5G Fronthaul Technologies (Especially, this document specifies the e-CPRI technology, because many telcos are now considering the eCPRI for the next fronthaul.)

1. 5G Fronthaul Technologies
2018
Kwang-koog Lee (Ph.D)
(kwangkoog.lee@kt.com)

2. Intro

3. 5 Years ago
출처: https://www.techquark.com

4. Yearly 22% ↑
출처: ETRI, 국내 모바일 트래픽 현황 및 전망 (18.1)

5. 5G is coming

6. On the road to 5G in Korea

7. 5G Deployment Plan
• 과학기술정보통신부 5G 구축 계획
• 3.5GHz
- 현 LTE와 동수준의 15만국 설정 (스몰셀, 중계기 포함)
- 3년 내 2만2500국(15%), 5년 내 4만5000국(30%) 의무구축
• 28GHz
- 스몰셀과 중계기를 포함해 10만국(대)
- 3년 내 1만5000국(대, 15%)를 의무 구축

8. 5G Features
출처: HSN2018 5G 네트워크 시범망 구축 (KT발표)

9. 5G Infra Requirements

10. 4G vs 5G Bandwidth
Radio frame / Technology LTE 5G
Subcarrier spacing (KHz) 15 75
Basic time unit Ts 1 / (15000 x 2048) seconds 1 / (75000 x 2048) seconds
Slot Tslot
TTI
15360 x Ts = 0.5 ms
1 ms
15360 x Ts = 0.1 ms
0.2 ms
Radio frame duration Tf
(150 x 2048) x Ts = 307200 x Ts = 10 m
s
(750 x 2048) x Ts = 1536000 x Ts = 10
ms
Maximum serving cells (CA) 5 8
Maximum aggregated bandwidth 5 x 20 = 100 MHz 8 x 100 = 800 MHz
Formula Maximum symbols / second NDL
symb . NRB
sc . NDL
RB . slots/frame . frames/sec . nb carriers
Maximum symbols / second 7 x 12 x 100 x 20 x 100 x 5 = 84M 7 x 12 x 100 x 100 x 100 x 8 = 672M
Maximum theorical throughput
MIMO 2 layers, 64 QAM (8 bits/symbol)
84M x 2 x 6
1.01 Gbits/s
672M x 2 x 6
8.06 Gbits/s

11. Ultra Reliable & Low Latency
출처: 에릭슨-LG URLLC 자료 발췌 (Dr. Janne Peisa)

12. Insight
• Giga-level Internet experience on mobile
• All-in-one infrastructure supporting numerous
services
• Starting point of the legacy infra. governance
All the business sectors may be integrated in 5G

13. Issue

14. C-RAN in LTE
Cell Site RUs
(hundreds of thousands sites)
e.g. 200,000
DU Pools
(hundreds of sites)
e.g. 300
SGW PGW
EPC
(several sites)
e.g. 2
Fronthaul (<25km) Backhaul
IP/MPLS
WDM
(option)
w/ Transport
(e.g. ROADM)
CPRI Option2 (1.25G)
CPRI Option3 (2.5G)
CPRI Option7 (9.8G)
• Domestic providers use C-RAN structure for serving LTE
- the central coordination is cost-effective and the management is easy
CPRI
CPRI
CPRI
CPRI
CPRI
CPRI
Eth EthEth Eth

15. C-RAN Issue
• 10MHz LTE or 20MHz LTE is using CPRI interface (16x more)
• If used in 5G, holistic CPRI bandwidth is necessary (100G CPRI?)
출처: 넷매니아즈 Tech-Blog (https://netmanias.com/ko/?m=view&id=blog&no=6241)

16. How Much CPRI BW?
출처: 정환석(ETRI), 모바일 네트워크를 위한 저지연 유무선 광액세스 기술 (KRNET 2018.6.25)

17. Architecture Evolution from 4G to 5G
• Main change is that the original BBU function is split into three parts
- RRU (Remote Radio Unit), DU (Distributed Unit), CU (Central Unit)
- Allows for decreased fronthaul line rates while meeting latency demands
- Parts of UP are moved to EPC to CU and DU
- Non-real-time (NRT) function from BBU to CU
- Real-time (RT) function from BBU to DU
- Two new created interfaces are referred to as
the high layer split point (Fronthaul II) and the
low layer split point (Fronthaul I)
출처: ITU-T GSTR-TN5G Technical Report – Transport Network Support of 5G (2018.2)

