Abstract:
A method for handling transmission errors in a hybrid automatic retransmission request transmitter, or a HARQ transmitter, of a wireless communications system includes creating a counter corresponding to a first packet when a first acknowledgement, called ACK, with respect to the first packet is received, and sending a local ACK to an automatic retransmission request transmitter, or an ARQ transmitter, when the counter reaches a predetermined maximum value.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/818,530, filed on Jul. 6, 2006 and entitled “Method and Apparatus for HARQ NACK to ACK Error Detection”, the contents of which are incorporated herein by reference. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The preset invention relates to methods and related communications devices for handling transmission errors in a wireless communications system, and more particularly to methods of handling transmission errors in a NACK-to-ACK error mechanism of a HARQ process in a wireless communications system and related communications devices that can avoid packet loss and reduce transmission delay of upper-layer packets. 
         [0004]    2. Description of the Prior Art 
         [0005]    The third generation mobile telecommunications system (called 3G system) provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission, and also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. 
         [0006]    Long Term Evolution wireless communications system (LTE system), an advanced high-speed wireless communications system established upon the 3G mobile telecommunications system, supports only packet-switched transmission, and tends to combine Radio Link Control (RLC) layer and Medium Access Control (MAC) layer into the same communication entity, so that the system structure becomes simple. 
         [0007]    In the 3G system, MAC entity provides a function of Hybrid Automatic Retransmission Request (HARQ), which is a technology combining Feed-forward Error Correction (FEC) and ARQ methods. In addition, RLC entity can apply specified mechanisms, such as sequence number checking, to provide an ARQ function, which has low retransmission efficiency due to complex operations, and is also called outer-ARQ. 
         [0008]    In the prior art, both outer-ARQ and HARQ will be used for LTE system. To decrease complexity of outer-ARQ to enhance retransmission efficiency, the prior art provides a method using the HARQ to assist the outer-ARQ. 
         [0009]    The method reveals that an HARQ transmitter provides local acknowledgement and local negative acknowledgement signals, local ACK/local NACK, to an ARQ transmitter upon different events. Local NACK is generated by the HARQ transmitter upon the following two events: 
         [0010]    1. When the HARQ transmitter gives up the HARQ transmission due to the maximum retransmission limit. 
         [0011]    2. When a NACK-to-ACK error is reported to the HARQ transmitter. In addition, local ACK is generated when none of above two events for an ARQ packet has taken place during a predefined time interval. The HARQ transmitter starts to count the predefined time interval while receiving an ACK. Thus, the predefined time interval is seen as a guard period to protect the HARQ process against the HARQ feedback transmission errors, namely NACK-to-ACK errors. 
         [0012]    According to the method of the prior art, the ARQ operation becomes simple, lost packets are detected more quickly, and the amount of feedback signaling is smaller. However, the method may miss the NACK-to-ACK error or misinterpret a legitimate transmission into the NACK-to-ACK error. 
         [0013]    In a HARQ process, the HARQ receiver assumes a NACK-to-ACK error when receiving a new transmission while the HARQ receiver expects a retransmission. This implies that after reporting an ACK, the HARQ receiver can determine if there is the NACK-to-ACK error until the next transmission packet is established by the HARQ transmitter and arrives at the HARQ receiver. However, in certain situations, such as heavy traffic load and bad radio condition of a cell, data transmission in queue due to QoS, or occupied buffer status of the HARQ transmitter, the next transmission packet may travel for more than the predefined time interval used in the prior art. In such a situation, even if the HARQ receiver determines a NACK-to-ACK error occurs, the HARQ transmitter has been sent a local ACK to the ARQ transmitter due to no NACK-to-ACK error reported during the predefined time interval. Therefore, the method to set the predefined time interval right after the HARQ transmitter receives an ACK can miss the NACK-to-ACK error due to the insufficient time interval. A solution is to lengthen the time interval. However, setting a long time interval for reducing the missing rate will delay the local ACK report. 
