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I have started working on TDMA algorithms for SDR utilizing narrow band waveforms, and I have started reading about narrowband waveforms. But I am confused about the concepts of channel bandwidth and occupying frequencies of narrow band signals. Narrow band channel bandwidth is 25 kHz and occupying frequency range is 30 - 512 MHz. But I have read so far that the bandwidth is the difference between maximum frequency, and minimum frequency and 25 kHz is not the difference of 512 MHz - 30 MHz = 482 MHz. Please elaborate the whole concept and difference?

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    $\begingroup$ Where did you read this? $\endgroup$ – Phil Frost - W8II Nov 7 '17 at 17:08
  • $\begingroup$ It is written in aselsan narrow band networking waveform document that narrow band operating frequency is 30-512 MHz and occupying bandwidth is 25KHz. $\endgroup$ – MentorGeek Nov 7 '17 at 17:12
  • $\begingroup$ Can you provide a web link to this? I think that's what Phil was asking for. And what is "aselsan"? $\endgroup$ – Mike Waters Nov 7 '17 at 17:19
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    $\begingroup$ that is just one supplier's own definition of "narrowband". I don't agree with that definition, on very many levels. Anyway, you're basing your research on a marketing brochure. That's really not a good place to start. $\endgroup$ – Marcus Müller Nov 7 '17 at 19:45
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    $\begingroup$ There's no single "narrow band" waveform. You need to define waveform for which application in which band solving which specific problems. Generally, I'd say, if you haven't, inhale the content of a communications engineering intro lecture – it really feels like you're trying to understand some very application-specific thing that you can't even put into precise words, just because you haven't gotten any of the basic theory of wireless communications. $\endgroup$ – Marcus Müller Nov 8 '17 at 6:11
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What that marketing brochure (a terrible way to start learning about a technical concept, by the way) means is that it uses narrowband channels from somewhere within that 30 to 512 MHz range.

That just means it allows you to pick one (or a few) of 25kHz pieces of spectrum to operate on.

"Narrowband" is not defined to be 25 kHz, by the way. The definition of narrowband depends on who you ask: For someone normally dealing with e.g. DVB-T signals, a 2 MHz channel might be considered narrow. For someone dealing with morse operation in HF, 150 Hz might be narrow. For someone doing modeling of channels, you'd typically expect them to say that a channel is narrow if it occupies significantly less than the coherency bandwidth – and that is something that will wildly vary between 30 MHz and 500 MHz. So, anyway you put it, calling 25 kHz "narrowband" is really just a marketing term here.

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  • $\begingroup$ I have been reading about SDR and its waveforms e.g Wide Band waveform and Narrow Band Waveform. I need to work on Medium Access Algorithm for Narrow Band Waveform. But i could not found more specific document that deals with the concepts of Narrow Band Waveform for SDR. I'll be much obliged if you share a document that will help me in building concepts. $\endgroup$ – MentorGeek Nov 8 '17 at 6:12
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    $\begingroup$ I've got nearly 10 years of experience with SDR, but I don't know what you're referring to when you say "its Wide Band and its Narrow Band waveform". Those aren't SDR terms – these are application-specific terms that someone uses. Software defined radio just says that you do as much as feasible of the signal processing in software. It doesn't define any waveforms. $\endgroup$ – Marcus Müller Nov 8 '17 at 6:13
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    $\begingroup$ so, ok, you will need to read up on the basics of communications. Because a) you keep calling it narrow band, b) because if you had the basic theory down, you'd see that you're really not giving us enough info for you to even help you and c) what am I even going to tell you that you are going to understand? Yes, you need a MAC, but it's totally unclear what kind of MAC you need, because you haven't written down sufficient requirements. Efficient MAC protocol is even harder, you haven't defined efficiency at all. $\endgroup$ – Marcus Müller Nov 8 '17 at 6:43
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    $\begingroup$ Right. Do i need to start with the wireless communications basics? $\endgroup$ – MentorGeek Nov 8 '17 at 6:46
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    $\begingroup$ How many times do you want me to repeat that? Yes. $\endgroup$ – Marcus Müller Nov 8 '17 at 6:48

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