Table of Contents

[[TOC]]

Functional Split Architecture

RCC: Radio-Cloud Center
RAU: Radio-Access Unit
RRU: Remote Radio-Unit
IF4.5 / IF5 : similar to IEEE P1914.1
FAPI (IF2) : specified by Small Cell Forum (open-nFAPI implementation)
IF1 : F1 in 3GPP Release 15

OpenAirInterface Block Diagram

OpenAirInterface 5G-NR Feature Set

General Parameters

The following features are valid for the gNB and the 5G-NR UE.

Static TDD, FDD
Normal CP
Subcarrier spacings: 15 and 30kHz (FR1), 120kHz (FR2)
Bandwidths: 10, 20, 40, 60, 80, 100MHz
Intermediate downlink and uplink frequencies to interface with IF equipment
Procedures for 2-layer DL and UL MIMO
Slot format: 14 OFDM symbols in UL or DL
Highly efficient 3GPP compliant LDPC encoder and decoder (BG1 and BG2 supported)
Highly efficient 3GPP compliant polar encoder and decoder
Encoder and decoder for short blocks
Support for UL transform precoding (SC-FDMA)

Furthermore, the gNB and UE support

"noS1" mode (DL and UL):
- Creates TUN interface to PDCP to inject and receive user-place traffic
- No connection to the core network
Standalone (SA) mode:
- UE can register with the 5G Core Network through the gNB, establish a PDU Session and exchange user-plane traffic

gNB PHY

15kHz and 30kHz SCS for FR1 and 120kHz SCS for FR2
Generation of NR-PSS/NR-SSS
NR-PBCH supports multiple SSBs and flexible periodicity
Generation of NR-PDCCH (including generation of DCI, polar encoding, scrambling, modulation, RB mapping, etc)
- common search space
- user-specific search space
- DCI formats: 00, 10, 01 and 11
Generation of NR-PDSCH (including Segmentation, LDPC encoding, rate matching, scrambling, modulation, RB mapping, etc).
- PDSCH mapping type A and B
- DMRS configuration type 1 and 2
- Single and multiple DMRS symbols
- PTRS support
- Support for 1, 2 and 4 TX antennas
- Support for up to 2 layers (currently limited to DMRS configuration type 2)
- Support for 256 QAM
NR-CSIRS Generation of sequence at PHY
NR-PUSCH (including Segmentation, LDPC encoding, rate matching, scrambling, modulation, RB mapping, etc).
- PUSCH mapping type A and B
- DMRS configuration type 1 and 2
- Single and multiple DMRS symbols
- PTRS support
- Support for up to 2 RX antenna
- Support for up to 2 layers
- Support for 256 QAM
NR-PUCCH
- Format 0 (2 bits, for ACK/NACK and SR)
- Format 2 (mainly for CSI feedback)
NR-SRS
- SRS signal reception
- Channel estimation (with T tracer real time monitoring)
- Power noise estimation
NR-PRS
- Rel16 Positioning reference signal(PRS) generation and modulation
- Multiple PRS resources, one per beam is supported in FR2 TDD mode
- FR1 and FR2 support with config file
NR-PRACH
- Formats 0,1,2,3, A1-A3, B1-B3
Highly efficient 3GPP compliant LDPC encoder and decoder (BG1 and BG2 are supported)
Highly efficient 3GPP compliant polar encoder and decoder
Encoder and decoder for short block

gNB MAC

MAC -> PHY configuration using NR FAPI P5 interface
MAC <-> PHY data interface using FAPI P7 interface for BCH PDU, DCI PDU, PDSCH PDU
Scheduler procedures for SIB1
Scheduler procedures for RA
- Contention Free RA procedure
- Contention Based RA procedure
  - Msg3 can transfer uplink CCCH, DTCH or DCCH messages
  - CBRA can be performed using MAC CE or C-RNTI
Scheduler procedures for CSI-RS
MAC downlink scheduler
- phy-test scheduler (fixed allocation and usable also without UE)
- regular scheduler with dynamic proportionally-fair allocation
- MCS adaptation from HARQ BLER
MAC header generation (including timing advance)
ACK / NACK handling and HARQ procedures for downlink
MAC uplink scheduler
- phy-test scheduler (fixed allocation)
- regular scheduler with dynamic proportionally-fair allocation
- HARQ procedures for uplink
Scheduler procedures for SRS reception
- Periodic SRS reception
- Channel rank computation up to 2x2 scenario
- TPMI computation based on SRS up 4 antenna ports and 2 layers
MAC procedures to handle CSI measurement report
- evalution of RSRP report
- evaluation of CQI report
MAC scheduling of SR reception
Bandwidth part (BWP) operation
- Handle multiple dedicated BWPs, supports one UE
- BWP switching through RRCReconfiguration method

