CommTech Talks: Optical Access Architectures for Backhauling of Broadband Mobile Networks

AGENDA

1. The data storm
2. Challenges and opportunities
3. Solutions: HetNet, small cells, BBU centralization
4. A closer look to BBU centralization
(CPRI backhauling)
5. BBU centralization CAPEX/OPEX analysis
6. Conclusions


The data storm

New Consumers New Devices/Ecosystem

5 Billion
people will be directly touched data munching devices exhausting data and
by connectivity in 2015 signaling capacity

New Connections New Communities and Cloud Services

25X
Global Mobile Traffic in 5 years
(forecast for period 2011-2016) 100s Millions
empowered users connected in social communities


Challenges …

Service Provider network economics
50

40
$/sub/month

30 Data ARPU
Network Cost
20 Data Traffic

10

0
2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

Source: Bell Labs Analysis


… and opportunities

Mobile backhaul connection by fiber reaching 42% in 2016.

Mobile Backhaul Connections by medium

10,000,000
9,000,000
8,000,000
7,000,000
copper
6,000,000
fiber
5,000,000
air
4,000,000
total
3,000,000
2,000,000
1,000,000
0
2010 2011 2012 2013 2014 2015 2016 2017

Source: Infonetics Research, March 2012


Solutions: HetNet

From homogeneous coverage paradigm to inhomogeneous
• Different wireless technologies, such as W-CDMA , LTE and Wi-Fi
• Flexible radio access options, such as macros, small cells and Wi-Fi.
• Cost-effective for capacity and coverage needs in all environments.
• Mitigates interference and allows for intelligent traffic management features


Solutions: small cells
NGNM definition: “Small cells are operator managed base stations with a lower
transmission power and coverage area than macro cells, used to complement them
in order to improve the service level by easing congestion with more capacity and
enhancing coverage”

Small cells typically below
rooftop 3-6m above street level
Macro In a Het-Net scenario, macro-
sites may double up as
aggregation sites for small cells
‘Last mile’ backhaul therefore
provides connectivity between
macro sites and small cell sites
Connection must meet QoS
requirements…

Typical Small
Cell locations


Solutions: mobile backhauling models

Remote
Radio Conventional BBU
Head (Macrocell)
(on tower)
IP

IP

All-in-one IP
(BaseBand
integrated IP mobile
in Radio Head) backhaul
Small cell
IP

Wireless
IP Controllers packet core
Multi-band
Remote CPRI
Radio Head over fiber
with any
BaseBand

Centralized baseband
RF only sites


Solutions: IP backhauling options and metrics

INFRASTRUCTURE AND TECHNOLOGY CAPABILITY
MEAN
Option Bandwidth (Mb/s) Latency (ms)
DSL - 2 pair bonding with vectoring and phantom mode 1500 m 100 down, 20 up 3
Copper DSL - 4 pair bonding with vectoring and phantom mode 1500 m 230 down, 40 up 3
DSL - 8 pair bonding with vectoring and phantom mode 1500 m 750 down, 150 up 3
305 down, 306 up per
11-23 GHz (up to 16 Km at 11 GHz) 254 bits per frame ∼ 0.15 per hop
Microwave radio
80 GHZ (up to 1.5Km) 1000 ∼ 0.15 per hop
10000 down, 2500 up
TDM PON ∼1
(shared among ONTs)
Fiber
B&W point to point 10000 0.005/Km
CWDM 8x 10000 per channel 0.005/Km


Solutions: BBU centralization (CPRI backhauling)
Traditional versus centralized architectures

Ethernet backhauling CPRI backhauling

RU RU
Cabinet CO

Backhaul network Backhaul network

BBU BBU
CPRI BH i/f CPRI CPRI


Common Public Radio Interface (CPRI)
Radio
Radio
Equipment CPRI Backhaul Equipment
Controller
(RE)
CPRI over fiber (REC)

Centralized Base
RF Only
Band Unit (BBU)

• The Common Public Radio Interface (CPRI) is an industry cooperation, operative since
2003, defining a publicly available specification for the internal interface of radio base
History stations between the Radio Equipment Control (REC) and the Radio Equipment (RE).
• Cooperating parties are: Ericsson AB, Huawei, NEC, Alcatel Lucent and Nokia Siemens
Networks (Nortel left on 2009)

