EQUIPMENT

TECHNICAL FIELD [001] Disclosed are embodiments related to handover optimization.

BACKGROUND

[002] Radio Access Technologies (RATs), such as, for example, GSM, WCDMA, and

LTE, have been used across the world to provide mobile communications. In many areas several RATs with multiple layers (i.e., carrier frequencies) are deployed. Different techniques are used to utilize parallel layers for a better user experience. This includes both session continuity and good enough bit rate for end user.

[003] To provide session continuity to a user equipment (UE) (i.e., a wireless communication device (WCD), such as, for example, a mobile terminal, a smartphone, a tablet, a smart sensor, a smart appliance, or any other device capable of wireless communication), a network node (e.g., a base station such as an eNodeB (eNB)) serving the UE may make use of signal level and signal quality measurements (e.g., RSRP and RSRQ measurements) from the UE with respect to the serving cell and neighbor cells to detect poor coverage and decide whether a mobility action is needed. A mobility action is normally a handover (HO) to a neighbor intra- RAT cell (intra-frequency or inter-frequency) or a neighbor inter-RAT cell.

[004] One of the recent techniques to improve bit rate and coverage, in LTE-advanced standards, is Advanced Antenna Systems (AAS). It is also valid for New Radio (NR) in 5G. It allows utilizing massive antenna techniques, such as UE-specific-beamforming.

[005] UE-specific-beamforming in LTE can be applied only for data channels (i.e.

PDSCH in DL), while the broadcast signals (PSS/SSS/CRS) and common control channels (PDCCH/PHICH/PBCH) should be accessible for all UEs and therefore cannot be beam formed for a specific UE. UE-specific-beamforming improves cell border SINR (for data channel) and consequently facilitating higher bit rate at the cell edge. SUMMARY

[006] In LTE, UE measurements of the source and neighbor signal level and quality

(RSRP and RSRQ) are based on the broadcasted reference signals (CRS) which are not subject to beamforming. In 5G, mobility mechanisms have not yet been decided in 3GPP. One proposal is to use Mobility Reference Signals (MRS) sent out on different beams in a cell, called Mobility Beams in this document. One can assume that the coverage ranges of UE specific beams and the Mobility Beams will not match completely.

[007] At the cell edge, a first UE configured with beamforming is expected to have a better SINR and a higher bit rate compared to a second UE at the cell edge that is not configured with beamforming. Both the first and second UEs, however, are likely to report poor coverage and may be relocated to another cell because the handover (HO) decision is based on CRS RSRP/RSRQ measurements and the CRS are not subject to beamforming (e.g., UE-specific beamforming).

[008] In some scenarios, the UE with beamforming (the first UE) would benefit by avoiding the handover and staying in the serving cell, whereas the other UE (the second UE) would benefit by being handed over to a neighbor cell.

[009] One scenario is when an inter-frequency handover could be avoided in favor of keeping the UE on the same frequency. The UE would benefit both from battery consumption (avoiding inter-frequency measurements) and potentially higher bit rate.

[0010] The disclosure describes embodiments for handover optimization - e.g., for preventing unnecessary inter-frequency handovers in favor of keeping certain UEs on the same frequency. As one example, the disclosure describes a serving cell (cell 1) that applies certain measurement parameters for UEs configured with beamforming. The goal of applying the certain measurement parameters for a certain set of the UEs being served is to avoid inter-frequency measurements and/or handovers. In some embodiments, the decision to use the certain measurement parameters as opposed to default measurement parameters, is based on information obtained from other network nodes (e.g., from a neighbor cell). In one specific embodiment, the X2AP Handover Report is used by a neighbor cell to inform the serving cell that unnecessary HOs to another frequency have been detected. That is the Handover Report is modified to include a new parameter: "Unnecessary HO to another frequency." As a result of receiving such a message from a neighbor cell (or another network node), the serving node may apply certain specific measurement parameters for poor coverage handling of UEs supporting transmission modes needed for beamforming.

[0011] Accordingly, in one aspect there is provided a method for HO optimization. In some embodiments, the method includes a first network node determining whether a condition is satisfied, wherein the first network node is serving a first UE located in a first cell operating on a first frequency. Determining whether the condition is satisfied comprises: i) the first network node determining whether the first UE possesses a certain transmission mode, TM, capability; and ii) the first network node determining whether an unnecessary inter-frequency HO to a second cell has been detected. As a result of determining that the condition is satisfied, the first network node reducing a likelihood that the first UE will trigger an inter-frequency HO of the first UE from the first cell to the second cell, which is operating on a different frequency than the first frequency on which the first cell is operating.

[0012] In some embodiments, the method further comprises: the first network node receiving a registration message from the first UE; and the first network node performing a registration procedure in response to receiving the registration message, wherein the steps of node reducing the likelihood that the first UE will trigger the inter-frequency HO is performed as part of the registration procedure.

[0013] In some embodiments, the method further comprises: the first network node transmitting to a second network node managing the second cell a HO request for the first UE; and the first network node receiving a HO reject transmitted by the first network node in response to the HO request, wherein the HO reject comprises information indicating that an unnecessary inter-frequency HO to a second cell has been detected. The step of reducing the likelihood that the first UE will trigger the inter-frequency HO is performed as a result of receiving the HO reject in some embodiments.

[0014] In some embodiments, reducing the likelihood that the first UE will trigger the inter- frequency HO comprises: i) selecting a measurement report triggering parameter, wherein the measurement report triggering parameter is a threshold and/or offset value; and ii) transmitting to the first UE a configuration message comprising the selected measurement report triggering parameter. The first UE is configured is some embodiments such that the first UE transmits a measurement report to the first network node as a result of determining that a determined value based on a measurement result of the first cell and a hysteresis value is less than the selected threshold value.

