WO2013010565A1

WO2013010565A1 - Network element and method of operating the same

Info

Publication number: WO2013010565A1
Application number: PCT/EP2011/062109
Authority: WO
Inventors: Bernhard Wegmann; Ingo Viering; Ahmad AWADA
Original assignee: Nokia Siemens Networks Oy
Priority date: 2011-07-15
Filing date: 2011-07-15
Publication date: 2013-01-24

Abstract

A network element for a communication network is provided, wherein the network element comprises a receiving unit and a processing unit, wherein the receiving unit is adapted to receive a data signal including an information element indicative of a determined value of a parameter wherein the value of the parameter is indicative for a gradient of a signal strength of a communication signal in the communication network. Furthermore, the processing unit is adapted to determine a threshold value based on the received information element.

Description

DESCRIPTION

TITLE

Network Element and Method of Operating the Same Field of Invention The present invention relates to a network element and a user equipment of a communication network, in particular a radio or mobile communication network. The invention further relates to a method of determining a threshold in a communication network and a method of operating the communication network. Furthermore, the invention relates to a protocol usable for performing

communication in a communication network, a program element and a computer readable medium.

Art Background One important area in the technical field of mobile radio communications relates to the handover of user equipment (UE) from a serving cell to a neighboring target cell and the optimization of the parameters controlling the handover. In this technical field SON (self optimizing networks) and in particular MRO (mobility robustness optimization) triggered by dual threshold measurement events consisting of two dedicated thresholds which have to be fulfilled are a main target. Such a dual threshold if for instance used for inter-RAT mobility (event B2 in LTE or 3A in UMTS), i.e. handover between different radio access technologies (RATs). In this technical field also intra-RAT mobility triggered by dual threshold measurement events (e.g. A5 in LTE) are of interest.

The target of MRO is to optimize those network configuration parameters (e.g. handover (HO) trigger parameters, HO thresholds or timers) such that radio link failures (RLF) due to handover are reduced. In order to make the right decision in terms of parameter optimization detailed root cause information is needed. Traditionally, the optimization of network configuration parameters in 2G or 3G networks is based on labor- and cost-intensive drive testing. For the first roll-out, network-wide default configuration parameters are used and if performance management (PM) counters are accumulating RLFs or even call drops in certain service areas, several optimization loops with drive testing are started to adapt parameters in a cell-specific manner.

The high costs and the huge effort are the reason for operator's demand for SON mechanisms where cell-specific parameters are autonomously optimized.

There are handovers which are triggered by a measurement event consisting of two thresholds which have to be mutually fulfilled, one belonging or being associated to serving cell of RAT A and one belonging to the neighboring or overlaying cell of RAT B. In case of LTE, there is, for instance, the inter-RAT trigger event B2 that is used to determine the point in time of a handover and that is defined as follows:

Inter-RAT trigger event B2:

Serving becomes worse than B2threshoid i ; and

Inter-RAT neighbor becomes better than B2_threshoi_d 2-

The corresponding inter-RAT measurement event on UMTS side triggering an inter-RAT HO is called 3A. In the LTE the MRO algorithm basically consists of a root cause analysis phase where cell or cell-pair specific KPI statistics are generated and a correction phase where values of the inter-RAT HO trigger parameters are adjusted. The HO problems normally result from bad timing, i.e. the handovers are either initiated too early or too late. For an inter-RAT handover two thresholds have to be simultaneously fulfilled. In case of LTE B2_threshoi_d ι (B2-1 ) is compared against the signal strength/quality of the own serving cell (Ms) and

B2_threshoid 2 (B2-2) is compared against the signal strength/quality of a neighboring cell of different RAT (Mn) and the handover is triggered if Ms < B2-1 AND Mn > B2-2.

That is, a handover is triggered in case the signal strength of the serving

communication link becomes worse than a threshold related to the serving signal and at the same time the signal strength of a neighboring communication link becomes better than a second threshold related to the neighbor signal, i.e. both criteria are fulfilled. The neighboring communication link may be a communication link connecting or belonging to a neighboring cell in a cellular network and/or a communication link which may relate to another mobile standard.

The measurement event B2 is typically not reported immediately but after a certain time interval TTT (time to trigger) where both conditions have to be fulfilled in order to make the decision more reliable. In particular, once the two conditions are met a timer is started (with a set time value) known as the time to trigger. This timer is used to check that, during this time, the two conditions are still met, thus ensuring that a handover decision is correct and can proceed and avoiding a ping pong effect.

Handover problems which might even cause radio link failures (RLFs) may occur in case the thresholds used have an inappropriate value. 3GPP has specified three categories of handover problems afflicted with a RLF:

a) Failures due to too late HO triggering b) Failures due to too early HO triggering c) Failures due to HO to a wrong cell In case of LTE inter-RAT mobility, as used here exemplarily, the reason for a too late HO can either be a too low threshold B2-1 or a too high threshold B2-2. This is schematically illustrated by Fig. 3 which shows this case for a too low B2-1 . In particular, Fig. 3A shows the signal strength of a communication signal over time for three communication links 301 , 302 and 303, wherein the graph corresponding to the first communication link 301 represents the serving communication path

(Ms), i.e. the communication link used for transmitting payload data. The second graph 302 represents the signal strength for the same user equipment but for a neighboring cell (Mn). The third graph 303 represents a further channel or communication link provided by the serving cell or base station of the service cell. The further or alternative channel may relate to a different mobile standard, for example. Additionally, the serving cell related threshold B2-1 and the neighbor cell related threshold B2-2 are indicated by the dotted lines 304 and 305, respectively. Furthermore, a rhomb 306 is used to indicate the point in time at which the time to trigger (TTT) period, which is schematically indicated by arrow 307, would run out after reaching the condition B2, i.e. Mn is higher than the threshold B2-2 and Ms is lower than the threshold B2-1 .

