quite low CQI and QPSK but high number of codes

[dgonzalez]

Hi Experts,

Is it possible a situation with a quite low CQI (16-18) and QPSK modulation and a quite high number of codes (8-10)?

Thanks!

BR

[twenty8]

Hi,

This is quite possible, depending if the UE HSDPA Category and the RAN features activated. In case Cat 7 -10 , the UE is capable to receive > 5 codes hence its possible to get these 8 - 10 codes. Based on the reported CQI, the scheduler will determine which TBS to allocate, and this would depend on the modulation and # of codes available.

[boring]

according to the standards it is completely fixed CQI and modulation scheme/number of codes (of course everything depends on UE capability)

for example a popular UE phone of category 7/8 (max codes = 10)

CQI = 14, QPSK, codes = 4
CQI = 15, QPSK, codes = 5
CQI = 16, 16QAM, codes = 5
CQI = 17, 16QAM, codes = 6
etc until it will reach the maximum code capability

hope this helps

[Philippe]

You can find the exact CQI mapping table (giving you for each CQI number the modulation, number of codes and power adjustment possible according to the UE category) in 3GPP TS25.214.

[Philippe]

You can find the exact CQI mapping table (giving you for each CQI number the modulation, number of codes and power adjustment possible according to the UE category) in 3GPP TS25.214.

For example with a UE category 12 that can only support QPSK and up to 5 codes, you can report some CQI higher than 15 and the HSDPA channel will still use QPSK (but not more than 5 codes) and adjust power.

For other UE categories (different from 11 and 12), 16QAM is used for CQI higher than 15.

Additionnally, 16QAM (and later 64QAM for HSPA+) is a equipment vendor feature that must be activated by licence on the HSDPA NodeB.

[keanchan]

You can find the exact CQI mapping table (giving you for each CQI number the modulation, number of codes and power adjustment possible according to the UE category) in 3GPP TS25.214.

For example with a UE category 12 that can only support QPSK and up to 5 codes, you can report some CQI higher than 15 and the HSDPA channel will still use QPSK (but not more than 5 codes) and adjust power.

For other UE categories (different from 11 and 12), 16QAM is used for CQI higher than 15.

Additionnally, 16QAM (and later 64QAM for HSPA+) is a equipment vendor feature that must be activated by licence on the HSDPA NodeB.

Hi Phlippe,
Is it possible to reverse calculate the possible CQI from measured RLC throughput, used modulation and UE Category?

/Kean

[Philippe]

It is more difficult as when assigning a given Transport Block size, modulation, number of codes and downlink power the effective data rate will still depend on radio environment (multipath, orthogonality).
Nevermind the CQI is reported by the UE so you can track it.