comm.DQPSKModulator

Modulate using DQPSK method

Description

The comm.DQPSKModulator System object™ modulates using the differential quadrature phase shift keying method. The output is a baseband representation of the modulated signal.

To modulate a signal using differential quadrature phase shift keying:

1. Create the comm.DQPSKModulator 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

dqpskmod = comm.DQPSKModulator

dqpskmod = comm.DQPSKModulator(Name=Value)

dqpskmod = comm.DQPSKModulator(phase,Name=Value)

Description

dqpskmod = comm.DQPSKModulator creates a modulator System object that modulates the input signal using the differential quadrature phase shift keying (DQPSK) method.

dqpskmod = comm.DQPSKModulator(Name=Value) sets properties using one or more name-value arguments.

dqpskmod = comm.DQPSKModulator(phase,Name=Value) creates a DQPSK modulator with the PhaseRotation 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.

PhaseRotation — Additional phase shift

pi/4 | real scalar

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

BitInput — Assume bit inputs

false or 0 (default) | true or 1

Option to provide input in 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 an integer column vector with values in the range [0, 3].

• When you set this property to true, the input must be a column vector of bit values whose length is an integer multiple of 2. This vector contains bit representations of integers in the range [0, 3].

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 group of two input bits to the corresponding modulated symbol. 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 m, between $$0\le m\le 3$$, shifts the output phase. This shift is (PhaseRotation + $$2\times \pi \times \raisebox{1ex}{$m$}\!\left/ \!\raisebox{-1ex}{$4$}\right.$$) radians from the previous output phase. The output modulated symbol is exp(j$$\times$$PhaseRotation + j$$\times$$$$2\times \pi \times \raisebox{1ex}{$m$}\!\left/ \!\raisebox{-1ex}{$4$}\right.$$)$$\times$$(previously modulated symbol).

Data Types: char | string

OutputDataType — Data type of output

"double" (default) | "single"

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

Data Types: char | string

Usage

Syntax

y = dqpskmod(x)

Description

y = dqpskmod(x) applies DQPSK modulation to the input data and returns the modulated DQPSK baseband signal.

Input Arguments

x — Input data

integer | column vector | bits

Input data, specified as an integer or column vector of integers or bits.

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

Output Arguments

y — DQPSK-modulated baseband signal

column vector

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

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

Modulate and Demodulate using DQPSK Method

Create a DQPSK modulator and demodulator pair.

dqpskmod = comm.DQPSKModulator(BitInput=true);
dqpskdemod = comm.DQPSKDemodulator(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 the processing loop. It consists of these main steps:

1. Generate 50 2-bit frames.

2. DQPSK-modulate.

3. Pass the signal through an AWGN channel with a signal-to-noise ratio of 9.

4. DQPSK-demodulate.

5. Collect error statistics.

for counter = 1:100
    txData = randi([0 1],100,1);
    modSig = dqpskmod(txData);
    rxSig = awgn(modSig,9);
    rxData = dqpskdemod(rxSig);
    errorStats = errorRate(txData,rxData);
end

Display the error statistics.

ber = errorStats(1)

ber = 
0.0183

numErrors = errorStats(2)

numErrors = 
183

numBits = errorStats(3)

numBits = 
9999

Algorithms

Integer-Valued Signals and Binary-Valued Signals

When you set the BitInput property to false, the valid input values are 0, 1, 2, and 3. In this case, the object accepts a scalar or column vector input signal. If the first input is m, then the modulated symbol is exp(jθ + jπm/2), where θ represents the PhaseRotation property. If a successive input is m, then the modulated symbol is the previous modulated symbol multiplied by exp(jθ + jπm/2).

When you set the BitInput parameter to true, the input contains pairs of binary values. In this case, the object accepts a column vector whose length is an even integer. The following figure shows the complex numbers by which the function multiplies the previous symbol to compute the current symbol, depending on whether you set the SymbolMapping property to "Binary" or "Gray". The following figure assumes that you set the PhaseRotation property to pi/4; in other cases, the two schematics would be rotated accordingly.

The following figure shows the signal constellation for the DQPSK modulation method when you set the PhaseRotation property to pi/4. The arrows indicate the four possible transitions from each symbol to the next symbol. The "Binary" and "Gray" options determine which transition is associated with each pair of input values.

More generally, if the PhaseRotation property has the form $$\frac{\Pi }{k}$$for some integer k, then the signal constellation has 2k points.

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