Random access based transmission control method, mobile station, and radio base station

Technical Field

0001The present invention relates to transmission control methods, mobile stations, and radio base stations.

Background Art

0002In a conventional mobile communication system, when a communication link is not established between a mobile station UE and a radio base station NodeB, the mobile station UE needs to transmit a signal to the radio base station NodeB by some means.

0003The mobile station UE can determine a transmission power to be used at the mobile station UE, by using a random access channel (hereinafter, RACH) at a physical layer

0004As an example of transmitting a signal to the radio base station NodeB through the RACH, a method using a power ramping can be considered. In this method, the mobile station UE transmits a single random access request as needed, and recognizes a failure of the transmission when an acknowledgment of the random access request transmitted from the radio base station NodeB cannot be received.

0005An example of the power ramping in the W-CDMA (Wideband Code Division Multiple Access) will be described. Firstly, the mobile station UE transmits, to the radio base station NodeB, a preamble signal as the random access request Here, the mobile station UE transmits the random access request while gradually increasing the transmission power.

0006The radio base station NodeB receives the random access request from the mobile station UE, and transmits a random access response for notifying the receipt of the random access request, to the mobile station UE through a downlink control channel.

0007In response to the receipt of the random access response from the radio base station NodeB, the mobile station UE stores the transmission power used for the most recent transmission of the random access request, which is transmitted to the radio base station NodeB.

0008Subsequent to the random access request, the mobile station UE transmits, to the radio base station NodeB, an allocation request for a control channel or the like, by using a transmission power equal to or higher than the stored transmission power.

0009The radio base station NodeB receives the allocation request from the mobile station UE, and transmits an allocation of a control channel or the like, to the mobile station UE. Thereby, the communication link is established between the mobile station UE and the radio base station NodeB (see Non-patent document 1 and Non-patent document 2, for example).

0010However, in the conventional mobile communication system, a collision can be occurred when multiple mobile stations UE simultaneously transmit signals to the radio base station NodeB by using the RACH (Random Access Channel), In that case, the conventional mobile communication system has a problem that the mobile station UE erroneously determines that the radio base station NodeB has received the random access request transmitted from the mobile station UE.

0011With reference to <figref idref="f0010">Fig. 11</figref>, an example in which the mobile station UE makes an erroneous determination will be described. In <figref idref="f0010">Fig. 11</figref>, neither a mobile station UE#1 nor a mobile station UE#2 has a communication link with a radio base station NodeB. Here, an example will be described for a case in which the mobile station UE#1 erroneously determines that an access request has been successfully transmitted to the radio base station NodeB although the transmission of the access request has not been successful.

0012In Step S2001, the mobile station UE#1 transmits a random access request to the radio base station NodeB through the RACH.

0013Here, assume that the base station NodeB has not received the random access request transmitted from the mobile station UE#1 for a reason that the transmission power is too small, or the like.

0014In addition, in Step S2001, the mobile station UE#2 transmits a random access request to the radio base station NodeB through the RACH at the same timing as the transmission of the random access request from the mobile station UE#1,

0015Here, each of the random access request transmitted from the mobile station UE#1 and the mobile station UE#2 collide with each other, and is transmitted to the radio base station NodeB.

0016In Step S2002, the radio base station NodeB receives the random access request, and transmits a random access response for notifying the receipt of the random access request, to the mobile station UE#1 through a downlink shared control channel corresponding to the RACH used for transmitting the random access request.

0017In addition, in Step S2002, the radio base station NodeB receives the random access request, and transmits a random access response for notifying the receipt of the random access request, to the mobile station UE#2 through the downlink shared control channel corresponding to the RACH used for transmitting the random access request.

0018In Step S2003, the mobile station UE#1 receives the random access response through the downlink shared control channel, and then transmits an allocation request to the radio base station NodeB.

0019Here, the mobile station UE#1 erroneously determines that the random access request transmitted from the mobile station UE#1 has been received at the radio base station NodeB. Moreover, the transmission power used for transmitting the allocation request from the mobile station UE#1 to the radio base station NodeB does not allow the allocation request to be received at the radio base station NodeB.

