Abstract:
Methods and apparatus for dynamically allocating HARQ processes are described. A wireless transmit/receive unit (WTRU) includes a receive unit configured to receive signaling and a transmit unit. The transmit unit is configured to transmit uplink data sequentially using a first integer number of hybrid automatic repeat request (HARQ) processes during normal HARQ operation and transmit uplink data using a second integer number of HARQ processes that is less than the first number of HARQ processes in response to receiving the signaling.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/841,156 filed Aug. 20, 2007, which claims the benefit of U.S. Provisional Application No. 60/839,172, filed Aug. 21, 2006, U.S. Provisional Application No. 60/829,457, filed Oct. 13, 2006, U.S. Provisional Application No. 60/863,543, filed Oct. 30, 2006, and U.S. Provisional Application No. 60/868,185, filed Dec. 1, 2006, the contents of which are hereby incorporated by reference herein. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention is related to a wireless communication systems. More particularly, a method and apparatus for dynamically allocating hybrid automatic repeat request (HARQ) processes for wireless transmit/receive units (WTRUs) in the uplink is disclosed. 
       BACKGROUND 
       [0003]    The uplink capacity in a code division multiple access (CDMA)-based system, such as high speed packet access (HSPA), or a single channel frequency division multiple access (SC-FDMA) system, such as an evolved universal terrestrial radio access network (E-UTRAN), is limited by interference. For a CDMA-based system, uplink interference at a specific cell site is typically generated by WTRUs, (i.e., users) connected to the cell as well as WTRUs connected to other cells. In the case of an SC-FDMA-based system, uplink interference stems primarily from WTRUs connected to other cells. To maintain coverage and system stability, a cell site can tolerate only up to a certain amount of uplink interference at any given instant in time. As a result, system capacity is maximized if interference can be kept constant as a function of time. This consistency allows a maximum of users to transmit and/or generate interference without having the uplink interference exceeding a predetermined threshold at any time. 
         [0004]    High-speed uplink packet access (HSUPA), as defined in the Third Generation Partnership Project (3GPP) Release 6, employs HARQ with synchronous retransmissions. When utilizing a 2 millisecond (ms) transmission timing interval (TTI), the minimum instantaneous data rate is often larger than the data rate offered by an application, due to the need to transmit a number of bits that is at least the size of a single radio link control (RLC) protocol data unit (PDU) in a given TTI. When this occurs, a WTRU can utilize only a subset of the available HARQ processes. As a result, the interference generated by a given active WTRU is not constant over a time span of eight (8) TTIs. During some TTIs, the WTRU transmits data and the interference it generates is high. During other TTIs, the WTRU may only transmit control information and, therefore, the interference it generates is low. In order to equalize interference across all TTIs, the system can restrict each WTRU to use a certain WTRU-specific subset of HARQ processes, and select different subsets for different WTRUs. 
         [0005]    Transmissions from a WTRU for a certain stream of data may be managed by non-scheduled transmissions or scheduling grants. With non-scheduled transmissions, the WTRU can freely transmit up to a fixed data rate in certain HARQ processes. With scheduling grants, the WTRU can also transmit up to a certain data rate on certain HARQ processes, but the maximum data rate is subject to change dynamically depending on the maximum power ratio signaled by a Node-B at a given time. 
         [0006]    When the network manages the transmission by allowing non-scheduled transmissions, the set of HARQ processes is signaled to the WTRU through radio resource control (RRC) signaling. The Node-B determines the set of HARQ processes and signals this information to the radio network controller (RNC), which then relays it to the user through RRC signaling. An advantage of managing delay-sensitive traffic with non-scheduled transmissions is that it eliminates the possibility of any additional delay that could be caused by insufficiency of the resources granted by the Node-B when managing the transmissions with scheduling grants. Another advantage is that it eliminates the signaling overhead due to the transmission of scheduling information that is required with scheduling grants. 
         [0007]    With the currently defined mechanisms for non-scheduled transmissions, however, the performance of the system is sub-optimal when the application mix is dominated by delay-sensitive applications that generate traffic patterns exhibiting periods of high activity alternated with periods of low activity. An example of this type of application is the voice over Internet protocol (VoIP) application, in which silence periods translate into a very low amount of traffic needing to be transmitted. When the cell or system is dominated by this type of application, capacity is maximized only if the network is capable of modifying the subset of HARQ processes used by a WTRU when its activity state changes, so that the interference is always equalized across the HARQ processes. Otherwise, the network has to restrict the number of WTRUs utilizing a certain HARQ process so that the threshold is not exceeded, even when they are all active at the same time, resulting in a much lower capacity. 
         [0008]    An issue when utilizing non-scheduled transmissions is that it allows modification of the subset of allowed HARQ processes only through RRC signaling, which typically involves latencies of several hundreds of milliseconds. This latency is significant compared to a typical interval between changes of activity for applications such as voice applications. Furthermore, RRC signaling in the current Release 6 architecture is controlled by the RNC. Therefore, the Node-B needs to signal the modification of the subset of allowed HARQ processes to the RNC beforehand. The interval of time between the change of activity state at the WTRU and the effective change of HARQ processes may well be larger than the duration of the activity state. Accordingly, this becomes unworkable for equalizing interference across HARQ processes. 
