CN105578506A - A switching method based on channel information in the high-speed mobile environment of rail transit - Google Patents

Abstract

The invention disclose a switching method base on channel information under track traffic high speed moving environment, comprising steps of setting a prediction switching position of a train, calculating the distance between the prediction switching position and a base station to be switched, calculating the path loss of the prediction switching position according to the calculated distance and a channel model corresponding to the prediction switching position, calculating the reception signal field intensity of the reception signal of the train arriving at the prediction switching position according to the path loss, determining whether the field intensity of the signal reception achieves the threshold, if the reception signal field intensity is stronger or equal to the preset threshold, preparing to switch in order to make the train switch to the base station to be switched when the train arrives at the prediction switching position, if the reception signal field intensity is smaller than the preset threshold, repeating the above steps until the received signal field intensity achieves the threshold. The invention can realize the fast, smooth and reliable switching under the high speed movement complex scene.

Description

A switching method based on channel information in the high-speed mobile environment of rail transit

technical field

The invention relates to the technical field of wireless mobile communication, in particular to a switching method based on channel information in a rail transit high-speed mobile environment.

Background technique

With the rapid development of rail transit systems such as railways, subways, intercity railways, and especially high-speed railways, providing reliable, real-time, and efficient broadband wireless network services for train passengers has become a hot spot in broadband mobile communication research at home and abroad. However, the rapid handover and frequent cell reselection caused by high-speed mobility will lead to the interruption of the wireless link connection, resulting in call drop and data transmission interruption, seriously affecting the communication quality and passenger experience. Especially for the rail transit system used to transmit train control information and video surveillance information to ensure the safe operation of the train, its reliable switching is of great significance.

Handover refers to the process of transferring the communication link between the current mobile user and the base station from the current base station to another base station while maintaining the communication without interruption.

The existing switching method based on level/power requires two basic conditions during switching: the level/power of the cell to be switched must be higher than the threshold value; the level of the cell to be switched must be higher than the power level of the previous cell; Ping/power several decibels. This kind of handover method, due to the impact of environmental changes or interference, will make the level/power of the cell to be handed over either not higher than the threshold value, or not higher than the level/power of the previous cell. talk.

The existing quality-based handover method is because the wireless coverage quality of the current cell is too poor. Therefore, regardless of the wireless coverage of the next handover cell, a forced handover is also performed, which leads to the fact that the wireless coverage quality after handover cannot be guaranteed at all. , especially edge coverage. In addition, the higher the moving speed, the shorter the time for crossing the overlapping area. When the time for the mobile station to cross the overlapping area is less than the minimum delay required for the system to process the handover, the handover process using this method cannot be completed, resulting in call drop.

The existing switching of position information based on satellite communication or GPS navigation cannot be positioned when the train passes through a high-speed railway such as a tunnel or a large marshalling yard with an awning, or a station; even if inertial navigation technology is used, the positioning accuracy will decrease. Poor; if using such as repeater relay station as ground communication switching means, in addition to bringing high costs and maintenance problems, it will also bring a large time delay when switching satellite or navigation signals to the ground network, which is also Will significantly affect the handover success rate. In addition, this type of technology judges the receiving field strength at a certain location by means of a drive test or calculation based on a traditional link budget model, which has poor accuracy. Therefore, this type of method is not suitable for rail traffic scenarios such as high-speed railways with complex scene characteristics of high-speed movement.

Moreover, the existing handover technology only starts to make handover judgment at the handover position, that is, the "handover trigger point", and initiates handover judgment and other processes, which is prone to handover interruption, difficult to guarantee communication quality, and takes a lot of time .

Therefore, research on fast and reliable switching algorithms suitable for high-speed mobile environments, providing reliable train control information for train control systems, and providing passengers with high-quality broadband network services anytime and anywhere, is of great significance to the construction and development of future rail transit systems. Great significance.

Contents of the invention

The purpose of the present invention is to provide a switching method based on channel information in the high-speed moving environment of rail transit, so as to realize fast, smooth and reliable switching in the high-speed moving scene.

