Handover based on signal stength trend

Abstract

Embodiments relate to an apparatus configured to perform a series of measurements indicative of a strength of signals from a neighbouring cell in a wireless communication network. The apparatus is further configured to determine a trend in the strength of signals from the neighbouring cell using the series of measurements and transmit a report to a serving cell supporting providing radio coverage to the apparatus in the wireless communication network for initiating a handover from the serving cell to the neighbouring cell in dependence on the trend.

Description

[0001] HANDOVER BASED ON SIGNAL STENGTH TREND

[0002] TECHNOLOGICAL FIELD

[0003] Various example embodiments relate to apparatus and methods for initiating a handover.

[0004] BACKGROUND

[0005] A key aspect in mobile networks is to assure service continuity for users moving across cells. Typically, within a specific frequency layer in the operator's network, unified configuration for handovers is applied and cell change is triggered if the strength of signals from a neighbor cell becomes greater than the strength of signals from the serving cell. The handover process is well known and well defined, but in challenging circumstances problems may arise, potentially compromising the cellular service quality and continuity.

[0006] BRIEF SUMMARY

[0007] The scope of protection sought for various example embodiments of the disclosure is set out by the independent claims. The example embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

[0008] According to various, but not necessarily all, example embodiments of the disclosure there is provided an apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: perform a series of measurements indicative of a strength of signals from a neighbouring cell in a wireless communication network; determine a trend in the strength of signals from the neighbouring cell using the series of measurements; and transmit a report to a serving cell supporting providing radio coverage to the apparatus in the wireless communication network for initiating a handover from the serving cell to the neighbouring cell in dependence on the trend.

[0009] A handover may be triggered by an A4 event, i.e., when neighbour cell signals become stronger than a threshold for a certain period of time (time to trigger). If a handover is triggered whilst serving cell signals are still stronger than the neighbouring cell signals, a handover back to the original serving cell (ping pong effect) may occur which can undesirably increase network signalling and, in the case of a high speed user equipment (UE) soon to leave the coverage of the original serving cell, reduce the time remaining for another handover to be performed before connection is lost to the original serving cell, thereby increasing the likelihood of radio link failure.

[0010] By basing the handover condition on the trend (i.e., the change or the rate of change) of the strength of signals from the neighbouring cell, undesirable handovers back to the original serving cell may be avoided even where a handover is performed to a neighbouring cell having weaker signals than the original serving cell. For example, on a high speed train moving away from the serving cell and towards the neighbouring cell, the trend in the strength of signals from the neighbouring cell is to increase and the trend in the strength of signals from the original serving cell is to decrease. Therefore, even if a handover from the serving cell to the neighbouring cell occurs when signals from the neighbouring cell are weaker, a backwards handover may not be initiated because the trend shows that the signal strength from the original serving cell (now a neighbouring cell) is decreasing. Therefore, undesirable ping-pong effect may be prevented or inhibited. Accordingly, embodiments may allow a handover to be triggered earlier than would otherwise be possible without risking ping pong, for example, when or soon after entering the neighbouring cell. In the case where there are many UEs travelling in the same direction and having to perform the same handover simultaneously, such as on a train, embodiments may provide more time for performing the handovers before leaving the coverage of the serving cell which can give the network sufficient time to complete the large number handovers, thereby reducing the likelihood of connection loss for UEs within the group.

[0011] Other example embodiments aim to improve A2 event handovers in which handovers are triggered by serving cell signals becoming worse than a threshold. In these example embodiments, rather than monitoring the trend of the neighbouring cell signals for determining whether to initiate a handover, such embodiments monitor the trend of the serving cell signals. The same advantages may be obtained.

[0012] In some example embodiments, the trend is indicative of a change of the strength of signals from the neighbouring cell. In other words, the trend is indicative of the absolute difference in signal strength between the time at which the signal strength meets a threshold and the signal strength after the time to trigger. The trend may be calculated using the formula: strength value at t2 - strength value at t1 . In some embodiments, the time difference may be different from the time to trigger. In some embodiments, more than two measurements over a time frame may be performed. In some example embodiments, the trend is indicative of a rate of change of the strength of signals from the neighbouring cell. In other words, the trend is indicative of the rate of change of the absolute difference which may be calculated using the formula: (strength value at t2 - strength value at t1 ) / (t2-t 1 ).

[0013] In some example embodiments, the apparatus is further caused to perform a second series of measurements indicative of a strength of signals from the serving cell; wherein the trend comprises a relative trend indicative of a change in a difference in the strength of signals from the serving cell and the strength of signals from the neighbouring cell.

[0014] In this way, embodiments may improve traditional handovers based on A3 or A5 events in which the relative strength of the neighbouring cell is used to trigger handovers. By monitoring the trend in the relative strength between signals from the serving cell and signals from the neighbouring cell, embodiments may prevent or inhibit undesirable ping- pong effects. For example, a handover to a neighbouring cell may be triggered due to the neighbouring cell signal strength trending upwards (or increasing) and / or the serving cell signal strength trending downwards (or decreasing). For a high speed UE, this trend is often expected to continue. Therefore, even where handover is performed to a neighbouring cell having a weaker signal strength, no handover back to the original serving cell is initiated because the trends indicate the relative strength of the original serving cell to be decreasing.

[0015] In some example embodiments, the relative trend is indicative of a rate of change of the difference in the strength of signals from the serving cell and the strength of signals from the neighbouring cell.

[0016] In some example embodiments, the apparatus is caused to transmit the report when the trend meets a handover condition.

[0017] In some example embodiments, the handover condition comprises indicating that the change is positive. In other words, the handover condition requires the trend to indicate that the strength of signals from the neighbouring cell is increasing. Where a relative trend is calculated, the handover condition requires the trend to indicate that the strength of signals from the neighbouring cell relative to the strength of signals from the serving cell is increasing. This may result from the strength of signals from the neighbouring cell increasing, the strength of signals from the serving cell decreasing, or a combination of both.

