CN100401838C - Handover Synchronization Method for Asynchronous Code Division Multiple Access System - Google Patents

Abstract

The present invention relates to the field of communication and discloses a switching-over synchronization method for an asynchronous CDMA system. Synchronizing information without a target district still can be switched over; therefore, switching-over success ratio and switching-over performance are ensured. The present invention of the switching-over synchronization method for an asynchronous CDMA system preserves relevant synchronizing information by storing a matrix list of Tcell of each NodeB and a matrix list of time difference and time stamp of NodeBs in a memory of an RNC. When a UE does not report the synchronizing information, the preserved information can still be used for switching over.

Description

Handover Synchronization Method for Asynchronous Code Division Multiple Access System

technical field

The invention relates to the communication field, in particular to the switching technology of an asynchronous code division multiple access system.

Background technique

With the increasingly mature technology, the practical prospect of the third generation mobile communication service is just around the corner. It has a similar network structure to the second-generation mobile communication network, and they can be divided into two parts: Radio Access Network ("RAN" for short) and Core Network ("CN" for short).

Among them, the RAN is mainly composed of a mobile station (Mobile Station, referred to as "MS"), a node B (NodeB) and a radio network controller (Radio Network Controller, referred to as "RNC"). In a mobile communication system, NodeB is also called a base station. Each NodeB covers a certain area with a diameter ranging from tens of meters to more than ten kilometers. It is responsible for the access of mobile phone signals in this area. The RNC is used to control several NodeBs, generally ranging from dozens to hundreds.

In the above mobile communication system, in order to improve the utilization rate of spectrum resources and the capacity of the whole system, the radio frequency power of the NodeB in the system is limited within the range of a cell. When the MS leaves a cell and enters another cell, the signal of the original cell received by the MS must become weaker and weaker, and the signal of the cell entering the cell received by the MS will also become stronger and stronger. In order to maintain the communication quality of the MS, it is necessary to connect the MS, that is, to switch from the original base station to the newly entered base station with stronger signal. This is the concept of handover in the cellular mobile communication system.

In the handover technology of mobile communication, there are hard handover and soft handover. Hard handover means that the MS first cuts off the connection with the original NodeB, and then connects with the new NodeB. The above process is prone to call drop. And soft handover means that when the MS moves or the NodeB currently communicating with the MS is busy so that the MS needs to communicate with a new NodeB, it does not interrupt the connection with the original NodeB first, but connects with the new NodeB first. After that, the connection with the original NodeB is interrupted, which is the classic Code Division Multiple Access (CDMA for short) technology. The above-mentioned soft handoff technology has the advantages of improving call quality and reducing call drop.

In a mobile communication system, handover is controlled by the following three methods, namely: Mobile Controlled Handover (MCHO), Network Controlled Handover (NCHO) and Mobile Assisted Handover (MAHO). The following is a brief introduction to these three methods:

MCHO is to continuously monitor the signal strength and quality of the base station (Base Station, referred to as "BS") through the MS. When the handover conditions are met, the MS selects the best handover candidate and sends a handover request. At present, Europe's Enhanced Digital Cordless Technology (DECT) and North America's Pacific Area Communication System (PACS) all use this switching control.

NCHO monitors the signal strength and quality through the BS, and when the signal deteriorates below a certain threshold, the network arranges to switch to a new BS. During this process, the network requires all BSs to monitor the signals from the mobile station and report the results to the network. When the network selects a new BS, it notifies the new and old BS to complete the handover at the same time, and the MS is passive during the handover process. The current TACS and AMPS systems all adopt this switching control.

MAHO can be said to be an evolution of NCHO. The network requires the MS to measure the signal strength of surrounding BSs and report to the old BS, and then the network determines whether to switch and which port to switch to. Therefore, MAHO uses the MS to measure the communication link, and the network controls the handover. During the handover process, the MS and the network participate in the handover at the same time. The MS is responsible for the measurement, and the network is responsible for the judgment. The current GSM and CDMA systems use this handover control.

