KR100594013B1 - Service quality-based handoff method - Google Patents

Abstract

In the handover method of the present invention, the terminal determines the handover to a specific base station based on the strength of the pilot signal received from the base stations and the quality of service that each base station can provide, and performs the handover to the base station. In the handover method of the present invention, the handover target base station is determined in consideration of the traffic load of each base station, thereby preventing traffic from concentrating on a specific cell and ensuring the best quality of service at all times.

Handover, Handover, Traffic Balancing, Quality of Service

Description

Handover Method Considering Quality of Service {SERVICE QUALITY-BASED HANDOFF METHOD}             

1 is a message flow diagram illustrating a handover procedure being considered in a next generation packet based wireless communication system;

2 is a message flow diagram illustrating a handover method according to a preferred embodiment of the present invention;

3 is a flowchart illustrating a handover method according to a preferred embodiment of the present invention;

FIG. 4 is a flowchart for explaining a quality of service handover procedure of FIG. 3. FIG.

5 is a flowchart illustrating a handover procedure based on the received signal strength of FIG. 3; And

FIG. 6 is a diagram illustrating a MAC state used as a reference for determining a traffic amount in a handover method according to an exemplary embodiment of the present invention.

7A is a schematic diagram showing a cellular environment to which a handover method according to a second embodiment of the present invention is applied;

7B is a graph for explaining a handover start point determination process when a UE moves from a cool spot to a hot spot in the handover method according to the second embodiment of the present invention;

FIG. 7C is a graph for explaining a handover start point determination process when a UE moves from a hotspot to a coolspot in the handover method according to the second embodiment of the present invention.

The present invention relates to a wireless communication system, and more particularly, to a handover method considering the quality of service in a wireless communication system.

The next generation of wireless communication, which is currently being standardized, aims to provide high-speed data services based on packet switching. In this packet switching scheme, unlike each user terminal assigned a dedicated resource in the circuit switching scheme, all users share resources, thereby enabling efficient use of limited resources. In other words, in a packet-switched communication system, multiple users can efficiently use resources by allocating resources to only those users when packets to be transmitted through packet scheduling do not allocate specific resources to specific users.

However, when the packet switching scheme is applied to the wireless communication network, the number of times that each terminal receives a service depends on the number of users present in the cell. In other words, if the number of users in the cell is small and the traffic load to be handled by the base station is small, the number of times that the terminal receives service increases, and as the number of users increases, the number of service receives relatively decreases.

Therefore, in the next generation wireless communication system based on the packet switched scheme, the quality of service that can be provided to the terminal varies according to the system capacity of the base station and the traffic load to be processed.

On the other hand, in a cellular communication system, a handover is performed when a mobile station moves from a base station service area (cell) currently being served to a service area of another neighboring base station.

The handover algorithm currently applied in the mobile communication system is a base station where the signal is sufficiently strong before the signal becomes weak enough not to be communicated mainly based on the received signal strength (RSS) to prevent the communication from being disconnected. It is designed to find and perform handovers. However, while the conventional handover algorithm can only support service at a stronger signal base station, the higher signal strength does not guarantee good service quality.

In other words, in the circuit-switched communication system, since the dedicated resources are allocated and used, the signal strength itself can be a measure of the quality of the allocated resources. Cannot be measured. Accordingly, a packet-based wireless communication system requires a handover method capable of guaranteeing the best service quality in consideration of not only the signal strength but also the service rate that the terminal can receive.

The present invention was devised to solve the above problems, and an object of the present invention is to provide a handover method in which a terminal can be guaranteed the best quality of service in a packet-based wireless communication system.

Still another object of the present invention is to provide a handover method capable of preventing traffic from being concentrated in a specific cell by determining a base station for handover in consideration of the traffic load of each base station.

Another object of the present invention is to determine the handover in consideration of the quality of service that can be provided by neighboring base stations even when the strength of the current signal from the base station is good, the handover that can always provide the best quality of service in a given environment To provide a way.

Another object of the present invention is to provide a handover method that can prevent traffic concentration on a specific cell by adjusting a handover start point in consideration of the traffic amount of base stations associated with handover in a handoff process based on received signal strength. To provide.

