|A pure modem do not get any ip address.|
Therefore, you have to use a router or PC/Laptop, to authenticate to your ISP.
So I assume, your modem isn't a modem but a router with integrated modem.
In that case, your router with integrated modem must support to act as a modem only.
Then the Huawai router must be configured, to authenticate to your ISP and should get the public ip address.