KR100337897B1 - Handoff method between frequency of mobile communication system - Google Patents

Abstract

The present invention relates to a method for inter-frequency handoff in a mobile communication system. The present invention relates to a condition determination step of determining whether a mobile station is a condition for handoff by checking a pilot strength, and when a condition for handoff occurs in the condition determination step. Transmitting the number of maximum frequencies that the control station receiving the pilot strength measurement message can serve in the target base station to the serving base station; and the serving base station transmitting in the step according to the call channel allocation request of the control station. Allocating the talk channel for inter-hard hard handoff to allocate the talk channel for hard handoff to the frequency with the least load among frequencies less than or equal to the maximum number of frequencies, and target the channel according to the call channel allocation request of the control station. For soft handoff, where the base station assigns a call channel for soft handoff A step of assigning a call channel, and a step of transmitting a handoff indication message by the control station transmitting a handoff indication message to the mobile station when the call channel allocation for the handoff is performed at the serving base station and the target base station after performing the step; According to the handoff indication message transmitted in the step of transmitting the handoff indication message, the mobile station performs a handoff between the base stations and performs a soft handoff with the target base station. .

Description

HANDOFF METHOD BETWEEN FREQUENCY OF MOBILE COMMUNICATION SYSTEM}

The present invention relates to a method for inter-frequency handoff in a mobile communication system. In particular, when a hard-to-frequency hard handoff request is made, a hard handoff and a soft handoff are not used repeatedly. The present invention relates to a method for inter-frequency handoff in a mobile communication system, which is performed to simultaneously increase the success rate of handoff.

One of the biggest features of the mobile communication system is to guarantee the mobility of the subscriber station, and the technology required to ensure the mobility includes a location registration technology and a handoff technology. It refers to a technology for switching a call path between a mobile station and a base station so that a call can be continuously maintained even when entering a service area of a base station or a sector away from a service area.

That is, soft handoff occurs when a talk channel having a frequency and frame offset currently allocated to a mobile station can be allocated in a service area of a neighboring base station or sector, and a frequency different from the frequency allocated to the mobile station occurs. Hard handoff occurs between frequencies, and when the frame offset is different, hard handoff occurs between frame offsets.

In the case of the inter-frequency hard handoff, the success rate is lower than that of the soft handoff because the mobile station must acquire the communication channel of the adjacent base station within 0.08 seconds.

1 is a block diagram of a general mobile communication system, which includes a mobile station 10, a serving base station 20-1, which is a base station to which the mobile station 10 is currently receiving service, and the mobile station ( 10) the hand of the mobile station 10 made between the target base station 20-2, which is a new base station to be provided with this service, and the serving base station 20-1 and the target base station 20-2. It consists of a control station 30 and an exchange station 40 that control the off procedure.

In this case, the serving base station 20-1 and the target base station 20-2 perform channel element (CE) 21-1 and 21-2 and BTS control processors 22-1 and 22-2. The control station 30 includes a transcoding selector bank (TSB) 31 and a call control processor (CCP) 32.

Referring to the frequency-to-frequency hard handoff method of the conventional mobile communication system as follows.

When the mobile station 10 moves from the serving base station 20-1 to the target base station 20-2, if the pilot strength of the target base station 20-2 is greater than the pilot signal detection threshold T_ADD, the serving base station 20-1 And a Pilot Strength Measurement Message or a Pilot Strength Report Message to the CCP 32 via the TSB 31 in the control station 30.

Subsequently, when the pilot strength measurement message or the pilot strength report message is analyzed by the CCP 32 of the control station 30, if a hard handoff occurs between frequencies, the same frequency as that provided by the target base station 20-2 is obtained. The frequency is detected at the frequency of the serving base station 20-1 and the serving base station 20-1 is requested to allocate a talk channel for hard handoff between frequencies.

Then, after the serving base station 20-1 assigns the frequency-to-frequency hard handoff communication channel to the detected frequency and reports the assignment result to the CCP 32 of the control station 30, the CCP 32 An inter-frequency hard handoff indication message is transmitted to the mobile station 10 via the serving base station 20-1.

Accordingly, the mobile station 10 performs the inter-frequency hard handoff at the serving base station 20-1, and then transmits the inter-frequency hard handoff completion message to the CCP 32 through the serving base station 20-1. do.

Subsequently, the CCP 32 of the control station 30 analyzes the pilot strength measurement message or the pilot strength report message transmitted from the mobile station 10 and softens the target base station 20-2 if it is a condition that a soft handoff occurs. Requires call channel allocation for handoff.

