Patent Publication Number: US-10312986-B2

Title: Flexible CSI RS configuration for FD-MIMO systems

Description:
CLAIM OF PRIORITY 
     This Application is a National Stage Entry of, and claims priority to, PCT Application Serial Number PCT/RU2015/000924, filed on Dec. 24, 2015 and entitled “Flexible CSI-RS Configuration For FD-MIMO Systems,” which claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 62/207,215 filed Aug. 19, 2015 and entitled “Flexible CSI-RS Configuration For FD-MIMO,” both of which are herein incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     Channel State Information Reference Signals (CSI-RS) were introduced for LTE-Advanced (Long-Term Evolution) in Release 10 of the 3GPP (3rd Generation Partnership Project) specification. To use this feature, an eNB (Evolved Node-B) establishes a wireless communications channel with a UE (User Equipment), after which CSI-RS symbols are transmitted from the eNB to the UE. The UE performs channel state information measurements on the CSI-RS symbols in order to calculate channel state information. The UE then returns the channel state information to the eNB, in order to provide information to the eNB about the downlink signal quality for the wireless communications channel. 
     Meanwhile, Release 8 of the 3GPP specification provides for MIMO (Multiple Input Multiple Output) antenna configurations, and subsequent enhancements in Release 10 and Release 11 extend these provisions. MIMO may support beamforming to increase downlink channel quality. For Release 10, UEs may support 2-port antennas, 4-port antennas, or 8-port antennas. Under Release 13, UEs may support antennas comprising more ports, such as 12-port and 16-port antennas. Antennas comprising even greater numbers of ports are contemplated for Release 14, such as 32-port and 64-port antennas. 
     Through Release 11, the 3GPP specification is designed to support MIMO antenna configurations that are capable of adaptation in azimuth (i.e., a radial angle with respect to a reference angle in a horizontal plane). In future releases, however, the 3GPP specification may support FD-MIMO (Full-Dimensional MIMO) antenna configurations that are capable of adaptation in both azimuth and elevation. 
     Non-precoded CSI-RS may support FD-MIMO by facilitating channel state information measurement at the UE, which may in turn facilitate precoding selection for eNB antennas. At the same time, Release 13 will support the use of non-precoded CSI-RS with 12- and 16-port antennas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of the disclosure will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the disclosure. However, while the drawings are to aid in explanation and understanding, they are only an aid, and should not be taken to limit the disclosure to the specific embodiments depicted therein. 
         FIGS. 1-3  illustrate embodiments of CSI-RS antenna port allocations within downlink RBs (Resource Blocks), detailing which REs (Resource Elements) within the subframe are associated with which CSI-RS antenna ports. 
         FIGS. 4-6  illustrate embodiments of eNB antenna and antenna port configurations, along with corresponding CSI-RS antenna port allocations. 
         FIG. 7  illustrates a variety of embodiments of antenna configurations. 
         FIG. 8  illustrates an embodiment of an eNB employing FD-MIMO beamforming to communicate with a plurality of UEs, as well as eNB antenna pairs that are generally available for transmission in general and eNB antenna pairs that are available to transmit to a specific UE. 
         FIGS. 9-10  illustrate embodiments of eNB antenna pairs that are available for transmission in general and eNB antenna pairs that are available to transmit to a specific UE, along with corresponding CSI-RS antenna ports. 
         FIGS. 11-13  illustrate embodiments of CSI-RS groups for use in configuring UE antennas. 
         FIG. 14  illustrates an embodiment of a protocol between an eNB and a UE for using CSI-RS groups to configure UE antennas. 
         FIG. 15  illustrates an embodiment of an eNB and an embodiment of a UE. 
         FIG. 16  illustrates an embodiment of a hardware processing circuitry for an eNB. 
         FIG. 17  illustrates an embodiment of a hardware processing circuitry for a UE. 
         FIGS. 18-19  illustrate embodiments of methods for using CSI-RS groups to configure UE antennas. 
         FIG. 20  illustrates example components of a UE device in accordance with some embodiments. 
         FIG. 21  illustrates a computing device with mechanisms to provide a flexible CSI-RS protocol, according to some embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The trend in 3GPP specification releases is to support wireless communication channels based upon higher numbers of antennas. In part, the trend toward higher numbers of antennas per channel is due to antenna configurations supporting MIMO, and in the future to antenna configurations supporting FD-MIMO. 
     A new CSI-RS protocol may advantageously support an ever-increasing numbers of antennas. At the same time, a new CSI-RS protocol may advantageously support more flexible assignment of antenna ports, which may lead to more optimal channel quality. 
     In the following description, numerous details are discussed to provide a more thorough explanation of embodiments of the present disclosure. It will be apparent to one skilled in the art, however, that embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring embodiments of the present disclosure. 
     Note that in the corresponding drawings of the embodiments, signals are represented with lines. Some lines may be thicker, to indicate a greater number of constituent signal paths, and/or have arrows at one or more ends, to indicate a direction of information flow. Such indications are not intended to be limiting. Rather, the lines are used in connection with one or more exemplary embodiments to facilitate easier understanding of a circuit or a logical unit. Any represented signal, as dictated by design needs or preferences, may actually comprise one or more signals that may travel in either direction and may be implemented with any suitable type of signal scheme. 
     Throughout the specification, and in the claims, the term “connected” means a direct electrical, mechanical, or magnetic connection between the things that are connected, without any intermediary devices. The term “coupled” means either a direct electrical, mechanical, or magnetic connection between the things that are connected or an indirect connection through one or more passive or active intermediary devices. The term “circuit” or “module” may refer to one or more passive and/or active components that are arranged to cooperate with one another to provide a desired function. The term “signal” may refer to at least one current signal, voltage signal, magnetic signal, or data/clock signal. The meaning of “a,” “an,” and “the” include plural references. The meaning of “in” includes “in” and “on.” 
     The terms “substantially,” “close,” “approximately,” “near,” and “about” generally refer to being within +/−10% of a target value. Unless otherwise specified the use of the ordinal adjectives “first,” “second,” and “third,” etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner. 
     For the purposes of the present disclosure, the phrases “A and/or B” and “A or B” mean (A), (B), or (A and B). For the purposes of the present disclosure, the phrase “A, B, and/or C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C). 
       FIGS. 1-3  illustrate embodiments of CSI-RS antenna port allocations within downlink RBs (Resource Blocks), detailing which REs (Resource Elements) within the subframe are associated with which CSI-RS antenna ports. As depicted in  FIG. 1 , a downlink resource block  100  in accordance with Release 10 of the 3GPP specification is composed of a plurality of subcarriers  110  in the frequency domain and a plurality of OFDM (Orthogonal Frequency-Division Multiplexing) symbols  120  in the time domain. For each subcarrier k and each OFDM symbol l, resource block  100  has a resource element  130 . 
     As shown, for each resource element  130  of downlink resource block  100  (i.e., for each subcarrier and OFDM symbol combination k &amp; l), a particular type of RE is defined. For example, resource element  130  at subcarrier  0  &amp; OFDM symbol  0  of resource block  100  is defined to be a PDCCH (Physical Downlink Control Channel) symbol, as are most of the other resource elements  130  of OFDM symbols  0  through  2 . Meanwhile, resource elements  130  at subcarriers  2 ,  5 ,  8 , and  11  &amp; OFDM symbols  0  and  1  are defined to be CRS (Cell-Specific Reference Symbols) symbols for various ports; resource elements  130  at subcarriers  3 ,  7 , and  11  &amp; OFDM symbol  3  are defined to be DMRS (Demodulation Reference Symbols) symbols in accordance with Release 8; and resource elements  130  at subcarriers  0 - 1 ,  5 - 6 , and  10 - 11  &amp; OFDM symbols  5 - 6  and  12 - 13  are defined to be DMRS in accordance with Release-9 and Release-10. Many of the remaining resource elements  130  are defined to be PDSCH (Physical Downlink Shared Channel) symbols. 
     Some resource elements  130  are defined to be CSI-RS symbols. More specifically, resource elements at all subcarriers &amp; OFDM symbols  9 - 10 , as well as resource elements at subcarriers  2 - 3  and  8 - 9  &amp; OFDM symbols  5 - 6  and  12 - 13 , are defined to be CSI-RS symbols.  FIG. 1  depicts a plurality of CSI-RS resource elements  150  for those combinations of subcarriers  110  &amp; OFDM symbols  120  which are defined to be CSI-RS symbols. 
     Each CSI-RS resource element  150  is enumerated  0  or  1 , and corresponds with an antenna port  15  or  16  of the eNB from which resource block  100  is transmitted. Similarly,  FIG. 2  depicts a plurality of CSI-RS resource elements  260  enumerated  0  through  3  and corresponding with antenna ports  15  through  18  of the transmitting eNB, and  FIG. 3  depicts a plurality of CSI-RS resource elements  370  enumerated  0  through  7  and corresponding with antenna ports  15  through  22  of the transmitting eNB. 
       FIG. 1  depicts CSI-RS resource elements  150  with 1-port or 2-port antennas,  FIG. 2  depicts CSI-RS resource elements  260  associated with 4-port antennas, and  FIG. 3  depicts CSI-RS resource elements  370  associated with 8-port antennas. The eNB can accordingly transmit CSI-RS symbols to a UE for wireless communication channels associated with 1 eNB antenna port, 2 eNB antenna ports, 4 eNB antenna ports, or 8 eNB antenna ports. 
     Antenna ports are logical constructs, as opposed to the physical antennas of an eNB or UE. Accordingly, an ordered set of antenna ports may correspond to a set of eNB antennas in a variety of ways.  FIGS. 4-6  illustrate embodiments of eNB antenna and antenna port configurations, along with corresponding CSI-RS antenna port allocations. (CSI reference signals may be transmitted on 1-port, 2-port, 4-port, and 8-port antennas using antenna ports numbered  15  through  22 ; accordingly, where  FIGS. 1-3  number the associated resource elements bearing CSI-RS symbols from  0  to  7 , the associated eNB antenna ports in  FIGS. 4-6  are numbered from  15  through  22 . The numbering of eNB from  15  through  22  reflects the numbering of CSI-RS configurations, which will be discussed further below.) 
       FIG. 4 , for example, depicts an eNB antenna configuration  410  and corresponding antenna port configuration  416  for an 8-port eNB antenna. Antenna configuration  410  includes a plurality of first antennas  412  having a first polarization and a plurality of second antennas  414  having a second polarization, where the second polarization is orthogonal to the first polarization. First antennas  412  and second antennas  414  are mapped to various eNB antenna ports in accordance with an antenna port configuration  416 , which shows that eNB antenna ports  15 - 18  correspond to first antennas  412  and eNB antenna ports  19 - 22  correspond to second antennas  414 . Accordingly, the antennas corresponding to eNB antenna ports  15 - 18  have a polarization orthogonal to the antennas corresponding to eNB antenna ports  19 - 22 . Corresponding resource block  400  depicts RE pairs  420  bearing CSI-RS symbols that are associated with each eNB antenna port (each RE pair being two adjacent OFDM symbols on one subframe). 
     In  FIG. 4 , all antennas ports associated with the 8-antenna channel correspond to RE pairs  420  bearing CSI-RS symbols. Individual RE pairs  420  correspond to antennas of the same polarization. As a result, if used in isolation, RE pairs  420  will not allow for CSI-RS measurement of orthogonally-polarized pairs of antennas. However, since CSI-RS for the 8-antenna channel span antenna ports  15 - 22 , and since the eNB antennas corresponding to antenna ports  15 - 18  and antenna ports  19 - 22  are orthogonally polarized, RE pairs  420  bearing CSI-RS symbols will allow for CSI-RS measurement of orthogonally-polarized pairs of antennas within the 8-antenna channel. This may be advantageous, since channel state information measurements of CSI-RS symbols transmitted by orthogonally-polarized antennas may lead to better channel performance. 
     In contrast,  FIG. 5  depicts an eNB antenna configuration  510  and corresponding antenna port configuration  516  for a 4-port eNB antenna. Unlike antenna configuration  410 , however, antenna configuration  510  only includes a plurality of first antennas  512  having a first polarization, and no second antennas  514  having a second polarization orthogonal to the first polarization. First antennas  512  are mapped to various antenna ports in accordance with an antenna port configuration  516 . Based upon codebook design principles, the antenna ports of antenna port configuration  510  are first mapped to antennas of one polarization and then to antennas of another polarization—which in this case means only antennas of one polarization. Corresponding resource block  400  depicts RE pairs  520  bearing CSI-RS symbols that are associated with each eNB antenna port. 
     Since antenna ports  15 - 18  are only mapped to first antennas  512 , the antenna ports corresponding to RE pairs  520  bearing CSI-RS symbols will not allow for CSI-RS measurement of orthogonally-polarized pairs of antennas for the 4-antenna channel. This may be disadvantageous, since channel state information measurements of CSI-RS symbols transmitted by antennas that are not orthogonally polarized may lead to suboptimal channel performance. 
     The embodiment depicted in  FIG. 6  has an eNB antenna configuration  610  and corresponding antenna port configuration  616  for an alternate 4-port eNB antenna. Here, antenna configuration  610  includes two first antennas  612  having a first polarization and two second antennas  614  having a second polarization orthogonal to the first polarization. Since antenna ports  15 - 18  are mapped to both first antennas  612  and orthogonally-polarized second antennas  614 , and since CSI-RS symbols transmitted by these antennas will be used for channel state information measurements, this embodiment may advantageously lead to better performance of the wireless communication channel associated with the 4-port eNB antenna. 
     However, the antenna ports associated with RE pairs  620  in corresponding resource block  400  have port assignments that are inconsistent with the CSI-RS antenna port assignments for 4-port antennas in  FIG. 2 . Based on  FIGS. 4-6 , a new, more flexible CSI-RS protocol capable of supporting a more flexible assignment of antenna ports may advantageously facilitate the establishment of higher quality wireless communication channels. 
     A new, more flexible CSI-RS protocol may also advantageously accommodate assignment of more suitable eNB antenna resources to wireless communication channels formed with specific UEs.  FIG. 7  illustrates a variety of embodiments of antenna configurations. Antenna configuration  710  is a 16-antenna array for an eNB, in which all 16 antennas are mapped to antenna ports for one wireless communication channel. In contrast, in antenna configuration  720 , only 12 antennas of the 16-antenna array are mapped to antenna ports for a wireless communication channel. Antenna configurations  730  and  740  show two different embodiments in which 8 antennas of the 16-antenna array are mapped to antenna ports for a wireless communication channel. More particularly, in antenna configuration  730 , 8 antennas of one column of the 16-antenna array are mapped to 8 antenna ports for a wireless communication channel, whereas in antenna configuration  740 ,  4  antennas from each of two columns are mapped to a total of 8 antenna ports for a wireless communication channel. A new, more flexible CSI-RS protocol may facilitate the assignment of the remaining antennas to one or more additional wireless communication channels, based upon the needs of the eNB. 
     A new, more flexible CSI-RS protocol may also advantageously support FD-MIMO, which may require adaptation in both azimuth and elevation.  FIG. 8  illustrates an embodiment of an eNB employing FD-MIMO beamforming to communicate with a plurality of UEs, as well as eNB antenna pairs that are generally available for transmission in general and eNB antenna pairs that are available to transmit to a specific UE. An eNB  800  is depicted at the top of  FIG. 8  as having established wireless communications channels with a UE  822 , a UE  824 , a UE  826 , and a UE  828 , which have differing azimuth and elevation relative to eNB  800 . 
     At the bottom of  FIG. 8 , beam diagram  840  depicts various antenna pairs  842  that are available for transmission in general, i.e., that are available for beamforming by eNB  800 . Antenna pairs  842  may accordingly be used as portions of one or more 1-port, 2-port, 4-port, or 8-port, or 16-port antennas. Similarly, beam diagram  850  depicts various antenna pairs  852  that are available for transmission in general, and also depicts various antenna pairs  854  that are not only available for transmission in general but are more promising for eNB  800  to use in forming a wireless communications channel with a specific UE, such as UE  822 , by creating a beamformed, FD-MIMO downlink. More particularly, antenna pairs  854  may be more promising in forming a wireless communications channel with UE  822  based upon the azimuth and elevation of UE  822  relative to eNB  800 . Antenna pairs  854  may accordingly be used to form a 1-port, 2-port, 4-port, 8-port, or 16-port antenna for eNB  800  to use in communicating with UE  822 . 
       FIGS. 9-10  illustrate embodiments of eNB antenna pairs that are available for transmission in general and eNB antenna pairs that are available to transmit to a specific UE, along with corresponding CSI-RS antenna ports.  FIG. 9  shows beam diagram  840  and antenna pairs  842  that are available for transmission in general, while corresponding resource block  900  includes RE pairs  942  that are available to transmit CSI-RS symbols for antenna pairs  842 . In  FIG. 10 , beam diagram  850  shows antenna pairs  852  that are available for transmission in general, and also shows antenna pairs  854  that may be more optimal for use in forming a wireless communications channel with UE  822 . Corresponding resource block  900  includes RE pairs  952  that are available to transmit CSI-RS symbols for antenna pairs  852 , of which RE pairs  954  correspond to antenna pairs  854 . A new, more flexible CSI-RS protocol may advantageously facilitate the use of antenna pairs which may be more optimal for supporting FD-MIMO. 
     A new, more flexible CSI-RS protocol may accordingly support an ever-increasing number of ports. A new protocol may also support a more flexible assignment of antenna ports, which may lead to more optimal channel performance, and may accommodate assignment of more suitable eNB antenna resources to wireless communication channels formed with specific UEs. 
       FIGS. 11-13  illustrate embodiments of CSI-RS groups for use in configuring UE antennas. In a new, more flexible CSI-RS protocol, the CSI-RS groups correspond with CSI configurations enumerated in 3GPP TS 36.211 (V10.7.0). Section 6.10.5 of TS 36.211 discusses “CSI reference signals.” Section 6.10.5.2 therein covers “Mapping to resource elements,” and ultimately provides a table that maps between CSI reference signal configurations and resource elements of a resource block. Section 6.10.5.2 begins by stating:
         In subframes configured for CSI reference signal transmission, the reference signal sequence r l,n     s   (m) shall be mapped to complex-valued modulation symbols a k,l   (p)  used as reference symbols on antenna port p according to       

