Patent Publication Number: US-2010113081-A1

Title: Mobile station, radio access network apparatus, and mobile communications system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to mobile stations, radio access network apparatuses, and mobile communications systems. 
     2. Description of the Related Art 
     As illustrated in  FIG. 1 , a mobile station UE transmits a Random access preamble to a radio access network apparatus eNB to request for starting a communication when the mobile station starts or restarts a communication with the radio access network apparatus in Long Term Evolution (LTE), which is being considered for 3G systems. Before multiple mobile stations can simultaneously transmit the Random access preambles, the radio access network apparatus reports, to the respective mobile stations, multiple Signatures available for the respective mobile stations. The mobile station randomly selects a Signature from the multiple Signatures reported in advance, and transmits the Random access preamble using the selected Signature. The radio access network apparatus which has detected one or more Signatures returns, on a shared data channel, one or more Random access responses to the detected one or more Signatures. 
     The radio access network apparatus which has received the Random access preamble cannot identify whether the mobile station is starting a new communication, making a new connection to a cell for handover to, or restarting a communication. Therefore, the following three types of communication setup information are newly assigned on a uniform basis to the respective Signatures received. 
     Uplink allocation resource (UL grant) 
     Uplink timing information (UL timing advance) 
     Cell-specific user-specific identifier (C-RNTI: Cell specific radio network temporal identifier) 
     The mobile station which has transmitted the Random access preamble receives the Random access response from the radio access network apparatus, and receives the UL grant, UL timing advance, and C-RNTI that are allocated to the Signature transmitted by the mobile station. 
     SUMMARY OF THE INVENTION 
     Problem(s) to be Solved by the Invention 
     In this way, when a communication is started using the Random access preamble, multiple mobile stations may select and use the same Signature, in which case, collision occurs among the Signatures and the multiple mobile stations end up using the same resource for transmitting. Thus, there is a problem that, in a radio access network apparatus, Scheduled Transmissions (( 3 ) in  FIG. 1 ) are simultaneously transmitted from the multiple mobile stations using the same uplink radio resource, so that a correct uplink signal cannot be received. 
     Moreover, in a Random access response in the LTE, the UL grant, Timing advance, and C-RNTI sent to the respective Signatures need to be returned in a uniform manner regardless of the state of the mobile station. Thus, even unnecessary information may be allocated for the mobile station which already has the C-RNTI of the cell for handover to, or a mobile station which already has the C-RNTI for restarting data transmission, so that downlink radio resources may be wasted. 
     Means for Solving the Problem 
     In order to solve the above problem, a radio access network apparatus is provided, which communicates with a mobile station using a dedicated uplink channel, a downlink shared data channel, and a downlink signaling control channel. The apparatus includes: 
     a dedicated uplink channel allocating unit which allocates, to a mobile station starting or restarting communications, on a downlink shared data channel, a dedicated uplink channel to be used by the mobile station; 
     a dedicated uplink channel reception detecting unit which detects, on the allocated dedicated uplink channel, a reception of an uplink transmission from the mobile station; and 
     a downlink transmitting unit which, when the dedicated uplink channel reception of the mobile station is detected, transmits a response, to the mobile station, using a downlink shared data channel and a downlink signaling control channel. 
     The radio access network apparatus makes it possible to efficiently utilize downlink radio resources. 
     Moreover, the mobile station is provided, which communicates with a radio access network apparatus using a dedicated uplink channel, a downlink shared data channel, and a downlink signaling control channel. The mobile station includes, 
     a dedicated uplink channel allocating information receiving unit which receives, on a downlink shared data channel, allocation information on a dedicated uplink channel to be used; 
     a dedicated uplink channel setting unit which sets the allocated dedicated uplink channel; 
     an uplink transmit unit for transmitting uplink on the set dedicated uplink channel; and 
     a data receive unit which receives downlink with a user-specific identifier after the end of the uplink transmission. 
     The mobile station makes it possible to efficiently utilize downlink radio resources. 
