simulate multipath rayleigh fading propagation channel - simulink

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Simulate multipath Rayleigh fading propagation channel

Multipath Rayleigh Fading Channel

Library

Channels

Description

The Multipath Rayleigh Fading Channel block implements a baseband simulation of a multipath Rayleigh fading

propagation channel. You can use this block to model mobile wireless communication systems. For details about fading

channels, see the references listed below.

This block accepts a scalar value or column vector input signal. The block inherits sample time from the input signal. The

input signal must have a discrete sample time greater than 0.

Relative motion between the transmitter and receiver causes Doppler shifts in the signal frequency. You can specify the

Doppler spectrum of the Rayleigh process using theDoppler spectrum typeparameter. For channels with multiple paths,

you can assign each path a different Doppler spectrum, by entering a vector of doppler objects in the Doppler spectrum

field.

Because a multipath channel reflects signals at multiple places, a transmitted signal travels to the receiver along several

paths, each of which may have differing lengths and associated time delays. In the block's parameter dialog box, the

Discrete path delay vector specifies the time delay for each path. If you do not check Normalize gain vector to 0 dB

overall gain, then the Average path gain vector specifies the gain for each path. When you check the box, the block

uses a multiple of Average path gain vector instead of the Average path gain vectoritself, choosing the scaling factorso that the channel's effective gain, considering all paths, is 0 dB.

The number of paths indicates the length of Discrete path delay vector or Average path gain vector, whichever is larger.

If both of these parameters are vectors, then they must have the same length if exactly one of these parameters contains

a scalar value, then the block expands it into a vector whose size matches that of the other vector parameter.

The block multiplies the input signal by samples of a Rayleigh-distributed complex random process. The scalar Initial

seed parameter seeds the random number generator and the block generates random numbers using the Ziggurat method.

Double-clicking this block during simulation or selecting Open channel visualization at start of simulationplots the

channel characteristics using the channel visualization tool. See Channel Visualization in Communications System

Toolbox User's Guide for details.

Dialog Box
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Maximum Doppler shift (Hz)

A positive scalar v alue t hat indicates the maximum Doppler shift.

Doppler spectrum type

Specifies the Doppler spectrum of the Rayleigh process.

This parameter defaults to Jakes Doppler spectrum. Alternatively, you can also choose any of the following types:

Flat

Gaussian

Rounded

Restricted Jakes

Asy mmetrical Jakes

Bi-Gaussian

Bell

For all Doppler spectrum types except Jakes and Flat, you can choose one or more parameters to control the shape

of the spectrum.
http://www.mathworks.com/help/comm/ref/doppler.bell.htmlhttp://www.mathworks.com/help/comm/ref/doppler.bigaussian.htmlhttp://www.mathworks.com/help/comm/ref/doppler.ajakes.htmlhttp://www.mathworks.com/help/comm/ref/doppler.rjakes.htmlhttp://www.mathworks.com/help/comm/ref/doppler.rounded.htmlhttp://www.mathworks.com/help/comm/ref/doppler.gaussian.htmlhttp://www.mathworks.com/help/comm/ref/doppler.flat.html


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You can also select Specify as dialog parameter for the Doppler spectrum type. Specify the Doppler spectrum

by entering an object in the Doppler spectrum field. See the doppler function reference in Communications System

Toolbox User's Guide for details on how to construct Doppler objects, and also for the meaning of the parameters

associated with the various Doppler spectrum types.

Discrete path delay vector (s)

A vect or t hat specif ies the propagation delay for each path.

Average path gain vector (dB)

A vect or t hat specif ies the gain f or each path.

Normalize gain vector to 0 dB overall gain

Checking this box causes the block to scale the Gain vector parameter so that the channel's effective gain

(considering all paths) is 0 dB.

Initial seed

The scalar seed for the Gaussian noise generator.

Open channel visualization at start of simulation

Select this check box to open the channel visualization tool when a simulation begins.

