CN100397943C - A method of inter-frequency switching in a code division multiple access communication system - Google Patents

Abstract

The invention discloses a method for inter-frequency handover of a CDMA system, which is applied to switching from the second carrier frequency of the source cell to the target cell, where both the source cell and the target cell have the first carrier frequency, including: The attribute of the second carrier frequency is set to the carrier frequency coverage edge; the absolute threshold value of the 2D event is set to be equal to the minimum signal-to-noise ratio to ensure the quality of service plus the signal-to-noise ratio between the second carrier frequency and the first carrier frequency of the source cell Maximum deviation; when a 2D event is triggered; the radio network controller judges whether the carrier frequency attribute of the source cell where the mobile station is located is the second carrier frequency at the carrier frequency coverage edge, and if so, hard handover from the second carrier frequency of the source cell to The first carrier frequency, and then soft handover from the first carrier frequency of the source cell to the first carrier frequency of the target cell. The invention also includes an access method. The invention avoids the impact on the system of starting the compression mode at the edge of the cell, and overcomes the impact of the extra burden on the system in the pseudo-pilot switching method.

Description

A method of inter-frequency switching in a code division multiple access communication system

technical field

The invention relates to code division multiple access (CDMA) communication technology, in particular to a method for inter-frequency switching in the CDMA communication system.

Background technique

In a cellular mobile communication system, when a mobile station (UE) moves from one cell to another, in order to maintain communication continuity, the communication link must be transferred from the source cell to the target cell, which is handover. In a CDMA communication system, handover can be divided into two categories: soft handover and hard handover.

The characteristic of soft handover is that when the UE starts to contact a new cell, it will not immediately interrupt the connection with the source cell, so it will not cause service interruption, and the handover success rate is high, which is a unique technology of CDMA communication system .

The characteristic of hard handover is that the UE first breaks the connection with the source cell, and then establishes the connection with the new cell, which will cause a short interruption of the communication link. When the carrier frequencies of the two cells are different, hard handover must be performed.

In the cell planning at the initial stage of network construction, a 3×1 NodeB configuration is generally adopted, that is, all three sectors are configured with the same carrier frequency. The handovers in this period are soft handovers or hard handovers at the same frequency. When the traffic volume in the coverage area cannot meet the actual needs, capacity expansion is required. One of the capacity expansion methods is to add a new carrier frequency in a sector to become a 3×2 NodeB configuration. In this way, the newly added carrier frequency forms a different-frequency same-coverage relationship with the original carrier frequency, and forms a different-frequency adjacent relationship with the original carrier frequency in the adjacent area.

If only a new carrier frequency f2 is added in one sector, as shown in Figure 1, when the UE has access to the f2 carrier frequency of cell b and moves from the edge of cell b to cell a or c, inter-frequency handover must be performed . If a carrier frequency f2 is added in several sectors at the same time, as shown in Figure 2, when the UE moves from the carrier frequency f2 of cell c to the edge, it can still perform intra-frequency handover. However, if the UE has already accessed the f2 carrier frequency of cell b or d, when the UE moves from the edge of cell b or d to cell a or e, an inter-frequency handover must be performed. For the sake of clarity, hereinafter, the originally accessed carrier frequency is referred to as the second carrier frequency, and the access carrier frequency of the target cell is referred to as the first carrier frequency.

The inter-frequency handover method commonly used at present is handover based on UE inter-frequency measurement. That is, the UE first measures the signal quality of the first carrier frequency of the target cell, and then switches to the target cell in different frequencies. The specific implementation process is:

1. After the UE establishes a dedicated channel on the second carrier frequency of the source cell, the radio network controller (RNC) sends 2D and 2F event measurement control to the UE to monitor the signal quality of the second carrier frequency of the source cell;

II. When the signal quality of the second carrier frequency of the source cell is lower than an absolute threshold, the UE reports a 2D event report, starts the compressed mode, and starts measuring the first carrier frequency of the target cell. If the signal quality of the second carrier frequency of the source cell returns to be higher than a certain threshold during the measurement of the first carrier frequency of the target cell, a 2F event is reported, and inter-frequency measurement and compressed mode are stopped.

