comm.ThermalNoise

Add thermal noise to signal

Description

The ThermalNoise object simulates the effects of thermal noise on a complex, baseband signal.

To add thermal noise to a complex, baseband signal:

Define and set up your thermal noise object. See Construction.
Call step to add thermal noise according to the properties of comm.ThermalNoise.

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

tn = comm.ThermalNoise creates a receiver thermal noise System object, H. This object adds thermal noise to the complex, baseband input signal.

tn = comm.ThermalNoise(Name,Value) creates a receiver thermal noise object, H, with each specified property set to the specified value. You can specify additional name-value pair arguments in any order as (Name1,Value1,...,NameN,ValueN).

Properties

expand all

`NoiseMethod` — Method used to set noise power
`'Noise temperature'` (default) | `'Noise figure'` | `'Noise factor'`

Method used to set the noise power, specified as 'Noise temperature', 'Noise figure', or 'Noise factor'.

`NoiseTemperature` — Receiver noise temperature
`290` (default) | nonnegative real scalar

Receiver noise temperature, specified in degrees K as a nonnegative real scalar. This property is available when NoiseMethod is equal to 'Noise temperature'. Noise temperature is typically used to characterize satellite receivers because the input noise temperature can vary and is often less than 290 K. Tunable.

`NoiseFigure` — Noise figure
`3.01` (default) | nonnegative real scalar

Noise figure, specified in dB as a nonnegative real scalar. This property is available when NoiseMethod is equal to 'Noise figure'. Noise figure describes the performance of a receiver and does not include the effect of the antenna. It is defined only for an input noise temperature of 290 K. The noise figure is the dB equivalent of the noise factor. Tunable.

`NoiseFactor` — Noise factor
`2` (default) | real scalar ≥ 1

Noise factor, specified as a real scalar greater than or equal to 1. This property is available when NoiseMethod is equal to 'Noise factor'. Noise factor describes the performance of a receiver and does not include the effect of the antenna. It is defined only for an input noise temperature of 290 K. The noise factor is the linear equivalent of the noise figure. Tunable.

`SampleRate` — Sample rate
`1` (default) | positive real scalar

Sample rate, specified as in Hz as a positive real scalar. The object computes the variance of the noise added to the input signal as kT×SampleRate. The value k is Boltzmann's constant and T is the noise temperature specified explicitly or implicitly via one of the noise methods.

`Add290KAntennaNoise` — Add 290 K antenna noise
`false` (default) | `true`

Add 290 K antenna noise to the input signal, specified as a logical scalar. To add 290 K antenna noise, set this property to true. This property is available when NoiseMethod is equal to 'Noise factor' or 'Noise figure'.

The total noise applied to the input signal is the sum of the circuit noise and the antenna noise.

Methods

step	Add receiver thermal noise

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

Examples

collapse all

Add Thermal Noise to QPSK Signal

Open Live Script

Create a thermal noise object having a noise temperature of 290 K and a sample rate of 5 MHz.

thNoise = comm.ThermalNoise('NoiseTemperature',290,'SampleRate',5e6);

Generate QPSK-modulated data having an output power of 20 dBm.

data = randi([0 3],1000,1);
modData = 0.3162*pskmod(data,4,pi/4);

Attenuate the signal by the free space path loss assuming a 1000 m link distance and a carrier frequency of 2 GHz.

fsl = (4*pi*1000*2e9/3e8)^2;
rxData = modData/sqrt(fsl);

Add thermal noise to the signal. Plot the noisy constellation.

noisyData = thNoise(rxData);
scatterplot(noisyData)

Add Antenna and Receiver Thermal Noise to 16-QAM Signal

Open Live Script

Create a thermal noise object having a 5 dB noise figure and a 10 MHz sample rate. Specify that the 290 K antenna noise be included.

thermalNoise = comm.ThermalNoise('NoiseMethod','Noise figure', ...
    'NoiseFigure',5, ...
    'SampleRate',10e6, ...
    'Add290KAntennaNoise',true);

Generate QPSK-modulated data having a 1 W output power.

data = randi([0 15],1000,1);
modSig = qammod(data,16,'UnitAveragePower',true);

Attenuate the signal by the free space path loss assuming a 1 km link distance and a 5 GHz carrier frequency.

fsl = (4*pi*1000*5e9/3e8)^2;
rxSig = modSig/sqrt(fsl);

Add thermal noise to the signal and plot its constellation.

noisySig = thermalNoise(rxSig);
scatterplot(noisySig)

