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Common mistakes using the 'pskmod' command in MATLAB

 

Sometimes, students incorrectly write code for phase shift keying modulation (PSK). They want to modulate the input bits. For example

 Method 1

N_Bits = 2520; % number of input bits
M = 4;
Phase = 0; % intial phase
input_bits = randi([0,1],N_Bits,1);
modData = pskmod(input_bits,M,Phase);

The above approach is correct once you're performing binary PSK or BPSK. The following code will work for higher-order modulation like 4-PSK, 8-PSK, 16-PSK, or 32-PSK.

 Method 2

N_Bits = 2520; % number of input bits
M = 4;
input_bits = randi([0,1],N_Bits,1);
data_temp = bi2de(reshape(input_bits,N_Bits/log2(M),log2(M)));
modData = pskmod(data_temp,M,Phase);

Another good approach is to generate random bits like this.

 Method 3

N_Symbols = 1000; % number of input symbols
M = 4;
Phase = 0; % intial phase
input_symbols = randi([0,(M-1)],N_Symbols,1);
modData = pskmod(input_symbols,M,Phase);

However, the above method could be more practical. It would be best to map input bits into symbols in most cases. So the second method is more important.

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