III. During inter-frequency measurement, when the signal quality of the first carrier frequency of the target cell is found to meet the handover condition, the UE is handed over to the cell in inter-frequency.

The 2D event is: the comprehensive quality of the active set on the currently used frequency is lower than a certain absolute threshold (“The estimated quality of the currently used frequency is below a certain threshold”), the 2F event is: the estimated quality of the currently used frequency is higher than a certain threshold Absolute threshold ("The estimated quality of the currently used frequency is above a certain threshold").

In this inter-frequency handover method, it is necessary to perform inter-frequency cell measurement. Therefore, the UE needs to be a dual-receiver or if the UE is a single-receiver, it must support the compressed mode; if the UE is a single-receiver and does not support the compressed mode, this strategy will fail and only calls will be dropped.

Another method to solve this inter-frequency handover is pseudo-pilot assisted hard handover. That is, the UE first measures the signal quality of the pseudo-pilot of the target cell, and then performs an inter-frequency handover to the target cell. The specific implementation process is:

1. Configure a pilot signal in the target cell, the frequency of the pilot signal is the same as the second carrier frequency, and its strength is determined by the first carrier frequency, so as to ensure that the pseudo pilot signal can correctly reflect the first carrier frequency of the target cell signal quality;

II. After the UE establishes a dedicated channel on the second carrier frequency of the source cell, the RNC sends the measurement control of the 1A event to the UE, and monitors the second carrier frequency of the source cell and the first carrier frequency pseudo-pilot signal of the target cell quality relationship;

III. When it is detected that the pseudo-pilot signal strength of the first carrier frequency of the target cell meets the handover requirement, directly switch from the second carrier frequency of the source cell to the first carrier frequency of the target cell.

The 1A event is: the quality of a dominant pilot signal enters the relative threshold report range, that is, the quality of a cell has been improved to be close to the best cell or the overall quality of the active set, and adding this cell to the active set can obtain a relatively high combining gain.

To implement this method, a pseudo-pilot must first be established, but the current agreement does not stipulate that the NodeB must support this function. If the NodeB does not support this function, this strategy cannot be implemented. Secondly, this method adds some pilot signals to the system, which brings additional interference to the system.

Contents of the invention

In view of this, the object of the present invention is to provide a method for inter-frequency handover in a CDMA communication system, which is applied to the scenario where the second carrier frequency of the source cell is switched to the target cell, and both the source cell and the target cell have the first carrier frequency The inter-frequency handover method in this method, under the premise of ensuring the handover success rate and service quality, can avoid the adverse impact on the system caused by starting the compression mode at the edge of the cell or adding pseudo-pilot signals, and does not require equipment to support special function.

In order to achieve the above object, the present invention provides an inter-frequency handover method in a code division multiple access communication system, which is applied to switching from the second carrier frequency of the source cell to the target cell, and both the source cell and the target cell have the first carrier frequency. In frequent scenarios, the method includes the following steps:

Set the attribute of the second carrier frequency of the source cell in advance as the carrier frequency coverage edge, and the adjacent cells of the source cell have the first carrier frequency but no second carrier frequency; set the absolute threshold value of the 2D event equal to the guaranteed service The minimum signal-to-noise ratio of the quality plus the maximum deviation of the signal-to-noise ratio between the second carrier frequency of the source cell and the first carrier frequency; the maximum deviation is based on the current downlink load conditions of the second carrier frequency and the first carrier frequency of the source cell Setting, if the downlink load of the second carrier frequency is greater than the downlink load of the first carrier frequency, the maximum deviation is taken as zero; if the downlink load of the second carrier frequency is smaller than the downlink load of the first carrier frequency, a positive signal quality deviation is added according to the load deviation ;

