KR20090049899A - Method for synchronizing a mobile station to different network in gsm/gprs system - Google Patents

Abstract

A mobile station operating in a packet transfer mode or a dual transfer mode (DTM) in a global system for mobile communication (GSM) / general packet radio service (GPRS) system provides a method for acquiring synchronization with another network cell. The method includes receiving a request message about a measurement report for another network cell from a base station and transmitting a measurable report message regarding whether the measurement of the other network cell is possible in view of the assigned timeslot. . The mobile station can prevent handover delay to other network cells by ensuring measurement of received signal size for synchronization acquisition for other network cells.

Description

Method for synchronizing a mobile station to different network in GSM / GPRS system}

The present invention relates to wireless communications, and more particularly, to a method in which a mobile station acquires synchronization for interoperability with other networks in a GSM / GPRS system.

Global System for Mobile communication (GSM) is one of the wireless technologies that has been developed based on many subscribers since it was created as one of the means to unify the wireless means of communication in Europe. General Packet Radio Service (GPRS) is introduced to provide a packet-switched data service in a circuit-switched data service provided by GSM.

EDGE (Enhanced Data Rate for GSM Evolution) is a method of using 8-PSK (Phase Shift Keying) as a modulation method instead of Gaussian Minimum Shift Keying (GMSK), which is a modulation method used in GSM. The implementation of GPRS through EDGE is called Enhanced GPRS (EGPRS). Since EGPRS is based on the same structure as GPRS, it is an evolution of GPRS. EGPRS optimizes the transmission rate by changing the modulation method and the coding method according to the wireless environment. Nine MCS (modulation and coding schemes) have been proposed to improve packet data communication.

The GSM / GPRS system is a system based on time division multiple access (TDMA). Information items transmitted in a communication relationship between a base station subsystem (BSS) and a mobile station (MS) arrive at a base station or mobile station in accordance with a timeslot. In the following, downlink means communication from a base station to a mobile station, and uplink means communication from a mobile station to a base station.

Meanwhile, when a GSM / GPRS system based on TDMA is a second generation wireless communication system, a universal mobile telecommunications system (UMTS) based on wideband code division multiple access (WCDMA) may be referred to as a third generation wireless communication system. In addition, standardization is being progressed for a Long Term Evolution (LTE) wireless communication system based on Orthogonal Frequency Division Multiple Access (OFDMA).

With the emergence of various kinds of wireless communication systems, interoperability between existing GSM / GPRS systems and new networks such as UMTS is a problem. Even if a new network system is introduced, compatibility with an existing GSM / GPRS system is convenient for the user and the operator can recycle existing equipment.

3GPP TS 25.212 V7.1.0 (2006-06) Technical Specification Group Radio Access Network; Multiplexing and channel coding (FDD) (Release 7) As shown in Section 4.4, UMTS supports a compressed mode to measure neighbor cells for networks with different frequencies. Compression mode refers to stopping transmission and reception for a while to perform measurements between different frequencies.

In order to prepare for handover from GSM / GPRS to another network, the mobile station needs to acquire synchronization with neighboring cells. In idle mode, the mobile station does not have much difficulty in acquiring synchronization even if the neighboring cells belong to different networks. However, during the transmission / reception of data such as the packet transmission mode, constraints are imposed on the mobile station to acquire synchronization with other network cells whose frequency or radio access method is different from the GSM / GPRS system.

If the mobile station is unable to acquire synchronization with another network cell and the base station does not know this continuously, the handover may be delayed or the service may be suspended.

Therefore, there is a need for a method in which a mobile station can efficiently acquire synchronization with another network in a GSM / GPRS system.

An object of the present invention is to provide a method for notifying a base station when a mobile station cannot measure another network cell in a GSM / GPRS system.

In one aspect, a method for a mobile station operating in a packet transfer mode or a dual transfer mode (DTM) in a Global System for Mobile communication (GSM) / General Packet Radio Service (GPRS) system to obtain synchronization with another network cell to provide. The method includes receiving a request message about a measurement report for another network cell from a base station and transmitting a measurable report message regarding whether the measurement of the other network cell is possible in view of the assigned timeslot. .

