KR100246547B1 - A method for reducing hard handoff between cells using hierarchical structure - Google Patents

Abstract

The present invention relates to a method for reducing inter-cell hard handoff using a hierarchical structure of micro cells and macro cells.

In a CDMA mobile communication system microcell environment, the processing of hard handoff between microcells is not only very difficult compared to the processing of soft handoff between microcells, but also has a high probability of dropping calls during handoff. have.

Accordingly, in the present invention, when a hard handoff occurs between the microcells using a hierarchical structure in which the microcells and the macrocells are superimposed, the handoff is performed by converting the hard handoff between the microcells and the macrocell, which is relatively simple to process. This method can improve the performance of the system with the effect of reducing the number of handoffs between micro cells. In this case, the frequency set for the micro cell and the frequency set for the macro cell are differently allocated, and the same frequency is allocated to the macro cells, but the frequency sets within the frequency set for the micro cell are allocated to the micro cells according to the traffic amount.

Description

A method for reducing hard handoff between cells using hierarchical structure

The present invention relates to a method for reducing hard handoff between cells in a code division multiple access (CDMA) mobile communication system. In particular, the present invention relates to a base station environment in which a micro cell and a macro cell overlap. The present invention relates to a method of processing a handoff by converting a hard handoff between microcells into a hard handoff between a microcell and a macrocell by allocating a frequency of a macrocell when a mobile terminal occurs during a call.

If a mobile terminal requires a hard handoff to switch the frequency of one microcell to an adjacent microcell during a call, the handoff is considerably less than the processing of soft handoff between microcells. Not only is it complicated, it is also very likely that the call will be dropped during the handoff.

In a hard handoff between microcells, since the mobile terminal does not know the time synchronizer of the neighboring cell to be handed off, it may take a long time to find out what the time synchronization is, thereby increasing the probability of handoff failure. Due to the nature of the cell, such hard handoffs frequently occur.

A method used to avoid hard handoff between conventional microcells is described as follows. Dividing the area within a cell into an inner area and an outer area allocates the original frequency of the cell to the inner area, and assigns the frequency allocated to the adjacent cell in addition to the original frequency to the outer area. Make it a hard handoff.

Accordingly, the present invention simplifies the handoff process by converting the hard handoff between the microcell and the macrocell into a hard handoff between the microcell and the macrocell using a hierarchical structure in which the microcell and the macrocell are superimposed. It is an object of the present invention to provide a method for reducing hard handoff between cells using a hierarchical structure capable of improving the quality of service by reducing the number of handoff between micro cells.

According to an aspect of the present invention, there is provided a method for configuring a plurality of micro cells and a macro cell including the micro cells, configuring a frequency set accordingly, and allocating a cell to the frequency set. Attempting to access a call to a base station of a micro cell to which the mobile terminal belongs, starting a call by allocating one code channel available among its frequencies to the mobile terminal, and performing the call. Requesting a handoff from a base station to which the mobile terminal first attempted a call to a neighboring base station by a start, and after requesting the handoff, a mobile terminal approaching a cell boundary moves a frequency currently used by the mobile terminal A first inspection step of checking whether the adjacent cell to be used is used, and the first inspection result A second check step of checking whether a frequency being used is a frequency of a macro cell when a frequency being used is used in an adjacent cell; and performing a soft handoff between macro cells if the frequency being used is a frequency of a macro cell. When the frequency being used is not the frequency of the macro cell, performing a soft handoff between the microcells, and then transitioning to a call attempting step; and when the frequency being used is not used by the neighboring cell, the base station of the macro cell. Performing a hard handoff, performing a handoff by assigning a frequency of a macro cell, and transitioning to the call attempting step; and terminating the call if the call is interrupted after the call attempt. It is done.

1 is a diagram illustrating a cell configuration method and a frequency allocation example of a hierarchical structure according to the present invention.

2 (a) and 2 (b) are diagrams showing an example of a case where a soft handoff between microcells and a hard handoff between microcells are converted into a hard handoff between a microcell and a macrocell according to the present invention.

3 is a flowchart of a method for call connection and handoff processing according to the present invention;

<Description of the symbols for the main parts of the drawings>

101: macro cell 102: micro cell

201: Soft handoff between micro cells

202 and 203: Microcell Hard Handoff

204: Hard handoff between micro cell and macro cell

205: Macro cell hard handoff

The present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating an example of a cell configuration method and a frequency allocation method of a hierarchical structure according to the present invention, in which a macro cell 101 and a micro cell 102 are formed of a hierarchical cell. One macro cell 101 manages an area of N micro cells, and FIG. 1 shows an example in which seven micro cells and one macro cell are overlapped. The frequencies assigned to the entire system are divided into frequency sets for micro cells and frequency sets for macro cells.