In the source cell, the radio network controller sends the measurement control of 2D events to the mobile station;

The 2D event is triggered, and the mobile station reports the 2D event;

The radio network controller judges the carrier frequency attribute of the source cell where the mobile station is located. If the attribute is the second carrier frequency at the edge of the carrier frequency coverage, then hard handover is performed from the second carrier frequency of the source cell to the first carrier frequency of the source cell. The first carrier frequency of the source cell is soft handed over to the first carrier frequency of the target cell; otherwise, a measurement-based handover is performed.

The first carrier frequency of the source cell is pre-configured as the hard handover target carrier frequency of the carrier frequency coverage edge; the hard handover from the second carrier frequency of the source cell to the first carrier frequency of the source cell is: the second carrier frequency of the source cell The carrier frequency is hard handed over to the hard handover target carrier frequency configured for the frequency coverage edge.

Further, after the attribute of the second carrier frequency of the source cell is set as the carrier frequency coverage edge in advance, before the radio network controller sends the measurement control of the 2D event to the mobile station, the present invention includes the following access steps:

a. When the mobile station located in the source cell sends an access request message to the second carrier frequency, the radio network controller receives the access request message from the mobile station on the second carrier frequency of the source cell;

b. The radio network controller judges the relationship between the signal-to-noise ratio of the pilot signal of the second carrier frequency and the absolute threshold value of the 2D event, and if it is less than the absolute threshold value of the 2D event, execute step c; otherwise, execute step d;

c. The radio network controller establishes the radio link of the mobile station on the first carrier frequency of the source cell;

d. The radio network controller establishes the radio link of the mobile station on the second carrier frequency of the source cell.

Preferably, in the radio network controller, the message block 11 of the source cell is pre-configured in the information element of the same-frequency measurement report reported by the random access channel and the information element of the maximum number of cells reported by the random access channel.

Preferably, the second carrier frequency attribute is set as the carrier frequency coverage edge in advance, then the step a further includes the following steps:

a1. The radio network controller receives a radio resource control connection establishment request from the mobile station;

a2. Judging the attribute of the second carrier frequency, if it is carrier frequency coverage edge, execute step b; otherwise, execute step d.

It can be seen from the above solution that the present invention realizes the handover from the source cell to the target cell with a different carrier frequency through one hard handover and one soft handover in the source cell. Therefore, there is no need to start inter-frequency measurement during the handover process. For a single receiver, there is no need to support and start the compressed mode, thereby avoiding the impact on the system of starting the compressed mode at the edge of the cell; The impact of an additional burden on the system. By setting the carrier frequency coverage edge and the hard handover target carrier frequency attribute for the carrier frequency, the correctness of the scene using the present invention and the correctness of the hard handover target are guaranteed. The setting of the 2D event threshold can ensure that the signal quality of the target carrier frequency meets the service requirements during hard handover and access, and reduces the synchronization time of the downlink during handover, thus reducing the service interruption delay. In addition, the access method provided in the present invention reduces the probability of inter-frequency switching and reduces the call drop rate.

Description of drawings

Figure 1 shows the expansion scenario 1;

Figure 2 shows the second expansion scenario;

Figure 3 shows the third expansion scenario;

Fig. 4 is the access flowchart of the present invention;

Fig. 5 is a switching flow chart of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings.