The UE is getting out-of-sync when signal quality (SINR) falls below a certain threshold Q_out- This is schematically depicted in Fig. 3B showing the SINR level 310 of the serving communication link and the SINR level 31 1 of the neighboring communication link. Additionally, the point in time of the occurrence of a radio link failure (RLF) is indicated by rhomb 312 in Fig. 3B which occurs in a specified time interval (T_Qout) after the SINR fell below threshold Q_out and is indicated by the arrow 313. Furthermore, Fig. 3C schematically illustrates the reconnection to a different RAT2 after losing the connection with RATI , which serves the communication during the beginning of the shown time period. RAT2 serves the communication during the end of the shown time period, i.e. after the reconnection. Between the two periods a period 320 is schematically indicated which is needed to recover the

communication after a radio link failure (RLF).

As described above, Fig. 3 shows a RLF due to a too low B2-1 . The RLF occurs before B2-1 has been fulfilled. The signal of the neighboring cell Mn is above threshold B2-2 already for a long time and therefore the missing B2 trigger event results obviously from too low B2-1 . However, as already mentioned, the reason for a too late inter-RAT HO could be also a too high B2-2, i.e. the second threshold was not fulfilled, while Ms has already exceeded B2-1 threshold. In case that one of the thresholds was fulfilled and the other not the root cause analysis and the subsequent correction is rather straightforward. That threshold which did not fulfill the criterion has to be adapted. In the example of Fig. 3 the threshold B2-1 has to be increased. Typically, SON algorithms are based on KPI statistics and do not react

immediately, i.e. the counter for this specific KPI indicating for instance that B2-1 is too low and has to be increased, is incremented.

Summary of the Invention

There may be a need to establish a mechanism for determining and/or transmitting information elements which may be used in a communication network in order to enable a reduction of handover failures.

This need may be met by a network element, a user equipment, a method of determining a threshold in a communication network, a method of operating the communication network, a protocol usable for performing communication in a communication network, a program element, and a computer readable medium according to the independent claims. Further embodiments are described in the dependent claims.

According to an exemplary aspect there is provided a network element for a communication network, wherein the network element comprises a receiving unit and a processing unit, wherein the receiving unit is adapted to receive a data signal including an information element indicative of a determined value of a parameter wherein the value of the parameter is indicative for a gradient of the signal strength of a communication signal in the communication network. Furthermore, the processing unit is adapted to determine a threshold or threshold value based on the received information element.

In particular, the processing unit may be adapted to determine the threshold or threshold value based directly on the information element. For example, the processing unit may be adapted to calculate or estimate a new threshold value or threshold level from the information element. Alternatively or additionally, the processing unit may be adapted to determine the threshold or threshold value in an indirect way, e.g. by using a counter for each specific information element and in case the a specific counter reaches or exceeds a specific number an event may be triggered which calculates, determines, defines or establish a new threshold or threshold value. That is, the term "determine a threshold or threshold value" may particularly denote that a value or data is determined which may be the threshold value itself or which may be used to afterwards determine or establish a threshold or threshold value, e.g. by using the information element to determine specific KPIs which may be fed to a MRO algorithm leading finally to an adaptation of the corresponding threshold. Thus, the term "determine" includes direct determining as well as indirect determining.

In particular, the network element may be a base station, a NodeB, an enhanced NodeB, a relay node, a pico station or the like. In particular, the information element may be a time stamp indicative for a point in time at which a

predetermined criterion is fulfilled and/or for a time interval indicative for a time difference between a point in time at which a radio link failure occurs and a point in time a predetermined threshold is reached. Furthermore, the network element may optionally be adapted to send a request message for requesting the data signal including the information element. Optionally, the processing unit may also be adapted to evaluate whether a predetermined criterion is fulfilled based on and/or with respect to the information element. In particular, the information element may be forwarded by another network element, base station, relay node or a user equipment. For example, the information element may be a result of a root cause analysis, may correspond to a directly measured value or may correspond to a pre-processed directly measured value, or the like. For example, the root cause analysis process may be one established in the network, e.g. according to a specific standard.

For example, the threshold value may be associated with a handover procedure in the communication network. In particular, the threshold value may correspond to a serving related threshold value, wherein a handover may be initiated in case the measured signal strength of a communication signal to and/or from a serving base station falls below the serving related threshold value. Additionally or alternatively the threshold value may correspond to a threshold value related to another serving, e.g. serving cell or serving channel, wherein a handover may only be initiated in case a measured signal strength of a communication signal to and/or from a neighbouring base station exceeds another respective threshold value.