The mobile station can prevent handover delay to other network cells by ensuring measurement of received signal size for synchronization acquisition for other network cells.

1 is a block diagram illustrating a wireless communication system. This represents a GSM (Global System for Mobile communication) / GPRS (General Packet Radio Service) based network. Hereinafter, the GPRS may include not only a general GPRS but also an enhanced GPRS (EGPRS). Wireless communication systems are widely deployed to provide various communication services such as voice, packet data, and the like.

Referring to FIG. 1, a mobile station (MS) 10 refers to communication equipment carried by a user and includes a user equipment (UE), a user terminal (UT), a subscriber station (SS), and a wireless device. Etc. may be called.

A base station subsystem (BSS) 20 includes a base transceiver station (BTS) 22 and a base station controller (BSC) 24. The BTS 22 communicates with the mobile station 10 in one cell area through an air interface, and performs functions such as synchronization with the mobile station 10. The BSC 24 interfaces at least one BTS 22 with the Mobile Switching Center (MSC) 30.

The MSC 30 connects a heterogeneous network such as a Public Switching Telephone Network (PSTN) 65 or a Public Land Mobile Network (PLMN) to the base station 20 through a Gateway MSC (GMSC) 60. The VLR (Visitor Location Register) 40 stores temporary user data and contains information about roaming of all mobile stations 10 in the MSC 30 service area. The Home Location Register (HLR) 50 contains information about all subscribers in the home network. The Serving GPRS Support Node (SGSN) 70 is responsible for mobility management of subscribers. The Gateway GPRS Support Node (GGSN) routes the packet to the current location of the mobile station 10 and interfaces with an external packet data network, such as a Public Data Network (PDN).

Hereinafter, the packet idle mode means that no temporary block flow (TBF) is provided, and the packet transfer mode means that a radio resource is allocated to a mobile station so that at least one TBF is provided. TBF refers to a physical connection used between two radio resource entities supporting unidirectional transmission of a Logical Link Control (LLC) Protocol Data Unit (PDU) on a packet data physical channel. At least one TBF is provided in a packet transfer mode. Temporary Flow Identity (TFI) is assigned to each TBF by the network and is unique among the TBFs that are concurrent in each direction.

In dedicated mode, the mobile station is provided with circuit-switched service, and in packet transmission mode, the mobile station is provided with packet-switched service. Dedicated mode provides GSM based service, and packet transfer mode provides GPRS or EGPRS based service. In dual transfer mode (DTM), the mobile station is in dedicated mode and packet transfer mode at the same time.

2 is an exemplary diagram illustrating a frame for synchronization acquisition of neighboring cells in a dedicated mode. This is the case where all neighboring cells are GSM / GPRS cells.

Referring to FIG. 2, the multi-frame in the dedicated mode includes 26 TDMA frames. One TDMA frame includes at least one timeslot. The 26 TDMA frames include 24 TDMA frames (T) containing bursts of traffic channels, 1 TDMA frame (S) and idle frame (I) reserved for the Slow Associated Control Channel (SACCH) control channel. .

The mobile station does not transmit and receive during the idle frame I, but performs peripheral cell measurement. Since the peripheral cell measurement is performed in the idle frame I, this idle frame I is also called a search frame.

Here, the thirteenth TDMA frame of the 26 TDMA frames is an idle frame I, but this is only an example. For example, the idle frame may be arranged in the 26th TDMA frame and the SACCH control channel may be arranged in the 13th TDMA frame.

In dedicated mode, the measurement period is 10 seconds. That is, the mobile station should attempt to acquire synchronization for neighboring cells as much as possible, as often as possible and at least once every 10 seconds of the measurement period. This synchronization acquisition process is performed during idle frames in a multiframe structure for 10 seconds.

3 is an exemplary diagram illustrating a frame for synchronization acquisition of neighboring cells in a packet transmission mode or a DTM.