     
       
         
           
             
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                                 m 
                                 + 
                                 
                                   ⌊ 
                                   
                                     
                                       
                                         N 
                                         RB 
                                         
                                           max 
                                           , 
                                           DL 
                                         
                                       
                                       - 
                                       
                                         N 
                                         RB 
                                         DL 
                                       
                                     
                                     2 
                                   
                                   ⌋ 
                                 
                               
                             
                           
                         
                       
                     
                   
                 
               
             
           
         
       
         
         
           
             The quantity (k′,l′) and the necessary conditions on n s  are given by Tables 6.10.5.2-1 and 6.10.5.2-2 for normal and extended cyclic prefix, respectively. 
           
         
       
    
     Section 6.10.5.2 then presents Table 6.10.5.2-1, which shows a mapping between CSI reference signal configurations and resource elements of a resource block. In the table, k′ corresponds with a subcarrier, l′ corresponds with an OFDM symbol, and n s  mod 2 corresponds with the slot, i.e., whether the OFDM symbol is in the lower half or upper half of a 14-symbol sub-frame. Table 6.10.5.2-1 is reproduced below as Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Mapping from CSI reference signal configurations (k′, l′) for normal cyclic prefix 
               
            
           
           
               
               
            
               
                   
                 Number of CSI reference signals configured 
               
            
           
           
               
               
               
               
               
            
               
                   
                 CSI reference signal 
                 1 or 2 
                 4 
                 8 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 configuration 
                 (k′, l′) 
                 n s  mod 2 
                 (k′, l′) 
                 n s  mod 2 
                 (k′, l′) 
                 n s  mod 2 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Frame 
                 0 
                 (9, 5) 
                 0 
                 (9, 5) 
                 0 
                 (9, 5) 
                 0 
               
               
                 structure 
                 1 
                 (11, 2)  
                 1 
                 (11, 2)  
                 1 
                 (11, 2)  
                 1 
               
               
                 type 1 and 2 
                 2 
                 (9, 2) 
                 1 
                 (9, 2) 
                 1 
                 (9, 2) 
                 1 
               
               
                   
                 3 
                 (7, 2) 
                 1 
                 (7, 2) 
                 1 
                 (7, 2) 
                 1 
               
               
                   
                 4 
                 (9, 5) 
                 1 
                 (9, 5) 
                 1 
                 (9, 5) 
                 1 
               
               
                   
                 5 
                 (8, 5) 
                 0 
                 (8, 5) 
                 0 
               
               
                   
                 6 
                 (10, 2)  
                 1 
                 (10, 2)  
                 1 
               
               
                   
                 7 
                 (8, 2) 
                 1 
                 (8, 2) 
                 1 
               
               
                   
                 8 
                 (6, 2) 
                 1 
                 (6, 2) 
                 1 
               
               
                   
                 9 
                 (8, 5) 
                 1 
                 (8, 5) 
                 1 
               
               
                   
                 10 
                 (3, 5) 
                 0 
               
               
                   
                 11 
                 (2, 5) 
                 0 
               
               
                   
                 12 
                 (5, 2) 
                 1 
               
               
                   
                 13 
                 (4, 2) 
                 1 
               
               
                   
                 14 
                 (3, 2) 
                 1 
               
               
                   
                 15 
                 (2, 2) 
                 1 
               
               
                   
                 16 
                 (1, 2) 
                 1 
               
               
                   
                 17 
                 (0, 2) 
                 1 
               
               
                   
                 18 
                 (3, 5) 
                 1 
               
               
                   
                 19 
                 (2, 5) 
                 1 
               
               
                 Frame 
                 20 
                 (11, 1)  
                 1 
                 (11, 1)  
                 1 
                 (11, 1)  
                 1 
               
               
                 structure 
                 21 
                 (9, 1) 
                 1 
                 (9, 1) 
                 1 
                 (9, 1) 
                 1 
               
               
                 type 2 only 
                 22 
                 (7, 1) 
                 1 
                 (7, 1) 
                 1 
                 (7, 1) 
                 1 
               
               
                   
                 23 
                 (10, 1)  
                 1 
                 (10, 1)  
                 1 
               
               
                   
                 24 
                 (8, 1) 
                 1 
                 (8, 1) 
                 1 
               
               
                   
                 25 
                 (6, 1) 
                 1 
                 (6, 1) 
                 1 
               
               
                   
                 26 
                 (5, 1) 
                 1 
               
               
                   