[0015] In some embodiments, reducing the likelihood that the first UE will trigger the inter- frequency HO comprises: i) selecting a first measurement report triggering parameter, wherein the first measurement report triggering parameter is a first cell specific offset value; and ii) transmitting to the first UE a configuration message comprising the selected first

measurement report triggering parameter. The configuration message in some embodiments configures the first UE such that the first UE uses the first cell specific offset value in calculating a first value and transmits a measurement report to the first network node as a result of determining that the first value is greater than a second calculated value. In some embodiments, reducing the likelihood that the first UE will trigger the inter-frequency HO further comprises selecting a second measurement report triggering parameter, wherein the second measurement report triggering parameter is a second cell specific offset value. The configuration message further comprises the selected measurement report triggering parameter, and further configures the first UE such that the first UE uses the second cell specific offset value in calculating a third value and transmits a measurement report to the first network node as a result of determining that the third value is greater than a fourth calculated value. In some embodiments, the first cell specific offset value is associated with the second cell, the second cell specific offset value is associated with a third cell that operates on the same frequency as the first cell, and the second cell specific offset value is greater than the first cell specific offset value.

[0016] In some embodiments, the method further comprises: the first network node transmitting to the first UE a first configuration message comprising a default measurement report triggering parameter, wherein the default measurement report triggering parameter is a default threshold value and the first UE is configured such that the first UE transmits a measurement report to the first network node as a result of determining that a determined value is less than the default threshold value; and the first network node receiving the measurement report transmitted by the first UE. In some embodiments, the step of reducing the likelihood that the first UE will trigger the inter-frequency HO is performed as a result of receiving the measurement report. In some embodiments, reducing the likelihood that the first UE will trigger the inter-frequency HO comprises: selecting a measurement report triggering parameter, wherein the selected measurement report triggering parameter is a selected threshold value that is less than the default threshold value; and transmitting to the first UE a configuration message comprising the selected measurement report triggering parameter. The configuration message in some embodiments configures the first UE such that the first UE transmits a measurement report to the first network node as a result of determining that a determined value based on a measurement result of the first cell and a hysteresis value is less than the selected threshold value.

[0017] In some embodiments, reducing the likelihood that the first UE will trigger the inter-frequency HO comprises: selecting a first cell specific offset value; selecting a second cell specific offset value; and transmitting to the first UE a configuration message comprising the selected first and second cell specific offset values. In some embodiments, the configuration message configures the first UE such that the first UE uses the first cell specific offset value in calculating a first value and transmits a measurement report to the first network node as a result of determining that the first value is greater than a second calculated value, and further configures the first UE such that the first UE uses the second cell specific offset value in calculating a third value and transmits a measurement report to the first network node as a result of determining that the third value is greater than a fourth calculated value. In some

embodiments, the first cell specific offset value is associated with the second cell, the second cell specific offset value is associated with a third cell that operates on the same frequency as the first cell, and the second cell specific offset value is greater than the first cell specific offset value.

[0018] In some embodiments, determining whether an unnecessary inter-frequency HO to a second cell has been detected comprises: the first network node receiving a message from another network node; and the first network node determining whether the message includes information indicating that an unnecessary inter-frequency HO to a second cell has been detected. In some embodiments, the message is a HO report transmitted by a neighbor network node managing a cell operating on the same frequency as the first cell. [0019] In another aspect there is provided a method for handover optimization in a network comprising a first network node serving a first cell, a second network node serving a second cell, and a third network node serving a third cell. In some embodiments, the method includes: the third network node receiving message, wherein the message includes UE history information for a UE. In some embodiments, the message is a HO request indicating that the second network node has determined that the UE should be handed over from the second cell served by the second network node to the third cell served by the third network node. In some embodiments, the method further comprises the third network node transmitting to the UE a UE information request, and the message is a UE information response transmitted by the UE in response to the UE information request. The method also includes the third network node determining, based on the UE history information included in the message, whether the UE has experienced an unnecessary inter-frequency HO from the first cell to the second cell. The method further includes, and as a result of determining that the UE has experienced an unnecessary inter-frequency HO from the first cell to the second cell, the third network node transmits to the first network node a report comprising information indicating that an

unnecessary inter-frequency HO from the first cell to another cell has been detected.

[0020] In another aspect there is provided a method for handover optimization. In some embodiments, the method includes a second network node receiving a HO request indicating that a first network node has determined that a UE should be handed over from a first cell served by the first network node to a second cell served by the second network node. The method further includes the second network node determining whether the requested HO is an unnecessary HO request. In some embodiments, determining whether the requested HO is an unnecessary HO request, comprises the second network node using HO statistical information together with location information identifying the location of the UE to determine whether the requested HO is an unnecessary HO request. The method also includes, as a result of determining that the requested HO is an unnecessary HO from the first cell to the second cell, the second network node transmitting to the first network node an HO reject comprising information indicating that an unnecessary HO from the first cell to another cell has been detected. In some embodiments, the HO reject comprises a cell identifier identifying a probable handover target. [0021] In another aspect there is provided a method for handover optimization in a network comprising a first network node serving a first cell, a second network node serving a second cell, a third network node serving a third cell, and a management node. In some embodiments, the method includes the management node receiving from various network nodes HO statistical information. The method also includes the management node using the received HO statistical information to detect presence of unnecessary inter-frequency HOs. The method further includes, in response to detecting an unnecessary inter-frequency HO from the first cell to the second cell, the management node transmitting to the first network node a HO optimization message indicating that an unnecessary inter-frequency HO from the first cell to another cell has been detected.

