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Transcript of ORAN Saidhiraj Amuru CeWit 5G KS · P } Ç Z ] } h v ] P } Ç Z ] } h v ] h^ rW o v t^ o ] W } ] v...
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5G NR gNB ArchitectureAn Open-RAN (ORAN) Perspective
Saidhiraj Amuru
Overview
• Evolution of RAN architectures
• O-RAN Architecture
• O-RAN functional splits
• O-RAN FrontHaul Interface
• O-RAN Transport Protocol
• O-RAN C-Plane and U-Plane Protocol
• O-RAN Delay Management(S-Plane)
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Traditional RAN Architecture
Everything is co-located
RRH: Remote Radio Head (RF + Antennas)BBU: Baseband Unit (Modem)CORE: Core Network
Centralized RAN Architecture
Remote Base Band Unit -typically proprietary closed platform
FrontHaul – CPRI/OBSAI/ORI
CPRI: Common Public Radio Interface, • a protocol for IQ data transmission between Radio Equipment (RE i.e., RRH) and Radio Equipment Controller (REC i.e., BBU) • via optical fibre • Wastage of resources (constant CPRI data streams are exchanged even when no traffic is present)• Fixed RRH-BBU mapping not good for virtualized BBU architecture• Highly inefficient – scales with number of antennas, not data rate i.e. 150Mbps data = ~2.5Gbps CPRI traffic • Requires very low latency – 200µs Optical transport; • RAN vendor proprietary format
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Cloud RAN Architecture
FrontHaul – CPRI/eCPRI/ IEEE 1914.3 RoEHighly efficient – 10x improvement over CPRITypically transported over Ethernet BBU: virtualization based; on-demand; centralized and coordinated
eCPRI: enhanced Common Public Radio Interface, • Advanced version of CPRI• Ethernet based IP packet flows; only when traffic is present (not point-to-point like CPRI)• BBU can be running on COTS platforms• Difficult to synchronize RRH and BBU due to bursty traffic
Cloud RAN – Supports More Splits
A CU may support multiple DUs and A DU may support multiple RUs.
Further disaggregate BBU into real-time and non-real-time functions into DU & CU
Move away from vendor lock-in, Reach out to open IP/Ethernet based technologies
RU: Radio UnitDU: Distributed/Data UnitCU: Control/ Centralized Unit
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Where to split CU-DU and DU-RU?
MidHaul – Option 2FrontHaul – Option 7 and 8
• Transport time/frequency domain IQ samples over FH • Scales with number of antennas/ streams (MIMO layers)• Variable data rates and variable latencies supported
Split between PDCP and RLC
BW requirement increases
Low latency requirements
Where to split CU-DU and DU-RU?
Options Option 6 Option 7.3 Option 7.2 Option 7.1 Option 8
Data Rates 100 Mbps 300 Mbps 300Mbps *(2*16)*P/8 1.2 Gbps* P*nTxRU 1.2 Gbps*P*nTxRu *nTx
Assumptions:• 100 Mbps MAC to PHY Data rate• 1/3 Coding Rate• 256 QAM Modulation Order (16 bits per I and Q)• P = Number of Antenna Ports• nTxRU = Number of RF chains• nTX = Number of transmission Antennas
NR perspective:
Option 7.2=> 3300*(2*16)*8 (layers)*13 (OFDM)/0.5 ms ~ 20 GbpsOption 8 => 61440 Msps*32*64/0.5 ms ~ 250 Gbps
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Enter X-RAN and O-RAN
• xRAN/O-RAN’s background• Started in June 2016 as xRAN Forum and later merged with C-RAN Alliance to form ORAN alliance in February 2018 • Operator driven: AT&T, China Mobile, Deutsche Telekom, NTT DOCOMO and Orange• Driven by openness and intelligence
• ORAN is not just open source software• Defines a white-box architecture• Open APIs• Open Architectures• Open Hardware• Open Interfaces
• Advantages• Multi-vendor deployment• Increases scalability• Decreases CAPEX & OPEX• Endless innovations
• Disadvantages• More effort in testing systems integration of multi-vendor systems
O-RAN Vision
• Two fold functional split• Horizontal split
• Splits radio protocol stack – various options• Vertical split
• Separates CP & UP functions
• Interfaces• Open FH between O-DU and O-RU• F1 between O-DU and O-CU• E1 between CU-CP and CU-UP• E2 between RIC RT and CU/DU• A1 between NMS and RIC RT
• RAN Intelligent Controller (RT-RIC)• RRM, mobility real time operations• Uses a machine learning model trained in the
non real time RIC
Figure courtesy: O-RAN Forum
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ORAN Standardization
• Operator Working Group• Technical Steering Committee• Working Groups
• WG1 - Use Cases and Overall Architecture Workgroup• WG2 - Non-real-time RIC and A1 Interface Workgroup• WG3 - Near-Real-time RIC and E2 Interface Workgroup• WG4 - Open Fronthaul Interfaces Workgroup• WG5 - Open F1/W1/E1/X2/Xn Interface Workgroup• WG6 - Cloudification and Orchestration Workgroup• WG7 - White-box Hardware Workgroup• WG8 - Stack Reference Design Workgroup
• Focus Groups• OSFG - Open Source Focus Group• SDFG - Standard Development Focus Group• TIFG - Test & Integration Focus Group
• O-RAN Software Community
O-RAN Split Architecture
• O-RAN has selected a single split point, known as “7-2x” but allows a small variation.
