Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation application of application Ser. No. 11/161,356, filed Aug. 1, 2005, which claims the benefit of U.S. Provisional Application No. 60/522,324, filed on Sep. 15, 2004, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to wireless communications. More particularly, the present invention relates to an enhanced polling mechanism and device in a 3GPP wireless communications system. 
         [0004]    2. Description of the Prior Art 
         [0005]    The surge in public demand for wireless communication devices has placed pressure upon industry to develop increasingly sophisticated communications standards. The 3 rd  Generation Partnership Project (3GPP™) is an example of such a new communications protocol. The 3 rd  Generation Partnership Project (3GPP) specification, 25.322 V6.1.0 (2004-06) Radio Link Control (RLC) protocol specification (referred to hereinafter as 3GPP TS 25.322), included herein by reference, provides a technical description of a Universal Mobile Telecommunications System (UMTS), and data transmission control protocols thereof. 
         [0006]    These standards utilize a three-layer approach to communications. Please refer to  FIG. 1 .  FIG. 1  is a block diagram of three layers in such a communications protocol. In a typical wireless environment, a first station  10  is in wireless communications with one or more second stations  20 . An application  13  on the first station  10  composes a message  11  and has it delivered to the second station  20  by passing the message  11  to a layer-3 interface  12 . The layer-3 interface  12  may also generate some layer-3 signaling messages  14  for the purpose of controlling layer-3 operations. The layer-3 interface  12  delivers either the message  11  or the layer-3 signaling message  14  to a layer-2 interface  16  in the form of layer-2 service data units (SDUs)  15 . The layer-2 SDUs  15  may be of any length. The layer-2 interface  16  composes the SDUs  15  into one or more layer-2 protocol data unit(s) (PDU)  17 . Each layer-2 PDU  17  is of a fixed length, and is delivered to a layer-1 interface  18 . (The required length of PDUs within a given communications system is dictated by the RLC layer of a transmitting station in accordance with above cited reference.) The layer-1 interface  18  is the physical layer, transmitting data to the second station  20 . The transmitted data is received by the layer-1 interface  28  of the second station  20  and reconstructed into one or more PDUs  27 , which is/are passed up to the layer-2 interface  26 . The layer-2 interface  26  receives the PDUs  27  and builds up one or more layer-2 SDU(s)  25  from the PDUs  27 . The layer-2 SDUs  25  are passed up to the layer-3 interface  22 . The layer-3 interface  22 , in turn, converts the layer-2 SDUs  25  back into either a message  21 , which should be identical to the original message  11  that was generated by the application  13  on the first station  10 , or a layer-3 signaling message  24 , which should be identical to the original signaling message  14  generated by the layer-3 interface  12 , and which is then processed by the layer-3 interface  22 . The received message  21  is passed up to an application  23  on the second station  20 . (As a note regarding terminology used throughout this disclosure, a PDU is a data unit that is used by a layer internally to transmit to, and/or receive from, a lower layer, whereas an SDU is a data unit that is passed up to, and/or received from, an upper layer.) 
         [0007]    There are three possible data transmission modes falling under the auspices of the abovementioned protocol specification, transparent mode (TM), acknowledged mode (AM) and unacknowledged mode (UM). As the present invention relates only to AM transmission, the scope of the prior art discussion herein is therefore limited to background relevant to AM transmission. 
