WO2015063626A1

WO2015063626A1 - Methods for handover configuration

Info

Publication number: WO2015063626A1
Application number: PCT/IB2014/064965
Authority: WO
Inventors: Konstantinos Dimou; Yu Yang
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2013-10-28
Filing date: 2014-09-30
Publication date: 2015-05-07
Also published as: EP3063986A1

Abstract

The dynamic determination of a handover trigger for triggering handover of a mobile terminal (300) m a wireless network (50) from a source base station (100) to a target base station. (200) is based on one or more Key Performance Indicators (KPIs). Each KPI indicates a quality of wireless services provided by the wireless network (50) responsive to a particular handover trigger. If an obtained parameter that indirectly or directly impacts handover performance passes a corresponding performance test, the mobile terminal (300) selects the handover trigger based on the KPIs. If the parameter fails the corresponding performance test, the source base station (100) selects the handover trigger based on the KPIs.

Description

METHODS FOR HANDOVER CONFIGURATION

BACKGROUND

During handover of a mobile terminal in a wireless communication netwo k_s control of an ongoing wireless communication session involving the mobile terminal k transferred ftom one network node, e.g., a source base station, to another network node, e.g., a. target base station. Handover is perfornjed as the mobile terminal moves out of the area covered by the source base sta tion and into the area covered by the target base statson.

Wireless networks typically use handover triggers to initiate or trigger handover oi the mobile terminal from the source base station to the target base station. Both sinndation results and field trials show that the optimal handover trigger substantially reduces the handover failure rale and improves system and service performance. Thus, overall performance of the wireless communication network relies on the careful choice of the handover tr.iggerls). This is particularly true for handover triggers associated witfe macro or pko cells, and for networks associated with different access technologies and/or standards (e.g., heterogeneous networks, which may include macro and pko cells), where the wrong handover trigger cause more pronounced problems than in homogeneous networks.

SUMMARY

The solution disclosed herein dynamically determines handover trigger for triggering handover of a mobile terminal m a wireless network from a source as station to target base st tion based oa one or more Key Performance Indicators

( -Pis). Each P! indicates a quality of wireless services provided by the wireless network responsive to a particular handover trigger. If an obtained parameter that indirectly or directly impacts handover performance passes a corresponding

performance test, the mobile terminal selects ^'the ^'handover trigger based on the 3*ls. If the parameter Ms the corresponding performance test, the source base station selects the handover trigger based on the f is. Exemplar}' PIs include, but are not limited to, a number of handover failures, a number of ping-pong handovers, a measurement of a time period where the mobile terminal is not in a preferred cell, a number of handover initiations, service performance parameter, a Refe nce Signal Received Power (RSKP), a Signal~pIus~Int ferenee to Noise Ratio (SINK), a Signal~to~Noise Ratio (SNR)_> a handover delay, and a Voice over Internet Protocol (VoIP) performance parameter that results .from or is otherwise . ssoc ated with a. particular handover trigger.

According to on exemplary method executed at a source base station, a first Key Perftnwi ce Indicator (KPI) is obtained for each of a first candidate trigger and a second candidate trigger. Each first KPI indicates, for the corresponding candidate trigger, a quality of wireless services provided by the wireless network to the mobil terminal. The method f¼i er includes obtaining a parameter associated with at least one of die mobile terminal and t he wireless network, wherein the parameter indirectly or directly Impacts handover performance. If the parameter passes a corresponding performance test, ^' the method includes sending the first KPls to the mobile terminal to facilitate a select ion at the mobile termi nal of one of the first and second candidate triggers as the handover trigger based on the first KPls. If the parameter fails the corresponding performance test, the method includes selecting one of the first and second candidate triggers as the handover trigger based on a first comparison between the .first KPls for the first and second candidate triggers.

An exemplary source base station comprises a KPi circuit, a parameter circuit, and a trigger circuit. The KPI circuit is configured to obtain a first KPI for each of a first candidate trigger and a second candidate trigger, wherein each first KPi indicates, for the corresponding candidate trigger, a quality of wireless services provided by the wireless network to the mobile terminal. The parameter circuit is configured to obtain a parameter associated with at least one of the mobile terminal and the wireless network, where the parameter indirectly or directly impacts handover performance. The trigger circuit is configured to send the first KPls to the mobile terminal to facilitate a selection a the mobile terminal of one of the first and second candidate triggers as the handover trigger based, on the first KPls if the parameter passes a corresponding performance test. If the parameter fails the corresponding performance test, the trigger circuit is configured to select one of the first and second candidate triggers as the handover trigger based on a first comparison between the first KPls for the first and second candidate triggers. According to an exemplary method executed at a mobile ^'terminal, a resource control message is received from the source base station. ^'The resource control message includes a first information element compris ng a first KPI for each, of a first candidate trigger and a second candidate trigger. Each first KM indicates, for the corresponding Candidate trigger, a qualify of wireless services provided b the wireless network to the mobile terminal The method further met tides selecting one of the first and second candidate triggers as the handover trigger based on a first comparison between the first PIs for the first, and second candidate triggers received in the resource control message.