End-to-End Latency Very strictRelaxed
FH Capacity RequirementLow Very high
F1 eCPRI
236 GbpsFew Gbps
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O-RAN FrontHaul Interface
Traffic is classified into two types: CUS-Plane and M-Plane
CUS Plane: Control / User / Synchronization Plane• Covers real-time control-plane communications between the DU and RU
• Covers user plane traffic in DL and UL between DU and RU
• Covers synchronization of the RU generally sources from the DU
• Uses Ethernet transport and eCPRI/IEEE 1914.3 radio application transport
M-Plane: Management Plane• Covers management of the Radio Unit (RU) as governed by the DU
• Provides all non-real-time control of the RU (Real time control uses the C-Plane)
• Uses Ethernet(UDP/IP) transport
CUS-Plane – Category A and Category B RUs
Two types of RU are considered
Category A:• Precoding function is in DU allowing the RU
design to be simple
• The FH interface will carry spatial streams in the DL which can be larger than layers
Category B:• Precoding is in RU which makes RU design
complex
• The FH interface will carry spatial layers which can be less data
• This category allows modulation compression which reduces the DL throughput much more
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CUS-Plane – Split Point 7-2x in DL for NR
Category A Radio Unit Category B Radio Unit
CUS-Plane – Split Point 7-2x in UL for NR
• Unlike in the DL case, the RU category makes no difference in UL
• FFT, CP removal and filtering in the O-RU
• Rest of all the PHY functions in the O-DU
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CUS-Plane – Encapsulation
Ethernet is the selected transport, and all radio application data is conveyed within the Ethernet Payload.
The radio transport header is used to convey some radio-specific transport information, while the radio transport payload carries the C-Plane & U-Plane information.
Destination MACAddress(6 Bytes)
Source MACAddress(6 Bytes)
Type/Length(Ethertype)(2 Bytes)
Payload(42…1500 Bytes)
FCS(4 Bytes)
VLAN Tag(4 Bytes)
Preamble(8 Bytes)
IFG(12 Bytes)
Native Ethernet frame with VLAN
all radio transport & application data
Radio transport Payload(up to 1444 bytes,
or longer for jumbo Ethernet frames)
Radio transportheader
(8 bytes)
Source: O-RAN FrontHaul Working Group: CUS Plane Specification
CUS-Plane – Radio Transport Header
• There are two possible radio transport mechanisms, eCPRI (mandatory) and IEEE 1914.3 RoE (optional).
• For ease of implementation, these are aligned as closely as possible to make implementing both as easy as possible.
• Both use 8-byte headers with the exact same information content and format in 6 of the 8 bytes; only the first two bytes differ
all section types
0 (msb) 1 2 3 4 5 6 7 (lsb) # of bytes
ecpriVersion ecpriReserved ecpriConcatenation
1 Octet 1
ecpriMessage 1 Octet 2
ecpriPayload 2 Octet 3Octet 4
ecpriRtcid 2 Octet 5Octet 6
ecpriSeqid 2 Octet 7Octet 8
dataDirection payloadVersion filterIndex 1 Octet 9
frameId 1 Octet 10
subframeId slotId 1 Octet 11
slotId startSymbolid 1 Octet 12
Octet M
all section types
0 (msb) 1 2 3 4 5 6 7 (lsb) # of bytes
subType 1 Octet 1
flowID (currently unused) 1 Octet 2
Length 2 Octet 3Octet 4
orderinfo 2 Octet 5Octet 6Octet 7Octet 8
dataDirection payloadVersion filterIndex 1 Octet 9
frameId 1 Octet 10
subframeId slotId 1 Octet 11
slotId startSymbolid 1 Octet 12
Octet M
eCPRI IEEE-1914.3
Source: O-RAN FrontHaul Working Group: CUS Plane Specification
Transport Header Radio Application Header
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C-Plane Specification – Section Types
• eCPRI message type-2 maps to C-plane message in ORAN
• In general there are “data sections” which identify which symbols / portions of symbols (e.g. PRBs) are addressed.