According to an exemplary aspect there is provided a user equipment for a communication network, wherein the user equipment comprises a determining unit and a sending unit, wherein the determining unit is adapted to determine a value of a parameter wherein the value of the parameter is indicative for a gradient of a signal strength of a communication signal in the communication network.

Furthermore, the sending unit is adapted to send a data signal including an information element indicative of the determined value of the parameter.

In particular, the gradient may be indicative for a temporally and/or locally development of the signal strength of a communication signal transmitted in the communication network. In particular, the signal strength itself or a parameter which is indicative of the signal strength may be measured over time and/or versus location or position, e.g. by a measuring unit of the user equipment. The signal of which the signal strength is measured may be a specific data portion or data block of a data signal specifically designed to be indicative of the signal strength and/or performance of the respective communication link the signal is transmitted, e.g. a pilot signal and/or a reference signal. Alternatively or additionally, the signal may relate to payload data.

In particular, the user equipment may be adapted to receive a request message relating to the information or requesting for sending the sent information. For example, the user equipment may receive the request message from a network element, e.g. base station, NodeB, enhanced NodeB, a relay node or the like. The user equipment may respond to this request message by sending the requested information, e.g. a time stamp, indicative for a time period between the reaching of a threshold value or threshold level and an occurred RLF. However, the user equipment may as well be adapted to send the data signal including the

information without receiving a request, i.e. in an autonomous way.

According to an exemplary aspect a communication network, e.g. a radio communication network or mobile communication network may be provided which comprises a network element according to an exemplary aspect and a user equipment according to an exemplary aspect.

According to an exemplary aspect of the invention a method of determining a threshold in a communication network is provided, wherein the method comprises receiving a data signal including an information element indicative of a determined value of a parameter wherein the value of the parameter is indicative for a gradient of a signal strength of a communication signal in the communication network, and determining a threshold or threshold value based on the received information element.

In particular, the determining of the threshold may directly be based on the information element or may be indirectly based on the information element as described above.

According to an exemplary aspect of the invention a method of controlling a communication in a communication network is provided, wherein the method comprises determining a value of a parameter wherein the value of the parameter is indicative for a gradient of a signal strength of a communication signal in the communication network, and sending a data signal including an information element indicative of the determined value of the parameter.

According to an exemplary aspect of the invention a communication protocol for a communication network is provided, wherein the communication protocol is adapted to support a message format including an information element indicative of a determined value of a parameter wherein the value of the parameter is indicative for a gradient of a signal strength of a communication signal in the communication network.

In particular, a user equipment and/or a network element may be adapted to implement the communication protocol. One adaptation of the UE may be that it can provide a time interval measurement and/or that it is configured to receive and send standardized signaling messages to carry out these measurements.

According to an exemplary aspect of the invention a program element is provided, which, when being executed by a processor, is adapted to control or carry out a method according to an exemplary aspect of the invention.

According to an exemplary aspect of the invention a computer-readable medium is provided, in which a computer program is stored which, when being executed by a processor, is adapted to control or carry out a method according to an exemplary aspect of the invention.

A gist of an exemplary aspect may be seen in providing information elements which are indicative of a gradient of a signal strength of a communication signal in the communication network. For example such a gradient may relate to a temporally and/or locally development of the signal strength. Therefore, the temporally development of a signal strength may be taken into account, for example, when adjusting threshold levels in a communication network. In particular, such gradients may provide additional information compared to the measured signal strengths of communication signals which may be useful for increasing the performance of a communication network, e.g. reducing radio link failures. Due to this additional information an adjusting of the thresholds may be improved or simplified.

In particular, it may be possible to avoid too late handover in case the signal strength of one signal, e.g. the signal relating to the serving communication link or channel, drops quite fast or has a steep gradient, while the other signal, e.g. the signal relating to a neighboring communication link, has a quite small gradient, e.g. raises quite slowly. In this case known methods depending on the signal strength only may decide that the threshold which has been less exceeded (i.e. signal with small gradient) is responsible for the failure and, therefore, leads to wrong direct or indirect determination of the threshold, e.g. by inducing wrong KPI counts which may finally lead to wrong threshold modifications.

Next further exemplary embodiments of the network element are described.

However, the embodiments also apply to the user equipment, the method of determining a threshold value in a communication network, the method of operating the communication network, the protocol usable for performing communication in a communication network, the program element, and the computer readable medium.

According to an exemplary embodiment of the network element the determination of the threshold or threshold value is based on the received information element and a further received information element.

For example, the received information element, e.g. a first information element and the further received information element, e.g. a second information element, may be received from a user equipment of the communication network. Both

information elements may be included or may be part of the same data signal received by the network element or may be part of different data signals. In case both information elements are provided from the same user equipment the first information element may relate to a first communication link while the second information may relate to a second communication link. According to an exemplary embodiment of the network element the received information element relates to a first communication link of the communication network and the further received information element relates to a second communication link of the communication network. For example, the first communication link and the second communication link may relate to communication links between the user equipment and different serving base stations, relay nodes or the like, e.g. relate to different cells of a cellular communication network. Additionally or alternatively, both communication links may relate to a communication between the user equipment and only one base station, relay node or the like (i.e. the same cell), but the communication links may relate to different standards, e.g. UMTS, LTE, GSM or the like. Thus, the two communication links may provide alternative communication paths for the user equipment. According to an exemplary embodiment of the network element the determination of the threshold comprises performing a root cause analysis and generating a value for a specific Key Performance Indicator based on the received information element.