         [0014]    As known from the above, the HARQ receiver assumes a NACK-to-ACK error when receiving a new transmission while the HARQ receiver expects a retransmission. However, the new transmission may be established due to giving up retransmission of a precious packet by the HARQ transmitter. The reason to giving up retransmission is that the HARQ receives a NACK associated with the previous packet and besides the maximum number of retransmission is reached. As a result, the result of the simple NACK-to-ACK error detection is incorrect. To avoid this situation so as to enhance the NACK-to-ACK error detection mechanism, the prior art defines a control bit carrying a cause value indicating the cause of the previous HARQ termination associated with each new transmission. For example, the cause value ‘0’ means the previous HARQ termination is because of ACK reception, and the cause value ‘1’ means the previous HARQ termination is not because of ACK reception, such as maximum retransmission number limit or schedule preemption. The schedule preemption is that a high-priority new transmission is allowed to preempt the transmission opportunity from a low-priority retransmission in the HARQ process. With indication of the cause value, the HARQ receiver can accurately determine whether a NACK-to-ACK error occurs or not. A misinterpreted NACK-to-ACK error due to maximum retransmission number limit or preemption can be avoided. Please be reminded that control signaling is expensive in terms of radio resources and thus should be kept on a minimal level in order not to affect system capacity too much. 
         [0015]    Instead of using the control signal of the cause value, the prior art proposes a method in which the HARQ receiver checks the maximum retransmission number by itself and thereby does not react with an outer ARQ feedback if the maximum retransmission number is reached and the related packet is failed to receive. The method is applied to a system in which a synchronous HARQ protocol is used and the maximum retransmission number is known at both HARQ transmitter and receiver. In this method of the prior art, if a NACK-to-ACK error occurs at the time when the maximum retransmission number is reached, the HARQ will not report the NACK-to-ACK error. On the other hand, the HARQ confirms the ACK due to no NACK-to-ACK error report and subsequently establishes a new transmission, resulting in packet loss. In addition, the method cannot cover a situation of schedule preemption supported in the HARQ transmitter side. Please be reminded that the schedule preemption allows a low-priority retransmission opportunity to be replaced by a high-priority new transmission. Thus, if a new transmission preempts an on-going retransmission, the HARQ receiver will report a NACK-to-ACK error due to the new transmission which is illegitimate to the HARQ receiver. 
       SUMMARY OF THE INVENTION 
       [0016]    Therefore, the present invention provides methods of handling transmission errors in a HARQ process in a wireless communications system and related communications devices that can avoid sending local ACKs mistakenly or missing NACK-to-ACK errors. 
         [0017]    The present invention discloses a method of handling transmission errors in a hybrid automatic retransmission request (HARQ) transmitter of a wireless communications system. The method includes creating a counter corresponding to a first packet when a first acknowledgement (ACK) related to the first packet is received and sending a local ACK to an ARQ transmitter when the counter reaches a maximum value. 
         [0018]    The present invention discloses a communications device of a wireless communications system utilized for accurately handling transmission errors in a HARQ process. The communications device includes a control circuit, a central processing unit and a memory. The control circuit realizes functions of the communications device. The central processing unit is installed in the control circuit and is used for executing a program code to operate the control circuit. The memory is coupled to the central processing unit and is used for storing the program code. The program code includes establishing a counter corresponding to a first packet when a first ACK related to the first packet is received; and sending a local ACK to an ARQ transmitter when the counter reaches a maximum value. 
         [0019]    The present invention discloses a method of handling transmission errors in a HARQ transmitter of a wireless communications system. The method includes receiving a first ACK from a HARQ receiver, where the first ACK is related to a first packet; creating a timer corresponding to the first packet when a second packet following the first packet is established; and sending a local ACK to an ARQ transmitter when the timer reaches at a predefined time. 
         [0020]    The present invention discloses a communications device of a wireless communications system utilized for accurately handling transmission errors in a HARQ process. The communications device includes a control circuit, a central processing unit and a memory. The control circuit realizes functions of the communications device. The central processing unit is installed in the control circuit and is used for executing a program code to operate the control circuit. The memory is coupled to the central processing unit and is used for storing the program code. The program code includes receiving a first ACK from a HARQ receiver, where the first ACK is related to a first packet; creating a timer corresponding to the first packet when a second packet following the first packet is established; and sending a local ACK to an ARQ transmitter when the timer reaches at a predefined time. 
         [0021]    The present invention discloses a method of handling transmission errors in a HARQ transmitter of a wireless communications system. The method includes creating a counter corresponding to a first packet when at least an event of plural events occurs; ignoring a NACK-to-ACK error report related to the first packet and deleting the counter when a report signal and the NACK-to-ACK error report are received; deleting the counter when the report signal is received and the NACK-to-ACK error report is not received; and deleting the counter when the counter reaches a maximum value. 
