QPSK Transmitter and Receiver in Simulink example question

Hello everyone,

I am trying to study on how can I simulate the digital communication using this example "QPSK Transmitter and Receiver in Simulink".

QPSK Transmitter and Receiver in Simulink - MATLAB & Simulink (mathworks.com)

I don't understand why in the example use data bit 2240 bits for 20 "Hello world ###" or 112 bits/message?

For my understanding. Each message is 15 char long (including 2 spaces) and ASCII characters are typically represented using 8 bits (1 byte) of information.

So, It should be 8*15 = 120 bits/ message ?

There is any reason for this? or I just misunderstood the ASCII representation concept?

Best Regards,

Fumihiko Sato

Answer 1

[Naren]

The original ASCII table is encoded on 7 bits and extended ASCII table uses 8-bit representation. However, in this example as the text doesn't contain any extended ASCII characters 7 bits are used.

Follow the steps to find out the bit representation used:

1. Go to the Simulink model of QPSK Transmitter.
2. Double click on the bit generation block.
3. Look at the properties of "Signal from Workspace" block.
4. A parameter named "Samples per frame" will contain the information on number of bits transmitted.

You can try changing the bit representation to 8 bits by editing the 'Samples per frame' parameter.

The length of the text is not 15, it will be 16 which includes the end character.

length = 16;
ASCII_bit_representation = 7;
thats '16*7 = 112 bits/message'.
no_of_messages = 20;
no_of_bits = 20*112 = 2240 bits.

Hope this resolves your problem.

[Fumihiko Sato]

Dear Naren,

Thank you for your explanation. That's resolved my question.

Really appreciate your help.

Best Regards,

Fumihiko Sato