Patent Publication Number: US-11395288-B2

Title: Dynamic transmission mode switching on the physical layer

Description:
RELATED APPLICATIONS 
     This U.S. Patent Application is a continuation of, and claims priority to, U.S. patent application Ser. No. 16/034,280, filed on Jul. 12, 2018, entitled “Dynamic Transmission Mode Switching on the Physical Layer,” which claims priority to provisional U.S. Patent Application No. 62/591,965, entitled “DYNAMIC SWITCHING OF TRANSMISSION MODES 9 AND 4 ON THE PHYSICAL LAYER,” filed on Nov. 29, 2017, the entirety of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     In a telecommunication network, user equipment (UE) can wirelessly connect to a base station in order to engage in voice calls, video calls, data transfers, or other types of communications. For example, a UE can connect to an eNode B (eNB) of a Long Term Evolution (LTE) network. 
     A base station can transmit radio frames that include data for a UE based on a selected transmission mode. The base station may select a particular transmission mode for a UE&#39;s data in a radio frame based on signal quality metrics reported by the UE, as some transmission modes can provide higher throughput to the UE than other transmission modes in different situations. However, the UE may only be able to correctly interpret a received radio frame if it has information about which transmission mode the base station actually selected and used for the UE&#39;s data in that radio frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description is set forth with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference numbers in different figures indicates similar or identical items or features. 
         FIG. 1  depicts user equipment (UE) in communication with a base station of a telecommunications network. 
         FIG. 2  depicts an exemplary radio frame. 
         FIG. 3  depicts an exemplary subframe. 
         FIG. 4  depicts a first example in which a UE knows that a base station supports Transmission Mode Four (TM4) and Transmission Mode Nine (TM9), and thus might be using either Downlink Control Information (DCI) format 2 or DCI format 2C, and finds its unique identifier using DCI format 2. 
         FIG. 5  depicts a second example in which a UE knows that a base station supports TM4 and TM9, and thus might be using either DCI format 2 or DCI format 2C, and finds its unique identifier using DCI format 2C. 
         FIG. 6  depicts an example system architecture for a UE. 
         FIG. 7  depicts an example system architecture for a base station. 
         FIG. 8  depicts a flow chart of an exemplary process through which a UE can dynamically identify, at the physical layer, which transmission mode a base station used to prepare data in a radio frame for the UE. 
     
    
    
