Patent Publication Number: US-2010124188-A1

Title: Methods utilized in mobile devices and base stations, and the mobile devices and base stations thereof

Description:
BACKGROUND OF THE INVENTION  
     1. Field of the Invention 
     The present invention relates to a wireless communication system, and more particularly, to methods utilized in mobile devices and base stations, and the mobile devices and base stations thereof. 
     2. Description of the Prior Art 
     A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs). 
     In LTE system, if a mobile device such as a mobile phone desires to connect to the Internet or communicate with other mobile phones via the LTE system, the mobile device firstly needs to be synchronized with a base station that serves the mobile device. The purpose of being synchronized with the base station is to prevent signals transmitted from the mobile device from colliding with other signals sent from other mobile devices under the coverage of the base station. 
     SUMMARY OF THE INVENTION  
     One of the objectives of the present invention is to provide at least one method, at least a mobile device, and a related base station used in a wireless communication system for efficiently processing a dedicated random access (RA) preamble when the mobile device tries to be synchronized with the base station; the dedicated RA preamble is allocated to the mobile device by the base station in the wireless communication system and therefore is regarded as a system resource. Another objective of the present invention is to provide at least one method, at least a mobile device, and a related base station used in a wireless communication system for preventing uplink (UL) data transmission from being delayed when the UL data transmission is initiated and downlink (DL) data arrival occurs at the base station but the mobile device is not synchronized with the base station on uplink. 
     According to an embodiment of the claimed invention, a method utilized in a mobile device is disclosed. The method comprises: transmitting a broadcasted random access (RA) preamble to a base station for initiating a first RA procedure; receiving a dedicated RA preamble from the base station after the first RA procedure is initiated; and transmitting the dedicated RA preamble to the base station for initiating a second RA procedure. 
     According to the embodiment of the claimed invention, a method utilized in a base station is further disclosed. The method comprises: receiving a broadcasted random access (RA) preamble used to initiate an RA procedure from a mobile device; assigning a dedicated RA preamble to the mobile device; transmitting an RA response corresponding to the broadcasted RA preamble to the mobile device and then receiving a scheduled transmission including a cell radio network temporary identity (C_RNTI) from the mobile device; and releasing the dedicated RA preamble when the C_RNTI or a media access control protocol data unit (MAC PDU) from the mobile device is received. 
     According to the embodiment of the claimed invention, a method utilized in a mobile device is further disclosed. The method comprises: transmitting an random access (RA) preamble to a base station; receiving a control message including downlink (DL) data arrival from the base station; transmitting a scheduled transmission message to the base station when an RA response from the base station is received and then starting a contention resolution timer; and before the contention resolution timer expires, transmitting a scheduling request message to the base station. 
     According to the embodiment of the claimed invention, a method utilized in a base station is further disclosed. The method comprises: determining whether an random access (RA) preamble is used for uplink (UL) data transmission; and sending a control message including a UL grant to the mobile device when the RA preamble is considered to be used for UL data transmission. 
     According to the embodiment of the claimed invention, a mobile device is disclosed. The mobile device comprises a communication unit for communicating with a base station and a control unit for controlling the communication unit. The control unit controls the communication unit to transmit a broadcasted random access (RA) preamble to a base station for initiating a first RA procedure. The communication unit receives a dedicated RA preamble from the base station after the first RA procedure is initiated. The control unit controls the communication unit to transmit the dedicated RA preamble to the base station for initiating a second RA procedure. 
     According to the embodiment of the present invention, a base station is disclosed. The base station comprises a communication module and a control module. The communication module is used for communicating with a mobile device, and the control module is used for controlling the communication module. The communication module receives a broadcasted random access (RA) preamble used to initiate an RA procedure from the mobile device. The control module controls the communication module to assign a dedicated RA preamble to the mobile device. The communication module transmits an RA response corresponding to the broadcasted RA preamble to the mobile device and then receives a scheduled transmission including a cell radio network temporary identity (C_RNTI) from the mobile device. The control module releases the dedicated RA preamble when the C_RNTI or a media access control protocol data unit (MAC PDU) from the mobile device is received by the communication module. 