In order to determine when to perform handover technology, a special pilot channel is used in the CDMA communication system to identify the coverage area of the cell, provide phase reference, and so on. The decision of soft handover is based on the MS's measurement of the pilot channel signal. The network end configures the threshold to the mobile station through signaling. When the user equipment (User Equipment, referred to as "UE") detects that the quality of the pilot signal of the monitoring set cell is higher than the threshold, it reports to the network end, and then the RNC decides Whether to initiate a soft handover.

In the existing asynchronous code division multiple access system, RNC and NodeB do not share a common time reference, therefore, the moment when they transmit signals is arbitrary, and there is no predetermined synchronization between them. In order to make the inter-cell asynchronous system perform soft handover normally, the MS to be handed over must be able to receive the signal of the target cell while receiving the signal of the source cell, so as to reduce the requirement on the buffer capacity. The MS calculates the time difference between the target cell and the source cell or the difference between the target cell and its own transmission time, and reports it to the network, and the network informs the target BS of the time difference through the RNC, so the target BS can adjust the transmit and receive signals to The time of the relevant MS is to compensate for this time difference and achieve synchronization.

In practical applications, the above solution has the following problems: in the current actual network operation, since the UE does not detect the frame header, not every UE can measure the synchronization information of the target cell, resulting in failure of synchronization. The failure of synchronization is a main reason for the handover failure during the handover process. Because during the soft handover process, if there is no synchronization information of the target cell, the soft handover cannot be triggered; while in the inter-frequency hard handover, if there is no synchronization information of the target cell, the inter-frequency hard handover can only perform asynchronous hard handover, which has worse performance than synchronous hard handover. switch. Therefore, how to configure correct synchronization parameters for UE and NodeB during handover is very necessary to ensure the success rate of handover, especially for asynchronous code division multiple access system.

Whether the synchronization information of the target cell is measured is controlled by the RNC. Take the Wideband Code Division Multiple Access (WCDMA) system as an example: when the RNC sends the same-frequency measurement and inter-frequency measurement control, the measurement control message Contains the neighbor cell list of the current cell that the UE is required to measure. These neighbor cell lists are configured in the RNC local database by network planning, and report the cell synchronization information reporting indicator (Cell synchronization information reporting indicator) in the measurement target cell report volume. If set to True, it is required to measure and report the synchronization information of the target cell. The same-frequency measurement will basically report synchronization information according to the synchronization indicator bit, but as mentioned above, there is also the possibility that synchronization information cannot be reported; inter-frequency measurement will basically not report synchronization information, because only dual-receiver UEs can report synchronization information, and For a single receiver, the compressed mode needs to be enabled, but the System Frame Number ("SFN" for short) of the inter-frequency cell cannot be read in the compressed mode.

The main reason for this situation is that the UE may not be able to measure the synchronization information of the target cell.

Contents of the invention

In view of this, the main purpose of the present invention is to provide a handover synchronization method for an asynchronous code division multiple access system, so that even if there is no synchronization information of the target cell, the handover can still be performed, thereby ensuring the handover success rate and handover performance.

To achieve the above object, the invention provides a handover synchronization method of an asynchronous code division multiple access system, comprising the following steps:

The A mobile station measures the synchronization parameters between the cells of the base stations, and reports the synchronization parameters to the radio network controller through the measurement report, and the radio network controller calculates the time difference information of the base stations according to the synchronization parameters, and saves the ;in,

Wherein, the synchronization parameter is the observation time difference information obtained by subtracting the system frame number of the target cell from the connection frame number at the time of transmission of the mobile station; or

Observation time difference information obtained after subtracting the system frame number of the source cell from the system frame number of the target cell;

B. When the mobile station needs to be handed over, the radio network controller acquires the stored base station time difference information of the target cell and the source cell, and configures the synchronization parameters of the target cell according to the base station time difference information;

C performs cell switching according to the synchronization parameters.

In the step A, it also includes the step of updating the time difference information between base stations according to the measurement report of the mobile station, marking it with a time stamp, and recording it in the radio network controller.

