KR20020039859A - Method for processing a hand-off by using site selection diversity transmission in mobile communication system - Google Patents

Abstract

PURPOSE: A hand-off method using an SSDT(Site Selection Diversity Transmission) of a mobile communication system is provided to reduce the call disconnection ratio by variably allocating the number of a hand off branch of a mobile communication terminal in case that a soft hand off is generated. CONSTITUTION: A mobile communication terminal monitors pilot channel receiving rating values through UTRAN in real time(S100) and judges hand off points(S102). In case that the mobile communication terminal is entered into a hand off area, the mobile communication terminal compares pilot channel receiving rating values of each base station with lower standard values(S104). In case that the pilot channel receiving rating value is lower than the lower standard value, base stations equipped with values higher than standard values of an existing soft hand off are selected(S106). The terminal receives data from the base stations selected(S108). It is judged whether there's a base station equipped with pilot channel receiving rating values higher than higher standard values(S110). The terminal selects base stations equipped with pilot channel receiving rating values lower than the higher standard values(S112). The terminal receives data from the base stations selected(S114). The terminal selects base stations equipped with the largest pilot channel receiving rating value among the base stations(S116). The terminal receives data for hand off from the base stations selected(S118).

Description

Hand off method using SDT of mobile communication system {METHOD FOR PROCESSING A HAND-OFF BY USING SITE SELECTION DIVERSITY TRANSMISSION IN MOBILE COMMUNICATION SYSTEM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a handoff method of a mobile communication system. In particular, when the mobile communication terminal enters the handoff area, the number of handoff branches for the mobile communication terminal is one to the maximum active set. The present invention relates to a handoff method using SSDT of a mobile communication system, which can be variably allocated as many times.

The most important thing in providing a personal mobile communication service is to ensure the maximum mobility of the personal mobile subscriber station. This is because the movement of the terminal occurs frequently due to the characteristics of personal mobile communication. For this reason, the handoff function is provided for the personal mobile communication service.

When the mobile subscriber moves from a cell initiating a call to an adjacent cell, the handoff function connects a new channel allocated from a base station in charge of the cell where the mobile subscriber is currently located to perform normal mobile call processing. It is classified into soft handoff and hard handoff.

Hard handoff is a function that occurs when a new base station cannot allocate a frequency channel, such as a frequency that is already in use, in an unavoidable situation due to movement during a call. The process of setting up a mobile communication system to acquire a new frequency channel as the frequency changes. This is a short but resumable, so when the transfer is over, the tones do not go smoothly and the subscriber hears a short interruption. The handoff supported by the exchange is the hard handoff described above.

In other words, the hard handoff is divided into handoff between frequency allocation (FA) or handoff between frame offsets, and handoff is implemented in the form of “break before make”. That is, when the base station that the mobile communication terminal is currently calling is called the source base station and the base station to be handed off is called the target base station, the “break before make” method cuts the source base station first and requests the call connection to the target base station. That's the way.

On the other hand, soft handoff uses a “make before break” scheme, and maintains the link between the source base station and the target base station while the mobile communication terminal is in the handoff area.

This is a function of changing the call right in a sector of a subscriber moving from one sector to another in a cell of a sectorized base station, and soft handoff is a function of maintaining a call of a subscriber moving between cells in a base station network. By setting up a new channel through the physical link already established between the two base stations before operating the existing channel, two or more channels are operated during the handoff period. The transfer is smooth enough to not know when to change the currency.

FIG. 1 shows that each base station transmits data to a mobile subscriber on a forward link during soft handoff according to the related art.

As shown in FIG. 1, the mobile communication terminal 1 transmits data downward from neighboring first to third base stations 2, 4, and 6. From two adjacent base stations.

However, in the above-described handoff scheme, since the mobile communication terminal maintains a link with up to six base stations while the mobile communication terminal is in the handoff region, the call disconnection rate is lowered, but the radio resources of the base station are unnecessary. Not only is it wasteful, but the interference of the forward link is increased.

In addition, in the conventional hard handoff method, since the mobile communication terminal maintains a link with one base station while it is in the handoff area, unnecessary waste of radio resources of the base station can be suppressed. In comparison with this, the call disconnection rate is a big problem.

Accordingly, the base station asynchronous scheme IMT-2000 (3GPP Specification) proposes a SSDT (Site Selection Diversity Transmission) scheme in order to take full advantage of the above two schemes.