                 27 
                 (4, 1) 
                 1 
               
               
                   
                 28 
                 (3, 1) 
                 1 
               
               
                   
                 29 
                 (2, 1) 
                 1 
               
               
                   
                 30 
                 (1, 1) 
                 1 
               
               
                   
                 31 
                 (0, 1) 
                 1 
               
               
                   
               
            
           
         
       
     
     With reference to  FIGS. 11-13 , a resource block  1100  extends across twelve subcarriers  1110  in the frequency domain (enumerated as 0-11) and fourteen OFDM symbols in the time domain (enumerated as 0-6 for both slots 0 and 1). Various RE pairs are enumerated to correspond with the various CSI-RS groups for 1-port, 2-port, 4-port, and 8-port antennas, as described in Table 6.10.5.2-1. More specifically,  FIG. 11  enumerates RE pairs corresponding to CSI-RS groups for 1-port and 2-port antennas,  FIG. 12  enumerates RE pairs corresponding to CSI-RS groups for 4-port antennas, and  FIG. 13  enumerates RE pairs corresponding to CSI-RS groups for 8-port antennas. 
     In the CSI-RS protocol, each of CSI reference signal configurations  0 - 19  listed in Table 6.10.5.2-1 is mapped to one of CSI-RS groups  1150  in  FIG. 11 , where k′ indicates the subcarrier within subcarriers  1110  of resource block  1100 , n s  mod 2 indicates either the lower slot (n s  mod 2=0) or the upper slot (n s  mod 2=1) within the subframe/OFDM symbol  1120  of resource block  1100 , and l′ indicates the OFDM symbol within the subframe/OFDM symbols. Similarly, each of CSI reference signal configurations  0 - 9  listed in Table 6.10.5.2-1 is mapped to one of CSI-RS groups  1160  in  FIG. 12 , and each of CSI reference signal configurations  0 - 4  listed in Table 6.10.5.2-1 is mapped to one of CSI-RS groups  1170  in  FIG. 13 . 
     The CSI-RS groups of  FIGS. 11-13  may be used to specify CSI-RS antenna ports that correspond, in aggregate, with an N-port antenna. For example, with reference to  FIGS. 6 and 11 , the RE pairs  620  associated with antenna ports  15 - 18  in  FIG. 6  correspond with (in order) number 11 and 10 of CSI-RS groups  1150  in  FIG. 11 . So, CSI configurations  11  and  10  specify, in order, the two RE pairs corresponding with antenna ports  15 , 16  and  17 , 18  in  FIG. 6 . 
     Accordingly, in the CSI-RS protocol, an eNB may send one or more configuration messages to a UE, and each configuration message may assign to the UE a CSI-RS group that specifies one or more CSI-RS antenna ports. The CSI-RS groups correspond with the CSI-RS configurations enumerated in Table 6.10.5.2-1. That is, each CSI-RS group may specify a 1-port, 2-port, 4-port, or 8-port CSI-RS antenna port. Depending up the number of eNB antennas making up the wireless communications channel between the eNB and the UE, any number of CSI-RS groups, in any order, may be assigned to the UE to correspond with the number of eNB antennas to be aggregated in forming the wireless communications channel. 
       FIG. 14  illustrates an embodiment of a protocol between an eNB and a UE for using CSI-RS groups to configure UE antennas. Under CSI-RS protocol  1400 , an eNB  1410  first establishes an ordered set of eNB antenna ports to be used for a wireless communications channel with a UE  1420 . eNB  1410  then sends one or more CSI-RS configuration messages to UE  1420 . Each CSI-RS configuration message assigns one or more CSI-RS groups to U  1420 , and each CSI-RS group specifies one or more CSI-RS antenna ports. UE  1420  then indexes an ordered list of CSI-RS antenna ports for at least part of the wireless communication channel, based on the CSI-RS antenna ports specified by the assigned CSI-RS groups. The order of the CSI-RS antenna ports within the ordered list is established by the order in which the CSI-RS configuration messages arrived at UE  1420 . 
     Having configured UE  1420  in this manner, eNB  1410  subsequently sends one or more CSI-RS symbols corresponding with the CSI-RS antenna ports specified by the CSI-RS groups sent to UE  1420 . UE  1420  then performs channel state information measurements on the indexed CSI-RS antenna ports. Based on the channel state information measurements, UE  1420  calculates channel state information, which it reports back to eNB  1410 . 
       FIG. 15  illustrates an embodiment of an eNB and an embodiment of a UE. More specifically,  FIG. 15  includes block diagrams of an eNB  1510  and a UE  1530  which are operable to co-exist with each other and other elements of an LTE network. High-level, simplified architectures of eNB  1510  and UE  1530  are described so as not to obscure the embodiments. It should be noted that in some embodiments, eNB  1510  may be a stationary non-mobile device. 
     eNB  1510  is coupled to one or more antennas  1505 , and UE  1530  is similarly coupled to one or more antennas  1525 . However, in some embodiments, eNB  1510  may incorporate or comprise antennas  1505 , and UE  1530  in various embodiments may incorporate or comprise antennas  1525 . 
     In some embodiments, eNB  1510  may include a physical layer circuitry  1512 , a MAC (media access control) circuitry  1514 , a processor  1516 , a memory  1518 , and a hardware processing circuitry  1520 . A person skilled in the art will appreciate that other components not shown may be used in addition to the components shown to form a complete eNB. 
     In some embodiments, physical layer circuitry  1512  includes a transceiver  1513  for providing signals to and from UE  1530 . Transceiver  1513  provides signals to and from UEs or other devices using one or more antennas  1505 . In some embodiments, MAC circuitry  1514  controls access to the wireless medium. Memory  1518  may be, or may include, a storage media/medium such as a magnetic storage media (e.g. magnetic tapes or magnetic disks), an optical storage media (e.g. optical discs), an electronic storage media (e.g. conventional hard disk drives, solid-state disk drives, or flash-memory-based storage media), or any tangible storage media or non-transitory storage media. Hardware processing circuitry  1520  may comprise logic devices or circuitry to perform various operations. In some embodiments, processor  1516  and memory  1518  are arranged to perform the operations of hardware processing circuitry  1520 , such as operations described herein with reference to logic devices and circuitry within eNB  1510  and/or hardware processing circuitry  1520 . 
     In some embodiments, antennas  1505  coupled to eNB  1510  may comprise one or more directional or omni-directional antennas, including monopole antennas, dipole antennas, loop antennas, patch antennas, microstrip antennas, coplanar wave antennas, or other types of antennas suitable for transmission of RF signals. In some MIMO (multiple-input and multiple output) embodiments, antennas  1505  are separated to take advantage of spatial diversity. 
       FIG. 15  also includes a block diagram of a UE  1530 . In some embodiments, UE  1530  may include a physical layer circuitry  1532 , a MAC circuitry  1534 , a processor  1536 , a memory  1538 , a hardware processing circuitry  1540 , a wireless interface  1542 , and a display  1544 . A person skilled in the art would appreciate that other components not shown may be used in addition to the components shown to form a complete UE. 
     In some embodiments, physical layer circuitry  1532  includes a transceiver  1533  for providing signals to and from eNB  1510  (as well as other eNBs). Transceiver  1533  provides signals to and from eNBs or other devices using one or more antennas  1525 . In some embodiments, MAC circuitry  1534  controls access to the wireless medium. Memory  1518  may be, or may include, a storage media/medium such as a magnetic storage media (e.g. magnetic tapes or magnetic disks), an optical storage media (e.g. optical discs), an electronic storage media (e.g. conventional hard disk drives, solid-state disk drives, or flash-memory-based storage media), or any tangible storage media or non-transitory storage media. Wireless interface  1542  is arranged to allow the processor to communicate with another device. Display  1544  provides a visual and/or tactile display for a user to interact with UE  1530 , such as a touch-screen display. Hardware processing circuitry  1540  may comprise logic devices or circuitry to perform various operations. In some embodiments, processor  1536  and memory  1538  may be arranged to perform the operations of hardware processing circuitry  1540 , such as operations described herein with reference to logic devices and circuitry within UE  1530  and/or hardware processing circuitry  1540 . 
     In some embodiments, antennas  1525  coupled to UE  1530  may comprise one or more directional or omnidirectional antennas, including monopole antennas, dipole antennas, loop antennas, patch antennas, microstrip antennas, coplanar wave antennas, or other types of antennas suitable for transmission of Radio Frequency (RF) signals. In some MIMO embodiments, antennas  1525  are separated to take advantage of spatial diversity. 
     Elements of eNB  1510  and UE  1530 , and elements of other figures having the same names or reference numbers, can operate or function in the manner described with respect to any such figures (although the operation and function of such elements is not limited to such descriptions). For example,  FIGS. 8, 14, 16-17, and 20  also depict embodiments of eNBs and/or UEs, and the embodiments described with respect to  FIG. 15  and  FIGS. 8, 14, and 20  can operate or function in the manner described with respect to any of the figures. 
     In addition, although eNB  1510  and UE  1530  are each described as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements and/or other hardware elements. In some embodiments of this disclosure, the functional elements can refer to one or more processes operating on one or more processing elements. Examples of software and/or hardware configured elements include Digital Signal Processors (DSPs), one or more microprocessors, DSPs, Field-Programmable Gate Arrays (FPGAs), Application Specific Integrated Circuits (ASICs), Radio-Frequency Integrated Circuits (RFICs), and so on. 
     In  FIG. 15 , eNB  1510  and UE  1530  are operable to communicate with each other on a network, such as a wireless network. More specifically, eNB  1510  and UE  1530  may be in communication with each other over a wireless communication channel  1550 , which has both a downlink path from eNB  1510  to UE  1530  and an uplink path from UE  1530  to eNB  1510 . eNB  1510  may send CSI-RS configuration messages, as well as the CSI-RS symbols themselves, over the downlink to UE  1530  over wireless communications channel  1550 . In turn, UE  1530  may transmit calculated channel state information back to eNB  1510  over wireless communications channel  1550 . 
       FIG. 16  illustrates an embodiment of a hardware processing circuitry for an eNB. With reference to  FIG. 15 , eNB  1510  (or various elements or components therein, or combinations of elements or components therein) may include a hardware processing circuitry  1600 . Hardware processing circuitry  1600  may comprise logic devices or circuitry to perform various operations. In some embodiments, processor  1516  and memory  1518  may be arranged to perform the operations of hardware processing circuitry  1600 , such as operations described herein with reference to devices and circuitry within hardware processing circuitry  1600 . For example, one or more circuits of hardware processing circuitry  1600  may be implemented by combinations of software-configured elements and/or other hardware elements. 
     In  FIG. 16 , and also with reference to various aspects of  FIGS. 11-15 , in some embodiments, hardware processing circuitry  1600  may comprise a set of antennas  1607 , and may also comprise an ordered set of antenna ports  1605  for at least part of a channel associated with a set of receiving antennas of the UE, such as eNB antenna ports associated with any of antennas  1607 , or antennas  1505 , or any other antennas that contribute to the formation of wireless communication channel  1550 . Hardware processing circuitry  1600  may also comprise a first circuitry  1610  operable to compose messages to UE  1530 , and a second circuitry  1620  operable to establish CSI-RS group assignments. First circuitry  1610  and second circuitry  1620  may be coupled to antenna ports  1605 . 
     Some messages composed by first circuitry  1610  may be configuration messages that assign to UE  1530  a CSI-RS group specifying one or more CSI-RS antenna ports. In some embodiments, first circuitry  1610  may compose a first CSI-RS configuration message assigning a first CSI-RS group to UE  1530 , and may compose a second CSI-RS configuration message assigning a second CSI-RS group to UE  1530 . In turn, the first assigned CSI-RS group and the second assigned CSI-RS group may each specify one or more CSI-RS antenna ports transmitted on various downlink sub-frames. 
     First circuitry  1610  may be operable to compose more than two CSI-RS configuration messages, and can compose any number of additional CSI-RS configuration messages assigning additional CSI-RS groups to UE  1530  in various embodiments. In some embodiments, first circuitry  1610  may be operable to compose a single CSI-RS configuration message assigning the first CSI-RS group, the second CSI-RS group, and any additional CSI-RS groups (as will be discussed in greater detail below). 
