KR20080058023A - Method of performing handover between cells in cdma networks implemented by different protocols - Google Patents

Abstract

A method for performing handover between cells in CDMA networks supporting different protocols is provided to allow a user to feel that he receives a service continuously by minimizing a service interruption. An MS(Mobile Station) located in a cell of an EV-DO(Evolution-Data Only) network receives parameters regarding handoff via a control channel(202). The MS checks whether cells in which every base station of an active set is located, including its currently located cell, correspond to boundary cells of the EV-DO network(204). If the size of a current pilot signal is smaller than a threshold value, a handdown timer is initiated and a certain time lapses(208). It is checked whether all of the base stations of the active set of the MS are still in the boundary cells of the EV-DO network and the pilot signal from a base station currently providing a service is smaller than the threshold value(210). If so, the MS performs handdown to receive a pilot signal with respect to a frequency allocated to a base station of a 1X network and measures its size(212). It is checked whether the measured size of the pilot signal is larger than the threshold value T-ADD(214). If the size of the pilot signal is larger than the threshold value, the connection with the EV-DO network is terminated and a connection to the 1X network is initiated to form a 1X data call(216).

Description

Handover method between CDMA network cells supporting heterogeneous protocols {METHOD OF PERFORMING HANDOVER BETWEEN CELLS IN CDMA NETWORKS IMPLEMENTED BY DIFFERENT PROTOCOLS}

1 is a diagram illustrating a plurality of geographically partitioned cells and a mobile station moving between these cells, according to an embodiment of the present invention;

2 is a flowchart illustrating a handoff procedure when moving from a cell of an EV-DO network to a cell of a 1X network while the hybrid mobile station is in a call.

3 is a flow chart illustrating a handoff procedure when moving from an EV-DO network to a 1X network while the hybrid mobile station is idle (IDLE).

<Description of the reference numerals for the main parts of the drawings>

102a-102d: CDMA 1X EV-DO Network Cell

104a-104c: CDMA 2000 1X Network Cells

106a-106d: CDMA 1X EV-DO Network Base Station

108a-108c: CDMA 2000 1X Network Base Station

110: mobile station

The present invention relates to a handoff method for a mobile station that moves between adjacent cells. More specifically, the present invention relates to a handoff method in which a mobile station rapidly performs a handoff to minimize service disconnection when a cell moves between a cell of a CDMA 1X EV-DO network and a cell of a CDMA 2000 1X network. A method of performing off.

With the rapid development of mobile communication technology, CDMA 2000 1X system (hereinafter referred to as 1X system), which corresponds to 2.5 generation mobile communication technology, has the same frequency bandwidth of 1.25 MHz to support higher data transmission rate. Another third-generation CDMA 1x EV-DO system that evolved into a different wireless protocol than the CDMA 2000 1X.

In other words, only the frequency bandwidth is the same, there is no compatibility between the two radio protocols.

CDMA 1X EV-DO generally refers to CDMA 2000 1X EV-DO Revision 0. To be precise, it refers to IS-856 Revision 0 protocol, which is developed based on IP technology and optimized for high-speed packet data service. The peak data rate is 2.4Mbps, much faster than the 144Kbps of the 1X system, and the average data rate is known as a broadband wireless technology ranging from 300 to 600kbps. In addition, the CDMA 1X EV-DO Revision 0 has evolved back to CDMA 1X EV-DO Revision A, which has a higher data transfer rate than the previous revision 0, which is 3.1 Mbps for the downlink and the reverse link. (uplink) provides a peak speed of up to 1.8Mbps and provides services such as video and video telephony as well as voice and data.

CDMA 1X EV-DO systems (hereinafter referred to as EV-DO systems) that provide such high-speed, high-capacity packet data services are gradually expanding their service ranges. In extending the service range of the EV-DO system, the service provider cannot install a nationwide network of EV-DO methods at a time, and thus expands the range of new networks gradually as a cluster is formed. Therefore, the hybrid mobile station supporting both EV-DO and 1X communication can move from the environment receiving the EV-DO network to the environment receiving the 1X network. It is necessary to switch from the EV-DO method to the 1X method.

