TECHNICAL FIELD The present invention relates to a network apparatus and a method for handover (HO) of a user equipment (UE) from a serving base station (BS) to a target BS. In particular, the network apparatus is configured to take a decision about handing over the UE, and may therefore also be referred to as a HO-decision-entity. BACKGROUND

In wireless networks, mobility management is a crucial feature to ensure ubiquitous quality of service to the end user in a mobility situation. In fact, a HO procedure is required for user association in case of mobility, particularly when it is necessary for a user to change from one coverage area to another, in order to avoid connection drops.

Fig. 13 summarizes a conventional HO procedure, and particularly shows that a HO decision, especially a determination of a target BS, is based on certain measurement reports sent by the UE in a mobility situation (as specified by the 3GPP standard 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Automatic Neighbour Relation (ANR) for UTRAN; Stage 2 (Release 10) 3GPP TS 25.484 VIO.0.0 (2011-06)).

According to this 3GPP standard, so far the only available HO-relevant information at the serving BS related to its neighbouring BSs, i.e. the possible target BSs, includes a Physical cell ID and downlink (DL) channel information.

Currently, the serving BS does not have any further information about the possible target BSs. Specifically, the serving BS does not know, whether a potential target BS is full duplex (FD) or half duplex (HD) capable. Furthermore, the serving BS does not, and currently cannot, use uplink (UL) signal information (e.g. an UL signal strength) in the HO procedure. However, this kind of currently not available information would be of great importance to the HO decision, given particularly the increasing importance of the FD feature (which allows to transmit and receive at the same time and same frequency band, i.e. in-band full-duplex) in wireless networks, particularly 5G networks.

This is, because the best BS in terms of signal quality, as perceived by a UE, might not be the best BS from a throughput point of view for many reasons, such as the FD/HD capabilities of the BSs. Currently, this fact is not taken into account in radio access technologies (RAT).

The impact of these parameters on user performance is shown in Figs. 14-16. In the network example depicted in Fig. 14, for instance, BS3 is better in terms of a received signal power (see right side of Fig. 14), but BS4 offers acceptable coverage and the advantage of FD (see left side of Fig. 14). Accordingly, BS4 could be a better choice for a moving user after HO from BS2, i.e. a better choice of a target BS, due to the FD capabilities.

Based on these considerations, advanced simulations were performed by the inventors. The simulations took into account FD attributes, particularly residual self-interference and inter user interference (see schematic in Fig. 15). In fact, the FD mode leads to self- interference and inter-user interference, which will impact performance and should thus be anticipated within the HO procedure. The effect that these two types of interferences have on throughput performance can only be measured using UL signals. As explained above, however, current networks only support DL measurements for the HO procedure.

As shown in Fig. 15, the self-interference affects the UL signal SINR of UEl. Measuring this UL SINR requires UL signal transmission from UEl. Inter-user interference further affects the DL signal SINR of UE2. Measuring this DL SINR also requires UL signal transmission from UEl.

With respect to Fig. 16, a scenario including one HD BS and one FD BS is considered. The focus here lies on a UE in a HO procedure, wherein the measured SINR of the FD BS is below the SINR level of the HD BS, i.e. SINR FD < SINR HD -

Following the conventional HO procedure, the UE will be associated to the HD BS based on its high level of measured SINR. However, the conventional procedure ignores the fact that a FD BS may be able to provide a larger throughput than a HD BS, even if the HD BS has a larger SINR. This behavior is analyzed in more detail according to simulations shown in Fig. 16, where user throughput after a HO is shown for two cases: (1) the user performs a HO to a HD BS and (2) the user performs a HO to a FD BS. The simulation assumptions and parameters are as follows:

SINRSZ = SIN Rfjn - Residual self, interference— inter. user interference

Variable Value A Fixed Value=0.5 dB

Based on Fig. 16, it can be concluded that: If the user switches to the BS offering the best SINR, then it will always connect to the HD BS. As shown, this HD BS may not provide the highest throughput after HO completion. Thus, parameters like bandwidth, self- interference, and inter-user interference have a high impact on the per-user throughput, and these parameters are completely neglected in the conventional HO procedure.

