KR20010057755A - Method for allocation channel in mobile communication system - Google Patents

Abstract

PURPOSE: A method for allocating a channel of a mobile communication system is provided to reduce generation of a hard hand-off and thereby improve service quality, by guaranteeing channel allocation with priority for a hand-off call even though there are a lot of calls. CONSTITUTION: When a user requests a call(S800), a base station determines whether the call is normal(S801). The number of normal-call limitation channels is calculated from the number of total usable channels and a channel limitation threshold value(S802). The number of the normal-call limitation channels is compared with that of currently used channels(S803). If the number of the normal-call limitation channels is larger than that of the currently used channels, one of idle channels is allocated to a requested normal call(S804). If the number of the currently used channels is larger than the number of the normal-call limitation channels, another procedure is executed(S806). If the requested call is the hand-off call, it is determined whether a usable idle channel exists in a corresponding CDMA channel(S805).

Description

Method for allocation channel in mobile communication system

TECHNICAL FIELD The present invention relates to mobile communications, and more particularly, to a channel assignment method of a mobile communication system, which is suitable for allocating channels to effectively handle handoff calls.

Generally, in a mobile communication system operating based on the EIA / TIA IS-95A or ANSI J-STD-008 standards, a base station uses one radio on a call-by-call basis for a normal or hand-off call requested by a user. Assign a call channel.

At this time, the base station allocates one wireless call channel to the call requested by the user, the CDMA channel divided by frequency band, the call channel set provided for each CDMA channel, and the frame defined in the IS-95A / J-STD-008 standard. Manage resources consisting of offset, Walsh code, and the power required to transmit data in the radio section.

This section describes the wireless call channel assignment procedure proposed by the EIA / TIA IS-95A or ANSI-STD-008 standard.

1 is a flowchart illustrating a procedure for allocating a wireless communication channel according to an EIA / TIA IS-95A or ANSI-STD-008 standard.

Referring to FIG. 1, in the conventional radio channel allocation procedure, when a call is requested from a user, a base station selects and assigns one available CDMA channel among CDMA channels divided by frequency bands (S100), and the allocated CDMA channel. Allocating a frame offset resource for (S101), and assigns one traffic channel that is not in use among the set of channels owned by the assigned CDMA channel to allocate the allocated frame offset resource (S102) enabling the call channel to use, assigning a Walsh code (S103), and allocating transmission power necessary for transmitting data to the wireless section through the assigned call channel ( S104).

In the step S100, the allocation of the CDMA channel means the allocation of frequency resources. In the current system, one frequency resource is allocated among eight frequency resources of 1750 MHz to 1780 MHz in the uplink and 1840 MHz to 1870 MHz in the downlink.

Steps S101 to S104 after the CDMA channel assignment step S100 are radio assignment procedures of a general CDMA mobile communication system, and thus description thereof is omitted.

FIG. 2A is a resource allocation diagram of available channels of the CDMA channel described with reference to FIG. 1, and FIG. 2B is a diagram illustrating radio channel resources managed for each CDMA channel managed by a conventional base station.

Referring to FIG. 2A, an available channel of a CDMA channel is divided into a normal call channel 200 that can be allocated to both a normal call and a handoff call, and a handoff call reservation channel 201 reserved for a handoff call only. . That is, the CDMA channel resource managed by the base station is composed of N _tot available channel elements in units of CDMA channels, and the base station includes the normal call channel 200 and the handoff call reservation channel as shown in FIG. 2A. Managed at 201.

Referring to FIG. 2B, in order to efficiently allocate and release each CDMA channel, the base station (BTS) may use the total number of available channels 202, the number of idle channels 203, the number of channels used 204, and the number of available channels 204 for each CDMA channel. A database of handoff call reservation channel count 205 and handoff call allocation channel count 206 is managed.

Here, the total number of available channels 202 is the total number of channels held for each CDMA channel, the number of idle channels is the number of channels currently allocated from the total number of available channels 202, and the number of available channels 204 is the total number of available channels. This is the number of channels currently in use at 202. The number of handoff call reservation channels 205 is the number of channels reserved for the handoff call, and the number of handoff call assignment channels 206 indicates the number of channels currently allocated to the handoff call.

3 is a flowchart illustrating a detailed process of allocating a CDMA channel shown in FIG. 1.

Referring to FIG. 3, the process of allocating a CDMA channel is a process of determining a possibility of assigning a call channel in a channel set included in the corresponding CDMA channel based on the database shown in FIG. 2B and updating the database when the allocation is possible. .

