KR100334798B1 - Softer Handoff Method in Cellular Mobile Communication Systems - Google Patents

Abstract

A method for softer handoff in a cellular mobile communication system using code division multiple access is disclosed. According to the method, when a mobile terminal provided with a mobile communication service reports a new active set to a base station controller, the base station controller refers to the active set and adds a second sector except for the first sector in the existing active set. Decide The base station controller instructs the base station to start sending the second sector and instructs the mobile terminal to add the second sector except the first sector in the existing active set. When the mobile terminal adds a second sector except the first sector in the existing active set through the handoff procedure and reports completion to the base station controller, the base station controller notified of completion completes the transmission of the first sector. Command and terminate the handoff procedure.

Description

Softer Handoff in Cellular Mobile Communication Systems

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a softer handoff method in a cellular mobile communication system, and more particularly to a method for preventing a softer handoff failure due to a decrease in radio link quality.

In general, a cellular mobile communication system is represented by a mobile communication system using a code division multiple access (CDMA) scheme. In such a CDMA mobile communication system, handoff is performed for normal service to a mobile station. Perform. Types of handoff in the CDMA mobile communication system include soft handoff, softer handoff, hard handoff, and the like. Among them, soft handoff means that the transfer of a call from an existing busy base station to the same scheduled base station is performed without forced disconnection of the existing busy channel. In other words, a cell serviced by a given base station is divided into a plurality of sectors, and a handoff required as a mobile station currently serving is moving between sectors is called a softer handoff.

1 is a diagram showing the configuration of a conventional CDMA mobile communication system.

Referring to FIG. 1, a configuration of a CDMA mobile communication system includes a base station transceiver that provides a mobile communication service to a mobile station (MS) 4 and 41 moving in a predetermined area of a cell. Subsystem: BTS (3) (31), Base Station Controller (BSC) 2 (21), which controls a plurality of base stations (3) (31), A plurality of base station controllers (2) (21) It includes a Mobile Switching Center (MSC) (1) for connecting to a Public Switched Telephone Network (PSTN) (11).

The forward link of the CDMA mobile communication system configured as described above refers to channels directed from the base station to the mobile terminal, and the reverse link refers to channels directed from the mobile terminal to the base station. All forward channels in one base station have the same Pseudorandom Noise (PN) Sequence Offset. Therefore, the PN offset becomes an identification signal for distinguishing several base stations.

The CDMA mobile communication system having the configuration as described above can improve the efficiency of insufficient frequency to serve more users. In addition, the concept introduced to further increase the frequency efficiency is a cell division technique, and one of such cell division techniques is sectorization. The sectorization means to divide a cell into a plurality of sectors and to perform a mobile communication service for each of the divided sectors. As an example of the sector-cell according to the sectorization, the cell may be divided into three parts by separating the 120 degree antenna from side to side. At this time, the mobile terminal recognizes one sector antenna as one base station.

As mentioned above, the CDMA mobile communication system allows a call to be continued by the handoff function when the mobile terminal enters a new area out of one service region (cell or sector). This is to ensure continuity of the call and provides various types of handoffs. In particular, a method of simultaneously connecting several call paths through one frequency band is called soft handoff, and soft handoff occurring between sectors is called softer handoff.

US Patent No. 5,625,876, "Method and apparatus for performing handoff between sectors of a common station," which demodulates and combines high frequency signals received from each sector and converts them into digital data to support inter-sector softer handoff. Is disclosed.

A CDMA mobile communication system supporting such a soft handoff currently manages several sectors to which a mobile terminal can establish a channel as one active set (AS). That is, the active set is used to easily perform the softer handoff by managing the sector to which the mobile terminal belongs and the sector to which the mobile terminal can move through the handoff.

On the other hand, the mobile terminal changes the active set from time to time by the command of the base station controller. That is, a sector in which the strength of the PN offset signal is gradually increased is added to the active set, and a sector in which the signal is far away, that is, the strength of the PN offset signal is weakened, is dropped in the active set.

