CN102300274A - Geographical-position-information-based fast handover method for time-division duplex long term evolution (TD-LTE) system - Google Patents

Abstract

A fast switching method for TD-LTE communication system based on geographic location information Aiming at the phenomenon of frequent cell switching in high-speed railway TD-LTE communication system, as well as the requirements of short switching time and high switching success rate, a method based on geographic location is proposed. TD-LTE fast switching method of information. According to the train's running position, speed and direction, after the network planning is completed, a list of neighboring cells is generated in advance, and the switching position of each cell is pre-set, that is, the longitude and latitude position information. When the train enters the overlapping area of the two cells and arrives When the handover position is predetermined, the source base station eNodeB performs handover according to the measurement report of the user terminal UE. The method can dynamically adjust the handover method according to the mobile speed of the user terminal UE, so as to solve the problem of fast handover in a high-speed mobile environment, reduce the number of communication drops, improve the handover success rate, enhance the service quality of high-speed broadband mobile services, and promote The development of multimedia broadband mobile Internet services in high-speed railway trains meets the growing needs of passengers for mobile communication services.

Description

A fast switching method of TD-LTE communication system based on geographic location information

Technical field:

The present invention aims at the high-speed railway Time-Division Duplex Long-Term Evolution technology (Time-Division Duplex Long-Term Evolution, TDD-LTE or TD-LTE) communication system with frequent cell handover, short handover time, and high handover success rate requirements, and proposes a geographically-based TD-LTE fast switching method for location information. The method can be applied to TD-LTE, Frequency-Division Duplex Long Term Evolution (Frequency-Division Duplex Long Term Evolution, FDD-LTE or FD-LTE) communication systems for fast handover in high-speed rail environments.

Background technique:

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

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

2. Switch decision (switching algorithm);

3. Switch execution;

The handover measurement is completed by the user terminal (User Equipment, UE) and the LTE base station, which is called an evolved node B (Evolved Node B, eNodeB). The entity (Mobility Management entity, MME) cooperates to complete. 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.

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 speeds, 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.

But on the other hand, the train-to-ground broadband communication link of high-speed railway 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. Reduce the complexity of system design and operation. And it can help reduce the complexity of some algorithms, obtain higher spectrum efficiency and transmission quality than general cellular communication under the same conditions, and improve the smoothness of cell handover.

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.

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.

Improving handover performance can be considered from the following three aspects:

(1) In terms of network planning, by adopting a reasonable wireless coverage scheme, the total number of handovers during the entire operation of the train is reduced, the length of the handover zone is ensured, and the handover area is reasonably set.

(2) In terms of network optimization, by adjusting parameter settings and improving the wireless coverage environment, the phenomenon of ping-pong switching is reduced, the rate of dropped calls is reduced, and the smooth completion of switching is ensured.

(3) In the selection of the handover algorithm, select an efficient and fast handover algorithm.

Invention content:

The content of the present invention is to support the requirement of fast handover of the high-speed railway TD-LTE communication system, and proposes a handover decision algorithm based on geographic location information to solve the handover method between adjacent cells.

The following is a description of the algorithm in the present invention:

According to the train's running position, speed and direction, after the network planning is completed, a list of neighboring cells is generated in advance, and the switching position of each switching zone is pre-set, that is, the longitude and latitude position information. When switching locations, the source base station eNodeB performs switching according to the measurement report of the user terminal UE.

1. Prerequisites for implementing TD-LTE fast handover algorithm based on geographic location information

1) The train is equipped with a Global Positioning System (Global Positioning System, GPS): This algorithm requires the user terminal UE to be able to report the train position and speed information to the source base station eNodeB.

2) Carry out measurement and statistics on the location when the train is switched, and obtain an estimated switching reference point. This point is the statistical average of multiple measurements of the position where the train triggers the switch; the statistics of the switch location need to be carried out frequently, and the switch reference point should also be updated regularly.

2. Basic concept of TD-LTE fast handover algorithm based on geographic location information

1) Handover reference point: a coordinate point obtained based on a large number of measurement statistical results, which is the statistical average of the position where the train triggers handover after multiple measurements.