         [0008]    Acknowledged Mode transmission is so called because a transmitting station requires acknowledgement from a receiving station, confirming that a message or part of a message has been successfully received. Based upon such information returned from the receiving station, the transmitting station either continues to transmit further packetized data as described above, or retransmits unconfirmed portions of previously transmitted data. The extra effort required to employ this transmission mode carries an additional overhead in terms of transmission airtime and system requirements. The RLC layer of the transmitting station therefore minimizes the impact of the above-mentioned overhead. This is managed by carefully controlling the number of requests made to the receiving station for confirmation messages, i.e. status reports. Status reports are requested, or ‘polled’, by the transmitting station setting a poll bit in the header of a protocol data unit (PDU) to be transmitted. Please refer to  FIG. 2 .  FIG. 2  is a block diagram showing the make-up of an acknowledged mode data (AMD) PDU  30 . The AMD PDU  30  comprises a predefined number of octets, i.e. 8-bit binary words, as each AMD PDU within a given communications system is of a fixed length as mentioned above. The first octet  31  of the AMD PDU  30  is composed of a data/control (D/C) bit  310 , this being used to indicate the PDU type, i.e. either ‘data’ or ‘control’, and the first seven bits of the twelve-bit PDU sequence number (SN)  311 . The second octet  32 , is composed of five further bits of the SN  320 , the poll bit  321 , and the header extension (HE) bits  322 . The twelve-bit SN is used by receiving stations to accurately re-construct original messages from received PDUs, while the HE bits (there are two) are used to indicate whether the following octet, i.e. the third octet  33 , is a data byte or a length indicator (LI) with extension bit. In the example AMD PDU  30  shown, the third octet  33  is an LI  330  with an extension bit  331 ; the LI  330  is used to map the position within the PDU  30  of the last byte of an SDU contained in the data block  35 . More than one LI may be included in an AMD PDU, therefore the extension bit  331 , is included to indicate whether the following octet is a data byte or another LI with extension bit. Hence there may be a number of LIs between the first LI  330  and the last LI  340 . Because each PDU must conform to a predefined length, the PDU  30  may not be foreshortened even if there is insufficient data  35  to completely fill the required number of octets, hence padding  36  is inserted into the remaining octets. 
         [0009]    Of particular relevance is the poll bit  321 , which is used to prompt the receiving station to reply with a status report upon successful receipt of any PDU in which the poll bit is set. Please refer to  FIG. 3 , which shows a message sequence chart representing AMD PDU transfer between a transmitting station  41  and a receiving station  42 , in a communications system  40  utilizing a 3-layer protocol as outlined above. A string of PDUs  400 ˜ 405  are transmitted sequentially from the transmitting station  41  to the receiving station  42 , the last PDU  405  being sent with poll bit set. Upon receiving the PDU  405 , the receiving station  42  responds by transmitting a status report  406  back to the transmitting station  41 . 
         [0010]    The designation of PDUs to be transmitted with poll bit set, is derived from the upper layers of each RLC entity in accordance with the cited protocol specification. The communications systems discussed herein can be configured to trigger a poll when any of the following events occur: 
         [0011]    1) The last PDU in the (first time) transmission buffer is transmitted. 
         [0012]    2) The last PDU in the re-transmission buffer is transmitted. 
         [0013]    3) Upon time-out of a ‘Poll_Timer’ function (triggers a poll function when a predefined period of time has elapsed following the initiation of a poll being sent out). 
         [0014]    4) An ‘Every Poll_PDU’ PDU is transmitted (triggers a poll function each time a predefined number of PDUs have been scheduled for transmission or retransmission). 
         [0015]    5) An ‘Every Poll_SDU’ SDU is transmitted (triggers a poll function each time a predefined number of SDUs have been scheduled for transmission). 
         [0016]    6) Conditions required by the ‘Poll_Window’ function are fulfilled (i.e. a “Window based trigger” is issued, which triggers a poll function when a predefined percentage of a transmission window has been reached). 
         [0017]    7) A predefined time period expires, i.e. a “timer based” function is configured (triggers a poll periodically). 
         [0018]    In addition to the above, the upper layers may configure a timer called ‘Timer_Poll_Prohibit’, which is then used to prohibit the transmission of polls within a predetermined period. If another poll is triggered while polling is prohibited by a current Timer_Poll_Prohibit function, transmission of the poll is delayed until Timer_Poll_Prohibit expires. Even if several polls were triggered while Timer_Poll_Prohibit was active, only one poll is transmitted when Timer_Poll_Prohibit expires. 
         [0019]    The polling process of the prior art set forth by 3GPP TS 25.322 can be summarized as the flow diagram shown in  FIG. 4 : 
         [0020]    Step  1000 : Process starts. 
         [0021]    Step  1001 : The system checks if there is a new PDU to be transmitted. If there is, the process proceeds to Step  1010 . Otherwise, the process proceeds to Step  1002 . 
         [0022]    Step  1002 : The system checks if there is negatively acknowledged PDU to be retransmitted. If there is, the process proceeds to Step  1011 . Otherwise, the process proceeds to Step  1003 . 
         [0023]    Step  1003 : The system checks if a polling function has been triggered. If yes, the process proceeds to Step  1004 . Otherwise, the process terminates via Step  1017 . 
