info

Characteristic information about fading channel object

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Syntax

S = info(obj)

Description

S = info(obj) returns a structure containing characteristic information about the fading channel System object™.

example

Examples

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Get comm.RayleighChannel Info

Open Live Script

Use the info object function to get information from a comm.RayleighChannel object.

Create a Rayleigh channel object with two paths and data to pass through the channel.

rayleighchan = comm.RayleighChannel( ...
    SampleRate=1000, ...
    PathDelays=[0 4e-3], ...
    AveragePathGains=[0 0])

rayleighchan = 
  comm.RayleighChannel with properties:

             SampleRate: 1000
             PathDelays: [0 0.0040]
       AveragePathGains: [0 0]
     NormalizePathGains: true
    MaximumDopplerShift: 1.0000e-03
        DopplerSpectrum: [1x1 struct]
       ChannelFiltering: true
    PathGainsOutputPort: false

  Use get to show all properties

data = randi([0 1],600,1);

Check the Rayleigh channel object information.

info(rayleighchan)

ans = struct with fields:
    ChannelFilterCoefficients: [2x5 double]
           ChannelFilterDelay: 0
          NumSamplesProcessed: 0

Pass data through the channel and check the object information again to see that the information structure accounts for the number of samples processed.

rayleighchan(data);
Sint = info(rayleighchan)

Sint = struct with fields:
    ChannelFilterCoefficients: [2x5 double]
           ChannelFilterDelay: 0
          NumSamplesProcessed: 600

Breaking down the group delay per path, the specified PathDelays times SampleRate results in ([0 4e-3]*1000) = [0 4] sample path delays. Since the requested path delays are all integer-valued, the implemented channel filter adds no excess delay to the channel output, and the ChannelFilterDelay field reports 0 samples for the delay. As configured, the channel results in a constant group delay equal to (PathDelays*SampleRate + ChannelFilterDelay) = ([0 4e-3]*1000 + 0) = [0 4] samples per path. Use the grpdelay function to confirm the group delay for each path.

figure
subplot(2,1,1)
grpdelay(Sint.ChannelFilterCoefficients(1,:),1)
title('Integer Path Delay: Group Delay for First Delay Path')
subplot(2,1,2)
grpdelay(Sint.ChannelFilterCoefficients(2,:),1)
title('Integer Path Delay: Group Delay for Second Delay Path')

$Figure contains 2 axes objects. Axes object 1 with title Integer Path Delay: Group Delay for First Delay Path, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Group delay (samples) contains an object of type line. Axes object 2 with title Integer Path Delay: Group Delay for Second Delay Path, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Group delay (samples) contains an object of type line.$

Release the object so you can update attributes. Change the second path delay to a noninteger value of 1.5e-3 seconds. Implementing a filter with a noninteger path delay introduces excess group delay. The info object function reports this excess delay in the ChannelFilterDelay field of the information structure. Recheck the object configuration and information.

release(rayleighchan)
rayleighchan.PathDelays = [0 1.5e-3]

rayleighchan = 
  comm.RayleighChannel with properties:

             SampleRate: 1000
             PathDelays: [0 0.0015]
       AveragePathGains: [0 0]
     NormalizePathGains: true
    MaximumDopplerShift: 1.0000e-03
        DopplerSpectrum: [1x1 struct]
       ChannelFiltering: true
    PathGainsOutputPort: false

  Use get to show all properties

rayleighchan(data);
Snonint = info(rayleighchan)

Snonint = struct with fields:
    ChannelFilterCoefficients: [2x16 double]
           ChannelFilterDelay: 6
          NumSamplesProcessed: 600

Breaking down the group delay per path, the specified PathDelays times SampleRate results in ([0 1.5e-3]*1000) = [0 1.5] sample path delays. Since the requested path delays contain at least one noninteger value, the channel filter implementation results in excess group delay at the channel output and the ChannelFilterDelay field now reports 6 samples for the delay. As configured, the channel results in a constant group delay equal to (PathDelays*SampleRate + ChannelFilterDelay) = ([0 1.5e-3]*1000 + 6) = [6 7.5] samples per path. Use the grpdelay function to confirm the group delay for each path.

