JP2008278037A - Mobile communication system, base station apparatus and mobile station apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten a time to be spent on a handover time while effectively utilizing a radio resource when a mobile station apparatus performs random access for handover. <P>SOLUTION: A mobile communication system is provided in which the mobile station apparatus 200 uses any signature of a predetermined signature group between the mobile station apparatus 200 and a base station apparatus 100 upon performing random access, wherein the signature to be used for random access to be performed by the mobile station apparatus 200 in handover is selected by the base station apparatus 100, and the signature selected by the base station apparatus 100 is used by the mobile station apparatus 200 for random access between the mobile station apparatus 200 and the base station apparatus 100. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a mobile communication system, a base station apparatus, and a mobile station apparatus that use a cellular radio system.

  At present, in 3GPP (3rd Generation Partnership Project), the W-CDMA system is standardized as a third generation cellular mobile communication system, and services are started sequentially. In addition, HSDPA (High Speed Downlink Packet Access), which further increases the communication speed, has been standardized and the service is about to start.

  On the other hand, in 3GPP, the evolution of third generation radio access (Evolved Universal Terrestrial Radio Access, hereinafter referred to as EUTRA) is being studied. An OFDM (Orthogonal Frequency Division Multiplexing) scheme has been proposed as a downlink of this EUTRA. Further, as an uplink of EUTRA, a single carrier communication method of DFT (Discrete Fourier Transform) -spread OFDM method has been proposed.

  As shown in FIG. 7, the EUTRA uplink is composed of an uplink pilot channel UPiCH (Uplink Pilot Channel), a random access channel RACH (Random Access Channel), and an uplink scheduling channel USCH (Uplink Scheduling Channel). (For example, refer nonpatent literature 1).

  The uplink random access channel RACH of E-UTRA includes an asynchronous random access channel and a synchronous random access channel. Here, the minimum unit of the asynchronous random access channel uses a 1.25 MHz band. For example, as shown in FIG. 8, a plurality of access channels are prepared so as to be compatible with a large number of accesses.

  The purpose of using the asynchronous random access channel is to synchronize between the mobile station apparatus (hereinafter referred to as “mobile station”) and the base station apparatus (hereinafter referred to as “base station”). In addition, it is also considered to shorten the connection time between the mobile station and the base station by transmitting several bits of information such as a scheduling request for allocating radio resources. On the other hand, the purpose of using synchronous random access is to make a scheduling request (see, for example, Non-Patent Document 2).

  In asynchronous random access, only the preamble is transmitted for synchronization. This preamble includes a signature which is a signal pattern representing information, and several bits of information can be specified by preparing several tens of signatures. At present, transmission of 6-bit information is assumed, and it is assumed that 64 types of signatures are prepared.

  It is assumed that information such as random ID for 5 bits, reason for random access, downlink path loss / CQI (Channel Quality Indicator), etc. is assigned to 6-bit information (for example, Non-Patent Document 3).

  FIG. 9 is a sequence chart for explaining an example of a conventional random access procedure. FIG. 9 shows a procedure of random access (asynchronous random access) when an asynchronous random access channel is used.

  As shown in FIG. 9, in a conventional random access procedure, first, a mobile station selects a signature based on a random ID, a reason for random access, downlink path loss / CQI information, and the like (step (hereinafter referred to as “step”). (Abbreviated as “ST”) 901). Then, a preamble (random access preamble) including the selected signature is transmitted through the asynchronous random access channel (ST902: message 1).

  When the preamble is received from the mobile station, the base station calculates a synchronization timing shift between the mobile station and the base station from the preamble and performs scheduling for transmitting an L2 / L3 (Layer2 / Layer3) message (ST903). . Then, C-RNTI is allocated to a mobile station that requires C-RNTI (Cell-Radio Network Temporary Identity) for random access reasons, and synchronization timing deviation information (synchronization information), scheduling information, signature ID number, and C-RNTI are assigned. A random access response including this is transmitted (ST904: Message 2).

  When receiving the information from the base station, the mobile station extracts a response from the base station including the transmitted signature ID number (ST905). Then, the L2 / L3 message is transmitted using the radio resource scheduled by the base station (ST906: Message 3). When receiving the L2 / L3 message from the mobile station, the base station transmits a contention resolution for determining whether or not there is a collision with the mobile station to the mobile station (ST907: message 4) ( For example, refer nonpatent literature 3).

  A problem of such random access is that a collision occurs when the same signature and random access channel are selected in a plurality of different mobile stations. When multiple mobile stations select the same signature and transmit using the same radio resource block having the same time and frequency, that is, the same random access channel, a collision occurs in the preamble (ST902) shown in FIG. To do.

  When the base station cannot detect the preamble (ST902) due to such a collision, a response (ST904) including synchronization information or the like cannot be returned. In this case, since the mobile station cannot receive a response (ST904) from the base station, it is necessary to select a signature and a random access channel again after a predetermined time and perform random access.