         [0024]    Step  1004 : The system checks if polling is prohibited. If polling is not prohibited, the process proceeds to Step  1005 . Otherwise, the process terminates via Step  1017 . 
         [0025]    Step  1005 : A polling function is activated and the polling bit of the next PDU to be transmitted is set to 1. 
         [0026]    Step  1006 : The system checks if there is no PDU scheduled for transmission or retransmission. If the checking result is yes, the process proceeds to Step  1007 . Otherwise, the process terminates via Step  1017 . 
         [0027]    Step  1007 : The system checks if the polling function checked at Step  1003  was triggered by “Poll timer” or “Timer based”. If yes, the process proceeds to Step  1008 . Otherwise, the process terminates via Step  1017 . 
         [0028]    Step  1008 : The system selects a suitable PDU for retransmission to carry the poll. 
         [0029]    Step  1009 : The system schedules the selected PDU for transmission. The process proceeds to Step  1016 . 
         [0030]    Step  1010 : The system schedules the new PDU for transmission. The process proceeds to Step  1012 . 
         [0031]    Step  1011 : The system schedules the negatively acknowledged (NACKed) PDU for retransmission. 
         [0032]    Step  1012 : The system checks if a polling function has been triggered. If yes, the process proceeds to Step  1013 . Otherwise, the process proceeds to Step  1015 . 
         [0033]    Step  1013 : The system checks if polling is prohibited. If polling is prohibited, the process proceeds to Step  1015 . Otherwise, the process proceeds to Step  1014 . 
         [0034]    Step  1014 : A polling function is activated and the polling bit of the next PDU to be transmitted is set to 1. 
         [0035]    Step  1015 : Polling function is not activated and the polling bit of the next PDU to be transmitted is set to 0. 
         [0036]    Step  1016 : The system submits the PDU to lower layer for transmission. 
         [0037]    Step  1017 : Process ends. 
         [0038]    Please refer to  FIG. 5 , which illustrates the above features via a similar message sequence chart to  FIG. 3 , and retaining like index numbers where appropriate. Assume that transmitting station configuration is determined by upper RLC layers such that the following five poll triggers are enabled: 
         [0039]    (1) “Last PDU in buffer (for first time transmission)”; 
         [0040]    (2) “Last PDU in Retransmission buffer”; 
         [0041]    (3) “Poll timer” (with Timer_Poll=200 ms); 
         [0042]    (4) “Every Poll_PDU PDU” (with Poll_PDU=4); and 
         [0043]    (5) “Every Poll_SDU SDU” (with Poll_SDU=4). 
         [0044]    Assume also that the ‘Window based’ trigger and ‘Timer based’ trigger are disabled, that the poll prohibit function is configured with Timer_Poll_Prohibit=250 ms, that one SDU is requested for transmission by an upper layer and an RLC transmission confirmation is requested by the upper layer when transmission of the SDU is positively acknowledged, and that the SDU is segmented into six PDUs. 
         [0045]    The transmitting station  41  will transmit the six PDUs  400 ˜ 405  (having sequential SNs: 0, 1, 2, 3, 4 and 5 for example) in sequence. When scheduling the fourth PDU  403  (SN=3) for transmission, the “Every Poll_PDU PDU” poll trigger will be activated and poll bit of the fourth PDU consequently set. The Timer_Poll 45 (200 ms) and Timer_Poll_Prohibit  43  (250 ms) functions are commenced simultaneously when PDU  403  (SN=3) is transmitted via lower layers. The transmitter continues to schedule the fifth (SN=4) and sixth (SN=5) PDUs,  404  &amp;  405  respectively, for transmission. When PDU  405  (SN=5) is transmitted, the “Last PDU in buffer” trigger is activated since there are no more PDUs to be transmitted, however, the poll trigger  48  is delayed because the poll prohibit function (Timer_Poll_Prohibit), according to the prior art, is still in effect, hence the sixth and last PDU  405  is transmitted without its poll bit set. Suppose that the third PDU  402  (SN=2) is lost during radio transmission. When the receiving station receives the fourth PDU (which has its poll bit set), the receiving station accordingly transmits a status report  406 , in this case to positively acknowledge that PDUs having SN values 0, 1 and 3, i.e. PDUs  400 ,  401  and  403  have been received successfully, but negatively acknowledging PDU  402  (SN=2). Suppose that the status report  406  is lost during radio transmission. 
