In this architecture, Central Unit (CU) and Distribution Unit (DU) can be defined as follows. The idea of decomposing a system’s speci cation along several ‘levels of abstrac-tion’ constitutes good practice in the eld of software engineering. Process, Functional Architecture, Logical Architecture, Technical Architecture, Model-Driven Architecture, Adaptive Cruise Control 1 Introduction Motivation. Here, High RLC segments RLC PDU based on the status reports while Low RLC segments RLC PDU into the available MAC PDU resources. 3GPP TR 38.801 Radio Access Architecture and Interfaces Release 14. In the DL, iFFT, CP addition, resource mapping and precoding functions reside in the DU, the rest of PHY functions reside in the CU. This description of separate workflows triggered by events is a logical view, not a physical one. In the downlink, iFFT and CP addition reside in the DU and the rest of the PHY resides in the CU. As a part of study item for New Radio (NR), 3GPP started studying different functional splits between central and distributed units. Option 2-1 Split U-plane only (3C like split): In this split option, RRC, PDCP are in the central unit. Distributed Unit (DU): This logical node includes a subset of the gNB functions, depending on the functional split option. Option 7-2 In this option the UL, FFT, CP removal, resource de-mapping and possibly pre-filtering functions reside in the DU, the rest of PHY functions reside in the CU. In addition, this option can be achieved by separating the RRC and PDCP for the CP stack and the PDCP for the UP stack into different central entities. The functional view de nes the functions that a user can invoke at the boundary of the system. The logical architecture of gNB is shown in figure below with Central Unit (CU) and Distributed Unit (DU). Distributed Unit (DU) also known with other names like RRH/RRU/RE/RU. Logical Decomposition Purpose The Logical Decomposition Process is used to: Improve understanding of the defined technical requirements and the relationships among the requirements (e.g. High RLC may be composed of receiving TM RLC entity, receiving UM RLC entity and a receiving side of AM except for the routing function and reception of RLC status reports, which are related to uplink transmission. The inter-cell interference coordination in the High-MAC sublayer will be in charge of interference coordination methods such as JP/CS CoMP. Central Unit (CU): It is a logical node that includes the gNB functions like Transfer of user data, Mobility control, Radio access network sharing, Positioning, Session Management etc., except those functions allocated exclusively to the DU. What is Inter Symbol Interference (ISI) in LTE, How Cyclic Prefix (CP) helps eliminating this problem ? It defines how the functions will operate together to perform the system mission(s). Functional architecture is described as “an architectural model that identifies system function and their interactions. Really, the only limitations are the performance and capabilities of the physical device. low latency, high throughput), Support of specific user density and load demand per given geographical area (which may influence the level of RAN coordination), Availability transport networks with different performance levels, from ideal to non-ideal, Application type e.g. Logical architecture is a structural design that gives as much detail as possible without constraining the architecture to a particular technology or environment. This option requires some kind of compression technique to reduce transport bandwidth requirements between the DU and CU. These functions can be used as a reference by different domain experts to develop IT-systems as part of a co-operative information-driven enterprise. Unlike these, however, logical architecture is quite broad in scope. Option 7-1 In this option the UL, FFT, CP removal and possibly PRACH filtering functions reside in the DU, the rest of PHY functions reside in the CU. RLC, MAC, physical layer and RF are in the distributed unit. Low RLC may be composed of segmentation functions; High RLC may be composed of ARQ and other RLC functions; Low RLC may be composed of transmitting TM RLC entity, transmitting UM RLC entity, a transmitting side of AM and the routing function of a receiving side of AM, which are related to downlink transmission. Fs-C and Fs-U provide control plane and user plane connectivity over Fs interface. Conceptual Architecture vs Logical Architecture : Conceptual Architecture: Logical Architecture: Definition: Architecture that includes as little detail as possible in order to plan or communicate basic structures. As adjectives the difference between functional and logical is that functional is in good working order while logical is (not comparable) in agreement with the principles of logic. logical architecture The logical architecture of a system is composed of a set of related technical concepts and principles that support the logical operation of the system. Features requirement at Radio Network level e.g. In this architecture, Central Unit (CU) and Distribution Unit (DU) can be defined as follows. The logical architecture of gNB is shown in figure below with Central Unit (CU) and Distributed Unit (DU). In a functional architecture, the basic unit is also a function, but a much larger business-oriented one that I like to call a workflow. Option 6 (MAC-PHY split): The MAC and upper layers are in the central unit (CU). MCS, Layer Mapping, Beamforming, Antenna Configuration, resource block allocation, etc.) The primary difference between logical and physical architecture documentation is that, while logical architecture's concerns end with identifying functional elements of the system, physical architecture takes an additional step, specifying actual devices that those functional elements execute on. Radio specific functions in the Low-MAC sublayer can for perform scheduling-related information processing and be reporting. High-MAC and Low-MAC), the services and functions provided by the MAC layer will be located in the Central Unit (CU), in the Distributed Unit (DU), or in both. Functional Decomposition • Functional decomposition is a cornerstone of systems engineering processes. As a noun functional Option 1 (RRC/PDCP, 1A-like split): In this split option, RRC is in the central unit while PDCP, RLC, MAC, physical layer and RF are kept in the distributed unit. In the DL, iFFT and CP addition functions reside in the DU, the rest of PHY functions reside in the CU. Some of the benefits of an architecture with the deployment flexibility to split and move New Radio (NR) functions between central and distributed units are below: The choice of how to split New Radio (NR) functions in the architecture depends on some factors related to radio network deployment scenarios, constraints and intended supported services. logical architecture. For the initial phase, 3GPP has taken LTE protocol stack as a basis for the discussion, until RAN2 defines and freezes the protocol stack for New Radio (NR). It defines how the functions will operate together to perform the system mission(s). Logical versus physical architecture. In the UL, FFT, and CP removal reside in the DU and for the two sub-variants, 7-1 and 7-2 are described below. Real-time or Non- Real Time. Option 4 (RLC-MAC split): In this split option, RRC, PDCP, and RLC are in the central unit. Option 7 (Intra PHY split): Multiple realizations of this option are possible, including asymmetrical options which allow obtaining benefits of different sub-options for UL and DL independently. Individual items identified in logical architecture may reside on common devices, physically.