0020In Step 2004, the mobile station UE#2 receives the random access response through the downlink control channel, and then transmits an allocation request to the radio base station NodeB.

0021In Step S2005, the radio base station NodeB transmits an allocation response for notifying the receipt of the allocation request, to the mobile station UE#2 through the downlink control channel.

0022As described above, the conventional mobile communication system has a problem that the mobile station UE may erroneously determine that the ' random access request transmitted from the mobile station UE has been received at the radio base station NodeB.

0023Further, in that case, another problem arises that a processing delay occurs at the mobile station UE until the determination made by the mobile station UE is turned out to be erroneous.

0024Moreover, in that case, still another problem arises that resource is wasted at the mobile station UE until the determination made by the mobile station U E turns out to be erroneous. <ul id="ul0001" list-style="none" compact="compact"><li>Non-patent document 1: 3GPP TS 25.213 V5.5.0</li><li>Non-patent document 2: 3GPP TS 25.211 V5.6.0</li></ul>

Disclosure of the Invention

0025The present invention has been made in view of the above-described problems, and has an object of providing a packet communication method, a mobile station, and a radio base station, which can reduce an occurrence of an erroneous determination made at the mobile station when a packet communication is initiated between the mobile station and the base station.

0026A first aspect of the present invention is summarized as including; transmitting, at a mobile station, a random access request that includes mobile station information assigned to the mobile station, to a radio base station through a random access channel allocated to a predetermined radio resource; receiving, at the radio base station, the random access request from the mobile station; and transmitting, at the radio base station, a random access response signal that notifies the receipt of the random access request and includes the mobile station information, to the mobile station through a downlink shared control channel corresponding to the random access channel.

0027The first aspect of the present invention may further includes; transmitting, at the mobile station, the random access request to the radio base station through the random access channel, by changing the radio resource used for transmitting the random access channel, when the mobile station fails to receive, from the radio base station, the random access response signal that includes the mobile station information.

0028A second aspect of the present invention is summarized as a mobile station, including: a random access request transmitter unit configured to transmit a random access request that includes mobile station information assigned to the mobile station, to a radio base station through a random access channel defined by a predetermined radio resource; and a random access response receiver unit configured to receive a random access response that includes the mobile station information.

0029A third aspect of the present invention is summarized as a radio base station, including: a random access receiver unit configured to receive a random access request that includes mobile station information assigned to a mobile station, from the mobile station through a random access channel defined by a predetermined radio resource; and a random access response transmitter unit configured to transmit a random access response signal that notifies the receipt of the random access request and includes the mobile station information, to the mobile station through a downlink shared channel corresponding to the random access channel.

Brief Description of the Drawings

0030<ul id="ul0002" list-style="none" compact="compact"><li>[<figref idref="f0001">Fig, 1] Fig. 1</figref> is an entire configuration diagram of a mobile communication system according to a first embodiment of the present invention.</li><li>[<figref idref="f0002">Fig. 2] Fig. 2</figref> is a functional block diagram of a mobile station according to the first embodiment of the present invention.</li><li>[<figref idref="f0002">Fig. 3] Fig. 3</figref> is diagrams each showing an example of the format of a RACH, the format being used in the mobile communication system according to the first embodiment of the present invention.</li><li>[<figref idref="f0003">Fig. 4] Fig. 4</figref> is a diagram showing an example of the format of mobile station information, the format being used in the mobile communication system according to the first embodiment of the present invention.</li><li>[<figref idref="f0004">Fig. 5] Fig. 5</figref> is a functional block diagram of a radio base station according to the first embodiment of the present invention.</li><li>[<figref idref="f0005">Fig. 6] Fig. 6</figref> is a diagram showing an allocation example of a resource of a radio uplink in the mobile communication system according to the first embodiment of the present invention.</li><li>[<figref idref="f0006">Fig. 7] Fig. 7</figref> is a diagram showing an allocation example of the resource of the radio uplink in the mobile communication system according to the first embodiment of the present invention,</li><li>[<figref idref="f0007">Fig. 8] Fig. 8</figref> is a diagram showing an allocation example of the resource of the radio uplink in the mobile communication system according to the first embodiment of the present invention.</li><li>[<figref idref="f0008">Fig. 9] Fig. 9</figref> is a diagram showing an allocation example of the resource of a radio downlink in the mobile communication system according to the first embodiment of the present invention.</li><li>[<figref idref="f0009">Fig. 10] Fig. 10</figref> is a sequence diagram showing operations in the mobile communication system according to the first embodiment of the present invention.</li><li>[<figref idref="f0010">Fig. 11] Fig. 11</figref> is a sequence diagram showing operations in a mobile communication system according to a conventional technique.</li></ul>

