Rank confusion in LTE

[eta004]

Case 1: 4x4 Rank 1 Transmit diversity:

Rank1 means: 1 unique layer of data ie even if Antenna config is 4 x 4 ie Enb has 4 Tx antenna & Ue has 4 Tx antenna (say Samsung S8)
Does all 4 antenna ports transmit the same data to the UE since it is rank1 & hence Transmit diversity?
Will all the 4 antennas be used for transmission?

The above 2 questions apply to the Ue receiver also...Do Ue receives in all its 4 antennas?


Case 2: 4x4 Rank 2 :

Rank2: 2 layers of unique data - Does all 4 txs and 4 rxs of Ue be used for communication

Case 3: Rank3 & 4

We have a case where rank3 is reported more than Rank4...Any specific reasons?
Max value of rank can be Rank 8 Since Cat 8 devices support 8 x 8 MIMO?

[jan74]

This has confused me in the past too. I believe (and will stand corrected because i never got a satisfactory answer to it) that you can get RI=1 more often when you enable TM4. But that doesn't mean slower throughout overall because DL noise is reduced significantly throughout the cell and particularly on the edge.

So as far as i understand it you can use RI=1 with TM4 and its not Tx Div....its supposed to be better than TxDiv... But i am struggling to understand how that can be(apart from the obvious.noise reduction). Im assuming its a similar case for 4*4....

[BlackX]

Case 3: Rank3 & 4

We have a case where rank3 is reported more than Rank4...Any specific reasons?

in our network we deploy L26 +L18 4X4 , and using U11 to do the static test.

In most case UE report RI =3 . The only one test Result we got RI=4 is we block all neighbor site and UE SINR is above 25 [ In test Result L18 SINR is 30 and L26 SINR is 26 ].

So i guess if you want to see RI=4 , the RF condition must very very good

[eta004]

Hi BlackX,

Yes, Convincing! I have a related query, when Rank is 3 as reported by RI, how many antennas does eNB & Ue use for this communication? Will both use all 4 Antenna ports or Only 3 antenna ports will be used and the 4th port is unused?




Case 3: Rank3 & 4

We have a case where rank3 is reported more than Rank4...Any specific reasons?

in our network we deploy L26 +L18 4X4 , and using U11 to do the static test.

In most case UE report RI =3 . The only one test Result we got RI=4 is we block all neighbor site and UE SINR is above 25 [ In test Result L18 SINR is 30 and L26 SINR is 26 ].

So i guess if you want to see RI=4 , the RF condition must very very good

[BlackX]

actually i not sure, i think this is depend on vendor's hardware and scheduler design

[eta004]

41457

This is a snap from XCAL MO PDSCH demapper Config.

Here M & N are given as Tx & Rx antennas, but not sure how it is calculated

[kobbyebo1]

The enb has the flexibility of using either 3 individual antenna ports or combining 2 ports into 1 in addition to the remaining 2. the second option is a combination of transmit diversity and the MIMO. But either depends on the RF condition of the UE.