Estimate the SNR.

mer = comm.MER;
snrEst1 = mer(rxSig,noisySig)

snrEst1 = 22.6611

Decrease the noise figure to 0 dB, and plot the resultant received signal. Because antenna noise is included, the signal is not completely noiseless.

thermalNoise.NoiseFigure = 0;
noisySig = thermalNoise(rxSig);
scatterplot(noisySig)

Estimate the SNR. The SNR is 5 dB higher than in the first case, which is expected given the 5 dB decrease in the noise figure.

snrEst2 = mer(rxSig,noisySig)

snrEst2 = 27.8658

snrEst2 - snrEst1

ans = 5.2047

Algorithms

Wireless receiver performance is often expressed as a noise factor or figure. The noise factor is defined as the ratio of the input signal-to-noise ratio, S_i/N_i to the output signal-to-noise ratio, S_o/N_o, such that

$F = \frac{S_{i} / N_{i}}{S_{o} / N_{o}} .$

Given receiver gain G and receiver noise power N_ckt, the noise factor can be expressed as

$\begin{matrix} F = \frac{S_{i} / N_{i}}{G S_{i} / (N_{c k t} + G N_{i})} \\ = \frac{N_{c k t} + G N_{i}}{G N_{i}} . \end{matrix}$

The IEEE defines the noise factor assuming that noise temperature at the input is T₀, where T₀ = 290 K. The noise factor is then

$\begin{matrix} F = \frac{N_{c k t} + G N_{i}}{G N_{i}} \\ = \frac{G k B T_{c k t} + G k B T_{0}}{G k B T_{0}} \\ = \frac{T_{c k t} + T_{0}}{T_{0}} . \end{matrix}$

T_ckt is the equivalent input noise temperature of the receiver and is expressed as

$T_{c k t} = T_{0} (F - 1) .$

The overall noise temperature of an antenna and receiver, T_sys, is

$T_{s y s} = T_{a n t} + T_{c k t},$

where T_ant is the antenna noise temperature.

The noise figure, NF, is the dB equivalent of the noise factor and can be expressed as

$N F = 10 \log_{10} (F) .$

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).

Documentation

comm.ThermalNoise

Description

Note

Construction

Properties

`NoiseMethod` — Method used to set noise power
`'Noise temperature'` (default) | `'Noise figure'` | `'Noise factor'`

`NoiseTemperature` — Receiver noise temperature
`290` (default) | nonnegative real scalar

`NoiseFigure` — Noise figure
`3.01` (default) | nonnegative real scalar

`NoiseFactor` — Noise factor
`2` (default) | real scalar ≥ 1

`SampleRate` — Sample rate
`1` (default) | positive real scalar

`Add290KAntennaNoise` — Add 290 K antenna noise
`false` (default) | `true`

Methods

Examples

Add Thermal Noise to QPSK Signal

Add Antenna and Receiver Thermal Noise to 16-QAM Signal

Algorithms

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

See Also

Introduced in R2012a

Communications Toolbox Documentation

Support

Documentation

comm.ThermalNoise

Description

Note

Construction

Properties

NoiseMethod — Method used to set noise power 'Noise temperature' (default) | 'Noise figure' | 'Noise factor'

NoiseTemperature — Receiver noise temperature 290 (default) | nonnegative real scalar

NoiseFigure — Noise figure 3.01 (default) | nonnegative real scalar

NoiseFactor — Noise factor 2 (default) | real scalar ≥ 1

SampleRate — Sample rate 1 (default) | positive real scalar

Add290KAntennaNoise — Add 290 K antenna noise false (default) | true

Methods

Examples

Add Thermal Noise to QPSK Signal

Add Antenna and Receiver Thermal Noise to 16-QAM Signal

Algorithms

Extended Capabilities

C/C++ Code Generation Generate C and C++ code using MATLAB® Coder™.

See Also

Introduced in R2012a

Communications Toolbox Documentation

Support

`NoiseMethod` — Method used to set noise power
`'Noise temperature'` (default) | `'Noise figure'` | `'Noise factor'`

`NoiseTemperature` — Receiver noise temperature
`290` (default) | nonnegative real scalar

`NoiseFigure` — Noise figure
`3.01` (default) | nonnegative real scalar

`NoiseFactor` — Noise factor
`2` (default) | real scalar ≥ 1

`SampleRate` — Sample rate
`1` (default) | positive real scalar

`Add290KAntennaNoise` — Add 290 K antenna noise
`false` (default) | `true`

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.