Referring to FIG. 3, in a packet transfer mode or DTM, multiple frames include 52 TDMA frames. Among the 52 TDMA frames, the 26th TDMA frame and the 52nd TDMA frame are idle frames (I).

In packet transmission mode or DTM, the mobile station performs synchronization acquisition or received signal size measurement on neighboring cells in the idle timeslot of the 25th TDMA frame, the 26th TDMA frame, the idle timeslot of the 51st TDMA frame, and the 52nd TDMA frame. . An idle timeslot refers to timeslots that are not allocated as uplink or downlink in one TDMA frame.

In the structure of FIG. 3, the 25 th TDMA frame is composed of eight timeslots, two timeslots are allocated for downlink transmission, and the other two timeslots are allocated for uplink transmission. Accordingly, the mobile station combines three timeslots of the 25th TDMA frame and eight timeslots of the 26th TDMA frame to perform synchronization acquisition or received signal size measurement for the neighboring cells during 11 consecutive timeslots. As a specific time, according to the GSM standard, since one TDMA frame has a length of 4.62 ms and one timeslot has a length of 0.577 ms, the mobile station performs synchronization acquisition or received signal size measurement for 6.35 ms.

The neighbor cell may be another network cell as well as a GSM / GPRS cell. The other network refers to a network system using a different frequency from the GSM / GPRS system, and may be, for example, a UMTS, LTE system, a system based on the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard, and the like. It is assumed that the mobile station supports not only GSM / GPRS but also other networks.

4 shows a radio frame structure in an E-UTRAN (Evloved-UMTS Terrestrial Radio Access Network). This includes: 3GPP TS 36.211 V8.0.0 (2007-09) Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); See section 4.1 Physical channels and modulation (Release 8).

Referring to FIG. 4, a radio frame includes 10 subframes, and one subframe includes two slots. One slot includes a plurality of OFDM symbols in the time domain. Here, one slot includes 7 OFDM symbols, but the number of OFDM symbols included in one slot may be changed according to a Cyclic Prefix (CP) structure.

The Primary Synchronization Channel (P-SCH) is located in the last OFDM symbol of the first slot and the tenth slot. P-SCH is used to obtain OFDM symbol synchronization or slot synchronization. The Secondary Synchronization Channel (S-SCH) is located in the last OFDM symbol in the last OFDM symbol of the first slot and the tenth slot. The S-SCH and the P-SCH may be located in contiguous OFDM symbols. S-SCH is used to obtain frame synchronization.

The mobile station needs to receive the P-SCH and the S-SCH present in one radio frame in order to measure the synchronization acquisition or reception signal size for the LTE cell, that is, the E-UTRAN.

When one slot is 0.5ms in length, the subframe consisting of two slots is 1ms in length. Therefore, the length of the radio frame consisting of 10 subframes is 10ms. In the structure of the radio frame shown in FIG. 4, the minimum window size w _min necessary for synchronization acquisition of the LTE cell is 10 slots + 1 OFDM symbol. The length of one slot is 0.5ms, and considering the length of the cyclic prefix (CP), the window size w _min is about 5.083ms (0.5ms + 0.083ms). The window size w _min of 5.083 ms corresponds to 8.81 timeslot (5.083 / 0.577 = 8.81). Accordingly, at least 8.81 timeslots are required for the mobile station to search for LTE cells in packet transfer mode or DTM. Moreover, while the mobile station actually performs data transmission and / or reception in the GSM / GPRS cell, additional time is required to change from the GSM / GPRS frequency to the LTE frequency in order to perform a synchronization acquisition operation for the LTE cell. . In conclusion, in order to perform a synchronization acquisition operation for an LTE cell in a packet transmission mode or a DTM, a minimum time (8.81) must be received at least one P-SCH and one S-SCH in a 10 ms radio frame of the LTE cell. Time slot) and the time for frequency change, a time corresponding to at least 10 timeslots is required.

Depending on the uplink time slot and / or downlink time slot configuration allocated by the mobile station in the packet transmission mode or the DTM state, it may not be possible to secure the minimum space required for synchronization acquisition or signal size measurement of another network cell.

