CQI stands for Channel Quality Indicator. As the name implies, it is an indicator carrying the information on how good/bad the communication channel quality is. This CQI is for HSDPA. (LTE also has CQI for its own purpose).
CQI is the information that UE sends to the network and practically it implies the following two:
1) Current Communication Channel Quality is this-and-that..
2) I (UE) wants to get the data with this-and-that transport block size, which in turn can be directly converted into throughput
In HSDPA, the CQI value ranges from 0 ~ 30. 30 indicates the best channel quality and 0,1 indicates the poorest channel quality. Depending which value UE reports, network transmit data with different transport block size. If network gets high CQI value from UE, it transmits the data with larger transport block size and vice versa.
CQI index |
modulation |
code rate x 1024 |
efficiency |
0 |
out of range |
||
1 | QPSK |
78 |
0,1523 |
2 | QPSK |
120 |
0,2344 |
3 | QPSK |
193 |
0,377 |
4 | QPSK |
308 |
0,6016 |
5 | QPSK |
449 |
0,877 |
6 | QPSK |
602 |
1,1758 |
7 | 16QAM |
378 |
1,4766 |
8 | 16QAM |
490 |
1,9141 |
9 | 16QAM |
616 |
2,4063 |
10 | 64QAM |
466 |
2,7305 |
11 | 64QAM |
567 |
3,3223 |
12 | 64QAM |
666 |
3,9023 |
13 | 64QAM |
772 |
4,5234 |
14 | 64QAM |
873 |
5,1152 |
15 | 64QAM |
948 |
5,5547 |
CQI Periodicity
Following is an example when CQI only is being transmitted. Npd and N_OFFSET,CQI configured by RRC Connection Setup and RRC Connection Reconfiguration and the value itself came from Table.
10*nf +[ns/2] – Noffset,CQI) mod (Npd)=0
nf = SFN
ns = Slot number within a radio frame
Noffset,CQI = Reporting Period Offset in subframes
Npd = Reporting Period in subframes
The equation itself will be quite simple, but just to double check your understanding, let me give you a short quiz. Don’t panic -:) Here you go.
Let’s try with some example for a FDD case.
If cqi-pmi-Configindex in RRC message is 13. What is Npd and N_OFFSET,CQI ?
This maps to the row of the table as follows. You can read Npd directly. It is 10. Then you need a little bit of math to get N_OFFSET,CQI. The value for this example is specified to be (I_CQI/PMI-7). It is “13 -7” which is 6. Now the last step is to apply these two values to the equation above to calculate the exact sub-frame number for CQI/PMI transmission.
ICQI/PMI |
Value of Npd |
Value of Noffset,CQI |
0 ≤ICQI/PMI≤1 |
2 |
ICQI/PMI |
2 ≤ICQI/PMI≤6 |
5 |
ICQI/PMI-2 |
7 ≤ICQI/PMI≤16 |
10 |
ICQI/PMI-7 |
17 ≤ICQI/PMI≤36 |
20 |
ICQI/PMI-17 |
37 ≤ICQI/PMI≤76 |
40 |
ICQI/PMI-37 |
77 ≤ICQI/PMI≤156 |
80 |
ICQI/PMI-77 |
157 ≤ICQI/PMI≤316 |
160 |
ICQI/PMI-157 |
ICQI/PMI=317 |
Reserved |
|
318 ≤ICQI/PMI≤349 |
32 |
ICQI/PMI-318 |
350 ≤ICQI/PMI≤413 |
64 |
ICQI/PMI-350 |
414 ≤ICQI/PMI≤541 |
128 |
ICQI/PMI-414 |
542 ≤ICQI/PMI≤1023 |
Reserved |
Additional info
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