To achieve the above object, the present invention adopts the following technical solutions:

A switching method based on channel information in a rail transit high-speed mobile environment, comprising the following steps:

S1. Set the predicted switching position of the train, and calculate the distance between the predicted switching position and the base station to be switched;

S2. Calculate the path loss of the predicted handover position according to the calculated distance and the channel model corresponding to the predicted handover position;

S3. Calculate the received signal field strength at which the train arrives at the predicted switching position according to the path loss;

S4. Judging whether the field strength of the received signal reaches a preset threshold;

S5-1. If the field strength of the received signal is greater than or equal to the preset threshold, prepare for handover, so that when the train reaches the predicted handover position, it is handed over to the base station to be handed over;

S5-2. If the field strength of the received signal is smaller than the preset threshold, repeat steps S1 to S4 until the field strength of the received signal reaches the preset threshold.

Preferably, step S1 includes:

Obtain the distance D ₁ between the train and the current base station;

Calculate the distance D ₂ between the predicted handover position and the base station to be handed over according to the following formula (1):

D ₂ =DD ₁ -D _p (1)

Wherein, D is the distance between the current base station and the base station to be switched, and D _p is the distance between the train and the predicted switching position.

Preferably, after setting the predicted switching position, the distance _Dp between the train and the predicted switching position is between 100m-500m.

Preferably, the step _of obtaining the distance D1 between the train and the current base station includes:

Obtain the distance D _ID between the transponder and the current base station;

measuring the relative distance D _r of the train to said transponder;

The distance D ₁ between the train and the current base station is equal to the sum of D _ID and D _r .

Preferably, a wheel-rail distance meter is used to measure the relative distance D _r between the train and the transponder.

Preferably, in step S2, the path loss is calculated according to the following formula (2):

PL(dB)＝A+Blog ₁₀ (D ₂ )(2)

Wherein, PL (dB) is the path loss, and D2 is the distance between the predicted handover position and the base station to be _handed over. For rivers, A and B are fixed parameters corresponding to the channel model.

Preferably, in step S2, the path loss is calculated according to the following formula (3):

PL(dB)＝Δ ₁ +74.52+26.16log ₁₀ (f)-13.82log ₁₀ (h _b )

(3)

-3.2log ₁₀ (11.75h _m ) ² +[44.9-6.55log ₁₀ (h _b )+Δ ₂ ]log ₁₀ (D ₂ )

Wherein, _f is the operating frequency, h _b and h _m respectively represent the effective height of the base station antenna to be switched and the effective height of the train antenna, and D is the distance between the predicted switching position and the base station to be switched, when the When the channel models are viaducts, road cuttings, stations, tunnels, urban areas, suburbs, villages and rivers, _Δ1 and _Δ2 are fixed parameters corresponding to the channel models.

Preferably, in step S3, the received signal field strength at which the train arrives at the predicted switching position is calculated according to the following formula (4):

P _R ＝P _T -(PL+L _BTX +L _MRX +F _T -G _b -G _m )(4)

Among them, P _R is the field strength of the received signal when the train arrives at the predicted switching position, _PT is the transmission power of the transmitter of the base station to be switched, PL is the path loss, and L _BTX is the transmission chain of the base station to be switched L _MRX is the device loss of the train receiving link, _FT is the total reserved margin, G _b and G _m represent the antenna gain of the base station to be switched and the antenna gain of the mobile station, respectively.

Preferably, the reserved total margin _FT is calculated by the following formula (5):

F _T ＝L _SF +L _MP +L _HM +L _IT +L _OA +L _TC (5)

Among them, L _SF is shadow fading margin, L _MP is multipath fading margin, L _HM is high-speed mobile fading margin, L _IT is interference margin, L _OA is device aging margin, L _TC is train control service margin Spend.

Preferably, the preset threshold is -85dB.

The present invention has the following beneficial effects:

The present invention predicts based on the channel model established for the rail traffic scene, and can predict the predicted switching position to be switched before the train reaches the "switching trigger point", so that the train is ready to switch the flow before reaching the predicted switching position, More time is reserved for the handover process, so that fast, smooth, and reliable handover can be achieved in complex high-speed mobile scenarios, which is of great significance for high-speed mobile environments.

