Unit I -Introduction of Wireless Channel

1. OUTDOOR PROPAGATION MODEL
 Several models have been developed to accurately model the received signal strength in
practical wireless scenario
 In mobile communication system radio transmission often takes place over irregular terrain
 So for estimation the Path Loss we consider terrain profile, which may vary from simple
curved earth profile to a highly mountainous profile also consider the presence of trees,
buildings & other obstacles.
 A number of propagation models are available to predict path loss over irregular terrain.
 Some of the models which are commonly used for outdoor propagation model are
1. Longly-Rice Model
2. Durkin’s Model-A case study
3. Okumura Model
4. Hata Model
5. PCS Extenssion to Hata Model

2. HATA MODEL
 The HATA Model [HAT90] is imperical formulation of graphical Path Loss data provided by
Okumura model
 Is valid from 150MHz to 1500 MHz
 Hata represents the urban area propagation loss
 Where,
fc - is frequency in MHz from 150MHz to 1500 MHz
- is effective transmitting (base station) antenna height( in m) from 30 m to 200m
- is effective receiving (mobile) antenna height( in m) from 1 m to 10 m
d - is the T-R separation distance (in km)
a( ) - is the correction factor for effective mobile antenna height which is the function of the size
of the coverage area
- 13.82 log - a( ) + (44.9 - 6.55 log ) logd

3. HATA MODEL
 For small and medium size city , the mobile antenna correction factor is given by
 To obtain the path loss in a suburban area , The standard Hata formula is modified as
a( ) - 0.7) - (1.56 - 0.8) dB
 and for large city , it is given by
a( ) 1.54 – 1.1 dB for ≤ 300 MHz
a( ) 11. - 4.97 dB for ≥ 300 MHz
- 5.4
open rural + 18.33
 Formulae for open rural area is modified as,
------ a
------ b
------ c

4. HATA MODEL
In Figure the simulated path loss in three types of environments are plotted

5. PCS EXTENSION TO HATA MODEL
 The proposed model for path loss is
 Where,
fc - 1500 MHz to 2000 MHz
- 30 m to 200m
- 1 m to 10 m
d - 1 km to 10 km
a( ) - is defined in equation a, b & c
- 13.82 log - a( ) + (44.9 - 6.55 log ) logd +
 The European cooperative for scientific & technology research (EURO-COST) formed the COST-
231 working committee to develop an extended version of Hata model.
 COST-231 proposed the following formulae to extend Hata’s model to 2 GHz.
0 dB for medium size city suburban areas
3 dB for metropolitan centres
=

6. RECEIVER NOISE COMPUTATION
 Noise at the receiver arises due to thermal effects is known as thermal noise.
 The noise Power Spectral Density (PSD) η denotes the noise power per
hertz of bandwidth. Hence, the total noise power is given as
 It is very important to accurately characterize noise power to compute the signal-to-noise power
ratio at the receiver and the resulting bit-error-rate performance.
Noise power = η × B
 Further, the noise power spectral density η can be derived as η = kTF
Where,
k = 1.38 × is the Boltzmann constant,
T - is the temperature in Kelvin,
F - is the noise figure.
 Thus Noise Power (Thermal noise power multiplied by noise figure) Noise power = kTF × B
 Noise temperature is the noise introduced by the receiver , is given as = (F-1)
(T is the room temperature)