Abstract:
A method and apparatus for scheduling transmissions via an enhanced dedicated channel (E-DCH) are disclosed. A scheduled power is calculated for scheduled data flows. A remaining transmit power is calculated for the E-DCH transmission. A rate request message is generated, wherein the scheduled power, remaining transmit power and rate request message are used to select transport format combinations (TFCs) and multiplex data scheduled for the E-DCH transmission. The remaining transmit power is calculated by subtracting from a maximum allowed power the power of a dedicated physical data channel (DPDCH), a dedicated physical control channel (DPCCH), a high speed dedicated physical control channel (HS-DPCCH), an enhanced uplink dedicated physical control channel (E-DPCCH) and a power margin.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/402,718 filed Apr. 12, 2006 which issued as U.S. Pat. No. 7,408,895 on Aug. 5, 2008, which claims the benefit of U.S. Provisional Application No. 60/673,076 filed Apr. 20, 2005, which is incorporated by reference as if fully set forth. 
    
    
     FIELD OF INVENTION 
     The present invention relates to wireless communication systems. More particularly, the present invention is related to a method and apparatus for scheduling transmissions via an enhanced dedicated channel (E-DCH). 
     BACKGROUND 
     Methods for improving uplink (UL) coverage, throughput, and transmission latency are currently being investigated in the third generation partnership project (3GPP). In order to achieve these goals, enhanced uplink (EU) transmissions have been proposed in 3GPP, in which control, (i.e., scheduling and assigning), of UL resources, (i.e., physical channels), is moved from a radio network controller (RNC) to a Node-B. 
       FIG. 1A  shows a conventional wireless transmit/receive unit (WTRU), (e.g., mobile station), side medium access control (MAC) architecture  100 . The WTRU MAC architecture  100  includes a MAC-es/MAC-e entity  105 , which comprises different independent sub-layer entities within the MAC. The MAC-es/-e functionality split is a result of how the MAC functionality is partitioned within the universal terrestrial radio access network (UTRAN). The WTRU MAC architecture  100  further includes a high speed MAC entity  110 , a MAC-c/sh  115 , a dedicated channel MAC (MAC-d)  120  and a MAC control service access point (SAP)  125 . The MAC-c/sh  115  controls access to all common transport channels, except the HS-DSCH transport channel  145 . The MAC-d  120  controls access to all dedicated transport channels, to the MAC-c/sh  115  and the MAC-hs  110 . The MAC-hs  110  controls access to the HS-DSCH transport channel  145 . 
     The MAC-es/MAC-e entity  105  controls access to an E-DCH  130 , whereby the MAC-d  120  may access the E-DCH  130  via a connection  135 , and the MAC control SAP  125  may access the E-DCH  130  via a connection  140 . 
       FIG. 1B  shows MAC interworking in the conventional WTRU of  FIG. 1A . As shown in  FIG. 1B , a radio link control (RLC) protocol data unit (PDU) enters the MAC-d on a logical channel. In the MAC-e header, a data description indicator (DDI) field, (6 bits), identifies the logical channel, MAC-d flow and MAC-d PDU size. A mapping table is signaled over radio resource control (RRC) signaling to allow the WTRU to set the DDI values. The N field, (fixed size of 6 bits), indicates the number of consecutive MAC-d PDUs corresponding to the same DDI value. A special value of the DDI field indicates that no more data is contained in the remaining part of the MAC-e PDU. The transmission sequence number (TSN) field (6 bits) provides the transmission sequence number on the E-DCH  130  shown in  FIG. 1A . The MAC-e PDU is forwarded to a hybrid-automatic repeat request (H-ARQ) entity, which then forwards the MAC-e PDU to layer  1  for transmission in one transmission time interval (TTI). 
     An efficient MAC architecture for scheduling the transmission of E-DCH data is desired. 