     Furthermore, a mobile communications system is provided, which communicates with a mobile station and a radio access network apparatus using a dedicated uplink channel, a downlink shared data channel, and a downlink signaling control channel. In the mobile communications system, the radio access network apparatus includes 
     a dedicated uplink channel allocating unit which allocates, to a mobile station starting or restarting communications, on the downlink shared data channel, a dedicated uplink channel to be used by the mobile station; 
     a dedicated uplink channel reception detecting unit which detects, on the allocated dedicated uplink channel, a reception of an uplink transmission from the mobile station; and 
     a downlink transmitting unit which, when the dedicated uplink channel reception of the mobile station is detected, transmits a response, to the mobile station, using a downlink shared data channel and a downlink signaling control channel, 
     and wherein the mobile station includes 
     a dedicated uplink channel allocating information receiving unit which receives on a downlink shared data channel allocation information to be used on a dedicated uplink channel; 
     a dedicated uplink channel setting unit which sets the allocated dedicated uplink channel; and 
     an uplink transmit unit which transmits uplink on the set dedicated uplink channel; and 
     a data receive unit which receives downlink with a user-specific identifier after the end of the uplink transmission. 
     The mobile communications system makes it possible to efficiently utilize downlink radio resources. 
     ADVANTAGE OF THE INVENTION 
     According to the embodiment of the present invention, eliminating unnecessary transmissions of UL grant, UL timing advance, or C-RNTI (Cell specific radio network temporal identifier) makes it possible to implement a mobile station, a radio access network apparatus, and a mobile communications system that allow an efficient use of downlink radio resources. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a sequence chart showing a sequence of starting and restarting a communication of a mobile station; 
         FIG. 2  is an overview diagram of a mobile communications system which includes a radio access network apparatus and a mobile station; 
         FIG. 3  is a functional block diagram of a mobile station according to an embodiment of the present invention; and 
         FIG. 4  is a functional block diagram of a radio access network apparatus according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Description of Notations 
     
         
         
           
               100  mobile station 
               102  data transmitter/receiver 
               104  dedicated uplink channel allocation information receiver 
               106  dedicated uplink channel setting unit 
               108  transmit signal generator 
               200  radio access network apparatus 
               202  data transmitter/receiver 
               204  downlink shared data channel/downlink signaling control channel generator 
               206  dedicated uplink channel selector 
               208  communications start and restart determining unit 
               210  dedicated uplink channel detector 
               212  mobile station specifying unit 
           
         
       
    
     BEST MODE OF CARRYING OUT THE INVENTION 
     In the following, best modes for carrying out the invention are described based on the following embodiments with reference to the drawings. Throughout the drawings for explaining the embodiments, the same letters are used for those elements having the same functions, so that repetitive explanations are omitted. 
     In LTE, a radio access network apparatus, when transmitting a handover request signal to a mobile station, allocates to the mobile station, together with the handover request signal, a user-specific Signature used at the time the mobile station connects to a cell for handover to in order to avoid a Signature collision. The mobile station which has received the handover request signal uses the allocated user-specific Signature to transmit a Random access preamble to the cell for handover to. Now an embodiment of the present invention is considered with respect to a sequence in which the radio access network apparatus which has detected the Random access preamble returns a Random Access Response. 
     A mobile communications system according to an embodiment of the present invention is described with reference to  FIG. 2 . 
     A mobile communications system  10  includes a mobile station  100  and a radio access network apparatus  200 . 
     The mobile station  100  and the radio access network apparatus  200  communicate using a dedicated uplink channel, a downlink shared data channel, and a downlink signaling control channel. 
     Now a mobile station  100  according to an embodiment of the present invention is described with reference to  FIG. 3 . 
     The mobile station  100  includes a data transmitter/receiver  102  with an antenna; a dedicated uplink channel allocation information receiver  104 , which is connected to the data transmitter/receiver  102 ; a dedicated uplink channel setting unit  106 , which is connected to the dedicated uplink channel allocation information receiver  104 ; and a transmit signal generator  108 , which is connected to the dedicated uplink channel setting unit  106  and the data transmitter/receiver  102 . 
     The data transmitter/receiver  102  transmits and receives data. For example, the mobile station  100  may determine whether the downlink signaling control channel is destined for the mobile station itself based on the C-RNTI received on the downlink signaling control channel. Moreover, information of a radio resource of a downlink data channel destined for the mobile station may be received from the downlink shared radio resource information transmitted on the downlink signaling control channel. 
     The dedicated uplink channel allocation information receiver  104  receives a dedicated uplink channel allocation information signal indicating dedicated uplink channel allocation information for the mobile station. For example, the dedicated uplink channel allocation information signal is transmitted on the downlink shared data channel as a part of a signal requesting for restarting downlink transmission or a handover request signal. Moreover, the dedicated uplink channel allocation information is communications setting information for setting any one of a mobile station-specific Signature used on the Access preamble, an identifier or a code number that is used for uplink, and an uplink radio resource. 