Best Mode for Carrying out the Invention

(Mobile communication system according to first embodiment of the present invention)

0031A configuration of a mobile communication system according to a first embodiment of the present invention will be described with reference to <figref idref="f0001 f0002 f0003 f0004">Figs. 1 to 5</figref>.

0032As shown in <figref idref="f0001">Fig. 1</figref>, the mobile communication system according to the present embodiment includes a plurality of radio base stations; radio base stations eNodeB #1 and eNodeB #2, and a central node (such as an access router, a radio network controller RNC or the like) that controls the plurality of radio base stations eNodeB #1 and eNodeB #2.

0033In the mobile communication system according to the present embodiment, each of a mobile station UE is configured to initiate a packet communication by a random access control, through a radio base station eNodeB and the central node (such as an access router or a radio network controller RNC). Here, the radio base station eNodeB controls a cell in which the mobile station UE is located.

0034As shown in <figref idref="f0002">Fig. 2</figref>, the mobile station UE is provided with a RACH information obtaining unit 11, a RACH information storage unit 12, a random access request transmitter unit 13, a random access response receiver unit 14, an allocation request transmitter unit 15, an allocation response receiver unit 16, a packet access request transmitter unit 17, a packet access response receiver unit 18, and a communication unit 19.

0035The RACH information obtaining unit 11 is configured to obtain RACH information and to store the obtained RACH information in the RACH information storage unit 12. Here, the RACH information is notified through a downlink shared channel allocated to the mobile station UE or a broadcast channel transmitted from a cell in which the mobile station UE is located.

0036For example, when the mobile station UE performs a handover, the RACH information obtaining unit 11 may be configured to obtain the RACH information from the radio base station eNodeB, which is a destination of the handover,

0037As the broadcast channel, such as a broadcast channel (BCH) defined in 3GPP, or the like can be assumed.

0038As the downlink shared channel, such as a downlink shared control channel or a downlink shared data channel or the like can be assumed.

0039The RACH information includes such as information for identifying the random access channel, mobile station information assigned, by the radio base station eNodeB, to the mobile station UE located in the cell controlled by the radio base station eNodeB, and the like.

0040Moreover, the RACH information may also include information for identifying the downlink shared data channel and the downlink shared control channel corresponding to the random access channel.

0041Furthermore, the RACH information may also include a transmission timing of a random access request.

0042Here, the mobile station information may be a preamble signal pattern (a RACH signature) to be used by the mobile station UE, the preamble signal pattern being specified when a handover is performed, by the radio base station eNodeB, which is the destination of the handover, (see <figref idref="f0003">Fig. 4</figref>).

0043Alternatively, the mobile station information may be identification information unique to the mobile station UE, a numerical value randomly generated, or a combination of QoS information and the numerical value randomly generated.

0044The mobile station information may also be information for specifying a sequence number to be used, of a numerical value table previously provided with the mobile station UE.

0045Here, as a random access channel (RACH) defined in 3GPP (3^rd Generation Partnership Project) or the like can be assumed to be the random access channel. Accordingly, the random access channel will be described as "RACH" hereinbelow.

0046Specifically, the RACH information includes information for specifying a radio resource allocated to the RACH, the downlink shared control channel corresponding to the RACH, or the downlink shared data channel.

0047Here, it is assumed that the information for specifying the radio resource specifies: a frequency resource (frequency band), a time resource (time slot or TTI), a code resource (spread code), or a combination of the above-described resources.

0048Further, the RACH information may include multiple pieces of information for specifying the above-described radio resources.