[0022] Advantages

[0023] Advantages of the disclosed embodiments include reduced RRC signaling because it is possible to reduce inter-frequency measurement configurations, measurement report and inter-frequency handovers. Another advantage is better UE and network performance. UE and network performance is increased because: a UE in poor coverage is subject to less RRC signaling and therefore lower radio link failure risk, higher bit rates are possible for UEs in poor coverage that are configured with beamforming, the possibility to keep UE in higher frequency layer with potentially higher capacity, and better utilization of network resources.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.

[0025] FIG 1 an example scenario with two frequency layers.

[0026] FIG 2 is a message flow diagram illustrating a process according to some embodiments.

[0027] FIG 3 is a message flow diagram illustrating a process according to some embodiments.

[0028] FIG 4 illustrates a management node providing a HO optimization messag network node. [0029] FIG. 5 is a message flow diagram illustrating a process according to some embodiments.

[0030] FIG. 6 is a message flow diagram illustrating a process according to some embodiments.

[0031] FIG. 7 is a flow chart illustrating a process according to some embodiments.

[0032] FIG. 8 is a flow chart illustrating a process according to some embodiments.

[0033] FIG. 9 is a flow chart illustrating a process according to some embodiments.

[0034] FIG. 10 is a flow chart illustrating a process according to some embodiments.

[0035] FIG. 11 is a flow chart illustrating a process according to some embodiments.

[0036] FIG. 12 is a block diagram of a computer apparatus according to some embodiments.

[0037] FIG. 13 is a diagram showing functional modules of a first network node according to some embodiments.

[0038] FIG. 14 is a diagram showing functional modules of a second network node according to some embodiments.

[0039] FIG. 15 is a diagram showing functional modules of a third network node according to some embodiments.

[0040] FIG. 16 is a diagram showing functional modules of a management node according to some embodiments.

[0041] FIG. 17 is a message flow diagram illustrating a process according to some embodiments.

DETAILED DESCRIPTION

[0042] In many multi-layer network deployments, higher frequency layers have higher capacity (larger bandwidth and/or less interference), resulting in better data rate offered to UEs. In such scenarios, it is advantageous to keep a UE on a higher frequency layer for as long as possible. On the other hand, higher frequencies cause higher path loss and therefore less coverage compared to lower frequencies. This may result in several inter-frequency HOs during the connection due to poor coverage detection on a higher frequency layer. [0043] FIG. 1 depicts such an example scenario with two frequency layers: Fl and F2. A first network node 101 (e.g., a base station) serves UEs located in cell-1 (e.g., UE 104) using frequency Fl, a second network node 102 serves UEs located in cell-2 using frequency F2, and a third network node 103 serves UEs located in cell-3 using frequency Fl. Preferably, nodes 101 and 103 are network nodes (e.g., eNB, gNB) in which UE specific beamforming can be supported. Node 102 can be any node conforming to any RAT.

[0044] As further shown in FIG. 1, network node 101 applies UE-specific beamforming for UE 104, which is close to the edge of cell-1. That is, for example, network node uses beam 106 to transmit downlink (DL) user plane data to UE 104. UE 104 detects poor coverage when passing the dashed line (representing RSRP or RSRQ threshold). When this occurs, UE 104 sends a measurement report to network node 101 serving cell-1, which may cause network node 101 instruct UE 104 to perform an inter- frequency measurement by transmitting a measurement configuration message to UE 104. This in turn may cause UE 104 to transmit to network node 101 a measurement report indicating information about cell-2, which may trigger an inter- frequency HO to cell-2, which is operating on frequency F2. While being served by network node 102 that services cell-2, UE 104 may detect good coverage on frequency Fl (cell-3), and the UE may trigger another inter-frequency HO (from F2 back to Fl, i.e., from cell-2 to cell-3). As described above, it is disadvantageous to have the UE perform these back-to-back handovers between cells operating at different frequencies. Accordingly, the embodiments herein address this issue.

[0045] In some embodiments, before network node 101 takes any actions to prevent or reduce the likelihood of these unnecessary HOs to another frequency, a "learning" phase is performed to determine whether such unnecessary HOs to another frequency is occurring.

[0046] FIG. 2 is a message flow diagram illustrating an example of the learning phase.

In step s200, UE 104 has detected poor coverage and sends a measurement report to network node 101. In one example, this measurement report sent in step s200 is based on an Event A2 configuration "Serving becomes worse than absolute threshold" (as described in 3GPP TS 36.311 v 14.1.0) which has been sent to UE during connection setup. Upon reception of the poor coverage report from UE, network node 101 transmits to UE 104 a measurement configuration message (e.g., an RRCConnectionReconfiguration or RRCConnectionResume) comprising measurement parameters (step s201). For example, the measurement parameters may include measurement report ("event") triggering parameters, such as a mobility threshold. In one example, the mobility threshold is an Event A4 threshold (A4: Neighbor becomes better than absolute threshold) as described in 3GPP TS 36.311 v 14.1.0 which may also include a cell specific offset of the neighbor cell. In other examples, other events such as A3, A5, B l, B2,etc. may be used to define mobility thresholds as described in 3GPP TS 36.311 v 14.1.0. these events may also include a cell specific offset of the neighbor cell.