2) Speed threshold: If the train running speed is higher than this speed threshold, this algorithm will be started, otherwise the normal switching procedure will be followed.

3. The specific implementation process is as follows:

1) The target cell designation method is applied to shield the cells behind the train. The cell information table broadcast by the source base station eNodeB to the user terminal UE through the system message only contains the only neighbor cell information, that is, the target base station eNodeB in front of the train.

2) Modify the content of the measurement report: In addition to the measurement results reported by the user terminal UE, the measurement results related to the receiving performance of the source base station eNodeB and the target base station eNodeB: Reference Signal Received Power (Reference Signal Receiving Power, RSRP) and received signal strength indication In addition to (Received Signal Strength Indication, RSSI), it will also contain the position and speed information of the user terminal UE. The location information includes the cell identification number, that is, the E-UTRAN Cell Global Identifier (ECGI) and the longitude and latitude location coordinates (x, y).

3) Modify the cell list in the base station eNodeB

The cell list has 4 attributes in total, which are:

a) The cell identification number ECGI, arranged smoothly according to the location of the cell.

b) The location coordinates of the handover reference point. There are two handover reference points in a certain cell and two neighboring cells.

c) Belonging base station eNodeB, indicating the home base station eNodeB of a certain cell.

d) The belonging mobile management entity MME/Serving Gateway S-GW (Serving Gateway), which indicates the belonging MME/S-GW of a cell base station eNodeB.

4) The source base station eNodeB extracts the position and speed information in the measurement report, namely ECGI, coordinates (x, y) and speed S, and S is compared with the speed threshold. If S≥speed threshold, it is decided to start the fast switching algorithm; if S<speed threshold, then use the conventional switching algorithm.

5) If the fast handover algorithm is used, when the user terminal UE moves to coordinates (x, y), the user terminal UE sends a measurement report to the source base station eNodeB, and the source base station eNodeB triggers handover according to the measurement report, and X2 interface handover is prioritized, if There is no X2 interface, and the S1 interface is used for switching.

6) The size of the cell handover overlap area should be positively correlated with the selected handover interface, that is, the X2 interface is adopted

The length of the overlapping area is smaller when the interface is switched than when the S1 interface is switched.

Description of drawings:

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

Figure 2 eNodeB Cell/Neighboring Cell List

Figure 3 Flow chart of TD-LTE fast handover algorithm based on geographic location information

Figure 4 is a signaling flow chart based on the S1 interface handover algorithm

Figure 5 Signaling flow chart based on X2 interface handover algorithm without S-GW relocation

Figure 6 Signaling flow chart with S-GW relocation handover algorithm based on X2 interface

Detailed ways:

The invention adopts the combination of theoretical analysis, simulation modeling and actual testing. Below in conjunction with accompanying drawing and embodiment, specific embodiment of the present invention is described in further detail:

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. Figure 2 is a list of eNodeB cells/neighboring cells.

Figure 3 is a flow chart of the TD-LTE fast handover algorithm based on geographical location information. According to this flow chart, when the UE receives the measurement quantities, including: the speed of the user terminal UE, latitude and longitude information, RSRP and RSSI of the source cell, if entering The handover zone also includes RSRP and RSSI of the target cell. The user terminal UE periodically reports the measurement amount, and the eNodeB of the serving cell 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 (1)

The source cell eNodeB will trigger a 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 handover point preset in the serving cell eNodeB meets the handover criterion requirement, that is, the distance difference between the two positions is less than a distance threshold Distance_threshold,

ΔL＜Distance_threshold (2)

The eNodeB of the source cell 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 eNodeB of the source cell is lower than the speed threshold Speed_threshold, a conventional handover judgment criterion is used for handover, and the algorithm description here is omitted in the flow chart.

In the LTE, the user terminal UE has two types of handover procedures in the active state, namely, the S1 interface handover procedure and the X2 interface handover procedure. According to different interfaces, describe the signaling process of this handover in detail.

