CN103491581A - Optimum switching reference point selecting method based on high speed railway fixed-point switching algorithm - Google Patents

Abstract

In order to solve the problem of selection of optimum switching reference points of a high speed railway fixed-point switching algorithm, the invention provides an optimum switching reference point selecting method. The method comprises the steps of firstly utilizing the RSRP and the BLER calculated by the RSRP for conducting initial selection of switching reference points, then, according to the switching reference point recording obtained by a large number of measurements, establishing a probability statistics model, and analyzing and obtaining the optimum switching reference points. According to the algorithm, the rapid switching problem under the high-speed mobile environment can be solved, the times of dropped calls of the communication can be reduced, the switching success rate is improved, the service quality of the high-speed broadband mobile service can be enhanced, conducting of multimedia broadband mobile internet services in high-speed trains is promoted, and the increasingly-growing requirements of passengers for mobile communication services are met.

Description

A kind of the best switching reference point choosing method based on high-speed railway fixed point handoff algorithms

Technical field:

The present invention is directed to high-speed railway time division duplex Long Term Evolution (Time-Division Duplex Long Term Evolution, TDD-LTE or TD-LTE) the community switching of communication system is frequent, switching time is short, the requirement that handover success rate is high, on the basis of the existing quick handoff algorithms based on geographical location information, definite method of the best switching reference point of a kind of power difference based on to the source and target cell reference signals and Block Error Rate has been proposed.The method can be applicable in TD-LTE, Frequency Division Duplexing (FDD) Long Term Evolution (Frequency-Division Duplex Long Term Evolution, FDD-LTE or FD-LTE) the quick handoff algorithms based on geographical location information of communication system under the high ferro environment.

Background technology:

Usually, the handoff procedure in the LTE system is divided into following three steps:

1. handover measurement (comprise measure filtering, algorithm triggers measurement report);

2. switch decision (handoff algorithms);

3. switching is carried out;

Handover measurement is by user terminal (User Equipment, UE) and the LTE base station, be called evolved Node B (Evolved Node B, base station) complete, switch decision carries out in the base station, base station, switching is carried out under the common cooperation of user terminal UE, base station, base station and mobile management entity (Mobility Management entity, MME) and is completed.For high-speed railway TD-LTE networking, dispose, what adopt at present is the identical networking scheme, and the center frequency point that neighbor cell adopts is identical.LTE system same frequency switch decision event criteria adopts the A3 event, work as the adjacent cell quality of measurement higher than the Serving cell quality, and difference surpasses certain thresholding, one section triggered time (Trigger to Time of this state continuance, TTT) after, user terminal UE reports the A3 event report to network side, after network side is received this report, carry out switch decision, after adjudicating successfully, adjacent cell is carried out to switching command, meet the A3 event report because synchronization may have a plurality of adjacent cells simultaneously, therefore, in the A3 report, can comprise the adjacent area that a plurality of cell quality meet switching condition simultaneously.For macrocellular, networking adopts this decision rule can meet the demand of system fully at present.

When train speed per hour reaches 350 kilometers/hour, the base station spacing of 10 kilometers, the time interval of switching between base station is reduced to 100 seconds, has caused frequently passing through of community.Because translational speed improves the lifting receiver threshold level that is bound to.For guaranteeing transmitting and certain efficiency of transmission, generally all need by dwindling the base station spacing, improve and cover field intensity and solved.But this is not unique method, if effectively suppress the lifting degree of at a high speed lower threshold level, maintain the existing base station spacing of 6-10 kilometer as far as possible, by laying Remote Radio Unit (Radio Remote Unit, RRU) will at utmost effectively utilize existing resource, reduce a large amount of engineerings and drop into, and be beneficial to maintenance.But, to the resource management of base station, switching time and quality propose higher requirement.

But then, the High Speed Railway Trains broadband communication link has himself characteristic:

Because the railway line strip distributes, so being different from the plane of general cellular communication, the distribution of base station covers characteristics.Thereby the predictability that causes base station distribution, can predicting of train operation circuit, train position can be predicted, but train passes through the time of community can be predicted etc. many to the helpful pre-known information of system, these information can be used for improving the performance of system, reduce the complexity of system and operation, and can contribute to reduce the complexity of some algorithms, acquisition, than general cellular communication higher spectrum efficiency and transmission quality under equal conditions, improves the flatness of community switching.

