[o-du/phy.git] / docs / Architecture-Overview_fh.rst

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.. |br| raw:: html

   <br />

Architecture Overview
=====================

.. contents::
    :depth: 3
    :local:

This section provides an overview of the xRAN architecture.

.. _introduction-1:

Introduction
------------

The front haul interface, according to the ORAN Fronthaul specification,
performs communication between O-RAN |br|
Distributed Unit (O-DU) and O-RAN
Radio Unit (O-RU) and consists of multiple HW and SW components.

The logical representation of HW and SW components is shown in Figure 1.

.. image:: images/Architecture-Block-Diagram.jpg
  :width: 600
  :alt: Figure 1. Architecture Block Diagram

Figure 1. Architecture Block Diagram

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|br|

From the hardware perspective, two networking ports are used to
communicate to the Front Haul and Back (Mid) Haul network as well as to
receive PTP synchronization. The system timer is used to provide a
“sense” of time to the gNB |br|
application.

From the software perspective, the following components are used:

-  Linux PTP provides synchronization of system timer to GPS time:

-  Ptp4l is used to synchronize oscillator on Network Interface
   Controller (NIC) to PTP GM.

-  Phc2sys is used to synchronize system timer to oscillator on NIC.

-  DPDK to provide the interface to the Ethernet port.

-  xRAN library is built on top of DPDK to perform U-plane and C-plane
   functionality according to the ORAN Fronthaul specification.

-  5GNR reference PHY uses the xRAN library to access interface to O-RU.
   The interface between the library and PHY is defined to communicate
   TTI event, symbol time, C-plane information as well as IQ sample
   data.

-  5G NR PHY communicates with the L2 application using the set of
   MAC/PHY APIs and the shared memory interface defined as WLS.

-  L2, in turn, can use Back (Mid) Haul networking port to connect to
   the CU unit in the context of 3GPP specification.

In this document, we focus on the details of the design and
implementation of the xRAN library with respect to providing Front Haul
functionality for both mmWave and Sub-6 scenarios

The xRAN M-plane is not implemented and is outside of the scope of this
description. Configuration files are used to |br|
specify selected M-plane
level parameters.

ORAN FH Threads
---------------

ORAN FH Thread Performs:

-  Symbol base “time event” to the rest of the system based on System
   Clock synchronized to GPS time via PTP

-  Baseline polling mode driver performing TX and RX of Ethernet packets

-  Most of the packet processing such as Transport header, Application
   header, Data section header and interactions with the rest of the PHY
   processing pipeline.

-  Polling of other call back function that was registered.

ORAN FH thread created the independent of usage of xRAN as an interface
to the Radio.

Communication between L1 and xRAN layer is performed using a set of
callback functions where L1 assigned callback and xRAN layer executes
those functions at a particular event or time moment. Detailed
information on callback function |br|
options and setting as well as design,
can be found in the sections below.

Sample Application Thread Model
-------------------------------

Configuration of a sample application for both O-DU and O-RU follows the
model of 5G NR l1app application in the |br|
section of xRAN only. No BBU or
FEC related threads are needed as minimal xRAN functionality is used
only.

.. image:: images/Sample-Application-Threads.jpg
  :width: 600
  :alt: Figure 3. Sample Application Threads

Figure 3. Sample Application Threads

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|br|

In this scenario, the main thread is used only for initializing and
closing the application. No execution happens on core 0 during run time.

Functional Split
----------------

Figure 1 corresponds to the O-RU part of the xRAN split. Implementation
of the RU side of the xRAN protocol is not |br|
covered in this document.

.. image:: images/eNB-gNB-Architecture-with-O-DU-and-RU.jpg
  :width: 600
  :alt: Figure 4. eNB/gNB Architecture with O-DU and RU

Figure 4. eNB/gNB Architecture with O-DU and RU

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|br|

More than one RU can be supported with the same implementation of the
xRAN library and depends on the configuration of gNB in general. In this
document, we address details of implementation for single O-DU – O-RU
connection.

The ORAN Fronthaul specification provides two categories of the split of
Layer 1 functionality between O-DU and O‑RU: Category A and Category B.

.. image:: images/Functional-Split.jpg
  :width: 600
  :alt: Figure 5. Functional Split

Figure 5. Functional Split

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Data Flow
---------

|br|

Table 3 lists the data flows supported for a single RU with a single
Component Carrier.