gNB RLC

Send/Receive operations according to 38.322 Rel.16
- Segmentation and reassembly procedures
- RLC Acknowledged mode supporting PDU retransmissions
- RLC Unacknowledged mode
- DRBs and SRBs establishment/handling and association with RLC entities
- Timers implementation
- Interfaces with PDCP, MAC
- Interfaces with gtp-u (data Tx/Rx over F1-U at the DU)

gNB PDCP

Send/Receive operations according to 38.323 Rel.16
- Integrity protection and ciphering procedures
- Sequence number management, SDU dicard and in-order delivery
- Radio bearer establishment/handling and association with PDCP entities
- Interfaces with RRC, RLC
- Interfaces with gtp-u (data Tx/Rx over N3 and F1-U interfaces)

gNB SDAP

Send/Receive operations according to 37.324 Rel.15
- Establishment/Handling of SDAP entities.
- Transfer of User Plane Data
- Mapping between a QoS flow and a DRB for both DL and UL
- Marking QoS flow ID in both DL and UL packets
- Reflective QoS flow to DRB mapping for UL SDAP data PDUs

gNB RRC

NR RRC (38.331) Rel 17 messages using new asn1c
LTE RRC (36.331) also updated to Rel 15
Generation of CellGroupConfig (for eNB) and MIB
Generation of system information block 1 (SIB1)
Generation of system information block 2 (SIB2)
Application to read configuration file and program gNB RRC
RRC can configure PDCP, RLC, MAC
Interface with GTP-U (tunnel creation/handling for S1-U (NSA), N3 (SA) interfaces)
Integration of RRC messages and procedures supporting UE 5G SA connection
- RRCSetupRequest/RRCSetup/RRCSetupComplete
- RRC Uplink/Downlink Information transfer carrying NAS messages transparently
- RRC Reconfiguration/Reconfiguration complete
- RRC Reestablishment/Reestablishment complete
- Support for master cell group configuration
- Interface with NGAP for the interactions with the AMF
- Interface with F1AP for CU/DU split deployment option
- Periodic RRC measurements of serving cell (no A/B events)

gNB X2AP

Integration of X2AP messages and procedures for the exchanges with the eNB over X2 interface supporting the NSA setup according to 36.423 Rel. 15
- X2 setup with eNB
- Handling of SgNB Addition Request/Addition Request Acknowledge/Reconfiguration Complete

gNB NGAP

Integration of NGAP messages and procedures for the exchanges with the AMF over N2 interface according to 38.413 Rel. 15
- NGAP Setup request/response
- NGAP Initial UE message
- NGAP Initial context setup request/response
- NGAP Downlink/Uplink NAS transfer
- NGAP UE context release request/complete
- NGAP UE radio capability info indication
- NGAP PDU session resource setup request/response
Interface with RRC

gNB F1AP

Integration of F1AP messages and procedures for the control plane exchanges between the CU and DU entities according to 38.473 Rel. 16
- F1 Setup request/response/failure
- F1 DL/UL RRC message transfer
- F1 Initial UL RRC message transfer
- F1 UE Context setup request/response
- F1 UE Context modification request/response
- F1 UE Context modification required
- F1 UE Context release req/cmd/complete
- F1 gNB CU configuration update
Interface with RRC
Interface with gtp-u (tunnel creation/handling for F1-U interface)

gNB E1AP

Integration of E1AP messages and procedures for exchange between CU-CP and CU-UP according to TS 38.463 Rel. 16
- E1 Setup (gNB-CU-UP initiated)
  - E1 Setup Request
  - E1 Setup Response
  - E1 Setup Failure
- E1 Bearer Context Setup (gNB-CU-CP initiated)
  - E1 Bearer Context Setup Request
  - E1 Bearer Context Setup Response
- Bearer Context Modification (gNB-CU-CP initiated)
  - E1 Bearer Context Modification Request
  - E1 Bearer Context Modification Response
Interface with RRC and PDCP

gNB GTP-U

New GTP-U implementation supporting both N3 and F1-U interfaces according to 29.281 Rel.15
- Interfaces with RRC, F1AP for tunnel creation
- Interfaces with PDCP and RLC for data send/receive at the CU and DU respectively (F1-U interface)
- Interface with SDAP for data send/receive, capture of GTP-U Optional Header, GTP-U Extension Header and PDU Session Container.