[0018] In some example embodiments, the handover condition comprises indicating that the change meets or exceeds a threshold value.

[0019] In some example embodiments, the apparatus is caused to perform the series of measurements in response to detecting that the neighbouring cell meets a trigger condition. In this way, trend monitoring may begin once the strength of the neighbouring cell meets a certain condition. The condition may be predetermined and indicated to the user equipment. The trigger condition may comprise an A4 event. In the example embodiments where the trend of the serving cell is monitored, the trigger condition may be an A2 event.

[0020] In some example embodiments, the trigger condition comprises the strength of signals from the neighbouring cell meeting or exceeding a threshold value.

[0021] In some example embodiments, the apparatus is caused to perform the second series of measurements in response to detecting that the neighbouring cell meets the trigger condition, the trigger condition comprising a relative strength, indicative of the difference in the strength of signals from the neighbouring cell and the strength of signals from the serving cell, meeting or exceeding a threshold value. In this way, trend monitoring may begin once the relative strength meets a certain condition. The condition may be predetermined and indicated to the user equipment. The trigger condition may comprise an A3 or A5 event.

[0022] In some example embodiments, the threshold value is negative such that the trigger condition is met when the strength of signals from the serving cell is greater than the strength of signals from the neighbouring cell.

[0023] The threshold value may be on or offset either side of the conceptual line at which the strength of signals from the serving cell is equal to the strength of signals from the neighbouring cell. A negative offset (or negative threshold value) is when the threshold value is set such that the series of measurements are triggered when the strength of signals from the serving cell is greater than the strength of signals from the neighbouring cell. Conversely, a positive offset (or positive threshold value) is when the threshold value is set such that the series of measurements are triggered when the strength of signals from the serving cell is less than the strength of signals from the neighbouring cell.

[0024] Whilst either a positive or negative offset (or no offset) may be implemented, when a negative offset is used, there may be more time for handover completion before connection to the serving cell is lost. Using a negative offset would normally lead to ping- pong handovers occurring as the user equipment still has a stronger connection to the serving cell than the neighbouring cell when the initial handover is performed. However, as embodiments monitor the trend in the strength of the connection of the apparatus to the neighbouring cell (or possibly the relative trend in strength of connections between the neighbouring cell and serving cell), in most high speed situations the trend would indicate that the connection to the neighbouring cell is getting stronger and / or the connection to the original serving cell is getting weaker. Thus, handovers back to the original serving cell (the ping-pong effect) can be prevented or are at least less likely to occur.

[0025] In some example embodiments, the user equipment is configured to receive the trigger condition from the serving cell in a radio resource management measurement configuration message. In some embodiments, the user equipment is configured to receive the trigger condition from the serving cell in a cell-wide broadcast. Accordingly, the UE may be informed of the conditions under which the series of measurements for monitoring the trend should be performed.

[0026] In some example embodiments, the apparatus is further caused to: monitor for signals from neighbouring cells, and measure a strength of any signals from the neighbouring cells detected whilst monitoring for signals. For example, the UE may monitor reference signals from the neighbouring cell to determine when the trigger conditions are met. In some example embodiments, the UE is configured to measure at least one of the following: RSRP, SINR and RSRQ as an indication of signal strength.

[0027] In some example embodiments, the apparatus is further caused to: monitor for signals from the serving cell, and measure a strength of one or more signals from the serving cell detected whilst monitoring for signals. For example, the UE may monitor reference signals from the serving cell to determine when the trigger conditions are met. In some example embodiments, the UE is configured to measure at least one of the following: RSRP, SINR and RSRQ as an indication of signal strength. In some example embodiments, the apparatus comprises a user equipment. The user equipment refers to any mobile end or terminal device that may be capable of wireless communication. By way of example rather than limitation, user equipment UE may also be referred to as a communication device, a terminal device, a Mobile Station (MS). The user equipment may include, but is not limited to, a mobile phone, a cellular phone, a smart phone, a tablet, a wearable terminal device, a personal digital assistant (PDA) , vehiclemounted wireless terminal devices, smart devices etc.

[0028] According to various, but not necessarily all, example embodiments of the disclosure there is provided an apparatus comprising: means for performing a series of measurements indicative of a strength of signals from a neighbouring cell in a wireless communication network; means for determining a trend in the strength of signals from the neighbouring cell using the series of measurements; and means for transmitting a report to a serving cell supporting providing radio coverage to the apparatus in the wireless communication network for initiating a handover from the serving cell to the neighbouring cell in dependence on the trend.

[0029] The means may perform the optional features set out in relation to the apparatus mentioned above.

[0030] According to various, but not necessarily all, example embodiments of the disclosure there is provided an apparatus comprising: circuitry configured to perform a series of measurements indicative of a strength of signals from a neighbouring cell in a wireless communication network; circuitry configured to determine a trend in the strength of signals from the neighbouring cell using the series of measurements; and circuitry configured to transmit a report to a serving cell supporting providing radio coverage to the apparatus in the wireless communication network for initiating a handover from the serving cell to the neighbouring cell in dependence on the trend.

[0031] The circuitry may be configured perform the optional features set out in relation to the apparatus mentioned above.

[0032] According to various, but not necessarily all, example embodiments of the disclosure there is provided an apparatus for supporting providing radio coverage to a user equipment in a wireless communication network, the apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: in response to receipt from a user equipment of a series of measurements indicative of a strength of signals received by the user equipment from a neighbouring cell in the wireless communication network, determine a trend in the strength of signals received by the user equipment from the neighbouring cell using the series of measurements; and transmit a message to the user equipment for initiating a handover from the apparatus to the neighbouring cell in dependence on the trend.