         [0022]    The present invention discloses a communications device of a wireless communications system utilized for accurately handling transmission errors in a HARQ process. The communications device includes a control circuit, a central processing unit and a memory. The control circuit realizes functions of the communications device. The central processing unit is installed in the control circuit and is used for executing a program code to operate the control circuit. The memory is coupled to the central processing unit and is used for storing the program code. The program code includes creating a counter corresponding to a first packet when at least an event of plural events occurs; ignoring a NACK-to-ACK error report related to the first packet and deleting the counter when a report signal and the NACK-to-ACK error report are received; deleting the counter when the report signal is received and the NACK-to-ACK-error report is not received; and deleting the counter when the counter reaches a maximum value. 
         [0023]    The present invention discloses a method of handling transmission errors in a HARQ transmitter of a wireless communications system. The method includes creating a timer corresponding to a first packet if at least an event of plural events occurs when a second packet following the first packet is established; ignoring a NACK-to-ACK error report related to the first packet and deleting the timer when a report signal and the NACK-to-ACK error report are received; deleting the timer when the report signal is received and the NACK-to-ACK error report is not received; and deleting the timer when the timer reaches at a predefined time. 
         [0024]    The present invention discloses a communications device of a wireless communications system utilized for accurately handling transmission errors in a HARQ process. The communications device includes a control circuit, a central processing unit and a memory. The control circuit realizes functions of the communications device. The central processing unit is installed in the control circuit and is used for executing a program code to operate the control circuit. The memory is coupled to the central processing unit and is used for storing the program code. The program code includes creating a timer corresponding to a first packet if at least an event of plural events occurs when a second packet following the first packet is established; ignoring a NACK-to-ACK error report related to the first packet and deleting the timer when a report signal and the NACK-to-ACK error report are received; deleting the timer when the report signal is received and the NACK-to-ACK error report is not received; and deleting the timer when the timer reaches at a predefined time. 
         [0025]    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 
         [0026]      FIG. 1  is a functional block diagram of a communications device. 
           [0027]      FIG. 2  is a diagram of the program code shown in  FIG. 1 . 
           [0028]      FIGS. 3-8  are flowchart diagrams of processes according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Please refer to  FIG. 1 , which is a functional block diagram of a communications device  100 . For the sake of brevity,  FIG. 1  only shows an input device  102 , an output device  104 , a control circuit  106 , a central processing unit (CPU)  108 , a memory  110 , a program code  112 , and a transceiver  114  of the communications device  100 . In the communications device  100 , the control circuit  106  executes the program code  112  in the memory  110  through the CPU  108 , thereby controlling an operation of the communications device  100 . The communications device  100  can receive signals input by a user through the input device  102 , such as a keyboard, and can output images and sounds through the output device  104 , such as a monitor or speakers. The transceiver  114  is used to receive and transmit wireless signals, delivering received signals to the control circuit  106 , and outputting signals generated by the control circuit  106  wirelessly. From a perspective of a communications protocol framework, the transceiver  114  can be seen as a portion of Layer  1 , and the control circuit  106  can be utilized to realize functions of Layer  2  and Layer  3 . Preferably, the communications device  100  is utilized in a third generation (3G) mobile communications system. 
         [0030]    Please continue to refer to  FIG. 2 .  FIG. 2  is a diagram of the program code  112  shown in  FIG. 1 . The program code  112  includes an application layer  200 , a Layer  3   202 , and a Layer  2   206 , and is coupled to a Layer  1   218 . The Layer  2   206  comprises two sub-layers: a radio link control (RLC) entity  224  and a media access control (MAC) entity  226 . A primary function of the RLC entity  224  is providing segmentation, reassembly, concatenation, padding, retransmission, sequence check, and duplication detection on transmitted data or control instructions based on different transmission quality requirements. The MAC entity  226  can match packets received from different logic channels of the RLC entity  224  to common, shared, or dedicated transport channels according to radio resource allocation commands of the Layer  3  (RRC layer)  202 , for performing channel mapping, multiplexing, transport format selection, or random access control. 