In the step A, the time difference information is stored in the second table of the matrix list for recording the time difference information and time stamps between base stations in the local memory of the radio network controller, and,

said second table is continuously updated by measurement reports received from said mobile station;

The time difference between the same base stations in the second table is constant at zero; and

The local memory also includes a first table for recording a list of cell timing delay matrices in each base station, and the first table is updated by the radio network controller when a cell is established.

When the time difference information is the observed time difference information obtained by subtracting the system frame number of the source cell from the system frame number of the target cell, the step of continuously updating the second table through the measurement report from the mobile station further includes the following Substeps:

The mobile station measures the system frame number of the target cell minus the system frame number of the source cell to observe time difference information;

When the target cell and the source cell can be handed over, according to the relationship between the Node B frame number and the system frame number, calculate the time difference information between the base stations where the two cells are located, put a time stamp on it, and then record the first The second table is updated.

Calculate the time difference information between the base stations where the two cells are located in the following manner:

(Node B frame number)i-(Node B frame number)k

=[(system frame number)ij-system frame number)ks]+[((cell timing delay)ij-(cell timing delay)ks]

in,

I represents the base station where the target cell is located, and j represents the target cell;

K represents the base station where the source cell is located, and s represents the source cell.

When the time difference information is the system frame number of the target cell minus the observation time difference of the connection frame number at the time of transmission of the mobile station, the step of continuously updating the second table through the measurement report from the mobile station further includes the following subsections: step:

The system frame number of the target cell measured by the mobile station minus the connection frame number at the time of transmission of the mobile station;

When the target cell and the source cell can be handed over, according to the relationship between the system frame number and the connection frame number at the time of transmission of the mobile station, calculate the time difference information between the base stations where the target cell and the source cell are located, put a time stamp on it, and accordingly The second table is updated.

Calculate the time difference information between the base stations where the two cells are located in the following manner:

(Node B frame number)i-(Node B frame number)k

=[Δij-Δks]+[((cell timing delay) ij-(cell timing delay)ks]

in,

I represents the base station where the target cell is located, and j represents the target cell;

K represents the base station where the source cell is located, and s represents the source cell;

Δij=(system frame number)ij-mobile station connection frame number at the time of transmission;

Δks = system frame number ks - connection frame number at the time of transmission of the mobile station.

Judging whether the two cells can be handed over according to the following conditions:

When the measured target cell and source cell do not belong to the same base station cell, and

When the target cell and the source cell are adjacent cells or the distance between the antennas of the target cell and the source cell is less than a predetermined value,

Then it can be determined that the target cell and the source cell can be handed over, otherwise the target cell and the source cell cannot be handed over; and,

When the target cell and the source cell cannot be switched, the time difference information between the base stations where the two cells are located is not updated.

In the step B, when the mobile station needs to be handed over, and the radio network controller has not received the synchronization information of the target cell measured by the mobile station, and the target cell and the source cell can be handed over, query the local From the first table and the second table in the memory, the corresponding time difference information between base stations and the corresponding time stamp information, and the timing delay of the cell are taken out, and the movement is calculated according to the relationship between the node B frame number and the system frame number. Synchronization parameters required for station switching.

When the synchronization parameter is the system frame number-system frame number time difference between the target cell and the source cell, it is calculated in the following manner:

(system frame number) ij-(system frame number) ks=[(B node frame number) i-(B node frame number) k]+[((cell timing delay) ks-(cell timing delay) ij],

in,

I represents the base station where the target cell is located, and j represents the target cell;

K represents the base station where the source cell is located, and s represents the source cell.

When the synchronization parameter is the time difference obtained after subtracting the connection frame number of the mobile station from the system frame number of the source cell, it is calculated in the following manner:

(system frame number) ij-(connection frame number)=[(B node frame number) i-(B node frame number) k]-[((cell timing delay) ij-(cell timing delay) ks]+Δks, in

Δks = (system frame number) ks - connection frame number at the time of transmission of the mobile station; and

I represents the base station where the target cell is located, and j represents the target cell;

K represents the base station where the source cell is located, and s represents the source cell.

