Patent Publication Number: US-2023164822-A1

Title: Partially overlapped csi-rs shifting

Description:
FIELD 
     The present disclosure relates to wireless communications, and in particular, to partially overlapped channel state information reference signal (CSI-RS) shifting. 
     BACKGROUND 
     NR Frame Structure 
     The Third Generation Partnership Project (3GPP) next generation mobile wireless communication system (3GPP 5 th  Generation (5G), also called New Radio or NR), supports a diverse set of use cases and a diverse set of deployment scenarios. The later includes deployment at both low frequencies (100s of MHz), similar to Long Term Evolution (LTE) today, and very high frequencies (millimeter (mm) waves in the tens of GHz). 
     Similar to LTE, NR uses OFDM (Orthogonal Frequency Division Multiplexing) in the downlink (i.e., from a network node, gNB, eNB, or base station, to a wireless device (WD) or user equipment or UE). The basic NR physical resource over an antenna port can thus be seen as a time-frequency grid as illustrated in  FIG.  1    for example, where a resource block in a 14-symbol slot is shown. A resource block corresponds to 12 contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth. Each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. 
     Different subcarrier spacing values are supported in NR. The supported subcarrier spacing values (also referred to as different numerologies) are given by Δf=(15×2{circumflex over ( )}α) kHz where α∈(0,1,2,3,4). Δf=15 kHz is the basic (or reference) subcarrier spacing that is also used in LTE. 
     In the time domain, downlink (DL) and uplink (UL) transmissions in NR may be organized into equally sized subframes of 1 millisecond (ms) each, similar to LTE. A subframe is further divided into multiple slots of equal duration. The slot length for subcarrier spacing Δf=(15×2{circumflex over ( )}α) kHz is ½{circumflex over ( )}α ms. There is only one slot per subframe at Δf=15 kHz and a slot includes 14 OFDM symbols. 
     Downlink transmissions are dynamically scheduled, i.e., in each slot the gNB transmits downlink control information (DCI) about which WD data is to be transmitted to and which resource blocks in the current downlink slot the data is transmitted on. This control information is typically transmitted in the first one or two OFDM symbols in each slot in NR. The control information is carried on the Physical Control Channel (PDCCH) and data is carried on the Physical Downlink Shared Channel (PDSCH). A WD first detects and decodes PDCCH and if a PDCCH is decoded successfully, it then decodes the corresponding PDSCH based on the decoded control information in the PDCCH. 
     In addition to PDCCH and PDSCH, there are also other channels and reference signals transmitted in the downlink. 
     Uplink data transmissions, carried on Physical Uplink Shared Channel (PUSCH), are also dynamically scheduled by the gNB by transmitting a DCI. In case of time division duplex (TDD) operation, the DCI (which is transmitted in the DL region) always indicates a scheduling offset so that the PUSCH is transmitted in a slot in the UL region. 
     Codebook-Based Precoding 
     Multi-antenna techniques can significantly increase the data rates and reliability of a wireless communication system. The performance is in particular improved if both the transmitter and the receiver are equipped with multiple antennas, which results in a multiple-input multiple-output (MIMO) communication channel. Such systems and/or related techniques are commonly referred to as MIMO. 
     The NR standard is currently evolving with enhanced MIMO support. A component in NR is the support of MIMO antenna deployments and MIMO related techniques such as spatial multiplexing. The spatial multiplexing mode aims to provide high data rates in favorable channel conditions. An illustration of a spatial multiplexing operation is provided in  FIG.  2   . 
     As seen, the information carrying symbol vector s is multiplied by an N T ×r precoder matrix W, which serves to distribute the transmit energy in a subspace of the N T  (corresponding to N T  antenna ports) dimensional vector space. The precoder matrix is typically selected from a codebook of possible precoder matrices, and typically indicated by means of a precoder matrix indicator (PMI), which specifies a unique precoder matrix in the codebook for a given number of symbol streams. The r symbols in s each correspond to a layer and r is referred to as the transmission rank. In this way, spatial multiplexing is achieved since multiple symbols can be transmitted simultaneously over the same time/frequency resource element (TFRE). The number of symbols r is typically adapted to suit the current channel properties. 
     NR uses OFDM in the downlink (and DFT precoded OFDM in the uplink) and hence the received N R ×1 vector y n  for a certain TFRE on subcarrier n (or alternatively data TFRE number n) is thus modeled by 
     
       
      
       y 
       n 
       =H 
       n 
       Ws 
       n 
       +e 
       n  
      
     
     where e n  is a noise/interference vector obtained as realizations of a random process. The precoder W can be a wideband precoder, which is constant over frequency, or frequency selective. 
     The precoder matrix W is often chosen to match the characteristics of the N R ×N T  MIMO channel matrix H n , resulting in so-called channel dependent precoding. This is also commonly referred to as closed-loop precoding and essentially strives for focusing the transmit energy into a subspace which is strong in the sense of conveying much of the transmitted energy to the WD. 
     In closed-loop precoding for the N R  downlink, the WD transmits, based on channel measurements in the forward link (downlink), recommendations to the network node, e.g., gNB, of a suitable precoder to use. The network node, e.g., gNB, configures the WD to provide feedback according to CSI-ReportConfig and may transmit CSI-RS and configure the WD to use measurements of CSI-RS to feedback recommended precoding matrices that the WD selects from a codebook. A single precoder that is supposed to cover a large bandwidth (wideband precoding) may be fed back. It may also be beneficial to match the frequency variations of the channel and instead feed back a frequency-selective precoding report, e.g. several precoders, one per subband. This is an example of the more general case of channel state information (CSI) feedback, which also encompasses feeding back other information than recommended precoders to assist the network node in subsequent transmissions to the WD. Such other information may include channel quality indicators (CQIs) as well as transmission rank indicator (RI). In NR, CSI feedback can be either wideband, where one CSI is reported for the entire channel bandwidth, or frequency-selective, where one CSI is reported for each subband, which is defined as a number of contiguous resource blocks ranging between 4-32 physical resource blocks (PRBs) depending on the band width part (BWP) size. 
     Given the CSI feedback from the WD, the network node, e.g., gNB, determines the transmission parameters it wishes to use to transmit to the WD, including the precoding matrix, transmission rank, and modulation and coding scheme (MCS). These transmission parameters may differ from the recommendations the WD makes. The transmission rank, and thus the number of spatially multiplexed layers, is reflected in the number of columns of the precoder W. For efficient performance, it is important that a transmission rank that matches the channel properties is selected. 
     2D Antenna Arrays 
     Some embodiments presented in this disclosure may be used with two-dimensional antenna arrays and some of the presented embodiments use such antennas. Such antenna arrays may be (partly) described by the number of antenna columns corresponding to the horizontal dimension N_h, the number of antenna rows corresponding to the vertical dimension N_v and the number of dimensions corresponding to different polarizations N_p. The total number of antennas is thus N=N_h N_v N_p. It should be pointed out that the concept of an antenna is non-limiting in the sense that it can refer to any virtualization (e.g., linear mapping) of the physical antenna elements. For example, pairs of physical sub-elements could be fed the same signal, and hence share the same virtualized antenna port. An example of a 4×4 array with cross-polarized antenna elements is illustrated in  FIG.  3   . 
     Precoding may be interpreted as multiplying the signal with different beamforming weights for each antenna prior to transmission. A typical approach is to tailor the precoder to the antenna form factor, i.e., taking into account N_h, N_v and N_p when designing the precoder codebook. 
     Channel State Information Reference Signals (CSI-RS) 
     For CSI measurement and feedback, CSI-RS are defined. A CSI-RS is transmitted on each transmit antenna (or antenna port) and is used by a WD to measure downlink channel between each of the transmit antenna ports and each of its receive antenna ports. The antenna ports are also referred to as CSI-RS ports. The supported number of antenna ports in NR are {1, 2, 4, 8, 12, 16, 24, 32}. By measuring the received CSI-RS, a WD can estimate the channel that the CSI-RS is traversing, including the radio propagation channel and antenna gains. The CSI-RS for the above purpose is also referred to as Non-Zero Power (NZP) CSI-RS. 
     CSI-RS can be configured to be transmitted in certain resource elements (REs) in a slot and certain slots.  FIG.  4    shows an example of CSI-RS REs for 12 antenna ports, where  1  RE per resource block (RB) per port is shown. 
     An antenna port is equivalent to a reference signal resource that the WD shall use to measure the channel. Hence, a network node, e.g., gNB, with two antennas could define two CSI-RS ports, where each port is a set of resource elements in the time frequency grid within a subframe or slot. The base station transmits each of these two reference signals from each of the two antennas so that the WD can measure the two radio channels and report channel state information back to the base station based on these measurements. 
     The sequence used for CSI-RS may be defined by 
     
       
         
           
             
               r 
               ⁡ 
               ( 
               m 
               ) 
             
             = 
             
               
                 
                   1 
                   
                     2 
                   
                 
                 ⁢ 
                 
                   ( 
                   
                     1 
                     - 
                     
                       2 
                       · 
                       
                         c 
                         ⁡ 
                         ( 
                         
                           2 
                           ⁢ 
                           m 
                         
                         ) 
                       
                     
                   
                   ) 
                 
               
               + 
               
                 j 
                 ⁢ 
                 
                   1 
                   
                     2 
                   
                 
                 ⁢ 
                 
                   ( 
                   
                     1 
                     - 
                     
                       2 
                       · 
                       
                         c 
                         ⁡ 
                         ( 
                         
                           
                             2 
                             ⁢ 
                             m 
                           
                           + 
                           1 
                         
                         ) 
                       
                     
                   
                   ) 
                 
               
             
           
         
       
     
     where the pseudo-random sequence is defined, for example, in clause 5.2.1 of 3GPP Technical Specification (TS) 38.211. The pseudo-random sequence generator may be initialized with c init =(2 10 (N symb   slot n s,f   μ +l+1)(2n ID +1)+n ID )mod 2 31  at the start of each OFDM symbol where n s,f   μ  is the slot number within a radio frame, l is the OFDM symbol number within a slot, and n ID  equals the higher-layer parameter scramblingID or sequenceGenerationConfig. 
     There are 18 different CSI-RS resource configurations in NR, where each has a specific number of ports X. See Table 1 below. The index k_i indicates which first subcarrier in the PRB that is used for mapping the CSI-RS sequence to resource elements, where the second subcarrier is k_i+1. This set (k_i, k_i+1) of subcarriers are denoted as a code division multiplexing (CDM) group for that particular OFDM symbol, where index i may be interpreted as the CDM group index. The index l_i indicates the OFDM symbol within the slot. Hence, for example the configuration given by row 4 is a X=4 port CSI-RS resource where two CDM groups are used, first starting at subcarrier k_0 and the second starting at subcarrier k_0+2 (=k_1), both in the same OFDM symbol l_0. (Note that k_i and l_i are parameters signalled from gNB to WD by radio resource control (RRC) signalling when configuring the CSI-RS resource). 
     Moreover, CSI-RS ports are numbered within a CDM group first and then across CDM groups. So, in this example, CSI-RS port 0 and 1 maps to the CDM group indicated by k_0 and port 2 and 3 maps to the CDM group indicated by k_0+2. 
     This is captured in the 3GPP specifications in which the CSI-RS port indices p are numbered as, 
     p=3000+s+jL; 
     j=0,1, . . . , N/L−1 
     s=0,1, . . . , L−1; 
     where s is the sequence index provided by Tables 7.4.1.5.3-2 to 7.4.1.5.3-5, below L∈{1,2,4,8} is the CDM group size, and N is the number of CSI-RS ports. The CDM group index j given in Table 1 and corresponds to the time/frequency locations ( k , l ) for a given row of the table. The CDM groups are numbered in order of increasing frequency domain allocation first and then increasing time domain allocation. 
     For some rows, more than two CDM groups are used and they can be individually mapped to subcarriers, an example is row 10 where three CDM group indices k_0, k_1 and k_2 are used in one and the same symbol given by the RRC configured parameter l_0. 
     A CDM group can refer to a set of 2, 4 or 8 antenna ports, where the set of 2 antenna ports occurs when only CDM in frequency-domain (FD-CDM) over two adjacent subcarriers is considered. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 CSI-RS locations within a slot. 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 Ports 
                 Density 
                   