That is, when a call is requested from the user, the base station checks whether there is an idle channel that can be allocated in the CDMA channel currently being used, and if there is an idle channel, allocates one of the idle channels to the UE (S300). Here, if the step S300 fails for the handoff call, soft hand-off is impossible.

If the channel assignment for the call requested by the user fails (i.e., the resource allocation fails on the CDMA channel requested by the user), the base station selects a CDMA channel of the other frequency band with the largest number of idle channels in all the CDMA channels in use. The idle channel of one of the selected CDMA channels is selected and assigned to the user (SS303).

However, if the channel allocation fails in step S303, the base station BTS does not allocate a radio channel for the requested call (S304, S305).

FIG. 4 is a flowchart illustrating a first embodiment of the process of allocating a CDMA channel shown in FIG. 3.

Referring to FIG. 4, the first embodiment describes a process of selecting and allocating an idle channel among CDMA channels currently used by a base station when a user requests a call.

First, the base station checks whether there is an idle channel among the CDMA channels in use (S400).

If the idle channel does not exist according to the check result, the base station fails to allocate the channel (S404). If the idle channel exists, the base station determines whether the call requested from the user is a normal call or a handoff call (S401).

If the call requested from the user is a normal call according to the determination result of step S401, the base station compares the current number of handoff call allocation channels and the number of handoff call reservation channels with each other (S402).

If the number of handoff call allocation channels is greater than or equal to the number of handoff call reservation channels, the base station BTS allocates one of the idle channels to the UE (S405 to S406).

However, if the number of handoff call allocation channels is less than the number of handoff call reservation channels, the base station (BTS) subtracts the number of handoff call allocation channels from the number of handoff call reservation channels and compares whether the result is greater than the number of idle channels. (S403).

As a result of the comparison, if the number of idle channels is large, the base station (BTS) allocates one of the idle channels except for the handoff call reservation channel to the UE (S405, S406). If the number of idle channels is small, the channel allocation fails (S404). ).

On the other hand, if the call requested from the user side (UE) in step S401 is a handoff call, the base station (BTS) reduces the number of idle channels by one and allocates one of the handoff call reservation channels to the user side (UE) (S407). S408).

FIG. 5 is a flowchart illustrating a second embodiment of the process of allocating a CDMA channel shown in FIG. 3.

Referring to FIG. 5, in a second embodiment, when a call is requested from a user side (UE), a base station (BTS) selects a CDMA channel having the most idle channels and selects and assigns an idle channel among the selected CDMA channels. Explain. This second embodiment applies when there is no idle channel among the CDMA channels currently used by the base station (BTS).

First, the base station (BTS) checks whether the call requested from the user side (UE) is a normal call or a handoff call (S500).

If the call requested from the UE (UE) is a normal call according to the result of the check, the base station (BTS) selects the CDMA channel having the largest idle channel among the CDMA channels of all the frequency bands in use (S501), and selects any of the selected CDMA channels. Select an idle channel and assign it to the user side (UE). If the selection of the CDMA channel with the most idle channels fails (S502), the base station (BTS) fails to allocate the CDMA channel (S505).

On the other hand, if the call requested from the user side (UE) in the step (S500) is a handoff call, the base station (BTS), like the normal call, selects the CDMA channel with the most idle channels among the CDMA channels of all frequency bands in use ( S506), an arbitrary idle channel is selected from the selected CDMA channel and assigned to the user side (UE). At this time, the number of idle channels is reduced and the number of handoff allocation channels is increased (S508, S509).

If the selection of the CDMA channel with the most idle channels fails, the base station (BTS) fails to allocate the CDMA channel (S505).

As described above, in the channel allocation procedure according to the IS-95A standard, channel resources already reserved for handoff calls are preferentially allocated whenever a handoff request is made. If the amount of the handoff call is larger than the channel resources reserved for handoff, the distinction between the normal call and the handoff call is lost.

Therefore, when the amount of calls requiring handoff increases, when the base station does not have enough radio channel resources, there is a problem in that a stable handoff cannot be performed because priority channel resource allocation cannot be guaranteed for the handoff call.

In addition, if a channel resource for a handoff call does not exist in a CDMA channel requested by a user, another CDMA channel may be allocated to the requested handoff call, but this causes hard handoff. This hard handoff has a problem that the call success rate is lower than that of the soft handoff, thereby increasing the probability that the call is dropped.

On the other hand, in order to avoid the above-mentioned problems, a method of increasing a handoff reservation call may be considered. However, increasing a handoff reservation call means that channel resources that can be allocated to a normal call are reduced, which wastes radio channel resources of the base station. Another problem arises.

