# Study Note 3 : O-RAN Fronthaul Interface (FHI) ###### tags: `Wireless Communications` ![](https://i.imgur.com/cdYepbJ.png) ## :notebook_with_decorative_cover: Studying Plan - [x] [O-RAN Introduction (04/11)](https://www.brighttalk.com/webcast/16515/359818?utm_source=brighttalk-portal&utm_medium=web&utm_content=Parallel%20Wireless&utm_campaign=webcasts-search-results-feed) - [x] [Enabling Interoperability & Adherence to O-RAN Fronthaul Interface (04/12)](https://files.keysightevent.com/files/2020KWT/(A6)%20Enabling%20Interoperability%20and%20Adherence%20to%20O-RAN%20Fronthaul%20Interface_Brian%20Su.pdf) - [x] [Overview of O-RAN Fronthaul Interface (04/12)](https://www.nttdocomo.co.jp/english/binary/pdf/corporate/technology/rd/technical_journal/bn/vol21_1/vol21_1_007en.pdf) <br> ## :notebook_with_decorative_cover: Introduction --- ### <center> **Why We Need O-RAN?**</center> --- :::info ![](https://i.imgur.com/jm8bSHg.png) <center>Fig.1 O-RAN Driving Forces, Objectives, and Expected Gains</center> ::: --- ### <center> **O-RAN General Explanation**</center> --- :::info There is a new technology that is currently on progress and will help radio access network virtualization called as Open-RAN or O-RAN. O-RAN architecture integrates a modular base station software stack on off-the-shelf hardware which **allows baseband and radio unit components from discrete suppliers to operate seamlessly together**. To understand more about the RAN evolution we can take a look at the image below. ::: ![](https://i.imgur.com/vupjkQX.png) <center>Fig.2. Disaggregation Of Access Network</center> <br> --- ### <center> **Distributed RAN, Virtualized RAN, And Open RAN Differences**</center> --- <i class="fa fa-book fa-fw"></i> **Distributed RAN** :::success - Proprietary RRU - Proprietary Interface - Proprietary BBU Hardware - Proprietary BBU Software ::: <br> <i class="fa fa-book fa-fw"></i> **Virtualized RAN** :::success - Proprietary RRU - Proprietary Interface - COTS BBU Hardware - Proprietary BBU Software ::: <br> <i class="fa fa-book fa-fw"></i> **Open RAN** :::success - Open RRU - Open Interface - COTS BBU Hardware - Proprietary BBU Software, Virtualized Function ::: <br> >[color=#ffa700]**Note :** >- **Commercial off-the-shelf (COTS)** means products are packaged and available for purchase in the commercial market >- **Remote Radio Unit (RRU)** is a remote radio transceiver that connects to an operator radio control panel via electrical or wireless interface >- **Baseband Unit (BBU)** is a unit that processes baseband in telecomm systems <br> ![](https://i.imgur.com/9BAUIx2.png) ## :notebook_with_decorative_cover: Open-RAN Fronthaul Interface --- ### <center> **Why O-RAN Fronthaul ?**</center> --- ![](https://i.imgur.com/vwXMa1o.png) <center>Fig.3. C-RAN Fronthaul Overview</center> <br> :::danger In general fronthaul means circuit between the baseband processing section in base station equipment and radio equipment using optical fiber. Common Public Radio Interface (CPRI) specification that have come to be used in conventional C-RAN do not sufficiently prescribe specifacations for fronthaul interfaces, and as a result, **there are now many regions having original specifications prescribed by different vendors. This state of affairs has made it difficult to achieve interoperability between baseband processing equipment and radio equipment from different vendors.** ::: <br> --- ### <center> **General Explanation of O-RAN FHI**</center> --- ![](https://i.imgur.com/HQmZZ9I.png) <center> Fig.4. gNB Disaggregation and O-RAN Splits</center> <br> :::info The Open RAN(O-RAN) fronthaul specifications were formulated against the problem above and are expected to help make multivendor RAN a reality in the 5G era. The new O-RAN fronthaul specifications include functional splitting called **Split Option 7-2x**. They also prescribe **Control, User and Synchronization Plane (C/U/S-Plane)**, and **M-Plane**. And we will talk about them one-by-one. ::: <br> >[color=#ffa700]**Note :** >- **Distributed Unit (DU)** is the distributed unit that sits close to the RU and runs the RLC, MAC, and parts of the PHY layer >- **Radio Unit (RU)** is the radio unit that handles the digital front end (DFE) and