OpenAirInterface 5G-NR UE Feature Set

NR UE PHY Layer

Initial synchronization
- the UE needs to know the position in frequency of the SSBs (via command line parameter in SA)
Time tracking based on PBCH DMRS
Frequency offset estimation based on PSS and SSS
15kHz and 30kHz SCS for FR1 and 120 kHz SCS for FR2
Reception of NR-PSS/NR-SSS
NR-PBCH supports multiple SSBs and flexible periodicity
- RSRP measurement for the strongest SSB
Reception of NR-PDCCH (including reception of DCI, polar decoding, de-scrambling, de-modulation, RB de-mapping, etc)
- common search space configured by MIB
- user-specific search space configured by RRC
- DCI formats: 00, 10, 01 and 11
Reception of NR-PDSCH (including Segmentation, LDPC decoding, rate de-matching, de-scrambling, de-modulation, RB de-mapping, etc).
- PDSCH mapping type A and B
- DMRS configuration type 1 and 2
- Single and multiple DMRS symbols
- PTRS support
- Support for 256 QAM
- Support for 1, 2 and 4 RX antennas
- Support for up to 2 layers (currently limited to DMRS configuration type 2)
Measurements based on NR-CSIRS
- RSRP measurements
- RI, PMI and CQI computation
- Support for up to 4 RX antennas
- Support for up to 2 layers
NR-PUSCH (including Segmentation, LDPC encoding, rate matching, scrambling, modulation, RB mapping, etc).
- PUSCH mapping type A and B
- DMRS configuration type 1 and 2
- Single and multiple DMRS symbols
- PTRS support
- Support for 256 QAM
- Support for up to 2 TX antenna
- Support for up to 2 layers
NR-PUCCH
- Format 0 (2 bits for ACK/NACK and SR)
- Format 2 (mainly for CSI feedback)
- Format 1 (limited testing)
- Format 3 and 4 present but old code never tested (need restructuring before verification)
NR-SRS
- Generation of sequence at PHY
- SRS signal transmission
NR-PRS
- PRS based Channel estimation with T tracer dumps
- Time of arrival(ToA) estimation based on channel impulse response(CIR)
- Finer ToA estimation by 16x oversampled IDFT for CIR
- Support for multiple gNB reception with gNBs synced via GPSDO
NR-PRACH
- Formats 0,1,2,3, A1-A3, B1-B3
Highly efficient 3GPP compliant LDPC encoder and decoder (BG1 and BG2 are supported)
Highly efficient 3GPP compliant polar encoder and decoder
Encoder and decoder for short block

NR UE FAPI

MAC -> PHY configuration via UE FAPI P5 interface
Basic MAC to control PHY via UE FAPI P7 interface
PHY -> MAC indication (needs some improvement)

NR UE Higher Layers

UE MAC

Minimum system information (MSI)
- MIB processing
- Scheduling of system information block 1 (SIB1) reception
Random access procedure (needs improvement, there is still not a clear separation between MAC and PHY)
- Mapping SSBs to multiple ROs
- Scheduling of PRACH
- Processing of RAR
- Transmission and re-transmission of Msg3
- Msg4 and contention resolution
DCI processing
- format 10 (RA-RNTI, C-RNTI, SI-RNTI, TC-RNTI)
- format 00 (C-RNTI, TC-RNTI)
- format 11 (C-RNTI)
- format 01 (C-RNTI)
UCI processing
- ACK/NACK processing
- Triggering periodic SR
- CSI measurement reporting
DLSCH scheduler
- Configuration of fapi PDU according to DCI
- HARQ procedures
ULSCH scheduler
- Configuration of fapi PDU according to DCI
- Logical channel prioritization of 'data from any logical channel'
NR-CSIRS scheduler
- Scheduling of NR-CSIRS reception
- Fill UCI for CSI measurement reporting
Scheduler procedures for SRS transmission
- Periodic SRS transmission
Bandwidth part (BWP) operation
- Operation in configured dedicated BWP through RRCSetup or RRCReconfiguration

UE RLC

Tx/Rx operations according to 38.322 Rel.16
- Segmentation and reassembly procedures
- RLC Acknowledged mode supporting PDU retransmissions
- RLC Unacknowledged mode
- DRBs and SRBs establishment and handling
- Timers implementation
- Interfaces with PDCP, MAC