     According to the embodiment of the claimed invention, a mobile device utilized is further disclosed. The mobile device comprises a communication unit for communicating with a base station and a control unit for controlling the communication unit. The control unit controls the communication unit to transmit a random access (RA) preamble to the base station; the communication unit receives a control message including downlink (DL) data arrival from the base station. The control unit controls the communication unit to transmit a scheduled transmission message to the base station when an RA response from the base station is received and then starts a contention resolution timer. The control unit controls the communication unit to transmit a scheduling request message to the base station before the contention resolution timer expires. 
     According to the embodiment of the claimed invention, a base station is further disclosed. The base station comprises a communication module for communicating with a mobile device and a control module for controlling the communication module to communicate with the mobile device. The control module determines whether an random access (RA) preamble is used for uplink (UL) data transmission, and controls the communication unit to send a control message including a UL grant to the mobile device when the RA preamble is considered to be used for UL data transmission. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a block diagram of a wireless communication system according to an embodiment of the present invention. 
         FIG. 2  is a block diagram of a user equipment (UE) and an evolved Node B (eNB) shown in  FIG. 1 . 
         FIG. 3  is a sequential diagram illustrating the interaction between the eNB and UE in  FIG. 2  according to the first example of this embodiment. 
         FIG. 4  is a sequential diagram illustrating another interaction between the eNB and UE in  FIG. 2  according to the first example of this embodiment. 
         FIG. 5  is a sequential diagram illustrating the interaction between the eNB and UE in  FIG. 2  according to a second example of this embodiment. 
         FIG. 6  is a sequential diagram illustrating another interaction between the eNB and UE in  FIG. 2  according to the second example of this embodiment. 
         FIG. 7  is a sequential diagram illustrating the interaction between the eNB and UE in  FIG. 2  according to a third example of this embodiment. 
         FIG. 8  is a sequential diagram illustrating the interaction between the eNB and UE in  FIG. 2  according to a fourth example of this embodiment. 
         FIG. 9  is a sequential diagram showing an interaction between the UE and eNB shown in  FIG. 2  according to a fifth example of this embodiment. 
     
    
    
     DETAILED DESCRIPTION  
     Please refer to  FIG. 1 .  FIG. 1  is a diagram of a wireless communication system  100  such as a beyond 3G communication system according to embodiments of the present invention. The communication system  100  offers the 3GPP Long Term Evolution (“LTE”) network, i.e. the next-generation network beyond 3G. The communication system  100  includes a core network (‘evolved packet core, EPC’ of LTE technology), and multiple base stations (‘evolved Node B, eNB’ of LTE technology) and may include many mobile stations/devices (named ‘user equipment’ in the LTE technology) such as mobile phones served by the base stations respectively. For simplicity, only a user equipment (UE)  110  is shown in  FIG. 1 . In order to communicate with the eNB  105   a  for DL data or UL data, it is necessary for the UE  110  to establish a point-to-point bidirectional connection between the Radio Resource Control (RRC) entities on the UE  110  and the evolved UMTS terrestrial radio access network (E-UTRAN), i.e. an RRC connection. When the RRC connection has been established and is still not released, the UE  110  is in an RRC_connected state; otherwise, the UE  110  is in an RRC_idle state. 