     The specific number and type of CSI-RS group assignments may be established by second circuitry  1620 , and may include any number of CSI-RS groups that in aggregate correspond with ordered set of antenna ports  1605 . Second circuitry  1620  may accordingly establish any number of 1-port or 2-port CSI-RS group assignments, any number of 4-port CSI-RS group assignments, and/or any number of 8-port CSI-RS group assignments, in any order, to correspond with ordered set of antenna ports  1605 . When aggregated, the CSI-RS antenna ports specified by the assigned CSI-RS groups may accordingly be an ordered list of CSI-RS antenna ports corresponding with ordered set of antenna ports  1605 . 
     So, in some embodiments, the ordered list of CSI-RS antenna ports may include one or more antenna ports specified by a first CSI-RS group assigned by a first CSI-RS configuration message, and one or more antenna ports specified by a second CSI-RS group assigned by a second CSI-RS configuration message. The ordered list of CSI-RS antenna ports may also, in various embodiments, include one or more antenna ports specified by any number of additional CSI-RS configuration messages. 
     The CSI-RS antenna ports specified by the assigned CSI-RS groups may be related to ordered set of antenna ports  1605  in a variety of ways. In some embodiments, the second circuitry may be operable to establish one or more antenna ports specified by a first assigned CSI-RS group as being associated with a first portion of ordered set of antenna ports  1605 , and to establish one or more antenna ports specified by a second assigned CSI-RS group as being associated with a second portion of ordered set of antenna ports  1605 , wherein the second portion follows the first portion in ordered set of antenna ports  1605 . In other words, all CSI-RS antenna ports specified by a first assigned CSI-RS group, followed by all CSI-RS antenna ports specified by a second assigned CSI-RS group (and followed by all CSI-RS antenna ports specified by any additional assigned CSI-RS groups) may correspond with at least part of ordered set of antenna ports  1605 . 
     In other embodiments, second circuitry  1620  may be operable (1) to establish a first CSI-RS antenna port specified by the first assigned CSI-RS group and a first CSI-RS antenna port specified by the second assigned CSI-RS group as being associated with a first portion of ordered set of antenna ports  1605 , and (2) to establish a second CSI-RS antenna port specified by the first assigned CSI-RS group and a second CSI-RS antenna port specified by the second assigned CSI-RS group as being associated with a second portion of ordered set of antenna ports  1605 , the second portion following the first portion in ordered set of antenna ports  1605 . Put another way, the CSI-RS antenna ports specified by a first assigned CSI-RS group, interleaved with CSI-RS antenna ports specified by a second assigned CSI-RS group (and interleaved with CSI-RS antenna ports specified by any additional assigned CSI-RS groups) may correspond with at least part of ordered set of antenna ports  1605 . 
     In still further embodiments, a first assigned CSI-RS group and a second assigned CSI-RS group may be contained in one message to UE  1530  having an information element (IE) that specifies each CSI-RS group as at least one asserted bit in an array of bits. In other words, a first assigned CSI-RS group and a second assigned CSI-RS group (along with any additional assigned CSI-RS groups) may be contained in one CSI-RS configuration message from eNB  1510  to UE  1530 . Such a message may include a set of bits, each of which may correspond to at least one 1-port, 2-port, 4-port, or 8-port CSI reference signal configuration as indicated by, for example, Table 6.10.5.2-1. 
     The CSI-RS protocol discussed herein may advantageously permit the establishment of more optimal wireless communication channels between eNB  1510  and UE  1530 . For example, in some embodiments, second circuitry  1620  may establish one or more antenna ports specified by the first assigned CSI-RS group as being associated with a first antenna coupled to eNB  1510 , and establish one or more antenna ports specified by the second assigned CSI-RS group as being associated with a second antenna coupled to eNB  1510 , the first antenna and the second antenna having orthogonal polarizations. In other words, an antenna of eNB  1510  associated with a CSI-RS antenna port specified by a first assigned CSI-RS group may have a polarization orthogonal to the polarization of an antenna of eNB  1510  associated with a CSI-RS antenna port specified by a second assigned CSI-RS group. Channel state information measurements of the associated CSI-RS symbols may then lead to more optimal channel performance. 
       FIG. 17  illustrates an embodiment of a hardware processing circuitry for a UE. With reference to  FIG. 15 , UE  1530  (or various elements or components therein or combinations of elements or components therein) may include a hardware processing circuitry  1700 . Hardware processing circuitry  1700  may comprise logic devices or circuitry to perform various operations. In some embodiments, processor  1536  and memory  1538  may be arranged to perform the operations of hardware processing circuitry  1700 , such as operations described herein with reference to devices and circuitry within hardware processing circuitry  1700 . For example, one or more circuits of hardware processing circuitry  1700  may be implemented by combinations of software-configured elements and/or other hardware elements. 
     In  FIG. 17 , and also with reference to various aspects of  FIGS. 11-15 , in some embodiments, hardware processing circuitry  1700  may comprise a set of antenna ports  1705 , which may be coupled to a set of antennas such as antennas  1707 , or antennas  1525 , or any other antennas that contribute to the formation of wireless communication channel  1550 . Hardware processing circuitry  1700  may also comprise a first circuitry  1710  operable to receive CSI-RS configuration messages from eNB  1510 , and a second circuitry  1720  operable to index assigned CSI-RS groups as an ordered list of CSI-RS antenna ports. First circuitry  1710  and second circuitry  1720  may be coupled to antenna ports  1605 . In addition, the set of antennas  1707  may be associated with at least part of the ordered list of CSI-RS antenna ports. 
     Some messages received by first circuitry  1710  may be configuration messages from eNB  1510  that assign to UE  1530  a CSI-RS group specifying one or more CSI-RS antenna ports. In some embodiments, first circuitry  1710  may receive, from eNB  1510 , the first CSI-RS configuration message assigning the first CSI-RS group and the second CSI-RS configuration message assigning the second CSI-RS group. First circuitry  1710  may also be operable to receive more than two CSI-RS configuration messages, and in various embodiments may receive any number of additional CSI-RS configuration messages assigning additional CSI-RS groups to UE  1530 . Furthermore, in some embodiments, first circuitry  1710  may be operable to receive a single CSI-RS configuration message assigning both the first CSI-RS group and the second CSI-RS group, as well as any additional CSI-RS groups. 
     After the CSI-RS configuration has been received, second circuitry  1720  may then index the CSI-RS antenna ports specified by the first assigned CSI-RS group and the CSI-RS antenna ports specified by the second assigned CSI-RS as an ordered list of CSI-RS antenna ports for at least part of a channel associated with set of antennas  1707 . The indexing done by UE  1530  should thus complement the manner in which the CSI-RS groups were established by second circuitry  1620  of eNB  1510 , so that the ordered list of CSI-RS antenna ports of UE  1530  may correspond with the ordered set of antenna ports of eNB  1510 . 
     Second circuitry  1720  may be operable to index the ordered list of CSI-RS antenna ports in a variety of ways. In some embodiments, second circuitry  1720  may be operable to index the ordered list of CSI-RS antenna ports beginning with all of the antenna ports specified by the first assigned CSI-RS group, then all of the antenna ports specified by the second assigned CSI-RS group. That is, second circuitry  1720  may index all CSI-RS antenna ports specified by each assigned CSI-RS group in the order in which they are received. 
     In other embodiments, second circuitry  1720  may be operable to index the ordered list of CSI-RS antenna ports beginning with (1) a first portion of the CSI-RS antenna ports specified by the first assigned CSI-RS group and a first portion of the CSI-RS antenna ports specified by the second assigned CSI-RS group, followed by (2) a second portion of the CSI-RS antenna ports specified by the first assigned CSI-RS group and a second portion of the CSI-RS antenna ports specified by the second assigned CSI-RS group. In other words, the first CSI-RS antenna port of each assigned CSI-RS group may be indexed, followed by the second CSI-RS antenna port of each assigned CSI-RS group, and so on, through the last CSI-RS antenna port of each assigned CSI-RS group. 
     In still further embodiments, the first assigned CSI-RS group and the second assigned CSI-RS group (along with any additional assigned CSI-RS groups) may be contained in the same message to UE  1530 , which may have an information element (IE) that specifies each CSI-RS group as at least one asserted bit in array of bits. Each bit in the array of bits may in turn correspond to at least one 1-port, 2-port, 4-port, or 8-port CSI reference signal configuration as indicated by, for example, Table 6.10.5.2-1. 
     After UE  1530  has had an opportunity to index the CSI-RS antenna ports of the various CSI-RS groups into the ordered list of CSI-RS antenna ports, eNB  1510  may transmit the CSI-RS symbols on the CSI-RS antenna ports of the ordered list. Second circuitry  1720  may then be operable to perform channel state information measurements on the ordered list of CSI-RS antenna ports. Based on the above discussion, each CSI-RS antenna port of the ordered list of CSI-RS antenna ports may correspond with a CSI-RS configuration for a 1-port, 2-port, 4-port, or 8-port antenna as defined in 3GPP TS 36.211 (V10.7.0). Furthermore, due to the flexibility of the CSI-RS protocol, the CSI-RS symbols for the ordered list of CSI-RS antenna ports may all be transmitted in the same downlink sub-frame. 
     After UE  1530  has performed the channel state information measurements, second circuitry  1720  may be operable to calculate channel state information based on the channel state information measurements, and to present the calculated channel state information to first circuitry  1710  via calculation interface  1725 . First circuitry  1710  may then be operable to compose a reporting message to eNB  1510  containing the calculated channel state information received via calculation interface  1725 . In a corresponding manner, first circuitry  1610  of eNB  1510  may be operable to receive the reporting message from UE  1530  containing the calculated channel state information for the channel, based upon the channel state information measurements on the ordered list of CSI-RS antenna ports. eNB  1510  may then use the channel state information to help manage its antenna resources for better performance. 
       FIGS. 18-19  illustrate embodiments of methods for using CSI-RS groups in accordance with the CSI-RS protocol. With reference to  FIG. 18 , a method  1800  to be performed by an eNB may comprise an establishment  1810  of CSI-RS groups, a transmission  1820  of CSI-RS configuration messages, a transmission  1830  of CSI-RS symbols, and a receipt  1840  of calculated channel state information. 
     In various embodiments, establishment  1810  may include establishing one or more CSI-RS antenna ports specified by a first CSI-RS group assignment and one or more CSI-RS antenna ports specified by a second CSI-RS group assignment as being an ordered set of antenna ports for eNB  1510 . The ordered set of antenna ports may in turn be at least part of a wireless communication channel associated with a corresponding set of receiving antenna ports for UE  1530 . 
     Method  1800  may, in some embodiments, comprise associating a first antenna coupled to eNB  1510  with one or more antenna ports specified by the first CSI-RS group assignment, and associating a second antenna coupled to eNB  1510  with one or more antenna ports specified by the second CSI-RS group assignment, where the first antenna and the second antenna have orthogonal polarizations. 
     In some embodiments, method  1800  may comprise associating a first portion of the ordered set of antenna ports of eNB  1510  with one or more CSI-RS antenna ports specified by the first CSI-RS group assignment, and associating a second portion of the ordered set of antenna ports of eNB  1510  with one or more CSI-RS antenna ports specified by the second CSI-RS group assignment, where the second portion follows the first portion in the ordered set of antenna ports of eNB  1510 . In other embodiments, method  1800  may comprise (1) associating a first CSI-RS antenna port specified by the first CSI-RS group assignment and a first CSI-RS antenna port specified by the second CSI-RS group assignment with a first portion of the ordered set of antenna ports of eNB  1510 , and (2) associating a second CSI-RS antenna port specified by the first CSI-RS group assignment and a second CSI-RS antenna port specified by the second CSI-RS group assignment with a second portion of the ordered set of antenna ports of eNB  1510 , where the second portion follows the first portion in the ordered set of antenna ports of eNB  1510 . 
     Transmission  1820  may include transmitting the first CSI-RS group assignment and the second CSI-RS group assignment to UE  1530 . Transmission  1830  may also include transmitting CSI-RS symbols to UE  1530 , for use in taking channel state information measurements and in calculating channel state information. Receipt  1840  may include receiving a reporting message from UE  1530  containing calculated channel state information for the channel. 
     With reference to  FIG. 19 , a method  1900  to be performed by a UE may comprise a receipt  1910  of CSI-RS configuration messages, an indexing  1920  of CS-RS antenna ports, a performance  1930  of channel measurements, and a calculation  1940  of channel state information. 