It is still another object of the present invention to provide a handover method that can increase the overall system capacity as well as prevent performance degradation due to overload of a specific base station by distributing traffic to neighboring cells during handover.

태인 단말의 수이다. 상기 온 상 태는 순방향과 역방향 트래픽 채널을 모두 가지고 있는 상태를 그리고 상기 홀드 상태는 순방향 채널과 얇은 역방향 채널을 가지고 있는 상태를 의미한다. 상기 핸드오버 시작점은 현재기지국의 트래픽 상태가 핸드오버 할 기지국보다 좋지 않은 경우 히스테리시스 발생 시점이 되고 핸드오버 할 기지국의 트래픽 상태가 현재기지국보다 좋지 않은 경우 히스테리상기 현재 기지국으로부터 수신되는 신호의 세기가 상기 임계값 보다 크지 않으면 단말은 수신신호 세기 기반의 핸드오버 절차를 수행한다. 상기 수신신호 세기 기반의 핸드오버 절차에서 단말은 인접 기지국 수신신호의 세기가 상기 임계값보다 작은지를 판단하고, 상기 인접 기지국 수신신호의 세기가 상기 임계값보다 작으면 인접 기지국 수신신호의 세기가 현재 기지국 수신신호의 세기보다 큰지를 판단하고, 상기 인접 기지국 수신신호의 세기가 현재 기지국 수신신호의 세기보다 크면 인접기지국으로의 핸드오버를 수행한다. 상기 인접 기지국 수신신호의 세기가 임계 수신신호의 세기보다 작지 않으면 현재 기지국과의 연결을 유지하고, 역시 상기 인접 기지국 수신신호의 세기가 현재 기지국 수신신호의 세기보다 크지 않으면 현재 기지국과의 연결을 유지한다. In the handover method according to the present invention in order to achieve the above object, the terminal determines the handover to a specific base station based on the strength of the pilot signal received from the base stations and the quality of service that each base station can provide, Handover to the base station is performed. In the handover decision process, the terminal compares the strength of the pilot signal received from the base station currently receiving the service with the strength of the pilot signal received from neighboring base stations, and the strength of the signal received from the base station is greater than a predetermined threshold. If it is determined that the size is large, and the strength of the signal currently received from the base station is greater than a predetermined threshold, the quality of service based handover procedure is performed. In the quality of service based handover procedure, the UE measures the service quality of the current base station and the neighboring base station, determines whether the service quality value of the neighboring base station is greater than the service quality value of the current base station, and the service quality of the neighboring base station is the current base station. If greater than the quality of service of the handover to the neighboring base station. The quality of service is measured using the traffic state information of the base station provided from each base station. The traffic state information is received through the pilot signal or via a separate downlink broadcast channel (DLBCH). The traffic state information is the number of UEs that are allocated both forward and reverse channels by the base station. The traffic state information of the terminal in which the medium access layer (MAC) state is ON or HOLD state in the service area of the base station. It is a number. The on state is a state having both a forward and a reverse traffic channel, and the hold state is a state having a forward channel and a thin reverse channel. The quality of service (SQ) is

This is the number of terminals. The on state means a state having both a forward and a reverse traffic channel, and the hold state means a state having a forward channel and a thin reverse channel. The handover start point is a hysteresis occurrence time when the traffic state of the current base station is worse than the base station to be handed over, and when the traffic state of the base station to be handed over is worse than the current base station, the strength of the signal received from the current base station is increased. If it is not larger than the threshold, the terminal performs a handover procedure based on the received signal strength. In the handover procedure based on the received signal strength, the terminal determines whether the strength of the neighbor base station received signal is less than the threshold value, and if the strength of the neighbor base station received signal is less than the threshold value, the strength of the neighbor base station received signal is present. It is determined whether the strength of the base station reception signal is greater than the strength of the base station reception signal, and if the strength of the neighbor base station reception signal is greater than the strength of the current base station reception signal, handover to the neighbor base station is performed. If the strength of the neighboring base station received signal is not less than the strength of the critical received signal maintains the connection with the current base station, and if the strength of the neighboring base station received signal is not greater than the strength of the current base station received signal maintains the connection with the current base station. do.