the parts of the PHY layer <br> --- ### <center> **Split Option 7-2x**</center> --- ![](https://i.imgur.com/OssG1oU.png) <center> Fig.5. Split Option 7-2x In General</center> <br> ![](https://i.imgur.com/M8846Wf.png) <center> Fig.6. Detail Information Of Split Option 7-2x</center> <br> :::info Split Option 7-2x is a specification to split O-RAN Distributed Unit (O-DU) and O-RAN Radio Unit (O-RU). In the downlink process flow, the user bit sequence received from the MAC layer and will be processed until it reaches analog BF block. In the uplink process flow, it will go from analog BF block until it reaches the decoding block. **There are some tradeoffs in O-DU and O-RU functional splitting that can be seen in Fig.7.** ::: ![](https://i.imgur.com/ViZKZlG.png) <center> Fig.7. Tradeoffs In O-DU and O-RU Functional Splitting</center> <br> --- ### <center> **U-Plane**</center> --- ![](https://i.imgur.com/JMQLVFc.png) <center>Fig.8. U-Plane Message Frame Format</center> <br> :::info In O-RAN, **U-Plane messages used for efficient data transfer** within the strict time limits. It also support data compression, used in I/Q data transfer and DL data precoding. ::: <br> --- ### <center> **C-Plane**</center> --- ![](https://i.imgur.com/k27rHQs.png) <center>Fig.9. C-Plane Message Frame Format</center> <br> :::info In O-RAN, **C-Plane messages define the scheduling, coordination required for data transfer, and beam-forming**. It also used in scheduling and beam-forming commands, DL precoding configuration, mixed numerology, and PRACH handling. ::: <br> --- ### <center> **S-Plane**</center> --- :::info In O-RAN, **S-Plane is responsible for the timing and sync aspects between the O-DU and O-RU**. It also used in topologies synchronization, PTP and SyncE profiles for synchronization, and time frequency sync guidelines. ::: <br> --- ### <center> **M-Plane**</center> --- ![](https://i.imgur.com/Rj8E7T4.png) <center>Fig.10. M-Plane Supported Models</center> <br> :::info In O-RAN, **M-Plane messages are used to manage the radio unit**. It also used in supporting hierarchical/hybrid model, C/U plane IP and delay management, and FCAPS including sync configurations and status. **There are two models that are supported in M-Plane architecture, they are hierarchical and hybrid model.** ::: <br> --- ### <center> **Protocol Stack**</center> --- ![](https://i.imgur.com/t2dWc4q.png) <center>Fig.11. Protocol Stack Of Each Plane</center> <br> :::info Protocol stack of each plane in O-RAN fronthaul are shown in Fig.11. We can conclude for the image that: - **C/U-Plane** - Support protocol stack that ransmits data used by eCPRI or Radio over Ethernet directly over Ethernet - Optional protocol stack that transmits the signal over UDP/IP - **S-Plane** - Support a protocol stack that transmits data used in Precision Time Protocol and SyncE over Ethernet - **M-Plane** - Support a protocol stack that transmits signals used in NETCONF over Ethernet with IP transported using TCP with Secure Shell (SSH) ::: <br> ## :notebook_with_decorative_cover: References :::info 1. [Enabling Interoperability & Adherence to O-RAN Fronthaul Interface](https://files.keysightevent.com/files/2020KWT/(A6)%20Enabling%20Interoperability%20and%20Adherence%20to%20O-RAN%20Fronthaul%20Interface_Brian%20Su.pdf) 2. [Overview of O-RAN Fronthaul Interface](https://www.nttdocomo.co.jp/english/binary/pdf/corporate/technology/rd/technical_journal/bn/vol21_1/vol21_1_007en.pdf) 3. [O-RAN Introduction](https://www.brighttalk.com/webcast/16515/359818?utm_source=brighttalk-portal&utm_medium=web&utm_content=Parallel%20Wireless&utm_campaign=webcasts-search-results-feed) 4. [O-RAN Fronthaul C-U/Sync/Mgmt Planes and Protocol Stack](http://www.techplayon.com/o-ran-fornthual-c-u-sync-mgmt-planes-and-protocols-stack/) 5. [O-RAN Fronthaul Split Option 7-2x](http://www.techplayon.com/o-ran-fronthaul-spilt-option-7-2x/) 6. [Baseband Unit Glossary](https://www.exfo.com/en/resources/glossary/baseband-unit/) 7. [Remote Radio Unit Glossary](https://www.exfo.com/en/resources/glossary/remote-radio-unit/) 8. [Open RAN 101–RU, DU, CU: Why, what, how, when? (Reader Forum) ](https://www.rcrwireless.com/20200708/open_ran/open-ran-101-ru-du-cu-reader-forum) :::