comm.DPSKModulator

Modulate using M-ary DPSK method

Description

The comm.DPSKModulator object modulates a signal using the M-ary differential phase shift keying method. The output is a baseband representation of the modulated signal.

To modulate a signal using differential phase shift keying:

1. Create the comm.DPSKModulator 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

dpskmod = comm.DPSKModulator

dpskmod = comm.DPSKModulator(Name=Value)

dpskmod = comm.DPSKModulator(M,phase,Name=Value)

Description

dpskmod = comm.DPSKModulator creates a modulator System object™ that modulates the input signal using the M-ary differential phase shift keying (M-DPSK) method.

dpskmod = comm.DPSKModulator(Name=Value) sets Properties using one or more name-value arguments.

dpskmod = comm.DPSKModulator(M,phase,Name=Value) creates an M-DPSK modulator object that has the ModulationOrder property set to M, the PhaseRotation property set to phase, and optional name-value arguments.

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.

ModulationOrder — Number of points in signal constellation

8 (default) | positive integer

Number of points in the signal constellation, specified as a positive integer.

Data Types: double

PhaseRotation — Additional phase shift

pi/8 (default) | scalar

Additional phase shift between the previous and current modulated symbols in radians, specified as a scalar. This value corresponds to the phase difference between the previous and current modulated symbols when the input is zero.

Data Types: double

BitInput — Input data as bits

false or 0 (default) | true or 1

Option to input data as bits, specified as a numeric or logical 0 (false) or 1 (true).

• When you set this property to false, the input to the System object requires a column vector of integer symbol values in the range [0, (M – 1)], where M represents the value of the ModulationOrder property.

• When you set this property to true, the input must be a column vector of bit values whose length is an integer multiple of log2(ModulationOrder). This vector contains bit representations of integers in the range [0, (M – 1)].

Data Types: logical

SymbolMapping — Constellation encoding

"Gray" (default) | "Binary"

Constellation encoding, specified as "Gray" or "Binary". This property controls how the object maps an integer or a group of log2(ModulationOrder) input bits to the corresponding modulated signal.

• When you set this property to "Gray", the object uses a Gray-encoded signal constellation.

• When you set this property to "Binary", the input integer L in the range [0, (M – 1)] shifts the output phase. M represents the value of ModulationOrder. This shift is (ϕ + 2×π×L / M) radians from the previous output phase. ϕ is the value of the PhaseRotation property. The output symbol is exp(j×ϕ + j×2×π×L / M)× (previously modulated symbol).

Dependencies

This property applies when you set the BitInput property to true.

OutputDataType — Data type of output

"double" (default) | "single"

Data type of output, specified as "double" or "single".

Usage

Syntax

Y = dpskmod(X)

Description

Y = dpskmod(X) returns the modulated DPSK baseband signal.

Input Arguments

X — Input data

integer | column vector | logical

Input data, specified as an integer or column vector of integers or bits with numeric or logical data types.

The setting of the BitInput property determines the interpretation of the input data.

Note

To process an input signal as binary elements, set the BitInput property to 'true'. For binary inputs, the number of rows must be an integer multiple of log₂(M). The function maps groups of log₂(M) bits onto a symbol, with the first bit representing the MSB and the last bit representing the LSB.

Output Arguments

Y — DPSK-modulated baseband signal

column vector (default)

DPSK-modulated baseband signal, returned as a column vector.

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)

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

8-DPSK Signal in AWGN

Create a DPSK modulator and demodulator pair.

bps = 3;   % Bits per symbol
M = 2^bps; % Modulation order  
dpskmod = comm.DPSKModulator(M,pi/8,BitInput=true);
dpskdemod = comm.DPSKDemodulator(M,pi/8,BitOutput=true);

Create an error rate calculator. Set the ComputationDelay property to 1 to account for the one bit transient caused by the differential modulation.

errorRate = comm.ErrorRate(ComputationDelay=1);

Run a loop processing frames of data that consists of these main steps:

1. Generate data frames of 150 3-bit symbols.

2. 8-DPSK-modulate the data.

3. Filter the data through an AWGN channel.

4. 8-DPSK-demodulate the data.

5. Collect error statistics.

numframes = 100; % Number of frames
spf = 150;       % Symbols per frame
snr = convertSNR(10,"ebno","snr",BitsPerSymbol=3);
for counter = 1:numframes
    txData = randi([0 1],spf,1);
    modSig = dpskmod(txData);
    rxSig = awgn(modSig,snr,'measured');
    rxData = dpskdemod(rxSig);
    errorStats = errorRate(txData,rxData);
end

Display the error statistics.

ber = errorStats(1)

ber = 
0.0095

numErrors = errorStats(2)

numErrors = 
143

numBits = errorStats(3)

numBits = 
14999

Algorithms

DPSK Modulation

DPSK is a noncoherent form of phase shift keying that does not require a coherent reference signal at the receiver. With DPSK, the difference between successive input symbols is mapped to a specific phase.

The disadvantage of DPSK is that it is approximately 3 dB less energy efficient than coherent PSK.

Integer-Valued Signals and Binary-Valued Signals

If the input is an integer, then valid input values are integers in the range [0 M-1]. In this case, the input can be either a scalar or a column vector. If the first input is k₁, then the modulated symbol is

$$\exp \left(j\theta +j2\pi \frac{k_1}{m}\right)$$

where θ represents the Phase Rotation property. If a successive input is k, then the modulated symbol is

$$\exp \left(j\theta +j2\pi \frac{k}{m}\right)\cdot (\text{previous modulated symbol})$$

If the input type is a bit input, the object accepts binary-valued inputs that represent integers.

The object collects binary-valued signals into groups of K = log₂(M) bits

where

K represents the number of bits per symbol.

The input vector length must be an integer multiple of K. In this configuration, the object accepts a group of K bits and maps that group onto a symbol at the output. The output is one modulated symbol for each group of K bits.

The input can be a column vector with a length that is an integer multiple of K.

In binary input mode, the Symbol Mapping property indicates how the object maps a group of K input bits to a corresponding phase difference. The "Binary" option uses a binary-coded-to-integer mapping, while the "Gray" option uses a Gray-coded assignment of phase differences. For example, the following table indicates the assignment of phase difference to three-bit inputs, for both the Binary and Gray options. θ is the Phase Rotation property. The phase difference is between the previous symbol and the current symbol.

Current Input	Binary-Coded Phase Difference	Gray-Coded Phase Difference
[0 0 0]	jθ	jθ
[0 0 1]	jθ + jπ/4	jθ + jπ/4
[0 1 0]	jθ + jπ2/4	jθ + jπ3/4
[0 1 1]	jθ + jπ3/4	jθ + jπ2/4
[1 0 0]	jθ + jπ4/4	jθ + jπ7/4
[1 0 1]	jθ + jπ5/4	jθ + jπ6/4
[1 1 0]	jθ + jπ6/4	jθ + jπ4/4
[1 1 1]	jθ + jπ7/4	jθ + jπ5/4

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 R2012a