In another aspect of the present invention, the process of performing the handover based on the received signal strength includes determining a handover start point in consideration of the traffic load of the base station to be handed over with the current base station. The traffic load is measured by using traffic state information received from each base station, and the traffic state information is received through a pilot signal or a separate downlink broadcast channel (DLBCH). The traffic state information is the number of terminals allocated to both the forward and reverse channels by the base station, and the medium access layer (MAC) state is ON or HOLD state in the service area of the base station. The number of terminals. The on state means a state having both a forward and a reverse traffic channel, and the hold state means a state having a forward channel and a thin reverse channel. The handover start point is a hysteresis occurrence time when the traffic state of the current base station is worse than the base station to be handed over, and a signal received from the current base station after the hysteresis occurs when the traffic state of the base station to be handed over is worse than the current base station. It is the time to reach.

Hereinafter, a handover method according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

1 is a message flow diagram illustrating a handover procedure considered in a next generation packet based wireless communication system.

As shown in FIG. 1, the terminal (MH) monitors the signal strength and signal-to-noise ratio of a signal from a base station to which it is currently connected, and when these parameters become weak, it is determined that a handover is necessary (S101). In case a new base station (hereinafter referred to as "NBS") can be predicted, the terminal tunnel initialization message (Host Tunnel INitiation) is referred to as a base station (Old Base Station, referred to as "OBS") to which the terminal is currently connected. "H-TIN" is transmitted (S102).

When receiving the H-TIN message, the base station (OBS) transmits a tunnel initialization message (TIN) to the candidate station (NBS) to which the terminal (MH) will handover (S103), and as a result, the base station (OBS) currently connected. And a tunnel is formed between the handover candidate station NBS (S104). After the tunnel is formed, the base station (NBS) receiving the tunnel initialization message (TIN) determines whether it can accept the handover and is ready for handover to the terminal (MH) if it can accept the handover. The UE transmits a handover hint message (Handoff Hint, hereinafter referred to as “HH”) in step S105.The UE having received the handover hint message determines a base station for handover (S106) and finishes a forward handover (S120). In case that forward handover is not performed, it is necessary to check whether the forward handover has occurred in the reverse handover process and compensate for the case where no forward handover has occurred.

If the UE does not know the new base station in advance, the reverse handover is performed. If the forward handover occurs, the handover process is performed to the end.

In the reverse handover, the terminal transmits a terminal handover request message (hereinafter, referred to as an "H-HR") to a base station to be handed over newly (S107). The base station (NBS) receiving the terminal handover request message (H-HR) checks the handover state (S108), if it is determined that the forward handover is performed, the reverse handover process is skipped and the forward handover is not performed. If not, transmits a handover request message (Handoff Request: HR) to the base station (OBS) to which the current terminal is connected (S109). The base station (OBS) receiving the handover request message transmits a handover initiation message (Handoff Initiation, hereinafter referred to as "HI") to the handover counter station (NBS) through a terminal authentication process (S110). A tunnel is formed between the OBS and the base station NBS to be handed over (S112). On the other hand, if the terminal authentication fails, the base station (NBS) to handover transmits a handover rejection message (hereinafter referred to as “HD”). The base station (NBS) receiving the handover rejection message sends a handover initialization message. By repeatedly transmitting the handover request message to the current base station (OBS) and receiving the handover initialization message, a tunnel is formed between the currently connected base station (OBS) and the handover target base station (NBS).

When the tunnel is formed, the handover target base station (NBS) transmits an update route message (Update route, hereinafter referred to as “UPD”) to the base station (OBS) to which the current terminal is connected to reset the data routing path (S113). A handover acknowledgment message (hereinafter referred to as "Hack") is transmitted to the terminal (MH) (S114) The base station (OBS) receiving the UPD message is referred to as an update acknowledgment (hereinafter referred to as "UPDA"). Is transmitted to the handover target base station (NBS) (S115) and the handover is completed (S120).

The present invention considers the traffic load of neighboring base stations to be handed over as well as the strength of the received signal strength (RS) from the base station during handover so that the terminal can be guaranteed the best quality of service.