So far, in fact, no specific mobility management method has been designed tailored to FD networks or mixed FD/HD deployed BSs.

SUMMARY

In view of the above-mentioned problems and disadvantages, the present invention aims to improve the conventional HO procedure. The present invention has especially the object to provide a network apparatus and a method, which are able to carry out an enhanced HO procedure, i.e. a more efficient HO procedure that takes benefit from the FD mode of the network elements (e.g. of BS and UE) and of the UL channel measurements. To this end, the present invention seeks to acquire additional information concerning the FD capabilities of BSs, especially of neighboring BSs of the serving BS serving a UE in a mobility situation. Further, the present invention intends to acquire additional information concerning the UL channel quality between the UE and the neighboring BSs of its serving BS.

The object of the present invention is achieved by the solution provided in the enclosed independent claims. Advantageous implementations of the present invention are further defined in the dependent claims.

In brief, the present invention proposes obtaining information on FD capabilities of the neighboring BSs of the serving BS. In the conventional HO procedure, knowledge of whether a neighboring BS is FD or HD is not available. Thus, the selection of the target BS for a UE in mobility is made only on the reported UE measurements, and is not at all correlated with the FD/HD capabilities of these BSs. Further, the present invention proposes triggering measurements of the UL channel quality between the UE in a mobility situation and the neighboring BSs. In the conventional HO procedure, the UE periodically measures the DL channel quality from its serving BS and from the neighboring BSs included in a list defined by the Automatic Neighbor Relation (ANR) function as specified in the 3GPP standard TS 25.484. These DL measurements are then reported by the UE to its serving BS, when a predefined condition is verified. UL channel quality measurements of the neighboring BSs of the serving BS is currently neither performed nor available.

A first aspect of the present invention provides a network apparatus configured to take a decision to HO a UE from a serving BS to a target BS, the network apparatus being configured to obtain FD capability information of each neighboring BS of the serving BS, request and receive an UL channel quality measurement for the UE from all or a subset of neighboring BSs, and determine a neighboring BS as the target BS based on the obtained FD capability information and the received UL channel quality measurements.

By obtaining additional FD capability information and UL channel quality measurements of all or a subset of (FD and/or HD capable) neighboring BSs, the network apparatus can take an enhanced HO decision, particularly a HO decision that take into account the FD capabilities of the different network entities. That is, overall a better decision can be taken, which allows benefits from FD capabilities in future networks. The enhanced HO decision significantly improves the overall network performance, and specifically improves UE performance after the HO operation is completed. It also reduces the number of HO failures.

The UL channel quality measurements can advantageously be requested and received from each FD capable neighboring BS of the serving BS. That is, one possible subset of neighboring BSs may include all FD capable neighboring BSs. However, the UL measurements can also be requested from, performed on, and then received from the HD neighboring BSs, and can be considered in the HO decision. That is, another possible subset of neighboring BSs may also include all HD capable neighboring BSs. The latter approach can also provide an enhanced HO decision with information about the measured UL quality. Of course, the UL channel quality measurements may also be obtained from each FD/HD capable neighboring BS.

In a first implementation form of the network apparatus according to the first aspect, the network apparatus is configured to extract the FD capability information from a neighbor relation table, NRT, available to at least the serving BS.

The NRT can be regularly updated, for instance, from the network side (e.g. a Radio Network Controller (RNC)). Integrating the information into the NRT provides an efficient solution, which does not require any additional signaling between BSs or BS and UE.

In a second implementation form of the network apparatus according to the first implementation form of the first aspect, the NRT includes a field specifying the FD capability of each neighboring BS of the serving BS.

In a third implementation form of the network apparatus according to the first or second implementation form of the first aspect, the NRT includes a field specifying supported bandwidths of each neighboring BS of the serving BS.

