CN103945479A - Throughput-based high-speed rail wireless special network cell switching optimal switching point determining method - Google Patents

Abstract

Aiming at the selection of the best handover reference point for the fixed-point handover algorithm of high-speed railway, a method for confirming the best handover reference point for high-speed railway wireless private network cell handover based on the throughput of the source and destination eNodeB is proposed. The train is loaded with downlink full-load business. The train implements a fixed-point switching process for each switching reference point, and records the difference in throughput for a certain period of time before and after the switching. Multiple running trains record and count the switching of each preset switching reference point candidate point The average difference of throughput before and after the handover is selected as the best handover reference point where the system throughput difference before and after the handover is the smallest. In engineering, use this method to establish all optimal switching reference points for the entire high-speed railway network, and use the switching method based on geographic location. The method can solve the problem of fast handover in a high-speed mobile environment, reduce the number of times of communication drop, improve the handover success rate, enhance the service quality of high-speed broadband mobile services, improve the handover success rate, and enhance the service quality of high-speed broadband mobile services.

Description

Confirmation method of optimal switching point for high-speed rail wireless private network cell handover based on throughput

Technical field:

The present invention aims at the high-speed railway wireless private network Time Division Duplex Long Term Evolution technology (Time-Division Duplex Long Term Evolution, TDD-LTE or TD-LTE) communication system with frequent handover, short handover time, and high handover success rate requirements. On the basis of the existing fast handover algorithm based on geographic location information, a method for confirming the best handover point for high-speed rail wireless private network cell handover based on the throughput of the source and target base stations is proposed. This method can be applied to TD-LTE, Frequency-Division Duplex Long Term Evolution (FDD-LTE or FD-LTE) communication system in the fast handover algorithm based on geographical location information in the high-speed rail environment. the

Background technique:

Generally, the handover process in an LTE system is divided into the following three steps:

1. Switch measurement (including measurement filtering, algorithm triggering, measurement report);

2. Switch judgment (switching algorithm);

3. Switch execution;

The handover measurement is completed by the user equipment (UE) and the LTE base station, which is called the evolved node B (Evolved Node B, eNode B). The handover decision is made in the base station, and the handover execution is performed in the user terminal UE, the base station, and the mobile management entity. (Mobility Management entity, MME) under the joint cooperation. For high-speed railway TD-LTE network deployment, the same-frequency network solution is currently used, that is, the central frequency points used by adjacent cells are the same. The decision event criterion for intra-frequency handover in the LTE system adopts the A3 event, that is, when the quality of the measured neighbor cell is higher than the quality of the serving cell, and the difference exceeds a certain threshold, after this state lasts for a period of trigger time (Trigger to Time, TTT), the user terminal UE Report the A3 event report to the network side. After receiving the report, the network side makes a handover judgment. After the judgment is successful, it executes the handover command to the adjacent cell. Since there may be multiple adjacent cells that meet the A3 event report at the same time, therefore, the A3 report Multiple neighboring cells whose cell quality meets the switching conditions can be included at the same time. At present, adopting this decision criterion for macro-cellular networking can fully meet the requirements of the system. the

When the train speed reaches 350 km/h and the distance between base stations is 10 km, the switching interval between base stations is reduced to 100 seconds, resulting in frequent crossing of cells. Due to the increase of moving speed, the receiving threshold of the receiver is bound to be raised. In order to ensure reliable transmission and a certain transmission efficiency, it is generally necessary to reduce the distance between base stations and increase the coverage field strength. But this is not the only way. If you can effectively suppress the rise of the receiving threshold at high speed, try to keep the existing base station distance of 6-10 kilometers, and maximize the effective use of the remote radio unit (RRU) by deploying Existing resources, reduce a lot of engineering investment, and facilitate maintenance. However, higher requirements are put forward for the resource management, switching time and quality of the base station. the

But on the other hand, the broadband communication link of high-speed railway trains has its own characteristics:

