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How does (if it does) frequency affect/relates to Data Rate.

Why for example using the same modulation, LoRa (in the physical layer),
you get somewhere around 250kbps at 2.4Ghz and only 20kbps at 868Hz ?

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    $\begingroup$ Welcome to DSP.se Christos K. ! Where did you get those numbers? To my knowledge, LoRa exclusively operates in the sub-Ghz ISM band (see, for example, ,blog.dbrgn.ch/2017/6/23/lorawan-data-rates). Also, note that LoRa is not a modulation scheme. The modulation scheme used by Lora is Chirp-Spread-Spectrum (CSS). $\endgroup$ – anpar Feb 5 at 19:42
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    $\begingroup$ also, there's simply no inherent relation between carrier frequency and data rate. This becomes obvious when you think about the complex baseband representation being the same, regardless of the carrier frequency, and that carrying identical information to the passband signal. $\endgroup$ – Marcus Müller Feb 5 at 20:52
  • $\begingroup$ More context is needed. $\endgroup$ – BlackMath Feb 5 at 21:35
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There's simply no inherent relation between carrier frequency and data rate.

I assume a classical comms engineering education here, but since that most often introduces the concept of equivalent baseband early, a good explanation would be:

This becomes obvious when you think about the complex baseband representation of a passband being the same, regardless of the passband's center frequency, and that the complex baseband carries identical information to the passband signal.

Thus, carrier frequency cannot have direct influence on the information transport capabilities of any system, given that you mix the same signal to these carriers.

Indirectly, there might be influences: Bandwidth is proportional to capacity; it's impossible to get 1 GHz bandwidth centered around 433 MHz, but cheap around 60 GHz.

Noise and interference are the other limit to capacity; these are different for different bands and technologies.

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  • $\begingroup$ Using an upper side band modulation you could get 1 GHz bandwith at a carrier frequency of 500 MHz or even at 10 kHz... Am I missing something ? (other than 10 kHz not suitable for RF, or existing broadcast standards) $\endgroup$ – Fat32 Feb 6 at 0:21
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    $\begingroup$ Hm, I tried to avoid this confusion by illustrating it as "1 GHz centered around 433 GHz". $\endgroup$ – Marcus Müller Feb 6 at 6:59
  • $\begingroup$ yes yes I saw that... I was actually referring to my own statement... $\endgroup$ – Fat32 Feb 6 at 11:23
  • $\begingroup$ ah, OK; but then, while your carrier would be 10 kHz, your central freq would still half the bandwidth plus 10 kHz, if you will. $\endgroup$ – Marcus Müller Feb 6 at 13:37
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    $\begingroup$ @BlackMath that's Double Side Band, but I was referring to Single Side Band anyway, this really is an impractical gedankenexperiment type of thing... $\endgroup$ – Fat32 Feb 6 at 19:19

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