Is 2nd ALPR -84dBc possible?

I'm designing a 1W OFDM radio. It will be tuned for 6MHz bandwidth channels from 500MHz to 700MHz.

To meet the MASK, 2nd ALPR need to be -84dBc. For the reason of cost reduction, there is no RF filter for each channel so it all relys on a high linear PA and low noise modulator design.

Sounds very challenge. Is it possible?

Yes, would be very challenging. Usually ACLR 2 in OFDM is in -50dBc range.

Assume it's -50dBc, How much DPD can help it improved?

I was thinking about RF filters, but all the researchs are unsuccessful. I hope DPD could somehow help.

Using Digital Predistortion can get improvement for ACLR2 in 20dB's range, more or less depending approach used and by transistor type. For example GaN HEMT get better ACLR than Si LDMOS.