0049In addition, in the mobile communication system according to the present embodiment, the radio resource allocated to the RACH or to the downlink shared control channel corresponding to the RACH may be predetermined.

0050Note that a random access response is transmitted through at least one of the downlink shared data channel and the downlink shared control channel corresponding to the RACH. Here, the random access response notifies the receipt of the random access request transmitted through the RACH.

0051The random access request transmitter unit 13 is configured to form and transmit a random access request that includes the mobile station information assigned to the mobile station UE.

0052For example, the random access request transmitter unit 13 may be configured to form and transmit a random access request that includes the above-described identification information unique to the mobile station UE, as the mobile station information.

0053Alternatively, the random access request transmitter unit 13 may be configured to form and transmit a random access request that includes the above-described RACH signature (see <figref idref="f0003">Fig. 4</figref>), as the mobile station information.

0054Specifically, the random access request transmitter unit 13 may be configured to form and transmit a random access request that includes the preamble signal pattern (for example, a 16-bit Hadamard sequence shown in <figref idref="f0003">Fig. 4</figref>) specified by the radio base station eNodeB such as when the handover is performed.

0055Moreover, the random access request transmitter unit 13 may be configured to form and transmit a random access request that includes the preamble signal pattern, through a predetermined RACH at a transmission timing, for example, the transmission timing specified as the RACH information by the radio base station eNodeB such as when the handover is performed, Here, the transmission timing is included in the RACH information obtained by the RACH information obtaining unit 11.

0056The RACH information storing unit 12 may be configured to form and transmit the random access request by using a value sequentially selected from the numerical value table previously provided or a numerical value table randomly generated, as the mobile station information assigned to the mobile station UE.

0057Alternatively, the RACH information storing unit 12 may be configured to form and transmit a random access request by using a value randomly selected from the numerical value table previously provided or the numerical value table randomly generated, as the mobile station information assigned to the mobile station UE.

0058The RACH information storing unit 12 may also be configured to refer to the RACH information obtained at the RACH information obtaining unit 11 through a broadcast channel or the downlink shared channel allocated to the mobile station UE, and to form and transmit a random access request that includes the above-described mobile station information.

0059Further, the RACH information storing unit 12 may be configured to form a random access request that includes the QoS information, as the mobile station information allocated to the mobile station UE.

0060The random access request transmitter unit 13 is configured to refer to the RACH information storing unit 12, and to transmit the random access request, to the radio base station eNodeB that controls the cell in which the mobile station UE is located, through the RACH to which a predetermined radio resource is allocated.

0061Note that the random access request transmitter unit 13 may be configured to change, by using an arbitrary method, the RACH used for transmitting the random access request, when the RACH information storage unit 12 stores a plurality of the information for identifying the RACH or the downlink shared control channel corresponding to the RACH.

0062Moreover, the random access request transmitter unit 13 may be configured to change, by using an arbitrary method, the RACH used for transmitting the random access request, when the RACH information storage unit 12 stores a plurality of the information for identifying the RACH or the downlink shared control channel corresponding to the RACH and when the random access response receiver unit 14 fails to receive the access response signal that includes the mobile station information assigned to the mobile station UE.

0063Further, the random access request transmitter unit 13 may be configured to change the RACH used for transmitting the random access request or a pattern constituting the random access request (such as the 16-bit Hadamard sequence shown in <figref idref="f0003">Fig. 4</figref>), based on a service class, a cell, or a purpose.

0064In other words, the random access request transmitter unit 13 may be configured to change the RACH used for transmitting the random access request or the pattern constituting the random access request, depending on the purpose of transmitting the random access request.

0065The random access request transmitter unit <b>13</b> may change the RACH for transmitting the random access request or the pattern constituting the random access request, depending on the purpose of the transmission, such as; a random access request transmitted when a handover is performed; a random access request transmitted for establishing a radio link between the mobile station UE and the radio base station eNodeB; and a random access request transmitted for adjusting a timing in the radio link established between the mobile station UE and the radio base station eNodeB.