                   
                 CDM group 
                   
                   
               
               
                 Row 
                 X 
                 ρ 
                 cdm-Type 
                 ( k ,  l ) 
                 index  j   
                 k′ 
                 l′ 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 1 
                 1 
                 3 
                 No CDM 
                 (k 0 , l 0 ), (k 0  + 
                 0, 0, 0 
                 0 
                 0 
               
               
                   
                   
                   
                   
                 4, l 0 ), (k 0  + 8, l 0 ) 
               
               
                 2 
                 1 
                 1, 0.5 
                 No CDM 
                 (k 0 , l 0 ), 
                 0 
                 0 
                 0 
               
               
                 3 
                 2 
                 1, 0.5 
                 FD-CDM2 
                 (k 0 , l 0 ), 
                 0 
                 0, 1 
                 0 
               
               
                 4 
                 4 
                 1 
                 FD-CDM2 
                 (k 0 , l 0 ), (k 0  + 2, l 0 ) 
                 0, 1 
                 0, 1 
                 0 
               
               
                 5 
                 4 
                 1 
                 FD-CDM2 
                 (k 0 , l 0 ), (k 0 , l 0  + 1) 
                 0, 1 
                 0, 1 
                 0 
               
               
                 6 
                 8 
                 1 
                 FD-CDM2 
                 (k 0 , l 0 ), (k 1 , l 0 ), 
                 0, 1, 2, 3 
                 0, 1 
                 0 
               
               
                   
                   
                   
                   
                 (k 2 , l 0 ), (k 3 , l 0 ) 
               
               
                 7 
                 8 
                 1 
                 FD-CDM2 
                 (k 0 , l 0 ), 
                 0, 1, 2, 3 
                 0, 1 
                 0 
               
               
                   
                   
                   
                   
                 (k 1 , l 0 ), (k 0 , l 0  + 
               
               
                   
                   
                   
                   
                 1), (k 1 , l 0  + 1) 
               
               
                 8 
                 8 
                 1 
                 CDM4 
                 (k 0 , l 0 ), (k 1 , l 0 ) 
                 0, 1 
                 0, 1 
                 0, 1 
               
               
                   
                   
                   
                 (FD2, TD2) 
               
               
                 9 
                 12 
                 1 
                 FD-CDM2 
                 (k 0 , l 0 ), (k 1 , l 0 ), 
                 0, 1, 2, 
                 0, 1 
                 0 
               
               
                   
                   
                   
                   
                 (k 2 , l 0 ), 
                 3, 4, 5 
               
               
                   
                   
                   
                   
                 (k 3 , l 0 ), (k 4 , l 0 ), 
               
               
                   
                   
                   
                   
                 (k 5 , l 0 ) 
               
               
                 10 
                 12 
                 1 
                 CDM4 
                 (k 0 , l 0 ), (k 1 , l 0 ), 
                 0, 1, 2 
                 0, 1 
                 0, 1 
               
               
                   
                   
                   
                 (FD2, TD2) 
                 (k 2 , l 0 ) 
               
               
                 11 
                 16 
                 1, 0.5 
                 FD-CDM2 
                 (k 0 , l 0 ), (k 1 , l 0 ), 
                 0, 1, 2, 3, 
                 0, 1 
                 0 
               
               
                   
                   
                   
                   
                 (k 2 , l 0 ), 
                 4, 5, 6, 7 
               
               
                   
                   
                   
                   
                 (k 3 , l 0 ), (k 0 , l 0  + 
               
               
                   
                   
                   
                   
                 1), (k 1 , l 0  + 1), 
               
               
                   
                   
                   
                   
                 (k 2 , l 0  + 1), 
               
               
                   
                   
                   
                   
                 (k 3 , l 0  + 1) 
               
               
                 12 
                 16 
                 1, 0.5 
                 CDM4 
                 (k 0 , l 0 ), (k 1 , l 0 ), 
                 0, 1, 2, 3 
                 0, 1 
                 0, 1 
               
               
                   
                   
                   
                 (FD2, TD2) 
                 (k 2 , l 0 ), (k 3 , l 0 ) 
               
               
                 13 
                 24 
                 1, 0.5 
                 FD-CDM2 
                 (k 0 , l 0 ), (k 1 , l 0 ), 
                 0, 1, 2, 3, 4, 5, 
                 0, 1 
                 0 
               
               
                   
                   
                   
                   
                 (k 2 , l 0 ), (k 0 , l 0  + 
                 6, 7, 8, 9, 
               
               
                   
                   
                   
                   
                 1), (k 1 , l 0  + 1), 
                 10, 11 
               
               
                   
                   
                   
                   
                 (k 2 , l 0  + 1), (k 0 , l 1 ), 
               
               
                   
                   
                   
                   
                 (k 1 , l 1 ), (k 2 , l 1 ), 
               
               
                   
                   
                   
                   
                 (k 0 , l 1  + 1), 
               
               
                   
                   
                   
                   
                 (k 1 , l 1 , + 1), 
               
               
                   
                   
                   
                   
                 (k 2 , l 1 , + 1) 
               
               
                 14 
                 24 
                 1, 0.5 
                 CDM4 
                 (k 0 , l 0 ), (k 1 , l 0 ), 
                 0, 1, 2, 3, 4, 5 
                 0, 1 
                 0, 1 
               
               
                   
                   
                   
                 (FD2, TD2) 
                 (k 2 , l 0 ), (k 0 , l 1 ), 
               
               
                   
                   
                   
                   
                 (k 1 , l 1 ), (k 2 , l 1 ) 
               
               
                 15 
                 24 
                 1, 0.5 
                 CDM8 
                 (k 0 , l 0 ), (k 1 , l 0 ), 
                 0, 1, 2 
                 0, 1 
               
               
                   
                   
                   
                 (FD2, TD4) 
                 (k 2 , l 0 ) 
                   
                   
                 1, 2, 3 
               
               
                 16 
                 32 
                 1, 0.5 
                 FD-CDM2 
                 (k 0 , l 0 ), (k 1 , l 0 ), 
                 0, 1, 2, 3, 
                 0, 1 
                 0 
               
               
                   
                   
                   
                   
                 (k 2 , l 0 ) 
                 4, 5, 6, 7, 
               
               
                   
                   
                   
                   
                 (k 3 , l 0 ), (k 0 , l 0  + 1), 
                 8, 9, 10, 11, 
               
               
                   
                   
                   
                   
                 (k 1 , l 0  + 1), 
                 12, 13, 14, 15 
               
               
                   
                   
                   
                   
                 (k 2 , l 0  + 1), 
               
               
                   
                   
                   
                   
                 (k 3 , l 0  + 1), 
               
               
                   
                   
                   
                   
                 (k 0 , l 1 ), (k 1 , l 1 ), 
               
               
                   
                   
                   
                   
                 (k 2 , l 1 ), (k 3 , l 1 ), 
               
               
                   
                   
                   
                   
                 (k 0 , l 1  + 1), 
               
               
                   
                   
                   
                   
                 (k 1 , l 1  + 1), 
               
               
                   
                   
                   
                   
                 (k 2 , l 1  + 1), 
               
               
                   
                   
                   
                   
                 (k 3 , l 1  + 1) 
               
               
                 17 
                 32 
                 1, 0.5 
                 CDM4 
                 (k 0 , l 0 ), (k 1 , l 0 ), 
                 0, 1, 2, 3, 
                 0, 1 
                 0, 1 
               
               
                   
                   
                   
                 (FD2, TD2) 
                 (k 2 , l 0 ), (k 3 , l 0 ), 
                 4, 5, 6, 7 
               
               
                   
                   
                   
                   
                 (k 0 , l 1 ), (k 1 , l 1 ), 
               
               
                   
                   
                   
                   
                 (k 2 , l 1 ), (k 3 , l 1 ), 
               
               
                 18 
                 32 
                 1, 0.5 
                 CDM8 
                 (k 0 , l 0 ), (k 1 , l 0 ), 
                 0, 1, 2, 3 
                 0, 1 
                 0, 1, 
               
               
                   
                   
                   
                 (FD2, TD4) 
                 (k 2 , l 0 ), (k 3 , l 0 ), 
                   
                   
                 2, 3 
               
               
                   
               
            
           
         
       
     
     In more strict mathematical terminology, the mapping of the sequence r(m) onto resource-elements a for CSI-RS antenna port p can be described by: 
     
       
         
           
             
               a 
               
                 k 
                 , 
                 l 
               
               
                 ( 
                 
                   p 
                   , 
                   μ 
                 
                 ) 
               
             
             = 
             
               
                 β 
                 CSIRS 
               
               ⁢ 
               
                 
                   
                     w 
                     f 
                   
                   ( 
                   
                     k 
                     ′ 
                   
                   ) 
                 
                 · 
                 
                   
                     w 
                     t 
                   
                   ( 
                   
                     l 
                     ′ 
                   
                   ) 
                 
                 · 
                 
                   
                     r 
                     
                       l 
                       , 
                       
                         n 
                         
                           s 
                           , 
                           f 
                         
                       
                     
                   
                   ( 
                   
                     m 
                     ′ 
                   
                   ) 
                 
               
             
           
         
       
       
         
           
             
               m 
               ′ 
             
             = 
             
               
                 ⌊ 
                 
                   n 
                   ⁢ 
                   α 
                 
                 ⌋ 
               
               + 
               
                 k 
                 ′ 
               
               + 
               
                 ⌊ 
                 
                   
                     
                       k 
                       _ 
                     
                     ⁢ 
                     ρ 
                   
                   
                     N 
                     sc 
                     RB 
                   
                 
                 ⌋ 
               
             
           
         
       
       
         
           
             k 
             = 
             
               
                 nN 
                 sc 
                 RB 
               
               + 
               
                 k 
                 _ 
               
               + 
               
                 k 
                 ′ 
               
             
           
         
       
       
         
           
             l 
             = 
             
               
                 l 
                 _ 
               
               + 
               
                 l 
                 ′ 
               
             
           
         
       
       
         
           
             α 
             = 
             
               { 
               
                 
                   
                     ρ 
                   
                   
                     
                       
                         for 
                         ⁢ 
                             
                         X 
                       
                       = 
                       1 
                     
                   
                 
                 
                   
                     
                       2 
                       ⁢ 
                       ρ 
                     
                   
                   
                     
                       
                         for 
                         ⁢ 
                             
                         X 
                       
                       &gt; 
                       1 
                     
                   
                 
               
             
           
         
       
       
         
           
             
               n 
               = 
               0 
             
             , 
             1 
             , 
             … 
                
           
         
       
     
     For the different CDM types, the following CDM weights are used, where w(k′,l′)=w f (k′)·w t (l′) corresponds to the resulting CDM weights formed by the multiplication of the frequency and time-domain CDM weight. 
     
       
         
           
               
             
               
                 TABLE 7.4.1.5.3-2 
               
             
            
               
                   
               
               
                 The sequences w f  (k′) and w t  (l′) for cdm-Type equal to ‘no CDM’. 
               
