CQI Interpretation

[fahmi]

Hi,
I am working on analyzing HSDPA Throughput and I want to corelate with CQI.
with huawei vendor, I found 31 counters indicating CQI (VS.CQI.0 -->VS.CQI.30).

so, how to interpretate these counters ? which one indicating a good CQI ?

What does a bad CQI reflect ? (interference, load , coverage ...) ?

thank you.

[Tomas Delgado]

Hi, mate. It supposed that CQI reports give feedback to the node B scheduler in order that the scheduler algorithm will give you the throughput you can get with the radio conditions reported in terms of CQI. Its supposed that CQI has a direct relation with the CPICH Ec/No the UE is measuring and with the power that the cell has for hsdpa. The best values are above 20 , regular ones between 15 and 20, bad ones less than 15 and no throughput if CQI =0. But in my personal experience with huawei equipment CQI is nothing, i manipulate parameters to get better reports but that didnt make any difference in the throughput. Hope it help.

[Philippe]

CQI levels are standardized in 3GPP documentation TS25.214 (I posted the document in an answer to the post quite low CQI and QPSK but high number of codes (http://www.finetopix.com/live-optimization/20928-quite-low-cqi-qpsk-but-high-number-codes.html) ). It gives you which modulation (QPSK, 16QAM or 64 QAM in HSPA+), which number of codes (from 1 to 15), which transport block set size (number of bits per TTI) will be used according to the CQI and the UE category.
For a given CQI, the effective throughput achieved will depend on the radio conditions (typically multipath and speed conditions) and on the UE receiver characteristics (simple RAKE receiver, advanced MMSE receiver, receiver with 2 way Rx diversity).
In any case, the higher CQI, the better throughput.

[oswe]

Hi,
I am working on analyzing HSDPA Throughput and I want to corelate with CQI.
with huawei vendor, I found 31 counters indicating CQI (VS.CQI.0 -->VS.CQI.30).

so, how to interpretate these counters ? which one indicating a good CQI ?

What does a bad CQI reflect ? (interference, load , coverage ...) ?

thank you.



appart from the good explanation given by the other colleagues, I give you an example... when you try to establish very high throughput to test the feature HSPA+ (which enables modulation 64QAM) you need at least CQI:26 in order to remain there...

best regards...:p

[FrankPintor]

Hi,
I am working on analyzing HSDPA Throughput and I want to corelate with CQI.
with huawei vendor, I found 31 counters indicating CQI (VS.CQI.0 -->VS.CQI.30).

so, how to interpretate these counters ? which one indicating a good CQI ?

What does a bad CQI reflect ? (interference, load , coverage ...) ?

thank you.


The CQI is essentially a specification of the transport block size the UE could receive which maintaining a BLER of <=10%.

So it's a measure of quality, and it's primarily affected by interference and coverage.

Operators typically specify a minimum CQI in urban areas of between 15 and 18, and in practice I see this as requiring a coverage density of 1.5km max. between sites (depends on topology, clutter, and tilts of course but this is just a rough rule of thumb).