Abstract:
A method and apparatus for logical channel prioritization in a wireless transmit receive unit (WTRU), including the WTRU receiving multiple streams of a multiple input/multiple output (MIMO) signal, a physical layer (PHY) of the WTRU providing an indicator for each of the multiple streams to a medium access control (MAC) layer of the WTRU, and the MAC layer performing logical channel multiplexing based on the indicator for each of the multiple streams.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/076,740, filed on Jun. 30, 2008 which is incorporated by reference as if fully set forth. 
    
    
     FIELD OF INVENTION 
     This application is related to wireless communications. 
     BACKGROUND 
     The long term evolution-advanced (LTE-A) project of the third generation partnership Project (3GPP) is working towards enhancements of the LTE program. For example, the LTE-A project anticipates the use of peak data rates of 0.5 Gbps in the uplink (UL) direction and 1 Gbps in the downlink (DL) direction. In order to achieve these data rates, UL multiple input/multiple output (MIMO) is being considered for the LTE-A project. 
       FIG. 1  shows an overview of an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)  100  in accordance with the prior art. As shown in  FIG. 1 , E-UTRAN  100  includes three eNodeBs (eNBs)  102 , however, any number of eNBs may be included in E-UTRAN  100 . The eNBs  102  are interconnected with each other by means of an X2 interface  108 . The eNBs  102  are also connected by means of an S1 interface  106  to the Evolved Packet Core (EPC)  104  that includes a Mobility Management Entity (MME)  108  and a Serving Gateway (S-GW)  110 . 
       FIG. 2  shows an LTE user-plane protocol stack  200  in accordance with the prior art. The protocol stack  200  is located in a WTRU  210  and includes the packet data control protocol (PDCP)  202 , the radio link control (RLC)  204 , the medium access control (MAC)  206  and the physical layer (PHY)  208 . The protocol stack  200  may also reside in an eNB (not shown). 
       FIG. 3  shows an LTE control plane protocol stack  300  of the WTRU  210  of  FIG. 2 . The control plane protocol stack  300  includes the non-access stratum (NAS)  302  and a radio resource control (RRC)  304 . Also included are the PDCP  306 , RLC  308  and MAC  310 , which together form the layer 2 sublayer  312 . 
     Logical channel prioritization is a procedure that is performed for each new transmission by a transmitting entity. The transmitting RRC entity controls the scheduling of UL data by giving each logical channel a priority. A higher priority value indicates a lower actual priority level. Additionally, each logical channel is given a prioritized bit rate (PBR). 
     The RRC of a wireless transmit receive unit (WTRU) may perform the logical channel prioritization procedure.  FIG. 4  shows a logical channel prioritization method  400  in accordance with the prior art. At step  402  the WTRU allocates resources to the logical channels. The WTRU, at step  404  allocates resources to the logical channels in a decreasing priority order up to a value such that on average, the served data rate for radio bearers that have data for transmission equals the configured PBR for the radio bearer. If the PBR of a radio bearer is set to “infinity”, the WTRU allocates resources for all the data that is available for transmission on the radio bearer before meeting the PBR of the lower priority radio bearers. At step  406  the WTRU, if any resources remain, serve all the logical channels in a strict decreasing priority order until either the data for that logical channel or the UL grant is exhausted, whichever comes first. 
     For the method  400  shown in  FIG. 4 , the WTRU may follow certain rules. For example, the WTRU should not segment a radio link control (RLC) service data unit (SDU), or partially transmitted SDU or retransmitted RLC protocol data unit (PDU), if the whole SDU, partially transmitted SDU or retransmitted RLC PDU fits into the remaining resources. Further, if the WTRU segments an RLC SDU from the logical channel, it may maximize the size of the segment to fill the grant as much as possible. Also, the WTRU may use as much data as it can to fill the grant, in general. However, if the remaining resources require the WTRU to segment an RLC SDU with size smaller than a certain number of bytes or smaller than the L2 header size, the WTRU may use padding to fill the remaining resources instead of segmenting the RLC SDU and sending the segment. 
     Logical channels configured with the same priority are served equally by the WTRU. Medium access control (MAC) control elements for buffer status reporting, with exception of padding BSR, have higher priority than user plane logical channels. At a serving cell change, the first UL dedicated control channel (DCCH) MAC SDU to be transmitted in the new cell has higher priority than MAC control elements for BSR. 