     DETAILED DESCRIPTION 
     Introduction 
     A telecommunication network can include base stations, such as eNode Bs (eNBs) in a Long Term Evolution (LTE) network, that wirelessly communicate with user equipment (UE) in cells serviced by the base stations. Some base stations can be configured to support multiple transmission modes. For example, base stations can be set up to select between 3GPP&#39;s Transmission Mode Four (TM4) or Transmission Mode Nine (TM9) when transmitting data for individual UEs in radio frames. In many cases, TM4 can lead to higher throughput than TM9 when a UE is closer to the base station, whereas TM9 can lead to higher throughput than TM4 when the UE is farther away from the base station. 
     A base station can select which transmission mode to use for a UE&#39;s data in one or more radio frames based on signal quality metrics reported by the UE. For example, a UE may report that it is receiving data from the base station at a good signal quality, which often occurs when the UE is relatively close to the base station and is considered to be “near-cell” or “mid-cell.” In this situation, the base station may choose to use TM4 for the UE&#39;s data in the next radio frame. However, if the UE reports that it is receiving data a lower signal quality, which can often occur if the UE is located at the edge of a cell, the base station may instead choose to use TM9 for the UE&#39;s data in the next radio frame, because TM9 can often lead to higher throughput at the cell edge than TM4. 
     In some existing systems, when a base station changes the transmission mode it is using for a particular UE, the base station informs the UE about the change in a Radio Resource Control (RRC) Reconfiguration message so that the UE knows which transmission mode to use when interpreting data in the radio frame. RRC messages are sent in data packets according to the Packet Data Convergence Protocol (PDCP), and are interpreted by UEs at the network layer. Accordingly, when an RRC message indicates a change to the transmission mode, a UE must process the RRC message at the network layer to discover the change and then pass information about the new transmission mode through the medium access control (MAC) layer to the physical layer so that received radio frames can be interpreted at the physical layer using the correct transmission mode. 
     However, in some cases network conditions experienced by a UE can change rapidly, and processing RRC messages that signal transmission mode changes can take too long for a UE to keep up. For example, when a UE is inside a vehicle driving within a cell, it may report poor signal strength while physically located near the cell edge. The base station may accordingly select TM9 for the next radio frame. However, by the time the UE would be able to receive and process an RRC Reconfiguration message from the base station indicating that the base station is now using TM9 for the UE, the UE may have been driven by the vehicle to a location closer to the base station. Accordingly, at that new position the UE may report better signal strength, and the base station may choose to use TM4 for the next radio frame. However, the UE would have just switched to TM9 according the RRC Reconfiguration message, and as such may not be able to keep up with the changing transmission modes. 
     This disclosure describes systems and processes for a UE to dynamically determine at the physical layer which transmission mode to use when interpreting a radio frame. Determining the transmission mode directly at the physical layer during interpretation of a radio frame can be faster than separately determining and implementing a transmission mode change in part through higher layers based on RRC message signaling. 
     In particular, a base station can use an RRC message to initially inform a UE about which transmission modes the base station supports. Each supported transmission mode can correspond to a different Downlink Control Information (DCI) format. The UE can receive this information about which transmission modes a base station supports, and which DCI formats correspond to those transmission modes, prior to interpreting subsequent radio frames. When a UE begins to receive subframes of a new radio frame, the UE can attempt to find the UE&#39;s unique identifier within DCI of individual subframes using the different DCI formats that correspond to the different transmission modes supported by the base station. Once the UE successfully finds its identifier in a subframe&#39;s DCI using one of the DCI formats, the UE can identify the transmission mode that corresponds to that DCI format and then interpret the UE&#39;s data in the remainder of the frame according to that transmission mode. 
     A UE being able to dynamically determine at the physical layer which transmission mode to use when interpreting a radio frame can improve the quality and retainability of individual communication sessions. For example, a voice call may be at risk of being dropped when a UE is at the edge of a cell and has a poor connection to a base station. In the existing systems described above, in which a base station must signal every change to the specific transmission mode it is using in an RRC Reconfiguration message, the voice call may be dropped by the time the UE receives a new RRC Reconfiguration message, analyzes it at higher layers to determine the specific transmission mode now being used, and then propagates information down to the physical layer that causes data to be interpreted using that new specific transmission mode. In contrast, when the UE can dynamically determine at the physical layer which transmission mode to use when interpreting a radio frame as described herein, the UE can directly use that transmission mode at the physical layer to interpret the received data without waiting for a message to be interpreted at a higher layer, thereby increasing the chances that the call will not be dropped. 
