comm.RicianChannel

Filter input signal through a Rician fading channel

Description

The RicianChannel System object™ filters an input signal through a Rician multipath fading channel. The fading processing per link is described in Methodology for Simulating Multipath Fading Channels.

To filter an input signal using a Rician multipath fading channel:

1. Define and set up your Rician channel object. See Construction.

2. Call step to filter the input signal through a Rician multipath fading channel according to the properties of comm.Ricianhannel. The behavior of step is specific to each object in the toolbox.

Note

Starting in R2016b, instead of using the step method to perform the operation defined by the System object, you can call the object with arguments, as if it were a function. For example, y = step(obj,x) and y = obj(x) perform equivalent operations.

Construction

H = comm.RicianChannel creates a frequency-selective or frequency-flat multipath Rician fading channel System object, H. This object filters a real or complex input signal through the multipath channel to obtain the channel impaired signal.

H = comm.RicianChannel(Name,Value) creates a multipath Rician fading channel object, H, with the specified property Name set to the specified Value. You can specify additional name-value pair arguments in any order as (Name1,Value1,...,NameN,ValueN).

Properties

SampleRate	Input signal sample rate (hertz) Specify the sample rate of the input signal in hertz as a double-precision, real, positive scalar. The default value of this property is 1 Hz.
PathDelays	Discrete path delay vector (seconds) Specify the delays of the discrete paths in seconds as a double-precision, real, scalar or row vector. The default value of this property is 0. When you set PathDelays to a scalar, the channel is frequency flat. When you set PathDelays to a vector, the channel is frequency selective.
AveragePathGains	Average path gain vector (decibels) Specify the average gains of the discrete paths in decibels as a double-precision, real, scalar or row vector. The default value of this property is 0. AveragePathGains must have the same size as PathDelays.
NormalizePathGains	Normalize average path gains to 0 dB When you set this property to true, the object normalizes the fading processes so that the total power of the path gains, averaged over time, is 0dB. The default value of this property is true.
KFactor	Rician K-factor scalar or vector (linear scale) Specify the K-factor of a Rician fading channel as a double-precision, real, positive scalar or nonnegative, nonzero row vector of the same length as PathDelays. The default value of this property is 3. If KFactor is a scalar, then the first discrete path is a Rician fading process with a Rician K-factor of KFactor. The remaining discrete paths are independent Rayleigh fading processes. If KFactor is a row vector, the discrete path corresponding to a positive element of the KFactor vector is a Rician fading process with a Rician K factor specified by that element. The discrete path corresponding to a zero-valued element of the KFactor vector is a Rayleigh fading process.
DirectPathDopplerShift	Doppler shift(s) of line-of-sight component(s) (hertz) Specify the Doppler shifts for the line-of-sight components of a Rician fading channel in hertz as a double-precision, real scalar or row vector. The default value of this property is 0. DirectPathDopplerShift must have the same size as KFactor. If DirectPathDopplerShift is a scalar, this value represents the line-of-sight component Doppler shift of the first discrete path. This path exhibits a Rician fading process. If DirectPathDopplerShift is a row vector, the discrete path corresponding to a positive element of the KFactor vector is a Rician fading process. Its line-of-sight component Doppler shift is specified by the corresponding element of DirectPathDopplerShift.
DirectPathInitialPhase	Initial phase(s) of line-of-sight component(s) (radians) Specify the initial phase(s) of the line-of-sight components of a Rician fading channel in radians as a double-precision, real scalar or row vector. The default value of this property is 0. DirectPathInitialPhase must have the same size as KFactor. If DirectPathInitialPhase is a scalar, this value represents the line-of-sight component initial phase of the first discrete path. This path exhibits a Rician fading process. If DirectPathInitialPhase is a row vector, the discrete path corresponding to a positive element of the KFactor vector is a Rician fading process. Its line-of-sight component initial phase is specified by the corresponding element of DirectPathInitialPhase.
MaximumDopplerShift	Maximum Doppler shift (hertz) Specify the maximum Doppler shift for all channel paths in hertz as a double-precision, real, nonnegative scalar. The default value of this property is 0.001 Hz. The Doppler shift applies to all the paths of the channel. When you set the MaximumDopplerShift to 0, the channel remains static for the entire input. You can use the reset method to generate a new channel realization. The MaximumDopplerShift must be smaller than SampleRate/10/fc for each path, where fc represents the cutoff frequency factor of the path. For a Doppler spectrum type other than Gaussian and bi-Gaussian, fc is 1. For Gaussian and bi-Gaussian Doppler spectrum types, fc is dependent on the Doppler spectrum object properties. Refer to the algorithm section of the comm.MIMOChannel for more details about how fc is defined.
