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…)