[0047] In step s202, UE 104 transmits to node 101 a measurement report (e.g., an Event

A3 or A4 or A5 report) indicating that neighbor cell cell-2 is a better cell (e.g., the report may indicate that cell-2 is offset better than the primary cell (i.e., cell-1 in this case)). As shown in FIG. 2, this measurement report triggers a HO from cell-1 to cell-2. For example, node 101 transmits to node 102 a HO request (step s203), including UE History Information IE containing Last Visited Cell Information as described in 3 GPP TS 36.423 v 14.0.0. In this case, node 102 accepts the HO request and transmits to node 101 a HO acknowledgement (ACK) (step s204). This then triggers node 101 to send to UE 104 a HO command (step s205a), which causes UE 104 to be handed over to cell-2 (i.e., UE 104 will now be served by node 102). In step s205b, node 102 transmits to UE 104 a measurement configuration message (e.g., an

RRCConnectionReconfiguration or RRCConnectionResume) comprising measurement parameters that cause UE 104 to make inter-frequency measurements. That is, the configuration message transmitted in step s205b is similar to the configuration message transmitted in step s201. In some embodiments, node 102 was triggered to send the configuration message transmitted in step s205b as a result of node 102 determining that i) UE 104 has beamforming capability and ii) UE 104 entered cell-2 via an inter-frequency HO. That is, node 102 may be configured such that whenever a UE enters cell-2, node 102 determines whether the UE has beamforming capability and determines whether the UE entered the cell via an inter-frequency HO. If both are true, then node 102 sends to the UE the configuration message for causing the UE to perform inter-frequency measurements.

[0048] A short while later, UE 104 transmits to node 102 measurement report (e.g., an

A3 report) indicating that neighbor cell cell-3 is better than the primary cell (i.e., cell-2 now) (step s206). As shown in FIG. 2, this second measurement report triggers a HO from cell-2 to cell-3. For example, node 102 transmits to node 103 a HO request (step s207), which includes UE history information (e.g., information indicating the amount of time the UE stayed in cell-2 and the previous cell that served the UE, which in this case is cell-1). In this case, node 103 accepts the HO request and transmits to node 102 a HO acknowledgement (ACK) (step s208). This then triggers node 102 to send to UE 104 a HO command (step s209).

[0049] Additionally, in step s210, node 103 determines whether or not a HO Report should be sent to node 101. For example, in step s210, node 103 detects whether an unnecessary HO to another frequency has occurred. In one embodiment, node 103 makes this determination based on UE history information included in the HO request transmitted by node 102 as well as capability information indicating transmission mode capabilities of UE 104. For example, if the UE history information included in the HO request transmitted by node 102 indicates that the UE stayed in cell-2 for not more than a threshold amount of time and the UE capability information indicates that UE 104 has certain beamforming capabilities, then node 103 determines that an unnecessary HO to another frequency has occurred. This threshold amount of time is configurable. In some embodiments, the threshold is not greater than a few minutes. In other embodiments, the threshold is not greater than 20 or 30 seconds).

[0050] As a result of detecting that an unnecessary HO to another frequency has occurred, node 103 transmits to node 101 a HO Report comprising information indicating that an unnecessary HO to cell-2 has occurred (step s211). This information may include an

"unnecessary inter-frequency HO" indicator and cell-2' s cell identifier. In this way, node 101 is able to determine that an unnecessary inter-frequency HO to a cell-2 has been detected.

[0051] FIG. 17 is a message flow diagram illustrating another example of the learning phase. As shown in FIG. 17, steps s200-s205, which are described above, are performed. After node 101 sends the HO command to UE 104 to cause UE 104 to be handed over to cell-2 (step s205), UE 104 enters an idle mode. Next, UE 104 performs a cell selection and decides to camp on cell-3 (step s253). Next (step s255), an RRC connection is established between UE 104 and node 103. Next (step s257), node 103 transmits to UE 104 a UE information request message. In response, UE 104 transmits to node 103 a UE information response message (step s259). The UE information response message transmitted in step s259 includes the UE history information. In step s261, node 103 determines whether or not a report should be sent to node 101. For example, in step s261, node 103 detects whether an unnecessary HO to another frequency has occurred. In one embodiment, node 103 makes this determination based on the UE history information included in the UE information response transmitted by the UE in step s259 as well as capability information indicating transmission mode capabilities of UE 104. For example, if the UE history information indicates that the UE stayed in cell-2 for not more than a threshold amount of time and the UE capability information indicates that UE 104 has certain

beamforming capabilities, then node 103 determines that an unnecessary HO to another frequency has occurred. As a result of detecting that an unnecessary HO to another frequency has occurred, node 103 transmits to node 101 a report comprising information indicating that an unnecessary HO to cell-2 has occurred (step s263). This information may include an

"unnecessary inter-frequency HO" indicator and cell-2' s cell identifier. In this way, node 101 is able to determine that an unnecessary inter-frequency HO to a cell-2 has been detected.

[0052] FIG. 3 is a message flow diagram illustrating yet another example of the learning phase. In step s300, node 102 obtains HO statistics regarding unnecessary inter-frequency HOs to a cell-2 from cell-1. In step s301, network node 101 transmits to UE 104 a measurement configuration message comprising measurement parameters (this measurement configuration message may be the same one shown in FIG. 2).

[0053] In step s303, UE 104 transmits to node 101 a measurement report (e.g., an Event

A3 report) indicating that neighbor cell cell-2 is better than the primary cell (i.e., cell-1 in this case). As shown in FIG. 3, this measurement report triggers a HO from cell-1 to cell-2. For example, node 101 transmits to node 102 a HO request (step s305).

[0054] In response to receiving the HO request, node 102 determines whether or not to accept the HO request based on information included in the request (e.g., UE capability information, information indicating the location of UE 104 when node 101 made the decision to send the HO request, etc.) and the obtained HO statistics (step s307). For example, the obtained HO statistics may indicate that a certain percentage of UEs that were located within a certain area of cell-1 when node 101 made the decision to HO the UEs to cell-2 spend not more than the threshold amount of time in cell-2 (e.g., such UEs are immediately handed over from cell-2 to cell-3). In such a scenario, if, based on the UE information included in the HO request, node 102 determines that i) UE 104 is located within the certain area of cell-1 and ii) node 103 and UE 104 both have beamforming capability, then node 102 rejects the HO request in some embodiments (i.e., node 102 transmits to node 101 a HO reject (step s309)). In such embodiments, the HO reject sent in step s309 may include a cause code indicating that the HO request is rejected due to unnecessary inter-frequency HO or unnecessary inter radio access technology (inter-RAT) HO if cell-2 is of a different RAT than cell-1. The HO reject may further include cell-3's identity to inform node 101 of the cell to which UE 104 will likely be handed over.