0066For example, the random access request transmitter unit 13 may use, as a pattern of the preamble signal included in the random access request transmitted when the handover is performed, the Hadamard sequences of P₀(n) to P₂(n), as shown in <figref idref="f0003">Fig. 4</figref>. Further, the random access request transmitter unit 13 may use, as a pattern of the preamble signal included in the random access request transmitted for establishing the radio link between the mobile station UE and the radio base station eNodeB, the Hadamard sequences P₃(n) to P₅(n) as shown in <figref idref="f0003">Fig.4</figref>. In addition, the random access request transmitter unit 13 may use, as a pattern of the preamble signal included in the random access request transmitted for adjusting the timing in the radio link established between the mobile station UE and the radio base station eNodeB, the Hadamard sequences P₃(n) to P₅(n) shown in <figref idref="f0003">Fig, 4</figref>.

0067The random access response receiver unit 14 is configured to receive the random access response for notifying the receipt of the random access request, from the radio base station eNodeB through at least one of the downlink shared control channel corresponding to the RACH used for transmitting the random access request, and the downlink shared data channel.

0068Note that the random access response may be configured to notify the uplink shared channel to be used for transmitting the packet access request (corresponding to the message part, for example) which requests an initiation of a packet communication.

0069In other words, the random access response may be configured to include information for specifying the radio resource allocated to the aforementioned uplink shared channel.

0070The allocation request transmitter unit 15 is configured to transmit an allocation request for requesting the radio base station eNodeB to allocate and notify the radio resource allocated to the uplink shared channel, when the random access response does not include the information for identifying the radio resource allocated to the uplink shared channel used for transmitting the packet random access request.

0071The allocation response receiver unit 16 is configured to receive an allocation response transmitted from the radio base station eNodeB in response to the allocation request. Note that the allocation response includes information for specifying the radio resource allocated to the uplink shared channel to be used for transmitting a packet random access request

0072The packet access request transmitter unit 17 is configured to transmit the packet access request for requesting an initiation of the packet communication, to the central node through the uplink shared channel notified by the random access response received at the random access response receiver unit 14,

0073Further, the packet access request transmitter unit 17 may be configured to transmit the packet access request for requesting the initiation of the packet communication, through the uplink shared channel notified by the random access response received at the allocation response receiver unit 16.

0074The packet access response receiver unit 18 is configured to receive a packet access response transmitted from the central node in response to the packet access request

0075When the packet access response is received at the packet access response receiver unit 18, the communication unit 19 is configured to set a link for transmitting and receiving user data (U-plane) between the mobile station UE and the central node, and to perform a communication through the link.

0076<figref idref="f0002">Fig. 3</figref> is a diagram showing an example of a format of the RACH used in the mobile communication system according to the first embodiment of the present invention.

0077As shown in <figref idref="f0002">Fig. 3(a)</figref>, the format of the RACH is configured to include a pilot signal, the mobile station information assigned to the mobile station UE, and the QoS (Quality of Service) information.

0078Alternatively, as shown in <figref idref="f0002">Fig. 3(b)</figref>, the format of the RACH may be configured to include the pilot signal and the mobile station information assigned to the mobile station UE while the QoS information is included in the mobile station information assigned to the mobile station UE.

0079An example of the mobile station information assigned to the mobile station UE will be shown in <figref idref="f0003">Fig. 4</figref>. The example of the mobile station information shown in <figref idref="f0003">Fig. 4</figref> is the preamble signal formed of the16-bit Hadamard sequence.

0080The preamble signal may be configured to be randomly selected by the random access request transmitter unit 13. Alternatively, the preamble signal may be configured to be sequentially selected by the random access request transmitter unit 13. Further, the preamble signal may be configured to be specified by the RACH information stored in the RACH information storing unit 12.

0081The radio base station eNodeB shown in <figref idref="f0004">Fig. 5</figref> is provided with a random access request receiver unit 31, a random access response transmitter unit 32, an allocation request receiver unit 33, an allocation response transmitter unit 34, a RACH information transmitter unit 35, and a resource management unit 36.

0082The random access request receiver unit 31 is configured to receive the random access request from the mobile station UE through the RACH to which the predetermined radio resource is allocated.

