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Dieter SchererConsultant
Broadband Wireless Technologies
Defining a Repeater for LMDS Deployment
Dieter Scherer
ConsultantBroadband Wireless Technologies
RAWCON 2001 August 20, 2001
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Acknowledgements
The author wishes to acknowledge Ralph Jones for assisting in the
isolation measurements and thanks Lucent Technologies formaking the data available.
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Outline
Key requirements for a LMDS repeater
Required repeater gain
Isolation measurements
Three proposals for repeater implementation
Design outline and key features of repeater with IF processing
Other repeater applications in LMDS deployment
Conclusions
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DS 8/15/01 LMDS deployment requires line-of-sight
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Broadband Wireless Technologies
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Reality of LMDS Deployment: Blocking buildings
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Key Requirements for a LMDS Repeater
Hub Site Shadowing
Highrise End
User
Site
Line-of-sight between hub/ repeater and end user/ repeater
Bi-directional operation
Repeater location anywhere between hub site and cell border
Entails:
Maximum Tx power for downstream: matching hub Tx powerMaximum Tx power for upstream: matching maximum subscriber Tx power
Rx sensitivities for up- and downstream: matching Rx sensitivities of hub and subscriber
Maintaining margin of operation
Transparent operation
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GRep = PRx Sens + Margin + 40log (4/)/)/)/)d0 + 20log d1/d0(1 - d1/d0) - PTx - GTx Ant - GRx Ant
Required Repeater Gain
Repeater SubscriberHub
d1 d0
GRep = Repeater gain including gain of repeater Rx and Tx antenna
PRx Sens = Threshold Rx power at BER = 10-6
Margin = Desired margin over threshold to account for rain fade
PTx = Transmit power of hubGTx Ant = Antenna gain of hub transmitter
GRx Ant = Antenna gain of subscriber receiver
= Wavelength of signal in md0 = Hub to subscriber distance in m
d1 = Hub to repeater distance in m
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70.0
80.0
90.0
100.0
110.0
120.0
130.0
140.0
0 10 20 30 40 50 60 70 80 90 100
% Distance of Repeater from Tx
R
epeaterGain[dB]
Repeater SubscriberHub
d1=
30% of d0
do
do=10000m
do=5000m
do=2500m
do=1000m
Required Gain as a Function of Location and Maximum Link Distance
Parameters affectingrepeater gain:
Link frequency =28GHz
PTx
= 20dbm
PRx Sens
= -85dBm
Margin =10dB
GTx Ant = 14dBGRx Ant = 32dB
Example:
5km link: 119dB required gain
10km link: 131dB required gain
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Isolation Requirements for Repeater
Forward Gain
Feedback
Stability requirement:
Isolation between repeater Tx output and Rx input needs to be
higher than the forward signal gain
Isolation may be achieved by
Frequency translation with channel filtering:
Drawback: Waste of valuable channel space
Complicated repeater deployment
High cost
Spatial isolation (direction and distance ):
Use of high directivity of signals at mm frequencies
Use of spatial separation
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Isolation Measurements
Result: Isolation between up- and downstream antenna at 28GHz: 139dB
0.6m
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Isolation Measurements, continued
Result: Isolation between up- and downstream antenna at 28GHz: 141dB
2m
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Isolation Measurements, continued
Result: Isolation between up- and downstream antenna (at 90o) at 28GHz: 136dB
0.6m
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Conclusions on Isolation Prospects at mm Frequencies
High isolation is achievable at mm frequencies between Tx and Rx antenna of arepeater.
At 28 GHz sufficient isolation was demonstrated to allow repeater operation in
links exceeding 10km.
Increasing the separation between Tx and Rx antenna of the repeater will
additionally increase isolation.
Minor peripheral features of the Tx and Rx antenna might have significant
effects on isolation.
Reflecting objects in the proximity of either Tx or Rx antenna could greatly
reduce isolation.