2 is a message flow chart illustrating a handover method according to a preferred embodiment of the present invention.

As shown in Figure 2, the terminal first compares the strength of the pilot signal received from the current base station and neighboring base stations, and calculates the quality of service that each base station can provide using the traffic information of the base stations. The terminal detects the handover with reference to the strength of the pilot signal and the quality of service and determines the handover to a base station capable of providing the best quality of service.

3 is a flowchart illustrating a handover method according to a preferred embodiment of the present invention.

In FIG. 3, the UE first sets the threshold received signal strength (RSS _THRESHOLD ) (S301) and the pilot signal strength received from several base stations adjacent to the strength of the pilot signal (RSS _CUR ) received from the base station currently being serviced (S301). RSS _NEIGHBOR ) is measured (S302) (S303). Subsequently, the terminal compares the strength of the current base station received signal (RSS _CUR ) with the strength of the threshold received signal (RSS _CRES ) and the strength of the current base station received signal (RSS _CUR ) is the strength of the critical received signal (RSS _THRESHOLD). (S304), if the strength of the current base station received signal (RSS _CUR ) is greater than the threshold received signal strength (RSS _THRESHOLD ) and performs a handover procedure based on the quality of service (S400), otherwise If not, a handover procedure is performed based on the received signal strength (S500).

FIG. 4 is a flowchart for describing a handover procedure based on the quality of service of FIG. 3.

As shown in FIG. 4, in a service quality based handover procedure (S400), the UE measures a current service quality (SQ _CUR ) of a current base station and a neighbor service quality (SQ _NEIGHBOR ) of a neighboring base station. (S401, S402) It is determined whether the neighbor service quality (SQ _NEIGHBOR ) value of the neighboring base station is greater than the current service quality (SQ _CUR ) value of the current base station (S403). If the neighbor service quality (SQ _NEIGHBOR ) value is larger than the current service quality (SQ _CUR ) value of the current base station, the UE performs a handover to the neighbor base station (S404). The handover decision procedure S400 ends.

FIG. 5 is a flowchart illustrating a handover procedure based on the received signal strength of FIG. 3.

As shown in FIG. 5, in a handover procedure based on the received signal strength (S500), the terminal determines whether the strength of the neighbor base station received signal (RSS _NEIGHBOR ) is smaller than the threshold received signal strength (RSS _THRESHOLD ) (S501). If the strength of the neighbor base station received signal (RSS _NEIGHBOR ) is less than the threshold received signal strength (RSS _THRESHOLD ), the terminal determines whether the strength of the neighbor base station received signal (RSS _NEIGHBOR ) is greater than the strength of the current base station received signal (RSS _CUR ) In operation S502, if the strength of the neighboring base station received signal (RSS _NEIGHBOR ) is greater than the strength of the current base station received signal RSS _CUR , handover to the neighboring base station is performed (S503). The determination procedure S500 ends.

Meanwhile, in step S501, the strength of the neighbor base station received signal RS _NEIGHBOR is not smaller than the threshold received signal strength RS _THRESHOLD , or in step S502, the strength of the neighbor base station received signal RS _NEIGHBOR is the strength of the current base station received signal. If not greater than the RSS _CUR ), the handover procedure based on the received signal strength (S500) is terminated without performing the handover.

In the process of performing the quality-based handover procedure, the UE considers the traffic load in the cell during handover to ensure the best quality of service.

In the handover method according to the preferred embodiment of the present invention, the quality of service (SQ) from the base station is represented by the number of times the service is received from the base station, and how often the service can be received is the amount of traffic existing in the cell when using a shared channel. Inversely proportional to load Therefore, the equation for obtaining the service quality proposed by the present invention is expressed as Equation 1 below.

는 서비스 품질이 가질 수 있는 최상 값이다.Where L is the amount of traffic present in the cell

Is the best value a service quality can have.

The traffic amount (L) of each cell is measured by the number of UEs in which a media access layer (MAC) state is on or held.

In the handover method according to the present invention, the traffic amount (L) is the number of terminals whose Media Access Layer (MAC) status is On or Hold in a cell which is a service area of a base station.