In particular, the root cause analysis may be an MRO root cause analysis. For example, the information element may be used to refine the MRO root cause analysis by generating or modifying a specific KPI value. Furthermore, the network element may be adapted to adapt or modify the threshold or threshold value based on a reached specific KPI value.

In particular, a root cause analysis may include or may result in determining specific KPIs. Based on the statistical analysis of the KPIs, the MRO algorithm may adapt the specific threshold in order to reduce the probability of a handover failure or radio link failure.

According to an exemplary embodiment of the network element the generated Key Performance Indicator value is indicative for one of the thresholds of a dual threshold measurement event.

According to an exemplary embodiment of the network element the root cause analysis is a part of an MRO algorithm. Furthermore, the network element is adapted to exchange information to determine a network element responsible for the failure and is further adapted to determine a corresponding Key Performance Indicator (KPI). Furthermore, the network element may optionally be adapted to decide which threshold of a plurality of thresholds is modified, wherein the deciding may be based or may depend on a statistical analysis of the Key Performance Indicator values or Key Performance Indicator.

In particular, the network element may be adapted to exchange information with other network elements, e.g. base stations, in the communication network, which exchanged information may then be used to determine the network element responsible for the failure.

In particular, the MRO algorithm may be adapted to perform the decision which threshold is modified. According to an exemplary embodiment of the network element the network element is further adapted to decide which threshold of a plurality of threshold is determined.

In particular, the determination may include the decision which of several thresholds is modified or changed in order to achieve a more stable

communication link or a handover procedure which is less prone to radio link failures due to a late handover.

For example one or more threshold value(s) may be adapted or modified based on the information element indicative of a gradient of a signal strength. In particular, the use of a gradient of a signal strength, e.g. a temporally development of a signal strength, may be advantageous compared to the use of the sole or pure signal strengths itself.

In particular, the network element may be adapted to transmit the determined threshold value to a user equipment. Additionally, the network element may optionally be adapted to transmit a request message to the user equipment. Next further exemplary embodiments of the user equipment are described.

However, the embodiments also apply to the network element, the method of determining a threshold value in a communication network, the method of operating the communication network, the protocol usable for performing communication in a communication network, the program element, and the computer readable medium.

According to an exemplary embodiment the user equipment further comprises a processing unit, wherein the processing unit is adapted to evaluate whether a predetermined criterion for the determined parameter is fulfilled.

In particular, a first predetermined criterion may indicate or may relate to the question whether a measured value equals and/or exceeds a corresponding predetermined threshold. A second predetermined criterion may indicate or may relate to the question whether a measured value equals or is lower than a corresponding threshold.

For example, the processing unit may be adapted in such a way that it determines or evaluates whether the measured signal value is equal or higher than an upper predetermined threshold in which case a first predetermined criterion may be considered to be fulfilled. At the same time the processing unit may be adapted in such a way that it determines or evaluates whether another measured signal value is equal or lower than a lower predetermined threshold, in which case a second predetermined criterion may be considered to be fulfilled.

Thus, the processing unit may be adapted to perform a processing of the measured value. For example, the processing unit may be adapted to calculate a time difference or time period between a first point in time and a second point in time. Additionally, the user equipment, e.g. the processing unit, may comprise a modulation unit and/or scheduler adapted to include the information element into the data signal to be sent by the user equipment. In this case the information element included in the data signal may be a time stamp or a

measured/determined point in time or time interval, for example.

For example, the determining unit and the processing unit may be formed by a single processor, CPU or computer or may be formed by separate elements or units. According to an exemplary embodiment of the user equipment the determined parameter is time.

In particular, the determined parameter may be a time period between a point in time at which the signal strength fulfils a predetermined criterion, e.g. reaches a threshold value, and a further, e.g. subsequent, point in time at which a radio link failure (RLF) occurs. That is, the parameter may be associated with a time period. For example, signal strength of a communication signal or on a communication link may be measured over time, i.e. an n-tuple or matrix including signal strengths and the corresponding times may be measured or determined. However, alternatively or additionally the measured parameter may be already the measured time of the RLF and/or the point in time at which the predetermined criterion may be fulfilled the first or the last time, e.g. the predetermined threshold is reached.

Thus, the predetermined criterion may relate to the reaching of a predetermined threshold and may be, in the case of a lower threshold or limit, relate to the point in time at which the signal strength falls below the predetermined lower threshold. In case of an upper threshold the criterion may relate to the point in time at which the signal strength exceeds the predetermined upper threshold.

Thus, in the present context the term "reaching" may denote the point in time at which the signal strength is equal or substantially equal to the predetermined threshold. In particular, it may depend on the application and/or the threshold whether the predetermined threshold is reached when the measured value reaches the predetermined threshold from below (exceeding the threshold), e.g. an upper limit, or reaches a predetermined threshold from above (falling below), e.g. a lower limit. According to an exemplary embodiment of the user equipment the information element is a time stamp.

