Page 399 - Integrated Wireless Propagation Models
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T h e l e e C o m p r e h e n s i v e M o d e l - I n t e g r a t i o n o f t h e T h r e e l e e M o d e l s 377
kind of losses will still be strong enough, and the noise floor must be kept as low as pos
sible. Therefore, we have to count all the noise sources, including the interference sources,
as one kind of noise. Usually, the interference is much higher than the thermal noise.
.
6.5.2 1 Thermal Noise-The thermal noise power is
N = kTB watts (6.5.2.1)
l
where k = Boltzmann's constant= -174 dBm/Hz at 7 °C, T = temperature in Kelvin, and
B b andwidth, in hertz.
=
6.5.2.2 Transmitter and Receiver Noises
The local oscillator phase noise, the AM-FM conversion noise in nonlinear devices, and the
IM noise, which the intermodulation (IM) products, appear within the bandwidth region.
6.5.2.3 Feeder Line Loss
The waveguide or cables between the receiving antenna and the receiver front contrib
ute both signal attenuation and thermal noise.
6.5.2.4 Atmosphere Loss
A primary atmosphere loss is from rainfall. The more intense the rainfall and the higher
the frequency, the more signal energy will be absorbed. Operating below 10 GHz, the
loss can be negligible.
6.5.2.5 Interference
Interference can be considered as one kind of noise. Based on the interfered power linkg
into the signal channel, the interference plus noise level would be used to compare with the
received signal level. Usually, the interference level is much higher than the thermal noise in
the cellular system due to the co-channel reuse scheme. The required signal-to-interference
ratio can provide an error probability from transmitting a signal that meets our system
requirement. The signal-to-interference ratio is a parameter to calculate the link budget. Sys
tem Interferences-System interference is formed by adjacent channel interference and co
channel interference. These types of interference can be predicted by the prediction model as
long as the input data are complete and accurate. Those data will be found in Sec. 6.5.5.
6.5.2.6 Antenna Efficiency and Gain
Antenna efficiency is the ratio of its effective aperture to its physical aperture. The
reduction of antenna efficiency is due to aperture tapering, aperture blockage, scatter
ing, re-radiation, spillover, edge diffraction, and dissipative loss. Antenna gain is the
ratio of the maximum radiation intensity from the subject antenna to the radiation
intensity from isotropic source with the same power input. The relationship between
antenna effective aperture A e and antenna gain G is
G = 4nAJA.2
All of these items would be used to calculate the link budget.
6.5.3 Received Signal Power and Noise Power
The received signal power after a distance d is
p = P, G,GmLo (6.5.3.1)
r A dY