I used E303 3g USB dongle , but you can call Huawei support line and the will give you all the usb 3g dongles compatible with this router. There are a few.
I got this router without checking if it supports LTE devices, and I had the E3276 LTE usb dongle, I had to do a work around which is flashing the E3276 dongle to be seen buy the the HG532c Router.