            
           
           
               
               
               
            
               
                 Index 
                 w f  (0) 
                 w t  (0) 
               
               
                   
               
               
                 0 
                 1 
                 1 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7.4.1.5.3-3 
               
             
            
               
                   
               
               
                 The sequences w f  (k′) and w t  (l′) for 
               
               
                 cdm-Type equal to ‘FD-CDM2’. 
               
            
           
           
               
               
               
            
               
                 Index 
                 [w f  (0) w f  (1)] 
                 w t  (0) 
               
               
                   
               
               
                 0 
                 [+1 +1] 
                 1 
               
               
                 1 
                 [+1 −1] 
                 1 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7.4.1.5.3-4 
               
             
            
               
                   
               
               
                 The sequences w f  (k′) and w t  (l′) for cdm-Type equal to ‘CDM4’. 
               
            
           
           
               
               
               
            
               
                 Index 
                 [w f  (0) w f  (1)] 
                 [w t  (0) w t  (1)] 
               
               
                   
               
               
                 0 
                 [+1 +1] 
                 [+1 +1] 
               
               
                 1 
                 [+1 −1] 
                 [+1 +1] 
               
               
                 2 
                 [+1 +1] 
                 [+1 −1] 
               
               
                 3 
                 [+1 −1] 
                 [+1 −1] 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7.4.1.5.3-5 
               
             
            
               
                   
               
               
                 The sequences w f  (k′) and w t  (l′) for cdm-Type equal to ‘CDM8’. 
               
            
           
           
               
               
               
            
               
                 Index 
                 [w f  (0) w f  (1)] 
                 [w t  (0) w t  (1) w t  (2) w t  (3)] 
               
               
                   
               
               
                 0 
                 [+1 +1] 
                 [+1 +1 +1 +1] 
               
               
                 1 
                 [+1 −1] 
                 [+1 +1 +1 +1] 
               
               
                 2 
                 [+1 +1] 
                 [+1 −1 +1 −1] 
               
               
                 3 
                 [+1 −1] 
                 [+1 −1 +1 −1] 
               
               
                 4 
                 [+1 +1] 
                 [+1 +1 −1 −1] 
               
               
                 5 
                 [+1 −1] 
                 [+1 +1 −1 −1] 
               
               
                 6 
                 [+1 +1] 
                 [+1 −1 −1 +1] 
               
               
                 7 
                 [+1 −1] 
                 [+1 −1 −1 +1] 
               
               
                   
               
            
           
         
       
     
     DFT-Based Precoders 
     A common type of precoding uses a Discrete Fourier Transform (DFT)-precoder, where the precoder vector used to precode a single-layer transmission using a single-polarized uniform linear array (ULA) with N antennas is defined as 
     
       
         
           
             
               
                 
                   w 
                   
                     1 
                     ⁢ 
                     D 
                   
                 
                 ( 
                 k 
                 ) 
               
               = 
               
                 
                   1 
                   
                     N 
                   
                 
                 [ 
                 
                   
                     
                       
                         e 
                         
                           j 
                           ⁢ 
                           2 
                           ⁢ 
                           
                             π 
                               
                             · 
                             0 
                             · 
                             
                               k 
                               QN 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         e 
                         
                           j 
                           ⁢ 
                           2 
                           ⁢ 
                           
                             π 
                             · 
                             1 
                             · 
                             
                               k 
                               QN 
                             
                           
                         
                       
                     
                   
                   
                     
                       ⋮ 
                     
                   
                   
                     
                       
                         e 
                         
                           j 
                           ⁢ 
                           2 
                           ⁢ 
                           
                             π 
                             · 
                             
                               ( 
                               
                                 N 
                                 - 
                                 1 
                               
                               ) 
                             
                             · 
                             
                               k 
                               QN 
                             
                           
                         
                       
                     
                   
                 
                 ] 
               
             
             , 
           
         
       
     
     where k=0, 1, . . . QN−1 is the precoder index and Q is an integer oversampling factor. A corresponding precoder vector for a two-dimensional uniform planar array (UPA) can be created by taking the Kronecker product of two precoder vectors as w 2D  (k,l)=w 1D (k)⊗w 1D (l). Extending the precoder for a dual-polarized user positioning accuracy (UPA) may then be performed as 
     
       
         
           
             
               
                 w 
                 
                   
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     where e jϕ  is a co-phasing factor that may for instance be selected from quadrature phase shift keying (QPSK) alphabet 
     
       
         
           
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               . 
             
           
         
       
     
     A precoder matrix W 2D,DP  for multi-layer transmission may be created by appending columns of DFT precoder vectors as 
         W   2D,DP [ w   2D,DP ( k   1   ,l   1 ,ϕ 1 ) w   2D,DP ( k   2   ,l   2 ,ϕ 2 ) . . .  w   2D,DP ( k   R   ,l   R ,ϕ R )],
 
     where R is the number of transmission layers, i.e., the transmission rank. In a common special case for a rank-2 DFT precoder, k 1 =k 2 =k and l 1 =l 2 =l, meaning that 
     
       
         
           
             
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             = 
             
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                   . 
                 
               
             
           
         
       
     
     Such DFT-based precoders are used for instance in NR Type I CSI feedback. The NR codebook thus assumes an antenna port indexing which maps ports first along the second dimension (identified by the index  1 , which may be the vertical dimension), then the first dimension (identified by the index k, which may be the horizontal dimension), and then the polarization dimension. 
     CSI Framework in NR 
     In NR, a WD can be configured with multiple CSI report settings and multiple CSI-RS resource settings. Each resource setting can contain multiple resource sets, and each resource set can contain up to 8 CSI-RS resources. For each CSI report setting, a WD feeds back a CSI report, either periodically or aperiodically (triggered by the network). 
     Each CSI report may contain at least:
         A CSI-RS resource set for channel measurement;   An IMR resource set for interference measurement;   Optionally, a CSI-RS resource set for interference measurement;   Time-domain behavior, i.e. periodic, semi-persistent, or aperiodic reporting   Frequency granularity, i.e. wideband or subband;   CSI parameters to be reported such as RI, PMI, CQI, and CSI-RS resource indicator (CRI) in case of multiple CSI-RS resources in a resource set;   Codebook types, i.e. type I or II, and eventual codebook subset restriction   Measurement restriction enabled or disabled; and   Subband size. One out of two possible subband sizes is indicated, the value range for a subband size depends on the configured bandwidth of the downlink bandwidth part (BWP). One CQI/PMI (if configured for subband reporting) is fed back per subband.       

     When the CSI-RS resource set in a CSI report setting includes multiple CSI-RS resources, one of the CSI-RS resources is selected by a WD and a CSI-RS resource indicator (CRI) is also reported by the WD to indicate to the gNB about the selected CSI-RS resource in the resource set, together with RI, PMI and CQI associated with the selected CSI-RS resource. The network may then transmit the different CSI-RS resources using different MIMO precoders or by using different beam directions. 
     For aperiodic CSI reporting in NR, more than one CSI report settings, each with a different CSI-RS resource set for channel measurement and/or different resource set for interference measurement can be configured and triggered at the same time, i.e., with a single trigger command in the downlink control channel from the gNB to the WD. In this case, multiple CSI reports are measured, computed, aggregated and sent from the WD to the gNB in a single physical uplink shared channel (PUSCH) message. 
     As a general classification, NR categorizes a CSI Report Setting into wideband and subband frequency-granularity as follows:
         wideband PMI/CQI reporting, beam reporting, hybrid CSI report, semi-open loop reporting and non-PMI feedback (with wideband CQI) is classified as wideband frequency-granularity CSI, whereas;   the other configurations of a CSI Report Setting are classified as having a subband frequency-granularity.       

     Only CSI Report Settings with wideband frequency-granularity are allowed to be periodically reported on short PUCCH. 
     CSI-RS Interference Issue 
     From over-the-air (OTA) testing of commercial NR WDs, an issue has been found related to MIMO performance near the cell edge. The issue has been detected for both 32 and 8 port CSI-RS and for two WDs with chipsets from different vendors. 
     This is a real-life network issue related to MIMO which may severely impact NR performance and may be summarized as:
         Near cell edge, while still connected to a serving cell, the NR WD selects a precoding matrix indicator (PMI) as if it was served by an interfering cell, hence false PMI selection and reporting.
           This leads to a sharp drop in physical downlink shared channel (PDSCH) throughput at cell edge.   PMI selection logged at the WD, hence this issue is not due to poor uplink control (UCI) feedback channel quality.   
           The problem may occur whenever a CSI-RS resource from the serving cell collides with a CSI-RS resource from a neighboring cell.
           The problem may occur even though a different seed is used for CSI-RS sequence generation in serving and interfering cell respectively.   Even if non-colliding CSI-RS is configured by the use of CSI-RS cell planning, colliding CSI-RS between different cells may be very hard to avoid in practical networks even if frequency reuse is adopted because the topology is much different from hexagonal and far away gNB with colliding CSI-RS still hits the WD.   
           One cause of the problem is due to the design in 3GPP Release 15 (Rel 15) that the same CSI-RS sequence is used for all CSI-RS ports in the CSI-RS resource.
           To mitigate this, the WD may perform more advanced channel estimation, which may be unnecessarily complex and may be avoided if the problem with the CSI-RS design is mitigated.   
               

     Simplified Mathematical Analysis of CSI-RS Interference 
     To simplify the analysis and to better understand the underlying reasons for the false PMI selection, it may be assumed in this theoretical analysis that orthogonal cover code (OCC) is not used to separate pairs of ports. In the next section, simulations were made using the true NR CSI-RS with both FD-OCC and TD-OCC to illustrate that the problem exists also in this case as was observed in OTA. 
     Start with assuming CSI-RS ports in one resource block where each CSI-RS port uses one RE. Assume the WD is connected to a desired cell A and experiences downlink interference from cell B. The CSI-RS sequence sample on subcarrier k for port p is sp (k) and s p   B (k) for the two cells, respectively. 
     In addition, the channels are h p   A  and h p   B  from cell A and B, respectively, (assuming the channel is flat in frequency and noise is negligible) overlapping CSI-RS and the received signal is then, for port p 
         y   p ( k )= s   p   A ( k ) h   p   A   +γs   p   B ( k ) h   p   B    
     where γ is square root of the power offset of the interferer versus the desired signal, i.e., the inverse of the SIR. The channel estimate of channel h p   A  is then, if averaging the channel estimate across K samples in frequency domain within an OFDM symbol (assuming the value K is sufficiently small so that the channel is flat across these samples): 
     
       
         
           
             = 
             
               
                 
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     where the attenuated cross-sequence term between cell A and B, is, 
     
       
         
           
             
               β 
               p 
               K 
             
             = 
             
               
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                 K 
               
               ⁢ 
               
                 
                   ∑ 
                   
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                     = 
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     Now, stack all channel estimates the WD makes from the N CSI-RS ports transmitted from the serving cell, cell A, into a column vector: 
         ĥ =[  . . .  ] T =[ h   1   A    . . . h   N   A ] T +[β 1   K   h   1   B β 2   K   h   2   B  . . . β N   K   h   N   B ] T   =h+e.  
 
     To reflect a design choice in NR in this modeling, assume that the same sequence s p   A (k) is used for all CSI-RS ports of a CSI-RS resource, hence s p   A (k)=s A (k), and β p   K =β K  and we can write: 
     
       
         
           
             
               
                 
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                       ⁢ 
                           
                       
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                       ⁢ 
                           
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                     ] 
                   
                   T 
                 
               
               = 
               
                 
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                   A 
                 
                 + 
                 
                   
                     β 
                     K 
                   
                   ⁢ 
                   
                     
                       h 
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                     . 
                   