In particular, the sent information element may be a time stamp corresponding or being indicative for the point in time when the predetermined criterion is fulfilled. For example, the information element may relate or indicate the point in time at which a predetermined criterion is fulfilled, e.g. a signal strength of a communication signal exceeds or falls below an upper threshold and/or a lower threshold. In particular, the time stamp may relate to the point in time at which a measured signal strength reaches, e.g. from above or below, a threshold the last time before a radio link failure occurs. Alternatively the time stamp may already be indicative of a time interval or time period between a point in time a threshold is reached and a subsequent radio link failure.

Such a time stamp may be indicative of a temporally development of a signal strength, i.e. a temporally gradient. In particular, in case the time stamp is associated with the time period between a reaching of a predetermined threshold and the occurring of a radio link failure, i.e. specifies a length of time, this time period may be indicative of the speed of changing of the signal strength, because it may be assumed that the signal strength changes faster or steeper in case the time period between reaching the threshold and occurring of the RLF is shorter.

Next further exemplary embodiments of the method of determining a threshold value in a communication network are described. However, the embodiments also apply to the network element, the user equipment, the method of operating the communication network, the protocol usable for performing communication in a communication network, the program element, and the computer readable medium.

According to an exemplary embodiment of the method of determining a threshold the information element is a time stamp indicative for a time period between the point in time at which the signal strength reaches a predetermined threshold value and the occurrence of a radio link failure.

According to an exemplary embodiment the method of determining a threshold further comprises receiving a further information element which is a further time stamp indicative for a further time period between the point in time at which a signal strength reaches a further predetermined threshold value and the occurrence of the radio link failure.

In particular, the further time period or second time period may relate or may be associated with the signal strength of another signal reaches a further threshold level. For example, the time period (first time period) may relate to a first communication link while the further or second time period may relate to another communication link of the same user equipment. Thus, the first time period or time interval and the second time period or time interval may be associated with different thresholds, e.g. one may be an upper threshold and one may be a lower threshold.

The further or second information element may be part of the same data signal or may be included in the same data signal.

According to an exemplary embodiment the method of determining a threshold further comprises determining which of the predetermined threshold and the further predetermined threshold is modified based on a comparison of the time stamp and the further time stamp.

In particular, a misconfigured threshold of a plurality of thresholds, e.g. the predetermined threshold and the further predetermined threshold, may be determined based on the comparison of the time stamp and the further time stamp. Such a misconfigured threshold may cause problems, e.g. causing RLFs, and may be modified or adapted after it is detected.

In particular, the smaller time stamp, i.e. the time stamp indicating the shorter time period, may be used to determine the specific threshold whose value is changed. That is, the predetermined threshold may be modified which corresponds to the smaller time stamp. For example, the time stamp is used to indirectly determine the specific threshold, e.g. by using the time stamps or a corresponding KPI value or statistic during a MRO algorithm. For example in case the time stamp

corresponding to the lower threshold, i.e. the threshold belonging or to be considered to the signal of the serving communication link, indicates a smaller time period, the lower threshold is increased. While in case the time stamp

corresponding to the upper threshold, i.e. the threshold belonging to the

neighboring communication link, indicates a smaller time period, the upper threshold is decreased. According to an exemplary embodiment the method, further comprises generating a specific KPI indicating the adaptation of the specific threshold and incrementing its corresponding counter for statistical analysis.

Summarizing, an idea of an exemplary specific embodiment may be seen in providing a mechanism for determining or modifying threshold levels, directly or indirectly, for a handover in a mobile or radio communication network. In particular, the mechanism takes into account the gradient of the signal change.

According to this exemplary embodiment an approach is proposed where a problematic threshold potentially causing the problem is determined by the comparison of a first time interval or time period Δίι and a second time interval Δί_2. The first time interval Δίι may correspond to a time interval passed between the point in time at which the signal level of the serving communication link reaches (e.g. falling below) the lower threshold T_B2-i and the time of occurrence of the RLF TRLF- The second time interval Δί₂ may correspond to a time interval passed between the point in time at which the signal level of the neighboring

communication link reaches (e.g. exceeds) the upper threshold T_B2-2 and the time of occurrence of the RLF T_RLF- That is, the UE may measure the following two time intervals:

Δίι = TRLF - T_B2-1

ΔΪ2 = TRLF - T_B2-2

The critical threshold is detected by the shorter time interval. Therefore a potential algorithm for determining which threshold should be adapted may be described by the following pseudocode:

IF (A ) < (Δί₂) THEN increment KPI "B2-1 too low"

ELSE IF (Δίι ) > (Δί₂) THEN increment KPI "B2-2 too high"

ELSE increment both KPIs "B2-1 too low" AND "B2-2 too high"

ENDIF

In particular, this approach or algorithm may not fail or at least may be less prone to failure if two measured signals, i.e. the signal strength of the serving link (Ms) and the signal strength of the neighboring link (Mn), change with different gradients, i.e. if for instance the signal strength of one signal (e.g. Ms) drops quite fast while the other signal (Mn) is slightly above the threshold since rather long time. For example, a method according to an exemplary embodiment may be part of the MRO SON feature and may require specific measurement configuration messages to the UE.