     Example Environment 
       FIG. 1  depicts user equipment (UE)  102  in communication with a base station  104  of a telecommunications network. A UE  102  can be any device that can wirelessly connect to a base station  104  in order to engage in communication sessions for voice calls, video calls, data transfers, or any other type of communication via the telecommunication network. For example, a UE  102  can be a smart phone, a cellular phone, a personal digital assistant (PDA), a personal computer (PC), a laptop, a desktop, a workstation, a media player, a tablet, a gaming device, a smart watch, or any other type of computing or communication device. An example UE  102  is illustrated in greater detail in  FIG. 6 , and is described in detail below with reference to that figure. 
     A base station  104  can provide network access to UEs  102  within a cell. A base station  104  can be based on, and/or provide network access through, one or more wireless access technologies. Such wireless access technologies can include fifth generation (5G) technology, Long Term Evolution (LTE)/LTE Advanced technology, High-Speed Data Packet Access (HSDPA)/Evolved High-Speed Packet Access (HSPA+) technology, Universal Mobile Telecommunications System (UMTS) technology, Code Division Multiple Access (CDMA) technology, Global System for Mobile Communications (GSM) technology, WiMax® technology, and WiFi® technology. For example, in an LTE network a base station  104  can be an eNode B (eNB). An example base station  104  is illustrated in greater detail in  FIG. 7 , and is described in detail below with reference to that figure. 
     Various types of data can be sent between the UE  102  and the base station  104 . For example, the base station  104  can transmit a series of radio frames  106  that can be received by one or more UEs  102 . The base station  104  can send Radio Resource Control (RRC) messages  108  to UEs  102  in at least some of the radio frames  106 , as will be described in more detail below. The UE  102  can also send data to the base station  104 , including signal quality measurements  110 . Signal quality measurements  110  can indicate how well the UE  102  is receiving data from the base station  104 . For example, signal quality measurements  110  can include a UE&#39;s indications of received signal quality and/or received signal strength, such as a channel quality indicator (CQI), signal to interference and noise ratio (SINR), or any other signal quality metric. 
     UEs  102  and base stations  104  can be configured to support multiple transmission modes at the physical layer, such as transmission modes defined by 3GPP standards. For example, UEs  102  and base stations  104  can be configured to support 3GPP&#39;s Transmission Mode Four (TM4) and 3GPP&#39;s Transmission Mode Nine (TM9). In some cases, the transmission modes a UE  102  or base station  104  supports can depend in part on the number of antennas it can use to send or receive data. For example, TM4 can be used for closed-loop spatial multiplexing for transmissions by multiple-input multiple-output (MIMO) devices with multiple antennas. TM9 can also be used for spatial multiplexing at up to eight layers by some MIMO devices. 
     Some transmission modes can provide greater throughput from a base station  104  to a UE  102  in certain situations. For example, in some cases TM9 can provide a throughput improvement of approximately 15% percent for UEs  102  near the edge of a cell compared to TM4, while TM4 can provide a throughput improvement of approximately 10% over TM9 for “mid-cell” UEs  102  closer to the base station  104  and a throughput improvement of approximately 30% over TM9 for “near-cell” UEs  102  that are very close to the base station  104 . A base station  104  can accordingly choose one of the multiple transmission modes it supports for a particular UE  102  based on the signal quality measurements  110  reported by that UE  102 . For example, if a UE  102  reports low signal quality measurements  110 , it may indicate that the UE  102  is on the edge of the cell, and the base station  104  can respond by selecting TM9. However, if the UE  102  reports higher signal quality measurements  110 , it may indicate that the UE  102  is at “mid-cell” or “near-cell,” and the base station  104  can respond by selecting TM4. 
     A base station  104  can select the transmission mode to use for a UE  102  for every group of one or more radio frames  106 . For example, a base station  104  can continue using a previous transmission mode or change to a different transmission mode at every radio frame  106 , at every ten radio frames  106 , or at intervals corresponding to any other number of radio frames  106 . 