  On the other hand, when the base station can detect the preamble (ST902), the base station calculates L2 / L3 message scheduling and synchronization timing deviation, and returns a response (ST904) to the mobile station. However, a plurality of mobile stations will receive a response (ST904) from the base station. For this reason, a plurality of mobile stations transmit the L2 / L3 message (ST906) using the scheduled radio resource, and as a result, a collision occurs in the L2 / L3 message (ST906).

  If the base station cannot detect the L2 / L3 message (ST906) due to such a collision, a response (ST907) cannot be returned. In this case, since the mobile station cannot receive a response (ST907) from the base station, it is necessary to select a signature and a random access channel again after a predetermined time and perform random access. In this way, when the same signature and random access channel are selected in a plurality of mobile stations, a collision can occur, and in the case where a collision occurs, the maximum number of times until the collision is detected is shown. The time until ST907 shown in Fig. 9 is required.

  By the way, when a mobile station capable of executing such random access exists at the position shown in FIG. 10, a handover is executed. Even when the handover is executed, the asynchronous random access as described above is performed.

  Here, an example of a random access procedure during handover execution will be described. FIG. 11 is a sequence chart for explaining an example of a random access procedure during handover execution. In addition, in FIG. 11, the procedure of the random access in the case of using an asynchronous random access channel is shown like FIG.

  As shown in FIG. 11, in the random access procedure at the time of handover execution, first, the mobile station measures the radio wave condition of the adjacent base station as a handover preparation stage (ST1101). Then, the measurement result (measurement report) is transmitted to the base station A of the base station that accommodates the mobile station itself (hereinafter referred to as “own base station” as appropriate) (ST1102).

  When receiving the measurement result from the mobile station, base station A selects the optimum base station from the measurement result (ST1103). Here, it is assumed that base station B is selected as the optimum base station. Then, base station A transmits a handover request message to handover destination base station B (ST1104).

  When receiving the handover request message from the base station A, the base station B allocates C-RNTI to the mobile station to be handed over (ST1105). Then, a handover request approval message including C-RNTI is notified to base station A as a response to the handover request (ST1106).

  When receiving the handover request approval message from base station B, base station A transmits a handover command message including C-RNTI to the mobile station (ST1107).

  When receiving the handover command message from base station A, the mobile station performs downlink synchronization of base station B, and confirms the position of the random access channel from the broadcast channel (ST1108). If downlink synchronization is performed, the mobile station selects one signature from signatures for which the reason for random access is handover (ST1109). Then, a preamble (random access preamble) including the selected signature is transmitted to the base station B through a random access channel (ST1110: message 1).

  When the signature is detected from the preamble received from the mobile station, the base station B calculates a synchronization timing shift, and performs uplink scheduling for transmitting a handover complete message from the mobile station (ST1111). Then, synchronization timing shift information (synchronization information), scheduling information, and signature ID number are transmitted (ST1112: message 2). When the handover is a reason for random access, the C-RNTI is not transmitted because the C-RNTI is notified in advance.

  When receiving the information addressed to the mobile station from the base station B, the mobile station corrects the synchronization timing shift based on the synchronization timing shift information (synchronization information) (ST1113). Then, a handover completion message is transmitted using the scheduled radio resource (ST1114: Message 3). When receiving the handover completion message from the mobile station, the base station B transmits a contention resolution for determining whether or not a collision has occurred with the mobile station to the mobile station (ST1115: message 4). .

Thus, since random access is performed also at the time of handover, collision is inevitable and there is a concern that it takes a long time to complete handover. To avoid this, the base station assigns a random access channel for handover to another physical release and notifies the mobile station to use the random access channel for handover, or the base station uses it for handover. Proposals have been made so that collisions do not occur in random access at the time of handover by performing random access by selecting a signature and notifying the mobile station. (For example, see Non-Patent Document 4 and Non-Patent Document 5)
R1-050850 “Physical Channel and Multiplexing in Evolved UTRA Uplink”, 3GPP TSG RAN WG1 Meeting # 42 London, UK, August 29-September 2, 2005 3GPP TR (Technical Report) 25.814, V7.0.0 (2006-06), Physical layer aspects for evolved Universal Terrestrial Radio Access (UTRA) 3GPP TS (Technical Specialization) 36.300, V0.90 (2007-03), Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Reverstrual ETC. R2-063082 “No-contention based handover execution”, 3GPP TSG RAN WG2 Meeting # 56 Riga, Latvia, November 6-10, 2006 R2-063225 “RACH Partitioning for Handover”, 3GPP TSG RAN WG2 Meeting # 56 Riga, Latvia, November 6-10, 2006

  However, as described above, when a random access channel for handover is used so as not to cause a collision, the physical channel is used only for a specific purpose, so the channel usage rate is low and radio resources are wasted. There is a problem of being consumed.