0083The random access response transmitter unit 32 is configured to refer to the resource management unit 36, and to transmit the random access response that includes the mobile station information assigned to the mobile station UE, so as to notify the receipt of the random access request.

0084Note that the random access response transmitter unit 32 is configured to refer to the resource management unit 36, and to notify, to the mobile station UE by the random access request, the uplink shared channel to be used for transmitting a packet random access request at the mobile station UE.

0085Specifically, the random access response transmitter unit 32 is configured to refer to the resource management unit 36, and to transmit, to the mobile station UE, the random access response that includes the information for specifying the radio resource allocated to the uplink shared channel to be used for transmitting the packet random access request at the mobile station UE.

0086The allocation request receiver unit 33 is configured to receive, from the mobile station UE through a channel to which the predetermined radio resource is allocated (such as the RACH and the uplink shared control channel), the allocation request for requesting the notification of the resource allocated to the uplink shared channel to be used for transmitting the packet random access request at the mobile station UE.

0087When the above-described allocation request from the mobile station UE is received at the allocation response transmitter unit 34, the allocation response transmitter unit 34 is configured to refer to the resource management unit 36, and to notify, to the mobile station UE by the allocation response, the uplink shared channel to be used for transmitting the packet random access request at the mobile station UE.

0088Specifically, the allocation response transmitter unit 34 is configured to refer to the resource management unit 36, and to transmit, to the mobile station UE, the allocation response that includes the information for specifying the radio resource allocated to the uplink shared channel to be used for transmitting the packet random access request at the mobile station UE.

0089The RACH information transmitter unit 35 is configured to refer to the resource management unit 36, and to notify the IZACH, the downlink shared control channel corresponding to the RACH, or the downlink shared data channel, to the mobile station UE through the broadcast channel or the downlink shared channel allocated to the mobile station UE.

0090Specifically, the RACH information transmitter unit 35 is configured to refer to the resource management unit 36, and to transmit, to the mobile station UE through the broadcast channel or the downlink shared channel allocated to the mobile station UE, the RACH information that includes the information for specifying the radio resource allocated to; the RACH, the downlink shared control channel corresponding to the RACH, or the downlink shared data channel.

0091Note that the RACH information transmitter unit 35 may be configured to change the RACH information to be notified to the mobile station UE (such as the radio resource allocated to; the RACH, the downlink shared control channel corresponding to the RACH, the downlink shared data channel), based on a cell, a service class, a purpose, or a reception level.

0092Further, the RACH information transmitter unit 35 may be configured to change the RACH information to be notified to the mobile station UE (such as the radio resource allocated to; the RACH, the downlink shared control channel corresponding to the RACH, and the downlink shared data channel), at a predetermined timing, depending on a traffic situation, a radio communication situation or the like.

0093The resource management unit 36 is configured to control each of the radio resources (a frequency resource, a time resource, and a code resource) allocated to respective channels in the uplink and the downlink. For instance, the resource management unit 36 is configured to control the radio resource allocated to the RACH, the downlink shared control channel corresponding to the RACH, or the downlink shared data channel.

0094<figref idref="f0005 f0006 f0007 f0008">Fig. 6 to Fig. 9</figref> each shows examples of the radio resources allocated by the resource management unit 36 to the respective channels in the uplink and the downlink.

0095Here, the examples shown in <figref idref="f0005 f0006 f0007 f0008">Fig. 6 to Fig. 9</figref> are configured such that the RACH is allocated in a frequency block A. Note that in the example of <figref idref="f0005">Fig. 6</figref>, multiple RACHs are multiplexed by code division multiple access (CDMA) in the frequency block A, while in the example in <figref idref="f0006">Fig. 7</figref>, multiple RACHs are multiplexed by time division multiple access (TDMA) in the frequency block A, and in the example in <figref idref="f0007">Fig. 8</figref> multiple RACHs are multiplexed by frequency division multiple access (FDMA) in the frequency block A, and in the example in <figref idref="f0008">Fig. 9</figref>, multiple RACHs are multiplexed by code division multiple access (CDMA) in the frequency block A.