• C-Plane:• sectionType=0 : DL idle/guard periods - allows Tx blanking for power savings• sectionType=1 : DL/UL Channels - provides mapping of beamforming index or weights to REs• sectionType=3 : PRACH and mixed-numerology channels• sectionType=5 : UE scheduling Info - provides UE co-scheduling info allowing real-time BF weight calculation on the
RU• sectionType=6 : UE channel info - provides UE channel info to guide real-time BF weight calculation on the RU• sectionType=7 : LAA Support – provides information specific to LAA especially listen-before-talk operation
Example: C-Plane Section Type 0
Values specific to idle/guard periodstimeOffset = number of samples from start of slot to start of CPframeStructure = 4 bits for FFT size, 4 bits for subcarrier spacingcpLength = cyclic prefix length, based on sample rate and m
Control information here describes empty-data PRBs allowing the RU to blank transmissions for energy-savings;
Section Type 0 : idle / guard periods0
(msb)1 2 3 4 5 6 7
(lsb)# of bytes
transport header 8 Octet 1dataDirection
payloadVersion filterIndex 1 Octet 9
frameId 1 Octet 10subframeId slotId 1 Octet 11
slotId startSymbolid 1 Octet 12numberOfsections 1 Octet 13
sectionType 1 Octet 14timeOffset 2 Octet 15
frameStructure 1 Octet 17cpLength 2 Octet 18reserved 1 Octet 20sectionId 1 Octet 21
sectionId rb symInc startPrbc 1 Octet 22startPrbc 1 Octet 23numPrbc 1 Octet 24reMask 1 Octet 25
reMask numSymbol 1 Octet 26reserved (16-bits) 2 Octet 27
…sectionId = P 1 Octet N
sectionId rb symInc startPrbc 1 N+1startPrbc 1 N+2numPrbc 1 N+3reMask 1 N+4
reMask numSymbol 1 N+5reserved (16-bits) 2 N+6
Octet M
Transport Header Radio Application Header Section Header #1 Section Header #n. . .
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Example: C-Plane Section Type 1
Common radio application header:Similar for all C-Plane messages
Repeated data sections as needed
transport header: eCPRI or IEEE-1914.3dataDirection: 0=UL, 1=DL
filterIndex points to channel filter in RU, usually 0x1frameId points to specific 10ms frame
SubframeId : points to specific 1ms subframe within a frameslotId : points to specific slot within a frame
numberOfsections : number of sections in this messageSectionType : msg applies to 1=DL, 2=UL radio channels
(only one sectionType per C-Plane message)
udCompHdr : states IQ bit width and compression method forchannel IQ data for all sections in this message
Upper 4 bits: iqWidth (range 1-16 bits)Lower 4 bits : compMeth compression method
section extension may be present based on “ef” valueSectionID : value allows matching of C and U plane msgs
rb : 0=use every PRB, 1=use every other PRBStartPrbc : first PRB this section applies to
numPrbc : number of PRBs this section applies toreMask : states population of REs in the PRB
numSymbol : number of symbols this section applies towf : 0 = no weights provided, 1 = weights follow the beamIdbeamId : index into predefined weight table for this section
section extension may be present based on “ef” value
Section Type 1 : DL/UL control msgs0
(msb)1 2 3 4 5 6 7
(lsb)# of bytes
transport header 8 Octet 1dataDirection
payloadVersion filterIndex 1 Octet 9
frameId 1 Octet 10subframeId slotId 1 Octet 11
slotId startSymbolid 1 Octet 12numberOfsections 1 Octet 13
sectionType 1 Octet 14udCompHdr 1 Octet 15
reserved 1 Octet 16sectionId 1 Octet 17
sectionId rb symInc startPrbc 1 Octet 18startPrbc 1 Octet 19numPrbc 1 Octet 20reMask 1 Octet 21
reMask numSymbol 1 Octet 22ef beamId 1 Octet 23
beamId 1 Octet 24<section extensions if any> 0-var
…sectionId = P 1 Octet N
sectionId rb symInc startPrbc 1 N+1startPrbc 1 N+2numPrbc 1 N+3reMask 1 N+4
reMask numSymbol 1 N+5ef beamId 1 N+6
beamId 1 N+7<section extensions if any> 0-var N+8
beamID value 0x0000 reserved specifically for “no beamforming”. This is primarily for SRS but could be used more generally too..