It has to be pointed out that of course any combination of features relating to different aspects of the herein disclosed subject matter is also possible. In particular, some embodiments have been described with reference to apparatus type claims whereas other embodiments have been described with reference to method type claims. However, a person skilled in the art will gather from the above and the following description that, unless other notified, in addition to any combination of features belonging to one aspect also any combination between features relating to different aspects or embodiments, for example even between features of the apparatus type claims and features of the method type claims is considered to be disclosed with this application. The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

Brief Description of the Drawings

Fig. 1 schematically shows a temporally course of signal strengths. Fig. 2 schematically shows another temporally course of signal strengths.

Fig. 3 schematically shows another temporally course of signal strengths. Fig. 4 schematically shows a communication network in which a network element according to an exemplary embodiment can be used.

Fig. 5 schematically shows a network element according to an exemplary embodiment.

Fig. 6 schematically shows a user equipment according to an exemplary embodiment. Detailed Description

The illustration in the drawings is schematic. It is noted that in different figures, similar or identical elements are provided with the same reference signs or with reference signs, which are different from the corresponding reference signs only within the first digit.

Fig. 1 schematically and exemplarily for the inter-RAT situation depicts time intervals which may have to be measured or determined by a user equipment in order to enable a threshold adjusting mechanism according to an exemplary embodiment. In particular, Fig. 1 A shows the signal strength of a communication signal over time for three communication links 101 , 102 and 103, wherein the graph corresponding to the first communication link 101 represents the serving communication path (Ms), i.e. the communication link used for transmitting payload data. The second graph 102 represents the signal strength for the same user equipment but for a neighboring cell (Mn). The third graph 103 represents a further channel or communication link provided by the serving cell or base station of the service cell. The further or alternative channel may relate to a different mobile standard, for example. Additionally, the serving cell related threshold B2-1 and the neighbor cell related threshold B2-2 are indicated by the dotted lines 104 and 105, respectively.

Furthermore, a rhomb 106 is used to indicate the point in time at which the time to trigger (TTT) period, which is schematically indicated by arrow 107, would run out after reaching the condition B2, i.e. that Mn is higher than the threshold B2-2 and Ms is lower than the threshold B2-1 . Furthermore, an arrow 108 is shown in Fig. 1 A corresponding to a time interval or time period At₂ corresponding to the time period between the point in time the signal Mn exceeds the threshold B2-2 and the occurrence of the radio link failure. Arrow 109 corresponds to a time interval or time period A corresponding to the time period between the point in time the signal Ms exceeds the threshold B2-2 and the occurrence of a RLF. It should be noted that the time periods or time intervals A and At₂ may

advantageously be defined by the threshold exceeding or underrun which is the one which occurred immediately before the radio link failure. That is, in case one of the two thresholds is several times reached by the respective signal (Ms or Mn) the time intervals are advantageously defined by the one which is the last one before the RLF. According to the example shown in Fig. Ι Α Δί-ι is lower than At₂. Radio link Failure (RLF) typically happens when signal quality (SINR) falls below a certain threshold Q_out- This is schematically depicted in Fig. 1 B showing the SINR level 1 10 of the serving communication link and the SINR level 1 1 1 of the neighboring communication link. Additionally, the point in time of a radio link failure is indicated by rhomb 1 12 in Fig. 1 B which RLP occurred some time (t_Qout) after the SINR fell below threshold Q_out which is indicated by the arrow 1 13.

Furthermore, Fig. 1 C schematically illustrates reconnection to a different RAT2 after losing the connection with RATI , which serves the communication during the beginning of the shown time period. RAT2 serves the communication during the end of the shown time period, i.e. after the reconnection. Between the two periods a period 120 is schematically indicated which is needed to recover the

communication after a radio link failure (RLF).

A key feature of an exemplary embodiment may be that the UE measures the time between fulfilling trigger conditions such as B2 condition 1 or 2 (or A5 condition 1 or 2), and an occurring RLF. This can be done via time stamps, or via directly measuring At. Furthermore, the UE may report this information element to a network element of a communication network, e.g. a base station BS. For instance, it can attach this info to the RLF report which already has been specified in 3GPP Release 9/10.

The critical threshold may be detected by the shorter time interval of Δίι and Δί₂. Therefore a potential algorithm for determining which threshold should be adapted may be written in pseudocode as following:

IF (Δίι) < (Δί₂) THEN increment KPI "B2-1 too low"

ELSE IF (A ) > (Δί₂) THEN increment KPI "B2-2 too high"

ELSE increment both KPIs "B2-1 too low" AND "B2-2 too high"

ENDIF

This approach may require slightly more complexity in terms of time stamp measurement on UE side, but may be more efficient in terms of determining the appropriate threshold (B2-2 or B2-1 ) which should be modified in order to reduce the probability of a too late handover.

In particular, a pure level based approach without this time information may make a wrong decision and mislead the MRO algorithm. A scenario in which a pure level based approach may lead to wrong decisions is schematically depicted in Fig. 2 which is in principle the same as the one shown in Fig. 1 .

In particular, Fig. 2A shows the signal strength of a communication signal over time for three communication links 201 , 202 and 203, wherein the graph

corresponding to the first communication link 201 represents the serving

communication path (Ms), i.e. the communication link used for transmitting payload data. The second graph 202 represents the signal strength for the same user equipment but for a neighboring cell (Mn). The third graph 203 represents a further channel or communication link provided by the serving cell or base station of the service cell. The further or alternative channel may relate to a different mobile standard, for example.

