I am new to wireless. From what I read, SISO serves only 1 client at a time and SU-MIMO can serve multiple clients but at different times.

So does SISO and SU-MIMO serve 1 client and then wait until it is fully done (disconnect) before it can serve another client?

Also, in SU-MIMO, how does it determine which devices should it serve first?

  • 1
    Channel access works with CSMA/CA and optionally RTS/CTS. There's nothing special for SISO or SU-MIMO. CSMA/CA is a competitive peer process while RTS/CTS is controlled by the WAP.
    – Zac67
    Apr 7 '20 at 11:17

I think you are referring to MU-MIMO (multi-user MIMO) when you talk about serving multiple clients. SU-MIMO deals with multiple streams of data for a single user. SISO deals with a single stream for a single user.

When you deal with multiple clients, each of the clients still compete for channel access (irrespective of whether they are going to employ SISO or MIMO) using CSMA/CA. Once a MIMO capable client has got access, the AP can decide whether to use MIMO features for boosting the SNR (using beamforming or diversity) or data rates (using spatial multiplexing).

  • i see, so more than 1 device can connect to SISO AP, and compete for channel using CSMA/CA?
    – Pokekman
    Apr 7 '20 at 15:33
  • That's correct. Whether or not the AP supports MIMO, more than one device can always connect to the AP. All the devices (including the AP) then compete for channel access. Once channel access is obtained, the AP and the device are free to use SISO or MIMO. This is how all types of devices (whether they are capable of MIMO or not) can coexist in the same BSS.
    – V-Red
    Apr 7 '20 at 19:54
  • I see, thank you. Do the devices use TDMA to determine each time slot that will be used for each of the devices?
    – Pokekman
    Apr 8 '20 at 2:38
  • That is a broad question, and it's up to the designer. In 802.11 systems, I'm not aware of any TDMA-based channel access protocol. Instead, a TXOP (Refer to en.wikipedia.org/wiki/… ) is assigned for a given transmission, and other stations set their NAV and back off. In LTE however, channel access is based on TDMA.
    – V-Red
    Apr 8 '20 at 19:55

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