       FIG. 2  depicts an exemplary radio frame  106 . As noted above, a base station  104  can transmit a series of radio frames  106  that can be received by one or more UEs  102 . Each radio frame  106  can include a plurality of subframes  202 . In some examples, one radio frame  106  can have a duration of ten milliseconds, and include ten distinct subframes  202  that each have a duration of one millisecond. The subframes  202  can each be identified by a subframe number. For example, a single radio frame  106  can include ten subframes  202  identified as subframe  0 , subframe  1 , . . . , and subframe  9 . 
       FIG. 3  depicts an exemplary subframe  202 . A subframe  202  can include data in a Physical Downlink Control Channel (PDCCH)  302  and data in a Physical Downlink Shared Channel (PDSCH)  304 . 
     The PDCCH  302  can be positioned at the beginning of a subframe  202 , and include information that UEs  102  can use to interpret and/or find data in the PDSCH  304  that follows the PDCCH  302  in the subframe  202 . For example, the PDCCH  302  can include Downlink Control Information (DCI)  306 , as will be discussed further below. 
     A subframe&#39;s PDSCH  304  can include data for one or more UEs  102 . For instance, the PDSCH  304  can be divided into multiple resource blocks located at different frequencies, and data for a particular UE  102  can be located at one or more of those resource blocks. A base station  104  can encode data for a particular UE  102  into a subframe&#39;s PDSCH  304  differently depending on which transmission mode it is using for that UE  102 . As discussed above, a base station  104  can change the transmission mode it uses for a particular UE  102  as frequently as every radio frame  106 . However, the base station  104  can use a consistent transmission mode for a UE  102  during each subframe  202  of a particular radio frame  106 . 
     In the PDCCH  302 , DCI  306  can include information that instructs UEs  102  how to locate and/or decode data in resource blocks of the PDSCH  304  that is intended for those UEs  102 . For instance, for a particular UE  102 , DCI  306  can indicate the location and/or number of resource blocks in the PDSCH  304  that are intended for that particular UE  102 , modulation and coding schemes used to encode data in those resource blocks, number of layers, and/or other types of information. 
     Because a subframe&#39;s PDSCH  304  can include data intended for more than one UE  102 , DCI  306  in the subframe&#39;s PDCCH  302  can be marked in part using unique identifiers for those UEs  102  to distinguish between DCI  306  intended for different UEs  102 . In some examples, the unique identifiers can be scrambled in the DCI  306  with a cyclic redundancy check (CRC), such that individual UEs  102  can only descramble the portion of the DCI  306  marked with their unique identifier. 
     In some examples, a UE&#39;s unique identifier can be a cell-radio network temporary identifier (C-RNTI) that is assigned to the UE  102  by a base station  104  when the UE  102  initially connects to that base station  104 . As such, DCI  306  within subframes  202  transmitted by a base station  104  can be marked with C-RNTIs to identify DCI  306  for corresponding UEs  102 . A particular UE  102  can accordingly use DCI  306  that is marked with its C-RNTI to locate and interpret resource blocks in the PDSCH  304  that contain data for that particular UE  102 . 
     When a UE  102  receives a new subframe  202  from a base station  104 , it may not know whether that particular subframe  202  contains any data for the UE  102 . Accordingly, the UE  102  can perform a blind search of the PDCCH  302  on the physical layer to determine if it contains any DCI  306  marked with the UE&#39;s identifier, such as the UE&#39;s C-RNTI, as described above. If it does, the UE  102  can use the DCI  306  marked with the UE&#39;s identifier to locate and/or decode data in the PDSCH  304  that is intended for that UE  102 . 
     As discussed above, data in the PDSCH  304  for a particular UE  102  can be encoded differently depending on the transmission mode selected for the radio frame  106  by the base station  104  for that UE  102 . Each of the multiple transmission modes can correspond to a different DCI format that can be used to encode the DCI  306  in the PDCCH  302 . For example, 3GPP&#39;s DCI format 2 can be associated with TM4, while 3GPP&#39;s DCI format 2C can be associated with TM9. Because the DCI  306  for a particular UE  102  can be encoded using different DCI formats depending on which transmission mode the base station  104  is actually using for the UE  102  in the current radio frame  106 , during a blind search of the PDCCH  302  the UE  102  may only be able to identify whether a subframe  202  contains DCI  306  marked with the UE&#39;s identifier if the UE  102  uses the correct DCI format to interpret the DCI  306 . 
     A base station  104  can send a UE  102  an RRC message  108 , such as an RRC Connection Setup message, RRC Reconfiguration message, or any other RRC message, that identifies which transmission modes are supported by the base station  104 . For example, a base station  104  can use an optional field in an RRC Reconfiguration message, such as an “antennaInfo-r10 explicitValue-r10” field, as follows to indicate that the base station  104  supports both TM4 and TM9: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 antennaInfo-r10 explicitValue-r10 : 
               