[0033] In contrast, to the example embodiments above, the UE may be configured to transmit measurements to an apparatus, such as a base station, for supporting providing radio coverage to the UE. The apparatus is configured to determine the trend from the signal strength measurements to determine when to initiate a handover. In this way, the trend monitoring for all or some UEs may be centralised which can reduce power consumption and the processing burden on the UEs. On the other hand, having a decentralised process, such as in the example embodiments above, processing is distributed to each UE which may be advantageous where there are lots of UEs requiring handover at the same time.

[0034] In some example embodiments, the trend is indicative of a change of the strength of signals received by the user equipment from the neighbouring cell. In other words, the trend is indicative of the absolute difference which may be calculated using the formula: value at t2 - value at t1 .

[0035] In some example embodiments, the trend is indicative of a rate of change of the strength of signals received by the user equipment from the neighbouring cell. In other words, the trend is indicative of the rate of change of the absolute difference which may be calculated using the formula: (value at t2 - value at t1 ) / (t2-t 1 ).

[0036] In some example embodiments, the trend comprises a relative trend indicative of a change in a difference in a strength of signals received by the user equipment from the apparatus and the strength of signals received by the user equipment from the neighbouring cell; the apparatus being cause to determine the trend in response to receipt of a second series of measurements indicative of the strength of signals received by the user equipment from the apparatus. In this way, embodiments may improve traditional handovers based on A3 or A5 events in which the relative strength of the neighbouring cell is used to trigger handovers. By monitoring the trend in the relative strength between signals from the serving cell and signals from the neighbouring cell, embodiments may prevent or inhibit undesirable ping- pong effects. For example, a handover to a neighbouring cell may be triggered due to the neighbouring cell signal strength trending upwards (or increasing) and / or the serving cell signal strength trending downwards (or decreasing). This trend is expected to continue for a high speed UE, for example, a UE on a train. Therefore, even where handover is performed to a neighbouring cell having a weaker signal strength, no handover back to the original serving cell is initiated because the trends indicate the relative strength of the original serving cell to be decreasing.

[0037] In some example embodiments, the relative trend is indicative of a rate of change of the difference in the strength of signals received by the user equipment from the apparatus and the strength of signals received by the user equipment from the neighbouring cell.

[0038] In some example embodiments, the apparatus is caused to transmit the message when the trend meets a handover condition.

[0039] In some example embodiments, the handover condition comprises indicating that the change is positive. In other words, the handover condition requires the trend to indicate that the strength of signals from the neighbouring cell is increasing. Where a relative trend is calculated, the handover condition requires the trend to indicate that the strength of signals from the neighbouring cell relative to the strength of signals from the serving cell is increasing. This may result from the strength of signals from the neighbouring cell increasing, the strength of signals from the serving cell decreasing, or a combination of both.

[0040] In some example embodiments, the handover condition comprises indicating that the change meets or exceeds a threshold value.

[0041] In some example embodiments, the apparatus is caused to determine the trend in response to detecting that the neighbouring cell meets a trigger condition. In this way, trend monitoring may begin once the strength of the neighbouring cell meets a certain condition. The condition may be predetermined and indicated to the user equipment. The trigger condition may comprise an A4 event. In the example embodiments where the trend of the serving cell is monitored, the trigger condition may be an A2 event.

[0042] In some example embodiments, the trigger condition comprises the strength of signals received by the user equipment from the neighbouring cell meeting or exceeding a threshold value.

[0043] In some example embodiments, the trigger condition comprises a relative strength, indicative of the difference in the strength of signals received by the user equipment from the neighbouring cell and the strength of signals received by the user equipment from the apparatus, meeting or exceeding a threshold value. In this way, trend monitoring may begin once the relative strength meets a certain condition. The condition may be predetermined and indicated to the user equipment. The trigger condition may comprise an A3 or A5 event.

[0044] In some example embodiments, the threshold value is negative such that the trigger condition is met when the strength of signals received by the user equipment from the apparatus is greater than the strength of signals received by the user equipment from the neighbouring cell.

[0045] The threshold value may be on or offset either side of the conceptual line at which the strength of signals from the serving cell is equal to the strength of signals from the neighbouring cell. A negative offset (or negative threshold value) is when the threshold value is set such that measurements are triggered when the strength of signals from the serving cell is greater than the strength of signals from the neighbouring cell. Conversely, a positive offset (or positive threshold value) is when the threshold value is set such that measurements are triggered when the strength of signals from the serving cell is smaller than the strength of signals from the neighbouring cell.

[0046] Whilst either a positive or negative offset (or no offset) may be implemented, when a negative offset is used, there may be more time for handover completion before connection to the serving cell is lost. However, using a negative offset would normally lead to ping-pong handovers occurring as the user equipment still has a stronger connection to the serving cell than the neighbouring cell when the initial handover is performed. However, as embodiments monitor the trend in the strength of the connection of the apparatus to the neighbouring cell (or possibly the relative trend in strength of connections between the neighbouring cell and serving cell), in most high speed situations the trend would indicate that the connection to the neighbouring cell is getting stronger and the connection to the serving cell is getting weaker. Hence, handovers back to the original serving cell (the ping-pong effect) will not occur.

[0047] In some example embodiments, the apparatus is further caused to transmit reference signals to the user equipment. In some embodiments, the reference signals are comprised within a cell-wide broadcast.

[0048] In some example embodiments, the apparatus comprises a base station supporting providing radio coverage to a serving cell of the user equipment. In some example embodiments, the apparatus comprises a gNodeB.

[0049] According to various, but not necessarily all, example embodiments of the disclosure there is provided an apparatus comprising: means for, in response to receipt from a user equipment of a series of measurements indicative of a strength of signals received by the user equipment from a neighbouring cell in the wireless communication network, determining a trend in the strength of signals received by the user equipment from the neighbouring cell using the series of measurements; and means for transmitting a message to the user equipment for initiating a handover from the apparatus to the neighbouring cell in dependence on the trend.