Thereby, the network apparatus is provided with further useful information, allowing it to take an even better HO decision, particularly in terms of throughput. Other useful information that can additionally or alternatively be included in a field of the NRT may be a mean value of inter-user interference at, for example, the neighboring and FD capable BSs.

In a fourth implementation form of the network apparatus according to the first aspect as such, the network apparatus is configured to obtain the FD capability information through a signaling exchange with each neighboring BS.

Accordingly, the network apparatus can obtain the FD capability information, without the necessity to change a conventionally used NRT design.

In a fifth implementation form of the network apparatus according to the fourth implementation form of the first aspect, the signaling exchange is performed through backhaul connections, for instance the X2 interface. Accordingly, existing connections may be used, and no further complexity is added to the system.

In a sixth implementation form of the network apparatus according to the first aspect as such or according to any previous implementation form of the first aspect, the network apparatus is configured to provide each neighboring BS with an identity of the UE for triggering the UL channel quality measurement between the respective neighboring BS and the UE.

In a seventh implementation form of the network apparatus according to the first aspect as such or according to any previous implementation form of the first aspect, the network apparatus is configured to receive a downlink, DL, channel quality measurement from the UE for all or a subset of neighboring BSs of the serving BS, and determine the target BS taking further into account the DL channel quality measurements. That is, the network apparatus may base the HO decision at least on the FD capability information and the combined DL and UL channel quality measurements of all or a subset of (FD and/or HD capable) neighboring BSs. Thereby, the HO decision is greatly improved. The network apparatus may also take into account other information, like a user state, a supported bandwidth, or the like. All information can be correlated with each other, and can be individually weighted as desired.

In an eighth implementation form of the network apparatus according to the first aspect as such or according to any previous implementation form of the first aspect, the network apparatus is configured to obtain FD capability information from the UE, and determine the target BS taking further into account the FD capability information of the UE.

In particular, depending on whether the UE is FD capable or not, the network apparatus can take the HO decision either favoring SINR or throughput.

In a ninth implementation form of the network apparatus according to the first aspect as such or according to any previous implementation form of the first aspect, the network apparatus is the serving BS or the network apparatus is included in or associated with the serving BS.

By including the network apparatus in at least one BS, multiple or each BS in a network may become capable of the enhanced HO procedure. A network apparatus may also be a separate entity, with which the network or BS are upgraded. The network apparatus may also be associated with multiple BSs.

In a tenth implementation form of the network apparatus according to the first aspect as such or according to any previous implementation form of the first aspect, the network apparatus is distributed over the serving BS and its neighboring BSs, wherein the serving BS is configured to obtain the FD capability information, request the UL channel quality measurement from all or a subset of neighboring BSs, and determine and notify a potential target BS based on the obtained FD capability information, and the potential target BS is configured to determine, whether it becomes the target BS for the HO of the UE, based on its FD capability and its UL channel quality measurement for the UE.

Thereby, a distributed approach is realized, wherein also the processing load is shared.

A second aspect of the present invention provides a method for HO of a UE from a serving BS to a target BS, the method comprising obtaining FD capability information of each neighboring BS of the serving BS, requesting and receiving an UL channel quality measurement for the UE from all or a subset of neighboring BSs, and determining a neighboring BS as the target BS based on the obtained FD capability information and the received UL channel quality measurements.

In a first implementation form of the method according to the second aspect, the method comprises extracting the FD capability information from a neighbor relation table, NRT, available to at least the serving BS. In a second implementation form of the method according to the first implementation form of the second aspect, the NRT includes a field specifying the FD capability of each neighboring BS of the serving BS.

In a third implementation form of the method according to the first or second implementation form of the second aspect, the NRT includes a field specifying supported bandwidths of each neighboring BS of the serving BS.

In a fourth implementation form of the method according to the second aspect as such, the method comprises obtaining the FD capability information through a signaling exchange with each neighboring BS.

In a fifth implementation form of the method according to the fourth implementation form of the second aspect, the signaling exchange is performed through backhaul connections, for instance the X2 interface.