     When a shortage occurs with respect to the dedicated uplink channel provided in advance at the radio access network apparatus, that the Random access preamble signal is to be used may be reported to the mobile station in the downlink shared data channel. 
     The dedicated uplink channel setting unit  106  sets a dedicated uplink channel according to dedicated uplink allocation information received at the uplink shared channel allocation information receiver  104 . 
     The transmit signal generator  108  generates a signal to be transmitted on the dedicated uplink channel which is set at the dedicated uplink channel setting unit  106 , and transmits the generated signal to the data transmitter and receiver  102 . The data transmitter and receiver  102  of the mobile station  100  wirelessly transmit the generated signal to the radio access network apparatus. In this way, the mobile station transmits, to the radio access network apparatus, an access preamble, for example. 
     The mobile station  100  which has transmitted the generated signal from the data transmitter/receiver  102  receives a downlink signaling control channel and a downlink shared data channel based on the C-RNTI. 
     Now a radio access network apparatus  200  according to an embodiment of the present invention is described with reference to  FIG. 4 . For convenience of explanation, a radio access network apparatus which wirelessly communicates with a mobile station is explained. However, more generally, the radio access network apparatus may communicate not only with a mobile station, but also user equipment (UE) including a fixed station. 
     The radio access network apparatus  200  includes a data transmitter/receiver  202 ; a downlink shared data channel/downlink signaling control channel generator  204 , which is connected to the data transmitter/receiver  202 ; a dedicated uplink channel selector  206 , which is connected to the downlink shared data channel/downlink signaling control channel generator  204 ; and a communication start/restart determining unit  208 , which is connected to the dedicated uplink channel selector  206 . Moreover, the radio access network apparatus  200  includes a dedicated uplink channel detector  210 , which is connected to the downlink shared data channel/downlink signaling control channel generator  204 ; and a mobile station specifying unit  212 , which is connected to the dedicated uplink channel detector  210 . 
     The communication start/restart determining unit  208  determines whether a mobile station to be managed by the radio access network apparatus starts or restarts communications. The communications start means that the mobile station being instructed to conduct a handover starts communications with the radio access network apparatus for handover to, for example. Moreover, the communications restart means a communications restart when downlink data to the mobile station performing intermittent reception is produced, for example. 
     For a mobile station which needs communications start or restart, the dedicated uplink channel selector  206  selects dedicated uplink channel allocation information to be used by the mobile station. The dedicated uplink channel allocation information is any one of an uplink radio resource, an uplink identifier or code number, and Signature of an Access preamble, for example. 
     If a shortage occurs with respect to the dedicated uplink channel provided in advance at the radio access network apparatus, that the Random access preamble signal is to be used for uplink may be reported to the mobile station in the downlink shared data channel. 
     The downlink shared data channel/downlink signaling control channel generator  204  generates a dedicated uplink channel allocation information signal indicating the dedicated uplink channel allocation selected at the dedicated uplink channel selector  206 . For example, the dedicated uplink channel allocation information signal is transmitted on the downlink shared data channel as apart of a signal requesting for restarting downlink data transmission or a handover request signal. 
     The dedicated uplink channel detector  210  receives the dedicated uplink channel allocation transmitted as a part of the signal generated at the downlink shared data channel/downlink signaling control channel generator  204 , and detects the presence/absence of uplink transmission in the dedicated uplink channel. The dedicated uplink channel is detected through a value of correlation with a Signature of access preamble allocated as dedicated uplink channel allocation information, for example. 
     The mobile station specifying unit  212  specifies the mobile station with the dedicated uplink channel detected at the dedicated uplink channel detector  210 . For example, when a mobile station-specific Signature used on an access preamble is allocated as an uplink shared channel, the mobile station is specified using the Signature. Moreover, when a mobile station specific code is allocated as dedicated uplink channel allocation information, the mobile station is specified based on the outcome of identifying the mobile station-specific code. 
