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I am working on a system whereby a smartphone may receive signals simultaneously from different sources. As we know, the fading and pathloss will make the transmitters send their traffic with different modulation schemes. I have also done some research on the transmission and reception for a smartphone and understand that a smartphone with single antenna can transmit and receive at the same time.

However, there is few materials mentions that if a smartphone can demodulate two signals modulated with different MCS simultaneously. The only paper I found(https://www.researchgate.net/publication/322615927_Reconfigurable_Modulation_Scheme_for_Communication_System) was published in 2018. It states that they are proposing a communication system that can use different modulation/demodulation schemes at a given point of time, but it also mentions that the "current system" can only use one scheme at a time.

My questions: Can a smartphone support different modulation/demodulation schemes with single receiver antenna at a time now? Or if multiple antennas are required to achieve this?

Thank you.

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  • $\begingroup$ Hello and welcome to ham.stackexchange.com! $\endgroup$
    – rclocher3
    Commented May 27, 2021 at 17:50

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The antenna has nothing to do with the modulation scheme.

The selection of antenna affects frequency and polarization. It may be tricky or very difficult to receive and transmit on the same antenna at the same time. Even with two antennas that are adjacent, this may be an issue, although careful placement, orthogonal polarizations, and good filter circuits would help.

Having said that, it is possible to have a wide band antenna that gets a wide range of frequencies, and antennas typically work at third harmonics of their base frequency, so it is trivial to work in multiple harmonic bands. Both of these involve compromises in directivity and sensitivity, but that may not be a big obstacle.

So other than that, I see no problem with dealing with multiple modulations on the same antenna. This is an issue for the demodulation portion of the phone, not the antenna. And most phones these days use SDR internally, so this becomes a software problem.

You aren't going to find many mentions of multiple modulations on the same antenna in technical literature, because it's not special. Where you will find mentions of this is in the data sheets for amateur radios, where supporting multiple modulations is common and ubiquitous, even before SDR made it trivial.

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  • $\begingroup$ Thanks for your answer! so the reason that I can find few resources on this topic is because demodulating different signals with different modulation schemes is not the task for the antenna, but the phone. An antenna is free to accept signals with different MCS. In addition, handling multiple signals with different MCS at a given point of time is possible for amateur radios in a phone and SDR makes it more trivial. It is correct? $\endgroup$
    – Yukinari
    Commented May 28, 2021 at 12:58
  • $\begingroup$ Partially right. Don't confuse demodulating multiple modes (one at a time) with demodulating multiple signals (all at once). And amateur radio isn't special here, it is just typically more flexible in what the product is designed to do. A non-sdr radio can demodulate one signal per receiver, but any mode it is designed for. SDR can demodulate as many signals at once (without respect to mode) as it has RF and cpu bandwidth for. $\endgroup$
    – user10489
    Commented May 28, 2021 at 22:55
  • $\begingroup$ I think I got it. In short, we can receive multiple signals at the same time, even if they are modulated with different MCS. Then the phone can demodulate these signals with their respected schemes one at a time. Also, a non-sdr radio can demodulate any signal with pre-defined modes, and signals of the same MCS is demodulated by a receiver at a time (if we have two signals with two MCS, we need two receivers.) . SDR can demodulate as many signals with their MCS at once if the RF and cpu bandwidth is enough. Am I missing something? $\endgroup$
    – Yukinari
    Commented May 29, 2021 at 8:51
  • $\begingroup$ Sounds about right. Multiple receivers per antenna is common. In an SDR radio, the demodulation is done in software, so a software update can add new modes. A non-sdr radio, the modes are predefined. $\endgroup$
    – user10489
    Commented May 29, 2021 at 13:15
  • $\begingroup$ Also, it is possible to stack modulations on top of each other. Such a signal must be demodulated multiple times, serially. For example, a stereo FM signal is demodulated with FM to get the main channel and the result filtered and AM demodulated and added to the main signal to get the left channel. $\endgroup$
    – user10489
    Commented May 29, 2021 at 13:23
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Modern mobile phones already receive many signals simultaneously: phone calls and notifications from the mobile phone towers (several bands), Wi-Fi (several bands), GPS, NFC, Qi, etc. Typically each use will use a different modulation scheme, and each will use its own band or bands. Phones typically have several different antennas to work on different frequency bands.

If you are asking if a phone can demodulate multiple signals with different modulation schemes on the same frequency or channel, then I would say yes, such a thing can be done theoretically. In practice, multiple signals using different modulation schemes are not used on the same channel for commercial purposes because it's inefficient; to one modulation scheme the other schemes are noise, which limit the distance the signals travel and reduce the bandwidth. (CDMA allows many phone signals to share the same channel simultaneously, but the signals all use the same modulation scheme and the power of each signal must be rapidly and continuously controlled by the mobile tower.) In practice it is more efficient to put each modulation scheme on its own band or bands. Each mobile phone company has the exclusive license to the channels it uses for phone calls in a particular location, in order to reduce inefficient competition to use the same channel.

It would be theoretically possible to design two or more modulation schemes that could coexist on the same channel, but it would require a great deal of work for very little benefit, so in practice this is seldom done for commercial purposes. (The military regularly uses modulation schemes that are designed to work when competing signals are on the same frequency.)

Two narrow-banded modulation schemes could be used on different channels on the same band. That has been done since vacuum tubes (valves) were created in the early days of radio.

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  • $\begingroup$ Thanks for commenting! Actually, the question I am asking is that if a smartphone can use single antenna to receive signals at the same transmission band(but different sub-bands), where these signals are transmitted at the same time and modulated by different MCS. Since you states that "a phone can demodulate multiple signals with different modulation schemes on the same frequency or channel", I think this is possible. Is my understanding correct? $\endgroup$
    – Yukinari
    Commented May 28, 2021 at 2:09
  • $\begingroup$ Yes, it is possible to decode multiple signals in the same band that are received with a single antenna. If the signals have more than one modulation scheme then the receiver must do more work to decode the signals, but it is certainly possible. $\endgroup$
    – rclocher3
    Commented May 28, 2021 at 22:41
  • $\begingroup$ Thank you for the answer! The comments are very helpful. $\endgroup$
    – Yukinari
    Commented May 29, 2021 at 14:54

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