figure
subplot(2,1,1)
grpdelay(Snonint.ChannelFilterCoefficients(1,:),1)
title('Noninteger Path Delay: Group Delay for First Delay Path')
subplot(2,1,2)
grpdelay(Snonint.ChannelFilterCoefficients(2,:),1)
title('Noninteger Path Delay: Group Delay for Second Delay Path')

$Figure contains 2 axes objects. Axes object 1 with title Noninteger Path Delay: Group Delay for First Delay Path, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Group delay (samples) contains an object of type line. Axes object 2 with title Noninteger Path Delay: Group Delay for Second Delay Path, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Group delay (samples) contains an object of type line.$

Get comm.RicianChannel Info

Open Live Script

Use the info object function to get information from a comm.RicianChannel object.

Create a Rician channel object with two paths and data to pass through the channel.

ricianchan = comm.RicianChannel( ...
    SampleRate=500, ...
    PathDelays=[0 2e-3], ...
    AveragePathGains=[0 0])

ricianchan = 
  comm.RicianChannel with properties:

                SampleRate: 500
                PathDelays: [0 0.0020]
          AveragePathGains: [0 0]
        NormalizePathGains: true
                   KFactor: 3
    DirectPathDopplerShift: 0
    DirectPathInitialPhase: 0
       MaximumDopplerShift: 1.0000e-03
           DopplerSpectrum: [1x1 struct]
          ChannelFiltering: true
       PathGainsOutputPort: false

  Use get to show all properties

data = randi([0 1],600,1);

Check the Rician channel object information.

info(ricianchan)

ans = struct with fields:
    ChannelFilterCoefficients: [2x2 double]
           ChannelFilterDelay: 0
          NumSamplesProcessed: 0

Pass data through the channel and check the object information again to see that the information structure accounts for the number of samples processed.

ricianchan(data);
Sint = info(ricianchan)

Sint = struct with fields:
    ChannelFilterCoefficients: [2x2 double]
           ChannelFilterDelay: 0
          NumSamplesProcessed: 600

Breaking down the group delay per path, the specified PathDelays times SampleRate results in ([0 2e-3]*500) = [0 1] sample path delays. Since the requested path delays are all integer-valued, the implemented channel filter adds no excess delay to the channel output, and the ChannelFilterDelay field reports 0 samples for the delay. As configured, the channel results in a constant group delay equal to (PathDelays*SampleRate + ChannelFilterDelay) = ([0 2e-3]*500 + 0) = [0 1] samples per path. Use the grpdelay function to confirm the group delay for each path.

figure
subplot(2,1,1)
grpdelay(Sint.ChannelFilterCoefficients(1,:),1)
title('Integer Path Delay: Group Delay for First Delay Path')
subplot(2,1,2)
grpdelay(Sint.ChannelFilterCoefficients(2,:),1)
title('Integer Path Delay: Group Delay for Second Delay Path')

Release the object so you can update attributes. Change the second path delay to a noninteger value, such as 2.2e-3 seconds. Implementing a filter with a noninteger path delay introduces excess group delay. The info object function reports this excess delay in the ChannelFilterDelay field of the information structure. Recheck the object configuration and information.

release(ricianchan)
ricianchan.PathDelays = [0 2.2e-3];
ricianchan(data);
Snonint = info(ricianchan)

Snonint = struct with fields:
    ChannelFilterCoefficients: [2x16 double]
           ChannelFilterDelay: 6
          NumSamplesProcessed: 600

Breaking down the group delay per path, the specified PathDelays times SampleRate results in ([0 2.2e-3]*500) = [0 1.1] sample path delays. Since the requested path delays contain at least one noninteger value, the channel filter implementation results in excess group delay at the channel output and the ChannelFilterDelay field now reports 6 samples for the delay. For a Rician channel, the filter is not symmetric which can be observed by variation in the group delay for the second path. As configured, the channel results in a group delay centered around (PathDelays*SampleRate + ChannelFilterDelay) = ([0 2.2e-3]*500 + 6) = [6 7.1] samples per path. Use the grpdelay function to confirm the group delay for each path.

figure
subplot(2,1,1)
grpdelay(Snonint.ChannelFilterCoefficients(1,:),1)
title('Noninteger Path Delay: Group Delay for First Delay Path')
subplot(2,1,2)
grpdelay(Snonint.ChannelFilterCoefficients(2,:),1)
title('Noninteger Path Delay: Group Delay for Second Delay Path')

Get comm.MIMOChannel Info

Open Live Script

Use the info object function to get information from a comm.MIMOChannel object.