         [0046]    At a time  46 , the Timer_Poll function  45  completes its countdown, however, because Timer_Poll_Prohibit  43  is still active, a poll trigger  49  that would otherwise be issued by the Timer_Poll function  45  is also delayed. When Timer_Poll_Prohibit  43  expires at a time  44 , even though there are two active delayed poll triggers ( 48  and  49 ), only one poll is issued and sent with a PDU  402   a , which is a re-transmission of a selected PDU  400  (SN=0) that has not yet been acknowledged yet (because the status report is lost). Upon receiving the PDU  402   a , the receiving station  42  responds by transmitting a status report  407  to the transmitting station  41  to positively acknowledge PDUs having SN 0, 1, 3, 4 and 5 and to negatively acknowledge PDU having SN 2. The prior art method can then retransmit the PDU  402  (SN=2) with its poll bit set (not shown in  FIG. 5 ) and proceed smoothly in this case. 
         [0047]    In  FIG. 5 , wherein there were no negatively acknowledged PDUs nor further SDUs requiring transmission and polling is not prohibited after Timer_Poll_Prohibit expires, the ‘timer based’ initiated poll would be sent with a re-transmission of a suitable PDU as described in Steps  1008 ,  1009  and  1016  in  FIG. 4 . The suitable PDU can be a PDU with SN=VT(S)−1, i.e. the sequentially last PDU that had been transmitted at least once (for example, PDU  405  in  FIG. 5 ). VT(S) is a ‘send state’ variable that is maintained by the transmitting station; it is incremented (by one) each time a PDU is transmitted for the first time, however, it is not incremented if a PDU is re-transmitted. 
         [0048]    In addition to the SN=VT(S)−1 PDU, in cases where “Configured_TX_Window_Size” is less than 2048, i.e. half the amount of different numbers that can be represented by a 12-bit SN, any PDU that has not yet been acknowledged (for example, PDUs  400 ,  401 ,  402 ,  403  and  404  in  FIG. 5 ) can be selected as the suitable PDU and scheduled for retransmission in order to carry the poll. ‘Transmission window size’ relates to parameters for the maximum number of PDUs, (in effect, a window size), that the transmitting station can transmit (and that the receiving station can receive) without receiving some form of status message from the receiving station. Again, the upper layers configure this parameter. 
         [0049]    Unfortunately, there are situations allowable in the prior art whereby ‘deadlock’ may arise. Please consider the following example, which assumes the same initial conditions as the example shown by  FIG. 5  above, i.e. that a transmitter is configured by upper layers to enable the following five poll triggers: 
         [0050]    (1) “Last PDU in buffer (for first time transmission)”; 
         [0051]    (2) “Last PDU in Retransmission buffer”; 
         [0052]    (3) “Poll timer” (with Timer_Poll=200 ms); 
         [0053]    (4) “Every Poll_PDU PDU” (with Poll_PDU=4); and 
         [0054]    (5) “Every Poll_SDU SDU” (with Poll_SDU=4). 
         [0055]    Again, as for the example shown by  FIG. 5  above, assume also that the ‘Window based’ trigger and ‘Timer based’ trigger are disabled, that the poll prohibit function is configured with Timer_Poll_Prohibit=250 ms, that one SDU is requested for transmission by an upper layer and an RLC transmission confirmation is requested by the upper layer when transmission of the SDU is positively acknowledged, and that the SDU is segmented into six PDUs. 
         [0056]    Please refer to  FIG. 6 , which illustrates the present example. The transactions between the transmitting station  41  and the receiving station  42  are identical to the example shown by  FIG. 5  regarding the initial transmission of PDUs  400 ˜ 405 , except that in this example the status report  406  positively acknowledges PDUs  400 ˜ 403  (SNs 0˜3) and the transmitting station  41  receives the status report successfully. According to the prior art, this has the affect of cancelling the Timer_Poll function  45  at a time  47 , and although a “Last PDU in buffer” poll trigger delayed until a time  44 , no PDU will be scheduled for transmission/re-transmission. This is because, in this case, there are no more SDUs (and hence, no more PDUs) to be transmitted, no negatively acknowledged PDUs to be re-transmitted, and a PDU with SN=VT(S)−1 may only be scheduled when a poll delayed by Timer_Poll_Prohibit is initiated by ‘poll timer’ or ‘timer based’ functions according to Steps  1006  and  1007  in  FIG. 4 . As the Timer_Poll function  45  is cancelled and no timer based function is configured, these conditions can not be met, and hence according to the prior art set forth by 3GPP TS 25.322 or by  FIG. 4  above, the transmitting station  41  will remain idle following receipt of the abovementioned status report  406 , without scheduling any PDUs for transmission or retransmission, i.e. there is no further traffic with which to transmit a poll. Without a status report acknowledging the successful receipt of the fifth and sixth PDUs, RLC transmission confirmation cannot be sent to the upper layers, consequently RLC layers at both the transmitter and the receiver stations cannot proceed to any further operations, i.e. the RLC layers are deadlocked. 