DopplerSpectrum	Doppler spectrum Specify the Doppler spectrum shape for the path(s) of the channel. This property accepts a single Doppler spectrum structure returned from the doppler function or a row cell array of such structures. The maximum Doppler shift value necessary to specify the Doppler spectrum/spectra is given by the MaximumDopplerShift property. This property applies when the MaximumDopplerShift property value is greater than 0. The default value of this property is doppler('Jakes'). If you assign a single Doppler spectrum structure to DopplerSpectrum, all paths have the same specified Doppler spectrum. If the FadingTechnique property is Sum of sinusoids, DopplerSpectrum must be doppler('Jakes'); otherwise, select from the following: doppler('Jakes') doppler('Flat') doppler('Rounded', ...) doppler('Bell', ...) doppler('Asymmetric Jakes', ...) doppler('Restricted Jakes', ...) doppler('Gaussian', ...) doppler('BiGaussian', ...) If you assign a row cell array of different Doppler spectrum structures (which can be chosen from any of those on the previous list) to DopplerSpectrum, each path has the Doppler spectrum specified by the corresponding structure in the cell array. In this case, the length of DopplerSpectrum must be equal to the length of PathDelays. To generate C code, specify this property to a single Doppler spectrum structure.
FadingTechnique	Fading technique used to model the channel Select between Filtered Gaussian noise and Sum of sinusoids to specify the way in which the channel is modeled. The default value is Filtered Gaussian noise.
NumSinusoids	Number of sinusoids used to model the fading process The NumSinuoids property is a positive integer scalar that specified the number of sinusoids used in modeling the channel and is available only when the FadingTechnique property is set to Sum of sinusoids. The default value is 48.
InitialTimeSource	Source to control the start time of the fading process Specify the initial time source as either Property or Input port. This property is available when the FadingTechnique property is set to Sum of sinusoids. When InitialTimeSource is set to Input port, the start time of the fading process is specified using the INITIALTIME input to the step function. The input value can change in consecutive calls to the step function. The default value is Property.
InitialTime	Start time of the fading process (s) Specify the time offset of the fading process as a real nonnegative scalar in seconds. This property applies when the FadingTechnique property is set to Sum of sinusoids and the InitialTimeSource property is set to Property. The default value is 0. InitialTime must be greater than the last frame end time. When InitialTime is not a multiple of 1/SampleRate, it is rounded up to the nearest sample position.
RandomStream	Source of random number stream Specify the source of random number stream as one of Global stream | mt19937ar with seed. The default value of this property is Global stream. If you set RandomStream to Global stream, the current global random number stream is used for normally distributed random number generation. In this case, the reset method only resets the filters. If you set RandomStream to mt19937ar with seed, the mt19937ar algorithm is used for normally distributed random number generation. In this case, the reset method not only resets the filters, but also reinitializes the random number stream to the value of the Seed property.
Seed	Initial seed of mt19937ar random number stream Specify the initial seed of an mt19937ar random number generator algorithm as a double-precision, real, nonnegative integer scalar. The default value of this property is 73. This property applies when you set the RandomStream property to mt19937ar with seed. The Seed reinitializes the mt19937ar random number stream in the reset method.
PathGainsOutputPort	Output channel path gains Set this property to true to output the channel path gains of the underlying fading process. The default value of this property is false.
Visualization	Enable channel visualization Specify the type of channel visualization to display as one of Off | Impulse response | Frequency response | Impulse and frequency responses | Doppler spectrum. The default value of this property is Off.
SamplesToDisplay	Specify percentage of samples to display You can specify the percentage of samples to display, since displaying fewer samples will result in better performance at the expense of lower accuracy. Specify the property as one of 10% | 25% | 50% | 100%. This applies when Visualization is set to Impulse response, Frequency response, or Impulse and frequency responses. The default value is 25%.
PathsForDopplerDisplay	Specify path for Doppler display You can specify an integer scalar which selects the discrete path used in constructing a Doppler spectrum plot. The specified path must be an element of {1, 2, ..., Np}, where Np is the number of discrete paths per link specified in the object. This property applies when Visualization is set to Doppler spectrum. The default value is 1.

