comm.BPSKModulator

Modulate using BPSK method

Description

The comm.BPSKModulator object modulates using the binary phase shift keying method. The output is a baseband representation of the modulated signal. The input signal must be a discrete-time binary-valued signal. If the input bit is 0 or 1, then the modulated symbol is exp(jθ) or -exp(jθ), respectively. The PhaseOffset property specifies the value of θ in radians.

To modulate a signal using BPSK method:

1. Create the comm.BPSKModulator 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

bpskmodulator = comm.BPSKModulator

bpskmodulator = comm.BPSKModulator(Name,Value)

bpskmodulator = comm.BPSKModulator(phase,Name,Value)

Description

bpskmodulator = comm.BPSKModulator creates a modulator System object™ to modulate input signals using the binary phase shift keying (BPSK) method.

bpskmodulator = comm.BPSKModulator(Name,Value) creates a BPSK modulator object 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).

bpskmodulator = comm.BPSKModulator(phase,Name,Value) creates a BPSK modulator object with the PhaseOffset property set to phase, and the other specified properties set to the specified values.

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.

PhaseOffset — Phase of zeroth point of constellation

0 (default) | scalar

Phase of zeroth point of the constellation in radians, specified as a scalar.

Data Types: double

OutputDataType — Output datatype

'double' (default) | 'single' | 'Custom'

Output datatype, specified as 'double', 'single' or 'Custom'.

Data Types: char

Fixed-Point Properties

CustomOutputDataType — Fixed-point data type of output

numerictype([],16) (default) | numerictype object

Fixed-point data type of the output, specified as a numerictype (Fixed-Point Designer) object with a signedness of Auto.

Dependencies

This property applies when you set the OutputDataType property to 'Custom'.

Usage

Syntax

waveform = bpskmodulator(data)

Description

waveform = bpskmodulator(data) applies BPSK modulation to the input data and returns the modulated BPSK baseband signal.

Input Arguments

data — Input signal data

column vector | matrix

Input signal data, specified as a column vector or matrix.

Data Types: double

Output Arguments

waveform — BPSK modulated baseband signal

column vector | matrix

BPSK modulated baseband signal, returned as a column vector or matrix of the same size as the input signal. For more information about the output datatype, see the OutputDataType property.

Data Types: double | single | fi
Complex Number Support: Yes

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.BPSKModulator

constellation

Calculate or plot ideal signal constellation

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

BPSK Data Scatter Plot

This example creates binary data, modulates it, and then displays the data using a scatter plot.

Create binary data symbols

data = randi([0 1],100,1);

Create a BPSK modulator System object

bpskModulator = comm.BPSKModulator;

Change the phase offset to pi/16

bpskModulator.PhaseOffset = pi/16;

Modulate and plot the data

modData = bpskModulator(data);
scatterplot(modData)

Algorithms

Phase modulation is a linear baseband modulation technique in which the message modulates the phase of a constant amplitude signal. Binary Phase Shift Keying (BPSK) is a two phase modulation scheme, where the 0’s and 1’s in a binary message are represented by two different phase states in the carrier signal

$$s_n(t)=\sqrt{\frac{2E_b}{T_b}}\cos \left(2\pi f_{c}t+{\varphi }_n\right),$$

for $$(n-1)T_b\le t\le n{T}_b,\text{ n}=\text{1},\text{2},\text{ 3},\dots$$where:

• ϕ_n = πm, m∈{0,1}.

• E_b is the energy per bit.

• T_b is the bit duration.

• f_c is the carrier frequency.

In MATLAB^®, the baseband representation of a BPSK signal is

$$s_n(t)=e^{-i{\varphi }_n}=\cos \left(\pi n\right).$$

The BPSK signal has two phases: 0 and π. The probability of a bit error in an AWGN channel is

$$P_b=Q\left(\sqrt{\frac{2E_b}{N_0}}\right),$$

where N₀ is the noise power spectral density.

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).

HDL Code Generation

Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.

double and single data types are supported for simulation, but not for HDL code generation.

To generate HDL code from predefined System objects, see HDL Code Generation from Viterbi Decoder System Object (HDL Coder).