Radio-to-Fiber Repeater Placement in Wireless Local-Loop Systems - Multiobjective Optimization Methodology: A Jumping Gene Approach - page 131

6.2 PathLossModel
To. evaluate. the. total. path. loss. and. satisfy. the. coverage. performance,. a.
path.loss.model,.based.on.the.Joint.Technical.Committee.(JTC).model.with.
some.modifications,.was.employed.to.adapt.for.the.WLL.system.[23]..In.this.
model,.the.power.loss.caused.by.multiple.diffractions.from.rows.of.building.
can.be.neglected.because.a.directional.antenna.is.used.as.the.WLL.repeater.
antenna..This.type.of.antennae.is.capable.of.improving.the.received.signal.
strength.
Since. WLL. systems. are. established. for. fixed. users,. there. is. no. mobil-
ity.effect..Assuming.that.the.WLL.base.station.antenna.is.located.above.
the. rooftop. levels. of. all. buildings. (see . Figure 6.1 ) ,. the. total. path. loss. is.
expressed.as

L = L + L . (6.1)

.

1 2

with.the.path.loss.due.to.free.space. L 1 and.the.diffraction.loss.from.rooftop.
to.street. L 2 given.by

λ
π .

(6.2)

L

= 20 log

4 R

.

and

2

λ
π

1 1

L = 10 log

θ −

. (6.3)

2

2

2 r 2 π + θ

.

2

( )

where.

= ∆ + ,.λ.is.the.wavelength,. R .is.the.dis-
tance.between.the.WLL.base.station.and.the.repeater,. d .is.the.horizontal.
distance. between. the. WLL. repeater. and. the. diffraction. edge,. and. Δ h r . is.
the. height. difference. between. the. rooftop. level. and. the. WLL. repeater.
antenna.
The. paths. of. radio. propagation. can. be. seen. in . Figure 6.1 . . To. satisfy. the.
coverage.performance.of.each.grid,

− 1 ∆ h

d

.and. r h d

2

θ = tan ( )

r

r

P G G L P

+ + − ≥

. . (6.4)

b r r

where. P 0 .is.the.WLL.base.station.transmission.power.(dBm),. G b .is.the.WLL.
base.station.antenna.gain.(dBi),. G r .is.the.WLL.repeater.antenna.gain.used.on.
the.grid.considered.(dBi),. L .is.the.total.path.loss.(dB),.and. P r .is.the.required.
minimum.received.signal.strength.at.the.WLL.repeater.(dBm).