For intra-LTE mobility, X2 handover occurs between eNodeBs. However, when there is no X2 interface between base station eNodeBs or the source base station eNodeB has initiated a handover to a specific base station eNodeB through the S1 interface, S1 handover will be triggered. Figure 4 shows the signal flow chart of the handover algorithm of the S1 interface, in which steps 2 to 16 are the handover preparation process, steps 17 to 19 are the handover execution process, and steps 20 to 26 are handover complete the process. During the handover preparation process, the user terminal UE periodically reports its own location information (latitude and longitude coordinates) and speed information, as well as the source cell or target cell (when the UE enters the handover zone) RSRP and RSSI measurement reports to the source base station eNodeB , according to the speed information, the source base station eNodeB decides whether to use the fast handover algorithm or the conventional handover algorithm. When the speed of the user terminal UE is greater than the speed threshold Speed_threshold, the source base station eNodeB initiates a fast handover, and when the distance difference between the longitude and latitude coordinates in the measurement report and the handover point coordinates is less than the distance threshold value Distance_threshold, the source base station eNodeB initiates a handover request to the source MME, Then the source MME sends a relocation request to the target MME, the target MME sends a session creation request to the target S-GW, and the target S-GW sends a session creation response to the target MME after receiving the request; then the target MME sends a handover request signaling to the target base station eNodeB, after receiving the handover request letter, the target base station eNodeB establishes a radio bearer and sends a handover request response to the target MME; then the target MME sends a request to create an indirect data forward tunnel to the target S-GW, and the target S-GW sends a create The indirect data fronthaul tunnel responds to the target MME; after receiving the response, the target MME sends a fronthaul location response to the source MME, and the source MME sends a request to the source S-GW to create an indirect data forward tunnel after receiving the response, and the source S-GW receives the request Reply to create an indirect data forward tunnel response to the source MME; after receiving the response, the source MME initiates a handover command to the source base station eNodeB, and then the source base station eNodeB sends the handover command to the user terminal UE after receiving the handover command, and completes the handover preparation process. Afterwards, the source base station eNodeB starts to send the state transition information of the base station eNodeB to the source MME. After receiving the information, the source MME sends the forward access context notification to the target MME, and the target MME sends the forward access context confirmation and sends the base station eNodeB state transition information to the target base station eNodeB. ; Then the source base station eNodeB starts to directly forward the data to the target base station eNodeB or forward the data to the target S-GW through the source S-GW, and the target S-GW sends the indirect data forwarding to the target base station eNodeB, and the handover execution process is completed at this point. The third part is the completion of the handover, which is mainly to update the tracking area (Tracking area updated, TAU) and release the resources of the source eNodeB, source MME and source S-GW.

Handover via the X2 interface can be triggered by default, unless no X2 interface is established or the serving cell eNodeB is configured to use S1 handover. X2 interface handover is divided into handover with and without S-GW relocation. Figure 5 is a signaling flow chart based on the X2 interface handover algorithm without S-GW relocation. In this process, the MME itself does not change and the MME determines the S-GW It is also used without changing the situation, using the X2 interface to switch a user terminal UE from the source base station eNodeB to the target base station eNodeB. Steps 2 to 7 are handover preparations, and the handover decision is the same as the S1 interface handover, the difference is that the handover request is directly sent by the source base station eNodeB to the target base station eNodeB through the X2 interface; steps 8 to 9 are handover execution During the process, the data that arrives at the source base station eNodeB but will not be delivered to the user terminal UE in the future is directly forwarded to the target base station eNodeB through the X2 interface; Steps 10 to 18 are the handover completion stage, and the target base station eNodeB sends a path switching request message to the MME. Notify the UE that the cell has been changed, including the Tracking Area Identity (TAI) + ECGI of the target cell, and that the Evolved Packet System (EPS) bearer list should be switched. The MME decides that the S-GW can continue to serve the UE. Then MME sends a modify bearer request to S-GW, S-GW sends a modify bearer request to the public data network (Public Data Network, PDN), PDN sends a confirmation response to S-GW after receiving it, and S-GW receives the response Afterwards, the bearer modification response information is sent to the MME, and the downlink data path is switched to the target base station eNodeB. In the following steps, the target eNodeB sends resource release information to the source eNodeB, and performs the tracking area update TAU process.

