Android LTE CQI API Type

Question

Ref: LTE Signal Strength.

3GPP defines UE may report different types of CQI, which are "wideband CQI" and "sub-band CQI".

Which CQI type displayed in android phone?

Answer 1

Based on the source code of the Android SDK 4.3(API 18), it uses "wideband CQI".

The CQI is maintained as a single integer in android.telephony.SignalStrength class. This class is the main class used to query the CQI by other classes(i.e. android.telephony.CellSignalStrengthLte)

The CQI is maintained as(line 64 in SignalStrength.java):

private int mLteCqi;

Now according to spec the wideband CQI is maintained in 4 bits and sent either in PUCCH or PUSH message. If that was using the "sub-band CQI" it would have to maintain the information for the sub band as well which cannot fit into an integer. It would be typically maintained in a vector like recommended at: http://my.safaribooksonline.com/book/electrical-engineering/communications-engineering/9780137033638/physical-layer-procedures-and-scheduling/ch09lev1sec2

Also more information that confimr this assumption is available at: http://lteuniversity.com/get_trained/expert_opinion1/b/hongyanlei/archive/2009/08/06/cqi-reporting-in-lte.aspx

Hope that helps.