18. Function Split in Fronthaul Link
The choice of optimal
5G NR split points
depends on specific
deployment scenarios
Small Cell Forum has
extended its specification
for the Functional API
(FAPI) multi-vendor
platform interface, which
has led to accelerated
deployments of small
cells,
출처: ITU-T GSTR-TN5G Technical Report – Transport Network Support of 5G (2018.2)

19. Start of Packet-based Fronthaul Era.
• NGFI/eCPRI interfaces are implemented on packet-
based technologies (Ethernet, IP)
- eCPRI group has focused its work on intra-PHY splits with data
transport over packet (Ethernet or IP) networks
- NGFI (Radio over Ethernet) provides standard fronthaul interfaces such as
native RoE, CPRI-aware/agnostic over Ethernet networks

20. eCPRI Fronthaul Example
• Split user payloads are encapsulated into eCPRI frame over Ethernet
Cell Site AUs
(Legacy or New Sites)
DUs
(Legacy LTE DU sites)
NGC
Mobile Core Cloud
(MCC)
Fronthaul (<20km) Backhaul
IP/
MPLS
TSN, OTN,
WDM
w/ Transport
(e.g. ROADM,
POTN)
CUs & NGC
Mobile Edge Cloud
(MEC)
MidHaul
Eth
EthEthIP or
전송
Eth
Eth
Eth
Eth
(optional) (optional)
(vUPF, vSMF, vPCF,
vAMF, … )
PHY-L PHY-H
PDCP
RRC
eCPRI eCPRI
vOS
H/W Box
ETH ETHDA SA Type Len eCPRI FCS
Ethernet Frame (Type: 0xAEFE)
NGC ComponentsRF
S/W
MAC
RLC
H/W Box

21. Tech.

22. eCPRI Introduction
• eCPRI is packet (Ethernet) based fronthaul interface connecting
eREC (eCPRI Radio Equipment Control) and eRE (eCPRI Radio
Element)
• Developed by CPRI forum (Ericsson, Huawei, Nokia, NEC)

23. Functional Decomposition
• Flexible radio base station system architecture
- eREC contains part of the PHY layer functions and higher layer
functions whereas eRE contains the other part of PHY layer
functions and the analog frequency functions

24. Choice of Function Split
• The functional split depends on
vendor specific choices
• Different implementations target
different objectives (radio or
fronthaul performance)
Bit rate estimation (100MHz, 4x4 MIMO, 256QAM, 1ms TTI)
Bit
oriented
Data
oriented
IQ
oriented

25. eCPRI Protocol Stack
EtherType (AEFE16)
Min Size 46 octets

26. eCPRI Message Format
• Four byte eCPRI common
header followed by a
variable length eCPRI
payload

27. Common Header Format
• “Protocol Revision” indicates the protocol version # (v1.0 → 000b)
• “Message Type” indicates the type of conveyed service
• “C” is eCPRI message concatenation indicator
• “Payload Size” is the size in bytes of the payload part (limited by the
maximum payload size of the underlying transport network)

28. Mapped to Transport Network
Example in which one
eCPRI message is mapped
onto a transport network
payload
Example in which two
eCPRI message are
concatenated and mapped
onto a transport network
payload

29. Message Types

30. Message Type #0: IQ Data
ID of a physical channel, a user,
a layer, an antenna port
ID of an OFDM symbol, a block
of sub-carriers
A sequence of IQ sample pairs

31. Message Type #1: Bit Sequence
ID of a physical channel, a user,
a layer, an antenna port
ID of an OFDM symbol, a block
of sub-carriers
A bit sequence of user data
(channel coded data before
modulation mapping)

32. Message Type #2: Real-Time Control Data
Vendor-specific real-time control message (various
types of control information associated with user
data (in form of IQ samples, bit sequence)
ID for message structure of specific
control/config/status/measurement
(request/response/indication)

33. Message Type #3: Generic Data Transfer
Used to transfer user plane data or related
control providing extended data sync support

34. Message Type #4: Remote Memory Access
Allows reading or writing from/to
a specific memory address on the
opposite eCPRI node
(e.g h/w driver updates)
A read/write request/response
sequence is an atomic procedure
ID used by the
Initiator of the request
A specific instance of
a generic h/w function

35. Message Type #5: One-way Delay Measurement
Without Follow_up With Follow_up
Seconds and nano-
Seconds parts
Measured by ns