Methods

info	Characteristic information about Rician Channel
reset	Reset states of the RicianChannel object
step	Filter input signal through multipath Rician fading channel

Common to All System Objects
release	Allow System object property value changes

Visualization

 Impulse Response

The impulse response plot displays the path gains, the channel filter coefficients, and the interpolated path gains. The path gains shown in magenta occur at time instances which correspond to the specified PathDelays property and may not be aligned with the input sampling time. The channel filter coefficients shown in yellow are used to model the channel. They are interpolated from the actual path gains and are aligned with the input sampling time. In cases in which the path gains are aligned with the sampling time, they will overlap the filter coefficients. Sinc interpolation is used to connect the channel filter coefficients and is shown in blue. These points are used solely for display purposes and not used in subsequent channel filtering. For a flat fading channel (one path), the sinc interpolation curve is not displayed. For all impulse response plots, the frame and sample numbers are shown in the display’s upper left corner.

The impulse response plot shares the same toolbar and menus as the System object it was based on, dsp.ArrayPlot.

In the figure, the impulse response of a channel is shown for the case in which the path gains are aligned with the sample time. The overlap between the path gains and filter coefficients is evident.

The case in which the specified path gains are not aligned with the SampleRate property is shown below. Observe that the path gains and the channel filter coefficients do not overlap and that the filter coefficients are equally distributed.

The impulse response for a frequency flat channel is shown below. You can see that the interpolated path gains are not displayed.

Note

• The displayed and specified path gain locations can differ by as much as 5% of the input sample time.

• The visualization display speed is controlled by the combination of the SamplesToDisplay property and the Reduce Updates to Improve Performance menu item. Reducing the percentage of samples to display and the enabling reduced updates will speed up the rendering of the impulse response.

• After the impulse response plots are manually closed, the step call for the Rician channel object will be executed at its normal speed.

• Code generation is available only when the Visualization property is Off.

 Frequency Response

The frequency response plot displays the Rician channel spectrum by taking a discrete Fourier transform of the channel filter coefficients. The frequency response plot shares the same toolbar and menus as the System object it was based on, dsp.SpectrumAnalyzer. The default parameter settings are shown below. These parameters can be changed from their default values by using the View > Spectrum Settings menu.

Parameter	Value
Window	Rectangular
WindowLength	Channel filter length
FFTLength	512
PowerUnits	dBW
YLimits	Based on NormalizePathGains and AveragePathGains properties

The frequency response plot for a frequency selective channel is shown.

Note

• The visualization display speed is controlled by the combination of the SamplesToDisplay property and the Reduce Plot Rate to Improve Performance menu item. Reducing the percentage of samples to display and the enabling reduced updates will speed up the rendering of the frequency response.

• After the frequency response plots are manually closed, the step call for the Rician channel object will be executed at its normal speed.

• Code generation is available only when the Visualization property is Off.

 Doppler Spectrum

The Doppler spectrum plot displays both the theoretical Doppler spectrum and the empirically determined data points. The theoretical data is displayed as a yellow line for the case of non-static channels and as a yellow point for static channels, while the empirical data is shown in blue. There is an internal buffer which must be completely filled with filtered Gaussian samples before the empirical plot is updated. The empirical plot is the running mean of the spectrum calculated from each full buffer. For non-static channels, the number of input samples needed before the next update is displayed in the upper left hand corner. The samples needed is a function of the sample rate and the maximum Doppler shift. For static channels, the text Reset fading channel for next update is displayed.

Note

• After the Doppler spectrum plots are manually closed, the step call for the Rician channel object will be executed at its normal speed.

• Code generation is available only when the Visualization property is Off.

Examples

Produce Same Rician Channel Output Using Different Random Number Generation Methods

The Rician Channel System object™ has two methods for random number generation. You can use the current global stream or the mt19937ar algorithm with a specified seed. By interacting with the global stream, the object can produce the same outputs from the two methods.