     For example, in various embodiments, receipt  1910  may include receiving in from eNB  1510  an assignment of a first CSI-RS group specifying one or more CSI-RS antenna ports, and an assignment of a second CSI-RS group specifying one or more CSI-RS antenna ports. Indexing  1920  may include indexing the one or more CSI-RS antenna ports specified by the first CSI-RS group assignment and the one or more CSI-RS antenna ports specified by the second CSI-RS group assignment as an ordered list of CSI-RS antenna ports for at least part of a channel associated with a set of receiving antennas of the UE. 
     Performance  1930  may include performing channel state information measurements for the channel, and calculation  1940  may include calculating channel state information for the channel. Method  1900  may also comprise composing a reporting message to eNB  1510  containing the calculated channel state information for the channel. 
     In some embodiments, indexing  1920  may begin with all antenna ports specified by the first CSI-RS group assignment, then all antenna ports specified by the second CSI-RS group assignment. In other embodiments, indexing  1920  may interleave the one or more REs of the first CSI-RS group assignment with the one or more REs of the second CSI-RS group assignment. In still further embodiments, the first CSI-RS group assignment and the second CSI-RS group assignment may be contained in one message from eNB  1510  having an information element (IE) that specifies each CSI-RS group assignment as at least one asserted bit in an array of bits. 
     Although the blocks in the flowchart with reference to  FIGS. 18-19  are shown in a particular order, the order of the actions can be modified. Thus, the illustrated embodiments can be performed in a different order, and some actions/blocks may be performed in parallel. Some of the blocks and/or operations listed in  FIGS. 18-19  are optional in accordance with certain embodiments. The numbering of the blocks presented is for the sake of clarity and is not intended to prescribe an order of operations in which the various blocks must occur. Additionally, operations from the various flows may be utilized in a variety of combinations. 
     Moreover, in some embodiments, machine readable storage media may have executable instructions stored thereon that, when executed, cause eNB  1510  to perform an operation comprising method  1800 . Similarly, in some embodiments, machine readable storage media may have executable instructions stored thereon that, when executed, cause UE  1530  to perform an operation comprising method  1900 . Such machine readable storage media may include any of a variety of storage media, like magnetic storage media (e.g. magnetic tapes or magnetic disks), optical storage media (e.g. optical discs), electronic storage media (e.g. conventional hard disk drives, solid-state disk drives, or flash-memory-based storage media), or any other tangible storage media or non-transitory storage media. 
       FIG. 20  illustrates example components of a UE device  2000  in accordance with some embodiments. In some embodiments, the UE device  2000  may include application circuitry  2002 , baseband circuitry  2004 , Radio Frequency (RF) circuitry  2006 , front-end module (FEM) circuitry  2008 , a low-power wake-up receiver (LP-WUR), and one or more antennas  2010 , coupled together at least as shown. In some embodiments, the UE device  2000  may include additional elements such as, for example, memory/storage, display, camera, sensor, and/or input/output (I/O) interface. 
     The application circuitry  2002  may include one or more application processors. For example, the application circuitry  2002  may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The processor(s) may include any combination of general-purpose processors and dedicated processors (e.g., graphics processors, application processors, etc.). The processors may be coupled with and/or may include memory/storage and may be configured to execute instructions stored in the memory/storage to enable various applications and/or operating systems to run on the system. 
     The baseband circuitry  2004  may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The baseband circuitry  2004  may include one or more baseband processors and/or control logic to process baseband signals received from a receive signal path of the RF circuitry  2006  and to generate baseband signals for a transmit signal path of the RF circuitry  2006 . Baseband processing circuitry  2004  may interface with the application circuitry  2002  for generation and processing of the baseband signals and for controlling operations of the RF circuitry  2006 . For example, in some embodiments, the baseband circuitry  2004  may include a second generation (2G) baseband processor  2004   a , third generation (3G) baseband processor  2004   b , fourth generation (4G) baseband processor  2004   c , and/or other baseband processor(s)  2004   d  for other existing generations, generations in development or to be developed in the future (e.g., fifth generation (5G), 6G, etc.). The baseband circuitry  2004  (e.g., one or more of baseband processors  2004   a - d ) may handle various radio control functions that enable communication with one or more radio networks via the RF circuitry  2006 . The radio control functions may include, but are not limited to, signal modulation/demodulation, encoding/decoding, radio frequency shifting, etc. In some embodiments, modulation/demodulation circuitry of the baseband circuitry  2004  may include Fast-Fourier Transform (FFT), precoding, and/or constellation mapping/demapping functionality. In some embodiments, encoding/decoding circuitry of the baseband circuitry  2004  may include convolution, tail-biting convolution, turbo, Viterbi, and/or Low Density Parity Check (LDPC) encoder/decoder functionality. Embodiments of modulation/demodulation and encoder/decoder functionality are not limited to these examples and may include other suitable functionality in other embodiments. 
     In some embodiments, the baseband circuitry  2004  may include elements of a protocol stack such as, for example, elements of an EUTRAN protocol including, for example, physical (PHY), media access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), and/or RRC elements. A central processing unit (CPU)  2004   e  of the baseband circuitry  2004  may be configured to run elements of the protocol stack for signaling of the PHY, MAC, RLC, PDCP and/or RRC layers. In some embodiments, the baseband circuitry may include one or more audio digital signal processor(s) (DSP)  2004   f  The audio DSP(s)  2004   f  may be include elements for compression/decompression and echo cancellation and may include other suitable processing elements in other embodiments. Components of the baseband circuitry may be suitably combined in a single chip, a single chipset, or disposed on a same circuit board in some embodiments. In some embodiments, some or all of the constituent components of the baseband circuitry  2004  and the application circuitry  2002  may be implemented together such as, for example, on a system on a chip (SOC). 
     In some embodiments, the baseband circuitry  2004  may provide for communication compatible with one or more radio technologies. For example, in some embodiments, the baseband circuitry  2004  may support communication with an evolved universal terrestrial radio access network (EUTRAN) and/or other wireless metropolitan area networks (WMAN), a wireless local area network (WLAN), a wireless personal area network (WPAN). Embodiments in which the baseband circuitry  2004  is configured to support radio communications of more than one wireless protocol may be referred to as multi-mode baseband circuitry. 
     RF circuitry  2006  may enable communication with wireless networks using modulated electromagnetic radiation through a non-solid medium. In various embodiments, the RF circuitry  2006  may include switches, filters, amplifiers, etc. to facilitate the communication with the wireless network. RF circuitry  2006  may include a receive signal path which may include circuitry to down-convert RF signals received from the FEM circuitry  2008  and provide baseband signals to the baseband circuitry  2004 . RF circuitry  2006  may also include a transmit signal path which may include circuitry to up-convert baseband signals provided by the baseband circuitry  2004  and provide RF output signals to the FEM circuitry  2008  for transmission. 
     In some embodiments, the RF circuitry  2006  may include a receive signal path and a transmit signal path. The receive signal path of the RF circuitry  2006  may include mixer circuitry  2006   a , amplifier circuitry  2006   b  and filter circuitry  2006   c . The transmit signal path of the RF circuitry  2006  may include filter circuitry  2006   c  and mixer circuitry  2006   a . RF circuitry  2006  may also include synthesizer circuitry  2006   d  for synthesizing a frequency for use by the mixer circuitry  2006   a  of the receive signal path and the transmit signal path. In some embodiments, the mixer circuitry  2006   a  of the receive signal path may be configured to down-convert RF signals received from the FEM circuitry  2008  based on the synthesized frequency provided by synthesizer circuitry  2006   d . The amplifier circuitry  2006   b  may be configured to amplify the down-converted signals and the filter circuitry  2006   c  may be a low-pass filter (LPF) or band-pass filter (BPF) configured to remove unwanted signals from the down-converted signals to generate output baseband signals. Output baseband signals may be provided to the baseband circuitry  2004  for further processing. In some embodiments, the output baseband signals may be zero-frequency baseband signals, although this is not a requirement. In some embodiments, mixer circuitry  2006   a  of the receive signal path may comprise passive mixers, although the scope of the embodiments is not limited in this respect. 
     In some embodiments, the mixer circuitry  2006   a  of the transmit signal path may be configured to up-convert input baseband signals based on the synthesized frequency provided by the synthesizer circuitry  2006   d  to generate RF output signals for the FEM circuitry  2008 . The baseband signals may be provided by the baseband circuitry  2004  and may be filtered by filter circuitry  2006   c . The filter circuitry  2006   c  may include a low-pass filter (LPF), although the scope of the embodiments is not limited in this respect. 
     In some embodiments, the mixer circuitry  2006   a  of the receive signal path and the mixer circuitry  2006   a  of the transmit signal path may include two or more mixers and may be arranged for quadrature downconversion and/or upconversion respectively. In some embodiments, the mixer circuitry  2006   a  of the receive signal path and the mixer circuitry  2006   a  of the transmit signal path may include two or more mixers and may be arranged for image rejection (e.g., Hartley image rejection). In some embodiments, the mixer circuitry  2006   a  of the receive signal path and the mixer circuitry  2006   a  may be arranged for direct downconversion and/or direct upconversion, respectively. In some embodiments, the mixer circuitry  2006   a  of the receive signal path and the mixer circuitry  2006   a  of the transmit signal path may be configured for super-heterodyne operation. 
     In some embodiments, the output baseband signals and the input baseband signals may be analog baseband signals, although the scope of the embodiments is not limited in this respect. In some alternate embodiments, the output baseband signals and the input baseband signals may be digital baseband signals. In these alternate embodiments, the RF circuitry  2006  may include analog-to-digital converter (ADC) and digital-to-analog converter (DAC) circuitry and the baseband circuitry  2004  may include a digital baseband interface to communicate with the RF circuitry  2006 . 
     In some dual-mode embodiments, a separate radio IC circuitry may be provided for processing signals for each spectrum, although the scope of the embodiments is not limited in this respect. 
     In some embodiments, the synthesizer circuitry  2006   d  may be a fractional-N synthesizer or a fractional N/N+1 synthesizer, although the scope of the embodiments is not limited in this respect as other types of frequency synthesizers may be suitable. For example, synthesizer circuitry  2006   d  may be a delta-sigma synthesizer, a frequency multiplier, or a synthesizer comprising a phase-locked loop with a frequency divider. 
     The synthesizer circuitry  2006   d  may be configured to synthesize an output frequency for use by the mixer circuitry  2006   a  of the RF circuitry  2006  based on a frequency input and a divider control input. In some embodiments, the synthesizer circuitry  2006   d  may be a fractional N/N+1 synthesizer. 
     In some embodiments, frequency input may be provided by a voltage controlled oscillator (VCO), although that is not a requirement. Divider control input may be provided by either the baseband circuitry  2004  or the applications processor  2002  depending on the desired output frequency. In some embodiments, a divider control input (e.g., N) may be determined from a look-up table based on a channel indicated by the applications processor  2002 . 
     Synthesizer circuitry  2006   d  of the RF circuitry  2006  may include a divider, a delay-locked loop (DLL), a multiplexer and a phase accumulator. In some embodiments, the divider may be a dual modulus divider (DMD) and the phase accumulator may be a digital phase accumulator (DPA). In some embodiments, the DMD may be configured to divide the input signal by either N or N+1 (e.g., based on a carry out) to provide a fractional division ratio. In some example embodiments, the DLL may include a set of cascaded, tunable, delay elements, a phase detector, a charge pump and a D-type flip-flop. In these embodiments, the delay elements may be configured to break a VCO period up into Nd equal packets of phase, where Nd is the number of delay elements in the delay line. In this way, the DLL provides negative feedback to help ensure that the total delay through the delay line is one VCO cycle. 