An exemplary mobile terminal comprises a receiver and a trigger selection circuit. The receiver is configured to receive a resource control message from he source base station, when a handover performance affectmg parameter associated with at least one of she mobile terminal and the wireless network passes a performance test. The resource control message includes a first information element comprising a first PI for each of a first candidate trigger and a second candidate trigger. Each first KM indicates, for the corresponding candidate trigger, a quality of wireless services provided by the wireless network to the mobile terminal. The trigger selection circuit is configured to select one of the first and second candidate triggers as the handover trigger based on a first comparison between the first f Pls for the first and second candidate triggers received is the resource control message.

BRIEF DESCRiPTION OF THE DRAWINGS

Figure 1 shows a wireless communication network.

Figure 2 shows a method for a source base station, according to one exemplary embodiment.

Figure 3 shows a method for a mobile terminal according to one exemplary embodiment.

Figure 4 shows an. exemplar resource control message.

Figure 5 shows a bloc k diagram of source base station according to one exemplary embodiment.

Figure 6 shows a block diagram of mobile terminal according to one exemplary embodiment. Figure 7 shows a method according to one exemplary embodiment

DETAILED DESCRIPTION

Figure J. shows the mam elements of an exemplary wireless network.50

invol ved in a handover of a mobile terminal 300 from a source base station 100 to a target base station 200. As used herein, wireless network 50 may comprise any network thai provides wireless services according to any known wireless protocol, e.g., Long Term Evolution (LIE), As used herein, the base stations 1.00, 200 may comprise any access point for the mobile terminal 300 within the wireless network 50, e..g., a NodeB, an eNodeS, etc. As used herein, the mobile terminal 300 may comprise an portable/movable device that includes a wireless transceiver for communicating within the wireless network SO, e,g.₅. a cellular telephone, tablet computer, lapto computer, automobile computer, etc. As long as the mobile terminal 300 is within the cell or area covered by the source base station 10 ₅ the source base station 100 controls some or ail communications to and from the mobile terminal 300. As the mobile terminal 300 moves within the network 50. e.c towards the target base station 200, the mobile terminal 300 mo ves out of the coverage area of the source base station 100, As a result, the overall quality of the wireless communications between the source base station 100 and the mobile terminal 300 deteriorates, in such scenarios, handover of the mobile terminal 300 to the target base station 200 prevents the mobile terminal 300 from experiencing a loss of wireless service..

A handover trigger represents one or multiple conditions that, if satisfied, will trigger a handover of a mobile terminal 300 from a source base statio 100 to a target base station 200, Thus, handover triggers facilitate the decision process regarding whether to handover a mobile terminal 300, Depending on the configuration of the wireless network 50, satisfaction of the handover trigger may be sufficient to trigger a handover, or the trigger may represent a subset, of the conditions considered when a handover i$ triggered. For example, a handover nigger may include one or both of a hysteresis value and a time to trigger (TIT) value. n such embodiments, a handover is triggered whe a signal strength measurement (c.g„ SRJP) for a target base station 200 exceeds a signal strength measurement for a source base station 100 by more than, an amount ndic ted by the hysteresis value for longer than a period o time indicat d by the TFT value.

i f handover trigger causes handover to occur more often than necessary- system performance may suffer.. If a h andover trigger causes .handover to occur less. often, than necessary, service performance associated, with individual mobile terminals 300 may suffer. Thus, it is important to choose a handover trigger that carefully balances system performance, service performance, and other wireless parameters, e.g., a desired .handover failure rate. Conventional systems attemp to achieve this balance by using a fixed handover trigger predetermined based on expected network conditions, expected network parameters, desired performance goals, etc. Because the

performance of a handover trigger fluctuates based on various parameters, however, such fixed handover: triggers cannot effectively Or optimally deal with all handover situations. For example, optimal handover triggers, tend- to vary with the source/target cef! size, source target cell load, mobile terminal speed, etc.

Embodiments of the solution disclosed herein determine whether the source base station 100 or mobile terminal 300, depending on the status of one or more variable network parameters, dynamically selects a handover trigger based on one or more Key Performance Indicators KPIs). Each network parameter directly or indirectly impacts handover performance. Exemplary parameters include, but are not. limited to, mobile- terminal speed, cell load, and network type. Each KM indicates a quality of wireless services pr ovided by the wireless network.50 responsi ve to a particular handove trigger. Exemplary KPIs include, but are not limited to:

« a number of handover failures;

* a n umber of ping-pong handovers;

a measurement of a time period where the mobile terminal 300 is not in. a preferred cell;

* a number of handover initiations;

service performance parameters (e.g. , packet delay, packet error rate);

a Reference Signal Received Power (R8RP);

a Signai-p!us-interference to Noise Ratio (SINR);

a Signal-to-Noise Ratio (SNR); 8

* a handover delay (e.g., the time difference between the time instant the handover decision Is made at the serving base station to the time instant the mobile terminal acknowledges receipt of a handover command message); and

» a Voice over Interne Protocol (V IP} performance parameter that results from or is otherwise associated with a particular handover trigger.

These KPIa may he determined by or may he available at the mobile terminal 300, the source base station 100, and/or another network node. By dynamically selecting the handover trigger based on the KPIs at the source base station 100 or mobile terminal 300 depending on the variable network paratneter(s), the handover trigger used to make handover decisions more accurately accounts for the variability of the network parameters. As a mult, the solution presented herein reduces the handover failnre rate, and improves system and service performances..

