Repeater Deployment

7/27/2019 Repeater Deployment

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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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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

Repeater Deployment

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