     SUMMARY 
     The present invention is related to a method and apparatus for scheduling transmissions via an E-DCH. A scheduled power is calculated for scheduled data flows. A remaining transmit power is calculated for the E-DCH transmission. A rate request message is generated, wherein the scheduled power, remaining transmit power and rate request message are used to select transport format combinations (TFCs) and multiplex data scheduled for the E-DCH transmission. The remaining transmit power is calculated by subtracting from a maximum allowed power the power of a dedicated physical data channel (DPDCH), a dedicated physical control channel (DPCCH), a high speed dedicated physical control channel (HS-DPCCH), an enhanced uplink dedicated physical control channel (E-DPCCH) and a power margin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding of the invention may be had from the following description of a preferred example, given by way of example and to be understood in conjunction with the accompanying drawings wherein: 
         FIG. 1A  shows a conventional WTRU side MAC architecture; 
         FIG. 1B  prior art MAC inter-working in the conventional WTRU of  FIG. 1A ; 
         FIG. 2  shows a WTRU MAC-e architecture configured in accordance with the present invention; 
         FIG. 3  is a flow diagram of a MAC-e scheduling process in accordance with the present invention; and 
         FIG. 4  shows an example of a pre-processed MAC-e PDU format in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereafter, the terminology “WTRU” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, the terminology “Node-B” includes but is not limited to a base station, a site controller, an access point or any other type of interfacing device in a wireless environment. 
     Hereinafter, the terminology “MAC-e” will be used to reference both MAC-e and MAC-es collectively. 
     The features of the present invention may be incorporated into an integrated circuit (IC) or be configured in a circuit comprising a multitude of interconnecting components. 
       FIG. 2  shows a WTRU MAC-e architecture  200  configured in accordance with the present invention. The WTRU MAC-e architecture  200  includes a scheduling grant processing unit  210 , a remaining transmit power computing unit  215  and a rate request processing unit  220 . 
     The scheduling grant processing unit  210  receives at least one scheduling grant from at least one radio link set (RLS) and derives a current scheduling grant. The scheduling grant may be an absolute grant  225  received from a serving E-DCH cell with a primary or secondary identifier, (i.e., an E-DCH radio network temporary identifier (E-RNTI) is used to determine if the absolute grant is primary or secondary), a relative grant  230  received from a serving E-DCH RLS or a relative grant  235  received from a non-serving E-DCH RLS. The scheduling grant processing unit  210  outputs a signal  240  indicating the amount of scheduled power for use by an E-TFC selection and multiplexing function for scheduled data MAC-d flows. 
     The amount of scheduled power may be identified as a ratio to the DPCCH power. For example, if the DPCCH power is P, the amount of scheduled power has a ratio of 2 to the DPCCH power. Thus, the amount of scheduled power is 2 P. Alternatively, the amount of scheduled power can be identified as the maximum transmit power that can be used for scheduled data to avoid the E-TFC selection and multiplexing function to be aware of DPCCH power measurements. Since DPCCH power changes rapidly, there is processing overhead if it has to be propagated to different entities within the MAC. Furthermore, it is complex to synchronize the timing. Therefore, having only one entity in the MAC-e aware of the DPCCH power is preferred since other scheduling related functions require knowledge of current DPCCH power. 
     When the MAC-e entity  105  invokes the MAC-e function, the scheduling grant processing unit  210  determines the current serving grant. The physical layer provides absolute grants  225  received from the AGCH, indicating whether the grant was received with a primary or secondary E- RNTI. The physical layer also provides relative grants  230 ,  235  received from each RLS, indicating if the RLS is either a serving E-DCH RLS or a non-serving E-DCH RLS. Absolute grants  225  are signaled as the ratio to the current UL DPCCH power. Absolute grants  225  received with a primary E-RNTI always reset the current serving grant. Absolute grants received with a secondary E-RNTI only affect the current serving grant if previously set by a secondary E-RNTI or the grant is set to zero. 
     Relative grants  230  from the serving E-DCH RLS adjust the serving grant in steps up, or down. Relative grants for the non-serving E-DCH RLS can only lower the serving grant by one step. When a relative grant down from a non-serving E-DCH RLS is received, a hysteresis period is started during which other relative grant downs are ignored. 
     The remaining transmit power computing unit  215  receives a signal  245  indicating current DPCCH power estimated by the physical layer, a signal  250  indicating an DCH TFC selected by the MAC-d or DPDCH power estimated by the physical layer, a signal  255  for indicating HS-DPCCH active from the physical layer and a signal  260  indicating maximum allowed power (with a power margin) from a lower layer management entity (LLME) configured by the radio resource controller (RRC). If the HS-DPCCH is active, its power (and power from other channels) must be subtracted from the maximum power to determine the remaining power. Based on signals  245 ,  250 ,  255  and  260 , the remaining transmit power computing unit  215  outputs a signal  265  indicating a remaining transmit power (P remain ) which is computed in accordance with the following equation (1):
 
 P   remain   =P   allowed   −P   DPDCH   −P   DPCCH   −P   HS-DPCCH   −P   E-DPCCH −Margin;  Equation (1)
 
where P DPCCH , P DPDCH , P HS-DPCCH  and P E-DPCCH  represent power requirements of the DPCCH, the DPDCH, the HS-DPCCH and the E-DPCCH, respectively. The rate request processing unit  220  monitors triggering events for rate requests, and triggers a scheduling information rate request when a triggering event occurs. The rate request processing unit  220  provides logic for triggering the rate request and logic for constructing a rate request message  270  including rate request bits.
