OQPSK Modulator Passband block

I have a problem with my zigbee model, that i wanna to send the modulated signal over 2.4 GHz carrier frequency band ,and that is not allowed at OQPSK Modulator baseband block. I searched about OQPSK Modulator Passband block on Mat. 2013 and 2015 and I couldn't find it .any help with that ??

Answer 1

[Walter Roberson]

It appears that R13SP2 was the last version that had that block. That is also the oldest version that you can still download from Mathworks.

[Asmaa Romia]

I searched about this block in this version and couldn't find it, any help with this ??

[Walter Roberson]

http://www.mathworks.com/help/releases/R13sp2/toolbox/commblks/ref/oqpskdemodulatorpassband.html#55719

Note: you would probably need a current support contract in order to be able to see that old documentation.

[Asmaa Romia]

thanks for your help . but why this block was removed from the newest matlab versions . and how can I built my model without it, if i use R2013a??

[Walter Roberson]

The block was removed in 2004, not in "newest MATLAB releases". I see that a number of passband functions were removed; I do not know why.

I do not know much at all about passband and baseband. Perhaps this example will help? https://www.mathworks.com/help/comm/examples/passband-modulation-with-adjacent-channel-interference.html

[Asmaa Romia]

thanks , that's very helpful for me. Appreciating your kind cooperation.

Answer 2

[Tasos Giannoulis]

Hi Asmaa and Walter,

Some important notes:

1) Indeed, the passband OQSPK modulator/demodulator has been removed and only a baseband OQPSK modulator/demodulator exists.

2) The motivation behind baseband processing is speed. It is much faster to generate or simulate a signal at baseband frequencies than at 2.4 GHz. Why exactly are you looking for passband operation? If you want to do the actual transmission at 2.4 GHz with a radio, then you can simply pass the baseband signal to the transmitter block (or System object) and this transmitter will do the upconversion to 2.4 GHz for you. No need to start with a passband OQPSK signal.

3) If you really need to do passband simulation (but please be sure about this first), then you can use the Digital Up/Down Converter blocks / System objects from the DSP System Toolbox in conjuction with the baseband OQSPK modulator/demodulator. Alternatively, the featured example that Walter showed, and this one for Simulink: https://www.mathworks.com/help/comm/examples/passband-modulation.html can show another way to upconvert baseband signals.

4) Be aware that ZigBee and IEEE 802.15.4 use half-sine pulses. The OQSPK tools of the Communication System Toolbox upsample the input signal (as of R2016b; see doc note), and a subsequent filtering operation will probably not produce the desired result. You will be better off if you conduct a joint modulation and filtering operation in this order (e.g., with a MATLAB Function block, or with 3 blocks in Simulink):

a. Split bits to odd (I) and even (Q)

b. Filter both I & Q streams for half-sine pulses

c. Delay the even-bit stream (Q) by half a simple and make a complex waveform I + j*Q

Tasos

[Walter Roberson]

Thanks for the remarks!

One question: I am not sure what "half a simple" is? Half a symbol perhaps?

[Asmaa Romia]

thanks alot about your reply. my question is about" if I don't transmitte over 2.4 GHz , what is the affect of the transmitted signal ?? if I need to study the interference any problem with that at this case?