[0050] The means may perform the optional features set out in relation to the apparatus mentioned above.

[0051] According to various, but not necessarily all, example embodiments of the disclosure there is provided an apparatus comprising: circuitry configured to, in response to receipt from a user equipment of a series of measurements indicative of a strength of signals received by the user equipment from a neighbouring cell in the wireless communication network, determine a trend in the strength of signals received by the user equipment from the neighbouring cell using the series of measurements; and circuitry configured to transmit a message to the user equipment for initiating a handover from the apparatus to the neighbouring cell in dependence on the trend.

[0052] The circuitry may be configured perform the optional features set out in relation to the apparatus mentioned above. According to various, but not necessarily all, example embodiments of the disclosure there is provided a method performed at a user equipment in a wireless communication network, the method comprising: performing a series of measurements indicative of a strength of signals from a neighbouring cell in the wireless communication network; determining a trend in the strength of signals from the neighbouring cell using the series of measurements; and transmitting a report to a serving cell supporting providing radio coverage to the user equipment in the wireless communication network for initiating a handover from the serving cell to the neighbouring cell in dependence on the trend.

[0053] In some example embodiments, the method further comprises performing a second series of measurements indicative of a strength of signals from the serving cell; wherein the trend comprises a relative trend indicative of a change in a difference in the strength of signals from the serving cell and the strength of signals from the neighbouring cell.

[0054] In some example embodiments, the method further comprises transmitting the report when the trend meets a handover condition.

[0055] In some example embodiments, the method further comprises performing the series of measurements in response to detecting that the neighbouring cell meets a trigger condition.

[0056] In some example embodiments, the method further comprises performing the second series of measurements in response to detecting that the neighbouring cell meets the trigger condition, the trigger condition comprising a relative strength, indicative of the difference in the strength of signals from the neighbouring cell and the strength of signals from the serving cell, meeting or exceeding a threshold value.

[0057] In some example embodiments, the method further comprises receiving the trigger condition from the serving cell in a radio resource management measurement configuration message. In some embodiments, the method further comprises receiving the trigger condition from the serving cell in a cell-wide broadcast.

[0058] In some example embodiments, the method further comprises monitoring for signals from neighbouring cells, and measuring a strength of any signals from the neighbouring cells detected whilst monitoring for signals. In some example embodiments, the method further comprises monitoring for signals from the serving cells, and measuring a strength of one or more signals from the serving cell detected whilst monitoring for signals.

[0059] According to various, but not necessarily all, example embodiments of the disclosure there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: performing a series of measurements indicative of a strength of signals from a neighbouring cell in the wireless communication network; determining a trend in the strength of signals from the neighbouring cell using the series of measurements; and transmitting a report to a serving cell supporting providing radio coverage to the user equipment in the wireless communication network for initiating a handover from the serving cell to the neighbouring cell in dependence on the trend.

[0060] The instructions may be for performing the optional features set out in relation to the method mentioned above.

[0061] According to various, but not necessarily all, example embodiments of the disclosure there is provided a method performed at a base station in a wireless communication network, the method comprising: in response to receipt from a user equipment of a series of measurements indicative of a strength of signals received by the user equipment from a neighbouring cell in the wireless communication network, determining a trend in the strength of signals received by the user equipment from the neighbouring cell using the series of measurements; and transmitting a message to the user equipment for initiating a handover from the base station to the neighbouring cell in dependence on the trend.

[0062] In some example embodiments, the trend comprises a relative trend indicative of a change in a difference in a strength of signals received by the user equipment from the apparatus and the strength of signals received by the user equipment from the neighbouring cell; and the method further comprises determining the trend in response to receipt of a second series of measurements indicative of the strength of signals received by the user equipment from the apparatus.

[0063] In some example embodiments, the method further comprises transmitting the message when the trend meets a handover condition. In some example embodiments, the method further comprises determining the trend in response to detecting that the neighbouring cell meets a trigger condition.

[0064] In some example embodiments, the method further comprises sending the trigger condition to the user equipment in a radio resource management measurement configuration message. In some embodiments, the method further comprises sending the trigger condition to the user equipment in a cell-wide broadcast.

[0065] In some example embodiments, the method further comprises transmitting reference signals to the user equipment.

[0066] According to various, but not necessarily all, example embodiments of the disclosure there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: in response to receipt from a user equipment of a series of measurements indicative of a strength of signals received by the user equipment from a neighbouring cell in the wireless communication network, determining a trend in the strength of signals received by the user equipment from the neighbouring cell using the series of measurements; and transmitting a message to the user equipment for initiating a handover from the base station to the neighbouring cell in dependence on the trend.

[0067] The instructions may be for performing the optional features set out in relation to the method mentioned above.

[0068] According to various, but not necessarily all, example embodiments of the disclosure there is provided computer program or computer program product comprising computer readable instructions which when executed by at least one processor of an apparatus are operable to control said apparatus to perform the method performed at a user equipment or the method performed at a base station.

[0069] The computer program or computer program product may cause performance of the optional features set out in relation to either of the methods mentioned above.

[0070] Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

[0071] Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

[0072] BRIEF DESCRIPTION

[0073] Some example embodiments will now be described with reference to the accompanying drawings in which:

[0074] FIGS. 1 A-C schematically illustrate different handover triggering points;

[0075] FIG. 2 schematically illustrates the signalling and the logic during a handover according to an example embodiment;

[0076] FIG. 3 schematically illustrates the signalling and the logic during a handover according to an example embodiment; and

[0077] FIG. 4 schematically shows a user equipment moving through a communication network according to an embodiment.

[0078] DETAILED DESCRIPTION

[0079] Before discussing the example embodiments in any more detail, first an overview will be provided.

[0080] The application is concerned principally with the situation where there are many UEs that need to handover at the same time and particularly where the UEs are travelling at a fast speed, so that the time in which a handover is to be performed, that is the time between the handover condition (A3 or A5 event for example) being met and coverage in the serving or source cell being lost is quite short. This problem may arise at cell boundaries on railway lines or highways.