Another factor that affects the high-speed railway covering is quick switching.Suppose that the switch area size is constant, the higher time of passing through switch area of translational speed is shorter so.Enough fast when user terminal UE translational speed, be less than to such an extent as to pass through the time of switch area the minimal time delay that system is processed switching, switching flow can't complete, and causes call drop.

Due to the particularity of high-speed railway channel circumstance and networking mode, above-mentioned A3 switch decision criterion can't adapt to the high-speed railway environment, and because train is run at high speed, switching time is shorter; In addition, the factors such as complicated landform and high-speed railway periphery electric equipment also can cause larger impact to channel circumstance, adopt A3 switch decision criterion can cause the frequent failure of switching, handover success rate reduces, communication quality descends, customer experience is poor, therefore must consider to adopt the decision rule that adapts to the high-speed railway environment.

Quick handoff algorithms based on geographical location information proposes for the particularity of above-mentioned high-speed railway channel circumstance and networking mode, to shorten handover delay, guarantee that user terminal UE is switched in rational position, meet the requirement of switching fast under high-speed condition.Quick handoff algorithms based on geographical location information crucial step in engineering practice is to determine the position of best switching reference point.The switching reference point locations is chosen the cutting off rate of the direct user of impact in handoff procedure.

Summary of the invention:

The present invention is intended to the requirement for the quick handoff algorithms based on geographical location information of high-speed railway TD-LTE communication system, definite method of the best switching reference point of a kind of power difference based on to the source and target cell reference signals and Block Error Rate has been proposed, the quick switching problem of solution under high-speed mobile environment, reduce the communication number of dropped calls, improve handover success rate, strengthen the service quality of high-speed wideband mobile service.

The present invention has realized that in the quick handoff algorithms based on geographical location information, the best is switched choosing of reference point, and concrete steps are as follows:

1, according to train operation position, speed and direction, after the network planning completes, generate in advance a adjacent cell list, and the switching position of pre-set each switching band, i.e. longitude and latitude positional information.

2, method is specified in the application target community, the community of shielding in the train operation rear, and the adjacent cell of reporting to train only comprises unique adjacent cell frequency point information, i.e. train operation ahead community.

3, train is according to measuring configuration to source cell base station periodicity report measurement information.When train enters the switching band of neighbor cell, the time train start to measure the reference signal power RSS of source cell base station and target cell base station _sand RSS _t, and report source cell base station together with speed now of train, positional information.

4, source cell base station is according to the metrical information of user terminal to send up, extracts the reference signal power value of the source and target community that train receives, and calculates the reference power difference △ P of train for Target cell reference power and cell-of-origin.

When power difference △ P is greater than difference power lower limit T1, and while being less than the higher limit T2 of difference power, meet:

T1≤RSS _t-RSS _s≤T2

Carry out next step, otherwise continue to wait for the user terminal to send up metrical information.

5, utilize general EESM algorithm comparatively commonly used can calculate the effective signal-to-noise ratio of UE at every sub-channels:

${\mathrm{\γ}}_{\mathrm{eff}}=-\mathrm{\β}\ln \left(\frac{1}{N_{\mathrm{sb}}}\underset{n=1}{\overset{N_{\mathrm{sb}}}{\mathrm{\Σ}}}\exp \left(\frac{{\mathrm{\λ}}_n}{\mathrm{\β}}\right)\right)$

Wherein β is for adjusting coefficient, N _sbfor the subcarrier number on every sub-channels, λ _nfor the SINR on each subcarrier.Just can calculate the Block Error Rate (Block Error Ratio, BLER) of UE on the every sub-channels of Target cell according to effective signal-to-noise ratio:

$\mathrm{BLER}=\frac{1}{2}[1-\mathrm{erf}\left(\frac{{\mathrm{\γ}}_{\mathrm{eff}}-b_m}{\sqrt{2}{c}_m}\right)]$

B wherein _mand c _mbe the adjustment coefficient after definite modulation coding mode (MCS), can obtain by inquiring about experience form commonly used.After finally the BLER of every sub-channels being averaged to processing, just obtained for the average BLER of the Target cell of switch decision.The ultimate source cell base station obtains train terminal respectively with respect to the BLER of source cell base station _sbLER with target cell base station _t.