  On the other hand, when using a signature for handover in order not to cause a collision, the number of signatures that can be used in one base station is limited to 64, and the number of signatures allocated for handover is small, When there are many handovers at the same time, there is a problem that the number of signatures for handover is insufficient. In addition, since signatures are assigned for handover, there is a problem that the number of signatures assigned for purposes other than handover is reduced, and the probability of collision between mobile stations is increased.

  The present invention has been made in view of such problems, and in the case where a mobile station apparatus performs random access for handover, the time spent during handover is effectively utilized while effectively utilizing radio resources. It is an object to provide a mobile communication system, a base station apparatus, and a mobile station apparatus that can be shortened.

  (1) In order to achieve the above object, the present invention has taken the following measures. That is, the mobile communication system according to the present invention is a mobile communication system in which any one of a predetermined signature group is used with a base station apparatus when the mobile station apparatus performs random access. The base station apparatus selects a signature used for random access performed at the time of handover, and the mobile station apparatus uses the signature selected by the base station apparatus for random access with the base station apparatus. It is a feature.

  In this way, when performing handover, the mobile station device can reduce the probability of collision between the mobile station devices by performing random access using the signature selected by the base station device. Processing time associated with reselecting a signature or a random access channel can be reduced, and the time spent at the time of handover can be reduced. In particular, since it is not necessary to prepare a random access channel and signature for handover, a situation where radio resources are consumed wastefully and a situation where the number of signatures is insufficient is not caused.

  (2) In the mobile communication system according to the present invention, when the base station apparatus receives a handover request message from another base station apparatus that is a handover source, the mobile station apparatus uses a signature used for random access performed at the time of handover. And the signature is notified to the mobile station apparatus via the other base station apparatus.

  Thus, since the mobile station apparatus selects a signature used for random access performed at the time of handover in response to a handover request message from another base station apparatus of the handover source, without requiring special processing, It is possible to select a signature to be used for random access performed by the mobile station device at the time of handover while maintaining normal processing at the time of handover execution.

  (3) In the mobile communication system of the present invention, when the base station apparatus receives a preamble including a signature from the mobile station apparatus, the base station apparatus adds a signature included in the preamble to a response to the preamble. It is characterized in that a flag indicating whether or not the selected signature is inserted.

  As described above, since the flag indicating whether or not the signature included in the preamble is the signature selected by the base station apparatus is inserted in the response to the preamble, the signature is transmitted from the base station apparatus in the mobile station apparatus. It is possible to easily determine whether the selected item is selected.

  (4) In the mobile communication system of the present invention, another mobile station apparatus that performs random access other than handover is a signature in which a signature included in the preamble is selected by the base station apparatus from a response to the preamble. When a flag indicating that the signature is detected is detected, a signature different from the signature is selected.

  As described above, when the signature included in the preamble is a signature selected by the base station apparatus, a signature different from the signature is selected by another mobile station apparatus, and therefore, the mobile station performs random access other than handover. Even when the same signature is selected with the station apparatus, it is possible to perform a handover while avoiding a collision between the mobile station apparatuses.

  (5) A base station apparatus according to the present invention is a base station apparatus connected to a mobile station apparatus that uses one of signatures of a predetermined signature group at the time of random access, and the mobile station apparatus performs handover A signature management unit for selecting a signature used for random access to be performed, and a flag indicating whether or not the signature included in the preamble from the mobile station apparatus is the signature selected by the signature management unit in response to the preamble And a preamble detector to be inserted.

  In this way, since the signature management unit selects a signature used for random access performed by the mobile station device during handover, the mobile station device uses the selected signature to perform random access, thereby moving The probability of collision between stations can be reduced. As a result, the processing time associated with the reselection of the signature and the random access channel can be reduced, and the time spent at the time of handover can be reduced. In addition, since a flag indicating whether or not the signature included in the preamble from the mobile station apparatus is the selected signature is inserted into the response to the preamble by the preamble detection unit, the signature is It is possible to easily determine whether the station apparatus has been selected.

  (6) In the base station apparatus of the present invention, when the preamble detection unit detects a plurality of preambles including the signature selected by the signature management unit, the timing that is most shifted in the timing at which the preamble is received is determined. And calculating as synchronization information with the mobile station apparatus performing handover.

  As described above, when the signature selected by the signature management unit and the signature included in the preamble from the mobile station apparatus that performs random access other than handover are the same, handover is performed based on the timing at which the preamble is received. Since synchronization information with the mobile station apparatus is calculated, even when the mobile station apparatus to be handed over cannot be specified because the selected signature is the same, it is based on the timing at which the preamble is received. It becomes possible to synchronize with the mobile station apparatus.

  (7) The mobile station apparatus of the present invention is a mobile station apparatus that uses any signature of a predetermined signature group with the base station apparatus at the time of random access, and is notified from the base station apparatus And a signature selection unit that selects a signature used for random access performed at the time of handover, and a preamble generation unit that generates a preamble including the signature selected by the signature selection unit.

