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2024 ITU Kaleidoscope Academic Conference





























              Figure 1- STAR-RIS assisted V2V NOMA system         Figure 2- AF relay assisted V2V NOMA system
           power levels of each vehicle to create a real-life scenario to      =    = ⋯ =    = 1.  For  effective  data  transmission,
                                                                               
                                                                1
                                                                    2
           compare the feasibility of both the models.        the  RIS's  reflection  phase  shift  matrix  and  the     ’s
                                                                                                             
                                                              transmitted  beam  configuration  work  jointly.  Since  the
                          2.  SYSTEM MODEL                    channel  follows  reciprocity,  the  channel  state  information
                                                              (CSI) acquired by uplink pilot training can congruently be
           2.1 RIS assisted NOMA V2V model                    utilized for transmission in downlink for all quasi-static flat
                                                              fading channels. If the reflected signal by RIS is twice or
           The system model for the proposed STAR-RIS assisted V2V   more,  the  path loss  of  the  signal  will  become  more
           network has been shown in Fig. 1.   In this arrangement, one   significant due to the multiple reflection of the transmitted
           vehicle     has been considered the source vehicle, this can  signal.  In  addition,  it  is  anticipated  that      has  full
                                                                                                       
                    
           be increased to any finite number of vehicles, which tries to   information of  the  CSI,  which  will  support  the  efficient
           communicate  with  the  destination  vehicles    ,  where    ∈  performance by STAR-RIS, this can be achieved using [14].
                                                   
           {1,2 … ,   }.  Let  us  assume  the  vehicle     is  single  antenna
                                              
           system and the     vehicle is also carrying single antenna each.  The received signal at vehicle     is given by
                                                                                         
                          
           It  is  assumed  that  there  is  no  cellular  link  for  direct
           communication  between  these  vehicles.  This  transmission       H      H  )
                                                                                        L
                                                                             h h  +
                                                                                            x +
           has  been  proposed  to  be  supported  via  a  reflected  path   y =  ( rl  sr  h sl    i i    , i  (2)
                                                                         l
           through RIS.                                                                 i= 1
                                                              Where  is the beamforming vector of     ℎ vehicle    ,     is
           The RIS used in this model have N discrete elements. It is   i                                      
           assumed that the transmission is carried out by means of a   the message signal transmitted by the source vehicle     and
                                                                                                            
           single  large  RIS  also  known  as  single  RIS-assisted       is  the  additive  white  Gaussian  noise  having  the  mean
                                                                 
                                                                                         2
           transmission  (SRAT)  through  dedicated  short-range   value as 0 and the variance of     [15]. At the receiver end
           communication (DSRC).                              the NOMA adopts the successive interference cancellation
                                                              technique  to  retrieve  the  source’s  information  [16].  The
           The channel between the source or transmitter vehicle    and  vehicle     decodes its signal     treating the rest information
                                                                                        
                                                                     1
                                                         
           the STAR-RIS is represented by ℎ  ∈ ℂ     1 , the channel  as noise. When    is more than or equal to 2, the user detects
                                           
           between RIS and     is given by ℎ ∈ ℂ 1      and the channel  each  signal  separately;  afterwards,  after  removing  other
                            
                                          
                                            
           between     and     is  given  by ℎ ∈ ℂ , which  can  be  the  vehicles detected signals from the actual received signal, it
                           
                     
                                         
           line of sight (LoS) path links. For N discrete elements, the   regains the signal amplitude and finds the remaining signals.
           reflection coefficients matrix of STAR-RIS can be written as   This  process  is  repeated  until  the  requested  signals  are
                                                              decoded.  The  sequence  of  the  receiver  vehicles  depends
                       =  diag  e j  1 , 2 e j  2 ,..., N e j N   (1)   upon  the  channel  condition,  as  the  distance  between  the
                                                              source  vehicle  and  the  destination  vehicles  increase  the
                             1
                                                              channel condition degrades which can be given by ‖ℎ ‖ ≤
                                                                                                           1
           Where                   is  the  reflection  coefficient  of  the      ℎ  ‖ℎ ‖ ≤ ‖ℎ ‖ ≤ ⋯ ≤ ‖ℎ ‖ ,  where      ℎ  vehicle  is  the
                                                                                       
                                                                  2
                                                                          3
                     
           reflecting  element  of  the  STAR-RIS  such  that     ∈ [0,1]  farthest and Vehicle     is the nearest one.
                                                                                1
                                                     
           whereas     is  the  phase  coefficient  of       ℎ element  and
                     
              ∈ [0, 2  ] .  Every  reflecting  element  on  the  RIS  is  The  signal  available  at  the  receive  vehicle      before  its
              
                                                                                                       
           considered to operate at maximum reflection, implying that   decoding can be written as
           each one's amplitude coefficient satisfies the relation
                                                          – 236 –
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