Create a PSK Modulator System object to modulate randomly generated data.

pskModulator = comm.PSKModulator;
channelInput = pskModulator(randi([0 pskModulator.ModulationOrder-1],1024,1));

Create a Rician channel System object. Set the RandomStream property to mt19937ar with seed using a name-value pair. Set the random number seed to 73.

ricianChan = comm.RicianChannel(...
    'SampleRate',1e6,...
    'PathDelays',[0.0 0.5 1.2]*1e-6,...
    'AveragePathGains',[0.1 0.5 0.2],...
    'KFactor',2.8,...
    'DirectPathDopplerShift',5.0,...
    'DirectPathInitialPhase',0.5,...
    'MaximumDopplerShift',50,...
    'DopplerSpectrum',doppler('Bell', 8),...
    'RandomStream','mt19937ar with seed', ...
    'Seed',73, ...
    'PathGainsOutputPort',true);

Filter the modulated data using the Rician channel System object, ricianChan.

[RicianChanOut1, RicianPathGains1] = ricianChan(channelInput);

Set the object to use the global stream for random number generation.

release(ricianChan);
ricianChan.RandomStream = 'Global stream';

Set the global stream to use the same seed that was specified for hRicianChan.

rng(73)

Filter the modulated data using hRicianChan for the case where the channel uses the global random number generator.

[RicianChanOut2,RicianPathGains2] = ricianChan(channelInput);

Verify that the channel and path gain outputs are the same for both function calls.

isequal(RicianChanOut1,RicianChanOut2)

ans = logical
   1

isequal(RicianPathGains1,RicianPathGains2)

ans = logical
   1

Rician Channel Impulse and Frequency Responses

This example shows how to create a frequency selective Rician channel and display its impulse and frequency responses.

Set the sample rate to 3.84 MHz and specify path delays and gains using ITU pedestrian B channel parameters. Set the Rician K-factor to 10 and the maximum Doppler shift to 50 Hz.

fs = 3.84e6;                                     % Hz
pathDelays = [0 200 800 1200 2300 3700]*1e-9;    % sec
avgPathGains = [0 -0.9 -4.9 -8 -7.8 -23.9];      % dB
fD = 50;                                         % Hz

Create a Rician channel System object with the previously defined parameters and set the Visualization property to Impulse and frequency responses using name-value pairs.

ricianChan = comm.RicianChannel('SampleRate',fs, ...
    'PathDelays',pathDelays, ...
    'AveragePathGains',avgPathGains, ...
    'KFactor',10, ...
    'MaximumDopplerShift',fD, ...
    'Visualization','Impulse and frequency responses');

Generate random binary data and pass it through the Rician channel. The impulse response plot allows you to easily identify the individual paths and their corresponding filter coefficients. The frequency selective nature of the pedestrian B channel is shown by the frequency response plot.

x = randi([0 1],1000,1);
y = ricianChan(x);

Selected Bibliography

[1] Oestges, C., and B. Clerckx. MIMO Wireless Communications: From Real-World Propagation to Space-Time Code Design, Academic Press, 2007.

[2] Correira, L. M. Mobile Broadband Multimedia Networks: Techniques, Models and Tools for 4G, Academic Press, 2006.

[3] Kermoal, J. P., L. Schumacher, K. I. Pedersen, P. E. Mogensen, and F. Frederiksen. “A stochastic MIMO radio channel model with experimental validation." IEEE Journal on Selected Areas of Communications. Vol. 20, Number 6, 2002, pp. 1211–1226.

[4] Jeruchim, M., P. Balaban, and K. S. Shanmugan. Simulation of Communication Systems, Second Edition, New York, Kluwer Academic/Plenum, 2000.

[5] Pätzold, Matthias, Cheng-Xiang Wang, and Bjorn Olav Hogstand. “Two New Sum-of-Sinusoids-Based Methods for the Efficient Generation of Multiple Uncorrelated Rayleigh Fading Waveforms.” IEEE Transactions on Wireless Communications. Vol. 8, Number 6, 2009, pp. 3122–3131.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

See System Objects in MATLAB Code Generation (MATLAB Coder).