                 
               
             
           
         
       
     
     To proceed, interest is in the outer product R ĥĥ  as it is well known with respect to optimization of norms and thus likely used in the PMI determination: 
         ĥĥ   H   =h   A ( h   A ) H +|β K | 2   h   B ( h   B ) H +2Re{β K   h   A ( h   B ) H }.
 
     The first term is due to the desired channel and the second term is due to the channel from the interfering cell B. The contribution from interfering cell is attenuated with the factor |β K | 2  and behaves in the limit as 
     
       
         
           
             
               
                 
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     since pseudo-orthogonal sequences are used in cell A and B. 
     The third term vanishes if an accumulation of outer products is performed, since each β K  is random per RB and the accumulation tends towards zero. Such accumulation typically is done when estimating the spatial covariance R ĥĥ , since ĥĥ H  is estimated per RB and R ĥĥ  is obtained by averaging the outer product over many RBs. 
     Now, if raw sample estimate for CSI-RS port channel estimation is used, then K=1 and |β 1 | 2 =γ 2  and 
         ĥĥ   H   =h   A ( h   A ) H +γ 2   h   B ( h   B ) H +2Re{β 1   h   A ( h   B ) H }  (2).
 
     Using the result that if the outer product ĥĥ H  is averaged over many RBs then the third term tends to zero, leaving the received spatial covariance converging towards this expression where the interference channel covariance is present: 
         R   ĥĥ   ˜h   A ( h   A ) H +γ 2   h   B ( h   B ) H .
 
     A more advanced WD may use some frequency domain processing to reduce the error e and remove some of the structure of the interference analyzed below. On the other hand, for large CSI-RS resources, such as 32 ports, it is more demanding from WD complexity perspective to perform this processing, while it may be more likely for smaller number of ports. Also, it may be difficult to perform such frequency domain processing in frequency selective channels. 
     Note also in equation (2) that the two first terms do not depend on the subcarrier k as there is no dependence on the factor β K . 
     From this expression (2) it can be seen that, for low and negative signal-to-interference (SIR), where γ 2 ≥1, the principal eigenvector of ĥĥ H  is dominated or strongly affected by the principal eigenvector of R ee ˜h B (h B ) H , which is exactly the outer product of the channel of interfering non-serving cell B. The interference is not spatially white, but has a strong colored structure. Hence, 
     
       
         
           
             
               
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                         arg 
                         ⁢ 
                            
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                     ⁢ 
                     
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                     ⁢ 
                     
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                     ⁢ 
                         
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                     ⁢ 
                         
                     
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             , 
           
         
       
     
     The consequence is that the selection of ŵ will, if the signal-to-interference-plus-noise ratio (SINR) is sufficiently low, start to follow the CSI-RS transmitted from the strongest interfering (non-serving) cell instead of the serving cell, even if a different scrambling sequence is used if raw channel estimates are used in the channel estimation (K=1). 
     If the channel estimation suppresses the interfering cell by selecting a K value larger than one, then the problem may be reduced as |β K | 2  may be significantly lower. 
     The root cause of the problem is thus the use of the same sequence of all p ports: s p   A (k)=s A (k). If the specification is changed, for example so that each port has its own sequence, then 
         ĥĥH˜h   A ( h   A ) H +[β 1   K   h   1   B β 2   K   h   2   B  . . . β N   K   h   N   B ] T [β 1   K   h   1   B β 2   K   h   2   B  . . . β N   K   h   N   B ]*  (3).
 