2A to 2C illustrate forward data transmission when the mobile communication terminal in the conventional concept of SSDT exists in the handoff area.

According to the conventional SSDT scheme, data transmission of the mobile communication terminal in the handoff region is as follows.

If the mobile communication terminal continuously monitors the reception strength values of the pilot channels of neighboring base stations and determines that the handoff time is determined, it is determined whether the SSDT is applied.

As a result of the determination, when the mobile communication terminal determines that the SSDT is applied, the mobile communication terminal uses the control channel on the reverse link between the base stations, and uses UTRAN (UMTS Terrestrial) as to which base station to use as the source base station to apply the SSDT to. Radio Access Network).

The UTRAN transmits user traffic on the forward link only to a specific base station performing SSDT based on information transmitted from the mobile communication terminal, and other base stations do not transmit user traffic.

When the first base station 2 has a reception strength value of the strongest pilot channel, as shown in FIG. 2A, the mobile communication terminal 1 receives data from the first base station 2 and the second base station. When (4) has the reception strength value of the strongest pilot channel, as shown in FIG. 2B, the mobile communication terminal 1 is receiving data from the second base station 4. When the third base station 6 has a reception strength value of the strongest pilot channel, as shown in FIG. 2C, the mobile communication terminal 1 receives data from the third base station 6.

The conventional SSDT scheme as described above has the advantage of reducing the amount of forward link interference of the base station, but there is a problem that the call disconnection rate is still higher than the conventional soft handoff.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and when the mobile communication terminal enters the handoff area, the number of handoff branches for the mobile communication terminal is one to the maximum active set. The present invention provides a handoff method using SSDT of a mobile communication system that can be variably allocated as many sets.

In order to achieve the above object, the method of the present invention performs a handoff between a mobile communication terminal and a base station by using a higher reference value and a lower reference value set for determining a handoff time point and signal strength values of pilot channels of each base station. A method comprising: detecting signal strength values of pilot channels provided from a plurality of neighboring base stations, comparing signal strength values of the detected pilot channels of each neighboring base station with the upper reference value and the lower reference value; And performing data communication for handoff with all of the plurality of neighboring base stations when all signal strength values of each detected pilot channel are less than the lower reference value, and signal strength values of each detected pilot channel. At least one signal strength value greater than the upper reference value among Performing data communication for handoff with my base station, and when there is no signal strength value greater than the higher reference value and at least one signal strength value greater than the lower reference value among the signal strength values of each detected pilot channel And performing data communication for handoff with the corresponding at least one base station.

1 is an exemplary diagram in which each base station transmits data to a mobile subscriber in a forward link during soft handoff according to the related art.

2A to 2C are exemplary diagrams of transmitting forward data when a mobile communication terminal according to a conventional SSDT concept exists in a handoff area;

3A and 3B are frame structure diagrams of a reverse link suitable for realizing handoff using SSDT in accordance with the present invention;

4 is a flowchart illustrating a process of providing a handoff using SSDT in a mobile communication system according to an embodiment of the present invention;

5 is an exemplary view illustrating a case of implementing 3GPP SSDT as an example according to the present invention;

6a to 6d are exemplary diagrams of transmitting forward data when the mobile communication terminal according to the concept of SSDT according to the present invention exists in a handoff area;

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

1: mobile communication terminal

2, 4, 6: base station

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

3A is a frame structure diagram of a reverse link suitable for realizing handoff using SSDT in accordance with the present invention.

The frame structure of the reverse link is composed of a dedicated physical control channel (DPCCH) as a control channel and a dedicated physical data channel (DPDCH) as a data channel.

The control channel DPCCH maintains synchronization between other adjacent base stations and the mobile communication terminal while the mobile communication terminal transmits forward with one base station having excellent reception performance when the mobile communication terminal enters the handoff area. It consists of a pilot channel, a FeedBack Indicator (FBI) field containing information of a base station to which SSDT is applied, and a Transmit Power Control (TPC) and Transport Format Combination Indicator (TFCI) field.

The structure of the FBI field is composed of the S field and the D field related to the SSDT, as shown in Fig. 3B. Here, the S field is allocated from 0 bits to 2 bits at maximum.

In addition, the mobile communication terminal determines whether to apply the SSDT by using the reception strength value of the pilot channel transmitted from the base station in the forward direction, that is, the base station Received Signal Code Power (RSCP).

4 is a flowchart illustrating a process of providing handoff using SSDT in a mobile communication system according to an exemplary embodiment of the present invention.