On the other hand, in the CDMA environment, each base station periodically transmits a pilot signal, and when the mobile station receives such a pilot signal, it acquires synchronization with the base station system. In particular, when there are a plurality of pilot signals that can be received, the mobile station acquires synchronization with a base station that provided the largest pilot signal among the pilot signals, accesses the base station, and receives a communication service therefrom. In addition, when the signal transmission state between the mobile station and the serving base station changes as the mobile station moves between cells, the control station performs a handoff to service the mobile station to another base station capable of providing appropriate service.

Handoff refers to changing a call path to a moved cell in order to continue to maintain a call when the mobile station moves out of the area of the serving base station to another base station. These handoffs include hard handoff, which involves disconnecting an existing line first and then connecting to a new base station, and soft handoff that supports a new call path with a new base station while maintaining the existing call path. Off is known as a handoff method that connects a call through an intermediate process of simultaneously acquiring a plurality of base station signals. In addition, hard handoff is a method of switching a service to a new base station by immediately disconnecting an existing circuit, and, alternatively, a handdown process of allowing an existing service base station to start service based on a frequency and an operation protocol by a new base station. There is a method of switching the base station by coarse soft handoff between cells.

Typically, hybrid mobile stations that support both EV-DO and 1X communication will not be able to detect EV-DO pilot signals as they move out of the service area of the EV-DO network. Terminates the connection to and then attempts to acquire synchronization for reconnection to the EV-DO system, and only after that fails attempts to acquire synchronization for the 1X system. Then, after successfully synchronizing with the 1X system, the data call through the 1X system is continued. As described above, according to the conventional hard handoff method, when the mobile station moves the boundary area between the EV-DO system and the 1X system, the service disconnection time becomes long, and the user is greatly inconvenienced.

Therefore, there is a need for a method of performing a fast handdown and handoff so that the mobile station can provide continuous service in the boundary area when the mobile station moves between the cells of the EV-DO network and the cells of the 1X network.

Accordingly, it is an object of the present invention to provide a method for performing handdown and handoff quickly so that service interruption is minimized when a mobile station moves between an EV-DO network and a 1X network supporting different radio protocols.

According to one aspect of the present invention, the present invention provides a handoff method performed for a mobile station supporting both first and second communication schemes in a mobile communication environment in which a plurality of cells exist. The cells are each serviced by one base station, and each of the base stations supports either a first communication scheme or a second communication scheme. According to the method of the present invention, the mobile station located in the cell served by the base station of the first communication scheme identifies the base station included in the active set, and checks whether the cell in which the identified base station is located is a boundary cell. The border cell refers to a cell adjacent to a cell serviced by the base station of the second communication method. Then in response to such confirmation, handoff is performed to the base station of the second communication scheme.

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

1 exemplarily illustrates a plurality of geographically divided cells and a mobile station moving between these cells according to an embodiment of the present invention. In this figure, a total of seven cells are shown and cells belonging to the same type of network are shown as being adjacent to each other, but a larger number of cells may exist and cells belonging to different types of networks may be randomly mixed. You need to know that.

The cells 102a-102d belong to a service network established by the EV-DO system (hereinafter referred to as EV-DO network) and the cells 104a-104c belong to a service network constructed by the CDMA 2000 1X system (hereinafter referred to as 1X network). Assume that you belong. The mobile station 110 is a hybrid scheme capable of supporting both the EV-DO system and the 1X system. The mobile station 110 is located in the cell 102d and is moving toward the cell 104b. It is also assumed that cells 102-102d are each serviced by one base station 106a-106d, and cells 104a-104c are each serviced by one base station 108a-108c.

When the mobile station 110 moves from the cell 102d of the EV-DO network to the cell 104b of the 1X network, a handoff for switching of the base station is required. The mobile station 110 is currently receiving a communication service from the base station of the EV-DO network in the cell 102d, but gradually moves to the cell 104b to perform a handoff to the base station of the 1X network at an appropriate time. According to the present invention, the mobile station 110 moves between cells 102d and 104b of heterogeneous networks that differ in their assigned frequency (FA) and communication protocol, so that the same by the base station 106d for switching between FA and communication protocol first. After performing a handdown process in the cell 102d, an inter-cell soft handoff is performed to the base station 108b, which will be described in more detail with reference to FIGS. 2 and 3 below.