     In order to transmit an RRC connection request message, the UE  110  has to use a random access (RA) procedure, which generally comprises an RA preamble (i.e. an RA request) sent by the UE  110  and followed by an RA response sent by the eNB  105   a , wherein the RA response is indicative of a grant of UL transmission. In general, RA procedures are classified to be two kinds of procedures: contention-based RA procedures and non-contention-based RA procedures. A contention-based RA procedure uses a broadcasted RA preamble including a broadcasted RA identifier (5 bits) while a non-contention-based RA procedure uses a dedicated RA preamble including a dedicated RA identifier (5 bits). The phrase ‘broadcasted’ means that the broadcasted RA identifier is broadcasted by an eNB to all UEs under the coverage of the eNB such as  105   a ; the phrase ‘dedicated’ signifies that the dedicated RA identifier is only assigned to a specific UE by the eNB  105   a . Each of the UEs including the UE  110  is noticed of available broadcasted RA preambles when each UE starts up. 
     After start-up of a UE and an RRC connection between the UE and the eNB has been established, even though the UE  110  is in the RRC_connected state, the UE such as  110  may not be synchronized with the eNB such as the eNB  105   a  since the UE  110  does not communicate with the eNB  105   a  during a period. In this situation, the UE  110  needs to initiate an RA procedure to get synchronization if the UE  110  desires to communicate with the eNB  105  again. For example, if the UE  110  desires to transmit data to the eNB  105   a  via uplink, the UE  110  has to use a contention-based RA procedure to transmit a broadcasted RA preamble to the UE  105   a  for UL synchronization. After receiving the broadcasted RA preamble, the eNB  105   a  responds to the broadcasted RA preamble of the UE  110  by sending an RA response to the UE  110 . The eNB  105   a  may receive the same broadcasted RA preamble from another UE and also send an RA response to this UE. However, only one of the two UEs is selected to be capable of communicating with the eNB  105   a . In other words, the selected UE can obtain UL synchronization while the other UE cannot be synchronized with the eNB  105   a  on uplink. Additionally, for example, if the eNB  105   a  desires to transmit data to the UE  110  on downlink, the eNB  105   a  assigns a dedicated RA identifier to the UE  110 . After receiving the dedicated RA identifier, the UE  110  uses an RA procedure to send a dedicated RA preamble including the dedicated RA identifier to the eNB  105   a  for UL synchronization. Under this condition, since no UE except the UE  110  receives the dedicated RA identifier, the dedicated RA preamble transmitted by the UE  110  does not collide with other RA preambles transmitted by other UEs. Accordingly, the dedicated RA identifier is regarded as a system resource of the eNB  105   a.    
     However, the prior art LTE communication system does not clearly specify how a UE and an eNB should operate if the eNB assigns a dedicated RA identifier for the UE almost at the time when the UE transmits a broadcasted RA preamble. It is probable the allocated dedicated RA identifier is not efficiently used by this UE. 
     Therefore, in this embodiment, in order to efficiently make use of dedicated RA identifiers, the UE  110  and eNB  105   a  have the following design. Please refer to  FIG. 2 .  FIG. 2  is a block diagram showing the eNB  105   a  and the UE  110  in  FIG. 1 . As shown in  FIG. 2 , the UE  110  comprises a communication unit  1101  for communicating with the eNB  105   a , a control unit  1102  for controlling the communication unit  1101 , and a counter  1103  (named ‘PREAMBLE_TRANSMISSION_COUNTER’ in the LTE technology) to count a number of transmission time(s) that an RA preamble is transmitted; the eNB  105   a  comprises a communication module  1051  for communicating with the UE  110  and a control module  1052  for controlling the communication module  1051 . The control unit  1102  of the UE  110  is used for controlling the communication unit  1101  to transmit a broadcasted/dedicated RA preamble, in order to initiate an RA procedure. The control module  1052  of the eNB  105   a  is utilized for controlling the communication module  1051  to receive an RA preamble and transfer data. 