[0055] In response to receiving the HO reject, node 101 selects one or more measurement report triggering parameters. For example, node 101 may select one or more Event A3 cell specific offsets (e.g., a cell specific offset for the cell identified in the HO reject message and/or a cell specific offset for cell-2). Additionally (or alternatively), node 101 selects a new Event A2 threshold (e.g., an Event A2 threshold that is less than the Event A2 threshold included in the configuration message sent in step s301). In step s311, node 101 transmits to UE 104 a further measurement configuration message that includes the selected measurement report triggering parameters. The selected measurement report triggering parameters are selected such that there is an increase in probability that UE 104 will transmit to node 101 a measurement report indicating that cell-3 is offset better than cell-1.

[0056] In step s313, using the new measurement report triggering parameters sent from node 101, UE 104 transmits to node 101 a measurement report indicating that neighbor cell cell-3 is offset better than cell cell-1. This report then triggers a HO to cell-3 as shown in steps s315, s317, and s319.

[0057] FIG. 4 illustrates another embodiment for the learning phase. In this embodiment, a management node 402 (e.g., an Operations Support System (OSS)) receives from various network nodes (e.g., node 102 and node 103) HO statistical information and uses the received information to detect presence of unnecessary inter-frequency HOs from cell-1 to cell-2. In response to detecting such unnecessary inter-frequency HOs from cell-1 to cell-2, node 402 transmits to node 101 a HO optimization message indicating that unnecessary inter-frequency HOs from cell-1 to cell-2 have been detected.

[0058] FIG. 5 is a message flow diagram illustrating a process performed by node 101 according to an embodiment. The process may begin with step s500, in which network nodes detects that an unnecessary inter- frequency HO from cell-1 to cell-2 has occurred. This step may consist of node 101 receiving a message indicating that that an unnecessary inter-frequency HO from cell-1 to cell-2 has occurred (e.g., the HO report transmitted by node 103 in step s211 of FIG. 2, the HO optimization message shown in FIG. 4, or other message).

[0059] At a later point in time, node 101 receives a registration message transmitted by

UE 104 (or another UE) (step s501). The registration message may be an LTE Attach Request, an LTE Tracking Area Update (TAU), a 5G Registration Request, or any other message for registering UE 104 with a network.

[0060] In step s503, in response to receiving the registration message, node 101 performs a registration procedure (e.g., Attach procedure, TAU procedure, or other registration

procedure). As illustrated in FIG. 5, a part of the registration procedure involves node 101 selecting measurement parameters, such as measurement report triggering parameters (MRTPs) (e.g., threshold values, offset values, and/or other MRTPs). In one embodiment, node 101 selects the measurement parameters by performing a process comprising: 1) determining whether a condition is satisfied, wherein determining whether the condition is satisfied comprises: a) determining whether the UE 104 possesses a certain transmission mode (TM) capability (e.g., determining whether UE 104 is configured for beamforming, such as UE-specific beamforming) and b) determining whether an unnecessary inter-frequency HO to cell-2 has been detected; and 2) performing one of: i) selecting a first set of one or more measurement parameters for UE 104 as a result of determining that the condition is satisfied and ii) selecting a different, second set of one or more measurement parameters for UE 104 as a result of determining that the condition is not satisfied.

[0061] For example, in one embodiment, the first set of measurement report triggering parameters includes a first Event A2 threshold value, the second set of measurement parameters includes a second Event A2 threshold value, and the first Event A2 threshold is less than the second Event A2 threshold. Accordingly, a first UE that receives the first set of measurement parameters is less likely than a second UE that receives the second set of selected measurement parameters to send an A2 measurement report indicating that the serving cell (i.e., cell-1 in this case) becomes worse than the Event A2 threshold, which in turn makes it less likely that the first UE will perform an inter- frequency measurement compared to the second UE. [0062] Additionally (or alternatively), the first and second sets of measurement report triggering parameters includes: a first cell specific offset value associated with cell-2 and/or a second cell specific offset value is associated cell-3, which operates on the same frequency as cell-1. Preferably, the offsets in each set are chosen such that, when the condition is determined to be satisfied, there will be a higher probability that UE 104 will be handed over to cell-3 instead of cell-2, thereby avoiding an inter-frequency HO. For instance, the cell specific offset value associated with cell-3 that is included in the first set of selected measurement parameters is greater than the cell specific offset value associated with cell-3 that is included in the second set of selected measurement parameters.

[0063] In step s505, node 101 generates a configuration message (e.g., an

RRCConnectionReconfiguration) and transmits to UE 104 the configuration message, wherein the configuration message includes the measurement report triggering parameters selected in step s503.

[0064] After node 101 transmits the configuration message, UE 104 may send to node

101 an Event A3 measurement report indicating that neighbor cell cell-3 is offset better than the primary cell (i.e., cell-1 in this case) (step s507). As shown in FIG. 5, this measurement report triggers a HO from cell-1 to cell-3 (i.e., node 101 sends a HO request for the UE to node 103 (step s509)). Hence, an inter-frequency HO is avoided.

[0065] FIG. 6 is a message flow diagram illustrating a process performed by node 101 according to another embodiment. The process may begin with step s500 described above.

[0066] At a later point in time, node 101 receives a registration message transmitted by

UE 104 (or another UE) (step s501), as described above.