  Thus, since the signature used for random access performed at the time of handover notified from the base station apparatus is selected and the preamble including the signature is generated, the probability of collision between mobile stations can be reduced. As a result, the processing time associated with the reselection of the signature and the random access channel can be reduced, and the time spent at the time of handover can be reduced.

  According to the present invention, when performing a handover, the mobile station apparatus can reduce the probability of collision between the mobile station apparatuses by performing random access using the signature selected by the base station apparatus. From this, it is possible to reduce the processing time associated with the reselection of the signature, the random access channel, etc., and thus it is possible to reduce the time spent during the handover. In particular, since it is not necessary to prepare a random access channel and signature for handover, a situation where radio resources are consumed wastefully and a situation where the number of signatures is insufficient is not caused. As a result, when the mobile station apparatus performs random access for handover, it is possible to reduce the time spent during handover while effectively utilizing radio resources.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The mobile communication system according to the embodiment of the present invention (hereinafter referred to as “communication system” as appropriate) is a signature that has been conventionally performed in a mobile station apparatus (hereinafter referred to as “mobile station” as appropriate) for handover. The selection is performed by a base station apparatus (hereinafter referred to as “base station” as appropriate), the selected signature is notified to the mobile station, and the mobile station performs random access using this signature.

  In this way, when performing handover, the mobile station can reduce the probability of collision between mobile stations by performing random access using the signature selected by the base station. Processing time associated with access channel reselection or the like can be reduced, and the time spent during handover can be reduced. In particular, since it is not necessary to prepare a random access channel and signature for handover, a situation where radio resources are consumed wastefully and a situation where the number of signatures is insufficient is not caused.

  In the communication system according to the present embodiment, a signature for handover is selected by the base station. In this case, since the signature selected by the base station is not a special signature, it can be selected by a mobile station that performs normal random access without performing handover. Therefore, the signature selected by the base station may be the same as the signature selected by the mobile station that performs normal random access. In this case, in the communication system according to the present embodiment, the mobile station is notified that the signature is selected by the base station, and causes the mobile station to select a different signature.

  As described above, even when the signature selected by the base station is the same as the signature selected by the mobile station that performs normal random access, the mobile station is notified that the signature is selected by the base station. By notifying, it is possible to reduce the time until the occurrence of a collision is determined, so it is possible to reduce the time spent at the time of handover.

  Hereinafter, configurations of a base station and a mobile station included in the communication system according to the present embodiment will be described. FIG. 1 is a block diagram showing an example of a configuration of a base station included in the communication system according to the present embodiment. FIG. 2 is a block diagram showing an example of the configuration of the mobile station included in the communication system according to the present embodiment.

  As shown in FIG. 1, the base station 100 includes a data control unit 101, an OFDM modulation unit 102, a scheduling unit 103, a radio unit 104, a channel estimation unit 105, a DFT-Spread-OFDM demodulation unit (DFT-S-OFDM demodulation unit). ) 106, a control data extraction unit 107, a preamble detection unit 108, and a signature management unit 109.

  The data control unit 101 receives input of control data and user data, and transmits control data according to an instruction from the scheduling unit 103 in the downlink common control channel, the downlink synchronization channel, the downlink pilot channel, and the downlink shared control signaling channel. On the other hand, transmission data (user data) for each mobile station is mapped to a shared data channel.

  The OFDM modulation unit 102 performs OFDM signal processing such as data modulation, serial / parallel conversion of input signals, IFFT (Inverse Fast Fourier Transform) conversion, CP (Cyclic Prefix) insertion, and filtering, and generates an OFDM signal.

  The scheduling unit 103 includes a DL scheduling unit 103a that performs downlink scheduling and a UL scheduling unit 103b that performs uplink scheduling. The DL scheduling section 103a performs scheduling for mapping user data to each downlink channel from CQI information notified from the mobile station and data information of each user notified from the higher layer. The UL scheduling section 103b performs scheduling for mapping user data to each uplink channel from the uplink radio channel estimation result from the channel estimation section 105 and the resource allocation request from the mobile station.

  The radio unit 104 up-converts OFDM-modulated data to a radio frequency and transmits it to the mobile station. Radio section 104 receives uplink data from the mobile station, down-converts it to a baseband signal, and receives the received data to channel estimation section 105, DFT-S-OFDM demodulation section 106, and preamble detection section 108. hand over.

  Channel estimation section 105 estimates radio channel characteristics from uplink pilot channel UPiCH, and passes the estimation result to DFT-S-OFDM demodulation section 106. In addition, the radio channel estimation result is passed to the scheduling unit 103 in order to perform uplink scheduling. The uplink communication scheme is assumed to be a single carrier scheme such as DFT-S-OFDM, but may be a multicarrier scheme such as the OFDM scheme.