         [0031]    An advanced wireless communications system, such as LTE, supports only packet-switched transmission, so that the RLC entity  224  and the MAC entity  226  are located in the same spot, such as a base station so that they can be combined into one communication entity for simplicity. Note that whether RLC entity  224  and MAC entity  226  are combined into one communication entity is only a modeling issue and is not relevant to the present invention. The present invention provides a transmission error handling program code  220  for improving the NACK-to-ACK error detection mechanism to avoid invalid local ACKs or NACK-to-ACK errors. Please refer to  FIG. 3 , which illustrates a schematic diagram of a process  30  according to an embodiment of the present invention. The process  30  is utilized for handling transmission error associated with the local ACKs in a wireless communications system, and can be complied into the transmission error handling program code  220 . The process  30  comprises the following steps:
       Step  300 : Start.   Step  302 : Create a counter corresponding to a first packet when a first ACK related to the first packet is received.   Step  304 : Send a local ACK to an ARQ transmitter when the counter reaches a maximum value.   Step  306 : End.       
 
         [0036]    According to the process  30 , the counter has a default value of 0. Furthermore, the counter value is increased by 1 for each of subsequent packets established after the first packet. The subsequent packets could be new packets or retransmission packets. When a second packet transmitted after the first packet is established, the local ACK to the ARQ transmitter is sent and the counter is deleted if an ACK or NACK signal related to the second packet is received and a NACK-to-ACK error is not received during a round trip time (RTT). In addition, a local NACK is sent to the ARQ transmitter and the counter is deleted if the NACK-to-ACK error is received before the counter reaches the maximum value. 
         [0037]    According to the process  30 , in a HARQ process, the HARQ transmitter executes a process  40  in each RTT after a counter is created for a packet that is acknowledged. Please refer to  FIG. 4 , which is a flowchart diagram of the process  40  according to another embodiment of the present invention. Assume a counter COUNT 1  has been created and has a default value of 0. The HARQ transmitter shall execute the process  40  in every RTT until the counter COUNT 1  is deleted. The process  40  can be compiled complied into the transmission error handling program code  220  and comprises the following steps:
       Step  400 : Start.   Step  402 : Determine if an ACK or a NACK is received. If so, go to Step  404 ; if not, go to Step  406 .   Step  404 : Determine if a NACK-to-ACK error is received. If so, go to Step  408 ; if not, go to Step  410 .   Step  406 : Determine if the counter COUNT 1  reaches a maximum value MAX 1 . If so, go to Step  410 ; if not, go to Step  414 .   Step  408 : Send a local NACK Local_NACK to an ARQ transmitter ARQ. Then, go to Step  412 .   Step  410 : Send a local ACK Local_ACK to the ARQ transmitter ARQ. Then, go to Step  412 .   Step  412 : Delete the counter COUNT 1 .   Step  414 : End.       
 
         [0046]    If the counter COUNT 1  is present, the HARQ transmitter increases the value of the counter COUNT 1  by 1 each time a new or retransmission packet is established. Step  402  indicates that the HARQ receiver responses with a report signal, the ACK or the NACK, to the transmission established by the HARQ transmitter. Therefore, through the counter COUNT 1 , after a packet is acknowledged, the HARQ receiver in the embodiment of the present invention can accurately determine NACK-to-ACK errors irrespective of how the next packet is delayed, and thereby will not affect the local ACK/NACK mechanism in the HARQ transmitter. 
         [0047]    Please refer to  FIG. 5 , which illustrates a schematic diagram of a process  50  according to an embodiment of the present invention. The process  50  mainly employs a timer to handle transmission error associated with the local ACKs in a wireless communications system, and can be complied into the transmission error handling program code  220 . The process  50  comprises the following steps:
       Step  500 : Start.   Step  502 : Receive a first ACK related to a first packet from a HARQ receiver.   Step  504 : Create a timer corresponding to the first packet when a second packet following the first packet is established.   Step  506 : Send a local ACK to an ARQ transmitter when the timer reaches at a predefined time.   Step  508 : End.       