First, while performing a call mode, the mobile communication terminal monitors pilot channel reception strength values in real time through the UTRAN with respect to neighboring base stations and determines a handoff time point (S100 and S102).

Referring to steps S100 and S102 in detail, the mobile communication terminal pilots the DPCCH, which is a control channel of the reverse link as shown in FIGS. 3A and 3B, received from base stations adjacent to the mobile communication terminal in preparation for entering the handoff area. Measure channel reception strength in real time.

The mobile terminal determines which base station is the source base station among the reception strengths of the pilot channel measured in real time from the base stations and transmits the temporary ID value of the source base station to the UTRAN in the reverse direction. In this case, the information for determining the temporary ID value of the source base station may refer to the "SSDT cell identity" contained in the "Cell update confirm" or "Physical channel reconfiguration" message transmitted downward from the UTRAN of the base station, the message The mobile communication terminal receives a temporary ID list for neighboring base stations.

The mobile communication terminal receiving the temporary ID from the UTRAN transmits the temporary ID value of the source base station to the UTRAN in the FBI field in the DPCCH, which is a control channel, as shown in FIG. 3A.

As a result of the determination in step S102, when the mobile communication terminal enters the handoff area, the mobile communication terminal continuously determines whether to use the pilot channel reception strength value of each base station monitored and whether to use SSDT or the existing handoff. The set lower reference value {T} _ {SSDT-lower} is compared (S104).

As a result of the comparison in step S104, when the reception strength value of the pilot channel of all neighboring base stations is smaller than the lower reference value {T} _ {SSDT-lower}, the pilot channel reception strength of all the base stations received by the mobile communication terminal Base stations having a value greater than {T} _ {SHO}, which is a reference value of the existing soft handoff, are selected (S106).

Subsequently, the mobile communication terminal receives data in a forward direction from the selected base stations (S108). At this time, while receiving data from the selected base station, the mobile communication terminal receives a pilot signal for synchronization from other nearby base stations.

That is, in the present invention, when the received strength values of pilot channels received from neighboring base stations are all smaller than the lower reference value {T} _ {SSDT-lower}, the soft handoff is performed as in the conventional method.

Next, the pilot channel reception strength value of the base stations whose pilot channel reception strength value is larger than the {T} _ {SSDT-lower} which is the lower reference value is compared with the {T} _ {SSDT-upper} which is the higher reference value proposed by the present invention. It is checked whether a base station having a pilot channel reception strength value greater than {T} _ {SSDT-upper} exists (S110).

As a result of the comparison in step S110, the mobile communication terminal selects base stations having a pilot channel reception strength value smaller than the upper reference value {T} _ {SSDT-upper} (S112) and receives data from the selected base stations. (S114).

In addition, if there is a base station with a pilot channel reception strength value greater than {T} _ {SSDT-upper}, the mobile communication terminal selects one having the largest pilot channel reception strength value among all base stations ( S116) Receive data for handoff from the selected base station (S118).

Figure 5 illustrates the implementation of the 3GPP SSDT proposed in the present invention.

Referring to FIG. 5, in the case of Example 1, since the pilot channel reception strength value of each neighboring base station does not have a value greater than the lower reference value {T} _ {SSDT-lower}, all base stations are mobile terminals according to the conventional method. Send data for handoff in the forward direction.

When there are three neighboring base stations of the mobile communication terminal, as shown in FIG. 6A, the mobile communication terminal 1 receives the pilot channel received from the base station 1 (2), the base station 2 (4), and the base station 3 (6). Compare the value of the intensity with the lower reference value {T} _ {SSDT-lower}. As a result of the comparison, since the received strength values of the pilot channels of the base station 1 (2), the base station 2 (4), and the base station 3 (6) are smaller than the lower reference value {T} _ {SSDT-lower}, the mobile communication terminal 1 ) Transmits data in a forward direction from base station 1 (2), base station 2 (4), and base station 3 (6).

In the case of Example 2, when the pilot channel reception strength value of each base station is greater than {T} _ {SSDT-lower}, the base station 1 and the base station 2 are the base station 1 and the base station {T} _ Since the base station smaller than {SSDT-upper} is the base station 2, only the base station 1 transmits data to the mobile communication terminal in the forward direction.