  The DFT-S-OFDM demodulation unit 106 demodulates the received data passed from the radio unit 104 according to the radio channel estimation result from the channel estimation unit 105.

  The control data extraction unit 107 separates the received data into user data (uplink shared data channel USDCH) and control data (uplink shared control signaling channel USCSCH). Then, among the separated control data, downlink CQI information is passed to the scheduling unit 103, and other control data and user data are passed to the upper layer.

  The preamble detection unit 108 detects a preamble, calculates a synchronization timing shift amount, and reports a signature ID number, a synchronization timing shift amount, and a base station designation flag to an upper layer. Here, the base station designation flag is a flag for identifying that the signature included in the preamble is a signature designated (selected) by the base station. When the signature included in the preamble is a signature designated by the base station, “1” is set in the base station designation flag, whereas when the signature is not designated by the base station, “0” is set in the base station designation flag. Is done.

  More specifically, if the signature ID number detected from the preamble is a signature notified from the signature management unit 109, the preamble detection unit 108 sets the base station designation flag to “1”, while In the case of a signature not notified from the management unit 109, the base station designation flag is set to “0”. If the signature ID number is a signature notified from the signature management unit 109, the signature management unit 109 is notified that a preamble including the signature ID number notified from the signature management unit 109 has been detected.

  When the preamble is detected, if it is confirmed that the preamble collides with another mobile station, the preamble detector 108 selects the largest amount as the amount of synchronization timing deviation, or the amount of deviation Calculate multiple and report to the upper layer. This is because the mobile station that performs handover is basically arranged at the cell boundary and the distance from the base station is assumed to be larger. It is based on what is considered to be a mobile station that performs.

  In this case, the mobile station that has received the notification of the plurality of synchronization timing deviation amounts sets the transmission timing from the largest amount as the transmission timing of the handover completion message. If no contention resolution (message 4) is returned, the transmission timing with the next largest shift amount is set.

  The signature management unit 109 selects a signature according to an instruction from the upper layer, and notifies the upper layer of the ID number (signature ID number) of the selected signature. In addition, the selected signature is notified to the preamble detector 108. Note that the signature is selected by checking the currently used signature ID number and excluding the used signature. The signature management unit 109 stores the selected signature ID number and deletes the signature detected by the preamble detection unit 108 from the stored content.

  On the other hand, as shown in FIG. 2, the mobile station 200 includes a data control unit 201, a DFT-S-OFDM modulation unit 202, a scheduling unit 203, a signature selection unit 204, a preamble generation unit 205, a synchronization correction unit 206, and a radio unit 207. , A channel estimation unit 208, an OFDM demodulation unit 209, and a control data extraction unit 210.

  The data control unit 201 receives input of user data and control data, and maps these data to an uplink scheduling channel according to an instruction from the scheduling unit 203.

  The DFT-S-OFDM modulation unit 202 performs data modulation, performs DFT-S-OFDM signal processing such as DFT conversion, subcarrier mapping, IFFT conversion, CP (Cyclic Prefix) insertion, and filtering, and performs a DFT-Spread-OFDM signal. Is generated. The uplink communication scheme is assumed to be a single carrier scheme such as DFT-Spread OFDM, but may be a multicarrier scheme such as the OFDM scheme.

  The scheduling unit 203 performs scheduling for mapping user data to each uplink channel from CQI information notified from a channel estimation unit 208 (to be described later) or scheduling information notified from an upper layer.

  The signature selection unit 204 selects a signature ID number used for random access in response to an instruction from an upper layer. The purpose of random access is notified as an instruction from the upper layer. When the notified purpose is handover, the signature ID number instructed by the upper layer is selected. On the other hand, when the notified purpose is other than the handover, the signature other than the handover is selected according to the purpose, and the selected signature ID number is passed to the preamble generation unit 205.

  In particular, when a signature ID is added to the handover command message received from the base station 100, the signature selection unit 204 selects a signature with the signature ID number, and passes the selected signature ID number to the preamble generation unit 205. .

  The preamble generation unit 205 generates a preamble using the signature ID number selected by the signature selection unit 204 and passes it to the DFT-S-OFDM modulation unit 202.

  The synchronization correction unit 206 determines the transmission timing from the synchronization information passed from the control data extraction unit 210, and passes the data modulated to match the transmission timing to the radio unit 207.

  Radio section 207 up-converts the modulated data to a radio frequency and transmits it to base station 100. Radio section 207 receives downlink data from base station 100, down-converts it to a baseband signal, and passes the received data to OFDM demodulation section 209.

  Channel estimation section 208 estimates the radio channel characteristics from the downlink pilot channel and passes the estimation result to OFDM demodulation section 209. In addition, in order to notify the base station 100 of the wireless channel estimation result, the base station 100 converts it to CQI information, and passes the CQI information to the scheduling unit 203.