0096Hereinbelow, with reference to <figref idref="f0006">Fig. 7</figref>, the allocation of the resources in the radio uplink in the mobile communication system according to this embodiment will be described.

0097In the example shown in <figref idref="f0006">Fig. 7</figref>, the multiple RACHs are multiplexed by the time division multiple access (TDMA) in the frequency block A.

0098In the example shown in <figref idref="f0006">Fig. 7</figref>, it is assumed that the mobile station UE acknowledges that the random access request transmitted through a RACH 50, which is multiplexed by the time division multiple access in the frequency block A, has not been received at the radio base station eNodeB.

0099Then, the mobile station UE is configured to change a frequency band resource used for the previous transmission at the mobile station UE, and to transmit the random access request to the radio base station eNodeB in a frequency band B through a RACH 51, which is multiplexed by the time division multiple access (TDMA).

0100In the example shown in <figref idref="f0007">Fig. 8</figref>, the multiple RACHs are multiplexed by the frequency division multiple access (FDMA) in the frequency block A

0101In the example shown in <figref idref="f0007">Fig. 8</figref>, the mobile station UE Is configured to change a time resource used for the previous transmission at the mobile station UE, and to transmit the random access request to the radio base station eNodeB in the frequency band B through a RACH 53, which is multiplexed by the frequency division multiple access (FDMA).

0102In the example in <figref idref="f0008">Fig. 9</figref>, the multiple RACHs are multiplexed by the code division multiple access (CDMA) in the frequency block A.

0103In the example shown in <figref idref="f0008">Fig. 9</figref>, the mobile station UE is configured to change a code resource used for the previous transmission at the mobile station UE, and to transmit the random access request to the radio base station eNodeB in the frequency band B through the RACH, which multiplexed by the code division multiple access (CDMA).

(Operations in mobile communication system according to first embodiment of the present invention)

0104Hereinbelow, an operation for a random access control in the mobile communication system according to this embodiment will be described with reference to <figref idref="f0009">Fig. 10</figref>.

0105In <figref idref="f0009">Fig. 10</figref>, neither the mobile station UE#1 nor the mobile station UE#2 has established a communication link with the radio base station eNodeB.

0106As shown in <figref idref="f0009">Fig. 10</figref>, in Step S1001, the mobile station UE#1 transmits a random access request that includes mobile station information assigned to the mobile station UE#1, to the radio base station eNodeB through a RACH to which a predetermined radio resource is allocated,

0107Further, in Step S1001, the mobile station UE#2 transmits a random access request that includes mobile station information assigned to the mobile station UE#2, to the radio base station eNodeB through the RACH to which the predetermined radio resource is allocated.

0108It is assumed that in Step 1001, the random access request transmitted from the mobile station UE#2 has not to been received at the base station eNodeB for a reason such as the transmission power is too small, or the like.

0109Here, each of the random access request transmitted from the mobile station UE#1 and the mobile station UE#2 collide with each other, and is transmitted to the radio base station NodeB.

0110In Step S1002, the radio base station NodeB transmits a random access response for notifying the receipt of the random access request, to the mobile station UE#1 through a downlink shared control channel corresponding to the RACH used for transmitting the random access request. Here, the random access response includes the mobile station information assigned to the mobile station UE #1.

0111Here, it is assumed that the radio base station eNodeB notifies, by the random access response, the uplink shared channel used for transmitting a packet random access request at the mobile station UE#1.

0112In addition, in Step S1002, the radio base station NodeB transmits the random access response for notifying the receipt of the random access request, to the mobile station UE#2 through at least one of the downlink shared data channel and the downlink shared control channel corresponding to the RACH used for transmitting the random access request. Here, the random access response includes the mobile station information assigned to the mobile station UE#1.

0113Here, the radio base station eNodeB also transmits the random access response to the mobile station UE#2, since the collided random access request has been received at the radio base station eNodeB.

0114Note that the radio resource allocated to the RACH or to the downlink shared control channel corresponding to the RACH may be predetermined.

