Presented by Prof. Andy Sutton, Principal Network Architect, BT Technology at The IET seminar, "5G 2020 - Unleashed" on 29 January 2020. A companion paper is available from Academia.edu website here: https://www.academia.edu/41625209/Design_and_Deployment_of_the_EE_5G_Network *** SHARED WITH PERMISSION ***

1. Backhauling the
5G Experience
1
Andy Sutton
Principal Network Architect
BT Technology
29th January 2020

2. Contents
• Pre-5G mobile backhaul
• The impact of 5G on macro-cell backhaul
• E2E multi-RAT backhaul network architecture
• Optical access and cell site gateways
• The introduction of E-band radio systems
• Future requirements for traditional microwave radio bands
• Summary
2
Note: This presentation is focused on 5G rollout to
the macro-cell layer, small cells are out of scope

3. Pre-5G mobile backhaul topology
- GSM & UMTS
• GSM backhaul utilised a high percentage of microwave links, circa 90%
• GSM backhaul topology included chains and stars from transport
nodes - some of these nodes accommodated BSCs
• UMTS increased the amount of fibre in the network however
microwave was still >50%
• UMTS drove migration to fibre as the technology evolved with HSPA
• GSM and UMTS use FDD spectrum and therefore required frequency
synchronisation, delivered via HDB3 on E1
• HSPA traffic levels drove adoption of Carrier Ethernet in support of E1
circuit emulation/pseudo-wires - fibre initially then Ethernet radio
3

4. Pre-5G mobile backhaul topology
- LTE
• LTE and the development of Gigabit Class LTE drove significant investment
in fibre connectivity, 1GE and even 10GE…
• Microwave connected sites reduced yet radio volumes increased due to
adoption of 2+0 XPIC configuration
• Use of wider radio channels resulted in the need for ETSI Class 4 antennas
to maximise link density
• 56 MHz channels with 512 QAM in XPIC configuration delivered >800Mbps
• LTE uses FDD spectrum and therefore required frequency synchronisation,
delivered via SyncE/IEEE 1588 v2
Note: We have some TDD spectrum however LTE focus to date has been on FDD
4

5. The impact on 5G on macro-cell backhaul
• 5G network is now live and supporting eMBB services, mainly to
smartphones
• EN-DC configuration supports the aggregation of 5G NR carrier with
up to 5 x LTE carriers
• 5G cell sites use 8T8R or 64T64R antenna systems - 16T16R and 32T32R
systems provide alternative options in the near-future
• Fibre connectivity is being upgraded to access DWDM with an initial
10GE for backhaul - fully distributed/aggregated RAN
• Wireless backhaul of >1Gbps is required - no standard configuration
available! - E-band offers a solution for short link lengths…
5

6. 5G within a multi-RAT network deployment - DRAN scenario
6
3G
4G1
5G
CSG NTU NTU
21C
PE
21C
PE
Mobile
core
networks2
21C IP/MPLS network
(P routers not illustrated)
Openreach Point to point
DWDM solution (OSA-FC)
n x λ
(can bypass
CSG & NTU)
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
Resilient PRTC
sync source
E-Band
D
W
D
M
D
W
D
M
Passive optical
filters
E-band millimetre
wave radio system

7. 7
Optical backhaul solutions
EAD1000
4G CSG
5G CSG
XG-210
16 CSM
OSA-FC
Note: Photo from lab environment, doesn’t represent actual deployed configuration

8. Frequency and phase synchronisation
8
3G
4G1
5G
CSG NTU NTU
21C
PE
21C
PE
Mobile
core
networks2
21C IP/MPLS network
(P routers not illustrated)
Openreach Point to point
DWDM solution (OSA-FC)
n x λ
(can bypass
CSG & NTU)
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
Resilient PRTC
sync source
E-Band
D
W
D
M
D
W
D
M
Passive optical
filters
E-band millimetre
wave radio system

9. The introduction of E-band radio systems
• Target architecture is a single E-band radio hop between a hub site and sub-
tended site (child site)
• Radio link to be planned to 99.99% atmospheric availability
• 1+0 and 2+0 configurations are allowed, based on deployment scenario
• Link can provide 6Gbps at up to 1.5km with 500 MHz channels and 256 QAM
in 2+0 XPIC configuration
• Recent regulatory changes offer opportunities for wider RF channels
9
E-band Frequency plan - source: Ofcom

10. The introduction of E-band radio systems
• E-band radio will take power from indoor mounted DC power source
• Traffic feeds to/from all outdoor E-band radio units will be via ng-CSG (10GE support)
• Radio unit will support PTP boundary clock for supply of phase sync to gNB slave clock
• Channel plan to be coordinated with network sharing partner to enable both operators to deploy on
shared sites with unilateral but parallel links (if required)
• Maximum of 3 sites to be supported from a fibre hub site in star topology (scale hub capacity
accordingly with 2nd 10GE)
• Two link chain topology to be supported as an exception, to be avoided wherever possible (scale
hub capacity accordingly)
10

11. E-band millimetre wave radio topology
11
Child site Hub site Child site
Child site Hub site
Child site Hub site Child site
Child site
Child site Child site Hub site
Chain of 2 E-band radio links in any of the agreed
topologies to be approved only as an exception,
when no other connectivity options are possible
Scale hub
capacity to
2 x 10GE*
Scale hub
capacity to
2 x 10GE*
*not required from day 1, monitor traffic and upgrade accordingly

12. Future requirements for traditional microwave radio bands
• A significant uplift in deployable capacity is required
• Wider RF channels, higher order modulations schemes and larger
antennas are options however none of these come without
challenges - technical and financial
• Dual-band concepts such as aggregating an E-band radio with a
traditional microwave band is an option we are studying however
this presents some user experience issues during E-band fade…
• Inter and intra-band carrier aggregation within traditional
microwave radio bands is of interest - target 2 to 5Gbps
• What’s the role of LoS MIMO and/or OAM? Other techniques?
12

13. So, what did we deliver during 2019?
13

14. 14
5G rollout during 2019 - 50 locations

15. Summary
• Mobile backhaul is an essential component of any mobile network; KPIs
are even more visible with 5G…
• Innovation in optical access has enabled high capacity and affordable
solutions for 10Gbps and beyond
• Microwave and millimetre wave radio systems will continue to play an
essential role in radio access network connectivity
• Future connectivity requirements will include; backhaul (S1/N2/N3),
midhaul (F1) and fronthaul interfaces (eCPRI/CPRI)
• Support for frequency and phase synchronisation is essential on CSG,
optical transmission and wireless backhaul solutions - network based
sync provides enhanced availability and performance
15

16. © British Telecommunications plc