  The OFDM demodulator 209 demodulates the received data passed from the radio unit 207 according to the radio channel estimation result received from the channel estimation unit 208.

  The control data extraction unit 210 separates received data into user data and control data. Scheduling information in the separated control data is passed to the scheduling unit 203, uplink synchronization information is passed to the synchronization correction unit 206, and other control data and user data are passed to the upper layer.

  Next, an example of a random access procedure at the time of executing handover in the communication system having the above configuration will be described. FIG. 3 is a sequence chart for explaining an example of a random access procedure at the time of executing handover in the communication system according to the present embodiment. Here, it is assumed that mobile station 200 is currently housed in base station 100A (hereinafter referred to as “base station A” as appropriate).

  As shown in FIG. 3, in the random access procedure at the time of executing handover in the communication system according to the present embodiment, first, mobile station 200 measures the radio wave conditions of adjacent base stations as a handover preparation stage. (ST301). Then, the measurement result (measurement report) is transmitted to base station A, which is its own base station (ST302).

  When receiving the measurement result from mobile station 200, base station A selects the optimum base station as the handover destination from the measurement result (ST303). Here, it is assumed that base station 100B (hereinafter referred to as “base station B” as appropriate) is selected as the optimum base station. Then, base station A transmits a handover request message to handover destination base station B (ST304).

  When receiving the handover request message from the base station A, the base station B selects one signature from the signatures (ST305). In this case, the base station B selects a signature from the signatures excluding the signature used in the base station B in order to avoid a collision between the mobile stations 200 that are handed over during random access. Then, after assigning C-RNTI to mobile station 200 to be handed over, a handover request approval message including signature ID number and C-RNTI is transmitted to base station A as a response to the handover request message (ST306).

  When receiving the handover request approval message from the base station B, the base station A transmits a handover command message including the signature ID number and the C-RNTI to the mobile station 200 (ST307).

  When receiving the handover command message from the base station A, the mobile station 200 performs downlink synchronization of the base station B and confirms the position of the random access channel from the broadcast channel (ST308). If downlink synchronization is performed, the mobile station 200 selects a signature ID number added to the handover command message, and randomly accesses a preamble (random access preamble: message 1) including the signature ID number. It transmits to the base station B through the channel (ST309).

  When the signature is detected from the preamble received from the mobile station 200 and it is confirmed that this signature is the signature designated in ST305, the base station B specifies the base station for identifying the signature designated by the base station B. The flag is set to 1 (ST310). Then, the amount of synchronization timing deviation is calculated, and scheduling for transmitting a handover complete message is performed (ST311). Then, a random access response (message 2) including a base station designation flag, synchronization timing deviation information (synchronization information), scheduling information, signature ID number, and C-RNTI is transmitted to mobile station 200 (ST312).

  In this case, since C-RNTI is notified in advance, the mobile station 200 does not need a signature number as identification information to be confirmed as data addressed to the mobile station 200, and may be C-RNTI.

  When receiving such information from the base station B, the mobile station 200 checks the base station designation flag. Here, when the base station designation flag is 1, the mobile station 200 recognizes the data addressed to itself and corrects the synchronization timing deviation from the synchronization information (ST313). Then, a handover completion message (message 3) is transmitted using the scheduled radio resource (ST314).

  When receiving the handover complete message from the mobile station 200, the base station B returns a contention resolution (message 4) including C-RNTI to the mobile station 200 accordingly (ST315). In this case, since there is no collision when the handover completion message (message 3) is transmitted, the contention resolution (message 4) may be omitted.

  Thus, when performing handover, the mobile station 200 can reduce the probability of collision between mobile stations by performing random access using the signature selected by the base station B. And the processing time associated with reselection of the random access channel can be reduced, and the time spent at the time of handover is shortened.

  Here, operations at the time of executing handover in base station 100 and mobile station 200 included in the communication system according to the present embodiment will be described. FIG. 4 is a flowchart for explaining the operation at the time of executing handover in base station 100 included in the communication system according to the present embodiment. FIG. 5 is a flowchart for explaining an operation at the time of executing handover in mobile station 200 included in the communication system according to the present embodiment. 4 shows the operation of the base station B (handover destination base station) shown in FIG. 3, and FIG. 5 shows the operation of the mobile station 200 shown in FIG.

  As shown in FIG. 4, when the base station B receives the handover request message from the base station A (ST401), the base station B assigns the C-RNTI of the mobile station 200 and selects the signature used by the mobile station 200 (ST402). , ST403). Then, a handover request approval message including the signature ID number and the C-RNTI is transmitted to the base station A as a response to the handover request message (ST404).

  When the handover request approval message is transmitted, it waits for the preamble (message 1) transmitted from the mobile station 200. If the preamble transmitted from mobile station 200 is received (ST405), it is determined whether the signature included in this preamble is the signature designated by base station B (ST406).

