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COPYRIGHT © 2011 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
Thomas Pfeiffer, Frank Schaich - Alcatel-Lucent Bell Labs StuttgartOFC/NFOEC wireless backhauling workshop - Los Angeles, 5.3.2012
OPTICAL ARCHITECTURES FORMOBILE BACK- AND FRONTHAULING
2
COPYRIGHT © 2011 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
Backhauling or fronthauling ? EPC : Evolved Packet CoreBBU : Baseband UnitRAN : Radio Access Network
IP backhaul or CPRI fronthaul ?=
conventional RAN or cloud RAN ?
… most likely both of them
core network
metro cellmetro cell(200 m diam.)(200 m diam.)
EPC
centralizedBBU
IP backhaul
CPRIfronthaul
macro cellmacro cell(1 km diam.)(1 km diam.)
IP backhaul
conventional RAN
cloud RAN
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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
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
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
totalMbps
# antennas / sector
MHz3 sectors
typ. for macro cell
CPRI bandwidth per site
0,1
1
10
100
1000
1 10
100
40
20
10
totalGbps
# antennas / sector
MHz3 sectors
* 8/15 in case ofWCDMA
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 lightRadioTM White Paper „Economic analysis“ (2011)
6
COPYRIGHT © 2011 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
Latency in LTE : limited by synchronous UL HARQ
n Orig. TX
n+4
n+8
NACK
1 st RTX
UE eNB
t [ms]
3 msec fixed delay defined by LTE standard
eNB processing1. PHY: UL frame decoding2. MAC: ACK/NACK creation3. PHY: DL frame creation
t [ms]
n Orig. TX
n+4
n+8
NACK
1 st RTX
UE eNB
reduced time for eNB processing
t [ms] t [ms]
RRH
round trip time (10 µsec / km)+ transport systemprocessing time
t [ms]
The allowed RRH eNB transmission time is limited to <<1 msecIt comes at the expense of a reduced processing time in the eNB
The allowed RRH eNB transmission time is limited to <<1 msecIt 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
powersplitte
r
Central Office
powersplitter
eNBs
1
4Route
r
12
8
OLT ONT
CO
serving area:diam. 6 km
macro cell:diam. 1 km
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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
metrocells
max. 20 km
hybrid splitter:10G - power splitter
GPON - cyclic AWG
Central Office eNBs
12
8 metro (8 x 64)
macro (32 x)10G-PON
GPON
macro area
12
16
diplexer
powersplitter
10G +j GPON
powersplitter
1
4
Route
r
WDM1r(diplexer)
GP
ON
#1
… #
81
0G
PO
N
cyclicAWG
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
L2RN
R-,B-ONUs
32...64 subs
10-20km
R-,B-ONUs
10-20km
L3RN
MCO 4 MCO 3
MCO 1
OLT
L1RN
L1RN
fixed/mobile coupler
eNB
R-,B-ONUs
L1RN
L1RN
metro mux street level coupler Macro Cell TRX (DWDM)Metro Cell TRX (CWDM)
SMCO
MCO 2
L2RN
R-,B-ONUs
32...64 subs
10-20km10-20km
R-,B-ONUs
10-20km10-20km
L3RN
MCO 4 MCO 3
MCO 1
OLT
L1RN
L1RNL1RN
fixed/mobile coupler
eNB
R-,B-ONUs
L1RN
L1RN
metro muxmetro mux street level coupler Macro Cell TRX (DWDM)Metro Cell TRX (CWDM)
MCO … Metro Central OfficeRN … remote node
macro BS fronthauling
metro BS fronthauling
guar
d
guar
d
US
FH
-DW
DM
1260 1300 1350 1400 1450 1550 1600
DS
XG
PO
N1
GP
ON
GP
ON
XG
PO
N1
X/G
PO
N o
verla
y
/nm(to scale)
*
* ... being stripped beforefixed-services ONUs
waterpeak
EDFA
DWDM Tunsbles
FH
-DW
DM
1500
macro BS fronthauling
metro BS fronthauling
guar
d
guar
d
US
FH
-DW
DM
1260 1300 1350 1400 1450 1550 1600
DS
XG
PO
N1
GP
ON
GP
ON
XG
PO
N1
X/G
PO
N o
verla
y
/nm(to scale)
*
* ... being stripped beforefixed-services ONUs
waterpeak
EDFA
DWDM Tunsbles
FH
-DW
DM
1500
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COPYRIGHT © 2011 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
Enable BBU pooling, but not via CPRI : alternatives
incre
ased
op
tical lin
k
ban
dw
idth
- simp
ler re
mote
un
it- p
ossib
le p
oolin
g g
ain
s - sim
ple
r rem
ote
un
it- p
ossib
le p
oolin
g g
ain
s
EPC
EPC
classical eNBclassical eNB
PDCP
RLC
PDCP
RLCRFRFMA
CMAC PHYPHY
BIP
variable
EPC
EPC
central unit (cluster)central unit (cluster)
PDCP
RLC
PDCP
RLC
MAC
MAC
slim eNBslim eNB
RFRFMAC
MAC PHYPHY
≥ BIP
variable
EPC
EPC
central unit (cluster)central unit (cluster)
PDCP
RLC
PDCP
RLC
MAC
MAC
PHY
PHY
extended RRHextended RRH
RFRFPHYPHY
e.g. 0.2 * BCPRI fixed
EPC
EPC
central unit (cluster)central unit (cluster)
PDCP
RLC
PDCP
RLC
MAC
MAC
PHY
PHY
CPRI
CPRI
RRHRRH
RFRFCPRI
CPRI
BCPRI
fixed
IP backhaulingIP backhauling
split within L1split within L1
CPRI fronthaulingCPRI fronthauling
split within L2split within L2
COPYRIGHT © 2011 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
COPYRIGHT © 2011 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
Back-Up
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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.
SB2SB1 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
CyclicWDM
wavelength sets
wavelength set
ONU 1
ONU 2
…
…
…
ONU n
I1
WS2
WS3
WS4
WS1
heating
50 GHz
wav
elen
gth
sets
Downstream : 4 x 10G TDM DWDM channels, 100GHz spacing, 1575-1580nm band
- OLT : -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