36. Message Type #6: Remote Reset
A “Remote Request” request sent by an eREC
triggers a reset of an eRE
Authentication or any parameters
to select a specific reset behavior

37. Message Type #7: Event Indication
Used when an event is either a raised or
ceased fault or a notification. An eCPRI node is
modelled as consisting of N elements

38. Synchronization and Timing
• An eCPRI node shall recover the frequency and
time/phase from its synchronization reference source
• eRE shall fulfill requirements
set by 3GPP
• In case of eREC,
requirements value depends
on vendor specific choices

39. Link Delay Management
• The goal of delay management is to avoid the
overflow/underflow of buffer memories and to
decrease the overall delay, the necessary size of buffer
memories Transport
network delay
The variation
of processing
time
The variation
of processing
time

40. Link Delay Management Example

41. Networking
• There is no longer a master port/slave classification at
physical level

42. Deploy

43. Deployment Scenarios - Initial
Eth
CUs & NGC (UPF) NGCDUs
Eth
RRUs
< 20-40km
• Independent RRU, DU, and CU (eCPRI not ready)
ROADM
(or POTN)
MPLS MPLS
80 km >
CPRICPRI
Eth
CPRI
CPRI
DWDM
Dark Fiber
CPRI
CPRI
RING MUX
< 20km
IP or
Transport
(Optional)

44. Deployment Scenarios - Middle
Eth
CUs & NGC (UPF) NGCDUs
Eth
RRUs
< 20-40km
• Independent RRU, DU, and CU (eCPRI ready)
MPLS MPLS
80 km >
Eth
DWDM
or RingMux
Dark Fiber
< 20km
IP or
Transport
(Optional)
Eth
Eth
Eth
Eth
Eth
PON
Eth
Eth
ROADM
(or POTN)

45. Deployment Scenarios - Final
Eth
BBUs (DU+CU) & NGC (UPF) NGC
Eth
RRUs
• More MECs plus Co-located DU and CU
- Middle-structure is still remains by CAPEX/OPEX (Mixed)
MPLS MPLS
80 km >
DWDM
or RingMux
Dark Fiber
< 20~30 km
Eth
Eth
PON
Eth
Eth
Eth
Eth
Towards Edge
ROADM
(or POTN)

46. Conclusion

47. Disruptive 5G
• All-in-one concept of 5G shakes the legacy infra.
- Just think about LoRa, NB-IoT in 5G era
• 5G features (mMTC, eMBB, URLLC) will change the traditional
choice for their company networks
- May not changed in 5G but it should be a starting point
• Giga-level realization on mobile bring people with more mobile-
oriented lives

48. From Providers’ Perspectives
• Providers consider as follows
(1) fronthaul, mid-haul, back-haul
(2) mobile edge cloud infra
(3) automated end-to-end networks (AU-DU-CU-NGC)
(4) virtualized 5G network function
(5) vendor-dependency (Cloud, SDN, NFV, Fronthaul)
※ providers should consider performances, cost-effectiveness,
and control & management about those items

49. From Vendors’ Perspectives
• The packet-based fronthaul is a new opportunity area for vendors
- The change from circuit to packet-structure is new business area
to current Ethernet players
- But, traditional transport players have to face with more
packet-based players (competition up↑)
- Vendors have to consider new technologies such as TSN, RoE,
because all packet-based world will be realized in 5G

50. References
[1] Antonio de la Oliva, et al., “An Overview of the CPRI Specification and Its Application to C-
RAN-Based LTE Scenarios,” IEEE Communications Magazine, Feb 2016
[2] 한국전자통신연구원, “국내 모바일 트래픽 현황 및 전망”, 2018.01
[3] Jong-Sik Lee, “KT 5G Deployment,” HSN 2018 워크숍
[4] 넷매니아즈 Tech-Blog, “C-RAN에서 DU와 RU간에 왜 초고용량 전송링크가 필요한가? (url:
“ https://netmanias.com/ko/?m=view&id=blog&no=6241)
[5] ITU-T GSTR-TN5G Technical Report – Transport Network Support of 5G (2018.2)
[6] 정환석(ETRI), 모바일 네트워크를 위한 저지연 유무선 광액세스 기술 (KRNET 2018.6.25)
[7] eCPRI Transport Network V1.1, “Requirements for the eCPRI Transport Network,” 2018.01.10