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> the higher the frequency, the higher the theoretical maximum bandwidth. This is not true and is unrelated to Shannon's theorem. Shannon's theorem shows us t
by makeworld 3y ago
> the higher the frequency, the higher the theoretical maximum bandwidth.
This is not true and is unrelated to Shannon's theorem.
Shannon's theorem shows us that wider bandwidths allow for larger bit rates. At higher frequencies our bandwidths can be bigger. For example a band from 1 to 2 terahertz is 1 terahertz wide, which is 1000 times larger than a band from 1 to 2 gigahertz (1 gigahertz wide).
The total bandwidth available (including multiple channels) for 2.4 GHz Wi-Fi is about 100 MHz. The total space available for this new standard is 800 to 1000 nm [0], which is 450 THz. That's 4.5 million times wider than Wi-Fi. That is why you get higher bit rates with this new standard, AKA more throughput, or more "bandwidth", when the term is used to mean data rate.
[0]: https://standards.ieee.org/ieee/802.11bb/10823/ https://standards.ieee.org/ieee/802.11bb/10823/
- metacritic12 3y agoI mean it sort of is true. If you're at 100THz, you can get a bandwidth of 1THz. If you're at 100KHz, you are not going to get a bandwidth of 1THz.
- Isamu 3y agoTrue, The “band” is a range of frequencies, from lower bound to upper bound. You can have a single frequency carrier that you modulate, in which case your bandwidth has more to do with your modulation scheme, and the rates implied by that
- deely3 3y agoCan I ask a noob question? Suppose we have 1Hz signal, what stopping us from sending/receiving 10 or 100 bits of info every second by modulationg amplitude of signal?
- p_j_w 3y agoWhen you modulate that 1 Hz signal you're generating power at frequencies other than your 1 Hz carrier. See https://en.wikipedia.org/wiki/Amplitude_modulation#Spectrum https://en.wikipedia.org/wiki/Amplitude_modulation#Spectrum
- deely3 3y agoSorry, its not clear for me. Modulated signal could be expressed as sum of signals with different frequencies, but will it be registered by receiver as signal at these frequencies? Suppose we send 1hz signal with length = 1 hour. In the middle we change amplitude of one wave to 1/2. Does recievers recieves mix of different frequencies?
- thfuran 3y agoThe only signal that contains only 1 Hz and no other frequencies is a perfect 1 Hz sine wave. As soon as you start modulating the amplitudes away from that sine wave, you're introducing content at higher frequencies. You can use that higher frequency content to transmit information at more than 1 bit per second, but you're not exactly using the 1 Hz signal to transmit information.
- megous 3y agohttps://en.wikipedia.org/wiki/Single-sideband_modulation https://en.wikipedia.org/wiki/Single-sideband_modulation No need for higher frequency content. But SNR will have to be good enough.
- BenjiWiebe 3y agoSSB still makes other frequencies. Viewed on a waterfall, it's just half of AM, minus the carrier. Still occupies a range of frequencies, approx half of what AM does.
- deleted 3y ago[deleted]
- pclmulqdq 3y agoYou can use FM, AM, QAM, or other multi-bit modulation schemes to send that information, but you need to have the signal-to-noise ratio to demodulate it. WiFi actually goes up to QAM-1024 (10 bits per symbol) in the more recent specs. However, the SNR you need to decode that is perfectly is something like 35 DB, while recovering a signal that sends 1 bit at a time needs ~3 DB. A 35 DB SNR is very hard to reach unless the RF environment is quiet (basically impossible in an apartment building, for example), but 3 DB is easy. Shannon's limit tells you about the total information capacity of a channel given its bandwidth and SNR. This is usually achieved by using deeper modulation than theoretical, and using error-correcting codes to recover the lost data.
- cycomanic 3y ago> > the higher the frequency, the higher the theoretical maximum bandwidth. > This is not true and is unrelated to Shannon's theorem. You are correct that it is unrelated to Shannon, but it is still true. The higher your carrier frequency the higher your theoretical maximum bandwidth (in the correct meaning, i.e occupied spectrum), you can never have negative frequencies, so modulation the maximum bandwidth you can modulate a 1Hz to is 2 Hz (modulation bandwidth extends to positive and negative frequencies). A 10 Hz carrier can be modulated to 20 Hz... > Shannon's theorem shows us that wider bandwidths allow for larger bit rates. At higher frequencies our bandwidths can be bigger. For example a band from 1 to 2 terahertz is 1 terahertz wide, which is 1000 times larger than a band from 1 to 2 gigahertz (1 gigahertz wide). So you are contradicting yourself? Not sure why you said the earlier statement is not treu?
- makeworld 3y agoMy point was that Shannon's theorem is defined in terms of bandwidth. I think speaking about frequency is misleading, even though it's true when discussing carrier/central frequencies. I shouldn't have said OP's statement was untrue, since it's strictly true as you say, that higher frequencies allow for wider bandwidth. They just don't have to have wider bandwidths, which I was trying to make clear. Thanks for the correction though!
- cycomanic 3y agoI think this all boils down to the confusion because people use bandwidth and capacity to really mean throughput. Talk about the capacity of a your internet connection to a communication theorist if you want to start a rant.