[0081] One way of addressing this would be to change the condition for the handover event to be triggered so that the condition is met earlier, that is before the target cell is better than the source cell. This would allow a longer time to handover before the source cell coverage is lost. A drawback of this is that there is an increased likelihood of a handover from the target cell back to the source cell (ping pong effect). This application addresses this problem by modifying the conditions of triggering the measurement report for initiating the handover. Specifically, embodiments propose triggering a handover based on the trend of the connection to the neighbouring cell and / or the serving cell. In other words, handover trigger conditions are based on whether connection to a target neighbouring cell is getting better and whether connection to the serving cell is getting worse. As a result, even when handovers are performed to a worse cell, i.e., a cell with weaker connection to the UE, a back handover may not be performed if the trend indicates the new cell is improving or is preferable to the previous serving cell.

[0082] As set out briefly above, for specific use cases (such as high speed trains, large numbers of cars travelling along highways, or even when providing cellular services to airplanes), where significant number of users located in the same area are traveling in the same predefined direction, it may be challenging to assure service continuity for all the users, due to processing power limitations offered by the source and target cells engaged in the handover process (finite number of handovers can be processed within certain period). The problem will be amplified in the future when the number of network devices will greatly increase due to, for example, wearables, RedCap (reduced capacity) devices, intelligent cars etc.

[0083] One aspect of the problem is the necessity to suddenly process large numbers of handover requests caused by the train / vehicle with tens to hundreds of passengers, or a vehicle having multiple loT devices on board travelling across cell boundaries. Another aspect of the problem is the high speed of the devices which imposes tight requirements on handover timing. A further aspect is that the standardized handover event is based on the principle that the UE crosses the handover threshold - typically because the neighbour cell becomes better than the serving one, and that this state is maintained for some time (Time to Trigger). This can cause difficulties including:

[0084] • the target cell has to be better than the serving one (might not be technically better if the negative offset is applied, but the principle is that the target cell goes above a certain threshold); and

[0085] • the Time to Trigger can’t be too long due to the high speed of the devices.

[0086] On top of these points, if handover is triggered to a worse cell, unwanted ping-pong effect (back handover) may occur introducing an even greater signalling load related to handover procedures. As a result, the connection of a number of users may be dropped due to lack of processing power by the base station. Embodiments disclosed herein propose ways for avoiding or at least impeding the back handover, particularly in case of handover to a worse cell, by modifying the conditions of triggering the measurement report for initiating the handover. Specifically, embodiments propose triggering a handover based on the trend of the strength of signals from the neighbouring cell and / or on the strength of signals from the serving cell. In some embodiments, the trend may indicate whether the relative strength compared to the serving cell or the absolute strength of signals from the neighbouring cell is improving or exceeds a threshold. Accordingly, when UEs are moving in a towards the neighbouring cell and away from the serving cell, a handover back to the serving cell may not be triggered because the trend is that the original serving cell is becoming worse and the neighbouring cell (now the serving cell) is becoming better, even where the connection to the original serving cell is stronger.

[0087] When handover occurs to a worse cell (when executed early, perhaps just when entering the coverage of the target cell), the cumulative time for execution of possible handovers between cells is increased. This extension of time may be crucial for users travelling in single group, in the same direction, at the same time because the base station transceiver (BTS) may offload (stretch) in time domain the processing associated with the large number of simultaneously executed handovers. In this way, the number of dropped users may be significantly reduced.

[0088] Legacy mobility events (prior to 3GPP ReL16) have long been used to provide intrafrequency, inter-frequency and inter-RAT mobility. The proposed idea is based on the use and possible extension of the A2, A3, A4 or A5 mobility events (relevant both to LTE and NR). Those events are specified as:

[0089] Event A1 (Serving becomes better than threshold) Event A2 (Serving becomes worse than threshold) Event A3 (Neighbour becomes offset better than SpCell (special cell)) Event A4 (Neighbour becomes better than threshold)

[0090] Event A5 (Serving becomes worse than threshold, Neighbour becomes better than threshold)

[0091] Event A6 (Neighbour becomes offset better than SCell)

[0092] It may be that a network covering the highways and the railways in a given country uses a single frequency layer, although the application is not limited to this. However, this is very often the case and thus, embodiments, focus on intra-frequency handover cases for simplicity sake, but the principles can be extended to any type of handover.

[0093] Current behaviour for event A3 based mobility is illustrated in Figs. 1 A - C.

[0094] In Fig. 1 A, handover initiation is triggered when the signal strength of the source cell (cell A) is equal to the signal strength of the target cell (cell B), sometimes referred to as the neighbouring cell. If handover initiation is triggered here, then in order for service not to be lost, it must be completed before radio coverage from the source cell is lost. Thus, the time for handover to occur is T1= L1 / v, where L1 = D / 2 that is half the diameter of the cell overlap and v is the velocity of the UE. As the trajectory of the UE is known and handover is only initiated when the target cell is better than the source cell, ping pong will likely not occur.

[0095] Fig. 1 B shows an alternative example where handover initiation is triggered when the target cell is a certain (positive) offset better than the source cell. This scenario is even safer with respect to possible ping pong but has a shorter time in which to perform the handover. In this case, the time available for handover before service is dropped is T2=L2 / v where L2 < 0.5D, so the time is shorter.

[0096] Fig. 1C shows a further alternative where handover is initiated early when the signal from the target cell is worse than the signal from the source cell by a predetermined negative offset. In this case, handover needs to be completed by T3 = L3 / v, where L3 > D, so there is a longer time in which handover can occur. However, as the signal strength from the target cell is less than the signal strength from the source cell when handover is initiated, the risk of ping pong back to the source cell is high.