UE PDCP

Tx/Rx operations according to 38.323 Rel.16
- Integrity protection and ciphering procedures
- Sequence number management, SDU dicard and in-order delivery
- Radio bearer establishment/handling and association with PDCP entities
- Interfaces with RRC, RLC

UE SDAP

Tx/Rx operations operations according to 37.324 Rel.15

Establishment/Handling of SDAP entities.
Transfer of User Plane Data
Reflective Mapping
RRC Signaling Mapping

UE RRC

Integration of RRC messages and procedures supporting UE 5G SA connection according to 38.331 Rel.16
- RRCSetupRequest/RRCSetup/RRCSetupComplete
- RRC Uplink/Downlink Information transfer carrying NAS messages transparently
- RRC Reconfiguration/Reconfiguration complete
- Support for master cell group configuration
- Reception of UECapabilityEnquiry, encoding and transmission of UECapability
Interface with PDCP: configuration, DCCH and CCCH message handling
Interface with RLC and MAC for configuration

UE NAS

Transfer of NAS messages between the AMF and the UE supporting the UE registration with the core network and the PDU session establishment according to 24.501 Rel.16
- Identity Request/Response
- Authentication Request/Response
- Security Mode Command/Complete
- Registration Request/Accept/Complete
- PDU Session Establishment Request/Accept
- NAS configuration and basic interfacing with RRC

OpenAirInterface 4G LTE eNB Feature Set

eNB PHY Layer

The Physical layer implements 3GPP 36.211, 36.212, 36.213 and provides the following features:

LTE release 8.6 compliant, and implements a subset of release 10
FDD and TDD configurations: 1 (experimental) and 3
Bandwidth: 5, 10, and 20 MHz
Transmission modes: 1, 2 (stable), 3, 4, 5, 6, 7 (experimental)
Max number of antennas: 2
CQI/PMI reporting: aperiodic, feedback mode 3 - 0 and 3 - 1
PRACH preamble format 0
Downlink (DL) channels are supported: PSS, SSS, PBCH, PCFICH, PHICH, PDCCH, PDSCH, PMCH, MPDCCH
Uplink (UL) channels are supported: PRACH, PUSCH, PUCCH (format 1/1a/1b), SRS, DRS
HARQ support (UL and DL)
Highly optimized base band processing (including turbo decoder)
Multi-RRU support: over the air synchro b/ multi RRU in TDD mode
Support for CE-modeA for LTE-M. Limited support for repeatition, single-LTE-M connection, legacy-LTE UE attach is disabled.

Performances

Transmission Mode, Bandwidth	Expected Throughput	Measured Throughput	Measurement Conditions
FDD DL: 5 MHz, 25 PRBS/ MCS 28	16 - 17 Mbit/s	TM1: 17.0 Mbits/s	COTS-UE Cat 4 (150/50 Mbps)
FDD DL: 10 MHz, 50 PRBS/ MCS 28	34 - 35 Mbit/s	TM1: 34.0 Mbits/s	COTS-UE Cat 4 (150/50 Mbps)
FDD DL: 20 MHz, 100 PRBS/ MCS 28	70 Mbit/s	TM1: 69.9 Mbits/s	COTS-UE Cat 4 (150/50 Mbps)

FDD UL: 5 MHz, 25 PRBS/ MCS 20	9 Mbit/s	TM1: 8.28 Mbits/s	COTS-UE Cat 4 (150/50 Mbps)
FDD UL: 10 MHz, 50 PRBS/ MCS 20	17 Mbit/s	TM1: 18.3 Mbits/s	COTS-UE Cat 4 (150/50 Mbps)
FDD UL: 20 MHz, 100 PRBS/ MCS 20	35 Mbit/s	TM1: 18.6 Mbits/s	COTS-UE Cat 4 (150/50 Mbps)

TDD DL: 5 MHz, 25 PRBS/ MCS XX	6.5 Mbit/s	TM1: 6.71 Mbits/s	COTS-UE Cat 4 (150/50 Mbps)
TDD DL: 10 MHz, 50 PRBS/ MCS XX	13.5 Mbit/s	TM1: 13.6 Mbits/s	COTS-UE Cat 4 (150/50 Mbps)
TDD DL: 20 MHz, 100 PRBS/ MCS XX	28.0 Mbit/s	TM1: 27.2 Mbits/s	COTS-UE Cat 4 (150/50 Mbps)

TDD UL: 5 MHz, 25 PRBS/ MCS XX	2.0 Mbit/s	TM1: 3.31 Mbits/s	COTS-UE Cat 4 (150/50 Mbps)
TDD UL: 10 MHz, 50 PRBS/ MCS XX	2.0 Mbit/s	TM1: 7.25 Mbits/s	COTS-UE Cat 4 (150/50 Mbps)
TDD UL: 20 MHz, 100 PRBS/ MCS XX	3.0 Mbit/s	TM1: 4.21 Mbits/s	COTS-UE Cat 4 (150/50 Mbps)

Number of supported UEs

16 by default
up to 256 when compiling with dedicated compile flag
was tested with 40 COTS-UE

eNB MAC Layer

The MAC layer implements a subset of the 3GPP 36.321 release v8.6 in support of BCH, DLSCH, RACH, and ULSCH channels.

RRC interface for CCCH, DCCH, and DTCH
Proportional fair scheduler (round robin scheduler soon), with the following improvements:
- Up to 30 users tested in the L2 simulator, CCE allocation in the preprocessor ; the scheduler was also simplified and made more modular
- Adaptative UL-HARQ
- Remove out-of-sync UEs
- No use of the first_rb in the UL scheduler ; respects vrb_map_UL and vrb_map in the DL
DCI generation
HARQ Support
RA procedures and RNTI management
RLC interface (AM, UM)
UL power control
Link adaptation
Connected DRX (CDRX) support for FDD LTE UE. Compatible with R13 from 3GPP. Support for Cat-M1 UE comming soon.

eNB RLC Layer

The RLC layer implements a full specification of the 3GPP 36.322 release v9.3.

RLC TM (mainly used for BCCH and CCCH)
- Neither segment nor concatenate RLC SDUs
- Do not include a RLC header in the RLC PDU
- Delivery of received RLC PDUs to upper layers
RLC UM (mainly used for DTCH)
- Segment or concatenate RLC SDUs according to the TB size selected by MAC
- Include a RLC header in the RLC PDU
- Duplication detection
- PDU reordering and reassembly
RLC AM, compatible with 9.3
- Segmentation, re-segmentation, concatenation, and reassembly
- Padding
- Data transfer to the user
- RLC PDU retransmission in support of error control and correction
- Generation of data/control PDUs

eNB PDCP Layer

The current PDCP layer is header compliant with 3GPP 36.323 Rel 10.1.0 and implements the following functions:

User and control data transfer
Sequence number management
RB association with PDCP entity
PDCP entity association with one or two RLC entities
Integrity check and encryption using the AES and Snow3G algorithms

eNB RRC Layer

The RRC layer is based on 3GPP 36.331 v15.6 and implements the following functions:

System Information broadcast (SIB 1, 2, 3, and 13)
- SIB1: Up to 6 PLMN IDs broadcast
RRC connection establishment
RRC connection reconfiguration (addition and removal of radio bearers, connection release)
RRC connection release
RRC connection re-establishment
Inter-frequency measurement collection and reporting (experimental)
eMBMS for multicast and broadcast (experimental)
Handover (experimental)
Paging (soon)
RRC inactivity timer (release of UE after a period of data inactivity)

eNB X2AP

The X2AP layer is based on 3GPP 36.423 v14.6.0 and implements the following functions:

X2 Setup Request
X2 Setup Response
X2 Setup Failure
Handover Request
Handover Request Acknowledge
UE Context Release
X2 timers (t_reloc_prep, tx2_reloc_overall)
Handover Cancel
X2-U interface implemented
EN-DC is implemented
X2AP : Handling of SgNB Addition Request / Addition Request Acknowledge / Reconfiguration Complete
RRC : Handling of RRC Connection Reconfiguration with 5G cell info, configuration of 5G-NR measurements
S1AP : Handling of E-RAB Modification Indication / Confirmation

eNB/MCE M2AP

The M2AP layer is based on 3GPP 36.443 v14.0.1:

M2 Setup Request
M2 Setup Response
M2 Setup Failure
M2 Scheduling Information
M2 Scheduling Information Response
M2 Session Start Request
M2 Session Start Response

MCE/MME M3AP

The M3AP layer is based on 3GPP 36.444 v14.0.1:

M3 Setup Request
M3 Setup Response
M3 Setup Failure
M3 Session Start Request
M3 Session Start Response

OpenAirInterface 4G LTE UE Feature Set

LTE UE PHY Layer