By comparison, it can be found that the difference between the technical solution of the present invention and the prior art is that the present invention stores a matrix list of Tcell in each NodeB and a matrix list of time difference and timestamps between NodeBs in the local memory of the RNC , to save information about the synchronization. When the UE does not report the synchronization information, the saved information can still be used for handover synchronization.

This difference in technical solutions brings obvious beneficial effects. Even if there is no synchronization information of the target cell, handover synchronization can still be performed, ensuring the handover success rate and handover performance.

Description of drawings

Fig. 1 is the flow chart that utilizes SFN-SFN time difference to refresh BFN-BFN according to an embodiment of the present invention;

Fig. 2 is the flow chart of using SFN-CFN time difference to refresh BFN-BFN according to an embodiment of the present invention;

Fig. 3 is a flowchart of a method for switching synchronization in an asynchronous code division multiple access system according to an embodiment 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.

In general, the method for handover synchronization in an asynchronous code division multiple access system proposed by the present invention first needs to save the SFN time difference between cells (hereinafter referred to as "SFN-SFN time difference") according to the synchronization information in the UE's measurement report ), and then according to the UE's intra-frequency or inter-frequency measurement report, if there is no synchronization information, configure the synchronization parameters of the target cell from the existing SFN-SFN time difference between cells to perform handover.

In the present invention, except above-mentioned SFN, also relate to following two kinds of frame numbers: NodeB frame number (NodeB Frame Number, be called for short " BFN ") and connection frame number (Connection Frame Number, be called for short " CFN "). In order to avoid the overlap of synchronization (SCH) between different cells in the same NodeB, the SFN in the cell is delayed by a cell timing delay value (Tcell) relative to the BFN. It is worth noting that there can be multiple cells under one NodeB, and the Tcell of each cell is fixed and configured by the RNC; in addition, in order to reduce the amount of data to save the SFN-SFN time difference, you can use the BFN time difference (hereinafter referred to as "BFN-BFN time difference") and the Tcell table of each NodeB instead of the SFN-SFN time difference have the same effect.

The above frame numbers constitute two synchronization parameters of the present invention: SFN-SFN time difference and SFN-CFN time difference.

In order to realize the technical effect of the present invention, firstly, the BFN-BFN time difference information between NodeBs is refreshed by using the SFN-CFN time difference or the SFN-SFN time difference, and a time stamp is added. To achieve this goal, a matrix list of Tcells in each NodeB and a matrix list of time differences and timestamps between NodeBs need to be stored in the local memory of the RNC, and the BFN-BFN time difference between the same NodeBs is always zero. The Tcell list is updated by the RNC when the cell is established.

As mentioned above, there are two ways to update the BFN-BFN time difference information, one is to use the SFN-SFN time difference to update, and the other is to use the SFN-CFN time difference to update. Both methods can achieve the purpose of refreshing the BFN-BFN. In the application, one of the methods will be selected according to the difference in the measurement and observation time difference reported by the UE.

The process of updating BFN-BFN by using the SFN-SFN time difference will be described below with reference to Fig. 1 .

First, in step 101, it is judged whether the two measured cells are the same NodeB cell. If yes, go to step 103, that is, do not update, because the BFN-BFN time difference between the same NodeBs is always zero; if not, go to step 102.

In step 102, according to the network planning configuration in the local database, it is judged whether the two measured cells are adjacent cells or whether the antenna distance between the two cells is smaller than a certain value. If yes, go to step 104; if not, go to step 103, that is, do not perform update processing, because if the two cells are not adjacent or the distance is too far, basically handover will not occur.

In step 104, the BFN-BFN time difference information of the NodeBs where the two cells are located is calculated by using the relationship between the BFN and the SFN. The specific process is as follows:

It is assumed that in (BFN)i, (SFN)ij, and (Tcell)ij, i represents the i-th NodeB, and j represents the j-th cell. Regardless of the same frequency cell or different frequency cell, it can be known that BFN and SFN satisfy the following relationship:

(SFN)ij=(BFN)i-(Tcell)ij

(1)

When the observation time difference of (SFN)ij-(SFN)ks is measured, the time difference of (BFN)i-(BFN)k can be calculated as

(BFN)i-(BFN)k

=[(SFN)ij+(Tcell)ij]-[(SFN)ks+(Tcell)ks]

=[(SFN)ij-SFN]ks]+[((Tcell)ij-(Tcell)ks)

(2)

Through the above steps, the time difference information between (NodeB)i and (NodeB)k can be calculated.

