Air Interface Link Budgets and Cell Planning

7/28/2019 Air Interface Link Budgets and Cell Planning

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OMNIAC M

OMNIAC M

TAWAPropagation and Cell

Planning


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OMNIAC M

OMNIAC M

DECT Standard :

High subscriber density

High traffic capacity

Low cost

Micro cellular deployment

Supports toll-quality voice service and high bit

rate data services

Introduction

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OMNIAC M

OMNIAC M

The sensitivity (defined as received power level at

which the Bit Error Rate is 10-3)

TAWA Enhancements

DECT Norm TAWA

FRS 83 dBm with BER=10-3 -91 dBm with BER=10-3

BS 86 dBm with BER=10-3 -91 dBm with BER=10-3

-73 dBm with BER=10-5 -86 dBm with BER=10-5

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OMNIAC M

OMNIAC M

The frequency of operation in DECT is around 1.9

GHz, at which the wavelength is only 15 cm Compact

Antenna:

Compact

High-gain

Several antennas have been specifically developed

for the TAWA system

Antennas (1)

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OMNIAC M

OMNIAC M

Sectoral antenna for FRS:

Gain: 10 dBi

Weigh: 150gm

Horizontal beam width = 80

Vertical beam width = 50

Antennas (2)

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OMNIAC M

OMNIAC MAntennas (3)

Sectoral antenna for BS and RBS:

Gain: 12,14, 16 or 18 dBi

Weigh: 300 gm

Horizontal beam width = 60


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OMNIAC MOMNIAC M

Omnidirectionnal antenna for BS and RBS:

Gain 6, 9 or 11 dB


Antennas (4)

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OMNIAC MOMNIAC M

-Transmit power Tx : 24 dBm

- Loss 1 m from antenna : +20log(/4) = -38

- BS antenna gain : +Gb- FRS antenna gain : +Gw

- BS and FRS cables loses : -Lc

- Propagation Loss : -Lp

- Fade margin : -Lf

Total : -14+Gb+Gw-Lc-Lp-Lf > -90 dBm(sensitivity limit for BER < 10-3)

FRS-BS Link Analysis

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OMNIAC MOMNIAC M

Path Loss:

LOS path : 6 dB loss for each doubling of distance (or20 dB every decade)

Wall / Floor : 7 dB loss for 9- 12 brick walls and 5 RCC

floorsTrees : 6-15 dB loss depending on canopy thickness

Cable Loss

BS : < 1 dB (short cable since antenna co-located with BS)

FRS : 1 5 dB (depending on cable lengthand type)

2 3 dB typical

Losses

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OMNIAC MOMNIAC M

Non-LOS links

At 2 GHz, signal fades by 20 dB in non-LOS situation due to

multi-path

With antenna diversity at BS, fade margin required is only 10

dB

no FRS installed with signal strength < -80 dBm

BER < 10-5 most of the time, occasionally dropping to

10-3

LOS Links

In LOS situations, multi-path fading is rare

5 dB margin is adequate

BER < 10-5 always

Fading

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OMNIAC MOMNIAC M

For 60 Sectors :

Antenna Gain Gb : 12 dB

Gw

: 7.5 dB

Cable Loss Lc : 3 dB (typical)

Fade Margin Lf : 10 dB (non-LOS)

Recd. Signal Strength = -14 + 12 + 7.5 - 3 - 10 - Lp

500 m propagation in free space 54 dB loss

28.5 dB margin in Lp for loss through walls / ceiling

4 walls / ceiling can be penetrated

Link Analysis Example : Roof-top Base

Station Cluster

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OMNIAC MOMNIAC M

Gb 12 dB

Gw 7.5 dB

Lc 6 dB (assume worst case cable losses of 1 + 5 dB)

Lp 80 dB (10 km)

Lf 5 dB (LOS case)

Received Signal Strength = -14 + 12 dB + 7.5 - 6 - 80 - 5

= 85.5 dBm

4.5 dB margin still available

Link Analysis Example : Long Distance BS

FRS Link at 10 km

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OMNIAC MOMNIAC M

BS

Roof-top BS cluster (macro-cell)

Street-level dispersed BS ( micro-cell) In-building multi-floor ( Pico-cell)

FRS

Integral whip antenna/indoor patch antenna

Window-mounted patch antenna

Roof-top patch antenna

Deployment Options

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OMNIAC MOMNIAC MSingle Omni Roof-top BS

Mount BS on a pole

Use 2/4/6 dBi omni antennas

vertical beam width decreases with gain

e.g. for 6 dBi antenna beam width, it is 100

shadow region in the vicinity of the BS

(where antenna has some lossinstead of gain)

shadow region increases in size with antenna height

and gain

)

Vert. beam width

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OMNIAC MOMNIAC MMultiple Omni Roof-top BS on a Pole (1)

Multiple BS can be co-located to increase capacity

1 BS with 12 channels gives 5.8 E (@ 1% GOS)

2 BS with 24 channels gives 15 E i.e 7.5 E per BS 4 BS with 48 channels gives 9 E per BS

Critical issues same as with single omni BS

In addition, spacing between antennas of different BS

should be about 50 cm

minimize parasitic effects

Suggested deployment geometries shown next, whether ontop of pole or otherwise

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OMNIAC MOMNIAC MMultiple Omni Roof-top BS on a Pole (2)

Could have a separate axially-mounted lightning interceptor (spikes) instead of industrial

antenna lightning protectors,

need to mount interceptor at a height sufficient to ensure that BS

antennas are within the protection funnel

Pole

Two OmniBS

Four Omni BS

Pole

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With Sectorised deployment, one can Increase frequency re-use by reducing interference in undesireddirections

can co-locate very large number of BSs

can deploy cell-sites every 1-2 kms to get high tele-density

Increase antenna gain at BS

easy to get 12 dB gain with compact antennas( ~ 60 cm length, < 1 kg weight)

Increase vertical beam-width despite high gain (~50)

Down tiltantenna (up to a few degrees less than

half of vertical beam width) reduce shadow region

reduce illumination above the horizon

reduce interference in neighbouring cells

Avoid shadowing due to tower/pole

Sectorised BS Cluster

Downtilt angle

Side view

)

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OMNIAC MOMNIAC MDiversity in Sectorised Deployment

45cm

45cm

45cm

Sectors illuminated by the pair ofdiversity antennas for each BS must beidentical

Diversity antennas can bemounted

a) side by side

b) one below the other

c) diagonally across

Antenna spacing in all cases atleast 45 cm

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OMNIAC MOMNIAC MNumber of Sectors

With 7.5 dB antennas, typical horizontal beam width =80- 90

4 to 5 sectors

With 12 dB antennas, horizontal beam width is 60

6 sectors

Each BS gives 5.8 E per sector @ 1% GOS

4-sectors

BS antennapair

) 60

6-sector

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