• A digitized and serial p2p radio interface, mapping the sampled antenna signals (I/Q
data), possibly related to different mobile technologies, into containers.
• Mobile technologies supported include: GSM, UMTS, WiMax, LTE …
• Single-hop and multi-hop topologies (between REC and RE) are allowed.
What is • Three different information flows (User Plane data, Control and Management Plane
data, and Synchronization Plane data) are TDM multiplexed over the CPRI.
• Seven different options for CPRI line bite rates are defined, as multiple of lower line
rate: (1) 614, 4 Mb/s, (2) 1228.8 Mbit/s, (3) 2457.6 Mbit/s, (4) 3072.0 Mbit/s, (5)
4915.2 Mbit/s, (6) 6144.0 Mbit/s, (7) 9830.4 Mbit/s.


CPRI throughput examples
How evaluating CPRI throughput:
• N. of sectors for each cell site: 3 5 MHz
WCDMA carriers LTE spectral bandwidth [MHz]
• N. of MIMO TX antennas 0 10 20 30
• for WCDMA: 2 0 0 5.530 11.059 16.614
1 737 6.267 11.796 17.351
• for LTE: 4 2 1.475 7.004 12.534 18.089
• Sampling rate: 7.68 Mb/s for WCDMA 3 2.212 7.741 13.271 18.826
4 2.949 8.479 14.008 19.563
15.36 Mb/s for LTE 10MHz
30.72 Mb/s for LTE 20MHz CPRI unidirectional throughput [Mb/s]
46.15 Mb/s for LTE 30MHz (non compressed)
• Sample width: 8 bit/sample for WCDMA 5 MHz
WCDMA carriers LTE spectral bandwidth [MHz]
15 bit/sample for LTE 0 10 20 30
• I/Q multiplication factor: 2 0 0 2.048 4.096 6.153
1 273 2.321 4.369 6.426
• Compression rate: 2.7 2 546 2.594 4.642 6.699
3 819 2.867 4.915 6.973
4 1.092 3.140 5.188 7.246

CPRI unidirectional throughput [Mb/s]
(compressed)


Centralized BBU Deployment Pros&Cons
Benefits: Challenges:
• Reduced OPEX (clustering): • CPRI backhaul demands
• Fewer cell site visits (e.g. high bandwidth capacity
centralized upgrades) CPRI (up to 10G) for circuit-
over fiber
• Reduced site costs (site based traffic
rental) and civil works for • Need for optical infra-
new sites structure
Centralized • Bandwidth
• Eliminate heating and BBU
cooling of enclosure compression
• Improved security (no algorithms can
cabinets to break into) effectively reduce costs
CPRI
• Improved X2 performance over fiber
• Strict transmission latency
(no transmission delay and jitter requirements
among BBUs in a pool) • Low entry cost with ability
• Load balancing lowers CAPEX Centralized
to scale
(pooling) BBU • Effectively leveraging
• Improved spectral efficiency existing fiber (e.g. GPON
(CoMP) overlay)


The business case for BBU centralization
source:

• The total incremental costs of a C-RAN architecture in urban environments reduce
after the first year, moving towards 70% of traditional RAN costs in the final years
• OPEX reduction eventually outweighs initial CAPEX increase


A synopsis of CPRI backhauling architectures

P2P
TREE
RING

P2P fibers RRH-BBU CPRI multiplexing

Y N Need for CPRI
P2P fibers Fiber rich multiplexing
RRH-BBU context at cell site

• Purely passive solution possible WDM WDM or TDM • Active solution
• CPRI compression not needed TDM • CPRI compression lowers costs
• With colored or colorless optics muxing • Proprietary or std multiplexing


CPRI backhauling functional model

Cell site Central Office

Transport network
CPRIs Line Line CPRIs
RRH(s) BBU Pool

CPRI CPRI
CPRI OPTICAL OPTICAL CPRI CPRI
(AxC) (AxC)
MUX NETWORK LINE MUX or SUB-CPRI
COMPR. COMPR.
DEMUX TERMINATION TERMINATION DEMUX SWITCHING
DECOMPR. DECOMPR.