FIG. 6 is a diagram illustrating a MAC state as a reference for determining a traffic amount in a handover method according to an exemplary embodiment of the present invention.

In FIG. 6, the ON state is a state of receiving data and the HOLD state is a state of waiting for traffic although not currently being transmitted. That is, where ON is a state having both downlink and uplink traffic channels, and HOLD is a state having both a forward channel and a thin uplink channel, and the UEs in the other states are It does not have a traffic channel. Therefore, in the handover method according to the preferred embodiment of the present invention, traffic amount determination is determined by the number of terminals whose MAC states are ON and HOLD states, and is obtained by Equation 2 below.

는 HOLD상태에 있는 사용자가 가지고 있는 채널 양을 얼마나 트래픽 양에 반영할 것인가를 나타내는 변수이다.Here, ON _current and HOLD _current represent the number of users who are currently in ON and HOLD states, respectively. And

Is a variable that indicates how much the channel amount of the user in HOLD state is reflected in the traffic amount.

Meanwhile, in the handover method according to another embodiment of the present invention, after a handover is determined to a specific base station in the received signal strength-based handover procedure (S500) of FIG. 5, the base station to handover with the current base station is a hotspot base station. And determining the base station to adjust the handover start point.

In the handover method according to the second embodiment of the present invention, the terminal adjusts the handover start point by determining whether the traffic load of the current base station and the base station to be handed over is a hot spot base station having a processing capacity or more or a cool spot base station having a processing capacity or less. . The determination of whether a hot spot base station or a cool spot base station is the traffic information received from the base stations, that is, the number of terminals whose MAC state is On or Hold in a cell which is a service area of the base station.

7A is a schematic diagram illustrating a cellular environment to which the handover method according to the second embodiment of the present invention is applied.

As shown in FIG. 7A, assuming that the terminal 10 moves from the cool spot cell 701 to the cool spot cell 703 again through the hot spot 702, based on the received signal strength according to the present invention. In the handover procedure, the parameters required for determining the handover start point vary depending on whether the terminal moves from the hotspot 702 to the coolspots 701 and 703 or from the coolspots 701 and 703 to the hotspot 702.

In other words, in the handover method according to the second embodiment of the present invention, when the terminal 10 moves from the hot spot 702 to the cool spot 703, the handover is performed quickly by starting the handover only by referring to hysteresis. On the contrary, when moving from the cool spot 701 to the hot spot 702, the handover proceeds slowly with reference to the hysteresis and the minimum threshold value Tmin of the received signal.

7B and 7C illustrate a handover start point determination process in the handover method according to the second embodiment of the present invention when the terminal 10 moves from a cool spot to a hot spot and moves from a hot spot to a cool spot, respectively. These are the graphs.

As shown in FIGS. 7A and 7B, when the terminal moves from the first cool spot 701 to the hot spot 702, the strength of the signal received from the base station 711 of the first cool spot 701 gradually decreases. The strength of the signal received from the base station 712 of the hot spot is gradually increased. In this case, the handover of the terminal 10 starts at the time when the signal received from the base station 711 of the first cool spot reaches the minimum threshold T_MIN after the hysteresis occurs on the graph.

Meanwhile, as shown in FIGS. 7A and 7C, when the terminal 10 moves from the hot spot 702 to the cool spot 703, the strength of the signal received from the base station 712 of the hot spot is gradually reduced and the cool spot is decreased. The strength of the signal received from the base station 713 at 703 becomes increasingly large. In this case, the terminal 10 starts handover at the time when hysteresis is detected from signals received from the two base stations 712 and 713.

As described above, in the handover method according to the second embodiment of the present invention, the handover time is delayed as much as possible for the terminal entering the hot spot in consideration of the traffic amount of the currently connected base station and the traffic amount of the base station to be handed over. For the outgoing UE, the traffic volume of the hotspot is distributed to neighboring cells by minimizing handover time.

As described above, in the handover method according to the present invention, since the handover target base station is determined in consideration of the traffic load of each base station, traffic concentration can be prevented in a specific cell.

In addition, in the handover method according to the present invention, even when the strength of the current signal from the base station is good, the terminal always provides the best quality of service in a given environment by determining the handover in consideration of the quality of service that can be provided by neighboring base stations. I can receive it.

