comm.MultibandCombiner

Frequency-shift and combine signals

Since R2021b

Description

The comm.MultibandCombiner System object™ interpolates, shifts input signals to the specified frequency bands, and then combines them into a single signal. For more information, see the Algorithms section.

To frequency-shift and combine signals:

1. Create the comm.MultibandCombiner object and set its properties.

2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

Creation

Syntax

multibandcombiner = comm.MultibandCombiner

multibandcombiner = comm.MultibandCombiner(Name,Value)

Description

multibandcombiner = comm.MultibandCombiner creates a multiband combiner System object to frequency-shift and combine input signals.

multibandcombiner = comm.MultibandCombiner(Name,Value) sets properties using one or more name-value arguments. For example, 'InputSampleRate',2e6 specifies an input signal sample rate of 2 MHz.

Properties

Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

InputSampleRate — Input signal sample rate

1e6 (default) | positive scalar

Input signal sample rate in Hz, specified as a positive scalar.

Data Types: double

FrequencyOffsets — Frequency offsets

[0 1e6] (default) | scalar | 1-by-N_chan vector

Frequency offsets in Hz, specified as one of these options.

• Scalar — Each channel of the input signal is frequency-shifted by this scalar value.

• 1-by- N_chan vector — Each channel of the input signal is frequency-shifted by the corresponding value in this vector. N_chan is the number of channels in the input signal x.

Data Types: double

OutputSampleRateSource — Source of output sample rate

'Auto' (default) | 'Property'

Source of the output sample rate, specified as one of these values.

• 'Auto' — The object interpolates the input signals to ensure that the resulting sample rate of the signals is sufficient to avoid distorting the frequency content of the original signals after they are frequency-shifted to produce the output signal.

• 'Property' — Specify the output sample rate by using the OutputSampleRate property.

Data Types: char | string

OutputSampleRate — Output signal sample rate

3e6 (default) | positive scalar

Output signal sample rate in Hz, specified as a positive scalar.

Tips

To avoid distortion, specify this value to be greater than or equal to the automatically computed output sample rate. To determine the automatically computed output sample rate, first run the object with the OutputSampleRateSource property set to 'Auto'.

Dependencies

To enable this property, set the OutputSampleRateSource property to 'Property'.

Data Types: double

Usage

Syntax

y = multibandcombiner(x)

Description

y = multibandcombiner(x) interpolates, frequency-shifts, and combines the input signal into one output signal.

Input Arguments

x — Input signals

N_samp-by-N_chan matrix

Input signals, specified as an N_samp-by-N_chan matrix. N_samp is the number of input samples per channel, and N_chan is the number of channels.

Data Types: double | single
Complex Number Support: Yes

Output Arguments

y — Output signal

N_out-by-1 vector

Output signal, returned as an N_out-by-1 vector of the same data type as input signal x. N_out is the number of output samples. For more information, see Algorithms.

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

Specific to comm.MultibandCombiner

info	Characteristic information about multiband combining

Common to All System Objects

step	Run System object algorithm
release	Release resources and allow changes to System object property values and input characteristics
reset	Reset internal states of System object

Examples

Combine QPSK and GMSK Signals

Combine two 60 KHz frequency bands that are adjacent to each other.

Set simulation parameters.

M = 4;      % QPSK modulation
N = 2000;   % Frame length
Fs1 = 60e3; % Input sample rate

Generate QPSK and GMSK signals.

data = randi([0,M-1],N,1);
modSig = pskmod(data,M,pi/4,"gray");
qpskTxFilter = comm.RaisedCosineTransmitFilter( ...
    OutputSamplesPerSymbol=2);
qpsksig = qpskTxFilter(modSig);

data = randi([0 1],N,1);
gmskMod = comm.GMSKModulator( ...
    BitInput=true, ...
    SamplesPerSymbol=2);
gmsksig = gmskMod(data);

Create a multiband combiner and two spectrum analyzer System objects. Use the info object function to determine the output sample rate for the combined signal. Use this output sample rate when configuring the spectrum analyzer objects.

mbc = comm.MultibandCombiner( ...
    InputSampleRate=Fs1, ...
    FrequencyOffsets=[-30e3 30e3], ...
    OutputSampleRateSource="Auto");
mbcInfo = info(mbc);
Fs2 = mbcInfo.OutputSampleRate

Fs2 = 
120000

sa = spectrumAnalyzer( ...
    SampleRate=Fs2, ...
    ShowLegend=true, ...
    ChannelNames=["qpsk","gmsk"]);
sacombined = spectrumAnalyzer( ...
    SampleRate=Fs2, ...
    ShowLegend=true, ...
    ChannelNames="combined");

Use the multiband combiner object to interpolate, frequency-shift, and combine the two signals.

combinedsig = mbc([qpsksig,gmsksig]);

Use the spectrum analyzer objects to view the individual signals at 60 kHz and the combined signal at 120 kHz.

sa(qpsksig,gmsksig);
release(sa);

sacombined(combinedsig)

Algorithms

Multiband Combiner

This figure shows how the multiband combiner algorithm processes input signal data.

When the output sample rate is greater than the input sample rate, the input signal is interpolated to avoid distortion in the frequency-shifted signal. Each column of the input signal is frequency-shifted by the corresponding value specified in the FrequencyOffsets property. The frequency-shifted signals are then added together into a single channel output signal. Each channel in the input must have the same number of samples.

Setting the OutputSampleRateSource to 'Auto' automatically configures the algorithm to compute the output sample rate as R_O = R_I × L, where:

• R_O is the output sample rate OutputSampleRate.

• R_I is the input sample rate InputSampleRate.

• L is the interpolation factor and is computed as L = ceil(2 × B_max/R_I).

• B_max is the maximum bandwidth and is computed as B_max = max(abs(FrequencyOffsets)) + (R_I/2).

Multiband Combining Delay

Multiband combining introduces a delay computed as delay = round(length(num)/2). The numerator coefficients, num, are computed as num = designMultirateFIR(L,1), where L is the interpolation factor.

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).

Version History

Introduced in R2021b