OPTICAL ARCHITECTURES FOR

qualtaghblurtingMobile - Wireless

Dec 12, 2013 (3 years and 3 months ago)

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COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.

Thomas Pfeiffer, Frank Schaich
-

Alcatel
-
Lucent Bell Labs Stuttgart

OFC/NFOEC wireless backhauling workshop
-

Los Angeles, 5.3.2012

OPTICAL ARCHITECTURES FOR

MOBILE BACK
-

AND FRONTHAULING

2

COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.

Backhauling or fronthauling ?

EPC : Evolved Packet Core

BBU : Baseband Unit

RAN : Radio Access Network

IP backhaul or CPRI fronthaul ?

=

conventional RAN or cloud RAN ?


… most likely both of them

core network

metro cell

(200 m diam.)

EPC

centralized

BBU

IP backhaul

CPRI

fronthaul

macro cell

(1 km diam.)

IP backhaul

conventional RAN

cloud RAN

3

COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.

Fiber transmission systems


protocol :

IP, CPRI, others
(digital; RoF not considered here)

direct or over PON, Ethernet, …


multiplexing :

TDM, WDM, TWDM, …


topology :

ptp, ptmp, ring


architecture:

dedicated ? overlay ? shared with FTTx ?


Metrics


technical metrics :

-
bandwidth (scaleability, user statistics), latency, jitter

-
environmental factors : temperature, humidity, mechanical

-
location factors : availability of local powering, footprint, accesseability


economic metrics :

-
infrastructure : ownership, availability of dark fibers, digging cost, leasing cost, opportunity for sharing

-
location factors : power supply and power consumption, rights of way

Choice of transmission technology : optical only

4

COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.

Backhauling and fronthauling bandwidth in LTE

IP backhauling =
variable bitrate

-

antennas may be grouped (e.g. beamforming) :


each group counts as one single element

-

user traffic statistics apply :


-

shown above are achievable peak rates on air i/f


-

avged. values may be less by an order of mag

CPRI fronthauling =
constant bitrate

-

each antenna counts separately (individual streams)

-

8B/10B can be removed for transport over Ethernet

-

compression can be applied to reduce to 1:3

IP peak bandwidth per site

100
1000
10000
100000
1
10
100
40
20
10
total
Mbps
# antennas / sector
MHz
3
sectors
typ. for macro cell

CPRI bandwidth per site

0,1
1
10
100
1000
1
10
100
40
20
10
total
Gbps
# antennas
/ sector
MHz
3
sectors
* 8/15

in case of

WCDMA

typ. for macro cell

5

COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.

Backhaul and fronthaul network dimensions and architecture shall account for
traffic statistics


traffic statistics per cell





statistical multiplex gain on IP backhaul


variations of total cell traffic over the day



load sharing (pooling gain) in cloud RAN

Impact from traffic statistics

taken from Alcatel
-
Lucent Technology lightRadio
TM

White Paper „Economic analysis“ (2011)

6

COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.

Latency in LTE : limited by synchronous UL HARQ

n

n+4

n+8

UE

eNB

t [ms]

3 msec fixed delay


defined by LTE standard


eNB processing

1. PHY: UL frame decoding

2. MAC: ACK/NACK creation

3. PHY: DL frame creation

t [ms]

n

n+4

n+8

UE

eNB

reduced time for

eNB processing

t [ms]

t [ms]

RRH

round trip time

(10 µsec / km)

+ transport system

processing time

t [ms]

The allowed RRH eNB t
ransmission time is limited to <<1 msec

It comes at the expense of a
reduced processing time in the eNB

7

COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.

Serving area around traditional CO


32 macro cells, backhauled by single dedicated 10G
-
PON


-

peak rate = 10Gbps per site;




sufficient even for extreme loads


-

average rate = 320 Mbps per site




can be increased by using multiple 10G
-
PONs, WDM
-
stacked


-

link length = 20 km





reaches any site within the area over realistic cable routes











Possible migration towards serving from consolidated Super
-
CO



via WDM stacking : hybrid WDM/TDM long reach 10G
-
PONs

(cf. PIEMAN, MUSE, SARDANA for example architectures + upcoming
NGPON2 standardisation for specs (tbd) )


IP backhaul by 10G
-
PON : urban area, macro cells

max. 20 km

power

splitter

Central Office

power

splitter

eNBs

1

4

Router

1

2

8

OLT

ONT

CO

serving area:

diam. 6 km

macro cell:

diam. 1 km

8

COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.

Scenario:
serving area around CO with

-
32 macro cells: 10G peak / 320M avge.



10G
-
PON,
1:32 split

(3 sectors * 8 antennas * 100 MHz)


(XGPON1 or XGPON2)

-
16 metros per macro : 1.7G peak / 26M avge.



8 x GPON,
1:64
split

each

(1 sector * 4 antennas * 100 MHz)


(stacking via low cost WDM)



low cost WDM
-
PON by cyclic wavelength allocation within 40 nm band



cf. Pöhlmann, Pfeiffer: ECOC 2011, paper We.9.C.1

IP backhaul (ct‘d) : urban area, macro + metro cells

CO

serving area:

diam. 6 km

macro cell:

diam. 1 km

metro

cells

max. 20 km

hybrid splitter:

10G
-

power splitter

GPON
-

cyclic AWG

Central Office

eNBs

1

2

8

metro

(8 x 64)

macro

(32 x)

10G
-
PON

GPON

macro area

1

2

16

dipl

exer

power

splitter

l

10G +

l
j

GPON

power

splitter

1

4

Router

WDM1r

(diplexer)

GPON #1 … #8

10G

PON

cyclic

AWG

OLTs

9

COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.


