LTE MIMO : RANK, LAYERS and Antenna ports

[fahmi]

Dear Experts,

When a UE reports a RI=3 for DL MIMO (4x2), could you explain the mapping of data stream to antenna ports ?

Is it true that, RI =3 means 3 differents data stream at the same time and means 3 layers that will be mapped to 3 antenna ports ? what about the 4th antenna ports in such case ?

Thanks

[abeloufa]

• Hello Fahmi, number of layers will definitivelly follow requested rank by the UE, if for instance Requested Ranks show 4 then MIMO CL/OL 2 Code Word mapped to 4-Layers should be used, yes this required 4 antenna ports (for both sides 4x4), (for all vendors there is a specific Counters for that).

[auto_art]

Dear Experts,

When a UE reports a RI=3 for DL MIMO (4x2), could you explain the mapping of data stream to antenna ports ?

Is it true that, RI =3 means 3 differents data stream at the same time and means 3 layers that will be mapped to 3 antenna ports ? what about the 4th antenna ports in such case ?

Thanks

iI asked the question to our 5G trainer, and He came back saying there would be 3 distinct paths in that case and what those three would be is configurable. e.g. a, b, c, c or a,a,b,c means one line will be duplicated other will be distinct.

[pathloss]

Yep, that's it. 3Layers where one is in TX Div.

[techfolkcmr]

We have UMTS network with single carrier of 5MHZ. My doubt is can MIMO(2*2) be enabled/implemented without second carrier or MIMO is the final option after availing second or third carriers and what will be the maximum achievable throughput if MIMO can be implemented with single carrier.

[firstmaxim]

But is it required to have TX diversity in the 3rd layer, while using MIMO for the other two? TX diversity is used when CQI is poor.

[mohsenJaz]

Enabling MIMO or activating second or third carriers are independent. In both cases you are increasing your available resources. It's up to you to select each of them based on the available hardware resources. Both policies have their own benefits. Enabling MIMO, you can benefit from diversity/multiplexing gain according to the rank of channel matrix, but when you activate another carrier, solely, you are increasing the capacity (throughput if dual carrier is configured in your network). In practice, average multiplexing gain of using MIMO is less than 2 (about 1.4-1.5).

We have UMTS network with single carrier of 5MHZ. My doubt is can MIMO(2*2) be enabled/implemented without second carrier or MIMO is the final option after availing second or third carriers and what will be the maximum achievable throughput if MIMO can be implemented with single carrier.

[mohsenJaz]

according to algebra theory, maximum rank in a 4*2 MIMO is 2. to be specific, in a m*n MIMO, maximum rank is min(m,n)

iI asked the question to our 5G trainer, and He came back saying there would be 3 distinct paths in that case and what those three would be is configurable. e.g. a, b, c, c or a,a,b,c means one line will be duplicated other will be distinct.

[techfolkcmr]

Enabling MIMO or activating second or third carriers are independent. In both cases you are increasing your available resources. It's up to you to select each of them based on the available hardware resources. Both policies have their own benefits. Enabling MIMO, you can benefit from diversity/multiplexing gain according to the rank of channel matrix, but when you activate another carrier, solely, you are increasing the capacity (throughput if dual carrier is configured in your network). In practice, average multiplexing gain of using MIMO is less than 2 (about 1.4-1.5).

so it is either MIMO or another carrier and its always best to use carrier option for better throughput and capacity.One more question MIMO or Modulation. 16QAM with MIMO or 64QAM without MIMO which is effective.And can MIMO coexist with high order Modulation.

[firstmaxim]

I think the questions posed are for R7 HSPA+. For LTE, you can have 64QAM and 4x4 MIMO simultaneous, if operator and UE supports. It will depend on the CQI value and RI reported.