     Note that even if raw channel estimates are used, K=1, each β p   1  is a pseudo-random QPSK symbol, this “destroys” the property of h B  (h B ) H  as each element is “scrambled” and appears closer to “spatially white” compared to the Rel 15 design, which makes the interference spatially colored. The expression (3) cannot be reduced to (2) in this case since the interference term now lies in a subspace that varies randomly from one subcarrier k to another; thus, spreading the interference energy rather isotropically in the entire vector space. 
     Hence, the principal eigenvector for [β 1   K h 1   B  β 2   K h 2   B  . . . β n   K h N   B ] T [β 1   K h 1   B  β 2   K h 2   B  . . . β n   K h N   B ]* which appears as the interference term in (3) is unrelated to the principal eigenvector of h B (h B ) H  which is very present in (2). 
     SUMMARY 
     Some embodiments advantageously provide methods, systems, and apparatuses for partially overlapped channel state information reference signal (CSI-RS) shifting. 
     In some embodiments, a method implemented in a network node includes configuring a channel state information reference signal (CSI-RS) resource of a set of candidate CSI-RS resources, the CSI-RS resource partially overlapping at least one other CSI-RS resource in the set; and optionally, transmitting CSI-RS signalling on the configured CSI-RS resource. 
     In some embodiments, a method implemented in a wireless device (WD) includes receiving a configuration of a channel state information reference signal (CSI-RS) resource of a set of candidate CSI-RS resources, the CSI-RS resource partially overlapping at least one other CSI-RS resource in the set; and optionally, receiving CSI-RS signalling on the configured CSI-RS resource. 
     According to an aspect of the present disclosure, a method implemented in a network node configured to communicate with a wireless device, WD, is provided. The method comprises configuring a first channel state information reference signal, CSI-RS, resource in a set of candidate CSI-RS resources, the first CSI-RS resource partially overlapping a second CSI-RS resource in the set of candidate CSI-RS resources, the first CSI-RS resource being associated with a first cell and the second CSI-RS resource being associated with a second cell; and transmitting CSI-RS signaling on the configured first CSI-RS resource. 
     In some embodiments, the first CSI-RS resource partially overlaps the second CSI-RS resource in at least one time-frequency resource within a slot. In some embodiments, each CSI-RS resource in the set of candidate CSI-RS resources occupies a set of time-frequency resource elements, REs, within a slot and a subset of resource elements of the first CSI-RS resource are occupied by a subset of resource elements of the second CSI-RS resource. In some embodiments, the first cell is a serving cell and the second cell is a neighboring cell. In some embodiments, each candidate CSI-RS resource in the set of candidate CSI-RS resources partially overlaps each of the other candidate CSI-RS resources in the set within a slot. 
     In some embodiments, the method further includes allocating a resource position for the first CSI-RS resource based on a physical cell ID, PCI, associated with the first cell. In some embodiments, allocating comprises allocating the resource position for the first CSI-RS resource based on the PCI modulus N, N being a number of resource positions for CSI-RS resources in the set of candidate CSI-RS resources. In some embodiments, the second CSI-RS resource is based on a PCI associated with the second cell. In some embodiments, the candidate CSI-RS resources in the set are shifted relative to each other within a slot based on an index value. In some embodiments, the first cell has a corresponding first index value and the second cell has a corresponding second index value, the second index value being different from the first index value. In some embodiments, the method further comprises applying a modulation and coding scheme, MCS, backoff in a slot on which the CSI-RS signaling is transmitted. 
     According to another aspect of the present disclosure, a network node configured to communicate with a wireless device, WD, is provided. The network node comprises processing circuitry. The processing circuitry is configured to cause the network node to configure a first channel state information reference signal, CSI-RS, resource in a set of candidate CSI-RS resources, the first CSI-RS resource partially overlapping a second CSI-RS resource in the set of candidate CSI-RS resources, the first CSI-RS resource being associated with a first cell and the second CSI-RS resource being associated with a second cell; and transmit CSI-RS signaling on the configured first CSI-RS resource. 
     In some embodiments, the first CSI-RS resource partially overlaps the second CSI-RS resource in at least one time-frequency resource within a slot. In some embodiments, each CSI-RS resource in the set of candidate CSI-RS resources occupies a set of time-frequency resource elements, REs, within a slot and a subset of resource elements of the first CSI-RS resource are occupied by a subset of resource elements of the second CSI-RS resource. In some embodiments, the first cell is a serving cell and the second cell is a neighboring cell. In some embodiments, each candidate CSI-RS resource in the set of candidate CSI-RS resources partially overlaps each of the other candidate CSI-RS resources in the set within a slot. In some embodiments, the processing circuitry is configured to cause the network node to allocate a resource position for the first CSI-RS resource based on a physical cell ID, PCI, associated with the first cell. 
     In some embodiments, the processing circuitry is configured to cause the network node to allocate by being configured to cause the network node to allocate the resource position for the first CSI-RS resource based on the PCI modulus N, N being a number of resource positions for CSI-RS resources in the set of candidate CSI-RS resources. In some embodiments, the second CSI-RS resource is based on a PCI associated with the second cell. In some embodiments, the candidate CSI-RS resources in the set are shifted relative to each other within a slot based on an index value. In some embodiments, the first cell has a corresponding first index value and the second cell has a corresponding second index value, the second index value being different from the first index value. In some embodiments, the processing circuitry is further configured to cause the network node to apply a modulation and coding scheme, MCS, backoff in a slot on which the CSI-RS signaling is transmitted. 
     According to yet another aspect of the present disclosure, a method implemented in a wireless device, WD, configured to communicate with a network node is provided. The method comprises receiving a configuration of a first channel state information reference signal, CSI-RS, resource in a set of candidate CSI-RS resources, the first CSI-RS resource partially overlapping a second CSI-RS resource in the set of candidate CSI-RS resources, the first CSI-RS resource being associated with a first cell and the second CSI-RS resource being associated with a second cell; and receiving CSI-RS signaling on the configured first CSI-RS resource. 
     In some embodiments, the first CSI-RS resource partially overlaps the second CSI-RS resource in at least one time-frequency resource within a slot. In some embodiments, each CSI-RS resource in the set of candidate CSI-RS resources occupies a set of time-frequency resource elements, REs, within a slot and a subset of resource elements of the first CSI-RS resource are occupied by a subset of resource elements of the second CSI-RS resource. In some embodiments, the first cell is a serving cell and the second cell is a neighboring cell. In some embodiments, each candidate CSI-RS resource in the set of candidate CSI-RS resources partially overlaps each of the other candidate CSI-RS resources in the set within a slot. 
     In some embodiments, the method further includes receiving an allocation of a resource position for the first CSI-RS resource, the resource position being based on a physical cell ID, PCI, associated with the first cell. In some embodiments, the resource position for the first CSI-RS resource is based on the PCI modulus N, N being a number of resource positions for CSI-RS resources in the set of candidate CSI-RS resources. In some embodiments, the second CSI-RS resource is based on a PCI associated with the second cell. In some embodiments, the candidate CSI-RS resources in the set are shifted relative to each other within a slot based on an index value. In some embodiments, the first cell has a corresponding first index value and the second cell has a corresponding second index value, the second index value being different from the first index value. In some embodiments, the CSI-RS signaling is received according to a modulation and coding scheme, MCS, backoff. 
     According to yet another aspect of the present disclosure, a wireless device, WD, configured to communicate with a network node is provided. The WD comprises processing circuitry. The processing circuitry is configured to cause the WD to receive a configuration of a first channel state information reference signal, CSI-RS, resource in a set of candidate CSI-RS resources, the first CSI-RS resource partially overlapping a second CSI-RS resource in the set of candidate CSI-RS resources, the first CSI-RS resource being associated with a first cell and the second CSI-RS resource being associated with a second cell; and receive CSI-RS signaling on the configured first CSI-RS resource. 
     In some embodiments, the first CSI-RS resource partially overlaps the second CSI-RS resource in at least one time-frequency resource within a slot. In some embodiments, each CSI-RS resource in the set of candidate CSI-RS resources occupies a set of time-frequency resource elements, REs, within a slot and a subset of resource elements of the first CSI-RS resource are occupied by a subset of resource elements of the second CSI-RS resource. In some embodiments, the first cell is a serving cell and the second cell is a neighboring cell. In some embodiments, each candidate CSI-RS resource in the set of candidate CSI-RS resources partially overlaps each of the other candidate CSI-RS resources in the set within a slot. In some embodiments, the processing circuitry is further configured to cause the WD to receive an allocation of a resource position for the first CSI-RS resource, the resource position being based on a physical cell ID, PCI, associated with the first cell. 
     In some embodiments, the resource position for the first CSI-RS resource is based on the PCI modulus N, N being a number of resource positions for CSI-RS resources in the set of candidate CSI-RS resources. In some embodiments, the second CSI-RS resource is based on a PCI associated with the second cell. In some embodiments, the candidate CSI-RS resources in the set are shifted relative to each other within a slot based on an index value. In some embodiments, the first cell has a corresponding first index value and the second cell has a corresponding second index value, the second index value being different from the first index value. In some embodiments, the CSI-RS signaling is received according to a modulation and coding scheme, MCS, backoff 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present embodiments, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG.  1    illustrates an example of a NR physical resource grid; 
         FIG.  2    illustrates an example transmission structure of precoded spatial multiplexing mode in NR; 
         FIG.  3    illustrates an example of a two-dimensional antenna array of cross-polarized antenna elements (N_P=2), with N_h=4 horizontal antenna elements and N_v=4 vertical antenna elements; 
         FIG.  4    illustrates an example of RE allocation for a 12-port CSI-RS in NR; 
         FIG.  5    illustrates an example of the observed problem from field testing with commercial WDs (the WDs served by gNB 1 are reporting PMI 1  instead of PMI D  where PMI 1  is the PMI the WD would report if served by gNB 2); 
         FIG.  6    is a schematic diagram of an exemplary network architecture illustrating a communication system connected via an intermediate network to a host computer according to the principles in the present disclosure; 
         FIG.  7    is a block diagram of a host computer communicating via a network node with a wireless device over an at least partially wireless connection according to some embodiments of the present disclosure; 
         FIG.  8    is a flowchart illustrating exemplary methods implemented in a communication system including a host computer, a network node and a wireless device for executing a client application at a wireless device according to some embodiments of the present disclosure; 
         FIG.  9    is a flowchart illustrating exemplary methods implemented in a communication system including a host computer, a network node and a wireless device for receiving user data at a wireless device according to some embodiments of the present disclosure; 
         FIG.  10    is a flowchart illustrating exemplary methods implemented in a communication system including a host computer, a network node and a wireless device for receiving user data from the wireless device at a host computer according to some embodiments of the present disclosure; 
         FIG.  11    is a flowchart illustrating exemplary methods implemented in a communication system including a host computer, a network node and a wireless device for receiving user data at a host computer according to some embodiments of the present disclosure; 
         FIG.  12    is a flowchart of an exemplary process in a network node according to some embodiments of the present disclosure; 
         FIG.  13    is a flowchart of an exemplary process in a wireless device according to some embodiments of the present disclosure; 
         FIG.  14    is a flowchart of an exemplary process in a network node according to some embodiments of the present disclosure; 
         FIG.  15    is a flowchart of an exemplary process in a wireless device according to some embodiments of the present disclosure; 
         FIG.  16    illustrates an example of partially overlapped CSI-RS resources according to some embodiments of the present disclosure; 
         FIG.  17    illustrates the 32-port CSI-RS pattern configuration A according to some embodiments of the present disclosure; 
         FIG.  18    illustrates the 32-port CSI-RS pattern configuration B according to some embodiments of the present disclosure; 
         FIG.  19    illustrates the 32-port CSI-RS pattern configuration C according to some embodiments of the present disclosure; 
         FIG.  20    illustrates the 32-port CSI-RS pattern configuration D according to some embodiments of the present disclosure; 
         FIG.  21    illustrates the 32-port CSI-RS pattern configuration E according to some embodiments of the present disclosure; 
         FIG.  22    illustrates the 32-port CSI-RS pattern configuration F according to some embodiments of the present disclosure; 
         FIG.  23    illustrates an example of serving and interfering cell CSI-RS resource positions within a CSI-RS reuse group; 
         FIG.  24    illustrates an example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  25    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  26    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  27    illustrates yet another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  28    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  29    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  30    illustrates yet another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  31    illustrates yet another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  32    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  33    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  34    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  35    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  36    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  37    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  38    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  39    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; 
         FIG.  40    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure; and 
         FIG.  41    illustrates another example of overlapping 16-port CSI-RS pattern configurations according to some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Due to the CSI-RS sequence design in NR 3GPP Rel-15, “false PMI reporting” due to pilot contamination occurs when colliding CSI-RS between serving cell and neighbor cell is used and the WD is in the handover region where the interfering cell is of similar power level as the serving cell. This may lead to high block error rate (BLER) and correspondingly severe WD throughput degradation since the serving cell may transmit in the wrong direction based on the false PMI report. 
     One way to reduce this interference is to apply a CSI-RS re-use pattern and transmit CSI-RS in neighboring cell in different slots so that they do not collide with each other. However, this leads to an increase in CSI-RS to physical downlink shared channel (PDSCH) interference which has a larger detrimental impact on performance than the CSI-RS interference itself. Thus, the solution is worse than the problem. 
     An inter-cell CSI-RS shifting method is proposed, where CSI-RS resources are partially overlapped between different cells in a CSI-RS reuse group. 
     Due to that, the interfering CSI-RS resource only partially overlaps with the serving CSI-RS resource, the structure of the interference becomes more spatially uncorrelated leading to lower chance of erroneous PMI determination by the WD, which improves WD DL performance in the handover region. Simultaneously, the excessive CSI-RS to PDSCH interference associated with the prior art CSI-RS reuse scheme may be avoided, which improves PDSCH performance. 
     Before describing in detail exemplary embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to partially overlapped channel state information reference signal (CSI-RS) shifting. Accordingly, components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Like numbers refer to like elements throughout the description. 
     As used herein, relational terms, such as “first” and “second,” “top” and “bottom,” and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the concepts described herein. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     In embodiments described herein, the joining term, “in communication with” and the like, may be used to indicate electrical or data communication, which may be accomplished by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling or optical signaling, for example. One having ordinary skill in the art will appreciate that multiple components may interoperate and modifications and variations are possible of achieving the electrical and data communication. 
     In some embodiments described herein, the term “coupled,” “connected,” and the like, may be used herein to indicate a connection, although not necessarily directly, and may include wired and/or wireless connections. 