         [0009]    It would therefore be beneficial to provide a method and apparatus for dynamically allocating HARQ processes in the uplink that would aid in optimizing capacity with non-scheduled transmissions. 
       SUMMARY 
       [0010]    Methods and apparatus for dynamically allocating HARQ processes are described. A wireless transmit/receive unit (WTRU) includes a receive unit configured to receive signaling and a transmit unit. The transmit unit is configured to transmit uplink data sequentially using a first integer number of hybrid automatic repeat request (HARQ) processes during normal HARQ operation and transmit uplink data using a second integer number of HARQ processes that is less than the first number of HARQ processes in response to receiving the signaling. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    A more detailed understanding of the invention may be had from the following description of a preferred embodiment, given by way of example and to be understood in conjunction with the accompanying drawings wherein: 
           [0012]      FIG. 1  shows an exemplary wireless communication system including a plurality of WTRUs, and a Node-B; 
           [0013]      FIG. 2  is a functional block diagram of a WTRU and the Node-B of  FIG. 1 ; 
           [0014]      FIG. 3A  is a flow diagram of a method of allocating processes; 
           [0015]      FIG. 3B  is a flow diagram of an exemplary implementation of the method of  FIG. 3A ; 
           [0016]      FIG. 4  is a flow diagram of a method of allocating processes, in accordance with an alternative embodiment; 
           [0017]      FIG. 5  is an exemplary diagram of system resource unit (SRU) allocation in accordance with the method of  FIG. 4 ; 
           [0018]      FIG. 6  is a flow diagram of a method of allocating processes, in accordance with an alternative embodiment; and 
           [0019]      FIG. 7  is a flow diagram of a method of allocating processes, in accordance with an alternative embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    When referred to hereafter, the terminology “wireless transmit/receive unit (WTRU)” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment. When referred to hereafter, the terminology “base station” includes but is not limited to a Node-B, a site controller, an access point (AP), or any other type of interfacing device capable of operating in a wireless environment. 
         [0021]      FIG. 1  shows an exemplary wireless communication system  100  including a plurality of WTRUs  110 , a Node-B (NB)  120 , and a radio network controller (RNC)  130 . As shown in  FIG. 1 , the WTRUs  110  are in wireless communication with the NB  120 , which is connected to the RNC  130 . Although three WTRUs  110 , one NB  120 , and one RNC  130  are shown in  FIG. 1 , it should be noted that any combination of wireless and wired devices may be included in the wireless communication system  100 . 
         [0022]      FIG. 2  is a functional block diagram  200  of a WTRU  110  and the NB  120  of the wireless communication system  100  of  FIG. 1 . As shown in  FIG. 2 , the WTRU  110  is in communication with the NB  120  and both are configured to perform a method of dynamic process allocation. 
         [0023]    In addition to the components that may be found in a typical WTRU, the WTRU  110  includes a processor  115 , a receiver  116 , a transmitter  117 , and an antenna  118 . The processor  115  is configured to perform a dynamic process allocation procedure. The receiver  116  and the transmitter  117  are in communication with the processor  115 . The antenna  118  is in communication with both the receiver  116  and the transmitter  117  to facilitate the transmission and reception of wireless data. 
         [0024]    In addition to the components that may be found in a typical NB, the NB  120  includes a processor  125 , a receiver  126 , a transmitter  127 , and an antenna  128 . The processor  115  is configured to perform a dynamic process allocation procedure. The receiver  126  and the transmitter  127  are in communication with the processor  125 . The antenna  128  is in communication with both the receiver  126  and the transmitter  127  to facilitate the transmission and reception of wireless data. 
         [0025]      FIG. 3A  is a flow diagram of a method  300  of allocating processes. In general, the method  300  involves signaling to the WTRU  110  a subset of allowed HARQ processes. This signaling is preferably used for those WTRUs  110  utilizing non-scheduled transmissions with 2 ms TTIs, and those enabled to utilize the method  300 . Also, preferably, the information required for enablement is communicated to the network through RRC signaling that is defined over one or more TTIs. 
         [0026]    In step  310 , HARQ processes to be activated or deactivated are identified and signaled to a WTRU  110  or group of WTRUs  110  (step  320 ). This signaling may be performed in a variety of ways. 
         [0027]    For example, in one preferred method, each time a signal command is sent, an individual HARQ process is either activated or deactivated, depending on its current activation state. In this way, the number of bits that require encoding depends on the maximum number of HARQ processes. For eight (8) HARQ processes, as are used in HSUPA, 3 bits would need to be signaled, plus an additional bit that indicates whether the HARQ process is to be activated/deactivated. It could also be implicit that the command signal toggles between activation and deactivation, where the last bit would be omitted since it would be unneeded. However, in this manner, the WTRU  110  would have to know beforehand how to interpret the signal. 
