MIMO 2x2 to 4x4 Change

[umutaltun13]

Hey everyone,

I have question about MIMO. What are the disvantages you see in your network of changing MIMO 2x2 to 4x4 ?


Thank you in advance.

[remoz_A]

mainly will be cost and installation

[longtermevolution]

If you have fixed RRU power which is now shared between 4 ports rather than 2 ports your coverage will shrink. if still having same power per port you will not face any negative impact.

Spatial layer cause mutual interference to each other so probably you might face:
SINR degradation, lower MCS and hence degraded capacity per layer compared to 2X2

[firstmaxim]

Less than 1percent of UEs in a cell would actually use MIMO 4x4. 50 percent of UEs. Only the UEs very close to the base station can be served with 4x4 MIMO because of the high S/N requirements.

[subway]

Less than 1percent of UEs in a cell would actually use MIMO 4x4. 50 percent of UEs. Only the UEs very close to the base station can be served with 4x4 MIMO because of the high S/N requirements.

To add to that, the fixed CRS overhead of your network will rise form 11-12% (2x2 MIMO) to almost 25%.

In my opinion, 4x4 MIMO only worth it where:

1. The amount of 4x4 capable UEs is high (at least 40-50%).
2. The sites are rather close to each other (dense urban).
3. And you have good reflective built environment.

In any other case, you will spend a lot of money, introduce a fixed speed penalty for most customers (CRS overhead), and will see very little gains.

To give you an example, our network is a rural WTTx one, everything is 4x4 capable yet it does not worth to turn it on.

If you can, think of beamforming, high order modulation (256QAM DL, 64QAM UL) and such instead of 4x4 MIMO. For example if you can do TM9 you can also exploit 4 spatial layers (compatible UEs required and a minimum of 8T8R antennas), but without the added fixed CRS overhead of the traditional 4x4 MIMO.

[felixj.alvarez]

To add to that, the fixed CRS overhead of your network will rise form 11-12% (2x2 MIMO) to almost 25%.

In my opinion, 4x4 MIMO only worth it where:

1. The amount of 4x4 capable UEs is high (at least 40-50%).
2. The sites are rather close to each other (dense urban).
3. And you have good reflective built environment.

In any other case, you will spend a lot of money, introduce a fixed speed penalty for most customers (CRS overhead), and will see very little gains.

To give you an example, our network is a rural WTTx one, everything is 4x4 capable yet it does not worth to turn it on.

If you can, think of beamforming, high order modulation (256QAM DL, 64QAM UL) and such instead of 4x4 MIMO. For example if you can do TM9 you can also exploit 4 spatial layers (compatible UEs required and a minimum of 8T8R antennas), but without the added fixed CRS overhead of the traditional 4x4 MIMO.

Your data is not very accurate:

For a 2-port antenna, CRSs consume 9.5% of air interface resources. Thisoverhead increases to 14.3% for a 4-port transmission configuration. Check here : https://www-file.huawei.com/-/media/...aper.pdf?la=en

[electron]

Hello friends,

Please note that deploying MIMO 4x4 in the network is not all about penetration of 4x4 support devices . When there is migration from 2x2 to 4x4 there is huge gain in spectral efficiency not only due to supportive 4x4 devices. It is mostly about diversity gain we achieve in both DL and UL which is directly interpreted to ~20% capacity gain. Aside the higher cost for operators caused by new RRU installment and other SW packages they need to purchase , Interference to other cells may increase for surrounding sites that may impact their efficiency.

B
R

[subway]

Hello friends,

... It is mostly about diversity gain we achieve in both DL and UL which is directly interpreted to ~20% capacity gain...
B
R

What you say about diversity is generally true, but has nothing to do with MIMO mode directly. For example if you have an 8T8R TD-LTE system (like we do), you can configure it as the following:

The cell is in 8T8R mode: 8R diversity is enabled for the uplink, and 8T is enabled for the downlink, but we are still on CRS2 (2x2 MIMO). In order to utilize diversity, you dont need to use higher order MIMO mode. You just need enough active antenna elements, and th relevant licenses for 4 or 8T8R diversity.

On 8T8R systems (especially if its not dense urban), the wise thing to do is TM9 with MUBF, this way you can selectively utilize the 4 spacial layers for capable UEs (and radio conditions) without the massive fixed CRS overhead of the classical 4x4 MIMO (TM3/TM4). If there are no TM9 capable UEs, keep it on CRS2, and use 4T4R or 8T8R in diversity mode, not in 4x4 MIMO mode.

[kaikunika]

the disadvantage is the cost . i dont think there will be a power problem even if you used fixed RRU

[electron]

What you say about diversity is generally true, but has nothing to do with MIMO mode directly. For example if you have an 8T8R TD-LTE system (like we do), you can configure it as the following:

The cell is in 8T8R mode: 8R diversity is enabled for the uplink, and 8T is enabled for the downlink, but we are still on CRS2 (2x2 MIMO). In order to utilize diversity, you dont need to use higher order MIMO mode. You just need enough active antenna elements, and th relevant licenses for 4 or 8T8R diversity.

On 8T8R systems (especially if its not dense urban), the wise thing to do is TM9 with MUBF, this way you can selectively utilize the 4 spacial layers for capable UEs (and radio conditions) without the massive fixed CRS overhead of the classical 4x4 MIMO (TM3/TM4). If there are no TM9 capable UEs, keep it on CRS2, and use 4T4R or 8T8R in diversity mode, not in 4x4 MIMO mode.

Well, It absolutely has correlation though never talked about MIMO mode diversity! Tell me how you can justify the gain of deploying MIMO 4x4 for the market which has negligible penetration of supportive 4x4 devices but you still see about 20% gain in efficiency? No doubt MIMO diversity gain for both DL and UL will reflect to spectral efficiency and higher capacity gain

B
R