[0097] Despite the high risk of ping pong, the option of Fig. 1C from better cell A to worse cell B provides the longest available time for a handover of the three examples and is therefore the most promising option in the context of cumulative time offered by the system for possible handovers, which may be required in particular where there is a group of UEs travelling in the same direction at the same time. For any given processing resources, execution of handovers can be distributed over more time because T3 > T1 > T2.

[0098] However, in the option of Fig. 1C, ping pong becomes a very real possibility.

[0099] Embodiments propose a solution for avoiding or at least reducing the ping-pong effect, particularly for handovers to a worse cell like in the scenario of Fig. 1 C. In some example embodiments, the conditions for causing a UE to transmit a measurement report for initiating a handover are modified to be based on the trend of the connections of the UE to the cells.

[0100] Fig. 2 illustrates the signalling and logic during a handover process according to an example embodiment. In step 1 , connection of the UE 10 to the source gNB 20 (sometimes referred to as serving cell or source cell) is established.

[0101] In step 2, RRC reconfiguration procedure for measurement configuration for a trendbased handover occurs. In this step, the UE 10 is informed by the source cell 20 of the modified conditions for triggering a handover.

[0102] In step 3, the UE 10 monitors for signals from the target gNB 30 (sometimes referred to as target cell or neighbouring cell) and the source cell 20 and measures the strength of any monitored signals. For example, the UE 10 may measure RSRP, RSRQ or SINR. In particular, the UE 10 determines whether the difference between the strength in signals from the neighbour cell 30 and the strength in signals from the serving cell 20 meets a threshold value for triggering monitoring of the trend of the connections to the serving cell 20 and the neighbouring cell 30. The threshold condition has been indicated to the UE during step 2.

[0103] As mentioned above, the threshold for triggering the trend monitoring may be positively or negatively offset (or not offset) relative to the conceptual line at which the strength of the connection to the serving cell 10 is equal to the strength of the connection to the target cell 30. In this embodiment, a negative offset is used to provide a longer time to complete the handover. This may be particularly advantageous when large groups of UEs all need to perform the same handover, for example, UEs on a train.

[0104] Once the trigger condition has been met, the time to trigger is started and the UE 10 begins to monitor the trend.

[0105] In step 4, the UE 10 determines whether or not the relative strength between signals from the target cell 30 and signals from the source cell 20 has increased by a threshold amount, DeltaAfterTTT, i.e., whether the trend indicates a sufficient increase in the relative strength for a handover condition to be met. In some example embodiments, rather than indicating the absolute difference in connection strength, the trend is indicative of the rate of change of the difference in strength and an appropriate threshold rate is set.

[0106] If the trend meets the handover condition, steps 5, 6 and 7 are performed. In steps 5 and 6, the UE 10 determines that the trend meets the handover condition and transmits an RRC measurement report to the serving cell 20 for initiating a handover. In step 7, a handover procedure is performed to establish a connection for the UE 10 to the target neighbour cell 30.

[0107] If the trend does not meet the handover condition, the UE 10 does not send an RRC measurement report and remains connected to the source cell 20 in step 8.

[0108] In this embodiment, 3GPP implementation changes may be required. For example, a modified event A3 (Neighbour becomes offset better than SpCell) may include:

[0109] Inequality A3-1a (Entering condition) (at which TimeToTrigger is started)

[0110] Mn + Ofn + Ocn - Hys > Mp + Ofp + Ocp + Off

[0111] Inequality A3-2 (Leaving condition)

[0112] Mn + Ofn + Ocn + Hys < Mp + Ofp + Ocp + Off

[0113] The variables in the formula are defined as follows:

[0114] • Mn is the measurement result of the neighbouring cell, not taking into account any offsets.

[0115] • Ofn is the measurement object specific offset of the reference signal of the neighbour cell (i.e. offsetMO as defined within measObjectNR corresponding to the neighbour cell).

[0116] • Ocn is the cell specific offset of the neighbour cell (i.e. celllndividualOffset as defined within measObjectNR corresponding to the frequency of the neighbour cell), and set to zero if not configured for the neighbour cell.

[0117] • Mp is the measurement result of the SpCell, not taking into account any offsets.

[0118] • Ofp is the measurement object specific offset of the SpCell (i.e. offsetMO as defined within measObjectNR corresponding to the SpCell). • Ocp is the cell specific offset of the SpCell (i.e. celllndividualOffset as defined within measObjectNR corresponding to the SpCell), and is set to zero if not configured for the SpCell.

[0119] • Hys is the hysteresis parameter for this event (i.e. hysteresis as defined within reportConfigNR for this event).

[0120] • Off is the offset parameter for this event (i.e. a3-Offset as defined within reportConfigNR for this event).

[0121] • Mn, Mp are expressed in dBm in case of RSRP, or in dB in case of RSRQ and RS- SINR.

[0122] Ofn, Ocn, Ofp, Ocp, Hys, Off are expressed in dB.

[0123] When entering conditions are valid for the TimeToTrigger, a Measurement Report for event A3 is sent.

[0124] For modified logic before sending the Measurement Report, the UE verifies whether the following handover conditions are met. Only when Inequality A3-1 b conditions are met is a Measurement Report is sent.

[0125] Inequality A3-1 b (Entering condition) (after which TimeToTrigger is stopped) Mn + Ofn + Ocn - Hys > Mp + Ofp + Ocp + Off + deltaAfterTTT

[0126] The parameter deltaAfterTTT is the minimum delta between the offset parameter and real offset measured by the UE after TimeToTrigger.

