and/or below.

This technique makes use of specific time domain measurement windows, where the UE is allowed to perform measurements, e.g. Radio Link Monitoring (RLM). <FIG> and <FIG> shows the structure of a DMTC window <NUM>, where a period and subframe offset parameter are configured. This may enable for example the cell to dynamically toggle 'on' and 'off' states.

The UE is configured with these parameters for example via Radio Resource Control (RRC) Signalling, so as to permit the UE to recognize the reference signal to be measured.

Therefore, the UE may measure the reference signal (e.g., PSS, SSS, CRS, CSI-RS, DRS) <NUM> after having known, from the RRC Signalling, configuration data of the DMTC window <NUM>.

A technique used by a base station for measuring the power of the signals from the UE(s) is here indicated.

In the case of Radio Resource Management, it may be beneficial for the base station to be able to understand the channel occupancy status or load of the carrier, e.g., to avoid the hidden node problem by correlating measurements by multiple UEs. The RMTC indicates the percentage of time, that RSSI was observed to be above a configured threshold for RRM reports. <FIG> illustrates the RMTC procedure.

The RMTC period <NUM> and offset may for example also be configured via RRC signalling (e.g., from the BS), so that the UE knows at which instants to perform the measurements. The RMTC is dependent on the on the measurements performed during the DMTC (RSRP and RSRQ).

A discussion on aspects of the invention is here presented.

The first cell (e.g., NR-U gNB/licensed gNB) <NUM> may provide the UE <NUM> with a measurement configuration (e.g., the assistance information <NUM> of <FIG>) via e.g. RRC signalling (e.g., <NUM> in <FIG> and <FIG>) including partial or full DMTC configurations of neighboring cells (e.g., <NUM> and/or <NUM>). The measurement configuration, defining a HO measurement occasion, may include at least one of:.

For NR the DRS can be assumed to include a combination of both SS/PBCH (Synchronization Signal Block) blocks and CSI-RS (channel state information reference signal), for example.

The following exemplary message defines the specifies information applicable for SS/PBCH block(s) intra/inter-frequency measurements or CSI-RS intra/inter-frequency measurements. <IMG>
<IMG>.

The following exemplary measurement reporting message for triggering the event of handover based on the DRS of the neighbouring cells is shown for NR, ReportConfigNR. This may for example be initially transmitted via system information and then updated via RRC signalling transmitted from the cell <NUM> to the UE <NUM>. Or it may simply be transmitted via RRC. <IMG>
<IMG>
<IMG>
<IMG>
<IMG>
<IMG>.

The measurements can be configured to be event-triggered as shown above with a set of common key parameters (highlighted in bold), where the event is a possible handover.

These measurement profiles are applicable for both neighbouring intra-frequency (operating on same carrier frequency) and inter-frequency (operating on different carrier frequency) base stations. It may also be assumed that these serving and neighbouring base stations either:.

so that the serving cell can provide updated DMTC configurations of neighbouring cells to the UE.

The UE <NUM> may measure the reference signal <NUM> (e.g., DRS) of neighboring cell <NUM> only in the measurement occasion and reports the measurement outcome back to the BS <NUM>. The measurement configuration (e.g., as provided by in the assistance information <NUM>) may additionally include information regarding where and when to report the measurement outcome, e. g, the UE <NUM> tries to initiate a COT with a PUSCH including corresponding RRC signaling after a defined time period after each HO measurement occasion.

Another example of when to report the measurement could be an event-triggered approach, where the UE transmits a measurement report only after the measured neighbouring cell(s) exceed a reference threshold. This still depends on whether the UE successfully initiates a COT via LBT.

The UE <NUM> may use the measurement information as performed at <NUM> to decide at <NUM> whether another cell (e.g., <NUM>) has a better link and may perform autonomously an initial access to this cell Additional triggers can be consistent LBT failures or high channel occupancy/load (CBR).

Scenario <NUM>: Unsuccessful Channel Access after a period of time / Measurement Configuration not received within a specific time due to high occupancy of the unlicensed channel, resulting in consecutive LBT failures.

The UE <NUM> may operate in an NR-U standalone scenario, with both Control-plane (C-plane) and User-plane (U-plane) links (connections) to a NR-U base station <NUM> as noted in the exemplary <FIG>.

