Repeater Deployment

Dieter Scherer

Consultant Broadband Wireless Technologies

Defining a Repeater for LMDS Deployment Dieter Scherer Consultant Broadband Wireless Technologies

RAWCON 2001

August 20, 2001


Dieter Scherer

Acknowledgements

The author wishes to acknowledge Ralph Jones for assisting in the isolation measurements and thanks Lucent Technologies for making the data available.

DS 8/15/01

2


Dieter Scherer

Outline

DS 8/15/01

•

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

3

Dieter Scherer

DS 8/15/01


LMDS deployment requires line-of-sight

4

Dieter Scherer


Reality of LMDS Deployment: Blocking buildings DS 8/15/01

5


Dieter Scherer

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 power Maximum 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 6

DS 8/15/01


Dieter Scherer

Required Repeater Gain Hub

Repeater

d1

Subscriber

d0

GRep = PRx Sens + Margin + 40log (4π/λ) π/λ)d π/λ) 0 + 20log d1/d0(1 - d1/d0) - PTx - GTx Ant - GRx Ant

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 hub GTx Ant = Antenna gain of hub transmitter GRx Ant = Antenna gain of subscriber receiver λ = Wavelength of signal in m d0 = Hub to subscriber distance in m d1 = Hub to repeater distance in m 7 DS 8/15/01


Dieter Scherer

Required Gain as a Function of Location and Maximum Link Distance 140.0 130.0

Repeater Gain [dB]

Parameters affecting repeater gain: Link frequency =28GHz PTx = 20dbm PRx Sens = -85dBm Margin =10dB GTx Ant = 14dB GRx Ant = 32dB

do=10000m do=5000m

120.0

do=2500m

110.0

do=1000m

100.0 90.0 80.0 70.0 0

10

20

30

40

50

60

70

80

90

100

% Distance of Repeater from Tx

Hub

Repeater

Example:

Subscriber

5km link: 119dB required gain 10km link: 131dB required gain

d1= 30% of d0 do

8 DS 8/15/01


Dieter Scherer

Isolation Requirements for Repeater •

Stability requirement: Isolation between repeater Tx output and Rx input needs to be higher than the forward signal gain

•

Isolation may be achieved by

Feedback Forward Gain

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 DS 8/15/01

9


Dieter Scherer

Isolation Measurements

0.6m

Result: Isolation between up- and downstream antenna at 28GHz: 139dB DS 8/15/01

10


Dieter Scherer

Isolation Measurements, continued

2m

Result: Isolation between up- and downstream antenna at 28GHz: 141dB DS 8/15/01

11


Dieter Scherer

Isolation Measurements, continued

0.6m

Result: Isolation between up- and downstream antenna (at 90o) at 28GHz: 136dB

DS 8/15/01

12

Dieter Scherer


Conclusions on Isolation Prospects at mm Frequencies •

High isolation is achievable at mm frequencies between Tx and Rx antenna of a repeater.

•

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.

DS 8/15/01

13

Dieter Scherer


Three Proposals for Implementing an LMDS Repeater

DS 8/15/01

•

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

14


Dieter Scherer

Proposal 1:

Repeater with mm Processing only

AC

Hub Site

DS 8/15/01

Shadowing Highrise

End User Site

Pro

Con

y Conceptually simple y Only roof access + AC required

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

15


Dieter Scherer

Proposal 2:

Repeater with IF Processing IF, Ref, -48V

Hub Tx/Rx

Hub Site

DS 8/15/01

D/C U/C

IF

IF

U/C D/C

AC

C P E

Shadowing Highrise

End User Site

Pro

Con

y Low 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

y Increased design complexity y Lack of access for level control and monitoring

16


Dieter Scherer

Proposal 3:

Repeater with Data Processing Hub Tx/Rx

CPE Hub Tx/Rx IF, Ref, -48V Control

IF, Ref, -48V Control CPE

Baseband Repeater

Hub Site AC

Standard CPE Modem

E1 10B-T

Shadowing Highrise

DS 8/15/01

Pro

Con

y Separable repeater Rx / Tx modules y High gain (isolation) possible with separate SRU / BRU y Data access y Full remote control and monitoring of up/ downstream Tx power

y y y y y

End User Site

Higher system cost Higher system complexity Additional SW design Indoor units required Indoor installation needed (or weatherized roof installation) y Only single channel is processed

17


Dieter Scherer

Favored Choice: Repeater with IF Processing

Proposal 2 was chosen to demonstrate a design because it has

DS 8/15/01

•

Minimal site requirements

•

High installation flexibility

•

Economic implementation of gain, gain control and filters at IF

18


Dieter Scherer

Design Outline of Repeater with IF Processing 3GHz WG Diplex

LNA

R

DC

I L

3GHZ

X-tal REF

100MHZ X-tal REF

Phase Locked DRO

Triplexer

2GHz in 3GHz out X-tal Ref.out -48DC in

AGC

xN Bias T AC/DC

X-tal REF

- 48V DC

L

PA

R

I

2GHz

up to 50m LMR400

A C

2GHz 3GHz X-tal REF

DC

2GHz out 3GHz in X-tal Ref.in -48DC in

Triplexer

2GHz R

I

WG Diplex

LNA

L

X-tal REF

Phase Locked DRO

xN

3GHz

X-tal REF

3GHz

L I

R

PA

19

AGC

DS 8/15/01

Transmit Level Adjust


Dieter Scherer

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 cochannel 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.

•

Modularity Basic split in up- and downstream module mm circuit and IF sub-modules Modular antenna attachment allowing point-to- point or point-tomultipoint use.

DS 8/15/01

20


Dieter Scherer

Other Repeater Applications in LMDS Deployment

•

Reach clusters of subscribers outside reqular grid.

•

Illuminate irregular uncovered areas outside grid with repeater linked to neighboring cell.

3 R

Reach sparsely populated areas with point-point repeaters in initial deployment.

•

PP-R

R

•

2

Use repeater as substitute hub. 1

DS 8/15/01

21


Dieter Scherer

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

DS 8/15/01

22

Repeater Deployment

Recommend Documents