Figure 2 shows an exemplary method 400, as executed by the source base station 100, for dynamically determining a handover trigger for triggering handover of the mobile terminal 300 from the soisrce base station 100 to the target base station 200, Method 400 includes obtai ning at least one KPI. for eac h of a first candidate trigger and a second candidate trigger (block 410}, and obtaining a parameter associated with the .mobile terminal.300 and/or the wireless network 50. Th obtained KPis may be determined by or may be made available to the mobile terminal 300, the source base station 100, and/or another network node. The obtained parameter comprises a parameter that directly or indirectly impacts handover performance, if the parameter passes a corresponding performance test (block 430), e.g., if the speed of the mobile terminal 300 equals or exceeds a speed threshold., the source base station 1 0 semis the KP!(s) to the mobile terminal 300 (block 440), e.g., as part of a resource control message. The mobile terminal 300 then selects the first or second candidate tri gger based on. the received KPIs. if, however, the parameter fails the corresponding performance test (block 430), e.g. , if the s eed of the mobile terminal 300 is less than the speed threshold, the source base station 100 selects the first or second candidate trigger based on the obtaine KPIs (block 450). For example, source base station 1 0 may compare the KPI(s) obtained for the first and second candidate triggers, and select the first or second candidate trigger bas d on the coreparlsonCs). In this scenario, source base station 1 0 may also inform the mobile terminal 300 of the selected handover trigger.

.Exemplary parameters used for the performance test include, hot are not limited to, the speed of the mob le terminal, cell load, network type, tc. Such parameters may be determined/obtained periodically according to some predetermined rate .

Alternatively, the parameter may be determined/obtained only under certain conditions, e.g., when data is being exchanged between the source base station 100 and the mobile terminal 300. For example, when the source base statio 100 and mobile terminal 300 are exchanging data, Doppfer frequency shifts estimation may be used to determine the speed of the mobile terminal 300. In either case, it will be appreciated that the network 50. e.g., the source base station 100, or the mobile terminal 300, .may determine the parameter It will -further be appreciated mat one or more of he obtained -parameters may be used to determine whether the source base station 100 or the mobile terminal 300 determines the handover trigger.

Figur 3 shows one exemplary method 500 executed at the mobile terminal 300 for selecting the handover trigger. Mobile terminal 300 receives a resource control message, e.g., a Radio Resource Control (RRC) message, from the source base station 100 (block 510). The -resource control message includes any neiwork-defermtned KPi^'s .necessary to enable the mobile terminal 300 to determine the handover trigger. The mobile terminal 300 selects the first or second candidate trigger based on the contents of the resource control message (block 520). More particularly, the mobi le terminal 300 compares the KP!(s) for the first and second candidate triggers, and selects the first or second candidate trigger based on the comparison(s). la one embodiment, the receipt of the resource control message at the mobile terminal 300 serves as an implicit instruction to the mobile terminal 300 to select the handover trigger. In another embodiment, the resource control message includes an explicit insn sction to the mobile terminal 300, e.g., handover selection flag, to select the handover trigger.

The mobile terminal 30 may store the K I(s) received from the source base station 100. if the mobile terminal 300 has multiple ones of the same KPl, e.g., multiple SNRs, the mobile terminal 300 only stores the most recently received Pf(s), or the mobile terminal 300 stores a filtered value taking into account the s ed KP!(s) and the most recently recei ved KPi(s). While not required,, the mo ile terminal 300 may also delete some or all of the stored KPIs once the handover trigger .has been determined, e.g., by the source base station 100 or the mobile terminal 300.

The resource control message used by the source base station 1.00 to provide the KPIs to the mobile terminal 300 comprises one or more information elements (IBs). While not required, the resource control message may comprise a Radio Resource Control (RRC) message as defined by Wideband Code Division Multiple Access (WCDMA) or Long Term Evolution (LTE). The source base station 1.00 may create a new resource control .message or may use an existing resource control message to provide the KPIs to the mobile terminal 300. One information element (IE) in the resource control m ssage comprises KPIs for each of the candidate trisaers. Fisure 4 shows one exemplary resource control message 600 comprisin one or more IBs 610- 040. A first IE 610 (IE #0) includes the KM(s) provided by the source base station 100 to the mobile terminal 300. Exemplary KPIs included in IE #0 610 axe those KPIs obtained by the source base station 1 0 and not already known by the mobile terminal 300, It will be appreciated that some KPIs used by the mobile terminal 300 to determine the handover trigger are determined by the mobile terminal 300, and therefore, are already known by the mobile terminal 300. When necessary, the mobile terminal 300 may convey such KPI(s) to the source base station I0O using another resource control message. While not required, the resource control message 600 may also include one or more additional lEs. For example, the resource control message 600 ma inchtde a mappin table IE 620 (IE #1 ), a liaiKiover trigger algorithm IE 630 (IE 2\ and/or a trigger selection instruction IE 640 (IE #3). The mapping table IE 620 includes one or more mapping tables that map different scenarios associated with different parameters to different handover triggers. The handover trigger algorithm IE 630 includes a sequence of steps to he executed by the mobile terminal 300 to deiermme the handover trigger based on the KPIs, e.g.,, the KPIs in the KPI IE 610, The trigger selection instruction IE 640 comprises an explicit instruction to the mobile terminal 300 to determine the handover trigger.

