This presentation explores the evolution of GSM, UMTS and LTE radio access network architectures before a detailed review of the RAN architecture options for 5G. The functional decomposition of the 5G radio access network presents the network designer with many challenges with regards placement of RU, DU and CU nodes, all of which are discussed. The presentation concludes with a review of BT UK plans for 5G launch with a fully distributed RAN in support of an EN-DC architecture.
Presented by Professor Andy Sutton CEng FIET, Principal Network Architect, Architecture & Strategy, BT Technology at IET 5G - the Advent conference on 30 January 2019 | IET London: Savoy Place
*** SHARED WITH PERMISSION ***
Prof. Andy Sutton: 5G RAN Architecture Evolution - Jan 2019
1. British Telecommunications plc 2018
5G Radio Access Network Architecture Evolution
Professor Andy Sutton CEng FIET
Principal Network Architect
Architecture & Strategy
BT Technology
30th January 2019
2. British Telecommunications plc 2018
Contents
• Lessons from the past - GSM, UMTS and LTE
• 5G RAN architecture evolution
• RAN functional decomposition
• Access network connectivity
• 5G network deployment
• 5G demo update
• Summary
2
3. British Telecommunications plc 2018
GSM - fully distributed RAN
• GSM BTS is a fully distributed radio base station
• All radio related protocols terminate in the BTS
• Radio interface encryption terminates in the BTS
• Distributed intelligence with centralised BSC
3
BTS Abis interface BSC
Nokia GSM Ultrasite BTS
Core network
NOTE: IP Sec GW used between BTS and BSC with IP Abis implementation
4. British Telecommunications plc 2018
UMTS - many centralised functions
• UMTS is a simple L2 radio base station (known as Node B)
• All radio related protocols terminate in the RNC
• Radio interface encryption terminates in the RNC
• Distributed radio with centralised intelligence
4
NodeB Iub interface RNC
Nokia UMTS Ultrasite BTS
Core network
5. British Telecommunications plc 2018
LTE - distribution wins again…
• LTE eNB is a fully distributed radio base station
• All radio related protocols terminate in the eNB
• Radio interface encryption terminates in the eNB
• X2 interface between adjacent eNBs, no centralised network controller
5
eNB S1 interface EPC
Huawei 3900 eNB (+GSM BTS)
eNB S1 interface SecGW Core network
2600
MHz
RRU
6. British Telecommunications plc 2018
LTE - RAN options
• LTE eNB is a fully distributed radio base station
• However, this radio (eNB) is made up of two components which can be
geographically separated
• RRU/RRH and BBU - separated by CPRI interface
6
RRU CPRI BBU
Huawei 3900 eNB (+GSM BTS)
RRU CPRI BBU S1 interface
2600
MHz
RRU
S1 interface
7. British Telecommunications plc 2018
Base station architecture - LTE
7
RRU BBU
RRU
S1 interface
BBU S1 interface
RRU BBU S1 interface
CPRI
CPRI
D-RAN with cabinet RFU
D-RAN with external RRU
C-RAN with centralised BBU
Note: a site may support
one or more base station
architectures for different
radio channels/bands
8. British Telecommunications plc 2018
RAN functional splits - protocol architecture
8
RRC
PDCP
Data
Low-
RLC
High-
MAC
High-
PHY
Low-
MAC
Low-
PHY RF
High-
RLC
RRC
PDCP
Data
Low-
RLC
High-
MAC
High-
PHY
Low-
MAC
Low-
PHY RF