Create a MIMO channel object with one path and data to pass through the channel.

mimo = comm.MIMOChannel( ...
    SampleRate=1000, ...
    PathDelays=4e-3, ...
    AveragePathGains=0)

mimo = 
  comm.MIMOChannel with properties:

                         SampleRate: 1000
                         PathDelays: 0.0040
                   AveragePathGains: 0
                 NormalizePathGains: true
                 FadingDistribution: 'Rayleigh'
                MaximumDopplerShift: 1.0000e-03
                    DopplerSpectrum: [1x1 struct]
    SpatialCorrelationSpecification: 'Separate Tx Rx'
          TransmitCorrelationMatrix: [2x2 double]
           ReceiveCorrelationMatrix: [2x2 double]
                   AntennaSelection: 'Off'
            NormalizeChannelOutputs: true
                   ChannelFiltering: true
                PathGainsOutputPort: false

  Use get to show all properties

data = randi([0 1],600,2);

Check the MIMO channel object information.

info(mimo)

ans = struct with fields:
    ChannelFilterCoefficients: [0 0 0 0 1]
           ChannelFilterDelay: 0
          NumSamplesProcessed: 0

Pass data through the channel and check the object information again to see that the information structure accounts for the number of samples processed.

mimo(data);
Sint = info(mimo)

Sint = struct with fields:
    ChannelFilterCoefficients: [0 0 0 0 1]
           ChannelFilterDelay: 0
          NumSamplesProcessed: 600

Breaking down the group delay, the specified PathDelays times SampleRate results in (4e-3*1000) = 4 sample path delay. Since the requested path delay is integer-valued, the implemented channel filter adds no excess delay to the channel output, and the ChannelFilterDelay field reports 0 samples for the delay. As configured, the channel results in a constant group delay equal to (PathDelays*SampleRate + ChannelFilterDelay) = (4e-3*1000 + 0) = 4 samples. Use the grpdelay function to confirm the group delay for the integer path delay.

grpdelay(Sint.ChannelFilterCoefficients,1)
title('Integer Path Delay: Group Delay')

Figure contains an axes object. The axes object with title Integer Path Delay: Group Delay, xlabel Normalized Frequency ( times pi blank rad/sample), ylabel Group delay (samples) contains an object of type line.

Release the object so you can update attributes. Change the path delay to a noninteger value, such as 2.5e-3 seconds. Implementing a filter with a noninteger path delay introduces excess group delay. The info object function reports this excess delay in the ChannelFilterDelay field of the information structure. Recheck the object configuration and information.

release(mimo)
mimo.PathDelays = 2.5e-3

mimo = 
  comm.MIMOChannel with properties:

                         SampleRate: 1000
                         PathDelays: 0.0025
                   AveragePathGains: 0
                 NormalizePathGains: true
                 FadingDistribution: 'Rayleigh'
                MaximumDopplerShift: 1.0000e-03
                    DopplerSpectrum: [1x1 struct]
    SpatialCorrelationSpecification: 'Separate Tx Rx'
          TransmitCorrelationMatrix: [2x2 double]
           ReceiveCorrelationMatrix: [2x2 double]
                   AntennaSelection: 'Off'
            NormalizeChannelOutputs: true
                   ChannelFiltering: true
                PathGainsOutputPort: false

  Use get to show all properties

Snonint = info(mimo)

Snonint = struct with fields:
    ChannelFilterCoefficients: [-0.0326 0.0403 -0.0504 0.0646 -0.0861 0.1238 -0.2101 0.6359 0.6359 -0.2101 0.1238 -0.0861 0.0646 -0.0504 0.0403 -0.0326]
           ChannelFilterDelay: 5
          NumSamplesProcessed: 0

