O-RAN Base Station O-DU & O-CU软件架构与API技术规范

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O-RAN.WG8.AAD.0-v02.00技术规范文档详细介绍了O-RAN堆栈参考设计中的基站O-DU（Optical DU）和O-CU（Central Unit）软件架构以及API（应用程序编程接口）。该文档由O-RAN联盟编制，版权属于2020年O-RAN联盟，用户在访问、下载或使用本规范的任何部分时，必须接受附录ZZZ中所述的O-RAN采纳者许可证协议条款。所有权利保留。 O-RAN（开放无线接入网）是一个致力于推动电信网络架构现代化的全球联盟，它倡导开放、标准化的无线接入网架构，以提高效率、降低成本和加快创新。这份技术规范着重于O-DU和O-CU的软件设计，这两个组件是O-RAN架构的核心部分： 1. **O-DU**：光分组单元，负责处理来自无线设备（如AAU）的射频信号，进行基带处理，并将其转换为适合传输到核心网络的数据包。O-DU包含硬件和软件，其中软件定义了如何与O-RAN的其他模块交互，以及处理和封装射频数据的逻辑。 2. **O-CU**：中央单元，主要负责控制面功能，包括网络功能虚拟化（NFV）、编解码、协议处理等。O-CU通过接口与O-RAN的其他组成部分如DU（ Distributed Unit）通信，确保网络的协调和一致性。 **修订历史**： - v01.0.0（2019年8月9日）：首次发布基站O-DU和O-CU软件架构及API的技术规范。 - V02.0.0（2020年2月14日）：O-RANWG8进行了第二次更新，这次更新可能包含了对现有规范的优化、新功能的添加、或对先前版本的改进，但具体描述中提到的"Release 2 updates"并未详述具体的变更内容。要深入理解和应用O-RAN的软件架构，开发者需要熟悉这些API的使用方法、接口设计以及遵循O-RAN采纳者许可证协议的要求。通过这种方式，O-RAN旨在创建一个开放、可扩展且可互操作的无线接入网络环境，促进电信行业的创新和发展。

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Your use is subject to the terms of the O-RAN Adopter License Agreement in Annex ZZZ

O-RAN.WG8.AAD.0-v02.00

 PDSCH, PDCCH, PBCH

 UL/DL Reference Signals (DMRS, PTRS, SRS, PSS, SSS)

 Fronthaul handler

 FAPI handler

 Hardware accelerator handler

 Timing sync

 L1 Task Control Module

In the following sections, the functional blocks are described in detail.

5.1 Physical Uplink Shared Channel

The uplink physical layer processing of transport channels consists of the following steps as described in [6]:

 Transport Block CRC attachment

 Code Block segmentation and Code Block CRC attachment

 Channel coding: LDPC coding

 Physical layer hybrid-ARQ processing

 Rate matching

 Scrambling

 Modulation: π/2 BPSK (with transform precoding only), QPSK, 16QAM, 64QAM and 256QAM

 Layer mapping, transform precoding (enabled/disabled by configuration), and precoding

 Mapping to assigned resources and antenna ports

The frequency domain IQ data received by the fronthaul module are sent to the L1 PUSCH processing functions and the

output of the PUSCH is the user bit stream. Figure 5-1 illustrates the PUSCH functional blocks.

Figure 5-1 PUSCH functional blocks

Resource Element (RE) Demapper: The RE Demapper function separates the DMRS REs and the user data REs. The

DMRS REs are provided to the channel estimation function.

Channel Estimation: The channel estimation functional block provides a channel estimate based on the DMRS of

resource elements of the user data.

MIMO Equalizer: The MIMO equalizer function processes the received IQ data signals to reverse the distortion

incurred during the signal transmission over the air. Using the channel information acquired via the channel estimation,

the equalizer tries to restore the IQ symbol sent by the transmitter. The symbols may be conveyed as log-likelihood

ratios (LLRs) for use by the LDPC decoder.

Rate Dematching: The rate dematching function performs the reverse operation steps of rate matching for LDPC code

in clause 5.4.2 in 3GPP TS38.212 [5].

LDPC Decoder: The LDPC decoder function uses received log-likelihood ratios (LLRs) to compute the data bits based

on selected decoder algorithm. The selection of the decoder algorithm is out of scope of this specification.