Due to the distribution of railway lines, the distribution of base stations is different from the planar coverage characteristics of general cellular communications. As a result, the predictability of the base station distribution, the predictability of the train running route, the predictable position of the train, the predictable time of the train crossing the cell, and many other predictable information that are helpful to the system design can be used to improve the performance of the system. It reduces the complexity of system design and operation, and can help reduce the complexity of some algorithms, obtain higher spectral efficiency and transmission quality than general cellular communication under the same conditions, and improve the smoothness of cell switching. the

Another factor affecting high-speed rail coverage is fast switching. Assuming that the size of the handover area remains the same, the higher the moving speed, the shorter the time to cross the handover area. When the mobile speed of the user terminal UE is fast enough, so that the time for crossing the handover area is less than the minimum delay for the system to process the handover, the handover process cannot be completed, resulting in call drop. the

Due to the particularity of the high-speed railway channel environment and networking mode, the above-mentioned A3 handover judgment criterion cannot adapt to the high-speed railway environment. Due to the high-speed running of the train, the handover time is short; in addition, factors such as complex terrain and surrounding electrical equipment on the high-speed railway The channel environment will also have a greater impact. Using the A3 handover judgment criterion will result in frequent handover failures, reduced handover success rate, lower communication quality, and poor customer experience. Therefore, it is necessary to consider adopting a judgment criterion suitable for the high-speed railway environment. the

The fast handover algorithm based on geographic location information is proposed for the particularity of the above-mentioned high-speed railway channel environment and networking mode, in order to shorten the handover delay, ensure that the user terminal UE is handed over at a reasonable location, and meet the requirements of fast handover under high-speed conditions. Require. The key step in the engineering practice of the fast handover algorithm based on geographic location information is to determine the position of the best handover reference point. The location selection of the handover reference point directly affects the call drop rate of the user during the handover process. the

Invention content:

The present invention aims at the requirements of the fast switching algorithm based on geographical position information of the TD-LTE communication system of the high-speed railway wireless private network, and proposes a method of switching the optimal switching point of the high-speed railway wireless private network cell switching based on the throughput of the source target cell The confirmation method solves the problem of fast switching in a high-speed mobile environment, reduces the number of dropped calls, improves the success rate of switching, and enhances the service quality of high-speed broadband mobile services. the

The present invention realizes the selection of the optimal switching point in the fast switching algorithm based on geographic location information, and the specific steps are as follows:

1. According to the train running position, speed and direction, after the network planning is completed, generate a list of neighboring cells in advance, and pre-set the switching position of each switching zone, that is, the longitude and latitude position information. the

2. Apply the target cell designation method to shield the cells behind the train running, and the adjacent cells reported to the train only contain the unique frequency point information of the adjacent cells, that is, the cells in front of the train running. the

3. The cell is divided into a handover zone and a non-handover zone according to a preset distance threshold. In the handover zone, the coverage overlapping area is divided into several equal parts according to the preset sampling point threshold, and the segment interval points are taken as the best handover reference point candidate point set. As shown in the figure, base station A is the source eNodeB, base station B is the target eNodeB, and the length of the coverage overlapping area is set to D meters. The overlapping area is divided into n equal parts, and there are n+1 handover reference points in total. Let the point that is L meters away from the source base station A be the first handover reference point candidate point, set as P ₁ , then the i-th handover reference point candidate point P _i is at a distance from base station A of d=L+(i-1) *D/n m.

4. In the experimental network, the train runs at high speed, and the long-term FTP download service test is carried out, that is, the train loads the downlink full traffic service. Since there is only one user of the train in the experimental network, the wireless resources of the cell can be allocated to the train. Therefore, The throughput of the train is directly determined by the quality of the wireless link between the train and the base station. When the quality of the wireless link of the train is better, the full load throughput of the train will be correspondingly greater. Therefore, the throughput parameter when the train is fully loaded can well reflect the wireless link communication quality of the train. For the train switching at a certain fixed point, the difference in the throughput of the train in the same period of time before and after the switch is to a certain extent The above reflects the performance of the train when switching at this point, that is, if the throughput before the switching is too large compared with the throughput after the switching, it means that the switching point is too early, otherwise it means that the switching is too late. Therefore, choosing a good handover reference point can be translated into selecting a handover point, so that the difference in throughput of full-load services before and after the handover obtained by the fixed-point handover of the train at this position is the smallest, and this point can be used as the handover reference point candidate for the current sampling The best switching reference point in the point set. the