     In some embodiments, synthesizer circuitry  2006   d  may be configured to generate a carrier frequency as the output frequency, while in other embodiments, the output frequency may be a multiple of the carrier frequency (e.g., twice the carrier frequency, four times the carrier frequency) and used in conjunction with quadrature generator and divider circuitry to generate multiple signals at the carrier frequency with multiple different phases with respect to each other. In some embodiments, the output frequency may be a LO frequency (fLO). In some embodiments, the RF circuitry  2006  may include an IQ/polar converter. 
     FEM circuitry  2008  may include a receive signal path which may include circuitry configured to operate on RF signals received from one or more antennas  2010 , amplify the received signals and provide the amplified versions of the received signals to the RF circuitry  2006  for further processing. FEM circuitry  2008  may also include a transmit signal path which may include circuitry configured to amplify signals for transmission provided by the RF circuitry  2006  for transmission by one or more of the one or more antennas  2010 . 
     In some embodiments, the FEM circuitry  2008  may include a TX/RX switch to switch between transmit mode and receive mode operation. The FEM circuitry may include a receive signal path and a transmit signal path. The receive signal path of the FEM circuitry may include a low-noise amplifier (LNA) to amplify received RF signals and provide the amplified received RF signals as an output (e.g., to the RF circuitry  2006 ). The transmit signal path of the FEM circuitry  2008  may include a power amplifier (PA) to amplify input RF signals (e.g., provided by RF circuitry  2006 ), and one or more filters to generate RF signals for subsequent transmission (e.g., by one or more of the one or more antennas  2010 . 
     In some embodiments, the UE  2000  comprises a plurality of power saving mechanisms. If the UE  2000  is in an RRC_Connected state, where it is still connected to the eNB as it expects to receive traffic shortly, then it may enter a state known as Discontinuous Reception Mode (DRX) after a period of inactivity. During this state, the device may power down for brief intervals of time and thus save power. 
     If there is no data traffic activity for an extended period of time, then the UE  2000  may transition off to an RRC Idle state, where it disconnects from the network and does not perform operations such as channel quality feedback, handover, etc. The UE  2000  goes into a very low power state and it performs paging where again it periodically wakes up to listen to the network and then powers down again. The device cannot receive data in this state, in order to receive data, it must transition back to RRC_Connected state. 
     An additional power saving mode may allow a device to be unavailable to the network for periods longer than a paging interval (ranging from seconds to a few hours). During this time, the device is totally unreachable to the network and may power down completely. Any data sent during this time incurs a large delay and it is assumed the delay is acceptable. 
       FIG. 21  illustrates a computing device with mechanisms to provide a flexible CSI-RS protocol, according to some embodiments of the disclosure. It is pointed out that those elements of  FIG. 21  having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such. 
     Computing device  2100  may be a smart device, smart phone, tablet, SoC, or computer system with mechanisms to provide a flexible CSI-RS protocol, according to some embodiments of the disclosure.  FIG. 21  illustrates a block diagram of an embodiment of a mobile device which may be operable to use flat surface interface connectors. In one embodiment, computing device  2100  may be a mobile computing device, such as a computing tablet, a mobile phone or smart-phone, a wireless-enabled e-reader, or other wireless mobile device. It will be understood that certain components are shown generally, and not all components of such a device are shown in computing device  2100 . 
     Computing device  2100  includes a first processor  2110  with mechanisms to provide a flexible CSI-RS protocol, according to some embodiments discussed. Other blocks of computing device  2100  may also include the mechanisms to provide a flexible CSI-RS protocol, according to other embodiments. The various embodiments of the present disclosure may also comprise a network interface within 2170 such as a wireless interface so that a system embodiment may be incorporated into a wireless device, for example a cell phone or personal digital assistant. 
     In some embodiments, processor  2110  can include one or more physical devices, such as microprocessors, application processors, microcontrollers, programmable logic devices, or other processing means. The processing operations performed by processor  2110  may include the execution of an operating platform or operating system on which applications and/or device functions may then be executed. The processing operations may also include operations related to one or more of the following: I/O (input/output) with a human user or with other devices; power management; connecting computing device  2100  to another device; audio I/O; and/or display I/O. 
     In some embodiments, computing device  2100  includes an audio subsystem  2120 , which represents hardware components (e.g., audio hardware and audio circuits) and software components (e.g., drivers and/or codecs) associated with providing audio functions to computing device  2100 . Audio functions can include speaker and/or headphone output as well as microphone input. Devices for such functions can be integrated into computing device  2100 , or connected to computing device  2100 . In one embodiment, a user interacts with computing device  2100  by providing audio commands that are received and processed by processor  2110 . 
     In some embodiments, computing device  2100  includes a display subsystem  2130 , which represents hardware components (e.g., display devices) and software components (e.g., drivers) that provide a visual and/or tactile display for a user to interact with computing device  2100 . Display subsystem  2130  may include a display interface  2132 , which may be a particular screen or hardware device used to provide a display to a user. In one embodiment, display interface  2132  includes logic separate from processor  2110  to perform at least some processing related to the display. In some embodiments, display subsystem  2130  includes a touch screen (or touch pad) device that provides both output and input to a user. 
     In some embodiments, computing device  2100  includes an I/O controller  2140  associated with hardware devices and software components related to interaction with a user. I/O controller  2140  is operable to manage hardware that is part of audio subsystem  2120  and/or display subsystem  2130 . Additionally, I/O controller  2140  may be a connection point for additional devices that connect to computing device  2100 , through which a user might interact with the system. For example, devices that can be attached to computing device  2100  might include microphone devices, speaker or stereo systems, video systems or other display devices, keyboard or keypad devices, or other I/O devices for use with specific applications such as card readers or other devices. 
     As mentioned above, I/O controller  2140  can interact with audio subsystem  2120  and/or display subsystem  2130 . For example, input through a microphone or other audio device can provide input or commands for one or more applications or functions of computing device  2100 . Additionally, audio output can be provided instead of, or in addition to, display output. In another example, if display subsystem  2130  includes a touch screen, the display device may also act as an input device, which can be at least partially managed by I/O controller  2140 . There can also be additional buttons or switches on computing device  2100  to provide I/O functions managed by I/O controller  2140 . 
     In some embodiments, I/O controller  2140  manages devices such as accelerometers, cameras, light sensors or other environmental sensors, or other hardware that can be included in computing device  2100 . The input can be part of direct user interaction, and may provide environmental input to the system to influence its operations (such as filtering for noise, adjusting displays for brightness detection, applying a flash for a camera, or other features). 
     In some embodiments, computing device  2100  includes a power management component  2150  that manages battery power usage, charging of the battery, and features related to power saving operation. 
     A memory subsystem  2160  includes memory devices for storing information in computing device  2100 . Memory subsystem  2160  can include nonvolatile memory devices (whose state does not change if power to the memory device is interrupted) and/or volatile memory devices (whose state is indeterminate if power to the memory device is interrupted). Memory subsystem  2160  can store application data, user data, music, photos, documents, or other data, as well as system data (whether long-term or temporary) related to the execution of the applications and functions of computing device  2100 . 
     Some portion of memory subsystem  2160  may also be provided as a non-transitory machine-readable medium for storing the computer-executable instructions (e.g., instructions to implement any other processes discussed herein). The machine-readable medium may include, but is not limited to, flash memory, optical disks, CD-ROMs, DVD ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, phase change memory (PCM), or other types of machine-readable media suitable for storing electronic or computer-executable instructions. For example, some embodiments of the disclosure may be downloaded as a computer program (e.g., BIOS) which may be transferred from a remote computer (e.g., a server) to a requesting computer (e.g., a client) by way of data signals via a communication link (e.g., a modem or network connection). 
     In some embodiments, computing device  2100  includes a network interface within a connectivity component  2170 , such as a cellular interface  2172  or a wireless interface  2174 , so that an embodiment of computing device  2100  may be incorporated into a wireless device such as a cellular phone or a personal digital assistant. In some embodiments, connectivity component  2170  includes hardware devices (e.g., wireless and/or wired connectors and communication hardware) and software components (e.g., drivers and/or protocol stacks) to enable computing device  2100  to communicate with external devices. Computing device  2100  could include separate devices, such as other computing devices, wireless access points or base stations, as well as peripherals such as headsets, printers, or other devices. 
     In some embodiments, connectivity component  2170  can include multiple different types of network interfaces, such as one or more wireless interfaces for allowing processor  2110  to communicate with another device. To generalize, computing device  2100  is illustrated with cellular interface  2172  and wireless interface  2174 . Cellular interface  2172  refers generally to wireless interfaces to cellular networks provided by cellular network carriers, such as provided via GSM or variations or derivatives, CDMA (code division multiple access) or variations or derivatives, TDM (time division multiplexing) or variations or derivatives, or other cellular service standards. Wireless interface  2174  refers generally to non-cellular wireless interfaces, and can include personal area networks (such as Bluetooth, Near Field, etc.), local area networks (such as Wi-Fi), and/or wide area networks (such as WiMax), or other wireless communication. 
     In some embodiments, computing device  2100  has various peripheral connections  2180 , which may include hardware interfaces and connectors, as well as software components (e.g., drivers and/or protocol stacks) to make peripheral connections. It will be understood that computing device  2100  could both be a peripheral device to other computing devices (via “to”  2182 ), as well as have peripheral devices connected to it (via “from”  2184 ). The computing device  2100  may have a “docking” connector to connect to other computing devices for purposes such as managing content on computing device  2100  (e.g., downloading and/or uploading, changing, synchronizing). Additionally, a docking connector can allow computing device  2100  to connect to certain peripherals that allow computing device  2100  to control content output, for example, to audiovisual or other systems. 
     In addition to a proprietary docking connector or other proprietary connection hardware, computing device  2100  can make peripheral connections  2180  via common or standards-based connectors. Common types of connectors can include a Universal Serial Bus (USB) connector (which can include any of a number of different hardware interfaces), a DisplayPort or MiniDisplayPort (MDP) connector, a High Definition Multimedia Interface (HDMI) connector, a Firewire connector, or other types of connectors. 
     Reference in the specification to “an embodiment,” “one embodiment,” “some embodiments,” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments. The various appearances of “an embodiment,” “one embodiment,” or “some embodiments” are not necessarily all referring to the same embodiments. If the specification states a component, feature, structure, or characteristic “may,” “might,” or “could” be included, that particular component, feature, structure, or characteristic is not required to be included. If the specification or claim refers to “a” or “an” element, that does not mean there is only one of the elements. If the specification or claims refer to “an additional” element, that does not preclude there being more than one of the additional element. 