This softer handoff basically acts as a swap handoff. That is, when a PN offset having a strength equal to or greater than a predetermined reference value is detected, one of the existing PN offsets is removed from the active set, and the newly detected PN offset is added to the active set.

A mobile terminal of a currently operating personal communication service (PCS) system can manage up to six PN offsets as an active set. Therefore, in consideration of radio resources and base station resources, up to two sectors are basically set in one cell. However, in the actual field, the multi-path phenomenon occurs due to the influence of the surrounding environment such as the terrain and the building around the base station, so that all three sectors may be randomly detected by the mobile terminal with sufficient strength. have.

Therefore, in the conventional case, if the mobile terminal is already adding two cells, that is, having two sector PN offsets in the active set, if another sector having a superior strength than the existing sector is detected, the base station is most Allow the mobile terminal to use only two sectors with good forward quality.

That is, the base station stops output of the sector having the smallest strength among the existing active sectors, and transmits the new sector. After the allocation of the radio resources is completed, the base station notifies the mobile station of a newly outputted sector (active set) and instructs a new active set to be configured. The PN offsets of the active set possessed by the mobile terminal must match the PN offsets to which the base station is transmitting a signal. A message flow diagram illustrating a procedure for soft handoff in a code division multiple access mobile communication system is shown.

Referring to FIG. 2, first, a mobile terminal 4 moving a service area of a base station 3 composed of sectors α, sector β, and sector γ is transmitted to the base station controller 2 through the base station 3. The change of the active set is reported (step 110). For example, the case where the mobile terminal 4 having [α, β] as the active set reports [α, γ] will be described.

The base station controller 2 determines whether or not the handoff is performed by referring to the changed active set (step 120). In this case, the base station controller 2 removes β included in the existing active set and decides to add γ. The base station controller 2 then changes its active set to [α, γ], and instructs the base station 3 to stop sending β and start sending γ (step 130). Then, the mobile terminal 4 The mobile terminal 4 changes the active set to [[alpha], [gamma]] through the handoff procedure only after receiving the command of the base station controller 2, and then the base station controller 2 Report the completion of the active set change (step 150).

However, in the prior art operating as described above, the forward quality of the newly added sector is degraded due to noise or terrain, so that the message is lost at the moment when the base station controller informs the mobile terminal of the new active set (step 140). Can be. Then, the mobile terminal may not be notified of the new active set from the base station controller, which may result in a situation in which the active set of the base station controller and the mobile terminal are inconsistent and the call is disconnected. In this case, the base station has already stopped transmitting β by the command of the base station controller, but the mobile terminal is not commanded to change the active set of the base station controller and will continue to search for β.

In addition, if the strength of the three sectors is constantly changing to a similar size, a continuous softer handoff occurs between the base station controller and the mobile terminal can increase the load on the system, the handoff processing speed of the base station controller and the mobile terminal The problem arises that the call can be truncated by not being able to keep up with the change in propagation and consequently adding inappropriate sectors.

Accordingly, an object of the present invention for solving the problems of the prior art operating as described above is only after the handoff of the mobile terminal is completed after starting transmission in a newly added sector when a soft swap handoff occurs in the base station controller. A soft handoff method is provided in a cellular mobile communication system for stopping transmission of an excluded sector.

Another object of the present invention is to provide a softer handoff method in a cellular mobile communication system in which only the added sector is added to the active set without exchanging the added sector and the excluded sector in order to cope with a constantly changing propagation environment. Is in.

The present invention according to the first aspect for achieving the above object is a code division multiple access mobile communication system comprising a mobile terminal, a base station and a base station controller for serving a cell consisting of a plurality of sectors, the mobile terminal, Receiving a change in the strength of the received signal corresponding to each of the sectors from the at least two sectors of the sectors according to the change in the strength of the received signal corresponding to each of the sectors to form a new active set; And requesting a change of an active set to the mobile terminal at the same time as starting transmission of a sector added to the new active set, and in response to the request for changing the active set, an active set change is completed from the mobile terminal. Stopping reporting of deleted sectors in the new active set if reported; If in response to the property set of the change request to change the active set from the mobile terminal is completed, the soap was not reported, including the step of stopping the transmission of the sector added to the new active set emitter implemented a handoff method.