5. Start to initialize the point selection method, set the first handover reference point candidate point P ₁ of the source eNodeB as the initial handover reference point, and write its geographic location parameter into the source eNodeB. The train starts to report the measurement report according to the measurement configuration. The measurement report includes the geographical location information of the train itself. When the train arrives at the designated handover candidate point, the source eNodeB decides to trigger the fixed-point handover event according to the measurement report reported by the train, and issues a fixed-point handover command to the UE. , perform fixed-point switching at the selected switching candidate point position _P1 , and record the average throughput of the FTP download service for a period of time t (for example, 50ms, depending on the actual engineering situation) before and after the switching, which are respectively recorded as T _hobefore and T _hoafter . Calculate the difference of the train throughput before and after the switch as ΔT, that is, ΔT=|T _hobefore -T _hoafter |.

6. After performing step 5 on a candidate point p _i in the handover candidate point set {p ₁ , p ₂ , p ₃ ...p _n }, artificially cut off the connection between the train and the target eNodeB, and switch the train back to the source eNodeB , and set the fixed-point handover reference point of the cell as the best handover reference point candidate point p _i+1 adjacent to it, so as to perform the steps shown in step 5 on the next handover candidate point p _i+1 adjacent to it In this way, the data of multiple candidate points can be measured when the train passes through the switching belt in one trip, and the work efficiency can be improved.

7. Since the train runs very fast and the distribution of candidate points is relatively dense, it may be that the time between the train passing through the switching reference point candidate point p _i and the switching reference point candidate point p _i+1 is not enough to implement the method described in step 6 , then according to the actual speed and the density of candidate points, consider skipping measurement, measure the candidate point p _j whose distance from the previous candidate point is enough to implement step 6, where ji>1, and switch the reference point candidate point p _j Set it as the reference point for the next measurement, which can reduce the number of repeated train runs in actual engineering practice and improve work efficiency.

8. The train repeatedly travels from the source eNodeB to the target eNodeB, repeats step 5 for multiple times, obtains multiple measurement data of each optimal handover reference point candidate point, and performs statistical averaging on each handover reference point candidate point data, The average value of the throughput difference of each handover reference point candidate point is recorded as Then take out the point with the smallest average value of the throughput difference among these points, and this point is the best switching reference point among these points. The denser the segmentation of the switching zone, the more accurate the optimal switching reference point will be, which can be divided according to the actual situation. If it needs to be precise, it can be divided more densely, and if it needs to reduce the complexity, it can be divided more sparsely.

Description of drawings

Figure 1 Schematic diagram of community coverage in high-speed rail scenarios

Figure 2 Flow chart of TD-LTE fast handover algorithm based on geographic location information

Figure 3 Schematic diagram of switching reference point division

Fig. 4 Flowchart of the optimal switching reference point selection method

Detailed ways

Below in conjunction with accompanying drawing and embodiment, specific embodiment of the present invention is described in further detail:

1. After the network planning along the high-speed railway is completed, you can get a district planning table along the high-speed railway. According to the planning table, you can pre-calculate the position of the handover overlapping coverage zone of each district along the railway, and the handover of each pair of adjacent districts By using the method shown in the content of the invention above, the optimal handover reference point of the fixed-point handover algorithm of the adjacent cell handover overlapping coverage zone is obtained, and finally a list of the best handover reference points of the fixed-point handover algorithm of the entire network is generated, and the base station of the corresponding cell Save the switching zone position and the best switching reference point position associated with itself. the

2. According to the obtained list of best handover reference point positions in the whole network, set up handover benchmarks (or sensors) at the best handover reference point (or range) of each adjacent cell handover zone, and install global The positioning system (GPS) and the corresponding sensors continuously use the measurement report information to report the position information to the source base station during the running of the train. When the train runs to the range of the best switching reference point, the train senses the best switching reference point through the sensor installed on the body. When the point marker exists, the train sends a handover request to the eNodeB, and the source eNodeB responds to the handover request and starts the fixed-point handover signaling process until the train is handed over to the target cell. the

