- Lab #4: - Completing our target system - Channel implementation

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Instructor : Jaewook Kang
At CSNL-GIST
E-mail: jwkkang@gist.ac.kr
2011, Apr. 8th
A Simple Communication System Design
Lab with MATLAB Simulink
- Lab #4: - Completing our target system
- Channel implementation

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Next time…Next time…
Place: IC203
Weeks Time Hour Instructor
1 week
Lab. #0
3.11
(13:00~
16:00)
3
- Overview of Development with Simulink
- QPSK Model with AWGN Channel/ Rayleigh Fading
Channel
- Development Example: Interference Cancellation for Satellite Communi
Junil Ahn
2 weeks
Lab. #1
3.18
(13:00~
14:20)
1.5 - Basic OFDM Junil Ahn
3.18
(14:30~
16:00)
1.5
- Introduction
- How to use Simulink with interleaver
implementation
Jaewook Kang
3 weeks
Lab. #2
3.25
(13:00~
16:00)
3
- How to use S-function builder
- PSF and Matched filter design
- Concept of upsampling and downsampling
Jaewook Kang
4 weeks
Lab. #3
4.1
(13:00~
16:00)
3
- Phase splitter
- Up conversion and down conversion
Jaewook Kang
5 weeks
Lab. #4
4.8
(13:00~
16:00)
3
- How to make subsystem
- Channel implementation
Jaewook Kang

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Summary of prev. lectureSummary of prev. lecture
Up conversions
By multiplying to BB signals, we can obtain PB signals
We usually use k=4 IF=pi/2
In case of down conversion, only sign of exponent is opposite.
2
( ) ( ) ( )
( ) ( )
2 2
Re[ ( )] cos( ) sin( )
2 2
Im [ ( )] sin( ) cos( )
BB
j n
k
PB BB
s n x n jy n
s n s n e
s t x n y n
k k
ag s n x n y n
k k
π
π π
π π
−
= +
=
= −
= +
2
j t
k
e
π
−
where 2, integerk ≥

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Summary of prev. lectureSummary of prev. lecture
Phase splitter
Since Tx only transmit real part of signals, we have to recover
the full complex signal from real part of the received signal.
When using FIR filter to implement Phase splitter, we have to
consider the delay of the filter (N-1)/2.

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Summary of prev. lectureSummary of prev. lecture
Hilbert transform
Find imaginary part of Xc(t) from real part only when Xc(t) is complex exponential.
02j f t
Ae π
Re[]
Hilbert TR
+
02j f t
Ae π
Xc Xr
Xi_hat
Xc_hat
X
j

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Today’s main pointsToday’s main points
Complete to make our target system
Let’s make a channel using simulink
How to use MATLAB function in sumulink
How to use variable from workspace

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Our target systemOur target system
Tx part
Rx part
Tx Source Interleaver
QAM
Mapper
PSF X
NCO
↑4
Phase
Splitter
Matched
filter
QAM
DemapperX
NCO
↓4
De-
Interleaver
Rx Source
:Real
:Complex

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Our target system in simulinkOur target system in simulink

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Channel ImplementationChannel Implementation
Rcvd signal = Trmtd signal x
( large scale fading) x (small scaling fading )
+AWGN
Today mainly talk about large scale fading.
We are going to use Block Rayleigh/Rician fading for small scale
fading.

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Fading channelFading channel
Tx
- is Rx
Large scale
fading
Small scale
fading
Fading channel = Large signal fading + small signal fading

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Signal
attenuation due
to propagation
distance
Fading channelFading channel
Multipath fading
< Only small scale >< Large + Small scale >

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Large scale fadingLarge scale fading
Log-distance path loss model
Aa one of the simplest model, we have use “log-distance path loss model”
Basically, the path loss is proportional to an nth-power of d/d0 in average sense.
Path loss is often represented by dB scale such that
0
0
where d is distance of two points to commni.
and d is the ref. distance (km)
p
d
L
d
∝
0
0
2
0
0 10
0 0
( ) ( ) 10 log( )
4 1
( ) 10log ,
p s
s
c
d
L dB L d n
d
d
L d
f u
π
λ
λ ε
= +
⎛ ⎞
= =⎜ ⎟
⎝ ⎠
0
0
0
d 1, for large cells
d 0.1, for micro cells
d 0.001, for indoor channels
=⎧
⎪
=⎨
⎪ =⎩
Path loss exponent, n
2, in free space
2, urban space, or place w/ many obstructions
n<2, w/ strong guided wave
n
n
−
=⎧
⎪
>⎨
⎪
⎩

