KR20020029815A - Method for processing a hand-off in an asynchronous mobile communication system - Google Patents

Abstract

PURPOSE: A handoff method in an asynchronous mobile system is provided to prevent a loss of data in the case of mode conversion and timing adaptation for handoff by using a compressed mode in an asynchronous mobile system. CONSTITUTION: An SRNC(Serving Radio Network Controller) transmits a compressed mode prepare message to node B and sets up parameters for a compressed mode operation. In response to the compressed mode prepare message, node B transmits a compressed mode ready message to the SRNC. The SRNC transfers a compressed mode commit message to inform node B of a data frame to be applied actually. Then, after calculating the difference(T_differ) value between a reference value(T_ref) from node B and a data received time from a UE(User Equipment), the SRNC transfers a USTS(Uplink Synchronous Transmission Scheme) scrambling code, a channel code and the time difference value(T_differ) to node B. Accordingly, node B prepares for conversion to a USTS mode, based on the allocated code information, and transfers a radio link reconfiguration ready message to inform the SRNC that preparation for mode conversion has been completed.

Description

METHODO FOR PROCESSING A HAND-OFF IN AN ASYNCHRONOUS MOBILE COMMUNICATION SYSTEM

The present invention relates to a handoff method in an asynchronous mobile communication system that can be used by an IMT-2000 terminal, and more particularly, to perform mode conversion and timing adaptation between a base station to which a mobile station newly enters and a corresponding mobile station when performing a handoff. A handoff method in an asynchronous mobile communication system suitable for performing effectively.

Currently, studies on uplink synchronous transmission scheme (USTS) technology have been conducted in various places in the CDMA mobile communication system, which has been widely commercialized, in order to increase system capacity and transmission performance.

Here, USTS is a technology that allows the base station to control the transmission time of the reverse data for the mobile stations in the cell managed by the base station so that the reverse signal of the mobile station using the orthogonal code can arrive simultaneously at the desired reference time. The technology can maximize the characteristics of the orthogonal code, thereby maximizing the transmission capacity in the cell.

On the other hand, when the above-described USTS technology is applied to the asynchronous IMT-2000 system, there are some technical problems in providing handoff.

That is, a handoff procedure is performed when a mobile station operating in USTS mode moves to another cell area. In the case of soft handoff, the mobile station should be able to receive data from two cells at the same time. .

However, when data is transmitted in the USTS mode, only one cell may be transmitted at a time, and thus, the new cell may be operated in the non-USTS mode. Thus, if the link with the previous cell communicating in USTS mode is deleted, the mobile station must convert the data frame transmission with the new cell operating in non-USTS mode to USTS mode, which is a scrambling code for USTS for the physical channel. This can be done by assigning and channel codes.

At this time, in order to operate in the USTS mode, the base station (the corresponding node) needs to readjust the difference value (T_differ) between the time reference value (T_ref) and the reception time of the mobile station data for each cell. In the proposed schemes, the timing is applied based on the first time reference value (T_ref) that appears after the start time of receiving the data frame of the mobile station.

However, in the conventional method as described above, if the transmission timing is advanced, there is a problem that a loss of the data frame occurs during the conversion from the non-USTS mode to the USTS mode. It acts as a trigger.

Accordingly, the present invention is to solve the problems of the prior art described above, by using the compressed mode (compressed mode) in the asynchronous mobile communication system to prevent the loss of data during mode conversion and timing adaptation for handoff It is an object of the present invention to provide a handoff method in an asynchronous mobile communication system.

According to one aspect of the present invention, there is provided a non-USTS / USTS mode conversion and timing between another mobile station and any mobile station when any mobile station belonging to a service area of any base station enters another adjacent base station. In a handoff method in an adaptive asynchronous mobile communication system, an idle time in frame data transmission is generated using a compression mode that temporarily increases a frame data transmission rate to reduce a transmission time of frame data, and generates the idle time. Provides a handoff method in an asynchronous mobile communication system characterized by adjusting the frame transmission timing for non-USTS / USTS mode conversion between the other base station and the corresponding mobile station using the time.

