1. www.mtigroup.com/mobilePublic
Cloud RAN fronthaul
Options, benefits and challenges.
Aleksandra Checko,
Industrial PhD student
Aleksandra.Checko@mtigroup.com
iJOIN Winter School "5G Cloud Technologies: Benefits and Challenges„
Bremen, 2015-02-23
www.fp7-harp.eu

2. www.mtigroup.com/mobile2 Public
Outline of today’s presentation
 Base station architecture evolution towards C-RAN
– Traditional base station (past)
– With RRH (present)
– Cloud RAN (C-RAN) (present/future)
 Fronthaul network
– Bitrate, delay and sync requirements
– Transport medium
– Transport solutions
 Fronthaul evolution
How?
Why?

3. www.mtigroup.com/mobile3 Public
Traditional base station
Base station evolution
Telecom Italia Demo
Base station with RRH

4. www.mtigroup.com/mobile4 Public
Through base station with Remote
Radio Head
 Currently deployed
 Power efficient
 Easy cooling
 For different standards
 Interface:
– Open Base Station Architecture Initiative (OBSAI)
– Common Public Radio Interface (CPRI) (some parts are vendor-
specific)
– Open Radio Equipment Interface (ETSI-ORI)
 Fiber up to 20-40 km, usually p2p
 Baseband Unit (BBU) a.k.a. Data Unit
BaseBand
Traditional Macro BS
Antenna
BS
cell
Transport
Control
Synch
RF
PA
BS with RRH
Antenna
cell
RRHRF
BBU
BaseBand
Transport
Control
Synch

5. www.mtigroup.com/mobile5 Public
To C-RAN architecture
 Proposed by IBM in 2010
 Cloud, Centralized processing, Cooperative radio, Clean
RF
RF
C-RAN with RRHs
Virtual BBU Pool
RRH
RRH
RRH
RF
BaseBand
Synch
Control
Transport
BaseBand
Synch
Control
Transport
BaseBand
Synch
Control
Transport
BaseBand
Transport
Control
Synch
Fiber – Digital BaseBand Coax cable – RF

6. www.mtigroup.com/mobile6 Public
Cloud RAN
Remote sites - RRH
FRONTHAUL
Source: http://www.mti-mobile.com/
Source: http://krnet.or.kr/
Data center – BBU Pool

7. www.mtigroup.com/mobile7 Public
Fronthaul transport network
- “link” between RRH and BBU
 P2P link for base station with RRH 
 Fronthaul network based on
– WDM
– Ethernet
– OTN

8. www.mtigroup.com/mobile8 Public
Requirements on bitrate & timing
 20 MHz LTE, 2x2 antennas (MIMO) – 150 Mbps for users, 2.5 Gbps on
fronthaul link (CPRI)
 Delay < 3 ms RRH-BBU-RRH (HARQ) ≈ 0.1- 0.2 ms on fronthaul
(CMCC)
 Jitter < 65 ns (MIMO, 36.104)
 Frequency error < 50 ppb (Macro BS, 36.104)
 BER < 10e-12 (CPRI, for specific application)

9. www.mtigroup.com/mobile9 Public
Which medium to choose?
Medium Bit rate Distance Remarks
Fiber 100Gbps + Tens km
Copper 10 Gbps 100 m
Microwave 1 Gbps (80GHz) 1.5 km LoS required
0
1
2
3
4
5
6
7
8
9
10
2011 2012 2013 2014 2015 2016
Million
Mobile Backhaul Connections by Medium
Air
Fiber
Copper
Source: Infonetics Research, March 2012
 Why to consider microwave, not fiber everywhere?

10. www.mtigroup.com/mobile10 Public
(Yes, people are working on
compression)
 Majority of algorithms
– Remove redundancies in spectral domain,
– Perform block scaling,
– Use non-uniform quantizer
– Up to 33% (3:1) compression ratio for 8% EVM
– ALU, IDT
 University of Texas at Austin
– rescaling,
– non-uniform quantization,
– noise-shaping error feedback
– Resampling
– 5:1 ratio
 One algorithm detects user activity – up to 7%! (14:1)
– Telefonica I+D

11. www.mtigroup.com/mobile11 Public
Transport solution
Technology is ready
(capacity not necessarily)
CPRI /
OBSAI
CPRI /
OBSAI
WDM
CPRI /
OBSAI
CPRI /
OBSAI
Microvawe
Compression Compression
Eth/CPRI/
OBSAI
Eth/CPRI/
OBSAI
Ethernet
CPRI/
OBSAI
CPRI/
OBSAI
OTN
BBU
Pool
RRH
CPRI / OBSAI
Point to point
WDM-PON

12. www.mtigroup.com/mobile12 Public
Ethernet enables to maximize
multiplexing gains
 Among others to reduce cost of BBU pool
A. Checko, et al. ” Cloud RAN for Mobile Networks - a Technology Overview”, IEEE Communications Surveys & Tutorials
0,0
0,5
1,0
1,5
2,0
0 10 20 30 40 50 60 70 80 90 100
Multiplexinggain
Office cells (%)
A. Checko, H. Holm, H. Christiansen, ” Optimizing small cell deployment by the use of C-RANs”, European Wireless 2014

