Page 98 - Kaleidoscope Academic Conference Proceedings 2020
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2020 ITU Kaleidoscope Academic Conference





           RUs are on different floors and DU is in the first floor of the same   Location(s) of 4G and NR units
           building


                                                                  CU is co-located with E-UTRA  DU and CU are co-located with   RU, DU, and CU are co-located
                                                                                   E-UTRA       with E-UTRA (*)
                                       (RU-DU)+CU
             RU+DU+CU          Managed by DU  Centralized 5G RAN
                      Centralized 5G RAN
                                                               4G Macro BS    CU
                                                                (MBS)       5G s gNB Units
                                                                5G s gNB Units  DU            CU is located at 4G site
                                                                4G BBU       RU    5G radio unit deployed  This is the lowest level of centralization
                                                                                      near 4G MBS   and is appropriate for low latency services
                                                                eNB         gNB
                                                            Note 1: CU can be deployed in the edge data center co-located with MEC
                                       (RU-DU-CU)           Note 2: It is less costly to co-locate 5G sites with 4G sites in distributed 5G RAN
               RU+(DU-CU)                                   Note 3: There are different options for centralized 5G RAN with different costs and latency constraints
                       Centralized 5G RAN  Distributed 5G RAN in the same location of 4G sites  Note 4: Placement of 5G RUs/DUs and centralization of CU depend on existing facilities and expected 5G traffic
                                                            Note 5: In scenario (*), although there are three separate units, some vendors may package DU and CU in one box
                                           Figure 3 – Deployment scenarios for gNBs.
                                    Table 2 – 5G RAN Deployment Paths for Different Locations

            Deployment Scenario  Path  Possible UPS  Advantages  Disadvantages            Examples
                         P1  UPS 1, UPS 5 – UPS 7  - Low cost radio equipment  - Moderate front-haul challenge
             Indoor Hotspot              - Centralization benefits                         -Offices, stadiums, malls, metro stations
                         P2  UPS 5- UPS 7  - Low cost radio equipment  - Front-haul challenges (less than P1)
                                         - Low cost radio equipment
                         P1  UPS 1, UPS 5 – UPS 9  - Centralization benefits  - High front-haul challenge
                                                              - Higher costs for radio equipment than P1
                         P2  UPS 1 – UPS 4  - Relaxed front-haul
                                                              - Less centralization benefits than P1
              Dense Urban                - Less front-haul challenges than P1  - Higher costs for radio equipment than P1
                         P3  UPS 1, UPS 5 – UPS 9                                         - City squares, commuter hubs
                                         - More centralization benefits than P2  - Less centralization benefits than P1
                         P4  UPS 2 – UPS 4  - Less costs for radio equipment than P2  - Smaller coverage than P1-P3
                                         - Relaxed front-haul
                                                              - Less centralization benefits
                                         - Less costs for radio equipment than P4
                         P5  UPS 5 – UPS 9                    - Moderate High front-haul challenges
                                         - More centralization benefits than P4
                Urban    P1  UPS 1 – UPS 4  - High coverage   - High cost for radio equipment (depending on UPS)  - Residential areas, universities
                Rural    P1  UPS 1       - High coverage      - High cost for radio equipment (depending on UPS)  - farms, inter-city roads
           In general, spectrum can be utilized either via time division  Depending on the number of user equipment (UE) in
           duplexing (TDD) or FDD, but in 5G, mid-band and mmWave  different locations, RAN deployment scenarios, called
           band are used exclusively via TDD. To avoid interference  location scenarios (LS) can be categorized as:
           between TDD networks and for efficient deployment of 5G  • Targeted hotspots, e.g., offices, stadiums, malls, and metro
           NR, synchronization and frame alignment in time are needed  stations
           in both UL and DL. In [11, 13], frame structures for 5G only  • Dense urban areas, e.g., city squares and commuter hubs
           and for 5G with 4G TDD (dual connectivity) are proposed.  • Urban areas, e.g., residential areas and universities

                                                              • Suburban and rural areas, and inter-city roads
           3.2 RAN Deployment
           Three scenarios for NG-RAN deployment are [14]:    RAN units (RU, DU, and CU) can be co-located or be in
                                                              different locations as described below (see also Figure 3)
           • Distributed RAN (D-RAN): RRH is on the tower and  [16]:
             BBU is in the same site;                         1. RU, DU, and CU are located in different places, denoted
           • Co-located RAT: both gNB and eNB are deployed in the  by RU+DU+CU.
             same site; and                                   2. RU and DU are co-located and CU is located in a different
           • Centralized RAN (C-RAN): several RRHs are served by  place, denoted by (RU-DU)+CU.
             a central BBU hotel (aggregation point.)
                                                              3. DU and CU are co-located and RU is located in a different
           RAN functions can be performed via D-RAN or C-RAN or  place, denoted by RU+(DU-CU).
           both, depending on the circumstances [15, 16]. In C-RAN,  4. RU, DU, and CU are co-located, denoted by (RU-DU-CU).
           the scheme is called functional splitting (FS), the extent of  The followings shall be satisfied in location scenarios [17]:
           which depends on TN technology and architecture; and gNB  • RU-DU latency (Front-haul): One-way RU-DU latency
           functions can be performed by the following units [16]:  must be below 0.5 ms, otherwise performance is impaired.
           • Central Unit (CU): A CU performs gNB’s upper layer  Also, RU-DU data rate must be 10 Gbps or more.
             functions and controls one or more distributed units.  • DU-CU latency (Mid-haul): One-way CU-DU latency
           • Distributed Unit (DU): each DU performs gNBs’ lower  must be below 3 ms [17].
             layer functions and is controlled by one CU.
           • Radio Unit (RU): each RU performs RF functions, i.e.,  In general, 5G deployment should be prioritized in locations
             the physical layer or low level RAN functions.   with more demand for the service. Below we describe 5G
                                                              RAN deployment scenarios for different cases (see Table 2).



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