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.

[subway]

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.

Enabling MIMO in UMTS will not give you much gain, as due to the coding/modulation scheme of UMTS, it is not very suitable for MIMO use. If you need to decide between MIMO or another carrier, I would suggest add a second carrier to your system. The fact the 2x2 MIMO theoretical maximum is 28Mbits, and the non-MIMO is 21.6 on UMTS it already gives you an impression of how little gain it will have.

[techfolkcmr]

Enabling MIMO in UMTS will not give you much gain, as due to the coding/modulation scheme of UMTS, it is not very suitable for MIMO use. If you need to decide between MIMO or another carrier, I would suggest add a second carrier to your system. The fact the 2x2 MIMO theoretical maximum is 28Mbits, and the non-MIMO is 21.6 on UMTS it already gives you an impression of how little gain it will have.
many thanks for your direct answer. One more scenario if the same 5MHZ of UMTS2100 is used for LTE what will be the theoretical throughput and practical throughout for a user.

[firstmaxim]

A rough back of the envelope estimate will yield a theoretical gross speed of 25 Mbps for 5MHz (approx 1Mbps per RB, considering no protection, 64QAM). If you add MIMO (m,n) to it then the SINR will determine the throughput gains from MIMO. Capacity = min (m,n) B log2 (1 + SINR)

[subway]

many thanks for your direct answer. One more scenario if the same 5MHZ of UMTS2100 is used for LTE what will be the theoretical throughput and practical throughout for a user.

Compared to UMTS, you will get higher speeds, despite the fact you use the same amount of bandwidth, due to the fact that:

- 2x2 MIMO is mandatory on LTE (for the DL), so either as transmit diversity or as space multiplexing, your clients will benefit
- frequency based scheduling (not possible in UMTS due to the single carrier nature of the modulation)
- faster TTI
- on the uplink you can introduce 64QAM and/or Rx diversity to extend your uplink coverage
- HARQ improved a lot (faster, more instances, more adaptive)

Based on the LTE capable UE penetration, I would definitely introduce 5MHz LTE instead of 5MHz UMTS. But you will need to consider if there is no VoLTE, your voice capacity will not be expanded by this (SRVCC/CSFB will still apply).

[techfolkcmr]

Compared to UMTS, you will get higher speeds, despite the fact you use the same amount of bandwidth, due to the fact that:

- 2x2 MIMO is mandatory on LTE (for the DL), so either as transmit diversity or as space multiplexing, your clients will benefit
- frequency based scheduling (not possible in UMTS due to the single carrier nature of the modulation)
- faster TTI
- on the uplink you can introduce 64QAM and/or Rx diversity to extend your uplink coverage
- HARQ improved a lot (faster, more instances, more adaptive)

Based on the LTE capable UE penetration, I would definitely introduce 5MHz LTE instead of 5MHz UMTS. But you will need to consider if there is no VoLTE, your voice capacity will not be expanded by this (SRVCC/CSFB will still apply).
Are you sure MIMO mandatory. Because part of our network changed to LTE with same architecture of UMTS on radio side (i.e) SISO only

[DJ Download]

It is mandatory from 3gpp specs point of view, meaning that MIMO has to be technically supported.

If operator wants to have SISO then its different story. MIMO feature can always be deactivated or otherwise no need to purchase the feature if its not needed.

[techfolkcmr]

It is mandatory from 3gpp specs point of view, meaning that MIMO has to be technically supported.

If operator wants to have SISO then its different story. MIMO feature can always be deactivated or otherwise no need to purchase the feature if its not needed.

Yup we are using SISO Only.The maximum throughput difference between UMTS-5MHZ SISO 64QAM (DL theoretically 21.4 Mbps) and LTE-5MHZ SISO (DL theoretically 25 Mbps) is very less and Pls justify (Just like an operator) why shifting to LTE is necessary with the same 2100 band and 5MHZ bandwidth of UMTS.

[firstmaxim]

3GPP specs are not mandatory for the operator. It is left to the operator's volition. It can be said that only regulations are mandatory.

[subway]

Are you sure MIMO mandatory. Because part of our network changed to LTE with same architecture of UMTS on radio side (i.e) SISO only

As it is already said, it is mandatory for the vendors (network element and UE manufacturers). So all UEs and enodeb will support it. Of coarse there can be special circumstances when you cannot use MIMO (you can, but not practical): like in an indoor DAS, or leaky feeder installation. Other than that, even the older 2100MHz RRUs are two chain units, and the old sector antennas are also having at least two chains. So given the fact LTE is capable to exploit this and present meaningful gains, why not to use it? Especially if the spectrum is limited (5MHz).

[DJ Download]

Hi,

I think the advantage of LTE over UMTS is not knly from data rate perspective ( although im not sure of UMTS suppory 256 QAM like LTE).

Basically OFDM technique that is used in LTE is better compared to WCDMA. SC-FDMA in the UL direction is also better than WCDMA.

UL in LTE is also orthogonal, meaning you dont have to worry about intra cell UL interference increase due to high load in the cell. I think LTE is also better in handling user capacity compared to UMTS.

Another advantage is also no RNC is needed so you get rid of a point of failure in a region and you dont need to invest in the hardware, software license for RNC (incl. license for extra capacity). Next to that you also save maintenance / resource cost to take care of RNC.

Security in LTE is also better as there is option to use IPSec.


/DJ D


Yup we are using SISO Only.The maximum throughput difference between UMTS-5MHZ SISO 64QAM (DL theoretically 21.4 Mbps) and LTE-5MHZ SISO (DL theoretically 25 Mbps) is very less and Pls justify (Just like an operator) why shifting to LTE is necessary with the same 2100 band and 5MHZ bandwidth of UMTS.

[subway]

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.

Its not required, but useful. If you have a 4T4R antenna and 4x4MIMO is not possible (due to radio conditions) - which is a likely scenario - the only way to benefit from your 4T4R system is Tx (and Rx) diversity. If you configure your cell to 4T4R, it will be Tx div on all non-MIMO channels. Of coarse you can configure your 4T4R antenna to 2T2R, but unless you save in terms of license, thats a waste of resources (you already payed for the 4T4R antenna, RRU and chains). In my view, you can benefit the most from a 4T4R system mainly with 4 way receive diversity (effectively doubles the uplink gain compared to 2 way, those improves the uplink imbalance), and beamforming. Switching on 4x4 MIMO is only realistic, if you have a large number of 4x4 MIMO capable UEs, and a reflective enough environment. In any other case turning on 4x4 MIMO will just increase the CRS overhead without much gains.

[tanz]

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) :)

You are right, purpose of 4X2 is to improve Receive Diversity. In terminology used above, this will be like a,a,b,b or a,b,a,b

[pathloss]

I'm looking forward to get experience with 4x4 and 4x2 MIMO, so far I see that network penetration of UE's that support 4x4 MIMO in general is low and due to this KPI,s for Rank 3 and Rank 4 utilization compared to Rank 1 and Rank 2 is very low. I’m convinced that for some time it's more important to focus on drive testing.

So here my questions:
1) What percentage of rank 3 and rank 4 utilization do you observe in your network?
See lot of cells that stay below 5% for rank 3 and that do only 0 to 1% for rank 4.
2) Which Transmission Mode did you implement? TM-3 OLSM or TM-4 CLSM?
3) What drive test solution do you use, in order to verify that 4x4 MIMO is properly working?
please name model of UE (eg. Galaxy S8, Galaxy S9,...) and what tool you use to post process the log files (TEM-S, NEM-O, SWISSQUA-L)

Pathloss