MIMO 2x2 versus 4x4r

Hello dear Experts,

When changing MIMO, from using MIMO 2x2 to MIMO 4x4, what are the advantages and disvantages in the network?

Thanks for any comment in advance.

You can get the advantages of the larger coverage and higher throughput, at the cost of higher complexity and power consumption.

Please @Wendy, can you give more details about coverage différence?

In the same channel condition and maintaining the same date rage, the maximum coverage advantage can be double (2x cover distance) or more if take into account all potential diversity gain in PHY layer.

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Thanks you

What is the additional gain with MIMO 4x4 compared to MIMO 2x2, in Uplink?

Is it 3 dB more?

Yes, additional gain is 3 dB.

So in Throughput (MBps) how much is increased?

What is increase 2x2 to 4x4? 4 MBps in UL or more?

We next consider the required transmit power of each user that is needed to reach a fixed spectral efficiency. Fig. 3 shows the normalized power (pu/σ2 ) required to achieve 1 bit/s/Hz per user for different M. The asymptotic curves are determined from Equations (29) for the case of perfect CSI, and (39) for the case of imperfect CSI. As expected, for large number of base station antennas, by doubling M, we can gain approximately 3 dB and 1.5 dB in power with perfect CSI and imperfect CSI, respectively. Furthermore, we can see that when M is large, i.e., M/K > 6, the difference in performance between MRC and ZF is less than 1 dB.


Fig. 3. Required power versus the number of base station antennas for 1 bit/s/Hz per user. Here K = 10.

Source: Uplink Power Efficiency of Multiuser MIMO with Very Large Antenna Arrays paper.