Description of drawings

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

FIG. 1 is a flowchart of a handover method provided by an embodiment of the present invention;

Fig. 2 is a schematic diagram of a chain coverage of a dedicated mobile communication network for rail transit;

Fig. 3 is a flow chart of the implementation process of the embodiment shown in Fig. 2 .

detailed description

In order to illustrate the present invention more clearly, the present invention will be further described below in conjunction with preferred embodiments and accompanying drawings. Similar parts in the figures are denoted by the same reference numerals. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not limit the protection scope of the present invention.

Embodiments of the present invention provide a switching method based on channel information in a rail transit high-speed mobile environment. As shown in FIG. 1, the switching method includes the following steps:

S1. Set the predicted switching position of the train, and calculate the distance between the predicted switching position and the base station to be switched;

S2. Calculate the path loss of the predicted handover position according to the calculated distance and the channel model corresponding to the predicted handover position;

S3. Calculate the received signal field strength at which the train arrives at the predicted switching position according to the path loss;

S4. Judging whether the field strength of the received signal reaches a preset threshold;

S5-1. If the field strength of the received signal is greater than or equal to the preset threshold, prepare for handover, so that when the train reaches the predicted handover position, it is handed over to the base station to be handed over;

S5-2. If the field strength of the received signal is smaller than the preset threshold, repeat steps S1 to S4 until the field strength of the received signal reaches the preset threshold.

The "predicted handover position" here refers to the predicted handover trigger position, that is, the base station is handed over when the train runs to this position. The present invention can accurately pre-determine the position where the train will perform base station handover by predicting the position of the handover trigger and combining the channel model at the predicted handover position. When the mobile terminal moves to this position, the handover will be triggered, effectively avoiding The handover interruption phenomenon is eliminated, and the communication quality of the next communication cell to be handed over is ensured.

Moreover, the present invention combines the rail traffic scene and channel modeling, and predicts the handover trigger point by predicting the field strength and multipath echo at the moving position of the train, that is, judging the predicted handover position, saving the existing handover methods. When reaching the handover trigger point, it starts to measure the level of adjacent cells, compare the field strength coverage of adjacent cells, select the optimal cell, and judge the handover trigger. This makes the handover delay very short and the handover process Smoother.

In addition, based on the characteristics of the chain coverage of railway base stations, in the prediction process, it is only necessary to predict the field strength of the next adjacent base station of the train, instead of the need to predict the field strength of all the surrounding cells of the mobile station as in the existing handover method. The field strength is estimated and the cell with the best field strength is selected for handover. Therefore, the method of the present invention can reduce switching time, make switching faster, and is more suitable for high-speed mobile environment.

Preferably, step S1 includes:

Obtain the distance D ₁ between the train and the current base station;

Calculate the distance D ₂ between the predicted handover position and the base station to be handed over according to the following formula (1):

D ₂ =DD ₁ -D _p (1)

Wherein, D is the distance between the current base station and the base station to be switched, and D _p is the distance between the train and the predicted switching position.

Further, the step _of obtaining the distance D1 between the train and the current base station includes:

Obtain the distance D _ID between the transponder and the current base station;

measuring the relative distance D _r of the train to said transponder;

The distance D ₁ between the train and the current base station is equal to the sum of D _ID and D _r .

Preferably, a wheel-rail distance meter is used to measure the relative distance D _r between the train and the transponder.

In the present invention, the positioning of the current position of the train is mainly realized based on the wheel-rail distance meter and the transponder, so it is not easily affected by tunnels and obstructions like GPS positioning. Moreover, due to the use of transponders, the prediction results of the field strength and multipath echoes at various positions of the train can change with the changes of the scene along the rail transit line, and the flexibility is high.

Preferably, after setting the predicted switching position, the distance _Dp between the train and the predicted switching position is between 100m-500m. Here, the distance D _p between the train and the predicted switching position is defined as "predicted distance". Generally, the longer the predicted distance, the longer the time for the train receiving station to prepare for switching, and the smoothness and accuracy of switching The better, the lower the switching interruption rate.