Table 1 shows one exemplary mapping table that may be included in IE #1 620 whe the mobile terminal 300 is approaching a macro neighbor cell. This mapping table maps the speed of the mobile terminal 300 to a handover trigger depending on the ceil load, where the handover trigger comprises a hysteresis value and a timet to trigger (T T) value. As previously noted, a handover is triggered when a signal strength measurement for a target base station 200 exceeds a signal strength measurement for a source base station .1.00 by more than an amount indicated by the hysteresis value for longer than the time indica ted by tbe TIT value.

Table 1 : Approaching Macro Neighbor {Target} Cell

Table 2 shows one exemplary mapping table thai may be .included in IE #1 620 when the mobile terminal.300 is approaching a pico neighbor cell.

Table I : Approaching Pico Neighbor (Target) Cell

As shown by Tables i and 2, the i her the. serving cell load (as measured in terms of percentage of Physical Resource Block (PRB) utilization), the easier it is io trigger handover. As shown by Table 2, more aggressive thresholds are typically used, when the mobile tsraiinal 300 is approaching a pico neighbor cell I n any event, the source base station. 100 or the mobile terminal. 300 may adjust one or mo e values (or ma default t one or more values) in such a .mapping table based on current Ki¾ to implement handover triggers that better account for the variable network parameters, e,g._s the speed of the mobile terminal

As noted above, the source base station 1.00 or th mobile terminal 300 selects one of the candidate triggers as the handover trigger based on one o more comparisons between the corresponding Pls for each candidate trigger. For exam le, assume ne KPI is obtained for each of two candidate triggers, e.g., KPI _f mi KPI ₉ > In this example, the candidate trigger associated with a better one of KPf._} and KPl when a difference between the KP!s

exceeds a predetermined margin may be selected as the handover trigger, if the source base station .100 selects the handover trigger,, the source base station 100 may transmit an indication of the selected handover trigger to the mobile terminal 300.

Figure 5 shows an. exemplary- source base station 100 for executing the method 400 of Figure 2, The source base station 100 comprises a KPI circuit 1 ID, a trigger selection circuit 120, a transceiver .130, and. a parameter circuit 1 0, KPI circuit 110 is configured to obtain the KPI(s) for each candidate trigger, while the parameter circuit 140 is configured to obtain at least one parameter associated with the mobile terminal 300 and/or the network 50, where the parameter indirectly or directly impacts handover performance. The KPI circuit 1 10 may obtain some or all of the Pl(s) from the mobile terminal 300 via transcei er 130, and/or the KPI circuit 1 10 may obtain some or all of the KM(s) by directly detemtmiag the KPi(s), For example, .the KPI circuit 1 t o may di rectly determine the number of p ing-pon handovers for each of the candidate triggers r n statistics stored in the network 50, or may measure the RSRP associated with each candidate trigger. The data used to determine the Hs ma he stored in the source base station 100, in the mobile terminal 300, or somewhere else in the network. 50.

If the obtained parameter passes, a corresponding performance test, a control message circuit 124 in the trigger selection circuit 120 is configured to generate a resource control message 600, which includes a first mfonnation element 610 comprising the obtained fCFICs), As noted above and shown i figure 4, the generated resource control message 600 may also include one or more additional JEs 620-640. The trigger selection circuit 1 0 then sends the generated resource control message to the mobile terminal 300 via transceiver 130 to facilitate a selection at the mobile terminal 300 of one of the candidate triggers based on comparison between the Pis performed by the mobile terminal 300. Otherwise, the trigger selection circuit 1.20 selects one of the candidate triggers as the handover trigger based -on a comparison between the KPis. As discussed further herein, ^'the trigger selection circuit 120 nmy include a ranking circuit 122 that ranks KPis based on a preferred emphasis. Other elements not explicitly shown in Figure 5 may also be present in the source base station IOC), e.g., a .network interface, memory, signal processing circuitry, etc.

Figure 6 shows an exemplary mobile terminal 300 for executing the -method 500 of Figure 3. Mobile terminal 300 comprises a transcei ver 310, trigger selection circ uit 320, and processor 330, The transceiver 310 receives a resoorce control -message from the source base station 100 when a variable network parameter passes a corresponding performance test . The trigger selection circuit 32 is configured to compare KPis, e.g. , the received- KPis. Based on the results of the

the trigger selection circuit 320 selects one of the candidate triggers. The processor 330 may also be configured to obtain KP!(s), e.g., by directly detetminmg the KPI(s), For example, processor 330 may measure the SRF, SNR, and/or SINR and associat the measured RSRP_? SNR, SINR (or an average or filtered value of multiple measurements) with the current .handover trigger being used by die mobile terminal 300. The mobile terminal 300 ma store the determined Pi(s) for the current handover trigger so that the determined F!(s) may be available to tire mobile terminal 300 for comparison with another like KPl obtained at a later time.

Regardless of whether the source base station 100 or the mobile terminal 300 determines die handover trigger, each candidate trigger may be associated with more than one KPI, and multiple KPis may be used to select the handover trigger . Figure 7 shows an exemplary method 700 where N KPis exist for each of two candidate triggers, e.g., KP.i_XA. for a first candidate trigger and JKPI^ for a second candidate triaster, where n -^~ I M . To determine the

the trigger selection circuit 120, 320 performs one or more KPI comparisons, e.g., b determining a difference between two corresponding R^'.PIs according to:

Equation (I ) uses the absolute value to ensure that tlte difference has a positive value. The trigger selection circuit 1 0, 320 subsequently makes the selection based on the set of KPis associated with the firs difference to exceed a predetermined margin. More part cularly, the trigger selection circuit 120, 320 determines a first ffere ce .DIFI] etween 8 .first pair of KFk (XPl_lA and KPJ )^■ according to

Equation (i), where »™Ι (block 710), and determines if BIf^'f] exceeds a

predetermined margin MARGIN,, (block 720). If DIFP\ > MARGM (Mock 720), the trigger selection circuit 120, 320 selects the better perfonmng candidate trigger, e.g., the candidate trigger associated with the better one of KPI and KPI_ls (block 730).