In a sixth implementation form of the method according to the second aspect as such or according to any previous implementation form of the second aspect, the method comprises providing each neighboring BS with an identity of the UE for triggering the UL channel quality measurement between the respective neighboring BS and the UE.

In a seventh implementation form of the method according to the second aspect as such or according to any previous implementation form of the second aspect, the method comprises receiving a downlink, DL, channel quality measurement from the UE for all or a subset of neighboring BSs of the serving BS, and determining the target BS taking further into account the DL channel quality measurements.

In an eighth implementation form of the method according to the second aspect as such or according to any previous implementation form of the second aspect, the method comprises obtaining FD capability information from the UE, and determining the target BS taking further into account the FD capability information of the UE.

In a ninth implementation form of the method according to the second aspect as such or according to any previous implementation form of the second aspect, the method is performed in the serving BS or the method is performed associated with the serving BS.

In a tenth implementation form of the method according to the second aspect as such or according to any previous implementation form of the second aspect, the method is performed distributed over the serving BS and its neighboring BSs, wherein the serving BS obtains the FD capability information, requests the UL channel quality measurement from all or a subset of neighboring BSs, and determines and notifies a potential target BS based on the obtained FD capability information, and the potential target BS determines, whether it becomes the target BS for the HO of the UE, based on its FD capability and its UL channel quality measurement for the UE.

With the method of the second aspect, all advantage of the network apparatus of the first aspect can be achieved. It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The above described aspects and implementation forms of the present invention will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which: Fig. 1 shows a network apparatus according to an embodiment of the present invention.

Fig. 2 shows a network apparatus according to an embodiment of the present invention, the network apparatus being configured to carry out a method according to an embodiment of the present invention.

Fig. 3 shows a general principle of the present invention.

Fig. 4 shows a NRT used in a network apparatus according to an embodiment of the present invention.

Fig. 5 shows a signaling exchange used by a network apparatus according to an embodiment of the present invention. Fig. 6 shows a procedure followed by a network apparatus according to an embodiment of the present invention.

Fig. 7 shows a schematic of a network apparatus according to an embodiment of the present invention.

Fig. 8 shows signaling used in a method according to an embodiment of the present invention. Fig. 9 shows a centralized implementation of a network apparatus according to an embodiment of the present invention.

Fig. 10 shows a distributed implementation of a network apparatus according to an embodiment of the present invention.

Fig. 11 shows an interaction between a RNC and O&M due to ANR according to the 3GPP standard TS 25.484. Fig. 12 shows ANR report forwarding according to the 3GGP standard TS 25.484.

Fig. 13 shows a conventional HO procedure.

Fig. 14 shows an example of a UE in a mobility situation.

Fig. 15 shows interference factors perceived in a FD BS.

Fig. 16 shows simulations of UE throughput as a function of number of users for

FD and HD BS configurations.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 shows a network apparatus 100 according to a general embodiment of the present invention. The network apparatus 100 is configured to decide about a HO of a UE 101 from a serving BS 102 to a target BS 103. The network apparatus 100 is particularly configured to determine one of the neighboring BSs 104 of the serving BS 102 as the target BS 103 for the UE 101 based on an enhanced HO procedure. The network apparatus 100 may be the serving BS 102 itself, or may be at least partly included in or associated with the serving BS 102.

For the enhanced HO procedure, as shown in Fig. 2, the network apparatus 100 is configured to obtain FD capability information of each neighboring BS 104 of the serving BS 102. Then, the network apparatus 100 is configured to request and receive an UL channel quality measurement for the UE 101 from all or a subset of (FD and/or HD capable) neighboring BSs 104. Finally, the network apparatus 100 is configured to determine a neighboring BS 104 as the target BS 103 based on the obtained FD capability information and the received UL channel quality measurements. These actions of the network apparatus 100, which are shown in Fig 2, correspond to a method 200 for an enhanced HO of the UE 101 from the serving BS 102 to the target BS 103 according to another general embodiment of the present invention. The method 200 comprises, in a first step, obtaining 201 the FD capability information of each neighboring BS 104 of the serving BS 102. In a second step, the method 200 comprises requesting and receiving 202 the UL channel quality measurement for the UE 101 from all or a subset of (FD and/or HD capable) neighboring BSs 104. In a third step, the method 200 comprises determining 203 a neighboring BS 104 as the target BS 103 based on the obtained FD capability information and the received UL channel quality measurements. As exemplarily illustrated in Fig. 2, the method 200 may be carried out by the network apparatus 100. However, the method 200 may also be carried out in a centralized manner by the serving BS 102 or by another HO-decision-entity of the network, or in a distributed manner by a collaboration of e.g. several BSs 102, 104.