[0067] In step s603, in response to receiving the registration message, node 101 performs a registration procedure. As discussed above, during the registration procedure node 101 selects measurement parameters. In this embodiment, node 101 does not select the measurement parameters based on whether or not the certain condition described above is satisfied. For example, in this embodiment, node 101 simply selects default measurement parameters regardless of whether or not an unnecessary inter-frequency HO to cell-2 has been detected. [0068] In step s605, node 101 transmits to UE 104 a configuration message comprising the measurement parameters selected in step s603.

[0069] At a later time, UE 104 may transmit to node 101 a report (e.g., the Event A2 measurement report) indicating that the serving cell (i.e., cell-1 in this case) becomes worse than the a threshold (e.g., the Event A2 threshold) (step s607). For example, In step s607, UE 104 calculates Ms + Hys, determines whether Ms + Hys is less than Thres, and transmits the report as a result of determining that Ms + Hys < Thres, where Ms is a measurement result of the serving cell, not taking into account any offsets, Hys is a hysteresis parameter, and Thres is a threshold.

[0070] In this embodiment, in response to receiving the measurement report, node 101 may select a new set of measurement parameters (step s609), as opposed to ordering UE 104 to perform an inter-frequency measurement. For example, in step s609, node 101 may perform the measurement parameter selection procedure described above with respect to step s503. If a new set of measurement parameters is selected, then in step s611 node 101 transmits to UE 104 a configuration message comprising the new set of measurement parameters. If, however, a new set of measurement parameters is not selected because the condition is not satisfied, then node 101 may instruct UE 104 to perform the inter-frequency measurement.

[0071] After node 101 transmits the configuration message in step s611, UE 104 may send to node 101 an Event A3 measurement report indicating that neighbor cell cell-3 is offset better than the primary cell (i.e., cell-1 in this case) (step s613). As shown in FIG. 6, this measurement report triggers a HO from cell-1 to cell-3 (i.e., node 101 sends a HO request for the UE to node 103 (step s615)). Hence, an inter-frequency HO is avoided.

[0072] FIG. 7 is a flow chart illustrating a process 700 according to some embodiments.

Process 700 may begin with step s702, in which node 101, which is serving UE 104 located in cell-1 which is operating on a first frequency, determines whether a condition is satisfied.

Determining whether the condition is satisfied comprises: i) node 101 determining whether UE 104 possesses a certain transmission mode (TM) capability (step s702a); and ii) node 101 determining whether an unnecessary inter- frequency HO to a second cell has been detected (step s702b). For example, in step s702a, node 101 determines whether node 101 can transmit data to UE 104 using beamforming (e.g., using dynamic UE- specific-beams or a set of fixed beam (known as grid of beams)). As a result of determining that the condition is satisfied, node 101 reduces the likelihood that UE 104 will trigger an inter- frequency HO of UE 104 from cell-1 to cell-2, which is operating on a different frequency than the first frequency on which cell-1 is operating.

[0073] In some embodiments, the process 700 further comprises: node 101 receiving a registration message from UE 104; and node 101 performing a registration procedure in response to receiving the registration message, wherein the step of node reducing the likelihood that UE 104 will trigger the inter-frequency HO is performed as part of the registration procedure.

[0074] In some embodiments, the process 700 further comprises: node 101 transmitting to a second network node managing the second cell a HO request for UE 104; and node 101 receiving a HO reject transmitted by the second network node in response to the HO request, wherein the HO reject comprises information indicating that an unnecessary HO to a second cell has been detected, wherein the step of reducing the likelihood that UE 104 will trigger the inter- frequency HO is performed as a result of receiving the HO reject.

[0075] In some embodiments, reducing the likelihood that UE 104 will trigger the inter- frequency HO comprises: i) selecting a measurement report triggering parameter, wherein the measurement report triggering parameter is a threshold and/or offset value; and ii) transmitting to UE 104 a configuration message comprising the selected measurement report triggering parameter. In some embodiments, UE 104 is configured such that UE 104 transmits a measurement report to node 101 as a result of determining that a determined value based on a measurement result of cell-1 and a hysteresis value is less than the selected threshold value.

[0076] In some embodiments, reducing the likelihood that UE 104 will trigger the inter- frequency HO comprises: i) selecting a first measurement report triggering parameter, wherein the first measurement report triggering parameter is a first cell specific offset value; and ii) transmitting to UE 104 a configuration message comprising the selected first measurement report triggering parameter. In some embodiments the configuration message configures UE 104 such that UE 104 uses the first cell specific offset value in calculating a first value and transmits a measurement report to node 101 as a result of determining that the first value is greater than a second calculated value. In such embodiments, reducing the likelihood that UE 104 will trigger the inter-frequency HO may further comprise selecting a second measurement report triggering parameter, wherein the second measurement report triggering parameter is a second cell specific offset value, the configuration message further comprises the selected measurement report triggering parameter, the configuration message further configures UE 104 such that UE 104 uses the second cell specific offset value in calculating a third value and transmits a

measurement report to node 101 as a result of determining that the third value is greater than a fourth calculated value, the first cell specific offset value is associated with cell-2, the second cell specific offset value is associated with cell-3 that operates on the same frequency as cell-1, and the second cell specific offset value is greater than the first cell specific offset value.