 
     The rate request may be triggered when new data on logical channels mapped to the E-DCH is received when there is no current scheduling grant, new data of a higher priority then last reported is received on a logical channel mapped to the E-DCH, when there is no scheduling grant and rate requests are updated and periodically generated, (which is configured by RRC procedures), and when a serving RLS acknowledgement (ACK) is not received for the previously transmitted rate request, an updated rate request is generated. 
     The rate request includes the total buffer occupancy for all scheduled MAC-d flows, the highest priority data buffer occupancy for any scheduled MAC-d flow, and a power headroom available for E-DCH transmission. 
     Referring to  FIG. 3 , a MAC-e scheduling process  300  is explained hereinafter. For each E-DCH TTI, the E-DCH is monitored and it is determined whether a scheduling information rate request trigger occurs and/or whether there is E-DCH data with a grant available (step  302 ). If no rate request trigger occurs or there is no E-DCH data available, the process waits until the next TTI. If the determination at step  302  is positive, it is further determined whether there is an H-ARQ process available (step  304 ). Availability of an H-ARQ process is required before E-TFC selection and E-DCH data transmission. If there is no available H-ARQ process, the process  300  waits until the next TTI. If an H-ARQ process is determined to be available at step  304 , a current scheduling grant and remaining transmit power calculation are requested from the scheduling grant processing unit  210  and the remaining transmit power computing unit  215 , respectively (step  306 ). In step  308 , a MAC-e control function invokes scheduling and E-TFC selection functions to generate a MAC-e PDU. In step  310 , the MAC-e PDU is then forwarded to the available H-ARQprocess with a unique power offset and maximum number of retransmissions. 
     In a separate embodiment to meet the timing requirement of the MAC-e PDU formation, pre-calculation of the possible MAC-e PDUs for speeding up the formation process is employed. When the MAC-e entity is requested with the remaining power budget for the E-DCH transmission, the formation process searches the pre-formatted MAC-e PDU table, (mainly its formatted MAC-e PDU header and appropriated data block PDUs), providing ready information to the H-ARQ/physical layer. There are a number of ways for performing the preprocessing, depending on the timing requirement. 
       FIG. 4  shows an example of a preprocessed MAC-e PDU format in accordance with the present invention. The preprocessed MAC-e PDU format consists of a power budget for E-DCH or equivalent, a fully formatted MAC-e PDU header optimally fitting the budget or equivalent, a list of transmission sequence numbers (TSNs) and data block pointers, scheduling information and padding bits. 
     The power budget for E-DCH includes a number of predicted power or equivalent situations based on the last transmission power and the prediction of the current possible power budget. The MAC-e PDU header is formatted based on this budget and the data priority on the same row. The fully formatted MAC-e PDU header describes the MAC-e PDU, with the logical channel priority considered, and the scheduled and non-scheduled data and budget considered. The header includes the DDI, N and the DDI-terminator. A list of the MAC-es PDUs descriptors, including the TSN and data pointers to the MAC-es data blocks, correspond to the same row pre-formatted PDU header. Scheduling information may go with the MAC-e PDU if it exists. Padding bits indicate the number of bits to be padded at the end of the MAC-e PDU for that particular row. The full formation can use the following partial formation: power budget for E-DCH or Equivalent, DDI, scheduled or non-scheduled. This sorted list is based on the data priority. Each row is a MAC-d-flow, (MAC-es PDUs). The power budget is a list of predicted power budget. The DDI represents the MAC-d-flow-ID, logical channel ID and the PDU size. The scheduled or non-scheduled column indicates that the PDUs consume the non-scheduled power budget or scheduled power budget. Non-scheduled data can also be used with scheduled information in the Mac-e PDU. 
     Although the features and elements of the present invention 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 of the present invention.