According to another aspect of the present invention, a mobile station belonging to a service area of an arbitrary base station performs non-USTS / USTS mode conversion and timing between another mobile station and any mobile station when entering another adjacent base station. A handoff method in an adaptive asynchronous mobile communication system, the method comprising: preparing to execute a compression mode in which the other base station temporarily increases a transmission rate of frame data to reduce a transmission time of frame data; Calculating a time difference value T_differ between a time reference value at the other base station and a data reception time from the mobile station; Transmitting a scrambling code and a channel code for the USTS and the calculated time difference value T_differ to the other base station; Notifying the base station controller that it is ready for mode conversion when the preparation for conversion to the USTS mode is completed based on the assigned code information; If the radio link reconfiguration is allowed from the base station controller, the USTS mode is converted using the scrambling code, the channel code, and the time difference value T_differ for the USTS, and the data frame transmission is adjusted by the time difference value. Adjusting timing; Transmitting a scrambling code, a channel code, a frame number for mode conversion, and a time difference value T_differ to the mobile station through the other base station; And adjusting a transmission timing of the data frame by adjusting the time difference value T_differ before transmitting the data frame having the frame number designated for the mode conversion. .

1 is a timing diagram illustrating an example of a case in which a transmission start time is advanced (T_differ1) for adapting timing synchronization for USTS.

2 is a timing diagram illustrating an example of a case where a transmission start time is delayed (T_differ2) for adaptation of timing synchronization for USTS;

3 is a timing diagram illustrating an example in which a transmission start time is advanced by using a compression mode for adaptation of timing synchronization for a USTS according to a preferred embodiment of the present invention;

4 is a timing diagram illustrating an example of a case where a transmission start time is delayed using a compression mode for adaptation of timing synchronization for a USTS according to a preferred embodiment of the present invention;

FIG. 5 is a timing chart illustrating a process of changing a non_USTS mode to a USTS mode using a compression mode during handoff according to an exemplary embodiment of the present invention. FIG.

<Description of the code | symbol about the principal part of drawing>

UE: mobile station Node B: base station

SRNC: Base Station Controller

The above and other objects and various advantages of the present invention will become more apparent from the preferred embodiments of the present invention described below with reference to the accompanying drawings by those skilled in the art.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

A key technical aspect of the present invention is a time reference value at a base station (ie, Node B) in the process of calculating a time difference value for converting a mode from non-USTS mode to USTS mode for handoff in an asynchronous mobile communication system. In selecting (T_ref), the flexibility to select a time reference value (T_ref) close to the start time of data frame reception from a mobile station (UE: user equipment) gives flexibility, that is, temporarily increases the data rate to reduce data transmission time. By using a compressed mode to generate an idle time for the mobile station to perform other tasks, it is easy to achieve the object of the present invention through this technical means.

Typically, when a mobile station supporting the USTS mode releases its link with a previous cell that has been communicating in USTS mode after the handoff procedure is completed, the mobile station can only transmit radio links that can transmit in the new cell and non-USTS mode. It exists.

Therefore, a mode conversion (switching) is required to operate the mobile station operating in the non_USTS mode in the USTS mode. For this purpose, the base station and the mobile station must be able to smoothly perform timing adaptation based on the time reference value (T_ref). do.

To this end, in a serving radio network controller (SRNC), a transmission start point of a dedicated physical control channel (DPCCH) transmitted from a cell of a base station to each mobile station, a round trip delay of a DPCH, and a time reference value (T_ref) The time difference value (T_differ1 or T_differ2) that needs to be adjusted is calculated using, for example. The time difference calculated here is used to adjust the starting point of the DPCCH transmitted to the base station and transmitted from the cell to the mobile station, and is also used to determine the starting point of the dedicated physical channel (DPCH) transmitted to the mobile station and transmitted from the mobile station to the base station. It is also used to adjust.

In this case, the synchronization of the transmission timing required for the USTS may be delayed (ie delayed) when the transmission start time is selected depending on the selection of the time reference value T_ref. An example of adaptation is shown in FIGS. 1 and 2.

FIG. 1 is a timing diagram illustrating an example of a case where the transmission start time is advanced (T_differ1) for adaptation of timing synchronization for USTS, and FIG. 2 is a delay of transmission start time for adapting timing synchronization for USTS (delay Is a timing diagram showing an example of the case (T_differ2).

1 and 2, slots in the upper portion of each channel display line show timing for operating in non_USTS mode, and slots in the lower portion operate in USTS mode (ie, after timing synchronization adaptation). The timing for the is shown.

