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NOTE : At high level view, it would not be difficult to understand overall concept of CSI. However, getting deeper into the details.. it would become much complicated .. and tooooooooooooo confusing (at least very confusing to me). That is one of the reason why I wrote multiple pages for the same topic (CSI). Multiple pages for the same topic can be additional confusion to some readers (even to me). However, I thought the page would get too big for download if I put everything in single page and I also thought it would not be bad to provide a little bit different aspect for the same topic with multiple post. But as I add more pages (post), I thought it would be good to write a page to provide high level view and help readers combine all those multiple pages that I wrote. Refer to CSI Overview page if you are not familiar with big picture of the CSI report.

 

 

CQI, PMI, RI Reporting Configuration - Details for Aperiodic Report

 

In most case, you would need more information for anything 'Aperiodic' implying 'irregular'. If something is periodic or regular, you may set a certain rule (like a mathematical formula) and pass a couple of parameters to the formula. But in case of Aperiodic, usually it would take more information to configure the behavior since it cannot be easily defined by a fixed rule (e.g, mathematical formula). Especially with the introduction of Carrier Aggregation and the number of Carrier gets larger, the amount of necessary information (e.g, when to send CSI, for which carrier it send CSI) gets larger.

 

In short, Aperiodic report is configured by two factors : one portion is configured in RRC message and the other portion is configured by DCI. The portion configured by RRC message is described in CQI/RI Feedback type page and the portion configured by DCI is described below in this page.

 

I assume that you have read through RRC portions of Aperiodic CQI configuration. Now let's look into DCI part of the configuration. The DCI can carry very short contents and it does not have enough space to carry all of those information.

 

Then, what would be the solution for this ?

The answer is a common old trick. They configure a complicated part in RRC message and lower layer (i.e, DCI in this case) just select a specific configuration defined in RRC message.

 

Now let's look into the details. The Aperidic CQI/CSI gets configured in RRC message as shown below. At the first glance, you would immediately have questions as below.

 

 

If you can answer these two questions, you already have overall mechanism of Aperiodic CSI report. The answers are as shown below.

 

 

Formal definition of aperiodicCSI-Trigger is defined in 36.331 as below.

 

36.331- aperiodicCSI-Trigger

 

Indicates for which serving cell(s) the aperiodic CSI report is triggered when one or more SCells are configured.

trigger1 corresponds to the CSI request field 10 and trigger2 corresponds to the CSI request field 11, see TS 36.213 table 7.2.1-1A. The leftmost bit, bit 0 in the bit string corresponds to the cell with ServCellIndex=0 and bit 1 in the bit string corresponds to the cell with ServCellIndex=1 etc. Each bit has either value 0 (means no aperiodic CSI report is triggered) or value 1 (means the aperiodic CSI report is triggered). At most 5 bits can be set to value 1 in the bit string. E-UTRAN configures value 1 only for cells configured with transmissionMode set in range tm1 to tm9. One value applies for all serving cells configured with transmissionMode set in range tm1 to tm9 (the associated functionality is common i.e. not performed independently for each cell).

 

 

< Example 1 >

 

Assumption : Carrier Aggregation is configured

 

Trigger in RRC Message

CSI Field

P Cell

S Cell1

trigger1 = 00000000

trigger2 = 00000000

00

No Report

No Report

01

Report

?? (To be confirmed)

10

No Report

No Report

11

No Report

No Report

 

 

< Example 2 >

 

Assumption : Carrier Aggregation is configured

 

Trigger in RRC Message

CSI Field

P Cell

S Cell1

trigger1 = 10000000

trigger2 = 00000000

00

No Report

No Report

01

Report

?? (To be confirmed)

10

Report

No Report

11

No Report

No Report

 

 

< Example 3 >

 

Assumption : Carrier Aggregation is configured

 

Trigger in RRC Message

CSI Field

P Cell

S Cell1

trigger1 = 11000000

trigger2 = 00000000

00

No Report

No Report

01

Report

?? (To be confirmed)

10

Report

Report

11

No Report

No Report

 

 

< Example 4 >

 

Assumption : Carrier Aggregation is configured

 

Trigger in RRC Message

CSI Field

P Cell

S Cell1

trigger1 = 11000000

trigger2 = 01000000

00

No Report

No Report

01

Report

?? (To be confirmed)

10

Report

Report

11

No Report

Report

 

 

 

< Influence of other MAC activities on CSI report >

 

Since there are some other periodic activities, those activities can influence Periodic/Aperidic CSI Report as described in CQI Report and DRX section. CSI report is triggered by DCI, so a certain DCI format can influence CSI Report as described in CQI Report and SR section.