Page 98 - Kaleidoscope Academic Conference Proceedings 2020

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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