0 (msb) 1 2 3 4 5 6 7 (lsb)iqWidth compMeth
range: 1-16 bits0 = 16 bits1= 1 bit…15 = 15 bits
0 = no compression1 = block floating point2 = block scaling3 = m-law compression4 = modulation compression5-15 = reserved
udCompHdr
Transport Header Radio Application Header Section Header #1 Section Header #n. . .
U-Plane Data
• The U-Plane is used to send actual IQ data as arranged in spatial streams or layers, already mapped into the resource elements
• Data is transported in compressed format if compression is enabled
• Data is transmitted symbol by symbol as U-Plane messages.
• There is no sectionType, reMaskor numberOfsections parameter for U-Plane messages;
• the sectionType and reMaskvalues are inferred from the matching C-Plane SectionId.
U-Plane Format – All Section Types0 (msb) 1 2 3 4 5 6 7 (lsb) # of
bytestransport header 8 Octet 1
datDirection
payloadVersion filterIndex 1 Octet 9
frameId 1 Octet 10subframeId slotId 2 Octet 11
slotId symbolId Octet 12sectionId 1 Octet 13
sectionId rb symInc startPrbu 1 Octet 14startPrbu 1 Octet 15numPrbu 1 Octet 16
compParam 1 Octet 17iSample (1st sample) 1 Octet 18qSample (1st sample) 1 Octet 19
…iSample (12th sample) 1 Octet 40
qSample (12th sample) + padding when needed 1 Octet 41compParam 1 Octet 42
iSample (1st sample) 1 Octet 43qSample (1st sample) 1 Octet 44
…iSample (12th sample) 1 Octet 65
qSample (12th sample) + padding when needed 1 Octet 66…
sectionId = P 1 Octet OsectionId=P rb symInc startPrbu 1 O+1
startPrbu 1 O+2numPrbu 1 O+3
compParam 1 O+5iSample (1st sample) 1 O+6qSample (1st sample) 1 O+7
…
Common radio application header:Same for all U-Plane messages
SectionID : value allows matching of C and U plane msgsrb : 0=use every PRB, 1=use every other PRB
StartPrbu : first PRB this section applies tonumPrbu : number of PRBs this section applies to
compParam* : compression parameter for following IQ samplesiSample, qSample : variable-length samples for I & Q data
(shown here, I or Q bit width = 8 bits)
Each PRB (12 REs) gets a new compression parameterNote each new compParam is always on a byte boundary regardless of
IQ sample size but for some compression methods the compParamvalue is not needed so the field is omitted
Octet count assumes 8-bit I and Q samples
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Subcarriers
CRS
CSI-RS
User data
symbols
Use of data sections in PRBs (LTE example)
0 1 2 3 4 5 6 7 8 9 10 11 12 13
11
10
9
8
7
6
5
4
3
2
1
0
SSS data
PSS data
PBCH data
zero data
UE#1 data
UE#2 data
SSS/PSS and PBCH shown although will not be in all PRBs. It is assumed those symbols will use the same broadcast beam so can share the same data section. UE#1 data is shown in two PRBs (would typically be more) and UE#2 data in one PRB. Punctured CRS and CSI-RS REs are shown though some of those REs will be zero.