Subsequently, when the target base station 20-2 allocates the soft handoff communication channel to the frequency provided by the target base station 20-2 and reports the allocation result to the CCP 32 of the control station 30, the CCP At 32, the soft handoff indication message is sent to the mobile station 10 via the serving base station 20-1.

Accordingly, the mobile station 10 performs soft handoff between the serving base station 20-1 and the target base station 20-2 between the same frequencies, and then performs soft handoff through the target base station 20-2. Send a message to CCP 32.

As described above, the control station instructs the serving base station to perform the inter-frequency hard handoff to perform the inter-frequency hard handoff first to make the soft handoff condition between the serving base station and the target base station, and then to the target base station. Inter-frequency hard handoff was performed by instructing soft handoff to perform soft handoff.

However, in performing the hard-to-frequency hard handoff method as described above, in the related art, in order to sequentially perform the hard-to-frequency hard handoff and soft handoff, the handoff-related messages are repeatedly transmitted and received, which adversely affects the wireless environment. there was.

That is, since the mobile station repeatedly transmits the pilot strength measurement message or the pilot strength report message to the control station, the control station repeatedly transmits the handoff indication message to the mobile station through the base station, which not only adversely affects the wireless environment, The likelihood of message loss between the control station and the control station increases.

The present invention has been made to solve the above problems, and an object thereof is to minimize the use of handoff-related messages such as a pilot strength measurement message, a pilot strength report message, a handoff indication message, and the like when a hard handoff between mobile stations is requested. The present invention provides a method for inter-frequency handoff in a mobile communication system that can perform a hard handoff and a soft handoff at a frequency with the least load, thereby improving the wireless environment and increasing the success rate of the handoff.

1 is a block diagram of a general mobile communication system;

2 is a flowchart illustrating an inter-frequency handoff method of a mobile communication system according to the present invention;

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

10: mobile station 20-1: serving base station

20-2: target base station 21-1, 21-2: CE

22-1, 22-2: BCP 30: control station

31: TSB 32: CCP

40: exchange office

In the inter-frequency handoff method of the mobile communication system of the present invention to achieve the above object, when the mobile station moves from the serving base station to the target base station, the condition that the hard-to-frequency hard handoff occurs by checking the pilot strength received from the target base station In the condition determination step of determining whether or not, and when the hard handoff between frequencies occurs in the condition determination step, the control station receives a pilot strength measurement message transmitted from the mobile station, analyzes the shape of the target base station, and Analyzing the pilot strength measurement message for finding the maximum number of frequencies that can be serviced and transmitting the same to the serving base station, and transmitting the number of frequencies to the serving base station; Analysis and frequency count transmission Allocate a channel with the least load among the frequencies less than or equal to the maximum number of frequencies transmitted from the system, allocate a talk channel for hard handoff between frequencies, and then transfer the allocation information to the control station. After performing the allocating step and allocating the call channel for hard handoff between the frequencies, the target base station allocates the call channel for soft handoff according to the soft handoff call channel allocation request of the control station, and then assigns the allocation information to the control station. After performing the soft handoff call channel assignment step and the soft handoff call channel assignment step, the control station handoffs to the mobile station when the handoff call channel assignments at the serving base station and the target base station are performed. Sending a handoff indication message to send an indication message and the handoff indication mesh; According to the handoff indication message transmitted in the transmission step the mobile station is to perform the inter-frequency hard handoff from the serving base station, and at the same time characterized by comprising the steps of: performing the handoff to the target base station and performing soft hand-off.

Hereinafter, an inter-frequency handoff method of a mobile communication system according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a flowchart illustrating an inter-frequency handoff method of a mobile communication system according to the present invention.

First, in the pilot strength reception and condition determination step (S1), when the mobile station 10 moves from the serving base station 20-1 to the target base station 20-2, the pilot strength is received from the target base station 20-2. It is determined whether a hard handoff between frequencies is a condition to occur.

That is, it is determined whether the received pilot signal is larger than the pilot signal detection threshold T_ADD.

If the pilot signal received from the target base station 20-2 is greater than the pilot signal detection threshold value T_ADD as a result of the determination in step S1, the mobile station 10 may serve the pilot strength measurement message transmission step S2. The pilot strength measurement message or the pilot strength report message is transmitted to the CCP 32 of the control station 30 via the TSB 31 in the base station 20-1 and the control station 30.

That is, the mobile station 10 transmits a pilot strength measurement message to the control station 30 when a condition that a hard handoff occurs between frequencies by satisfying the following conditions.

