Lecture07_ChannelSounding

8/13/2019 Lecture07_ChannelSounding

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Channel Modelling ETI 085Lecture no:

7

Fredrik Tufvesson

Department of Electrical and Information Technology

Lund University, Sweden

[email protected]

2008-11-20 Fredrik Tufvesson - ETI 085 1

Why directional channel models? The spatial domain can be used to increase the spectral

e c ency o t e system

Smart antennas

Need to know directional properties

Which directions?

Model inde endent on s ecific antenna attern


Double directional impulse responseTX position RX position number of multipath components

h t r r Nr

h t r r

for these positions

1

delay direction-of-departure

- -

h t,r

TX,r

RX,,

,

|a

|ej


Physical interpretation

l



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Angular spreadEs, , ,s , , , P s, ,,

double directional delay power spectrum

an ular dela ower s ectrum

, , s , , ,

ADPS, DDD PS, , GMSd

l

angular power spectrum

APS APDS, d

power

P APS d


Directional models

The double directional delay power spectrum is sometimes factorized

. . . , .

DDDP S, , APSBS

APSMS

PDP

Often in reality there are groups of scatterers with similar DoD and DoA

clustersDDD PS P

cAPS

c,BS APS

c,MS PD P

c

k


Angular dispersion At the base station the angular spread is often modeled as

ap ac an

0ex 2APS

=

S

Typical rms angular spread:

Indoor office: 10-20 deg

n us r a : - eg

Microcell 5-20 deg LOS, 10-40 deg NLOS

Rural: 1-5 de


Laplacian distribution example Angular spreads 5, 10, 20, 40 degrees

0.09

0.1

0.07

0.08

.

0.05

0.06

pdf

.

0.03

0.04

0

0.01

.


200 150 100 50 0 50 100 150 200

Angle


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Geometry-based stochastic channel models Assign positions for scatterers

Derive impulse response given

the scatterers and distributions

for the signal properties.

Used in the COST 259

,

model the 3GPP

spatial channel

,

WINNER model


Channel measurementsIn order to model the channel behavior we need to measure

its properties

Time domain measurements mpu se soun er

correlative sounder

Fre uenc domain measurements

Vector network analyzer

rec ona measuremen s

directional antennas

multiplexed arrays

virtual arrays


Impulse sounder

hmeasti, phti,

impulse responseof sounder

impulse response

of channel


Correlative sounder Transmit a pseudo-noise sequence and correlate with the same

Compare conventional CDMA systems

Correlation peak for each delayed multipath component

(

Tc-Tc

correlation eak im ulse res onse measured im ulse res onse



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Frequency domain measurements Use a vector network analyzer or similar to determine the

trans er unct on o t e c anne

* *H H H H=

Time domain properties via FFT

meas antenna c anne antenna

Using a large frequency band it is possible to get good time

resolution

s or me oma n measuremen s, we nee o now e

influence of the measurement system


Channel sounding directional antenna Measure one impulse

response or eacantenna orientation


Channel sounding antenna array

response for each antennaelement

Ambi uit with linear arra

d d dlinear array

h( ) h( ) h( )h( )

x=0 x=d x=2d x=(M-1)d

spatially resolved impulse response


Real multiplexed and virtual arrays Real array: simultaneous

measuremen a a

antenna elements RX RX RX

Multiplexed array: short

time intervals between

Digital Signal Processing

measurements at different

elements RX

Virtual array: long delay


no problem with mutual

coupling RX




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Directional analysis The DoA can, e.g., be

received signals with steering

vectors.

1

expjk0dcos

a exp j2k0dcos

expjM 1k0dcos

An element spacing of d=5.8 cm

and an an le of arrival of =20d sin degrees gives a time delay of

6.610-11 s between neighboring


elements

High resolution algorithms In order to get better angular resolution, other techniques

or est mat ng t e ang es are use , e.g.:

MUSIC, subspace method using spectral search ,

MVM (Capons beamformer), rather easy spectral search method

SAGE, iterative maximum likelihood method

Based on models for the propagation

Rather com lex, one measurement oint ma take 15

minutes on a decent computer


RUSK LUND our broadband MIMO channelsounderounder

measurement system for

radio propagation

,GHz and 5 GHz.

Financed by Knut and Alice

Wallenbergs stiftelse, FOI

and LTH

switches, currently 32

elements at each side.


Its all about measuring some delays...y In MIMO systems we use the fact

between the transmitter and

receiver

These paths are characterized by a time delay,

hase shift,

attenuation,

angle of departure and

angle of arrival

The angle of departure and angle

of arrival result in a slight

difference in time delay for each of

the antenna elements



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The measurement system

measurements

,

frequencies

2 se arate PCs to mana e the data flow from the A/D

converters

Oven controlled rubidium clocks to maintain

synchronization during wireless measurements

GPS and wheel sensors to position the system Broadband patch antennas with 128 antenna ports at 2.6

GHz


Circular 300 MHz antennas with a diameter of 1.5 m

RUSK LUND transmitter bandwidths: u to 240 MHz

frequency grid 10 MHz

max. power 500 mW, withpossibility for 10 W externalamplifier

carrier frequency ranges 2200 2700 MHz,

Baseband (Arbitrary Wave Form)

235-387 MHz (20W)

Power Supply 24 V DC and 230 VAC

Signal Generator

Frequency Synthesizer

Rubidium Reference Modulator

Power Amplifier

MIMO Control Unit


RUSK LUND receiver GPS Receiver

Odometer Interface

total amplification 72 dB

AGC dynamic range 51 dB ,

a us a e n s eps, intermediate frequency 160 MHz

bandwidth 240 MHz

-

High Speed ADC

Automatic Gain Control (AGC)

MIMO Control Unit

Rubidium Reference

High Speed Data Recorder 320MByte/s, 500 GByte


Antennas

To get good

resolution we want

4x16 dualpolarized circular 4x8 dualpolarized


rec angu ar array


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Antennas cont.

PDA device

sleeve antenna array


RUSK LUND Key Parameters Power: TX

235-387 MHz

2200 2700 MHz, 5150 5750 MHz

20 W (300 MHz)

500 mW and 10 W high powerextension (2 and 5 GHz)

RF carrier frequency grid:

1 MHz (300 MHz)

10 MHz (2 and 5 GHz)

Antennas:

7+1 circular monopole antennaarray (300 MHz),

Measurement bandwidth up to 240MHz (null-to-null bandwidth)

MIMO capabil ity:

x e emen p anar array, uapolarized (2 GHz)

4x16 element circular array, dualpolarized (2 GHz)

16 TX antennas and 8 RX antennas(300 MHz)

32 TX antennas and 32 RX

various application specificantennas

GHZ)


Lecture07_ChannelSounding

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