Source: X-RAN FrontHaul Tutorial
Use of data sections in PRBs (LTE example)
UE#1 data
UE#2 data
1 2 3 4 5 6 7 8 9
1 A B C D E F G H
Seventeen sections needed to specify these PRBs:sectionId 1: reMask = 1111 1111 1111 (broadcast beam for SSS, PSS, PBCH)sectionId 2: reMask = 1011 1111 1111 (UE#1 REs, all REs are user data)sectionId 3: reMask = 0110 1101 1011 (UE#1 REs, numbered from bottom)sectionId 3: reMask = 1001 0010 0100 (CRS REs, complementary reMask) sectionId 4: reMask = 1111 1111 1111 (UE#1 REs)sectionId 5: reMask = 0110 1101 1011 (UE#1 REs, numbered from bottom)sectionId 5: reMask = 1001 0010 0100 (CRS REs, complementary reMask) sectionId 6: reMask = 1111 1111 1111 (UE#1 REs)sectionId 7: reMask = 1111 1100 0011 (UE#1 REs)sectionId 7: reMask = 0000 0011 1100 (CSI-RS REs)sectionId 8: reMask = 0110 1101 1011 (UE#1 REs, numbered from bottom)sectionId 8: reMask = 1001 0010 0100 (CRS REs, complementary reMask) sectionId 9: reMask = 1111 1111 1111 (UE#1 REs)sectionId A: reMask = 1011 1111 1111 (UR#2 all REs are user data)sectionId B: reMask = 0110 1101 1011 (UE#2 REs, numbered from bottom)sectionId B: reMask = 1001 0010 0100 (CRS REs, complementary reMask) sectionId C: reMask = 0000 1111 1111 (UE#2 REs)SectionId C: reMask = 1111 0000 0000 (CSI-RS REs)sectionId D: reMask = 1111 1111 1111 (UE#2 REs)sectionId E: reMask = 0110 1101 1011 (UE#2 REs, numbered from bottom)sectionId E: reMask = 1001 0010 0100 (CRS REs, complementary reMask) sectionId F: reMask = 1111 1100 0011 (UE#2 REs)sectionId G: reMask = 0110 1101 1011 (UE#2 REs, numbered from bottom)sectionId G: reMask = 1001 0010 0100 (CRS REs, complementary reMask) sectionId H: reMask = 1111 1111 1111 (UE#2 REs)
Source: X-RAN FrontHaul Tutorial
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U-Plane Data: Compression
• The data rates increase linearly with spatial streams (or layers) in split option 7.2x.
• Various compression methods are currently supported.• No Compression, Block Floating Point, Block Scaling, μ -law compression, Modulation Compression
• The block compression methods are performed on Physical Resource Block (PRB = 12 subcarriers) basis
• Example:• 16 bits I and Q• 9 bits mantissa – includes 1 sign bit• 8 bits exponent (4 for I and 4 for Q)
• Without BFP compression• 1 PRB = 12 (Subcarriers) * 16 (bits) * 2 (I and Q) = 384 bits
• With BFP compression• 1 PRB = 12 (Subcarriers) * 9 (bits) * 2 (I and Q) + 8 (exponent) = 224 bits
• Compression Ratio = 0.5833
#1 #2 #3 #4 #12
384 bits
#1 #2 #3 #4 #12 Exp
224 bits
C/U-Plane – message timing
• In general, C-Plane messages precede U-Plane messages, and a single C-Plane message may cover multiple U-Plane messages.
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IQ Data Transfer Procedure
Delay Management (S-plane)
• The transmission windows and reception windows are determined based on:• The processing time• Receiver buffer lengths• Transport network delay variation
• In Downlink, the DU has to send data early enough to ensure the corresponding symbol time and also that it does not send data too early, risking overflow of the RU buffers
• In Uplink, the data must be received early enough to ensure the DU can process the data in time to meet HARQ loop restrictions.
• Not all U-Plane data is delay managed.
• Non-Delay managed traffic such as SRS data are sent on “best-effort” basis.
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Delay Management: DL
Source: O-RAN FrontHaul Working Group: CUS Plane Specification
ORAN Advantages and Summary
• Interface simplicity: Transfer of user plane data is based on Resource Elements / Physical Resource Blocks, which reduces complexity
• Transport Bandwidth Scalability: • Lower split options (e.g., splits 7-1 and 8) scale based on number of antennas. • In contrast, 7-2x interface scales based on “streams”, which allows using high number of antennas
without higher transport bandwidth. • User data transfer can be optimized to send only PRBs that contain user data for purpose of reducing
transport bandwidth (DMRS etc generated in RU)
• Less user specific parameters are used at split 7-2x (when compared to higher split options) -> simplified design
• Moves away from single-vendor design lock-in for operators
• Several new companies can contribute to individual portions of the entire design• Better enhanced start-up community
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Back Up Slides
U-Plane Data: Modulation Compression
• To represent the constellation points as I and Q values that also overlap allowing multiple constellation sizes to be represented by a single word-width, the constellations are “shifted” to allow a twos-complement I and Q value to represent any constellation point.