T_ADD <Pilot strength of target base station 20-2

T_DROP (pilot signal rejection threshold)> pilot strength of serving base station 20-1

The pilot strength of the serving base station 20-1 < the pilot strength of the target base station 20-2 + T_COMP (Active set versus candidate set comparison threshold) * 0.5 dB

Subsequently, after the pilot strength measurement message transmission step S2, the pilot strength measurement message analysis and frequency number transmission step S3 are performed, and the control station 30 transmits the pilot strength transmitted from the mobile station 10 in step S2. After analyzing the measurement message to analyze the shape of the target base station 20-2, and transmits the maximum number of frequencies that can be serviced by the target base station 20-2 to the serving base station 20-1.

That is, the CCP 32 of the control station 30 analyzes the " PILOT_PN_PHASE " and " PILOT_STRENGTH " fields of the pilot strength measurement message transmitted from the mobile station 10 in step S2 to determine that it is the target base station 20-2. It recognizes whether the target base station 20-2 is a beacon base station that artificially outputs only a pilot signal by reading PLD (Program Loading Data) of the target base station 20-2.

If the target base station 20-2 is not a beacon base station, a soft handoff procedure is performed. If the target base station 20-2 is a beacon base station, the serving base station searches for the maximum number of frequencies that can be serviced by the target base station 20-2. 20-1).

Subsequently, after analyzing the pilot strength measurement message and transmitting the frequency number (S3), the process proceeds to the call channel allocation step (S4) for hard handoff between frequencies, and from the control station 20 to the serving base station 20-1, Requesting allocation of talk channel for hard handoff between frequencies at the frequency with the least load among frequencies less than or equal to the maximum number of frequencies transmitted in S3), and the serving base station 20-1 transmits the maximum in step S3. Among the frequencies less than or equal to the number of frequencies, the frequency with the least load is selected to allocate a talk channel for hard handoff between frequencies, and the allocation information is transmitted to the control station 30.

Subsequently, after the step of assigning the talk channel for hard handoff (S4), the process proceeds to the step of assigning the talk channel for soft handoff (S5), and the serving base station 20-1 of the step S4 is performed by the control station 20. After receiving the inter-frequency hard handoff call channel assignment information from the target base station 20-2, the target base station 20-2 requests a soft handoff call channel assignment so that the soft handoff can occur. After allocating a handoff call channel, the allocation information is transmitted to the control station 30.

After the soft channel call channel allocation step (S5), the handoff instruction message transmission step (S6) is performed, and the control station 30 performs handoff at the serving base station 20-1 and the target base station 20-2. If the call channel assignment is good, the mobile station 10 transmits a handoff indication message.

After the handoff instruction message transmission step S6, the mobile station 10 receives the handoff instruction message of step S6 by proceeding to the handoff execution step S7, and then the serving base station 20-1 receives the inter-frequency hard signal. Handoff is performed and soft handoff is performed with the target base station 20-2 at the same time.

As described above, the present invention performs hard handoff between frequencies at the serving base station, and simultaneously performs soft handoff with the target base station to prevent duplication of the handoff indication message, and to perform handoff at the frequency with the least load. The success rate of the off can be increased.

As described above, the present invention minimizes the use of handoff-related messages when the mobile station requests hard handoff between frequencies, and simultaneously improves the wireless environment by simultaneously performing hard handoff and soft handoff at a frequency with the least load. It is possible to improve the success rate of the handoff, thereby providing a stable and continuous call service to the subscribers of the mobile station.

Claims (1)

When the mobile station moves from the serving base station to the target base station, checking the pilot strength received from the target base station to determine whether the inter-frequency hard handoff is a condition to occur; In the condition determination step, when a hard handoff occurs between frequencies, the control station receives a pilot strength measurement message transmitted from the mobile station, analyzes the shape of the target base station, and determines the maximum number of frequencies that the target base station can service. Analyzing and transmitting a pilot strength measurement message to find and transmit to a serving base station; The serving base station selects a frequency with the least load among frequencies less than or equal to the maximum number of frequencies transmitted in the pilot strength measurement message analysis and frequency number transmission step according to the control channel allocation request for frequency hard handoff. Assigning a talk channel for hard handoff between frequencies and assigning a talk channel for hard handoff between frequencies for transmitting allocation information to the control station; After performing the step of assigning the call channel for hard handoff between the frequencies, the soft base station transmits the allocation information to the control station after the target base station allocates the call channel for soft handoff according to the soft channel call request for soft handoff. Assigning a call channel for off; After the soft handoff call channel assignment step, when a handoff call channel assignment is performed at the serving base station and the target base station, the control station transmits a handoff indication message to the mobile station; , According to the handoff instruction message transmitted in the step of transmitting the handoff instruction message, the mobile station performs a hard handoff between frequencies at the serving base station, and at the same time comprises a handoff performing step of performing a soft handoff with the target base station A method for handoff between frequencies in a mobile communication system.