     Furthermore, the particular features, structures, functions, or characteristics may be combined in any suitable manner in one or more embodiments. For example, a first embodiment may be combined with a second embodiment anywhere the particular features, structures, functions, or characteristics associated with the two embodiments are not mutually exclusive. 
     While the disclosure has been described in conjunction with specific embodiments thereof, many alternatives, modifications and variations of such embodiments will be apparent to those of ordinary skill in the art in light of the foregoing description. For example, other memory architectures e.g., Dynamic RAM (DRAM) may use the embodiments discussed. The embodiments of the disclosure are intended to embrace all such alternatives, modifications, and variations as to fall within the broad scope of the appended claims. 
     In addition, well known power/ground connections to integrated circuit (IC) chips and other components may or may not be shown within the presented figures, for simplicity of illustration and discussion, and so as not to obscure the disclosure. Further, arrangements may be shown in block diagram form in order to avoid obscuring the disclosure, and also in view of the fact that specifics with respect to implementation of such block diagram arrangements are highly dependent upon the platform within which the present disclosure is to be implemented (i.e., such specifics should be well within purview of one skilled in the art). Where specific details (e.g., circuits) are set forth in order to describe example embodiments of the disclosure, it should be apparent to one skilled in the art that the disclosure can be practiced without, or with variation of, these specific details. The description is thus to be regarded as illustrative instead of limiting. 
     The following enumerated examples pertain to further embodiments. Specifics in the examples may be used anywhere in one or more embodiments. All optional features of the apparatus described herein may also be implemented with respect to a method or process. 
     Example 1 provides a User Equipment (UE) operable to communicate with an Evolved Node-B (eNB) on a network. The UE may include hardware processing circuitry comprising a set of antennas, a first circuitry, and a second circuitry. The first circuitry may be operable to receive Channel State Information Reference Signal (CSI RS) configuration messages from the eNB that assign to the UE a CSI RS group specifying one or more CSI RS antenna ports. The second circuitry may be operable to index a first set of CSI RS antenna ports specified by a first assigned CSI RS group and a second set of CSI RS antenna ports specified by a second assigned CSI RS group as an ordered list of CSI RS antenna ports for at least part of a channel associated with the set of antennas. 
     In example 2, the UE of example 1 is provided, in which the second circuitry may be operable to perform channel state information measurements on the ordered list of CSI RS antenna ports. The first assigned CSI RS group may correspond with a CSI RS configuration having 2, 4, or 8 antenna ports as defined in TS 36.211 v.  10 . 7 . 0 , and CSI RS symbols for the ordered list of CSI RS antenna ports are transmitted in the same downlink subframe. 
     In example 3, the UE of example 2 is provided, in which the second circuitry may be operable to calculate channel state information based on the channel state information measurements. In example 4, the UE of example 3 is provided, in which the first circuitry may be operable to compose a reporting message to the eNB containing the calculated channel state information. 
     In example 5, the UE of any of examples 1 through 4 is provided, in which the second circuitry may be operable to index the ordered list of CSI RS antenna ports beginning with all antenna ports specified by the first assigned CSI RS group, then all antenna ports specified by the second assigned CSI RS group. 
     In example 6, the UE of any of examples 1 through 4 is provided, in which the second circuitry may be operable to index the ordered list of CSI RS antenna ports beginning with a first portion of the antenna ports specified by the first assigned CSI RS group and a first portion of the antenna ports specified by the second assigned CSI RS group, followed by a second portion of the antenna ports specified by the first assigned CSI RS group and a second portion of the antenna ports specified by the second assigned CSI RS group. 
     In example 7, the UE of example 6 is provided, in which the first portion of the antenna ports may be a first half of the antenna ports, and the second portion of the antenna ports may be a second half of the antenna ports. 
     In example 8, the UE of any of examples 1 through 4 is provided, in which the first assigned CSI RS group and the second assigned CSI RS group may be contained in one message from the eNB having an information element (IE) that specifies each CSI RS group as at least one asserted bit in an array of bits. 
     In example 9, the UE of any of examples 1 through 8 is provided, in which the first circuitry and the second circuitry may be part of a baseband circuitry of the UE. 
     In example 10, a device comprising an application processor, a memory, one or more antennas, a wireless interface for allowing the application processor to communicate with another device, and a touch-screen display may be provided, the device including the UE of any of examples 1 through 9. 
     Example 11 provides an apparatus of a User Equipment (UE) comprising an application processor, a memory, a set of antennas, and a wireless interface for allowing the application processor to communicate with another device. The apparatus may include a first circuitry and a second circuitry. The first circuitry may be operable to receive Channel State Information Reference Signal (CSI RS) configuration messages from the eNB that assign to the UE a CSI RS group specifying one or more CSI RS antenna ports. The second circuitry may be operable to index a first set of CSI RS antenna ports specified by a first assigned CSI RS group and a second set of CSI RS antenna ports specified by a second assigned CSI RS group as an ordered list of CSI RS antenna ports for at least part of a channel associated with the set of antennas. 
     In example 12, the apparatus of the UE of example 11 is provided, in which the second circuitry may be operable to perform channel state information measurements on the ordered list of CSI RS antenna ports. The first assigned CSI RS group may correspond with a CSI RS configuration having 2, 4, or 8 antenna ports as defined in TS 36.211 v. 10.7.0. CSI RS symbols for the ordered list of CSI RS antenna ports may be transmitted in the same downlink subframe. 
     In example 13, the apparatus of the UE of example 12 is provided, in which the second circuitry may be operable to calculate channel state information based on the channel state information measurements. 
     In example 14, the apparatus of the UE of example 13 is provided, in which the first circuitry may be operable to compose a reporting message to the eNB containing the calculated channel state information. 
     In example 15, the apparatus of the UE of any of examples 11 through 14 is provided, in which the second circuitry may be operable to index the ordered list of CSI RS antenna ports beginning with all antenna ports specified by the first assigned CSI RS group, then all antenna ports specified by the second assigned CSI RS group. 
     In example 16, the apparatus of the UE of any of examples 11 through 14 is provided, in which the second circuitry may be operable to index the ordered list of CSI RS antenna ports beginning with a first portion of the antenna ports specified by the first assigned CSI RS group and a first portion of the antenna ports specified by the second assigned CSI RS group, followed by a second portion of the antenna ports specified by the first assigned CSI RS group and a second portion of the antenna ports specified by the second assigned CSI RS group. 
     In example 17, the apparatus of the UE of example 16 is provided, in which the first portion of the antenna ports may be a first half of the antenna ports, and the second portion of the antenna ports may be a second half of the antenna ports. 
     In example 18, the apparatus of the UE of any of examples 11 through 14 is provided, in which the first assigned CSI RS group and the second assigned CSI RS group may be contained in one message from the eNB having an information element (IE) that specifies each CSI RS group as at least one asserted bit in an array of bits. 
     In example 19, the apparatus of the UE of any of examples 11 through 18 is provided, in which the apparatus may be a baseband circuitry of the UE. 
     Example 20 provides an Evolved Node-B (eNB) operable to communicate with a User Equipment (UE) on a network. The eNB may include hardware processing circuitry may comprise an ordered set of antenna ports, a first circuitry, and a second circuitry. The ordered set of antenna ports may be for at least part of a channel associated with a set of receiving antennas of the UE. The first circuitry may be operable to compose CSI RS configuration messages that assign to the UE a Channel State Information Reference Signal (CSI RS) group specifying one or more CSI RS antenna ports. The second circuitry may be operable to establish CSI RS group assignments for an ordered list of CSI RS antenna ports corresponding with the ordered set of antenna ports of the eNB. The ordered list of CSI RS antenna ports may include one or more antenna ports specified by a first assigned CSI RS group, and may include one or more antenna ports specified by a second assigned CSI RS group. 
     In example 21, the eNB of example 20 is provided, in which the first circuitry may be operable to receive a reporting message from the UE containing calculated channel state information for the channel based on channel state information measurements on the ordered list of CSI RS antenna ports. 
     In example 22, the eNB of either of examples 20 or 21 is provided, in which the second circuitry may be operable to establish the one or more antenna ports specified by the first assigned CSI RS group as being associated with a first antenna coupled to the eNB, and may be operable to establish the one or more antenna ports specified by the second assigned CSI RS group as being associated with a second antenna coupled to the eNB. The first antenna and second antenna may have orthogonal polarizations. 
     In example 23, the eNB of any of examples 20 through 22 is provided, in which the second circuitry may be operable to establish the one or more antenna ports specified by the first assigned CSI RS group as being associated with a first portion of the ordered set of antenna ports of the eNB, and may be operable to establish the one or more antenna ports specified by the second assigned CSI RS group as being associated with a second portion of the ordered set of antenna ports of the eNB. The second portion may follow the first portion in the ordered set of antenna ports of the eNB. 
     In example 24, the eNB of example 23 is provided, in which wherein the first portion of the antenna ports may be a first half of the antenna ports, and the second portion of the antenna ports may be a second half of the antenna ports. 
     In example 25, the eNB of any of examples 20 through 22 is provided, in which the second circuitry may be operable to establish a first antenna port specified by the first assigned CSI RS group and a first antenna port specified by the second assigned CSI RS group as being associated with a first portion of the ordered set of antenna ports of the eNB, and may be operable to establish a second antenna port specified by the first assigned CSI RS group and a second antenna port specified by the second assigned CSI RS group as being associated with a second portion of the ordered set of antenna ports of the eNB. The second portion may follow the first portion in the ordered set of antenna ports of the eNB. 
     In example 26, the eNB of any of examples 20 through 22 is provided, in which the first assigned CSI RS group and the second assigned CSI RS group may be contained in one message to the UE having an information element (IE) that specifies each CSI RS group as at least one asserted bit in an array of bits. 
     In example 27, the eNB of any of examples 20 through 25 is provided, in which the first assigned CSI RS group is transmitted in a first message to the UE and the second assigned CSI RS group is transmitted in a second message to the UE. 
     Example 28 provides a machine readable storage media having machine executable instructions stored thereon that, when executed, cause a User Equipment (UE) to perform an operation. The operation may comprise receiving in the UE, from an Evolved Node-B (eNB), an assignment of a first Channel State Information Reference Signal (CSI RS) group specifying one or more CSI RS antenna ports, and an assignment of a second CSI RS group specifying one or more CSI RS antenna ports. The operation may also comprise indexing the one or more antenna ports specified by the first CSI RS group assignment and the one or more antenna ports specified by the second CSI RS group assignment as an ordered list of CSI RS antenna ports for at least part of a channel associated with a set of receiving antennas of the UE. 
     In example 29, the machine readable storage media of example 28 is provided, in which the operation may comprise performing channel state information measurements for the channel. The operation may also comprise calculating channel state information for the channel. The operation may also comprise composing a reporting message to the eNB containing the calculated channel state information for the channel. 