Accordingly, in order to convert from the non_USTS mode to the USTS mode, the base station controller SRNC transmits the USTS time reference value T_ref, that is, the synchronization reference point and the downlink (DL) DPCCH frame, for the corresponding cell of the base station Node B. A time difference value T_differ with a synchronization reference point is calculated based on timing information about a start point of a start point and an arrival start point of an uplink (UL) DPCH frame. In this case, two reference time reference points T_ref may be selected based on the time when the UL DPCH data frame starts to arrive at the base station Node B.

This is the reference time reference point that appears immediately before and the reference time reference point that will appear immediately after, based on the time when the UL DPCH data frame starts to arrive. Based on these reference points, the base station controller SRNC can obtain time difference values T_differ1 and T_differ2, and these time difference values have values corresponding to 1 to 256 chips, respectively.

In this case, when the selection criterion of the time reference point T_ref is fixed to T_ref which appears immediately after the UL DPCH data frame starts arriving at the base station Node B, the initial time difference value T_differ_init is set. After calculation, the smaller of this value and 256 chip-T_differ_init value can be selected as the final T_differ. At this time, if T_differ_init calculated first is set to T_differ, transmission delay of T_differ is required for synchronization adaptation. If 256 chip-T_differ_init value is selected as the final value, transmission timing should be advanced by T_differ.

In addition, when the selection criterion of the time reference point T_ref is fixed to T_ref that appears immediately before the UL DPCH data frame starts to arrive at the base station Node B, the initial time difference value T_differ_init is set. After calculation, the smaller of this value and 256 chip-T_differ_init value can be selected as the final T_differ. At this time, if T_differ_init calculated first is set to T_differ, the transmission timing should be advanced as much as T_differ for synchronization adaptation. If 256 chip-T_differ_init value is selected as the final value, transmission delay as much as T_differ is required.

Here, the selection of the reference reference point T_ref and the calculation of the time difference value T_differ may be selected from any of the above-described methods.

However, for initial timing synchronization adaptation, the transmission of the DPCH frame needs to be adjusted by the time difference value T_differ. If the transmission of the DPCH data frame has to be delayed by the time difference value T_differ, the transmission is stopped by the T_differ time. However, in the case of advancing the transmission of the DPCH data frame, data loss occurs because it overlaps with a portion of the DPCH data frame transmitted immediately before switching to the USTS mode.

Therefore, in this case, a method for preventing data loss is required. An alternative may be to use a compressed mode used for frequency / system handoff in a W-CDMA system.

On the other hand, the compression mode used in the W-CDMA system, for example, temporarily increases the data rate for a transmission frame of 10 ms, thereby reducing the actual data transmission time by up to 5 ms and using the remaining idle time for different mobile stations. This mode allows you to perform tasks. Control of these idle times is controlled on a slot basis based on information transmitted through a Node B Application Protocol (NBAP) message and an RRC (radio resource control) message of the Iub interface. Therefore, when applied to two data frames consecutively, it is possible to interrupt transmission for up to 10 ms.

In this case, when the compression mode is applied to the timing value adjustment for the USTS, the parameter may be adjusted to include the last slot (slot # 15) or the first slot (slot # 1) of the data frame.

FIG. 3 is a timing diagram illustrating an example of advancing a transmission start time using a compression mode for adaptation of timing synchronization for a USTS according to a preferred embodiment of the present invention, and FIG. 4 is a preferred embodiment of the present invention. FIG. 9 is a timing diagram illustrating an example in which a transmission start time is delayed using a compression mode for adaptation of timing synchronization for a USTS.

As can be seen from Figures 3 and 4, in the present invention, the transmission rate is increased until the slot in which the transmission is stopped by the compression mode (slot # 14), and the timing synchronization is performed in the slot in which the transmission is stopped (slot # 15). Adaptation for them. 3 and 4, the upper portion of the line indicating each channel represents a case where normal transmission is performed, and the lower portion represents a case of using the compression mode.

That is, when the compression mode is not applied, the data rate for each slot of the data frame is the same. However, when the compression mode is applied according to the present invention, when the data rate applied to each slot transmission of the data frame is normal. In comparison, the time required for the actual data transmission is less than 10 ms.

Thus, applying timing adjustment to slots where transmission is interrupted in compression mode enables timing synchronization adaptation without loss of data. That is, the adaptation to the time difference value T_differ required to operate in USTS mode is applied to the first slot (slot # 1) or the last slot (slot # 15) of the data frame in which the actual data transmission is not performed in the compression mode. The adjustment is performed as much as the time difference value T_differ.