               
                   
                 { 
               
            
           
           
               
               
            
               
                   
                 transmissionMode-r10 tm4, 
               
               
                   
                 transmissionMode-r10 tm9, 
               
               
                   
                 ue-TransmitAntennaSelection release : NULL 
               
            
           
           
               
               
            
               
                   
                 }. 
               
               
                   
                   
               
            
           
         
       
     
     The UE  102  can use the information in the RRC message  108  about which transmission modes a base station  104  supports to identify which corresponding DCI formats might be used by the base station  104  in a subframe&#39;s PDCCH  302 . For example, if a UE  102  receives the RRC Reconfiguration message shown above, which indicates that a base station  104  supports TM4 and TM9, the UE  102  can determine that the base station  104  will use DCI format 2 when it has selected TM4 for the UE  102 , and DCI format 2C when it has selected TM9 for the UE  102 . 
     When the UE  102  receives the first subframe  202  of a new radio frame  106 , it may not yet know which transmission mode the base station  104  is using for the UE&#39;s data in that radio frame  106 . However, the UE  102  may know from an earlier RRC message  108  that a base station  104  supports at least two transmission modes, and thus might be using any of at least two DCI formats that correspond to the supported transmission modes. The UE  102  can perform blind searches on the physical layer using DCI formats corresponding to the supported transmission modes. to determine if it can find its unique identifier in the subframe&#39;s DCI  306 . Once the UE  102  finds its unique identifier using one of the DCI formats, the UE  102  can identify the transmission mode that corresponds to that DCI format, and use the identified transmission mode to interpret the subframe  202  and subsequent subframes  202  of the current radio frame  106 . 
     In some examples, the UE  102  can perform blind searches at the physical layer during different DCI formats in an order determined by the order of the transmission modes listed in a base station&#39;s RRC message  108 . For example, a UE  102  can perform a first blind search using a first DCI format corresponding to a first transmission mode listed in the RRC message  108 , and then move on to performing a second blind search using a second DCI format corresponding to a second transmission mode listed in the RRC message  108  if the first blind search is unsuccessful. In other examples, the UE  102  can perform a first blind search using a DCI format that was used to successfully find the UE&#39;s identifier in a previous radio frame  106 , and then move on to performing one or more other blind searches using different DCI formats if the first blind search was unsuccessful. 
       FIG. 4  depicts a first example in which a UE  102  knows from an earlier RRC message  108  that a base station  104  supports TM4 and TM9, and thus might be using either DCI format 2 or DCI format 2C. The UE  102  can perform a blind search of the PDCCH  302  in a first subframe  202  using DCI format 2 in an attempt to find the UE&#39;s C-RNTI in the DCI  306 . In this example, the UE  102  successfully finds its C-RNTI using DCI format 2 in DCI  306  in the first subframe  202 . The UE  102  can accordingly use TM4, which corresponds to DCI format 2, to interpret data for the UE  102  in the first subframe&#39;s PDSCH  304 . 
     In the example of  FIG. 4 , because the base station  104  does not change transmission modes between subframes  202  of the same radio frame  106 , the UE  102  can continue using DCI format 2 when performing blind searches for its C-RNTI in subsequent subframes  202  of the same radio frame  106 , and continue using TM4 to interpret data for the UE  102  in the PDSCH  304  of those subframes  202 . If the UE  102  does not find its C-RNTI in the PDCCH  302  of a subsequent subframe  202  using DCI format 2, then there is no data for the UE  102  in that subframe&#39;s PDSCH  304  and the UE  102  can wait until the next subframe  202 . If the UE  102  does find its C-RNTI in the PDCCH  302  of a subsequent subframe  202  using DCI format 2, the UE  102  can interpret data for the UE  102  in the subframe&#39;s PDSCH  304  using TM4. 
       FIG. 5  depicts a second example in which a UE  102  knows from an earlier RRC message  108  that a base station  104  supports TM4 and TM9, and thus might be using either DCI format 2 or DCI format 2C. Like  FIG. 4 , the UE  102  performs a blind search of the PDCCH  302  in a first subframe  202  using DCI format 2 in an attempt to find the UE&#39;s C-RNTI in the DCI  306 . However, in this example the UE  102  is unable to find its C-RNTI using DCI format 2, but retries the blind search using DCI format 2C and is able to successfully find its C-RNTI in DCI  306  in the first subframe  202  using DCI format 2C. The UE  102  can accordingly use TM9, which corresponds to DCI format 2C, to interpret data for the UE  102  in the first subframe&#39;s PDSCH  304 . 
     In the example of  FIG. 5 , because the base station  104  does not change transmission modes between subframes  202  of the same radio frame  106 , the UE  102  can continue using DCI format 2C when performing blind searches for its C-RNTI in subsequent subframes  202  of the same radio frame  106 , and continue using TM9 to interpret data for the UE  102  in the PDSCH  304  of those subframes  202 . If the UE  102  does not find its C-RNTI in the PDCCH  302  of a subsequent subframe  202  using DCI format 2C, then there is no data for the UE  102  in that subframe&#39;s PDSCH  304  and the UE  102  can wait until the next subframe  202 . If the UE  102  does find its C-RNTI in the PDCCH  302  of a subsequent subframe  202  using DCI format 2C, the UE  102  can interpret data for the UE  102  in the subframe&#39;s PDSCH  304  using TM9. 