Accordingly, an object of the present invention is to provide a channel allocation method of a mobile communication system for allocating a wireless channel to efficiently handle handoff in view of the above-mentioned problems of the prior art.

According to an aspect of the present invention for achieving the above object, the channel allocation method of the mobile communication system comprises a first step of setting a first channel limit threshold for the first channel set, and the first channel set A second step in which a call is required; a third step of calculating a number of first normal call limited channels of the first channel set using the set first channel limit threshold; and a first use channel of the first channel set. A fourth step of calculating the number, a fifth step of comparing the calculated size of the first normal call restriction channel number with the first used channel number, and whether or not to allocate a channel to the requested call according to the comparison result The sixth step is to decide.

Preferably, the seventh step of setting a second channel limit threshold for the second channel set when the calculated first number of used channels is greater than the calculated normal call limit channel number and the requested call is a normal call; An eighth step of calculating the number of second normal call limited channels of the second channel set by using the set second channel limit threshold; a ninth step of calculating the number of second used channels of the second channel set; And a tenth step of comparing the calculated size of the second normal call limited channel number with the number of second used channels, and an eleventh step of determining whether to allocate a channel to the requested call according to the comparison result. Is done.

1 is a flowchart illustrating a procedure for allocating a wireless call channel according to the EIA / TIA IS-95A or ANSI-STD-008 standard.

FIG. 2A is a resource allocation diagram for an available channel of the CDMA channel described in FIG.

2B is a diagram illustrating radio channel resources managed for each CDMA channel managed by a conventional base station.

3 is a flow chart showing in detail the allocation process of the CDMA channel shown in FIG.

FIG. 4 is a flowchart showing a first embodiment of the process of allocating a CDMA channel shown in FIG.

FIG. 5 is a flowchart showing a second embodiment of the process of allocating a CDMA channel shown in FIG.

6 is a resource allocation diagram for an available channel of a CDMA channel according to the present invention.

7 is a diagram illustrating radio channel resources managed by a base station for each CDMA channel according to the present invention.

8 illustrates a first procedure of a channel allocation method according to the present invention.

9 illustrates a second procedure of the channel allocation method according to the present invention;

Hereinafter, a configuration and an operation according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

The allocation of radio channel resources from a base station can be broadly divided into a case where a call is received / outgoed from a corresponding base station or a call originated / received from another base station is handed off to a corresponding base station. This handoff call includes a soft handoff that uses the existing CDMA channel and frame offset (FO) and a hard handoff that changes the CDMA channel and frame offset (FO).

This hard handoff has a lower success rate than soft handoff, so if a hard handoff continues to occur to a moving user, the probability of a call drop is increased. This greatly affects the call quality felt by the user. Therefore, there is a need for a channel allocation method for reducing the occurrence of hard handoff with limited channel resources at the base station.

Accordingly, the present invention proposes a channel allocation method for assigning a radio channel to a handoff call preferentially so as to efficiently handle the handoff.

To this end, the present invention implements stable channel allocation for the handoff call by setting the first channel limit threshold and the second channel limit threshold and adjusting the set thresholds according to the ratio of the normal call and the handoff call.

6 is a resource allocation diagram for an available channel of a CDMA channel according to the present invention.

Referring to FIG. 6, each CDMA channel according to the present invention is a first channel 600 that can be allocated to all required calls, regardless of a normal call or a handoff call, and a limited number of first assignable channels to a normal call. It is divided into two channels 601 and a third channel 602 which can be assigned only to a handoff call.

Here, the number of first channels 600 is determined by the first channel limiting threshold, the number of second channels 601 is determined by the first channel limiting threshold and the second channel limiting threshold, and the third The number of channels 602 is determined by the remaining channels except for the first channel 600 and the second channel 601 in all available channels of the corresponding CDMA channel.

As such, the reason for setting the first channel limit threshold and the second channel limit threshold so as to distinguish the first channel 600 from the second channel 601 is to limit the channel assignment for the normal call and to the handoff call. This is to prioritize channel allocation.

7 illustrates radio channel resources managed by a base station for each CDMA channel according to the present invention.

Referring to FIG. 7, the CDMA channel managed by the base station according to the present invention includes the total number of available channels (N _tot ) 700, the number of idle channels (N _idle ) 701, and the number of normal call allocation channels (N _normal). ) 702, the number of handoff call allocation channels (N _handoff ) 703, the first channel limit threshold N _{1st_th} 704, and the second channel limit threshold N _{2st_th} 705. Are distinguished.

