What is difference between TM4 in 2x2 MIMO and TM4 in 4x4 MIMO? Which should have better gain?

4G LTE
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Actually TM4 (closed loop MIMO - PMI Feedback from UE) is working for MIMO mode whether in 2x2 or 4x4 MIMO but the difference is in PMI codebook size in case of TM4 (Closed-loop MIMO):

  • TM4 in 2x2 MIMO —> have PMI codebook size = 4 for 2-antenna-port
  • TM4 in 4x4 MIMO —> have PMI codebook size = 16 for 4-antenna-port

So TM4 in 4x4 MIMO have better gain than 2x2 MIMO due to large available codebook size.

References:

  • 3GPP TS 36.211 version 14.2.0 Release 14,
  • 3GPP TS 36.213 version 10.4.0 Release 10

What is difference between TM4 in 2x2 MIMO and TM4 in 4x4 MIMO
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