In this regard, first looking further at the soft handoff process, the mobile station searches for currently receiveable pilot channels to detect a currently accessible CDMA channel. In accordance with such a search, the mobile station selects a pilot set of pilot channels, each of which is an active set of base stations with which the mobile station is currently calling, and a base station with which pilot channels of sufficient strength are detected, which are not currently being called. (Candidate Set), a neighbor set of neighbor base stations that do not belong to the current active or candidate set but are likely candidates for future handoff, and a remaining set of all remaining base stations in the system. Manage by dividing. Therefore, the active set of the mobile station in the call should always include at least one base station, and the large number of base stations belonging to the active set means that many base stations have been assigned a forward traffic channel for the mobile station.

To determine the active set, the mobile station periodically reports its location information and the information obtained by estimating the surrounding wireless link to the control station. The control station obtains a plurality of pilot information (i.e., information about the pilot channel received by the mobile station from the surrounding base stations) from the received information, and the mobile station depends on a predetermined criterion, for example, whether the pilot signal is sufficient in size. Determine the base stations that may be included in the active set of ie the communication traffic channel can be established with the current mobile station.

2 is a flowchart illustrating a handoff procedure when moving from a cell of an EV-DO network to a cell of a 1X network while the hybrid mobile station is in a call.

First, a mobile station located in a cell of the EV-DO network receives parameters related to handoff via a control channel (202). Such parameters include information about each base station that may be included in the mobile station's current active set, candidate set, neighbor set and remaining set. In particular, such information may include a flag indicating whether each base station is located at a boundary cell of the EV-DO network, that is, whether the base station services a cell of the EV-DO network located at the boundary between the EV-DO network and the 1X network. . According to an embodiment of the present invention, information on whether each of these base stations is located in a boundary cell may be conveyed by an overhead message transmitted by the base station to the mobile station through a control channel, for example, a NeighborList message.

The mobile station then determines whether the cells in which all base stations in the active set, including the cell at the current location, are located correspond to the boundary cells of the EV-DO network (204). If all of the base stations in the active set are located in the border cell, then the mobile station will be in a state of high probability of leaving the current EV-DO network. If all of the base stations in the active set are located in the boundary cell of the EV-DO network as a result of the determination, it is determined whether the pilot signal of the cell of the current position is smaller than a predetermined threshold (206). According to one embodiment of the invention, such a determination may be made by Ec / lo and PilotAdd + PilotCompare, where lo is the total signal magnitude received at the mobile station and Ec is the pilot signal magnitude received from the base station of the cell at the current location. to be. PilotAdd is a threshold of pilot signal magnitude to be a base station providing communication service to a mobile station in an EV-DO network, and PilorCompare is a value determined to prevent an excessively frequent handoff.

In step 206, if it is determined that the magnitude of the current pilot signal is less than the predetermined threshold, the handdown timer is started and a predetermined time (e.g., 3 seconds) elapses (208). After a predetermined time has elapsed, the pilot signal (e.g., Ec / lo) from the base station, where all of the base stations in the active set of the mobile station are still located in the boundary cell of the EV-DO network and is currently providing a service, may receive the threshold (e.g., PilotAdd). (PilotCompare) is less than (210). If so, the mobile station performs a handdown to receive a pilot signal for a frequency (FA) assigned to the base station of the 1X network and measure its size (212). Then, the mobile station compares the magnitude of the pilot signal received by the frequency FA assigned to the base station of the 1X network with the threshold T-ADD. The T-ADD determines whether it is greater than or equal to a threshold of pilot signal magnitudes to become a base station providing communication service to a mobile station in a 1X network (214). If the size of the pilot signal is determined to be greater than or equal to the threshold as a result of the determination, the connection with the EV-DO network is terminated, and then the connection to the 1X network is initiated to form a 1X data call (216). As a result, handoff is performed from a boundary cell of the EV-DO network to a cell of the 1X network.

3 is a flowchart illustrating a handoff procedure when a hybrid mobile station moves from an EV-DO network to an 1X network in an idle state (IDLE).

