802.11b DSSS Waveform Generator not showing bell shaped spectrum

I expect a 20MHz bell shaped curve when transmitting 802.11b DSSS using the Matlab IEEE 802.11b/g waveform generator. Instead the spectrum is flat with 11MHz bandwidth. any idea why?

Matlab:

Expected:

[akshatsood]

Hi @yesihaveaquestion,

Could you please confirm whether the expected waveform was creating using a RRC filter?

[yesihaveaquestion]

Yes the settings are the default filter settings shown in the screenshot. RRC Oversampling 4, rolloff factor 0.2, filter span 10 symbols.Changing the filter span to 1 symbol gives a bell shape.

[akshatsood]

Hi @yesihaveaquestion,

Thanks for the response. Though, I was referring to the "Expected" waveform which you have attached for comparing the results generated in the Wireless Wave Generator app. Perhaps, your response says that your query is solved. If not, do let me know any additional details you seek help in.

Answer 1

[Naren]

Hello,

The flat response observed with an 11MHz bandwidth when using the 802.11b Waveform generator can be due to the specified Filtering Configuration.

Consider adjusting the parameters within the filtering configuration, such as the Rolloff factor to achieve a bell-shaped curve with 20 MHz bandwidth.

Regards,

Naren

[yesihaveaquestion]

I believe filtering should only impact out of band lobes. Below is a diagram from Rohde-Shwartz