FIG. 6 is a signaling flow chart of an S-GW relocation handover algorithm based on an X2 interface. This process is used when the MME itself does not change and the MME decides that the S-GW should be relocated, using the X2 interface to switch a UE from the source base station eNodeB to the target base station eNodeB. Steps 2 to 7 are handover preparations, and the handover decision is the same as the S1 interface handover, the difference is that the handover request is directly sent by the source base station eNodeB to the target base station eNodeB through the X2 interface; steps 8 to 9 are handover execution In the process, the data that arrives at the source base station eNodeB but will not be delivered to the user terminal UE in the future is directly forwarded to the target base station eNodeB through the X2 interface; Steps 10 to 17 are the handover completion stage, and the target base station eNodeB sends a path switching request message to the MME. Inform the user terminal that the UE has changed the cell, including the ECGI of the target cell, and update the EPS bearer list. The MME decides that the S-GW is relocated and selects a new S-GW to serve the UE. Then the MME sends a session creation request to the target S-GW, and the target S-GW sends a modify bearer request to the PDN. After receiving the request, the PDN sends a confirmation response to the target S-GW. After receiving the response, the target S-GW sends it to the MME to create a session. Session response information, the downlink data path is switched to the target base station eNodeB. After receiving the information, the MME sends a path switching request response to the target base station eNodeB, and then the uplink data is sent to the PDN through the target base station eNodeB and the target S-GW, and then the target base station eNodeB sends a release The resource information is sent to the source base station eNodeB, and resources are released between the MME and the source S-GW, the session request is deleted, and the tracking area update TAU process is performed.

To sum up, the fast handover method of TD-LTE communication system based on geographic location information can 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. This patent can effectively improve the handover success rate, and can dynamically adjust the handover algorithm according to the speed of the user terminal UE to ensure the quality of wireless communication services.

The above descriptions are only examples of the present invention, and do not mean that the present invention is limited to these described embodiments. For those skilled in the art, it is possible to improve the specific implementation of the present invention or perform equivalent replacements and modifications to some contents without departing from the spirit of the technical solution of the present invention, and all of them should be included in the scope of the claims of the present invention Inside. At the same time, it should be noted that the technical solution of the present invention is not specifically aimed at the TD-LTE wireless communication system. It is equally applicable to the wireless communication system of FD-LTE.

Claims (5)

1. fast switch over method based on the TD-LTE communication system of geographical location information, be used for supporting of the requirement of high-speed railway TD-LTE communication system to quick switching, a kind of switch decision algorithm based on geographical location information has been proposed, with the function that realizes switching fast between neighbor cell.

2. according to right 1 described method, its thought is: according to train operation position, speed and direction, after the network planning is finished, generate a adjacent cell list in advance, and the position of pre-set each switching band, be the longitude and latitude positional information, when train entered overlapping region, two sub-districts and arrive predetermined switching position, source base station eNodeB switched according to the measurement report of user terminal UE.

3. according to the precondition of right 2 described these methods:

1) train is installed gps system

Statistics is measured in place when 2) train being switched, obtains the switching reference point of an estimation

4. according to right 3 described preconditions, the concrete implementation step of this method comprises:

A) method is specified in the application target sub-district, and shielding is in the sub-district at train operation rear.

B) user terminal UE revises the measurement report content

C) revise the interior cell list of base station eNodeB

D) source base station eNodeB extracts position and the velocity information in the measurement report

E) judge the quick handoff algorithms of execution according to speed

F) switching the overlay region size for the sub-district should be relevant with the switching interface type of selecting

5. switch implementation step fast according to right 4 described TD-LTE, be divided into the flow chart of two big class signalings according to the different this patents of the interface that switches: 1) based on the TD-LTE quick switch signaling flow chart of S1 interface; 2) based on the TD-LTE quick switch signaling flow chart of X2 interface; And switch for X2 interface, according to the reorientation whether S-GW is arranged in handoff procedure, this patent comprises the signaling process figure of two classes based on X2 interface: 1) do not have S-GW reorientation hand off signaling flow chart based on X2 interface; 2) based on X2 interface S-GW reorientation hand off signaling flow chart is arranged.

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