To this end, it is necessary to deliver accurate timing values for a user equipment (UE) and a base station (Node B), and for this purpose, it is necessary to add this information to an RRC message and an NBAP message. This timing transmission can be applied to other slots in which the transmission is stopped in the compression mode instead of the first and last slots of the data frame. In this case, it is necessary to calculate and apply the correct timing for the slot.

In this case, when timing is adjusted using a slot in which transmission is stopped in the compression mode, the length of the slot may be lengthened or shortened by T_differ, and information about the slot may be determined by the base station Node B and the mobile station before applying the compression mode. UE). Therefore, when timing adjustment is completed, the data frame can be transmitted in the USTS mode for subsequent transmission.

FIG. 5 is a timing chart illustrating a process of changing a non_USTS mode to a USTS mode using a compression mode during handoff according to an exemplary embodiment of the present invention.

First, when the mobile station US moves from a base station Node A in a service area to another base station Node B, the mobile station US notifies the base station Node A and the base station controller SRNC. Regarding handoff processing for processes of mode conversion (non-USTS mode to USTS mode) and timing adaptation between a base station Node B and a corresponding mobile station UE while the controller SRNC is aware of this. will be.

That is, in FIG. 5, a part described as completing the handoff procedure means a state in which control of the mobile station UE is transferred to the base station Node B, and thereafter, between the base station Node B and the mobile station UE. Processes for mode conversion and timing adaptation.

Referring to FIG. 5, the base station controller (SRNC) determines the scrambling code and channel code for the USTS and the mode conversion timing required to operate as the USTS. Whether the mode conversion is performed on a data frame to which the compression mode is applied (transmission interruption) Frame number to apply the compression mode depending on whether the interval includes slot # 15) or whether the mode conversion is applied from the data frame after applying the compression mode (if the transmission interrupt interval includes slot # 1). The CFN and the frame number CFN to which the mode conversion is applied are determined.

In general, when slot # 15 is included in the transmission interruption interval, the frame number CFN to apply the compression mode has a value smaller than 1 by the frame number CFN to be applied for mode conversion. If 1 is included, it has the same frame number (CFN) value.

To this end, the base station controller SRNC transmits a compressed mode prepare message to the base station Node B to set parameters for a compressed mode operation, and in response, the base station Node B responds to a compressed mode preparation response. (Compressed Mode Ready) message is transmitted to the base station controller (SRNC) to inform that the compression mode operation is ready, then the base station controller (SRNC) forwards the Compressed Mode Commit message to the base station (Node B) Informs a data frame.

Subsequently, the base station controller SRNC calculates a difference value T_differ between the reference reference value T_ref at the base station Node B and the data reception time from the mobile station UE, and then prepares for a radio link reconfiguration. A scrambling code, a channel code, and a time difference value T_differ (or chip offset value) for a USTS are transmitted to a base station Node B through a Prepare message.

Accordingly, the base station Node B prepares for the conversion to the USTS mode based on the assigned code information, and transmits a radio link reconfiguration ready message to the base station controller SRNC. Announce that you are ready for

In response, the base station controller SRNC transmits a frame number CFN to perform the mode conversion to the base station Node B through a Radio Link Reconfiguration Commit message. Accordingly, the base station Node B performs a process of adjusting the transmission timing by advancing or delaying data frame transmission by a time difference value (or chip offset value) after the conversion to the USTS mode.

In addition, the base station controller (SRNC) may use a scrambling code and channel code, a time difference value (T_differ) (or chip offset value), and a frame number (CFN) to perform mode conversion through a physical channel reconfiguration message. , And transmit the compressed mode operation information to the mobile station (ie, via the base station Node B).

Next, when the compression mode is performed, the base station Node B adjusts the chip offset by the time difference value T_differ for the data frame for mode conversion, and then adjusts the data frame in which the chip offset is adjusted. UE).

Here, timing adjustment is performed in the transmission interruption interval of the compression mode. When the transmission timing is pulled, the next data frame is transmitted by T_differ time for the last slot in which the transmission interruption is made. In addition, when delaying the transmission timing, delay the T_differ time for the last slot in which the transmission is interrupted, and then transmit the next data frame to the mobile station UE.

Similarly, the mobile station UE adjusts the time difference value T_differ before transmitting the data frame having the frame number CFN designated for mode conversion, and then transmits the data frame to the base station Node B. That is, the UL DPCH transmission at the mobile station (UE) always occurs after T0 from the time it starts to receive the DL DPCH.