  Here, if the signature is designated by the base station B, the base station designation flag is set to “1” (ST407). Then, the amount of synchronization timing deviation is calculated and scheduling for transmitting a handover complete message is performed, and a preamble response (message 2) including a base station designation flag, synchronization information, scheduling information, signature ID number, and C-RNTI is performed. ) Is created (ST408). Then, this preamble response is transmitted to mobile station 200 (ST409).

  When the preamble response is transmitted, it waits for a handover completion message (message 3) transmitted from the mobile station. If the handover complete message transmitted from mobile station 200 is received (ST410), a contention resolution (message 4) including C-RNTI is created (ST411). Then, this contention resolution is transmitted to mobile station 200 (ST412).

  On the other hand, if it is not the signature designated by base station B in ST406, the base station designation flag is set to “0” (ST413). The case where the signature is not designated by the base station B corresponds to the case where the mobile station 200 randomly selects a signature. For example, when a signature is selected in the mobile station 200 that performs normal random access without handover, a signature different from the signature designated by the base station B is detected.

  If the base station designation flag is set to “0”, the synchronization timing deviation amount is calculated and scheduling for transmitting the schedule transmission message is performed, and the base station designation flag, synchronization information, scheduling information, signature ID number, A preamble response (message 2) including temporary C-RNTI is created (ST414). Then, this preamble response is transmitted to mobile station 200 (ST415).

  When the preamble response is transmitted, a schedule transmission message (message 3) transmitted from the mobile station 200 is waited. If the schedule transmission message transmitted from the mobile station is received (ST416), a contention resolution (message 4) including C-RNTI or temporary C-RNTI is created (ST417). Then, this contention resolution is transmitted to mobile station 200 (ST418).

  On the other hand, as shown in FIG. 5, when receiving a handover command message from base station A (ST501), mobile station 200 performs downlink synchronization with base station B (ST502). If downlink synchronization is performed, the signature with the signature ID number included in the handover command message is selected (ST503). That is, the signature designated by the base station B is selected. Then, a preamble (message 1) including the selected signature is transmitted to base station B (ST504).

  If a preamble has been transmitted, it is determined whether a preamble response (message 2) transmitted from base station B has been received (ST505). If the random access response transmitted from the base station B is received, it is confirmed that the base station designation flag included therein is “1” (ST506). If a preamble response including the transmitted signature ID number cannot be received within a certain time, the process returns to ST504 and the preamble is transmitted again.

  If it is confirmed that the base station designation flag is “1”, a handover complete message (message 3) including C-RNTI is created (ST507). Then, this handover complete message is transmitted to base station B (ST508). When the handover complete message is transmitted, the contention resolution (message 4) is transmitted from the base station B, and is received (ST509).

  As described above, according to the communication system according to the present embodiment, when performing handover, mobile station 200 selects a signature selected by base station B and performs random access, so Since the probability of collision can be reduced, it is possible to reduce the processing time associated with the reselection of the signature and the random access channel, and it is possible to reduce the time spent during the handover.

  Particularly, since it is not necessary to prepare a random access channel and signature for handover as in the prior art, a situation where radio resources are consumed wastefully and a situation where the number of signatures is insufficient is not caused.

  Here, an operation when mobile station 200 included in the communication system according to the present embodiment performs normal random access other than handover will be described. FIG. 6 is a flowchart for explaining an operation when mobile station 200 included in the communication system according to the present embodiment performs normal random access.

  As shown in FIG. 6, when performing normal random access, the mobile station 200 first selects a signature randomly (ST601). Then, a preamble (message 1) including the selected signature is transmitted to base station B (ST602).

  If a preamble has been transmitted, it is determined whether a preamble response (message 2) transmitted from base station B has been received (ST603). Here, when the preamble response cannot be received from the base station B within a predetermined time, the process returns to ST601, and the preamble is transmitted again.

  If the preamble response transmitted from the base station B is received, the base station designation flag included in this is determined (ST604). Specifically, it is determined whether the base station designation flag is “1” or “0”. If the base station designation flag is “1”, it is determined that a collision has occurred with the mobile station to be handed over, and the process returns to ST601. Then, the signature is selected again and the preamble is transmitted again.

  Note that the case where the base station designation flag is “1” means that the signature selected by the mobile station 200 that executes the flow shown in FIG. 6 corresponds to the other mobile station 200 that executes the handover first. This corresponds to the case where the signature is the same as that selected by the base station B in response to the request message. When the base station designation flag is “0”, the signature selected by the mobile station 200 that executes the flow shown in FIG. 6 is not selected by the base station B, or the handover is executed first. This corresponds to a case where the signature is not the same as the signature selected by the base station B in response to the handover request message corresponding to another mobile station 200.

  On the other hand, if the base station designation flag is “0”, a schedule transmission message (message 3) is created (ST605). Then, this schedule transmission message is transmitted to base station B (ST606). When the schedule transmission message is transmitted, the contention resolution (message 4) is transmitted from the base station B, and is received (ST607).