BBU clustering

: move BBU hardware from BTS into common central space

-
simplified hardware

at antenna sites (footprint, electrical power) and in BBU (indoor specs)

-
„zero latency“ links between BBUs allow for implementing CoMP and ICIC algorithms



BBU pooling

: share hardware elements between multiple colocated BBUs

-
additional benefit : ease of load
-
sharing between clusters



Either variant requires CPRI links to remote antenna sites

-
transmission bandwidths easily reach levels that render TDM
-
PON unattractive

-
small split factors (1:2 or 1:4)

-
constant bitrate, i.e. no statistical multiplex gain

-
strict latency limits (<<1 msec) require zero framing/buffering etc. delays


-
most viable solutions employ ptp
-
links via

-
fiber, if available …

-
wavelength : ptp
-
WDM overlay on TDM
-
PON or „pure“ WDM
-
PON

Centralized processing : variants and benefits

COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.

CPRI fronthaul via WDM overlay on LR
-
PON

(ACCORDANCE project)

SMCO
MCO 2
L2
RN
R
-
,B
-
ONUs
32...64 subs
10
-
20km
R
-
,B
-
ONUs
10
-
20km
L3
RN
MCO 4
MCO 3
MCO 1
OLT
L1
RN
L1
RN
fixed/mobile coupler
eNB
R
-
,B
-
ONUs
L1
RN
L1
RN
metro mux
street level coupler
Macro Cell TRX (DWDM)
Metro Cell TRX (CWDM)
SMCO
MCO 2
L2
RN
R
-
,B
-
ONUs
32...64 subs
10
-
20km
10
-
20km
R
-
,B
-
ONUs
10
-
20km
10
-
20km
L3
RN
MCO 4
MCO 3
MCO 1
OLT
L1
RN
L1
RN
L1
RN
fixed/mobile coupler
eNB
R
-
,B
-
ONUs
L1
RN
L1
RN
metro mux
metro mux
street level coupler
Macro Cell TRX (DWDM)
Metro Cell TRX (CWDM)
MCO … Metro Central Office

RN … remote node

macro BS
fronthauling
metro BS
fronthauling
guard
guard
US
FH
-
DWDM
1260
1300
1350
1400
1450
1550
1600
DS
XGPON1
GPON
GPON
XGPON1
X/GPON overlay
l
/
nm
(to scale)
*
* ... being stripped before
fixed
-
services ONUs
wate
rpeak
EDFA
DWDM Tunsbles
FH
-
DWDM
1500
macro BS
fronthauling
metro BS
fronthauling
guard
guard
US
FH
-
DWDM
1260
1300
1350
1400
1450
1550
1600
DS
XGPON1
GPON
GPON
XGPON1
X/GPON overlay
l
/
nm
(to scale)
*
* ... being stripped before
fixed
-
services ONUs
wate
rpeak
EDFA
DWDM Tunsbles
FH
-
DWDM
1500
11

COPYRIGHT © 2011 ALCATEL
-
LUCENT.

ALL RIGHTS RESERVED.


Enable BBU pooling, but not via CPRI : alternatives

increased optical link bandwidth

-

simpler remote unit

-

possible pooling gains

core

network

EPC

classical eNB

PDCP

RLC

RF

MAC

PHY

B
IP

variable

core

network

EPC

central unit (cluster)

PDCP

RLC

MAC

slim eNB

RF

MAC

PHY


B
IP

variable

core

network

EPC

central unit (cluster)

PDCP

RLC

MAC

PHY

extended RRH

RF

PHY

e.g. 0.2 * B
CPRI


fixed

core

network

EPC

central unit (cluster)

PDCP

RLC

MAC

PHY

CPRI

RRH

RF

CPRI

B
CPRI

fixed

IP backhauling

split within L1

CPRI fronthauling

split within L2

COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.

COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.

Back
-
Up

14

COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.

Conventional Approach

Example XG
-
PON1 upstream, 4 Wavelength Subbands SB1


SB4

DFB laser wavelength can be tuned by heating or cooling by ≈ 0.08nm/K. Tuning range up to 3nm.




SB2

SB1

SB3

SB4

1260nm


1265nm 1270nm 1275nm 1280nm

1260nm


1265nm 1270nm 1275nm 1280nm

Wavelength band is separated in
four subbands
for wavelength stacking

Randomly distributed
DFB laser wavelengths in the 20nm band

15

COPYRIGHT © 2011 ALCATEL
-
LUCENT. ALL RIGHTS RESERVED.

TWDM 40/10G with ultra
-
low cost WDM upstream

(ALU proposal, ECOC 2011)

CO
feeder
RN
OLT
1
OLT
3
OLT
2
OLT
4
Cyclic
WDM
wavelength sets
wavelength set
ONU 1
ONU 2



ONU n
I
1
WS2
WS3
WS4
WS1
heating
50 GHz
wavelength sets

Downstream

: 4 x 10G TDM


DWDM channels, 100GHz spacing, 1575
-
1580nm band

-

OLT :
l
-
stabilised DFB transmitter

-

ONU : FP based tunable filter



Upstream

: 4 x 2.5G TDMA


wavelength sets, 50GHz grid, 1260
-
1280nm band

-

OLT : filtered with cylical AWG

-

ONU : partially tunable DFB with integrated heater

WSDM

(wavelength set division multiplexing)


Operational principle:

-

cyclic optical filter at Rx, 50 or 100 GHz grid

-

narrow range Tx tuneability instead of full band

-

accomplished by integrated heater stripe (no TEC)

-

otherwise conventional transmitter technology