For example, if KPI , and KPI_W represent a signal-to-nois ratio for the respective candidate triggers, the frigger selection circuit 120, 320 will select the candidate trigger associated with the largest signal -to-noise ratio as the handover trigger when

DIFF, > MARGIN,■ i MFF_t < MARGIN, (block 720), however, the trigger selection circui 120, 320 determines the difference BIFF between the next pai of KPls (block 740), and determines if BIFF, exceeds a second predetermined margin (block 750). if DJFF > MARGIN., (block 650), the trigger selection circuit 120, 320 selects the better performing candidate trigger, e.g., the candidate trigger associated with the better one of KP!_l and .KM^ (block 730). for example, if KFL_A and KPI_W represent a number of handover failures or a handover Mure rate for the respective candidate triggers, the trigger selection circuit 120, 32 will select the candidate trigger associated with the smallest number of handover failures or the smalles handover failure rate as the handover trigger when. DJFF, > MARGIN, . If DJFF≤ MA RGIN, (block 750), however, the trigger selection circuit 120, 320 moves on to the next pair of KPls. This process continues for each pair of KPls until the trigger selection circuit 1,20, 320 finds a pair of KPls having a difference exceeding a predetermined margin, or until the trigger selection circuit 120, 320 determines the difference DiFF for the last pair of KPls (block 760) and determines that DIFF*≤ MARGIN* (block 770). In that scenario, the trigger selection circuit 120, 320 may select a default trigger (block 780) For example, the default handover trigger may comprise a current handover trigger currently used by the mobile terminal 300,

In some embodiments, trigger selection circuit 1 0, 320 executes the KPI comparisons accoatmg to some random order. In other embodiments, the trigger selection circuit 120_f 320 may rank the KPls and sequentially execute the KPI IS

comparisons in the order defined by tie raitfctng. In this erribodimenr, tbe trigger selection circuit 120, 320 may comprise a ranking circuit 122, 322 configured to rank each -pair of KPls based o» a preferred emphasis in descending order. For example, when the handover failure rate has beets determined to be tbe most important parameter, followed, by the stgnai-to-Botse ratio (SNR), and then, the reference signal received power (RSRP), the ranking circuit 122, 322 may rank the pair of handover failure rate KPIs higher than the pair of SNR KPls, which are ranked higher than the pair of SRP KPIs. The trigger sel ection ci rc uit 1.20, 320 then executes the process of Figure 7 according to this ranking, e.g., such that blocks 710 and 720 deal, with the handover failure rate KPls, blocks 740 and 750 deal with the SNR KRI^'s, and blocks 760 and 770 deal with the RSRP KPIs.

While the embodiments a d examples disclosed herein present the solution, in terms of two candidate trigger , any number of candidate tri ggers may be used. For example, one or more KPte may be obtained for each of two or more candidate triggers, where each set of KPIs comprises a KPI corresponding to the same parameter for a different candidate trigger. The trigger selection circuit 120, 320 selects the handover trigger based on a comparison between the KPIs in a set of KP s. in one embodi ment , the comparisons ma comprise simultaneous comparisons of all of the KPls in a set of KPls, e.g., all of the SNR KPls. Alternatively, the comparison may comprise- multiple evaJuatlons c mpansoas of subsets of the set of PIs, e.g., subsets of the SNR KPls.

In some embodiments, the source base station 100 may store the KPls and the corresponding candidate triggers so as to create a database of information regarding the handover performance associated with different triggers. While the information in sach a database may vary torn base station to base sta tion, some or all of tbe database information may be exchanged and/or shared among base stations, e.g., using an X2 or Si interface. Such an exchange of information may be used to assis with initial handover settings and/or for future handover trigger selection.

The solution disclosed herein enables handover performance to be evaluated from a comprehensive viewpoint. The performance can be evaluated automatically, both « t the mobile terminal and at th network, such that the handover trsggeris) may he dynamically adapted and adjusted to get a good handover performance. Thus, the solution, disclosed herein reduces the handover failure rate as well as improves system and service performance.

The mobile terminal 300 (or another suitable component of wireless network SO) may initiate handover of a communication session associated with the mobile terminal 300 between a source base station 100 and target base station 200, based on the selected handover trigger. For example, as explained above, the selected handover trigger ma represent or Include a hysteresis value and a TXT value in particular embodiments, in such embodiments, mobile terminal 300 ma detect that a signal strength measurement for targe base station 200 exceeds a signal strength

measurement for source base station 100 by more than an amount indicated by the hysteresis value of the selected handover trigger for longer than a period of time indicated by the TTT value of the selected handover trigger. In response to detecting this, mobile terminal 300 may notify the source base station 10 via a measurement report and start performing the handover to the target base station 200.