[0077] In some embodiments, process 700 further comprises: node 101 transmitting to

UE 104 a first configuration message comprising a default measurement report triggering parameter, wherein the default measurement report triggering parameter is a default threshold value and UE 104 is configured such that UE 104 transmits a measurement report to node 101 as a result of determining that a determined value is less than the default threshold value; and node 101 receiving the measurement report transmitted by UE 104, wherein the step of reducing the likelihood that UE 104 will trigger the inter- frequency HO is performed as a result of receiving the measurement report. In such an embodiment, reducing the likelihood that UE 104 will trigger the inter-frequency HO may comprise: selecting a measurement report triggering parameter, wherein the selected measurement report triggering parameter is a selected threshold value that is less than the default threshold value; and transmitting to UE 104 a configuration message comprising the selected measurement report triggering parameter, wherein the configuration message configures UE 104 such that UE 104 transmits a measurement report to node 101 as a result of determining that a determined value based on a measurement result of cell-1 and a hysteresis value is less than the selected threshold value. Additionally, in such an embodiment, reducing the likelihood that UE 104 will trigger the inter-frequency HO may comprise: selecting a first cell specific offset value; selecting a second cell specific offset value; and transmitting to UE 104 a configuration message comprising the selected first and second cell specific offset values. This configuration message configures UE 104 such that UE 104 uses the first cell specific offset value in calculating a first value and transmits a measurement report to node 101 as a result of determining that the first value is greater than a second calculated value. This configuration message further configures UE 104 such that UE 104 uses the second cell specific offset value in calculating a third value and transmits a measurement report to node 101 as a result of determining that the third value is greater than a fourth calculated value. In some embodiments, the first cell specific offset value is associated with cell-2, the second cell specific offset value is associated with cell-3,which that operates on the same frequency as the first cell, and the second cell specific offset value is greater than the first cell specific offset value.

[0078] In some embodiments, determining whether an unnecessary inter-frequency HO to a second cell has been detected comprises: node 101 receiving a message from another network node; and node 101 determining whether the message includes information indicating that an unnecessary inter-frequency HO to a second cell has been detected. In some

embodiments, the message is a HO report transmitted by a neighbor network node (e.g., cell-3) managing a cell operating on the same frequency as cell-1.

[0079] FIG. 8 is a flow chart illustrating a process 800 according to some embodiments.

Process 800 may begin in step s802, in which node 101 receives a message transmitted by UE 104 (e.g., the registration message sent in step s501, the report sent in step s607, or other message). In response to receiving the message, node 101 determines whether a condition is satisfied. In this example, node 101 first determines whether UE 104 is configured for beamforming. If UE 104 is not so configured, process 800 proceeds to step s810, otherwise the process proceeds to step s806. In step s806, node 101 determines whether an unnecessary inter- frequency HO has been detected. For example, node 101 determines whether it has received a message (e.g., a message from node 102) indicating that the node has detected an unnecessary inter-frequency HO. If no unnecessary inter-frequency HOs have been detected, then the process proceeds to step s808 otherwise it proceeds to step s810. In step s808, node 101 selects the above described first set of measurement parameters (i.e., it selects parameters that reduce the likelihood of an inter-frequency HO, thus increasing the chance of an intra- frequency HO); and in step s810 node 101 selects the above described second set of measurement parameters.

[0080] FIG. 9 is a flowchart illustrating a process 900 according to some embodiments.

Process 900 may begin with step s902, in which node 103 receives a message. The message may be a HO request indicating that node 102 has determined that UE 104 should be handed over from cell-2 to cell-3 (see e.g., the HO request transmitted in step s207) or it may be a UE information response (see e.g., the UE information response transmitted in step s259). As discussed above with respect to steps s207 and s259, the HO request and UE information response each includes UE history information. In step s904, based on the UE history

information included in the message, node 103 determines whether UE 104 has experienced an unnecessary inter- frequency HO from cell-1 to cell-2 (this is also described above with respect to steps s210 and s261). As a result of determining that UE 104 has experienced an unnecessary inter-frequency HO from cell-1 to cell-2, node 103 in step s906 transmits to node 101 a report (e.g., an HO report) comprising information indicating that an unnecessary inter-frequency HO from cell-1 to cell-2 has been detected. In some embodiments, process 900 further comprises the node 103 transmitting to UE 104 a UE information request, and the message is a UE information response transmitted by UE 104 in response to the UE information request.

[0081] FIG. 10 is a flowchart illustrating a process 1000 according to some

embodiments. Process 1000 may begin with step sl002, in which node 102 receives a HO request indicating that node 101 has determined that UE 104 should be handed over from cell-1 to cell-2 (see e.g., the HO request transmitted in step s305).

[0082] In step sl004, node 102 determines whether the requested HO is an unnecessary

HO request (e.g., an unnecessary inter- frequency HO or an unnecessary inter-RAT HO). For example, as explained above with respect to steps s307 and s309, in performing step sl004, node 102 may use HO statistical information together with location information identifying the location of UE 104 to determine whether the requested HO is an unnecessary HO request.

[0083] In step sl006, as a result of determining that the requested HO is an unnecessary

HO from cell-1 to cell-2, node 102 transmits to node 101 an HO reject comprising information indicating that an unnecessary HO from cell-1 to cell-2 has been detected (e.g., the information included in the HO reject may indicate that an unnecessary inter- frequency HO has occurred). In some embodiments, extra information could be added to the HO reject message to cell-1 to assist the adjustment of mobility thresholds in cell-1 for the specific UEs. Such information could include probable handover target (i.e., cell-2 in this example) with or without correlation with UE position information. UE position could be acquired either through positioning nodes, or via implicit information available in the eNB (any combination of RSRP/RSRQ, CQI, PMI, TA, etc.). [0084] In another embodiment, node 102 could provide more detailed information to node 101 regarding the coverage overlap between the neighboring cells on the two frequencies (Fl and F2). Node 102 may select some candidate UEs coming from cell-1 to perform

continuous inter-frequency measurement on F2 and report good enough targets continuously. This information could be gathered to make sure that there is good enough continuous coverage on F2 and it is possible to keep the UE in F2 and avoiding the inter-frequency handover. Node 102 could notify node 101 about the best intra- frequency neighbor for handover for different positions. Positions could be identified with some index identifying an area, related to any combination of RSRP/RSRQ range, CQI, TA, PMI, or any other information available.