     The term “network node” used herein can be any kind of network node comprised in a radio network which may further comprise any of base station (BS), radio base station, base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), g Node B (gNB), evolved Node B (eNB or eNodeB), Node B, multi-standard radio (MSR) radio node such as MSR BS, multi-cell/multicast coordination entity (MCE), integrated access and backhaul (IAB) node, relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), a core network node (e.g., mobile management entity (MME), self-organizing network (SON) node, a coordinating node, positioning node, MDT node, etc.), an external node (e.g., 3rd party node, anode external to the current network), nodes in distributed antenna system (DAS), a spectrum access system (SAS) node, an element management system (EMS), etc. The network node may also comprise test equipment. The term “radio node” used herein may be used to also denote a wireless device (WD) such as a wireless device (WD) or a radio network node. 
     In some embodiments, the non-limiting terms wireless device (WD) or a user equipment (UE) are used interchangeably. The WD herein can be any type of wireless device capable of communicating with a network node or another WD over radio signals, such as wireless device (WD). The WD may also be a radio communication device, target device, device to device (D2D) WD, machine type WD or WD capable of machine to machine communication (M2M), low-cost and/or low-complexity WD, a sensor equipped with WD, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), an Internet of Things (IoT) device, or a Narrowband IoT (NB-IOT) device, etc. 
     Also, in some embodiments the generic term “radio network node” is used. It can be any kind of a radio network node which may comprise any of base station, radio base station, base transceiver station, base station controller, network controller, RNC, evolved Node B (eNB), Node B, gNB, Multi-cell/multicast Coordination Entity (MCE), IAB node, relay node, access point, radio access point, Remote Radio Unit (RRU) Remote Radio Head (RRH). 
     In some embodiments, the term “overlap” means overlap of at least part of a time-frequency resource. 
     The term “signaling” used herein may comprise any of: high-layer signaling (e.g., via Radio Resource Control (RRC) or a like), lower-layer signaling (e.g., via a physical control channel or a broadcast channel), or a combination thereof. The signaling may be implicit or explicit. The signaling may further be unicast, multicast or broadcast. The signaling may also be directly to another node or via a third node. 
     Signaling may generally comprise one or more symbols and/or signals and/or messages. A signal may comprise or represent one or more bits. An indication may represent signaling, and/or be implemented as a signal, or as a plurality of signals. One or more signals may be included in and/or represented by a message. Signaling, in particular control signaling, may comprise a plurality of signals and/or messages, which may be transmitted on different carriers and/or be associated to different signaling processes, e.g. representing and/or pertaining to one or more such processes and/or corresponding information. An indication may comprise signaling, and/or a plurality of signals and/or messages and/or may be comprised therein, which may be transmitted on different carriers and/or be associated to different acknowledgement signaling processes, e.g. representing and/or pertaining to one or more such processes. Signaling associated to a channel may be transmitted such that represents signaling and/or information for that channel, and/or that the signaling is interpreted by the transmitter and/or receiver to belong to that channel. Such signaling may generally comply with transmission parameters and/or format/s for the channel. 
     Configuring a Radio Node 
     Configuring a radio node, in particular a terminal or user equipment or the WD, may refer to the radio node being adapted or caused or set and/or instructed to operate according to the configuration. Configuring may be done by another device, e.g., a network node (for example, a radio node of the network like a base station or eNodeB) or network, in which case it may comprise transmitting configuration data to the radio node to be configured. Such configuration data may represent the configuration to be configured and/or comprise one or more instruction pertaining to a configuration, e.g. a configuration for transmitting and/or receiving on allocated resources, in particular frequency resources, or e.g., configuration for performing certain measurements on certain subframes or radio resources. A radio node may configure itself, e.g., based on configuration data received from a network or network node. A network node may use, and/or be adapted to use, its circuitry/ies for configuring. Allocation information may be considered a form of configuration data. Configuration data may comprise and/or be represented by configuration information, and/or one or more corresponding indications and/or message/s. 
     Configuring in General 
     Generally, configuring may include determining configuration data representing the configuration and providing, e.g. transmitting, it to one or more other nodes (parallel and/or sequentially), which may transmit it further to the radio node (or another node, which may be repeated until it reaches the wireless device). Alternatively, or additionally, configuring a radio node, e.g., by a network node or other device, may include receiving configuration data and/or data pertaining to configuration data, e.g., from another node like a network node, which may be a higher-level node of the network, and/or transmitting received configuration data to the radio node. Accordingly, determining a configuration and transmitting the configuration data to the radio node may be performed by different network nodes or entities, which may be able to communicate via a suitable interface, e.g., an X2 interface in the case of LTE or a corresponding interface for NR. Configuring a terminal (e.g. WD) may comprise scheduling downlink and/or uplink transmissions for the terminal, e.g. downlink data and/or downlink control signaling and/or DCI and/or uplink control or data or communication signaling, in particular acknowledgement signaling, and/or configuring resources and/or a resource pool therefor. In particular, configuring a terminal (e.g. WD) may comprise configuring the WD to perform certain measurements on certain subframes or radio resources and reporting such measurements according to embodiments of the present disclosure. 
     A resource element may represent a smallest time-frequency resource, e.g. representing the time and frequency range covered by one symbol or a number of bits represented in a common modulation. A resource element may e.g. cover a symbol time length and a subcarrier, in particular in 3GPP and/or LTE standards. A data transmission may represent and/or pertain to transmission of specific data, e.g. a specific block of data and/or transport block. 
     A cell may be generally a communication cell, e.g., of a cellular or mobile communication network, provided by a node. A serving cell may be a cell on or via which a network node (the node providing or associated to the cell, e.g., base station or eNodeB) transmits and/or may transmit data (which may be data other than broadcast data) to a user equipment, in particular control and/or user or payload data, and/or via or on which a user equipment transmits and/or may transmit data to the node; a serving cell may be a cell for or on which the user equipment is configured and/or to which it is synchronized and/or has performed an access procedure, e.g., a random access procedure, and/or in relation to which it is in a RRC_connected or RRC_idle state, e.g., in case the node and/or user equipment and/or network follow a 5G or LTE-standard. One or more carriers (e.g., uplink and/or downlink carrier/s and/or a carrier for both uplink and downlink) may be associated to a cell. 
     Note that although terminology from one particular wireless system, such as, for example, 3GPP LTE and/or New Radio (NR), may be used in this disclosure, this should not be seen as limiting the scope of the disclosure to only the aforementioned system. Other wireless systems, including without limitation Wide Band Code Division Multiple Access (WCDMA), Worldwide Interoperability for Microwave Access (WiMax), Ultra Mobile Broadband (UMB) and Global System for Mobile Communications (GSM), may also benefit from exploiting the ideas covered within this disclosure. 
     Note further, that functions described herein as being performed by a wireless device or a network node may be distributed over a plurality of wireless devices and/or network nodes. In other words, it is contemplated that the functions of the network node and wireless device described herein are not limited to performance by a single physical device and, in fact, can be distributed among several physical devices. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Referring again to the drawing figures, in which like elements are referred to by like reference numerals, there is shown in  FIG.  6    a schematic diagram of a communication system  10 , according to an embodiment, such as a 3GPP-type cellular network that may support standards such as LTE and/or NR (5G), which comprises an access network  12 , such as a radio access network, and a core network  14 . The access network  12  comprises a plurality of network nodes  16   a ,  16   b ,  16   c  (referred to collectively as network nodes  16 ), such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area  18   a ,  18   b ,  18   c  (referred to collectively as coverage areas  18 ). Each network node  16   a ,  16   b ,  16   c  is connectable to the core network  14  over a wired or wireless connection  20 . A first wireless device (WD)  22   a  located in coverage area  18   a  is configured to wirelessly connect to, or be paged by, the corresponding network node  16   a . A second WD  22   b  in coverage area  18   b  is wirelessly connectable to the corresponding network node  16   b . While a plurality of WDs  22   a ,  22   b  (collectively referred to as wireless devices  22 ) are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole WD is in the coverage area or where a sole WD is connecting to the corresponding network node  16 . Note that although only two WDs  22  and three network nodes  16  are shown for convenience, the communication system may include many more WDs  22  and network nodes  16 . 
     Also, it is contemplated that a WD  22  can be in simultaneous communication and/or configured to separately communicate with more than one network node  16  and more than one type of network node  16 . For example, a WD  22  can have dual connectivity with a network node  16  that supports LTE and the same or a different network node  16  that supports NR. As an example, WD  22  can be in communication with an eNB for LTE/E-UTRAN and a gNB for NR/NG-RAN. 
     The communication system  10  may itself be connected to a host computer  24 , which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm. The host computer  24  may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. The connections  26 ,  28  between the communication system  10  and the host computer  24  may extend directly from the core network  14  to the host computer  24  or may extend via an optional intermediate network  30 . The intermediate network  30  may be one of, or a combination of more than one of, a public, private or hosted network. The intermediate network  30 , if any, may be a backbone network or the Internet. In some embodiments, the intermediate network  30  may comprise two or more sub-networks (not shown). 
     The communication system of  FIG.  6    as a whole enables connectivity between one of the connected WDs  22   a ,  22   b  and the host computer  24 . The connectivity may be described as an over-the-top (OTT) connection. The host computer  24  and the connected WDs  22   a ,  22   b  are configured to communicate data and/or signaling via the OTT connection, using the access network  12 , the core network  14 , any intermediate network  30  and possible further infrastructure (not shown) as intermediaries. The OTT connection may be transparent in the sense that at least some of the participating communication devices through which the OTT connection passes are unaware of routing of uplink and downlink communications. For example, a network node  16  may not or need not be informed about the past routing of an incoming downlink communication with data originating from a host computer  24  to be forwarded (e.g., handed over) to a connected WD  22   a . Similarly, the network node  16  need not be aware of the future routing of an outgoing uplink communication originating from the WD  22   a  towards the host computer  24 . 
     A network node  16  is configured to include a configuration unit  32  which is configured to configure a channel state information reference signal (CSI-RS) resource of a set of candidate CSI-RS resources, the CSI-RS resource partially overlapping at least one other CSI-RS resource in the set; and optionally, transmit CSI-RS signalling on the configured CSI-RS resource. 
     A wireless device  22  is configured to include a measurement unit  34  which is configured to receive a configuration of a channel state information reference signal (CSI-RS) resource of a set of candidate CSI-RS resources, the CSI-RS resource partially overlapping at least one other CSI-RS resource in the set; and optionally, receive CSI-RS signalling on the configured CSI-RS resource. 
     Example implementations, in accordance with an embodiment, of the WD  22 , network node  16  and host computer  24  discussed in the preceding paragraphs will now be described with reference to  FIG.  7   . In a communication system  10 , a host computer  24  comprises hardware (HW)  38  including a communication interface  40  configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system  10 . The host computer  24  further comprises processing circuitry  42 , which may have storage and/or processing capabilities. The processing circuitry  42  may include a processor  44  and memory  46 . In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry  42  may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor  44  may be configured to access (e.g., write to and/or read from) memory  46 , which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). 
     Processing circuitry  42  may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by host computer  24 . Processor  44  corresponds to one or more processors  44  for performing host computer  24  functions described herein. The host computer  24  includes memory  46  that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software  48  and/or the host application  50  may include instructions that, when executed by the processor  44  and/or processing circuitry  42 , causes the processor  44  and/or processing circuitry  42  to perform the processes described herein with respect to host computer  24 . The instructions may be software associated with the host computer  24 . 
     The software  48  may be executable by the processing circuitry  42 . The software  48  includes a host application  50 . The host application  50  may be operable to provide a service to a remote user, such as a WD  22  connecting via an OTT connection  52  terminating at the WD  22  and the host computer  24 . In providing the service to the remote user, the host application  50  may provide user data which is transmitted using the OTT connection  52 . The “user data” may be data and information described herein as implementing the described functionality. In one embodiment, the host computer  24  may be configured for providing control and functionality to a service provider and may be operated by the service provider or on behalf of the service provider. The processing circuitry  42  of the host computer  24  may enable the host computer  24  to observe, monitor, control, transmit to and/or receive from the network node  16  and/or the wireless device  22 . The processing circuitry  42  of the host computer  24  may include a monitor unit  54  configured to enable the service provider to observe, monitor, control, transmit to and/or receive from the network node  16  and/or the wireless device  22 . 
     The communication system  10  further includes a network node  16  provided in a communication system  10  and including hardware  58  enabling it to communicate with the host computer  24  and with the WD  22 . The hardware  58  may include a communication interface  60  for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system  10 , as well as a radio interface  62  for setting up and maintaining at least a wireless connection  64  with a WD  22  located in a coverage area  18  served by the network node  16 . The radio interface  62  may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers. The communication interface  60  may be configured to facilitate a connection  66  to the host computer  24 . The connection  66  may be direct or it may pass through a core network  14  of the communication system  10  and/or through one or more intermediate networks  30  outside the communication system  10 . 
     In the embodiment shown, the hardware  58  of the network node  16  further includes processing circuitry  68 . The processing circuitry  68  may include a processor  70  and a memory  72 . In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry  68  may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor  70  may be configured to access (e.g., write to and/or read from) the memory  72 , which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). 
     Thus, the network node  16  further has software  74  stored internally in, for example, memory  72 , or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the network node  16  via an external connection. The software  74  may be executable by the processing circuitry  68 . The processing circuitry  68  may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by network node  16 . Processor  70  corresponds to one or more processors  70  for performing network node  16  functions described herein. The memory  72  is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software  74  may include instructions that, when executed by the processor  70  and/or processing circuitry  68 , causes the processor  70  and/or processing circuitry  68  to perform the processes described herein with respect to network node  16 . For example, processing circuitry  68  of the network node  16  may include configuration unit  32  configured to perform network node methods discussed herein, such as the methods discussed with reference to  FIG.  12    as well as other figures. 
     The communication system  10  further includes the WD  22  already referred to. The WD  22  may have hardware  80  that may include a radio interface  82  configured to set up and maintain a wireless connection  64  with a network node  16  serving a coverage area  18  in which the WD  22  is currently located. The radio interface  82  may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers. 
     The hardware  80  of the WD  22  further includes processing circuitry  84 . The processing circuitry  84  may include a processor  86  and memory  88 . In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry  84  may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor  86  may be configured to access (e.g., write to and/or read from) memory  88 , which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). 
