CN1244998A

CN1244998A - Controlling handover in a mobile communication network

Info

Publication number: CN1244998A
Application number: CN 96180580
Authority: CN
Inventors: J·卡勒弗
Original assignee: Nokia Telecommunications Oy
Current assignee: Nokia Oyj
Priority date: 1996-12-04
Filing date: 1996-12-04
Publication date: 2000-02-16

Abstract

A methd and system of controlling handover in a mobile communication network is described. According to the described technique, the selection of one of a plurality of handover alternatives is based on pre-stored probability indicators which indicate a likely probability of success if handover is effected tot hat handover alternative. The technique also involves the use of a monitoring period which monitors both the instant and the selected traffic channel for a period surrounding handover to provide data for subsequent use in selecting handover alternatives.

Description

Handoff Control in the mobile radio communication

The present invention relates to a kind of method and system of control handover in the mobile radio communication.

In mobile radio communication, each dedicated mode travelling carriage is all followed base station communication by Traffic Channel, and the interference of choosing the signal of launching between signal level, travelling carriage and the base station of depending between the residing environment of travelling carriage, travelling carriage and the base station of Traffic Channel and processing influence the other factors of the signal between travelling carriage and the base station when calling out.Here be illustrated in the term Traffic Channel and set up a channel that is used for signal communication between travelling carriage and the base station.In standard GSM tdma system, Traffic Channel is used for characteristic frequency of signal transmission and a particular time-slot of distribution defines, and perhaps defines with a frequency hop sequences in the frequency hopping situation.In some more complicated systems, it can also define with the radiation direction that resembles in the so-called SDMA system.

In the discussion to handoff techniques, what should be understood that discussion generally is the frequency of Traffic Channel hereinafter, is to distribute to travelling carriage in the frequency hopping situation perhaps, is called to move a class frequency of distributing (mobileallocation).That is to say that term frequency, frequency channel or channel all represent to carry a frequency of signal of communication.

Have Several Factors in the calling procedure and require to change Traffic Channel.During the travelling carriage motion, it is always changing with the relation of base station, and the signal parameter of communicating by letter between travelling carriage and the base station also changes thereupon.According to existing handoff techniques, monitor in these signal parameters one or several, therefrom detect handoff trigger condition (trigger condition), when trigger condition is detected, just switch to another Traffic Channel.These signal parameters may comprise: the i) signal quality of up link and down link, the ii) signal level of up link and down link, iii) timing advance amount information (it is a travelling carriage has a tolerance how far from the base station with its communication just), the iv) traffic rank of this area and the v) consideration of power budget aspect (power budget considerations).

Selection will be switched Traffic Channel in the past and be relied on multiple different handoff algorithm, and these algorithms all depend on communication environment.Be enhanced if switch the back call quality, this handover decisions is good.Yet handover decisions is all bad under many situations, call out or go offline, or deterioration.The main cause that this phenomenon occurs is that handover decisions all is based on the signal level information that will switch channel in the past.

Therefore the objective of the invention is to improve handoff decisions, make most of the calling after switching, keep good quality.

According to an aspect of the present invention, a kind of method of control handover in the mobile radio communication is provided, wherein the Traffic Channel of just using (aninstant traffic channel) that communication is provided between travelling carriage and the base station is carried out monitoring, therefrom detect the trigger condition that switches to another different business channel, this different business channel chooses in some switchings are selected, this one of selection from described a plurality of switchings are selected is based on switching with each of storage in advance as described different business channel and selects relevant probability pointer (probabilityindicator), and each probability pointer represents to carry out the probability that this switching is chosen to merit.

Switch the probability pointer of selecting by storing each, in this particular environment, just might utilize these to switch and select, make handover decisions with the highest probability of success.

In above-mentioned embodiment, each of one group of cell pattern has all been stored these switchings and has been selected and corresponding probability pointer, and each cell pattern all comprises one group of neighbor cell in the network.Here these cell patterns all are taken as service mode (Server Pattern), comprise that Serving cell and three neighbor cells can have nearly four sub-district, and they have the signal level of best report.Here switch and select to be taken as a service mode probability vector (SPPV) with relevant probability pointer.Therefore each service mode all has a relevant service mode probability vector in preferred embodiment.