     Please refer to  FIG. 3 .  FIG. 3  is a sequential diagram illustrating the interaction between the eNB  105   a  and UE  110  according to the first example of this embodiment. In the first example, it is assumed that the UE  110  is in the RRC_connected state but not synchronized with the eNB  105   a  on uplink, and the UE  110  and eNB  105   a  both have data to be transmitted to each other almost simultaneously. Suppose that at time t 0  the UE  110  transmits a broadcasted RA preamble RA 1  including a broadcasted RA identifier ID 1  to the eNB  105   a  for initiating a first RA procedure. After sending/transmitting the broadcasted RA preamble RA 1 , the control unit  1102  of the UE  110  sets a period of a TTI window, which is defined by a beginning time named RA_WINDOW_BEGIN and an end time named RA_WINDOW_END, and initiates monitoring the physical downlink control channel (PDCCH) associated with the random access radio network temporary identity (RA-RNTI) for a RA response at time t′, which is determined by the beginning time RA_WINDOW_BEGIN; the phrases “RA_WINDOW_BEGIN” and “RA_WINDOW_END” are specified in 3GPP LTE MAC specification 36.321. The first RA procedure is failed when the period of the TTI window expires. As shown in  FIG. 3 , the broadcasted RA preamble RA 1  is not received by the eNB  105   a , so the eNB  105   a  does not transmit an RA response to the UE  110  correspondingly. In general, the UE  110  has to re-transmit the broadcasted RA preamble RA 1  in a second RA procedure at time t 1 , wherein time t 1  is determined by the end time RA_WINDOW_END of the TTI window in 3GPP LTE MAC specification 36.321. However, after the first RA procedure is initiated, the eNB  105   a  assigns a dedicated RA identifier ID′ to the UE  110  via the PDCCH because the eNB  105  has DL data to be transmitted to the UE  110 . Once the UE  110  receives the dedicated RA identifier ID′, the UE  110  transmits a dedicated RA preamble RA′ including the dedicated RA identifier ID′ at time t 1  for initiating the second RA procedure, instead of re-transmitting the broadcasted RA preamble RA 1 . Therefore, the system resource (i.e. the dedicated RA identifier ID′) can be efficiently used. It should be noted that the dedicated RA preamble RA′ is transmitted when the first RA procedure is failed. The above-mentioned second RA procedure is used when a radio resource control (RRC) connection with the eNB  105   a  is established and the UE  110  is not synchronized with the eNB  105   a.    
     Furthermore, please refer to  FIG. 4 .  FIG. 4  is a sequential diagram illustrating another interaction between the eNB  105   a  and UE  110  according to the first example of this embodiment. As shown in  FIG. 4 , at time t 0 , the UE  110  uses a first RA procedure to transmit the broadcasted RA preamble RA 1  including the broadcasted RA identifier ID 1  to the eNB  105   a . In this scenario, the broadcasted RA preamble RA 1  is successfully received by the eNB  105   a , so the eNB  105   a  transmits an RA response corresponding to the broadcasted RA preamble RA 1  to the UE  110 . After receiving the RA response, the UE  110  sends a scheduled transmission message including a Cell Radio Network Temporary Identity (C_RNTI) to the eNB  105   a  and initiates a contention resolution timer at time t′, and waits for a response of the eNB  105   a . However, as shown in  FIG. 4 , the scheduled transmission message is not successfully received by the eNB  105   a , so the UE  110  waits for expiration of the contention resolution timer and then initiates a second RA procedure for UL synchronization at time t 1 . Since the eNB  105   a  assigns a dedicated RA identifier ID′ to the UE  110  via the PDCCH during the first RA procedure, the UE  110  is designed to transmit a dedicated RA preamble RA′ using the dedicated RA identifier ID′ instead of the broadcasted RA identifier ID 1  when initiating the second RA procedure. That is, the system resource (i.e. the dedicated RA identifier ID′) assigned to the UE  110  is utilized in the following RA procedure if any transmission about the ongoing RA procedure fails. The dedicated RA preamble RA′ is transmitted by the UE  110  for initiating the second RA procedure when the first RA procedure is failed. 