The purpose of the present invention is to provide an inter-frequency handover method applied in a CDMA communication system for switching from the second carrier frequency of the source cell to the target cell, and both the source cell and the target cell have the first carrier frequency. First of all, if there is a cell x with the first and second carrier frequencies, and there is a cell in the adjacent cell with the first carrier frequency but no second carrier frequency, then the second carrier frequency attribute of the x cell is set in the RNC Set as "carrier frequency coverage edge", and set the first carrier frequency of cell x as the "hard handover target carrier frequency" corresponding to the "carrier frequency coverage edge". Then set the absolute threshold of the 2D event of the carrier frequency with the attribute of "carrier frequency coverage edge" as follows: the absolute threshold value of the 2D event is equal to the minimum signal-to-noise ratio to ensure the quality of service plus the difference between the carrier frequency and the first carrier frequency of the same cell The maximum deviation of the signal quality between. The maximum deviation is set according to the current downlink load of the second carrier frequency and the first carrier frequency of the source cell. If the downlink load of the second carrier frequency is greater than the downlink load of the first carrier frequency, the maximum deviation is taken as zero; if the downlink load of the second carrier frequency If it is less than the downlink load of the first carrier frequency, a positive signal quality deviation is added to the maximum deviation according to the load deviation. The signal quality may be the signal-to-noise ratio or the received signal chip power (RSCP). In this embodiment, the signal quality is the signal-to-noise ratio as an example for illustration. However, in a specific implementation process, the signal-to-noise ratio hereinafter may also be replaced by RSCP accordingly. Then configure the information element in its corresponding message block 11: "RACH reports the same frequency measurement report" ("Intra-frequency reporting quantity for RACH reporting") and "Maximum number of reported cells on RACH" ("Maximum number of reported cells on RACH"), the UE is required to report the signal-to-noise ratio of the carrier frequency pilot channel in the RRC connection establishment request.

As shown in Figure 4, the UE access steps are as follows:

Step 401, the UE sends an access request message to a certain carrier frequency of a certain cell;

Step 402, after the RNC receives the access request message, judge whether the attribute of the carrier frequency is "carrier frequency coverage edge", if the judgment result is yes, execute step 403, otherwise execute step 405;

Step 403, judging whether the signal-to-noise ratio of the carrier frequency is lower than the absolute threshold value of the 2D event, if the judging result is yes, go to step 404, otherwise go to step 405;

Step 404, establishing the radio link of the UE on the first carrier frequency of the cell;

Step 405, directly establish the radio link of the UE on the carrier frequency requested for access in step 401.

As shown in Figure 5, the handover steps of the UE are as follows:

Step 501, when the UE establishes a dedicated channel on a certain carrier frequency, the RNC sends the measurement control of the 2D event to the UE;

Step 502. If the signal-to-noise ratio of the carrier frequency is lower than the absolute threshold value of the 2D event, which means that the signal quality of the cell is low and handover is required, the UE reports the 2D event to the RNC;

Step 503: After the RNC receives the 2D event report, it judges whether the attribute of the carrier frequency currently establishing a connection with the UE is "carrier frequency coverage edge", if the judgment result is yes, execute step 504, otherwise execute step 508;

Step 504, the RNC controls the UE to perform hard handover to the "hard handover target carrier frequency" configured for the carrier frequency, and then sequentially execute steps 505, 506, and 507;

Step 505, after the UE switches to the "hard handover target carrier frequency", the RNC sends the measurement control of the 1A event to the UE;

Step 506, when the 1A event is triggered, the signal quality of the first carrier frequency of the adjacent cell meets the requirements, and soft handover is required, and the UE reports the 1A event to the RNC;

Step 507: After receiving the 1A event reported by the UE, the RNC controls the UE to perform soft handover to the first carrier frequency of the adjacent cell;

Step 508, perform measurement-based handover.

The measurement-based handover in step 508 may be soft handover, or inter-frequency handover using compressed mode or dummy pilot.

During the implementation process, many situations may arise, and the following three situations are listed to illustrate:

The first case: as shown in Figure 1, the f2 carrier frequency attribute of cell c is set to "carrier frequency coverage edge".

The second case: as shown in Figure 2, the f2 carrier frequency attributes of cells b and d are set to "carrier frequency coverage edge". Set it to "Carrier Coverage Edge". When the UE has established a link on the f2 carrier frequency of b or d, and switches from the right edge of cell b or d to cell a or e, the switching steps in the present invention are adopted. When switching from the left edge of cell b or d to cell c or between cells b and d, if the soft handover is triggered prior to the handover method of the present invention, soft handover is performed; otherwise, the handover method of the present invention is performed.