Fig. 3 shows that the above general embodiments of the present invention include two main parts. A first part concerns BS related information, specifically the obtaining of the neighboring BSs 104 FD capabilities. A second part concerns UE related information, specifically the obtaining of the UL channel quality between the UE 101 and the neighboring BSs 104, specifically all or a subset of these neighboring BSs 104. Details of the first, BS related part are now explained in detail.

In a conventional HO procedure, a serving BS associated with a UE in a mobility situation has only a list of possible neighboring BSs, to which the UE can be handed over. Only neighboring cell identifiers are stored at the level of the network, and no further information is available.

Particularly, the Automatic Neighbor Relation (ANR) is defined in 3GPP TS 25.484 (3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Automatic Neighbor Relation (ANR) for UTRAN; Stage 2 (Release 10) 3GPP TS 25.484 VIO.0.0 (2011-06)). As shown in Fig. 11, the ANR function resides in the RNC of a base station, and is composed of the Neighbor Relation Table (NRT) Management Function, Neighbor Detection Function, and Neighbor Removal Function. The Neighbor Detection Function detects new neighbors, and adds them to the NRT. The Neighbor Removal Function removes outdated neighbors. Also, a Neighbor cell Relation (NR) between a base UTRAN Cell and a Neighbor Cell exists under a set of predefined conditions (details in section 4.1 in of TS 25.484). As shown in Fig. 12, an ANR measurement report provided by a UE to a receiving RNC of a potential target BS for HO is forwarded to a base RNC of the serving BS. However, no information related to FD duplex capabilities of the neighboring BSs is forwarded.

According to the embodiments of the present invention, the network apparatus 100 (which in the following is exemplarily in the serving base station 102), is made aware of the FD capabilities of the neighboring BSs 104. To this end, two possible implementations are proposed. For the first implementation, the standardized NRT is changed by adding additional information. For the second implementation, an additional message exchange and signaling is provided.

As shown in Fig. 4, for the first implementation, preferably a new field 401 is added to NRT 400, which NRT 400 is at least available to the serving BS 102. This new field 401 specifies the FD capabilities of the neighboring BSs 104, and optionally other useful information such as (but not limited to) the supported bandwidth size, on which FD can be performed. The network apparatus 100 can extract the FD capability information, and optionally the additional useful information, from the NRT 400.

As shown in Fig. 5, for the second implementation, in order to get the FD attributes of the neighboring BSs 104 (without changing the NRT 400), additional signaling 500 may be carried out, wherein the network apparatus 100 in the serving BS 102 is configured to ask the neighboring BSs 104 for their FD attributes, and to receive their replies through 'standardized' signaling. This signaling 500 is, for instance, exchanged through existing backhaul connections such as wired/optical/wireless through the X2 interface, for example, that is commonly used for HO request operation (however, any other backhaul or inter-BS interface may also be used). That is, the network apparatus 100 is configured to obtain the FD capability information through a signaling exchange with each neighboring BS 104.

Details of the second UE related part are now described.

With current radio access standards, it is not possible to estimate an UL channel quality between a given UE (notably in a HO situation) and a possible target (neighboring) BS, which is not currently serving this UE. With respect to Fig. 6, however, the following enhanced procedure may be applied according to an embodiment of the present invention.