 
         [0053]    According to the process  50 , after the first ACK related to the first packet is received, the HARQ transmitter creates the counter corresponding to the first packet when the second packet is established, following the first packet. The HARQ transmitter sends a local NACK to the ARQ transmitter and deletes the timer if a NACK-to-ACK error is received before the timer expires. Besides, the HARQ transmitter sends the local ACK to the ARQ transmitter and deletes the timer if an ACK or NACK signal related to the second packet is received and the NACK-to-ACK error is not received during a round trip time before the timer reaches at the predefined time. Preferably, the predefined time is set to be a multiple of the round trip time. 
         [0054]    In the prior art, the HARQ transmitter starts the timer at the time the previous packet (the first packet) is acknowledged. In this situation, if the time the next packet (the second packet) arrives the HARQ receiver exceeds the predefined time, the HARQ transmitter cannot receive a NACK-to-ACK error in time if the NACK-to-ACK error occurs. The HARQ transmitter may have sent the local ACK to the ARQ transmitter before the HARQ receiver reports the NACK-to-ACK error. In the meantime, packet loss occurs. Compared to the prior art, in the embodiment of the present invention, the HARQ transmitter starts the timer when the next packet (the second packet) is established. Therefore, if the next packet is delayed, the HARQ receiver can still report the NACK-to-ACK error in time. Accordingly, the HARQ transmitter can accurately send the local ACK or NACK error. 
         [0055]    Assume that the HARQ transmitter creates a timer TIMER 1  for an acknowledged packet when a subsequent packet is established. The HARQ transmitter then shall execute a process  60  in each RTT until the timer TIMER 1  is deleted. Please refer to  FIG. 6 , which is a flowchart diagram of the process  60  according to another embodiment of the present invention. The process  60  can be compiled complied into the transmission error handling program code  220  and comprises the following steps:
       Step  600 : Start.   Step  602 : Determine if an ACK or a NACK is received. If so, go to Step  604 ; if not, go to Step  606 .   Step  604 : Determine if a NACK-to-ACK error is received. If so, go to Step  608 ; if not, go to Step  610 .   Step  606 : Determine if the timer TIMER 1  reaches at a predefined time T 1 . If so, go to Step  610 ; if not, go to Step  614 .   Step  608 : Send a local NACK Local_NACK to an ARQ transmitter ARQ. Then, go to Step  612 .   Step  610 : Send a local ACK Local_ACK to the ARQ transmitter ARQ.   Then, go to Step  612 .   Step  612 : Delete the timer TIMER 1 .   Step  614 : End.       
 
         [0065]    In the process  60 , Step  602  indicates that the HARQ transmitter has transmitted a packet and then the HARQ receiver responds with a report signal, the ACK or NACK, to the packet. Before the timer TIMER 1  expires, the HARQ transmitter sends the local ACK Local_ACK to the ARQ transmitter ARQ if any NACK-to-ACK error is received. If no NACK-to-ACK error is received when the timer TIMER 1  expires, the HARQ transmitter also sends the local ACK Local_ACK. But if any NACK-to-ACK error is received in each RTT, the HARQ transmitter sends the local NACK Local_NACK. Through the process  60  executed in each RTT, the HARQ receiver can report the NACK-to-ACK error in the predefined time, and doest not affect the local ACK/NACK mechanism in the HARQ transmitter. 
         [0066]    Please refer to  FIG. 7 , which illustrates a schematic diagram of a process  70  according to an embodiment of the present invention. The process  70  is utilized for handling transmission error associated with the NACK-to-ACK error reports in a wireless communications system, and can be complied into the transmission error handling program code  220 . The process  70  comprises the following steps:
       Step  700 : Start.   Step  702 : Create a counter corresponding to a first packet when at least an event of plural events occurs.   Step  704 : Ignore a NACK-to-ACK error report related to the first packet and delete the counter when a report signal and the NACK-to-ACK error report are received.   Step  706 : Delete the counter when the report signal is received and the NACK-to-ACK error report is not received.   Step  708 : Delete the counter when the counter reaches a maximum value.   Step  710 : End.       
 
         [0073]    In the process  70 , the counter has a default value of 0. The plural events may cause the HARQ transmitter to receive invalid NACK-to-ACK error reports. Preferably, the plural events are that a maximum retransmission number in the HARQ transmitter is reached and thereby a retransmission related to the first packet is canceled, and that a retransmission opportunity related to the first packet is replaced by a new transmission. When any of the plural events occurs, a HARQ receiver may misinterpret a legitimate transmission (the second packet) into the invalid NACK-to-ACK error when the HARQ receiver expects a new packet while receiving a retransmission packet. Thus, after the counter is created, the HARQ transmitter determines whether an ACK or NACK signal is received and a NACK-to-ACK error report related to the first packet is also received during an RTT. If the ACK or NACK signal and the NACK-to-ACK error report are both received, the HARQ transmitter ignores the NACK-to-ACK error report and deletes the counter. This is because the NACK-to-ACK error report here is a misinterpreting result of the HARQ receiver so that the HARQ transmitter shall do no reaction with the error report. On the other hand, the HARQ transmitter also deletes the counter if the report signal is received but no NACK-to-ACK error report is received. If neither report signal nor NACK-to-ACK error report is received, and besides the counter value is smaller than the maximum value, the counter value is increased by 1 when a packet transmitted after the first packet is established, where the packet could be a new packet or a retransmission packet. When the counter reaches the maximum value, the HARQ transmitter deletes the counter. Thus, through the process  70 , the embodiment of the present invention does not require extra control signals to indicate the HARQ receiver the cause of the previous HARQ termination and also can avoid invalid NACK-to-ACK errors. Moreover, the process  70  is applied to wireless communications systems with preemption functionality. Therefore, the embodiment of the present invention can avoid packet retransmission due to invalid NACK-to-ACK errors and thereby conserve radio resources. 
         [0074]    Please refer to  FIG. 8 , which illustrates a schematic diagram of a process  80  according to an embodiment of the present invention. The process  80  is utilized for handling transmission error associated with the NACK-to-ACK error reports in a wireless communications system, and can be complied into the transmission error handling program code  220 . The process  80  comprises the following steps:
       Step  800 : Start.   Step  802 : Create a timer corresponding to a first packet if at least an event of plural events occurs when a second packet following the first packet is established.   Step  804 : Ignore a NACK-to-ACK error report related to the first packet and delete the timer when a report signal and the NACK-to-ACK error report are received.   Step  806 : Delete the timer when the report signal is received and the NACK-to-ACK error report is not received.   Step  808 : Delete the timer when the timer reaches at a predefined time.   Step  810 : End.       
 
         [0081]    In the process  80 , the plural events may cause the HARQ transmitter to receive invalid NACK-to-ACK error reports. Preferably, the plural events are that a maximum retransmission number in the HARQ transmitter is reached and thereby a retransmission related to the first packet is canceled, and that a retransmission opportunity related to the first packet is replaced by a new transmission. When any of the plural events occurs, a HARQ receiver may misinterpret a legitimate transmission (the second packet) into the invalid NACK-to-ACK error when the HARQ receiver expects a new packet while receiving a retransmission packet. Thus, after the timer is started, during each RTT, the HARQ transmitter determines whether an ACK or NACK signal is received and a NACK-to-ACK error report related to the first packet is also received. If the ACK or NACK signal and the NACK-to-ACK error report are both received, the HARQ transmitter ignores the NACK-to-ACK error report and deletes the counter. This is because the NACK-to-ACK error report here is a misinterpret result of the HARQ receiver so that the HARQ transmitter shall do no reaction with the error report. On the other hand, the HARQ transmitter also deletes the counter if the report signal is received but no NACK-to-ACK error report is received. If neither report signal nor NACK-to-ACK error report is received, and the timer has not expired, the counter value is increased by 1 when a packet transmitted after the first packet is established, where the packet could be a new packet or a retransmission packet. When the timer reaches at the predefined time, the HARQ transmitter deletes the counter. The predefined time is preferably set to be a multiple of the round trip time. Thus, through the process  80 , the embodiment of the present invention does not require extra control signals to indicate the HARQ receiver the cause of the previous HARQ termination and also can avoid invalid NACK-to-ACK errors. Moreover, the process  80  is applied to wireless communications systems with preemption functionality. Therefore, the embodiment of the present invention can avoid packet retransmission due to invalid NACK-to-ACK errors and thereby conserve radio resources. 
         [0082]    In summary, regarding the local ACK generation mechanism, the present invention can reduce a missing rate of NACK-to-ACK errors without delaying the local ACK report. Regarding NACK-to-ACK detection mechanism, the present invention can avoid the control signaling and also cover the situation of schedule preemption. 
         [0000]    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.