The third case: as shown in Figure 3, the f2 and f3 carrier frequency attributes of g cell are set to "carrier frequency coverage edge", and the "hard handover target carrier frequency" configured for it is f1 carrier frequency of g cell.

Appropriate improvements can be made to the method according to the present invention in the specific implementation process to meet the specific needs of specific situations. Therefore, it can be understood that the specific implementation manners according to the present invention are only exemplary, and are not intended to limit the protection scope of the present invention.

Claims (5)

1. A method for inter-frequency handover in a code division multiple access communication system, which is applied to handover from the second carrier frequency of the source cell to the target cell, and both the source cell and the target cell have the first carrier frequency in the scene, its characteristics The method comprises the following steps: setting the attribute of the second carrier frequency of the source cell as the carrier frequency coverage edge in advance, and the adjacent cell of the source cell has the first carrier frequency but no second carrier frequency; setting the absolute gate of the 2D event The limit value is set to be equal to the minimum signal-to-noise ratio for ensuring service quality plus the maximum deviation of the signal-to-noise ratio between the second carrier frequency of the source cell and the first carrier frequency; the maximum deviation is based on the second carrier frequency of the source cell and the first carrier frequency. The current downlink load of the carrier frequency is set. If the downlink load of the second carrier frequency is greater than the downlink load of the first carrier frequency, the maximum deviation is set to zero; Last positive signal quality deviation; In the source cell, the radio network controller sends the measurement control of the 2D event to the mobile station; The 2D event is triggered, and the mobile station reports the 2D event; The radio network controller judges the carrier frequency attribute of the source cell where the mobile station is located. If the attribute is the second carrier frequency at the edge of the carrier frequency coverage, then hard handover is performed from the second carrier frequency of the source cell to the first carrier frequency of the source cell. The first carrier frequency of the source cell is soft handed over to the first carrier frequency of the target cell; otherwise, a measurement-based handover is performed. 2. The method according to claim 1, wherein the first carrier frequency of the source cell is set in advance as the hard handover target carrier frequency of the carrier frequency coverage edge; The hard handover from the second carrier frequency of the source cell to the first carrier frequency of the source cell is: hard handover from the second carrier frequency of the source cell to the hard handover target carrier frequency configured for the frequency coverage edge. 3. The method according to claim 1, characterized in that after setting the attribute of the second carrier frequency of the source cell as the carrier frequency coverage edge in advance, before the radio network controller sends the measurement control of the 2D event to the mobile station , the method further includes the following access steps: a. When the mobile station located in the source cell sends an access request message to the second carrier frequency, the radio network controller receives the access request message from the mobile station on the second carrier frequency of the source cell; b. The radio network controller judges the relationship between the signal quality of the pilot signal of the second carrier frequency and the absolute threshold value of the 2D event, and if it is less than the absolute threshold value of the 2D event, execute step c; otherwise, execute step d; c. The radio network controller establishes the radio link of the mobile station on the first carrier frequency of the source cell; d. The radio network controller establishes the radio link of the mobile station on the second carrier frequency of the source cell. 4. The method according to claim 3, wherein the step a further comprises, in advance, in the radio network controller, configuring a random access channel in the message block 11 of the source cell to report the same-frequency measurement report information element And the information element of the maximum number of cells reported by the random access channel. 5. The method according to claim 3, wherein the second carrier frequency attribute is set as the carrier frequency coverage edge in advance, and said step a further comprises the following steps: a1. The radio network controller receives the radio resource control connection establishment request of the mobile station; a2. Judging the carrier frequency attribute of the second carrier frequency, if it is the carrier frequency coverage edge, execute step b; otherwise, execute step d.

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