         [0028]    Another alternative method could be that each time the command signal is sent, one HARQ process is activated and another HARQ process is deactivated. In this method, enough bits to encode two HARQ processes, (e.g., six (6) bits), would be required. In this manner, a HARQ process that is deactivated may be activated and a HARQ process that is activated may be deactivated. Alternatively, all active HARQ processes may be deactivated, and all deactivated HARQ processes may be activated. 
         [0029]    Steps  310  and  320  of method  300  may also be performed by implicitly signaling the activation or de-activation of an individual HARQ process by the transmission time of the signaling, such as the frame and sub-frame. For example, a rule may be pre-established between the frame/sub-frame number of the signaling command and the HARQ process involved. In this way, no bit is necessarily required to specify an individual HARQ process, but the NB  120  would be constrained to activate/de-active the individual HARQ process only at a specific frame or sub-frame. However, a single bit may be utilized if desirable to signal whether a process is activated or deactivated. Alternatively, a combination of methods may be used, such as by indicating de-activation of an individual process by the transmission time and indicating the activation of a process by using a bit or bits, or vice versa. 
         [0030]    Yet another alternative for employing steps  310  and  320  of the method  300  of  FIG. 3A  is to utilize the signaling command to specify the activation or deactivation of all HARQ processes at once. This may be accomplished by defining a bit map where each bit represents a HARQ process and the value of the bit indicates whether or not the process should be activated or deactivated, or the active/deactive state of the process merely switched. 
         [0031]    It should be noted that in the current state of the art, HARQ process numerators, also referred to as HARQ process indices, are WTRU specific. However, the RNC  130  may align the numerators so that broadcast information may be used by all WTRUs  110  in communication with the RNC  130 . Alternatively, a particular WTRU  110  may be signaled before the correspondence between each bit of the bitmap and each HARQ process numerator. 
         [0032]    For example, there are eight (8) possible HARQ processes for each WTRU that are identified with an index, (e.g., from 1 to 8). As the WTRUs  110  are not synchronized with one another, HARQ process N for a particular WTRU  110  is generally not transmitted at the same time as HARQ process N for another WTRU  110 . However, the NB  120  may desire to activate or deactivate HARQ processes for multiple WTRUs  110  that are transmitted at a specific time. To enable this signaling to take place in a “broadcast” scenario, the HARQ process indices of the different WTRUs  110  should be synchronized so that HARQ process N for one particular WTRU  110  is transmitted at the same time as HARQ process N for any other WTRU  110 . Alternatively, each WTRU  110  may be made aware in advance which process index should be turned on or off if the NB  120  signals that all processes being transmitted at a given time, that may be specified by some common reference, should be turned on or off. 
         [0033]    In another way of performing steps  310  and  320  of the method  300  of  FIG. 3A , the WTRU  110  may be permitted to utilize an individual process that has been “toggled off” under conditions pre-specified or signaled from the network beforehand. One of these conditions may include the buffer occupancy of data for uplink transmission by the WTRU  110 . The number of bits associated with each individual process could vary and may indicate a priority of usage in that different priorities would correspond to respective different sets of conditions for usage of each individual process. 
         [0034]    The number of bits may be equal to the maximum number of HARQ processes. For example, eight (8) bits are used for HSUPA. Alternatively, the required number of bits could be reduced if the set of HARQ processes that can potentially be activated for a particular WTRU  110  is smaller than the maximum number of possible HARQ processes. The set of potentially activated HARQ processes could be signaled to the WTRU  110  through higher-layers, (e.g., RRC) in the same way that a set of restricted HARQ processes is signaled. 
         [0035]    The signaling command may also specify the set of allowed HARQ processes, (i.e., those HARQ processes that the WTRU  110  can use for uplink transmission), taking effect immediately or at a fixed delay from when the information is received by the WTRU  110 . Alternatively, the updated set of allowed processes can take effect at a time specified in the signaling message itself. Preferably, the set of allowed HARQ processes is signaled as an index into a table where multiple sets of allowed HARQ processes are already pre-defined and known at the WTRU  110 . The number of bits representing the index will limit the number of sets that can be pre-defined. The mapping between the index and set of allowed HARQ processes can be pre-configured through higher layer signaling or the set of allowed HARQ processes can be explicitly signaled to the WTRU  110  by enumerating the specific allowed process numbers. 
         [0036]    Another way to perform steps  310  and  320  of the method  300  of  FIG. 3A  is for the signaling to specify the probabilities for which the WTRU  110  should turn on or off individual HARQ processes. Preferably, a single probability value is signaled per HARQ process, (e.g., turn off), and a second probability value, (e.g., turn on), is calculated by using the signaled value according to a predefined rule. Alternatively, both the off and on probabilities may be explicitly signaled to the WTRU  110 . 
         [0037]    For any of the above described methods, the signaling commands may be sent (step  320 ), or directed, to an individual WTRU  110  or to a plurality of WTRUs  110 . 
         [0038]    In one preferred embodiment, the functionality of the enhanced dedicated channel (E-DCH) absolute grant channel (E-AGCH) may be extended by defining additional interpretation of the information bits. The correct interpretation may be known to the WTRU  110  by time multiplexing in different TTIs and/or by using different spreading codes. The times and codes may be signaled to the WTRU  110  by the network. Additionally, the interpretation may be implied by an identification code embedded in the E-AGCH such as the WTRU ID. This is equivalent to defining a new physical channel with a new name, (e.g., enhanced active process indicator channel (E-APICH), that may be time and/or code-multiplexed with the E-AGCH. 