High-
RLC
Option
1
Option
2
Option
3
Option
4
Option
5
Option
6
Option
7
Option
8
Relaxed Very low
End to end
latency
Traffic/capacity related Very high
Capacity
requirement
Higher layer splits Lower layer splits
S
1
CPRI
Reference 3GPP TR 38.801
9. British Telecommunications plc 2018
RAN functional decomposition
9
gNB
RU* DU CU
* RU could be integrated within AAU (mMIMO) or standalone RU (RRU/RRH)
with coaxial connections to passive antenna (typically 8T8R)
CPRI
eCPRI
F1
interface
S1 interface (EPC+)
N2/N3 interfaces (NGC)
NR (air)
interface
10. British Telecommunications plc 2018
RAN functional decomposition - E1 interface
10
gNB
RU* DU
CU-c
* RU could be integrated within AAU (mMIMO) or standalone RU (RRU/RRH)
with coaxial connections to passive antenna (typically 8T8R)
CPRI
eCPRI
F1-c
NR (air)
interface
CU-u
F1-u
N2
N3
E1
Additional work is on-going on:
• DU-CU split for LTE (W1
interface)
• E2 interface between CU and
RAN Intelligent Controller (RIC)
• A1/O1 interface between RIC
and NMS & Orchestration layer
12. British Telecommunications plc 2018
Base station architecture - 5G - EN-DC (Option 3x)
12
RU CU
RU
S1 interface
DU
RU DU
D-RAN with AAU/RRU
C-RAN with option 2 split
C-RAN with option 7/8 split
and further CU centralisation
DU
CPRI
eCPRI
CU S1 interface
F1CPRI
eCPRI
CU S1 interface
F1CPRI
eCPRI
Note: a site may support
one or more base station
architectures for different
radio channels/bands
Note: In full C-RAN configuration the DU and CU may be co-located or on separate sites
13. British Telecommunications plc 2018
RAN functional splits - protocol architecture (EN-DC)
13
RRC
PDCP
Data
Low-
RLC
High-
MAC
High-
PHY
Low-
MAC
Low-
PHY RF
High-
RLC
RRC
PDCP
Data
Low-
RLC
High-
MAC
High-
PHY
Low-
MAC
Low-
PHY RF
High-
RLC
Option
1
Option
2
Option
3
Option
4
Option
5
Option
6
Option
7
Option
8
Relaxed Very low
End to end
latency
Traffic/capacity related Very high
Capacity
requirement
Higher layer splits Lower layer splits
S
1
CPRIeCPRIF1
Reference 3GPP TR 38.801
14. British Telecommunications plc 2018
Base station architecture - 5G - Next Generation Core (NGC)
14
RU CU
RU
N2/N3 interface
DU
RU DU
D-RAN with AAU/RRU
C-RAN with option 2 split
C-RAN with option 7/8 split
and further CU centralisation
DU
CPRI
eCPRI
CU N2/N3 interface
F1CPRI
eCPRI
CU N2/N3 interface
F1CPRI
eCPRI
Note: a site may support
one or more base station
architectures for different
radio channels/bands
Note: In full C-RAN configuration the DU and CU may be co-located or on separate sites (as illustrated)
15. British Telecommunications plc 2018
RAN functional splits - protocol architecture (NGC)
15
RRC
SDAP/
PDCP
Data
Low-
RLC
High-
MAC
High-
PHY
Low-
MAC
Low-
PHY RF
High-
RLC
RRC
SDAP/
PDCP
Data
Low-
RLC
High-
MAC
High-
PHY
Low-
MAC
Low-
PHY RF
High-
RLC
Option
1
Option
2
Option
3
Option
4
Option
5
Option
6
Option
7
Option
8
Relaxed Very low
End to end
latency
Traffic/capacity related Very high
Capacity
requirement
Higher layer splits Lower layer splits
N
2
-
N
3
CPRIeCPRIF1 Note:
Service Data Adaptation
Protocol (SDAP), has been
introduced to the NR user
plane to handle flow-based
Quality of Service (QoS)
framework in RAN, such as
mapping between QoS flow
and a data radio bearer, and
QoS flow ID marking.