Additionally, the serving cell related threshold B2-1 and the neighbor cell related threshold B2-2 are indicated by the dotted lines 204 and 205, respectively.

Furthermore, a rhomb 206 is used to indicate the point in time at which the time to trigger (TTT) period, which is schematically indicated by arrow 207, would run out after reaching the condition B2, i.e. that Mn is higher than the threshold B2-2 and Ms is lower than the threshold B2-1 .

Furthermore, in Fig. 2A a determined difference (Mn - B2-2) between the measured signal strength Mn and the threshold B2-2 is indicated by arrow 208. Additionally, in Fig. 2A a determined difference (B2-1 - Ms) between the measured signal strength Ms and the threshold B2-1 is indicated by arrow 209. In particular, according to Fig. 2A B2-1 - Ms > Mn - B2-2.

Radio link Failure (RLF) typically happens when signal quality (SINR) falls below a certain threshold Q_out- This is schematically depicted in Fig. 2B showing the SINR level 210 of the serving communication link and the SINR level 21 1 of the neighboring communication link. Additionally, the point in time of a radio link failure is indicated by rhomb 212 in Fig. 2B which RLP occurred some time (t_Qout) after the SINR fell below threshold Q_out which is indicated by the arrow 213. Furthermore, Fig. 2C schematically illustrates the reconnection to a different RAT2 after losing the connection with RATI , which serves the communication during the beginning of the shown time period. RAT2 serves the communication during the end of the shown time period, i.e. after the reconnection. Between the two periods a period 220 is schematically indicated which is needed to recover the

communication after a radio link failure (RLF).

According to the pure level based approach it would be proposed to adapt that threshold where the difference between measurement and threshold is smaller. The corresponding algorithm is given below in pseudocode: IF (B2-1 - Ms) < (Mn - B2-2) THEN increment KPI "B2-1 too low" ELSE IF (B2-1 - Ms) > (Mn - B2-2) THEN increment KPI "B2-2 too high"

ELSE increment both KPIs "B2-1 too low" AND "B2-2 too high"

ENDIF

According to this pure level base approach simply already existing measurements can be used. The thresholds are known (provided by measurements configuration messages) and the current signal measurements (Ms and Mn) when RLF occurred are provided to UE with the RLF report.

But a problem of this pure level base approach may be that this level based approach fails if the two measured signals change with different gradients, i.e. if for instance the signal strength of one signal (e.g. Ms) drops quite fast while the other signal (Mn) is slightly above the threshold since rather long time (see Fig. 2). The algorithm would propose to decrease threshold B2-2 even though that criterion was fulfilled already all the time. Lowering the B2-2 would not change the situation for this problem case. In contrast, it would probably lead to too early HO problem in other areas of the corresponding cell. Thus, in order to overcome the problem associated with the pure level base approach according to an exemplary embodiment of the invention a gradient of the measured signal strengths Ms and Mn may be taken into account when deciding which threshold is changed. In particular, the decision may be based only indirectly on the measured signal strengths, e.g. by using the signal strengths and

information elements derived from these signal strengths which are then used for determining a KPI value, e.g. by upcounting a respective counter, in the course of a MRO algorithm.

In particular, according to an exemplary embodiment takes into account the gradient of a signal change, e.g. the rate at which the signal strength changes, A user equipment, e.g. a mobile phone, may measure the time between fulfilling trigger conditions for handover, e.g. a serving signal strength is below a lower threshold while a neighboring signal strength is above an upper threshold, and an occurring RLF either by using time stamps or by directly measuring a time change. The trigger condition which is associated with the shorter time interval may then be adjusted, either by increasing or decreasing the appropriate threshold. In this way a future too late or too early handover may be avoidable.

Fig. 4 schematically shows a communication network or communication system

400 in which a network element or a user equipment according to an exemplary embodiment may be used. In particular, Fig. 4 shows four network elements, e.g. base stations 401 , 402, 403, and 404. Additionally, five user equipments 405, 406, 407, 408, and 409 are schematically depicted in Fig. 4. Furthermore, two serving cells 410 and 41 1 are indicated by the respective dotted lines. The base stations

401 to 404 may be adapted to perform a method of determining a threshold in a communication network according to an exemplary embodiment, while the user equipments 405, 406, 407, 408, and 409 may be adapted to perform a method of controlling a communication in a communication network according to an exemplary embodiment. For example, the user equipments may be adapted to perform a measurement or determination of a value of a parameter wherein the value of the parameter is indicative for a gradient of a signal strength of a communication signal in the communication network. In particular, the two user equipments 408 and 409 may be in the coverage of both of the cells 410 and 41 1 . Thus, the performing of method of controlling communication in a communication network with respect to one of these two user equipments may be advantageous. Fig. 5 schematically shows a network element 500 according to an exemplary embodiment. The network element may be a base station, a relay node, a pico station or the like. In particular, the network element comprises a receiving unit

501 , e.g. an antenna, and a processing unit 502 which may be formed by a computer chip, a CPU or a processor of a computer. The receiving unit is adapted to receive a data signal including an information element indicative of a determined value of a parameter wherein the value of the parameter is indicative for a gradient of a signal strength of a communication signal in the communication network.