The UE <NUM> may be configured with an NR-U channel access timer after which the NR-U base station <NUM> can trigger a fast-track C-plane split bearer connection (supported for SRB1 and SRB2) for the said UE <NUM> over a licensed carrier to the strongest neighbouring base station (e.g., <NUM>) based on a set of criteria (low load, best signal quality, etc.), in order to provide robust control signalling for the NR-U UE <NUM> as shown in <FIG>. This is especially important for the timely reception of critical measurement reports required by the NR-U gNB <NUM>. The NR-U base station <NUM> would again be assumed to be synchronized with the NR base station <NUM> and thus all related base station signalling could be exchanged via the appropriate interface (e.g. X2, Xn, Xw).

<FIG> shows the conceptual signal flow diagram <NUM>. The licensed base station <NUM> and NR-U base station <NUM> may agree beforehand for the admittance of at least a set of UEs (in particular, UE <NUM>) based on pre-determined criteria (low load, best signal quality, etc).

This could also enable the addition of the licensed base station as secondary cell (SCell) to exploit an additional robust control signalling link.

The UE <NUM> may be configured with a channel access timer via system information to trigger the split bearer C-plane connection as seen in the exemplary messages below:
<IMG>
<IMG>
<IMG>
<IMG>.

Scenario <NUM>: The concept of switching C-plane connections in Scenario <NUM> can also apply to synchronous NR-U gNBs. Although, the key reason to initiate DC to another NR-U cell would be due to a lightly loaded cell (with low traffic). The same LBT vulnerabilities would be present when performing a NR-U dual connectivity with the advantage of double LBT opportunities for receiving control plane signalling.

Generally, examples may be implemented as a computer program product with program instructions, the program instructions being operative for performing one of the methods when the computer program product runs on a computer. The program instructions may for example be stored on a machine readable medium.

Other examples comprise the computer program for performing one of the methods described herein, stored on a machine readable carrier.

In other words, an example of method is, therefore, a computer program having a program instructions for performing one of the methods described herein, when the computer program runs on a computer.

A further example of the methods is, therefore, a data carrier medium (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. The data carrier medium, the digital storage medium or the recorded medium are tangible and/or non-transitionary, rather than signals which are intangible and transitory.

A further example of the method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may for example be transferred via a data communication connection, for example via the Internet.

A further example comprises a processing means, for example a computer, or a programmable logic device performing one of the methods described herein.

A further example comprises a computer having installed thereon the computer program for performing one of the methods described herein.

A further example comprises an apparatus or a system transferring (for example, electronically or optically) a computer program for performing one of the methods described herein to a receiver.

In some examples, a programmable logic device (for example, a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some examples, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods may be performed by any appropriate hardware apparatus.

The above described examples are merely illustrative for the principles discussed above. It is understood that modifications and variations of the arrangements and the details described herein will be apparent. It is the intent, therefore, to be limited by the scope of the impending claims and not by the specific details presented by way of description and explanation of the examples herein.

Claim 1:
A user equipment, UE (<NUM>), configured for exchanging control signals, in uplink, UL, and/or downlink, DL, with a first cell (<NUM>, <NUM>) and at least one second cell (<NUM>), wherein the first cell (<NUM>, <NUM>) is a licensed or unlicensed cell and the at least one second cell (<NUM>) is an unlicensed cell,
wherein the UE (<NUM>) is configured to exchange control signals (<NUM>) with the first cell (<NUM>, <NUM>) and, meanwhile:
receive, from the first cell (<NUM>, <NUM>), assistance information (<NUM>) for assisting the UE (<NUM>) in receiving a discovery reference signal (<NUM>, <NUM>), wherein the assistance information (<NUM>) includes at least timing information regarding a timing of the discovery reference signal (<NUM>, <NUM>) periodically sent by the at least one second cell (<NUM>);
perform (<NUM>) at least one measurement on the discovery reference signal (<NUM>, <NUM>) as acquired by the UE (<NUM>), from the at least one second cell (<NUM>), using the timing information included in the assistance information (<NUM>),
characterized by being further configured to perform a handover, HO, decision by deciding whether to initiate a HO procedure (<NUM>), so that the UE (<NUM>) communicates (<NUM>) with the at least one second cell (<NUM>), wherein the HO procedure is based on the performed at least one measurement on the discovery reference signal (<NUM>),
wherein the HO decision (<NUM>) is based at least on the performed at least one measurement (<NUM>) on the discovery reference signal (<NUM>) as acquired, so that the HO decision (<NUM>) follows the performed at least one measurement (<NUM>) being over a measurement threshold indicative of an increased quality.