First, an idle mobile station located in a boundary cell of an EV-DO network receives a message indicating that a cell providing a current service is a cell of an EV-DO network boundary region through a control channel (302). According to an embodiment of the present invention, such a message may be made through an overhead message for transferring information on a sector configuration, for example, a predetermined field (PDCHSupportedInclude or FPDCHSupported Field) of a SectorParameter message according to the IS-856 standard. However, the present invention is not so limited, and the mobile station should be aware that any cell in any message over the control channel may be informed that the cell currently being served is a cell in the EV-DO network boundary region. do.

The mobile station then initiates a handdown to measure the magnitude of the pilot signal from the base station of the 1X network along with the magnitude of the pilot signal from the base station of the EV-DO network (304). The mobile station then determines 306 if the magnitude of the pilot signal from the 1X network is greater than or equal to a predetermined threshold compared to the pilot signal magnitude from the EV-DO network, and returns to step 304 otherwise. In step 306, if it is determined that the magnitude of the pilot signal from the 1X network is greater than or equal to the threshold compared to the magnitude of the pilot signal from the EV-DO network, the mobile station terminates the EV-DO session and then returns to the base station of the 1X network. A connection is established and service is provided from the corresponding base station of the 1X network (308). As a result, handoff is performed from a boundary cell of the EV-DO network to a cell of the 1X network.

In the present specification, the hybrid mobile station has been described with reference to the embodiment related to handoff when moving from the EV-DO network toward the 1X network. However, the present invention is similarly applied to the case where the mobile station moves from the 1X network to the EV-DO network. It should be understood that this may apply.

As described above, embodiments of the present invention for understanding the present invention have been described, but as will be appreciated by those skilled in the art, the present invention is not limited to the examples described herein but is not limited to the scope of the present invention. It can be variously modified, reconfigured and replaced. Therefore, it is intended that the present invention cover all modifications and variations that fall within the true spirit and scope of the present invention.

According to the present invention, a mobile station moving between an EV-DO network environment and a 1X network environment recognizes in advance that a cell at a current location corresponds to a boundary area and that handoff is likely to occur, so that service disconnection is minimized. Perform a handoff, thereby allowing the user to feel like receiving ongoing service.

Claims (10)

In a mobile communication environment in which a plurality of cells, the cells are each serviced by one base station, and the base stations support one of the first communication method and the second communication method, respectively, A handoff method performed for all supporting mobile stations, Identifying a base station included in an active set by a mobile station located in a cell serviced by the base station of the first communication scheme, Identifying whether the cell where the identified base station is located is a border cell, wherein the border cell refers to a cell adjacent to a cell served by the base station of the second communication scheme; and In response to the confirmation, performing a handoff to the base station of the second communication scheme; Handoff method comprising a. The method of claim 1, And the checking step further comprises the mobile station receiving, via a control channel, a message indicating whether the cell in which the identified base station is located is in a boundary cell. The method of claim 1, Performing the handoff step is performed when a cell in which the identified base station is located is a boundary cell and a pilot signal of the first communication scheme received at the mobile station remains below a threshold for a predetermined period. The method of claim 2, The message is a handoff method transmitted in a SectorParameter Message according to the IS-856 standard or a neighborlist message according to the IS-856 standard. The method of claim 4, wherein The message is transmitted using the FPDCHSupportedInclude or FPDCHSupported Field of the SectorParameter Message. The method of claim 4, wherein The message is included in a predetermined field in the SectorParameter Message or the Neighborlist Message and transmitted. The method of claim 1, The performing of the handoff may further include determining whether the pilot signal of the second communication scheme is greater than or equal to a threshold. The method of claim 1, The performing of the handoff may further include comparing a magnitude of the pilot signal of the first communication method and a pilot signal of the second communication method. The method of claim 1, The first communication method is a CDMA 1X EV-DO communication method, and the second communication method is a CDMA 2000 1X communication method. The method of claim 9, The CDMA 1X EV-DO communication method is a communication method supporting a protocol version of Revision A or higher, and the second communication method is a communication method supporting a protocol version of less than Revision C.

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