devm bluetooth

Recently, in Bluetooth V2.0 EDR, a parameter called DEVM (Differential Error Vector Magnitude) has been introduced.

Is standard EVM still measured first and then DEVM is derived from it?

Also, does anyone have any dood documentation on DEVM measurement and theory?

Any help anyone?

DEVM is similiar to EVM but it is not derived from EVM. Bluetooth applies DPSK(differential encoded phase shift keying). Because DPSK's phase information is naturally related to its prior one, We are more interested in bluetooth's DEVM than in EVM.

The explaination of DEVM is very straightforward. See my attachment.