• For Decompression, un-shift the constellation and multiply with a scale factor based on modulation order
• Applicable only to DL
• Data rates almost same as split option 7.3
• Completely lossless compression
X X X X X X X X
X X X X X X X X
X X X X X X X X
X X X X X X X X
X X X X X X X X
X X X X X X X X
X X X X X X X X
X X X X X X X X
BPSK (normal, p/ 4, p/ 2)encodes 1 user bit
X X X X
X X X X
-3/4 -1/4 1/4 3/4
X X X X
X X X X
X X
-1/2 1/2
X X
I is represented by 2 bitQ is represented by 2 bits(-1/ 2, 0, and 1/ 2 are needed)
modulat ion-compression:from 32 bit s (16I and 16Q)to 4 bit s (2I and 2Q)
I is represented by 1 bitQ is represented by 1 bit
modulat ion-compression:from 32 bit s (16I and 16Q)to 2 bit s (1I and 1Q)
I is represented by 2 bitsQ is represented by 2 bits
modulat ion-compression:from 32 bits (16I and 16Q)to 4 bit s (2I and 2Q)
I is represented by 3 bitsQ is represented by 3 bits
modulat ion-compression:from 32 bit s (16I and 16Q)to 6 bit s (3I and 3Q)
QPSKencodes 2 user bits
16 -QAMencodes 4 user bits
64-QAMencodes 6 user bits
X X-1/2 1/2
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U-Plane Data: Modulation Compression
Assumptions: 64 TRX, Max Qm = 256 QAM, 100 MHz, 16 Spatial streams
• W/O modulation compression using block compression methods• 1 PRB = 12 x 2 x 8 bits mantissa + 8-bits exponent = 200 bits• DL data rate: 14 (symbols) x 273 (PRBs) x 200 x 16 (spatial streams) / 0.5 ms = 24.46 Gbps
• W/ modulation compression:• 1 PRB = 12 x 8 bits = 96 bits• DL data rate: 14 (symbols) x 273 (PRBs) x 96 x 16 (spatial streams) / 0.5 ms = 11.74 Gbps
FH: eCPRI data rates
• Throughput: 3/1.5 Gbps (downlink/uplink, end-user data rate, transport block from/to MAC)
• Air bandwidth: 100 MHz (5 * LTE20) -> 500 PRB
• Number of downlink MIMO-layers: 8 Number of uplink MIMO-layers: 4 (with 2 diversity streams per uplink MIMO layer)
• MU-MIMO: No
• TTI length: 1 ms
• Digital beamforming where BF-coefficients calculation is performed in O-DU
• Rate matching assumptions: Code rate: ~0.80
• Modulation scheme (Downlink & Uplink): 256 QAM
• Number of antennas: 64
• Sub-carrier spacing: 15 kHz
• IQ sampling frequency: 122.88 Msps (3.84*32)
• IQ-format: 30 bits per IQ-sample
• No IQ compression
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eCPRI
• Open protocol for fronthaul
• Allows data transfer over packet based network: IP or ethernet
• Allows various split options option 7.1, 7.2, 8 etc• CPRI does only Option 8
• Analog IQ has high BW requirement for 5G and hence CPRI breaks• eCPRI based on split has data rate requirements ranging from 10G to 200G (Option 8)
• eCPRI has C-plane, M-Plane, U-Plane, S-Plane• Control and management plane manage DU and RU -> Operation, maintenance, not time critical• U-plane carries 5G NR control channels, data channels• S-plane is for synch between DU and RU, frame and time alignment
• eCPRI allows different message types• 256 message types
• Packing of messages, forming of messages is where ORAN comes into picture
Functional Decomposition (eCPRI)
• Intra Phy splits ID, IID Iv
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Functional Splits – 7.X
Delay Management: Model
Model uses reference points from CPRI delay model• Downlink: R1 – DU transmit port
R2 – RU receive portT12 – Transmission time
• Uplink: R3 – RU transmit port; R4 – DU receive port;T34 – Transmission time
• Transport Variation in network (T12max – T12min)All transmit/ receive times relative to antenna (“Ra”)
• Model defines transmission/ reception in terms of symbol time over the air• T1a – Transmit time from DU relative to transmission over the air • T2a – Receive time at RU relative to transmission over the air• Ta3 – Transmit time from RU relative to reception over the air• Ta4 – Receive time at RU relative to reception over the air
• Since transmission time (T12/ T34) varies, T2a/ Ta4 MUST vary• Receive window at: RU (T2a_max – T2a_min); DU (Ta4max – Ta4min)• Transmission Window: Earliest/ latest transmit time to ensure reception in corresponding (DL/ UL) reception window
Reception Window Transmission Window Transport Variation
Downlink T2amax – T2amin T1amax – T1amin T12max – T12min
Uplink Ta4max – Ta4min Ta3max – Ta3min T34max – T34min