Like in a conventional HO procedure, a UE 101 measures 601 a channel quality of its serving and neighboring cells, i.e. it collects, for example, DL RSRP measurements. If a predefined HO condition is verified 602, the UE 101 reports 603 the measurements (e.g. the RSRP of the BSs in a NRT table) to its serving BS 102. Here, exemplarily, the network apparatus 100 is again in the serving BS 102.

A new function is then activated at the network apparatus 100, the function being called FD aware HO trigger function 700 (see also Fig. 7). Its preferred role is to identify the FD capable neighboring BSs 104 of the serving BS 102, in order to trigger all or a subset of these BSs 104 to perform UL channel measurements. The FD capable neighboring BSs 104 may be identified based on the NRT table or through signaling. The FD aware HO trigger function may also trigger all or a subset of HD capable neighboring BSs 104 to perform the UL channel measurements. The network apparatus 100 is then configured to inform 604 each FD capable (and/or each HD capable) neighboring BS 104, i.e. each potential target BS 103, about the ID of the UE 101, which is to be handed over, and of other necessary information, in order to initiate the UL measurements. That is, the network apparatus 100 is configured to trigger UL channel quality measurements between the respective neighboring BSs 104 and the UE 101. All informed neighboring BSs 104 accordingly assess 605 the UL channel quality, e.g. UL RSRP measurements, for the considered UE 101.

The network apparatus 100 is then configured to initiate 606 the HO procedure, and to determine the newly selected target BS 103 including a link type supported by the UE 101 (FD capable or not). The target BS 103 may then assess 607, whether it can properly serve the considered UE 101, e.g. by assessing UL and DL quality and availability, and may report 608 back the type of link to be established (FD/HD; Totality of the band/only Up/Down bands; ...). Then, when the target BS 103 confirms 609, that it can serve the UE 101, resource pre- allocation and a standard HO procedure based on the selected options are carried out 610.

Fig. 7 shows a schematic of a network apparatus 100 with the FD aware HO trigger function 700. The network apparatus 100 may receive FD capabilities of the neighboring BSs 104 via a modified NRT 400. The FD aware HO trigger function 700 of the network apparatus 100 chooses, based on the modified NRT 400, a set of FD (and/or HD) capable neighboring BSs 104, from which it requests UL measurements. The network apparatus 100 receives these UL measurements from the neighboring BSs 104, and may also receive DL measurements from the UE 101, either directly (if the network apparatus 100 is in the serving BS 102) or via the serving BS 102. Fig. 8 shows signaling exchanged in this respect. Then, the network apparatus 100 selects the target BS 103 based on the received measurements, and requests HO to this target BS 103.

Two implementations of the network apparatus 100 are shown with respect to the Figs. 9 and 10, respectively. The implementation shown in Fig. 9 is based on a centralized approach, wherein the network apparatus 100 (here exemplarily provided in the serving BS 102) collects all the measurements including those in the UL performed by other potential target BSs (neighboring BSs 104), and decides upon the target BS 103 for HO based on the reported measurements (conventional DL measurements and the UL measurements reported by the neighboring BSs 104). Notably, the network apparatus 100 may also be the serving BS 102, but could also be a separate entity associated with the serving BS 102.

The implementation shown in Fig. 10 is based on a distributed approach, wherein the network apparatus 100 (exemplarily provided partly in the serving BS 102) selects a set of potential target BSs (neighboring BSs 104) for HO. Then one selected potential target BS is contacted, and this potential target BS decides, if it can accept, or not, the HO (taking into account UL measurements for the considered UE 101). That is, here the network apparatus 100 is provided partly in the serving BS 102 and partly in the neighboring BSs 104, i.e. is distributed over these BSs 102, 104.

In summary, whereas a conventional handover decision procedure considers as input only DL measurements reported by the UE, the embodiments of the present invention consider extra information about the FD capabilities of the neighboring BSs 104 and UL measurements of all or a subset of neighboring BSs 104 for the UE 101. The respective enhanced HO procedure follows a two-stage output. First, the network apparatus 100 requests or is informed of the extra information. Second, a suitable target BS 103 is selected considering the FD capabilities and the UL measurements.

The present invention has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed invention, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.