According to a further aspect in the invention, provide a kind of method of implementing the handover in the mobile radio communication, it may further comprise the steps:

Monitoring is for providing first Traffic Channel of communication, so that detect the handoff trigger condition between travelling carriage and the base station;

After detecting trigger condition, in some switchings are selected, select second Traffic Channel of communication is provided, and switch to second Traffic Channel;

During the monitoring that after detecting trigger condition, begins, monitor first and second Traffic Channel and other remaining switching and select; With

The channel data of collecting in during the monitoring is stored, be used for later handover.

Monitor the Traffic Channel of just using by utilization and switch the channel data of collecting in the cycle of selecting with all the other, the feature of this respect of the present invention and the feature of first aspect can integrate, thus definite and renewal probability pointer.

Monitoring periods can start from detecting the registration point of trigger condition.Whether successful it can end at selection the evaluation point of determining Traffic Channel, and success is used for determining with failure and renewal probability pointer.

Also for realizing that in mobile radio communication handover provides a system, this system comprises this one side of the present invention:

Be used to monitor first Traffic Channel that communication is provided between travelling carriage and base station, therefrom detect the device of handover triggering condition;

Be used to detect after the trigger condition, selection provides the device of second Traffic Channel of communication in selecting from some switchings;

Be used to implement to switch to the switching device shifter of second Traffic Channel from first Traffic Channel;

Be used in during the monitoring that begins to detect trigger condition monitoring first and second Traffic Channel and all the other switch the device of selecting; With

The channel data of collecting in preserving during monitoring is used for a memory of later switching.

Another aspect of the invention is provided for a system of the Handoff Control of mobile radio communication, and this system comprises:

Be used to monitor the Traffic Channel of just using that communication is provided between travelling carriage and base station, therefrom detect the device of the trigger condition that switches to the different business channel;

Be used for switching the device of selecting different Traffic Channels from some;

Be used to preserve with relevant some of the corresponding probability pointer of storage in advance and switch the memory of selecting, each probability pointer declaration switches to a switching and selects probability of successful, and wherein said choice device is selected different Traffic Channels according to the probability pointer.

According to a further aspect of the present invention, provide a mobile radio communication, it comprises that some base stations are used for limiting the sub-district and at least one base station controller is used to control the base station at network, and base station controller comprises the system of a control handover, and this system comprises:

Be used to monitor the Traffic Channel of just using that communication is provided between travelling carriage and base station, therefrom detect the device of the trigger condition that switches to a different business channel;

Be used for switching the device of selecting the different business channel in the selection from some;

In order to understand the present invention better and to illustrate how it implements, will be by example reference the following drawings:

Fig. 1 is the block diagram of a system of control handover in the mobile radio communication;

Fig. 2 is the more detailed block diagram of the circuit in the base station controller; With

Fig. 3 be handover with relevant monitoring during sequential chart.

Fig. 1 represents to be designated as in the cellular mobile telecommunication system four sub-districts of A, B, C, D.Each sub-district all belongs to the base station that several sub-districts can be arranged, but for the sake of simplicity in this example each base station of supposition have only a sub-district.Symbol A, B, C, D can be used for representing the sub-district and also can be used for representing the base station like this.Each sub-district can have one or more transceivers.In this example, sub-district A has a transceiver 6, and sub-district B has three

transceivers

8,10,12, and sub-district C has two

transceivers

14,16, and sub-district D has two

transceivers

18,20.

Each all has an area of coverage among sub-district A, B, C, the D, and these areas of coverage can be defined as the zone that travelling carriage can be kept connection (calling) by this sub-district.The area of coverage of supposing A, B, C, D in this example all has overlapping.Therefore travelling carriage is reported service mode ABCD in this overlay region.The actual Serving cell and the order of three neighbor cells are unimportant.For example server A and adjacent BCD, and server B and adjacent DAC use same service mode ABCD to represent.

Has only a mobile station MS in Fig. 1.Actual network has several travelling carriages certainly.This mobile station MS works in dedicated mode, is just utilizing the transceiver 12 of sub-district B to communicate by Traffic Channel TCH1.In this embodiment, suppose that each transceiver only provides a frequency, it is with representing that the letter of sub-district and transceiver plane No. identify.Except preface partly introduce, can think that each frequency all provides the Zone channel on the basis of sub-district.In fact according to GSM standard, each frequency all will be supported nearly 8 (during half rate 16) time-division Traffic Channels.All use the Traffic Channel of same channel different time-gap that similar quality of connection is all arranged usually, therefore all regard of equal value the switching as and select.So in the example shown, each all represents several Traffic Channels and several selection among the frequency B1 of sub-district B, B2, the B3.

The work of transceiver among sub-district A, B, C and the D is also controlled in the work of the several base stations of base station controller (BSC) 22 controls in above-mentioned embodiment.Base station controller 22 comprises the monitoring calling and makes the circuit of handoff decisions.This circuit comprises a meter 24, and it receives the report that comprises measurement data from the travelling carriage that each works in dedicated mode.Handoff decisions is made and monitored to a control circuit 26 that is connected to meter.Switch option table (HOAT) 28 and link to each other, and Be Controlled circuit 26 is used to select switching channels with control circuit 26.Control circuit comprises a microprocessor, and it can move handover decisions program (HODMP) 30 and handover evaluation program (HOEMP) 32, hereinafter will introduce in detail.Fig. 1 schematic illustration the output of handover evaluation program 32 be sent to and switch option table 28, the output of handover decisions program is used to change the Traffic Channel of travelling carriage with base station communication.In the example in Fig. 1, travelling carriage is switched to Traffic Channel 2 TCH2 by the transceiver 14 of sub-district C, channel C2 in other words from Traffic Channel 1 TCH1.The transceiver 12 of sub-district B is followed base station communication by an A-bis interface 3.The transceiver 14 of sub-district C is then followed base station communication by another A-bis interface 4, dots among the figure.

Drawn the in more detail circuit of base station controller 22 li of Fig. 2.To illustrate how to implement handover in embodiment of the present invention with reference to this figure.

Base station controller 22 is collected the measurement data of each ongoing calling in the meter, and these data are by mobile station MS and Serving cell (sub-district B) report.Mobile station MS utilizes Traffic Channel TCH1 to report to Serving cell B, and sub-district B utilizes A-bis interface 3 to send one and reports to base station controller then.This report merges with the measurement data of travelling carriage and transceiver 12 in the B of sub-district.In the above-described embodiment, report data is based on GSM standard, and these data comprise the information such as signal level of downlink signal level, uplink signal level, up link and downlink quality, six best neighbor cells.Base station controller optionally keeps some reports, and for example 32, they are used to follow the tracks of these parameters.Control circuit 26 comprises an observation circuit 34, these parameters of this monitoring circuit monitors, and utilize one of them or more, trigger to switch according to handoff algorithms.Existing gsm system is using such handoff algorithms, wherein switches and selects all to come divided rank according to the measurement report in the meter 24.But,, set up a registration point RP, for example as shown in figs. 1 and 3 triggering the point that switches according to existing handoff algorithms according to above-mentioned new system.At registration point RP, start handover decisions program 30.This program 30 is taken out data for 28 li from switching option table, and utilizes these data to select Traffic Channel, for example a TCH2 for switching.Utilize to switch implement circuit 38 then and start these Traffic Channels, like this, travelling carriage is to use the transceiver 14 of Traffic Channel TCH2 by sub-district C to communicate basically, and sub-district C then follows base station controller 22 to communicate with A-bis interface 4.Represent the enforcement of switching with HO in Fig. 1 and Fig. 3, but do not introduce here, because all know in this area.Timer 36 is set during the monitoring, ends at evaluation point EP during this period.The number of the report of determining with the user during the monitoring of receiving from travelling carriage is measured.In evaluation point, start handover evaluation program 32 and assess the success and the failure of handover, and revise the data of switching 28 li storages of option table in view of the above.Like this, each switch all to upgrade once switch option table, thereby provide one always in the reference of variation for later handoff decisions.This has greatly increased the handover decisions possibility of success.

As shown in Figure 3, implement the back dropped calls if switch HO, just stop in this point during the monitoring, the failure of handover decisions then is used for upgrading switching option table 28.

Table I is an example that switches option table.Switch option table and preserve a service mode probability vector SPPV for each service mode.Each service mode is the group that four sub-districts are arranged, and it comprises three best neighbor cells that a Serving cell and travelling carriage are reported at registration point RP place.In this example, HOAT includes 15000 records of different SP and relevant SPPV.These service modes are set up according to the report of the travelling carriage in the zone of base station controller 22 controls and are upgraded.Service mode probability vector SPPV provides a probability pointer in the optional channel of that sub-district each, and this probability pointer declaration switches to the Traffic Channel possibility of success that channel is supported in this service mode.In the example of Table I, supposing has 10 optional channels in each sub-district, represents to 10 with the letter and number 1 of representing the sub-district.The probability pointer of these channels is represented (sub-district letter-numeral) with P heel channel code name.For example, the probability pointer of channel A1 is P (A1) in the service mode ABCD.The service mode probability vector of service mode ABCE illustrates with the shadow region.

Corresponding to the probability of success of switching, they all get from-127 to 127 value to each probability pointer according to Table II.Span is that-127 to 127 benefit is, the probability pointer can be only with a byte representation.Relevant probability pointer upgrades at each handover evaluation point EP.This realizes by the value in the specific span relevant with specific handover event is added up to.Table III is an example of handover event and analog value.

Value in the Table III should be regarded as the different performance of selection or the marks (Credit Points) of performance estimation of switching.

Level/quality is good in the Table III/and bad relevant with average value measured with some threshold value.Can adopt different definition, for example:

● if the mean value of the sampling value of report is more than or equal to a predetermined threshold during the monitoring, and level is good so, otherwise is exactly bad.

● if predetermined percentage is arranged more than or equal to a predetermined threshold in the sampling of report, quality is good so, otherwise is exactly bad.

Known have a similar definition, and they are used to existing handoff algorithms, therefore no longer provides more details here.

The handover decisions of the first half supposition from channel B1 to channel C2 of Table III is successful.Monitored the level and the quality of signal in during the monitoring, each channel has all provided mark.Table III has illustrated channel, span and has been added in value in the scope on the probability pointer as mark.

For channel C2 during the monitoring go up that signal quality is good, level might as well situation, be defined as maximum 16 for channel C2, if but the signal level of a channel and quality are all good in a certain specific cell, other channel of just supposing same sub-district also has corresponding signal levels and quality, so selective value 4.

If during signal monitoring, detected bad signal level and quality, so with regard to predetermined channel C2 and channel C1 value-4 all from channel C2.

If during signal monitoring, detected the signal level that bad signal quality is become reconciled from channel C2, with regard to predetermined channel C2 value-8, but predetermined channel C1 value 4.That is to say, suppose the signal level of channel in the common cell similar be reasonably, although the quality difference.

If the calling in during monitoring on the channel C2 (after successfully switching) goes offline, with regard to predetermined channel C2 value-16, channel C1 value-8.

Have the situation of good signal level, value 4 for the channel in neighbor cell B and the D.For example, channel D1, D2, B2 and the B3 in seeing Table.Predetermined channel B1 value 0 because switch to other channel from this channel, so although the B1 channel level can, but the supposition certain trigger condition is arranged, thereby caused switching.So a less value is suitable.

For the bad signal level on the channel of neighbor cell, regulation value-6 sees Table channel D1, D2, B1, B2 and B3 among the III.

For from channel B1 to the unsuccessful switching of channel C2, can adopt similar process.For the successfully calling of Return Channel B1, regulation C2 gets low value-16.If the signal during monitoring on the channel B1 has good signal quality and level, just stipulate the channel value 4 in all sub-districts.Go up bad signal level and quality for channel B1 in during the monitoring, all channels in this sub-district are all got low value-4.Go up the level that bad signal quality is become reconciled for channel B1 during the monitoring, channel B1 value-8, but channel B2 just gets relative higher value 4 with B3, and another signal level that those channels are described may be fine, but can not pre-determine signal quality.

If dropped calls, channel B1 and C2 just get low value-16.

Obviously, can adopt value system arbitrarily, in fact can leave the user for and go regulation.

Adding the value that remains on the SPPV credit by basis switching dependent event as shown in Table III can determine.The probability pointer of each channel in the service mode ABCD.For example suppose P in the ABCD SPPV (C2)=78, after successfully switching to C2, if the signal quality of C2 and level are all good, the new value of SPPV is P (C2)=78+16=94 so, if get nowhere but switch, dropped calls, so new value is P (C2)=78-16=62.If the gained sum goes beyond the scope,, just get immediate permissible value for example less than-127 or greater than 127.In this way, every handover decisions is once all upgraded the probability pointer one time, like this, all changes service mode probability vector SPPV for each service mode.Therefore, service mode probability vector SPPV is a useful tool selecting switching channels.Resemble and always select the highest channel of SPPV mark for use, perhaps select mark to be better than the such simplex criteria of any SPPV channel of a predetermined value, can be used for replacing or additional existing switching selection criterion.

To depend on the number of SPPV in the HOAT to the requirement of internal memory.The size of HOAT can be estimated as the function of the mean value of the sub-district number of BSC management and each sub-district neighbor cell number in the given BSC.For example, 100 sub-districts are arranged, all there are average 16 neighbor cells each sub-district, and such BSC needs 14000 HOAT clauses and subclauses.Just in case the space that keeps is not enough, HOAT is full, then can abandon the oldest SPPV of time mark when new SP has been arranged, sees Table I.

Above-mentioned handoff technique has several advantages.

Realize that this technology does not need to change the GSM index.The existing report of just using travelling carriage to send that needs by the adjunct circuit in the base station controller.

Requirement to internal memory and amount of calculation is appropriate.As previously discussed, the probability pointer can be stored with being no more than 1 byte, can use very simple algorithm to upgrade and the probability of use pointer.

This handoff technique can be used for additional or replace existing handover decision algorithm gradually.So it can make together with prior art and be used for strengthening prior art and can not influence existing handover decision algorithm.Table I

Table II

Value	Probability (%)
Value	Probability (%)	-127	?0
?0	?50	-127	?0
?0	?50	?127	?100

Table III

Incident	Channel	Scope	Value
Incident	Channel	Scope	Value	The successful switch of B1 → B2 ● the quality of C2 and level are all good during the monitoring ● the level of C2 (and quality) is bad during the monitoring ● poor quality's level of C2 is good ● C2 goes offline during the monitoring ● the level of D is good during the monitoring ● the level of B is good during the monitoring ● the level of D is bad during the monitoring ● the level of B is bad during the monitoring	?C2 ?C1 ?C1，C2 ?C2 ?C1 ?C2 ?C1 ?D1，D2 ?B1 ?B2，B3 ?D1，D2 ?B1，B2，B3	8…24 0…8 -8…0 -12…-4 0…8 -24…-8 -12…-4 0…8 -4…4 0…8 -8…-4 -8…-4	16 4 -4 -8 4 -16 -8 4 0 4 -6 -6
The unsuccessful switching of B1 → B2 ● return B1 ● the level of B1 and quality are all good during the monitoring ● the level of B1 (quality) is bad during the monitoring ● poor quality's level of B1 is good during the monitoring ● dropped calls access success	?C3 ?B1，B2，B3 ?B1，B2，B3 ?B1 ?B2，B3 ?B1，C2	-24…-8 0…8 -8…0 -12…-4 0…8 -24…-8	-16 4 -4 -8 4 -16				16 4 -4 -8 4 -16 -8 4 0 4 -6 -6

Claims

1. A method for controlling handover in a mobile communication network, wherein the traffic channel that is being used to provide communication between the mobile station and the base station is monitored, and a trigger condition for switching to another traffic channel is detected therefrom, this other A traffic channel is selected from a number of handover options from which one is selected as another traffic channel based on pre-stored probability pointers associated with each handover option, each probability pointer representing a handover to that handover option probability of success.

2. The method of claim 1, wherein those handover choices and corresponding probability pointers are stored for each set of cell patterns, each cell pattern comprising a set of neighboring cells in the network.

3. The method of claim 2, wherein the number of cells in each group is four.

4. The method of claim 2 or 3, wherein the different traffic channels are selected from handover options stored with one of the cell patterns, said one of the cell patterns being determined by including the serving cell and some adjacent The cell pattern is selected from a group of cells whose reported mobile station signal level is optimal when a handover trigger condition is detected.

5. The method of any one of the preceding claims, wherein the triggering condition is detected at the registration point in order to implement the handover, and wherein the monitoring period begins at the registration point, during which period, the active use of the communication between the mobile station and the base station is provided. traffic channels are monitored before and after handover.

6. The method of claim 5, during a monitoring period not only the traffic channel being used but also the remaining channels in said handover selection are monitored.

7. The method of claim 6, wherein data collected while monitoring traffic channels in use and remaining handover options during the monitoring period is used to determine and update the probability indicator.

8. The method of claim 5, 6 or 7, wherein the monitoring period terminates at an evaluation point to determine the success of the selected traffic channel, which is used to determine and update the probability indicator for the handover.

9. A system for controlling handover in the mobile communication network, the system includes:

means for monitoring a traffic channel in use providing communication between the mobile station and the base station, and detecting a trigger condition for switching to another traffic channel;

means for selecting another traffic channel from a number of switching options;

A memory for storing handover options related to pre-stored probability pointers, each probability pointer indicating the probability of success of handover to that handover option, wherein the selecting means selects another traffic channel based on the probability pointers.

10. The system of claim 9, wherein said memory stores handover selections and associated probability pointers for each set of cell patterns, each cell pattern comprising a set of neighboring cells in the network.

11. The system according to claim 9 or 10, wherein said monitoring means can monitor the traffic channel in use and the handover selection for providing communication between the mobile station and the base station during the monitoring period and before and after the handover, and the system also includes collecting based on the monitoring period The data update probability pointer means.

12. A mobile communication network comprising base stations defining cells in the network and at least one base station controller for controlling said base stations, the base station controller comprising a system for controlling switching, the system comprising:

means for monitoring a traffic channel in use providing communication between a mobile station and a base station, and detecting a trigger condition for switching to another traffic channel;

means for selecting another traffic channel from a number of switching options;

A memory for storing some handover options associated with pre-stored probability pointers, each probability pointer indicating the possibility of successful handover to which handover option, wherein the selecting means selects the other traffic channel based on the probability pointers.

13. A method for implementing handover in a mobile communication network, comprising the following steps:

Monitor the first traffic channel that provides communication between the mobile station and the base station, and detect handover trigger conditions from it;

after detecting said handover trigger condition, selecting a second traffic channel for providing said communication from a number of handover options, and handover to the second traffic channel;

Monitoring the first and second traffic channels and remaining handover options during a monitoring period starting from the detection of the trigger condition; and

The channel data collected during the monitoring period is stored for future switching.

14. A system for implementing handover in a mobile communication network, the system comprising:

A device that monitors the first traffic channel that provides communication between the mobile station and the base station, and detects handover trigger conditions therefrom;

means for providing a second traffic channel for said communication, selected from a number of handover options after detection of said handover trigger condition;

Switching means for switching from a first traffic channel to a second traffic channel;

means for monitoring the first and second traffic channels and remaining handover options during a monitoring period commencing from the detection of the trigger condition; and

The channel data collected during the monitoring period is stored for future switchover.