In addition, the handover method according to the present invention can prevent the concentration of traffic in a specific cell by adjusting the handover time in consideration of the traffic amount of the base stations associated with the handover in the handoff process based on the received signal strength.

In addition, in the handover method according to the present invention, by distributing traffic to neighbor cells during handover, not only the performance degradation caused by the overload of a specific base station can be prevented, but the overall system capacity can be increased.

Claims (23)

In a mobile communication system of a packet-based cellular environment consisting of a plurality of terminals and base stations, Analyze the strength of the pilot signal received from the base station currently being served and the strength of the pilot signal received from the neighbor base station; Determine whether the strength of the signal currently received from the base station is greater than a predetermined threshold; If the strength of the signal received from the current base station is greater than a predetermined threshold, perform a quality of service based handover procedure; And performing a received signal strength based handover procedure if the strength of the signal received from the current base station is not greater than the threshold. delete The method of claim 1, wherein the quality of service handover procedure comprises: Measure a service quality of a current base station and a neighboring base station; Determine whether the quality of service value of the neighboring base station is greater than the quality of service value of the current base station; And performing a handover to the neighbor base station if the quality of service of the neighbor base station is greater than that of the current base station. 4. The handover method of claim 3, wherein the quality of service is measured from traffic state information of a base station provided from each base station. The handover method of claim 4, wherein the traffic state information is received through the pilot signal. 5. The handover method of claim 4, wherein the traffic state information is received through a DLBCH. 5. The handover method of claim 4, wherein the traffic state information is a number of terminals allocated to both forward and reverse channels by the corresponding base station. The handover method as claimed in claim 4, wherein the traffic state information is the number of terminals in which a medium access layer (MAC) state is in an ON state or a HOLD state in a service area of a corresponding base station. 9. The handover method of claim 8, wherein the on state is a state having both forward and reverse traffic channels. 9. The handover method of claim 8, wherein the hold state is a state having a forward channel and a thin reverse channel. 5. The method of claim 4, wherein the quality of service (SQ) is

Is calculated by Where L is the amount of traffic present in the service area of the base station,

Is the highest value of quality of service, and ON _current and HOLD _current are the number of users currently in ON and HOLD states,

The handover method is a variable indicating how much of the traffic amount of the channel amount of the user in the HOLD state to reflect. delete The method of claim 1, wherein the received signal strength based handover procedure is: Determining whether the strength of the neighbor base station received signal is less than the threshold; If the strength of the neighbor base station received signal is less than the threshold, determines whether the strength of the neighbor base station received signal is greater than the strength of the current base station received signal; And performing a handover to an adjacent base station if the strength of the neighbor base station received signal is greater than the strength of the current base station received signal. The handover method of claim 13, wherein the connection with the current base station is maintained if the strength of the neighbor base station received signal is not less than the strength of the threshold received signal. 14. The handover method of claim 13, wherein the connection with the current base station is maintained if the strength of the neighbor base station received signal is not greater than that of the current base station received signal. The handover method of claim 13, wherein the performing of the handover based on the received signal strength includes determining a handover start point based on a traffic load of a base station to be handed over with a current base station. 17. The handover method of claim 16, wherein the traffic load is measured using traffic state information received from each base station. 18. The handover method of claim 17, wherein the traffic state information is received through a pilot signal or a separate downlink broadcast channel (DLBCH). 19. The handover method of claim 18, wherein the traffic state information is a number of terminals allocated to both forward and reverse channels by a corresponding base station. 19. The handover method of claim 18, wherein the traffic state information is a number of terminals in which a medium access layer (MAC) state is in an ON state or a HOLD state in a service area of a corresponding base station. 21. The method of claim 20 wherein the on state is a state having both forward and reverse traffic channels. 21. The handover method of claim 20, wherein the hold state is a state having a forward channel and a thin reverse channel. 17. The method of claim 16, wherein the handover start point is a point of time when hysteresis occurs when the traffic state of the current base station is worse than that of the base station to be handed over. Handover method characterized in that it is the time when the received signal reaches the minimum threshold.

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