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Three Proposals for Implementing an LMDS Repeater
Repeater with gain and gain control based on mm processing only
Repeater with most of gain and gain control at IF
Repeater based on data retrieval and re-transmission
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Proposal 1:
Repeater with mm Processing only
Shadowing
HighriseHub Site
AC
End
UserSite
Pro
yConceptually simple
y Only roof access + AC required
Con
y High cost (mm gain blocks,gain control, filter)
y Tx/Rx difficult to separate
(requiring waveguides)
y Lack of access for level control
and monitoring
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Proposal 2:
Repeater with IF Processing
IF, Ref, -48V
AC
D/C
U/C
IF
D/C
U/C IF
Shadowing
HighriseHub Site End
UserSite
Hub
Tx/Rx
C
P
E
Pro
yLow cost (economical design of IF gain,filters, level control)
y Separable repeater Rx / Tx modules
y High gain (isolation) possible with long
IF cable
y Only roof access + AC required
Con
y Increased design complexityy Lack of access for level control
and monitoring
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Proposal 3:
Repeater with Data Processing
AC
Hub
Tx/RxCPE
Baseband
Repeater
IF, Ref, -48V
Control
E1
10B-T
Shadowing Highrise
IF, Ref, -48V
Control
Hub Site End
User
Site
CPE
Hub
Tx/Rx
Standard
CPE Modem
Pro
y Separable repeater Rx / Tx modules
y High gain (isolation) possible withseparate SRU / BRU
y Data access
y Full remote control and monitoring of
up/ downstream Tx power
Con
y Higher system cost
y Higher system complexityy Additional SW design
y Indoor units required
y Indoor installation needed (or
weatherized roof installation)
y Only single channel is processed
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Favored Choice: Repeater with IF Processing
Proposal 2 was chosen to demonstrate a design because it has
Minimal site requirements
High installation flexibility
Economic implementation of gain, gain control and filters at IF
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WG
Di-
plex
Phase
Locked
DRO
x N
LNARI
L
PARIL
3GHz
2GHz out
3GHz inX-tal Ref.in
-48DC in
2GHz
3GHz
AGC
Transmit Level Adjust
Tri-
plexer
DC
X-tal REF
X-tal REF
AGC
Tri-
plexer
Phase
Locked
DRO
x N
LNA R I
L
PA R IL
DC
Bias T
AC/DC
- 48V
DCA
C
WG
Di-
plex
3GHz
2GHz
100MHZX-tal REF
3GHZ
up to 50m
LMR4002GHz
3GHz
X-tal REF
X-tal REF
X-tal REF
2GHz in
3GHz out
X-tal Ref.out
-48DC in
Design Outline of Repeater with IF Processing
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Key Features of Repeater Design
Phase coherent up- and down-conversion
Reference signal (100MHz) is shared via IF cable. Upstream transmit level control
Forward level control loop is linked to downstream receive signal.
Downstream transmit level setting
Tx level is set according to repeater proximity to cell border (to avoid co-
channel interference with frequency re-use).
IF bandwidth
The choice of up-and downstream IF is determined by cable loss limits,
desired bandwidth, isolation and economic filter realization.
ModularityBasic split in up- and downstream module
mm circuit and IF sub-modules
Modular antenna attachment allowing point-to- point or point-to-
multipoint use.
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Other Repeater Applications in LMDS Deployment
Reach sparsely populated areas with
point-point repeaters in initial
deployment.
Reach clusters of subscribers
outside reqular grid.
Illuminate irregular uncovered
areas outside grid with repeater
linked to neighboring cell.
Use repeater as substitute hub.
R
R
PP-R
2
1
3
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Conclusions
Fixed wireless at mm-wave has the greatest potential for providing
broadband access.
Lack of line-of-sight is a major obstacle in urban deployment.
Line-of-sight blockage can be effectively overcome with repeaters.
Repeaters will become an indispensable component of LMDS deployment
if designed to be
transparent in use
easy to install
inexpensive compared to base station equipment