5 is an exemplary diagram illustrating an example of timeslot allocation.

Referring to FIG. 5, if a mobile station receives six timeslots in downlink and one timeslot in uplink from a TDMA frame immediately before an idle frame in a packet transmission mode, only the idle frame is included in the idle frame for measurement of an LTE cell. Only 8 timeslots are reserved. Therefore, according to the currently assigned timeslot configuration, the mobile station cannot measure the LTE cell because 10 timeslots, which are the minimum timeslots required for LTE cell measurement, cannot be obtained.

6 is a flowchart illustrating a measurement report method according to an embodiment of the present invention.

Referring to FIG. 6, the base station transmits a message to the mobile station requesting reporting on synchronization acquisition or received signal size measurement for another network cell such as an LTE cell (S210). At this time, the mobile station is in packet transfer mode or DTM.

 The mobile station determines whether measurement is possible for another network cell in consideration of downlink timeslots and uplink timeslots allocated from the network (S220). That is, it is determined whether or not the minimum space necessary for acquiring synchronization with other network cells is secured. For example, if the cell to be measured is an LTE cell, it is determined whether 10 timeslots, which are the minimum number of timeslots necessary for the measurement, are secured.

The mobile station transmits a measurable report message indicating whether it can be measured (S230). The measurable report message may confirm whether it is measurable, or may be transmitted to the base station only when measurement is impossible. For example, if the minimum number of timeslots is not secured, the mobile station can measure information indicating that it is impossible to acquire synchronization or measure signal size for the LTE cell according to the currently allocated downlink timeslot and uplink timeslot configuration. The report message is transmitted to the base station.

 If packet acquisition mode or DTM cannot acquire synchronization or receive signal size measurements for other network cells according to downlink timeslots and uplink timeslots allocated from the network, the mobile station informs the network that this is the case. . The network receiving this information reallocates a downlink time slot and / or an uplink time slot to the mobile station to enable the mobile station to acquire synchronization or receive signal size measurements for other network cells. Thus, the mobile station can enable synchronization acquisition or measurement of received signal size for other network cells.

The mobile station can prevent handover delay to other network cells by ensuring measurement of the received signal size for synchronization acquisition for other network cells.

The invention can be implemented in hardware, software or a combination thereof. In hardware implementation, an application specific integrated circuit (ASIC), a digital signal processing (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, and a microprocessor are designed to perform the above functions. , Other electronic units, or a combination thereof. In the software implementation, the module may be implemented as a module that performs the above-described function. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

As mentioned above, preferred embodiments of the present invention have been described in detail, but those skilled in the art to which the present invention pertains should understand the present invention without departing from the spirit and scope of the present invention as defined in the appended claims. It will be appreciated that various modifications or changes can be made. Accordingly, modifications to future embodiments of the present invention will not depart from the technology of the present invention.

1 is a block diagram illustrating a wireless communication system.

2 is an exemplary diagram for a method of synchronizing neighboring cells in a dedicated mode.

3 is an exemplary diagram illustrating a frame for synchronization acquisition of neighboring cells in a packet transmission mode or a DTM.

4 shows a radio frame structure in an E-UTRAN.

5 is an exemplary diagram illustrating an example of timeslot allocation.

6 is a flowchart illustrating a measurement report method according to an embodiment of the present invention.

Claims (4)

A method for a mobile station operating in a packet transfer mode or a dual transfer mode (DTM) in a global system for mobile communication (GSM) / general packet radio service (GPRS) system to obtain synchronization with another network cell, Receiving a request message regarding a measurement report from another base station to another network cell; And Transmitting a measurable report message regarding whether the measurement of the other network cell is possible in view of the assigned timeslot. The method of claim 1, And determining whether or not measurement is possible according to whether a minimum number of timeslots required for measurement of the other network cell are secured. The method of claim 2, And wherein the minimum number of timeslots are contiguous. The method of claim 2, Wherein the total length of the minimum number of timeslots is greater than a window size for receiving a Primary Synchronization Channel (P-SCH) and a Secondary Synchronization Channel (S-SCH) for the other network cell.

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