         [0057]    There is a need then for a method which, when implemented in a 3GPP radio communications system, will circumvent the abovementioned RLC layer deadlock situation. 
       SUMMARY OF THE INVENTION 
       [0058]    A method of polling in a wireless communications system includes prohibiting polling within a first predetermined period and triggering a poll function while polling is prohibited. After the first predetermined period has expired the method determines that there are no protocol data units (PDUs) scheduled for transmission or re-transmission and that there is at least a transmitted PDU that is not acknowledged yet, and selects a PDU to schedule for re-transmission to fulfill the triggered poll function. The trigger to trigger a polling function includes a trigger that triggers a poll function when a last PDU in a buffer for first-time transmission is scheduled for transmission, a trigger that triggers a poll function when a last PDU in a buffer for re-transmission is scheduled for re-transmission, a trigger that triggers a poll function when every first predetermined number of PDUs are scheduled for transmission or re-transmission, a trigger that triggers a poll function when every second predetermined number of service data units (SDUs) are scheduled for transmission, and a trigger that triggers a poll function when a predetermined percentage of a transmission window is reached. 
         [0059]    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 
         [0060]      FIG. 1  is a block diagram of the three layers typical of a communications system according to the 3 rd  Generation Partnership Project (3GPP™) communications protocol. 
           [0061]      FIG. 2  is a block diagram showing an example of an acknowledged mode data protocol data unit (AMD PDU) according to the prior art. 
           [0062]      FIG. 3  is a message sequence chart representing AMD PDU transfer between a transmitting station and a receiving station according to the prior art. 
           [0063]      FIG. 4  is a flow diagram of the polling process according to the prior art. 
           [0064]      FIG. 5  is a message sequence chart representing AMD PDU transfer between a transmitting station and a receiving station according to the prior art. 
           [0065]      FIG. 6  is a message sequence chart representing an example of deadlock in a wireless communications system according to the prior art. 
           [0066]      FIG. 7  is a message sequence chart representing a preferred embodiment method of AMD PDU transfer according to the present invention. 
           [0067]      FIG. 8  is a message sequence chart representing a preferred embodiment method handling a lost poll situation according to the present invention. 
           [0068]      FIG. 9  is a flow diagram of a preferred embodiment of the present invention method. 
       
    
    
     DETAILED DESCRIPTION 
       [0069]    In order to overcome the prior art problems described above, a preferred embodiment method of the present invention is described by example below. 
         [0070]    Assuming the configuration of the transmitting and the receiving stations is the same as that given in the prior art examples illustrated by  FIGS. 5 and 6  above, i.e. the transmitter is configured by upper layers to enable the following five poll triggers: 
         [0071]    (1) “Last PDU in buffer (for first time transmission)”, 
         [0072]    (2) “Last PDU in Retransmission buffer”, 
         [0073]    (3) “Poll timer” (with Timer_Poll=200 ms), 
         [0074]    (4) “Every Poll_PDU PDU” (with Poll_PDU=4), and 
         [0075]    (5) “Every Poll_SDU SDU” (with Poll_SDU=4). 
         [0076]    And also assuming that: ‘window based’ triggers and ‘timer based’ triggers are disabled, the poll prohibit function is configured with Timer_Poll_Prohibit=250 ms, one SDU is requested for transmission by an upper layer and an RLC transmission confirmation is requested by the upper layer when transmission of the SDU is positively acknowledged, and that the SDU is again segmented into six PDUs (having sequential SNs: 0, 1, 2, 3, 4 and 5). 