     The mobile station specifying unit  212  transmits the mobile station-specific result to the downlink shared data channel/downlink signaling control channel generator  204 . The downlink shared data channel/downlink signaling control channel generator  204  determines whether transmission, to the specified mobile station, is required of two types of communications setting information (UL grant, UL timing advance), or only the UL timing advance, and transmits required information in the downlink shared data channel/downlink signaling control channel using a mobile station-specific identifier (C-RNTI). For example, the radio access network apparatus  200  determines that the two types of communications settings are required at the time of handover, and determines that the UL timing advance only is required at the time of restarting downlink data transmission. 
     According to the embodiment of the present invention, eliminating unnecessary transmissions of UL grant, UL timing advance, or C-RNTI (Cell specific radio network temporal identifier) makes it possible to implement a mobile station, a radio access network apparatus, and a mobile communications system that allow an efficient use of downlink radio resources. 
     As described above, in order to reduce the probability of multiple mobile stations selecting the same Signature and thereby, causing collision, a dedicated signature provided in advance is allocated, for a certain period, to a mobile station already having C-RNTI. Typical examples of such a mobile station are: (1) a mobile station to which is allocated, at the time of handover, a dedicated signature and C-RNTI of a cell for handover to as a part of a handover command from a cell for handover from; and (2) a mobile station already having C-RNTI and to which mobile station is allocated, at the time of restarting downlink data transmission, a dedicated preamble used at the time of establishing uplink synchronization. 
     However, with such a method of decreasing the collision probability, if all of the dedicated channels or dedicated preambles are in use, it is necessary to wait for a dedicated preamble allocation until the dedicated preamble becomes available, causing a delay in the transmit timing of the handover command, and a delay in the restart of the downlink data transmission. 
     Then, if all the Dedicated preambles are being used (or if there is a shortage), a base station eNB instructs the mobile station UE to transmit a Random access preamble using one Signature randomly selected. More specifically, (1) as a part of a signal transmitted to the mobile station by the base station, some indicator (this may be called a Random access preamble transmission indicator, for example) indicating that the Random access preamble is to be transmitted or (2) a special Dedicated signature representing that a random access preamble is to be used in such a condition may be specified. For example, the Random access preamble transmit identifier (in (1)) may be expressed as a flag bit such as ON or OFF, or the Dedicated signature number may be set to zero (in other words, “0” is specified so that it corresponds to “Random access preamble”.) 
     In this way, even if all dedicated preambles are being used, a mobile station can rapidly establish uplink synchronization and start or restart communications without delaying handover command transmission and downlink data transmission. 
     On the other hand, the mobile station which has received (1) a Random access preamble transmission indicator, or (2) a Dedicated signature number indicating that a Random access preamble is to be transmitted randomly selects one Signature out of Signatures transmittable as the Random access preamble according to an instruction from the base station. 
     As described above, while the present invention is described with reference to specific embodiments, the respective embodiments are merely exemplary, so that a skilled person will understand variations, modifications, alternatives, and replacements. While specific numerical value examples are used to facilitate understanding of the present invention, such numerical values are merely examples, so that any appropriate value may be used unless specified otherwise. For convenience of explanation, while the apparatus according to the embodiments of the present invention is explained using functional block diagrams, such an apparatus as described above may be implemented in hardware, software, or a combination thereof. The present invention is not limited to the above embodiments, so that variations, modifications, alternatives, and replacements are included in the present invention without departing from the spirit of the present invention. 
     The mobile station, radio access network apparatus, and mobile communications system according to the present embodiments may be applied to mobile communications systems. 
     As described above, while the present invention is described with reference to specific embodiments, the respective embodiments are merely exemplary, so that a skilled person will understand variations, modifications, alternatives, and replacements. While specific numerical value examples are used to facilitate understanding of the present invention, such numerical values are merely examples, so that any appropriate value may be used unless specified otherwise. Breakdown of the respective embodiments is not essential to the present invention, so that two or more embodiments may be used as needed. For convenience of explanation, while the apparatus according to the embodiments of the present invention is explained using functional block diagrams, such an apparatus as described above may be implemented in hardware, software, or a combination thereof. The present invention is not limited to the above embodiments, so that variations, modifications, alternatives, and replacements are included in the present invention without departing from the spirit of the present invention. 
     The present international application claims priority based on Japanese Patent Application No. 2007-28627, filed on Feb. 7, 2007, the entire contents of which are hereby incorporated by reference. 
     The present international application also claims priority based on Japanese Patent Application No. 2007-167008, filed on Jun. 25, 2007, the entire contents of which are hereby incorporated by reference.