A presentation on Cloud RAN fronthaul, current deployment Options, benefits and challenges. This was presented in the iJOIN Winter School "5G Cloud Technologies: Benefits and Challenges", Bremen, 2015-02-23

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

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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

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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

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

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Fronthaul transport network
- “link” between RRH and BBU
 P2P link for base station with RRH 
 Fronthaul network based on
– WDM
– Ethernet
– OTN

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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)

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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?

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(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

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HARP optimization
 Looking when to use C-RAN
 Combining fiber and microwave
 Optimizing cell-BBU assignment

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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

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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

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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

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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

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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

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Wrap Up

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 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

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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

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Deployment scenarios
A. Checko, et al. „Cloud RAN for Mobile Networks - a Technology Overview”, IEEE Communications Surveys & Tutorials

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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