     Thus, the WD  22  may further comprise software  90 , which is stored in, for example, memory  88  at the WD  22 , or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the WD  22 . The software  90  may be executable by the processing circuitry  84 . The software  90  may include a client application  92 . The client application  92  may be operable to provide a service to a human or non-human user via the WD  22 , with the support of the host computer  24 . In the host computer  24 , an executing host application  50  may communicate with the executing client application  92  via the OTT connection  52  terminating at the WD  22  and the host computer  24 . In providing the service to the user, the client application  92  may receive request data from the host application  50  and provide user data in response to the request data. The OTT connection  52  may transfer both the request data and the user data. The client application  92  may interact with the user to generate the user data that it provides. 
     The processing circuitry  84  may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by WD  22 . The processor  86  corresponds to one or more processors  86  for performing WD  22  functions described herein. The WD  22  includes memory  88  that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software  90  and/or the client application  92  may include instructions that, when executed by the processor  86  and/or processing circuitry  84 , causes the processor  86  and/or processing circuitry  84  to perform the processes described herein with respect to WD  22 . For example, the processing circuitry  84  of the wireless device  22  may include a measurement unit  34  configured to perform WD methods discussed herein, such as the methods discussed with reference to  FIG.  13    as well as other figures. 
     In some embodiments, the inner workings of the network node  16 , WD  22 , and host computer  24  may be as shown in  FIG.  7    and independently, the surrounding network topology may be that of  FIG.  6   . 
     In  FIG.  7   , the OTT connection  52  has been drawn abstractly to illustrate the communication between the host computer  24  and the wireless device  22  via the network node  16 , without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from the WD  22  or from the service provider operating the host computer  24 , or both. While the OTT connection  52  is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network). 
     The wireless connection  64  between the WD  22  and the network node  16  is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the WD  22  using the OTT connection  52 , in which the wireless connection  64  may form the last segment. More precisely, the teachings of some of these embodiments may improve the data rate, latency, and/or power consumption and thereby provide benefits such as reduced user waiting time, relaxed restriction on file size, better responsiveness, extended battery lifetime, etc. 
     In some embodiments, a measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection  52  between the host computer  24  and WD  22 , in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection  52  may be implemented in the software  48  of the host computer  24  or in the software  90  of the WD  22 , or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which the OTT connection  52  passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software  48 ,  90  may compute or estimate the monitored quantities. The reconfiguring of the OTT connection  52  may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect the network node  16 , and it may be unknown or imperceptible to the network node  16 . Some such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary WD signaling facilitating the host computer&#39;s  24  measurements of throughput, propagation times, latency and the like. In some embodiments, the measurements may be implemented in that the software  48 ,  90  causes messages to be transmitted, in particular empty or ‘dummy’ messages, using the OTT connection  52  while it monitors propagation times, errors etc. 
     Thus, in some embodiments, the host computer  24  includes processing circuitry  42  configured to provide user data and a communication interface  40  that is configured to forward the user data to a cellular network for transmission to the WD  22 . In some embodiments, the cellular network also includes the network node  16  with a radio interface  62 . In some embodiments, the network node  16  is configured to, and/or the network node&#39;s  16  processing circuitry  68  is configured to perform the functions and/or methods described herein for preparing/initiating/maintaining/supporting/ending a transmission to the WD  22 , and/or preparing/terminating/maintaining/supporting/ending in receipt of a transmission from the WD  22 . 
     In some embodiments, the host computer  24  includes processing circuitry  42  and a communication interface  40  that is configured to a communication interface  40  configured to receive user data originating from a transmission from a WD  22  to a network node  16 . In some embodiments, the WD  22  is configured to, and/or comprises a radio interface  82  and/or processing circuitry  84  configured to perform the functions and/or methods described herein for preparing/initiating/maintaining/supporting/ending a transmission to the network node  16 , and/or preparing/terminating/maintaining/supporting/ending in receipt of a transmission from the network node  16 . 
     Although  FIGS.  6  and  7    show various “units” such as configuration unit  32 , and measurement unit  34  as being within a respective processor, it is contemplated that these units may be implemented such that a portion of the unit is stored in a corresponding memory within the processing circuitry. In other words, the units may be implemented in hardware or in a combination of hardware and software within the processing circuitry. It is also understood that implementations of the various embodiments can be made without reliance on the OTT aspects, i.e., without the inclusion of the host computer  24  and the connection  28 . 
       FIG.  8    is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of  FIGS.  6  and  7   , in accordance with one embodiment. The communication system may include a host computer  24 , a network node  16  and a WD  22 , which may be those described with reference to  FIG.  7   . In a first step of the method, the host computer  24  provides user data (Block S 100 ). In an optional substep of the first step, the host computer  24  provides the user data by executing a host application, such as, for example, the host application  50  (Block S 102 ). In a second step, the host computer  24  initiates a transmission carrying the user data to the WD  22  (Block S 104 ). In an optional third step, the network node  16  transmits to the WD  22  the user data which was carried in the transmission that the host computer  24  initiated, in accordance with the teachings of the embodiments described throughout this disclosure (Block S 106 ). In an optional fourth step, the WD  22  executes a client application, such as, for example, the client application  92 , associated with the host application  50  executed by the host computer  24  (Block S 108 ). 
       FIG.  9    is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of  FIG.  6   , in accordance with one embodiment. The communication system may include a host computer  24 , a network node  16  and a WD  22 , which may be those described with reference to  FIGS.  6  and  7   . In a first step of the method, the host computer  24  provides user data (Block S 110 ). In an optional substep (not shown) the host computer  24  provides the user data by executing a host application, such as, for example, the host application  50 . In a second step, the host computer  24  initiates a transmission carrying the user data to the WD  22  (Block S 112 ). The transmission may pass via the network node  16 , in accordance with the teachings of the embodiments described throughout this disclosure. In an optional third step, the WD  22  receives the user data carried in the transmission (Block S 114 ). 
       FIG.  10    is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of  FIG.  6   , in accordance with one embodiment. The communication system may include a host computer  24 , a network node  16  and a WD  22 , which may be those described with reference to  FIGS.  6  and  7   . In an optional first step of the method, the WD  22  receives input data provided by the host computer  24  (Block S 116 ). In an optional substep of the first step, the WD  22  executes the client application  92 , which provides the user data in reaction to the received input data provided by the host computer  24  (Block S 118 ). Additionally or alternatively, in an optional second step, the WD  22  provides user data (Block S 120 ). In an optional substep of the second step, the WD provides the user data by executing a client application, such as, for example, client application  92  (Block S 122 ). In providing the user data, the executed client application  92  may further consider user input received from the user. Regardless of the specific manner in which the user data was provided, the WD  22  may initiate, in an optional third substep, transmission of the user data to the host computer  24  (Block S 124 ). In a fourth step of the method, the host computer  24  receives the user data transmitted from the WD  22 , in accordance with the teachings of the embodiments described throughout this disclosure (Block S 126 ). 
       FIG.  11    is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of  FIG.  6   , in accordance with one embodiment. The communication system may include a host computer  24 , a network node  16  and a WD  22 , which may be those described with reference to  FIGS.  6  and  7   . In an optional first step of the method, in accordance with the teachings of the embodiments described throughout this disclosure, the network node  16  receives user data from the WD  22  (Block S 128 ). In an optional second step, the network node  16  initiates transmission of the received user data to the host computer  24  (Block S 130 ). In a third step, the host computer  24  receives the user data carried in the transmission initiated by the network node  16  (Block S 132 ). 
       FIG.  12    is a flowchart of an exemplary process in a network node  16  according to some embodiments of the present disclosure. One or more Blocks and/or functions and/or methods performed by the network node  16  may be performed by one or more elements of network node  16  such as by configuration unit  32  in processing circuitry  68 , processor  70 , radio interface  62 , etc. according to the example method. The example method includes configuring (Block S 134 ), such as via configuration unit  32 , processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , a channel state information reference signal (CSI-RS) resource of a set of candidate CSI-RS resources, the CSI-RS resource partially overlapping at least one other CSI-RS resource in the set. The method includes optionally, transmitting (Block S 136 ), such as via configuration unit  32 , processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , CSI-RS signalling on the configured CSI-RS resource. 
     In some embodiments, the CSI-RS resource partially overlaps the at least one other CSI-RS resource in a same slot. In some embodiments, each candidate CSI-RS resource in the set of candidate CSI-RS resources partially overlaps each of the other candidate CSI-RS resources in the set. In some embodiments, the method includes receiving CSI feedback, such as a CSI feedback report based on WD  22  measurements of the CSI-RS signalling. 
       FIG.  13    is a flowchart of an exemplary process in a wireless device  22  according to some embodiments of the present disclosure. One or more Blocks and/or functions and/or methods performed by WD  22  may be performed by one or more elements of WD  22  such as by measurement unit  34  in processing circuitry  84 , processor  86 , radio interface  82 , etc. The example method includes receiving (Block S 138 ), such as via measurement unit  34 , processing circuitry  84 , processor  86  and/or radio interface  82 , a configuration of a channel state information reference signal (CSI-RS) resource of a set of candidate CSI-RS resources, the CSI-RS resource partially overlapping at least one other CSI-RS resource in the set. The method includes optionally, receiving (Block S 140 ) CSI-RS signalling on the configured CSI-RS resource. 
     In some embodiments, the CSI-RS resource partially overlaps the at least one other CSI-RS resource in a same slot. In some embodiments, each candidate CSI-RS resource in the set of candidate CSI-RS resources partially overlaps each of the other candidate CSI-RS resources in the set. In some embodiments, the method includes performing measurements on the received CSI-RS signalling and transmitting CSI feedback, such as a CSI feedback report based on the WD  22  measurements of the CSI-RS signalling. 
       FIG.  14    is a flowchart of an exemplary process in a network node  16  according to some embodiments of the present disclosure. One or more Blocks and/or functions and/or methods performed by the network node  16  may be performed by one or more elements of network node  16  such as by configuration unit  32  in processing circuitry  68 , processor  70 , radio interface  62 , etc. according to the example method. The example method includes configuring (Block S 142 ), such as by configuration unit  32  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , a first channel state information reference signal, CSI-RS, resource in a set of candidate CSI-RS resources, the first CSI-RS resource partially overlapping a second CSI-RS resource in the set of candidate CSI-RS resources, the first CSI-RS resource being associated with a first cell and the second CSI-RS resource being associated with a second cell. The method includes transmitting (Block S 144 ), such as by configuration unit  32  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , CSI-RS signaling on the configured first CSI-RS resource. 
     In some embodiments, the first CSI-RS resource partially overlaps the second CSI-RS resource in at least one time-frequency resource within a slot. In some embodiments, each CSI-RS resource in the set of candidate CSI-RS resources occupies a set of time-frequency resource elements, REs, within a slot and a subset of resource elements of the first CSI-RS resource are occupied by a subset of resource elements of the second CSI-RS resource. In some embodiments, the first cell is a serving cell and the second cell is a neighboring cell. In some embodiments, each candidate CSI-RS resource in the set of candidate CSI-RS resources partially overlaps each of the other candidate CSI-RS resources in the set within a slot. In some embodiments, the method further includes allocating, such as by configuration unit  32  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , a resource position for the first CSI-RS resource based on a physical cell ID, PCI, associated with the first cell. 
     In some embodiments, allocating comprises allocating, such as by configuration unit  32  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , the resource position for the first CSI-RS resource based on the PCI modulus N, N being a number of resource positions for CSI-RS resources in the set of candidate CSI-RS resources. In some embodiments, the second CSI-RS resource is based on a PCI associated with the second cell. In some embodiments, the candidate CSI-RS resources in the set are shifted relative to each other within a slot based on an index value. In some embodiments, the first cell has a corresponding first index value and the second cell has a corresponding second index value, the second index value being different from the first index value. In some embodiments, the method further includes applying, such as by configuration unit  32  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , a modulation and coding scheme, MCS, backoff in a slot on which the CSI-RS signaling is transmitted. 
       FIG.  15    is a flowchart of an exemplary process in a wireless device  22  according to some embodiments of the present disclosure. One or more Blocks and/or functions and/or methods performed by WD  22  may be performed by one or more elements of WD  22  such as by measurement unit  34  in processing circuitry  84 , processor  86 , radio interface  82 , etc. The example method includes receiving (Block S 146 ), such as by measurement unit  34  in processing circuitry  84 , processor  86  and/or radio interface  82 , a configuration of a first channel state information reference signal, CSI-RS, resource in a set of candidate CSI-RS resources, the first CSI-RS resource partially overlapping a second CSI-RS resource in the set of candidate CSI-RS resources, the first CSI-RS resource being associated with a first cell and the second CSI-RS resource being associated with a second cell. The method includes receiving (Block S 148 ), such as by measurement unit  34  in processing circuitry  84 , processor  86  and/or radio interface  82 , CSI-RS signaling on the configured first CSI-RS resource. 
     In some embodiments, the first CSI-RS resource partially overlaps the second CSI-RS resource in at least one time-frequency resource within a slot. In some embodiments, each CSI-RS resource in the set of candidate CSI-RS resources occupies a set of time-frequency resource elements, REs, within a slot and a subset of resource elements of the first CSI-RS resource are occupied by a subset of resource elements of the second CSI-RS resource. In some embodiments, the first cell is a serving cell and the second cell is a neighboring cell. In some embodiments, each candidate CSI-RS resource in the set of candidate CSI-RS resources partially overlaps each of the other candidate CSI-RS resources in the set within a slot. 
     In some embodiments, the method further includes receiving, such as by measurement unit  34  in processing circuitry  84 , processor  86  and/or radio interface  82 , an allocation of a resource position for the first CSI-RS resource, the resource position being based on a physical cell ID, PCI, associated with the first cell. In some embodiments, the resource position for the first CSI-RS resource is based on the PCI modulus N, N being a number of resource positions for CSI-RS resources in the set of candidate CSI-RS resources. In some embodiments, the second CSI-RS resource is based on a PCI associated with the second cell. 
     In some embodiments, the candidate CSI-RS resources in the set are shifted relative to each other within a slot based on an index value. In some embodiments, the first cell has a corresponding first index value and the second cell has a corresponding second index value, the second index value being different from the first index value. In some embodiments, the CSI-RS signaling is received according to a modulation and coding scheme, MCS, backoff Having described the general process flow of arrangements of the disclosure and having provided examples of hardware and software arrangements for implementing the processes and functions of the disclosure, the sections below provide details and examples of arrangements for partially overlapped channel state information reference signal (CSI-RS) shifting, which may be implemented by the network node  16 , wireless device  22  and/or host computer  24 . 
     As explained in the introduction above, a reason why false PMI reporting occurs with colliding CSI-RS is that the ports of the interfering CSI-RS resource directly collide the ports of the serving CSI-RS resources, as described by the below formula: 
     