The present invention according to the second aspect for achieving the above object is a code division multiple access mobile communication system comprising a mobile terminal, a base station and a base station controller for serving a cell consisting of a plurality of sectors, the mobile terminal, Receiving a change in the strength of the received signal corresponding to each of the sectors from the at least two sectors of the sectors according to the change in the strength of the received signal corresponding to each of the sectors to form a new active set; And requesting a change of an active set to the mobile terminal at the same time as starting transmission of a sector added to the new active set, and in response to the active set change request, reporting the completion of the active set change from the mobile terminal. By the mobile terminal and the mobile terminal in response to the active set change request. A soft handoff method is implemented including stopping the transmission of a sector added to the new active set if the active set change completion report is not performed.

1 is a diagram showing the configuration of a typical code division multiple access mobile communication system.

2 is a message flow diagram illustrating a procedure performed for softener handoff in a code division multiple access mobile communication system.

3 is a message flow diagram illustrating a procedure performed for softer handoff according to a preferred embodiment of the present invention.

4 is a message flow diagram illustrating a procedure performed for softer handoff according to another exemplary embodiment of the present invention.

Hereinafter, described in detail with reference to the accompanying drawings in accordance with an embodiment of the present invention. First, in the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

In addition, two embodiments of the present invention will be described below. The first embodiment is to prevent the case where the active set of the base station and the mobile station is inconsistent, and the second embodiment is to prevent the case where the handoff process cannot keep up because the radio wave continuously changes rapidly. .

First, a method for preventing a case where an active set of a base station and a mobile station are inconsistent according to an embodiment of the present invention will be described.

3 is a diagram illustrating a message flow showing a procedure performed for softer handoff according to an exemplary embodiment of the present invention.

Referring to Figure 3 described in detail the operation according to an embodiment of the present invention as follows.

The mobile terminal 4 reports the change of the active set to the base station controller 2 (step 210), i.e., the mobile terminal 4 determines the strength of the signal received from each sector constituting the cell to which it belongs. The change is reported to the base station controller 2. For example, the case where the mobile terminal 4 having [α, β] as the active set reports [α, γ] to the base station controller 2 will be described.

The base station controller 2 determines whether or not the handoff is performed by referring to the signal strengths of the changed sectors α, β, and γ reported from the mobile terminal 4 (step 220). After determining whether to perform the handoff and performing the softer handoff, if the signal strength of the two sectors of the reported active set [α, β] is the weakest and the active set does not include the signal Determine the other sectors with superior strength. The sector with the weakest signal strength determined as described above is removed from the active set, and other sectors with the superior signal strength are included in the active set. For example, assuming that the sector with the weakest signal strength is β sector and another sector with superior signal strength is a sector γ, the active set will change as follows. That is, it is determined to remove the β sector having the smallest signal strength from the existing active set, and to add the γ sector which is much stronger in the signal strength. The base station controller 2 changes its active set to [α, γ] and instructs the base station 3 to start transmitting γ. (Step 230) Then, the mobile terminal 4 changes the active set. Command (step 240).

The mobile terminal 4 changes the active set to [α, γ] through a handoff procedure only after receiving the active set change command from the base station controller 2, and changes the active set to the base station controller 2. The base station controller 2 instructs the base station 3 to stop transmitting β, and terminates the handoff procedure (step 260).

On the other hand, the base station controller 2 may not receive the completion of the active set change report from the mobile terminal 4 in step 250 may occur. The reason for not receiving the active set change completion report is that the mobile terminal 4 does not receive the active set change command from the base station controller 2 and the active set change complete report from the mobile terminal 4 is not received. It may be the case that the base station controller 2 does not receive it. In this case, the base station controller 2 instructs the base station 3 to stop transmitting the newly started β. Therefore, if the softer handoff is performed as described above, the call may be prevented from being disconnected even when the active set change command message of the base station controller or the active set change complete report message of the mobile station is lost.

Next, a method of preventing a case in which handoff processing cannot be followed because the change of the radio wave continuously changes rapidly according to another embodiment of the present invention is as follows.

4s is a diagram illustrating a message flow showing a procedure performed for softener handoff according to another exemplary embodiment of the present invention.

Referring to FIG. 4, another embodiment of the present invention will be described in detail.

First, the mobile terminal 4 reports the change of the active set to the base station controller 2 (step 310). That is, the mobile terminal 4 receives a signal received from each sector constituting the cell to which it belongs. The change in intensity is reported to the base station controller 2. Hereinafter, for example, the mobile terminal 4 having [α, β] as the active set reports [α, γ] to the base station controller 2. One case will be described.

The base station controller 2 determines the type of sector to be added by referring to the signal strengths of the changed sectors α, β, and γ reported from the mobile terminal 4 (step 320). The sectors having good reception strength are determined by measuring the strength of signals received from other sectors except the two sectors of the reported active set [α, β]. Sectors with good signal strength as determined above are included in the active set. For example, if another sector having a good signal strength is assumed to be a sector, the sector will be added to the active sector in sectors α and β. In this case, the base station controller 2 changes its active set to [α, β, γ] and instructs the base station 3 to start transmitting γ. (Step 330) Then, the mobile terminal 4 Instruct the user to change the active set (step 340).

The mobile terminal 4 changes the active set to [[alpha], [beta], [gamma]] through the handoff procedure and reports the completion of the active set change to the base station controller 2. (Step 350) The base station controller 2 Terminates the handoff procedure.

However, if the base station controller 2 does not report the completion of the active set change from the mobile terminal 4 in step 350, the base station controller 2 stops the transmission of the new transmission γ in step 330. Command Therefore, when the softer handoff is performed as described above, it is possible to prevent the case where the handoff process cannot keep up because the radio wave changes continuously and rapidly.

Meanwhile, the present invention may be variously modified from the above-described embodiments, may take various forms, and the detailed description of the present invention has been described only with respect to specific embodiments thereof. However, it should be understood that the present invention is not limited to the particular forms mentioned in the detailed description of the invention. It is also to be understood that all modifications, equivalents and substitutions are within the spirit and scope of the invention as defined by the appended claims.

The present invention operating as described above maintains good call quality by performing an appropriate handoff even when noise is generated in a single sector or when an influence such as a terrain occurs or a change in propagation changes momentarily rapidly.

That is, the call quality is improved by preventing the inconsistency of the active set of the base station and the mobile terminal. In addition, the handoff processing speed of the base station and the mobile terminal improves call quality by coping with a continuously changing radio wave.

Claims (2)

A method for performing softer handoff in a code division multiple access mobile communication system comprising a mobile terminal, a base station and a base station controller serving a cell consisting of a plurality of sectors, The mobile terminal receives a change in the strength of the received signal corresponding to each of the sectors from the mobile terminal, and determines at least two sectors of the sectors according to the change in the strength of the received signal corresponding to each of the sectors to form a new active set. Composition process, Requesting a change of an active set to the mobile terminal at the same time as starting transmission of a sector added to the new active set; Stopping transmission of a sector deleted from the new active set when it is reported that the active set change is completed from the mobile terminal in response to the active set change request; And stopping transmission of a sector added to the new active set if it is not reported that the active set change is completed from the mobile terminal in response to the active set change request. Softener handoff method. A method for performing softer handoff in a code division multiple access mobile communication system comprising a mobile terminal, a base station and a base station controller serving a cell consisting of a plurality of sectors, The mobile terminal receives a change in the strength of the received signal corresponding to each of the sectors from the mobile terminal, and determines at least two sectors of the sectors according to the change in the strength of the received signal corresponding to each of the sectors to form a new active set. Composition process, Requesting a change of an active set to the mobile terminal at the same time as starting transmission of a sector added to the new active set; Ending by an active set change completion report from the mobile terminal in response to the active set change request; And stopping transmission of a sector added to the new active set if the active set change completion report is not made from the mobile terminal in response to the active set change request. Softener handoff method.