         [0077]    As in the prior art example, in the example illustrated by  FIG. 7 , the receiving station  72  successfully receives all six PDUs  700 ˜ 705  (SN=0˜5), but also sends a status PDU  706  positively acknowledging the PDUs having SNs=0˜3, the fourth PDU  703  (SN=3) having been received with a poll. The transmitting station  71  receives this status report  706  successfully at a time  77  before the current instance of the Timer_Poll function  75  expires, thereby canceling the Timer_Poll function  75 , thus no poll is issued at the time  76  when the Timer_Poll function  75  countdown was due to expire. However, when the Timer_Poll_Prohibit function  73  expires, the transmitting station  71  finds that a delayed poll  78  (having been triggered by a “Last PDU in buffer for first-time transmission” trigger when PDU  705  (SN=5) was scheduled for transmission, but not sent because the Timer_Poll_Prohibit function  73  was still active) is awaiting transmission. Again, there are no more PDUs scheduled for transmission or re-transmission, and under the prior art scheme, no PDU can be scheduled because the relevant poll was not triggered by a “Poll Timer” or “Timer based” function (Step  1007  in  FIG. 4 ). Note also that, because the existing Timer_Poll function  75  is canceled by the status report  706  positively acknowledging the first four PDUs  700 ˜ 703 , there is no likelihood of a suitable poll trigger occurring due to the “Poll timer” function. Hence, in the method of the present invention, upon expiration of the Timer_Poll_Prohibit function  73 , PDU status is checked, i.e. whether there is at least one PDU that has been transmitted but not acknowledged by a status PDU. In this example, it can be seen that since transmitted PDUs  704  and  705  have not been acknowledged, the test will be positive and, according to the present invention method, the transmitting station  71  will re-transmit a suitable PDU  705   a , which can be the last PDU  705  (SN=5), this being the current SN=VT(S)−1 PDU with poll bit set. When the receiving station  72  receives the re-transmission of the last PDU  705  (SN=5), i.e., the PDU  705   a , this time including a poll, the receiving station  72  will send a status report  707  to positively acknowledge the successful receipt of all PDUs up to and including SN=5. Upon receiving the status report  707 , the transmitting station  71  can send confirmation of SDU receipt to the upper layer (not shown in  FIG. 7 ) so that the upper layer can proceed to subsequent processes, thus avoiding the deadlock situation inevitable under the prior art scheme. 
         [0078]    Otherwise, as may be the case outside of the above example, if the check is negative because all transmitted PDUs have been acknowledged, then no PDU will be transmitted; this feature is capable of circumventing the transmission of superfluous polls as described below. 
         [0079]    If the receiving station  72  does not receive the retransmitted PDU  705   a  (SN=5) with poll as illustrated by  FIG. 8 , or the status report  707  in  FIG. 7  gets lost during radio transmission (not shown in  FIG. 8 ), the Timer Poll mechanism will ensure that a poll will be sent again by retransmission of a suitable (e.g., SN=VT(S)−1 if no new traffic is scheduled) PDU  705   b  when a current Timer_Poll function  75   a  expires. In the case illustrated by  FIG. 8 , this would be by retransmitting PDU  705  with poll bit set, and hence prompting the issuance of status report PDU  707   a . Thus, employing the method of the current invention can circumvent the deadlock shown to occur when the prior art method is applied to such a scenario and can also circumvent the transmission of superfluous polls. 
         [0080]    The present invention method can be implemented as software or firmware in a wireless communications system, incorporated in the architecture of, for example, a monolithic communications microchip for use in the same, or realized in the structure of supporting discrete or programmable logic device(s). The present invention method can be summarized in the following process ( FIG. 9  refers): 
         [0081]    In  FIG. 9 , Step  1006  in  FIG. 4  is replaced by  1006   a  and there is no Step  1007  shown in  FIG. 4 . Thus, the process of this invention proceeds from Step  1006   a  to Step  1008  when the checking result in Step  1006   a  is yes. In other words, if the polling function checked at Step  1003  is triggered by polling functions other than “Poll timer” and “Timer based”, the system still retransmits a suitable PDU to carry the poll bit. Only Step  1006   a  is described below since all the other steps are exactly the same as those in  FIG. 4 . 
         [0082]    Step  1006   a : The system checks if there is no PDU scheduled for transmission or retransmission and there is a transmitted PDU that is not acknowledged (neither positively nor negatively) yet. If the checking result is yes, the process proceeds to Step  1008 . Otherwise, the process terminates via Step  1017 . 
         [0083]    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. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

Technology Category: 5