As an embodiment of the present invention, in step S2, the path loss of the predicted switching position is calculated according to the following formula (2):

PL(dB)＝A+Blog ₁₀ (D ₂ )(2)

Wherein, PL (dB) is the path loss, and D2 is the distance between the predicted handover position and the base station to be _handed over. For rivers, A and B are fixed parameters corresponding to the channel model.

Further, in step S2, the path loss may be calculated by the following formula (3):

PL(dB)＝Δ ₁ +74.52+26.16log ₁₀ (f)-13.82log ₁₀ (h _b )

(3)

-3.2log ₁₀ (11.75h _m ) ² +[44.9-6.55log ₁₀ (h _b )+Δ ₂ ]log ₁₀ (D ₂ )

Wherein, _f is the operating frequency, h _b and h _m respectively represent the effective height of the base station antenna to be switched and the effective height of the train antenna, and D is the distance between the predicted switching position and the base station to be switched, when the When the channel models are viaducts, road cuttings, stations, tunnels, urban areas, suburbs, villages and rivers, _Δ1 and _Δ2 are fixed parameters corresponding to the channel models. The specific numerical values of the above fixed parameters will be given below.

Further, in step S3, the received signal field strength at which the train arrives at the predicted switching position is calculated according to the following formula (4):

P _R ＝P _T -(PL+L _BTX +L _MRX +F _T -G _b -G _m )(4)

Among them, P _R is the field strength of the received signal when the train arrives at the predicted switching position, _PT is the transmission power of the transmitter of the base station to be switched, PL is the path loss, and L _BTX is the transmission chain of the base station to be switched L _MRX is the device loss of the train receiving link, _FT is the total reserved margin, G _b and G _m represent the antenna gain of the base station to be switched and the antenna gain of the mobile station, respectively.

Wherein, described reserve total margin _FT calculates by following formula (5):

F _T ＝L _SF +L _MP +L _HM +L _IT +L _OA +L _TC (5)

In formula (5), L _SF is shadow fading margin, L _MP is multipath fading margin, L _HM is high-speed mobile fading margin, L _IT is interference margin, L _OA is device aging margin, L _TC For the train control business margin.

Preferably, the preset threshold in the method of the present invention is -85dB. That is, in the present invention, the -85dB specified by the International Union of Railways UIC can be used as the preset threshold for judgment. If the received signal field strength at the predicted switching position is greater than or equal to the preset threshold, the switching preparation will be carried out in advance. When the actual position reaches the predicted switching position, the switching is started immediately, and sufficient switching time is reserved for the switching process, thereby ensuring a high switching success rate.

The specific implementation process of the present invention will be described in detail below.

Fig. 2 is a schematic diagram of chain coverage of a mobile communication network dedicated to rail transit, where B1 represents the current base station, B2 represents the base station to be switched, and P1 represents the predicted switching position. Fig. 3 is a flow chart of the implementation process of the embodiment shown in Fig. 2 .

First, get the current position of the train. The transponder sends its own ID to the train to obtain the distance D _ID between the transponder and the current base station. At the same time, the wheel-rail distance meter is used to obtain the relative distance D _r between the train and the transponder according to the rotation of the wheel. Then the train and The current distance D ₁ between base stations can be obtained by the formula D ₁ =D _ID +D _r .

The current location of the train based on the wheel-rail rangefinder and transponder is not as susceptible to the influence of tunnels and obstructions as GPS positioning. Moreover, due to the use of transponders, the prediction results of the field strength and multipath echoes at various positions of the train can change with the changes of the scene along the rail transit line, and the flexibility is high.

Because the trajectory of the rail transit train is fixed, the distance between the base stations of the communication network is also fixed, that is, the distance between the current base station B1 and the base station B2 to be switched is D. As mentioned above, P1 represents the predicted switching position, then the distance between the train and the predicted switching position P1 is D _p . According to the graphical relationship in Figure 2, the distance between the predicted switching position P1 and the base station B2 to be switched can be obtained, that is, the formula (1) mentioned above:

D ₂ =DD ₁ -D _p (1)

Among them, D _p is preferably set between 100m-500m, the longer the predicted distance, the longer the time for the train receiving station to prepare for switching, the better the smoothness and accuracy of switching, and the lower the switching interruption rate.