When there are three neighboring base stations of the mobile communication terminal, as shown in FIG. 6B, the mobile communication terminal 1 receives the pilot channel received from the base station 1 (2), the base station 2 (4), and the base station 3 (6). Compare the value of the intensity with the lower reference value {T} _ {SSDT-lower}. As a result of the comparison, base station 1 (2) and base station 2 (4) having a pilot channel value larger than the lower reference value of {T} _ {SSDT-lower} are larger than the higher reference value of {T} _ {SSDT-upper}. Since there is a base station 2 (4) which is a base station having a value, the mobile communication terminal 1 receives data from the base station 2 (4) in the forward direction.

In the case of Example 3, when the pilot channel reception strength value of each base station is larger than the lower reference value {T} _ {SSDT-lower}, the base station 1 and the base station 2 are respectively higher, and the pilot channel reception strength values of the base station 1 and the base station 2 are higher. Since the reference value is less than {T} _ {SSDT-upper}, the base station 1 and the base station 2 transmit data in the forward direction to the mobile communication terminal.

When there are three neighboring base stations of the mobile communication terminal, as shown in FIG. 6C, the mobile communication terminal 1 receives the pilot channel received from the base station 1 (2), the base station 2 (4), and the base station 3 (6). Compare the value of the intensity with the lower reference value {T} _ {SSDT-lower}. As a result of the comparison, base station 1 (2) and base station 2 (4) having a pilot channel value larger than the lower reference value of {T} _ {SSDT-lower} are larger than the higher reference value of {T} _ {SSDT-upper}. Since there is no base station having a value, the mobile communication terminal 1 receives data from the base station 1 (2) and the base station 2 (4) in the forward direction.

In the case of Example 4, when the pilot channel reception strength value of each base station is greater than {T} _ {SSDT-lower}, the base station 1, the base station 2 and the base station 3, and the pilot of the base station 1, base station 2 and base station 3 Since the channel reception strength value is larger than {T} _ {SSDT-upper}, the base station 3 having the largest reception strength of the pilot channel among the base station 1, the base station 2, and the base station 3 forwards data to the mobile terminal in a forward direction. Send.

When there are three neighboring base stations of the mobile communication terminal, as shown in FIG. 6D, the mobile communication terminal 1 receives the pilot channel received from the base station 1 (2), the base station 2 (4), and the base station 3 (6). Compare the value of the intensity with the lower reference value {T} _ {SSDT-lower}. As a result of the comparison, the base station 1 (2), the base station 2 (4) and the base station 3 (6) having the reception value of the pilot channel larger than the lower reference value {T} _ {SSDT-lower} are all the {T} _ {SSDT-upper} has a value larger than that of the base station 1 (2), the base station 3 (6) having the largest pilot reception strength value by comparing the pilot channel reception strength value of the base station 2 (4) and base station 3 (6) ), The mobile communication terminal 1 receives data in the forward direction.

As described above, in the handoff method of the mobile communication terminal, an example of three neighboring base stations is described, but the case of six neighboring base stations having a maximum active set is described in the same manner as described above.

As described above, according to the present invention, when the soft handoff occurs, the call disconnection rate is variably allocated by assigning the number of handoff branches to the mobile communication terminal from one to the maximum number of active sets. By minimizing this, there is an effect of improving call quality and reducing waste of radio resources.

On the other hand, the present invention is not limited to the above-described embodiment, various modifications are possible by those skilled in the art within the spirit and scope of the present invention described in the claims to be described later.

Claims (2)

A method of performing handoff between a mobile communication terminal and a base station by using an upper reference value and a lower reference value set for handoff timing determination and signal strength values of pilot channels of each base station, Detecting signal strength values of pilot channels provided from a plurality of adjacent base stations; Comparing signal strength values of the detected pilot channel of each neighboring base station with the upper reference value and the lower reference value; Performing data communication for handoff with all of the plurality of neighboring base stations when all of the detected signal strength values of each pilot channel are less than the lower reference value; Performing data communication for handoff with at least one corresponding base station when there is at least one signal strength value greater than the upper reference value among the signal strength values of each detected pilot channel; And When there is no signal strength value greater than the higher reference value among the signal strength values of each detected pilot channel and at least one signal strength value greater than the lower reference value exists, data communication for handoff with at least one corresponding base station The handoff method using the SSDT of the mobile communication system comprising the step of performing. The method of claim 1, wherein the method is further configured to perform data communication for handoff with one base station corresponding to the largest signal strength value among the large signal strength values when there are a plurality of signal strength values greater than the upper reference value. Hand off method using the SSDT of the mobile communication system, characterized in that.