Breaking down the group delay, the specified PathDelays times SampleRate results in (2.5e-3*1000) = 2.5 sample path delay. Since the requested path delay contains a noninteger value, the channel filter implementation results in excess group delay at the channel output and the ChannelFilterDelay field now reports 5 samples for the delay. As configured, the channel results in a constant group delay equal to (PathDelays*SampleRate + ChannelFilterDelay) = (2.5e-3*1000 + 5) = 7.5 samples. Use the grpdelay function to compare the group delay for the integer and noninteger path delay.

figure
subplot(2,1,1)
grpdelay(Sint.ChannelFilterCoefficients,1)
title('Integer Path Delay: Group Delay')
subplot(2,1,2)
grpdelay(Snonint.ChannelFilterCoefficients,1)
title('Noninteger Path Delay: Group Delay')

$Figure contains 2 axes objects. Axes object 1 with title Integer Path Delay: Group Delay, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Group delay (samples) contains an object of type line. Axes object 2 with title Noninteger Path Delay: Group Delay, xlabel Normalized Frequency (\times\pi rad/sample), ylabel Group delay (samples) contains an object of type line.$

Model MIMO Channel Using Sum-of-Sinusoids Technique

Open Live Script

Show that the channel state is maintained for discontinuous transmissions by using MIMO channel System objects configured to use the sum-of-sinusoids fading technique. Observe discontinuous channel response segments overlaid on a continuous channel response.

Set the channel properties.

fs = 1000;               % Sample rate (Hz)
pathDelays = [0 2.5e-3]; % Path delays (s)
pathPower = [0 -6];      % Path power (dB)
fD = 5;                  % Maximum Doppler shift (Hz)
ns = 1000;               % Number of samples
nsdel = 100;             % Number of samples for delayed paths

Define a continuous time span and three discontinuous time segments over which to plot and view the channel response. View a 1000-sample continuous channel response starting at time 0 and three 100-sample channel responses starting at times 0.1, 0.4, and 0.7 seconds, respectively.

to0 = 0.0;
to1 = 0.1;
to2 = 0.4;
to3 = 0.7;
t0 = (to0:ns-1)/fs;      % Transmission 0
t1 = to1+(0:nsdel-1)/fs; % Transmission 1
t2 = to2+(0:nsdel-1)/fs; % Transmission 2
t3 = to3+(0:nsdel-1)/fs; % Transmission 3

Create a flat-fading 2-by-2 MIMO channel System object, disabling channel filtering and specifying a 1000 Hz sampling rate, the sum-of-sinusoids fading technique, and the number of samples to view. Specify a seed value so that results can be repeated. Use the default InitialTime property setting so that the fading channel is simulated from time 0.

mimoChan1 = comm.MIMOChannel('SampleRate',fs, ...
    'MaximumDopplerShift',fD, ...
    'RandomStream','mt19937ar with seed', ...
    'Seed',17, ...
    'FadingTechnique','Sum of sinusoids', ...
    'ChannelFiltering',false, ...
    'NumSamples',ns);

Create a clone of the MIMO channel System object. Change the number of samples for the delayed paths and the source for the initial time so that you can specify the fading channel offset time as an input argument when calling the System object.

mimoChan2 = clone(mimoChan1);
mimoChan2.InitialTimeSource = 'Input port';
mimoChan2.NumSamples = nsdel;

Save the path gain output for the continuous channel response by using the mimoChan1 object and for the discontinuous delayed channel responses by using the mimoChan2 object with initial time offsets provided as input arguments.

pg0 = mimoChan1();
pg1 = mimoChan2(to1);
pg2 = mimoChan2(to2);
pg3 = mimoChan2(to3);

Compare the number of samples processed by the two channels by using the info method. The results show that mimoChan1 processed 1000 samples and that mimoChan2 processed only 300 samples.