Then enter step 105, and mark the time stamp. Thus, the process of refreshing the BFN-BFN by using the SFN-SFN time difference is completed.

The process of updating the BFN-BFN by using the SFN-CFN time difference is described below with reference to Fig. 2 . It is worth noting that the SFN-CFN observation time difference is the difference between the SFN of the target cell and the CFN at the UE transmission time. If a user obtains the SFN-CFN time difference information through measurement, the following steps are carried out:

First, in step 201, it is judged whether the two measured cells are the same NodeB cell. If yes, go to step 203, that is, do not update, because the BFN-BFN time difference between the same NodeBs is always zero; if not, go to step 202.

In step 202, according to the network planning configuration in the local database, it is judged whether the two measured cells are adjacent cells or whether the antenna distance between the two cells is smaller than a certain value. If yes, go to step 204; if not, go to step 203, that is, do not perform update processing, because if the two cells are not adjacent or the distance is too far away, basically handover will not occur.

In step 204, the BFN-BFN time difference information of the NodeBs where the two cells are located is calculated by using the relationship between the SFN and the CFN. The specific process is as follows:

The SFN-CFN observation time difference is defined as Δij, the Δij of the target cell is measured by the UE, Δij=(SFN)ij-CFN; and the Δks of the source cell is known according to the requirement of establishing a wireless link, Δks=(SFN)ks - CFN. So

(SFN)ij-(SFN)ks=Δij-Δks

(3)

According to formula (2), the time difference information between (NodeB)i and (NodeB)k can be calculated: (BFN)i-(BFN)k

=[(SFN)ij-SFN]ks]+[((Tcell)ij-(Tcell)ks)

=[Δij-Δks]+[((Tcell)ij-(Tcell)ks)

(4)

Through the above steps, the time difference information between (NodeB)i and (NodeB)k can be calculated.

Then enter step 205, and stamp the time stamp. Thus, the process of refreshing the BFN-BFN time difference by using the SFN-CFN time difference is completed.

After explaining how to obtain the BFN-BFN time difference, the following describes the steps of using the BFN-BFN time difference to realize handover synchronization according to the principle of the present invention.

When the UE needs to perform handover, if it can receive the synchronization information of the target cell measured by the UE, it will directly use this information to perform handover timing processing. If the relevant synchronization information cannot be obtained, the corresponding BFN-BFN time difference and the accompanying time stamp information are taken out from the BFN-BFN table. The timestamp is used to judge whether the BFN-BFN time difference information has exceeded the validity period. If it has not expired, the time difference information is calculated according to the relationship between the BFN and the SFN, and switching timing processing is performed.

Below in conjunction with accompanying drawing 3 illustrate relevant process:

First, in step 301, the UE enters the connected state, and the RNC generally issues intra-frequency measurement control or inter-frequency measurement control to the UE to measure adjacent intra-frequency cells or adjacent inter-frequency cells for soft handover or Inter-frequency hard switching. Then go to step 302 .

In step 302, when the measurement report satisfies the trigger condition, the UE will report the intra-frequency or inter-frequency measurement report to the RNC. Then go to step 303 .

In step 303, the RNC judges whether the measurement report contains synchronization information. If yes, go to step 304; if not, go to step 305.

In step 304, the BFN-BFN time difference and timestamp will be refreshed and saved. There are two ways to realize this step, one is to use the SFN-SFN time difference, refer to step 101 to step 105 for the specific process; the other is to use the SFN-CFN time difference, refer to step 201 to step 205 for the specific process. In the application, one of the methods will be selected according to the difference in the measurement and observation time difference reported by the UE. There are two types of time difference reported by the UE as mentioned above: SFN-SFN time difference and SFN-CFN time difference.