[0127] It will be appreciated that Fig. 2 depicts one possible example using an A3 event where the threshold for triggering monitoring of the trend is indicated to the UE in an RRM MeasureConfig message and the UE is configured to determine if the trend meets a certain handover condition. In other example embodiments, an A4 event which only requires the neighbouring cell connection to be monitored or an A2 event which only requires the serving cell connection to be monitored may be used to trigger the trend monitoring. In the case of an A4 event, trend monitoring may be triggered when the neighbouring cell connection becomes stronger than a threshold. In the case of an A2 event, trend monitoring may be triggered when the serving cell connection falls below a certain threshold value. In some example embodiments, mobility for non-high speed UEs can rely on event A5 radio conditions where the thresholds indicate absolute values of RSRP / RSRQ / SINR. In other example embodiments, it is the serving cell 20 rather than the UE 10 which determines that the trigger condition has been met and which monitors the trend. In the latter case, the UE would send multiple measurement reports and the serving cell would be in charge of determining the measurement trend and taking the decision to launch the handover. Where a cell’s trend is determined by the gNB based on consecutively received measurements, no changes in measurement configuration may be required and the cell trend-based handover can rely on Measurement Reports applicable for existing events A3, A4, A5. In such embodiments, the source cell 20 may initiate a handover once it determines that the trend meets a certain handover condition.

[0128] Fig. 3 shows similar signalling and logic during a handover as Fig. 2 but further details the handover steps. Steps 101 , 102 and 103 comprise steps 2, 3, 4 and 5 of Fig. 2 whilst step 103 is the same as step 6. Therefore, these steps will not be described again.

[0129] Step 6 in Fig. 2 comprises steps 104 to 111 of Fig. 3. In step 104, the serving cell 20 sends a handover required message to the AMF 40 based on the decision to trigger a handover. In step 105, the AMF 40 transmits a handover request message to the target cell 30. In step 106, the handover request is acknowledged by the target cell 30. In step 107, the AMF 40 sends a handover command to the source cell 20. In step 108, an RRC reconfiguration message is sent by the source cell 20 to the UE 10. In step 109, the UE 10 performs a random access procedure to the target cell 30. In step 110, the UE 10 transmits an RRC reconfiguration complete message to the target cell 30 once the random access procedure is complete. In step 111 , the UE is connected to the target cell 30 which may send a new or updated measurement configuration to the UE 10. It will be appreciated that this is just one example of a handover process and that the general principles of the application may be applied to other handover processes.

[0130] Fig. 4 schematically shows UE 10 moving from a source cell 23 supported by source node 20 towards target cell 33 supported by target node 30. UE 10 comprises one or more processors 12, one or more data stores 14 and a transceiver 16. Source node 20 comprises a transceiver 22, one or more processors 24 and one or more data stores 26. Target node 30 comprises a transceiver 38, one or more processors 36 and one or more data stores 37. It should be noted that the target node is a target node for the UE 10 but may be a source or serving node for other UEs. Similarly, source or service node 20 may be a target node for other UEs. Thus, these nodes may be configured with the functionality of both a target and source node according to some example embodiments.

[0131] In other words, the application proposes a new type of measurement event, allowing triggering of a handover from a cell which becomes weaker (based on RSRP / RSRQ trend) to cell which becomes stronger (based on RSRP / RSRQ trend). Such a trend-based handover event gives the possibility to trigger a handover (even to worse cell) without the risk of ping-pong effect. Cumulative time for execution of possible handovers between cells can be increased which may be crucial for users travelling in single group, in the same direction, at the same time.

[0132] The proposed trend-based measurement event is based on collecting a series of subsequent measurements and processing them to derive the trend (increase or decrease). The proposed embodiments cover at least four aspects:

[0133] 1 . which mobility event to use: A2, A3, A4 or A5;

[0134] 2. which physical signal can be used as a basis for the measurements (RSRP, SINR, perhaps RSRQ);

[0135] 3. which node will determine the triggering condition. This could be the UE or the BTS (gNB). In the former case, it's the UE that is performing internally multiple measurements to determine if the trend of the measured signal justifies triggering the measurement report. This would require the UE to be provided with the decision threshold. In the latter case, the UE would send multiple measurement reports and the BTS would be in charge of determining the measurement trend and possibly taking the decision to launch handover. If it's the UE that determines the measurement trend, it will require modification of the UE (new UE capability). The advantage of this approach is that processing load needed to determine cells' trends is decentralized (from serving gNB POV) and spread over the UEs. This may result also in a lower number of RRC Measurement Reports sent by the UEs (Measurement Report is sent only when cell trends are detected). For the second approach, where cells' trend is determined by the gNB based on consecutively received measurements, no changes in measurement configuration are required; the cell trend based handover can relay on Measurement Reports applicable for existing events A3, A4, A5.

[0136] 4. the way in which to provide the UE with a decision threshold (if needed). This could be done per-UE as an additional field in the RRM MeasConfig, or by broadcasting the cell-wide threshold in an appropriate message. Both approaches would require modification of 3GPP 38.331 . If the RRM MeasConfig is modified, it will require the UE to be able to read an additional field and act upon it. Another possibility is to reuse the solution for RRM measurement relaxation, but to apply it not only and solely for RedCap UEs. This could be done by broadcasting the thresholds intended for RedCap devices, but not broadcasting the indication that the specific cell supports the RedCap devices. This would prevent the RedCap devices from applying these thresholds.

[0137] A person of skill in the art would readily recognize that steps of various above-described methods can be performed by programmed computers. Herein, some embodiments are also intended to cover program storage devices, e.g., digital data storage media, which are machine or computer readable and encode machine-executable or computerexecutable programs of instructions, wherein said instructions perform some or all of the steps of said above-described methods. The program storage devices may be, e.g., digital memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media. The embodiments are also intended to cover computers programmed to perform said steps of the above-described methods. The tern non-transitory as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g. RAM vs ROM).

[0138] As used in this application, the term “circuitry” may refer to one or more or all of the following:

[0139] (a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and

[0140] (b) combinations of hardware circuits and software, such as (as applicable):

[0141] (i) a combination of analog and / or digital hardware circuit(s) with software / fi rmware and

[0142] (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

[0143] (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0144] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0145] Although example embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

[0146] Features described in the preceding description may be used in combinations other than the combinations explicitly described.