     Please refer to  FIG. 5 .  FIG. 5  is a sequential diagram illustrating the interaction between the eNB  105   a  and UE  110  according to the second example of this embodiment. In the second example, the UE  110  is also in the RRC_connected state but not synchronized with the eNB  105   a  on uplink, and the UE  110  and eNB  105   a  both also have data to be transmitted to each other almost simultaneously. After sending the broadcasted RA preamble RA 1 , the control unit  1102  of the UE  110  sets a period of a TTI window, which is defined by a beginning time named RA_WINDOW_BEGIN and an end time named RA_WINDOW_END. The UE  110  of the second example is designed to transmit the dedicated RA preamble RA′ to the eNB  105   a  for immediately initiating a second RA procedure after receiving the assignment message of the dedicated RA identifier ID′ coming from the eNB  105   a . That is, regardless of whether the UE  110  detects failure of the first RA procedure due to that no RA response containing a RA 1  is received within the TTI window from the beginning time t 1  to the end time t 2 , the dedicated RA preamble RA′ is transmitted to initiate the second RA procedure. That is, the dedicated RA preamble RA′ is transmitted when the first RA procedure is ongoing. As shown in  FIG. 5 , before the UE  110  detects failure of the first RA procedure due to no RA response containing a RA 1  is received in the TTI window from t 1  to t 2 , the UE  110  immediately sends the dedicated RA preamble RA′ at time t′ when receiving the assignment message of the dedicated RA identifier ID′. In other words, whether the first RA procedure succeeds or fails, the second RA procedure is immediately initiated to send the dedicated RA preamble RA′ once the dedicated RA identifier ID′ is assigned to the UE  110 . An advantage of this example is that the eNB  105   a  can process an RA response with either the broadcasted RA preamble RA 1  or the dedicated RA preamble RA′, depending on which one of the preambles is successfully received; the UE  110  has a higher chance to connect to the eNB  105   a . In this scenario, the eNB  105   a  sends an RA response associated with the RA preamble RA 1  to the UE  110 ; however, this is not a limitation of the present invention. 
     Please refer to  FIG. 6 .  FIG. 6  is a sequential diagram illustrating another interaction between the eNB  105   a  and UE  110  according to the second example of this embodiment. As shown in  FIG. 6 , the UE  110  transmits the broadcasted RA preamble RA 1  at the time t 0  for initiating the first RA procedure, and sets a period of a TTI window defined by a beginning time RA_WINDOW_BEGIN (i.e. t 1 ) and an end time RA_WINDOW_END (t 2 ) after transmitting the broadcasted RA preamble RA 1 . The UE  110  also immediately transmits the dedicated RA preamble RA′ at time t′ for initiating a second RA procedure after receiving the assignment message of the dedicated RA identifier ID′, and sets a period of another TTI window defined by a beginning time RA_WINDOW_BEGIN (i.e. t 1 ′) and an end time RA_WINDOW_END (t 2 ′) after sending the dedicated RA preamble RA′. In other words, if the first RA procedure fails, the dedicated RA preamble RA′ is transmitted to initiate the second RA procedure before the UE  110  detects failure of the first RA procedure due to that no RA response containing the broadcasted RA preamble RA 1  is received within the TTI window from the beginning time t 1  to the end time t 2 . The UE  110  maintains the TTI window from the beginning time t 1 ′ to the end time t 2 ′ for a RA response containing the dedicated RA preamble RA′. The eNB  105   a  is arranged to respond to the broadcasted and dedicated RA preambles RA 1  and RA′ by sending RA responses corresponding to RA 1  and RA′ respectively. In this scenario, only the RA response corresponding to the dedicated RA preamble RA′ is successfully received by the UE  110 , so the UE  110  enters a status of processing the RA response corresponding to the dedicated RA preamble RA′. Then, the eNB  105   a  transmits a control message including a C_RNTI and a DL grant via the PDCCH, and sends DL data (i.e. MAC PDU) to the UE  110 . If the broadcasted RA preamble RA 1  is not received within the TTI window from the beginning time t 1  to the end time t 2 , the broadcasted RA preamble RA 1  is not considered valid for reception. If a PUCCH for scheduling request (SR) is configured, the UE  110  sends an SR message to the eNB  105   a  after the UE  110  receives the RA response containing the dedicated RA preamble RA′, in order to request UL data transmission. Otherwise, the UE  110  initiates a RA procedure to request UL data transmission. 