• Optional • TDM/WDM • P2P • P2P • TDM/WDM • Optional • Optional
• Proprietary • PON • PON • Proprietary • Proprietary
• Ring • Ring if sub-CPRI

Optimized TDM based CPRI backhauling architecture

WDM based CPRI backhauling architecture


CPRI backhauling CAPEX/OPEX analysis
Models

CPRI multiplexing: BBU stack
Active TDM MX/DX
• TDM up to 10Gb/s
• CPRI compression
(about 3 times on
LTE signals) B&W pt-to-pt
Cell site (20÷40 Km) CO

CPRI multiplexing: BBU stack
Passive WDM
1. Fixed DWDM MX/DX (AWG)
2. Colorless DWDM
(SS-WDM)
WDM pt-to-pt
Cell site (20÷40 Km) CO
WDM colored e/o converters


Minimally loaded configuration

Normalized network cost
• Variable number of cell sites 6
5.5

• 2 scenarios: 5
4.5

1. Minimally loaded: 4
3.5
3

• mix of CPRI interfaces globally 3
2.5
conveying 33Gb/s (16Gb/s after 2
4

compression) 1.5 2
1
2. Maximally loaded: 0.5
1

0
• mix of CPRI interfaces globally 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Number of cell sites
conveying 88Gb/s (40Gb/s after Maximally loaded configuration
compression) 6

Normalized network cost
5.5
5

Legenda: 4.5
) 4
1) p2p fibers connecting RUs and BBUs; ) 3.5
) 3
2) TDM multiplexing (with compression); ) 2.5
3

3) WDM multiplexing with fixed WDM; 2
1.5
4
2
4) WDM multiplexing with colorless WDM 1
1
0.5
(SS-WDM) 0
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
x
Number of cell sites


OPEX considerations

Reliability Scalability Installation aspects In-field
upgrades

TDM Acceptable if Limited by TDM Either in cabinet or on tower, Needed
careful box capacity; it with need for power supply if
electronic scales with boxes not cooling; indoor/outdoor
design versions needed
Fixed Very good; only Limited by the No power/cooling needs for Not
WDM passive WDM number of λs on WDM de-mux; complex needed
de-multiplexer a fiber (up to management of WDM modules
at cell site 80+80 using C+L (spares for each λ, need for
(beyond RRHs) bands) management of fixed colors)

SS-WDM Very good; only Limited by the No power/cooling needs for Not
passive WDM number of λs on WDM de-mux; very simple needed
de-multiplexer a fiber (up to management of WDM modules
at cell site 80+80 using C+L (only one spare type, no
(beyond RRHs) bands) management of fixed colors)


Colorless DWDM technology
SS-WDM: principle of operation

Distribution Fiber
Feeder Fiber
Data modulation

Reflective-SOA
Remote mirror
ONU transmitter WDM MX/DX
(AWG or TFF)

Self-seeding Laser cavity

Colorless transmitter self-aligns to any available channel of the AWG grid
without needing wavelength control and tracking system:
1. The fiber between the R-SOA and the AWG mirror forms a laser cavity
2. The laser wavelength is selected by the AWG port channel
3. The R-SOA is directly modulated with the ONU data stream


Colorless DWDM technology
SS-WDM: R-SOA operations in the self-seeding cavity

The R-SOA in the cavity performs simultaneously 3 operations:
• Sustain lasing – optical amplification
• ONU data modulation – direct gain modulation
• Cancellation of re-circulating modulation – Nonlinear Gain saturation


Conclusions

• Some mobile market evolution trends have been depicted in their main lines,
showing how a sustainable growth constantly needs to leverage on innovation, in
order to make operators’ costs and revenues meet on a fair basis
• Specifically, a new mobile backhauling paradigm (BBU centralization or CPRI
backhauling) has been described
- Suitable both for macro and small cells
- Allowing for significant OPEX savings at the expense of initial CAPEX increase
• Results from a CAPEX/OPEX analysis have been reported:
- TDM (active) solutions with compression can be generally designed at lower cost than
WDM ones and allow for “CPRI independent” monitoring of the optical line
- Low cost/short distance WDM solutions, like SS-WDM, look promising thanks to the
possibility of a pure passive add-ons in the cell site; the auto-tuning facility is key for
eliminating the OPEX burden implied by the management of different devices for
distinct colours


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