dpskmod

Differential phase shift keying modulation

Syntax

y = dpskmod(x,M)

y = dpskmod(x,M,phaserot)

y = dpskmod(x,M,phaserot,symorder)

Description

y = dpskmod(x,M) modulates the input signal using differential phase shift keying (DPSK) with modulation order M.

y = dpskmod(x,M,phaserot) specifies the phase rotation of the DPSK modulation.

y = dpskmod(x,M,phaserot,symorder) also specifies the symbol order.

Examples

DPSK Demodulation

Demodulate DPSK data in a communication channel in which a phase shift is introduced.

Generate a 4-ary data vector and modulate it using DPSK.

M = 4;                          % Alphabet size
dataIn = randi([0 M-1],1000,1); % Random message
txSig = dpskmod(dataIn,M);      % Modulate

Apply the random phase shift resulting from the transmission process.

rxSig = txSig*exp(2i*pi*rand());

Demodulate the received signal.

dataOut = dpskdemod(rxSig,M);

The modulator and demodulator have the same initial condition. However, only the received signal experiences a phase shift. As a result, the first demodulated symbol is likely to be in error. Therefore, you should always discard the first symbol when using DPSK.

Find the number of symbol errors.

errs = symerr(dataIn,dataOut)

errs = 
1

One symbol is in error. Repeat the error calculation after discarding the first symbol.

errs = symerr(dataIn(2:end),dataOut(2:end))

errs = 
0

Input Arguments

x — Input signal

vector | matrix

Input signal, specified as a vector or matrix of positive integers. The elements of x must have values in the range of [0, M – 1].

Data Types: double

M — Modulation order

integer power of two

Modulation order, specified as an integer power of two.

Example: 2 | 4 | 16

Data Types: double

phaserot — Phase rotation

0 (default) | scalar | []

Phase rotation of the DPSK modulation, specified in radians as a real scalar. The total phase shift per symbol is the sum of phaserot and the phase generated by the differential modulation.

If you specify phaserot as empty, then dpskmod uses a phase rotation of 0 degrees.

Example: pi/4

Data Types: double

symorder — Symbol order

'bin' (default) | 'gray'

Symbol order, specified as 'bin' or 'gray'. This argument specifies how the function assigns binary vectors to corresponding integers.

• If symorder is 'bin', the function uses binary-coded ordering.

• If symorder is 'gray', the function uses a Gray-coded ordering.

Data Types: char

Output Arguments

y — DPSK-modulated output signal

vector | matrix

Complex baseband representation of a DPSK-modulated output signal, returned as vector or matrix of complex values. The columns represent independent channels.

Note

An initial phase rotation of 0 is used in determining the first element of the output y (or the first row of y if it is a matrix with multiple rows), because two successive elements are required for a differential algorithm.

Extended Capabilities

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

Version History

Introduced before R2006a