Complex path gains portSelect this check box to create a port that outputs the values of the complex path gains for each path. In this N-by-M

multichannel output, N represents the number of samples the input signal contains and Mrepresents the number of

discrete paths (number of delays).

Channel filter delay port

Select this check box to create a port that outputs the value of the delay (in samples) that results from the filtering

operation of this block. This delay is zero if only one path is simulated, but can be greater than zero if more than one

path is present. See Methodology for Simulating Multipath Fading Channels: in Communications System Toolbox User's

Guide for a definition of this delay, where it is denoted as .

Algorithm

This implementation is based on the direct-form simulator described in Reference [1]. A detailed explanation of the

implementation, including a review of the different Doppler spectra, can be found in [4].

Some wireless applications, such as standard GSM (Global System for Mobile Communication) systems, prefer to specify

Doppler shifts in terms of the speed of the mobile. If the mobile moves at speed v making an angle of with the direction

of wave motion, then the Doppler shift is

f = (vf/c)cos

where f is the transmission carrier frequency and c is the speed of light. The Doppler frequency represents the maximum

Doppler shift arising from motion of the mobile.

Example

Generating Ideal Theoretical BER Results for a Rayleigh Fading Channel

This example illustrates how to generate ideal theoretical BER results for a flat Rayleigh fading channel. The model uses

reproduces known theoretical results and shows the correct BER performance for a flat Rayleigh fading channel. In this

example, you will run the model and compare the simulation results to the BERTool theoretical results for verification

purposes. Note that the EbNo value for the model's AWGN block is 5 dB. You can change the noise power by double-

clicking the AWGN block and entering another numeric value in the EbNo parameter.

Opening the Model

N1

d
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You can open the model by clicking here in the MATLAB Help browser. Alternatively, you can type

doc_qpsk_rayleigh_derotated at the MATLAB command line.

Running the Model and Comparing Results

1. You can run the example by clicking Simulation > Run.

2. After the model collects more than 5000 errors, click the stop button.

3. Close the three scopes.

4. In the Simulink model window, double-click the Transmitter Output block. In the mask window, click the Figure

Properties tab, uncheck Open scope at start of Simulation, then click OK.

5. In the Simulink model window, double-click the Rayleigh Channel Output block. In the mask window, click the Figure

Properties tab, uncheck Open scope at start of Simulation, then click OK.

6. In the Simulink model window, double-click the Noisy Rayleigh Channel Output block. In the mask window, click the

Figure Properties tab, uncheck Open scope at start of Simulation, then clock OK.

7. In the Simulink model window, double-click the Error Rate Calculation block, check Stop simulation, enter 5000 for

Target number of error, then click OK.

8. Click the play button to rerun the example.

9. Open BERTool by typing bertool at the MATLAB command line.

10. In BERTool, click the Theoretical tab and make the following selections:


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For Eb/No range enter 0:10

For Channel type, select Rayleigh

For Diversity Order enter 1

For Modulation Type, select PSK

For Modulation order, select 4

11. Click Plot.

12. Since the Simulink model uses an EbNo value of 5 dB, verify the probability of error on the BERTool curve at 5 dB.

The two values should be approximately equal.


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Click the Data Cursor button (second from right) and clic k on the BERTool curve at 5dB.

See Also

Rayleigh Noise Generator, Multipath Rician Fading Channel, doppler

References

[1] Jeruchim, Michel C., Balaban, Philip, and Shanmugan, K. Sam, Simulation of Communication Systems, Second

edition, New York, Kluwer Academic/Plenum, 2000.

[2] Jakes, William C., ed. Microwave Mobile Communications, New York, IEEE Press, 1974.

[3] Lee, William C. Y., Mobile Communications Design Fundamentals, 2nd Ed. New York, Wiley, 1993.

[4] Iskander, Cyril-Daniel,A MATLAB-based Object -Oriented Approach t o Multipath Fading Channel Simulation, a

MATLAB Central submission available from www.mathworks.com.

Introduced before R2006a
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simulate multipath rayleigh fading propagation channel - simulink

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