     In example 30, the machine readable storage media of either of examples 28 or 29 is provided, in which the indexing may begin with all antenna ports specified by the first CSI RS group assignment, then all antenna ports specified by the second CSI RS group assignment. 
     In example 31, the machine readable storage media of either of examples 28 or 29 is provided in which the indexing may interleave the one or more REs of the first CSI RS group assignment with the one or more REs of the second CSI RS group assignment. 
     In example 32, the machine readable storage media of any of examples 28 through 31 is provided, in which the first CSI RS group assignment and the second CSI RS group assignment may be contained in one message from the eNB having an information element (IE) that specifies each CSI RS group assignment as at least one asserted bit in an array of bits. 
     Example 33 provides a machine readable storage media having machine executable instructions stored thereon that, when executed, cause an Evolved Node-B (eNB) to perform an operation. The operation may comprise establishing one or more Channel State Information Reference Signal (CSI RS) antenna ports specified by a first CSI RS group assignment and one or more CSI RS antenna ports specified by a second CSI RS group assignment as being an ordered set of antenna ports of the eNB for at least part of a channel associated with a set of receiving antennas for a User Equipment (UE). The operation may also comprise transmitting to the UE the first CSI RS group assignment and the second CSI RS group assignment. 
     In example 34, the machine readable storage media of example 33 is provided, in which the operation may comprise receiving a reporting message from the UE containing calculated channel state information for the channel. 
     In example 35, the machine readable storage media of either of examples 33 or 34 is provided, in which the operation may comprise associating a first antenna coupled to the eNB with the one or more antenna ports specified by the first CSI RS group assignment. The operation may also comprise associating a second antenna coupled to the eNB with the one or more antenna ports specified by the second CSI RS group assignment, the first antenna and the second antenna having orthogonal polarizations. 
     In example 36, the machine readable storage media of any of examples 33 through 34 is provided, in which the operation may comprise associating a first portion of the ordered set of antenna ports of the eNB with one or more antenna ports specified by the first CSI RS group assignment, and may comprise associating a second portion of the ordered set of antenna ports of the eNB with one or more antenna ports specified by the second CSI RS group assignment. The second portion may follow the first portion in the ordered set of antenna ports of the eNB. 
     In example 37, the machine readable storage media of any of examples 33 through 35 is provided, in which the operation may comprise associating a first antenna port specified by the first CSI RS group assignment and a first antenna port specified by the second CSI RS group assignment with a first portion of the ordered set of antenna ports of the eNB, and may comprise associating a second antenna port specified by the first CSI RS group assignment and a second antenna port specified by the second CSI RS group assignment with a second portion of the ordered set of antenna ports of the eNB. The second portion may follow the first portion in the ordered set of antenna ports of the eNB. 
     Example 38 provides a method performed by a User Equipment (UE) to communicate with an Evolved Node-B (eNB) on a network. The method may comprise receiving in the UE, from an eNB, an assignment of a first Channel State Information Reference Signal (CSI RS) group specifying one or more CSI RS antenna ports, and an assignment of a second CSI RS group specifying one or more CSI RS antenna ports. The method may also comprise indexing the one or more antenna ports specified by the first CSI RS group assignment and the one or more antenna ports specified by the second CSI RS group assignment as an ordered list of CSI RS antenna ports for at least part of a channel associated with a set of receiving antennas of the UE. 
     In example 39, the method of example 38 is provided. The method may comprise performing channel state information measurements for the channel. The method may also comprise calculating channel state information for the channel. The method may also comprise composing a reporting message to the eNB containing the calculated channel state information for the channel. 
     In example 40, the method of either of examples 38 or 39 is provided, in which the indexing may begin with all antenna ports specified by the first CSI RS group assignment, then all antenna ports specified by the second CSI RS group assignment. 
     In example 41, the method of either of examples 38 or 39 is provided, in which the indexing may interleave the one or more REs of the first CSI RS group assignment with the one or more REs of the second CSI RS group assignment. 
     In example 42, the method of any of examples 38 through 41 is provided, in which the first CSI RS group assignment and the second CSI RS group assignment may be contained in one message from the eNB having an information element (IE) that specifies each CSI RS group assignment as at least one asserted bit in an array of bits. 
     In example 43, a machine readable storage media is provided, wherein the media has machine executable instructions stored thereon that, when executed, cause one or more processors (such as one or more processors of the UE) to perform a method according to any of examples 38 through 42. 
     Example 44 provides a method performed by an Evolved Node-B (eNB) to communicate with one or more User Equipments (UEs) on a network. The method may comprise establishing one or more Channel State Information Reference Signal (CSI RS) antenna ports specified by a first CSI RS group assignment and one or more CSI RS antenna ports specified by a second CSI RS group assignment as being an ordered set of antenna ports of the eNB for at least part of a channel associated with a set of receiving antennas for a User Equipment (UE). The method may also comprise transmitting to the UE the first CSI RS group assignment and the second CSI RS group assignment. 
     In example 45, the method of example 44 is provided. The method may comprise receiving a reporting message from the UE containing calculated channel state information for the channel. 
     In example, 46, the method of either of examples 44 or 45 is provided. The method may comprise associating a first antenna coupled to the eNB with the one or more antenna ports specified by the first CSI RS group assignment, and may comprise associating a second antenna coupled to the eNB with the one or more antenna ports specified by the second CSI RS group assignment. The first antenna and the second antenna may have orthogonal polarizations. 
     In example 47, the method of any of examples 44 through 46 is provided. The method may comprise associating a first portion of the ordered set of antenna ports of the eNB with one or more antenna ports specified by the first CSI RS group assignment, and may also comprise associating a second portion of the ordered set of antenna ports of the eNB with one or more antenna ports specified by the second CSI RS group assignment. The second portion may follow the first portion in the ordered set of antenna ports of the eNB. 
     In example 48, the method of any of examples 44 through 46 is provided. The method may comprise associating a first antenna port specified by the first CSI RS group assignment and a first antenna port specified by the second CSI RS group assignment with a first portion of the ordered set of antenna ports of the eNB, and may comprise associating a second antenna port specified by the first CSI RS group assignment and a second antenna port specified by the second CSI RS group assignment with a second portion of the ordered set of antenna ports of the eNB. The second portion may follow the first portion in the ordered set of antenna ports of the eNB. 
     In example 49, a machine readable storage media is provided, wherein the media has machine executable instructions stored thereon that, when executed, cause one or more processor (such as one or more processors of the eNB) to perform a method according to any of examples 44 through 48. 
     Example 50 provides a User Equipment (UE) operable to communicate with an Evolved Node-B (eNB) on a network, the UE including hardware processing circuitry that may comprise means for receiving in the UE, from an eNB, an assignment of a first Channel State Information Reference Signal (CSI RS) group specifying one or more CSI RS antenna ports, and an assignment of a second CSI RS group specifying one or more CSI RS antenna ports. The hardware processing circuitry may also comprise means for indexing the one or more antenna ports specified by the first CSI RS group assignment and the one or more antenna ports specified by the second CSI RS group assignment as an ordered list of CSI RS antenna ports for at least part of a channel associated with a set of receiving antennas of the UE. 
     In example 51, the UE including hardware processing circuitry of example 50 is provided, in which the hardware processing circuitry may comprise means for performing channel state information measurements for the channel. The hardware processing circuitry may also comprise means for calculating channel state information for the channel. The hardware processing circuitry may also comprise means for composing a reporting message to the eNB containing the calculated channel state information for the channel. 
     In example 52, the UE including hardware processing circuitry of either of examples 50 or 51 is provided, in which the indexing begins with all antenna ports specified by the first CSI RS group assignment, then all antenna ports specified by the second CSI RS group assignment. 
     In example 53, the UE including hardware processing circuitry of either of examples 50 or 51 is provided, in which the indexing interleaves the one or more REs of the first CSI RS group assignment with the one or more REs of the second CSI RS group assignment. 
     In example 54, the UE including hardware processing circuitry of any of examples 50 through 53 is provided, in which the first CSI RS group assignment and the second CSI RS group assignment are contained in one message from the eNB having an information element (IE) that specifies each CSI RS group assignment as at least one asserted bit in an array of bits. 
     In example 55, an Evolved Node-B (eNB) operable to communicate with a User Equipment (UE) on a network is provided, the eNB including hardware processing circuitry that may comprise means for establishing one or more Channel State Information Reference Signal (CSI RS) antenna ports specified by a first CSI RS group assignment and one or more CSI RS antenna ports specified by a second CSI RS group assignment as being an ordered set of antenna ports of the eNB for at least part of a channel associated with a set of receiving antennas for a User Equipment (UE). The hardware processing circuitry may also comprise means for transmitting to the UE the first CSI RS group assignment and the second CSI RS group assignment. 
     In example 56, the eNB including hardware processing circuitry of example 55 is provided, in which the hardware processing circuitry may comprise means for receiving a reporting message from the UE containing calculated channel state information for the channel. 
     In example 57, the eNB including hardware processing circuitry of example 55 or 56 is provided, which may comprise means for associating a first antenna coupled to the eNB with the one or more antenna ports specified by the first CSI RS group assignment. The hardware processing circuitry may also comprise means for associating a second antenna coupled to the eNB with the one or more antenna ports specified by the second CSI RS group assignment, the first antenna and the second antenna having orthogonal polarizations. 
     In example 58, the eNB including hardware processing circuitry of examples 55 through 57 is provided, in which the hardware processing circuitry may comprise means for associating a first portion of the ordered set of antenna ports of the eNB with one or more antenna ports specified by the first CSI RS group assignment. The hardware processing circuitry may also comprise means for associating a second portion of the ordered set of antenna ports of the eNB with one or more antenna ports specified by the second CSI RS group assignment, the second portion following the first portion in the ordered set of antenna ports of the eNB. 
     In example 59, the eNB including hardware processing circuitry of any of examples 55 through 57, in which the hardware processing circuitry may comprise means for associating a first antenna port specified by the first CSI RS group assignment and a first antenna port specified by the second CSI RS group assignment with a first portion of the ordered set of antenna ports of the eNB. The hardware processing circuitry may also comprise means for associating a second antenna port specified by the first CSI RS group assignment and a second antenna port specified by the second CSI RS group assignment with a second portion of the ordered set of antenna ports of the eNB, the second portion following the first portion in the ordered set of antenna ports of the eNB. 
     An abstract is provided that will allow the reader to ascertain the nature and gist of the technical disclosure. The abstract is submitted with the understanding that it will not be used to limit the scope or meaning of the claims. The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment.