modnorm

Scaling factor for normalizing modulation output

Syntax

normfactor = modnorm(refconst,type,power)

Description

normfactor = modnorm(refconst,type,power) returns a scale factor for normalizing a PAM or QAM modulator output using the specified reference constellation, normalization type, and output power.

Examples

Normalize Power of QAM Signal

Generate a 16-QAM reference constellation.

refconst = qammod(0:15,16);

Generate random symbols and apply 16-QAM modulation.

x = randi([0 15],1000,1);
y = qammod(x,16);

Plot the constellation.

h = scatterplot(y);

Compute the normalization factor so that the output signal has a peak power of 1 W.

nf = modnorm(refconst,'peakpow',1);
z = nf*y;

Confirm that no element of the normalized signal has a power greater than 1 W.

max(z.*conj(z))

ans = 
1.0000

Add the normalized constellation to the scatter plot.

hold on
scatterplot(z,1,0,'ro',h)
hold off

Input Arguments

refconst — Reference constellation

vector

Reference constellation, specified as a vector of complex elements that comprise the reference constellation points.

Example: qammod(0:15,16)

Data Types: double
Complex Number Support: Yes

type — Normalization type

'avpow' | 'peakpow'

Normalization type, specified as either 'avpow' or 'peakpow'.

• If type is 'avpow', the normalization factor is calculated based on average power.

• If type is 'peakpow', the normalization factor is calculated based on peak power.

Data Types: char

power — Target power

scalar

Target power, specified as a real scalar. The target power is the intended power of the modulated signal multiplied by normfactor.

Data Types: double

Output Arguments

normfactor — Normalization factor

scalar

Normalization factor, returned as a real scalar. When a modulated signal is multiplied by the normalization factor, its average or peak power matches the target power. The function assumes that the signal you want to normalize has a minimum distance of 2.

Version History

Introduced before R2006a