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|br|

Table 3. Supported Data Flow

+---------+----+-----------------+-----------------+----------------+
| Plane   | ID | Name            | Contents        | Periodicity    |
+---------+----+-----------------+-----------------+----------------+
| U-Plane | 1a | DL Frequency    | DL user data    | symbol         |
|         |    | Domain IQ Data  | (PDSCH),        |                |
|         |    |                 | control channel |                |
|         |    |                 | data (PDCCH,    |                |
|         |    |                 | etc.)           |                |
+---------+----+-----------------+-----------------+----------------+
|         | 1b | UL Frequency    | UL user data    | symbol         |
|         |    | Domain IQ Data  | (PUSCH),        |                |
|         |    |                 | control channel |                |
|         |    |                 | data (PUCCH,    |                |
|         |    |                 | etc.)           |                |
+---------+----+-----------------+-----------------+----------------+
|         | 1c | PRACH Frequency | UL PRACH data   | slot or symbol |
|         |    | Domain IQ Data  |                 |                |
+---------+----+-----------------+-----------------+----------------+
| C-Plane | 2a | Scheduling      | Scheduling      | ~ slot         |
|         |    | Commands        | information,    |                |
|         |    |                 | FFT size, CP    |                |
|         |    | (Beamforming is | length,         |                |
|         |    | not supported)  | Subcarrier      |                |
|         |    |                 | spacing, UL     |                |
|         |    |                 | PRACH           |                |
|         |    |                 | scheduling      |                |
+---------+----+-----------------+-----------------+----------------+
| S-Plane | S  | Timing and      | IEEE 1588 PTP   |                |
|         |    | Synchronization | packets         |                |
+---------+----+-----------------+-----------------+----------------+

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.. image:: images/Data-Flows.jpg
  :width: 600
  :alt: Figure 6. Data Flows

Figure 6. Data Flows

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|br|

Information on specific features of C-Plane and U-plane provided in
Section 6.0. Configuration of S-plane used on test |br|
setup for simulation
is provided in Appendix Appendix 2.

Data flow separation is based on VLAN (applicable when layer 2 or layer
3 is used for the C/U-plane transport.)

#. The mechanism for assigning VLAN ID to U-Plane and C-Plane is assumed
to be via the M-Plane.

VLAN Tag is configurable via the standard Linux IP tool (refer to
Appendix Appendix 1).

No Quality of Service (QoS) is supported.

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|br|

.. image:: images/C-plane-and-U-plane-Packet-Exchange.jpg
  :width: 600
  :alt: Figure 7. C-plane and U-plane Packet Exchange

Figure 7. C-plane and U-plane Packet Exchange

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|br|

Timing, Latency, and Synchronization to GPS
-------------------------------------------

The ORAN Fronthaul specification defines the latency model of the front
haul interface and interaction between O-DU and 0-RU. This
implementation of the xRAN library supports only the category with fixed
timing advance and Defined Transport method. It determines O-DU transmit
and receive windows based on pre-defined transport network |br|
characteristics, and the delay characteristics of the RUs within the
timing domain.

Table 4 below provides default values used for the implementation of
O-DU – O-RU simulation with mmWave scenario. Table 5 and Table 6 below
provide default values used for the implementation of O-DU – O-RU
simulation with |br|
numerology 0 and numerology 1 for Sub6 scenarios.
Configuration can be adjusted via configuration files for sample |br|
application and reference PHY. However, simulation of the different
range of the settings was not performed, and |bR|
additional implementation changes might be required as well as testing with actual O-RU. |br|
The
parameters for the front haul network are out of scope as a direct
connection between O-DU and 0-RU is used for simulation.

|br|
|br|

Table 4. Front Haul Interface Latency (numerology 3 - mmWave)

+------+------------+-------------------+-------------------+----------------+------------+
|      | Model      | C-Plane           | U-Plane           |                |            |
|      | Parameters |                   |                   |                |            |
+------+------------+-------------------+-------------------+----------------+------------+
|      |            | DL                | UL                | DL             | UL         |
+------+------------+-------------------+-------------------+----------------+------------+
| O-RU | T2amin     | T2a_min_cp_dl=50  | T2a_min_cp_ul=50  | T2a_min_up=25  | NA         |
+------+------------+-------------------+-------------------+----------------+------------+
|      | T2amax     | T2a_max_cp_dl=140 | T2a_max_cp_ul=140 | T2a_max_up=140 | NA         |
+------+------------+-------------------+-------------------+----------------+------------+
|      |            | Tadv_cp_dl        | NA                | NA             | NA         |
+------+------------+-------------------+-------------------+----------------+------------+
|      | Ta3min     | NA                | NA                | NA             | Ta3_min=20 |
+------+------------+-------------------+-------------------+----------------+------------+
|      | Ta3max     | NA                | NA                | NA             | Ta3_max=32 |
+------+------------+-------------------+-------------------+----------------+------------+
| O-DU | T1amin     | T1a_min_cp_dl=70  | T1a_min_cp_ul=60  | T1a_min_up=35  | NA         |
+------+------------+-------------------+-------------------+----------------+------------+
|      | T1amax     | T1a_max_cp_dl=100 | T1a_max_cp_ul=70  | T1a_max_up=50  | NA         |
+------+------------+-------------------+-------------------+----------------+------------+
|      | Ta4min     | NA                | NA                | NA             | Ta4_min=0  |
+------+------------+-------------------+-------------------+----------------+------------+
|      | Ta4max     | NA                | NA                | NA             | Ta4_max=45 |
+------+------------+-------------------+-------------------+----------------+------------+

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Table 5. Front Haul Interface Latency (numerology 0 - Sub6)