         [0039]    Currently, the E-AGCH identifies WTRUs  110  by masking the cyclic redundancy code (CRC) with enhanced radio network temporary identifiers (E-RNTIs) of 16 bits. This approach could be extended by defining additional E-RNTIs for non-scheduled transmissions for the WTRUs  110  that use both scheduled and non-scheduled transmissions. The WTRU  110  should respond to more than one E-RNTI. It is also possible to separate scheduled and non-scheduled operations in time. For processes that have been allowed use by the RNC  130  for non-scheduled operation, the AGCH utilizes the bit interpretation as described in the embodiments above, while in other processes it utilizes the bit interpretation as utilized in the current state of the art. 
         [0040]    Additionally, the network may define groups of WTRUs  110  and E-RNTI values for these groups. This allows faster signaling in case some HARQ processes need to be deactivated for multiple WTRUs  110 . Accordingly, a particular WTRU  110  can be associated with a set of E-RNTI values, among which some may be common to multiple WTRUs  110 . Further processing may be similar to what is currently defined for the E-AGCH, such as convolutional encoding followed by rate matching. There are additional possibilities in terms of coding rate, amount of rate matching, size of CRC, and the like, to fit the required number of information bits on the E-AGCH or E-APICH. Preferably, the coding rate and rate matching should be kept the same as the prior art E-AGCH to simplify decoding operation at the WTRU  110 . By way of example, the E-AGCH may contain the WTRU ID information (E-RNTI)/CRC (16 bits) and 6 bits of payload. Depending on how many bits are needed to encode the instructions, one or more E-AGCH transmissions may be combined by concatenating their available bits. In another example, the E-RNTI/CRC field may be reduced from 16 bits to a smaller number of bits to increase the available number of bits. 
         [0041]    Another way of signaling the WTRU  110  in step  320  may be to extend the E-RGCH/E-HICH functionality, or multiplex a newly defined channel with these channels by utilizing distinct orthogonal sequences to contain the new signaling. This option allows the transmission of a binary value every TTI. One or more WTRUs  110  is identified by an orthogonal sequence (signature). It is also possible to transmit three (3) binary values by not combining the sequences in each of the three (3) slots of the TTI. However, this way may require greater transmission power. If the number of orthogonal sequences required to support the new signaling and the existing enhanced relative grant channel (E-RGCH)/enhanced HARQ indicator channel (E-HICH) is insufficient, a different spreading code may be utilized to contain the new signaling, allowing the reuse of the orthogonal sequences of the E-RGCH/E-HICH. 
         [0042]    Alternatively, the format of the high speed shared control channel (HS-SCCH) may be modified to include activation/de-activation commands. The format for the additional bits may be similar to the methods set forth above for the E-AGCH. 
         [0043]    In addition to the signaling methods for step  320  described above, various other techniques may be utilized. For example, the existing broadcast control channel (BCCH)/broadcast channel (BCH) may be extended to include the signaling information related the activation/de-activation of individual HARQ processes. The existing RRC control signaling may be extended to convey information related to the activation/de-activation of individual HARQ processes. The high speed medium access control (MAC-hs) header may be modified to include activation/de-activation commands, with the format for the additional bits potentially being similar to one of the options described above for the E-AGCH. For this particular example, as retransmissions are asynchronous in the downlink (DL), and since the WTRU  110  can typically only decode the information once the downlink PDU decoding is successful, signaling options where an individual HARQ process is implicitly indicated by the signaling time should preferably refer to the transmission time of the HS-SCCH that corresponds to the first transmission for this downlink PDU. 
         [0044]    To make the signaling compatible with the use of discontinuous reception (DRX) or discontinuous transmission (DTX) at the WTRU  110 , it may be required to impose rules to force the WTRU  110  to listen, (i.e., not be in DRX), during TTIs where it would otherwise be in DRX, when certain conditions are met. 
         [0045]    For example, the WTRU  110  could be required to not utilize DRX for a certain period of time immediately following resuming or interruption of voice activity, so that the NB  120  may modify the activated HARQ processes if needed. Alternatively, it could be required that the WTRU  110  listens periodically during certain TTIs when it would otherwise be in DRX, according to a pre-determined pattern. By way of another example, a WTRU  110  could be required to stop DRX, (i.e., listen in all TTIs), when the NB  120  deactivates a HARQ process until another HARQ process is activated. Thus, the NB  120  that desires to modify the HARQ process allocation of a particular WTRU  110  would start by de-activating one of the HARQ processes knowing that the WTRU  110  will be listening for the activation of the new HARQ process. The converse rule, (activate first and deactivate second), is also possible. More generally, a rule could be established that allows the WTRU  110  to activate DRX only when it has a specified number of HARQ processes activated. 
