CHANNEL MODEL for INFOSTATIONS
Can this be the model for outdoors?
Andrej Domazetovic,WINLAB – February, 23
OBJECTIVE
Assuming that the channel is Ricean and using the
measurements by Feuerstein, Rappaport et. al. in San
Francisco (2-ray model) try to develop the channel model
proposal described as the behavior of Ricean K-factor with
respect to transmitter-receiver distance.
INITIAL ASSUMPTIONS
Low transmitter antenna heights (3, 4 and 5m) Receiver antenna height 1.7m Clear line of sight path - no shadowing Carrier frequency 5.1 GHz Channel bandwidth 100 MHz Omnidirectional antennas No mobility (yet)
OUTLINE
Brief overview of standard 2-ray propagation model Brief overview of Propagation over the earth Closer look into propagation issues Modified model Link to Ricean K-factor Real antenna pattern Conclusions/Questions
Standard 2-ray propagation model
Source:
[] Rappaport - Wireless Communications
L
GGd
PdP rttr1
4
2
Friis free space equation:
Relation between power and electric field: fs
d R
E
d
EIRPP
2
24
Where: EIRP - effective isotropic radiated power, E - magnitude of radiating portion of electric field in the far field, Rfs - free space intrinsic impedance and Ae - antenna effective aperture
eedr AE
APdP120
2
Standard 2-ray propagation model
Source:
[] Rappaport - Wireless Communications
GRLOSTOT EEE The electric field at receiver:
c
dt
d
dE
c
dt
d
dEtdE ccTOT cos)1(cos, 0000
4
22
d
hhGGPP rtrttr
assuming: large distance from the transmitter, Taylor series approximations, perfect ground reflection...
Standard 2-ray propagation model
Source:
[] Feuerstein, Rappaport et. al. - Path loss, Delay spread and Outage models as Functions of Antenna Height for Microcellular System Design - TVEH, Aug, 1994
In measurements performed in San Francisco, it was shown that 2-ray model is fairly good model for microcellular urban environment
It was also shown that the path loss within first Fresnel zone clearance is purely due to spherical spreading of the wave front:
decreases as d-2 and not d-4
(10m being the minimum T-R distance)
Standard 2-ray propagation model
Source:
[] Feuerstein, Rappaport et. al. - Path loss, Delay spread and Outage models as Functions of Antenna Height for Microcellular System Design - TVEH, Aug, 1994
Standard 2-ray propagation model
Source:
[] Feuerstein, Rappaport et. al. - Path loss, Delay spread and Outage models as Functions of Antenna Height for Microcellular System Design - TVEH, Aug, 1994
42
22222
222
1
fdrt
rt
hh
hh
Fresnel zone clearance
Propagation over a plane earth
Source:
[] W.C. Jakes - Microwave Mobile Communications
Propagation over smooth, conducting, flat earth Bullington:
22
....)1(14
jj
rttr eAReRGGd
PP
Where:first term - direct wavesecond term - reflected wavethird term - surface waverest - induction field and ground secondary effects - phase difference between reflected and direct paths
ASSUMTIONS
Source:
[] Rappaport - Wireless Communications
L
GGd
PdP rttr1
4
2
Friis free space equation:
• The formula is a valid predictor for Pr for d which are in the far-field of the transmitting antenna - Fraunhofer region i.e. when inductive and electrostatic fields become negligible and only radiation field remains
df=2D2/ , df>>D and df>>• For fc = 5.1GHz and the antenna size D = 10cm
df=33.9cm , df>>10cm and df>>5.9cm
• If D (largest linear dimension of antenna) and fc increase, so does df - attention must be paid
ASSUMTIONS
First Fresnel zone distance:
Antenna height: fd: for fc=5.1GHz3m 70.47m Mobile height:1.7m
4m 118.29m
5m 179.6m
Since wavelength=5.9cm, the Bullington equation also holds (surface wave can be neglected)
Source:
[] Feuerstein, Rappaport et. al. - Path loss, Delay spread and Outage models as Functions of Antenna Height for Microcellular System Design - TVEH, Aug, 1994
[] W.C. Jakes - Microwave Mobile Communications
Ricean K-factor
Source:
[] Rappaport - Wireless Communications
[] Steele - Mobile Radio Communications
componentscatteredofPower
componentspecularofPowerK
td
dERt
d
dEtdE ccTOT coscos, 0000
2
ddR
dK
22
22
rt
rt
hhdd
hhdd
Propagation Mechanisms
Source:
[] Rappaport - Wireless Communications
ii r r
tt
Ei
Er
Et
Ei Er
Et
E-field in plane of incidenceVertical polarization
E-field normal to plane of incidenceHorizontal polarization
Propagation Mechanisms
Source:
[] Rappaport - Wireless Communications
[] W.C. Jakes - Microwave Mobile Communications
Reflection coefficient (Fresnel) depends on material properties, frequency, incident angle…
fjr
20
Type of surface (S/m) Poor ground 0.001 4
Average ground 0.005 15
Good ground 0.02 25
Sea water 5 81
Fresh water 0.01 81
Brick 0.01 4.44
Limestone 0.028 7.51
Glass at 10 GHz 0.005 4
It is often related to relative permittivity value: (for lossy dielectric) - some energy absorbed
If material is good conductor (f</r0)
- not sensitive to f
For lossy dielectrics:
- 0, r - const. with f
but may be sensitive
Propagation Mechanisms
Source:
[] Rappaport - Wireless Communications
From Maxwell’s equations and Snell’s Law:
irir
irir
snR
2
2
||cos
cossin
iri
iriR
2
2
cossin
cossin
When the first medium is free space and 21
ir REE
Reflection coefficient
Reflection coefficient
Reflection coefficient
Reflection coefficient
Reflection coefficient
Ricean K-factor
Ricean K-factor
Ricean K-factor
Ricean K-factor
Real antenna issues
Ricean K-factor - antenna
Ricean K-factor - antenna
Close scatters – practical issue
Assuming 100MHz bandwidth 200Msamples/second 1.5m path distance in order to detect another path wave
Some hints that look promising
Source:
[] IEEE Communication magazine, Jan 2001.
Conclusions/Questions
1. What do you think IMW or JFAI?
2. What to pursuit?
- If this idea holds, how to prove it?
- If not, should COSTs/ITUs/etc. be investigated better and picked one of those models?
2. If the channel is really that good why OFDM?
- Simplicity for Downlink (no PAPR headache, implementable on Winlab hardware)
- DS-CDMA (no near-far, fully orthogonal code set, multiple access…)