13. www.mtigroup.com/mobile13 Public
Timing in fronthaul
 Timing is really important
 Frequency of transmission
 Handover, coding
00
01
02
00
01
02
Device A Device B
 Solution: timing distribution
 GPS
 PHY layer clock – SyncEth
 Packet-based timing
 IEEE 1588v2 (PTP)
 Multiple
 Requirements
 Phase error LTE-A with eICIC/CoMP:
± 1.5 - 5 μs, MIMO: 65 ns
 Frequency error LTE – A TDD/FDD:
±50 ppb

14. www.mtigroup.com/mobile14 Public
Shared Ethernet is even better for
cost-saving
Access network -
fronthaul
Aggregation
network -
backhaul
BBU
Pool
CPRI /
OBSAI
Remote
Radio
Heads
CPRI /
OBSAI
Aggregation network
- fronthaul
Aggregation
network -
backhaulRemote
Radio
Heads
IQ over
Eth
CPRI2Eth
Gateways
BBU
Pool
GPS, 1588, ect
RRH
CPRI
GPS?, 1588?,
new solution?
Variable delay
RRH++
BBU Pool++
Traditional
fronthaul
Packet-based
fronthaul
Sync delivered together
with data (CPRI)
New Sync
solution needed
BBU
 Switching
 Multiplexing
 Widely deployed (reuse!)
! Fronthaul cost savings vs problems with delays
! Synchronous CPRI vs asynchronous Ethernet

15. www.mtigroup.com/mobile15 Public
HARP optimization
 Looking when to use C-RAN
 Combining fiber and microwave
 Optimizing cell-BBU assignment

16. www.mtigroup.com/mobile16 Public
Deploying C-RANs
 Trade off
– Fiber length
– Cells in the C-RAN
– Multiplexing gain
 TCO vs. capacity
A. Checko, H. Holm, H. Christiansen, ” Optimizing small cell deployment by
the use of C-RANs”, European Wireless 2014

17. www.mtigroup.com/mobile17 Public
Optimization model
 To maximize multiplexing gain and minimize fiber cost
 In multi C-RANs scenario
Aggregated
Traffic (h)
Aggregated
Traffic (h)
24 h
24 h

18. www.mtigroup.com/mobile18 Public
Partial C-RANs
 Partial C-RAN
– Some sites are excluded from the
C-RAN and are backhauled to
the nearest C-RAN site by MWR
R. Al-obaidi; et. Al. ”C-RAN deployment scenarios”, DTU, 2014
Backhaul
network
Base
Stations
LTE
MWR
Fronthaul network Backhaul
network
BBU
Pool
CPRI
Remote
Radio
Heads
MWR
Fiber
Aggregated
Traffic (h)
24 h
S1

19. www.mtigroup.com/mobile19 Public
Updates from industry
 No more CPRI?!
 4G towards 5G

20. www.mtigroup.com/mobile20 Public
It is time to rethink fronthaul
towards 5G
 New functional split between BBU
and RRH
– To reduce fronthaul data rate
– Decoupling user-processing and
cell-processing
 No more CPRI? Need for interface
supporting:
– Variable bit rate (traffic
dependent to enjoy multiplexing
gain)
• To increase scalability
– Packet-based
• Synchronization is a challenge
– Multipoint to multipoint
– Fully standardized
BBU Pool--
RRH
BBU Pool
Current C-RAN
Future C-RAN
10 Gbps
10 Gbps
2 Gbps
2 Gbps
2 Gbps
RRH++
BBU Pool--
2 Gbps
3 Gbps
3 Gbps
Vendor A
Vendor A
Vendor A
Vendor B
Vendor C

21. www.mtigroup.com/mobile21 Public
Timely topic
 IEEE 1904.3 - encapsulation and mapping of IQ data over Ethernet
 IEEE 802.1 – CPRI fronthaul discussion with Time Sensitive Networking
task force
 CPRI  CPRI2?
 3GPP - proposal on a study item on variable rate multi-point to multi-
point packet-based fronthaul interface supporting load balancing

22. www.mtigroup.com/mobile22 Public
Wrap Up

23. www.mtigroup.com/mobile23 Public
 Costs
– 2x2 MIMO, 20 MHz LTE,
15+1 CPRI 2.5 Gbps
– 3 sectors?  7.5 Gbps
– Tens of BS over long
distance? 100s Gbps
Costs vs savings
Fever
BBUs?Fronthaul
cost?
 Savings
– Equipment
– Energy
Re-define fronthaul

24. www.mtigroup.com/mobile24 Public
Base station architecture evolution
BaseBand RF
a) Traditional Macro BS
Antenna
RF
RF
c) C-RAN with RRHs
Virtual BBU Pool
BaseBand
BaseBand
RRH
RRH
RRH
RF
Fiber – Digital BaseBand Coax cable – RF
BS
cell
BaseBand
RF
b) BS with RRH
Antenna
cell
RRH
BBU
RF
RF
d?) Possibly C-RAN with new function split between BBU and RRH
Virtual BBU Pool
BaseBandBaseBand
--
RRH
RRH
RRH
RF
BB
BB
BB
FH network

25. www.mtigroup.com/mobile25 Public
Deployment scenarios
A. Checko, et al. „Cloud RAN for Mobile Networks - a Technology Overview”, IEEE Communications Surveys & Tutorials

26. www.mtigroup.com/mobile26 Public
Take away points
 Fronthaul network capacity is a deal breaker for introducing C-RAN
 Fronthaul solutions so far rely on legacy deployments
 Industry is working on “redefining” fronthaul – towards switchable,
multipoint-to-multipoint connections, with a strong focus on Ethernet-
based solutions
Thank you for your attention
www.fp7-harp.eu