         [0046]    To ensure that the new set of HARQ processes corresponds to the DRX/DTX pattern the WTRU  110  is using, the network may signal DRX activate and/or DTX activate from the NB  120  to the WTRU  110 . Alternatively, signaling could be done by higher layers. Since individual or group WTRU signaling to enable or disable a process exists in the current state of the art, it can be extended to indicate conditions for usage of multiple processes. 
         [0047]    The embodiments may also support macrodiversity. For example, a particular WTRU  110  may be in a state where it transmits to one or more NBs  120  (additional NBs not shown) in an active set in addition to its serving NB  120 , which then sends the data to the RLC to be macro-combined. If the serving NB  120  changes the allocated HARQ processes, the other cells in the active set may blindly detect uplink transmissions from the WTRU  110  in the new HARQ processes, or the serving NB  120  may signal changes to the RNC  130  which then relates them to other NBs  120  in the active set. 
         [0048]    Due to power control, all WTRUs  110  may be considered interchangeable with respect to their contribution to uplink interference. The NB  120 , therefore, has the ability to choose which WTRU  110  it transfers between processes. Accordingly, the NB  120  can choose not to change the HARQ process allocation of WTRUs  110  in handover. 
         [0049]    As WTRUs  110  move within the system, changes of E-DCH serving NB  120  will be required periodically. In order to support this mobility, several alternatives exist for the behavior of the WTRU  110  and NB  120  during this period. In one example, the WTRU  110  is allowed to transmit on any HARQ process that is not restricted by higher layers, (i.e., all processes are active), until it receives activation/de-activation commands from the new serving NB  120 . Alternatively, the WTRU  110  may be disallowed to transmit on any HARQ process, (i.e., all processes are inactive), until it receives activation commands from the new serving NB  120 . 
         [0050]    In another preferred embodiment, however, the WTRU  110  maintains the same active/inactive state of each of its HARQ processes upon change of E-DCH serving NB  120 . The new E-DCH serving NB  120  then sends an activation/de-activation command that changes the state of each HARQ process. If the new serving NB  120  sends a de-activation command for a HARQ process that was already inactive, or an activation command for a HARQ process that was already active, the WTRU  110  may ignore the command. Optionally, the new serving NB  120  may signal the active/inactive state of HARQ processes of the WTRU  110  by the RNC  130  upon setup of the radio link through Iub. Such signaling would require that the old serving NB  120  signals this information to the RNC  130 , again through Iub, prior to or upon the change of E-DCH (enhanced data channel handler) serving Node-B. 
         [0051]    The WTRU  110  then reacts to signaling that it receives (step  330 ). This reaction may include several variations. In one example, the WTRU  110  may listen at least when the MAC-e state changes from no uplink data to uplink data. A change from no data to data is indicated when N1 TTIs have elapsed where new data has arrived in the buffer. A change from data to no data is indicated when N2 TTIs have elapsed without new data arriving in buffer. N1 and N2 may be signaled beforehand by the network to the WTRU  110 . If signaled specifically the WTRU  110  must then enable or disable the processes as instructed. 
         [0052]    In an alternative example, if the WTRU  110  is signaled as a part of a group of WTRUs, the WTRU  110  may decide randomly whether to execute the instruction utilizing a probability that may be signaled by the network. In order to support synchronous retransmissions within a HARQ process, preferably the WTRU  110  should only be allowed to switch to a different HARQ process once the current HARQ process is complete, that is, once a positive ACK has been received or the maximum number of retransmissions has been met. Alternatively, if signaled as part of a group, the WTRU  110  may wait a random amount of time before executing the instruction, where the random amount of time may be signaled to the WTRU  110  beforehand by the network. 
         [0053]    When DRX or DTX is activated, and if the WTRU  110  was previously instructed to behave so by higher layer signaling, the WTRU  110  adjusts the reference for its DRX and DTX pattern to correspond to the time of the last DRX or DTX activation signal, respectively. Alternatively the WTRU  110  adjusts the DRX/DTX pattern to correspond to the set of HARQ processes signaled. The mapping of HARQ processes to DRX/DTX patterns could be pre-determined, or could be signaled ahead of time by higher layer signaling. 
         [0054]    In the current 3GPP Release 6 architecture, the RRC layer is terminated at the RNC  130 . When leaving control of the HARQ process activation to the NB  120 , the NB  120  may require information about the quality of service (QoS) requirements of the WTRU  110  to avoid an excessive reduction in the number of activated processes. Such a reduction of the number of activated processes in a non-scheduled operation would undesirably force the WTRU  110  to increase its instantaneous data rate during its active processes and reduce the area over which it can meet its QoS. Accordingly, it may be useful to have the RNC  130  communicate information to the NB  120  regarding the WTRUs  110 , or have the NB  120  acquire the information in some other way. 
         [0055]    For example, the RNC  130  may estimate the minimum number of HARQ processes that need to be activated at a given time to support the WTRU  110  transmissions. The RNC  130  has the capability of performing this estimation since it knows what the guaranteed bit rate is and has control over the throughput of the HARQ process through outer-loop power control and HARQ profile management. The RNC  130  communicates this number of HARQ processes to the NB  120  through NBAP signaling. The NB  120  ensures that the WTRU  110  has at least this number of HARQ processes activated at any time. Because of the simplicity, this process may be desirable for the NB  120 . 