     Although  FIGS. 4 and 5  depict examples in which a UE  102  successfully finds its C-RNTI in DCI  306  of a first subframe  202  using either DCI format 2 or DCI format 2C, in some cases the UE  102  may not find its C-RNTI in the first subframe  202  using any of the DCI formats that correspond to transmission modes supported by the base station  104 . In these cases, the first subframe  202  may not contain any data for the UE  102 , and the UE  102  can retry the blind search for its C-RNTI using the different DCI formats in subsequent subframes  202 . For example, if the first data for a UE  102  in a radio frame  106  is contained in the third subframe  202 , the UE  102  can perform blind searches for its C-RNTI using both DCI format 2 and DCI format 2C at the first and second subframes  202  without success. However, at the third subframe  202  the UE  102  can successfully find its C-RNTI using one of the DCI formats. The UE  102  can then continue with that successful DCI format and its corresponding transmission mode for the remainder of the subframes  202  in the radio frame  106 . 
     Example Architecture 
       FIG. 6  depicts an example system architecture for a UE  102 , in accordance with various examples. As shown, a UE  102  can include a memory  602  that stores modules and data  604 , processor(s)  606 , radio interfaces  608 , a display  610 , output devices  612 , input devices  614 , and/or a drive unit  616  including a machine readable medium  618 . 
     In various examples, memory  602  can include system memory, which may be volatile (such as RAM), non-volatile (such as ROM, flash memory, etc.) or some combination of the two. Memory  602  can further include non-transitory computer-readable media, such as volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. System memory, removable storage, and non-removable storage are all examples of non-transitory computer-readable media. Examples of non-transitory computer-readable media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium which can be used to store the desired information and which can be accessed by the UE  102 . Any such non-transitory computer-readable media may be part of the UE  102 . In some examples, memory  602  can also include a SIM (subscriber identity module) card, which is a removable memory card used to identify a user of the UE  102  to a telecommunication network. 
     The modules and data  604  can be utilized by the UE  102  to perform or enable performing any action taken by the UE  102 . The modules and data  604  can include a UE platform and applications, and data utilized by the platform and applications. The modules and data  604  can also include information about transmission modes that are supported by a particular base station  104 , and information about corresponding DCI formats, which the UE  102  can identify after receiving an RRC message  108  containing information about supported transmission modes from a base station  104 . 
     In various examples, the processor(s)  606  can be a central processing unit (CPU), a graphics processing unit (GPU), or both CPU and GPU, or any other type of processing unit. Each of the one or more processor(s)  606  may have numerous arithmetic logic units (ALUs) that perform arithmetic and logical operations, as well as one or more control units (CUs) that extract instructions and stored content from processor cache memory, and then executes these instructions by calling on the ALUs, as necessary, during program execution. The processor(s)  606  may also be responsible for executing all computer applications stored in the memory  602 , which can be associated with common types of volatile (RAM) and/or nonvolatile (ROM) memory. 
     The radio interfaces  608  can include one or more transceivers, modems, receivers, transmitters, antennas, error correction units, symbol coders and decoders, processors, chips, application specific integrated circuits (ASICs), programmable circuit (e.g., field programmable gate arrays), firmware components, and/or other components that perform or assist in exchanging radio frequency (RF) communications with a base station  104 . For example, a UE  102  can have one or more radio interfaces  608  that are compatible with a base station  104 , such as one or more antennas configured to send data to the base station  104  and/or receive data from the base station  104 . In some examples, a processor  606 , other modules and data  604 , and/or other components of the UE  102  can perform or assist in transmitting and/or receiving data, and/or pre-processing or post-processing of such data, instead of or in combination with the radio interfaces  608 . 
     In particular, the radio interfaces  608 , processors  606 , and/or other modules and data  604  can perform operations at the physical layer to analyze subframes  202  of radio frames  106  received from a base station  104  as described above. For example, the UE  102  can use its radio interfaces  608 , processors  606 , and/or other modules and data  604  to perform blind searches at the physical layer for the UE&#39;s unique identifier in DCI  306  of a subframe  202  based on one or more DCI formats that correspond to transmission modes supported by the base station  104 , and/or interpret data for the UE  102  in the PDSCH  304  of subframes  202  according to an identified transmission mode. 
     The display  610  can be a liquid crystal display or any other type of display commonly used in UEs  102 . For example, display  610  may be a touch-sensitive display screen, and can then also act as an input device or keypad, such as for providing a soft-key keyboard, navigation buttons, or any other type of input. 
     The output devices  612  can include any sort of output devices known in the art, such as a display  610 , speakers, a vibrating mechanism, and/or a tactile feedback mechanism. Output devices  612  can also include ports for one or more peripheral devices, such as headphones, peripheral speakers, and/or a peripheral display. 
     The input devices  614  can include any sort of input devices known in the art. For example, input devices  614  can include a microphone, a keyboard/keypad, and/or a touch-sensitive display, such as the touch-sensitive display screen described above. A keyboard/keypad can be a push button numeric dialing pad, a multi-key keyboard, or one or more other types of keys or buttons, and can also include a joystick-like controller, designated navigation buttons, or any other type of input mechanism. 
     The machine readable medium  618  can store one or more sets of instructions, such as software or firmware, that embodies any one or more of the methodologies or functions described herein. The instructions can also reside, completely or at least partially, within the memory  602 , processor(s)  606 , and/or radio interface(s)  608  during execution thereof by the UE  102 . The memory  602  and the processor(s)  606  also can constitute machine readable media  618 . 
       FIG. 7  depicts an example system architecture for a base station  104 , in accordance with various examples. As shown, a base station  104  can include processor(s)  702 , memory  704 , and transmission hardware  706 . 
     In various examples, the processor(s)  702  can be a central processing unit (CPU), a graphics processing unit (GPU), both CPU and GPU, or any other type of processing unit. Each of the one or more processor(s)  702  may have numerous arithmetic logic units (ALUs) that perform arithmetic and logical operations, as well as one or more control units (CUs) that extract instructions and stored content from processor cache memory, and then executes these instructions by calling on the ALUs, as necessary, during program execution. The processor(s)  702  may also be responsible for executing all computer applications stored in the memory  704 , which can be associated with common types of volatile (RAM) and/or nonvolatile (ROM) memory. 
     In various examples, memory  704  can include system memory, which may be volatile (such as RAM), non-volatile (such as ROM, flash memory, etc.) or some combination of the two. The memory  704  can also include additional data storage devices (removable and/or non-removable) such as, for example, magnetic disks, optical disks, or tape. Memory  704  can further include non-transitory computer-readable media, such as volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. System memory, removable storage, and non-removable storage are all examples of non-transitory computer-readable media. Examples of non-transitory computer-readable media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium which can be used to store the desired information and which can be accessed by the base station  104 . Any such non-transitory computer-readable media may be part of the base station  104 . 
     The transmission hardware  706  can include one or more modems, receivers, transmitters, antennas, error correction units, symbol coders and decoders, processors, chips, application specific integrated circuits (ASICs), programmable circuit (e.g., field programmable gate arrays), firmware components, and/or other components that can establish connections with one or more UEs  102 , transmit data, and monitor the connections. For example, in an LTE network, the transmission hardware  706  can establish and manage connections with one or more UEs  102 . The transmission hardware  706  can handle transmissions and protocol exchanges on the baseband, such as a physical LTE connection, as well as the physical (PHY) and media access control (MAC) layers of a protocol stack. 
     The transmission hardware  706  can support multiple transmission modes, such that the base station  104  can select a particular transmission mode to use for data for particular UEs  102  when transmitting radio frames  106 . As discussed above, the base station&#39;s selection of a particular transmission mode for a particular UE  102  can be based on signal quality measurements  110  reported by that UE  102  to the base station  104 . The processors  702  and/or transmission hardware  706  can accordingly perform operations that prepare and transmit radio frames  106  using the selected transmission modes, including encoding DCI  306  for particular UEs  102  using DCI formats corresponding to the selected transmission modes. The transmission hardware  706  can also be used to transmit RRC messages  108  in radio frames  106  that indicate to UEs  102  which transmission modes are supported by the base station  104 . 
     Example Operations 
       FIG. 8  depicts a flow chart of an exemplary process through which a UE  102  can dynamically identify, at the physical layer, which transmission mode a base station  104  used to prepare data in a radio frame  106  for the UE  102 . Prior to using the process of  FIG. 8  to analyze subframes  202  of a new radio frame  106 , the UE  102  can have received an RRC message  108  from the base station  104  that identifies a plurality of transmission modes that the base station  104  is configured to use. From this RRC message  108 , the UE  102  can determine which transmission modes, and which corresponding DCI formats, the base station  104  may be using to prepare data for the UE  102  within radio frames  106 . 
     At block  802 , the UE  102  can receive a new subframe  202  of a radio frame  106  from a base station  104 . In some examples, this new subframe  202  can be the first subframe  202  of the radio frame  106 , although the new subframe  202  can be a later subframe  202  in the radio frame  106  if the UE  102  cannot find its unique identifier in the first subframe  202  using the process of  FIG. 8 . 