Wherein, the SFN-SFN time difference can be obtained as the following formula (5), where (SFN)ij is the SFN of the target cell, (SFN)ks is the SFN of the source cell, then:

(SFN)ij-(SFN)ks

=[(BFN)i-(Tcell)ij]-[(BFN)k-(Tcell)ks]

=[(BFN)i-(BFN)k]+[((Tcell)ks-(Tcell)ij)

(5)

The SFN-CFN time difference can be obtained according to the following formula (6), assuming that the SFN-CFN observation time difference is defined as Δij, and Δij of the target cell = (SFN)ij-CFN, which can be deduced according to formula (4), where Δks is the source cell The SFN-CFN value, configured when the radio link of the source cell is established, can be stored in the local memory of the RNC:

(SFN)ij-CFN

=Δij

=[(BFN)i-(BFN)k]-[((Tcell)ij-(Tcell)ks)+Δks

(6)

After refreshing and saving the BFN-BFN time difference and time stamp, it will enter step 309 .

In step 305, according to the network planning configuration in the local database, it is judged whether the two measured cells are adjacent cells or whether the antenna distance between the two cells is smaller than a certain value. If yes, go to step 306; if not, go to step 307, that is, fail to obtain the time difference, because basically handover will not occur if the two cells are not adjacent or too far apart.

In step 306, it shows that the report does not contain synchronization information at this time, so the BFN-BFN time difference table and Tcell table stored locally are searched at the RNC, and the corresponding BFN-BFN time difference and the accompanying timestamp information are taken out from the BFN-BFN table . Then go to step 308 .

In step 308, it is judged whether the BFN-BFN time difference information has expired. If yes, go to step 307, which means that the acquisition of the time difference fails; if not, go to step 309.

In step 309, configure handover synchronization parameters, and then enter step 310 to execute the handover process.

In addition to the above method, the present invention can also be extended as follows: because the UE measures the synchronization information of the target cell, the measurement resources of the UE are generally consumed. In order to save the measurement resources of the UE and achieve the purpose of saving energy and time, a Part of the UEs in the cell, such as 20% of the UEs, set the synchronization information of the target cell to be measured in the measurement control, and the rest of the UEs are set not to measure the synchronization information of the target cell.

To sum up, in the present invention, when the RNC receives the UE's measurement report and decides to issue a handover request, it will preferentially use the timing information measured by the UE; if the UE does not report the timing relationship, it will use the synchronization between cells stored on the network side. Relationship configuration toggle synchronization parameters.

Although the present invention has been illustrated and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein, and without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (11)

1. A switching synchronization method of asynchronous CDMA system is characterized in that it includes following steps:

a, a mobile station measures synchronous parameters among base station cells, reports the synchronous parameters to a wireless network controller through a measurement report, and the wireless network controller calculates and obtains base station time difference information according to the synchronous parameters and stores the base station time difference information; wherein,

the synchronization parameter is observed time difference information obtained by subtracting the mobile station transmitting moment connection frame number from the target cell system frame number; or subtracting the system frame number of the source cell from the system frame number of the target cell to obtain observation time difference information;

b, when the mobile station needs to be switched, the wireless network controller acquires the stored base station time difference information of the target cell and the source cell, and configures the synchronization parameter of the target cell according to the base station time difference information;

and C, carrying out cell switching according to the synchronization parameters.

2. The method for synchronizing handover in an asynchronous cdma system as claimed in claim 1, wherein the step a further comprises the steps of updating inter-base station time difference information based on the measurement report of the mobile station, time-stamping the time-stamped information, and recording the time-stamped information in the rnc.

3. The handover synchronization method of an asynchronous code division multiple access system according to claim 2, wherein in the step A, the base station time difference information is stored in a second table of a matrix list for recording inter-base station time difference information and time stamps in the radio network controller local memory, and,

the second table may be continuously updated by measurement reports received from the mobile station;

the time difference between the same base stations in the second table is constant to zero; and is

The local memory also contains a first table for recording a cell timing delay matrix list in each base station, and the first table is updated by the radio network controller when the cell is established.