     With the introduction of UL MIMO in LTE-advanced, enhanced MAC logical channel prioritization and multiplexing mechanisms may be needed to handle multiple transport blocks (TBs) within the same transmission time interval (TTI). 
     SUMMARY 
     A method and apparatus for logical channel prioritization in a wireless transmit receive unit (WTRU) is disclosed. This may include the WTRU receiving multiple streams of a multiple input/multiple output (MIMO) signal. This may also include a physical layer (PHY) of the WTRU providing an indicator for each of the multiple streams to a medium access control (MAC) layer of the WTRU and the MAC layer performing logical channel multiplexing based on the indicator for each of the multiple streams. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein: 
         FIG. 1  shows an overview of an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN) in accordance with the prior art; 
         FIG. 2  shows an LTE user-plane protocol stack in accordance with the prior art; 
         FIG. 3  shows an LTE control plane protocol stack of the WTRU  210  of  FIG. 2 . 
         FIG. 4  shows a logical channel prioritization method  400  in accordance with the prior art. 
         FIG. 5  shows a wireless communication system  200  including a plurality of WTRUs  210  and an e Node B (eNB)  220 ; and 
         FIG. 6  is a functional block diagram of the WTRU and the eNB of the wireless communication system of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     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. 
       FIG. 5  shows a wireless communication system  500  including a plurality of WTRUs  510  and an e Node B (eNB)  520 . As shown in  FIG. 5 , the WTRUs  510  are in communication with the eNB  520 . Although three WTRUs  510  and one eNB  520  are shown in  FIG. 5 , it should be noted that any combination of wireless and wired devices may be included in the wireless communication system  500 . 
       FIG. 6  is a functional block diagram  600  of a WTRU  510  and the eNB  520  of the wireless communication system  500  of  FIG. 5 . As shown in  FIG. 5 , the WTRU  510  is in communication with the eNB  520 . The WTRU  510  is configured with a PHY layer, MAC layer, RRC layer and an RLC layer. The WTRU  510  is further configured to perform logical channel prioritization as required. 
     In addition to the components that may be found in a typical WTRU, the WTRU  510  includes a processor  615 , a receiver  616 , a transmitter  617 , and an antenna  618 . The WTRU  510  may also include a user interface  618 , which may include, but is not limited to, an LCD or LED screen, a touch screen, a keyboard, a stylus, or any other typical input/output device. The WTRU  510  may also include memory  619 , both volatile and non-volatile as well as interfaces  620  to other WTRU&#39;s, such as USB ports, serial ports and the like. The receiver  616  and the transmitter  617  are in communication with the processor  615 . The antenna  618  is in communication with both the receiver  616  and the transmitter  617  to facilitate the transmission and reception of wireless data. 
     In addition to the components that may be found in a typical eNB, the eNB  520  includes a processor  625 , a receiver  626 , a transmitter  627 , and an antenna  628 . The receiver  626  and the transmitter  627  are in communication with the processor  625 . The antenna  628  is in communication with both the receiver  626  and the transmitter  627  to facilitate the transmission and reception of wireless data. The eNB  520  is configured with a PHY layer, a MAC layer and an RRC layer. The eNB  520  is further configured to perform logical channel prioritization upon transmission as required. 
     The PHY layer within a transmitting entity, for example, a WTRU or an eNB, may provide certain indications to the MAC layer with the transmitting entity. For example, the PHY may indicate to the MAC, for each MIMO stream, channel conditions and/or information on physical allocation so that the modulation and coding scheme (MCS), transmit power, and TB size can be determined for each MIMO stream. 
     The transmit power and TB size may depend on the MCS and on the particular MAC data flow or combination of data flows assigned to each MIMO stream. For a selected MAC data flow or combination of flows, the choice of MCS, transmit power, and TB size may be dependent on the channel quality of the MIMO stream and channel allocation information of the MIMO stream. The MAC may choose these parameters so that the Quality of Service (QoS) is normalized on each MIMO stream. An intended result is for the residual hybrid retransmission request (HARQ) process error rate to be similar on each MIMO stream when the same data flow or flows are assigned. 