Furthermore, the processing unit is adapted to determine a threshold based on the received information element. Fig. 6 schematically shows a user equipment 600, e.g. a mobile phone, a PDA, a laptop or the like, according to an exemplary embodiment. The user equipment 600 for a communication network comprises a determining unit 601 , and a sending unit 602, e.g. an antenna. The determining unit is adapted to determine or measuring a value of a parameter wherein the value of the parameter is indicative for a gradient of a signal strength of a communication signal in the communication network. Furthermore, the sending unit is adapted to send a data signal including an information element indicative of the determined value of the parameter.

It should be noted that the term "comprising" does not exclude other elements or steps and the "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

Further the examples and embodiments should not be construed as limiting the scope of the claims. Further, many variations are possible without leaving the scope of the appended claims.

List of reference signs:

101 serving signal

102 neighboring signal 03 further signal

104 lower threshold

105 upper threshold

106 run out of I I I

107 I I I

108 At₂

109 A

1 10 SINR serving signal

1 1 1 SINR neighboring signal

1 12 radio link failure

1 13 tQout

120 trecovery

201 serving signal

202 neighboring signal

203 further signal

204 lower threshold

105 upper threshold

206 run out of I I I

207 I I I

208 B2-1 - Ms

209 Mn - B2-2

210 SINR serving signal

21 1 SINR neighboring signal

212 radio link failure

213 tQout

220 trecovery

301 serving signal

302 neighboring signal

303 further signal 304 lower threshold

305 upper threshold

306 run out of I I I

307 TTT

310 SINR serving signal

31 1 SINR neighboring signal

312 radio link failure

313 tQout

320 trecovery

400 communication network

401 -404 base stations

405-409 user equipment

41 1 cell

412 cell

500 network element

501 receiving unit

502 processing unit

600 user equipment

601 determining unit

602 sending unit

Claims

CLAIMS:

1 . A network element (402, 403, 404, 405; 500) for a communication network (400), the network element (402, 403, 404, 405; 500) comprising: a receiving unit (501 ); and a processing unit (502), wherein the receiving unit (501 ) is adapted to receive a data signal including an information element indicative of a determined value of a parameter wherein the value of the parameter is indicative for a gradient of a signal strength of a communication signal in the communication network (400); and wherein the processing unit (502) is adapted to determine a threshold based on the received information element.

2. The network element (402, 403, 404, 405; 500) according to claim 1 , wherein the determination of the threshold is based on the received information element and a further received information element.

3. The network element (402, 403, 404, 405; 500) according to claim 2, wherein the received information element relates to a first communication link of the communication network (400) and the further received information element relates to a second communication link of the communication network (400).

4. The network element (402, 403, 404, 405; 500) according to any one of the claims 1 to 3, wherein the determination of the threshold comprises; performing a root cause analysis and generating a value for a specific Key Performance Indicator based on the received information element.

5. The network element (402, 403, 404, 405; 500) according to claim 4, wherein the generated Key Performance Indicator value is indicative for one of the thresholds of a dual threshold measurement event.

6. The network element (402, 403, 404, 405; 500) according to claim 4 or 5, wherein the root cause analysis is a part of an MRO algorithm, and wherein the network element is adapted to exchange information to determine a network element responsible for the failure and is further adapted to determine a corresponding Key Performance Indicator.

7. A user equipment (405-409; 600) for a communication network (400), the user equipment (405-409; 600) comprising: a determining unit (601 ), and a sending unit(602), wherein the determining unit (601 ) is adapted to determine a value of a parameter wherein the value of the parameter is indicative for a gradient of a signal strength of a communication signal in the communication network (400), and wherein the sending unit (602) is adapted to send a data signal including an information element indicative of the determined value of the parameter.

8. The user equipment (405-409; 600) according to claim 7, wherein the determined parameter is time.

9. The user equipment (405-409; 600) according to claim 7 or 8, wherein the information element is a time stamp.

10. Method of determining a threshold in a communication network (400), the method comprising: receiving a data signal including an information element indicative of a determined value of a parameter wherein the value of the parameter is indicative for a gradient of a signal strength of a communication signal in the communication network (400); and determining a threshold based on the received information element.

1 1 . The method according to claim 10, wherein the information element is a time stamp indicative for a time period between the point in time at which the signal strength reaches a predetermined threshold value and the occurrence of a radio link failure.

12. The method according to claim 1 1 , further comprising: receiving a further information element which is a further time stamp indicative for a further time period between the point in time at which a signal strength reaches a further predetermined threshold value and the occurrence of the radio link failure.

13. The method according to claim 12, further comprising: determining which of the predetermined threshold and the further predetermined threshold is modified based on a comparison of the time stamp and the further time stamp.

14. Method of controlling a communication in a communication network (400), the method comprising: determining a value of a parameter wherein the value of the parameter is indicative for a gradient of a signal strength of a communication signal in the communication network (400), and sending a data signal including an information element indicative of the determined value of the parameter.

15. A communication protocol for a communication network (400), wherein the communication protocol is adapted to support a message format including an information element indicative of a determined value of a parameter wherein the value of the parameter is indicative for a gradient of a signal strength of a communication signal in the communication network (400)