CRC Check: The CRC function block checks the parity bits using the generator polynomials in Subclause 5.1 of 3GPP

TS38.212 [5]. Refer to the 3GPP specification for details.

Low-PHY

Precoder/

Beamforming

Demapper

Channel

Estimation

Equalizer Demodulation Descrambler

Rate

Dematching

LDPC

Decoder

CRC

Check

DMRS

Channel Info

IQ data

FFT/CP

Removal

Library APIs

Bit Stream

IQ samples

________________________________________________________________________________________________

Your use is subject to the terms of the O-RAN Adopter License Agreement in Annex ZZZ

O-RAN.WG8.AAD.0-v02.00

5.2 Uplink Control Channels

Physical Uplink Control Channel (PUCCH) conveys Uplink Control Information (UCI) and supports all the formats

defined in clause 6.3.2 of 3GPP TS38.211 specification [4]. Refer to this specification for details of the formats as well

as the control message including:

 HARQ-ACK (Hybrid Automated Repeat Request Acknowledgement).

 Scheduling Request (SR)

 Channel State Information (CSI)

5.3 Uplink Reference Signals

5G NR introduces the following reference signals.

 Demodulation Reference Signal (DMRS) for PUSCH and PUCCH

 Phase Tracking Reference Signal (PTRS)

 Sounding Reference Signal (SRS)

Refer to clause 6.4.1 in 3GPP TS38.211 specification [4] for more details of the reference signals.

5.4 Physical Downlink Shared Channel

The downlink physical layer processing of transport channels consists of the following steps as described in [6]:

 Transport Block CRC attachment

 Code Block segmentation and Code Block CRC attachment

 Channel coding: LDPC coding

 Physical-layer hybrid-ARQ processing

 Rate matching

 Scrambling

 Modulation: QPSK, 16QAM, 64QAM and 256QAM

 Layer mapping

 Mapping to assigned resources and antenna ports

Figure 5-2 illustrates the functional blocks of the PDSCH.

Figure 5-2 PDSCH Functional Blocks

Cyclic Redundancy Check Generation: The CRC function block computes the parity bits using the generator

polynomials in Subclause 5.1 of 3GPP TS38.212 [5]. Refer to the 3GPP specification for details.

Segmentation: The transport block is segmented when it exceeds the code block size specified by 3GPP TS38.212 [5].

Refer to Subclause 7.2.3 for details.

LDPC Encoder: Refer to Subclause 5.3.2 in 3GPP TS38.212 [5] for details.

Rate Matching: Refer to Subclause 5.4.2 in 3GPP TS38.212 [5] for details.

Scrambler: Refer to Subclause 7.3.1.1 in 3GPP TS38.211 [4] for details.

Modulation Mapper: Refer to Subclause 7.3.1.2 in 3GPP TS38.211 [4] for details.

Low-PHY

CRC

Generation

Segmentati

LDPC

Encoder

Rate

Matching

Scrambler

Modulation

Mapper

Layer Mapper

Precoder/

Beamforming

RE Mapper iFFT

Transport

Block

FH Libray APIs

IQ Samples

________________________________________________________________________________________________

Your use is subject to the terms of the O-RAN Adopter License Agreement in Annex ZZZ

O-RAN.WG8.AAD.0-v02.00

Layer Mapper: Refer to Subclause 7.3.1.3 in 3GPP TS38.211 [4] for details.

RE Mapper: Refer to Subclause 7.3.1.5 and Subclause 7.3.1.6 in 3GPP TS38.211 [4] for details.

5.5 Physical Downlink Control Channel

A Physical Downlink Control Channel (PDCCH) carries control information (DCI) such as scheduling information and

resource grant to UEs. The PDCCH includes one or more Control Channel Elements (CCE, consists of 6 resource

element group) based on the aggregation level defined by 3GPP specification [4]. The PDCCH processing flow is

similar to the PDSCH. The PDCCH uses a polar code instead of LDPC. QPSK modulation is the designated modulation

scheme for the PDCCH bits block.

5.6 Downlink Reference Signals

The Downlink Reference Signals include:

 Demodulation Reference Signal (DMRS) for PDSCH, PDCCH and PBCH.