Afterwards, the channel model corresponding to the predicted switching position P1 is determined, and the path loss at the predicted switching position P1 is calculated. As mentioned above, the path loss of the predicted switching position P1 can be calculated according to formula (2) or formula (3):

PL(dB)＝A+Blog ₁₀ (D ₂ )(2)

PL(dB)＝Δ ₁ +74.52+26.16log ₁₀ (f)-13.82log ₁₀ (h _b )

(3)

-3.2log ₁₀ (11.75h _m ) ² +[44.9-6.55log ₁₀ (h _b )+Δ ₂ ]log ₁₀ (D ₂ )

Among them, PL (dB) is the path loss, D ₂ is the distance between the predicted switching position P1 and the base station B2 to be switched, f is the operating frequency, h _b and h _m represent the effective height and train height of the base station antenna to be switched respectively The effective height of the antenna.

When the channel models are viaducts, cuttings, stations, tunnels, urban areas, suburbs, villages and rivers, A and B (or Δ ₁ and Δ ₂ ) are fixed parameters corresponding to the channel models. Table ₁ shows the values of Δ1 and _Δ2 in formula (3).

Table 1

It can be understood that, according to the values of Δ1 and _Δ2 in Table ₁ , by sorting the formula (3), the corresponding values of A and B in the formula (2) can be obtained, which will not be repeated here.

Afterwards, wireless link calculation is performed to obtain the field strength of the received signal at the predicted train arrival switching position P1. Since the downlink can be based on the test of the broadcast channel BCCH signal and can meet the requirements of Lee's sampling criterion, the wireless link budget of the dedicated mobile communication network for rail transit is usually based on the downlink.

As mentioned above, the received signal field strength at the train arrival prediction switch position P1 can be calculated according to formula (4):

P _R ＝P _T -(PL+L _BTX +L _MRX +F _T -G _b -G _m )(4)

Among them, P _R is the field strength of the received signal when the train arrives at the predicted switching position, _PT is the transmission power of the transmitter of the base station to be switched, PL is the path loss, and L _BTX is the transmission chain of the base station to be switched L _MRX is the device loss of the train receiving link, _FT is the total reserved margin, G _b and G _m represent the antenna gain of the base station to be switched and the antenna gain of the mobile station, respectively.

The reserved total margin _FT can be calculated by formula (5):

F _T ＝L _SF +L _MP +L _HM +L _IT +L _OA +L _TC (5)

Among them, L _SF is shadow fading margin, L _MP is multipath fading margin, L _HM is high-speed mobile fading margin, L _IT is interference margin, L _OA is device aging margin, L _TC is train control service margin Spend.

Finally, compare the obtained received signal field strength P _R with the preset threshold, if the received signal field strength _PR at the predicted switch position P1 is greater than or equal to the preset threshold, then perform tasks such as preparing for distribution and activating a new signal in advance. Command channel, prepare to allocate, activate a new traffic channel, prepare to start timer and other processes. Then when the train arrives at the predicted switching position P1 from the actual position, the switching is started immediately, and enough switching time is reserved for the switching process to ensure a high switching success rate.

The preset threshold here can be -85dB stipulated by the International Union of Railways UIC. If the received signal field strength P _R at the predicted switching position P1 is lower than the preset threshold, a predicted switching position is repeatedly set, and the above steps are repeated until the received signal field strength at the set predicted switching position meets the switching requirement.

It should be noted that, as shown in FIG. 3 , before the train arrives at the predicted switching position, the predicted switching position can also be set again to achieve faster, higher quality, and smoother switching.

The invention combines the characteristics of the rail transit system running on a fixed track, and its running track is fixed, and the train is accurately positioned by using the wheel-rail range finder and the transponder; Based on the channel model and environmental information at the position, the handover trigger point that meets the handover requirements is predicted in advance (that is, the handover position is predicted, and the received signal field strength at this position is greater than or equal to the preset threshold), so that the handover is performed at the predicted handover position , to achieve fast, smooth and reliable switching in high-speed moving and complex rail transit scenarios.