     Additionally, as mentioned above, the UE  110  uses the counter  1103  to count a number of time(s) of transmission of a RA preamble. Once the previous RA procedure fails and the number of transmission time(s) reaches a maximum value, the UE decides whether to try to connect to the eNB and then resets the counter to zero. Please refer to  FIG. 7 .  FIG. 7  is a sequential diagram illustrating the interaction between the UE  110  and eNB  105   a  according to a third example of this embodiment. As shown in  FIG. 7 , the counter  1103  of the UE  110  has reached 2 before the broadcasted RA preamble RA 1  is transmitted at time t 0 , so the counter  1103  counts to 3 after the broadcasted RA preamble RA 1  is transmitted; this RA procedure of transmitting the broadcasted RA preamble RA 1  at time t 0  is named as a first RA procedure herein. After sending the broadcasted RA preamble RA 1 , the control unit  1102  sets a period of a TTI window defined by a beginning time t 1  and an end time t 2 . In this scenario, the broadcasted RA preamble RA 1  of the first RA procedure is not received by the eNB  105   a  successfully, and the eNB  105   a  assigns the dedicated RA identifier ID′ to the UE  110  during the first RA procedure. Thus, the UE detects the failure of the first RA procedure due to that no RA response containing the broadcasted RA preamble RA 1  is received within the TTI window from the beginning time t 1  to the end time t 2 , and the UE  110  is arranged to transmit the dedicated RA preamble RA′ including the dedicated RA identifier ID′ to the eNB  105   a  at time t′, in order to initiate a second RA procedure. The UE  110  is designed to reset the counter  1103  to zero in response to a receipt of the assigned dedicated RA identifier ID′; actually, the counter  1103  is reset when the assignment message of the dedicated RA identifier ID′ is received before the end time RA_WINDOW_END of the TTI window (i.e. time t 2 ). That is, the counter  1103  is reset before a failure of the first RA procedure. It is expected that the number of transmission times using the dedicated RA preamble RA′ should reach the maximum value if a final result indicates that the UE  110  cannot connect to the eNB  105   a , when the dedicated RA identifier ID′ is assigned to the UE  110  by the eNB  105   a . Usually, when assigning the dedicated RA identifier ID′to the UE  110 , the eNB  105   a  starts a dedicated preamble validity timer. The eNB  105   a  expects that the UE  110  should try to connect to the eNB  105   a  with the dedicated RA preamble RA′ until the dedicated preamble validity timer expires. Therefore, the control unit  1102  of the UE  110  resets the counter  1103  once a dedicated RA identifier is received. This can avoid a UE transmitting a dedicated RA preamble at a time (for initiating an RA procedure) and then deciding to not try to connect with an eNB if this RA procedure fails. For instance, suppose that the maximum value is set as 4. If the UE  110  did not reset the counter  1103  when receiving the dedicated RA identifier ID′ and the second RA procedure failed, the UE  110  might not try to initiate another RA procedure for re-transmitting the dedicated RA preamble RA′ to the eNB  105   a.    