The mobile terminal 30 may send a measurement report, e.g., including measured signal strengths associated with neighbor base stations, to the source base station 1 0 to enable the source base station 100 to make the handover decision, 1» this case, the handover performance may further be Improved by reducing the size of the measurement report sent by th mobile terminal 300, depending on one or more variable network parameters, e.g., mobile terminal speed, in this embodiment, the processor 330 in the mobile terminal 300 may measure the strength of a signal received from each of a plurality of neighbor base stations. The processor 330 may further obtain a parameter that indirectly or directly impacts the handover performance. For example, the processor 330 may receive information from the source base station 100 indicating the speed of the mobile terminal 300. The processor 330 then determines which and/or how many of the measured signal strengths should be included in a measurement report to be sent to the source base station .100 based on whether the obtained parameter passes a corresponding per formance test. For examp le, if the speed of the mobile terminal 300 exceeds a speed threshold, the processor may include on ly a subset of the signal strength measurements. The subset may include as few as one signal strength measurement or as many as one less than the total available signal strength measurements. The processor 330 may e.g., opt to include the » strongest signal strength measurements where n represents the size of the subset, when the speed exceeds a threshold. Subsequently, the transceiver 310 trmtsmits the

measurement report to the source base station 100. By reducing the size of the measurement report, e.g., when the mobile tercninal 300 is mov ng at a high rat -of speed, the mobile tewnmal 300 increases the robustness of the handover measurement reporting, which in turn reduces the possibility of handover failures. In this embodiment, the source base station 100 may be configured to blindly decode the received measurement repor by assuming both a default size (including all of the signal strength measurements) and reduced size of the measurement report.

The KM circuit. 1 10, trigger selection circuit, ϊ 20, 320, performance parameter circuit 1 0, processor 330, and/or ranking circuit. 122, 322 ma he implemented in hardware and/or software. In all embodiments, the functionality provided by the described "circuits'^* or "proces ors" in the drawing figures, e.g.., the Pl circuit 110, trigger selection circuit 120, 320, performance parameter circuit 140, processor 330, and/or mikin circuit 2 , 322, eto., may more generally be implemented as dedicated hardware circuits (either analog or digital) as n the example of Figures 4 and 5; as programmable logic together with appropriate firmware; as software modules executed o one or more stored-program processors or digital signal processors (DSP); or in an combination, thereof. Additionally., each, of the described circuits may represent in part or in whole, the same physical components as one or more of the other circuits. Thus, for example,, KM circuit 1 10, trigger selection circuit 120. performance parameter circuit 140, and/or ranking circuit 122 may, in some embodiments, all represent a single circuit or a common set. of circuits while, in other embodiments, they may each represent separate independent circuits. Similarly, trigger selection circuit 320, processor 330, and/or ranking circuit 322 may, in some embodiment, all represent a single circuit or a common set of circuits while, in other embodiments, they may each ^•represent separate independent circuits.

In all embodiments, the transceiver 1 0, 330 may comprise a receiver and transmitter interface used to communicate with one or more other transceivers via a Radio Access Network according to one or more communication protocols known in the art or that may bo developed, e.g., IEEE 802.xx, CDMA, WCDMA, GSM, LTE, UTRA , WiMax, or the like.. The transceiver 530 implements transmitter and receiver functionality appropriate to the Radio Access Network links (e.g., frequency allocations and the like). The transmitter and receiver functions may share circuit components and/or software, or alternatively tnay be implemented separately.

The present invention may, of course, be carried out in other ways man those specifically set forth herein without depart tag from, essential characteristics of the invention. The present embodiments are to he considered in all respects as illustrat ve and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to he embraced there in.

Claims

1?

What Is claimed is;

.1. A method, executed at a source base station ( 100), of determining a handover trigger for triggering handover of a mobile terminal (300) in. a wireless network (SO) from the source base station ( 00) to & target, base station. (200), the method

characterized by:

obtaining a first e Performance Indicator ( PI) for each of a first candidate trigger and a second candidate trigger, wherein each first KM indicates, for the corresponding candidate trigger, a quality of wireless services provided by the wireless network (50) to the mobile terminal (300); obtaining a parameter associated with at least one of the mobile terminal (300) arid the wireless network. (SO), wherein the parameter indirectly or directly impacts handover performance;

if the parameter passes a corresponding performance test, sending the first KPIs to the mobile terminal (300) to facilitate a selection at the mobile terminal (300) of one of the first and second candidate triggers as the handover trigger based on the first KPIs; and

if the parameter fails the corresponding performance test, selec t ing one of the first and second candidate triggers as the handover trigger based on a first comparison between the first KPIs for the first and second candidate triggers.

2, The method of claim 1 wherein sending the first KPIs to the mobile terminal 1300) comprises:

generatin a resource control message {600) includin a first information.

element (610) comprising the first KPIs; and

sending the resource control message (600) to the mobile terminal (300),

3, The method of claim 2 further comprising including a second information element (640) in the resource control message (000), sak! second information element (640) comprising an explicit instruction directing the mobile terminal (300) to select one of die first and second candidate triggers as the handover trigger based on the first PIs in the first information element (6 if)).

4. The method of claim 2 further comprising including one or more ddit n l information elemen s (620, 630) in the resource control, message (600), -each of said one or more additional information elements (620, 630) comprising on of a mapping table and a handover trigger algorithm, wherein the mapping table maps different scenarios of one or more of the parameters to different handover triggers, and wherein the handover trigger algorithm comprises a sequence of steps to he executed by the mobile terminal (300) to determine the handover trigger based on the first KPIs in the first information element (61 ).