     The PHY may also indicate to the MAC a ranking of the different TBs, for example, from the most preferred to the least preferred. The ranking may be based on the quality of the TB or underlying MIMO stream. For example, a higher quality TB may be ranked ahead of a lower quality TB. The ranking may also be based on a size of the TB, the MCS, one or more of the link adaptation parameters such as power and/or MCS, the likelihood for correct reception, and/or HARQ acknowledge/non-acknowledge (ACK/NACK) results and statistics. The PHY may indicate the TBs in sequence to the MAC, for example, from the most preferred to the least preferred. Alternatively, PHY can indicate a pointer to a predetermined TB set rather than send a list. 
     The MAC will may use the indications from the PHY layer to perform logical channel multiplexing on the TBs. Within the transmitting entity, when given multiple TB&#39;s within the same TTI, the MAC logical channel prioritization procedure may populate and/or multiplex traffic on a TB according to the MIMO stream quality and physical channel allocation information, or according to the ranking indicated from the PHY layer. For example, if a determination is made that the first TB to be populated is TB 1  and that the second TB to be populated is TB 2  and so on, the MAC will perform the operation. MAC multiplexing/logical channel prioritization on multiple TB&#39;s may be according to a certain order. The ranking or ordering criteria can be used to optimize and improve the performance of uplink transmissions in a way that can enhance the quality of service (QoS) and the uplink throughput. 
     A transmitting entity may receive, for each MIMO stream, an MCS for each of the multiple TBs, size for each of the multiple TBs, transmission power for each of the multiple TBs, UL radio resources, such as frequency and time or space location of radio resource blocks, for example, an UL preceding MIMO index such as a pre0-coding matrix index (PMI) or MIMO channel coefficients, for example, information regarding HARQ processes used for UL transmission and HARQ feedback (ACK/NACK) for each of the multiple TBs. The information may be received in an UL scheduling grant, for example, which is carried on an DL control channel, such as the physical downlink control channel (PDCCH), for example. For each MIMO stream, the information may be signaled explicitly or implicitly. If signaled implicitly, some information may be derived from other signaled parameters. For example, a TB size may be derived from the MCS and allocated resource blocks. 
     The order or location of the parameters in the control channel may indicate the order of the TB&#39;s to be populated by the MAC. For example, the first TB (TB 1 ) may correspond to the first codeword and the second TB (TB 2 ) may correspond to the second codeword, and so on. A MAC multiplexing function may populate TB 1  first, then TB 2  and so on, in accordance with the order implied from or indicated in the signaling channel. Accordingly, the ranking or ordering criteria of populating the TB&#39;s by the MAC multiplexing function corresponds to the order that will be implied/derived from the signaling. 
     When a transmitting entity, such as a WTRU, for example, is processing multiple TBs within the same TTI, the MAC logical channel prioritization procedure may populate or multiplex traffic on the TBs according to a particular order. The population may be performed in a round-robin fashion, for example. The order shifts or circulates in every defined time period, whether the time period is, for example, every TTI, or every TTI allocated. Alternatively, the population may be performed randomly or arbitrarily. 
     The MAC may perform a logical channel prioritization and multiplexing operation on each of the TB&#39;s in the TTI, independent of the other TBs. The MAC may perform logical channel (LC) prioritization and multiplexing, and create a MAC PDU for TB 1 , and perform the same procedure to create a MAC PDU for TB 2 . 
     This operation is equivalent to running the LC prioritization and multiplexing logic in one TTI, and rerunning the same logic for another TTI. However, the rerunning of the same logic occurs twice in the same TTI. The LC prioritization and multiplexing of different TBs to be transmitted in the same TTI can be operated simultaneously or sequentially. 
     The MAC evaluates the sizes of all TB&#39;s within the TTI, and performs prioritization and multiplexing of LC&#39;s on the TBs jointly. Rather than prioritizing logical channels on TB&#39;s according to the priority/order of the TBs, the WTRU may map data from different logical channels on any of the TB&#39;s in such a way that will minimize the overhead, such as the RLC segmentation overhead, for example. For example, the WTRU may maximize the size of the RLC PDU and minimize the need for segmentation. 