Fig. 1 is a schematic diagram of cell coverage in the high-speed rail scene in the present invention. According to the linear distribution of the high-speed rail, the mobile communication network along the high-speed rail adopts chain-like dedicated cell coverage. In order to reduce the number of handovers, the baseband of BBU (Baseband Unit)+RRU is adopted Deployment mode of unit + distributed remote radio unit. the

Fig. 2 is a flow chart of TD-LTE fast handover algorithm based on geographic location information. This switching algorithm requires the user terminal UE to install a GPS positioning system in order to report the train position and speed information to the source base station. the

According to this flow chart, the user terminal UE periodically reports measurement information, including the reference signal received power of the source eNodeB and the target eNodeB, train speed and position information. The source base station triggers the handover procedure according to the speed of the user terminal UE. When the speed of the user terminal UE is greater than the set speed threshold Speed_threshold:

s＞Speed_threshold

The source eNodeB will trigger the fast handover procedure. When the distance between the longitude and latitude position coordinates uploaded by the user terminal UE and the longitude and latitude position coordinates of the preset handover point in the source base station meets the handover criterion requirements, that is, the distance difference between the two positions is less than a distance threshold Distance_threshold:

ΔL＜Distance_threshold

The source eNodeB initiates fast handover signaling to handover the user terminal UE to the target cell. If the speed reported by the user terminal UE obtained by the source eNodeB is less than the speed threshold Speed_threshold, the conventional handover judgment criterion is used for handover. the

Fig. 3 is a schematic diagram of optimal handover reference point division. As shown in the figure, the cell handover overlapping zone has a distance of D meters, which is divided into n equal parts, and there are n+1 handover reference point candidates in total. The distance between the first candidate handover reference point p ₁ and the source eNodeB is L meters, and the i-th handover reference point P _i is at a distance of d=L+(i-1)*D/n meters from the base station A. The train travels from the source eNodeB to the target eNodeB at high speed.

Fig. 4 is a flowchart of a method for selecting an optimal handover reference point. the

Claims (8)

1. A method for selecting the best handover reference point in the process of high-speed railway fixed-point handover algorithm, which is suitable for the selection and determination of the best handover reference point in high-speed railway fixed-point handover, and proposes a high-speed railway based on throughput A method for confirming the best handover reference point for wireless private network cell handover, so as to realize the fast handover function based on geographic location information of adjacent cells in high-speed railways. 2. The method according to claim 1, the idea of which is: according to the UE average throughput difference before and after a period of switching point switching, select the minimum point of the throughput difference before and after switching as the best switching reference point. 3. The method according to claim 2, according to the preset sampling point interval, the cell coverage overlapping area is divided into several equal parts, and the segmentation interval point is taken as the best handover reference point candidate point set, based on this point Set the optimal switching reference point selection algorithm. 4. The method according to claim 3, when the train enters the handover zone between the two cells, the train is loaded with downlink full-load services, occupying all the resources of the cell, so that the train's downlink throughput reaches the maximum value, so as to perform the measurement and calculation of the next step . 5 . The method according to claim 4 , wherein the throughput difference is calculated for each optimal handover reference point candidate in turn, and the measurement data is recorded. 6. according to the described method of claim 5, repeat the described method of claim 5, obtain multiple throughput measurement data and carry out statistical average, select the minimum point of throughput difference before and after handover as the best handover reference point of this subdistrict. 7. Since the wireless link propagation environment is different for every two different handover cells, the position of the best handover reference point for different wireless propagation environments will also be different. For different cell handover zones, the best handover reference point should be re-measured select. 8. According to the preceding claims, its engineering practice is as follows: After the network planning along the high-speed railway line is completed, a community planning form of the high-speed railway is obtained, and the position of the handover zone of each community along the railway line is calculated in advance. For each pair of handover zones of adjacent communities, all The best handover reference point of the adjacent cell handover zone, and generate a list of the best handover reference points for the entire network. Further set up a handover benchmark (or sensor) at the best handover reference point (or range) of each adjacent cell handover zone, and install the Global Positioning System (GPS) and corresponding sensors on the train in advance. The range of the optimal handover point is sensed, the handover request is sent to the source base station, and the fixed-point handover signaling process is started until the handover is made to the target cell.