5. The method of cl im h

wherein obtaining die parameter comprises obtaining a speed of the mobile terminal (300);

wherein the performanc test comprises a speed threshold test; and

wherein sending the first KF s to the mobile terminal (300) comprises sending the first KPIs to the mobile terminal (300) to facilitate & selection of one of the first and second candidate triggers as the handover trigger if the obtained speed exceeds speed threshold.

6. The method of claim ! wherein if the parameter fails the corresponding performance test; the method fiinl comprising informing the mobile terminal (300) of the selected handover trigger.

7. A source base station (1 0) configured, to determine a handover trigger for triggering handover of mobile terminal (300) in a. wireless network (50) from the source base station (1 0) to a target base station (200), the source base station (t 00) characterized by;

a Key Performance .Indicator (KPI) circuit (1 }ø) configured to obtain first KPI for each of a first candidate trigger and a second candidate trigger, wherein each first ΡΪ indicates, for the corresponding candidate trigger. 10

a quality of w ireless services provided by the w ireless network (50) to the mobile terminal (300);

a parameter circuit (140) configured to obtain a parameter associated with at least one of the mobile terminal (300) and the wireless network (50), wherein the parameter indirectly or directly impacts handover performance; and

a trigger circuit (1.20) configured to:

send the first KPh to the mobile terminal (300) to facilitate a selection at the mobile terminal (300) of one of .be first and second candidate triggers as the handover trigger based on the first KPIs if the parameter passes a corresponding performance test; and select one of the first and second candidate triggers as the handover trigger based oa a first comparison between the first KPIs for the first and second candidate triggers if the parameter rails the corresponding performance test.

8. The source base station ( 300) of claim 7 further comprising a control message circuit 124) configured to generate a resource control message ο0ϋ) including a first information element (010) comprising the first KI¾ wherein the trigger circuit (120) is configured to send the first KPIs to the mobile terminal (300) by sending the resource control message (600) to the mobil terminal (300).

9. The source base station (100) of claim 8 wherein the control message c ircuit (124) is forther configured to include a second information element (640) ia the resource control message (600), said, second information element (640) comprising an explicit instruction directing the mobile terminal (300) to selec one of the first and second candidate triggers as the handover trigger based on the first KPIs in the first information element (610),

10. The source base station (100) of claim 8 wherein the control message circuit (1 4) is further configured to include one or more additional information elements (620, 30) in the resource control message (600), each -of said one or more additional information elements (620, 630) ^'comprising one of a^' mapping table sod handover trigger algorithm, wherein the mapping table maps different scemdos of one or more of the parameters to different handover triggers, and wherein the handover trigger algorithm comprises a sequence of steps to be executed by the mobile terminal (300) to determine the handover trigger based on the first KFis in the first information element (610). 1 , The source base station (100) of claim ?:

wherein the parameter comprises a speed of the mobile terminal (300);

wherein the performance test comprises a speed threshold test; and

wherein the irisser circuit (120) is configured to send the first KMS bv sending the first Ki¾ to the mobile terminal (300) to facilitate a selection of one of the first and second candidate triggers as the handover trigger if the obtained speed exceeds a speed threshold.

12, The source base station (100) of claim 7 wherein if the parameter fails the corresponding performance test, the trigger selection circuit (120) is further configured to inform the mobile terminal (300) of the selected handover trigger. 1 Γ A .method of determining a handover trigger at a mobile terminal (300) for triggering handover of the mobile terminal (300) in a wireless network (50) from a. source base station (1 0) to a target, base station (200), the method characterized by: receiving a. resource control message (600) from the source base station (100), the resource control message (600) including a first uitbrroatiort element (610) comprising a first Key Performance Indicator (KM) for each of a first candidate trigger and a second, candidate trigger, wherein each first Pi indicates, for the corresponding candidate trigger, quality of wireless services provided, by the wireless network (50) to the mobile terminal (300); and

selecting one of the first and second candidate triggers s the handover trigger based on a first comparison between the first i Ms for the first and second candidate triggers received in the resource control message

(600),

14. The .method of claim 1.3 wherein selecting one of the first nd second cimdidate triggers comprises selecting, as the handover trigger, the candidate trigger associated with a better one of the first KPIs when a difference between the first K Is exceeds a predeterin ed margin .

15. The method of claim 13 wherein the resource control message (600) further includes a second information element (640) comprising an explicit Instruction directing the mobile terminal (300) to select one of the first and second candidate triggers a the handover trigger based on the first KPIs in the first information element (6.1.0). 16. The method of claim 13 wherein, the resource- control message (600) further includes one or more additional information elements (620, 6M) each comprising one of a mapping table and a handover trigger algorithm, wherein the mapping table maps different scenarios of one or more parameters to different handover triggers, and wherein the handover trigger algorithm comprises -a sequence of steps to he executed by the mobile terminal (300) to determine the handover trigger based oa the first KPIs in the first information element (610).