Here, the total number of available channels (N _tot ) 700 is the number of all channels available in the CDMA channel, the number of idle channels (N _idle ) 701 is the number of channels currently available, and the number of normal call allocation channels (N _normal ) 702 is the number of channels assigned to the normal call, the handoff call allocation channel number N _handoff 703 is the number of channels currently assigned to the handoff call, and the first channel limit threshold. (N _{1st_th} ) 704 is a threshold of a channel that can be allocated to both a normal call and a handoff call in the total number of available channels 700, and the second channel limit threshold (N _{2st_th} ) 705 is limited to normal. The threshold of channels that can be assigned to the call.

The first channel limit threshold 704 and the second channel limit threshold 705 are parameters for preferentially assigning a handoff call when the amount of calls required is large.

Meanwhile, the base station sets a threshold adjustment parameter N _delta for adjusting the channel limit thresholds 704 and 705 according to the ratio of the normal call allocation channel number 702 and the handoff call allocation channel number 703. To manage.

8 is a diagram illustrating a first procedure of a channel allocation method according to the present invention.

Referring to FIG. 8, when a call is requested from the user (S800), the base station determines whether the requested call is a normal call (S801).

If the required call is a normal call according to the determination result of step S801, the base station determines whether there is an available idle channel that can be allocated to the normal call in a given set of CDMA channels.

At this time, it is determined whether there is an idle channel available according to the following steps.

First, the first normal call limited channel number N _{1st_th} is calculated from the total number of available channels N _tot and the first channel limited threshold value T _{1st_th} (S802).

At this time, the number of first normal call restriction channels is calculated according to the following equation.

Number of first normal call limit channels = total number of available channels × first channel limit threshold

Next, the number of _busy channels N _busy is calculated from the number of normal call allocation channels N _normal and the number of handoff call allocation channels N _handoff .

At this time, the number of channels currently in use is calculated according to the following equation.

Number of channels in use = number of normal call allocation channels + number of allocation channels after handoff

Subsequently, the size of the first normal call limit channel number N _{1nd_th} and the number of channels N _busy currently obtained according to Equation 1 and Equation 2 are compared with each other (S803).

If the number of first normal call restriction channels is greater than the number of channels being used according to the comparison result, any one of the idle channels is allocated to the required normal call (S804). However, if the number of channels being used is greater than the first normal call restriction channel according to the comparison result, the second procedure of the channel allocation method shown in FIG. 9 is performed (S806).

This means that the normal call is limited and the handoff call is allocated when the number of channels being used is greater than the number of first normal call restricted channels according to the comparison result, and when the number of first normal call limited channels is larger than the number of channels being used. Means allocating to both normal and handoff calls.

On the other hand, if the requested call is a handoff call according to the determination result of step S801, it is determined whether an available idle channel exists in the corresponding CDMA channel (S805), and if there is an available idle channel (that is, zero or more) Then assigns any idle channel to the requested handoff call. However, if there is no idle channel available, the second procedure shown in FIG. 9 is performed next (S806).

In this first procedure, if the CDMA channel allocation process for the normal call is successful, the number of normal call allocation channels (N _normal ) is increased. Likewise, if the CDMA channel allocation process for the handoff call is successful, the handoff call allocation channel is successful. The number N _handoff increases.

9 is a view showing a second procedure of the channel allocation method according to the present invention.

Referring to FIG. 9, the base station first selects a CDMA channel having the largest idle channel among all the CDMA channels in use (S900).

Then it is determined whether the requested call is a normal call (S901).

If the requested call is a normal call according to the determination result of the step S901, it is determined whether there is an idle channel available in the CDMA channel selected in the step S900. At this time, it is determined whether the available idle channel exists as follows.

First, the second normal call limited channel number N _{1st_th} is calculated from the total number of available channels N _tot and the second channel limited threshold value T _{1st_th} (S902).

In this case, the number of second normal call restriction channels is calculated according to the following Equation 3.

2nd normal call limit channel number = total number of available channels x 2nd channel limit threshold

Next, the number of _busy channels N _busy is calculated from the number of normal call allocation channels N _normal and the number of handoff call allocation channels N _handoff .

At this time, the number of channels currently in use is calculated according to the following equation.

Number of channels in use = number of normal call allocation channels + number of allocation channels after handoff

Subsequently, the size of the second normal call limit channel number N _{2nd_th} and the number of channels N _busy currently used according to Equation 3 and Equation 4 are compared with each other (S903).