Assign cells to frequency sets. The frequency set of the microcell is A = {F ₁ , F ₂ ,. , F _m }, and the macro cell frequency set is B = {F _{m + 1} ,... , F _n }, the micro cells are a ₁ , a ₂ ,..., Which is a subset of frequency set A for the micro cells. , a _m is assigned, and macro cells are assigned frequencies of frequency set B and true subset b for the macro cell. All macro cells are assigned the same frequency, and micro cells have a set of frequencies a ₁ , a ₂ ,... As the traffic volume of each cell increases. , a _m is assigned in this order.

That is, a ₁ = {F ₁ }, a ₂ = {F ₁ , F ₂ },... , a _m = {F ₁ , F ₂ ,... , F _m } is assigned, and b = {F _{M + 1} ,... , F _n } is assigned.

2 (a) and 2 (b) are diagrams showing an example of a case where a soft handoff between microcells and a hard handoff between microcells are converted into a hard handoff between a microcell and a macrocell according to the present invention. In this case, four types of handoffs that can occur between cells to which frequencies are allocated are shown.

The first type is a soft handoff 201 between microcells 102 as shown in Fig. 2 (a), which is a time synchronization of adjacent cells since the handoff is made from the F1 frequency to the F1 frequency, ie the same frequency. Is easy to find.

The second type is the hard handoffs 202 and 203 between the microcells 102, as shown in FIG. 2 (a), with handoffs from F3 to F2 frequency 202 and from F2 frequency to F1 frequency. (203). This handoff is changed to a frequency of a neighboring micro cell that is different from the frequency currently used by the mobile terminal, and has a high probability of handoff failure because of the hassle of finding time synchronization of neighboring cells.

The third type is a hard handoff 204 between the micro cell 102 and the macro cell 102, as shown in FIG. 2 (b), from the F3 frequency assigned to the micro cell to the F4 frequency assigned to the macro cell. Handoff is made. This is a hard handoff similar to the second type, a hard handoff between micro cells, but it is easier to find time synchronization.

As a last type, soft handoff 205 between macro cells 101 as shown in Fig. 2 (b), a handoff is made from the F4 frequency assigned to the macro cell to the F4 frequency. This is the same method as soft handoff 201 between microcells except that the frequency set is different.

As we saw in the four types, soft handoff does not change the frequency in use, while hard handoff must change the frequency in use.

3 is a flowchart for call connection and handoff processing according to the present invention. After configuring a cell and a frequency set and allocating a cell to the frequency set, the mobile terminal attempts to access a call to a base station of a micro cell to which the mobile station belongs for a call (301). The base station allocates one available code channel of its frequency to the mobile terminal (302) and the call begins (303). All new calls are assigned a frequency of microcells. Once the call is initiated, the mobile terminal has a characteristic of moving during the call, so a handoff from the base station to which the call was first attempted to the neighboring base station is required (304). The mobile terminal approaching the cell boundary checks whether the current frequency used by the mobile terminal is used in the neighboring cell to be moved (305). As a result of the check, if the frequency being used is used in the adjacent cell, it is checked whether the frequency being used is the frequency of the macro cell (306). As a result of the test, if the frequency being used is the frequency of the macro cell, soft handoff is performed between macro cells (308). If the frequency being used is not the frequency of the macro cell, soft handoff is performed between the micro cells (307). The process then advances to step 303. As a result of the check in step 305, if the frequency being used is not used in the neighboring cell, a hard handoff is attempted to the base station of the macro cell, the handover is performed by being assigned the frequency of the macro cell (309), and the transition to step 303 is performed. do. End the call if you interrupt the call.

As described above, according to the present invention, when a mobile terminal requests a hard handoff to a neighboring microcell during a call, when a hard handoff occurs between the microcells using a hierarchical structure in which the microcells and the macrocells are superimposed, the processing is relatively difficult. By converting into a simple handoff between the microcell and the macrocell, the handoff is performed to simplify the handoff process, reduce the number of handoffs between the microcells, and reduce the possibility of call dropping, thereby preventing deterioration in service quality. Have

Claims (1)

Configuring a plurality of micro cells and a macro cell including the micro cells, configuring a frequency set accordingly, and allocating cells to the frequency sets; Attempting to access a call to a base station of a micro cell to which the mobile terminal belongs in the system environment configured as described above; The base station of the micro cell assigns one code channel available among its frequencies to the mobile terminal to initiate a call; Requesting a handoff from a base station to which the mobile terminal first attempted a call to an adjacent base station by the start of the call; A first checking step of checking whether a mobile terminal approaching a cell boundary after requesting the handoff uses a frequency currently being used by a neighboring cell to be moved; A second test step of checking whether a frequency being used is a frequency of a macro cell when the frequency being used is used in an adjacent cell as a result of the first test; When the frequency being used is the frequency of the macro cell as a result of the second test, the soft handoff is performed between the macrocells, and when the frequency being used is not the frequency of the macrocell, the soft handoff is performed after the microcells. Steps, Attempting a hard handoff to a base station of a macro cell, performing a handoff by assigning a frequency of a macro cell when the frequency being used is not used in an adjacent cell, and transitioning to the call attempting step; And ending the call if the call is interrupted after the call attempt.

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