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Table of Contents

  1. Functional Split Architecture
  2. OpenAirInterface Block Diagram
  3. OpenAirInterface 4G-LTE eNB Feature Set
    1. eNB PHY Layer
    2. eNB MAC Layer
    3. eNB RLC Layer
    4. eNB PDCP Layer
    5. eNB RRC Layer
    6. eNB X2AP
    7. eNB/MCE M2AP
    8. MCE/MME M3AP
  4. OpenAirInterface 4G-LTE UE Feature Set
    1. LTE UE PHY Layer
    2. LTE UE MAC Layer
    3. LTE UE RLC Layer
    4. LTE UE PDCP Layer
    5. LTE UE RRC Layer
  5. OpenAirInterface 5G-NR gNB Feature Set
    1. General Parameters
    2. gNB Physical Layer
    3. gNB Higher Layers
  6. OpenAirInterface 5G-NR UE Feature Set
    1. UE Physical Layer
    2. UE Higher Layers

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

Functional Split Architecture

OpenAirInterface Block Diagram

Block Diagram

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

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)
  • Max number of antennas: 2
  • CQI/PMI reporting: aperiodic, feedback mode 3 - 0 and 3 - 1
  • PRACH preamble format 0
  • All downlink (DL) channels are supported: PSS, SSS, PBCH, PCFICH, PHICH, PDCCH, PDSCH, PMCH
  • All uplink (UL) channels are supported: PRACH, PUSCH, PUCCH (format 1/1a/1b), SRS, DRS
  • LTE MBMS-dedicated cell (feMBMS) procedures subset for LTE release 14 (experimental)
  • LTE non-MBSFN subframe (feMBMS) Carrier Adquistion Subframe-CAS procedures (PSS/SSS/PBCH/PDSH) (experimental)
  • LTE MBSFN MBSFN subframe channel (feMBMS): PMCH (CS@1.25KHz) (channel estimation for 25MHz bandwidth) (experimental)

LTE UE 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
  • HARQ Support
  • RA procedures and RNTI management
  • RLC interface (AM, UM)
  • UL power control
  • Link adaptation
  • MBMS-dedicated cell (feMBMS) RRC interface for BCCH
  • eMBMS and MBMS-dedicated cell (feMBMS) RRC interface for MCCH, MTCH

LTE UE RLC Layer

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

LTE UE PDCP Layer

The current PDCP layer is header compliant with 3GPP 36.323 Rel 10.1.0.

LTE UE RRC Layer

The RRC layer is based on 3GPP 36.331 v14.3.0 and implements the following functions:

  • System Information decoding
  • RRC connection establishment
  • MBMS-dedicated cell (feMBMS) SI-MBMS/SIB1-MBMS management

LTE UE NAS Layer

The NAS layer is based on 3GPP 24.301 and implements the following functions:

  • EMM attach/detach, authentication, tracking area update, and more
  • ESM default/dedicated bearer, PDN connectivity, and more

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
  • 30 kHz subcarrier spacing
  • Bandwidths: 10, 20, 40, 80, 100MHz (273 Physical Resource Blocks)
  • Intermediate downlink and uplink frequencies to interface with IF equipment
  • Single antenna port (single beam)
  • 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)

gNB PHY Layer

  • 30KHz SCS for FR1 and 120 KHz 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)
  • 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 1 RX antenna
    • Support for 1 layer
  • NR-PUCCH
    • Format 0 (2 bits, for ACK/NACK and SR)
    • Format 2 (up to 11 bits, mainly for CSI feedback)
  • 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 Higher Layers

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 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 allocation
    • HARQ procedures for uplink
  • MAC procedures to handle CSI measurement report
    • evalution of RSRP report
    • evaluation of CQI report
  • MAC scheduling of SR reception

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 RRC

  • NR RRC (38.331) Rel 16 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
    • Support for master cell group configuration
    • Interface with NGAP for the interactions with the AMF
    • Interface with F1AP for CU/DU split deployment option

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
    • F1 DL/UL RRC message transfer
    • F1 Initial UL RRC message transfer
    • F1 UE Context setup request/response
    • F1 gNB CU configuration update
  • Interface with RRC
  • Interface with gtp-u (tunnel creation/handling for F1-U interface)

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)

OpenAirInterface 5G-NR UE Feature Set

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

NR UE PHY Layer

  • Initial synchronization
  • Time tracking based on PBCH DMRS
  • Frequency offset estimation
  • 30KHz SCS for FR1 and 120 KHz SCS for FR2
  • Reception of NR-PSS/NR-SSS
  • NR-PBCH supports multiple SSBs and flexible periodicity
  • 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 1, 2 and 4 RX antennas
    • Support for up to 2 layers (currently limited to DMRS configuration type 2)
  • 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 1 TX antenna
    • Support for 1 layer
  • NR-PUCCH
    • Format 0 (2 bits for ACK/NACK and SR)
    • Format 2 (up to 64 bits, mainly for CSI feedback)
    • Format 1, 3 and 4 present but old code never dested (need restructuring before verification)
  • NR-PRACH
    • Formats 0,1,2,3, A1-A3, B1-B3
  • NR-SRS
    • Old code never dested (need restructuring before verification)
  • SS-RSRP
    • RSRP measured on synchronization SSB (ok only for single SSB)
  • 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 (SSB RSRP only)
  • DLSH scheduler
    • Configuration of fapi PDU according to DCI
    • HARQ procedures
  • ULSCH scheduler
    • Configuration of fapi PDU according to DCI

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 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
  • 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

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