     At block  804 , the UE  102  can select a DCI format to use. As described above, the UE  102  can have previously determined from an RRC message  108  that the base station  104  supports a plurality of transmission modes. The UE  102  can accordingly determine that the base station may be any one of a plurality of DCI formats that correspond to those supported transmission modes, depending on which transmission mode is being used for the current radio frame  106 . As such, at block  804 , the UE  102  can select one of the DCI formats it has determined the base station  104  may be using for the current radio frame  106 . 
     In some examples, during a first pass through block  804 , the UE  102  can select a DCI format corresponding to the first transmission mode listed in the base station&#39;s RRC message  108 , and then select a different DCI format during each subsequent pass through block  804  in an order corresponding to the order of the transmission modes listed in the base station&#39;s RRC message  108 . In other examples, during a first pass through block  804 , the UE  102  can select a DCI format corresponding to a transmission mode found to have been used in a previous radio frame  106 . For example, if the UE  102  determines that TM9 was used in the preceding radio frame  106 , the UE  102  can initially select corresponding DCI format 2C during a first pass through block  804  for the current radio frame  106  even if TM9 is listed second in the base station&#39;s RRC message  108 . During subsequent passes through block  804 , the UE  102  can select other DCI formats known to correspond with other transmission modes supported by the base station  104 . In still other examples, the UE  102  can select the DCI format randomly or in any other during initial and/or subsequent passes through block  804 . 
     At block  806 , the UE  102  can use the currently selected DCI format to perform a blind search at the physical layer of the subframe&#39;s PDCCH  302  for DCI  306  marked using a unique identifier for the UE  102 , such as its C-RNTI. In some examples, the UE  102  may attempt to descramble the DCI  306  in addition to using the currently selected DCI format when looking for its unique identifier. 
     At block  808 , the UE  102  can determine if it was able to find its unique identifier in the DCI  306  of the subframe  202  using the currently selected DCI format. If the UE  102  was not able to find its unique identifier using the currently selected DCI format, the UE  102  can move to block  810 . However, if the UE  102  was able to find its unique identifier using the currently selected DCI format, the UE  102  can move to block  812 . 
     At block  810 , when the UE  102  could not find its unique identifier in the DCI  306  of the subframe  202  using the currently selected DCI format during the previous pass through blocks  804  through  808 , the UE  102  can determine if there are additional DCI formats the UE  102  has not yet tried at the current subframe  202  that correspond to transmission modes supported by the base station  104 . If there are such additional DCI formats that the UE  102  has not yet tried, the UE  102  can return to block  804  and select a different one of those DCI formats. However, if the UE  102  has tried all of the possible DCI formats corresponding to transmission modes supported by the base station  104  during different passes through blocks  804  through  808 , and the UE  102  has not found its unique identifier in the DCI  306  of the subframe  202  using any of those DCI formats, the UE  202  can determine that there is no data in the current subframe  202  for the UE  102 , and can wait for the first subframe  202  of the next radio frame  106  to begin again at block  802 . 
     At block  812 , when the UE  102  has found its unique identifier in the DCI  306  of the subframe  202  using the currently selected DCI format, the UE  102  can identify the transmission mode that corresponds to the currently selected DCI format. For example, if the UE  102  found its unique identifier in the DCI  306  using DCI format 2, the UE  102  can identify TM4 as the corresponding transmission mode. As another example, if the UE  102  found its unique identifier in the DCI  306  using DCI format 2C, the UE  102  can identify TM9 as the corresponding transmission mode. The UE  102  can then use the currently selected DCI format and the corresponding transmission mode to interpret data for the UE  102  in the current subframe  202 , and in any subsequent subframe  202  of the current radio frame  106 . For example, if the currently selected DCI format and corresponding transmission mode are DCI format 2 and TM4, the UE  102  can continue to use DCI format 2 to perform blind searches for its unique identifier in DCI  306  of subsequent subframes  202  within the same radio frame  106 , and if it finds its unique identifier in any subsequent subframe  202  using DCI format 2, it can use TM4 to interpret data for the UE  102  in that subframe&#39;s PDSCH  304 . After interpreting data in the current subframe  202  and remaining subframes  202  of the current radio frame  106  according to the currently selected DCI format and corresponding transmission mode at block  812 , the UE  102  can begin again at block  802  for the next radio frame  106 . 
     Conclusion 
     As described above, a UE  102  can, at the physical layer, determine from a subframe&#39;s DCI  306  which transmission mode was used by a base station  104  to prepare data in the radio frame  106  for the UE  102 , by determining which DCI format allows the UE to find its unique identifier in the DCI  306  and identifying which transmission mode corresponds to that DCI format. Accordingly, the UE  102  can directly use that transmission mode identified at the physical layer to interpret data for the UE  102  in the subframe  202  and subsequent subframes  202  of the same radio frame  106 . This allows the UE  102  to determine and use the correct transmission mode directly at the physical layer, without waiting for a message to be processed at higher layers that indicates the specific transmission mode used by the base station  104 . 
     Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example embodiments.