         [0056]    Additionally, the RNC  130  may provide the guaranteed bit rate to the NB  120  through NBAP signaling. Based on the guaranteed bit rate, the NB  120  estimates how many active HARQ processes are required at a given time and activates individual processes accordingly. The NB  120  may also determine to deactivate certain processes during periods of inactivity. 
         [0057]    Alternatively, the RNC  130  may not provide any information to the NB  120 . Instead, the NB  120  may endeavor to maintain the number of active HARQ processes for a given WTRU  110  to the smallest possible value with the constraint that it never has to transmit more than one RLC PDU at a time unless all HARQ processes are already activated. The NB  120  could detect the transmission of more than one RLC PDU by inspecting the content of successfully decoded MAC-e PDUs. This approach provides significant flexibility to the NB  120 , but may be more complex to implement. 
         [0058]    Any HARQ process allocation changes and resulting DRX/DTX pattern or reference changes determined by NB  120  may be signaled to the RNC  130 , which may signal those changes to a target NB  120  in case of handover. 
         [0059]    In the current state of the art, the set of HARQ processes that the WTRU  110  is allowed to use is indicated by the RNC  130  through L3 signaling. This signaling could be maintained, indicating the allowed HARQ processes for the WTRU  110 , which may be activated or deactivated by the NB  120  as per the various schemes described above. In addition, the RNC  130  could indicate to the WTRU  110  the initial set of HARQ processes to be activated. 
         [0060]      FIG. 3B  is a flow diagram of an exemplary implementation  305  of the method  300  of  FIG. 3A . In particular, the implementation  305  allows the RNC  130 , NB  120  and WTRU  110  to optimize capacity, such as for VoIP or any other delay sensitive application. Upon call setup initiation (step  370 ), a particular WTRU  110  is preferably provided with a list of potentially activated HARQ processes (step  375 ). Alternatively, if a list is not provided, the WTRU  110  may assume that it can potentially use all HARQ processes. The RNC  130  also provides information to the NB  120 , preferably through NBAP to aid the NB  120  in determining the required number of HARQ processes. 
         [0061]    After the WTRU  110  commences transmission, the NB  120  begins de-activating HARQ processes for which the interference in the system is the greatest (step  380 ). Additionally, the NB  120  maintains as active the HARQ processes for which interference was minimal. 
         [0062]    The NB  120  then continuously monitors the activity of all admitted WTRUs  110  in the system with non-scheduled transmissions (step  385 ) and tries to maintain the interference across all HARQ processes below a particular threshold by changing the active HARQ processes as a function of activity (step  390 ). There are numerous ways in which to perform step  390 . 
         [0063]    One way is that when the NB  120  detects that a previously inactive WTRU  110  becomes active, the NB  120  changes the set of active HARQ processes for this WTRU  110  to HARQ processes where the interference is the least. Alternatively, if a previously active WTRU  110  becomes inactive, it can swap its set of active HARQ processes with the set of another active WTRU  110 . Additionally, the NB  120  could also deactivate most HARQ processes of a particular WTRU  110  that has become inactive, and activate other HARQ processes, such as where interference is minimal, when activity resumes. 
         [0064]    Another alternative is that the NB  120  may monitor the interference on each HARQ process and periodically re-allocate one of the HARQ processes of one WTRU  110  from the most interfered HARQ process to the least interfered HARQ process, provided that the maximum level of interference over all processes does not increase. That is, a most interfered with HARQ process in the WTRU  110  is deactivated and a least interfered with HARQ process in the WTRU  110  is activated. 
         [0065]      FIG. 4  is a flow diagram of a method  400  of allocating processes, in accordance with an alternative embodiment. Since the purpose of the E-APICH is to maintain an uplink interference profile that is as uniform as possible between HARQ processes, a group-wise allocation of system resources is possible to the WTRUs  110 . 
         [0066]    In step  410  of the method  400  of  FIG. 4 , a system resource unit (SRU) is defined. Preferably, the SRU is defined to be a combination of a HARQ process and a granular amount of an interfering system resource, such as rate or power. The interfering system resource is preferably defined by considering that in an interference limited system, such as a CDMA uplink, there is only a finite amount of power or rate that can be utilized by transmitters simultaneously. Usage of more resources than is available will cause interference and likely loss of packets. Although in a preferred embodiment, the interfering system resource is typically measured using rate or power, other measures can be used. Additionally, required signal-to-interference ratio (SIR), received power, uplink load, (i.e., a fraction of UL pole capacity) are measures that may also be utilized. 
         [0067]    In step  420  of the method  400  of  FIG. 4 , the SRUs are allocated to the WTRUs  110 . In fact, all allocation in the present alternative embodiment of the invention is done using SRUs. Preferably, a group of WTRUs  110  is selected and allocated the same non-scheduled SRUs. Depending on how the SRU is defined this can be performed in a variety ways. For example, if SRU=(HARQ process, power), then HARQ processes can be allocated via RRC signaling, where power is allocated via a mechanism such as the E-AGCH. All SRU processes within a group are assumed active, and therefore, all HARQ processes are active. Fast allocation is used only to allocate SRUs within the group. Optional “banning” of SRUs in a group is possible to make sure that no WTRU  110  in a group uses a particular HARQ process at a given time. 
         [0068]    The allocation of SRUs to WTRU groups may be performed by allocating SRUs to single groups such that if this is the only group transmitting, system resources are now exceeded and successful communication is assured. However, when multiple groups are present, the total number of SRUs allocated in a cell may exceed the total number of available SRUs. 
         [0069]      FIG. 5  is an exemplary diagram of system resource unit (SRU) allocation in accordance with the method  400  of  FIG. 4 . In the example shown in  FIG. 5 , it may be assumed that a system supports 8 HARQ processes and only 3 SRUs can be supported simultaneously. No WTRU group is allocated SRUs such that it can induce self-interference. However, a total of twice as many SRUs as are available have been allocated, making it possible that interference will occur if the WTRUs  110  all transmit at the same time. As shown in  FIG. 5 , the SRUs are allocated to groups of WTRUs  110  designated as Group 1, Group 2, Group 3, and Group 4. However, it should be noted that the depiction of four groups is exemplary, and any number of groups could be envisioned. By allocating one or several SRUs to groups of WTRUs  110 , fast allocation of SRUs is then signaled by the NB  120 , preferably using the E-APICH, where the NB  120  ensures that no two WTRUs  110  in a particular group are allocated the same SRU. 
         [0070]    There are several advantages and challenges to a group-wise approach as described in method  400 . By grouping the WTRUs  110 , scheduling in the NB  120  may be simplified. For example, HARQ allocations are semi-static between groups and dynamic only within a group. On the other hand, a group provides both sufficient freedom and sufficient response time to keep the interference profile relatively stable. 
         [0071]    Additionally, signaling overhead may be reduced since only a single E-APICH per group is required. All WTRUs  110  in a group monitor the same E-APICH. Moreover, there is no need for individual “power grant” to a WTRU  110 . A particular WTRU  110  can always be granted more or less power in a given HARQ process by providing it more SRUs or by removing some. 
         [0072]    However, as WTRUs  110  enter and leave the cell, a group may need to be updated, which may lead to an increase in signaling overhead. This problem may be mitigated by not updating a full group every time a WTRU  110  enters or leaves a group. Because a particular WTRU  110  only needs to know its own group and its ID within a group the group update overhead can be reduced. 
         [0073]    For example, if a WTRU  110  leaves a cell, it group is maintained intact, but the NB  120  does not allocate any SRUs to that WTRU  110 . Similarly, if a WTRU  110  enters a cell, it may be added to a group which has an opening, for example due to a WTRU in a group previously leaving a cell, or a new group may be created, with this WTRU  110  as the only member. Other WTRUs  110  may subsequently be added to the newly created group. In any case, the NB  120  may occasionally have to reconfigure the groups. However, this will likely be a very infrequent event. 
         [0074]    Depending on the scheduler of the NB  120 , the rate required or services supported by the group size of the WTRUs  110  may vary. Therefore, there are a variety of ways in which to form the groups. 
         [0075]    For example, the total SRUs per group may be fixed. The number of WTRUs  110  per group may be fixed. The total of a particular individual resource, (e.g., rate, power, HARQ processes) per group may be fixed. A group may be comprised of WTRUs  110  with similar receiver characteristics, (e.g. Multi-in-Multi-out (MIMO) enabled, Type-x receiver). A group may also be comprised of WTRUs  110  with similar channel qualities. 
         [0076]    Although multiplexing and signaling options for group-wise E-APICH are similar to those described above for the per-WTRU fast allocation, the signaling options may need to be modified. Since all HARQ processes are assumed active for a group, the E-AGCH in a given TTI includes the group index of the WTRU  110  to which this process is allocated. A special index or non-existing WTRU index may be used to ban the HARQ process for all WTRUs  110  in a group. 
         [0077]    Additionally, implicit signaling via timing of transmission may not be practical for a group, although it may be used as an overlay for banning the HARQ process. Also, instead of a bit field, a symbol, (i.e., multi-bit), field is used, where each symbol indicates which WTRU  110  is permitted a particular HARQ process and a special symbol or non-existing WTRU index may be used to ban the process. For example, each WTRU  110  may be assigned a position of a bit field. A “0” may indicate that the WTRU assigned to this position cannot use the process while a “1” may indicate that the WTRU can use the particular process. Additionally, one of the positions of the bit field might be assigned to no specific WTRU  110 , and rather be used to indicate that the process either can or cannot be used by any, or all, of the WTRUs  110 . 
         [0078]      FIG. 6  is a flow diagram of a method  600  of allocating processes, in accordance with an alternative embodiment. In the present alternative embodiment, non-scheduled operation may be enhanced by sending minimal downlink signaling that includes enough information to a WTRU  110  for dynamically changing HARQ processes within the constraints specified in the downlink signaling. The current RRC signaling of HARQ allocation for non-scheduled operation may be made such that the HARQ processes are restricted and staggered for the WTRUs  110  so that there is a smooth WTRU load distribution across the HARQ processes. However, this does not smooth out the voice activity variations which can cause high interference during some HARQ processes. 