     If there is sufficient data, the transmitting MAC may multiplex a number of RLC PDUs. The number may be as close as possible to the number of TB&#39;s in a TTI. For example, if there are 2 TBs per TTI, 2 RLC data PDUs should be multiplexed, that is, one in each TB. This may prevent excessive segmentation and may maximize the RLC PDU sizes. 
     If the WTRU is scheduling 2 or more RLC SDUs, the WTRU may compare the size of each of the RLC SDU with the size of each of the TB&#39;s. For each of the SDUs, the WTRU multiplexes an RLC SDU on the TB that will not require segmentation of the RLC SDU and/or will lead to minimizing the occurrence of segmentation of the other RLC SDUs that will be multiplexed on the other TBs. The WTRU may not segment an RLC SDU if the whole SDU fits into any of the TBs in the TTI, or if it fits into any of the remaining un-assigned/un-populated TB&#39;s of the TTI. If the WTRU segments an RLC SDU from the logical channel, it maximizes the size of the segment to fill the TB as much as possible. If the WTRU has an option to perform segmentation or re-segmentation on at least one RLC SDU, the WTRU may select or segment the RLC PDU that will result in the lowest segmentation overhead. For example, if the WTRU has the option of segmenting an RLC SDU for the first time, or resegmenting an RLC PDU for the first time, then the WTRU may segment the former and retransmit the latter as is, rather than transmitting the former as is and resegmenting the latter, because the overhead due to resegmentation is typically higher. 
     In another embodiment, the WTRU may select the permutation or mapping that minimizes the occurrence of segmentation and/or resegmentation. For example, assume that the WTRU is scheduling data (Di) from an LC&#39;s (LCi) and has 2 TBs of size TBS 1  and TBS 2 . The WTRU may consider the sizes TBS 1  and TBS 2  in order to find the permutation or mapping that minimizes the occurrence of segmentation on all Di. The WTRU may view this in terms of a bin-packing problem, whereby the TBs are the bins, and the MAC SDUs and/or MAC CE&#39;s are the objects to be packed in the two bins of sizes TBS 1  and TBS 2 , with the exceptions that the size of one or more of the objects to be packed can be changed and the process is constrained by the goal of minimization of total segmentation overhead and/or padding. 
     Alternatively the MAC may choose data flows to be multiplexed into TBs based on the quality and/or resource allocation of each MIMO channel. The MAC may chose the data flow or combination of data flows to multiplex for each TB mapped to a MIMO stream based on the data flow quality and/or data rate requirements. 
     MAC control elements CEs may be transmitted on any of the TBs. However, in order to improve the reception of MAC CEs, the WTRU can transmit then on the TB with the highest quality. The MAC CEs may be handled as the highest priority traffic by the MAC multiplexing logic. However, the MAC CEs may also be distributed among the TBs in such a way that will minimize the occurrence of segmentation for the other MAC PDUs. 
     In another alternative embodiment, an information element (IE) sent over RRC signaling can include configuration information regarding a mapping of LCs onto TBs. The WTRU may restrict or allow a group of LCs to be multiplexed on a given TB, while allowing another group of LCs to be multiplexed on another TB. 
     For example, RRC signaling may specify which LCs should be mapped to the first TB, and which LCs should be mapped to the second TB. The first and second TB can be determined by the WTRU. For example, the first TB may be a preferred TB because it is, for example, a high quality TB, and not necessarily the first one available. The WTRU may perform logical channel multiplexing in accordance with the mapping, and if any resources remain, and no more data is available from one of the LC groups, then it may include/multiplex data from the other group onto the TB configured for the other LC group. 
     By way of example, a WTRU may receive a signal that a first LC group, including, for example, LC 1 , LC 3 , and LC 4 , are to be multiplexed on the first TB, while a second LC group, including, for example, LC 2  and LC 5  are to be multiplexed on the second TB. The WTRU will multiplex the traffic on the TBs in a way that adheres to the signaled mapping. As an optional optimization, if the WTRU does not have sufficient data to transmit from one LC group, then data from the other group may be sent on the other TB. Some LCs may be present in more than one group. As another alternative, L2 signaling can be used to configure the mapping or grouping of LC&#39;s onto TBs. 
     Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. The methods or flow charts provided herein may be implemented in a computer program, software, or firmware incorporated 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). 
     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. 
     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) or Ultra Wide Band (UWB) module.