     In addition, in this embodiment, the control module  1052  of the eNB  105   a  can appropriately stop the dedicated preamble validity timer and release the dedicated RA identifier ID′ allocated to the UE  110  under certain conditions. Please refer to  FIG. 8   FIG. 8  is a sequential diagram illustrating the interaction between the UE  110  and eNB  105   a  according to a fourth example of this embodiment. As shown in  FIG. 8 , the UE  110  transmits a broadcasted RA preamble RA 1  to the eNB  105   a  at time t 0  for initiating a first RA procedure, and the eNB  105   a  assigns a dedicated RA identifier ID′ to the UE  110  during the first RA procedure; however, the assignment message of the dedicated RA identifier ID′ is not successfully received by the UE  110 . When assigning the dedicated RA identifier ID′ to the UE  110  via the PDCCH, the eNB  105   a  starts the dedicated preamble validity timer. In the following, the eNB  105   a  replies to the broadcasted RA preamble RA 1  by sending an RA response corresponding to RA 1  to the UE  110 , and then the UE  110  transmits a scheduled transmission message including the C_RNTI to the eNB  105   a  after receiving this RA response. The eNB  105   a  transmits a UL resource assignment message to the UE  110  via the PDCCH once the scheduled transmission message is received. When the UE  110  successfully receives the UL resource assignment message, the contention resolution procedure succeeds and then the UE  110  transmits UL data such as medium access control protocol data unit(s) (MAC PDU) to the eNB  105   a . In this scenario, the eNB  105   a  cannot be actively aware that the assignment message of the allocated dedicated RA identifier ID′ is not successfully received by the UE  110 . The eNB  105   a  can be designed to release the system resource (i.e. the dedicated RA identifier ID′) early and may allocate the system resource to another UE if the eNB  105   a  knows that the synchronization between the UE  110  and eNB  105   a  is established. In the fourth example, the eNB  105   a  is arranged to stop the dedicated preamble validity timer and release the dedicated RA identifier ID′when successfully receiving a signal from the UE  110 . For example, when successfully receiving the scheduled transmission message including the C_RNTI transmitted by the UE  110  at time t 1 , the eNB  105   a  can be aware that the RA procedure associated with RA 1  succeeds and the synchronization between the UE  110  and the eNB  105   a  is established. Accordingly, the eNB  105   a  can stop the dedicated preamble validity timer and release the dedicated RA identifier ID′, when receiving the scheduled transmission message sent from the UE  110 . In addition, the eNB  105   a  (also?) can be arranged to stop the dedicated preamble validity timer and release the dedicated RA identifier ID′, when successfully receiving a MAC PDU sent from the UE  110  at time t 2 . This MAC PDU can be the first MAC PDU or the other MAC PDU received by the eNB  105   a  after the C_RNTI is received. In other words, the control module  1052  of the eNB  105   a  releases the dedicated RA preamble associated with the dedicated RA identifier ID′ when the C_RNTI or a MAC PDU from the UE  110  is received by the communication module  1051 ; the MAC PDU is received later than the receipt of the C_RNTI. The modifications obey the spirit of the present invention. 
     Moreover, according to an accepted agreement in the 3GPP meeting, when a UE uses a contention preamble (i.e. an RA preamble) and has an C_RNTI, and the random access channel (RACH) is not triggered by a PDCCH order, only a PDCCH information with the C_RNTI containing a UL grant shall be considered as indicating successful contention resolution. That is to say, when the UE uses an RA preamble to perform an RA procedure for sending UL data to an eNB, a contention resolution is considered to be successful only when the UE receives a UL grant from the eNB via the PDCCH. If the UE does not receive the UL grant before the contention resolution timer expires, then the contention resolution fails. Thereafter, the UE may initiate an RA procedure once again to try to transmit UL data; however, the UL data transmission has been delayed. 