If the number of second normal call restriction channels is greater than the number of channels being used according to the comparison result, any one of the idle channels is allocated to the required normal call (S904). However, if the number of channels being used is greater than the second normal call limit channel number according to the comparison result, the CDMA channel allocation for the required normal call fails (S906).

On the other hand, if the call required according to the determination result of the step S901 is a handoff call, it is determined whether an available idle channel exists in the corresponding CDMA channel (S905), and if there is an available idle channel (that is, zero or more) Then assigns any idle channel to the requested handoff call. However, if there is no idle channel available, CDMA channel allocation for the requested handoff call fails (S906).

In this second procedure, if the CDMA channel allocation process for the normal call is successful, the number of normal call allocation channels (N _normal ) is increased. Likewise, if the CDMA channel allocation process for the handoff call is successful, the handoff call allocation channel is successful. The number N _handoff increases.

On the other hand, according to the first procedure of the channel allocation method according to the present invention, if the _busy channel N _busy is greater than the first normal call limit channel number N _{1nd_th} , the normal call cannot be allocated to the CDMA channel requested by the user. It is allocated to another CDMA channel with an idle channel assignable to it.

In this case, since the call success rate is lowered, the present invention _adjusts the first channel limit threshold value N _{1st_th in accordance} with a procedure such that the normal call and the handoff call require different rates for each base station and time zone.

First, the sizes of the normal call allocation channel number N _normal and the handoff call allocation channel number N _handoff are compared.

If the normal call allocation channel number N _normal is greater than the _handoff call allocation channel number N _handoff according to the comparison result, the first channel limit threshold value N _{1st_th} is used with the threshold adjustment parameter N _delta . It increases by the product of the ratio of the normal calls among the _busy channels (N _busy ).

That is, the first channel limit threshold N _{1st_th} is adjusted according to the following equation.

However, if the handoff call allocation channel number N _handoff is greater than the normal call allocation channel number N _normal according to the comparison result, the first channel limit threshold N _{1st_th} is not adjusted.

As described above, the channel allocation method of the mobile communication system according to the present invention has the following effects.

First, even when a large amount of calls are required, it is possible to provide a certain quality call service to the user by reducing the frequency of hard handoffs by ensuring priority channel allocation for handoff calls.

Second, by setting the first channel limit threshold, it is possible to provide a stable communication service by preventing a certain amount of calls from being concentrated on a specific CDMA channel.

Third, it is possible to prevent the phenomenon that the normal call is unnecessarily limited by adjusting the first channel limit threshold according to the ratio of the normal call and the handoff call.

Claims (6)

Setting a first channel limit threshold for the first set of channels; A second step in which a call is required to the first channel set; A third step of calculating the number of first normal call limited channels of the first channel set by using the set first channel limited threshold value; A fourth step of calculating a number of first channels used in the first channel set; A fifth step of comparing the calculated size of the first normal call limited channel number with the first used channel number, And a sixth step of determining whether to allocate a channel to the requested call according to the comparison result. The method of claim 1, wherein the first step, Comparing the size of the normal call allocation channel number N _normal of the first channel set with the handoff call allocation channel number N _handoff ; When the number of normal call allocation channels N _normal is greater than the number of _handoff call allocation channels N _handoff , the set first channel limit threshold is set to a preset threshold adjustment parameter N _delta and a channel in use. and multiplying by the ratio occupied by the normal call among the _{busy calls} . The method of claim 1, wherein in the third step, And the first normal call limited channel number is calculated as a product of the set first channel limited threshold value and the total number of available channels of the first channel set. The method of claim 1, wherein in the fourth step, And the first number of used channels is calculated as the sum of the number of normal call allocation channels and the number of handoff call allocation channels in the first channel set. The method of claim 1, wherein in the sixth step, Allocating a channel for the requested call when the calculated first normal call limited channel number is greater than the first used channel number, Mobile communication characterized by not assigning a channel when the requested call is a normal call when the calculated first used channel number is larger than the first normal call restriction channel, and assigning a channel when the requested call is a handoff call. How the system allocates channels. The method of claim 1, wherein when the calculated first number of used channels is greater than the calculated normal call limit channel number and the requested call is a normal call, Setting a second channel limit threshold for the second channel set; An eighth step of calculating the number of second normal call limited channels of the second channel set by using the set second channel limited threshold value; A ninth step of calculating a number of second used channels of the second channel set; A tenth step of comparing the calculated size of the second normal call limited channel number with the second used channel number; And an eleventh step of determining whether to allocate a channel to the requested call according to the comparison result.