 Phase Tracking Reference Signal (PTRS)

 Channel State Information Reference Signal (CSI-RS)

 Primary Synchronization Signal (PSS)

 Secondary Synchronization Signal (SSS)

Refers to clause 7.4.1 in 3GPP TS38.211 specification [4] for more details related to the reference signals. The PSS and

SSS combined with PBCH is known as SS/PBCH block, which consists of:

 1 symbol PSS, 1 symbol SSS and 2 symbol PBCH.

5.7 Physical Broadcast Channel

PBCH carries 5G NR system information for UEs. UEs need to decode the PBCH information in order to access the 5G

cell. PBCH information includes: downlink bandwidth, SFN, timing information in radio frame and SS burst

periodicity. Polar codes are used as error correcting code for PBCH.

PBCH

Payload

Generation

Scrambling

CRC

attachment

Channel

Encoding

Rate

Matching

Data

Scrambling

Data

Modulation

BCH

Resource

Element

Mapping

DMRS

Sequence

Generation

DMRS

Scrambling

DMRS

Modulation

DMRS

Figure 5-3: PBCH processing flow diagram

PBCH Payload Generation: Creates the PBCH payload message, Refer to Subclause 7.1.1 in 3GPP TS38.212 [5] for

details.

Scrambling: Refer to Subclause 7.1.2 in 3GPP TS38.212 [5] for details.

CRC attachment: Refer to Subclause 7.1.3 in 3GPP TS38.212 [5] for details.

Channel Encoding: Refer to Subclause 7.1.4 in 3GPP TS38.212 [5] for details.

Rate Matching: Refer to Subclause 7.1.5 in 3GPP TS38.212 [5] for details.

Data Scrambling: Refer to Subclause 7.3.1.3 in 3GPP TS38.211 [4] for details.

Data Modulation: Refer to Subclause 7.3.3.2 in 3GPP TS38.211 [4] for details.

Resource Element Mapping: Refer to Subclause 7.3.3.3 in 3GPP TS38.211 [4] for details.

DMRS Generation: Refer to Subclause 7.4.1.4 in 3GPP TS38.211 [4] for details.

________________________________________________________________________________________________

Your use is subject to the terms of the O-RAN Adopter License Agreement in Annex ZZZ

O-RAN.WG8.AAD.0-v02.00

DMRS Scrambling: Refer to Subclause 7.4.1.4 in 3GPP TS38.211 [4] for details.

DMRS Modulation: Refer to Subclause 7.3.3.2 in 3GPP TS38.211 [4] for details.

5.8 Physical Random Access Channel

Physical Random Access Channel (PRACH) is used to carry preamble from UE to gNB. Based on PRACH, gNB is able

to calculate the timing advance of each UE and make adjustments on Rx timing for all UEs. PRACH adopts ZC (Zero

Correlation) sequences as preamble. It supports two sequence lengths (139 and 839) with various formats targeted for

different deployment scenarios. As O-RAN fronthaul separates the PRACH processing into two parts, the CP removal,

frequency shift, samples decimation/filter, FFT and de-mapping function are handled by O-RU; the O-DU PRACH

processing flow is shown in Figure 5-4.

O-DU

Correlation

iFFT

Antenna

Combination

Noise

Estimation

Peak Search

Preamble

Detection & TA

Estimation

Root

Sequence

Figure 5-4: PRACH processing flow diagram

Each O-DU PRACH processing function blocks are described below. The details of the PRACH signal generation,

formats are described in 3GPP specifications.

Root Sequence Generation: Refer to Subclause 6.3.3.1 in 3GPP TS38.211 [4] for details.

Correlation: Perform correlation operation between root sequence and received signals.

iFFT: Perform the iFFT operation of received signals.

Antenna Combination: Combine the received signals from all the antennas.

Noise Estimation: Perform the noise estimation operation

Peak Search: Detect the peak for different root sequences.

Preamble Detection and Timing Advance (TA) Estimation: Determine the preamble sequence and timing advance

estimation.

5.9 L1 Tasks Processing Flow

The L1 function processes are described in previous sections. Those processing blocks focus on specific task that needs

to be completed in a timely fashion. Figure 5-5 shows the L1 related task processing blocks.

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