Accordingly, when timing adjustment using the time difference value T_differ is completed, the mobile station UE generates a physical channel reconfiguration complete message and transmits the message to the base station controller SRNC via the base station Node B. By doing so, all handoff processing is completed.

As described above, according to the present invention, in selecting a time reference value from the mobile station in the process of calculating a time difference value for converting from non-USTS mode to USTS mode for handoff in an asynchronous mobile communication system, Gives you the flexibility to choose a time reference value that is close to the start time of receiving the data frame, ie by using compression mode to temporarily increase the data rate to reduce data transfer time, thereby creating idle time for the mobile station to perform other tasks. In addition, the idle time may be used to perform mode conversion and timing adaptation without losing frame data, thereby preventing deterioration of service quality due to handoff in an asynchronous mobile communication system.

Claims (10)

A handoff method in an asynchronous mobile communication system that adapts non-USTS / USTS mode conversion and timing between another mobile station and any mobile station when any mobile station belonging to a service area of any base station enters another neighboring base station. Create an idle time in frame data transmission by using a compression mode that temporarily increases the frame rate of the frame data to reduce the transmission time of the frame data, and uses the generated idle time to generate a non-USTS between the other base station and the mobile station. A method of handoff in an asynchronous mobile communication system characterized by adjusting the frame transmission timing for the / USTS mode conversion. 2. The asynchronous mobile communication system of claim 1, wherein the method adjusts the transmission timing by reducing a transmission stop time for the last slot in which the transmission is stopped in the compression mode to advance the transmission timing. Hand off way. 2. The asynchronous mobile communication system according to claim 1, wherein the method adjusts the transmission timing by increasing the transmission stop time for the last slot in which the transmission is stopped in the compression mode to delay the transmission timing. Handoff method in 4. The method according to claim 1, 2 or 3, wherein the method further comprises: when performing a mode conversion on a data frame to which the compression mode is to be applied, the applied frame number of the compression mode is 1 than the applied frame number of the mode conversion. A handoff method in an asynchronous mobile communication system, characterized in that it is set to a value as small as. The method according to claim 1, 2 or 3, wherein the method further comprises: when applying mode conversion from a data frame after applying the compression mode, the application frame number of the compression mode is applied to the application frame number of the mode conversion. A handoff method in an asynchronous mobile communication system, characterized in that the same setting. A handoff method in an asynchronous mobile communication system that adapts non-USTS / USTS mode conversion and timing between another mobile station and any mobile station when any mobile station belonging to a service area of any base station enters another neighboring base station. Preparing the other base station to execute a compression mode that temporarily increases a transmission rate of frame data to reduce transmission time of frame data; Calculating a time difference value T_differ between a time reference value at the other base station and a data reception time from the mobile station; Transmitting a scrambling code and a channel code for the USTS and the calculated time difference value T_differ to the other base station; Notifying the base station controller that it is ready for mode conversion when the preparation for conversion to the USTS mode is completed based on the assigned code information; If the radio link reconfiguration is allowed from the base station controller, the USTS mode is converted using the scrambling code, the channel code, and the time difference value T_differ for the USTS, and the data frame transmission is adjusted by the time difference value. Adjusting timing; Transmitting a scrambling code, a channel code, a frame number for mode conversion, and a time difference value T_differ to the mobile station through the other base station; And And adjusting the transmission timing of the data frame by adjusting the time difference value T_differ before transmitting the data frame having the frame number designated for the mode conversion. 7. The system of claim 6, wherein the method adjusts the transmission timing by reducing the transmission interruption time for the last slot in which the transmission is interrupted in the compression mode to advance the transmission timing. Hand off way. 7. The asynchronous mobile communication system of claim 6, wherein the method adjusts the transmission timing by increasing the transmission stop time for the last slot in which the transmission is stopped in the compression mode to delay the transmission timing. Handoff method in The method of claim 6, 7, or 8, wherein the method further comprises: when performing a mode conversion on a data frame to which the compression mode is to be applied, the applied frame number of the compression mode is 1 than the applied frame number of the mode conversion. A handoff method in an asynchronous mobile communication system, characterized in that it is set to a value as small as. The method according to claim 6, 7, or 8, wherein when the mode conversion is applied from the data frame after applying the compression mode, the method applies the frame number of the compression mode to the application frame number of the mode conversion. A handoff method in an asynchronous mobile communication system, characterized in that the same setting.