       
         
           
             
               
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     However, if the CSI-RS resources are only partially overlapping, the ports of the interfering CSI-RS resource will not collide directly with the same ports of the serving CSI-RS resource, as illustrated by the formula below: 
     
       
         
           
             
               
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     This may reduce the effect of pilot contamination and erroneous PMI reporting. 
     To achieve a trade-off between the degree of pilot contamination and the degree of CSI-RS to PDSCH interference, some embodiments propose a method for CSI-RS transmission for network node  16  cells in a communication network. Each network node  16  cell is allocated a CSI-RS resource position from a set of candidate CSI-RS resource positions. Each CSI-RS resource occupies certain time-frequency resource elements within a slot. 
     The CSI-RS resource positions in the set may be characterized by that at least some of the CSI-RS resource positions partially overlap within the same slot. Where a partial overlap between a CSI-RS resource A and another CSI-RS resource B is defined such that resource A and B partially overlap if a strict subset of the resource elements of CSI-RS resource B is also occupied by a subset of the resource elements of CSI-RS resource A, but where some resource elements of CSI-RS resource B are not occupied by CSI-RS resource A. That is, CSI-RS resource A and CSI-RS resource B are not fully overlapping. 
     An example of partially overlapping CSI-RS resources is shown in  FIG.  16   . Here, a serving cell 8-port CSI-RS with 8×1 pattern is positioned with starting RE (k 0 ,l 0 )=(0,5), while an interfering cell CSI-RS resource also with an 8×1 pattern is positioned with starting RE (k 0 ,l 0 )=(2,5). The two resources are thus overlapping on subcarriers k=2, 3, 4, 5, 6, 7 but not on k=0, 1 and k=8, 9 which are occupied only by the serving cell CSI-RS and the interfering cell CSI-RS, respectively. 
     In one embodiment, all of the CSI-RS resource positions in the set are mutually partially overlapping, meaning that each resource in the set partially overlaps with any of the other resources in the set. In another embodiment, only some of the resources in the set are mutually overlapping while other resources are non-overlapping (meaning that they occupy disjoint sets of resource elements). 
     In one embodiment, network node  16  cells may be allocated different CSI-RS resource positions based on the Physical Cell ID (PCI) associated with the cell according to a certain re-use pattern. For instance, if the number of CSI-RS resource positions in the set is N, such that the CSI-RS resources n=0, 1, . . . N−1, may be indexed and a cell with PCI=PCI 0  may be allocated CSI-RS resource position PCI 0  mod N. 
     One benefit with the proposed method compared to the known CSI-RS reuse method based on non-overlapping CSI-RS resource positions is that CSI-RS to PDSCH interference may be reduced, especially compared to whether an inter-slot CSI-RS reuse pattern is used in the prior art. By the use of partially overlapping CSI-RS resources, all CSI-RS interference is concentrated to a single slot, resulting in that only a single slot is affected by excessive CSI-RS to PDSCH interference and resulting in higher BLER, instead of multiple slots. 
     Example CSI-RS Shifting Patterns 
     The CSI-RS resource positions within the slot are shifted with respect to the look-up table index (LUTindex) as described by the table below. Each LUTindex corresponds to one network node  16  cell in a CSI-RS reuse group. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
               
               
                 LUTindex 
                 0 
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                 CSI-RS pattern configuration 
                 A 
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                 bitmask “other” 
                 ‘001111’ 
                 ‘011110’ 
                 ‘111100’ 
                 ‘001111’ 
                 ‘011110’ 
                 ‘111100’ 
               
               
                 firstOFDMSymbolInTimeDomain 
                 5 
                 5 
                 5 
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                 7 
               
               
                 firstOFDMSymbolInTimeDomain2 
                 7 
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     32 Port CSI-RS Patterns 
       FIGS.  17 - 22    illustrate examples of 32-port CSI-RS patterns according to the LUT index in the table above.  FIG.  17    illustrates the 32-port port CSI-RS pattern configuration A.  FIG.  18    illustrates the 32-port port CSI-RS pattern configuration B.  FIG.  19    illustrates the 32-port port CSI-RS pattern configuration C.  FIG.  20    illustrates the 32-port port CSI-RS pattern configuration D.  FIG.  21    illustrates the 32-port port CSI-RS pattern configuration E.  FIG.  22    illustrates the 32-port port CSI-RS pattern configuration F. Note that the legend provided in  FIG.  17    applies to  FIGS.  18 - 22   . 
     For example, if the serving cell supported by network node  16  is allocated the configuration A CSI-RS position, REs within the CSI-RS slot impacted by CSI-RS interference from within the cell reuse group is illustrated in  FIG.  23   . 
     Since the CSI-RS to PDSCH interference in this slot may be severe, ways to mitigate this effect can be considered. 
     In one embodiment, multiple ZP CSI-RS resources are configured in the CSI-RS slot such that the resource elements where the interfering cells CSI-RS patterns which are not colliding with the serving cell CSI-RS patterns are covered. This removes those resource elements to be used by PDSCH, which may improve the link adaption. 
     In another embodiment, a modulation and coding scheme (MCS) backoff is applied in the slot where the CSI-RS is transmitted, to take into account that a subset of the resource elements will be interfered by neighboring cell CSI-RS. 
     16 Port CSI-RS Patterns 
       FIGS.  24 - 41    illustrate examples of 16-port CSI-RS patterns according to some embodiments of the present disclosure. In some embodiments, each of the patterns may correspond to an index in a table, such as the LUTindex table above. In some embodiments, each of the 16-port CSI-RS patterns may at most partially overlap (e.g., in the same time/frequency resources in the slot) with one or more of the other 16-port CSI-RS patterns depicted in  FIGS.  24 - 41   . Note that the legend provided in  FIG.  24    applies also to  FIGS.  25 - 29   , and the legend provided in  FIG.  30    applies also to  FIGS.  31 - 41   . 
     Some embodiments may include one or more of the following: 
     Embodiment A1. A network node configured to communicate with a wireless device (WD), the network node configured to, and/or comprising a radio interface and/or comprising processing circuitry configured to: 
     configure a channel state information reference signal (CSI-RS) resource of a set of candidate CSI-RS resources, the CSI-RS resource partially overlapping at least one other CSI-RS resource in the set; and 
     optionally, transmit CSI-RS signaling on the configured CSI-RS resource. 
     Embodiment A2. The network node of Embodiment A1, wherein the CSI-RS resource partially overlaps the at least one other CSI-RS resource in a same slot. 
     Embodiment A3. The network node of Embodiment A1, wherein each candidate CSI-RS resource in the set of candidate CSI-RS resources partially overlaps each of the other candidate CSI-RS resources in the set. 
     Embodiment B1. A method implemented in a network node, the method comprising: 
     configuring a channel state information reference signal (CSI-RS) resource of a set of candidate CSI-RS resources, the CSI-RS resource partially overlapping at least one other CSI-RS resource in the set; and 
     optionally, transmitting CSI-RS signaling on the configured CSI-RS resource. 
     Embodiment B2. The method of Embodiment B1, wherein the CSI-RS resource partially overlaps the at least one other CSI-RS resource in a same slot. 
     Embodiment B3. The method of Embodiment B1, wherein each candidate CSI-RS resource in the set of candidate CSI-RS resources partially overlaps each of the other candidate CSI-RS resources in the set. 
     Embodiment C1. A wireless device (WD) configured to communicate with a network node, the WD configured to, and/or comprising a radio interface and/or processing circuitry configured to: 
     receive a configuration of a channel state information reference signal (CSI-RS) resource of a set of candidate CSI-RS resources, the CSI-RS resource partially overlapping at least one other CSI-RS resource in the set; and 
     optionally, receive CSI-RS signaling on the configured CSI-RS resource. 
     Embodiment C2. The WD of Embodiment C1, wherein the CSI-RS resource partially overlaps the at least one other CSI-RS resource in a same slot. 
     Embodiment C3. The WD of Embodiment C1, wherein each candidate CSI-RS resource in the set of candidate CSI-RS resources partially overlaps each of the other candidate CSI-RS resources in the set. 
     Embodiment D1. A method implemented in a wireless device (WD), the method comprising: 
     receiving a configuration of a channel state information reference signal (CSI-RS) resource of a set of candidate CSI-RS resources, the CSI-RS resource partially overlapping at least one other CSI-RS resource in the set; and 
     optionally, receiving CSI-RS signaling on the configured CSI-RS resource. 
     Embodiment D2. The method of Embodiment D1, wherein the CSI-RS resource partially overlaps the at least one other CSI-RS resource in a same slot. 
     Embodiment D3. The method of Embodiment D1, wherein each candidate CSI-RS resource in the set of candidate CSI-RS resources partially overlaps each of the other candidate CSI-RS resources in the set. 
     As will be appreciated by one of skill in the art, the concepts described herein may be embodied as a method, data processing system, computer program product and/or computer storage media storing an executable computer program. Accordingly, the concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects all generally referred to herein as a “circuit” or “module.” Any process, step, action and/or functionality described herein may be performed by, and/or associated to, a corresponding module, which may be implemented in software and/or firmware and/or hardware. Furthermore, the disclosure may take the form of a computer program product on a tangible computer usable storage medium having computer program code embodied in the medium that can be executed by a computer. Any suitable tangible computer readable medium may be utilized including hard disks, CD-ROMs, electronic storage devices, optical storage devices, or magnetic storage devices. 
     Some embodiments are described herein with reference to flowchart illustrations and/or block diagrams of methods, systems and computer program products. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer (to thereby create a special purpose computer), special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     These computer program instructions may also be stored in a computer readable memory or storage medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
     The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     It is to be understood that the functions/acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows. 
     Computer program code for carrying out operations of the concepts described herein may be written in an object oriented programming language such as Java® or C++. However, the computer program code for carrying out operations of the disclosure may also be written in conventional procedural programming languages, such as the “C” programming language. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer. In the latter scenario, the remote computer may be connected to the user&#39;s computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
     Many different embodiments have been disclosed herein, in connection with the above description and the drawings. It will be understood that it would be unduly repetitious and obfuscating to literally describe and illustrate every combination and subcombination of these embodiments. Accordingly, all embodiments can be combined in any way and/or combination, and the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them, and shall support claims to any such combination or subcombination. 
     Abbreviations that may be used in the preceding description include: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Abbreviation 
                 Explanation 
               
               
                   
                   
               
             
            
               
                   
                 CP 
                 Cyclic Prefix 
               
               
                   
                 CRS 
                 Common RS 
               
               
                   
                 CSI-RS 
                 Channel State Information RS 
               
               
                   
                 DM-RS 
                 Demodulation RS 
               
               
                   
                 ID 
                 Identifier 
               
               
                   
                 NR 
                 New Radio 
               
               
                   
                 RS 
                 Reference signal 
               
               
                   
                 TRS 
                 Tracking RS 
               
               
                   
                   
               
            
           
         
       
     
     It will be appreciated by persons skilled in the art that the embodiments described herein are not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope of the following claims.