6, as the BLER calculated _sand BLER _twhile all being less than the threshold value Q of some Block Error Rates, meet:

BLER _s<Q&BLER _t<Q

The candidate point that this position is best switching reference point.Each time is through the overlapping cover tape of switching, and train can access a lot of satisfactory best switching reference point candidate points according to said method, records the positional information of train through all points that meet the demands in the process of switching band.

7, train repeatedly drives towards Target cell from cell-of-origin, a plurality of optimal candidate points that at every turn obtain are deposited in best switching reference point candidate point table, then the best switching reference point table is carried out to probability statistical analysis, the location probability Distribution Statistics that can obtain best switching reference point candidate point is approximately Gaussian Profile, with computer, the probability statistical distribution obtained is carried out to gaussian curve approximation, obtain the mean value of this Gaussian Profile, the position of mean value is made as to the best switching reference point of this switching band.

The accompanying drawing explanation

Fig. 1 high ferro scene community covers schematic diagram

The flow chart of the TD-LTE quick handoff algorithms of Fig. 2 based on geographical location information

The best switching of Fig. 3 reference point choosing method flow chart

Embodiment

Below in conjunction with drawings and Examples, specific embodiment of the present invention is described in further details:

1. after the line of high-speed railway network planning, can obtain the plot planning table of a line of high-speed railway, can precompute the position of the overlapping cover tape of switching of each community of Along Railway according to planning table, switching band to every a pair of neighbor cell uses method shown in the foregoing invention content, obtain the best switching reference point that neighbor cell switches the fixed point handoff algorithms of overlapping cover tape, finally generate the best switching reference point list of the fixed point handoff algorithms of a the whole network, and switching band position and best switching reference point locations that the respective cell base station is preserved and oneself is associated.

2. according to the list of the best switching of resulting the whole network reference point locations, the best switching reference point place (or scope) at each neighbor cell switching band sets up switching mark post (or transducer), and global positioning system (GPS) and corresponding transducer be installed in advance ON TRAINS, in train travelling process, constantly utilize measurement report information to the source base station report position information, when the scope of train operation to best switching reference point, the sensor sensing that train is installed by vehicle body is to the existence of best switching reference point mark post, train just sends handover request to source cell base station, source cell base station response handover request starts to start fixed point hand off signaling flow process, until train is switched to Target cell.

3. the list of the best of line of high-speed railway the whole network switching reference point can regularly be upgraded and be revised, after train puts into effect, in train travelling process constantly to the corresponding source cell base station information that reports in, with positional information, the positional information to train is judged in the corresponding switching of source cell base station utilization oneself storage, when train enters in the switching overlap zone, source base station sends the signaling of measuring best switching reference point candidate point to train, train starts to use the method for content of the present invention to start to report the reference power received to source cell base station, source cell base station starts to carry out determining and record of best switching reference point candidate point, train by the respective cell highway section has many at set intervals, can accumulate a certain amount of best switching reference point candidate point data, thereby at set intervals or the best switching reference point candidate point that new record has occurred when larger change causes the previous the best switching reference point list generated not accurately just can to re-use when the propagated environment carry out best statistics again and calculating of switching reference point, to the best switching reference point, list is upgraded and is revised.

Fig. 1 is that in the present invention, high ferro scene community covers schematic diagram, according to the wire of high-speed railway, distribute, the mobile communications network of line of high-speed railway adopts the chain dedicated cell to cover, in order to reduce the number of times of switching, adopt BBU(Baseband Unit)+deployment way of the Base Band Unit of RRU+distributed Remote Radio Unit.

Fig. 2 is based on the flow chart of the quick handoff algorithms of TD-LTE of geographical location information.This handoff algorithms needs user terminal UE that the GPS navigation system is installed, in order to train position and velocity information are reported to source base station.

According to this flow chart, user terminal UE is report measurement information periodically, includes source base station and Reference Signal Received Power, train running speed and positional information the purpose base station.Source base station triggers changeover program according to the speed of user terminal UE, when user terminal UE speed is greater than the speed threshold value Speed_threshold of setting:

s>Speed_threshold

Source base station will trigger quick changeover program.In longitude and latitude position coordinates that user terminal UE uploads and source base station, the distance value of the longitude and latitude position coordinates of default switching point meets the switching criterion requirement, two positions be less than the threshold value Distance_threshold of a distance apart from difference:

△L<Distance_threshold

Base station initiated quick switch signaling, be switched to Target cell by user terminal UE.If the speed that the user terminal UE that source base station obtains reports is less than speed threshold value Speed_threshold, adopt conventional switching determination criterion to be switched.

Claims (6)

1. the system of selection for the best switching reference point of high-speed railway fixed point handoff algorithms process, be applicable in high-speed railway fixed point switching the selection of optimal reference switching point and determine, definite method of the best switching reference point of a kind of power difference based on to the source and destination cell reference signals and Block Error Rate has been proposed, to realize the rapid switching function of neighbor cell in high-speed railway.

2. method according to claim 1, its thought is: when train enters Liang Ge community overlapping area, i.e. switching with the time train reference signal power size that starts to measure source cell base station and purpose cell base station be respectively RSS _sand RSS _tand report source cell base station, be greater than some difference power lower limits and be less than the difference power higher limit for the reference signal power difference of purpose cell reference signals power and cell-of-origin when source cell base station calculates train.

3. the RSRP measurement report that the source cell base station utilization receives calculates the Block Error Rate of train for cell-of-origin and purpose community, when the Block Error Rate of source and destination community all is less than the threshold value of some Block Error Rates, determines the candidate point that this point is best switching reference point.

4. according to claim 2,3 described thoughts, while it is characterized in that train carries out the selection of optimum switching point, each time is through the switching band, train method according to claim 2 can access a lot of satisfactory best switching reference point candidate points, should further from these satisfactory candidate points, choose best switching reference point to these best switching reference point candidate points, further comprise following steps:

Train repeats to run to the purpose community repeatedly from cell-of-origin, a plurality of optimal candidate points that at every turn obtain are deposited in best switching reference point candidate point table, then the best switching reference point table is carried out to probability statistical analysis, the location probability Distribution Statistics that can obtain best switching reference point candidate point is approximately Gaussian Profile, with computer, the probability statistical distribution obtained is carried out to gaussian curve approximation, obtain the mean value of this Gaussian Profile, the position of mean value is made as to the best switching reference point of this switching band.

5. according to claim 4, every two different switching cells are due to propagated environment difference, the Gaussian Profile that the probability statistical distribution of best switching reference point candidate point is obeyed is also by difference, switch the position of reference point also by difference for different wireless propagation environment the bests, to different community switching bands, best switching reference point should re-start to measure to be chosen.

6. according to claim 5, its engineering concrete practice is:

After the line of high-speed railway network planning, obtain the plot planning table of a high-speed railway, precompute the switching band position of each community of Along Railway, to the switching band of every a pair of neighbor cell according to the described right method of right 1,2,3,4, obtain the best switching reference point of all neighbor cell switching bands, generate the best switching reference point list of a the whole network.

Further at the best switching reference point place (or scope) of each neighbor cell switching band, set up switching mark post (or transducer), and global positioning system (GPS) and corresponding transducer be installed in advance ON TRAINS, when the optimum switching point scope is arrived in train operation, perceive the existence of mark post, send handover request to source base station, start fixed point hand off signaling flow process, until be switched to Target cell.

The best switching reference point list of the whole network can regularly be upgraded and be revised, after train puts into effect, each just start claim 1,2,3 through neighbor cell switching band and carry out determining and record of best switching reference point candidate point, at set intervals or the best switching reference point candidate point that new record has occurred when larger change causes the previous the best switching reference point list generated not accurately just to re-use when the propagated environment carry out best renewal and correction of switching reference point.

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