16. British Telecommunications plc 2018
RAN access network connectivity
16
RU DU CU
S1 or N2/
N3 interface
F1CPRI
eCPRI
Terms; Fronthaul, mid-haul and backhaul as defined by MEF (Metro Ethernet Forum)
Fronthaul Mid-haul Backhaul
Backhaul (in common use)
CPRI, eCPRI or
Non-ideal
fronthaul
17. British Telecommunications plc 2018
5G within a multi-RAT network deployment - DRAN scenario
17
3G
4G1
5G
CSG
OSA
-FC
OSA
-FC
21C
MSE
D
W
D
M
D
W
D
M
21C
MSE
Mobile
core
networks2
21C IP/MPLS network
(P routers not illustrated)
Openreach Point to point
DWDM solution
Future-proofed for network
sharing and RAN evolution
n x λ
(can bypass
CSG)
1 - 2G is supported on the same base station as 4G (SRAN/Multi-RAT)
2 - Includes RNC for 3G and IP Sec GW for 4G and 5G
PRTC
sync source
18. British Telecommunications plc 2018
5G within a multi-RAT network deployment - DRAN scenario
18
3G
4G1
5G
CSG
OSA
-FC
OSA
-FC
21C
MSE
D
W
D
M
D
W
D
M
21C
MSE
Mobile
core
networks2
21C IP/MPLS network
(P routers not illustrated)
Openreach Point to point
DWDM solution
n x λ
(can bypass
CSG)
1 - 2G is supported on the same base station as 4G (SRAN/Multi-RAT)
2 - Includes BSC for 2G, RNC for 3G and IP Sec GW for 2G, 4G and 5G
PRTC
sync source
E-Band
19. British Telecommunications plc 2018
5G within a multi-RAT network deployment - DRAN scenario
19
3G
4G1
5G
CSG
OSA
-FC
OSA
-FC
21C
MSE
D
W
D
M
D
W
D
M
21C
MSE
Mobile
core
networks2
21C IP/MPLS network
(P routers not illustrated)
Openreach Point to point
DWDM solution
n x λ
(can bypass
CSG)
1 - 2G is supported on the same base station as 4G (SRAN/Multi-RAT)
2 - Includes BSC for 2G, RNC for 3G and IP Sec GW for 2G, 4G and 5G
PRTC
sync source
E-Band
E-band link(s) could connect directly
to a wavelength on OSA-FC product
20. British Telecommunications plc 2018
5G within a multi-RAT network deployment - Edge enabled
20
3G
4G1
5G
CSG
OSA
-FC
OSA
-FC
21C
MSE
D
W
D
M
D
W
D
M
21C
MSE
Mobile
core
networks2
21C IP/MPLS network
(P routers not illustrated)
Openreach Point to point
DWDM solution
n x λ
(can bypass
CSG)
1 - 2G is supported on the same base station as 4G (SRAN/Multi-RAT)
2 - Includes BSC for 2G, RNC for 3G and IP Sec GW for 2G, 4G and 5G
3 - Enables RAN functional decomposition, distributed UPF and service platforms
PRTC
sync source
E-Band
E-band link(s) could connect directly
to a wavelength on OSA-FC product
5G Edge Cloud3
21. British Telecommunications plc 2018
5G demo at Canary Wharf
21
Highlights
• 1.3Gbps to test equipment (30 MHz LTE + 40 MHz NR)
• 600Mbps to Huawei 5G CPE (5 MHz LTE + 40 MHz NR)
• 4T4R LTE (15 MHz 2100 + 15 MHz 2600) with 64T64R NR
22. British Telecommunications plc 2018
Summary
• The functional decomposition of the RAN is at an advanced stage in standards,
industry fora and implementation (XRAN/ORAN, 3GPP, ONAP)
• Traditional 4G centric CRAN (CPRI based) is popular in Asia due to availability of dark
fibre, this brings radio optimisation benefits through centralised scheduling etc.
• CPRI doesn’t scale for 5G due to amount of spectrum and antennas therefore eCPRI
was developed by the same industry partners who developed CPRI
• Several industry groups are working towards a virtualised RAN to disaggregate the
hardware from software for many functions, also enables innovative new entrants to
market
• Major RAN vendors offer a range of different RAN architectures to meet various
deployment scenarios
• BT is currently rolling out the radio, backhaul and core network infrastructure
necessary to be a leader in 5G and converged networks
22
https://www.ngmn.org/fileadmin/ngmn/content/downloads/Technical/2018/180226_NGMN_RANFSX_D1_V20_Final.pdf