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Large scale fadingLarge scale fading
Log-distance path loss model
However, model just provide average of path loss.
It is necessary to provide for variations about the mean such that
we have log-normal model.
Then, how to make use it in simulation ?
0
0
( ) ( ) 10 log( )p s
d
L dB L d n
d
= +
2
0
0
( ) ( ) 10 log( ) where ~ (0, )p s
d
L dB L d n X X N
d
σ σ σ= + +
2
0
10 10 10
0
2
10
10
0
2
10
0
2
10
0
4
( ) 10log 10log ( ) log 10
4
10log ( ) 10
4
(linear scale) ( ) 10
4
(path loss gain)= ( ) 10
Xn
p
Xn
Xn
p
Xn
d d
L dB
d
d d
d
d d
L
d
d d
K
d
σ
σ
σ
σ
π
λ
π
λ
π
λ
π
λ
−
−
−
⎛ ⎞
= + +⎜ ⎟
⎝ ⎠
⎛ ⎞
= ⎜ ⎟
⎝ ⎠
⎛ ⎞
= ⎜ ⎟
⎝ ⎠
⎛ ⎞
⎜ ⎟
⎝ ⎠

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Small scale fadingSmall scale fading
Block Rayleigh fading
A well-known and one of the simplest channels.
By CLT, sum of a large number of stochastic components follows zero mean
complex Gaussian with unit variance.
Block fading channel
2 2 1
~ (0,1)
~ , tan ~ ( , )
Let C X jY X and Y N
Y
r X Y Rayleigh uniform
X
θ π π−
= +
= + = −

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Small scale fadingSmall scale fading
Block Rician fading
If LOS exist, the small scale fading channel is called Rician fading channels.
2 2 1
~ (0,1)
( ) ( )
) ( ) ~ , tan ~ ( , )
2 2
where A is magnitude of LOS
Let X and Y N
Then C X A j Y A
A A Y
r X Y Rician uniform
X
θ π π−
= + + +
= + + + = −
Y
X
var=1
Y
X
var=1
0
( , )
2 2
A A
A
< Rician >< Rayleigh >

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Channel ImplementationChannel Implementation
Let implement your own channel model using
simulink
Let do it together !!

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Channel ImplementationChannel Implementation
Block to use MATLAB functions
The first block works like a MATLAB function.
The second function is used like m-script by writing
down combination of functions and parameters.
The 3rd block is user-defined version of the first one

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Channel ImplementationChannel Implementation
How to bring variables from the workspace
In order to bring data from the workspace,
you should change the data format to “struct” type.
The structure should includes time and signal
field.
In addition, the signal field also should have
field for values and dimension of the signal.
An example
% make channel data in structure type.
hSR=sqrt(1/2)*(randn(NumOfsym,1)+A+j*(randn(NumO
fsym,1)+A) );
hSRout.time=1:length(hSR);
hSRout.signals.values=hSR;
hSRout.signals.dimensions=1;

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Channel ImplementationChannel Implementation
How to make subsystem
1) Specify your inputs and outputs in the block

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Channel ImplementationChannel Implementation
How to make subsystems
2) Select all block to compose the subsystem and click “Create
subsystem”.

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Channel ImplementationChannel Implementation
How to make subsystems
3-1) Click Mask subsystem
3-2) Specify your block and port names
3-3) Set parameters and put some description for your block.

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Wrapping upWrapping up
Try again to make your own channel block and use it in your
simulation.
Retry to make blocks which are not completed in previous class.
Thank you for attending this class.
This is the end of the Simulink education program.
If you have some question while doing your project using simulink,
please bring food with your trouble.