[0147] Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

[0148] Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

[0149] Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not particular emphasis has been placed thereon.

[0150] LIST OF ABBREVIATIONS

[0151] BTS - Base Station Transceiver gNB - next generation Node B (5G base station) HST - High Speed Train RedCap - Reduced Capacity (device) RRM - Radio Resource Management RSRP - Reference Signal Received Power RSRP - Reference Signal Received Quality SIB - System Information Broadcast SINR - Signal to Interference Ratio UE - User Equipment

[0152] U2N - User to Network (relay node)

Claims

CLAIMS1 . An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: perform a series of measurements indicative of a strength of signals from a neighbouring cell in a wireless communication network; determine a trend in the strength of signals from the neighbouring cell using the series of measurements; and transmit a report to a serving cell supporting providing radio coverage to the apparatus in the wireless communication network for initiating a handover from the serving cell to the neighbouring cell in dependence on the trend.

2. An apparatus according to claim 1 , wherein the trend is indicative of a change of the strength of signals from the neighbouring cell.

3. An apparatus according to claim 1 , wherein the apparatus is further caused to: perform a second series of measurements indicative of a strength of signals from the serving cell; wherein the trend comprises a relative trend indicative of a change in a difference in the strength of signals from the serving cell and the strength of signals from the neighbouring cell.

4. An apparatus according to any one of claims 1 to 3, wherein the apparatus is caused to transmit the report when the trend meets a handover condition.

5. An apparatus according to claim 4 when dependent on claim 2 or claim 3, wherein the handover condition comprises indicating that the change is positive.

6. An apparatus according to claim 4 or claim 5, when dependent on claim 2 or claim 3, wherein the handover condition comprises indicating that the change meets or exceeds a threshold value.

7. An apparatus according to any preceding claim, wherein the apparatus is caused to perform the series of measurements in response to detecting that the neighbouring cell meets a trigger condition.

8. An apparatus according to claim 7, wherein the trigger condition comprises the strength of signals from the neighbouring cell meeting or exceeding a threshold value.

9. An apparatus according to claim 7 when dependent on claim 3, wherein the apparatus is caused to perform the second series of measurements in response to detecting that the neighbouring cell meets the trigger condition, the trigger condition comprising a relative strength, indicative of the difference in the strength of signals from the neighbouring cell and the strength of signals from the serving cell, meeting or exceeding a threshold value.

10. An apparatus according to claim 9, wherein the threshold value is negative such that the trigger condition is met when the strength of signals from the serving cell is greater than the strength of signals from the neighbouring cell.

11. An apparatus according to any preceding claim, wherein the apparatus comprises a user equipment.

12. An apparatus for supporting providing radio coverage to a user equipment in a wireless communication network, the apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: in response to receipt from a user equipment of a series of measurements indicative of a strength of signals received by the user equipment from a neighbouring cell in the wireless communication network, determine a trend in the strength of signals received by the user equipment from the neighbouring cell using the series of measurements; and transmit a message to the user equipment for initiating a handover from the apparatus to the neighbouring cell in dependence on the trend.

13. An apparatus according to claim 12, wherein the trend is indicative of a change of the strength of signals received by the user equipment from the neighbouring cell.

14. An apparatus according to claim 12, wherein the trend comprises a relative trend indicative of a change in a difference in a strength of signals received by the user equipment from the apparatus and the strength of signals received by the user equipment from the neighbouring cell; the apparatus being cause to determine the trend in response to receipt of a second series of measurements indicative of the strength of signals received by the user equipment from the apparatus.

15. An apparatus according to any one of claims 12 to 14, wherein the apparatus is caused to transmit the message when the trend meets a handover condition.

16. An apparatus according to claim 15 when dependent on claim 13 or 14, wherein the handover condition comprises indicating that the change is positive.

17. An apparatus according to claim 15 or claim 16, when dependent on claim 13 or claim 14, wherein the handover condition comprises indicating that the change meets or exceeds a threshold value.

18. An apparatus according to any one of claims 12 to 17, wherein the apparatus is caused to determine the trend in response to detecting that the neighbouring cell meets a trigger condition.

19. An apparatus according to claim 18, wherein the trigger condition comprises the strength of signals received by the user equipment from the neighbouring cell meeting or exceeding a threshold value.

20. An apparatus according to claim 18, when dependent on claim 14, wherein the trigger condition comprises a relative strength, indicative of the difference in the strength of signals received by the user equipment from the neighbouring cell and the strength of signals received by the user equipment from the apparatus, meeting or exceeding a threshold value.21 . An apparatus according to claim 20, wherein the threshold value is negative such that the trigger condition is met when the strength of signals received by the user equipment from the apparatus is greater than the strength of signals received by the user equipment from the neighbouring cell.

22. An apparatus according to any one of claims 12 to 21 , wherein the apparatus comprises a base station supporting providing radio coverage to a serving cell of the user equipment.

23. A method performed at a user equipment in a wireless communication network, the method comprising: performing a series of measurements indicative of a strength of signals from a neighbouring cell in the wireless communication network; determining a trend in the strength of signals from the neighbouring cell using the series of measurements; and transmitting a report to a serving cell supporting providing radio coverage to the user equipment in the wireless communication network for initiating a handover from the serving cell to the neighbouring cell in dependence on the trend.

24. A method performed at a base station in a wireless communication network, the method comprising: in response to receipt from a user equipment of a series of measurements indicative of a strength of signals received by the user equipment from a neighbouring cell in the wireless communication network, determining a trend in the strength of signals received by the user equipment from the neighbouring cell using the series of measurements; and transmitting a message to the user equipment for initiating a handover from the base station to the neighbouring cell in dependence on the trend.

25. A computer program comprising computer readable instructions which when executed by at least one processor of an apparatus are operable to control said apparatus to perform the method of claim 23 or claim 24.

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