Page 64 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 6 – Wireless communication systems in beyond 5G era
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ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 6



























                    Fig. 14 – Position of UE (y-direction) and         Fig. 16 − CDF of channel capacity multi-hop vs
                       channel capacity (         = 185)                       single-hop vs w/o hop

                                                               3)  Grid environment

                                                               Fig. 16 shows the Cumulative Distribution Function
                                                               (CDF) of channel capacities for cases of multi-hop,
                                                               single-hop,  and  w/o  hop.  Channel  capacity  is
                                                               calculated  every  5  m  in  a  gridded  arrangement
                                                               shown  in  Fig.  8.  Results  show  that  without  RSs,
                                                               channel  capacity  is  0Gbps,  namely  mmWave
                                                               communications are not available in around 80% of
                                                               the area in the environment. On the other hand, by
                                                               hopping  with  RSs,  channel  capacity  is  greatly
                                                               improved  and  100%  coverage  is  available.
                                                               Compared with the single-hop case, the multi-hop
                                                               case can further improve channel capacity of about
                                                               12  Gbps  with  about  10%  cumulative  probability.
               Fig. 15 – Position of UE (y-direction) and number of   More importantly, the steepness of the curve of the
                          streams (         = 185)
                                                               multi-hop case also indicates that it does not only
          with w/o hop. In the multi-hop case by multiple RSs,   improve channel capacity but also provides stable
          the proposed system significantly improves channel   mmWave communications regardless of locations.
          capacity compared with the single-hop and w/o hop    4.3  Discussions
          cases. Channel capacities of more than 20 Gbps are
          archived  in  all  positions.  The  improvement  is   In  the  previous  subsections,  we  have  shown  the
          particularly    obvious     at      intersections    effectiveness  of  the  proposed  mmWave  massive
          (   UE =  −30,0,30),  where  the  number of streams is   analog relay MIMO system in a simple scenario with
          greatly  improved  by  using  a  large  number  of  RSs   a single  BS  and single  UE.  At the  last  part of  this
          deployed  along  the  x-direction.  Compared  with   section,  generalization  of  the  proposed  system  to
          single-hop,  the  multi-hop  case  further  increases   scenarios  with  multiple  UEs  and  multiple  BSs  is
          about 15 Gbps channel capacity in all positions. In   discussed.
          Fig. 15, in the w/o hop case, in most of the positions,
          the communication is not possible due to blockage    With  respect  to  the  multiple  UEs,  the  proposed
          by  buildings.  On  the  other  hand,  the  number  of   system can be applied directly in the case of Time
          streams in single-hop and multi-hop is more  than    Division Multiple Access (TDMA) of UEs or TDMA of
          three,  so  that  the  MIMO  transmission  can  be   groups of UEs. This scenario includes an urban city
          performed.  In  addition,  multi-hop  relay  obtains   environment with multiple moving hotspots such as
          more  streams  than  single-hop,  which  leads  to   buses  where  multiple  UEs  in  a  hotspot  create  a
          further improvement in channel capacity. It can also   group  to  share  the  same  beams  and  routes.  In
          be  seen  that  the  number  of  streams  increases   addition to the algorithms developed in this paper,
          especially at the intersections in NLOS.             further  discussions  about  synchronous  beam





          52                                 © International Telecommunication Union, 2021
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