Apparently, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those of ordinary skill in the art can also make It is impossible to exhaustively list all the implementation modes here, and any obvious changes or changes derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims (10)

1. under track traffic high-speed mobile environment based on a changing method for channel information, it is characterized in that, comprise the following steps:

The prediction switching position of S1, setting train, and calculate the distance between described prediction switching position and to be switched base station;

S2, according to the described distance that calculates and channel model corresponding to described prediction switching position, calculate the path loss of described prediction switching position;

S3, arrive the Received signal strength field intensity at described prediction switching position place according to described path loss calculation train;

S4, judge whether described Received signal strength field intensity reaches pre-determined threshold;

If S5-1 described Received signal strength field intensity is more than or equal to described pre-determined threshold, then carries out switching and prepare, when reaching described prediction switching position to make train, be switched to described to be switched base station;

If S5-2 described Received signal strength field intensity is less than described pre-determined threshold, then repeat step S1 to step S4, till described Received signal strength field intensity reaches described pre-determined threshold.

2. changing method according to claim 1, is characterized in that, step S1 comprises:

Obtain the distance D between train and current base station ₁;

The distance D between described prediction switching position and to be switched base station is calculated according to following formula (1) ₂:

D ₂＝D-D ₁-D _p(1)

Wherein, D is the distance between described current base station and described to be switched base station, D _pfor the distance between train and described prediction switching position.

3. changing method according to claim 2, is characterized in that, after setting described prediction switching position, and the distance D between train and described prediction switching position _pbetween 100m-500m.

4. changing method according to claim 2, is characterized in that, obtains the distance D between train and current base station ₁step comprise:

Obtain the distance D between transponder and current base station _iD;

Measure the relative distance D of train and described transponder _r;

Distance D between train and current base station ₁equal D _iDwith D _rsum.

5. changing method according to claim 4, is characterized in that, adopts the relative distance D of wheel track stadia surveying train and described transponder _r.

6. changing method according to claim 1, is characterized in that, in step s 2, calculates described path loss according to following formula (2):

PL(dB)＝A+Blog ₁₀(D ₂)(2)

Wherein, PL (dB) is described path loss, D ₂for the distance between described prediction switching position and to be switched base station, when described channel model be respectively overpass, cutting, station, tunnel, city, suburb, rural area and river time, A with B is the preset parameter corresponding with described channel model.

7. changing method according to claim 1, is characterized in that, in step s 2, calculates described path loss according to following formula (3):

PL(dB)＝Δ ₁+74.52+26.16log ₁₀(f)-13.82log ₁₀(h _b)

(3)

-3.2log ₁₀(11.75h _m) ²+[44.9-6.55log ₁₀(h _b)+Δ ₂]log ₁₀(D ₂)

Wherein, f is operating frequency, h _band h _mrepresent the effective depth of described to be switched antenna for base station and the effective depth of train antenna respectively, D ₂for the distance between described prediction switching position and to be switched base station, when described channel model be respectively overpass, cutting, station, tunnel, city, suburb, rural area and river time, Δ ₁and Δ ₂for the preset parameter corresponding with described channel model.

8. changing method according to claim 1, is characterized in that, in step s3, calculates according to following formula (4) the Received signal strength field intensity that train arrives described prediction switching position place:

P _R＝P _T-(PL+L _BTX+L _MRX+F _T-G _b-G _m)(4)

Wherein, P _rfor train arrives the Received signal strength field intensity at described prediction switching position place, P _tfor the transmitting power of described to be switched base station transmitter, PL is described path loss, L _bTXfor the device loss of described to be switched Base Transmitter link, L _mRXfor the device loss of train receiver, F _tfor retaining total nargin, G _band G _mrepresent described to be switched bs antenna gain and mobile portable antennas gain respectively.

9. changing method according to claim 8, is characterized in that, the total nargin F of described reservation _tcalculated by following formula (5):

F _T＝L _SF+L _MP+L _HM+L _IT+L _OA+L _TC(5)

Wherein, L _sFfor shadow fading nargin, L _mPfor multipath fading nargin, L _hMfor high-speed mobile fade margin, L _iTfor interference nargin, L _oAfor device aging nargin, L _tCfor row control business nargin.

10. changing method as claimed in any of claims 1 to 9, is characterized in that, described pre-determined threshold is-85dB.