+------+----------+----------+----------+----------+----------+
|      | Model    | C-Plane  | U-Plane  |          |          |
|      | Pa       |          |          |          |          |
|      | rameters |          |          |          |          |
+------+----------+----------+----------+----------+----------+
|      |          | DL       | UL       | DL       | UL       |
+------+----------+----------+----------+----------+----------+
| O-RU | T2amin   | T        | T        | T2a_mi   | NA       |
|      |          | 2a_min_c | 2a_min_c | n_up=200 |          |
|      |          | p_dl=400 | p_ul=400 |          |          |
+------+----------+----------+----------+----------+----------+
|      | T2amax   | T2       | T2       | T2a_max  | NA       |
|      |          | a_max_cp | a_max_cp | _up=1120 |          |
|      |          | _dl=1120 | _ul=1120 |          |          |
+------+----------+----------+----------+----------+----------+
|      |          | Ta       | NA       | NA       | NA       |
|      |          | dv_cp_dl |          |          |          |
+------+----------+----------+----------+----------+----------+
|      | Ta3min   | NA       | NA       | NA       | Ta3      |
|      |          |          |          |          | _min=160 |
+------+----------+----------+----------+----------+----------+
|      | Ta3max   | NA       | NA       | NA       | Ta3      |
|      |          |          |          |          | _max=256 |
+------+----------+----------+----------+----------+----------+
| O-DU | T1amin   | T        | T        | T1a_mi   | NA       |
|      |          | 1a_min_c | 1a_min_c | n_up=280 |          |
|      |          | p_dl=560 | p_ul=480 |          |          |
+------+----------+----------+----------+----------+----------+
|      | T1amax   | T        | T        | T1a_ma   | NA       |
|      |          | 1a_max_c | 1a_max_c | x_up=400 |          |
|      |          | p_dl=800 | p_ul=560 |          |          |
+------+----------+----------+----------+----------+----------+
|      | Ta4min   | NA       | NA       | NA       | T        |
|      |          |          |          |          | a4_min=0 |
+------+----------+----------+----------+----------+----------+
|      | Ta4max   | NA       | NA       | NA       | Ta4      |
|      |          |          |          |          | _max=360 |
+------+----------+----------+----------+----------+----------+

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Table 6. Front Haul Interface Latency (numerology 1 - Sub6)

+------+------------+-------------------+-------------------+----------------+------------+
|      | Model      | C-Plane           | U-Plane           |                |            |
|      | Parameters |                   |                   |                |            |
+------+------------+-------------------+-------------------+----------------+------------+
|      |            | DL                | UL                | DL             | UL         |
+------+------------+-------------------+-------------------+----------------+------------+
| O-RU | T2amin     | T2a_min_cp_dl=285 | T2a_min_cp_ul=285 | T2a_min_up=71  | NA         |
+------+------------+-------------------+-------------------+----------------+------------+
|      | T2amax     | T2a_max_cp_dl=429 | T2a_max_cp_ul=429 | T2a_max_up=428 | NA         |
+------+------------+-------------------+-------------------+----------------+------------+
|      |            | Tadv_cp_dl        | NA                | NA             | NA         |
+------+------------+-------------------+-------------------+----------------+------------+
|      | Ta3min     | NA                | NA                | NA             | Ta3_min=20 |
+------+------------+-------------------+-------------------+----------------+------------+
|      | Ta3max     | NA                | NA                | NA             | Ta3_max=32 |
+------+------------+-------------------+-------------------+----------------+------------+
| O-DU | T1amin     | T1a_min_cp_dl=285 | T1a_min_cp_ul=285 | T1a_min_up=96  | NA         |
+------+------------+-------------------+-------------------+----------------+------------+
|      | T1amax     | T1a_max_cp_dl=429 | T1a_max_cp_ul=300 | T1a_max_up=196 | NA         |
+------+------------+-------------------+-------------------+----------------+------------+
|      | Ta4min     | NA                | NA                | NA             | Ta4_min=0  |
+------+------------+-------------------+-------------------+----------------+------------+
|      | Ta4max     | NA                | NA                | NA             | Ta4_max=75 |
+------+------------+-------------------+-------------------+----------------+------------+

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|br|

IEEE 1588 protocol and PTP for Linux\* implementations are used to
synchronize local time to GPS time. Details of the configuration used
are provided in Appendix Appendix 2. Local time is used to get Top of
the Second (ToS) as a 1pps event for SW implementation. Timing event is
obtained by performing polling of local time using |br|
clock_gettime(CLOCK_REALTIME,..)

All-time intervals are specified with respect to GPS time which
corresponds to OTA time.

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|br|
|br|

Virtualization and Container-Based Usage
----------------------------------------

xRAN implementation is deployment agnostic and does not require special
changes to be used in virtualized or |br|
container-based deployment options.
The only requirement is to provide one SRIOV base virtual port for
C-plane and one port for U-plane traffic per O-DU instance. This can be
achieved with the default Virtual Infrastructure Manager (VIM) as well
as using standard container networking.