G = info(mimoChan1);
H = info(mimoChan2);
[G.NumSamplesProcessed H.NumSamplesProcessed]

ans = 1×2

        1000         300

Convert the path gains into decibels for the path corresponding to the first transmit and first receive antenna.

pathGain0 = 20*log10(abs(pg0(:,1,1,1)));
pathGain1 = 20*log10(abs(pg1(:,1,1,1)));
pathGain2 = 20*log10(abs(pg2(:,1,1,1)));
pathGain3 = 20*log10(abs(pg3(:,1,1,1)));

Plot the path gains for the continuous and discontinuous cases. The results show that the gains for the three segments match the gain for the continuous case. The alignment of the two shows that the sum-of-sinusoids technique is ideally suited to the simulation of packetized data because the channel characteristics are maintained even when data is not transmitted.

plot(t0,pathGain0,'r--')
hold on
plot(t1,pathGain1,'b')
plot(t2,pathGain2,'b')
plot(t3,pathGain3,'b')
grid
title('Continuous and Discontinuous Channel Response')
xlabel('Time (sec)')
ylabel('Path Gain (dB)')
legend('Continuous','Discontinuous','location','nw')

Figure contains an axes object. The axes object with title Continuous and Discontinuous Channel Response, xlabel Time (sec), ylabel Path Gain (dB) contains 4 objects of type line. These objects represent Continuous, Discontinuous.

Input Arguments

collapse all

`obj` — System object to get information from
System object

System object to get information from, specified as a comm.MIMOChannel, comm.RayleighChannel, or comm.RicianChannel System object.

Output Arguments

collapse all

`S` — Structure containing object information
structure

Structure containing these fields with information about the System object.

`ChannelFilterDelay` — Excess filter delay
positive integer

Excess filter delay in samples, returned as a positive integer.

If you configure the PathDelays property of your channel object with all integer-valued delays, the implemented channel filter adds no excess delay to the channel output. In this case, the ChannelFilterDelay field reports 0 for the excess path delay.
If you configure the PathDelays property of your channel object with any noninteger-valued delays, the implemented channel filter may add excess delay to the channel output. In this case, the ChannelFilterDelay field may report a nonzero value for the excess path delay.

`ChannelFilterCoefficients` — Channel filter coefficients
matrix

Channel filter coefficients, returned as a matrix. The time varying path gains are applied as gains to this non-varying filter to produce the channel output over time

`NumSamplesProcessed` — Number of samples processed by the channel object
positive integer

Number of samples processed by the channel object since the last reset, returned as a positive integer.

`LastFrameTime` — Last frame ending time
positive scalar

Last frame ending time in seconds, returned as a positive scalar. Use this value to confirm the simulation time.

Dependencies

This property applies when the FadingTechnique property is 'Sum of sinusoids' and the InitialTimeSource property is 'Input port'.

Version History

Introduced in R2012a

info

Syntax

Description

Examples

Get comm.RayleighChannel Info

Get comm.RicianChannel Info

Get comm.MIMOChannel Info

Model MIMO Channel Using Sum-of-Sinusoids Technique

Input Arguments

`obj` — System object to get information from
System object

Output Arguments

`S` — Structure containing object information
structure

`ChannelFilterDelay` — Excess filter delay
positive integer

`ChannelFilterCoefficients` — Channel filter coefficients
matrix

`NumSamplesProcessed` — Number of samples processed by the channel object
positive integer

`LastFrameTime` — Last frame ending time
positive scalar

Dependencies

Version History

See Also

Objects

info

Syntax

Description

Examples

Get comm.RayleighChannel Info

Get comm.RicianChannel Info

Get comm.MIMOChannel Info

Model MIMO Channel Using Sum-of-Sinusoids Technique

Input Arguments

obj — System object to get information from System object

Output Arguments

S — Structure containing object information structure

ChannelFilterDelay — Excess filter delay positive integer

ChannelFilterCoefficients — Channel filter coefficients matrix

NumSamplesProcessed — Number of samples processed by the channel object positive integer

LastFrameTime — Last frame ending time positive scalar

Dependencies

Version History

See Also

Objects

`obj` — System object to get information from
System object

`S` — Structure containing object information
structure

`ChannelFilterDelay` — Excess filter delay
positive integer

`ChannelFilterCoefficients` — Channel filter coefficients
matrix

`NumSamplesProcessed` — Number of samples processed by the channel object
positive integer

`LastFrameTime` — Last frame ending time
positive scalar