[0085] FIG. 11 is a flowchart illustrating a process 1100 according to some

embodiments. Process 1100 may begin with step si 102, in which node 402 receives from various network nodes (e.g., node 102 and node 103) HO statistical information. In step si 104 node 402 uses the received HO statistical information to detect presence of unnecessary inter- frequency HOs (e.g., an unnecessary inter- frequency HO from cell-1 to cell-2). In response to detecting an unnecessary inter-frequency HO from cell-1 to cell-2, node 402 transmits to node 101 a HO optimization message indicating that an unnecessary inter-frequency HO from cell-1 to cell-2 has been detected (step si 106).

[0086] In some embodiments, before initiation of intra-frequency handover a

Coordinated Multi Point (CoMP) technique in which UE can be served from both cell-1 and cell- 3 is applied. This is done to improve UE performance at cell border where the UE can receive same signal from both cell-1 and cell-3 and also get an improved UL by multipoint reception. Intra-frequency handover could be triggered later on when the radio condition in cell-3 is good enough.

[0087] Additionally, in some embodiments, key performance indicators (KPIs) are monitored and used as an input to select the event triggering parameter values that are sent to the UEs so that optimized values can be sent to the UEs.

[0088] FIG. 12 is a block diagram of a computer apparatus 1200 according to some embodiments for implementing the above described network nodes 101, 102, 103, 402. As shown in FIG. 12, the computer apparatus may comprise: a data processing apparatus (DPA) 1202, which may include one or more processors (P) 1255 (e.g., a general purpose microprocessor and/or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like); a network interface 1248 comprising a transmitter (Tx) 1245 and a receiver (Rx) 1247 for enabling the computer apparatus to transmit data to and receive data from other nodes connected to a network 110 (e.g., an Internet Protocol (IP) network) to which network interface 1248 is connected; circuitry 1203 (e.g., radio transceiver circuitry) coupled to an antenna system 1204 for wireless communication with UEs); and local storage unit (a.k.a., "data storage system") 1208, which may include one or more non-volatile storage devices and/or one or more volatile storage devices (e.g., random access memory (RAM)). In embodiments where computer apparatus includes a general purpose microprocessor, a computer program product (CPP) 1241 may be provided. CPP 1241 includes a computer readable medium (CRM) 1242 storing a computer program (CP) 1243 comprising computer readable instructions (CRI) 1244. CRM 1242 may be a non-transitory computer readable medium, such as, but not limited, to magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory), and the like. In some embodiments, the CRI 1244 of computer program 1243 is configured such that when executed by data processing apparatus 1202, the CRI causes computer apparatus to perform steps described herein (e.g., steps described herein with reference to the flow charts and/or message flow diagrams). In other embodiments, computer apparatus may be configured to perform steps described herein without the need for code. That is, for example, data processing apparatus 1202 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be

implemented in hardware and/or software.

[0089] FIG. 13 is a diagram showing functional modules of network node 101 according to some embodiments. As shown in FIG. 13, the network node 101 includes a determining module 1302 for determining whether a condition is satisfied and a HO optimization module 1304 reducing a likelihood that the first UE will trigger an inter- frequency HO of the first UE from the first cell to the second cell, which is operating on a different frequency than the first frequency on which the first cell is operating.

[0090] FIG. 14 is a diagram showing functional modules of network node 102 according to some embodiments. As shown in FIG. 14, the network node 102 includes: 1) an HO request processing module 1402 configured to process a received HO request indicating that a first network node (e.g., node 101) has determined that a UE (e.g. UE 104) should be handed over from a first cell (e.g., cell-1) served by the first network node to a second cell (e.g., cell-2) served by a second network node (e.g., node 102); 2) a determining module 1404 configured to determine whether the requested HO is an unnecessary HO request; and a transmitting module 1406 configured such that, as a result of the determining module 1404 determining that the requested HO is an unnecessary HO from the first cell to the second cell, the transmitting module 1406 employs a transmitter (e.g., transmitter 1245 to transmit to the first network node an HO reject comprising information indicating that an unnecessary HO from the first cell to another cell has been detected.

[0091] FIG. 15 is a diagram showing functional modules of network node 103 according to some embodiments. As shown in FIG. 15, the network node 103 includes: 1) a determining module 1502 configured to determine whether a UE has experienced an unnecessary inter- frequency HO from a first cell (e.g., cell-1) to a second cell (e.g., cell-2) based on UE history information included in a message received at network node 103; and 2) a transmitting module 1504 configured such that, as a result of the determining module 1502 determining that the UE has experienced an unnecessary inter-frequency HO, the transmitting module 1504 employs a transmitter (e.g., transmitter 1245) to transmit to the a network node (e.g. node 101) a report comprising information indicating that an unnecessary inter-frequency HO from the first cell (cell-1) to another cell has been detected.

[0092] FIG. 16 is a diagram showing functional modules of network node 402 according to some embodiments. As shown in FIG. 16, the network node 402 includes: 1) a HO statistics obtaining module 1602 for obtaining the HO statistics, as explained with respect to FIGs. 4 and 11, 2) an unnecessary HO detecting module 1604 configured to use the obtained HO statistical information to detect presence of unnecessary inter-frequency HOs, and 3) a reporting module 1606 configured such that, in response to the detecting module 1604 detecting an unnecessary inter- frequency HO from cell-1 to cell-2, the reporting module 1606 employs a transmitter 1245 to transmit to node 101 a HO optimization message indicating that an unnecessary inter- frequency HO has been detected (e.g., as described above with respect to FIGs. 4 and 11). [0093] While various embodiments of the present disclosure are described herein

(including the appendices), it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[0094] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.