What is the advantage if the MISO (Multiple Input Single Output) technology in communications? I have been searching it on the internet, but there are just about their model and full name.

For example, What is its application? Is it used in 5G or IoT?

  • $\begingroup$ What advantages? Many advantages, depending on the application. I don't know what you're actually after, because the half sentence "but there are just about their model and full name" indicates you've been looking into products rather than searching literature for basics. What application? Wireless communication devices. Many SISO systems can be improved by becoming MISO systems in term of e.g. robustness or average power constumption or speed. Used in 5G? Yes. And in 4G. And in 3G, at least rudimentarily. In IoT? IoT doesn't actually mean anything specific, so yes. $\endgroup$ – Marcus Müller Dec 17 '18 at 14:28
  • $\begingroup$ Do you understand what MISO is? From there it'd be easier to explain advantages. Could you explain your level of understanding of MISO? I'll mark this question as "too broad" in the meantime, to remind myself to check back on whether you've demonstrated your background – only if we know what level we need to start explaining on would it make sense to write an answer. $\endgroup$ – Marcus Müller Dec 17 '18 at 14:29

Multiple input single output refers to the scenario where you have a transmitter with multiple antennas and a receiver with a single antenna. That is, the channel sees multiple inputs from the multiple transmit antennas and a single output at the single receiver antenna. With that being said there are many benefits of multiple antennas:

  1. Wireless channels undergo what is called fading and can sometimes experience a so called "deep fade" in which the channel strength drops low enough to a point where reliable communication is no longer possible. Say we have 10 antennas at the transmitter and a single antenna at the receiver, then there are 10 wireless channels, one for each transmit antenna. Intuitively you can think the probability of a deep fade event should now be less since all 10 channels would have to experience a deep fade at the same time. This is referred to as transmit diversity.
  2. With multiple antenna elements we can perform what is called beamforming. Beamforming allows us to amplify signals we send in certain directions and can even further attenuate signals in different directions (pointing a null beam). Many beamforming techniques have been developed including adaptive algorithms which perform beam pointing "on-the-fly" to try to maximize SINR for example.
  3. Multiple transmit antennas are necessary for certain space-time block codes (STBC) which boil down to transmitting specially modified versions of the same signal during the different time slots of transmission. A common and simple STBC is the Alamouti scheme.

These are just the first few that came to my mind but, multiple antenna systems are an active research area and with 5G pushing massive MIMO there are many groups doing work in this area.

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  • $\begingroup$ so "Beamforming allows us to amplify signals we send in certain directions and can even further attenuate signals in different directions" Does it means that we can broadcast the signal to farer place and try not to let this signal influence the other signal ? $\endgroup$ – electronic component Dec 18 '18 at 7:40
  • $\begingroup$ Right. It allows for the signal energy to be concentrated in a certain direction which would mean it could reach farther away targets. I describe in such broad strokes here because from your question it was not clear how much you wanted but there are many resources to learn about beamforming and much of it comes down to modeling it as a linear algebra problem. Also, when learning something new I suggest playing with it in MATLAB which has toolboxes which can implement and then from there you can work to write your own functions. $\endgroup$ – Engineer Dec 18 '18 at 13:51

Multiple-input, single-output (MISO) wireless communications basically mean that the transmitter has multiple antennas, and the receiver has only one.

Wireless channels are very challenging. For instance, they have random deep fades, where the received signal has almost zero power. Under those conditions, there is very little that can be done to keep the data flow going.

One solution to the fading problem is to create diversity: send the signal through multiple channels, hoping that at least one of them is not in a deep fade. In wireless systems, it is possible to create these multiple channels without increasing the bandwidth or the transmit power.

For example, one could have multiple receiver antennas (this would be a SIMO system). Under some conditions, each receiver antenna sees a different channel. The receiver can then combine all the received signals and get a very significant performance improvement.

However, sometimes it is unfeasible to have multiple antennas in the receiver. One example would be the base-station to mobile channel. One would like to have many antennas on the base station, where there is ample space and power, and only one in the receiver, which is very limited.

MISO systems try to create diversity when the transmitter has multiple antennas. This is much more challenging than the SIMO case, because it requires either channel knowledge at the transmitter, or specially designed signals such as the Alamouti space-time code.

I recommend getting "Introduction to Wireless Communications" by R. Heath. It's a very good book, covers all of this material, and is not too expensive.

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