     In order to solve this problem, the UE  110  of the above-mentioned embodiment has an additional design. Please refer to  FIG. 9 , which illustrates a sequential diagram showing an interaction between the UE  110  and the eNB  105   a  shown in  FIG. 2  according to a fifth example of this embodiment. As shown in  FIG. 9 , the UE  110  is in the RRC_connected state but not synchronized with the eNB  105   a  on uplink; the UE  110  has UL data to be transmitted the eNB  105   a . DL data arrival occurs at the eNB  105   a  almost at the same time. In this case, since the eNB  105   a  does not assign any dedicated RA identifier to the UE  110 , the control unit  1102  of the UE  110  controls the communication unit  1101  to transmit the broadcasted RA preamble RA 1  to the eNB  105   a  for initiating a first RA procedure to achieve the UL data transmission. For the eNB  105   a , the RA preamble RA 1 , however, may be considered an RA preamble regarding DL data transmission but not for the UL data transmission. Therefore, the communication unit  1101  of the UE  110  transmits a scheduled transmission message including the C_RNTI to the UE  110  when an RA response from the eNB  105   a  is received and then starts a contention resolution timer. The eNB  105   a  may send control messages including the C_RNTI and a DL grant via the PDCCH and then sends DL data (i.e. MAC PDU) to the UE  110 . Once the UE  110  receives the DL data, the UE  110  may acknowledge a Hybrid ARQ acknowledgement (ACK)/negative acknowledgement (NACK) message to the eNB  105   a  via the physical uplink control channel (PUCCH). In addition to the Hybrid ARQ ACK/NACK message, if the PUCCH for SR is configured, the control unit  1102  of the UE  110  is arranged to control the communication unit  1101  to transmit an SR message from the UE  110  to the eNB  105   a  via the PUCCH at the same time, in order to notify the eNB  105   a  that the UE  110  has UL data to be transmitted (i.e. the RA preamble is used for UL data transmission). In other words, the UE  110  transmits the SR message to the eNB  105   a  before the contention resolution timer expires, and the SR message is transmitted with an ACK message or a NACK message. It should be noted that the PUCCH is available in this case since the UL synchronization between the UE  110  and eNB  105   a  is established after the C_RNTI via PDCCH is successfully received by the UE  110 . Additionally, in this embodiment, the UE  110  is designed to keep transmitting the SR message to the eNB  105   a  when the contention resolution timer is running. That is, the UE  110  sends the SR message as long as the UE  110  itself desires to acknowledge the Hybrid ARQ ACK/NACK to the eNB  105   a  and the contention resolution timer does not expire yet; however, this design is not intended to be a limitation of the present invention. In other words, the UE  110  in other embodiments can be arranged to send the SR message at a time or at many times, to notify the eNB  105  that it has data to be transmitted. Please note that any modification of sending a message to notify the eNB  105   a  when the contention resolution timer is running should obey the spirit of the present invention. Note that if the UE  110  was not arranged to send the SR message, the eNB  105   a  may be unable to know that the RA preamble RA 1  is used for UL data transmission but not for DL data transmission before the contention resolution timer expires. 
     Furthermore, at a point of view of the eNB  105   a , an alternative design to solve the above problem is proposed for the eNB  105   a  to distinguish an RA procedure for UL data transmission or an RA procedure for DL data transmission. The eNB  105   a  considers that an RA preamble is used for the UL data transmission if the RA preamble is received by the eNB  105   a  within n subframes after the eNB  105   a  sends the control message including the C_RNTI and a DL data arrival via the PDCCH. That is, the control module  1052  of the eNB  105   a  is arranged to determine whether the RA preamble is for the UL data transmission. Once the RA preamble is considered as an RA preamble for the UL data transmission, the control module  1051  is arranged to control the communication module  1051  to transmit a control message including a UL grant from the eNB  105   a  to the UE  110  via the PDCCH. Therefore, the UL data transmission will not be delayed. The number n is determined by a sum of the DL transmission time via the PDCCH, the processing time of the UE  110 , the delay time due to the physical random access channel (PRACH) allocation, and the UL transmission time via the random access channel (RACH). The delay time due to the PRACH allocation is indicative of that the UE  110  may still wait for a time t 0  send an RA preamble after receiving the control message including a DL data arrival via the PDCCH. This is because the eNB  105   a  specifies that a UE such as  110  can send an RA preamble to perform an RA procedure only at a particular subframe in 10 mini-seconds. Note that the example of 10 mini-seconds is only used for illustrative purposes, and is not meant to be a limitation of the present invention. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.