  As described above, according to the communication system according to the present embodiment, when the signature selected by mobile station 200 performing normal random access and the signature selected by base station B are the same, the base station designation flag Is set to “1”, the mobile station 200 is notified that the signature is selected by the base station B, and the mobile station is made to select a different signature. As a result, the time required to determine the occurrence of a collision between mobile stations can be shortened, so that the time spent during handover can be shortened.

  The present invention is not limited to the embodiment described above, and can be implemented with various modifications. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effect of the present invention is exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  For example, the above embodiment shows a case where the base station 100 selects a signature and notifies the mobile station 200 of the signature ID number with a handover command message. In this case, when selecting a signature, only the frequency band position of the random access channel is selected. However, the object selected by the base station 100 is not limited to this and can be changed as appropriate. For example, in addition to the frequency band position of the random access channel, the time position may be selected, and these may be included in the handover command message for notification.

  Further, in the above embodiment, the case where a signature for handover as described in the background art is used is not assumed, but when the signature for handover is used in this way, It can also be used as a method of complementing when the signature is insufficient.

It is a block diagram which shows an example of a structure of the base station apparatus which the communication system which concerns on this Embodiment has. It is a block diagram which shows an example of a structure of the mobile station apparatus which the communication system which concerns on the said embodiment has. It is a sequence chart for demonstrating an example of the random access procedure at the time of handover execution in the communication system which concerns on the said embodiment. It is a flowchart for demonstrating the operation | movement at the time of handover execution in the base station apparatus which the communication system which concerns on the said embodiment has. It is a flowchart for demonstrating operation | movement at the time of the handover execution in the mobile station apparatus which the communication system which concerns on the said embodiment has. It is a flowchart for demonstrating operation | movement in case the mobile station apparatus which the communication system which concerns on the said embodiment has performs normal random access. It is a figure for demonstrating the structure of the uplink of EUTRA. It is a figure for demonstrating the random access channel of the uplink of E-UTRA. It is a sequence chart for demonstrating an example of the procedure of the conventional random access. It is a figure for demonstrating arrangement | positioning of the base station in which a handover generate | occur | produces. It is a sequence chart for demonstrating an example of the procedure of the random access at the time of the conventional handover execution.

Explanation of symbols

100 Base station equipment (base station)
DESCRIPTION OF SYMBOLS 101 Data control part 102 OFDM modulation part 103 Scheduling part 104 Radio | wireless part 105 Channel estimation part 106 DFT-S-OFDM demodulation part 107 Control data extraction part 108 Preamble detection part 109 Signature management part 200 Mobile station apparatus (mobile station)
201 Data control unit 202 DFT-S-OFDM modulation unit 203 Scheduling unit 204 Signature selection unit 205 Preamble generation unit 206 Synchronization correction unit 207 Radio unit 208 Channel estimation unit 209 OFDM demodulation unit 210 Control data extraction unit

Claims (7)

A mobile communication system in which a mobile station device uses any one of a predetermined signature group at the time of random access with a base station device,
The base station device selects a signature to be used for random access performed by the mobile station device during a handover, and the mobile station device uses the signature selected by the base station device for random access with the base station device. A mobile communication system characterized by being used.   When the base station apparatus receives a handover request message from another base station apparatus that is a handover source, the base station apparatus selects a signature used for random access performed by the mobile station apparatus at the time of handover, and passes through the other base station apparatus. The mobile communication system according to claim 1, wherein the mobile station apparatus is notified of the signature.   When the base station apparatus receives a preamble including a signature from the mobile station apparatus, a flag indicating whether or not the signature included in the preamble is a signature selected by the base station apparatus in response to the preamble. The mobile communication system according to claim 2, wherein the mobile communication system is inserted.   When another mobile station apparatus that performs random access other than handover detects a flag indicating that the signature included in the preamble is a signature selected by the base station apparatus from the response to the preamble, 4. The mobile communication system according to claim 3, wherein different signatures are selected.   Signature management for selecting a signature to be used for random access performed by a mobile station device at the time of handover, which is connected to a mobile station device that uses any one of a predetermined signature group at the time of random access And a preamble detection unit that inserts a flag indicating whether or not the signature included in the preamble from the mobile station apparatus is the signature selected by the signature management unit into a response to the preamble. A characteristic base station apparatus.   The preamble detection unit, when detecting a plurality of preambles including the signature selected by the signature management unit, the timing that is most deviated in the timing at which the preamble is received from the mobile station apparatus that performs handover 6. The base station apparatus according to claim 5, wherein the base station apparatus calculates the synchronization information. A mobile station device that uses any signature of a predetermined signature group at the time of random access with a base station device,
A signature selection unit that selects a signature used for random access performed at the time of handover notified from the base station apparatus; and a preamble generation unit that generates a preamble including the signature selected by the signature selection unit. A featured mobile station apparatus.

Images