0115In Step S1003, the mobile station UE#1 receives the random access response that includes the mobile station information assigned to the mobile station UE#1, through the downlink shared control channel corresponding to the RACH used for transmitting the random access request, and can acknowledge that the random access request has been received at the radio base station eNodeB.

0116In Step 1004, the mobile station UE#1 transmits the packet random access request to the radio base station eNodeB through the uplink shared channel notified by the aforementioned random access response.

0117In Step S1005, the radio base station eNodeB transfers the packet random access request to the central node.

0118In Step S1006, the central node transmits, to the radio base station, a packet random access response for notifying the receipt of the packet random access request

0119in Step S1007, the radio base station eNodeB transfers the aforementioned packet random access response to the mobile station UE#1.

0120In Step S1008, when the packet random access response is received at the mobile station UE#1, a link for transmitting and receiving user data (U-plane) is established between the mobile station UE#1 and the central node.

0121In Step S1008, the mobile station UE#2 receives the random access response that includes the mobile station information assigned to the mobile station UE#1, through at least one of the downlink shared data channel and the downlink shared control channel corresponding to the RACH used for transmitting the random access request.

0122The mobile station UE#2 acknowledges that the random access request transmitted from the mobile station UE#2 has not been received at the radio base station eNodeB since the received random access response includes the mobile station information assigned to the mobile station UE#1.

0123Note that the mobile station UE#2 may acknowledge that the random access request has not been received at the radio base station eNodeB, when the mobile station UE#2 has not received the random access response for a predetermined period, the random access response that includes the mobile station information assigned to the mobile station UE#2.

0124In Step S1010, the mobile station UE#2 transmits the random access request to the radio base station eNodeB through a RACH to which a radio resource different from the radio resource used in Step S1001 is allocated,

0125In Step S1011, the radio base station eNodeB transmits a random access request that notifies the receipt of the random access request and includes the mobile station information assigned to the mobile station UE#2, to the mobile station UE#2 through at least one of the downlink shared data channel and the downlink shared control channel corresponding to the RACH used for transmitting the random access request.

0126The operations in Steps S1012 to S1016 are same as those in the above-described Steps S1004 to S1008, and hence, descriptions of the operations are omitted.

(Advantageous effects of mobile communication system according to first embodiment of the present invention)

0127The mobile communication system according to this embodiment includes; transmitting, at a mobile station, a random access request that includes mobile station information assigned to the mobile station, to a radio base station through a random access channel allocated to a predetermined radio resource; receiving, at the radio base station, the random access request from the mobile station; and transmitting, at the radio base station, a random access response signal that notifies the receipt of the random access request and includes the mobile station information, to the mobile station through a downlink shared control channel corresponding to the random access channel. According to the above-described configuration, the mobile station UE can acknowledge that the random access request transmitted from the mobile station UE has been received at the radio base station eNodeB. Thus, an occurrence of an erroneous determination made at the mobile station UE can be reduced.

0128It is also possible to reduce a processing delay until the determination made by the mobile station UE is turned out to be erroneous. Further, it is possible to reduce the resource wasted at the mobile station UE until the determination made by the mobile station UE is turned out to be erroneous.

0129Moreover, the mobile communication system according to this embodiment includes; transmitting, at the mobile station, the random access request to the radio base station through the random access channel, by changing the predetermined radio resource for transmitting the radio resource, when the mobile station fails to receive, from the radio base station, the random access response signal that includes the mobile station information. According to the above-described configuration, the mobile station UE can transmit the random access request to the radio base station eNodeB while avoiding a collision when a reason that the mobile station UE fails to receive, from the radio base station eNodeB, the random access response signal that includes the mobile station information is owing to the collision.

0130Moreover, when the reason that the mobile station UE fails to receive, from the radio base station eNodeB, the random access response signal that includes the mobile station information is owing to the collision, the above-described configuration makes it possible to avoid an occurrence of continuous collisions. As a result, a frequency diversity effect can be obtained.

Industrial Applicability

0131As described above, the present invention makes it possible to provide a packet communication method, a mobile station, and a radio base station, which can reduce an occurrence of erroneous determination made at the mobile station when a packet communication is initiated between the mobile station and the base station.