17, The method of claim 13 wherein the first information element (010) further comprises a second KM for each of die first and second candidat triggers, wherein selecting one of the first and second candidate triggers comprises selecting one of the frrst and second candidate triggers as the handover trigger based on at least one of the first comparison between the first KPIs for the first and second candidate triggers and a second comparison between the second KPIs for the first and second candidate triggers. 18. The- method of claim I ? wherein selecting one of the first and second candidate triggers based on at least one of the first and second comparisons comprises: selecting, as the ^'handover trigger, the caiididate trigger associated with a better one of the first KPIs if a first difference between the first KPh exceeds a first predetermined margin; and

if the first difference does not exceed the first predetermined margin, selecting, as the ^'handover trigger, the- candidate trigger associated with a better one of the second iPs if a second difference between the second PIs exceeds a second predetermined margin.

1 . The method, of claim 1 § further comprising, if neither the first, difference nor second difference exceed the respective first and second predetermined margins, selecting a default trigger as the handover trigger.

The method of claim 17:

further comprising ranking die first and second KPis based on a preferred

emphasis m one of the first and second KPis;

wherein selecting one of the first and second candidate triggers comprises: sequentially executing at least one of the first and second comparisons according to the ranking; and

selecting, as the handover trigger, one of the first and second candidate triggers based on one or more of the sequentially executed first and second comparisons.

The method of claim 13 ioniser comprising:

measuring a -strength of a signsl received from each of a pluralit of neighbor base stations;

obtaining a parameter that indirectly or directly impacts handover performance; determining which of the measured signal s rengths should be included in a measureme t report to be sent to the source base station ( 00) based on whether the obtained parameter passes a corresponding performance test; and

sending the measurement report to the source base station (100),

22. A .mobile terminal (300) configured to determine a handover trigger for triggering handover of the mobile terminal (300) in a wireless network (50) from a source base station (100) to a target, base station (200), the mobile terminal (300) characterized by^*

a receiver (310) configured to receive a resource control, message (600) from fh source base station (100) when a handover performance affecting parameter associated with at least one of the mobile terminal (300) and the wireless network (50) passes a performance test, the resource contra message (600) including a first mformation element (61.0) comprising a first Key Perfonnance Indicator (KPI) for each of a first candidate trigger and a second candidate trigger, wherein each first KPI indicates, for the .corresponding candidate trigger, a qu l f of wireless services provided by the wireless network (50) to the mobile terminal (300): and a trigger selection circuit (320) configured to sel ect one of the first and second candidate triggers as the handover trigger based on a first comparison between the first KP for the first and second candidate triggers received in the resource control message (600).

23, The -mobile terminal (300) of claim 22 wherein the trigger selection circui (320) is configured to select one of the first and second candidates by selecting, as the handover trigger, the candidate trigger associated with a better one of the first Kl¾ when a difference between the first f PIs exceeds a predetermined margin.

24. The mobile terminal (300) of claim 22 wherein the resource control message (600) further includes a second information element (640) comprising an explicit mstructton directing the mobile terminal (300) to select one of the first and second candidate triggers as the handover trigger based on the first KPT* the first information element (610),

25, The- mobile terminal (300) of claim 22 wherein the resoarce control message (600) farther includes one or more additional infonnation elements (620, 630) each comprising one of a mapping table and a handover trigge algorithm, wherein the mapping table maps ^'different scenarios of one or more parameters to different handover diggers, and wherein the handover trigger algorithm comprises a sequence of steps to be executed by the mobile terminal (300) to determine the handover trigger based on the first KPis in the firs information element (6.10).

26. The mobile terminal (300) of claim 22 wherein the first information element (610) fttrthec comprises a second KFI for each of the first and second candidate triggers, wherein the trigger selectio circuit (320) is configured to select one of the first and second candidate triggers by selecting one of the first and second candidate triatters as the handover triaaer based on at least one of the first comparison between the first KPis for the first and second candidate triggers and a second comparison between the- second KPis for the first and second candidate triggers,

27. The mobile terminal (300) of claim 26 wherein the trigger selection circuit (320) is configured to select one of the first and second candidate triggers based on at least one of the first and second comparisons by:

selecting, as the handover trigger, the candidate nigger associated with a better one of the first KPis if a first difference between the first KPis exceeds a first predetermined margin; and

if the first difference does not exceed the first predetermined margin, selecting, as the handover trigger, the candidate trigger associated with a better one of the second KIPs if a second difference between the second KPis exceeds a second predetermined margin.

28. The mobile terminal (300) of claim, 27 wherein the trigger selection circuit (320) is further configured to, if neither the first difference nor the second difference exceed the respective first and second predetermined margins, select a default trigger as the handover trigger.

29, The mobile terminal (300) of claim 26: the trigger selection circuit (320) comprises a tanking circuit (322) configured to rank the fust and second PIs based on a preferred emphasis on one of the first and second P!s; and

wherein, the trigger selection circuit (320) is configured to select one of the first arid second candidate triggers by:

sequentially executing at least one of the first a d second comparisons according to the ranking; and

selecting, as the handover trigger, one of the first and second candidate triggers based on one or more of the sequentially ex ec uted first and second comparisons, The mobile terminal (300) of claim 22 further comprising:

a processor (330) configured to:

measure a strength of a signal received from each of a plurality of

neighbor base stations;

obtai a parameter that indirectly or directly impacts handover

performance; sad

determine which of the measured signal strengths should be incl uded in a^dmeasurement report to be sent to the source base station (100) based on whether the obtained, parameter passes a corresponding performance test: and

a transmitter ( 10) configured, to send the measurement repon to the source base station (100).