4. The method for synchronizing handoffs in an asynchronous code division multiple access system as claimed in claim 3, wherein when said time difference information is observed time difference information obtained by subtracting a source cell system frame number from said target cell system frame number, the step of continuously updating said second table with measurement reports from said mobile station further comprises the substeps of:

the mobile station measures the observation time difference information of the system frame number of the target cell minus the system frame number of the source cell;

and when the target cell and the source cell can be switched, calculating time difference information between base stations where the two cells are located according to the relation between the B node frame number and the system frame number, stamping a time stamp, and updating the second table according to the time difference information.

5. The method of claim 4, wherein the time difference information between the base stations of the two cells is calculated according to the following method:

(node B frame number) i- (node B frame number) k

(system frame number) ij (system frame number) ks + [ (cell timing delay) ij (cell timing delay) ks ]

Wherein,

i represents a base station where the target cell is located, and j represents the target cell;

k represents the base station where the source cell is located, and s represents the source cell.

6. The method for synchronizing handover in asynchronous cdma system as claimed in claim 3, wherein when said time difference information is an observed time difference obtained by subtracting a mobile station transmit time connection frame number from said target cell system frame number, the step of continuously updating said second table by measurement report from said mobile station further comprises the sub-steps of:

the mobile station measuring the system frame number of the target cell minus the connection frame number of the mobile station at the transmitting moment;

when the target cell and the source cell can be switched, calculating the time difference information between the base stations of the target cell and the source cell according to the relation between the system frame number and the connection frame number of the mobile station at the transmitting moment, stamping a time stamp, and updating the second table according to the time difference information.

7. The method of claim 6, wherein the time difference information between the base stations of the two cells is calculated according to the following method:

(node B frame number) i- (node B frame number) k

(Δ ij- Δ ks) + [ (cell timing delay) ij- (cell timing delay) ks ]

Wherein,

i represents a base station where the target cell is located, and j represents the target cell;

k represents a base station where the source cell is located, and s represents the source cell;

Δ ij ═ (system frame number) ij — mobile station transmission time connection frame number;

Δ ks-system frame number ks-mobile station transmit time connection frame number.

8. The handover synchronization method of an asynchronous cdma system according to claim 5 or 7, wherein the determination of whether the two cells can perform handover is based on the following conditions:

when the measured target cell and the source cell do not belong to the same base station cell, and

when the target cell and the source cell are adjacent cells or the distance between the antennas of the target cell and the source cell is less than a predetermined value,

the target cell and the source cell can be judged to be switched, otherwise, the target cell and the source cell can not be switched; and,

and when the target cell and the source cell can not be switched, updating the time difference information between the base stations of the two cells.

9. The handover synchronization method of an asynchronous cdma system as claimed in claim 8, wherein in step B, when the ms needs handover, and the rnc does not receive the synchronization information of the target cell measured by the ms, and the target cell and the source cell can perform handover, the rnc queries the first and second tables in the local memory of the rnc, extracts the corresponding inter-bs time difference information, the corresponding timestamp information, and the cell timing delay, and calculates the synchronization parameters needed for handover of the ms according to the relationship between the node B frame number and the system frame number.

10. The method of claim 9, wherein when the synchronization parameter is a time difference obtained by subtracting the system frame number of the source cell from the system frame number of the target cell, the method comprises:

(system frame number) ij- (system frame number) ks

═ node B frame number i- (node B frame number) k ] + [ (cell timing delay) ks- (cell timing delay) ij ],

wherein,

i represents a base station where the target cell is located, and j represents the target cell;

k represents the base station where the source cell is located, and s represents the source cell.

11.The method of claim 10, wherein when the synchronization parameter is the time difference obtained by subtracting the mobile station transmit time connection frame number from the source cell system frame number, the method comprises:

(system frame number) ij- (connection frame number)

(node B frame number) i- (node B frame number) k ] - [ (cell timing delay) ij- (cell timing delay) ks ] + Δ ks, where

Δ ks ═ system frame number (system frame number) ks — mobile station transmit time connection frame number; and is

i represents a base station where the target cell is located, and j represents the target cell;

k represents the base station where the source cell is located, and s represents the source cell.

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