Questions to MIMO synchronisation

[senmeis]

Hi,

In attachment a slide about MIMO implementation is shown.

Question 1: Why must digital back end be synchronized? As far as I know random signals are ideal for MIMO.

Question 2: Why beamforming here? Shall beamforming not only be used for conventional arrays?

Senmeis

 

[weetabixharry]

1) To be honest, I'm more confused as to why they say the RF front end should be unsynchronised. For example, if local oscillators are not frequency locked between the multiple receive chains, then coherent processing at the receiver becomes practically impossible. This would, for example, destroy the performance of MIMO WiFi (802.11n/ac).

I would argue that it is much easier to guarantee uncorrelated signals when the whole system is coherent (because then you can just design uncorrelated signals in the digital domain). Where did you find this slide and what technology is it talking about? When they refer to "optimum performance" like this, they must be referring to some specific application.

2) No, you can do whatever you want in MIMO, including beamforming.