         [0079]    The RRC signaling of restricted and staggered HARQ allocation may be utilized to enhance non-scheduled operation. In step  610  of method  600 , the RNC  130  makes a HARQ allocation. Once that HARQ allocation is made, a known-controlled pattern/hopping allocation may be utilized (step  620 ). This known-controlled pattern/hopping may be used to move the WTRUs  110  that are on top of the RNC  130  allocation in such a way that the load of WTRUs per HARQ process remains as before, but the voice activity is smoothed out across HARQ processes. Preferably, the known-controlled pattern/hopping distributes and smooths the variations of voice activity while not disturbing the WTRU load distribution benefits achieved by restriction and staggering of HARQ processes. Additionally, it may be bounded below by a non-scheduled HARQ process allocation that is restricted and staggered. 
         [0080]    The known-controlled pattern/hopping is sent to a particular WTRU  110  (step  630 ) in a variety of ways. For example, it may be sent by RRC signaling or other downlink signaling, such as by the new physical channel E-APICH signaling described above. The pattern may be signaled at call setup time or during a call/session on a semi-static basis which may be needed to fine tune previous allocations due to changes in the system such as in load-variations. 
         [0081]    Additionally, the known-controlled pattern/hopping may take the form of any pattern that generally preserves the load balance of the WTRUs  110  across the HARQ processes, as provided by the RRC allocation of non-scheduled operation. For example, it may take the form of sequential hopping of HARQ processes, from the initial RNC allocation, based on a multiple of TTI period that may be specified in RRC or other downlink signaling. The sequential hopping is circular over the maximum number of HARQ processes and the hopping direction is picked randomly, for example, with a 0.5 probability. 
         [0082]    Alternatively, the RRC may initially allocate a set of HARQ processes to the WTRU  110  and the WTRU  110  may “hop” among them periodically with some multiple of TTIs specified in the RRC or other downlink signaling. In another alternative, the WTRU  110  hopping may be randomized based on a pseudo-random pattern and the hopping period specified by RRC or other downlink signaling. 
         [0083]    In yet another alternative, the WTRU  110  may randomly select a signaled number of processes to be used in each cycle of 8 processes, for example, or the WTRU  110  may randomly decide, each TTI, whether to transmit or not according to a probability that may be signaled to the WTRU  110  beforehand. In another alternative, the probability could depend on the WTRU uplink buffer occupancy that is defined by the network and signaled beforehand. 
         [0084]      FIG. 7  is a flow diagram of a method  700  of allocating processes, in accordance with an alternative embodiment. In the method  700  described in  FIG. 7 , HARQ processes uses for uplink (UL) transmissions are randomly selected by particular WTRUs  110  during selection opportunities. Thes selection opportunities occur every M TTIs, where M is preferably a multiple of the total number of HARQ processes, (e.g., 8, 16). The WTRU should be pre-configured through higher layers to select P HARQ processes on which it is allowed to transmit until the next selection opportunity. 
         [0085]    In step  710 , the RAN assigns a selection opportunity to each HARQ process. Preferably, the RAN provides a selection probability between 0 and 1 for each of the allowed HARQ processes, where the sum of the probabilities for all HARQ processes equals 1. This allows the RAN to favor some processes over others, based on such factors as interference generated from scheduled WTRUs  110  and intercell interference. The random distribution that is used to select the HARQ processes is signaled by the RAN to the WTRU  110  or WTRUs  110 . The signaling of these parameters may be achieved using any of the signaling mechanisms described above. The parameters can be signaled individually to each WTRU  110 , to a group of WTRUs  110  or for all WTRUs  110  at once. Preferably, updates to the parameters may be made at the frequency at which WTRUs  110  select HARQ processes or at a slower frequency. 
         [0086]    At every selection opportunity, the WTRU  110  should retrieve the latest set of parameters signaled from the RAN (step  720 ). The WTRU  110  then selects a first HARQ process by randomly selecting a HARQ process among potential processes (step  730 ), taking into consideration the selection probability of each process. 
         [0087]    If another process is required (step  740 ), then the WTRU  110  randomly selects among the remaining processes (step  730 ), taking into consideration the selection probability of the remaining processes. The process continues until the number of processes on which the WTRU is allowed to transmit until the next selection opportunity (P) have been selected. 
         [0088]    In order to support synchronous retransmissions within a HARQ process, preferably the WTRU  110  should only be allowed to select a different HARQ process once the current HARQ process is complete, for example once a positive ACK has been received or the maximum number of retransmissions has been met. 
         [0089]    Although the features and elements are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements. The methods or flow charts provided may be implemented in a computer program, software, or firmware tangibly embodied in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). 
         [0090]    Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine. 
         [0091]    A processor in association with software may be used to implement a radio frequency transceiver for use in a wireless transmit receive unit (WTRU), user equipment (UE), terminal, base station, radio network controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a videophone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, a Bluetooth® module, a frequency modulated (FM) radio unit, a liquid crystal display (LCD) display unit, an organic light-emitting diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any wireless local area network (WLAN) module.